Interpretation of PEA Output Signal in a Multilayer Specimen

The aim of the present work is to evaluate the acoustic waves behavior within the Pulsed Electro-Acoustic (PEA) cell, in case of a multilayer specimen, in order to avoid misinterpretation of the output signal. Due to the reflection phenomenon of the acoustic waves travelling within the PEA cell, the output signal could be distorted. Because this aspect, for a given PEA cell with certain ground electrode and absorber thicknesses, depends on the sound velocity and thickness of the specimen under test, the latter must be carefully sized. For this aim, some useful relationships, that must be taken into account are given and described. In particular, a three layers sample simulating an air void defect within an insulating material has been realized, and the space charge pattern has been detailed analyzed. Measurement result, shown that despite the specimen layers thicknesses has been chosen in accordance to the provided relationships, a reflection within the specimen itself overlaps one the main charge peak