Near-Field Acoustic Emission Sensing Performance of Piezoelectric Film Strain Sensor

This article deals with near-field acoustic emission (AE) signal sensing with a low-profile piezoelectric film strain sensor. In general, AE signals can be represented as a summation of moment tensor (dipoles or double couples) weighted Greens’ functions. Basic theories of the Green's function and moment tensor are introduced first. The formulation presented here extends the AE elastodynamic solution to stress-wave induced surface strain response in half space. As a special case with potential use for sensor calibration, stress wave-induced surface strain response to a surface pulse load is presented. To verify the derivation, experiments were carried out with glass capillary breakage on a large steel block. The experimental result matches the theoretical prediction fairly well. Based on the surface pulse case study, the characteristics of strain and displacement signals are illustrated for both P and Rayleigh wave arrivals, which could provide insights for such strain sensor design and implementation. Due to the finite sensing area of piezoelectric film strain sensor, its aperture effect cannot be neglected in practical use, especially in higher frequency AE signal sensing, which is also investigated in this article.