This paper describes a simple simulation of the signal pathway in an ultrasonic A-scan. It includes transient diffraction acoustic field, transducer response, and frequency dependent absorption in the field medium. The approach selected here aim to develop digital computer simulations of the physical processes that underlie these effects. The soft tissue is considered as a viscoelastic medium and the relaxation theory has been used to calculate the absorption data and dispersion in the tissue. The simulation is used to estimate the degradation in range of resolution due to wave absorption.

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An active acoustic power control method for three-dimensional space was investigated both theoretically and experimentally. In this paper, the focus is on the typical case of a single primary and two secondary point sources, and methods of minimizing the power output were considered. Suitable arrangements of the sources and microphone were proposed on the basis of theoretical estimations. The authors call this the acoustic nodal point method. The power reducing performance was verified by applying the method to the noise radiating from a duct opening.

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Acoustic scattering of an arbitrary wave incident on a finite submerged cylindrical shell is studied theoretically and experimentally, where the term arbitrary wave is referred to non-plane, non-spherical wave-front emanating from an actual transducer driven by a single frequency. An analytical solution for the spherical wave incidence is extended by introducing the concepts of “insonified window” and “shape parameter.” A simplysupported cylindrical shell for the experiment may be modeled as an infinite shell whose insonified length is restricted by the insonified window. The shape parameter defines the difference in the shape of wave-front between the spherical wave and the wave from an actual transducer. The measurement of scattering on a simply-supported, waterfilled shell is carried out using Scattering Generalized Near-field Acoustical Holography (SGENAH). The validity of our approximate theory is confirmed by good agreement between theoretical and experimental results.

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A three dimensional intensity probe using four microphones is proposed. Four microphones are placed at apexes of a regular tetrahedron. One is placed in the front and three others consisting a vertical regular triangle are in the back. The microphones are attached at the tips of parallel thin tubes. The microphone arrangement is not the conventional face to face type. The aim of this type of microphone arrangement is to design a sound intensity probe with a simple structure, which is essential for reducing the diffraction problem. Algorithms for three dimensional intensity components from cross spectra are given as well as for leakage components. Measurements of sensitivity characteristics in an anechoic room using two types of probes with 60mm and 20mm microphone separations show that sensitivity fluctuations are small enough (less than 1dB) for the practical application of the sound intensity method. The leakage errors of approximately 5%(-13dB) seem also acceptable. The measurement results indicate that sensitivity and leakage errors will become smaller if a more ideal plane wave field in an anechoic room is achieved.

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The measurement method for the acoustic nonlinearity parameter B/A of a liquid sample inserted in the focal regioh has been presented, where the acoustic wave of focused Gaussian beam observed with a concave receiver which is set perpendicular to the acoustic axis within the postfocal region is utilized. Both the amplitudes and phase difference of the fundamental and second harmonic components in the signal detected with a concave receiver set at the position, where the obtained signal amplitude attains the maximum for each the case with and without insertion of the sample, are transformed to the values expected for the axial pressure at the range corresponding to the maximum position for the case with the insertion of the sample. Then the previously presented method utilizing the axial pressure turns out to be applicable. Using a 1.9-MHz focusing source and a concave receiver, the confirmation of validity of the present method was intended through the experiment employing the samples of alcohol and glycerin. The result verified the capability of the present method to measure the B/A.

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