A reconfigurable monolith chip-type microwave gas sensor for ultrasensitive NH3 detection

Microwave gas sensors (MGSs) have attracted the interest of researchers because of their low power consumption, non-contact operation, and room temperature detection capabilities. However, the practical use of sensitive circuits is currently inadequate. In this context, we propose a reconfigurable rectangular waveguide microwave gas sensor (RWMGS). This RWMGS is achieved by designing a high Q-factor waveguide sensitive circuit and employing an In₂O₃/Al₂O₃ monolith as the sensitive material. The prepared RWMGS exhibited an ultra-low detection limit of 10 ppb, high selectivity for NH₃, and a remarkable sensitivity of 116.1 dB ppm⁻¹ for concentrations lower than 50 ppb. Importantly, we introduce a chip-type sensor mode that can be used for complex system detection. This simplifies the sensing system and provides significant advantages in MGS design. These advantages can be attributed to the unique hierarchical porous structure of the monolith and the high Q-factor waveguide resonator.