High-Power Piezoelectrics and Loss Mechanisms

Abstract

Abstract Heat generation is one of the significant problems in piezoelectrics for high power density applications. In this chapter, we review first the loss phenomenology in piezoelectrics first, including three losses—dielectric, elastic and piezoelectric losses—followed by the equivalent circuit approach with these three losses. Third, heat generation analysis is discussed in piezoelectric materials for pseudo-DC and AC drive conditions. Heat generation at off-resonance is attributed mainly to intensive dielectric loss tan δʹ, while the heat generation at resonance is mainly originated from the intensive elastic loss tan ϕʹ. Fourth, various experimental techniques (high power characterization system, HiPoCS) are introduced to measure dielectric, elastic, and piezoelectric losses separately, including admittance/ impedance spectrum analysis and burst/transient response method. Mechanical quality factors (QA at resonance and QB at antiresonance) are primarily measured as a function of vibration velocity. Fifth, based on the results received by HiPoCS, new driving schemes (antiresonance drive, etc.) are proposed in order to minimize the losses and maximize the transducer efficiency. Sixth, loss mechanisms are discussed from the materials science viewpoint, particularly from the domain dynamics models. Then, practical high-powered “hard” Pb(Zr,Ti)O3 (PZT)-based materials are described, which exhibit vibration velocities close to 1 m/s (rms), leading to the power density capability 10 times that of the commercially available hard PZTs. We propose an internal bias field model to explain the low loss and high power origin of these materials. Finally, we also introduce the polarization angle dependence of losses (sample geometry), and DC bias electric field dependence of losses (sample driving technique) for the high-powered applications.