Research On Modulated Thermal Wave Detection Method For Photothermal Properties Of Semitransparent Materials

Semitransparent media has a wide range of applications in aerospace,industrial manufacturing,biomedical and other fields,such as high temperature resistant devices,thermal protection materials,flames of the engine tail.The photothermal characteristics of semitransparent media are the basis for describing the transmission process of photothermal radiation.Therefore,the related measurement research has important application value for non-destructive testing,biological tissue medical imaging,clinical diagnosis and treatment of high-tech components.Based on the current thermal properties measurement method,infrared thermal wave radar detection technology and inverse problem optimization algorithm,this paper investigates the measurement method of photothermal characteristics of semitransparent medium using modulated heat wave.The main research contents include the following three aspects:Firstly,the method for solving the positive and negative problems for the measurement of photothermal characteristics of semitransparent media is introduced.For positive problems,different positive problem models are established according to the different heat transfer processes in the medium,and the finite volume method is used to solve the pure heat conduction model.For the coupled model of radiation heat conduction,the finite volume method-discrete coordinate method is used for coupling solution.For the inverse problem,the objective function is established according to the measurement signal obtained from the positive problem.According to the number and correlation of the parameters to be inverted,the intelligent optimization algorithm is selected.The sequence quadratic programming algorithm is optimized,and the phenomenon that the algorithm cannot converge is improved.Secondly,the photothermal characteristics of the one-dimensional medium excited by modulated heat flow are studied.For the pure thermal conductivity model,based on the principle of periodic heat flow method,combined with numerical simulation and signal processing method,the thermal conductivity of the medium is calculated,and the influence of the characteristics of the excitation heat flow,the physical properties of the medium to be tested and the feature size on the measurement results are obtained.The method of improving the measurement accuracy is introduced.For the radiation-thermal coupling model,the inverse problem optimization algorithm is introduced.The temperature information of each point in the medium is used as the measurement signal to invert the photothermal parameters of the medium,and the internal parameters of the medium are uniformly distributed and linearly distributed.The calculations were carried out separately and accurate results were obtained,and the practicability of using this method for physical property measurement was verified.Finally,the photothermal characteristics of the two-dimensional medium under the excitation of modulated heat flow are studied.The two-dimensional heat transfer model of semitransparent medium containing defects is established,the basic principle of infrared thermal wave radar detection technology is introduced,the characteristic images of three signal processing algorithms are compared,the best method is selected for information extraction,and the excitation heat source and defects are analyzed.The influence of characteristic parameters on the detection capability enables fast locking of internal defects,and combined with the sequence quadratic programming algorithm to complete the reconstruction of the internal photothermal parameter field of the medium,and for ZnS and SiC containing different numbers and distributions of internal defects.The reconstruction of thermal conductivity and absorption coefficient of the materials verified the effectiveness of the method and finally measured the photothermal properties of the materials.