Locating the acoustic source in an anisotropic plate

By analyzing the arrival times of guided waves, the acoustic source in a plate is predicted. Solving this problem is important for continuous health monitoring of structures. Several techniques based on the triangulation principle have been proposed for this purpose but they do not work for anisotropic plates. The popular triangulation technique assumes that the wave velocity is the same in all directions, which is not true for anisotropic plates. An alternative method based on the optimization scheme was proposed by Kundu et al. (Kundu T, Das S and Jata KV. Point of impact prediction in isotropic and anisotropic plates from the acoustic emission data. J Acoust Soc Am 2007; 122(4): 2057–2066; Kundu T, Das S, Martin SA and Jata KV. Locating point of impact in anisotropic fiber reinforced composite plates. Ultrasonics 2008; 48(3): 193–201; Kundu T, Das S and Jata KV. Health monitoring of a thermal protection system using lamb waves. Struct Health Monit: Int J 2009; 8(1): 29–45; Kundu T, Das S and Jata KV. Detection of point of impact on a stiffened plate by the acoustic emission technique. Smart Mater Struct 2009; 18(3): 1–9) to locate the point of impact in anisotropic plates by analyzing the times of arrival of the ultrasonic signals received by the passive sensors attached to the plate. Recently, Hajzargarbashi et al. (Hajzargarbashi T, Kundu T and Bland S. An improved algorithm for detecting point of impact in anisotropic inhomogeneous plates. Ultrasonics 2010; 51(3): 317–324.) improved that technique. Following their modification, in this article, the acoustic source point in an anisotropic plate is predicted from the acoustic emission data with some additional modifications. Experiments are carried out with a carbon–epoxy plate. A parallel pre-stressed actuator is used as the acoustic source and the acoustic signals at different locations are received by adhesively bonded acoustic sensors. The source point is then predicted and compared with its actual location. Related theory and computed results of wave propagation in anisotropic plate are also presented and the theoretical predictions experimentally verified at frequencies higher than what is typically generated by the simple impact phenomenon.