Measurement of internal charge distribution in dielectrics using the pulsed electro-acoustic method in non contact mode

We introduce a pulsed electro acoustic (PEA) device enabling space charge measurement inside dielectric films without the need of sample to excitation unit contact. The new device -called open PEA because one face of the film is at a floating potential- has been used to investigate the internal charge of electron beam irradiated dielectrics. Details are given on the system and its calibration for performing quantitative charge measurements. Charge distributions in electron beam irradiated polytetrafluoroethylene (PTFE) films are compared using the classical and the open PEA. Due to the short-circuit condition in the classical PEA, the implanted charges measured using the two systems are drastically different. Surface potential and current measurements performed during irradiation have been used to validate the measurement in the open configuration which is well suited to investigate the behaviour of dielectrics in space environment.