Complex electromechanical coefficients of piezoelectric composites: Applications to passive vibration damping

A modified resonance technique was used to measure the complex electromechanical property coefficients of lossy 0-3 composite samples comprised of ceramic lead zirconate titanate (PZT) powder dispersed in different polymer matrices.;An increase in the loss tangents of the dielectric, elastic and piezoelectric coefficients was observed near the glass transition temperatures of the polymer phases. In the case of a PZT-polyvinylidene fluoride (PVDF) composite, it was possible to measure the electromechanical coefficients using 31 and thickness mode resonances over a range of temperatures spanning the glass transition temperature of the polymer. The principle of time-temperature superposition was used to explain the frequency and temperature dependences of the coefficients. The relaxation behavior of the properties of 0-3 composites, predicted theoretically by a simple cubes model representing the composite structure, was found to be in partial agreement with the experimental data.;Due to electromechanical coupling, an imaginary part in a piezoelectric coefficient implies an imaginary part in a corresponding elastic coefficient which in turn implies lossy mechanical behavior. A dissipative mechanism like electrical conductivity in a piezoelectric material results in a mechanical loss tangent and associated dissipation of mechanical energy and damping of mechanical vibrations.;This concept of passive piezoelectric damping was developed and the effect of internal conductivity simulated by connecting external resistors across poled piezoceramic elements with large piezoelectric coupling. The damping characteristics of a stack specimen comprised of several such elements were optimized. The properties measured using electrical resonance and mechanical vibration experiments agreed with predictions from theory. It was possible to obtain a large mechanical stiffness coefficient (;Suggestions as to the utilization of the above damping effect have been made with respect to the design of ceramic-metal composites, inducing electrical conductivity in piezoceramics, use of active electronic circuits to enhance and obtain greater control over the damping properties and the possible use of magnetostrictive materials possessing large magnetomechanical coupling coefficients.