Dual-mode anti-interference humidity detection: Differential microwave sensor based on microstrip circuit

Monitoring humidity is indispensable to ensure industry and health safety. However, humidity sensors usually suffer from interference by environmental variation. Differential measurement is an effective way to improve the anti-interference of devices in which the circuit design is the key point. The flexible circuit structures and unique dual port characteristics of microwave circuits make it candidates for differential measurement. Herein, a differential microwave humidity sensor based on microstrip circuit is proposed in this paper, which combines the anti-interference ability and the high sensitivity. Commercial polyvinyl alcohol (PVA) is applied as sensitive material. The proposed sensor exhibits a high dual-mode response for both frequency (1.5 MHz/%RH) and magnitude (0.39 dB/%RH) for the humidity range (25% RH – 85% RH). Moreover, the anti-interference measurement confirms the performance of baseline correction to enhance the sensor accuracy. Meanwhile, the sensor mechanism is proposed by the propagation of electromagnetic wave for the first time. This work provides a novel solution of anti-interference differential sensors for monitoring humidity.