Capacitive monitoring of bio and neuro signals

Capacitive electrode is emerging as a useful tool for the inconspicuous monitoring of bio- and neuro-signal. It operates with the displacement currents instead of the real charge currents, and its electrolytic electrode-skin interface is replaced by a dielectric material, an electrically insulated layer or air. Here, we introduce the basic principles of capacitive recording of biosignals and categorize the various capacitive recording methods as 'built-in', 'helmet', 'band and film' and 'pad and chip' type, and describe the detailed features of each method. Each type is designed according to the signal type and anatomical position. Especially the 'built-in' type is focused on electrocardiogram (ECG) in our real life. Insulators in the applications are also selected by various materials and we described. A recent progress in microelectromechanical system (MEMS) technology enabled the capacitive measurement of bio and neuro signals and we briefly mention the contribution of MEMS technology. Conclusively, we describe the future potential applications of capacitive monitoring beyond the laboratory environment.