Dual-Band Microwave Circuits for Selective Binary Gas Sensing System

A noninvasive contactless binary gas sensing system is enabled using coupled passive flexible tag integrated with porous adsorbent beads tower. The platform is based on two flexible passive tags coupled with a dual-reader resonator operating at 4.86 GHz, while the distance between passive reader and tags can be extended to 10 mm. The sensor demonstrates the capability of detecting and monitoring more than one gas simultaneously and independently from each other. Various concentrations of methyl ethyl ketone (MEK) and humidity have been detected distinctively by using a hyper cross-linked polymer as volatile organic compounds (VOCs) and silica gel as humidity adsorbent beads. Selective accumulation of the gas molecules in the beads' pores is monitored with less than 5% error and by separate coupled tags and their associated resonant frequencies. The proposed structure offers a low-cost conformal solution and has the potential for real-time contactless multiple gas sensing in environmental applications. The structure demonstrates the sensitivity of 0.18 MHz/ppm in VOC sensing and 0.19 MHz/ppm while performing selective binary sensing.