Impact localization on a metal plate using matched field processing and a microphone array

Acoustic waves are well-suited for remote sensing applications and structural health monitoring because they convey information about their source and can be recorded using non-contacting methods. An important structural health monitoring task is localization of an impact excitation. However, traditional array signal processing techniques for source localization are ill-suited for many structural engineering applications because of geometrical complexity, dispersive acoustic wave propagation in structures, and the coupling of the vibrating structure and the surrounding medium. Plus, many traditional methods use contacting sensors, which can permanently alter the structure. This study utilizes Bartlett matched field processing (MFP), a localization technique initially developed for underwater acoustics, to localize an impact source on a metal plate. A 14-microphone array recorded the sound radiated by a 0.64-cm-thick 91.4-cm-diameter round aluminum plate after the impact of a 1.3-cm-diameter stainless-steel ball bearing. MFP and a physics-based finite-element acoustic environment model were used to localize the impact on the plate. Results are presented as ambiguity surfaces where the predicted source location was typically found to be within 1.1 cm of the true source location. Localization performance was also assessed in a noisy environment, with success down to a signal-to-noise ratio of -7.5 dB.