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A measurement technique for infrared emissivity of epoxy-based microwave absorbing materials



Derek A. Houtz, Dazhen Gu


Infrared emissivity is a critical parameter for modeling and predicting heat transfer by radiation. Microwave absorbing materials, having a high emissivity in the microwave spectrum, are crucial in a wide array of applications such as electromagnetic interference mitigation, stealth technology, and microwave remote sensing and radiometer calibration. Accurate knowledge of the thermal properties of these materials is necessary for efficient design and optimization of these types of systems. Typical microwave absorbing materials consist of a dielectric epoxy base material impregnated with a lossy material such as iron or carbon. We study a novel cryogenically compatible epoxy-based absorber material that has been loaded with varying concentrations of carbonyl iron powder. We study six materials with carbonyl iron powder concentrations of 0%, 5%, 10%, 20%, 30%, and 50% by tap volume. We use a commercial infrared camera with sensitivity in the range 7.5 µm to 13 µm to measure the radiance of the samples and a waterbath infrared blackbody at ten temperatures between about 19 C and 45 C. A linear Deming fitting is performed, considering uncertainties in both measured parameters, and the slope of the linear fit is shown to be the infrared emissivity, averaged over the spectral response of the camera. The emissivity ranges between 0.868 and 0.757 decreasing monotonically as a function of iron carbonyl concentration between 0% and 50%. The uncertainty of the emissivity determination method is derived and presented. The uncertainty of the presented method is shown to be no larger than 3.3% for all the measured samples.
IEEE Geoscience and Remote Sensing Letters


microwave radiometry, calibration, thermal properties, microwave absorber, infrared imagery


Houtz, D. and Gu, D. (2017), A measurement technique for infrared emissivity of epoxy-based microwave absorbing materials, IEEE Geoscience and Remote Sensing Letters, [online], (Accessed April 15, 2024)
Created December 4, 2017, Updated July 2, 2018