Table of contents

Acoustic wave sensors are highly sensitive in detecting the properties of solid or fluid materials in contact with their surfaces, including the surface mass change, liquid density, liquid viscosity and electrical conductivity. In this paper, primarily, the commonly used acoustic wave sensors are reviewed and their mass sensitivities are compared. The fundamentals of the sensing system using the shear horizontal surface acoustic wave (SH-SAW) sensor on a 36° rotated Y-cut X-propagating LiTaO₃ are described. Since the high sensitivity of the electrical perturbation is a significant advantage of the SH-SAW sensor, its applications based on acoustoelectric interaction are also presented.

Primary frequency standards with stated inaccuracies of δf/f∼10^-15 or slightly better are in use today in several national timing laboratories. These standards, which are the most accurate in the world today, use laser-cooled cesium atoms to obtain this level of performance. We discuss the operation of these standards as well as possible future improvements that should see the inaccuracy of the realization of the second fall to the 10^-16 level over the next 5–10 years.

This short article is an introductory review and guidance on nonlinear acoustics, the study of which dates back to the 18th century. First, interpretation is made for the meaning and research field of nonlinear acoustics. Second, two typical model equations are presented describing finite-amplitude sound beams radiated in a viscous fluid from unfocused and focused powerful sources with finite apertures. The three basic characteristics of a wave, diffraction, dissipation, and nonlinearity are combined successfully in the model equations. Third, an innovative application referred to as a parametric acoustic array is shortly reviewed. Numerical demonstration shows specifically the sharp directivity of the parametric array.

A molecular dynamics computer simulation has been carried out for a monatomic, anharmonic, and two-dimensional hexagonal model crystal. Central forces between the nearest neighbor atoms and anharmonic forces up to the third order are considered. Pulse input displacements are applied to the line of atoms at one end of a rectangular crystal, and the atomic excitations propagating in the crystal are observed. The excitations are shown to be phonons or solitons when the applied pulse is small or large, respectively. A mass defect – an atom of which the mass is lighter or heavier than that of the lattice atoms – is placed near the center of the crystal. The excitation is scattered by the defect, and the simulations are made for various cases of large and small inputs, and light and heavy mass defects. The obtained results are represented using two-dimensional maps. The intention of the study and the significance of the results are briefly discussed.

The domain switching characteristics of a congruent LiTaO₃ (CLT) single crystal are investigated mainly with respect to switching speed. It is found that fast nanosecond domain switching can be achieved by reducing the sample thickness, even for CLT, which has been thought to be unsuitable for high-speed switching. As an example, the authors successfully obtain a polarization inverted domain dot with a radius of 7.9 nm in a 60-nm-thick CLT plate by application of a 4 ns, 10 V pulse. These results demonstrate that the speed of polarization reversal is closely related to the thickness of the medium.

On a direction-variable beam generated from an annular transducer array, the effects imparted to the shape of the beam when the decentering ratio of each element in the source is fluctuated are examined. A nondiffracting beam propagating with a sharp profile is formed by an annular transducer array in which each element has a width corresponding to the J₀ function. The sound source constructed by this method has clearances between each neighboring element, and the radiation direction of the beam becomes variable by utilizing these clearances in order to decenter the elements. Numerical calculations are carried out using five kinds of arrays the fluctuation of decentering ratio of each element of which differs. A slight deviation and bending in radiated beams appear, and these could be regarded as originating from the fluctuation of the decentering ratio in individual elements.

An impulse representation for calculating a diffraction wave due to a rigid wedge is described. The method is an approximation of the Biot-Tolstoy rigorous closed-form solution for the diffraction of point source radiation by an infinite rigid wedge. The band-limited time-domain function can be reconstructed to the original waveform if it satisfies the sampling theorem, which assumes that sampling takes place at the lowest permissible sampling rate. Therefore, if the energy is concentrated between the first sampling intervals immediately after the rise time of the time-domain function, the rigorous solution can be approximated as a delta function. This paper shows the description methods of the diffraction field near the ridge in three-dimensional space. Using the proposed impulse representation, numerical simulation was performed and the calculation accuracy was examined.

The authors have been researching the promotion of lactic acid fermentation by ultrasonic irradiation. In the past research, it was proven that ultrasonic irradiation is effective in the process of fermentation, and the production of yoghurt and kefir was promoted. In this study, the effect of the ultrasonic frequency in this fermentation process was examined. In the frequency range of this study, it was found that the action of fermentation promotion was exponentially proportionate to the irradiated ultrasonic frequency.

Stable plasma can be generated in a liquid hydrocarbon such as n-dodecane or benzene by simultaneous microwave and ultrasonic irradiation. The authors refer to this plasma as "sonoplasma" and distinguish it from "sonoluminescence" on the basis of the continuity of emission. The temperature in the plasma was obtained by measuring two specified emission intensities from the plasma which reached approximately 5000 K. To analytically estimate the temperature, numerical simulations of the behavior of a single bubble in sound field, taking into account the absorption of microwave energy, were carried out. The temperature inside the bubble in n-dodecane reached approximately 8000 K. In benzene, the temperature inside the bubble, which continued expanding through absorption of microwave energy, exceeded 2000 K.

A method that uses underwater ultrasonic waves to promote sedimentation of fine particles dispersed in suspension, such as pigments, has been experimentally studied. Relationships among factors such as concentration of suspension before ultrasonic irradiation (0.1–1%), sound pressure (0–100 kPa) and irradiation time (0–180 s), and promotion of sedimentation of dispersed fine particles upon irradiation of ultrasonic waves were experimentally examined using abrasive particles (silicon carbide) with average particle sizes of 4–10 µm.

We tried to remove a liquid leaked into a narrow channel immediately by radiating high-intensity aerial ultrasonic waves (at a frequency of 20 kHz) onto the liquid to atomize and disperse it into the atmosphere. Channels of 0.3 to 2 mm width and 1 to 10 mm depth with and without a bottom were used. The results of experiments showed that an ultrasonic radiation of 170 dB or more could remove a liquid in each of the channels immediately, by atomizing and dispersing it. The processes of atomization and dispersion of the liquid in each channel without a bottom largely varied, depending on the channel width and depth as well as the ultrasonic radiation intensity.

When ultrasonic waves are applied, the heat transfer at a heated surface in water increases markedly. The origin of this increase in heat transfer is thought to be due to the agitation effect from the microjets of cavitation and from acoustic streaming. The method in which four vibrators are used has the ability of further enhancing heat transfer. This paper presents the method using four vibrators to eject an acoustic stream jet at a selected position in the vessel. Analyses of this method are performed to establish it theoretically and to compare with an experiment previously conducted. The analyses shown in this research indicate that the aspects of acoustic streaming generated by the four vibrators in the vessel can be correctly predicted and provide a foundation for the development of using this method for the enhancement of heat transfer.

An electric discharge phenomenon in a high-intensity ultrasound field is influenced by a vibration from a medium in a boundary layer of an electrode. Static pressure is also a component that affects the discharge phenomenon. An intermittent spark discharge unit was set in a high-intensity standing wave field at 164 dB SPL and waveforms of electric discharge were measured. It was found that a prebreakdown current wave existed in a pilot plant; this is one of the important factors for describing the mechanism of the discharge in a high-intensity standing wave field.

In this paper, we propose a method for leveling viscous fluids–photoresist, for example–on substrates using ultrasound. We expect this technology to supersede the spin-coat method, particularly for large substrates. Ultrasonic leveling using standing waves is presented first, followed by a leveling method using traveling waves. The uneven thickness distribution produced through slit nozzle application can be eliminated using the proposed method. The experimental evaluation of these methods was performed, and the results demonstrate the positive effect on the surface nonflatness of a photoresist. In particular, the traveling wave method has an advantage of the freedom of orientation of the slit nozzle movement.

We present a method of fabricating a near-field optical probe with a nickel film whose thickness gradually decreases to a few tens of nanometers toward the apex. This method involves etching an optical fiber and electroless nickel plating with ultrasonic agitation. Using 1 MHz ceramic transducers, we have reproducibly fabricated the probe with a tip diameter of less than 40 nm. This reproducibility is high compared to those for Langevin-type transducers.

A new ultrasonic suction pump is described in this paper. The pump uses the suction force of a rigid cylinder tube vibrating at an ultrasonic frequency and has no physically moving parts. The pump consists of a longitudinal bolt-clamped Langevin transducer (BLT) combined with a stepped horn working at a resonance frequency of 24 kHz. A glass tube with the length of the half-wavelength-resonance is glued at the tip of the horn. To enhance pump performance, we introduced a reflection plate and a thin rod installed to the end of the glass tube with a small gap. Maximum pressures of 7.2 kPa and 23.5 kPa were recorded using the reflection plate and the thin rod, respectively. In this study, we experimentally investigate the characteristics of the pump and the operating physics. The maximum pressure is a function of the vibration velocity of the end surface of the glass tube and of the gap.

The three-dimensional (3D) finite-difference time-domain (FDTD) method is applied to acoustics analysis in this paper. The disadvantages of its method are large memory requirement and long calculation time. We developed the 3D-FDTD method using parallel computing with the Message-Passing Interface (MPI) in the personal computer (PC) cluster because it could shorten the calculation time and could treat larger memory. In this paper, basic algorithm of the proposed method is described. The acoustic fields of point sources and the real aerial sensor are calculated for verifying the validity of the method.

This paper deals with a piezoelectric ceramics ultrasonic motor of rectangular plate type using double resonance modes of longitudinal (L₁) and width-bending (B₁) vibrations. First, the motor construction and its operating principle are described, and second, the measured characteristics of this prototype motor are presented.

In this paper, we report an ultrasonic motor capable of high-velocity revolution applicable for long continuous high operation as a microfan. This study is a response to the new challenge of developing a new field of applications for an ultrasonic motor. Ultrasonic motors using a longitudinal-flexural coupling-vibration mode of a thin plate with a vibrating piece or step-horn are considered. A stator vibrator consists of a metal plate sandwiched by two thin unipoled piezoelectric ceramic plates, the electrodes of which are not divided, and this ultrasonic motor can be driven by a single ac source. Not only the coupling between a longitudinal vibration and flexural one but also the transformation of a longitudinal vibration velocity by a vibrating piece λ/4 long and step-horn λ/2 long are used. They will be effective at making the rotary speed fast. As a result, an ultrasonic motor 0.55 mm thick rotated a shaft 1.5 mm in diameter over 8,000 rpm under conditions of an applied voltage of 30 Vp-p and an input power of only 0.16 W.

A piezoelectric linear motor using a (R,1)-((1,1)) mode disk has practical requirements, such as high-speed movement, high thrust characteristic and simple construction of thin shape. However, two resonance vibration modes, namely, (R,1) and ((1,1)), do not have vibration nodes common to their movement, and therefore, a stable support of the motor could not be realized. Thus, we devised a new stator vibrator to which a stable and good support method can be applied. That is, the construction is such that it is equipped with T-type support jigs on the two positions of the disk circumference. This structure suffers almost no influence from the support, because the resonance frequencies of T-type support jigs are made equal to the frequencies of the two resonance modes of the stator vibrator. In this paper, we deal with this new type of linear motor using the (R,1)-((1,1)) mode disk and report on the simulated and measured characteristics of the proto type motor.

A multidegree-of-freedom (MDOF) ultrasonic motor using the multimode of a disk vibrator is realized. A spherical rotor can rotate around arbitrary axes. However, at the beginning of research on the MDOF ultrasonic motor, the MDOF ultrasonic motor did not have any mechanisms for supporting a spherical rotor. Since the preload was given by only the rotor's own weight, the friction between the rotor and the stator vibrator was very small, but the torque characteristics of the MDOF motor were insufficient for practical use. The purpose of this study is to improve the motor performance further. In this paper, some support and preload mechanisms using a support plate were examined for the improvement of the motor performance. In addition to these methods, a sandwich structure in which two stator vibrators hold a spherical rotor is proposed. This structure has both a rotor support mechanism and a preload mechanism, and high torque by the torque composition of two stator vibrators can be obtained.

The configurations of large-capacity 27 kHz ultrasonic complex vibration sources with multiple longitudinal transducers are proposed and studied. Ultrasonic complex vibration systems are effective for various types of metal welding and essential for new applications in various industries. The large-capacity vibration source consists of a complex transverse rod with a welding tip (titanium alloy), a complex vibration rod with a flange and a stepped part for holding the system (stainless-steel), a one-wavelength longitudinal vibration disk (aluminum alloy) and six bolt-clamped Langevin type piezo-electric ceramic (PZT) transducers (BLTs) installed along the circumference of the disk at an angle difference of 60°. The vibration source is driven using three driving systems with three transformers at a phase difference of 120°, and the disk is driven in a circular locus. The transverse vibration rod installed at the center of the disk is driven transversally and the welding tip of the rod vibrates in a circular locus.

Vibration and welding characteristics of a 94 kHz ultrasonic plastic welding system are studied. The 94 kHz ultrasonic plastic welding systems consist of a 30-mm-diameter bolt-clamped Langevin-type PZT longitudinal transducers with four PZT rings, a stepped horn (vibration transform ratio N = 3.0) with a supporting flange at a nodal position and a catenoidal horn (N = 3.13) with an 8-mm-diameter welding tip. Maximum vibration velocity of the 94 kHz welding tip was 3.2 m/s (peak-to-zero value) at loaded condition. The welding characteristics of the 1.0-mm-thick polypropylene sheet specimens using the 94 kHz welding system were studied. Using the 94 kHz system, a weld strength of more than 370 N per one welded area was obtained at a vibration velocity of 2.7 m/s_p-0 (peak-to-zero value), welding time of 0.8 s and static pressure of 600 kPa.

The vibration and load characteristics of an ultrasonic motor using a circular vibration disk with three longitudinal transducers have been studied. Three bolt-clamped Langevin type piezoelectric ceramic (PZT) longitudinal transducers (BLT) 20 mm in diameter were installed along the circumference of the circular disk, and complex transverse vibration rods were installed normally in the center of the circular disk. A complex transverse vibration rods are driven simultaneously using three power amplifiers with a phase difference of 120°. The transducers could also be driven using only one power amplifier in the case where the resonance frequencies were slightly different. A rotor disk installed on the free edge of the transverse vibration rod was pressed statically to a driving surface using a system for inducing static pressure. A maximum torque over 0.12 Nm was obtained using three power amplifiers under a static pressure of 1.7 MPa. A maximum rotation of 280 rpm and an efficiency of 1.13% were obtained using one power amplifier under a static pressure of 1.4 MPa.

Shear and compressional wave velocities in (Ba_0.996Y_0.004)TiO₃ semiconductive ceramics were accurately measured by the pulse transmission method over the temperature range between 20°C and 210°C. The temperature dependence of the ultrasonic wave velocities exhibits a marked feature at the characteristic temperatures of transition in resistivity. The elastic moduli were calculated using ultrasonic data.

Ultrasonic atomic force microscopy (UAFM) was used to investigate the elasticity variation on domain boundary (DB) in lead zirconate titanate (PZT). The UAFM imaged the change in contact stiffness not only among grains but also on the DB. According to an analysis, the contact stiffness of the DB was approximately 10% lower than that within the domain. This is the first direct evidence of the variation of the elasticity due to the DB. The implication of this finding is that the low stiffness at the DB may affect the piezoelectricity of PZT and the easy mobility of the DB under a stress and electric field, which are important for not only actuator applications but also high-speed writing memory applications.

A composite material consists of two or more materials and its optimum acoustic properties can be designed by selecting its constituents. Unidirectional composite materials have a very low transverse Poisson's ratio of less than 0.1. By considering such composite material features, the applications of carbon fiber-epoxy and highly crystalline polyethylene fiber-polyurethane composite materials to a medical transducer array are proposed. The sound velocities and densities of the composite materials are measured and their transverse Poisson's ratios are calculated from experimental data.

Reflection-induced ΘA Brillouin scattering (RIΘA) is introduced to investigate the opto-acoustic anisotropy of uniaxially stretched polyvinylidene fluoride (PVDF) films (0.04 mm in thickness). Although the films are not perfectly transparent, their elastic and optical anisotropy could be investigated nondestructively. The optical anisotropy, which is observed as birefringence, showed a clear decrease near the Curie temperature (T_c).

The complex reflectance function of acoustic waves in the incidence angle range from 0 to 60° was calculated for polymer thin films on glass substrates with different Young's modulus and density values. A characteristic phase change of the complex reflectance function was observed due to the existence of the polystyrene thin film on the glass substrate. The phase change appeared when the thickness of the polymer thin film was more than 0.9 µm at 300 MHz. The normalized wave number of the characteristic phase change varied sensitively with Young's modulus and the density of the polymer thin film. The contour map of the normalized wave number was obtained from these results. The determination method of Young's modulus of the polymer thin film by the characteristic phase change was proposed.

Ultrasonic absorption in aqueous solutions of sodium p-toluene sulfonate and dodecyltrimethyl ammonium bromide was measured in the frequency range from 0.2 to 7 MHz. The ultrasonic relaxation spectra showed a single relaxation process in both the spherical and rodlike micelle solutions, which was identified as the relaxation due to the micelle-monomer exchange process. The relaxation time and strength were discussed in terms of Teubner's theory.

The use of ultrasonic wave technology was anticipated as an important technology in monitoring the health of composite materials and/or structures. However, the propagation of ultrasonic wave becomes very complicated in polymer-based composite materials due to reflection, transmission, dispersion and other behaviors, which may occur at the interface of the matrix and reinforcements. Therefore, in this study, the elastic wave motion equation is evaluated using finite element analysis; then the propagation of ultrasonic waves in several model composite materials was simulated. The influences of the fiber/matrix interface, fiber size and other fiber properties on wave propagation were clarified. Moreover, the complicated propagation resulting from reflection, transmission and refraction on the fiber/matrix interface was visualized, and the influences of the arrangement of the fibers, the debonding position at the interface, and the volume fraction of fiber are discussed.

The photoacoustic (PA) spectra of porous Si (PS) were measured using a microphone under various surface treatments such as vibration during anodisation, vibration during rinsing, and acid surface treatment before contact deposition. The Fourier transform infrared (FTIR) spectra were also compared for the estimation of surface conditions. To obtain good contacts for electroluminescence (EL) devices, where a large injection current during operation is required, the vibration during rinsing in distilled (DI) water and hydrochloric (HCl) acid surface treatment are important. The PA signals increase with such vibration because of the enhancement of the pressure effects in pores of PS. Moreover, the decrease in PA signals caused by the surface change of pores can be also observed with the surface treatments. As the good contacts are obtained both by the vibration and surface treatments, the surface states in the pores seem to be important for the contacts to PS. This process can be monitored by PA spectroscopy in a noncontact manner because the PA signals from the PS are enhanced in the pores by the pressure effects, and PA spectroscopy can be sensitive to the change in surface of pores of PS.

Photoacoustic (PA) spectra for Zn_1-xCo_xO mixed-crystal powders with various Co concentrations and sintering temperatures were measured. The PA spectra showed three peaks of Co²⁺ absorption between 560 nm and 660 nm. On the other hand, the PA spectra between 800 nm and 1000 nm were almost flat, and these are expected to be dominated by light scattering effects. The PA spectra were normalized by using the Co²⁺ absorption peaks in order to compare the sample size and the PA signals intensity, and the sintering temperature dependence of the PA spectra is discussed. The PA signal intensity decreased with the increase of the sintering temperature. The decrease of the PA spectra seems to be caused by small light scattering effects for the large clusters under higher temperature sintering, where the grains and clusters size increase. We could evaluate the grain growth in the sintering processes by PA spectroscopy in a noncontact mode.

In this study, the nondestructive testing (NDT) of tilting surface defects has been demonstrated using a photoacoustic microscope (PAM). The tilting surface defects were fabricated on a metal plane specimen by mechanical processing. The obtained signal strength distribution was affected by the tilt angle of the surface defects, and it is possible to estimate the tilt angle of the surface defects from the gradient of the obtained signal strength distribution.

Room-temperature piezoelectric photothermal spectroscopy (PPTS) measurements were carried out for the single-quantum-well (SQW) structures of GaInNAs. Four as-grown samples with thicknesses of 10, 7, 5 and 3 nm were used to investigate the quantum confinement effect in the SQW. The exciton contribution was clearly distinguished from the two-dimensional step like band-to-band transition. The thickness dependence of PPT signal peak energy were well understood by quantum mechanics. The decrease in well thickness results in increases in quantized energy level and exciton binding energy. The present results showed that the newly developed PPT methodology is a unique and powerful tool for investigating the optical absorption spectra of extremely thin quantum well structures.

Two types of nanostructured titanium dioxide (TiO₂) electrodes were prepared with anatase TiO₂ nanoparticles of different sizes (average diameters of 15 and 27 nm). CdSe quantum dots were adsorbed onto each of the two types of TiO₂ electrodes, by a chemical deposition (CD) technique, the average sizes of which increased to 7 nm on increasing the deposition time. Optical absorption and photoelectrochemical properties were characterized by using photoacoustic (PA) and photoelectrochemical (PEC) current methods. Redshift of the PA and PEC current spectra with increasing CdSe sizes was clearly observed, which indicates quantum confinement effects and photosensitization by the CdSe quantum dots. It was found that the PEC current spectra in the visible region were quite different for the two types of TiO₂ electrodes for the same deposition time, although the PA spectra were very similar to each other. The correlation of the PEC current spectra with the microstructures of the two types of TiO₂ electrodes was discussed, which provided information that could lead to the optimization of dye-sensitized solar cells (DSSC).

The fidelity of ultrasonic phase conjugate waves has been experimentally investigated at the wavefront level. Phase conjugate waves at 3.7 MHz were generated via nonlinear piezoelectricity of PZT (PbZr_xTi_1-xO₃) ceramics, and wavefronts of the incident wave and the phase conjugate wave were visualized by the schlieren method. Wavefronts of an incident wave and those of the phase conjugate wave agreed with the errors of 1/6 the wavelength. A possible cause of the error is the diffraction effect due to the finite aperture of the phase conjugator. Some additional, noise-like ultrasonic fields were detected in schlieren images.

Waveguide-type acoustooptic (AO) switches can switch optical waves wavelength-selectively for wavelength-division-multiplexed (WDM) signals. The switches can be expected to be used in WDM photonic networks. In this paper, finite-difference time-domain (FDTD) analysis is presented for wavelength-selective switching with a collinear weighted AO device consisting of an optical directional coupler, input/output Y-branches and a tapered surface acoustic wave (SAW) waveguide. The FDTD simulated results are compared with the result from the coupled mode theory. It is shown that a sidelobe level as low as -20 dB in the filtering characteristics is realized by using weighted AO interaction. It is also shown that the sidelobe structure is affected by the characterisitcs of the input Y-branch.

The piezoelectric photothermal (PPT) signals from hydrogenated microcrystalline silicon (µc-Si:H) films were measured and the effects of the deposition rate on the optical properties were investigated. Increasing the deposition rate resulted in (i) a decrease in optical absorption coefficient, (ii) a shift in effective energy gap to the higher photon energy side, and (iii) a increase in the density of localized states originating from a structural disorder. These results led to a reduction in the photovoltaic conversion efficiency of the solar cells for high-deposition-rate samples. The usefulness of the PPT method for investigating the optical properties of thin and transparent µc-Si:H films was also demonstrated.

A wavelength-switchable and tunable fiber ring laser has been proposed to implement an optical source of a fiber Bragg grating (FBG) vibration sensor array based on intensity modulation technique. The laser consists of an erbium-doped fiber amplifier (EDFA) and an optical switch with tuning FBGs, in which the lasing output is coupled out from a selected tuning FBG and serves as an optical source of one of the multiplexed FBG vibration sensor elements. By changing the channel of the optical switch, the lasing wavelength can be chosen for the sensing FBG of the respective sensor element. In addition, the temperature effects on the sensor outputs due to environmental temperature can be eliminated when the temperature changes are applied commonly to both the tuning and sensing FBGs. In the experiment, multipoint vibration detection with a temperature-insensitive operation is successfully demonstrated by constructing two sensor elements arranged in parallel.

Due to a strong quantum confinement effect, the thermal conductivity and heat capacity per unit volume of a nanocrystalline silicon (nc-Si) layer prepared by electrochemical anodization are extremely low when compared to those of single crystal silicon (c-Si). These large differences in the thermal properties between nc-Si and c-Si make it possible to produce an efficient ultrasound emitter device based on thermo-acoustic conversion without any mechanical vibration. In this paper, the fundamental ultrasound characteristics of a fabricated thermally induced nc-Si ultrasound emitter are explained with regard to an application as an ultrasound speaker. Ultrasound generated at the same frequency as the input signal exhibits a flat frequency response over a wide range and is non-directional. This behavior is totally different from that of conventional airborne ultrasound devices such as piezoceramic transducers.

Mechanical and dielectric losses were measured by the measurement method proposed in this paper in a piezoelectric transducer with input and output terminals. These losses must be considered in designing piezoelectric transformers used as power sources. In the method proposed here, the losses can be obtained using the experimental results of resonance angular frequency, quality factor and the resistive component of input impedance when the output terminals are short-circuited and opened, and using the measured phase angle difference between current and voltage when the output terminals are opened. In the method, a resonance frequency tracking circuit is utilized. Hence, there is an advantage that the measurement can be performed easily and in a short time. The results obtained by this method have also been used in the evaluation of the efficiency of piezoelectric transformers.

The contact mechanism for a quartz-crystal tuning-fork tactile sensor has been investigated both theoretically and experimentally. We assume that the L-shaped right half of a quartz-crystal tuning fork is described by Sezawa's model and the torsion spring model. The frequency of the tuning-fork tactile sensor is analyzed by considering the lateral clamping force of an acrylic resin case and Winkler's foundation of the object in contact. The calculations are performed under two boundary conditions at one end of the bar which corresponds to the center of the base. Five metals (brass, copper, aluminum, stainless steel, and iron) are investigated in the present experiment. The calculated results are in reasonable agreement with the experimental ones.

In this paper, we describe a novel atomization system using surface acoustic wave (SAW) devices. The SAW radiates its energy into a liquid, if the liquid is loaded on the SAW propagating surface. The various liquid motions, such as vibration, flow and droplet formation, due to interaction between SAW and liquid are called SAW streaming. The liquid dynamics depends on the SAW input power. First, the relationships between input voltage to the SAW device and water dynamics are observed. For atomization, an input voltage larger than 30 V_P-P is required. Second, a stable method of generating a mist is discussed. The thin liquid layer plays an important role in continuous mist generation. The fundamental properties, such as the angle and height of mist, are measured using a filter paper to keep a thin liquid layer on the surface. We also demonstrate the control of mist direction with an electrostatic field. Based on these fundamental experiments, a practical atomization system is designed and performed.

In this study, the propagation characteristics of a pure shear-horizontal-type surface acoustic wave on rotated Y-cut 90° X propagation langasite (at Euler angles of (0°, θ, 90°)) with a high-density thin film, such as a gold (Au) film or a tantalum pentoxide (Ta₂O₅) dielectric film, are investigated. The theoretical analysis showed that, by loading with these films, coupling factor increases to about 1.0% for a certain condition. In fact, the measured coupling factors for θ=20° were 0.80% and 0.61%, for the samples with a Au film thickness of 0.015 wavelength (λ) and a Ta₂O₅ film thickness of 0.047 λ, respectively. For both films, the measured frequency shifts in the temperature change for θ=20° showed that a temperature characteristic with a zero temperature coefficient of delay in the same as the ST-90°X quartz with a free surface can be obtained by appropriately choosing the film thickness.

Evanescent acoustic fields which decay exponentially from the plate surface can be created in the vicinity of a piezoelectric bending vibrator. When an object is brought into this evanescent field, the electric admittance of the vibrator undergoes some change depending on the vibrator-to-object distance d. The authors' group has found so far that as an object comes into close proximity with the plate end, an unexpected phenomenon occurs such that the Q-factor which once decreased starts to increase in the range where d becomes small. In this study, this unique phenomenon is examined in detail by experiments and some new findings are shown on the variation of bending-vibrator characteristics. Also, theoretical explanations are given to conjecture the mechanism of this phenomenon by using a simple model.

In this study, we focus on a flatly supported gyro sensor using a double-ended tuning fork quartz resonator set in parallel with the rotating plane. The resonator has the advantages of flat form, high precision and strong shock resistance; moreover, fundamentally, the resonator is able to detect two-axial angular velocities. We clarified the features of the resonator by discussing the advantages and disadvantages of the resonator as a gyro sensor. The resonator was designed to have high detection efficiency, applying the vibration theory and using the finite element method. The resonator was finely fabricated by photolithography and wet etching. As a result, the resonators, without any problem as a gyro sensor, have been fabricated; we also confirmed experimentally that the practical angular velocity could be detected by the prototype gyro sensor. Consequently, we can conclude that the double-ended tuning fork quartz resonator could be used as the flatly supported gyro sensor.

Using a conventional RF magnetron sputtering system, we have obtained two types of ZnO films on various kinds of substrate. One is a film with the c-axes of crystallites unidirectionally aligned in the substrate plane {(110) textured film}. The other is a film with c-axes parallel and perpendicular to the plane (mixed texture film). The former is expected to realize a shear wave transducer on the surfaces of various materials. The alignment of c-axes of crystallites in the plane was then carefully investigated by the X-ray pole figure analysis. The elastic anisotropy in the film has been successfully measured by the Brillouin scattering method. The (110) textured film did not excite the elastic waves; however, comparatively strong shear waves were actually excited by the mixed texture film.

Multilayer ceramic resonators using a piezoelectric longitudinal-effect flexural vibration mode have been developed. The resonators are able to be designed in a much smaller format while maintaining high performance than the multilayer longitudinal resonators which we previously presented. Utilizing internal divided electrodes and floating electrodes makes it possible to generate a flexural vibration mode without complicating the process of connecting electrodes or polarizing. The relationship between the ratio of piezoelectric area in the length direction and the bandwidth, and the effects of the gap and distance from the internal electrodes on the resonator characteristics, are analyzed by the finite element method. Resonators and ladder filters are investigated and their superior characteristics and small size have been demonstrated.

We numerically analyze the two-dimensional (2-D) coupled vibrations of a doubly rotated quartz plate with tilted edges. An efficient technique that uses a combination of 1-D and 2-D finite element methods is developed to solve coupled vibrations in the Y'-Z' cross section of a parallelogram shape. When the orientation of a quartz plate is described using the IEEE notation, as (YXwlt)φ/θ/ψ, the third rotation ψ about the plate normal is selected such that the Z'-width faces are parallel to the particle motion of a slow-shear wave propagating in the Y'-thickness direction. For SC-cut plates operating in the fundamental slow thickness-shear mode, we evaluate the effect of tilted edges on the frequency spectra and the first frequency-temperature coefficients, and verify the strong decoupling effect on the thickness-shear and face-shear modes. The optimal inclination angle of tilted edges for SC and FC cuts is appropriately defined as the equiphase plane of the main displacement of the face-shear traveling wave.

In this paper, we calculated the mode-coupling characteristics of multistepped bi-mesa resonators and compared them with those of beveled resonators. Calculation results showed that increasing the number of mesa steps red to reduced coupling between the thickness-shear and thickness-flexure modes. These results indicate that the multistepped bi-mesa resonator has a good mode-decoupling effect, and its performance characteristics approach those of the beveled resonator.

Lamb waves propagating on an AT-cut quartz substrate were studied. In this study, we propose a high-frequency resonator using a Lamb wave. A Lamb wave is excited on an extremely thin AT-cut quartz substrate which thickness is comparable to the wavelength of an elastic wave propagating on a substrate. This Lamb wave propagates at a higher phase velocity mode than surface acoustic waves. This realizes an RF resonator operable in a high frequency range in which a conventional quartz resonator hardly operates. A theoretical analysis of the reflection coefficient of a Lamb wave with a grating reflector was conducted. The analysis results and experimental results are compared and discussed in this study. A reflection coefficient which is 10 to 20 times higher than that for a Rayleigh-type surface acoustic wave is obtained.

The methodology to trap the vibrational energy of an axially polarized surface-shear wave (axial-shear wave) in a stepped cylindrical rod is presented. The central part of the rod where the resonance vibration was trapped had a slightly larger diameter. The magnetostriction effect of steel enabled us to generate and detect the resonance with noncontacting. An approximated analysis was used to derived a resonance equation and displacement distribution of trapped axial-shear-wave modes. The displacement was measured along the axial direction and it exponentially decreased with the distance from the center. This trend agreed with the theoretical calculation.

Surface acoustic wave (SAW) filters employing a unidirectional interdigital transducer (UIDT) show low loss, wide band properties. In this paper we describe a new single phase unidirectional transducer (UDT) of about λ/4 electrode width with the best transducer efficiency. The new UDTs are fabricated on the very thin dielectric grating or very shallow groove grating SAW substrates. The electromechanical couplings (k²) of electrodes on SiO₂ gratings decrease rapidly for film thickness. Therefore the good properties of UDT are obtained for very thin SiO₂ (about 0.3 µm and 0.03 µm at 100 MHz and 1 GHz, respectively). The calculation results show wide-band, low-loss filters with various k² materials. Also, the electrodes of λ/2 width have large reflection coefficients of SAW. The calculation and experimental results of SAW resonators with λ/2 electrode width and λ-period using susceptance changes are described.

We are studying the response of a strip-type LiTaO₃ shear wave resonator in polymer liquid in MHz range. The element size is small (1.0×7.4×0.49 mm³). The side surfaces of the resonator were covered with a highly viscous silicone rubber material. Using Newton fluid theory, the characteristic mechanical impedance of the shear wave in the liquid was derived for the equivalent circuit of the resonator. The analytical values of glycerin were roughly consistent with the experiment using only 0.1 cm³. The polymer liquid used for the measurement was silicone oil. The static viscosity was from 9.8 to 94,720 mPa·s. The resonance frequency change was from 0.05% to 0.07%. The resonance resistance change was from 57 Ω to 190 Ω. The experiment results were examined using Mason's equivalent circuit with Maxwell model of a viscoelastic polymer.

In this paper, the characteristics of the acceleration sensor utilizing the resonance frequency change in the flexural vibrator are examined experimentally. The sensor sample was produced using stainless steel. It was confirmed that the relationship between the applied acceleration and the resonance frequency change becomes linear and almost coincides with the theoretical value by the finite element analysis. The sensor sensitivities of approximately 2800 ppm/G and 2150 ppm/G are measured in the cases of using the 1st and 2nd modes, respectively. It was clarified experimentally that the spurious vibrations do not appear in the vicinity of the resonance frequency f₀. Moreover, it is shown that this sensor can also be used as an inclination angle sensor.

Using a 3×4×5 mm torsional microtransducer attached to a 30-cm long, 0.3-mm diameter flexible stainless steel wire, torsional vibration and coupled torsional-flexural vibration is transmitted to a remotely-placed rotor. The torsional microtransducer uses flat, thickness-poled lead zirconate titanate (PZT) elements attached to the surface of a square-sided prism with a tapered horn and tip; the elements twist the structure and generate torsional vibration amplified by the horn and tip at 150–260 kHz. Swaged to the wire–the `acoustic waveguide'–torsional vibration is transmitted into the wire, and flexural vibration is developed in the wire due to strong torsional-flexural coupling, demonstrated by measurement of the vibration velocity. Standing wave vibration was generated (standing wave ratio, SWR≈7.5) in the waveguide with nothing on the waveguide tip, but upon using a rotor, traveling wave vibration transmitted energy to the rotor (SWR≈4), which acted essentially as a loss; by placing a damping material on the tip instead of a rotor, very similar traveling wave motion was obtained (SWR≈1.5). The few torsional resonances of the transducer were found to be greatly increased in number by the waveguide, and rotors, with a contact radius of 300 µm, were found to rotate for most of these resonances in either direction at up to 11,500 rpm and 3.5 µN-m.

In this paper, we present an analysis of the viscoelastic characteristics of a silicone rubber test piece for a tactile sensor using the finite element method. The calculated characteristics of stress relaxation and dynamic viscoelasticity agree well with the experimental values. The results can be used for designing a standard test piece for the evaluation of the measurement accuracy of a tactile sensor.

By applying a new shear horizontal (SH)-type leaky surface acoustic wave (LSAW) excited by interdigital transducers (IDTs) and reflectors made of Ta or W on an ST-cut 90°X-propagation (direction perpendicular to X-axis) quartz substrate, we succeeded in fabricating very small resonator filters (1/5–1/4 of conventional device sizes). However, the Ta and W films used in our filters were β-Ta and β-W, which have resistances higher than that of an Al film. α-Ta and α-W films with very low resistivities have been successfully deposited in place of β-Ta and β-W films. The insertion loss of resonator filters consisting Ta- or W-electrode/ST-90°X quartz has been improved by 1.5–8 dB using the α-Ta or the α-W film electrode.

This paper deals with a new type of slope sensor using a thin plate piezoelectric bending vibrator loaded with moment impedance. This sensor is fabricated on the basis of the gyro-moment motor already reported by one of the authors. In the first part of this paper, the construction of this sensor and its operation principle are described. In the second part, basic experimental results proving the principle are presented. Moreover, we show the results of finite element method simulations of some constructions of the slope sensor.

In this paper, we present the relationship between the transmission function and the terminating resistances of a triple tuned coupled band-pass filter. It is possible to estimate the change of the transmission function by changing only the terminating resistances continuously while keeping the other equivalent circuit parameters fixed. The following results were obtained. When terminating resistances are changed continuously over a wide range, the well-known equal ripple, maximally flat and flat delay characteristics appear dispersedly. There is a combination of parameters which shows the group delay resembling a Gaussian distribution. The group delay at the center frequency becomes minimum when the filter function exhibits the maximally flat in attenuation. It is convenient that the terminating resistances can be changed continuously as an independent variable, because it enables some evaluation criteria to be satisfied.

In order to give a wide beam width characteristic to a vibrating element, acoustic convex lenses were fabricated and the diverged acoustic field was investigated experimentally. To design the acoustic lenses, an acoustic field estimation method was proposed by using an angular spectrum method. It was confirmed that the estimation of the diverged acoustic field is possible using the suggested method and the acoustic convex lens can achieve the wide beam width characteristics of the vibrator.

In ultrasonic computed tomography (UCT), it is necessary to synthesize a plane wave using waves emitted from sound sources arranged in the interior surface of a cylinder. In order to transmit a plane wave into a cylindrical surface, an ultrasonic transducer which has many vibrating elements with piezoelectric transverse effect arrayed on an arc surface is proposed. To achieve a wide beam width, the elements should have a small radiation area with a much narrow width. The measured electroacoustic efficiency for the elements was approximately 40% and the beam width defined by -3 dB level from the maximum was as wide as 120 deg. It was confirmed that plane wave synthesis is possible using the proposed transducer array.

This paper discusses the application of Love mode propagating on Cu-grating/rotated YX-LiNbO₃-substrate structure to the development of ultra-wideband and low-loss RF surface acoustic wave (SAW) filters. Theoretical analysis suggested that high performance resonators with very small capacitance ratio would be realised using Cu gratings with a thickness of several percent of wavelength. It was also suggested that in particular, on 15°YX-LiNbO₃-substrate structure, the spurious response due to Rayleigh mode could effectively be suppressed. An IDT-type one-port SAW resonator and a ladder-type SAW filter were fabricated on the Cu-grating/15°YX-LiNbO₃-substrate structure, and their high performances are demonstrated with discussion.

Propagation of surface acoustic waves (SAWs) was investigated on a single lithium niobate (LiNbO₃) ball of 1 inch diameter. We found ten specific routes, on which the roundtrips of SAWs are observed, and one or more specific routes, on which the multiple reflections of bulk waves are observed. Since the temperature coefficient is similar on each route of the SAW, one route can be used to correct the temperature dependency of all other routes, and the other routes can be used as multiple-gas sensors by coating various reactive thin films along each route.

Noncontact air-coupled ultrasonic systems for measuring micrometer- or submicrometer-order displacements are newly constructed at frequencies of 40 and 400 kHz. The phase detection accuracy of the displacement measurements under several thousandths of ultrasonic wavelengths λ is markedly improved by the introduction of phase differences between the reference waves and the transmitting wave signal. To verify our system, the displacement of the reflector, which is translated by a high-precision mechanical stage, is measured using a single piezoelectric ceramic transducer in the reflection mode. Resolutions of displacement of better than 1 µm or 0.1 µm (λ/8500) using ultrasonic waves of 40 or 400 kHz in air, respectively, are achieved.

In pulse compression methods used with ultrasonography, when a small signal is reflected by a small target positioned near a large target, the small-target reflected signal can be obscured by the sidelobes of the large-target reflected signal. We apply a digital subtraction method using zero-padding to detect the small signal.

Final aim of this study is to estimate the corrosion-induced wall reduction of the bottom plate in storage tanks from the outside of the tank. We excited strong S₀-mode Lamb waves by impacting the center of the edge plane of a plate, and monitored both the amplitude and arrival time of the S₀-mode reflected from artificial slits by a low frequency receiver mounted at the edge plane. The amplitude of reflected S₀-mode Lamb waves increased proportionally with slit depth. Locations of defects, calculated from the arrival time of reflected S₀-mode Lamb waves, were estimated as the locations of actual slits with an error below 2%.

Cracks in solids can be detected by ultrasound if they are open. However, their detection is not easy when they are closed with a closure stress, and thus it is a fundamental problem in ultrasonic testing. Subharmonics with half the input frequency is potentially useful in the detection and evaluation of such cracks, although quantitative analysis has not been established. In this work, we develop analytical and numerical theories accounting for the crack parameters, such as closure stress and crack surface conditions, for the first time. We proved their validity by comparison with experiments on a well-defined fatigue crack in aluminum alloy, finding reasonable agreements. Based on these theories, it will be possible to estimate important parameters of partially closed cracks by fitting measured waveforms to theoretical predictions, which solves the fundamental problem in ultrasonic testing of cracks.

For the measurement of very high viscosity, we attempted to use a cantilever-type viscosity sensor using a triangular bimorph with a needle. Thus, the frequency-phase characteristics of the sensor in each viscosity were investigated at a low frequency range by changing the length of the triangular bimorph. As a result, it was clarified that we could develop a viscosity sensor with high sensitivity for very high viscosities up to 100,000 mm²/s(=cSt), using frequencies below 100 Hz.

An acoustical method for temperature measurement of large-scale spaces in a wind field is described. The real-time thermometry in a long span of 100 m was realized by the adoption of a bidirectional sound probe as a temperature sensor and a wireless local area network for controlling sensors. The probe mainly consists of two loudspeakers and two microphones. An accurate mean spatial temperature was measured without the interference of the wind in the area by the bidirectional probe. We carried out numerical simulations to confirm the validity of our method. The mean temperature was satisfactorily measured by this principle under various distributions of wind velocity. In field measurements, mean spatial temperature along a 100-m-long baseline was measured by the system with a conventional thermometer as a reference. The temperature change over one hour at 30 s intervals was compared to the change in the reference temperature at the center of the baseline. The results indicated that the system recorded a long periodic change in air temperature without the effects of local turbulence and wind. The advantages of the proposed system compared to a conventional thermometer are real-time, wireless and noncontact measurements.

In this paper, we describe temperature measurement using acoustic reflectors. The reflectors increased the number of sound paths to five. The temperature distribution was measured with one loud speaker (SP) and one microphone (MIC) utilizing a radial transmission of the SP and specular reflections of sounds. The propagation paths of the sounds could be used as the sound probes and their directions could be changed using the acoustic reflectors with plane surfaces. By adjusting the angles of the acoustic reflectors as the propagation paths reached one of the MICs, the temperature distribution of an arbitrary and partial space in the measurement object could be measured. The temperature distribution of a horizontal space partitioned into five unit cells was measured with one SP, one MIC and ten acoustic reflectors. The -6 dB beam width of the SP was approximately 80 deg, thus the received signals maintained sufficient amplitudes. Experimental results showed a good agreement with the temperature distribution results measured with thermocouples.

In this paper, we describe a visualization method of wind velocity and direction distributions for micrometeorology measurement. The wind velocity and direction were measured in a noncontact mode within a measurement area using acoustic probes, on the basis of differences of the time of flight of sound. To reconstruct a two-dimensional distribution, eight acoustic transducers were installed at equal intervals along the circumference of a turntable. The reliability of the system was tested in a wind tunnel. The test was performed for two patterns: increasing wind velocity under a constant wind direction, and rotating wind direction under a constant wind velocity. For the two experimental patterns, two-dimensional distributions of the wind velocity and direction could be reconstructed. Compared with a reference measured with an ultrasonic anemometer, our results showed good agreement.

Real-time imaging of dynamical movement or stress distribution across living tissues by physiological internal or clinical external stress forces could be a promising tool for clinical diagnosis as visualized palpation. However, the transversal components of tissue local motion across an ultrasonic beam cannot be obtained utilizing conventional beam scanning. We proposed the combined algorithm of phase sensitive spatial cross-correlation between two sequential speckle echo frames and signal processing for a synthetic aperture of an array transducer which realizes a uniform spatial resolution through these echo frames. The two-dimensional local motion vector can be directly calculated from the sequentially estimated local phase changes by successive irradiation of different point sources. The accuracy and the statistical variance of the estimated two-dimensional displacement were investigated for the simulated random tissue and the received speckle echo frames from it. The obtained results showed the excellent performance of the proposed algorithm, both for local values and for the entire distribution of estimated displacement vectors throughout the measured medium.

A scanning acoustic microscope (SAM) and a photoacoustic microscope (PAM) operating on a unified software environment was designed and fabricated. Welded steel plates, in which the welding condition was changed by varying the amount of current and its duration, were used as specimens. SAM and PAM measurements for this specimen were carried out, and the obtained images were compared. This system has the advantage of complementary measurement using both SAM and PAM.

A new theory is proposed to extend the limit of the application of bulk ultrasonic pulses, which have been thought to be unsuitable for the evaluation of sound velocity in thin coating layers because of interference with echoes. This extension is accomplished by introducing the new concept of the group delay spectrum. We first made a model representing waves reflected from a coating layer and found that many acoustic properties, for example, sound velocity, acoustic impedance, and coating density, can be derived easily by a group delay analysis. Next, the theory was applied to the analysis of a layer plasma-sprayed coated with alumina particles on a stainless steel substrate. To confirm the validity of the theory, we prepared coated specimens of varying thicknesses which covered from 0.16 mm to 0.48 mm, and we succeeded in evaluating sound velocity and coating density.

We show an advanced technique for measuring elastic constants C_ij of thin films deposited on substrates. Thin films often show anisotropy between the in-plane and out-of-plane directions because of their columnar structure, residual stress, texture, and incohesive bond. Then, thin films show macroscopically transverse isotropy and have five independent C_ij. All the film C_ij affect free-vibration resonance frequencies of the film/substrate layered specimen. Therefore, measuring the resonance frequencies permits us to determine the thin-film C_ij with the other known parameters. In order to yield reliable C_ij of thin films, we have to measure the resonance frequencies with sufficient accuracy and identify vibration modes of the measured resonance frequencies. We overcome these problems by developing a tripod and using a laser-Doppler interferometer, respectively. We applied the present technique to a copper thin film. Measured C_ij are smaller than those of bulk and show elastic anisotropy. We attribute these features to the incohesive bond regions.

A nonlinear resonant ultrasonic method using water immersion has been developed to detect micro defects in solids. This method allows us to reduce the strong nonlinearity of water and amplify the weak second harmonics generated at internal micro defects. In this method, both the fundamental and second harmonic frequencies are selected to match the resonant frequencies based on the resonant spectra of a sample. The detection of the micro defects in SiC_f/Ti composite has been demonstrated.

Monopolar C-mode imaging using a concaved polyvinylidene fluoride (PVDF) transducer was developed. The basic characteristics of the spreading of the ultrasound field are measured and discussed with respect to the imaging, along with the spatial resolution, and the C-mode image of a printed circuit board (PCB) surface.

The adhesive strength of polycrystalline chemical vapor deposition (CVD)-synthesized diamond films deposited on sintered SiC substrates was estimated using laser spallation. A strong pulse expansion wave was produced on the surface opposite the diamond film by the pulse laser breakdown of silicone grease confined by a silica plate and used to cause Mode-I fracture at the interface between the diamond and SiC. The amplitude of the expansion wave was monitored by a fast laser interferometer as a function of laser characteristics and the confining method. The critical laser energy for causing film spallation changed depending on the diameter of the laser beam and the thickness of the energy-absorbing layer (grease) confined by the silica plate. The driving force of the spallation was estimated to be the tensile stress of the expansion wave following the first compression wave, and it was changed significantly by the dynamics of dielectric breakdown. This was demonstrated by the waveform simulation of the out-of-plane displacement using a theoretical Green's function of the second kind for the dipole source. A pulse dipole source with short rise and decading times generates strong expansion waves.

In an attempt to obtain the eigenvalues of local modes in a range-dependent ocean environment, the Wigner distribution function (WDF) is exploited in the range-wavenumber domain, instead of in the time-frequency domain, in analogy with time-dependent signal processing. In the first place, it is confirmed that the WDF can extract the exact eigenvalues for the acoustic field simulated in a horizontally stratified environment. Then, the WDF is applied to a range-dependent field simulated using the parabolic equation model. Consequently, the WDF peaks are recognized to evolve laterally in the same manner as local modes; however, some of the small peaks are difficult to identify due to the affection of false images generated in the WDF. As a result of applying a technique to enhance the amplitude of those peaks, their identification can be improved.

A double-layered piezoelectric disk-type transducer (DLPT) without a backing and/or an intermediate layer is newly constructed and analyzed to generate short ultrasonic pulses. One of the disks is excited for the purpose of transmission and the other is used for canceling the ringing of the pulse. The driving conditions of the system, including the DLPT and the peripheral electronic component for generating the short ultrasonic pulse, are optimized by analysis using the cascade connection of a transmission line model. Experiments using the active ringing cancellation method with DLPT in water are also demonstrated. The analysis and experimental results were mostly in agreement with each other. A short ultrasonic pulse having a pulse width of 1.5 wavelengths is achieved.

Underwater acoustic digital communication was investigated by simulation under conditions of various distortions which seem to degrade communication performance, such as multipath or Doppler shift. M-sequence data was used as transmission data. The signal band was 20 kHz±4 kHz, and the modulation method was 16-quadrature amplitude modulation (16-QAM). The received data was demodulated using a multichannel decision feedback equalizer (DFE). In this paper, the effect of feedforward tap allocation on communication performance under an intensive multipath condition is considered. It became clear that the communication performance is advanced by utilizing multipaths, that this advantage is distinguished when the signal-to-noise ratio (SNR) of the input signal is small, that it is necessary to consider the trade-off between this advantage and the instability caused by a large number of taps, and that this advantage is available if ever there is Doppler shift or few multipaths.

An experiment on high-speed underwater acoustic data communication was carried out at real sea as a time-variant multipath channel. Demodulation was processed by a multichannel decision feedback equalizer (DFE) demodulator with adaptive filtering. The modulation method used was 16-quadrature amplitude modulation (16-QAM), transmitting rate was 32 k bit per second (bps), carrier frequency was 20 kHz, and bandwidth was 8 kHz (16–24 kHz). Good demodulation results were obtained at a sea trial despite the presence of high-level multipaths. At real sea, we proved that high-speed (32 kbps) acoustic communication can be realized even in a multipath fading channel with 16-QAM. Therefore, it is expected that the flexibility of the design of underwater equipment will be improved, because the influence of a circumferential structure can be neglected.

The revolutionary concept of using ocean ambient noise positively to detect objects, called acoustic daylight imaging, has attracted much attention. The authors attempted the detection of a silent target object using ambient noise and a wide-band beam former consisting of an array of receivers. In experimental results obtained in air, using the wide-band beam former, we successfully applied the delay-sum array (DSA) method to detect a silent target object in an acoustic noise field generated by a large number of transducers. This paper reports some experimental results obtained by applying the multiple signal classification (MUSIC) method to a wide-band beam former to detect silent targets. The ocean ambient noise was simulated by transducers decentralized to many points in air. Both MUSIC and DSA detected a spherical target object in the noise field. The relative power levels near the target obtained with MUSIC were compared with those obtained by DSA. Then the effectiveness of the MUSIC method was evaluated according to the rate of increase in the maximum and minimum relative power levels.

In a phased array, the interval between the centers of the sound source elements which adjoin each other is set below half the wavelength in order to suppress the gratinglobe. At this interval, the array sound source can gain strong radiation power. The estimation of radiation impedance is important in the analysis of the radiation power. The Greenspon's method which is a radiation impedance calculation method of rectangular pistons on a cylinder is explained, and some defects of this method are clarified. For the evaluation of Greenspon's method, we introduce the combined Helmholtz integral equation formulation (CHIEF) method. The radiation impedance is calculated using both Greenspon's method and the CHIEF method, and the results are compared. On the basis of comparison of the radiation power measured while driving the cylindrical phased array with the theoretical value of radiation power determined using the caluculated value of radiation impedance, it is considered that Greenspon's method and the CHIEF method give accurate estimations.

The underwater imaging sonar system with an acoustic lens is again receiving considerable attention because it does not require a complex beam-forming circuit. The lens system used in this type of sonar was designed by the ray theory or by a hybrid method of the ray and wave theories. In this report, a basic analysis was performed by an analytical method using a wave theory and by a numerical method using the parabolic equation (PE) method, to determine the convergent characteristics of a biconcave lens. The pressure field focused by the biconcave lens was measured in a water tank. The biconcave lens used in the experiment is made of acrylic resin with a radius of 20 cm and a radius of curvature of 20 cm. Measurements was conducted in a water tank at a frequency of 500 kHz. Sound pressure fields around the focal region measured by the experiments agreed well with the calculated ones by the analytical and PE methods.

Ocean acoustic tomography (OAT) is a powerful approach for observation of mesoscale ocean fluctuations. The precise estimation of travel time is required for ocean current measurement. We previously proposed the measurement of travel time using phase information. In this paper, we present the theoretical analysis of phase deviation using the Rice distribution. We then propose a new measurement technique of travel time termed as the complex vector method. We also demonstrate the ability of this method by computer simulation and received signals from OAT experiment in 1999. The preliminary results are promising. We conclude that the proposed estimated method is useful in long-range ocean transmission.

In marine research, measures against self-noise of an observatory ship are important. Generally, the self-noise is measured after the completion of ships. It is difficult to predict this noise level beforehand. Then, an attempt is made to determine the noise emitted from various elements of a structure. The finite difference time domain method is applied to obtain sound fields, including that of a plate in water. The time behavior of the sound wave emitted from a sound source placed near the upper part of a plate is investigated. As a result, the reflected and re-radiated waves from the plate including the head wave resulting from the longitudinal and traverse waves in the plate are able to be visualized. In the case of the plate with a branch plate, the suppression of the wave which propagates at the inside of the plate with the length of the branch plate is shown.

We have studied on the convergence property of time reversal waves (which are equal to phase conjugate waves) in the ocean, particularly in time domain with various configurations of time reversal array (TRA) through simulations and tank experiments. In this paper, the property of time reversal waves under noisy environment is discussed. Simulations were carried out with various sound velocity profiles using the Pekeris solution of the normal mode method and the parabolic equation (PE) method, and tank experiments were also conducted to compare with the simulation results. Results revealed the following. Time reversal waves even at very low signal noise to ratio (SNR) can converge and send the desired signal to the focus at high SNR. The focusing effect of time reversal waves is higher when the horizontal range is extended. If the sound velocity profile is different, the focusing effects are not considerably affected.

The relative positions of moving distributed sources are estimated by the Doppler frequency shift estimate of each source using the extended Kalman filter (EKF). Each source is assumed to radiate a different frequency with a different spatial position. The Doppler frequency shift of each source along the Closest Point of Approach (CPA) is unique with respect to time and frequency and this is mapped with respect to each source position. Since the Doppler frequency shift should be estimated with a high time resolution and a high frequency resolution particularly for a moving source with a relatively fast time-varying amplitude, the EKF frequency-amplitude estimator is proposed to fulfill this goal. The performance of the technique is examined by an illustrative numerical example and is verified by an experiment using loudspeaker sources on the roof of a car.

In order to determine the size of the vibrating surface of an individual element and the spaces among elements in a cylindrically arrayed ultrasonic transducer, enormous calculations for mutual- and self-radiation impedances should be accomplished within a limited time. However, the direct application of the equation of Greenspon and Sherman to such numerical calculations requires a very long time to obtain high accuracy. In this study, an effective calculation algorithm was investigated by introducing subintervals into the integration of the Greenspon and Sherman's equation. As results, limits of subintervals improving computation time and accuracy were fitted as functions of the size of the vibrating surface of the element and the size of the baffle.

Whales found in the north Pacific are known to migrate over several thousand kilometers, from the Alaskan coast where they heartily feed during the summer to low latitude waters where they breed during the winter. Therefore, it is assumed that whales are using the "deep sound channel" for their long-distance communication. The main objective of this study is to clarify the behaviors of baleen whales from the standpoint of acoustical oceanography. Hence, authors investigated the possibility of long distance communication in various species of baleen whales, by simulating the long-distance propagation of their sound transmission, by applying the mode theory to actual sound speed profiles and by simulating their transmission frequencies. As a result, the possibility of long distance communication among blue whales using the deep sound channel was indicated. It was also indicated that communication among fin whales and blue whales can be made possible by coming close to shore slopes such as the Island of Hawaii.

To characterize tissues in atherosclerotic plaques, we have developed a method, the phased tracking method, for measuring the strain (change in wall thickness) and elasticity of the arterial wall. However, some types of tissue, such as lipids and blood clots, cannot be discriminated from each other based only on elasticity due to the small difference in their elasticity. For more precise tissue characterization, we have measured the regional viscoelasticity. To obtain the viscoelasticity, in this study, elastic moduli at multiple frequencies were measured with ultrasound by generating the change in internal pressure due to remote cyclic actuation. Furthermore, the viscoelasticity of the arterial wall was estimated from the measured elastic moduli at multiple actuation frequencies.

When an ultrasonic vibrator is forced to come into contact with a static load, it is known that the resonance frequency and quality factor of the vibrator are influenced by the reaction of the object. On the basic of this phenomenon, a study to measure the physical constants, such as the elastic modulus of materials, is under way. However no report concerning the accurate analysis of the relationship between the said change and the physical constants has been available. In this paper, we present the analytical result of the relationship equations. The resonance frequency is increased in the case that the body in contact is sufficiently hard, whereas it is decreased in the case that the body is soft. Frequency equations expressing both the phenomena referred to above were obtained in a unified manner. Furthermore, the appropriateness of the said equations was confirmed by experiments. It is concluded from the studied that the analytical results are in agreement with the experimental results.

When micro bubbles flow into an ultrasonic wave field, the microbubbles often produce bubble aggregation. The aggregated bubbles create an inherent aggregate pattern depending on the bubbles, ultrasonic wave frequency and sound pressure. To evaluate the microbubble aggregation, which is produced by ultrasonic waves, the Bjerknes force which is produced by aggregated bubbles is derived. We assume that 2n+1 bubbles are aligned with a separation shorter than the wavelength and that they oscillate independently producing secondary ultrasonic waves around the bubbles. The relative phase between the secondary wave radiation of the aggregated bubbles and the radial oscillation of a single neighboring bubble is an important parameter for characterizing the bubble aggregation. Based on this discussion, a novel method of measuring the relative phase between the secondary wave radiation and the radial oscillation is proposed. This method is applied to micro bubbles with polyvinyl chloride shells.

The destruction of microcapsules having an elastic thin shell is discussed. An optical observation of the capsule destruction using a high-speed video camera is carried out. As the driving pressure is increased, the microcapsules trapped at the antinode of an acoustic standing wave show circling movements, and then the microcapsules eventually collapse. At the moment of destruction, it is found that the microcapsules change in shape and the internal gas jets out of the capsule rapidly. The sound pressure threshold for the capsule destruction is the lowest under the resonant condition. The capsule destruction also depends on the existence of free bubbles in the surrounding media. It is found that the mechanism of capsule destruction can be categorized into two types: one is due to the increasing driving sound pressure and the other is due to the existence of the free bubbles in the surrounding media. It is considered that the destructions of multicapsules depend on some parameters; however, these two types of capsule destruction are dominant factors.

We have developed the phased tracking method [H. Kanai, M. Sato, Y. Koiwa and N. Chubachi: IEEE Trans. UFFC 43 (1996) 791.] for measuring the minute change in thickness during one heartbeat and the elasticity of the arterial wall with transcutaneous ultrasound. When this method is applied to a plane perpendicular to the axis of the artery (short-axis plane) using a linear-type probe, only an ultrasonic beam which passes through the center of the artery coincides with the direction of the change in thickness. At other beam positions, the wall motion cannot be accurately tracked because the direction of wall expansion slips off the beam. To obtain the cross-sectional image of elasticity in the short-axis plane using transcutaneous ultrasound, in this paper, the directions of ultrasonic beams are designed so that each beam always passes through the center of the artery; thus, they always coincide with the direction of the wall expansion. In basic experiments, the accuracy in elasticity measurement was evaluated using a silicone rubber tube. In in vivo experiments, the minute change in wall thickness was measured along each ultrasonic beam, and the cross-sectional image of elasticity was obtained in the short-axis plane with transcutaneous ultrasound.

The purpose of this study is to quantify the characterization of myocardial tissue using the method of surrogate echo data and chaos analysis. Myocardium RF ultrasonic echo signals were obtained from healthy subjects and patients with dilated cardiomyopathy (DCM). This surrogate method is a null hypothesis test to differentiate a deterministic process from a stochastic one using translation error. The result of the translation error from the obtained data was about half of that from the surrogate data sets. Since the obtained data showed a higher degree of determinism, we confirmed that myocardial dynamics is dominated by a deterministic process, and found that there are significant differences in deterministic values between healthy subjects and DCM patients. These results suggest that the proposed nonlinear dynamic analysis from the reconstructed echo signals is useful in myocardial tissue characterization.

With the aim of avoiding the concentration of second harmonic generation at the focus, a modified focusing source designed to minimize the fundamental amplitude at the focus is examined. The present source consists of two coaxially arranged confocal transducers: An inner disk transducer and an outer ring transducer whose areas are the same. They have been polarized in the thickness direction opposite to each other, and are connected in parallel. The theoretical and experimental results show that the second harmonic amplitude attains a maximum at three locations including two positions where the fundamental amplitude takes peak values. A relatively sharp second harmonic beam is demonstrated. Provided the radius of curvature is relatively small, since the three maximum positions are close to each other, the second harmonic beam effectively focuses long. Suppression of side lobes by weighting the source excitation is also discussed.

Unconstrained health monitoring systems have received much considerable attention in medical applications, because such system can examine a subject without constraint. In this study, we propose a detection method based on a fuzzy logic for evaluating heart rate using our ultrasonic vibrograph. In the experiment for confirming heart rate, our method has been successfully used to detect the heart rates of four subjects, compared with a method using an electrocardiograph.

As a quantitative imaging tool for ultrasonic endoscopy with high lateral resolution, we proposed a new measurement method for tissue acoustic impedance utilizing the adjacent near-field at one end of a quartz fiber. In this note, the fine prospect for matching layer design at a fiber end with a diameter less than wavelength of ultrasound transmitted into a tissue medium is reported. Real-time simulations by the three dimensional finite element method ensure that the shear wave propagation is dominant in the matching layer, and the reflection coefficient obtained from echoes at the matching frequency is very sensitive for the evaluation of tissue acoustic impedance.

Real-time imaging of tissue dynamic response caused by internal or external stress forces acting across a living tissue is promising for improving diagnostic quality and accuracy of clinical palpation as an "ultrasonic visualized palpation". Thus we have investigated a real-time imaging system of local tissue displacement along an ultrasonic beam scanned across the living tissue, which realized straightforward but tissue-oriented physiological and dynamic color imaging on a conventional B-mode screen. System performance is fairly supported by a flexible design of a digital signal processor for real-time local cross correlation between successive two-dimensional complex speckle echo frames. Propagation of shear waves raised by external stress in a tissue phantom was clearly observed, so that real-time observation of shear wave traveling across a physiological liver tissue locally stressed by heartbeats was studied. As a result, we could confirm the characteristic shear wave propagation pattern by internal stress synchronous with heartbeat.

The methods of suppressing cancer cell proliferation by ultrasound exposure were investigated to develop a new minimally invasive cancer treatment. A stainless-steel diaphragm with a bolt-clamped Langevin-type transducer (BLT) was attached to the bottom of a water tank in the ultrasound exposure system used in this study. Cancer cells of a mouse T lymphoma (EL-4) in a flask were exposed to ultrasound under various conditions of exposure time, ultrasound frequency, ultrasound waveform, and so forth. The number of cancer cells exposed to ultrasound decreased during the culturing process. In this study, it was proved by electrophoresis, enzyme activity measurement and morphological observation that cancer cell proliferation can be suppressed by apoptosis induction in cancer cells by ultrasound exposure.

The abnormalities of myocardial wall motion caused by changes in wall stiffness often appear in the early stage of ischemic heart disease. Since the myocardium exhibits complex and large motion, a two-dimensional (2D) or three-dimensional (3D) assessment of stiffness distribution is required for accurate diagnosis. Although a 3D assessment is ultimately required, as a stepped approach for practical use, we propose novel methods for tracking the 2D motion using a one-dimensional (1D) phased array and for assessing myocardial malfunction by visualizing the invariant of a strain tensor. The feasibilities of the proposed methods were evaluated by numerically simulating the short-axis imaging of a 3D myocardial model. This model includes a hard infarction located between 1 and 3 o'clock, which is difficult to detect by conventional tissue Doppler and strain rate imaging, and the motions of the model were assigned by referring to actual myocardial motion. These results revealed that the proposed imaging methods clearly depicted the hard infarction area which conventional imaging could not detect.