Table of contents

The fundamental acoustic properties of amorphous Ta₂O₅ and Nb₂O₅ thin films prepared by RF sputtering were evaluated using a Rayleigh-type surface acoustic wave (SAW) on 128° YX-LiNbO₃ and a shear-horizontal-type SAW on 36° YX-LiTaO₃. The elastic constants c₁₁ and c₄₄ of the thin films were determined from the measured phase velocities of two SAW modes with mutually perpendicular particle motion. Although the elastic constants of the Ta₂O₅ thin film were found to be approximately 14–17% larger than those of the Nb₂O₅ thin film, it was clarified that the Ta₂O₅ thin film has a stronger SAW trapping effect than the Nb₂O₅ thin film because the density of the former was measured to be 1.5 times higher than that of the latter. On the other hand, the Nb₂O₅ thin film has a smaller propagation loss for a Rayleigh-type SAW, a lower temperature coefficient of delay, and a higher refractive index than the Ta₂O₅ thin film.

The complete sets of elastic constants C_ij and piezoelectric coefficients e_ij for LiNbO₃ and LiTaO₃ single crystals have been determined by resonant ultrasound spectroscopy (RUS) from ambient temperature to 6 K. Both C_ij(T) and e_ij(T) of the two crystals monotonically increased as the temperature decreased. The Einstein temperature estimated from Varshni's equation revealed that e₁₅ and e₂₂ of LiNbO₃ have remarkably low values compared with the acoustic Debye temperature. In addition, the lattice anharmonicity of these piezoelectric coefficients was also extraordinarily low. An analysis based on the group theory and lattice dynamics revealed that both LiNbO₃ and LiTaO₃ crystals have three types of internal displacement modes: A₁, A₂, and E, and only the E mode affects e₁₅ and e₂₂. Therefore, it is reasonable to suppose that the E mode internal displacement is responsible for the unusual behaviors of the tow piezoelectric coefficients.

We have developed a theory that determines a complete set of stress field, σ_ij, in a freely vibrating two-dimensional isotropic medium within the framework of the calculus of variation. Our formulation is based on the Airy stress function φ and the minimization of the complementary strain energy under the constrain condition || φ|| ²_L²=const. By the Ritz method, the constrained variational problem becomes a linear eigenvalue problem. Numerical analysis yields 36 types of the stress functions φ_i. Unlike the stress fields determined from the conventional resonant ultrasound spectroscopy theory, the stress fields derived from the stress functions φ_i explicitly satisfy the stress-free natural boundary condition and the equilibrium equation. It is also confirmed that the 36 resonant modes can be classified into four groups according to the parity of the coefficient of the basis function. Furthermore, the stress functions φ_i are orthogonal in the sense of the L² inner product. These features are similar to those of the conventional resonant ultrasound spectroscopy (RUS) theory.

A numerical study of switchable frequency band gaps in two-dimensional phononic crystal (PnC) slabs consisting of piezoelectric inclusions in an isotropic matrix is presented. Instead of changing the geometry or orientation of the PnC units or inclusions, electrical boundary conditions are used to actively control the frequency band gaps. The electrical open and short boundary conditions are considered in this paper. With different electrical boundary conditions imposed on the surfaces of the piezoelectric inclusions, the dispersion relations can be modulated and the band gaps can be switched. The validity of switchable transmission and the dependence of its characteristics on the incident slab wave modes and electrical boundary conditions are investigated as well. Using the switchable frequency gaps, switchable linear PnC slab waveguides, which show the confined propagation of slab waves, are demonstrated. As a result, the confined wave energy flows can be switched on/off by changing the imposed electrical boundary conditions. The methodology presented here enables designing PnC structures of active controlled transmission, guiding, switching, and emission for slab waves.

We demonstrate the performance of a newly developed viscosity measurement system, especially designed for liquid samples with low viscosities. The electromagnetically spinning (EMS) viscometer operated with a floating disk rotor enables the determination of viscosity with 1% accuracy for dilute aqueous solutions of various materials. In the article, we report the concentration dependence of the viscosity of a water/ethanol mixture. Accuracy required for a viscometer from the viewpoint of ultrasonic spectroscopy is also discussed.

Optical switching of high-bit-rate pulse trains using collinear acoustooptic (AO) devices is theoretically discussed. Since the collinear AO devices have wavelength selectivity, the switched optical pulse trains suffer from distortion when the bandwidth of the pulse train is comparable to the pass bandwidth of the AO device. As the AO device, a sidelobe-suppressed device with a tapered surface-acoustic-wave (SAW) waveguide and a Butterworth-type filter device with a lossy SAW directional coupler are considered. Distortion of optical pulse trains at 40 to 100 Gbps is numerically analyzed. Although filtering characteristics of collinear AO devices for continuous wave or narrow-bandwidth signals have been reported so far, distortion of short pulse trains having wide bandwidth is clarified for the first time.

By using a sequential evaporation method, Cu(In,Ga)Se₂ (CIGS) thin films with a high Ga/(Ga+In) mole ratio were fabricated on Mo/soda-lime glass substrates. The bandgap energy (E_g) estimated by the photoreflectance (PR) and piezoelectric photothermal (PPT) methods shifted to the higher photon energy side with increasing Ga/(Ga+In) mole ratio. Although PR signals could not be observed, the PPT method could determine E_g even for high Ga/(Ga+In) mole ratio samples. A broad photoluminescence peak originating from band-to-band or impurity level was also observed for all samples. The present experimental results imply that the Ga/(Ga+In) mole ratio of CIGS thin films can easily be controlled by a sequential evaporation method, and that the PPT method is a powerful method for determining the E_g of low crystallinity samples.

We developed a stable picosecond-ultrasound-spectroscopy system with a fiber-laser light source. A linearly polarized light pulse with 532 nm wavelength is split into pump and probe light pulses using a polarized beam splitter (PBS). The ultrahigh-frequency acoustic waves excited by the pump light pulse are successfully detected using the delayed probe light pulse with a signal-to-noise ratio higher than that of the traditional titanium–sapphire pulse laser. The wavelength used allows deep inspection of silicon because of less light absorption. The developed system is also applied to a biosensor with an ultrathin Pt film resonator, which shows significantly improved stability at 100 GHz. The amount of frequency change caused by the adsorption of target molecules is of the order of 10^-2, which is much higher than that detected with conventional oscillator biosensors by a factor of 10⁴.

We measured the longitudinal-wave velocity and its attenuation in SrTiO₃ between 20 and 300 K using picosecond ultrasound spectroscopy. From the temperature dependence of the velocity and attenuation, we monitored the cubic–tetragonal phase transition of SrTiO₃ near 100 K, whereas no more transitions were indicated below 100 K. From the measured attenuation coefficients, we estimate the relaxation time τ. Because of the ultrahigh frequency measurements, the product ωτ is larger than unity, where the traditional theory for phonon–phonon interaction fails to explain the relaxation time. We then derived the relationship between the relaxation time and attenuation for ωτ>1.

We improved the apparatus for measuring frequency-dependent complex strain-optical coefficient using ultrasonically induced depolarized light diffraction. Measurements were performed at frequencies from 5 to 75 MHz. The upper frequency limit is three times larger than that obtained in our previous study. We also measured shear relaxation spectra at frequencies from 5 to 205 MHz and compared the results with strain-optical coefficients of 4-cyano-4'-pentylbiphenyl (5CB). The resulting spectra suggest that 5CB has second a relaxation at a high frequency, which has not been observed by heterodyne dynamic light scattering.

Accuracy in measuring surface temperature distributions by a laser ultrasonic method is examined. Surface temperature distributions of an aluminum plate whose single side is heated up to 110 °C are estimated by the inverse analysis coupled with surface acoustic wave (SAW) measurements, and the results are compared with those measured by an infrared radiation method. A random fluctuation in the temperature estimated by the ultrasonic method is observed and decreases with an increase in the distance from the heating area. The standard deviation in fluctuation is estimated to be about 2 °C at the heating area. Furthermore, the systematic errors in the temperature estimation due to the deviations in the temperature dependence of SAW velocity and thermal diffusivity are investigated. It is found that the temperature dependence of SAW is an important factor affecting the systematic error, but the influence of the deviation in thermal diffusivity is negligible.

The perfectly matched layer (PML) is introduced into the wave equation finite difference time domain (WE-FDTD) method. The WE-FDTD method is a finite difference method in which the wave equation is directly discretized on the basis of the central differences. The required memory of the WE-FDTD method is less than that of the standard FDTD method because no particle velocity is stored in the memory. In this study, the WE-FDTD method is first combined with the standard FDTD method. Then, Berenger's PML is combined with the WE-FDTD method. Some numerical demonstrations are given for the two- and three-dimensional sound fields.

An evaluation method of the hydrophone spatial averaging effect in near field measurement using numerically calculated ultrasonic fields for determining the mechanical index related to diagnostic ultrasound is proposed. To demonstrate that the accurate evaluation can be achieved using the method, it is investigated whether a difference between acoustic pressures of an ultrasonic field radiated from a plane circular transducer measured by hydrophones with two different active element sizes is reduced by the correction using the evaluation. The results confirmed that the proposed method is available for evaluating the effect quantitatively.

A staggered grid for velocity–stress formulation is presented for modeling elastic waves in anisotropic solids by the finite-difference time domain method. To simply impose boundary conditions on numerical models, our grid is derived by applying a finite integration technique to a single control volume satisfying Newton's law instead of interleaved control volumes for conventional staggered grids. Computed results for the numerical dispersions of the new grid for propagating vertically polarized shear and longitudinal waves in an isotropic solid show that the numerical dispersions of the new grid can be suppressed to the same levels as those of the conventional staggered grids by using a third-degree bi-polynomial interpolation.

The transport properties of bulk and guided acoustic waves travelling in a lead zirconate titanate (PZT) disc, originally manufactured to serve as ultrasonic transducer, have been monitored by scanned Coulomb coupling. The images are recorded by excitation and detection of ultrasound with local electric field probes via piezoelectric coupling. A narrow pulse has been used for excitation. Broadband coupling is achieved since neither mechanical nor electrical resonances are involved. The velocities of the traveling acoustic waves determined from the images are compared with characteristic velocities calculated from material properties listed by the manufacturer of the PZT plate.

Detections of second-harmonic components generated from fatigue-tested plates using finite amplitude Lamb waves were carried out using a double-layered piezoelectric transducer (DLPT) with a pulse-echo method. Three pure magnesium (Mg) plates subjected to fatigue tests of 0, 1×10⁵, and 2×10⁵ cycles were used in this experiment. In a received waveform from the plate subjected to the fatigue test of 2×10⁵ cycles, a second-harmonic component was increased by 10 dB compared with that in the case of an unstressed plate. The usefulness of the DLPT system for detecting second-harmonic components of Lamb waves in the pulse-echo method was confirmed.

We report the results of an experiment on measuring the viscosities and densities of several liquids using a single piezoelectric sensor, since only the numerical results obtained by finite element analysis were reported in our previous paper. The novelty of the sensor is that the viscosity and density can be inferred simply by measuring resonance frequencies in liquid for the vibration in the tangential and normal directions with respect to the contact surface between the sensor and the liquid, while the method suggested as reference requires measurements of resonance frequency and damping of a single vibration mode. By comparing the viscosities and densities measured by the proposed and conventional methods using food oil, the densities were found to correspond to the values measured using a weight meter with an error within 1% and the viscosity was evaluated to be higher than that measured using a viscometer with an error within 10%. The results suggest the possibility of measuring liquid density and viscosity by the proposed method.

In this paper, a hygrometer operated by acoustic means is proposed. It is important to measure spatial average humidity for environmental management in a room. In a large space, it is difficult to determine spatial average humidity because conventional sensors measure only local humidity at the measurement point. The proposed acoustic hygrometer utilizes the relationship between the sound attenuation coefficient and humidity. To measure the sound attenuation coefficient, reverberation time in a room is utilized. An acoustic hygrometer based on reverberation time achieves a noncontact measurement of spatial average humidity. As a practical examination, relative humidity (RH) was measured on the basis of reverberation time in a chamber, and compared with reference values. The humidity measurement accuracy of the hygrometer was evaluated by statistical means because the measured reverberation time showed variability. From the results, the possibility of humidity measurement with an accuracy of about 5% RH at 50% RH or more using this hygrometer was verified. Here, the unit of RH is % RH.

Microphone arrays have been used for estimating the direction of arrival (DOA). Owing to intercorrelation among direct and reflected sounds, there are difficulties in estimating DOA using microphone array in highly reverberant environments. The purpose of this research is to estimate the correct DOA in such environments using a small number of microphones with the aid of signal processing. The proposed signal processing uses the relationship that direct signals always arrive earlier than reflected signals. By comparing the delayed-sum signals corresponding to candidate direct signals, the DOA of direct sounds could be determined correctly. We have confirmed the usefulness of the proposed method by conducting several experiments. This proposed method is different from conventional methods because it has high tolerance to the effect of reverberation; it not only enables estimation of DOA but can also be applied to the measurement of the delay of time of flight in reverberant environments.

An ultrasonic tissue mimicking phantom is a useful tool for the performance testing and calibration of ultrasonic medical devices. However, it is hard to estimate the thermal distribution caused by the ultrasound in the human body using a conventional phantom. In this study, a tissue mimicking phantom to visualize the thermal distribution was developed by using thermochromic particles. The acoustic characteristics of the phantom were investigated according to the ingredient ratio of the phantom. Changing the ingredient ratio, the acoustic characteristics of the phantom can be adjusted to those of human tissue.

The residual particle distribution in pure water could be a problem in the nanoscience fields because nanoparticles are usually suspended in pure water such as deionized or distilled water. The effect of ultrasound on the residual particle distribution in pure water should be analyzed because the nano particles used in nanoscience are usually dispersed using ultrasound power. In this study, using a cylindrical piezoelectric vibrator, a noncontact-type focusing ultrasound system was fabricated to keep the purity of the water. The residual particle distribution in pure water was investigated. The number of residual particles increased as the ultrasound exposure time increased.

Although in previous studies were examined the ultrasonic reflection behaviors at a nano-air gap using a relatively small optical Newton's ring specimen and a commercial acoustic lens, the details of the quantitative ultrasonic behaviors at a nano-air gap have remained unqualified until now. Since the accuracy of estimating these behaviors is directly related to the accuracy of industrial ultrasonic crack sizing, we tried to measure more accurately quantitative ultrasonic behaviors at a nano-air gap in this study. For this purpose, a special highly focused acoustic lens was designed and fabricated and applied to a large optical Newton's ring specimen to obtain accurate and reliable experimental results. Comparisons between the experimental and the conventional small gap theoretical results for a nano-air gap were also carried out. As a result, ultrasonic transmission was found to begin to occur from 60–70 nm air gaps in all the measurements. This finding was largely different from that based on the gap theory. Regarding the cause of this large difference between the experimental and theoretical results, we also examined the influence of the surface roughness of contact plates.

Conventional ultrasonic flowmeters have a problem in measuring the small open channel fluid flow. To solve this problem, a lateral observation technique using a single transmitter/receiver transducer attached at the bottom of the pipe was proposed. Pulse echo signals scattered from the particles in the medium were repetitively recorded with a constant time interval. From the slope of the correlation peak amplitude with the variation in pulse echo excitation time, the flow speed of the medium was estimated. The method has an advantage in that the variation in flow speed in the vertical depth direction is directly measured with a minimum measurement space. Moreover, the fluctuations caused by the turbulent water can be avoided compared with the case of a conventional method based on the time estimation method. Bubbles were generated by an aspirator and flour powder was mixed with water as scatterers in the imitated drainage water. The flow speed of water was measured with respect to the inflowing fluid volume. Moreover, vertical flow speed profiles were measured and compared with fluid flow simulation results. The results showed that the precision of the measured flow speed was satisfactory and tolerant against the turbulence of the water flow medium.

A finite-difference time-domain technique for nonlinear elastic media is proposed, which can be applied to analyze finite amplitude elastic waves in solids. The kinematic and the material nonlinearities are considered, employing a general expression for the strain energy of an isotropic solid containing the second- and third-order terms of the strain components. The accuracy of the proposed technique is demonstrated by comparison with the analytical solution for the plane longitudinal wave propagation with finite amplitude. Two-dimensional simulations are performed to demonstrate the effectiveness of this formulation for Lamb waves. First, numerical simulations without the nonlinear effects are carried out, and the spectral peaks obtained from the calculated waveforms are shown to agree well with the theoretical dispersion curves of Lamb waves. As an example with the nonlinear effects, the harmonic generation in Lamb wave propagation is also demonstrated. The results show that the growth of the second-harmonic mode occurs for an incident-wave frequency selected in accordance with the analytical phase matching condition.

Closed stress corrosion cracks (SCCs) have been generated in Ni-based alloy weld metal in nuclear power plants. The ultrasonic inspection is difficult because of the crack closure. For the application of new inspection methods and training/educating of inspection engineers, realistic closed SCC specimens are required. However, there is no means for forming such SCC specimens in a reasonable amount of time. Here, we present a two-step method. The first step is to form an open SCC in chemical solution. The second step is to close the SCC by generating oxide films between the crack faces in high-temperature pressurized water (HTPW). To verify the crack closure, we used a closed-crack imaging apparatus, the subharmonic phased array for crack evaluation (SPACE). Consequently, we found that parts of the SCC after 1321 h immersion were closed in the HTPW. Thus, we verified the two-step method for forming realistic closed SCC specimens in a reasonable amount of time.

A new measurement system for detecting microcrack tips was investigated for the nondestructive evaluation of thin plates. In this system, we combined two different techniques. One technique is the use of a low-power pulsed laser to induce ultrasonic pulse waves, which are generated by the thermoelastic effect. The other technique is the vibration of samples using a symmetric mode Lamb wave at low frequencies, which causes the fluctuation of crack tips. Taking account of the Lamb wave propagation in the plate sample, laser-induced waves were excited to pass through plane cracks under two different fluctuation conditions (compression and extension). The characteristic difference between the frequency spectra of these waves gave us information on fluctuating cracks. Using an acrylic sample, we confirmed that the difference in phase could be used for the detection of crack tips.

We have proposed an ultrasonic computerized tomography method using the time-of-flight (TOF) of a longitudinal wave as a defect detection method for a steel billet. However, it took a long time to measure the TOFs because the transmissions were made one by one from the requirement of independent signal transmission. In this study, to speed up the TOF measurement, we proposed a simultaneous measurement method of TOFs using the phase-modulated signals by Gold sequences, and evaluated the ability of simultaneous measurement by an experiment. The reflected wave from the billet surface had a very adverse effect on the measurement of TOF, so a short signal was required as the transmitted signal. To make the transmitted signal short, a half-sine pulse phase-modulated by a Gold sequence was employed. As a result, five simultaneous transmissions were possible to be used for the inspection of the billet. When five simultaneous transmissions are made, the total measurement time can be decreased to 1/5 of the previous one.

Subharmonic waves realize a high selectivity for closed cracks. However, when a short-burst wave is used to achieve a high temporal resolution, not only closed cracks but also linear scatterers appear in the subharmonic image owing to leakage in frequency filtering. They are ghosts that degrade the selectivity for closed crack in the subharmonic image. Here, we propose an amplitude difference phased array (ADPA), where the ghosts are eliminated by subtracting a subharmonic image at a small input multiplied by the input amplitude ratio from that at a large input. We verified the ADPA method by a two-dimensional simulation based on the finite difference time domain (FDTD) method with damped double nodes (DDNs) for subharmonic imaging of closed cracks. Furthermore, the ADPA method was experimentally verified in a closed-crack specimen.

High-density perovskite titanate zirconate-modified potassium niobate solid solutions 0.92(Na_0.5K_0.5)NbO₃–xBaZrO₃–(0.08-x)(Bi_0.5K_0.5)TiO₃ (BBK) and Mn-added BBK have been prepared by the solid-state reaction method. The phase diagram summarized from the dielectric measurement reveals that there exists a tetragonal–rhombohedral morphotropic phase boundary (MPB) for both solid solutions. The piezoelectric properties show enhanced behavior at around the tetragonal–rhombohedral MPB. Mn addition could increase Q_m as well as k_p and d₃₃. The behavior is attributed to oxygen vacancy formation and grain size growth, respectively.

In the underwater imaging field, the control of the focal length of a transducer is very useful. As one of the control methods, we suggested an ultrasonic array transducer with adjustable curvature by using air pressure. The curvature of the transducer was investigated according to the air pressure level in the back space of the transducer. Concave-, planar-, and convex-type transducers were obtained with different air pressure levels. The acoustic fields of the transducer were measured for different shapes of the radiation surface.

Conventional annular array transducers designed with Fresnel divided elements have a limited maximum size of the aperture of the transducer. In this study, we designed and fabricated a prototype of a large-aperture annular array transducer to inspect next-generation semiconductors. A new annular array pattern was designed with a wide focal range and a large focal length using equal areas for the inner elements and equal stroke widths for the outer elements. The prototype was fabricated by epoxy bonding with a patterned metal electrode on a flexible printed circuit and a piezoelectric copolymer. As a result of evaluation, we obtained a fine spatial resolution below 100 µm and a narrow relative sensitivity variation of 6.5 dB for a large focal length and a wide focal range from 10 to 30 mm.

The authors have presented a new sensing device that employs a piezoelectric thickness vibrator operating in a trapped-energy mode for detecting slight variation in liquid level. To simulate its sensor operation, the device should be expressed by an equivalent electric network. In this study, the sensor is modeled by modifying an equivalent electric network representing the propagation of a thickness-vibration mode along the piezoelectric plate, and thereby its operation is simulated. The variation in G with the liquid level has been computed using this network model, and the feasibility of the model is confirmed.

The characteristics of the coupled bending vibrator that linearly connects the two bending vibrators are analyzed by the finite-element method, and then the characteristics of the coupled bending vibrator used as a force sensor are investigated. The coupled bending vibrator is applied to an acceleration sensor as a force sensor. The vibration mode in which the two vibrators of the coupled vibrator are out of phase is used here and is very stable because it does not couple with other vibration modes. When the axial force is applied, the amplitude of one vibrator of the coupled vibrator decreases with increase in compressive force. The amplitude of the other vibrator also decreases when the force is applied in the opposite direction. Therefore, the coupled vibrator is used as a force sensor that can estimate the axial force as a change in the amplitude of the vibrator.

The characteristics of a frequency-change-type two-axis acceleration sensor must be improved on the point that an undesirable signal from the other axis direction is detected. The signal is caused by the rotation of mass in the sensor. Two methods for improving the characteristics are proposed here and investigated by finite-element analysis. First, the center of gravity in the sensor was moved to realize a linear motion of mass. As a result, the signal became very small from 5.1 to 0.4%, but the volume of the sensor increased by 28%. Next, the other method of adjusting the dimensions of a bent-type support bar was proposed to realize a linear motion of mass. The rotation was not observed when the signal was decreased to almost zero. The method is very useful from the standpoint of realizing the same volume as the sensor of the prototype.

A gyroscope using two pairs of degenerate modes for wide-range sensing is proposed. We focused on a coaxial resonator composed of a cylinder and a column. To evaluate the characteristics of the proposed gyroscope, we analyzed its frequency response and rotational response both experimentally and numerically. From the frequency response under rotation, there was a difference between the shifts of resonance frequencies of two detecting modes. We also found that the lower-frequency mode had higher sensitivity and the higher-frequency mode had a wider linear region from the rotation response of each mode. These results suggest that high sensitivity for low-speed rotation and a wide linear region for high-speed sensing can be attained simultaneously by a single resonator with the help of two different pairs of degenerate modes.

Wideband ultrasonic transducers are required for acoustic imaging and nondestructive evaluation. In this study, we have fabricated transducer consisting of c-axis tilted ZnO/c-axis normal ZnO multilayer on the Au(111)/Ti/silica glass substrate. We have investigated the crystalline orientations and frequency characteristics of the multilayer transducer. An X-ray diffraction analysis and a scanning electron microscopy analysis of the transducer revealed that the c-axis normal ZnO layer was grown on the Au(111) layer during the initial stage of ZnO layer deposition. As ZnO grain growth proceeded, c-axis normal growth change to the c-axis tilted ZnO layer growth. This multilayer transducer excited second-overtone modes of longitudinal and shear waves as well as the fundamental mode in the UHF range. Therefore, the frequency bandwidth of the multilayer transducer was broader than that of a single layer transducer consisting of a c-axis tilted ZnO layer.

We developed a coaxial-type fixture for precisely measurement of the impedance characteristics of small surface-mounted quartz crystal units. This fixture is applicable to the one-port S-parameter reflection method proposed in IEC60444-5, and measures the frequency impedance characteristics of a device under test (DUT) from its reflection coefficients. This measurement fixture uses a 65 GHz coaxial connector and calibrators with a 1.85 mm inside diameter. Using a "zero-length" coaxial center pin method, this fixture can be applied to up to 2 GHz devices without the need for electrical length compensation.

We present contour-mode AlN resonator structure and fabrication process for high quality factor (Q-factor). The vibrational energy should be confined to the resonant part of the radial extensional (RE) resonator in order to obtain a high Q-factor and high coupling factor (k²) from devices made using micro electro mechanical systems (MEMS) technology. In this paper, we discuss how to form a support for the resonant part in a high-precision process. We fabricated simple RE resonators and clarified through experimentation that it is difficult to avoid deterioration of the Q-factor because the RE vibration energy leaks from the resonant part into the silicon substrate through the supporting points. Next, we fabricated tuning-fork RE resonators by using the three-etching-process method and clarified through experimentation that this method is useful for forming the resonant part into the correct circular shape and avoiding energy leakage.

We examined the suppression of spurious responses beneath the resonant frequency in an aluminum-nitride-based thin-film bulk acoustic resonator (FBAR) by a two-dimensional (2D) finite element method (FEM) and dispersion analysis of waves. The results confirmed that the 0th-order asymmetric mode (A₀ mode) influences the resonance characteristics. As a result of these findings, we propose a structure having a thin ring on the electrode edge to take advantage of this A₀ mode in suppressing spurious responses.

Polarization control of the optical guided wave in a new configuration using a reverse-proton-exchanged (RPE) LiNbO₃ straight waveguide and a leaky surface acoustic wave (LSAW) which propagates perpendicular to the straight waveguide was proposed. First, the perturbation of the dielectric tensor was estimated by using coupled mode theory. When a Love-type SAW on a proton-exchanged layer/YX-LiNbO₃ was assumed, comparable perturbations to those in conventional Bragg diffraction due to a Rayleigh wave were confirmed. Next, a sample device with an LSAW wavelength Λ of 136 µm was fabricated on YX-LiNbO₃ using an RPE channel waveguide. It was found that the incident linearly polarized wave was rotated by -90° in addition to the inherent rotation due to the perturbation of the LSAW without adding the LSAW wavenumber vector to the propagation constant of the incident optical guided mode. The maximum conversion efficiencies for optical wavelengths of 633, 532, and 473 nm were 87, 43, and 40%, respectively. The measured response time of 280 ns was almost equivalent to the time required for the propagation of the LSAW through the interdigital transducer width.

In this paper, we describe a new boundary acoustic wave structure employing multilayered metal electrodes with a high-density metal and a low-density metal. By using this structure, such as Pt/Al/Pt, the electromechanical coupling coefficient (k²) and temperature coefficient of frequency (TCF) of the boundary acoustic wave can be changed. We theoretically studied the dependence of the energy distribution of the boundary wave on the position of the total electrode gravity center when the electrode layer structure is changed. It was experimentally confirmed that k² and TCF can be changed simultaneously. By using this structure, we developed a novel filter with good electrical characteristics, and a very small variation of the filter characteristic with temperature (almost zero TCF) was successfully realized.

The authors reported band-pass (BP)-type tunable filters composed of ultrawide band (17%) surface acoustic wave (SAW) resonators composed of grooved Cu electrodes on 4°YX-LiNbO₃ and interdigital capacitors (IDCs) on the same LiNbO₃ substrate. However, the frequency of the tunable filter did not shift continuously because the capacitance of the IDCs was fixed. This time, the tunable filter with the frequency tunable range of 6.1% shifting continuously was obtained for the first time by applying voltage to the variable capacitance diode. The authors discuss the mechanical quality factor (Q) of variable capacitors and characteristics of the tunable filters.

In this paper, we describe a suppression technique of transverse-mode spurious responses for a surface acoustic wave (SAW) resonator with a near zero temperature coefficient of frequency (TCF) on a SiO₂/Al/LiNbO₃ structure. We investigated the thinning of SiO₂ on the dummy electrode region and studied how the transverse-mode responses change with remaining SiO₂ thickness h on the dummy electrode region. As the results, we clarified that the remaining SiO₂ thickness h on the dummy electrode region has an optimum value and could suppress the transverse-mode spurious responses completely when H and h are set at 0.35 λ and 0.20 λ, respectively. It was demonstrated that the selective SiO₂ removal technique is effective to suppress transverse-mode spurious responses for SAW resonators employing the SiO₂/Al/LiNbO₃ structure for a wide range of SiO₂ thicknesses, provided that the SiO₂ thickness at the dummy electrode region is adjusted properly.

This study provides the relationship between cut angles of the rotated Y–X LiTaO₃ (LT) substrate and characteristics of surface acoustic wave (SAW) resonators with shape-controlled SiO₂ in the SiO₂/Al/LT system. The 32–48° Y-cut of LT is well known as the leaky-SAW (LSAW) cut of LT. The propagation characteristics of an LSAW are affected by the surface condition of the substrate, and the optimum cut of LT should be determined with respect to such condition. In this study, we investigated the dependence of SAW resonator characteristics on the shape of SiO₂ and on the cut angle of LT by simulation and experiment. The dependence of the reflection coefficient and coupling factor on the shape of SiO₂ is not changed by the cut angle of LT, but the dependence of the quality factor (Q-factor) on the shape of SiO₂ is changed by the cut angle of LT. Additionally, the dependence of the Q-factor on the cut angle at resonance frequency was different from that at antiresonance frequency. It was shown that LT with the rotation angle of 39–42° gives the optimal balance in this system.

The longitudinal-type leaky surface acoustic wave (LLSAW) is one of the SAW modes that is advantageous for application to high-frequency SAW devices. However, the LLSAW has huge inherent attenuation. In this study, to reduce the attenuation of the LLSAW, we proposed a layered structure of air, a bulk LiNbO₃ (LN) layer, and an elastically softened LN substrate. When the layered structure was applied to X–36°Y LN with a large coupling factor K² for the LLSAW, the calculated attenuation for the metallized surface decreased at a certain depth of the bulk layer. To realize such a layered structure, a reverse proton exchange (RPE) process was applied to X–36°Y LN, and the propagation and resonance properties of the LLSAW were evaluated. A "good region" existed on the RPE wafer, in which the value of K² for the Rayleigh wave was recovered to approximately 80% of that of the virgin wafer. In comparison with the virgin wafer, the propagation loss for the free surface of the good region on the RPE wafer was decreased threefold, the insertion loss was decreased drastically, and the resonance properties were improved markedly.

A supercritical fluid is a fluid at a temperature and pressure above its critical point. Supercritical CO₂ functions as a moderate solvent, has zero surface tension, and has high permeability in fine structures. These properties are regarded as ideal for the processing of nano- and microscale substances. A problem of applying supercritical fluids is fluctuations in their density. By utilizing a surface acoustic wave (SAW), it may be possible to realize a sensor for measuring the density fluctuation. In this study, the resonance property of a shear-horizontal-type SAW resonator fabricated on a 36° Y–X LiTaO₃ substrate and the impedance of an interdigitated electrode (IDE) fabricated on a nonpiezoelectric substrate were measured in high-pressure CO₂. Abrupt changes in the resonance property owing to discontinuous changes in the density and viscosity were observed at a certain CO₂ pressure between gas and liquid phases. The impedance change of the IDE owing to discontinuous changes in the permittivity was also observed.

A liquid-phase sensor is realized that uses a shear horizontal surface acoustic wave (SH-SAW) device. The advantage of using an SH-SAW sensor is the simultaneous detection of liquid properties, such as density, viscosity, permittivity, and conductivity. In this study, the SH-SAW sensor is applied as a methanol (MeOH) sensor for a direct methanol fuel cell (DMFC). As the generation efficiency of the DMFC depends on the methanol concentration, the monitoring of MeOH concentration is needed. The SH-SAW sensor is applied to the MeOH sensor to measure the electrical properties. The efficiency of the DMFC is also influenced by materials contained in the fluid. If a component of the SH-SAW sensor is eluted into the fuel, the SH-SAW sensor cannot be used in the DMFC. The SH-SAW sensor was dipped into the fuel at 80 °C and it was found that the concentration of eluted components from the SH-SAW sensor was low and that the efficiency was not influenced by such components. Then, the temperature characteristics of the SH-SAW sensor with various MeOH solutions were measured. The maximum operating temperature of the DMFC is 80 °C and the minimum temperature depends on the place of installation. In this work, the minimum temperature is assumed to be -5 °C. Thus, the SH-SAW sensor must measure the MeOH concentration from -5 to 80 °C without malfunction. The results indicate that the MeOH concentration can be measured when the temperature is lower than 60 °C. If the temperature is higher than 60 °C, bubbles are generated on the sensor surface and the sensor is influenced by them. A liquid flow system was demonstrated to reduce the influence of bubbles.

Direct methanol fuel cells (DMFCs) offer promising future power sources. Operating DMFCs at ideal conditions, fuel concentration management is required, and therefore, devices for methanol concentration measurement are considered important to DMFC systems. Shear-horizontal surface acoustic wave (SH-SAW)-based methanol concentration sensors can be used as DMFCs offering advantages such as miniature size, mass-production ability, and reliability. The objective of this study was to develop and evaluate an easy to install SH-SAW sensor in a wide variety of DMFC systems. In this paper, we describe the detailed structure and measurement characteristics of the developed sensor system. The evaluations were focused on the linearity and response to methanol concentration change. Through the evaluations, theoretically predicted response linearity to the methanol concentration change was confirmed on the developed sensor. It was found that the response speed of the sensor was so quick that even a transient phenomenon of methanol spreading into water could be detected. These measurement abilities will be useful for accurate fuel control of DMFC systems, and should be able to extend the application range of SH-SAW sensors.

A shear horizontal type of surface acoustic wave (SAW) magnetic sensor composed of a magnetostrictive Ni electrode and an ST-cut 90°X quartz substrate was fabricated. In this study, in order to obtain a higher magnetic sensitivity, one-port SAW resonators composed of three kinds of Ni electrode structures on the ST-cut 90°X quartz, namely, (a) grooved Ni electrodes, (b) additional overlaid Ni films on grooved Ni electrodes, and (c) Ni electrodes on the quartz, were fabricated and measured. In addition to these, a SAW resonator composed of a magnetostrictive TbFe₂ film electrode, which has a larger magnetostrictivity than the Ni film, on the ST-cut 90°X quartz was also fabricated. Their characteristics are examined.

Although portable gas chromatographs (GCs) have been developed for the monitoring of volatile organic compounds (VOCs) in working environments, they still need high power consumption for the heating column. Thus, we previously developed a portable surface acoustic wave (SAW) GC equipped with a ball SAW sensor and a micro-electromechanical-system column (ball SAW GC) and proved the usefulness of the forward flush (FF) method for realizing the fast analysis of multiple gases without a heater. However, its ability to measure ten kinds of VOCs at ppm order and automatic continuous measurement were not demonstrated. In this study, a ball SAW GC employing the FF method and equipped with a gas sampler for continuous injection was developed. Then, the performance of monitoring multiple gases in working environments was verified by measuring ten kinds of VOCs with maximum acceptable concentrations. Moreover, real-time monitoring of seven kinds of VOCs with a linear change in the response value to concentration changes was demonstrated.

We developed a highly sensitive strain sensor employing a surface acoustic wave (SAW) resonator for a wireless sensing system. The aim of this study is to monitor the distribution of the strain in the earth crust or giant infrastructures, such as bridges, skyscrapers and power plants, for disaster prevention. A SAW strain sensor was fabricated using LiNbO₃ and a quartz substrate, and applied in a tensile test by attaching the steel specimen based on Japanese Industrial Standards (JIS Z2441-1). The results confirmed that the developed sensor could detect a strain of 10^-6 order with linearity.

In the field of environmental measurement and security, a portable gas chromatograph (GC) is required for the on-site analysis of multiple hazardous gases. Although the gas separation column has been downsized using micro-electro-mechanical-systems (MEMS) technology, an MEMS column made of silicon and glass still does not have sufficient robustness and a sufficiently low fabrication cost for a portable GC. In this study, we fabricated a robust and inexpensive high-precision metal MEMS column by combining diffusion-bonded etched stainless-steel plates with alignment evaluation using acoustic microscopy. The separation performance was evaluated using a desktop GC with a flame ionization detector and we achieved the high separation performance comparable to the best silicon MEMS column fabricated using a dynamic coating method. As an application, we fabricated a palm-size surface acoustic wave (SAW) GC combining this column with a ball SAW sensor and succeeded in separating and detecting a mixture of volatile organic compounds.

The fundamental and second harmonic components in a focused sound transmitting through a layer of an inhomogeneous medium with a nonuniform sound speed are analyzed. The nonlinear wave equation including the perturbation of the sound speed is solved with a successive approximation. The influence of the nonuniformity on the measurement of the acoustic nonlinearity parameter B/A in biological samples inserted in the focal region is also investigated. The axial sound-speed variation causes the relative uncertainty of the measured B/A to be the same as the rate of the sound speed within the sample. On the other hand, since the sound beam is refracted owing to the lateral variation of the sound speed, the second harmonic amplitude of the sound detected with the receiver noticeably decreases. Thus, the B/A is underestimated by half the rate of change of the sound speed within a lateral range equivalent to the sample thickness.

A nonlinearity parameter can be used for the estimation of the gas void fraction in gassy sediment. If two primary acoustic waves of different frequencies are incident on gassy sediment, nonlinear acoustic waves can be generated at the difference frequency. In the present study, the parametric acoustic array theory for the difference frequency wave was employed to estimate the nonlinearity parameters of gas-bubble-contained sands under laboratory conditions. The nonlinearity parameters of the sands were estimated between 10³ and 10⁴. Then, the estimated gas void fractions in the sands were between 10^-6 and 10^-4. They were similar to those estimated through the sound speed variation method. However, this linear acoustic method could not be applied to gas-bubble-contained sand with a low gas void fraction, because the sound speed variation was not observed in the sand. This study suggests that the nonlinear acoustic method seems very feasible to estimate the gas void fraction in gassy sediment with a low gas content.

We have been studying measurement techniques of acoustic cavitation using a cavitation sensor. Cavitation was investigated using broadband integrated voltage (BIV) calculated from broadband noise. In this study, the distribution of BIV in the vertical direction in a water vessel was measured with a novel cavitation sensor with improved spatial resolution. As a result, it was found that the pattern of standing wave acoustic field could be measured with the novel cavitation sensor. Also, the values of BIV measured in the vertical direction agreed well with sonochemical luminescence. The novel sensor has potential as a tool for accurate evaluation using acoustic cavitation in several fields.

A size distribution measurement method of the oscillating cavitation bubbles using the diffraction pattern of the bubbles has been studied by the authors. This method can measure the diameter distribution of the small oscillating bubbles. However, it has a disadvantage in that the measurement result of the method is disturbed by the acousto-optic effect. In this study, the influence of the acousto-optic effect on the measurement was experimentally investigated. As a result, it was found that the diffraction pattern tended to be disturbed along the direction of the ultrasound propagation. It was also recognized that the disturbance could be reduced using the diffraction pattern along the unsusceptible direction. Consequently, it was indicated that the diameter distribution of the oscillating bubbles was correctly measured using the diffraction pattern along the unsusceptible axis by comparison with the reference value measured by the stroboscopic imaging method.

Sonochemical reactions were demonstrated using a commercial ultrasonic atomizer at 2.4 MHz. The influences of experimental conditions, bottom shape and glass thickness of reactors, irradiation method, and liquid height on the sonochemical yield were discussed. The sonochemical effect was evaluated by potassium iodide dosimetry and degradation of methylene blue. Direct and indirect irradiations were examined. The former had the highest yield. In the latter case, sonochemical yield decreased in the solution because glass prevented the transmission of ultrasonic waves. Poly film, on the other hand, could transmit ultrasonic waves very well without damage.

In this work, we examined the influence of transducer structure on the mechanical and chemical effects of 20 kHz sonication, where the dissipated power measured by calorimetry was kept constant (5 W). The mechanical effects were evaluated from the degradation rate of poly(ethylene oxide) in aqueous solution, and the chemical effects were measured with potassium iodide solution. The mechanical effects for a bath-type apparatus with the transducers fixed at a node with a diameter of 50 mm are nearly equal to those for a horn-type apparatus. The former transducer showed the strongest chemical effects among the transducers investigated here.

The degradation of dichloroacetonitrile (DCAN) by means of the processes of sonolysis, ozonolysis and sonolytic ozonolysis was studied, and degradation rate constants were evaluated at various frequencies and power densities of ultrasound. The ultrasonic frequencies used were 35, 170, 283, 450, and 935 kHz. The power densities were in the range of 9.5 to 20 W/L. The degradation rate constants for the sonolytic ozonolysis were (3.1–4.4)×10^-3 min^-1 with the power density of 9.5 W/L and the ozone dose of 3.7 g/h. And the synergistic effect in sonolytic ozonolysis was significant at 35 and 283 kHz among the five frequencies. The sonolytic ozonolysis provided an extra oxidation mechanism by generating additional hydroxyl radicals, giving significant enhancement on the process. The calculated values of synergistic effect were 2.56 and 2.15 at 35 and 283 kHz, respectively.

1,4-Dioxane is regarded as a priority pollutant because it is hardly degraded by conventional methods of wastewater treatment. In this study, the degradation of 1,4-dioxane in water by the combined use of ultrasound and ozone microbubbles has been investigated. 1,4-Dioxane degradation by ultrasound and/or ozone followed a first-order reaction kinetics. The reaction constant for ozone microbubbles was higher than that for ozone millibubbles. The synergistic effect on reaction constant has been observed by the combined use of ultrasound and ozone microbubbles. The effect of hydroxyl radicals on reaction has also been investigated. Compared with the direct reactions of ultrasound and ozone, hydroxyl radicals play a major role in 1,4-dioxane degradation. The synergistic effect is enhanced with increasing ultrasonic input power and ozone concentration. Empirical equations of the relationships between ultrasonic input power, ozone concentration, and reaction rate constant have been established.

Few studies using high frequencies have been carried out on the sono-TiO₂ process, and consistent results based on the specific experimental conditions have not been reported thus far. Therefore, in the present work the effects of power density and dose on the kinetic constant of diethyl phthalate at 500 and 35 kHz using TiO₂ have been evaluated. The slopes of kinetic constants depending on the power density regardless of TiO₂ were increased and they were shown to be linear. However, the enhancement percentage according to the frequencies at 500 kHz was lower than that at 35 kHz, though clear discussions on the enhancement in the presence of TiO₂ have not yet been produced. Also, the optimal dose was 1 g/L, which was not changed according to the frequency.

The application of micelles as a drug carrier for chemical reaction processes was investigated from the viewpoint of process intensification. The effects of ultrasonic stimulation and thermal stimulation on the effluence of internal hydrophobic dye from Pluronic micelles were investigated by measuring the absorbance of sample solutions. Internal substances could be released from the micelle rapidly by ultrasonic irradiation, and the ultrasonic physical effect is important for the effluence of internal substances. The possibility of new chemical reaction process using Pluronic micelles as a reactant carrier is revealed.

This study investigated degradation of the hormone estriol by sonolysis, photolysis and sonophotolysis at various UV wavelengths. Degradation was determined with UVA (365 nm), UVC (254 nm), or VUV (185 nm) irradiation and/or ultrasound exposure (283 kHz). The pseudo-first order degradation rate constants were in the order of 10^-1 to 10^-4 min^-1 depending on the processes. The dominant reaction mechanism of estriol in sonolysis was estimated as hydroxyl radical reaction by the addition of tert-butanol (t-BuOH), which is a common hydroxyl radical scavenger. Photolytic and sonophotolytic estriol degradation rate also were high at shortest UV wavelength (VUV) due to the higher energy of photons, higher molar absorption coefficient of estriol and increased hydroxyl radical generation from the homolysis of water. Small synergistic effects were observed for sonophotolytic degradation with UVA and UVC irradiation. No synergy was observed for sonophotolysis with VUV irradiation.

The acceleration of water content reduction by vibrational energy was investigated with a series of laboratory tests. Vibration was generated with a poly(vinylidene fluoride) (PVDF) film as a flexible transducer at various frequencies. Test conditions included the power and duration of sonic energy, and the soil type. Test results showed a significant increase in dewaterability when ultrasound was applied. The time required for the outflow of the same amount of water was shorter for the sonicated conditions. The degree of enhancement varied with the test conditions. Using the test results, we discuss the potential development of a new method that can reduce the dewatering period.

In this study, the sonochemical oxidation of cyanide in the presence of peroxydisulfate (PDS) ions has been investigated. As a result of experiments, sulfate anion radicals (·SO₄^-) and hydroxide radicals (·OH) produced by PDS ions in acoustic cavitation could readily oxidize and even mineralize cyanide in an aqueous environment. When the frequency of ultrasound and PDS ions were applied at 450 kHz and 60 mg·L^-1, the efficiencies of mineralization for free cyanide (CN^-) and thiocyanate (SCN^-) were 99.3 and 99%, respectively. The kinetics of total organic carbon (TOC) reduction for CN^- and SCN^- oxidation were interpreted using the modified pseudo-first-order kinetic model. In this study, carbonate and nitrate were found to be by-products of CN^- oxidation while sulfate, carbonate and nitrate were by-products of SCN^- oxidation.

We investigated the effect of ultrasound irradiation at 200 kHz on As(III) and As(V) removal using jarosite. When the solution containing As(V) was irradiated in air, Ar, or O₂ atmospheres, As(V) removal rate increased with irradiation time as compared with treatment by stirring. Likewise, when the solution containing As(III) was sonicated in Ar or O₂ atmospheres, the As removal rate increased with irradiation time because As(III) was oxidized to As(V) by the sonication and As(V) was removed from the solution by the adsorption onto jarosite. However, in air, the removal rate increased only slightly with irradiation time. This is partly because As(III) removal was interfered by the adsorption of HNO₃, which was generated during sonication, onto jarosite. Therefore, As(V) removal by the simultaneous application of jarosite and ultrasound irradiation can be performed in air, Ar and O₂ atmospheres, while As(III) removal can be performed efficiently in either Ar or O₂ atmosphere.

This study aims to investigate the sonophotochemical oxidation of As(III) to As(V) using the synergistic effect of a strong oxidant that is a hydroxyl radical. The rate constant, k, in the ultrasound (US), ultraviolet C (UV-C), and US/UV-C processes was found to be 1.65×10^-4, 3.65×10^-4, and 8.31×10^-4 s^-1 respectively. The highest power densities were 21.26, in the case of UV-C, and 26.27 W L^-1 for US. Finally, the combined US/UV-C system gave a synergistic effect value of 1.57. This was similar to the synergistic effect value of the production of hydroxyl radicals with potassium iodide (KI) solution using the same combined process. Moreover, the reaction rate of the As(III) oxidation to As(V) in the US/UV-C process increased with a gradual increase in pH. The reaction rates were found to be 1.88×10^-3 at pH 11 and 8.31×10^-4 s^-1 at pH 7. Therefore, the reaction rate at pH 11 was 2.3 times faster than that at pH 7.

Thermoacoustic systems have several advantages owing to their simple structure driven by heat energy such as waste heat and solar heat. However, because their energy conversion efficiency is low, they have not been developed for practical use. Therefore, to improve energy conversion efficiency, a method of system design development is examined in this report using numerical calculations. First, calculation results obtained using the transfer-matrix methods are compared with experimentally obtained results, which confirms their good agreement. Secondly, calculated results of each heat flow element in the stack show that heat flow proportional to the temperature gradient Q_D, which decreases the performance of the system, is dominant. Finally, the installation position of the stack is changed to reduce the ratio that Q_D occupies in the heat flow. Results show a decrease in the ratio obtained by moving the stack installation position closer to the center of the tube. Energy conversion efficiency was increased eight times.

A standing-wave thermoacoustic prime mover and a traveling-wave one realize cooling systems of not having moving parts. The prime movers have a challenge of being miniaturized for a practical use. For the miniaturization, in contrast to lower energy conversion efficiency than the traveling-wave thermoacoustic prime mover, the standing-wave one has some advantages of its simple structure and no acoustic streaming. The efficiency depends on the amplification quantity of sound intensity in the stack. However, the intensity measurement in the stack is difficult. In this paper, for improving the efficiency of the standing-wave thermoacoustic prime mover, the amplification quantity of sound intensity in the stack is calculated and discussed especially with the acoustic impedance in the stack. Consequently, results show that the efficiency improves when the absolute value of the acoustic impedance is low in the stack.

Oil sands are attractive as an energy resource. Bitumen, which is found in oil sands, has high viscosity, so that it does not flow. Most oil sands are underground and are developed with a method called steam-assisted gravity drainage (SAGD). Hot steam is injected underground to fluidize bitumen and promote its recovery. However, the preheating time is too long. One way of reducing running costs is by shortening the preheating time. Previous studies have found that bitumen can be extracted from oil sands efficiently by applying ultrasonic irradiation, but SAGD was not applied directly in these cases. Thus, the purpose of this study is to apply ultrasonic irradiation to SAGD, thereby shortening the preheating time of oil sands. As a model experiment for SAGD, heat transfer experiments in a sand layer made with Toyoura sand and silicone oil were conducted and the thermal effect with ultrasound was investigated.

Recently, developments have improved methods employing aerial ultrasonic waves for detecting defects in solid materials such as metals, pipe walls, and fiber-reinforced plastics. These methods can be performed using a noncontacting aerial ultrasonic probe. In a previous study, we developed a new method using high-intensity aerial ultrasonic waves to successfully detect peeling, artificially created by inserting an air gap between tiles and concrete plates. In the present study, we use the same method to detect the depth and size of defects in a homogeneous medium.

Air pollutants can cause health problems, such as bronchitis and cancer, and are now recognized as a social problem. Hence, a method is proposed for the collection and removal of gaseous air pollutants by aerial ultrasonic waves and water mist. Typically, gas removal effects are studied using lemon oil vapor ("lemon gas"), which is a hydrophobic gas. Previous experiments using lemon gas have shown that a removal rate of up to 40% can be achieved in an intense standing wave at 20 kHz, for an amount of water mist of 1.39 cm³/s and an electrical input power of 50 W. Increasing the surface area of the water mist leads to greater removal of hydrophobic gas. In this study, the effects of gas removal are examined by conducting experiments using intense aerial ultrasonic waves to disperse two kinds of water mists, each composed of particles of different sizes: small particles (diameter: ≈3 µm) and conventional large particles (diameter: ≈60 µm).

The influence of air humidity and water particles on dust control was examined using ultrasonic atomization at 2.4 MHz, an acrylic box (61 L), and four types of ore dust samples: green tuff (4 µm), green tuff (6 µm), kaolin, and silica. It was clearly demonstrated that ultrasonic atomization was effective in raising humidity rapidly. However, at high relative air humidity, the water particles remained stable in the box without changing to water vapor. Ultrasonic atomization was applied to suppress dust dispersion and 40–95% dust reduction was achieved at 83% relative air humidity. Dust dispersion was more effective with ultrasonic atomization than without.

A new method using a polishing slurry together with ultrasonic longitudinal and torsional vibrations from a source with a diagonal slit vibration converter is developed for the hole machining of brittle materials. We predict that removal rate and machining accuracy will be improved using ultrasonic longitudinal–torsional vibration when compared with using conventional longitudinal vibration machining. In experiments, soda-lime glass is used as the processing material, and hole roundness error and machining time are measured to assess the hole machining characteristics. We find that machining accuracy is improved using ultrasonic longitudinal–torsional vibration.

To clarify the mechanism of an ultrasonically forced insertion (USFI), frictional stresses and displacements on the contact surface of a metal rod and a metal plate in the USFI process were analyzed by finite element method. Frictional stresses under two conditions were compared. One of the conditions was a horn and the metal rod moving with static displacement. The other was the horn and the metal rod moving with vibrational displacement. The amplitude and distribution of frictional stresses under the vibrational condition were small and almost flat, respectively. Axial and radial displacements of the plate and rod on the contact surface in a USFI process were also analyzed. As results, it was clarified that the USFI had the effect of reduction of frictional stress.

In this study, an ultrasonic motor for use at ultralow temperatures has been fabricated and evaluated. The motor has a bolt-clamped Langevin-type transducer using lead magnesium niobate–lead titanate (PMN–PT) single crystal. The transducer is proposed as an oscillator for use at ultralow temperatures by simulation of the thermal stress and evaluation of the pre-load. The thermal effect of the transducer was evaluated when the temperature was changed. As a result, the pre-load of the transducer was concluded to be affected by thermal stress. In addition, the ultrasonic motor using the transducer was fabricated and evaluated. By adjusting the contact pre-load between the rotor and the transducer, the motor has successfully rotated at an ultralow temperature. The rotation speed was 144 rpm at 4.4 K when the applied voltage was 150 V_p–p. This rotation speed is larger than that of previous same size actuators that can be used at ultralow temperatures.

The properties of miniature cantilever-type ultrasonic motors using lead-free array-type multilayer piezoelectric ceramics of (Sr,Ca)₂NaNb₅O₁₅ (SCNN) developed using the design rule were investigated under high input power by comparison with the high-power properties of SCNN ceramics. The frequency dependence of the revolution speed reflected the nonlinear behavior of SCNN ceramics with the hard-spring effect and showed a mirror-reversed image relative to that of the motor of Pb(Zr,Ti)O₃ (PZT) ceramics. The output power increased linearly with increasing input power up to 110 mW without heat generation, and the driving properties were almost the same as the expectations under low input power. The output power density characteristics of the motors were high in comparison with those of the commercialized motors of PZT ceramics. It appeared that the motors have a high potential as an environmental friendly piezoelectric device with excellent properties, reflecting the high-power properties of SCNN ceramics.

A medical ultrasound imaging technique with a high spatial resolution and a high signal-to-noise ratio (SNR) is strongly required for precise diagnosis. To obtain high-resolution images, tissue harmonic imaging (THI) can be effectively adopted because of its wide bandwidth characteristics compared with fundamental imaging. However, the amplitude of harmonic components is much smaller than that of a fundamental component. Additionally, frequency dependent attenuation is severe, especially for harmonic components. These phenomena mean that THI is susceptible to noise. From these considerations, in this study, we propose a method for improving the SNR of THI by reducing noise using a signal processing technique. The proposed method is constructed based on the Bayesian inference using fundamental components of echoes, and it can hold the high-resolution nature of THI. We show the effectiveness of the proposed method through simulations.

The authors have developed a multiple frequency imaging system using a multiple resonance transducer (MRT) consisting of 1–3 composite materials with a low mechanical quality factor Q bonded together. The MRT has a structure consisting of thin and thick piezoelectric plates, two matching layers, and a backing layer. This makes it possible to obtain B-mode images of satisfactory resolution using ultrasonic pulses owing to their short duration. In this paper, the vibration property of the MRT derived through equivalent-circuit analysis is first shown. By utilizing the result, an MRT capable of transmitting ultrasonic pulses for generation of the images of biological tissues with satisfactory resolution is designed and prototyped. Setting the prototype transducer in the mechanical sector probe of commercial ultrasonic diagnosis equipment, the speckle reduction effect is demonstrated using images of various phantoms to mimic biological tissues and a human thyroid.

Photoacoustics (PA) enables obtaining functional information like optics and depth information similarly to ultrasonics. The prospect of PA has already been discussed in previous studies, but there is a current demand for PA imaging that works as real-time imaging to acquire multispectral information in simultaneous irradiation with a high signal-to-noise ratio. We propose coded excitation using Gold codes that have good autocorrelation and cross-correlation properties to satisfy this demand. In this study, we also demonstrate the feasibility through simulations of RF signals and linear scanning B-mode imaging, and conduct an experiment to determine the feasibility of Gold codes for PA imaging. Our results show similarity to the theoretically predicted value, supporting the effective use of Gold codes.

Laparoscopic surgery is one of the most challenging surgical operations, because inside information about the target organ cannot be fully understood from the laparoscopic image. Therefore, a fusion technique of laparoscopic and ultrasonic images is proposed for guidance during laparoscopic surgery. The proposed technique can display the internal organ structure by overlaying a three-dimensional (3D) ultrasonic image over a 3D laparoscopic image, which is acquired using a stereo laparoscope. The registration of the 3D images is performed by registering the surface of the target organ, which is found in the two 3D images without requiring the use of an external position detecting device. The proposed technique was evaluated experimentally using a tissue-mimicking phantom. Results obtained led to registration accuracy better than 2 cm. The total computation time was 3.1 min on a personal computer (Xeon processor, 3 GHz CPU). The structural information permits the visualization of target organs during laparoscopic surgery.

Integrated backscatter (IB) from the heart wall is gaining attention as a quantitative tissue characterization method and the cyclic variation (CV) in IB during a cardiac cycle offers potential for the evaluation of myocardial contractility. Since there is large motion in the heart wall owing to the heartbeat, in the conventional method, the position of the region of interest (ROI) for calculating the IB is manually assigned in each frame during one cardiac cycle. Moreover, the change in the size of the ROI during contraction and relaxation of the myocardium is not considered. In this study, the phased tracking method was applied to multiple points in the heart wall for automatic tracking of the position and size of the ROI and, then, IB in the same site of the heart wall was measured in each frame by improving temporal resolution and spatial resolution in the axial direction. As a result, cyclic variations, which differed site by site, were found. Furthermore, the rate of change in thickness was estimated by using the interference cycle obtained by applying the discrete Fourier transform (DFT) to IB signals. According to the results, the rate of change in thickness estimated using the interference cycle of IB was in good agreement with that estimated by the phased tracking method. These results indicate the possibility of estimating the rate of change in thickness using the IB signal.

For noninvasive and quantitative measurements of global two-dimensional (2D) heart wall motion, speckle tracking methods have been developed and applied. In these conventional methods, the frame rate is limited to about 200 Hz, corresponding to the sampling period of 5 ms. However, myocardial function during short periods, as obtained by these conventional speckle tracking methods, remains unclear owing to low temporal and spatial resolutions of these methods. Moreover, an important parameter, the optimal kernel size, has not been thoroughly investigated. In our previous study, the optimal kernel size was determined in a phantom experiment under a high signal-to-noise ratio (SNR), and the determined optimal kernel size was applied to the in vivo measurement of 2D displacements of the heart wall by block matching using normalized cross-correlation between RF echoes at a high frame rate of 860 Hz, corresponding to a temporal resolution of 1.1 ms. However, estimations under low SNRs and the effects of the difference in echo characteristics, i.e., specular reflection and speckle-like echoes, have not been considered, and the evaluation of accuracy in the estimation of the strain rate is still insufficient. In this study, the optimal kernel sizes were determined in a phantom experiment under several SNRs and, then, the myocardial strain rate was estimated such that the myocardial function can be measured at a high frame rate. In a basic experiment, the optimal kernel sizes at depths of 20, 40, 60, and 80 mm yielded similar results: in particular, SNR was more than 15 dB. Moreover, it was found that the kernel size at the boundary must be set larger than that at the inside. The optimal sizes of the correlation kernel were seven times and four times the size of the point spread function around the boundary and inside the silicone rubber, respectively. To compare the optimal kernel sizes, which was determined in a phantom experiment, with other sizes, the radial strain rates estimated using different kernel sizes were examined using the normalized mean-squared error of the estimated strain rate from the actual one obtained by the 1D phase-sensitive method. Compared with conventional kernel sizes, this result shows the possibility of the proposed correlation kernel to enable more accurate measurement of the strain rate. In in vivo measurement, the regional instantaneous velocities and strain rates in the radial direction of the heart wall were analyzed in detail at an extremely high temporal resolution (frame rate of 860 Hz). In this study, transition in contraction and relaxation was able to be detected by 2D tracking. These results indicate the potential of this method in the high-accuracy estimation of the strain rates and detailed analyses of the physiological function of the myocardium.

In line with the fact that the intima–media thickness (IMT) of the carotid arterial wall is the most frequently used indicator to diagnose atherosclerosis by ultrasound, it is essential to accurately estimate the thickness of the intima–media complex (IMC) boundaries, i.e., the lumen–intima boundary (LIB) and media–adventitia boundary (MAB). In this study, an improved adaptive model of an ultrasonic echo was developed for the model to realize better fitting to the reference RF echo, which is measured from a glass plate, using a Gaussian window for the envelope function of the adaptive model. Using the mean squared error (MSE) method, the envelope of the improved adaptive model (multiply the sinusoidal wave with the Gaussian window) was fitted with the envelope of an RF echo measured in vivo to estimate the boundaries of the carotid arterial wall. Firstly, a computer simulation of the carotid arterial wall was conducted to evaluate the accuracy of boundary detection using the envelope of the improved adaptive model. In the simulation, IMT was set at 0.50 mm in a 7.2-mm-long short segment in the longitudinal direction. The IMT estimated by the proposed method was 0.54 mm. The 8% error between the true and detected IMTs showed the high accuracy of the envelope of the improved adaptive model in boundary detection. In the in vivo measurement, for the 4.8-mm-long short segment in the longitudinal direction, the average IMT automatically estimated by the proposed method was 0.57 mm. The result was compared with those obtained by the previous method and manually. The IMT estimated by the previous method, which uses an RF adaptive model, was 0.59 mm and the manually determined IMT was 0.56 mm. The smaller difference between the results obtained by the proposed method and manually verified that boundary detection by the proposed method was better than that by the previous method.

It would be useful to measure the minute surface roughness of the carotid arterial wall to detect the early stage of atherosclerosis. In conventional ultrasonography, the axial resolution of a B-mode image depends on the ultrasonic wavelength of 150 µm at 10 MHz because a B-mode image is constructed using the amplitude of the radio-frequency (RF) echo. Therefore, the surface roughness caused by atherosclerosis in an early stage cannot be measured using a conventional B-mode image obtained by ultrasonography because the roughness is 10–20 µm. We have realized accurate transcutaneous estimation of such a minute surface profile using the lateral motion of the carotid arterial wall, which is estimated by block matching of received ultrasonic signals. However, the width of the region where the surface profile is estimated depends on the magnitude of the lateral displacement of the carotid arterial wall (i.e., if the lateral displacement of the arterial wall is 1 mm, the surface profile is estimated in a region of 1 mm in width). In this study, the width was increased by combining surface profiles estimated using several ultrasonic beams. In the present study, we first measured a fine wire, whose diameter was 13 µm, using ultrasonic equipment to obtain an ultrasonic beam profile for determination of the optimal kernel size for block matching based on the correlation between RF echoes. Second, we estimated the lateral displacement and surface profile of a phantom, which had a saw tooth profile on its surface, and compared the surface profile measured by ultrasound with that measured by a laser profilometer. Finally, we estimated the lateral displacement and surface roughness of the carotid arterial wall of three healthy subjects (24-, 23-, and 23-year-old males) using the proposed method.

Since clinical diagnosis using ultrasonic B-mode images depends on the skill of the doctor, the realization of a quantitative diagnosis method using an ultrasound echo signal is highly required. We have been investigating a quantitative diagnosis technique, mainly for hepatic disease. In this paper, we present the basic experimental evaluation results on the accuracy of the proposed quantitative diagnosis technique for hepatic fibrosis by using a simple ultrasonic phantom. As a region of interest crossed on the boundary between two scatterer areas with different densities in a phantom, we can simulate the change of the echo amplitude distribution from normal tissue to fibrotic tissue in liver disease. The probability density function is well approximated by our fibrosis distribution model that is a mixture of normal and fibrotic tissue. The fibrosis parameters of the amplitude distribution model can be estimated relatively well at a mixture rate from 0.2 to 0.6. In the inversion processing, the standard deviation of the estimated fibrosis results at mixture ratios of less than 0.2 and larger than 0.6 are relatively large. Although the probability density is not large at high amplitude, the estimated variance ratio and mixture rate of the model are strongly affected by higher amplitude data.

We have proposed a new modulation method that can generate modulated RF signals with oscillation in two mutually orthogonal directions over a wide, deep area using a small-aperture probe. We had also shown the validity of the method by numerical simulations in a previous work. In this study, we applied the method to an experimental system and validated it by phantom experiments. In numerical simulation, point-source transmission has been performed, but in practical measurement, it does not acquire a sufficient signal-to-noise ratio (SNR) for estimating displacement because of its low output power. A spatially coded excitation, Hadamard spatial coding, was employed to increase SNR. An experiment on wire targets indicated that the proposed method can modulate the RF signal correctly, and an experiment on elasticity imaging suggested that it enables us to estimate displacement in axial and lateral directions with high precision.

Precise evaluation of the stage of chronic hepatitis C with respect to fibrosis has become an important issue to prevent the occurrence of cirrhosis and to initiate appropriate therapeutic intervention such as viral eradication using interferon. Ultrasound tissue elasticity imaging, i.e., elastography can visualize tissue hardness/softness, and its clinical usefulness has been studied to detect and evaluate tumors. We have recently reported that the texture of elasticity image changes as fibrosis progresses. To evaluate fibrosis progression quantitatively on the basis of ultrasound tissue elasticity imaging, we introduced a mechanical model of fibrosis progression and simulated the process by which hepatic fibrosis affects elasticity images and compared the results with those clinical data analysis. As a result, it was confirmed that even in diffuse diseases like chronic hepatitis, the patterns of elasticity images are related to fibrous structural changes caused by hepatic disease and can be used to derive features for quantitative evaluation of fibrosis stage.

In tissue diagnosis, both elasticity and viscosity are important indexes. Therefore, we propose a method for evaluating tissue viscoelasticity by applying vibration that is usually performed in elastography and using an ultrasound coupler gel with known viscoelasticity. In this method, we use three viscoelasticity parameters based on the coupler strain and tissue strain: the strain ratio as an elasticity parameter, and the phase difference and the normalized hysteresis loop area as viscosity parameters. In the agar phantom experiment, using these viscoelasticity parameters, we were able to estimate the viscoelasticity distribution of the phantom. In particular, the strain ratio and the phase difference were robust to strain estimation error.

Tissue elasticity measurements by an ultrasonic wave are a promising technique for the qualitative diagnosis of tumors and liver diseases. The viscoelastic characteristics in soft tissue can be quantitatively evaluated by considering the frequency dependence of the velocity of the shear wave propagating in the tissue. To improve the reliability of the in vivo viscoelasticity measurement, we propose a novel elasticity imaging method using continuous vibration wave excitation, which was realized by developing a three dimensional ultrasonic (3D US) wave Doppler measurement system with multiple-frequency excitation. In vivo experiments on the brachial muscle were carried out in order to demonstrate the validity and effectiveness of the developed system. The experimental results show that this system can successfully measure the velocity of a shear wave propagating through a muscle layer. This system has the potential to obtain viscoelastic information from a target with high repeatability and reliability.

In our previous study, the stress–strain relationship of the radial arterial wall was measured and the viscoelasticity of the intima–media region was estimated from the stress–strain relationship. Furthermore, the transient change in viscoelasticity due to flow-mediated dilation (FMD) was estimated by the automated detection of wall boundaries. In the present study, the strain rate was adaptively filtered to improve the accuracy of viscoelasticity estimation by decreasing the high-frequency noise. Additionally, in a basic experiment, this method was validated using a silicone tube (simulating artery). In the basic experiment, the elasticity was estimated with a mean error of 1.2%. The elasticity measured at each beam position was highly reproducible among measurements, whereas there was a slight variation in measured elasticity among beams. Consequently, in in vivo measurements, the normalized mean square error (MSE) was clearly decreased. Additionally, the stress–strain relationship of the radial arterial wall was obtained and the viscoelasticity was estimated accurately. The inner small loop, which corresponds to the negative pressure wave caused by the closure of the aortic valve, can be observed using the adaptive low-pass filtering (LPF). Moreover, the transient changes in these parameters were similar to those in the previous study. These results show the potential of the proposed method for the thorough analysis of the transient change in viscoelasticity due to FMD.

It is important for regenerative medicine to evaluate the maturity of regenerating tissue. In the maturity evaluation of regenerating cartilage, it is useful to measure the temporal change of elasticity because the maturity of regenerating tissue is closely related to its elasticity. In this study, an elasticity evaluation method for the extracted regenerating cartilage sample, which is based on the laser Doppler measurement of ultrasonic particle velocity, was experimentally investigated using agar-based phantoms with different elastic moduli and the regenerating cartilage samples extracted from beagles in animal experiments. In addition, the experimentally-obtained elasticity was compared with the result of a static compression test. These results verified the feasibility of the proposed method in the elasticity evaluation of regenerating cartilage samples.

An effective method in static elastography for improving the nonuniformity of stress applied by the shape of a transducer head is to insert a damper between the tissue being analyzed and the transducer head. We previously demonstrated the effectiveness of inserting a damper through computer simulations of structural and acoustic analyses on tissue models with flat surfaces. In this study, the optimal values were obtained for two parameters of the damper: Young's modulus and damper thickness. An effective damper shape was also determined through structural analyses.

Accurate testing of an instrument by phantoms requires a tissue-mimicking material that has the acoustic velocity and density defined in the International Electrotechnical Commission (IEC) standard, and furthermore the tissue-mimicking material must be stable over time. To achieve the tissue-mimicking materials with the desired acoustic velocity and density defined in the IEC standard, new materials have been developed. The form of tissue-mimicking materials reported comprised polystyrene and poly(methyl methacrylate) (PMMA) particles dispersed in segmented polyurethane gel. They were stable over a period of 40 days and the changes in weight and acoustic velocity did not exceed 0.5%.

We present a blood-mimicking fluid (BMF) for the Doppler test object of medical diagnostic instruments. Accurate measurement in a flow Doppler test requires a BMF that has the acoustic velocity and density defined in the International Electrotechnical Commission (IEC) standard, and furthermore, they must be stable over time. To formulate a fluid with the desired density and acoustic velocity, we have developed a new fluid made of glycerine and water-soluble silicone oil. The new BMF includes dispersed polystyrene particles as scatterers. The density of the liquid can be adjusted to maintain it at the same value as that of the polystyrene particles, thus ensuring neutral buoyancy of the particles. The MBF was stable over a period of 2 weeks, during which the density and acoustic velocity did not change.

Fast and slow longitudinal waves can propagate through cancellous bone in the direction of the strong trabecular orientation. In in vivo experiments, the cortical bone layer surrounding cancellous bone is considered to affect the fast and slow wave propagations. In this study, the effects of the cortical bone layer were investigated using the stratified models of cancellous bone. In the experimental and simulated results, it was shown that the boundary condition between the cancellous and cortical bone regions affected both the fast and slow waves, particularly the slow wave. The slow wave could be clearly observed for the stratified bone model with a distinct boundary, but the slow wave amplitude decreased as the boundary became less distinct. This was because the generation of the slow wave was interrupted by the gradually varying pore spaces. Moreover, it was shown that the reflected waves within the cortical bone layer could affect the observation of the fast and slow waves. Despite the effects of the cortical bone layer, both the fast and slow waves could be observed for all stratified bone models.

Hypersonic wave velocity was measured in the cortical bone of bovine femur using a micro-Brillouin scattering technique. Using thin plate specimens, wave velocities propagating in the bone axis direction were measured. Next, focusing on the hydroxyapatite (HAp), which is one of the main components of bone, we estimated the relationship between wave velocity and HAp content. The decalcification caused a clear wave velocity decrease from 5.06×10³ to 3.28×10³ m/s, showing the strong effects of HAp on the elasticity of bone. The micro-Brillouin scattering technique would be helpful for the evaluation of bone characterization in a small area.

In this study, we investigated the propagation velocity of bone-conducted ultrasound (BCU) in a living human head. The propagation velocity was calculated using the pattern of acoustic interference, which was extracted from the distribution of the acceleration responses induced as a function of frequency and inter lateral phase difference of bilaterally presented BCU stimuli. Stepped sine signals from 28 to 32 kHz in 100 Hz steps with an interlateral phase difference from -2π to 2π in π/8 steps were used as excitation signals. The estimated propagation velocities were approximately 300 m/s. Furthermore, a simple numerical simulation for the bilateral presentation of BCU stimuli using the estimated velocity was conducted. The simulated acoustic interference pattern was similar to the results of the actual measurements, supporting the fact that the acoustical interference of BCU stimuli induced by bilateral presentation can be estimated with this model.

Bone-conducted ultrasound (BCU) is perceived even by the profoundly sensorineural deaf. A novel hearing aid using the perception of amplitude-modulated BCU (BCU hearing aid: BCUHA) has been developed; however, further improvements are needed, especially in terms of articulation and sound quality. In this study, the intelligibility and sound quality of BCU speech with several types of amplitude modulation [double-sideband with transmitted carrier (DSB-TC), double-sideband with suppressed carrier (DSB-SC), and transposed modulation] were evaluated. The results showed that DSB-TC and transposed speech were more intelligible than DSB-SC speech, and transposed speech was closer than the other types of BCU speech to air-conducted speech in terms of sound quality. These results provide useful information for further development of the BCUHA.

In triggered high-intensity focused ultrasound (HIFU) treatment, cavitation clouds are produced by extremely high intensity trigger pulses and enhance the effect of following heating waves. The ultrasound intensity must be quickly changed from that for trigger pulses to that for heating waves before cavitation clouds vanish. We newly designed and constructed a class D amplifier based on a staircase voltage drive concept, which has the capability of outputting high voltage waves for trigger pulses and continuous waves for heating waves and the capability of fast switching between the two modes. Its efficacy was confirmed by an experiment with a BSA containing polyacrylamide gel.

For therapeutic ultrasound array transducers, it is necessary to reduce the electrical impedance of their elements so that the transducer can produce high ultrasonic power at a relatively low drive voltage. For this purpose, a new concept of a breathing-mode piezoceramic transducer element has been proposed. Numerical simulation showed its low electric impedance as well as good acoustical coupling between the concave hemispherical piezoceramic shell, with a diameter on the order of a wavelength in water, and the volume of a water sphere half enclosed by the shell. In the preparation of a prototype transducer, the effect of additional load masses of the flange supporting the shell and the electric contact for driving the element was numerically analyzed in this paper.

High-intensity focused ultrasound (HIFU) is used for the treatment of tumors such as prostate cancer. In the development of this technique, an accurate and fast measurement of the HIFU pressure field is important. A hydrophone is generally used for the measurement, but it might disturb the pressure field and scanning it in the field takes a long time. On the other hand, optical ultrasonic field mapping has the advantages of speed and its nature of not by interfering with the acoustic field. In this study, we reconstructed an asymmetric ultrasound field by optical measurement using a computed tomography (CT) algorithm. The asymmetric field was generated by a focused transducer with four elements. Also, the absolute measurement of ultrasonic pressure was checked by measuring the center of the field of the charge-coupled device (CCD) camera. The results showed overall agreement with those of hydrophone measurement.

High-intensity focused ultrasound (HIFU) is a noninvasive therapeutic application that focuses ultrasound to the target tissue, such as a malignant tumor, and thermally coagulates it. Monitoring methods for evaluating the formation of thermal lesions induced by HIFU are required to perform safe and accurate HIFU treatment. However, the conventional ultrasonic B-mode image incurs difficulties in assessing the formation of HIFU-induced lesions. In this study, ultrasound RF signals were acquired during HIFU exposure. A correlation coefficient was used to evaluate the changes occurring in the RF signals backscattered from the thermal lesion. Also, a block matching algorithm has been implemented to compensate the tissue motion during HIFU exposure. The experimental results show that correlation coefficients in the focal spot decreased significantly with HIFU exposure, which indicates that the backscattered RF signals changed owing to tissue coagulation.

High-intensity focused ultrasound (HIFU) causes selective tissue necrosis through heating and is used as a noninvasive treatment in cancer therapy. However, there is a problem that it takes several hours to treat a large tumor. To shorten the treatment time, there is need for the development of a highly efficient method. It is known that cavitation bubbles generated by HIFU enhance the heating effect of ultrasound. In this study, the enhancement of the heating effect due to cavitation was considered in the bio-heat transfer equation (BHTE) by increasing the absorption coefficient in the region of generated cavitation. The absorption coefficient was calculated by curve fitting between the temperature rise at the focal point in the experiment and that in the simulation. The results show that the increased absorption can simulate the enhancement of the temperature rise by cavitation bubbles.

When an ultrasonic wave with sound pressure less than the threshold level of bubble destruction irradiates microbubbles, the microbubbles aggregate by an acoustic radiation force and form bubble clouds. The cavitation of bubble clouds produces a large number of microhollows (microdips) on the flow channel wall. In this study, microhollow production by bubble cloud cavitation is evaluated using a blood vessel phantom made of N-isopropylacrylamide (NIPA) gel. Microbubble dynamics in bubble cloud cavitation is observed by a microscope with a short pulse light emitted diode (LED) light source. Microhollows produced on the flow channel wall are evaluated by a confocal laser microscope with a water immersion objective. It is observed that a mass of low-density bubbles (bubble mist) is formed by bubble cloud cavitation. The spatial correlation between the bubble mist and the microhollows shows the importance of the bubble mist in microhollow production by bubble cloud cavitation.

Ultrasound-mediated gene transfection in the presence of microbubbles is a recently developed promising nonviral gene delivery method. The main obstacle towards its clinical application is its low transfection efficiency. In this work, we investigate the effect of the complexation of plasmid DNA (pDNA) into polyplex micelles on the transfection efficiency. Complexation changes the structure of pDNA and results in the condensation in size and enhanced stability. Both naked and complexed pDNAs were transfected into cultured cells using ultrasound in the presence of microbubbles. The transfection rate using complexed pDNA is considerably enhanced (from ∼0.92 to ∼1.67%, by ∼82%) compared with the rate using naked pDNA. Our method provides an alternative for the improvement of the transfection efficiency of the ultrasound-mediated method.

Mid-frequency bottom loss measurements over a grazing angle range of 25 to 70° at frequencies of 6, 8, and 10 kHz were made off the east coast of Korea in October 2008. In this paper, geoacoustic parameters including the sediment sound speed, density, attenuation coefficient, and thickness of the surficial sediment layer are estimated via comparison between the measured bottom loss and a bottom reflection forward model based on the two-layered fluid sediment structure. A global search is performed over the search space of geoacoustic parameters by a genetic algorithm method, in which the weighted squared error between the data and the model predictions is used as an objective function to be minimized. The inversion result shows that a thin lower sound speed layer with a thickness of 0.4 m overlies the higher sound speed sediment. This result is consistent with marine geological observations conducted at the experimental site.

Experimental results, measured in the open ocean using a real target for true target echo signal separation from a mixture of reverberations and noises are presented. The proposed modified independent component analysis (ICA) in conjunction with principal component analysis (PCA), which can preserve the original source signal amplitude, separated the true target echoes from the reflected active sonar signals. In addition, the signal-to-noise ratio (SNR) of the proposed method output was about 3 dB better than that of the conventional beamforming technique.

It is important to estimate the range between a transmitter and a receiver in the sea in position monitoring and navigation. For precise range estimation, the synchronous signal between the transmitted signal and the received signal must be extracted. However, it is difficult because of interference due to the multipath propagation. In this paper, we considered the direct-sequence spread-spectrum (DSSS) system with binary phase shift keying (BPSK) modulation generally adopted for range estimation in the deep sea and discuss the three different simulation results of range estimations from peak detection with cross-correlation. To examine how the transmitter characteristics affect the range estimation performance, the range estimation performance of DSSS signals with BPSK is simulated first with only random noise, then with random noise and the transducer band-limited frequency response, and finally with random noise and the inverse filter of the transducer. It is found that the frequency response characteristics of the transmitter affect the range estimation accuracy.

This paper is about the underwater acoustic (UWA) communication using orthogonal signal division multiplexing (OSDM) in shallow water, whose environment is time spread and frequency spread. In this paper, the Doppler effect – Doppler shift and spread – for UWA communication using OSDM is mainly considered. The effects of Doppler shift and Doppler spread are evaluated in a test tank with a moving platform on a stable water surface and with a stable platform with a moving water surface, respectively. Doppler shift correction, which has been considered in simulation-based studies, is found to work effectively. In relation to the effect of Doppler spread, the experimental result well agrees with the simulation result. Through this study, it is confirmed that a smaller frame length is preferable because it enables the measurement of the UWA channel frequently so that it can keep up with channel changes.

The constrained interpolation profile (CIP) method, a type of method of characteristics (MOC), is a novel low-dispersive numerical scheme. In an earlier study, we applied the CIP method to quantitative analyses of sound wave propagation. However, a new grid system is important for the CIP simulation of complicated heterogeneous media or large-scale simulations of wave propagation. In this study, we examined a subgrid technique for use with acoustic wave simulation using the type-M and type-C CIP methods. The results indicate that this technique for the CIP methods has advantages of small memory requirements and faster calculation.

In this study, we examine the acoustic simulation method combining the wave equation finite difference time domain (WE FD-TD) method and compact FDs (CPFDs) for the second derivative. The wave equation compact finite difference time domain (WE CPFD-TD) method does not require calculation of the particle velocity; therefore, it can reduce the calculation time and memory used. Furthermore, for acceleration of simulation, we employ the recursive filtering algorithm and graphics processing unit (GPU) computing. As a result, we clarified that the three-dimensional WE CPFD-TD acoustic simulation using GPU is ca. 25–30 times faster than that using CPU with OpenMP.

The wave equation finite difference time domain (WE-FDTD) method is applied to the analysis of the long range sound wave propagation in the deep ocean. In the WE-FDTD method, the wave equation in the cylindrical coordinate is directly discretized on the basis of the central differences. The method is then implemented on a graphics processing unit (GPU) cluster system, which consists of 32 GPUs. Assuming the axisymmetric field, two-dimensional numerical models whose region size is 1000 km × 5000 m are developed for various cell sizes (1–3 m). Some numerical demonstrations are made for sound wave propagation in the deep ocean under the assumption of the Munk profile, which is known as the sound speed profile of the mid-latitude of the Pacific Ocean. The numerical results are compared with the results obtained using the ray-tracing method. It is found that the numerical dispersion error appears strikingly in the WE-FDTD solutions when the points per wavelength are less than 20 p.p.w., while the WE-FDTD solutions show good agreement with the ray-tracing solutions in the propagation time when the points per wavelength are more than 20 p.p.w. It is confirmed that the WE-FDTD method can be applied to the analysis of long range sound wave propagation in the deep ocean with reasonable accuracy.

A sound propagation experiment in very shallow water was conducted at Hashirimizu port in 2009. We transmitted 5 kHz sinusoidal waves with M-sequence modulation. As a result, we found that the travel time concentrated in two time frames. When comparing the travel time with the tide level, the travel time was dependent on the tide level. In terms of the wave patterns, most of the wave patterns have two peaks. As the tide level changed, the biggest peak switched within two peaks. To discuss this, numerical simulation by finite difference time domain (FDTD) method was carried out. The result agreed with the experimental result. Finally, we changed the material of the quay wall in the FDTD simulation and concluded that the first peak is a multireflected combination wave and the effect of its reflected wave at a quay wall has superiority in the second peak.

The seawater temperature and wind dependences and diurnal variation of the ambient noise at the snapping shrimp colony in shallow water of the southern sea of Korea were investigated. The ambient noise levels are significantly affected by the snapping shrimp sound, when the bottom seawater temperature increases and the wind speed decreases. However, they are not exceptively almost affected by the snapping shrimp sound when the wind speed decreases at low seawater temperatures (<10 °C). In diurnal variation, the ambient noise levels are also significantly affected by the snapping shrimp sound in the morning and night time zones. This study shows that the activity of the snapping shrimp affecting the variation in ambient noise level in shallow water can be related to the wind speed as well as the seawater temperature. This study also shows that the snapping shrimp in diurnal activity can be more active in the morning and night time zones.

We have already designed and fabricated an aspherical lens with an aperture diameter of 1.0 m to develop a prototype system for ambient noise imaging (ANI). It has also been verified that this acoustic lens realizes a directional resolution, which is a beam width of 1° at the center frequency of 120 kHz over the field of view from -7 to +7°. In this study, a sea trial of silent target detection using the prototype ANI system was conducted under only natural ocean ambient noise at Uchiura Bay, in November of 2010. There were many transients in the received sound. These transients were classified roughly into directly received noises and target scatterings. We proposed a classification method to extract transients of only target scatterings. By analyzing transients extracted as target scatterings, it was verified that the power spectrum density levels of the on-target directions were greater than those of the off-target directions in the higher frequency band over 60 kHz. These results showed that the targets are successfully detected under natural ocean ambient noise, mainly generated by snapping shrimps.

We developed a planate acoustic lens with a phononic crystal structure for acoustic imaging technology in ocean. To determine the properties of the planate acoustic lens, we simulated the sound field converged by the lens using a finite difference time domain (FDTD) method. In addition, we manufactured a prototype of the planate acoustic lens using stainless-steel rods. In this study, we performed a small-scale trial to reduce the scale to one-tenth the original size of the lens. We measured the sound field converged by the manufactured prototype lens in a water tank. A burst pulse with a frequency of 740 kHz radiated from a transducer. Measurement results agree well with analysis results. The focal distances of measurement and analysis were 12.5 and 11.7 mm, respectively. The measured -3 dB beam width at 3.1 mm almost agrees with the analysis result at 2.3 mm.

An aplanatic Straubel mirror was designed for underwater acoustic imaging. However, there was a problem in that incident sound waves coming into the aplanatic Straubel mirror were interrupted by a receiver array placed in front of the mirror. An off-axis Straubel mirror is proposed to solve this problem. In this study, an off-axis aplanatic Straubel mirror is designed and evaluated using numerical calculation to verify the feasibility of the off-axis design. Upon comparison of the off-axis and ordinary aplanatic Straubel mirrors, the off-axis mirror shows almost the same convergence property as the ordinary one when a receiver array exists. The off-axis aplanatic Straubel mirror is compared with an aplanatic Fresnel lens because this lens is not affected by the receiver. The results show that the off-axis mirror showed a smaller aberration than the aplanatic Fresnel lens at a wider angle of view.

See pdf for details

See pdf for details