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

Although modified lead-titanate ceramics exhibit a negligible d₃₁ piezoelectric coefficient, piezoelectric-rod/polymer-matrix composites made from them exhibit a substantial d₃₁. A theoretical analysis shows that the composite´s enhanced d₃₁ 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 d₃₃. For hydrophone applications, this enhanced d₃₁ suppresses the hydrostatic response so that the composite´s hydrophone figure of merit, d_hg_h, is less than that of the constituent ceramic. Nevertheless, the composite´s still substantial d_hg_h, high g_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 k₃₃ is nearly the same as its k_t. These expectations are in good agreement with measurements on 1-3 modified lead-titanate/polymer composites made by the dice-and-fill technique