Research On The Measurement Technology Of Directional Polarized Spectral Emissivity And Its Application In Radiation Thermometry

Emissivity is one of the important thermal physical parameters used to characterize the emission capability of an object,and is widely applied in a lot of applications,such as military and national defense,material science,and industrial and agricultural production.In recent years,the directional polarized spectral emissivity of materials has drawn more and more attentions from many researchers with the rapid development of technologies like infrared stealth,2-D materials,microstructure metasurfaces,and radiation thermometry.Compared with the unpolarized emissivity,the polarized emissivity of material can be used to explore the regulation mechanism of the microstructure on the surface radiation,to study the material recognition technology based on the polarized spectrum,and to establish new methods for further improving the accuracy of radiation temperature measurement.Therefore,studying the directional polarized spectral emissivity measurement method with high-precision and establishing the corresponding measurement apparatus are of great significance for different fields,for example material polarization modulation engineering,surface heat transfer calculation,and radiation thermometry.However,the polarized radiation signals are much weaker than the unpolarized radiation signals,thus are more difficult to be measured.Accurately measuring the directional polarized spectral emissivity requires effectively eliminating the effect of background radiation,accurately calibrating the system response function,and precisely correcting the measurement deviation of sample surface temperature.This research,supported by the National Natural Science Foundation of China "The measurement of polarized spectral emissivity and its application in radiation thermometry" and the National Science Foundation of China's Major National Scientific Research Instrument Development Project "The spectral emissivity measurement apparatus at cryogenic temperature",proposed the methods for solving the three problems and established the corresponding experimental apparatus for accurately measuring the directional polarized spectral emissivity in a wide waveband.In addition,the application of polarization radiation measurement technology in radiation thermometry was explored,and a new multi-angular polarized spectrum thermometry was proposed.The research mainly covers the following four parts of work:1.The background and the significance of directional polarized spectral emissivity was introduced.The research actuality of the directional spectral emissivity and the directional polarized spectral emissivity was summarized in detail.The difficulties in accurately measuring the directional polarized spectral emissivity was analyzed.The method for calibrating the spectral response of the emissivity measurement system was presented,and the sample surface temperature measurement methods used in the spectral emissivity measurement were carefully studied.2.A polarized spectral emissivity measurement method was proposed by eliminating the influence of background radiation based on a thermostatic cold plate.And a method for calculating the surface temperature of sample by correcting the effect of contact thermal resistance was proposed to improve the emissivity measurement accuracy.A new measurement apparatus was established to accurately measure the directional polarized spectral emissivity of solid material in 4-20 ?m under a controlled environment.The spectral response of the apparatus was calibrated in different polarization directions by the improved two-temperature blackbody method,and the linearity of the response function was verified.The reliabilities of the measurement method and the experimental apparatus were verified by measuring a highpurity SiC sample and comparing the measured result with the literature data.The measurement results show that the relative uncertainty is less than 4.1% except the spectral bands related to the absorptions of air and beam splitter when measuring the directional polarized spectral emissivity of SiC sample in the range of 300-700 ?.3.Aiming at solving the problem in measuring the weak radiation signals in the mid-infrared and farinfrared wavebands,a method to measure the mid-infrared and far-infrared polarized spectral emissivity was proposed based on the multi-temperature calibration method.For reducing the influence of the sample surface temperature gradient on the measurement results at large emission angle,a temperature correction method for the unequal temperature measurement area was proposed to further improve the accuracy of the polarized emissivity measurement.A new apparatus for measuring the directional polarized spectral emissivity in the wavelength range of 20-50 ?m was established in air.The reliabilities of the measurement method and the measurement apparatus were proved by measuring the polarized spectral emissivity data of SiC at different temperatures and comparing the measurement results with the mid-infrared measurement data and the international data.4.A new multi-angular polarized spectrum thermometry based on the optimal wavelength selection was proposed to accurately invert the surface temperature of smooth sample.The optimal inversion model was determined by comparing the inverted results of different inversion models.The multi-angular polarized spectral radiance of a smooth SiC sample was measured using the built-up measurement apparatus,and the optical constants and the surface temperature of the SiC sample were inverted by the proposed method.The reliability of the multi-angular polarized spectrum thermometry was proved by comparing the inverted temperature with the temperature results calculated by the one-dimensional heat conduction and the Christiansen thermometry.The result shows that the sample temperature deviation inverted at the optimal wavelength by using the optimal inversion model is less than 1%.