A highly sensitive humidity sensor was prepared by the coating of epoxy resin on a quartz crystal sensor surface. The probe was adapted to a ventilated chamber-type apparatus for the measurement of water evaporation from human surfaces. In the range from 0 to 50% relative humidity (RH), the relationship between RH and resonant frequency showed good linearity with high resolution, ≤0.1% RH. By alternation between standard air (10% RH) and humidified air (12.5, 22.5, 32.5% RH), the time to reach steady state was determined to be less than 120 sec for both absorption and desorption processes. The frequency at the steady state was very stable.
This newly developed humidity sensor was used to measure water evaporation rates from human forearm, cheek, palm of hand and ocular surface. The observed rates were 10.7±0.5, 35.0±1.3, 40.2±1.6 and 298.9±4.0g/m2
·hr (mean±standard deviation) respectively. These values and regional differences were consistent with those previously reported. The sensitivity and responsiveness of the new probe was best seen when measuring evaporation from the ocular surface. After achieving steady state, oscillations of the resonant frequency coincided with blinks of the eye at 5 sec intervals. Therefore, this new system that utilizes an epoxy-coated quartz crystal sensor will very useful to evaluate dynamic changes of water evaporation rate. It may have both clinical and industrial uses.