Portable sweat rate sensors integrated with air ventilation actuators

Abstract

Two types of the portable sweat rate sensors (miniaturized prototype, wearable prototype) integrated with thermo-pneumatic actuators for automatic ventilation have been proposed and experimentally verified their performances. The previous forced ventilation sweat rate sensors using external ventilating devices had the problem of the bulky size with the lack of portability. The previous natural ventilation sweat rate sensors with portable sizes meanwhile required a manual ventilation per each measurement. The total weight of the miniaturized prototypes is 6.4 % of that of the previous forced ventilation sweat rate sensors. The integrated thermo-pneumatic actuator lifts the humidity measuring chamber above the skin for automatic natural ventilation. The miniaturized prototypes, fabricated in a size of $41 \pm 0.5 mm - width \times 38 \pm 0.5 mm$ - height $\times 29.5 \pm 0.5 mm$ - thickness with a total weight of $63 \pm 1$ g, measure the sweat rate with a sensitivity of 0.056 (pF/sec)/ $(g/m^2h)$ and a linearity of 99.1 % in the sweat rate range of 3.76~137.68 $g/m^2h$. To improve applicability, the wearable prototypes are developed. The total weight of the wearable prototypes is 47.6 % of that of the miniaturized prototypes. The wearable prototypes are operated by 6 V of the two commercialized batteries by reducing the consuming power from 12.5 W to 1.6 W. The wearable prototypes, fabricated in a size of $35 \pm 0.5 mm - diameter \times 25 \pm 0.5 mm$ - thickness with a total weight of $30 \pm 1$ g, measure the sweat rate with a sensitivity of 0.039 (pF/sec)/ $(g/m^2h)$ and a linearity of 97.9 % in the sweat rate range of 3.76~137.68 $g/m^2h$ . The present two type sensors are insensitive to the wind effect of the gentle wind (1.0 m/s) and the human walking speed (1.5 m/s), respectively, and thus demonstrates high potential for mobile human thermoregulatory status monitoring applications, such as human monitoring jackets and cognitive air-conditioning systems based on human sweat.