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 In 2 O 3 facilitates gas diffusion , further enhancing sensing performance. Herein, a microwave gas sensor is designed by applying porous monolithic In 2 O 3 and waveguide resonator . By adjusting the content of the polymer PVP, In 2 O 3 with different pore sizes is synthesized in which hierarchical porous In 2 O 3 sample with a PVP content of 3.0 g (3.0-HPS In 2 O 3 ) exhibits the best NH 3 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.