PIEZOCERAMICS FOR HIGH-FREQUENCY (20 TO 100 MHZ) SINGLE-ELEMENT IMAGING TRANSDUCERS

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.