Abstract
A real-time humidity sensor based on a microwave resonator coupled with a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) conducting polymer (CP) film is proposed in this paper. The resonator is patterned on a printed circuit board and is excited by electromagnetic field coupling. To enhance the sensitivity of the sensor, the CP film is located in the area with the strongest electric field in the resonator. To investigate the performance, the proposed sensor is placed alongside a reference sensor in a humidity chamber, and humidity is injected at room temperature. The experimental results indicate that the electrical properties of the resonator with the CP film, such as the transmission coefficient (S21) and resonance frequency, change with the relative humidity (RH). Specifically, as the RH changes from 5% to 80%, S21 and the resonance frequency change simultaneously. Moreover, the proposed sensor exhibits great repeatability in the middle of the sensing range, which is from 40% to 60% RH. Consequently, our resonator coupled with the CP film can be used as a real-time humidity-sensing device in the microwave range, where various radio-frequency devices are in use.
Highlights
Humidity sensors have recently been receiving considerable attention due to their usefulness in various fields, such as agriculture, manufacturing, environmental sciences, medicine[1,2], and so on
The mask layer was composed of photoimageable solder resist ink, which is widely used in the printed circuit board (PCB) process
A chemical reaction between the PEDOT:polystyrene sulfonate (PSS) conducting polymer (CP) film and humidity can clearly be observed via the microwave electrical properties, S21 and the resonance frequency
Summary
Humidity sensors have recently been receiving considerable attention due to their usefulness in various fields, such as agriculture, manufacturing, environmental sciences, medicine[1,2], and so on These humidity sensors should possess good performance characteristics, such as high accuracy, good repeatability, wide sensing range, fast response time, easy fabrication process, and low production cost. The final class includes chemically sensitive field-effect transistor (ChemFET)[12,13] sensors, which substitute the gate region of the transistor with the sensing material and measure the drain current Various sensing materials such as carbon nanotubes[14,15], crystals[16], graphene[17,18,19], ceramics[20,21], silicon[22], organic polymers[23,24], and composite materials[25,26], have been studied. When the RH changes from 5% to 80%, S21 and the resonance frequency are immediately changed by 0.18 dB and −35.4 MHz,respectively
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