High-frequency acoustic characterization of porous lead zirconate titanate for backing applications

Abstract

An original method to measure the acoustic properties of porous Pb(Zr 0.53 Ti 0.47 )O 3 (PZT) backings at high-frequencies (HF, i.e. between 15 and 25 MHz), was developed. To this end, a piezoelectric PZT-based thick film was deposited onto the porous ceramic backing and directly used to generate an acoustic signal in water. Here, the considered signal is the one that was generated in water, reflected on a target, back toward the multilayer structure, transmitted through the piezoelectric thick film and then to the rear face of the porous backing and finally back to the active film. This method avoids the overlap of the electrical excitation and the measured signal. In this study, two types of porous PZT backings with 1.5 and 10 micrometers pore sizes (volume fraction around 20%) were characterized. For both samples, group velocities were around 3500 m/s and for the 10 micrometers pores size sample, the measured acoustic attenuation coefficient was 1.7 dB/mm/MHz in the frequency range of the transducer bandwidth. Finally, this method is found to be an easy way to determine, in operating conditions, the minimum required thickness of the porous PZT to be used as a backing (in order to be considered as a semi-infinite medium) for HF transducer applications.