Atsuo Iida

Electro-sound transducer eliminating acoustic multi-reflection, and ultrasonic diagnostic apparatus applying it

An ultrasonic diagnostic apparatus protected from multi-reflection of sound echoes. Multi-reflection is avoided by eliminating the reflection from the surface of an electro-sound transducer. This invention eliminates the surface reflection of the transducer by following three methods: (a) changing a direction of each surface of an array of transducer elements to direct the reflected sound wave away from the main direction of the sound beam; (b) applying an acoustic matching layer to a surface of a piezo-electric device of the transducer to cancel out phases of sound waves reflected by the surfaces of the layer and the device; and (c) providing an acoustic matching surface on a front or back face of the piezo-electric device to cancel out phases of sound waves reflected by the surface of the device.

Effect of saw-cut depth on characteristics of array transducer

The authors suggest that saw-cut depth affects the electroacoustic conversion characteristics of an array transducer. To investigate this, they made several samples and measured the impedance of the sawed part of the backing. The results indicate that this impedance is less than that of the solid backing because the acoustic velocity of the sawed part is decreased. Assuming that the sawed part acts as a pseudolayer between the PZT (lead zinc titanate) elements and backing, the authors calculated transducer conversion characteristics by computer simulation. On the basis of the simulation, they built transducers and measured their characteristics. Excellent agreement between the simulation and experiment supports the pseudolayer theory. It is concluded that by making good use of the saw-cut-depth effect, high-efficiency broad-bandwidth transducers can be made.<<ETX>>

Intravascular Ultrasonic Imaging with a Micromotor

This paper reports a new intravascular imaging system with a micromotor, revolution characteristics of the micromotor and experimental results using a plastic tube. In this system, an ultrasonic beam is scanned radially by the micromotor instead of a scanning wire. The experimental results show that a cross-sectional image of the tube is reconstructed and that this system has a possibility of application to the observation of the inside of a blood vessel.

The effect of delay error on the sidelobe level in synthetic aperture imaging

The synthetic aperture method, which synthesizes a large aperture by multiplexing a small transmit/receive aperture, is known to have two major advantages: (1) mainlobe narrower than one-way dynamic focusing in reception, and (2) a hardware volume smaller than in the synthetic focusing method, which requires that every element receives a reflected signal for each transmitting element. This paper describes the influence of delay error on the sidelobe in the synthetic aperture method. The simulation results show that in order to suppress the sidelobe level below -40 dB at 3.5 MHz, the combined delay fluctuations among the small apertures caused by the wavefront distortion in the medium and by the electronics should be less than 3 ns. As the propagation time inhomogeneity in a typical medium such as a phantom test object or a human body causes fluctuations of more than 15 ns of arrival time among the small apertures, the results lead to the conclusion that the synthetic aperture method is not effective on such a medium.

Variation of acoustic impedance caused by a cut in ultrasonic transducers

The authors describe the measurement of the acoustic impedance of the backing of an ultrasonic array transducer consisting of piezoelectric ceramic and backing and matching layers. The transducer is made by sawing the piezoelectric ceramic into array elements. The backing is also cut slightly so that each element can be driven independently, without acoustic cross-coupling between elements. The authors devised a way to measure the acoustic impedance of the sawn part of the backing, which presented difficulties because of its small size. The method uses the reflection coefficient spectrum at the surface of the sawn backing. The measured impedance of the sawed part was 5.33*10/sup 6/ kg/m/sup 2/ s, and that of the solid part was 6.35*10/sup 6/ kg/m/sup 2/ s. It is shown that the impedance of the sawn part of the backing is less than that of the solid backing, even though the material is the same. From this, the array transducers electroacoustic conversion characteristics were obtained by computer simulation, accounting for the effect of the sawn part of the backing, and were in excellent agreement with experiment.<<ETX>>

A New Ultrasonic Transducer to Decrease the Multi-Reflections Which Cause Artifacts on B-Mode Imaging

We propose a design that decreases the acoustic energy reflected by an ultrasonic t ransducer f or medical use. Multi-reflections must be reduced to achieve good images without artifacts. This can be done by decreasing the transducers r eflection coefficient. The reflection coefficient is important, and must be taken into a ccount t ogether with efficiency and bandwidth when considering design. Input acoustic impedance is assumed to be that seen from the transducers surface to the backing material through the matching layers a nd piezoelectric ceramic (PZT). Input acoustic impedance at the center frequency is designed to equal t he acoustic impedance of the load. We analized the reflection c oefficients of several transducers by computer simulation. We found a structure that provides a small reflection coefficient, good efficiency, and a wide bandwidth. The reflection coefficient of the thin-disk transducer we fabricated is 10 dB lower than that of a conventional transducer.