Yeo Junho, Kwon Younghwan
Department of Artificial Intelligence, Daegu University, 201 Daegudae-ro, Gyeongsan-si 38453, Republic of Korea.
Department of Energy System Engineering, Daegu University, 201 Daegudae-ro, Gyeongsan-si 38453, Republic of Korea.
Sensors (Basel). 2024 Sep 28;24(19):6286. doi: 10.3390/s24196286.
In this paper, the humidity-sensing characteristics of gelatin were compared with those of poly(vinyl alcohol) (PVA) at L-band (1 ~ 2 GHz) microwave frequencies. A capacitive microwave sensor based on a defected ground structure with a modified interdigital capacitor (DGS-MIDC) in a microstrip transmission line operating at 1.5 GHz without any coating was used. Gelatin is a natural polymer based on protein sourced from animal collagen, whereas PVA is a high-sensitivity hydrophilic polymer that is widely used for humidity sensors and has a good film-forming property. Two DGS-MIDC-based microwave sensors coated with type A gelatin and PVA, respectively, with a thickness of 0.02 mm were fabricated. The percent relative frequency shift (PRFS) and percent relative magnitude shift (PRMS) based on the changes in the resonant frequency and magnitude level of the transmission coefficient for the microwave sensor were used to compare the humidity-sensing characteristics. The relative humidity (RH) was varied from 50% to 80% with a step of 10% at a fixed temperature of around 25 °C using a low-reflective temperature and humidity chamber manufactured with Styrofoam. The experiment's results show that the capacitive humidity sensitivity of the gelatin-coated microwave sensor in terms of the PRFS and PRMS was higher compared to that of the PVA-coated one. In particular, the sensitivity of the gelatin-coated microwave sensor at a low RH from 50% to 60% was much greater compared to that of the PVA-coated one. In addition, the relative permittivity of the fabricated microwave sensors coated with PVA and gelatin was extracted by using the measured PRFS and the equation was derived by curve-fitting the simulated results. The change in the extracted relative permittivity for the gelatin-coated microwave sensor was larger than that of the PVA-coated one for varying the RH.
在本文中，对明胶与聚乙烯醇（PVA）在L波段（1~2 GHz）微波频率下的湿度传感特性进行了比较。使用了一种基于缺陷接地结构且带有改进型叉指电容器（DGS-MIDC）的电容式微波传感器，该传感器位于微带传输线中，工作频率为1.5 GHz，且未进行任何涂层处理。明胶是一种基于动物胶原蛋白的天然聚合物，而PVA是一种高灵敏度的亲水性聚合物，广泛用于湿度传感器，具有良好的成膜性能。分别制备了两个涂有A型明胶和PVA的基于DGS-MIDC的微波传感器，涂层厚度均为0.02 mm。基于微波传感器传输系数的谐振频率和幅度水平的变化，使用相对频率偏移百分比（PRFS）和相对幅度偏移百分比（PRMS）来比较湿度传感特性。使用由聚苯乙烯泡沫塑料制成的低反射温度湿度室，在约25℃的固定温度下，将相对湿度（RH）以10%的步长从50%变化到80%。实验结果表明，就PRFS和PRMS而言，涂有明胶的微波传感器的电容式湿度灵敏度高于涂有PVA的传感器。特别是，在50%至60%的低相对湿度下，涂有明胶的微波传感器的灵敏度比涂有PVA的传感器高得多。此外，通过使用测量得到的PRFS并对模拟结果进行曲线拟合推导方程，提取了涂有PVA和明胶的制成的微波传感器的相对介电常数。对于不同的相对湿度，涂有明胶的微波传感器提取的相对介电常数的变化大于涂有PVA的传感器。
