An improved technique for locating the point of impact from the acoustic emission data

Triangulation technique for impact point location works very well when the acoustic emission sensors are placed at a relatively large distance from the point of impact. In this situation the time of arrival measurement is not affected significantly by the small error that might arise from not being able to pinpoint the exact time of arrival of the acoustic signal. The conventional technique also requires that the wave speed in the medium is well-known and non-dispersive in the frequency range of interest. If the receiving wave is a P-wave or S-wave or a non-dispersive Rayleigh wave then the conventional triangulation technique is reliable. In this paper it is shown that the conventional triangulation technique is not very reliable for locating the impact point in a plate when the sensors are placed close to the striking point for two reasons - first, it is difficult to pin point the exact time of arrival of the signal and secondly the Lamb modes in a plate are dispersive. Dispersive signals attenuate differently at various frequencies and propagate with different speeds causing distortions in the received signals and thus introduce more error in the time of flight measurement. In this paper an alternative approach is proposed to locate the impact point more accurately. Experiments are carried out with an aluminum plate. The impact points predicted by the conventional triangulation technique and the proposed modified method are compared.