Waveguide microwave gas sensor based on monolithic In₂O₃ for enhanced ammonia detection

For commonly used chemical resistance sensors, achieving room-temperature detection often results in reduced performance. Microwave gas sensors have been rapidly expanding in recent years, attributed to their advantages of room-temperature operation and low power consumption. Waveguide, as a three-dimensional microwave circuit with separated electric and magnetic field distributions, resulting in high quality factor, is expected to significantly enhance the sensitivity of microwave sensors. Additionally, the hierarchical porous structure of monolithic In₂O₃ facilitates gas diffusion, further enhancing sensing performance. Herein, a microwave gas sensor is designed by applying porous monolithic In₂O₃ and waveguide resonator. By adjusting the content of the polymer PVP, In₂O₃ with different pore sizes is synthesized in which hierarchical porous In₂O₃ sample with a PVP content of 3.0 g (3.0-HPS In₂O₃) exhibits the best NH₃ sensing properties, including a wide concentration range (0.01-2000 ppm), a low limit of detection (LOD) of 7 ppb, excellent selectivity, good moisture resistance, and long-term stability. This study offers a promising approach for the development of room-temperature ammonia gas sensors with an extended detection range and has preliminarily explored the influence of pore sizes on gas sensing performance.