Mj. Zipparo et al., PIEZOCERAMICS FOR HIGH-FREQUENCY (20 TO 100 MHZ) SINGLE-ELEMENT IMAGING TRANSDUCERS, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 44(5), 1997, pp. 1038-1048
The performance of transducers operating at high frequencies is greatl
y influenced by the properties of the piezoelectric materials used in
their fabrication. Selection of an appropriate material fur a transduc
er is based on many factors, including material properties, transducer
area, and operating Frequency. The properties of a number of piezocer
amic materials have been experimentally determined by measuring the el
ectrical impedance of air-loaded resonators whose thickness correspond
s to resonance frequencies from 10 to 100 MHz. Materials measured incl
ude commercially available compositions of lead zirconate titanate (PZ
T) with relatively high dielectric constants and a modified lead titan
ate (PT) composition with a much lower dielectric constant. In additio
n, materials which have been designed or modified to result in improve
d properties at high frequencies are studied. Conclusions concerning t
he influence of the microstructure and composition on the frequency de
pendence of the material properties are made from the calculated prope
rties and microstructural analysis of each material. Issues which affe
ct transducer performance are discussed in relation to the properties.
For transducers larger than about 1 mm in diameter, the use of a lowe
r dielectric constant material is shown to result in a better electric
al match between the transducer and a standard 50 Omega termination. F
or transducers whose impedance is close to that of the connecting cabl
es and electrical termination, equivalent circuit model simulations sh
ow improved performance without the need for electrical matching netwo
rks. Measurements of fabricated transducers show close agreement with
the simulations, validating the measurements and showing the performan
ce benefits of electrically matched transducers.