Textile-based Passive Sensor for Air Humidity

In this paper, the manufacturing parameters of a passive ultra-high frequency (UHF) radio frequency identification (RFID)-based air humidity sensor were studied and optimized to reach the highest sensing ability. The sensor is fabricated by 3D printing combined with embroidering technology. In a high humidity environment, the sensor tag permanently changes its shape from flat to curved, which has a significant effect on the sensor tag read range and received signal strength indicator (RSSI) value. By modifying the infill percentage of the 3D-printed pattern and the stretching percentage of the elastic textile, the curving of the sensor tag can be modified. Based on the study, the stretching percentage of the elastic textile has the most significant influence on the sensor performance. As a result, the wireless performance of the sensor tag with optimized manufacturing parameters has a significant change in curvature after exposure to 60 % relative humidity for one hour. This passive sensor can provide cost-effective and flexible monitoring of air humidity for versatile application fields.