Evaluation of Piezoelectric Ceramics for use in Miniature Histotripsy Transducers

Five piezoelectric ceramics were evaluated for use in miniature broadband histotripsy transducers. The materials tested were PZT-5A, PZT-5H (CTS 3203HD), Pz39, Pz54 and PMN-38. 5 MHz, 1-3 dice and fill piezo/epoxy composites were fabricated for all except for Pz39, which is a low acoustic impedance porous ceramic. Four air-backed transducers for each material were built by bonding the composite to an 8 mm machined aluminum lens with a 7 mm focus and depositing a Parylene-C matching layer. The performance of each material was evaluated by measuring the transducers' transmitting sensitivity, cavitation threshold voltage in water and surface pressure versus drive voltage, and then testing them to failure. Measured sensitivities were compared to FEM model results, and HITU Simulator V2.0 was used to non-linearly extrapolate the results. Transducers were tested using 8-cycle, 1 kHz PRF pulses. As expected, the measured sensitivity for transducers of each material increased with increasing dielectric constant, while cavitation threshold voltages in water decreased. All Pz39 transducers failed when driven at or above 264 Vpp. All PMN38 transducers failed due to high instantaneous current. The most common failure mode was Parylene delamination.