Power and energy characteristics of solid-state induced-strain actuators for static and dynamic applications

The power and energy characteristics of solid-state induced-strain actuators are studied. Piezoelectric (PZT), electrostrictive (PMN) and magnetostrictive (TERFENOL) actuators are considered. The principles and internal construction of solid-state induced-strain actuators are briefly reviewed. Typical performance curves are presented and discussed. The basic equations of piezoelectricity and piezomagnetism are presented. A linearization procedure is adopted whereby apparent values for the piezoelectric and piezomagnetic constants are derived from full-stroke vendor data using the secant approximation principle. Values for the apparent electromagnetic conversion coefficient for full-stroke operation are obtained. The static analysis considers the one-directional operation of the induced strain actuators against an external spring load. It is found that the maximum energy output from the induced-strain actuator is obtained when the internal and external stiffnesses are matched. Expressions for the maximum energy output, and the energy densities per unit volume, mass, and cost are derived. Numerical examples and comparative charts are given for a number of piezoelectric, electrostrictive and magnetostrictive actuators. The influence of casing and pre-stress mechanism on the overall energy density values is also highlighted. The electromechanical conversion efficiency is studied, and two separate expressions are derived, one for the best efficiency, and another for the conversion efficiency at the stiffness match point. The dynamic analysis considers the cyclic motion of the induced-strain actuators about a midpoint bias position. The dynamic full-stroke is found approximately one-half the static full-stroke. The correspondingly maximum output energy and energy densities under dynamic conditions are calculated. The dynamic energy conversion efficiency is studied and the influence of bias voltage or current is included. Numerical examples and comparative charts are given for a number of piezoelectric, electrostrictive and magnetostrictive actuators operating under dynamic conditions.