Normalisation procedure in thermal wave approach of thermal diffusivity measurement of solids using pyroelectric sensor

Abstract

The theory of thermal wave interference in generation of photoacoustic signal suggested by Bennett and Patty [Appl. Opt. 21 (1982) 49] was applied to measure thermal diffusivity of optically opaque sample using photopyroelectric technique. To determine thermal diffusivity with precision, one needs to work with frequencies high enough in order to be in a thermally thick regime. However, this condition cannot always easily be fulfilled due to the great attenuation of the amplitude signal at high frequency resulting in decrease in signal-to-noise ratio. In this work, we proposed thermal diffusivity measurements to be carried out with the thermal wave probing starting from the sample–pyroelectric interface towards the thermally thick region of the sample. Reflection of thermal wave in the pyroelectric coatings, which was ignored in previous models, was considered in the generation of photopyroelectric signal. Normalisation procedure was used to eliminate the number of media parameters of photopyroelectric cell that otherwise need to be known before one can determine the thermal diffusivity of the sample. With the appropriate sample–pyroelectric detector dimension, the thermal diffusivity of any solid sample is readily being determined. The method was experimentally tested for aluminum, copper, and nickel, and the values obtained were close to the literature values.