Influence of Elastic Loss on Measured Dielectric-Loss-Angle of High-Coupling Piezoelectric Material

A dielectric loss angle of piezoelectric materials measured at sufficiently low frequencies contains an excess angle resulting from an elastic loss brought by the quasi-static strains. This paper presents an experimental verification of this effect in transducers made of high-coupling piezoelectric ceramics with a low mechanical Q-factor, where the excess loss-angle becomes fairly large. Taking account of both dielectric and elastic losses, an advanced equivalent circuit is also derived, which is useful for estimating the excess loss-angle through the free immitance measurements. In this circuit, the excess loss-angle can be evaluated by a resistance equal to k2/ωCdQB) added in series to the clamped impedance.