Acoustic Properties of Porous Lead Zirconate Titanate Backing for Ultrasonic Transducers

For transducer design, it is essential to know the acoustic properties of the materials in their operating conditions. At frequencies over 15 MHz, standard methods are not well adapted because layers are very thin and backings have very high attenuation. In this article, we report on an original method for measuring the acoustic properties in the 15-25 MHz frequency range, corresponding to typical skin-imaging applications, using a backing/piezoelectric multilayer structure. Onto a porous Pb(Zr0.53Ti0.47)O-3 (PZT) substrate, a piezoelectric PZT-based layer with a thickness of similar to 20 mu m was deposited and directly used to excite an acoustic signal into water. Herein, the measured signal corresponds to the wave that is first reflected on a target in water, then propagates back to the multilayer structure, and is transmitted through the thick film and further to the rear face of the porous backing, where it is again reflected and returns to the piezoelectric thick film, thus avoiding overlap with the electrical excitation signal. Two types of PZT backings with similar porosity of similar to 20% and spherical pores with size of 1.5 and 10 mu m were processed. The ultrasound groupvelocitiesweremeasuredat similar to 3500m/s for both samples. The acoustic attenuation of the backingswith pore size of 1.5 and 10 mu m were 12 and 33 dB/mm, respectively, measured at 19 MHz. This advanced measuring technique demonstrated potential for the simple measurements of acousticpropertiesof backing at high frequencies in operating conditions. Importantly, this method also enables rapid determination of the minimum required thickness of the backing to act as a semi-infinitemedium, for high-frequency transducer applications.