Space Charge Measurement by the Laser-Induced Pressure Pulse Technique 1
Three non-destructive techniques currently exist to determine the space charge in a solid insulator using the propagation or production of a pressure wave. These are the electroacoustic PEA (Pulsed Electro Acoustic) method described in the previous chapter, a method using propagation of a pressure wave generated by a piezo: PIPS or PIPP (Piezoelectrically Induced Pressure Step or Pulse), and a method using propagation of a pressure wave induced by the impact of a laser beam, called the LIPP (Laser Induced Pressure Pulse) technique. The method of production of this pressure wave is the parameter which distinguishes these different techniques. In PIPPS, PIPP and LIPP techniques, the acoustic wave is generated in a mechanical way, either by a piezo transducer, or by a laser impact on a target fixed on the sample to be tested. This impulse acoustic wave propagates throughout the insulator, thus modifying the relative position of the charges it encounters. A variation of induced charges then appears at the electrodes, whose effect is the outbreak of a pulse voltage or current in the measurement circuit.
After a brief discussion of the development history of this method’s principle, the equations connecting the measured external pulse current or voltage magnitude to the internal charges distribution will be described. A description of the experimental setup as well as the expected performances ...