Luo Mengxue, Liu Zhangming, Wang Qi, Liu Rui, Xu Yuan, Wang Ke, Shi Xinzhi, Ye Shuangli
School of Printing and Packaging, Wuhan University, Wuhan 430072, Hubei Province, People's Republic of China.
Electronic Information School, Wuhan University, Wuhan 430072, Hubei Province, People's Republic of China.
ACS Appl Mater Interfaces. 2022 Apr 13;14(14):16621-16630. doi: 10.1021/acsami.2c00503. Epub 2022 Mar 31.
In this work, surface engineering is applied to polyimide (PI) films to fabricate low-cost Ag/PI wireless humidity sensors with a resonant frequency of 2.45 GHz. The sensors were obtained by in situ metallization technique coupled with inkjet printing, where PI plays triple roles as a flexible substrate, ion-exchange surface, and sensing material to moisture. Moreover, the humidity sensitivity can be enhanced by the improvement of hydrophilicity via loading with different ions on the PI surface, which has been demonstrated by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The wireless humidity sensor loaded with K ions has the maximum sensitivity of 97.7 kHz/% RH at a low relative humidity range of 20-65% and 359.7 kHz/% RH at a high relative humidity of 65-90%, respectively. Accordingly, a sensing mechanism of the fabricated humidity sensor has been discussed in detail. On the other hand, the characteristics of the humidity sensor such as response and recovery speed and stability are analyzed. The mechanical performance tests show that the humidity sensor displays excellent flexibility and good mechanical stability. A strong adhesion between the Ag antenna and PI substrate can be found as well. The passive wireless humidity sensor described in this work has the advantages of having a simple structure, low cost, high sensitivity, long-term stability, and good mechanical properties, which has potential applications in automated industry and healthcare with real-time humidity monitoring.
在这项工作中，通过表面工程对聚酰亚胺（PI）薄膜进行处理，以制造具有2.45 GHz谐振频率的低成本Ag/PI无线湿度传感器。这些传感器是通过原位金属化技术与喷墨印刷相结合获得的，其中PI兼具柔性基板、离子交换表面和湿度传感材料这三种功能。此外，通过在PI表面负载不同离子来提高亲水性，可以增强湿度敏感性，这已通过傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）和接触角测量得到证实。负载K离子的无线湿度传感器在20-65%的低相对湿度范围内灵敏度最高可达97.7 kHz/%RH，在65-90%的高相对湿度下为359.7 kHz/%RH。据此，详细讨论了所制备湿度传感器的传感机制。另一方面，分析了湿度传感器的响应、恢复速度和稳定性等特性。机械性能测试表明，该湿度传感器具有出色的柔韧性和良好的机械稳定性。同时还发现Ag天线与PI基板之间具有很强的附着力。本文所述的无源无线湿度传感器具有结构简单、成本低、灵敏度高、长期稳定性好以及机械性能优良等优点，在自动化工业和实时湿度监测的医疗保健领域具有潜在应用价值。
