Non-destructive evaluation of multi-layer actuators

This paper describes the use of impedance spectroscopy as a means of non-destructively detecting delaminations and damage in piezoelectric multi-layer actuators. The method is based on a test developed to examine multi-layer capacitor devices. Impedance spectra are reported on conventional multi-layer actuators and multi-layers that contain delaminations or have been subjected to damage. The defects within the devices are characterised by ultrasonic evaluation and microscopy. Impedance analysis reveals that the resonance behaviour of the actuator is altered by the presence of defects. By examining impedance data using a complex impedance plot the change in resonance behaviour of a multi-layer actuator due to defects can be observed. The method could be employed as a means of quality control during production or for monitoring the state of the actuator whilst in service, e.g. whether there has been fatigue of the device or it has be subjected to an unacceptably high stress.