Biased Lead Zirconate-Titanate as a High-Power Transducer Material

In considering applications for high-power, electrostrictive transducer materials such as lead magnesium niobate, one should not overlook the possibility of biased operation of conventional high-power materials, such as Navy Type III lead zirconate-titanate PZT. Because of the high electrical impedance of this material, very large electric fields will be required, with concommitant transducer design problems, but 10-dB increases in energy density over that obtainable with conventional, unbiased Type III piezoceramic might be achievable. Measurements of the strain and charge density for prestressed samples of Type I and Type III, subjected to compressive prestress up to 10 ksi and peak electric field intensities as much as 2 MVm, indicate substantial increases in the relative permittivity E33 TE0, with increasing bias field. On the other hand, the elastic compliance coefficient s33E and the piezoelectric strain coefficient d33 do not deviate greatly from their small-signal values. Therefore, the energy density may be expected to increase in a roughly proportional manner to the square of the ac drive field intensity. However, the coupling factor k33 would be expected to decrease with increasing bias field because of the increasing permittivity, and so the bandwidth obtainable from biased PZT will be reduced from that of conventionally driven material.