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Thermal return reflection method for resolving emissivity and temperature in radiometric measurements

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2 Author(s)
Woskov, P.P. ; MIT Plasma Science and Fusion Center, Massachusetts Institute for Technology, 167 Albany Street, Cambridge, Massachusetts 02136 ; Sundaram, S.K.

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A radiometric method for resolving emissivity ϵ and temperature T in thermal emission measurements is presented. Thermal radiation from a viewed source is split by a beamsplitter between a radiometer and a mirror aligned to return a part of the thermal radiation back to the source. The ratio of the thermal signal with and without a return reflection provides a measurement of the emissivity without need of any other probing sources. The analytical expressions that establish this relationship are derived taking into account waveguide/optic losses and sources between the radiometer and viewed sample. The method is then applied to thermal measurements of several refractory materials at temperatures up to 1150 °C. A 137 GHz radiometer is used to measure the emissivity and temperature of an alumina brick, an Inconel 690 plate, and two grades of silicon carbide. Reasonable temperature agreement is achieved with an independent thermocouple measurement. However, when the emissivity approaches zero, as in the case of the Inconel plate, radiometric temperature determinations are inaccurate, though an emissivity near zero is correctly measured. This method is expected to be of considerable value to noncontact thermal analysis applications of materials. © 2002 American Institute of Physics.

Published in:

Journal of Applied Physics  (Volume:92 ,  Issue: 10 )