P1J-4 Evaluation of Small Ultrasonic Probe Using Lead Zirconate Titanate Film Deposited by Hydrothermal Method
Recently, our laboratory has explored the possibility of using lead zirconate titanate [PZT] polycrystalline film deposited hydrothermally on titanium substrate to fabricate a small actuator and ultrasound sensor. Hydrothermally deposited PZT polycrystalline films have piezoelectricity without a poling process, and it is easy to deposit PZT polycrystalline films on substrates that are tiny or complexly shaped. We confirmed that hydrothermally synthesized PZT polycrystalline films have wideband frequency characteristics with sensitivities in the megahertz band. It is thought that miniature ultrasound probes with wide- frequency band characteristics can be fabricated using hydrothermally synthesized PZT polycrystalline films. In our last report we assessed methods to produce a miniature ultrasound probe and transceiver characteristics. Here, the reception and transmission directivities of such a probe were measured at 5, 10, 15, and 20 MHz. The results showed that, except at 5 MHz, the theoretical and experimental values agreed. The difference at 5 MHz is attributed to the effect of the resonance frequency of the diameter direction.
Development of Miniature Needle-Type Hydrophone with Lead Zirconate Titanate Polycrystalline Film Deposited by Hydrothermal Method
A needle-type miniature hydrophone was developed using hydrothermally deposited lead zirconate titanate (PZT) polycrystalline films on a titanium (Ti) wire with a diameter of 0.3 mm in this study. Two types of hydrophones were fabricated as a trial for this paper. One is a hydrophone with hydrothermally deposited PZT polycrystalline films on the end surface and side surface near the end of the Ti wire. The other one is a hydrophone with hydrothermally deposited PZT polycrystalline films only on the end surface of the Ti wire. We measured the frequency characteristics of the relative receiving sensitivity and directivity of the fabricated hydrophones. The frequency characteristics of the relative receiving sensitivities of the fabricated hydrophone type A or B were measured in the frequency range from 1 to 20 MHz. Our hydrophone with deposited PZT films on the end and side faces of the Ti wire had problems in the directivity of relative receiving sensitivity. The relative sensitivity of the side direction was higher than that of the front direction. The directivity of our hydrophone with hydrothermally deposited PZT films only on the end surface of the Ti wire was improved remarkably.
Dielectric and Piezoelectric Properties of 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 Piezoelectric Single Crystals for Medical Array Transducers
Dielectric and piezoelectric properties of 0.93Pb(Zn1/3Nb2/3)O3–0.07PbTiO3 (PZNT 93/7) piezoelectric single crystals (PSC) have been investigated. The PZNT 93/7 single crystals (SC) with diameters of 40 mm were grown successfully by the Bridgman method with PbO flux. The dielectric constant of PZNT 93/7 SC at room temperature was about 3500, which is slightly larger than that of PZNT 91/9 SC. Phase-transition temperature, Trt, of PZNT 93/7 SC was 108°C, which is about 40°C higher than that of PZNT 91/9 SC; however, the Curie temperature, Tc, of PZNT 93/7 SC was 170°C, which is about 10°C lower than that of PZNT 91/9 SC. The coupling factor of rectangular bar mode, k33′, of PZNT 93/7 SC was 84% at room temperature, which is as large as that of PZNT 91/9 SC. The k33′ value of PZNT 93/7 SC hardly changed up to about 100°C and then decreased gradually towards the Curie temperature, Tc. The degradation temperature of the k33′ value was roughly in agreement with the phase-transition temperature, Trt, from the rhombohedral to tetragonal phase, measured using the poled PZNT SC. Moreover, no dielectric hysteresis was observed in PZNT 93/7 SC in the temperature range from 0°C to 80°C, although a dielectric hysteresis was observed in PZNT 91/9 SC in the same temperature range. Therefore, the Trt is thought to be important for guaranteeing a high k33′ value and minimum dielectric hysteresis. PZNT 93/7 SC with a reduced Ti content had not only a higher Trt but also its piezoelectric properties were as good as those of PZNT 91/9 SC near the morphotropic phase boundary (MPB). Therefore, PZNT 93/7 SC achieves the optimum balance of piezoelectric properties and their thermal stability for certain applications performed at comparatively high temperatures.