Loss mechanisms in piezoelectrics and resonance/antiresonance

Abstract

Losses in piezoelectrics are considered in general to have three different mechanisms: dielectric, mechanical and piezoelectric losses. This paper deals with the phenomenology of losses, first, then how to measure these losses experimentally. We will discuss two methods for measuring the electrical, mechanical, and piezoelectric coupling losses separately: (1) strain versus stress and field and displacement versus stress and field curves, and (2) a resonance/antiresonance technique. Also, one can measure heat generation at an off-resonance frequency to obtain a total loss. By combining the above methods, we can investigate the loss mechanisms in practical piezoelectric materials and their consequences in devices. It will be shown that heat generation is caused mainly by the dielectric loss, not by the mechanical loss. Furthermore, a drastic decrease in mechanical Q with an increase of vibration level is observed in resonant piezoelectric ceramic devices, a result not observable using conventional impedance analyzers at low power. Based on this loss knowledge, we will discuss the differing situations between piezoelectric resonance and antiresonance states. In particular, since the mechanical quality factor at an antiresonance frequency is larger than that at a resonance frequency the antiresonance mode seems to be superior for high-power applications.