Radiation conversion results: (a) Radially symmetrical model of radiation converter cell (1 is the fiberglass plastic, 2 is the top nickel layer of the metamaterial cell, 3 is detected THz radiation, 4 is IR radiation, 5 is the bottom nickel layer of the metamaterial cell and 6 is the graphite emitting layer). The temperature at the converter perimeter is 293.15 K. Electromagnetic and thermal calculation results obtained in the Microwave Studio CST environment. (b) Heat flow density of converted THz radiation for three graphite layer thicknesses (0.2, 1 and 2 μm). The best result was obtained for the 0.2 μm thick graphite layer as it delivers the highest heat flow density and hence the greatest image contrast on the focal plane array matrix of the thermal imaging system. Images of (c) surface heat flow density and (d) bulk heat flow density suggest that it is the emitting layer in the radiation converter that provides for heat emission