Behaviour of acoustic emission sensors using broadband calibration techniques

For a quantitative study of acoustic emission signals or for the analysis of transient waveforms the transfer function of the sensors both in Rayleigh and longitudinal wave sound fields has to be known. To this end, the reciprocity calibration is applied to measure the response of acoustic emission sensors to the normal displacement velocity of Rayleigh and longitudinal waves. In this method neither a reference acoustic source nor a calibrated sensor is needed. The sensitivity is obtained through electrical measurements only, with three transducers alternately working as the sound source and receiver. Our contribution to this well-established calibration technique (the reciprocity method) comes from the use of spectral analysis techniques with short pulses, which enables the efficient determination of both the phase and the amplitude of the sensitivity in a broad frequency range. This study focuses on three points. First, we compare this method with laser interferometry calibration. Then we use the reciprocity technique to study the following points: the aperture effect and the fact that for quantitative acoustic emission analyses it is very important to take account of the material under test.