  The miniaturization of infrared gas sensors is largely hindered by expensive
and bulky laser sources as well as the use of optical filters. In this work, we
propose a dual-band, directional thermal emitter based on compact W-Si-Cu
metasurfaces to address this issue. This metasurface emitter is designed to
support two nondispersive magnetic polariton modes that exhibit distinct
directional thermal emission profiles, thus enabling dual-band detection
without the need of optical filters. Specifically, we evaluate the feasibility
of such dual-band filterless detection by adapting the metasurface emitter to
CO2 sensing. The model of sensing system shows a selective relative sensitivity
of CO2 which is 3.2 times higher than that using a blackbody emitter, and a
relative sensitivity of temperature of emitter about 1.32%/K.
