Wearable Perspiration Volume Sensor Using Dual-Frequency Impedance Measurement

In recent years, the increase in the number of heat stroke patients has become a social problem. Heat stroke occurs indoors at home in many cases. This paper focuses on the measurement of sweat rate using a wearable device to prevent heat stroke in the indoor environment. In the proposed method, textile-based electrodes impregnated in fiber materials are used to measure the impedance of the skin. As sweating lowers the impedance of the skin, the amount of sweating can be estimated from the impedance change between the electrodes. However, the method using impedance has a problem in distinguishing the effects of water volume and salinity. To address this problem, dual-frequency impedance measurement is proposed in this paper. The proposed method utilizes the fact that impedance variations due to water volume and salinity changes have different frequency characteristics. The measurement results indicate that the proposed method can measure impedance while considering changes in the water volume and salinity.