Losses in piezoelectrics derived from a new equivalent circuit

Abstract

Miniaturization of piezoelectric devices such as ultrasonic motors, transformers, and sound projectors requires high power density maintained in the piezoelectric materials. During operation, heat generation due to material losses, however, hinders the realization of high power density. As a result, it is very important to understand the loss mechanisms in piezoelectric materials to successfully realize device miniaturization and at the same time maintain a good device performance. There are three fundamental losses in piezoelectric materials: dielectric, elastic, and piezoelectric. The first two components have been intensively investigated, whereas piezoelectric loss has not received much attention, which leaves some phenomena inexplicable. To verify its significance, in this paper, a new methodology has been presented to calculate the dielectric, elastic and piezoelectric losses based on a new equivalent circuit (EC) deduced from the revised Hamilton’s Principle. The improvement of the new methodology lies in the fact that all the three losses, including the piezoelectric loss, have been fully taken in consideration. The derivations and the calculation results indicate that the piezoelectric loss is not only non-negligible, but is also larger than other two components for hard PZT materials. The significance of the piezoelectric loss component has been therefore verified. During the above verification process, an elegant and concise measuring procedure of all the losses, including piezoelectric component, has been presented from an EC aspect for the first time. The calculation and measurement also indicate that the largest mechanical quality factor exists at a frequency between resonance and antiresonance, which may suggest a new optimal working frequency for piezoelectric devices from the loss reduction viewpoint.