Spiral-shaped piezoelectric sensors for Lamb waves direction of arrival (DoA) estimation

A novel strategy to design piezoelectric sensors suited for direction of arrival (DoA) estimation of incoming Lamb waves is presented in this work. The designed sensor is composed by two piezoelectric patches (P1, P2) to be bonded on the structure to be inspected. In particular, by exploiting the Radon Transform, the proposed procedure computes the shape of P2 given the shape of P1 so that the difference in time of arrival (DToA) of the Lamb waves at the two patches is linearly related to the DoA while being agnostic of the material dispersion curves. With a dedicated processing procedure, the waveforms acquired and digitized from the two electrodes can be used to retrieve DoA information. Numerical and experimental results show that DoA estimation performed by means of the proposed shaped transducers is extremely robust.