An indirect skin emissivity measurement in the infrared thermal range through reflection of a CO$_{2}$ laser beam

Abstract

An indirect procedure to measure human skin emissivity is proposed. This procedure uses a 10.6 $\mu $m CO$_{2}$ laser, to project a controlled energy on the skin, and a power meter to measure the projected, reflected, emitted and background energies. To eliminate the effects of background radiation, two power measurements are taken: one of the skin and background emission and another that includes the skin emission itself, the background radiation, as well as the reflection of the laser beam by the skin. Those two measurements are subtracted to obtain the reflected energy and, with this, the corresponding reflectivity of the skin. With such subtraction, background and other sources of noise are eliminated, and using the Kirchhoff law the emissivity is calculated. The emissivity values obtained with this procedure were corroborated using a theoretical blackbody. Both methods give practically the same values, which validates our procedure. In addition, our values are in accordance with those previously reported by other researchers, but our procedure is simpler, faster and innocuous. An additional contribution of this work is the analysis of the way the skin reflects the infrared radiation, in the mid range. It was found that the reflection of the skin is more specular than Lambertian, for the wavelength that was used in this work.