Electrostrictive ceramics for low-frequency active transducers

Electrostrictive ceramics based on Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/ have demonstrated promise as low-frequency active materials. They broaden the range of design options by providing a mix of properties unavailable in traditional piezoceramics. Typical properties are: 1000 microstrain on the interval 0-1 MV/m with a k/sub 33/ of 0.5; high-field electrical impedance /spl sim/5 times that of traditional piezoelectrics; graceful, predictable, and repeatable property variation with temperature, frequency, and prestress; recoverable change of properties with temperature. Unipolar excitation at fields less than 1 MV/m is typical to provide direct frequency conversion and prevent corona discharge and reliability issues within transducers. Although electrostrictive ceramics are not direct replacements for traditional piezoceramics, they have many similarities in physical and chemical properties. The differences are most obvious in the electromechanical response behavior with changes in bias field, drive level, frequency, and prestress. In addition, the "rules-of-thumb" for traditional piezoceramics, both processing and use, do not wholly apply to electrostrictive ceramics. The development and present state of the art in electrostrictive ceramics for low-frequency uses are detailed.