Measurement Of Thermal Diffusivities Of Various Materials Using Photo-thermal Radiometry Backward Detection Technology

The thermal diffusivities of various metal bulk materials and thin metal layers havebeen measured by the photothermal radiometry backward detection (PTR BD)technique, based on a simplified single-layer model of PTR theory in this paper. Thethermal diffusivity can be accurately and effectively measured by this PTR BD method.The experimental results obtained from the measurement of different samples by PTRBD system are accurate and effective.(1) The thermal diffusivities of various metal bulk materials have been measuredby the PTR BD experimental system. Firstly, based on the3D heat conduction theoryand gray body radiation theory, the simplified single-layer model of PTR theory hasbeen introduced in this paper, which is the PTR BD technique’s theoretical basis.Secondly, the corresponding PTR BD experimental system has been designed andcreated. By measured thermal diffusivities of two standard samples (copper andaluminum), it has verified the validity and accuracy of the PTR BD experimentalsystem. Comparing with the traditional PTR method, this PTR BD experimental systemis simplified. The results show that the output signals from the rear of samples arereliable and stable. The SNR is improved. The experimental data accord well with thetheoretical curves. The experimental values of two samples are consistent with thereference values. The values obtained from phase data are more accurate than fromamplitude data. Thirdly, the thermal diffusivities of other materials have been measuredby this experimental system. The experimental values have been determined by thephase data of the measured PTR signals. The relative error between the experiment dataand the reference data are less than3％.The experimental results show that thecoefficient of determination of six samples are more than97％and variance of thefitting are less than0.01. The PTR BD technique provides an accurate and effective wayto determine the thermal diffusivity of materials.(2) The thermal diffusivities of thin metal layers have been measured by the PTRBD experimental system. Firstly, the temperature distribution of different thicknessaluminum thin layers has been simulated by ANSYS thermal analysis. The results analyzed by the temperature field show that the thermo-physical properties of thinlayers influenced by variation of the thickness are different from them of bulk materials,when the thickness of the materials is reduced to micrometers. Secondly, by testing thedifferent thickness aluminum and copper thin layers, the experimental data is inaccordance with the academic calculation. The best fitted thermal diffusivity values for40um and20um aluminum thin layers are78.999mm~2/s and68.271mm~2/s, respectively.The best fitted thermal diffusivity values for20um and10um copper thin layers are90.059mm~2/s and83.131mm~2/s, respectively. The coefficient of determination ofdifferent samples are more than97％and variance of the fitting are too small.Compared with the result measured by the traditional PTR system, the result measuredby this PTR BD system is more reliable. When the thickness of the thin layer is reducedto micrometers, the thermal diffusivity of the thin layer is less than it of the bulkmaterial.The experimental results show that the PTR BD technique provides an accurateand effective way to determine the thermal diffusivity of materials. The values obtainedfrom phase data are more accurate than from amplitude data. When the thickness of thethin layer is reduced to micrometers, the thermal diffusivity of the thin layer is less thanit of the bulk material.