Wearable Antenna Sensor Based on EBG Structure for Human Body Area Humidity Monitoring

The humidity levels surrounding the human body surface can impact both comfort and overall health. This article designs and manufactures a wearable antenna sensor that utilizes an electromagnetic bandgap (EBG) array. The sensor operates within the 5.8-GHz industrial, scientific, and medical (ISM) band, enabling the monitoring of humidity levels on the surface of the human body. The antenna and EBG array are structurally integrated with the "Fu," "Tai Chi," and "Xi" characters of traditional Chinese culture, ensuring the optimal performance of the antenna and enhancing its artistry. The antenna adopts a flexible polyimide (PI) substrate to meet the wearing needs of the human body. The EBG array temporarily uses FR-4 as the substrate material due to its ease of fabrication and stable performance. The incorporation of the EBG array effectively broadens the antenna's operating bandwidth from 5.787–5.864 to 5.703–5.881 GHz. Additionally, it boosts the peak gain from 5.75 to 8.77 dB and reduces the specific absorption rate (SAR) by approximately 30%. Notably, the resonant frequency of the antenna gradually decreases with increased relative humidity (RH) levels in the environment. The humidity sensitivity of the antenna can reach 1.64 MHz/RH% at 40%RH–90%RH. The actual measurement and simulation results of the antenna sensor produced fit well. The experimental results indicate that the antenna sensor is suitable for humidity monitoring in human areas.