Fabrication and Characterization of a Wavenumber-Spiral Frequency-Steerable Acoustic Transducer for Source Localization in Plate Structures

This paper reports on the fabrication and the experimental characterization of a wavenumber frequency-steerable acoustic transducer (WS-FSAT). Here, the transducer is employed for the localization of broadband acoustic events corresponding to the propagation of guided elastic waves in an isotropic plate. The WS-FSAT records the plate response and defines the source location through a time-frequency analysis of the received signal. This is achieved by exploiting the frequency selective response of the transducer which directly maps the dominant component of the received signal to the direction of arrival of the incoming wave. This feature is the result of the spatial filtering effect produced by the characteristic shape of the sensing surface, which is designed in the wavenumber domain. Experiments are performed on a prototype fabricated on a polyvinylidene fluoride substrate mounted on an aluminum test plate. Tests are conducted for various source locations, and with multiple sources activated simultaneously. The results highlight the robustness of the proposed device, its good sensitivity and angular resolution, as well as the low complexity of hardware and signal processing. This paper suggests the WS-FSAT as an attractive solution for the detection of broadband acoustic events, such as impacts on structural substrates, and its potential use as part of active structural health monitoring systems based on pitch-catch or pulse-echo operations.