Contactless GSR Sensing Using mmWave Radar

The galvanic skin response (GSR), which is a manifestation of the activity in eccrine sweat glands, has always been an important psychological test to evaluate emotional arousal and mental stress. Although researches have focused on the radio reflections of skin and revealed that sweat gland activity can change the reflection signal of skin, the complicated experimental settings including vector network analyzer (VNA) and even optical path design limit further daily life application. In this article, we demonstrate the potential of using commodity millimeter-wave (mmWave) multiple-input multiple-output (MIMO) radar for contactless GSR sensing. To simulate the reflected signals of the frequency-modulated continuous-wave (FMCW) radar to the skin of different individuals, a four-layered skin model focused on the sweat duct is used and the change in conductivity in sweat ducts is regarded as mapping of sweat gland activity. Extensive experiments are conducted, consisting of three different physiological statuses: relaxing status, mental stress status, and physical stress status. We design a beamformer to transform the raw signal to the space domain so that the reflection signals from the palm are separated. The principal components of the processed signal are extracted to eliminate the interference caused by breathing and random noise. We evaluate the performance in terms of the correlation between the radar signal and the GSR before and after stress-induced events. The experimental results preliminarily verify the feasibility of contactless GSR sensing.