An investigation of detection metrics for the remote acoustic sensing of mechanical changes in a vibrating plate

Abstract

Acoustic radiation from a mechanical structure due to broadband forcing is inherently dependent on the structure’s material, geometry, and boundary conditions. Measurements of the radiated field can be used to detect mechanical changes (i.e., defects) when compared to known baseline measurements of the same structure. However, there are many available options for evaluating these changes, and each presents benefits and liabilities. In this presentation, several detection metrics are evaluated for the remote acoustic detection of mechanical changes in a 0.3-m-square by 3-mm-thick aluminum plate with 100 to 2000 Hz broadband forcing. The radiated acoustic field from the vibrating plate is recorded with a 15-element receiver array used to reconstruct an estimate of the plate’s acoustic response. This response is then quantitatively compared to previous baseline responses using cross-correlation, spectral analysis, wavelet analysis, frequency response function analysis, and other relevant detection techniques. The performance of each detection metric is evaluated and ranked by considering the minimum detectible size of a change, required a priori knowledge of the system, and ease of implementation. The feasibility of classification of the detected changes is also considered. [Sponsored by NAVSEA through the NEEC, and by the US DoD through an NDSEG Fellowship.]