Study of mechanical and dielectric losses contribution to the surface-acoustic-wave attenuation in piezoelectric ceramics

Abstract

The surface-acoustic-wave (SAW) propagation losses of two ceramics, a lead zirconate titanate composition and a modified lead titanate composition, are studied. Contrary to crystals, where only mechanical losses contribute, dielectric losses and scattering at the grain boundaries have to be taken into account. A first-order perturbation theory is extended to include dielectric losses to calculate the surface attenuation. Based on the measurement of the mechanical and the dielectric losses of the two ceramics as a function of frequency, the frequency behavior of the SAW propagation losses of each material is theoretically calculated and values are compared to those obtained experimentally at 25 MHz. Both results show that the modified lead titanate ceramic has low SAW propagation losses, 0.22 dB/mm at 25 MHz, while the lead zirconate titanate has propagation losses of 2 dB/mm at 25 MHz. Using results published in literature, the effect of the scattering contribution is evaluated. Finally, other SAW properties of ceramics, i.e., the free-surface-wave velocity, the surface coupling coefficient, and the surface permittivity are measured and reported. All these results are discussed and the suitability of both materials for SAW applications is examined.