Table of contents

Molecular dynamics computer experiments have been carried out for two-dimensional hexagonal mass-spring model crystals. Anharmonic forces up to the third order were taken into account, and central forces were considered between the nearest neighbor atoms. Input pulse displacements were given to atoms on the crystal surface, and induced displacements and velocities of all atoms in the crystal were computed. Solitons were produced as the atomic excitation, and the propagation velocity and the strength of solitons were enumerated. The dependences of these two quantities on the pulse application direction and on two parameters, the magnitudes of the input pulse and the higher order force constant, were investigated. Two crystallographic directions were taken for the input pulse direction, and values of the two parameters were widely varied. On the basis of the results of the simulation, a possible laboratory experiment of soliton production was considered.

We carried out ultrasonic birefringence and dynamic light scattering measurements to estimate the anisotropic shape of particles suspended in an aqueous solution. Since these techniques independently give the hydrodynamic radius and the anisotropy of the particle, we can uniquely determine the anisotropic shape of the ellipsoid particles. The result obtained for TiO₂ sol well reproduces the actual shape. However, the model cannot explain the result obtained for the V₂O₅ sol, suggesting some other soft anisotropic structure of V₂O₅ particles.

The acoustic field of a parametric focusing source is experimentally examined. It is found that the theoretical beam sharpness and focusing of the difference frequency sound are primarily due to a less-cumulative sound generated near a strong virtual source located at the focus. Since the amplitude of the difference frequency sound on the focal plane is very weak compared to the primary sound, the signals received by a hydrophone may be dominated by false signals due to the nonlinear response of the hydrophone. Employing the primary sound of frequencies as high as 5 MHz to attain high conversion efficiency, the characteristic of the narrow beam at the focus is demonstrated by observing the signal reflected by a small reflector set at the focal plane. When a highly dissipative medium covers a target to be detected by the parametric focusing source, the difference frequency sound is markedly reduced and the beam sharpness is significantly degraded at the range of the target.

Urick's theory of viscous liquid suspensions has been applied to investigate the ultrasonic wave properties in small-particle dispersed agarose gels. Based on the idea of apparent shear viscosity of the gel medium, the theoretically estimated velocity showed good agreement with the experimental data in the MHz range. The characteristic velocity decrease in viscous suspensions, due to the increase of volume concentration or density of particles, was also observed clearly in the particle-dispersed gels. This phenomenon becomes clearer in the region aβ≪7, where a is the radius of the particles and β is described by angular frequency ω, density ρ and fluid viscosity η.

The observed time traces for a heat pulse experiment on vitreous silica decay exponentially with a characteristic decay time of 30 µs in the power density range from 10^-3 to 10^-2 W/mm², suggesting quasidiffusive phonon propagation. The experimental observation of quasidiffusion in Si requires a low excitation density in order to avoid the emergence of a localized source of low-frequency phonons at high density. The observed density is more than three orders of magnitude below the excitation density in weakly photoexcited Si.

By introducing a common parameter space for sonic crystals and photonic crystals, we have classified them uniformly. Both are artificial crystals made of a periodic array of scatterers with a lattice constant of approximately a half wavelength. Then, we predicted that sonic crystals composed of solid cylinders in air have full band gaps with a filling ratio larger than 0.44, developing a finite-difference time-domain (FDTD) method numerically to analyze acoustic wave propagation in a finite periodic structure. Next, we constructed in air a two-dimensional array of 10 ×10 acrylic cylinders with a radius of 10.2 mm and a lattice constant of 24.0 mm, and observed a full band gap between 6.8 kHz and 9.5 kHz with a transmission ratio smaller than -25 dB using a tone burst, which agrees well with the numerical predictions. To our knowledge, no other report of clear and direct measurements of the full band gap of sonic crystals made of solid scatterers in air has been published.

Compressional and shear wave velocities and attenuation in magnetite, which was sintered in N₂ gas atmosphere, were accurately measured to investigate the Verwey transition by the pulse transmission method using a dual acoustic path across the temperature range between 78 K and 300 K. The temperature dependence of the compressional and shear wave velocities of the sintered magnetite exhibited a depression at ∼ 85 K. The low transition temperature corresponds to a large nonstoichiometry very close to the oxidation limit of magnetite. Using the measured ultrasonic data, the elastic properties of sintered magnetite are discussed.

The shear moduli of methylcellulose gels were measured by means of the surface wave method with different molecular weights and degrees of substitution, i.e., average number of methoxy groups in a glucose unit. Measurements obtained ranged in concentration from 3 to 15 wt%. The effects of molecular weight and degree of substitution on the shear modulus were discussed.

The numerical solution of ordinary differential equations has been widely used in many fields including wave propagation analysis. To represent a continuous function in terms of its discrete sampled values in a sequence, it should satisfy the sampling theorem. However, in conventional wave propagation analysis, the experiential finite difference technique has generally been used. In this paper, the sampling extension which converges more rapidly than in the case of classical cardinal series is proposed. The extension and aliasing errors including the truncation error are described specifically. The sampling extention is also generalized to include the sampled values of the derivative and integral of the signal.

A rapid calculation method for the radiated sound field from a rectangular transducer is proposed. The radiated field is calculated using the convolution integral between the driving signal of the transducer and the time derivative of the spatial impulse response. The proposed method partitions the integral interval with the driving signal of the transducer and approximates the spatial impulse response as a straight line. The time derivative of the response takes constant values. These constant values are separately multiplied by integrated values of the driving signal prepared in advance. The convolution integral is expressed in a very brief form using several basic mathematical operations. Therefore, the time required for the entire calculation is markedly reduced. It becomes at least about 1/40 of that in which the convolution is directly calculated using the conventional method.

Propagation characteristics of a Lamb wave in a nematic liquid-crystal cell are examined by numerical analysis and experimental investigation. The directional dependence of the viscosity coefficients of the nematic liquid-crystal is taken into account for both compressional and shear vertical components of the Lamb wave in the numerical analysis. Higher order modes of Lamb wave are dispersive and the 6th mode of Lamb wave is most sensitive to the director-orientation change of the nematic liquid crystal in the examined frequency region. The electric field dependences of the acoustic phase delay and the propagation loss are measured for three kinds of initial orientations of the nematic liquid crystal. The director orientation in the nematic liquid-crystal cell is evaluated from the phase velocity of the Lamb wave, which is related to the acoustic phase-delay change.

The transmission of ultrasound through a layered structure into a liquid is controlled by the effective reflection coefficient of the layered structure. Under the conditions of resonant transmission, the effective reflection coefficient coincides with the reflection coefficient in the layer at the end of the layered structure that is in contact with the liquid. When the total number of layers increases, the resonant transmission disappears and the transmission rate of ultrasound oscillates rapidly with respect to the change of frequency. However, in the case of actual transmission measurements, this oscillation is difficult to observe. Furthermore, in the case where the substrate of the layered structure has lower acoustic impedance, the observed transmission rate has a large mismatch with the transmission rate given by the theoretical predictions.

Brillouin spectra of monohydric alcohols were examined in the liquid and the supercooled liquid regions using an angular dispersion-type Fabry-Perot interferometer. Relaxation effects became enhanced with increasing alkyl chain length at a constant temperature, reflecting the increase of the viscosity due to the hindrance effect. The velocity dispersion was negligible in the temperature range where the relaxation frequency of the Debye-type α process of each alcohol passes through the Brillouin frequency window. Considering the temperature dependence of the relaxation time obtained from the analysis using a simple viscoelastic theory based on a single-relaxation-time approximation, the coupling between the density fluctuation modes and the secondary β process, instead of the dominant α process, seems to be dominant in the liquid phase. The temperature dependence of the relaxation time in octanol deviated from the high-temperature Arrhenius behavior below a certain temperature, indicating the limitation of the single-relaxation-time approximation used in the present analysis.

The existence of the hysteresis loop between the sound pressure and the light intensity of single bubble sonoluminescence (SBSL) appearing at low air concentration is discussed. The light intensity rises spontaneously at the sound pressure of the starting of the sonoluminescence (SL). Pause time is given just after the SL turns off by the decrease in the sound pressure. The sound pressure is increased after the pause time. Then the relationship between the restarting sound pressure of the SL and the pause time is observed. The pause time is shorter, and the sound pressure at which the bubble starts luminescing shifts to the lower range. The effects of argon rectification are discussed using these observed results. It is shown that the observed results support the argon rectification hypothesis.

The decomposition of water was performed using a sono-catalytic reaction system, which is a joint system of sonochemical and catalytical reactions. By sono-catalysis, overall water splitting was accomplished through the combined effect of these reactions. Water-soluble ferric (Fe(III)) compounds, Pt-black, and metal oxides such as titanium oxide (TiO₂) and iron oxide (Fe₂O₃) were used as catalysts. Homogeneous Fe(III) catalyst was effective for oxygen (O₂) generation under sonication, particularly iron ammonium sulfate (iron alum, (FeNH₄(SO₄)₂). Hydrogen (H₂) was also evolved by sonication. Thus, overall water (H₂O) splitting was accomplished using the sono-catalytic technique. Furthermore, a photosynthesis-like system under sonication is discussed.

The purpose of this study is to clarify experimentally the influence of streaming induced by ultrasonic vibration on heat transfer using a horn-type ultrasonic vibrator. A horn tip of 6 mm diameter and 60.7 kHz resonant frequency was used as the ultrasonic transducer. Heat transfer experiments for a downward-facing horizontal heating surface with ultrasonic vibration from below were carried out in a natural convection region. The acoustic jet in the water from the horn tip of the transducer regarded as a nozzle exit was induced by this transducer, and as a result, up to a ten-fold increase in heat transfer coefficient was obtained by application of 20 W in both tap water and degassed water. It was found that the mechanism of heat transfer enhancement by ultrasonic vibration in tap water can be classified into four categories. In degassed water, heat transfer enhancement is influenced not by the acoustic jet, but by small-scale perturbations by cavitation microjets.

The aim of our study is to examine a new high-intensity aerial ultrasonic source to radiate alternate ultrasonic waves of two similar frequencies with one source set. The ultrasonic source has two conditions of independent resonance and is capable of driving two resonance frequencies. For that purpose, the source has slits that almost reach the center driving point of a striped mode vibrating plate, to divide the transverse vibrating plate into two components. It is clarified that this ultrasonic source drives finely when the resonance frequency of longitudinal vibration is about 600 Hz higher than the two resonance frequencies of a striped mode.

The motion of high-intensity aerial converged ultrasonic waves (frequency: 20 kHz) as studied as they entered a perforation which had a smaller diameter than the wavelength of the radiated acoustic waves (approx. 17.4 mm). In addition, the characteristics of the sound field created in the perforation were studied experimentally. The acoustic waves incident upon the perforation were convergent, having a spreading angle of approx. 90°. As a result, it was elucidated that the acoustic waves favorably entered the perforation with a sufficiently smaller diameter (5 mm max) than the wavelength of the acoustic waves. A sound field of standing waves was created with the sound pressure being the maximum at the bottom of the perforation. The sound pressure increased in the ratio of the 0.5th power of the electric power supplied to the sound source. When the electric power supplied to the sound source was 50 W, a very powerful ultrasonic field of approx. 170 dB was created at the bottom of the perforation.

In recent years, we have attempted ultrasonic ceramic joining for the purpose of extending the application field of ultrasonic joining. We attempted ultrasonic joining of silicon nitride (Si₃N₄) plates and alumina (Al₂O₃) plates. We joined these ceramic plates without using any adhesive material in the case where the plates were of the same material. The maximum joint strength was 33 MPa for Si₃N₄ plates and 30 MPa for Al₂O₃ plates. However, there color the changes on the surface of the joined parts. We surmised that the changes are significant for clarifying the joining processes; thus, we also measured the composition of the joined parts by X-ray photoelectron spectroscopy. In this paper, we show the X-ray spectroscopic data of the joined parts, and discuss the relationship between the process of the joining and the change of composition.

The welding characteristics of aluminum and copper plate specimens welded using a 19 kHz ultrasonic welding system with a complex-vibration welding tip were studied. The welding tip part vibrates in an elliptical or circular locus. The seam welding system uses a rotating circular disk welding tip and a shifting stage for continuous welding of the metal sheets. Using the complex-vibration system, metal plates of various thicknesses can be welded continuously at multiple positions with large and uniform welded areas and large weld strengths independently of the welding position and direction. The required complex-vibration amplitude is less than one-half of that of a conventional linear-vibration system. Aluminum-aluminum, aluminum-copper and copper-copper plate specimens were welded with weld strengths almost equal to the specimen strength.

The welding characteristics of 40 kHz ultrasonic plastic welding system using fundamental and higher-resonance-frequency vibrations were studied. At high frequency, welding characteristics can be improved due to the larger vibration loss of plastic materials. The 40 kHz welding tip vibrates at a maximum velocity of more than 3.0 m/s (peak-to-zero value) at a fundamental resonance frequency and there are several higher resonance frequencies up to 107 kHz whose vibration velocities are more than one-fourth that of the fundamental frequency. The welding characteristics of lapped 0.5-mm-thick polyvinyl chloride and 1.0-mm-thick polypropylene sheets were measured in the cases where the vibration system was driven using combined driving voltages of both fundamental and higher resonance frequencies. The welded area and weld strength increased as fundamental and higher resonance frequencies were driven simultaneously. The welding characteristics of ultrasonic plastic welding were improved significantly by driving fundamental and higher resonance frequencies simultaneously.

This paper describes a method of simultaneously executing both observations using a charge-coupled device (CCD) camera with stroboscopic light and measurement of bubble radius with light scattering. This optical system consists of a beam splitter inserted between a lens and the CCD camera, and a photomultiplier tube (PMT) mounted at the beam splitter. It is confirmed that this system is useful for the simultaneous observation of the bubble size, shape and translational motion.

A high-speed and direct observation system for single bubble motion in acoustic fields is introduced. It produces high-speed and detailed imaging in the ms and µm range. Sonoluminescing bubble motion is observed especially in detail at the rebounding phase. Radius versus time curves are compared with theoretical results calculated by Keller's equation. Disagreement appears at the rebounding phase where rapid decreases in the amplitude and period of rebounds are observed in the experimental values.

A same-phase drive-type ultrasonic motor requires a single power source for its operation. In particular, self-oscillation driving is useful for driving a small ultrasonic motor. This type of ultrasonic motor has a spurious mode close to the operation frequency on its stator vibrator. The spurious vibration mode affects the oscillation frequency of a self-oscillation drive circuit. Hence the spurious vibration mode should be restrained or moved away from the neighborhood of the operation frequency. In this paper, we report that an inductor connected at an electrical control terminal provided on standby electrodes for the reverse rotation operation controls only the spurious vibration mode. The effect of an inductor connected at the control terminal was clarified by the simulation of an equivalent circuit and some experiments.

Ultrasonic levitation in a gravity field was tested using a viscous liquid at a frequency range from 20 kHz to 28 kHz. Red ink and glycerin droplets havingdiameters in the range of 3 mm to 5 mm were placed at a node of a standing wave. As a result, the droplets were not only flattened like a disk, but also found to contain fine air bubbles. Additionally, the droplets continuously changed their location moving from node to node while maintaining a constant volume.

To improve the operating stability and controllability of a high-power ultrasonic linear motor, the authors propose a mechanism to hold the vibrator using the resonance of stepped horns. The new holding system can support the motor firmly, without affecting the longitudinal and bending vibration modes. The resonance frequency of the supporting system is designed to be very near to that of the motor. By using the proposed system, the residual vibrations and the settling time in the transient state have been reduced markedly. When supported by the resonance support mechanism, the no-load speed and the maximum thrust force of the motor were not changed even after 8000 complete back-and-forth cycles, while with the one-point support system, the no-load speed fell rapidly and the motor failed after 20 to 30 cycles.

The vibration and load characteristics of ultrasonic motors that use a longitudinal-torsional vibration converter and various nonlinear springs were studied. Ultrasonic motors have one-dimensional longitudinal-torsional converters with a diagonally slitted part. The vibration characteristics were markedly improved using nonlinear springs for inducing static pressure on the driving surface. Using a nonlinear static pressure source, the frictional driving force of a rotor increases during the forward duty cycle, and that during the opposite retracting cycle decreases, resulting in small frictional loss. The nonlinear static and dynamic characteristics of various material springs were measured. The nonlinear static pressure source may be applied to any types of ultrasonic motor.

The ultrasonic decomposition of a mixture of two hydrophilic organic compounds, phenol and p-chlorophenol, in aqueous solution was investigated. The effect of the initial concentration of phenol and p-chlorophenol on the overall decomposition rate was examined experimentally. The overall decomposition rate constant of p-chlorophenol became lower as the initial concentration of phenol increased. The overall decomposition rate constant of phenol decreased with increasing initial concentration of p-chlorophenol, and remained unchanged when the initial concentration of p-chlorophenol was above a certain value. It was considered that phenol was decomposed by thermal degradation in addition to OH radical degradation. The decomposition of a mixture of phenol and p-chlorophenol in aqueous solution was simply modeled and kinetic analysis was performed. It was found that the initial decomposition rate of p-chlorophenol was higher than that of phenol due to OH radical degradation. The OH radicals were effectively used to decompose p-chlorophenol and phenol.

In recent years, applications of ultrasound to food processing have been of interest. Fermentation is a typical example of food processing which has been used, since ancient times, on milk and is utilized for processing various dairy products, e.g., yoghurt. In this study, ultrasonic irradiation to shorten the time of fermentation in yoghurt production is attempted. It is proven that shortening the fermentation time is possible by employing ultrasonic irradiation.

Results of ultrasonic power measurements using a radiation force balance system constructed at National Institute of Advanced Industrial Science and Technology (AIST) are described. The aim of this research is to establish the ultrasonic power standard for medical ultrasonics. The experimental results of the linearity of the system under 1 mW to about 60 mW for the continuous and the burst waves are presented. It is also confirmed that the measured ultrasonic power is not affected by the repetition rate of the burst wave.

A (110)-plane epitaxial ZnO film is deposited on an R-plane ((012)-plane) sapphire substrate. In order to generate a shear bulk wave using the ZnO film, metal electrodes are required at both planes of the ZnO film; namely, the top plane on the top surface of the ZnO film and the bottom plane at the boundary between the ZnO film and the R-sapphire substrate. A c-plane ((0001)-plane) polycrystal ZnO film is conventionally deposited on the metal film on the R-sapphire substrate. Thus, the (110)-plane epitaxial ZnO film for the shear bulk transducer has not been realized until now. The authors realized a (110)-plane epitaxial ZnO film with low electrical resistivity (ρ of the order of 10^-4 Ω·cm) on an R-sapphire substrate by doping with an impurity such as Al, Ga, or V as a substitute for the metal electrode, and a (110)-plane piezoelectric epitaxial ZnO film with high electrical resistivity (ρ>10⁺¹⁰ Ω·cm) on this epitaxial ZnO film with low electrical resistivity for fabricating a shear wave transducer. An Al electrode was deposited on the piezoelectric ZnO film. By using the Al electrode as the top-plane electrode and a (110)-plane epitaxial ZnO film with low electrical resistivity as the bottom-plane electrode substituting for the metal film, strong shear bulk waves have been generated.

The Ta₂O₅ thin film is a novel piezoelectric thin film, and its application as a surface acoustic wave communication element is expected. Thus, we attempted to grow the single crystal thin film on an amorphous substrate. In this study, a uniaxial orientation film was established on both an amorphous substrate and a single crystal substrate using the RF sputtering method. A new heating method for fabricating a single crystal thin film was proposed, and the basic examination was carried out. As a result, a high-quality crystal thin film was obtained on both kinds of substrates.

We have previously proposed a piezoelectric sensor configuration using an optical-access method. However, optical measurement of the resonance frequency is difficult. In this paper, we discuss an optical measurement method that uses the refraction index deviation caused by piezoelectric vibration. In the corresponding detection configuration, a resonator sample is inserted into the optical path of a Mach-Zehnder interferometer. The resonance frequency can be accurately measured using an optical fiber. This detection configuration is applicable to the measurement of a resonator array. Resonance frequencies of the array were optically measured simultaneously and with high accuracy.

The sensitivity factors of polyvinylidene fluoride (PVDF) transducers between 5 and 50 MHz were measured based on reciprocity and self-reciprocity calibration methods. The results showed that the tendencies of the sensitivity factors over this frequency range by both methods were in good agreement.

In order to develop a high-performance aerial back sonar for a car, we predicted the waveforms of the received pulse using the finite difference time domain (FDTD) method. The echo pulses reflected from the target were calculated as a function of the target's height in air at an inhomogeneous temperature. The maximum amplitudes of the pulse train changed with the target's height. The amplitude and propagation time of the reflected pulse markedly differed with shape of targets at a constant temperature. The result shows that an aerial sensor should be able to detect a square target at an inhomogeneous temperature such as that in summer. However, it is very difficult to detect a slanted target.

Many methods have been developed in order to measure precisely the velocities of elastic waves in materials. However, most of them assume that elastic waves are not distorted when propagating through a medium. In real materials, such a case is rare or only approximately valid. As a result, it is difficult to obtain sound velocities precisely. In this study, in order to solve this problem, we attempt to improve the cross-correlation method, that is, we first extend ultrasonic pulses into analytic signals and then develop the theory of the cross-correlation function between those analytic signals. Consequently, we found a method to measure the precise time difference between pulses. This method is applicable to the following cases: 1) no dispersion exists in medium; 2) not dispersion but constant phase shift exists; 3) not dispersion but frequency-dependent attenuation ratio exists; 4) there exists dispersion whose group velocity is constant; and finally 5) includes all cases from 2) to 4).

A synchronous Schlieren system for observation of ultrasound wavefronts was developed. Since high-intensity and short-response-time GaN/InGaN green light-emitting diodes (LEDs) are suitable light sources of a Schlieren system, we constructed such a system by pulsed illumination synchronized to ultrasound. We used it to observed progressive plane waves and their transmission through a thin plate. Moreover, we used it to observe Lamb waves in the plate by imaging the ultrasonic field in the fluid in its vicinity. The results obtained showed the effectiveness of this system. It has also been proven to be useful for overviewing the spatial distribution of the phase factor of an ultrasonic field, which may be similar to that of ultrasonic power.

The application of a two-dimensional correlation filter to the mode shape visualization of piezoelectric devices is described. The filter extracts the vibrational patterns from two laser-speckle images of the driven and resting phases. The experimental results demonstrate clearly the feasibility of the proposed technique.

The sound pressure distribution of underwater ultrasonic waves is measured by real-time stroboscope holographic interferometry using bismuth silicon oxide single crystal. Stroboscopic sub-microsecond irradiation of laser light enables the recording of the stationary holographic interferogram of refractive index changes of water by ultrasonic waves for the frame time of a charge coupled device camera. The fringe order distribution is calculated from the interferogram by Fourier transform fringe analysis. The optical path differences caused by sound field along the optical path are converted into local field values of sound pressure, which is displayed as a gray scale distribution image. In the experiment, the sound pressure distributions of ultrasonic waves through rectangular and circular apertures are observed. They are compared with the theoretical sound pressure distribution. The sound pressure values obtained by a hydrophone show good agreement with the measured values obtained by this method. The converging and diverging sound pressure fields realized by an acoustic lens are measured.

This paper describes how to achieve an adjustment-free mirage instrument with components assembled in a compact package. The deflection angle amplifier that we previously developed for mirage detection is assembled in this instrument. The features of this instrument are: 1) no optical table, 2) adjustment-free design, and 3) an extremely compact structure for mobile use. The volume of our compact mirage instrument is at least 1/25 times that of the conventional mirage instrument. The capability of the compact mirage instrument is also verified. The results show good potential for using the technique for apparatus commercialization.

To quantitatively improve brain SPECT (single photon emission computed tomography), we propose a noninvasive method for determining the speed of sound in skull bone and its thickness. We assume a spherical shell structure for the skull, and the speed of sound to be constant in the bone layer. Small ultrasonic transducers are arranged on the outer surface of the bone layer to form a transducer array. The array is excited to produce an ultrasonic pulse wave focused at a point on the inner surface by assigning an appropriate time delay to each of the transducers. The pulse is propagated to the focal point, and a reflected spherical pulse wave is produced at that point. The reflected pulse wave is detected by the same transducers, and the output from each transducer is added to give a summed signal. When the time delays are optimized, we obtain the maximum envelope amplitude for the signal. A simulation study is conducted to confirm the method, and the potential error is examined for ideal conditions. From the simulation results, we conclude that the proposed method is suitable for SPECT if the transducers are arrayed with a sufficiently large aperture.

A transducer consisting of two bonded Pb(Zr, Ti)O₃ (PZT) disks is applied to measure the nonlinearity distribution in a layered biological tissue and an in vivo measurement method using the transducer is also investigated. The measured results of nonlinearity parameters of B/A are compared with the theoretical results calculated using equations in the literature, and good agreement between them is obtained. Consequently, the usefulness of the transducer in measuring the nonlinearity of biological media is successfully demonstrated.

A method was proposed to estimate the elastic moduli of materials from the sound produced by impact. To measure the elastic moduli, we have to estimate the natural frequencies of the material's vibration from the observed impact sound waveform. In the conventional method, we estimate the elastic moduli from the estimated natural frequencies by numerical solution. However, the precision of measured natural frequencies was often decreased in ceramics composites at high temperatures, because of the high attenuation of vibration. In this paper, we introduce a neural network approach to the process of estimating elastic moduli from the measured natural frequencies of vibration. Then, we demonstrate the estimation of the correct elastic moduli from the observed ambiguous natural frequencies.

In this study, the author analyzed the deviation factor and the temperature-compensation factor of a new simple ultrasonic solution-concentration sensor which automatically eliminates temperature dependence using the phase-locked loop method (PLLM) and the phase difference method (PDM). The deviation factor is an essential specification for designing a voltage-controlled oscillator (VCO), a phase detector (PD) and an acoustic cell (AC). It was proved that the deviation factor obtained using the empirical equation is always the same, regardless of the center frequency (f_O) of the VCO in the PLLM and the frequency of the driving oscillator (OSC) (f_D) for the transmitter in the PDM. The deviation factor for a 0.0–1.0% NaCl solution determined by both PLLM and PDM was 0.0078. Moreover, it became clear that the same temperature-compensation factor can be used for determining the concentrations of both NaCl and sugar solutions; this factor is derived from the empirical equations of sound velocity. Specifically, its value in a 0.0–1.0% NaCl solution at f_O=2.15 MHz for PLLM is 3.381 kHz/°C, and that in a 0.0–5.0% sugar solution is 3.379 kHz/°C.

Analyses of the performance of piezo-microactuators for various thicknesses of piezoelectric layers are presented. If the value of the Young's modulus of the piezoelectric layer is not more than five time less than that of nonpiezoelectric layers, to realize maximum displacement of the actuator it is better to use a piezoelectric layer as thin as possible (thickness 2–5 µm) with a high breakdown electrical field property. A unimorph lead zirconate titanate (PZT)/stainless steel actuator was successfully fabricated using the aerosol deposition method (ADM) and its performance was investigated for various thicknesses of piezoelectric layers. The electrical energy consumption of actuators when they deflect with the same displacement did not strongly depend on the thickness of the piezoelectric layer. A breakdown electrical filed of more than 500 kV/cm for a lead zirconate titanate [Pb(Zr_0.52,Ti_0.48)O₃] film with thickness ranging from 2 to 80 µm was reported as well.

We propose an alternative 2 Dimensional acoustical array transducer which enables one to generate an arbitrary transmitting beam with a very small number of signal channels. The array with N×M elements can be controlled by N+M signal channels by edge-connected array. In this paper, an edge-connected array composed of nonlinear acoustic devices such as electrostrictive transducers is proposed. Each element of our array can be controlled independently, in contrast to conventional edge-connected arrays. We adopted a spice model of an electrostrictive material (PMN-Pt) to evaluate the characteristics of the array. The performance of the single transducer and the ability of the edge-connected array to perform 3 dimensional imaging were demonstrated by SPICE simulation. In addition to simulation, we performed preliminary experiments using PMN-Pt as a test sample.

The piezoelectric constants of a Pb(Zr, Ti)O₃ (PZT) transducer are experimentally determined using the transient response. When a step voltage is applied to the transducer, the resonance frequency f_r of the transducer is determined from the frequency spectrum of the motional transient-current waveform under a low-electrical-source-impedance condition. Under a high electrical source impedance, the antiresonance frequency f_a and the free capacitance C^F of the transducer can also be determined. Piezoelectric constants obtained by our method agree well with those obtained by the conventional method.

Photoacoustic (PA) spectra have been investigated using a piezoelectric device and a tunable laser for CuInS₂ crystals grown by the traveling heater method. The PA spectrum at 9 K shows two dips located at 1.536 and 1.556 eV corresponding to "A" and "B" free excitons, respectively. The dips of the PA spectrum indicate an increase in the probability of radiative recombination for resonantly excited electron-hole pairs with free exciton energies.

The temperature dependence of the piezoelectric photothermal (PPT) signal intensity of semi-insulating (SI) GaAs from 160 to 297 K was measured. One peak at 205 K was observed in the temperature dependence of the PPT signal. Curve fitting to experimental results by a theoretical analysis based on the rate equations of electrons in the conduction band and a corresponding deep level was carried out. The temperature dependence of the quasi-Fermi level in the band gap of SI-GaAs was also taken into account in the present theoretical model for the first time. We then identified that the observed PPT peak was due to the nonradiative electron transitions through the deep level EL6 in GaAs. It is demonstrated that the deep level was clearly characterized in SI-GaAs by using the PPT measurement.

In this study, the measurement of subsurface defect shape has been demonstrated using photoacoustic microscopy. Two types of subsurface defects are prepared. Using photoacoustic signal intensity distribution with varying thermal diffusion length, the feasibility of the present scheme for estimating the shape of the subsurface defect is shown.

The photoacoustic (PA) spectra of GaAs fine powder whose particle size was of the micrometer order were measured. The PA spectra show a broad peak and this peak shifts to the high-energy region as the sample particle size decreases. The band gap shift can be observed for the large-particle-size samples in the PA spectra. On the other hand, the PA peak shift for the small-particle samples is caused by the light penetration effect causing the decrease of the PA signals, where the particle size is smaller than the light absorption length. Although careful elucidation of the band gap shift in the fine powder samples from the PA measurement is required, the light absorption spectra above the band gap energy can be estimated.

We report the effect of voltage in a concentrated KCl electrolyte applied to highly porous, polycrystalline TiO₂ films during their final preparation processes on photoacoustic (PA) and photoelectrochemical (PEC) current spectra. The PA signal intensities of the TiO₂ films with different applied voltage treatments are higher than those without the treatments below the band-gap region, suggesting an inner-band transition due to an increase in carrier concentration by the voltage treatments. The PA intensity below the band-gap region increases with the increase of the applied voltage, indicating the increase in the carrier concentration due to the formation of donor levels by partially reduced Ti ions (Ti⁴⁺→Ti³⁺). The PEC spectra for the applied voltage treatments with -1.5 V and without the treatments show broad bands at approximately 3.31 eV. The PEC spectra for the applied voltage treatments over -1.5 V show two peaks at approximately 3.31 eV and 3.88 eV. The PEC intensities at each peak position increase rapidly above the applied voltage of -1.5 V (eight times larger for the voltage of -3.5 V than those without the treatments), which is similar to that of the PA intensity at a photon energy of 2.0 eV. The increase of the PEC intensity with different applied voltage treatments implies an increase in carrier concentration due to the formation of donor levels by the treatments. These results suggest that TiO₂ electrodes suitable for the sensitization by dyes or quantum-sized semiconductors can be obtained by applying the voltage treatments.

Piezoelectric photothermal spectroscopy (PPTS) is a powerful tool for investigating optical properties of semiconductors. Temperature dependence of the PPT signal intensity of the Co-doped ZnO semiconductor was measured from 4.2 to 300 K. The Co concentration dependence of the PPT signal intensity was also studied to clarify the effect of doping with transition metals. In the case of doping at a low level, Co atoms form deep impurity levels in the ZnO matrices in the spectral region from 1.2 to 1.7 eV. However, for samples doped at higher levels, many crystal field split-off levels from localized Co²⁺ ions appeared at approximately 0.7–1.2 and 1.7–2.4 eV and these two bands became dominant in the spectra. The doping effect was investigated from the point of view of nonradiative transition for the first time.

The surface wave velocity of the SiC layer on the Si substrate was investigated by the Brillouin scattering method. The quasi Rayleigh wave on the SiC layer was clearly observed, showing velocity dependence on the crystalline structure.

The temperature variation of the piezoelectric photo-thermal (PPT) signal intensity of N-type Ni-doped Si was measured in the range from 100 to 300 K. We observed one distinctive peak at 150 K in the Ni doped sample. Since no intense peak could be observed for the control sample, we consider that this 150 K peak is due to Ni impurity. The activation energy, electron capture cross section and concentrations are obtained by fitting the observed curve to that from the theoretical analysis based on the rate equations for electrons. The best-fitted parameters are in good agreement with those obtained by conventional deep defect levels transient spectroscopy (DLTS) measurements. The usefulness of PPT measurements for studying the deep level in semiconductors is pointed out.

Photoacoustic (PA) spectra for the Sb₂O₃-doped ZnO varistors were measured to study the Sb₂O₃ doping effects on their nonradiative properties and deep levels, where the Sb₂O₃-doped ZnO varistors had the highly nonohmic current-voltage feature. For the samples without the Sb₂O₃ doping, the PA spectra are almost flat between 750 nm and 950 nm. When the ZnO varistors were doped with Sb₂O₃, a decrease in the intensities of the PA signals above 800 nm with increasing wavelength is observed. The Sb₂O₃ doping generates the spinel phase, which suppresses the concentration of Co dissolution into the ZnO grains; the PA peaks of Co in ZnO observed between 800 nm and 1000 nm appear to be low. The small peak at approximately 950 nm is observed for the Sb₂O₃-doped samples. This peak corresponded to the deep level caused by the Sb₂O₃ doping. The analysis of this level helps in the estimation of the properties of ZnO varistors.

The optical absorption spectra of ZnS:Mn nanocrystals can be obtained by applying photoacoustic (PA) spectroscopy, which is a powerful technique for detecting small amounts of highly scattered materials. The peak position in PA difference spectra increases linearly within experimental accuracy with the decrease of Mn²⁺ ion concentration. These results correspond to the following possibilities, \ding172 the increase of the higher excited energy states relative to the ground state of ⁶A₁, \ding173 the increase of state density for the higher excited states and \ding174 the increase of transition probability from the ⁶A₁ state to the higher excited states. These possibilities suggest the hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn²⁺ ion impurity. The peak position of the PL spectrum (the transition from ⁴T₁ to ⁶A₁ states) is ∼ 2.08 eV with a half width of 0.24 eV, similar to that of the bulk ZnS:Mn, and it is independent of the Mn²⁺ ion concentration. This result might be attributed to the fact that the Mn²⁺ emission is due to phonon assisted transition. Hence, there might be a slight shift of the peak position with increase of Mn²⁺ ion concentration due to hybridization of the s-p states of the ZnS nanocrystal host and the d state of the Mn²⁺ ion impurity. The peak intensity of the PL spectrum shows a maximum at a certain value of Mn²⁺ ion concentration and it decreases with the increase of concentration of Mn²⁺ ion impurities (concentration quenching).

In this study, an appropriate negative impedance converter (NIC) circuit is designed to improve the receiving sensitivity of a flexural-type piezoelectric sensor. The negative electric elements of the NIC circuit reduce the mechanical resistance of the sensor in resonance, and consequently control the vibration characteristics. Experimental results show that the receiving sensitivity of the designed sensor with the NIC circuit can be improved such that it is much higher than that of a sensor without the circuit.

One of the key elements in succeeding in the development of the piezoelectric gyro-sensor is considered to be the reduction of the leakage output caused by complicated couplings, such as harmful mechanical coupling between the drive vibration mode and the detection vibration mode [N. Ishida and Y. Tomikawa: Jpn. J. Appl. Phys. 38 (1999) 3228]. In this report we describe the realization of the monolithic piezo-type tuning fork resonator which applies two types of poling, horizontal and vertical poling, as a means of reduction of the leakage output. The establishment of the V-groove edge clamp support method for the piezo-resonator and photolithographic patterning method for the piezo-electrodes are also described. Realization of the monolithic piezo-type tuning fork resonator enabled the reduction of dispersion of characteristics because of the high tooling accuracy for resonator dimensions. The V-groove edge clamp support structure enabled the stabilization of the leakage output. The photolithographic patterning method enabled small dispersion of the sensor characteristics in the production stage, because of the high accuracy of electrode patterning. Moreover, the success in photolithographic patterning on piezoceramics enabled not only the use of aluminum wire bonding as signal wiring but also the minimization of the influence of signaling wire on the characteristics of the gyro-sensor. With the development of these core technologies, the subminiature monolithic piezoelectric gyro-sensor was realized.

A new trapped-energy vibratory gyroscope, which uses the thickness-shear vibrations in a piezoelectric ceramic plate with a plano-mesa structure, is proposed and its principle of constitution is presented. This gyroscope has three electrodes for excitation and detection of the thickness-shear vibrations, and these electrodes are deposited in the central region of a piezoelectric ceramic plate with a plano-mesa structure, where only the plate thickness of the central region is partially increased. A trapped-energy vibratory gyroscope on a lead zirconate titanate (PZT) ceramic plate of 25×25 mm² area and 2 mm thickness is constructed and studied, and its experimental results are presented. The results show that a highly reliable gyroscope with a simple solid structure can be realized, and a detection sensitivity of 1.7 mV/deg/s, which is proportional to the applied angular velocity, can be obtained when the driving voltage is 2 V_p-p and the total gain of the detecting circuit is 66 dB.

Gyrosensors, which are now practically used but are still under development, can only detect one-axis angular velocity. Therefore, if three-axes angular velocities must be detected, we have to apply at least three gyrosensors of one-axis detection type. In such a case, the space occupied by the gyrosensors in the apparatus increases. Thus, we studied a one-chip style gyrosensor that can detect three-axes angular velocities: that is, we developed a one-chip three-axes gyrosensor using a quartz crystal trident-type tuning fork resonator. In this paper, we discuss the operation principle of such a gyrosensor and the finite element method simulations of its characteristics.

We have already proposed a new one-chip-style quartz crystal motion sensor which detects one-axis angular velocity and one-axis acceleration. This sensor is aimed to be used as a small wristwatch-type instrumentation unit to monitor some motions of the human body. From the results of some simulations of its characteristics, it has been clarified that the sensor is effective; however some problems, such as nonobjective axis sensitivity of angular velocity detection and unstable vibration characteristics of the acceleration sensor part, have remained. Therefore, for solving these problems, we propose here a newly improved sensor structure. The simulations of the newly improved sensor show that it has a very low sensitivity to nonobjective angular velocity and stable vibration characteristics. Furthermore, the vibration characteristics of a prototype sensor were measured using a laser Doppler vibrometer. Some vibration characteristics of the prototype sensor are similar to the simulated ones.

We numerically studied both the mass-loading and elastic effects of Au-electrodes on the fundamental thickness-shear (TS) mode of a very thin plate. To solve the two-dimensional forced vibrations of an infinite AT-cut quartz plate with infinite strip Au-electrodes, an efficient technique that utilizes the one-dimensional finite element method was developed. Using the technique, the piezoelectrically induced admittance Y_p of the plate was derived with a complex value, and then the frequency f₁ and the equivalent inductance L₁ of the fundamental TS resonance were calculated as a function of the Au-electrode thickness. The results show that the influence of Au-elasticity on f₁ and L₁ is negligible compared with mass-loading R, in the wide range of R=0.04–0.36, and that the change of L₁ is proportional to R. We also find that the single wave approximation, which was considered to hold only for small R<0.1, holds well even for large mass-loading R=0.36.

In order to evaluate the `resonance intensities' and resonance frequencies of piezoelectric transducers driven `partially', two mathematical methods are considered: One is the evaluation of `speed of divergence' at the resonance of Mason's equivalent circuit which is applied appropriately using the conventional concept of a distributed-parameter circuit, and the other is a superposition of complex dynamical variable η to form complex infinite geometric series in which |η|<sup>2</sup> corresponds to the stored energy in the transducer and in which the way of superposition reflects the electrical and mechanical boundary conditions of the transducer. The resonance intensity is related to the effective power at the resonance. The `partial drive' can induce resonance modes other than a set of odd-degree modes, with various resonance intensities due to a nondissipative cause, on appropriate boundary conditions. The calculation results of the two methods agree with each other satisfactorily, and thus suggest the physical reasonableness of both methods.

We developed a method for analyzing the frequency of a quartz-crystal tuning fork using a torsion spring model. In order to calculate the frequency near the actual frequency of the tuning fork, we approximated the right half of the tuning fork as an L-shaped bar in which two bars acting as the base and the arm undergo bending vibration. Furthermore, we applied the torsion spring model with torsion spring constant R to the joint of beam A corresponding to the base and beam B corresponding to the arm. A comparison was made between frequencies calculated by this method and experimental results, and the relationship between R and the width of the base was discussed.

We are aiming at developing a Langevin longitudinal transducer without a bolt using a single crystal. The Z plate of the LiNbO₃ single crystal was used as a piezoelectric material. We selected epoxy resin for bonding a piezoelectric disc (10 mmφ) and stainless blocks (12.5 mm in length) as trial samples. The resonant frequency is about 94 kHz and the Q factor is about 1000. The material constants of the adhesive were derived for the finite element method (FEM) analysis. We measured the marked decrease in the Q factor due to temperature rise. It became clear that the measurement for high-voltage operation by continuous wave was limited within 4 cm/s of the edge surface velocity. We drove transducers using a burst signal and suppressed the temperature rise of the transducer. This method extended the measurement limitation to 40 cm/s. To clarify the problems of this transducer, the relationship between the bonding layer and the resonance resistance, and the stress in the bonding layer were determined using FEM. A thin crystal disc was also found to decrease the resonance resistance using FEM.

This paper presents piezoelectricity in germanium-doped silica (germanosilicate) films produced by poling treatment. The germanosilicate films were prepared on Si substrates by RF magnetron sputtering. The films were poled by electric fields of 2–4 ×10⁷ V/m at a temperature above 300°C. Before the poling, no piezoelectric response was observed. After the poling, a 0piezoelectric response caused by normal stress T₃₃ on the film surface appeared. The maximum value of the piezoelectric constant d₃₃ of the poled film was larger than d₁₁ of quartz by 20–30%. Various applications of the piezoelectric Ge:SiO₂ film are expected to emerge.

A new structure of flat force sensors using the resonant frequency shift of a flexurally vibrating bar by the axial force is proposed in this paper. The sensor structure is composed of only one flexurally vibrating bar called a central arm and two short arms flatly arranged on both sides at both ends. As the displacements at the base ends can be extremely reduced by balancing these arms, the structure is not affected by a support. The dimensions of the force sensor are determined by the finite-element analysis when using the out-of-plane modes. The resonant frequency changes with application of the axial force to the both base ends. The rate of change for the first mode is larger than that for the second mode. This structure is suitable for mass production, and therefore will be expected as a low-cost force sensor with high stability and sensitivity.

In this paper, the resonance frequency of a vibrating resonator used as a force sensor has been considered. The value of resonance frequency change of the resonator deformed by the axial force is calculated using the finite element method. Then, the resonance frequency change considering the stress distribution of the resonator by the axial force is also calculated. The difference between the two kinds of resonance frequency changes is quantitatively clarified.

A nanoliter dispensing head based on a novel principle has been proposed. In this dispensing head, a piezo ceramics transducer moves a glass capillary holding liquid in the direction of dispensation. As a result of this movement, pressure waves are generated in the capillary, resulting in the dispensing of a small droplet from the nozzle. In order to understand the basic performance of this head, we have studied the effect of voltage waveform application to the piezo ceramics transducer on droplet formation. We have also studied the effect of sample liquid volume in the capillary on droplet formation and the effect of sample liquid viscosity on droplet properties. Under typical dispensing conditions, the volume of a drop was 1 nl and the coefficient of variation was 5%.

A new structure for low-frequency flat-type piezoelectric vibratory gyroscopes is proposed, and is analyzed by the finite-element method. The H-type vibrator is arranged at the center of the vibratory gyroscope, and is connected to two 3-arm-type vibrators by a central arm. In-plane modes of vibration are used for driving and detecting in this structure. The structure is negligibly affected by a support because the displacements at the support part become very small. Using the metal structure with the piezoelectric ceramics for driving and detecting, it was clarified that the vibratory gyroscope operates as an angular rate sensor.

To confirm the effect of stepped bi-mesa structures on the decoupling of thickness-shear and thickness-flexure modes, we fabricated stepped bi-mesa resonators and measured their frequency-temperature behavior. The results showed that stepped bi-mesa resonators have better temperature characteristics than bi-mesa resonators. These results confirmed that the stepped bi-mesa structure can reduce the influence of mesa edges and improve the characteristics of bi-mesa resonators.

Expanding electrical communication systems demand new acoustic wave devices that can be used in high frequency ranges. The solidly mounted piezoelectric thin film resonator is a candidate for such devices. In this study, first, acoustic properties of a number of thin films are evaluated and a combination of SiO₂ and ZnO is shown to be suitable for such devices as quarter-wave multilayer materials. Then, piezoelectric thin film resonators consisting of a ZnO piezoelectric film on alternately deposited SiO₂ and ZnO quarter-wave multilayers are designed and fabricated. Their measured characteristics are presented and discussed.

Generally, the phase difference between center and edge in a flexural type vibrator leads to high side-lobe levels when the vibrator is used in a parametric source. To decrease the side-lobe level, an arrayed method is investigated in which the vibrators are arrayed at an angle to the array surface. To analyze the radiation characteristics, a one-dimensional model of the vibrator is derived. Using the method, a side-lobe level can be reduced to about 20 dB for the secondary wave in the parametric source.

In this paper, we propose a method of analyzing the excitation and detection of leaky modes in a surface acoustic wave (SAW) waveguide structure. These properties could not be directly evaluated by the conventional scalar potential theory and mode expansion. In the present theory, the SAW excitation and detection are taken into account in the scalar potential theory, and then the SAW signal transfer between input and output ports is estimated in a form of the Fourier transform in the wavenumber domain. Finally, the contribution of each mode is estimated by the residue theorem. This method is effective in estimating the contribution of complete spectra, including leaky modes as well as non-leaky guided modes.

Vibration of a liquid droplet is easily controlled by the Rayleigh surface acoustic wave (SAW). In the vibration of a liquid droplet, two cases are considered: free vibration and forced vibration when it is excited without and with SAW excitation, respectively. For the free vibration, the theoretical and experimental results have already been reported. In the forced vibration, when input excitation was increased, we had determined experimentally that vibration of a liquid droplet shows two nonlinear phenomena. One is, with the increase in SAW input voltage, resonance frequency decreases and vibration amplitude exhibits jump phenomenon. The other, in addition to the fundamental frequency, second and third harmonics, and 1/2 and 3/2 subharmonics are observed. In this report, we explain the two nonlinear phenomena qualitatively using the Duffing equation including the term of a nonlinear spring.

The computed parameters of coupled-mode equations are presented for natural single phase unidirectional transducers (NSPUDTs) on La₃Ga_5.5Ta_0.5O₁₄ substrates with Euler angles (0°, 140°, 23°) and (12.7°, 150.1°, 36.3°). The aluminum electrode width and height dependences of the coefficients of coupled-mode equations are investigated in detail. Numerical results show that the amplitude of mutual-coupling coefficient κ₁₂ for an NSPUDT on a (0°, 140°, 23°) La₃Ga_5.5Ta_0.5O₁₄ substrate is larger than that on a (12.7°, 150.1°, 36.3°) La₃Ga_5.5Ta_0.5O₁₄ substrate for the same electrode width and height within the range of 0.5≤w/p and 0.04 ≤h/p. Our results of the insertion loss for a filter which consists of an NSPUDT and two split interdigital transducers on a (0°, 140°, 23°) La₃Ga_5.5Ta_0.5O₁₄ substrate agree well with previous experimental results.

Computed results of all the coefficients of coupled-mode equations are presented for interdigital transducers with solid electrodes of gold, silver, tantalum, or tungsten alloy on a 50° Y-25° X La₃Ga₅SiO₁₄ substrate. The electrode thickness and width dependences of the coefficients for tantalum or tungsten electrodes are investigated in detail. Numerical results show that the phase of the mutual-coupling coefficient for natural single phase unidirectional transducers (NSPUDTs) with tantalum or tungsten electrodes do not increase monotonically with increasing electrode height. Our results of the effective velocity and the difference between the phase of the mutual-coupling coefficient and two times the phase of the transduction coefficient agree well with the earlier experimental results.

We have developed a poly-crystalline diamond film whose grain size is about 0.5 µm, which is smaller than that of our previously studied diamond films applied in surface acoustic wave (SAW) devices. Using the small-grain diamond, three kinds of narrow-band SAW filters were fabricated with the SiO₂/interdigital-transducer (IDT)/ZnO/diamond/Si structure at the center frequencies from 2.488 to 5.0 GHz. The insertion losses of these filters were lower by 1.3 to 3.2 dB and the Q values were 200 higher than those obtained using the standard diamond. The Q value is defined as the center frequency divided by the bandwidth at a loss level 3 dB lower than the minimum insertion loss. "Standard diamond" refers to our previously studied diamond. The propagation loss, electro-mechanical coupling coefficient (K²), phase velocity and temperature coefficient of frequency (TCF) were investigated on the basis of the measured characteristics of these filters. It was found that the propagation loss was about two thirds of that obtained using the standard diamond film while TCF, K² and phase velocity were almost the same as those obtained using the standard diamond.

In this study, in order to improve the temperature coefficient of frequency (TCF), the propagation characteristics of SiO₂/Rotated Y-cut, X-propagating LiNbO₃ leaky surface acoustic wave (SAW) substrates with a large electromechanical coupling coefficient (k²), zero attenuation and zero TCF are theoretically investigated. The results showed a large k² of more than 0.2 (zero k² of Rayleigh mode), zero TCF and zero propagation attenuation for leaky SAW in the case of a short boundary at a thin film thickness of H/λ\fallingdotseq0.15–0.25 (H: SiO₂ film thickness, λ: SAW wavelength). The experimental results agreed with the theoretical ones.

In this study, we investigate a future high-speed real time analog signal processing circuit by co-integrating a semiconductor active array device with a surface acoustic wave (SAW) device in one chip. We propose a novel semiconductor coupled SAW functional device with a traveling wave amplifier structure and show basic characteristics of the devices using a circuit simulator. Using epitaxial liftoff film bonding technology, we fabricated a basic test device on LiNbO₃ substrate and measured the basic characteristics of the functional device.

Equivalent circuit parameters of surface-acoustic-wave transducers are reported for the [interdigital-transducer (IDT)]/ZnO/diamond, ZnO/IDT/diamond, SiO₂/IDT/ZnO/diamond and SiO₂/ZnO/IDT/diamond structures. The admittance mismatch, normalized susceptance and transformer turns ratio are calculated for each structure by applying the finite-element method (FEM). Their dependences on the thicknesses of the aluminum electrode, ZnO and SiO₂ are examined. Experiments are also carried out to evaluate the admittance mismatch, the results of which agree with the calculated data. It is shown that these structures have large values of admittance mismatch compared with those of conventional surface acoustic wave (SAW) materials such as LiTaO₃, LiNbO₃ and quartz.

The propagation characteristics of leaky surface acoustic waves on rotated Y-cut langasite with a thin dielectric film, such as those of tantalum pentoxide (Ta₂O₅) and silicon dioxide (SiO₂), are investigated theoretically and experimentally, mainly in terms of the attenuation. The theoretical analysis showed that, for a certain range of the cut angle, the attenuation can be reduced by choosing the appropriate material and thickness of the film. In fact, the estimated propagation loss of the leaky surface acoustic wave on (0°, 140°, 42°)-cut langasite with RF-sputtered Ta₂O₅ film decreased to approximately one-tenth that of the sample without the thin film.

Although resonant ultrasound spectroscopy is useful for testing the surface and inside of objects, the resonance properties (resonance frequency and mode amplitude ratio) are disturbed by the contact with supports and transducers. To eliminate this disturbance, we propose the floating resonance method in which the resonance property is evaluated after floating the objects, while avoiding contact to supports and transducers. Thus, using laser ultrasonics, completely noncontact resonance measurement is realized for the first time. In a preliminary application to bearing balls, we succeeded in floating an 8-mm-diameter steel bearing ball using controlled air flow and in improving the reproducibility of resonance frequency to better than 0.005%. A defect was detected by observing the difference in resonance frequencies with and without the defect, which was difficult under the supported condition.

Underground imaging using a stacking method of reflected scattered waves has been studied. A sound source made of aluminum has already been employed in the hammer method. However, the amplitude of the reflected scattered waves is not stable. Therefore, we propose a new sound source comprising a super-magnetostriction vibrator whose displacement is 100 times larger than that of a conventional magnetostriction transducer. The experimental results show the potential of this new sound source.

The acoustic intensity distribution and radiation power of a flat-plate phased-array sound source consisting of Tonpilz-type transducers were measured. This study shows that the active acoustic intensity is skewed in the direction of wave propagation. In addition, it clarifies that if the measurement is carried out in the immediate vicinity of the sound source, the reactive acoustic intensity distribution is effective for identifying the positions of the individual sound source elements. Experimental values of active radiation power agree well with theoretical values. Conversely, experimental values of reactive radiation power do not agree with theoretical values; it is clear that they fluctuate significantly with distance from the radiating surface. The reason for this is explained in the case of a point sound source.

The autonomous underwater vehicle mounted on the forward obstacle avoidance sonar is developed to investigate ocean environments such as that of the Arctic Ocean. In order to obtain real time, high efficiency and clear acoustic images, the acoustic lens sonar system has been adopted. Usually, the design of the acoustic lens as well as that of the optical lens is based on geometrical optics theory. In this paper, the acoustic characteristics of the acoustic lens are studied by using the two- and three-dimensional parabolic equation methods.

In this study, the acoustic wave reflection characteristics from the surface of water-saturated and air-saturated sediments are calculated using the Biot-Stoll model. These sediments are silt and medium sand. The calculated results for the water-saturated and the air-saturated silt and medium sand are compared. Additionally the reflection characteristics from the surface of sediments with the top transition layer are obtained using OASES (Biot-Stoll model). The effects of the transition layer depending on the frequency are investigated. Moreover, the effects of the slow wave in the air-saturated sediment on the reflection characteristics are considerd.

We analyzed the effect of a sound speed structure near the ocean surface on sound propagation in a deep sound channel in the ocean by ocean acoustic tomography (OAT), using the normal mode theory. The time structure of the received pulse train in the deep sound channel varies according to the sound speed structure near the ocean surface. In the analysis of the inverse problem in OAT, attention must be paid to the sound speed structure near the ocean surface in the ocean area of interest.

We present the stability estimation results of the reciprocal acoustic transmission data collected during the tomography experiment performed by Japan Marine Science and Technology Center (JAMSTEC) in 1999 in the Central Equatorial Pacific. Travel-time perturbations due to ocean currents are correspondingly one to two orders of magnitude smaller than travel-time signals due to sound-speed perturbations. It is important to estimate the stability of signals of reciprocal transmission. The standard deviation of the phase of the ray signal is very stable within 130 s. Between reciprocal transmissions, the overall structures of the signal are similar, however, the fine structures are different. The standard deviation of the effective phase is a useful index for determining whether or not the ray exists. The received signal is judged as an arrived ray when the standard deviation of the effective phase of 13 consecutive shots is less than 1 rad. The combination of the amplitude and phase information is effective for observing the ocean structure change.

The purpose of this paper is to describe an accurate computational method for underwater acoustic propagation problems in shallow water. Most of the available computational methods consider only longitudinal wave in a fluid model. These methods, however, may not be applied to all kinds of oceans because of the influence of shear wave in shallow water. In this paper, an elastic parabolic equation combined with the rotated Pade series for an accurate solution is derived. To confirm the validity of the proposed method, typical examples of sound propagation underwater are calculated in comparison with the conventional fluid PE method. Estimations of propagation pulse waveforms are performed under the condition that the propagation path is 5000 m in an ocean of 300 m depth. The result shows the difference of pulse waveforms between elastic and fluid PE models. It is also shown that consideration of the influence of shear wave in an elastic bottom is very important for an accurate calculation.

Lamb waves are normally utilized for inspecting thin metal sheets, and a wheel type probe with piezoelectric oscillators is used as the sensor, although it has a few serious disadvantages such as a dramatic change in sensitivity. We then studied a useful electromagnetic acoustic transducer (EMAT) without a couplant. The trial EMAT consists of a meandering coil with a narrow distance between the intervals which can generate Lamb waves of variable wavelengths corresponding to the frequency range from approximately 150 kHz to 4.0 MHz. This transducer, for example, can select Lamb waves with optimum wavelengths on the factory line that produces thin sheets with variable thicknesses. The described EMAT can be used to inspect steel sheets of different thicknesses. It is also shown that the S₀-mode Lamb wave with the longer wavelength is the most effective for a thick sheet (up to 6 mm).

An interface scanning method is proposed for imaging of underground interfaces, such as during the exploration of comparatively large archaeological sites or the interfaces of different earth layers. The path lengths of ultrasonic waves from the sound source to each receiver corresponding to an interface to be calculated are derived according to the shortest path propagating principle. The corresponding amplitudes and polarities are derived from signals of each channel. The image magnitude of the interface to be calculated can then be calculated by the amplitude correlation synthesis processing method. The compared imaging results of an underground interface derived by the previous point scanning method and by the interface scanning method using both the numerical simulation and experiments are presented. The interfaces with different angles of declination are imaged clearly by the interface scanning method while only a blurred image at the center of the interface is obtained by the point scanning method.

Ultrasonic force microscopy allows the local mapping of elasticity in atomic force microscopy by the application of ultrasonic vibration to the cantilever or sample. In an attempt to analyse the results of ultrasonic force microscopy in a quantitative fashion, a force-distance curve measurement is done with ultrasonic vibration applied to the cantilever base, and the results are compared with a model of the cantilever dynamics and tip-sample interaction based on the finite-difference technique.

It is essential for advanced nondestructive evaluation that single mode of acoustic waves be selectively generated. We have proposed the phase velocity scanning (PVS) method for this purpose. In this work, we improved the PVS method by using an acoustooptic deflector to scan a laser beam at high velocity with high repeatability. In aluminum plates, we succeeded to generate narrow-band single-mode Lamb waves, which propagated a distance more than 1.7 m. We propose to apply this method to detection of defects on large plate structures.

In order to develop a tool for designing on the ultrasonic probe and its peripheral devices for tissue-harmonic-imaging systems, a study is carried out to compare the calculation and observation results of nonlinear acoustic fields for a diagnostic ultrasound system. The pulsed ultrasound with a center frequency of 2.5 MHz is emanated from a weakly focusing sector probe with a 6.5 mm aperture radius and a 50 mm focal length into an agar phantom with an attenuation coefficient of about 0.6 dB/cm/MHz or 1.2 dB/cm/MHz. The nonlinear acoustic field is measured using a needle-type hydrophone. The calculation is based on the Khokhlov-Zabolotskaya-Kuznetsov(KZK) equation which is modified so that the frequency dependence of the attenuation coefficient is the same as that in biological tissue. This equation is numerically solved with the implicit backward method employing the iterative method. The measured and calculated amplitude spectra show good agreement with each other.

A method using ultrasonic velocity change due to light absorption was investigated in order to realize practical optical computed tomography. The phase shift of ultrasonic wave was observed even in the medium with a scattering coefficient equivalent to that of the human brain when ultrasonic wave passed through absorption object under light illumination. The optical image of the absorption region in a scattering medium was reconstructed from the projection data of ultrasonic phase shift due to light illumination. The shape of the absorbing object hidden in the chicken tissue was recognized by detecting the ultrasonic phase shift due to light illumination.

When a microbubble oscillates under an ultrasonic wave, the bubble radiates a secondary ultrasonic wave around it. This wave produces the secondary Bjerknes force between the neighboring bubbles and it assists in the aggregation of bubbles to make bubble clouds if the phases of the vibrations are the same. In this paper, a novel technique to characterize the secondary ultrasonic wave radiated from a bubble is proposed. This method is based on the observation of the interference fringe pattern which is produced by small bubbles trapped around the bubble of interest. A method to estimate the frequency, phase and amplitude of the secondary ultrasonic wave is discussed. Experiments are carried out for bubbles produced by an ultrasonic wave contrast agent. The results show that aggregated bubbles of a few tens of micrometers radiate approximately 7th- to 8th-order harmonic waves at 200 kPa sound pressure.

In this study, the change in thickness of the arterial wall caused by the heartbeat was measured by the phased tracking method [IEEE Trans. UFFC. 43 (1996) 791] for noninvasive assessment of the regional elasticity of the arterial wall. In the phased tracking method, the change in thickness of the arterial wall is obtained from the difference between displacements of two points set along an ultrasonic beam. The displacement during the pulse repetition interval is determined by the phase of the complex correlation between the quadrature modulated ultrasonic waves. For suppressing noise components, the complex correlation function is spatially averaged in the region, which corresponds to the ultrasonic wavelength. However, spatial averaging of displacements is not desirable for measurement of the change in thickness, because the change in thickness is caused by the spatial inhomogeneity of displacements. In this paper, the phased tracking method was modified for direct estimation of the change in thickness without spatial averaging of displacements.

In this paper, a new parameter that quantifies the intensity of tissue nonlinear elasticity is introduced as the nonlinear elasticity parameter. This parameter is defined based on the empirical information that the nonlinear elastic behavior of soft tissues exhibits an exponential character. To visualize the quantitative nonlinear elasticity parameter, an ultrasonic imaging procedure involving the three-dimensional finite element method (3-D FEM) is presented. Experimental investigations that visualize the nonlinear elasticity parameter distribution of a chicken gizzard and a pig kidney embedded in a gelatin-based phantom were performed. The values extracted by ultrasound and 3-D FEM were compared with those measured by the direct mechanical compression test. Experimental results revealed that the nonlinear elasticity parameter values extracted by ultrasound and 3-D FEM exhibited good agreement with those measured by the mechanical compression test, and that the intensity of tissue nonlinear elasticity could be visualized quantitatively by the defined nonlinear elasticity parameter.

Since an ultrasound (US) imaging system can image in real-time and interactively, it can be used as an image guidance assisting magnetic resonance imaging (MRI) for minimally invasive therapy. The effects of MRI-compatible US probes on MRI monitoring were evaluated, and it was found that the MRI-compatible US probes, whose backing material contained 100 ppm ferrite, did not disturb MR monitoring except at a few mm radius from the US probe's position. MRI temperature monitoring of a swine liver irradiated with a high-intensity focused US beam from an MRI-compatible therapeutic transducer with US image guidance was then performed, and the potential usefulness of such a therapeutic system in minimally invasive therapy was demonstrated.

To realize a quantitative diagnosis of liver cirrhosis, we have been analyzing the characteristics of echo amplitude in B-mode images. Realizing the distinction between liver diseases such as liver cirrhosis and chronic hepatitis is required in the field of medical ultrasonics. In this study, we examine the spatial correlation, with the coefficient of correlation between the frames and the amplitude characteristics of each frame, using the volumetric data of RF echo signals from normal and diseased liver. It is found that there is a relationship between the tissue structure of liver and the spatial correlation of echo information.

This paper describes the presentation of a three-dimensional (3D) ultrasound heart image on an immersive projection system (IPS). A 3D image was reconstructed from B-mode images that were acquired by transesophagel echocardiography. The reconstructed 3D image was presented on the IPS and the observer can see a stereoscopic image. The immersive environment could present a large field of view and enables interactive browsing and free movement of an eye position. Therefore, our developed system has the potential to be used as a visual interface in future robot surgery.

For the application of the ultrasound inverse scattering imaging method to medical diagnosis, measurement under a limited viewing range is strongly desired. To achieve this, we present an inverse scattering image reconstruction method based on the reflection and transmission data obtained by placing a reflector plate behind an object. The reflection and transmission data are measured while rotating the transmitter/receiver pair around a half-circumference of the object. We can simultaneously obtain two different directional data from one observation of the object through this method, therefore enabling us to reduce the range of the views to half compared with the conventional transmission method. In this paper, the reflection and transmission inverse scattering image reconstruction method using multifrequency illumination is proposed in order to improve the robustness of the method against the restriction of the viewing range. The validity of the method is examined using simulation data assuming an irregularly shaped triangular specimen. As a result, it was established that the precision of the sound speed values and reproducibility of the object shape in the reconstructed image were satisfactory although the aperture viewing range was limited to around 100 deg.

Ultrasound tissue-mimicking material using oil gel for a phantom is proposed. As the material has advantages in that bacteria do not propagate in it and organic liquids contained in it tend not to evaporate, its characteristics are stable with time. The oil gel is manufactured from ethylene glycol and propylene glycol or polypropylene glycol. The sound velocities and the densities of the organic materials for making the oil gel are measured for evaluation of phantom materials.

In this paper, we propose the power supply and the bi-directional information transmission system using ultrasonic. Ultrasonic does not interfere with the electronic circuits of implanted devices and is safe for a living body. Previously, we have clarified experimentally that ultrasonic is applicable to power and information transmission. This study deals with improving information transmission speed from the inside to the outside of the body. The new system uses two transmission paths, Path 1 and Path 2. Each path consists of a pair of piezo oscillators. Path 1 transmits a carrier wave and Path 2 echoes back the inside information. As a result, the transmission speed increases to 9.6 Kbps from 600 bps without errors. Additionally, several types of information, such as text, static and motion image files can be transmitted. The proposed system can be applied to various medical applications.

The phenomenon physically occurring within the head for bone-conducted sound of various stimulation locations has been calculated using the finite-difference time-domain (FDTD) technique; three slightly different stimulation locations near the left mastoid were set for audible and ultrasonic frequency stimulation. Calculated sound fields at the plane including the cochleae showed considerably different characteristics at different stimulation frequencies. For audible frequency stimulation, their distribution negligibly differed for each stimulation location. On the contrary, for ultrasonic frequency stimulation, their distribution shifted considerably for each different stimulation location. These results indicated the characteristics of the shifting sound image perceived for bone-conducted ultrasound and the negligibly shifting sound image perceived for bone-conducted audible sound, from the slight changes in their stimulation locations.

The 2-dimensional (2-D) ultrasonic imaging of static strain or elasticity in soft tissues with quantitative images of distributed parameters has been developed for medical diagnosis. However it is very hard to realize the quantitative image of stationary elastic parameters because living tissues are always affected by dynamical pressure change under the pulsatile blood circulation. Thus to replace the static image dynamically limited to local tissue substances the straightforward, physiological dynamic image of slight local motion during a frame interval, which cannot be visualized in conventional B-mode images, was pursued in this study. In the overall performance analysis of estimated axial displacement on accuracy, variance and spatial resolution, physiological dynamic images, which recorded velocity and acceleration between successive echo frames, were demonstrated by using real-time clinical data acquired from hepatohemangeoma. These images proved that real-time imaging is a practical and promising approach toward achieving an advanced version of clinical palpation, ultrasonic visualized palpation.

We previously developed a method for measuring small changes in thickness of the arterial wall during one cardiac cycle. Knowledge of this change in thickness is useful for in vivo assessment of the regional elasticity of the arterial wall. In this study, from computer simulations, it is found that measurement error depends on the distance of the ultrasonic beam from the center of the artery and it can be reduced by optimally setting the focal position. In basic experiments using a silicone rubber tube and in in vivo experiments with a human carotid artery, it is found that by optimizing the focal position, measurement of the change in thickness becomes more robust against mispositioning of the ultrasonic beam. From these results, it is demonstrated that optimum focal positioning provides more robustness in measurement, even if there is arterial wall motion causing the position of the ultrasonic beam to deviate from the center of the artery.

Development of ultrasound transducers with double-peak-type frequency characteristics for harmonic imaging and subharmonic imaging is reported in this paper. The peak on the low-frequency side in the frequency characteristics is used to transmit ultrasound into tissues or microbubble ultrasound contrast agents, and another peak on the high-frequency side is used to receive the second harmonic component in the ultrasound transducer with double-peak-type frequency characteristics for harmonic imaging. On the other hand, the peak on the high-frequency side in the frequency characteristics is used to transmit ultrasound and another peak on the low-frequency side is used to receive the 1/2 subharmonic component in the ultrasound transducer with double-peak-type frequency characteristics for subharmonic imaging. The results of the transducer design based on numerical calculation are reported in this paper.