Modeling and testing of PZT and PVDF piezoelectric wafer active sensors

Abstract

Piezoelectric wafer active sensors (PWAS) used in structural health monitoring (SHM)applications are able to detect structural damage using Lamb waves. PWAS are small,lightweight, unobtrusive and inexpensive. They achieve direct transduction between electricand elastic wave energies. PWAS are charge mode sensors and can be used as bothtransmitters and receivers. The focus of this paper is to find a suitable in situ piezoelectricactive sensor for sending and receiving Lamb waves to be used in the SHM of structureswith a curved surface. Current SHM technology uses brittle piezoceramic (PZT) waferactive sensors. Since piezoceramics are brittle, this approach could only be used on flatsurfaces. The motivation of our research was to explore the use of flexible piezoelectricmaterials, e.g. piezoelastic polymers such as PVDF. However, PVDF stiffnessis orders of magnitude lower than the PZT stiffness, and hence PVDF Lambwave transmitters are much weaker than PZT transmitters. Thus, our researchproceeded in two main directions: (a) to model and understand how piezoelectricmaterial properties affect the behaviour of piezoelectric wafer active sensors; and(b) to perform experiments to test the capabilities of the flexible PVDF PWAS incomparison with those of stiffer but brittle PZT PWAS. We have shown that, withappropriate signal amplification, PVDF PWAS can perform the same Lamb wavetransmission and reception functions currently performed by PZT PWAS. Theexperimental results of PZT-PWAS and PVDF-PWAS have been compared with aconventional strain gauge. The theoretical and experimental results in this study gave abasic demonstration of the piezoelectricity of PZT-PWAS and PVDF-PWAS.