Executive Summary : | Emittance of infra-red (IR) radiation from a hot object is used to great advantage in night vision devices. Recently-developed band-selective metamaterial (MTM) IR absorbers (or emitters) represent a great opportunity in this context as they can be applied to a surface to obtain required absorptivity/emissivity at specified bands. Thermal imaging principally makes use of the 3–5 ?m (MWIR) and 8-12 ?m (LWIR) wavelength bands. Emission of IR is also essential for radiative cooling of systems (vehicles, human etc.). Hence, the ideal camouflage would need spatially varying emissivity in the above imaging bands to resemble background clutter and high emissivity in the intermediate band for radiative cooling. Attempts at IR camouflage are made principally by IR camouflage paints or by actively cooling panels with thermoelectric coolers placed on tanks. The PI’s group has developed band specific IR MTMs for high absorption including flexible MTMs using transparent conductive oxides for integration with optical camouflage. A technology demonstrator for IR camouflage will be developed using band selective emissive MTMs. This requires fabrication of the microstructured MTMs over large areas for which we have recently developed some new MTM designs utilizing soft-lithography methods. MTM panels (~100 sq. cm areas) with specified IR emissivities will fit together to make a composite screen, which would appear as a patchwork of high and low emissive regions to resemble the thermal clutter of the background. The IR images of the screen using LWIR and MWIR cameras will be used to evaluate the camouflage efficacies. Such IR MTMs allow for incorporation onto helmets, bullet-proof jackets, skirtings for tanks and other vehicles as these MTMs are transparent at visible wavelengths and can blend in with presently available optical camouflage patterns. This new technology is critically important for our armed forces and DRDO will be involved at a future stage. |