Wearable humidity sensor with porous membrane by soft-MEMS techniques

An electric conductimetric sensor (thickness: 80 μm) constructed in a sandwich configuration with a hydrophilic poly-tetrafluoroethylene membrane placed between two gold deposited layers was evaluated for use as a moisture sensor. The humidity level was measured by electrical conductivity of the device using the multifrequency LCR-meter at frequencies ranging from 100 Hz to 100 kHz, the device was calibrated at 100 Hz against the moisture air over the range of 30-85 % RH, which includes normal humidity level in the atmosphere and physiologic air such as breath and sweating. The response sensitivity of the conductimetric device was extremely high (i.e. less than 1 sec. for conductivity shift between humid air of 80 % RH and dried air of -60 °C dew point) even for recovery to dried air. The sensor performance was reproducible over multiple measurements, showing the highly reproducibility with a coefficient of variation of 1.77 % (n = 5).