High-resolution acoustic localization of changes in spatially-distributed coherent sources for structural health monitoring.

Abstract

Localization of acoustic sources is a common remote sensing goal. When multiple sources are present and coherent, high-resolution localization typically becomes more challenging. The spectral estimation method with additive noise (SEMWAN) is an existing technique for high-resolution localization of incoherent monopole sources in low-signal-to-noise environments. SEMWAN utilizes a reference measurement to incoherently suppress background noise, but its performance suffers in applications involving spatially-distributed coherent sources, such as like a vibrating plate. However, by subtracting a reference measurement and using subarray averaging, SEMWAN can be extended to localization of small changes in distributed coherent sources. This revised approach, the spectral estimation method with coherent background removal (SEMCBR), permits remote acoustic localization of damage in a vibrating structure. A simple multi-source experiment using an 8-by-8 planar square microphone array with 6-cm spacing in both horizontal directions was performed to validate SEMCBR at a frequency of 5.0 kHz. Additional SEMCBR experimental results are reported for the same array placed 1.0 m above a 30 cm × 30 cm vibrating plate with and without damage. Cuts, boundary failures and delamination of a composite plate were successfully located with conventional spherical-wave beamforming and SEMCBR using a 0.1 to 6.0 kHz bandwidth. However, SEMCBR provides 4 to 6 times better resolution.