Study On Measurement Of Thermal Diffusivity Of Opaque Material By PTR Method

Photothermal Radiometry (PTR) is based on photoacoustic (PA) technology. It is a new detection technique with high sensitivity and without damaging effects. This method is applied in measurement of optics and parameter of thermal diffusion. For several years, the PTR technique has attracted much attention in the nondestructive evaluation of surface and subsurface features of solid. In this paper, a new method of measuring thermal diffusivity and thermal conductivity tensor at room temperature with photothennal signal is presented. In the first part, a method for measuring thermal diffusivity of opaque materials by a modulated PTR technology is introduced. Based on theory of PTR, we show the linear relation between signal phase and modulated frequency under special condition. The thermal diffusivity is determined by fitting the experimental data. Photothermal signals from anisotropic media, which is irradiated by a modulated laser beam, are analyzed in the second part. The temperature field and thermal diffusivity tensor of anisotropic media is theoretically studied. With photothernial radiometry (PTh) method we measure and determine the thermal conductivity tensor of anisotropic media. In analysis of isotropic and anisotropic material, PTR method has advantages compared with Mirage and JR method in theories and experiments. PTR method is proved to be an important tool in measurements of thermal characters of materials.