Free emissivity temperature investigations by dual color applied physics methodology in the mid- and long-infrared ranges

In this work a free emissivity (dual color) thermographic technique, based on the ratio of monochromatic emissive power, is investigated. It can be performed by equipping the InfraRed (IR) camera of two band pass filters in such a way to consider the emissivity parameter as a constant value. Two colour technique can reveal its utility in fields of applied physics where intrusive techniques are not allowed and/or materials are characterized by unknown emissivity. This physics methodology can be really useful, for example, in temperature determination of (Aero) Space materials (such as TPS-Thermal Protection Systems), tested on ground Plasma Wind Tunnel, solid targets temperature determination due to ions bombarding by means of accelerators for nuclear (Astro) Physics and/or environmental physics applications. In this paper, temperature measurement investigations based on the choice of central wavelength distances of two filters are reported. In particular a numerical model simulation, experimentally validated in the Long and Mid (LW, MW) e Wavelength ranges, was built and used to determine the feasibility of the technique and to choose the best filters combinations. In addition, after the verification capability in MW range, the temperature measurements on an aluminium plate were carried out with the dual colour technique. Moreover the verified numerical model was used to analyze errors of the two color technique in MW range using different curves of materials with variable emissivity. The study was carried out up to 500 C and the results show that this innovative technique allows measurements of surface temperatures with errors of few % in MW range