A Simple High-Sensitivity Radiometer in the Infrared for Measurements of the Directional Total Emissivity of Opaque Materials at Near-Ambient Temperatures

A novel device for direct determination of the total directional emissivity of solid surfaces at near-ambient temperatures is described. The method of operation is based on comparing the radiation emitted by the surface with that emitted by a reference. The primary sensor is a solid-state, thermopile detector, and the signal recovery is achieved by phase-sensitive detection techniques, using a mechanical chopper. The device is simple and does not use any cooling. Experimental results are preseInted using a test sample of clear float glass, kept at 323 K (50°C), with black paint on a float glass substrate as the reference. These results, likely the first for the directional total emissivity of float glass at such low temperatures obtained without cooling, compare well with values in the literature.