Portable wireless humidity sensor based on hyperbranched polysiloxane for multifunctional non-contact sensing

Non-contact sensing is an immediate research focus as a much greener and hygienic human-machine interface. Nonetheless, much research remains to be done on fast and stable non-contact sensors based on humidity signals. Hence, in this paper, hyperbranched sulfonated polysiloxane (HPS) with carboxyl groups at the end was synthesized by polycondensation reaction . The resulting polymer was compounded with LiCl and fabricated into humidity sensors . Benefiting from the tailored hydrophilicity/hydrophobicity of the material, flexible siloxane backbones and ionized LiCl, the sensor exhibited five orders of magnitude impedance changes over a wide humidity test range (11–98% RH) with rapid response (1–2 s) and small humidity hysteresis (3% RH). The results of continuous cyclic test confirmed the good reproducibility and stability of the material. Moreover, the sensor was able to distinguish and respond to fingers at different distances, respirations with altered frequencies and various commands. By integrating humidity sensors into the circuit, a low-cost, portable and wireless non-contact monitoring device was developed. The detector enables real-time display of data on a cell phone , which is of great potential value for non-contact distance detection, command recognition and respiration monitoring.