Mamoru Izumi

Ultrasonic probe and ultrasonic diagnosing system using ultrasonic probe

An ultrasonic diagnosing system includes a probe having an vibrator made of a plurality of spaced piezoelectric; material elements arranged in a matrix, first electrodes arranged on one surface of the vibrator in an array of rows parallel to each other, and second electrodes arranged on another surface of the vibrator in an array of rows parallel to each other and orthogonally to the first electrodes. Particularly, the piezoelectric material elements are spaced by spacer segments arranged between the electrode rows and formed from a high molecular weight material with less acoustic impedance than the piezoelectric material, a Shore hardness D50 or more (JIS) and a thickness of about 1/10 to 1/2 of the piezoelectric elements. The ultrasonic diagnosing system uses a phased array technique to provide tomograms at mutually orthogonal and spatially close positions with sufficient sensitivity.

Shockwave generator using a piezoelectric element

A shockwave generator is adapted to be coupled to an object through a liquid medium for ultrasound transmission to generate a shockwave in the object. The shockwave generator comprises a piezoelectric element having an ultrasound radiating surface, an acoustic matching layer formed on the ultrasound radiating surface of the piezoelectric element, a fluorine-resin coating layer formed on the acoustic matching layer and a bag provided in front of the ultrasound radiating surface of the piezoelectric element and holding water for ultrasound transmission, where the water is held in contact with the fluorine-resin coating layer.

Development of Under-sodium Three-dimensional Visual Inspection Technique Using Matrix-arrayed Ultrasonic Transducer

We have developed an advanced under-sodium ultrasonic visual inspection technique in order to observe in-vessel structures in a Fast Breeder Reactor (FBR) whose reactor vessel is filled with opaque liquid sodium. The final goal of this work is achievement of resolution equivalent to that of an image obtained by optical fiber scope. The under-sodium ultrasonic visualizing system consists of a matrix-arrayed transducer and a signal- processing device. The matrix-arrayed transducer, in which 36x36 piezoelectric elements are arranged with 5 mm interval and sealed by a thin metal diaphragm, can realize a 3-dimensional image with high resolution. Regarding signal processing, the 3-dimensional image synthetic processing and the cross correlation processing for the purpose of improving S/N ratio of ultrasonic echoes are implemented on a high-speed parallel processor. Under-sodium imaging test was carried out, and it was confirmed that a 3-dimensional image of the blind target, which was prepared without information beforehand, could be visualized clearly with less than 2.0 mm resolution under-sodium.

A Low-Impedance Ultrasonic Probe Using a Multilayer Piezoelectric Ceramic

An ultrasonic probe employing a multilayer ceramic is proposed for improving the S/N ratio. The S/N ratio is degraded when the probe impedance rises in relation to parallel combined impedances of cable and receiver circuits. The impedance of n layers of ceramic can be reduced to 1/n2 of a single ceramic layer, thus permitting the S/N ratio to be raised. A co-firing multilayer method is introduced to achieve a multilayer ceramic with large adhesive strength. As a result, the S/N ratio has been improved as much as 8 dB over that of conventional probes under the same drive voltage.

Temperature Dependence of Dielectric and Piezoelectric Properties of Pb(Zn1/3Nb2/3)O3–PbTiO3 Piezoelectric Single Crystals

Temperature dependence of the dielectric and piezoelectric properties of xPb(Zn1/3Nb2/3)O3–yPbTiO3 (PZNT 100x/100y) piezoelectric single crystals (PSC) was investigated to estimate the heat stability of their properties. The coupling factor rectangular bar mode k33′=81% of PZNT 91/9 decreased sharply at about 70°C and then decreased gradually toward the Curie temperature, Tc. On the other hand, the k33′=62% of PZNT 95.5/4.5 hardly changed up to 110°C, although it was lower than that of PZNT 91/9 at room temperature. The degradation temperatures of the k33′ value were roughly in agreement with the phase-transition temperature, Trt, from rhombohedral to tetragonal, measured using the poled PZNT PSC. A large dielectric hysteresis was observed when PZNT PSC was heated to a temperature higher than the Trt, measured using poled PZNT PSC. Although PZNT 95.5/4.5 with reduced Ti content had a higher Trt, the obtained piezoelectric properties were inferior to those of PZNT 91/9 near the morphotropic phase boundary (MPB). Therefore, it is necessary to design the PSC composition carefully, considering specific applications in order to achieve the optimum balance between piezoelectric property and its heat stability.

Acoustic emission and piezoactivity during poling in PZT-like ferroelectric ceramics

Abstract Acoustic Emission (AE) induced by poling field was observed in the PZT-like ferroelectric ceramics at the room temperature. Relationships between AE characteristics and electromechanical coupling coefficients as the measure of poling show that domains in grains have the various levels of charactersitic threshold field to reverse their polarization directions or to move domain walls. Reversals of domain states with higher threshold field levels occur large amplitude acoustic emissions.

A dual frequency ultrasonic probe for medical application.

A dual frequency probe employing two ceramic layers for medical ultrasonic diagnostic equipment has been developed for simultaneously obtaining both a high‐resolution tomogram and a high S/N Doppler mode image. This ceramic vibrator, which has opposite poling directions and different individual thicknesses, has enabled the excitement of a second harmonic in addition to the fundamental resonance. Therefore, only a pair of electrical terminals are enough to excite dual frequencies. Ultrasonic attenuation in a human body is reduced, since the Doppler reference frequency can be set below the tomogram center frequency. Moreover, the two relative resonant levels are widely controllable by changing the thickness ratio of the two layers. An optimum thickness ratio of 1:0.7 has been obtained by computer simulation under Mason’s model. A cofiring multilayer method has been developed to achieve a multilayer ceramic with a large adhesive strength. As a result, the S/N of the Doppler mode has been improved as much as ...

A Dual Frequency Ultrasonic Probe

A dual frequency probe using a multilayer ceramic is proposed for simultaneously obtaining a high resolution B mode and a high S/N Doppler mode image. This ceramic consists of 2 layers in which the poling directions are opposite and the individual thicknesses are different. It has been shown that the intima of the carotid artery can be distinguished by an actually fabricated probe with dual frequencies of 3.75 and 7.5 MHz. Also, the S/N of this probe in the Doppler mode has been improved as much as 5 dB over that of a conventional one at the popliteal artery located 5 cm deep from the surface.

Fabrication of phased array probe using 0.93Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.07PbTiO/sub 3/ piezoelectric single crystals

Single crystals of 0.93Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.07PbTiO/sub 3/ (PZNT 93/7) with diameters of 40 mm were gown successfully by the solution Bridgman method with PbO flux. The PZNT 93/7 single crystal (SC) had excellent dielectric and piezoelectric properties equivalent to those of PZNT 91/9 SC and better thermal stability of the properties because of its high phase transition temperature, Trt. Moreover, phased array probes using the PZNT 93/7 SC were fabricated. The echo amplitudes and the bandwidths of the probes were almost the same as those of PZNT 91/9 SC probes. Therefore, we think that the PZNT 93/7 SC achieves the optimum balance between piezoelectric properties and their thermal stability and it is very suitable for medical transducers.

A two-dimensional array probe using an insulating layer and a signal line on the vibrator

A two-dimensional array probe using a newly developed method for drawing out signal lines is proposed. In this probe, an insulating layer and a conductive layer with about 10 µm total thickness are deposited on one electrode of a vibrator. The insulating layer has a through-hole to connect the electrode to the conductive layer. The conductive layer is patterned to inner signal lines that are terminated at both edges on the side of the vibrator. An outer signal line is drawn from each signal line terminal of the vibrator by wire bonding. The specifications of the fabricated two-dimensional array probe are 5 MHz, 30×5 elements and two acoustic matching layers. The pulse-echo characteristic and directional response of an element were evaluated, and a -6 dB bandwidth of 64% and -20 dB pulse-echo directional response of 10° were obtained. This measured bandwidth was not drastically reduced as compared with that of a conventional probe, and the measured directional response became slightly narrower as compared with the calculated result.