High-precision Directional Spectral Emissivity Measuring Device Based On Integrating Sphere

Spectral emissivity is an important parameter to describe the thermal radiation characteristics of objects.It is widely used in radiation heat transfer calculation,photovoltaic materials,spacecraft insulation,satellite remote sensing and other fields.The emissivity of materials is a variable quantity,which is affected by many factors such as temperature,wavelength and roughness.In recent years,with the rapid development of infrared technology,the original emissivity data has been unable to meet the requirements of current scientific research and practical application in terms of accuracy,temperature range and wavelength range.Therefore,accurate measurement of material emissivity data over a wide wavelength range and a wide temperature range is crucial.The emissivity measurement methods are divided into calorimetric method,energy method,reflection method and multi-wavelength method.Among the measurement methods,the energy method is widely concerned because of its high measurement accuracy.According to the measurement principle of the energy method,the sample radiation signal and the blackbody radiation signal should be consistent in temperature,wavelength,light path,environment and other measurement conditions.The ideal situation should be to use a detector to measure the radiation of the blackbody and the sample simultaneously.However,it is not easy to achieve simultaneous measurement in practical applications.Emissivity measurement device based on energy method to date generally adopts the method of measuring sample radiation signal and blackbody radiation signal progressively,the signal switching is achieved by the interplay between the plane mirror,parabolic mirror and displacement platform.This way may have an impact on the accuracy of emissivity measurement.In this paper,a high-precision directional spectral emissivity measurement device for simultaneous measurement of the blackbody and the sample radiation with only one detector is established based on an integrating sphere reflectometer,and the radiation properties of different materials are investigated thoroughly.The main work of this paper is as follows:1.Based on the energy method,a set of directional spectral emissivity measurement device is established.The device is composed of four parts: sample heating furnace,blackbody,optical system,and signal acquisition system.The sample heating furnace and the blackbody belong to the radiation signal source in the device;the optical system mainly includes the aperture diaphragm,filter,off-axis parabolic mirror and integrating sphere reflectometer;the rotating module that comes with the sample heating furnace can realize the radiation measurement of the sample to be tested at different angles;the hardware part of the signal acquisition system includes a detector,two choppers and two lock-in amplifiers,which are used for radiation signal acquisition,modulation,demodulation and amplification respectively.The software part is developed based on Lab VIEW and is aimed at the acquisition and storage system of the output signal of the lock-in amplifier.2.Several situations that may affect the measurement accuracy of the experimental device are analyzed systematically: the temperature uniformity inside the blackbody radiation cavity,the radiation distribution inside the sample heating furnace,the temperature distribution of the effective measurement area on the sample surface under the limit measurement angle condition,and the optical path difference calibration coefficient for systematic error.3.According to the difference of the measured samples,two methods for determining the surface temperature of the samples are proposed,and the accuracy of the methods is verified via specific experiments.4.The emissivity of four different material samples have been measured,including silicon,silicon carbide,Armco iron and pure copper.The measurement results are compared with the related emissivity measurement data reported in the reference.The experimental measurement results are analyzed,and the uncertainty of the device is evaluated.