ANALYSIS OF AC TEMPERATURE WAVE DURING THE MEASUREMENT OF THERMAL-DIFFUSIVITY OF 2-LAYERED PLATE-LIKE SAMPLES

A theoretical consideration of two-dimensional ac temperature waves in a two-layered platelike sample for application to thermal diffusivity measurement parallel to a sample surface using an ac calorimetric met hod is presented. The analysis is based on the Fourier-transformed Gre en's function technique. it is concluded that this thermal system devi ates from an apparent one-layered system of which the thermal diffusiv ity parallel to a sample surface is calculated based on steady state h eat flow under the following conditions: (a) the frequency of the supp lied ac thermal energy is high, (b) the difference between the thermal diffusivities of the layers is large, and (c) the layer with higher t hermal diffusivity is thin. This deviation is due to the inhomogeneous ac temperature distribution normal to the sample surface. If experime ntal conditions are the reverse of conditions (a)-(c), an ac calorimet ric method can be used to measure the thermal diffusivity of thin samp les on substrates. (C) 1996 American Institute of Physics.