Development of ac Calorimetric Method for Thermal Diffusivity Measurement. II. : Sample Dimension Required for the Measurement

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Abstract
In an ac light-irradiated method for thermal diffusivity measurements of rectangular plate-like samples partly shadowed by a mask, the required dimensions are considered. The contour length around the cross-section (given by the thickness times the width) should be so long that the sample has a proper amount of heat capacity; then, the external thermal relaxation time becomes sufficiently long so as not to dissipate ac thermal energy. The thickness, however, should be thin enough so as to obtain a uniform temperature across the sample during oscillations (as discussed in detail previously). For the sample length, the distance between the thermocouple and the sample boundary on which ac light is irradiated should be sufficiently long so that the thermal waves reflected at the boundary decay. However, there is no restriction on the other bourtdary shadowed by the mask, i.e., the thermocouple can be placed at the boundary.