Physical working principles and main parameters of converter: (a) Salisbury screen [31] consisting of a thick screening metallic layer coated with a dielectric layer having a specially selected thickness and a thin transparent metallic screen; (b) frequency selective surface in the form of a 2D array of metallic elements on a dielectric substrate which reflects or absorbs electromagnetic waves at the preset frequency depending on the surface topology; (c) the metaatom considered herein is in the form of three superimposed layers with square cross-sections having the following dimensions: L1 = 0.535 mm, L2 = Ld = 0.585 mm, and thicknesses s1 = s2 = 0.024 mm and sd = 0.067 mm. The overall thickness of the metamaterial is 0.115 mm; (d) frequency selective surfaces of two topologies and their equivalent circuits. Tiles are used in the low-frequency range, and grid is used at high frequencies; (e) the top and bottom conducting layers in the metaatom are nickel, the dielectric being fiberglass plastic. The bottom surface of the metamaterial is coated with graphite for radiation conversion; (f) example of THz converter application in security domain. The person 2 is in the inspection zone between the 96 GHz electromagnetic source 1 and the screen 3 which is the THz converter. The radiation passes through the transparent media and is incident on the terahertz converter for further conversion to IR radiation. The infrared radiation of the converter is read by the IR camera 4