Behavior of a PZT ring under non-uniform mechanical stress

Ring-shaped lead zirconate titanate (PZT) piezoelectric vibrators were subjected to non-uniform mechanical stress applied by bolt clamping. The effect of mechanical stress on the effective electromechanical coupling factor (k_eff) and mechanical quality factor (Q_m) of the thickness and wall thickness modes was studied by an equivalent electric circuit analysis. The initiation and propagation of cracks under mechanical stress were also discussed based on the resonance method and the indentation technique. k_eff for both the thickness and wall thickness modes decreased with increase in mechanical stress due to de-poling of the PZT. Q_m of the thickness mode dropped sharply with increase in mechanical stress while Q_m of the wall thickness mode remained almost unchange. Existence of microcracks in a PZT vibrator can be detected by the occurrence of spurious vibrations at the wall thickness mode in the electrical impedance vs. frequency spectra.