Demonstration experiments for active thermal imaging using a millimeter-wave source (ATIMS)

Summary form only given. Thermal infrared imaging provides a powerful means for analyzing and identifying objects. While passive thermal imaging is useful in many situations where there is a large temperature differential between the target and background, it is less useful in situations where the target is at nearly the same temperature as the background. A method for enhancing the thermal contrast in targets or objects at long ranges is presented by R. Hubbard, et al. in the 33rd International Conference on Plasma Science. This paper describes several demonstration experiments for active thermal imaging using a millimeter-wave source (ATIMS). Our test setup relies upon the NRL millimeter-wave materials processing laboratory featuring a 20 kW, 83 GHz gyrotron oscillator and a mid-wavelength infrared (IR) camera. During and after the targets are irradiated with power levels of 50-200 W over an area of approximately 100 cm², the IR sensitive camera captures a time-resolved history of the target's temperature. The target was located 1.6 m from the source while the IR camera was located 1.2 m from the target. Experiments were also performed where liquid crystal paper in thermal contact with the target scenario was used as the detector in lieu of the IR camera. We present data taken for a variety of objects and configurations, including situations where metallic and dielectric objects have been obscured, buried in sand, and covered by several layers of cloth. Since temperature differences of a few hundredths of a degree can be detected, temperature changes are often visible almost immediately after the radiation has been initiated. Initial results show that objects can be imaged underneath several layers of cloth or buried under sand