Spira Mirabilis: A shaped piezoelectric sensor for impact localization

In this work, a novel piezoelectric sensor for guided waves detection on laminate composite and metallic structures is presented. The sensor is composed by two electrodes (E1 and E2) on the top surface of the device, plus a common electrode (EC) on the bottom surface, which is bonded to the structure to be inspected. E1 has a circular shape, whereas E2 is shaped as a segment of a logarithmic spiral (or spira mirabilis). Because of this asymmetric shaping, the wavefront of a generic acoustic event (e.g. the one generated by an impact) hits the electrodes in two points whose distance D varies with the Direction of Arrival (DoA) of the wave itself. With a dedicated processing procedure, the information about the distance D first, and then about the DoA can be retrieved from the waveforms acquired and digitized at the two electrodes E1 and E2. In particular, the procedure computes the cross-correlation of the dispersion compensated signals, and extracts the distance D by looking at the position of the maximum of the cross-correlation envelope. Here, a first experimental test is performed to validate the effectiveness of the proposed technology.