Structural health monitoring method based on the entropy of an ultrasonic sensor network for a plate-like structure

Abstract

Piezoelectric ultrasonic sensors used to propagate guided waves can potentially be implemented to inspect large areas in engineering structures. However, the inherent dispersion and noise of the guided acoustic signals, multiple echoes in the plate as well as a lack of an approximate or exact model limits their use as a continuous structural health monitoring system. In this work, the implementation of a network of piezoelectric sensors randomly placed on a plate-like structure to detect and locate artificial damage is studied. A sensor network of randomly located 1MHz transducers working in a pitch-catch configuration was set on an aluminum thin plate 1.9 mm in thickness. Signals were analyzed in time-scale domain by the continuous wavelet transform. The objectives in this work were twofold, first to develop a damage index using the entropy of the ultrasonic waves generated by a sensor network; and second to implement time of arrival (TOA) and time-difference of arrival (TDOA) algorithms on the gathered signals for damage location of an artificial circular discontinuity. Our preliminary test results show that the proposed methodology provides sufficient information for damage detection which, once combined with the TOA and TDOA algorithms, allows localization of the damage.