Numerical Simulation of the Influence of Ambient Temperature and Humidity on Skin Sweating and Electrical Characteristics

Abstract:
Transcutaneous electrical nerve stimulation (TENS) is widely used in areas such as tactile sensation restoration, rehabilitation medicine, and neuromodulation. It is crucial for optimization design of electrical stimulation devices to understand the mechanisms of how ambient temperature and humidity alter skin conductivity through influencing human sweating processes. This study establishes a skin sweating model and a finger conductivity model based on the theory of heat and mass transfer in porous media as well as skin conductivity. Through numerical simulation and analysis, we investigate the sweating, heat and mass transfer, and finger conductivity under different ambient temperature and humidity conditions. The temperature and humidity distributions in various skin layers are obtained, as well as the current and voltage distributions under different skin humidity. The results show both temperature and humidity variations influence skin temperature and humidity distributions by altering skin heat conduction, sweating, and sweat evaporation processes. The current is concentrated in the superficial skin layers between electrodes under electrical stimulation. Each 12.5% increase in ambient humidity leads to an approximate 1V increase in voltage at the neurons between the epidermis and dermis while each 4deg C rise in ambient temperature results in a voltage increase of approximately 0.8V, all having a significant impact on the effectiveness of TENS.