Piezoceramics for high-frequency (50 to 100 MHz) single-element imaging transducers

The properties of piezoelectric materials operating at high frequencies greatly influence the level of transducer performance which is achievable. Selection of the appropriate material can be made based on the transducer area and operating frequency. The properties of a number of piezoceramic materials have been experimentally determined by measuring the electrical impedance of air-loaded resonators whose thickness corresponds to resonance frequencies from 10 to 100 MHz. Materials measured include commercially available high dielectric lead zirconate titanate (PZT) and lower dielectric modified lead titanate (PT) ceramics, as well as materials which have been designed or modified to result in improved properties at high frequencies. Conclusions regarding the influence of the microstructure and composition on the frequency dependence of the properties are made based on the calculated properties and microstructural analysis of each material. Issues which affect transducer performance are discussed in relation to the measurements. For larger area transducers the use of a lower dielectric constant material is shown to result in a better electrical match between the transducer and standard 50 Omega terminations. For transducers whose impedance is close to that of the connecting cables and electrical terminations, KLM model simulations show improved performance without the need for electrical matching networks which can narrow the bandwidth and introduce additional losses. Measurements of actual transducers show close agreement with the simulations, verifying the material property measurements and the performance benefits of electrically matched transducers.