Kenji Kawabe

Ultrasonic equipment and its catheter-type ultrasonic probe

An Ultrasonic Equipment and its Catheter-type Ultrasonic Probe can be inserted in capillaries such as blood vessels, and comprises a catheter-type ultrasonic probe for generating ultrasonic waves by a piezoelectric transducer arrayed at its tip. A plurality of the piezoelectric transducer segments are arrayed on a two-dimensional plane, perpendicular or approximately perpendicular to the insertion direction of the probe into a capillary with their ultrasonic wave emitting surface faced in the insertion direction. A part of the plane is cut out to provide a guide unit for passing a treating catheter or a guide wire in the insertion direction.

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.

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.

Acoustic characteristics of PVA gel

Polyvinyl (PVA) alcohol gel is a rubbery material with a high water content, an extremely low acoustic attenuation, and an acoustic impedance close to that of the human body. These characteristics make PVA gel a good candidate as an acoustic coupler between the body and probe during ultrasonic diagnosis. Nonlinearity in acoustic-pressure propagation between pressure input and output was measured for PVA gel. Measurements of the acoustic characteristics of PVA gel show that PVA gel has nonlinearity similar to that of water. It also has extremely low attenuation and good impedance matching to the body.<<ETX>>

An ultrasonic transducer apodized by polarization

In attempting to improve the quality of images produced by ultrasonic diagnostic equipment, the authors tried to narrow the width of the ultrasound beam in the scanning direction and the short axis perpendicular to the scanning direction, and to shorten the pulse duration. The beamwidth, especially in the short axis, is markedly broad. To narrow the width, the transmitting acoustic sound pressure was apodized by polarizing the piezoelectric ceramic element of an array-type transducer in a stepped manner. A transducer using this apodization had its beamwidth decreased from 50% to 80% compared to the conventional transducer.<<ETX>>

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>>

Improved SQUID Magnetometer with an External Feedback Circuit

The large magnetic noise and weak magnetic signal level of the heart and brain in magnetic measurement require that a magnetometer have a wide dynamic range and be highly sensitive. The single-chip digital SQUID magnetometer proposed by Fujirnaki (Fujirnaki, 1988) featured an internal superconducting feedback circuit that made it compact (3.0 mm × 3.5 mm), but its dynamic range was limited by the volume of magnetic flux stored in the superconducting feedback loop.