Modelling and measurement of piezoelectric fibres and interdigitated electrodes for the optimisation of piezofibre composites

Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72. Measurements of the piezoelectric induced strain constants (d(33) and d(31)), relative dielectric constants (epsilon(33)), longitudinal coupling factors (k(33)) and stiffness' (s(33)) of the varying volume fraction composites are compared to analytical expressions in order to extract the fibre properties. Results show 1-3 composite data accurately follows the analytical trends. The Viscous Plastic Process (VPP) fibres are found to exhibit optimum material properties, which approach bulk material values. Reduced piezoelectric activity in extruded fibres is thought to be associated with a small grain size and high porosity. A second study, an optimisation of interdigitated electrode design, was performed using the finite element software ANSYS. The effect of the IDE geometry (electrode width and spacing) and PZT substrate thickness on the strain output of bulk PZT substrates was modelled. Results show optimal actuation occurs at electrode widths equal to half the substrate thickness, and for thin substrates the electrode finger spacing can be reduced to enable lower driving voltages.