Piezo-electric Thick Films for Sensing

Monolithic piezoelectric sensors commonly used for acoustic emission and ultrasonic inspection are non-conforming, bulky, costly and heavy. This means they do not fit well to complex geometries, they can be susceptible to damage, and on larger structures their cost and weight can be prohibitive. An alternative to this is the use of piezo-electric thick films, which comprise of piezo-electric particles suspended in a matrix material. Such materials could provide “paint on” or “printable” sensors and sensor networks that are low profile, easy to mount and very cheap. In this work we explore the potential of piezo-electric thick films to sense and actuate for Acoustic Emission and ultrasonic applications. Sensors were produced by dispersing PZT 5a particles within water based acrylic and epoxy matrix materials with up to 70% fill by weight. The PZT films were applied to steel and their responses to artificial AE sources (Hsu-Nielson) were assessed and three-dimensional laser vibrometry was used to study the frequency response and mode shapes of the sensors under excitation. The results showed that although less sensitive than monolithic piezoelectric transducers, the thick film sensors can excite and detect ultrasonic waves for SHM applications and there is great potential for the development of a low cost, printed sensor network for SHM.