Detection Based On Laser-induced Thermal Diffusivity

In this thesis, based on laser-induced detection methods, the revised photoacoustic piezoelectric (PAPE) technique and the photothermal radiometry (PTR) technique which including the time and frequency domain have been studied. The thermal diffusivities of engineering plastics and metal film materials have been measured effectively.1. The measurement of engineering plastics'diffusivity by the revised PAPE technique. Firstly, the revised PAPE method was proposed based on the traditional PAPE theory and the corresponding experimental system was set up. Secondly, the experimental system was calibrated and tested by investigating the diffusivity of pure aluminum and PTFE. Finally, the thermal diffusivities of eight kinds of engineering plastics were measured by the revised PAPE method. The results show that engineering plastics have excellent insulation properties and the diffusivities are under 0.4mm2/s. The theoretical and experimental results show that the revised PAPE method can be used to accurately measure the thermal diffusivity of engineering plastics.2. The measurement of metal film materials'diffusivity by the frequency domain PTR technique. Firstly, the temperature and radiation field theory of frequency domain PTR method was established. Secondly, the design and fabrication of the vacuum chamber was introduced and the corresponding experimental system was set up. Thirdly, three metal film materials: stainless steel, brass, copper were measured under different vacuum, and the results show that the air has great influence on PTR signals, thus the use of vacuum chamber is necessary. Finally, the experimental data on the vacuum of 10-3 Pa was fitted to the theoretical curve. The results show that the frequency-domain PTR method could accurately measure the diffusivity of metal film material.3. The measurement of metal film materials'diffusivity by the time domain PTR technique. Firstly, the temperature and radiation field theory of time domain PTR method was established according to the theory of frequency domain PTR technique and Superposition theorem. Secondly, experimental system was built according to the theoretical model, and the experimental results of the three kinds of metal film materials were obtained at different modulation frequencies. Finally, the experimental data were processed and fitted to theoretical curve. Fitting results are poor, and the time-domain PTR theory need to be improved. Through this thesis, the following conclusions were obtained: the revised PAPE method in regard to the traditional detection method has higher accuracy and can accurately detect the thermal diffusivity of engineering plastics and other soft materials; The frequency domain PTR technique can effectively measure the thermal diffusivity of metal film materials; the time domain PTR technique has got good experimental data, but the theory needs further study.