Localisation of continuous acoustic emission sources using time-reversal signal processing

Reliable acoustic emission (AE) source localisation is one of the most important inverse problems in non-destructive testing (NDT) and structural health monitoring of engineering structures. Standard AE source localisation techniques often fail when applied to complicated structures that exhibit wave dispersion, velocity and/or geometry changes. The localisation of continuous AE signals, for example generated by leakage, is still a challenge compared to the localisation of short-burst signal sources. An effective tool to overcome these problems is time-reversal (TR) signal processing, which results in space-time wave focusing, partial source signal reconstruction and more precise source localisation. In this paper, the TR procedure is used to improve the signal-to-noise ratio (SNR) and the cross-correlation function (CCF) to locate continuous signal sources. The proposed TR-based AE source location procedure is verified using an artificial AE source, ie a piezoelectric transducer emitting a continuous noise signal, acting on an aluminium (Al) plate with circular holes. The signal simulating the leak was recorded at different positions on the plate, time-reversed and retransmitted back into the structure. For precise localisation, detailed surface scanning around the roughly estimated source position was necessary. The experimental results show new possibilities for TR signal processing in practical engineering applications.