Wearable Multifunction Sensor for the Detection of Forehead EEG Signal and Sweat Rate on Skin Simultaneously

In this paper, we designed a multifunction wearable sensor for detecting electroencephalogram (EEG) and sweat rate simultaneously. Conductive fabric electrode was combined on the multifunction sensor for EEG signal measurement. The conductive material on the fabric was metallic Ag, which has low contact impedance and noise. The EEG electrode was connected to an EEG signal recording module, which was based on ADS1299 converter. There were 8 signal recording channels on the module. One of the channels was connected to the multifunction sensor and the other 7 channels could be connected to independent EEG electrodes. Because of the gaps between the fibers, the conductive fabric electrode could record EEG signals while allowing sweat to permeate through it. The sweat passed through EEG electrode could get into the internal of multifunction sensor. A piece of microporous PDMS was used to accelerate the evaporation of sweat in the multifunction sensor. The microporous PDMS was coated with super hydrophilic coating to help sweat diffusion in it. CaCl ₂ desiccant was used in the sensor to absorb sweat vapor continuously and generate a humidity diffusion gradient. A circuit board based on SHT20 chip was embedded in the sensor for relative humidity measurement in the path of sweat vapor diffusion. The sweat rate was measured by indirect estimation from relative humidity. By measuring the relative humidity in the multifunction sensor, we could realize the continuously measurement of sweat rate simultaneously with EEG signal recording. Both the EEG signal and sweat rate data could be transferred out wirelessly.