Thermal waves interferences for space charge measurements in dielectrics

As a new improvement to increase accuracy and resolving power of our ATWM, we proposed the use of two simultaneous thermal waves applied on the two opposite faces of the sample. The resulting temperature oscillation at each abscissa is the sum of the two temperature oscillations due to the two disturbances, taking into account amplitude and phase. A kind of stationary thermal waves is created. By acting on the phase of the two disturbances, several temperature distributions may be obtained for each frequency with specific current response what ought to facilitate the determination of the entire space charge distribution. The interference technique is convenient if the used thermal wavelength is about or greater of sample thickness. A thickness of quarter of wavelength seems to be efficient. Thermal interferences occur in the middle of the sample as the attenuation is not excessive. The theoretical shapes of different temperature distributions which may be obtained for some common values of the phase are given in this work showing the possible expansions of this technique. Actually, our measuring cell becomes operative. The two thermal disturbances are produced by thermo electrical modules and, as seen above, it is not difficult to act on the phase of the thermal wave by acting on the phase of the two controlling currents. Currently different dielectric materials are being studied. The results will be given in a next work.