Shiroh Saitoh

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.

A dual frequency ultrasonic probe for medical applications

A dual frequency probe using a multilayer ceramic is proposed for simultaneously obtaining a high resolution B mode and a high sensitivity Doppler mode image. This ceramic consists of two layers in which the poling directions are opposite and the individual thicknesses are different. It is possible to control the values of relative electromechanical coupling factors in the fundamental and the second harmonic by changing the thickness ratio. A thickness ratio of 1:0.7 was decided from computer simulation based on the Masons model. A sufficient resolution has been shown from the fact that the intima of the carotid artery could be distinguished by an actually fabricated probe with dual frequencies of 3.75 and 7.5 MHz. Also, the sensitivity of this probe in the Doppler mode at 5 cm depth from the surface has been improved as much as 5 dB over that of a conventional one.<<ETX>>

An Improved Phased Array Ultrasonic Probe Using 0.91Pb(Zn1/3Nb2/3)O3?0.09PbTiO3 Single Crystal

A 96-channel phased array probe for echocardiography using a single-plate, 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 (PZNT 91/9) single-crystal transducer with dimensions of 14×20 mm has been fabricated to realize greater sensitivity and broader bandwidth properties. The center frequency of the probe, 3.5 MHz, was selected to cover the bandwidths of two conventional lead zirconate titanate (PZT) ceramic probes with center frequencies of 2.5 and 3.75 MHz. A solder paste was used to connect a flexible printed circuit to the PZNT 91/9 transducer. The echo amplitude of the PZNT 91/9 probe is about 6 dB higher than that of the two PZT probes, and the fractional bandwidths are 30 and 25 percentage points wider, respectively. The B-mode image quality of the PZNT 91/9 probe is comparable to that of the two PZT probes, and the Doppler sensitivity of the PZNT 91/9 probe is almost equal to that of the 2.5 MHz PZT probe, which means that the PZNT 91/9 probe matches both the penetration of the 2.5 MHz PZT probe and the resolution of 3.75 MHz PZT probe.

A 3.7 MHz phased array probe using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/

A novel 128-channel phased array probe for echocardiography with a center frequency of 3.7 MHz using 0.91Pb(Zn(1/3)Nb(2/3))O(3)-0.09PbTiO(3 ) (PZN-9%PT) single crystal has been fabricated to realize greater sensitivity and broader bandwidth properties. The echo amplitude of the PZN-9%PT single-crystal probe is about 5 dB higher than that of the conventional lead airconate titanate (PZT) ceramic probe, and the fractional bandwidth is about 25 percentage points broader. The quality of B mode images obtained by the PZN-9%PT probe satisfies the performance of the two types of conventional PZT ceramic probes that have center frequencies of 2.5 and 3.75 MHz. At the reference frequency of 3 MHz, the Doppler sensitivity of the PZN-9%PT probe is about 5 dB higher than that of the 3.75 MHz PZT probe; the blood flow of a pulmonary vein in a hard-to-image patient is much more clearly imaged than in the case of using the PZT probe. These superior images are attributable to the use of sufficiently large PZN-9%PT single crystals obtained by the self-flux method.

A 20 MHz single-element ultrasonic probe using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/ single crystal

A 20 MHz single-element ultrasonic probe using 0.91Pb(Zn(1/3 )Nb(2/3))O(3)-0.09PbTiO(3) (PZN-PT 91/9) single crystal has been fabricated. The single crystal of PZN-PT 91/9 orientated to the (001) plane has longitudinal coupling factor of k(33)>90%, which is much larger than the k(33)=70 to 80% of conventional Pb(Zr(1-x),Ti(x))O(3) (PZT) based ceramics. A single crystal of PZN-PT 91/9 without inclusion or crack has been grown with dimensions of about 25x15x5 mm by the self-flux method. Because mechanical strength in the fabrication of disk transducers orientated to the (001) plane was sufficiently strong, under the same conditions as are applied to conventional PZT ceramics, a piston single-element probe with a diameter of 2.0 mm and a frequency of 20 MHz was successfully fabricated. The bandwidth of the PZN-PT 91/9 probe was 13-26 MHz, which was 4 MHz broader than that of the conventional PZT probe.

Crystal Growth of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Using a Crucible by the Supported Bridgman Method

Piezoelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 (PZNT 91/9) single crystals with diameters of 40 mm were successfully grown from solution by the Bridgman method with a PbO flux supported on the bottom of the crucible. This type of Bridgman method is more suitable for growing large and heavy crystals than the hanging-type Bridgman method. Using a modified supporting method, a PZNT 91/9 single crystal was grown. The crystals were grown in a platinum crucible heated to 1,130°C, and the growth rate was 0.20–0.50 mm/h. The obtained crystals were about 40 mm in diameter×20 mm in length (200 g) and were light brown in color. The Curie temperature, Tc, ranged from 170 to 175°C. These results confirm that the Bridgman method using a supported crucible is useful for the mass production of large crystals of PZNT 91/9.

Forty-channel phased array ultrasonic probe using 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/ single crystal

A 0.91Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-0.09PbTiO/sub 3/ (PZN-PT) single crystal with high electromechanical coupling factor (k/sub 33/)>90% has been used to fabricate a 40-channel phased array ultrasonic probe with greater sensitivity and broader bandwidth than conventional probes. This probe has a center frequency of 3.5 MHz and an aperture of about 6.0/spl times/7.5 mm. The standard probe fabrication process was modified for PZN-PT. The dispersion of echo signals was within /spl plusmn/20% of the mean value. After recovery poling, the echo amplitude of the PZN-PT single-crystal probe is 8 and 5 dB higher than that of one- and two-matching-layer PZT probes, respectively. Moreover, the fractional bandwidth of the single-matching-layer PZN-PT probe is broader than that of the two-matching-layer PZT probes. The PZN-PT single crystals provide great improvements in the sensitivity and bandwidth of phased array probes.

Simulation and Fabrication Process for a Medical Phased Array Ultrasonic Probe using a 0.91Pb(Zn1/3Nb2/3)O3–0.09PbTiO3 Single Crystal

Medical array ultrasonic probes using a 0.91Pb(Zn1/3Nb2/3)O3-0.09PbTiO3 (PZN-PT) single crystal exhibiting a high electromechanical coupling factor (k33) >90% have been studied in order to realize both a higher sensitivity and broader bandwidth properties. Pulse echo characteristics of the array probes, each transducer of which has dimensions of 6.0 mm×0.14 mm with a center frequency of 3.5 MHz, are simulated using the dielectric and the piezoelectric constants of the grown PZN-PT single crystals. Simulated echo amplitudes of the PZN-PT probes have been improved by as much as 7 dB compared with those of the conventional Pb(Zr1-x,Tix)O3 (PZT) ceramic ones. Moreover, the bandwidth of the PZN-PT probe is expected to be about 25% broader than those of the conventional PZT probes. It has been shown by simulation that the low acoustic impedance as well as the high coupling factor of the PZN-PT crystal contribute in broadening the bandwidth of the probe. The fabrication process of the array probe was investigated. A conventional method in which the dicing conditions are optimized and a novel dicing process are proposed.

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.

Crystal Growth and Mechanical Properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Single Crystal Produced by Solution Bridgman Method

High-quality, 40-mm-diameter piezoelectric Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals (PZNT91/9) were successfully grown by the solution Bridgman method. Vickers hardness and fracture toughness of a PZNT91/9 wafer cut from a crystal were investigated by a microindentation technique. The Vickers hardness of PZNT91/9 was 2.6 GPa (transparent area) and 2.2 GPa (opaque area). The Vickers hardness of the transparent area in PZNT91/9 was equivalent to that of PZT ceramic. The fracture toughness of the transparent area of PZNT91/9 was markedly different depending on the domain direction: KIC=0.80 MPam1/2 (vertical to the domain wall); and KIC=0.38 MPam1/2 (parallel to the domain wall). Although the fracture toughness of PZNT91/9 is smaller than that of PZT ceramic, it is possible to cut the crystals for fine-pitch dicing, as required to produce array-type medical transducers, without serious problems.