Enhanced lateral electromechanical coupling in lead-titanate-rod/polymer piezoelectric composites

Although modified lead-titanate ceramics exhibit a negligible d/sub 31/ piezoelectric coefficient, piezoelectric-rod/polymer-matrix composites made from them exhibit a substantial d/sub 31/. A theoretical analysis shows that the composite's enhanced d/sub 31/ coefficient arises from lateral stress on the polymer phase being transferred to a longitudinal stress along the ceramic rods by the Poisson effect in the polymer, thus producing a charge through the ceramic's d/sub 33/. For hydrophone applications, this enhanced d/sub 31/ suppresses the hydrostatic response so that the composite's hydrophone figure of merit, d/sub h/g/sub h/, is less than that of the constituent ceramic. Nevertheless, the composite's still substantial d/sub h/g/sub h/, high g/sub h/ coefficient, remarkable pressure stability, low density, formability, and availability in thick sheets provide advantages for naval applications. In ultrasonic transducer applications, the composite structure provides no enhancement in electromechanical coupling, since the modified lead-titanate's k/sub 33/ is nearly the same as its k/sub t/. These expectations are in good agreement with measurements on 1-3 modified lead-titanate/polymer composites made by the dice-and-fill technique.<>