An Improved Shear-Horizontal Wave AE Sensor and an Explanation of SH Wave Mechanics

Abstract

An improved torsional SH wave sensor is introduced that provides sensitivity to shear horizontal-type guided wave acoustic emissions. This sensor provides benefits that makes them excellent supplements for, and in some cases replacements for, conventional AE sensors. The SH wave sensors provide benefits including simpler velocity settings, more consistent source localization, and reduced environmental noise from sources such as rain and wind-driven particles. These advantages arise due to the distinct differences in the wave mechanics of the SH wave modes compared to Lamb wave modes (A0 and S0, for example). Note that the SH0 mode is non-dispersive with the highest group velocity of all SH-type modes and it features pure in-plane vibration. Another benefit of the SH AE sensors is that they provide sensitivity to the SH wave modes that are produced from almost every type of AE source, but have been almost entirely neglected during AE testing. This otherwise neglected wave mode carries significant portions of energy and information contained in acoustic emissions. The inability to detect this mode creates a limitation in source detection and characterization. The SH AE sensor can be used with conventional (Lamb-type) AE sensors for source detection, localization, and characterization.