A technique for determining the polarization distribution in thin polymer electrets using periodic heating

The variation in the polarization distribution through the thickness of a polymer electret is determined by heating each electrode of the sample with a laser beam which is modulated at various frequencies between 0.1 and 100 kHz. The periodic heating induces temperature waves which are attenuated exponentially as a function of both depth in the sample and frequency of modulation. The resulting “thermal probe” heats regions having different polarizations and produces an AC pyroelectric current. A linear least-squares analysis of the experimental current-frequency data gives the polarization distribution.