Laser-direct-writing assisted preparation of flexible humidity sensors based on semi-interpenetrating polymer network for applications in non-contact human-machine interaction

Flexible sensors for non-contact human-machine interaction (HMI) received great attention recently due to increasing requirements for cross-infection of bacteria or virus, which is prominent considering the disaster brought about by COVID-19. Herein, a semi-interpenetrating network of poly(dimethyl diallyl ammonium chloride)/crosslinked poly(vinyl alcohol)/graphene oxide (PDDA/c-PVA/GO) was deposited on polytetrafluoroethylene membrane with interdigital electrodes constructed by reducing GO with laser-direct-writing technology to prepare a flexible humidity sensor (FHS). As-prepared PDDA/c-PVA/GO FHS showed excellent sensing performance, including high response magnitude over wide range of relative humidity (RH) (impedance change of three orders of magnitude between 10 % and 90 % RH), good sensing linearity (R-2 = 0.991) on a semilogarithmic scale, small hysteresis (similar to 4.4 % RH) and resistance to humid environment. Moreover, the FHS exhibited good performance in various scenarios of non-contact HMI, including prompt differentiation of respiration status, speech recognition, accurate measurement of fingertip movement (as small as 2 mm). Specially, a 3 x 3 FHS sensor array could realize accurate non-contact positioning. This work provides a new approach for developing high performance flexible sensors with great application potentials in non-contact HMI.