In this study, an ultrafast and high-sensitivity humidity sensor is designed and analyzed based on microwave dual-band resonator functionalized with belt-shaped MoO3 nanomaterial. Two sensitive frequencies for water vapor were selected in the frequency band of 2–12 GHz using the developed interdigital capacitor. The proposed dual-band resonator structure was optimized to achieve higher response and improved quality factor (Q-factor) for sensitivity enhancement. To investigate the humidity sensing performance of the sensor, the sensing element deposited with sensitive material MoO3 was placed inside a humidity chamber with the humidity generator to yield five humidity levels at room temperature. Results indicate that the insertion loss linearly varies with the humidity level ranging from 10% to 90% relative humidity (RH) with sensitivity of 0.069 and 0.022 dB/% RH for 7.3 and 9.1 GHz, respectively. Moreover, the sensor exhibits sensitivity of 1.938 and 2.062 MHz/% RH for the two sensitive frequencies. The dynamic kinetics of response and recovery time was less than 5 s and the humidity hysteresis was about 0.25% RH. The humidity sensing mechanism was discussed from the perspective of sensitive material and microwave transduction. This study provides a facile approach for the implementation of microwave humidity sensors with high sensitivity and fast response speed.
