Analysis of thermal diffusivity by parameter estimation in converging thermal-wave technique

The in-plane thermal diffusivity of several kinds of metal foils was measured by the converging thermal-wave technique. This is a typical technique which can obtain the thermal diffusivity by taking the temperature evolution at the center of pulsed annular laser beam when the beam irradiates the surface of the samples. The thermal diffusivity is normally calculated using the maximum time tm or half-maximum time t1/2 when the temperature evolution is half and maximum, respectively, however, the rapid temperature increase and the nonlinearity of the infrared detector in the earlier part, convection heat loss from the sample surface, and some times the low signal to noise ratio can produce errors. In this study, a nonlinear least-square regression was performed to estimate the optimal values of several separate parameters by fitting the data to the theoretical equation. The thermal diffusivity of the samples obtained from the optimal values of the estimated parameters was compared with the values from tm and t1/2, and the reference values, and it shows that the thermal diffusivity obtained by this parameter estimation technique agrees quite well with the reference data within 3.4% at maximum.