Clamping effect on the piezoelectric responses of screen-printed low temperature PZT/Polymer films on flexible substrates

摘要

This paper introduces a new flexible lead zirconate titanate (PZT)/polymer composite material that can be screen-printed onto fabrics and flexible substrates, and investigates the clamping effect of these substrates on the characterization of the piezoelectric material. Experimental results showed that the optimum blend of PZT/polymer binder with a weight ratio of 12:1 provides a dielectric constant of 146. The measured value of the piezoelectric coefficient d(33) was found to depend on the substrate used. Measured d(33clp) values of 70, 40, 36 pC N-1 were obtained from the optimum formulation printed on Polyester-cotton with an interface layer, Kapton and alumina substrates, respectively. The variation in the measured d(33clp) values occurs because of the effect of the mechanical boundary conditions of the substrate. The piezoelectric film is mechanically bonded to the surface of the substrate and this constrains the film in the plane of the substrate (the 1-direction). This constraint means that the perpendicular forces (applied in the 3-direction) used to measure d(33) introduce a strain in the 1-direction that produces a charge of the opposite polarity to that induced by the d(33) effect. This is due to the negative sign of the d(31) coefficient and has the effect of reducing the measured d(33) value. Theoretical and experimental investigations confirm a reduction of 13%, 50% and 55% in the estimated freestanding d(33fs) values (80 pC N-1) on Polyester-cotton, Kapton and alumina substrates, respectively. These results demonstrate the effect of the boundary conditions of the substrate/ PZT interface on the piezoelectric response of the PZT/polymer film and in particular the reduced effect of fabric substrates due to their lowered stiffness.