Human respiration monitoring using humidity and temperature dual-modal sensors for temperature-insensitive humidity sensing and synchronous temperature sensing

Humidity and temperature are two inseparable basic environmental physical quantities. The flexible humidity and temperature sensors play a crucial role in human health monitoring. However, their cross-sensitivity to temperature and relative humidity (RH) variations usually leads to unwanted signal interference, which significantly hinders their practical application. Moreover, the manufacturing cost of flexible humidity and temperature sensors also greatly limits their wide application. Herein, we fabricated humidity and temperature dual-mode sensors by simple printing and spraying processes, and their sensitive materials are completely derived from graphene oxide (GO), which achieved temperature-insensitive humidity sensing and synchronous temperature sensing. In the RH range of 20–90 %, the resistance of the humidity sensor was decreased by four orders of magnitude. While at applied frequency of 100 Hz, capacitance of the humidity sensor was increased from 9.51 pF to 76.05 pF in the range of 20–90 %RH. The temperature sensor exhibits a high sensitivity of 1.66 % /℃ in the range of 25–45 ℃. Remarkably, benefiting from the fact that the humidity sensor is insensitive to the test temperature in the capacitive working mode, and the packaging strategy of temperature sensor isolates the external humidity change, the dual-modal sensors can distinguish the temperature and humidity change at the same time. Finally, the humidity and temperature dual-modal sensors have been successfully applied to the detection of human respiratory frequency. This provides an important method for developing low-cost and integrated multifunctional flexible sensors.