A new class of super wideband, nonresonant and high efficiency ultrasound imaging transducers is described. The design developed uses PVDF piezoelectric material and exhibits pulse-echo sensitivity on a par with that achievable with a conventional, resonant design employing PZT or PZT composite material. The transducers can operate at virtually any clinically relevant frequency which minimizes the trade-off between the achievable penetration depth and desired image resolution and are well suited for both conventional medical imaging in the frequency range 2-12 MHz and high frequency imaging such as ultrasound backscatter microscopy using the frequencies between 20 and 100 MHz. Both simulation results and preliminary experimental data are presented and show very good agreement. The potential for using this approach as a technological breakthrough in the imaging array design is pointed out.

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A new method of measuring the viscosity of liquid, using a triangular bimorph transducer, has been proposed and has been successfully used for measuring the viscosity of various liquids over a wide range of viscosities. This viscometer is a vibration type and consists of a triangular bimorph transducer and a small circular plate. The bimorph is effectively used for both as a driving transducer and a detecting transducer, and the viscosity of liquid can be gotten by measuring the electrical phase difference between both transducers. It was found out that the phase difference of the triangular bimorph transducer appeared largely in the off-resonance frequency band, and so the viscosities of various liquids were measured by using this bimorph. This viscometer is simple in the operation and is expected to have a high accuracy.

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A precise target strength measurement system in an indoor tank is constructed. A target is rotated in pitch plane by a computer controlled stepping motor and measurements are done automatically from the start to the end. Echo data in the range between -50 and 50 degrees are stored at intervals of 1 degree on the hard disk built in an oscilloscope. Spreading loss and absorption loss are compensated for in a software to calculate precise target strength. Because all echo sounders with both output terminals of transmitting trigger signal and of echo signal are available as a transmitter and receiver of this system, precise target strength measurements are possible at any frequency for many kinds of physical models and fish. Target strength patterns of several prolate spheroidal models precisely made of expanded polystyrene are measured, and the results are compared with the exact theory of a soft prolate spheroid scattering model to ascertain accuracy and precision of the measurements. The experimental results agreed very well with the theoretical results and the correlation coefficients are almost unity.

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To fabricate a bolt-clamped large diameter Langevin torsional vibrator as designed is usually difficult. A torsional vibrator tightened with an outside bolt is proposed in which the designed characteristics in the resonant vibration of the normal mode is achieved. A torsional vibrator 80 millimeters in diameter with a calculated resonant frequency of 28kHz has been fabricated. The resonant frequency of the torsional vibrator is 26.1kHz, the quality factor is 890 and the maximum angular velocity is 4.1 rad/s. It is confirmed that the vibration characteristics obtained with the externally-bolted transducer are improved compared with the torsional transducer tightened with an inside bolt.

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Ultrasound energy losses due to viscosity in a fluid induce acoustic streaming globally and elevate temperature locally. Generally, the flow induced in the beam reduces the elevation of temperature by cooling. The present report seeks to clarify the cooling effect of streaming on the ultrasound heating in three kinds of fluid with different viscosities. Numerical examples of the streaming velocity and temperature elevation are given along and across the beam axis for a Gaussian focusing system. The effect of buoyancy on the generation of acoustic streaming is usually neglected. However, the streaming significantly changes the spatial distribution of the temperature, in particular, in a fluid with high viscosity.

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We discuss the spacing of the transducer elements of transmitter and receiver arrays to sample sufficient data for ultrasonic diffraction tomography. We intend to save fairly the data acquisition time of our prior method by replacing the mechanical scanning of the pair of a transmitter and a receiver with the electrical switching of the both arrays. One of the most important parameters of the arrays is the spacing of the elements. In the previous paper we used the equation of the spacing derived from the theory of acoustical holography for convenience, though the prerequisites might not fit for the case. We now newly obtain the equation by calculating the phase of the received signal. New result proves 3 times narrower than the previous one. We confirm the feasibility of the new result by the numerical calculation and the experiment.

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A method of realizing an amplitude-phase modulation using a travelling type ultrasonic device is described. A shear horizontal (SH) plate-mode wave device is composed of four interdigital transducers (IDTs). The first and the forth IDTs are used for the carrier signal input, and device output. The another two IDTs located at the central part of the SH-wave device are used as an attenuator and a phase-shifter for amplitude and phase modulation, respectively. The operation principle that is analyzed with the equivalent circuit model for the amplitude-phase modulator, is given with experimental confirmation. At the frequency of 1.20MHz, the device performs as amplitude modulator and phase modulator, simultaneously.

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A new technique to remove hand motion artifacts in pulsed Doppler is proposed. The instantaneous phase difference between two consective echoes is estimated and is supposed to be dominated by the hand motion component. The phase difference is then used to compensate the phase of the next echo. The same procedure is repeated in every transmit/receive cycle. Implementation of this technique is accomplished on a medical imaging system with a pulsed Doppler processor. The results observed shows that hand motion artifacts have been greatly reduced.

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Nondestructive evaluation of formability (r-value) in cold-rolled steel sheet with an electromagnetic acoustic transducer (EMAT) for the fundamental shear horizontal plate wave (SH₀-wave) has been developed. First, the principle of nondestructive r-value measurement is described. Next the characteristics of the magnetostrictive type EMAT and the Lorenz force type EMAT for the SH₀-wave were evaluated to permit an optimum sensor for nondestructive measurement. Based on the results, the system with the magnetostrictive type EMAT was fabricated and the capability for measuring r-values was evaluated using many samples. The system was confirmed to measure r-values with an accuracy of 1σ=0.065 nondestructively.

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