Electric Impedance of Piezoelectric Ceramics under Acoustic Loads

Abstract

The electric impedance of piezoelectric ceramics is influenced by variations in the acoustic load. This situation is very common for ultrasonic applications in medicine where the irradiated media can present different interfaces and impedances to the propagating acoustic energy. In this work we analyzed the behavior of the resonances, anti-resonances and the effective electromechanical coupling factor of a piezoelectric ceramic ring vibrating in thickness mode. The analysis is based on equivalent electric circuits and considers variations in the acoustic load. The results showed that the electric impedance of the ceramic is altered with the length of the acoustic load, resulting in new resonances and changing the effective electromechanical coupling factor. Electronic circuits for driving piezoelectric transducers must be able to correct the frequencies if acoustic loads vary.