Design of Passive Humidity Sensor Based on Polyimide as Substrate

In this article, the relevant principles of substrate integrated waveguide are analyzed, and a passive humidity sensor based on polyimide as the substrate is designed. Subsequently, the sensor is modeled, simulated, and optimized. The sensor employs a polyimide substrate that features flexibility and operates. The sensor prototype was fabricated and tested using an environmental testing chamber, network analyzer, and other equipment. The test results indicate that the sensor can achieve detection in the humidity range of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20-95 \% \text{RH}$</tex>, with a sensitivity of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$865 \text{kHz} / \% \text{RH}$</tex> at the temperature of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$25^{\circ} \mathrm{C}$</tex>.