Metal-insulator transition-induced adaptive multispectral infrared camouflage (Conference Presentation)

Performance of adaptive infrared camouflage is usually parameterized in terms of cycle-ability, response time, actuation mechanism, stability etc., however, one of the key components that has not been addressed so far is the spatial density of infrared information that can be encoded and actively manipulated for camouflaging. We report an adaptive infrared camouflage system that can be engineered to operate at any desired wavelength in the technologically relevant, infrared transparent 3 – 5 µm and 8 – 12 µm bands. We exploit the metal-insulator phase transition in VO2 to design an optical cavity coupled infrared absorber where the cavity length can be altered by controlling the VO2 phase. Cavity tuning is done by strategically placing the VO2 layer inside the optical cavity composed of a tri-layer architecture. In its insulating state VO2 is transparent to infrared such that incident light couples to the entire cavity length, however in the metallic state, VO2 behaves like a mirror and shortens the cavity length by reflecting ~80% of incident light. The Maxwell Garnett EMT describes the phase transition dependent optical response of the absorber better than the Bruggeman EMT when compared to the experimental results. We tailor the device parameters to demonstrate adaptive thermal camouflage of multispectral encoded infrared information on a pixelated designer surface with a pixel resolution (~20 µm) and density comparable to the industry standard for infrared sensors. We envision this work will pave the way for novel tunable optical devices for technological advancements in infrared tagging, camouflaging and anti-counterfeiting efforts.