A high-sensitive microwave humidity sensor based on one-step laser direct writing of dielectric silver nanoplates

Microwave technology has emerged as an appealing alternative for building humidity sensors with multiple detection parameters. This paper demonstrates the one-step laser direct writing fabrication of microwave humidity sensors. Silver nanoplates were used as both the humidity-sensitive material and a precursor to highly conductive Ag electrodes. Particularly, the unirradiated silver nanoplates film shows an unusual lossy dielectric nature, with the effective complex dielectric permittivity being dramatically tuned by humidity stimuli. Through a laser-induced sintering mechanism, laser irradiation bursts the conductivity by approximately 10 orders of magnitude with a maximum conductivity value of 9.7 x 106 S/m. A prototype microwave humidity sensor is designed and fabricated and its humidity sensing performances are comparatively studied and discussed. The measured results show that the sensor displays a high humidity sensitivity of up to 12.61 MHz/RH or 0.288 dB/ RH. This work suggests a good candidate approach for the realization of high-performance microwave humidity sensors with a fast and simplified advantage.