Flexible Antenna Sensor Based on Vertical Graphene for Wireless Humidity Monitoring and IoT Applications

Some special environments, such as closed or harsh spaces, require contactless and real-time humidity monitoring. A flexible 920-MHz antenna sensor with vertical graphene (VG) as a sensitive film is proposed, which can measure humidity and transmit data wirelessly in real time. When the humidity changes, the number of H2O molecules absorbed by the graphene film will vary, which affects the permittivity of the antenna patch, and results in shifts in the resonant frequency. Remote humidity monitoring can be realized by analyzing the frequency response at the receiver. By depositing VG film on the antenna patch, the sensitivity can be improved from 16.3 to 32.6 kHz/% RH (linear range: 0%–57% RH) and from 145 to 290.5 kHz/% RH (57%–90% RH). During humidity change, the radiation direction of the VG-based antenna sensor remains stable, and the maximum wireless transmission distance reaches 100 m. For the first time, the model of the antenna sensor is established. Furthermore, the flexible sensor can conform to various installation shapes. The experimental results show that the wireless VG-based antenna sensor is a good candidate for remote humidity monitoring and the Internet of Things.