Development of a capacitive coupling electrode for bioelectrical signal measurements and assistive device use

The human body is known to produce several different electrical patterns and signals derived from bioelectrical activity. Bioelectrical signals such as the cardioelectrical and myoelectrical signals have several medical applications. In order to acquire those signals, low impedance contact electrodes are commonly used. However, because these sensors require skin preparation or application of conductive gels, placing these sensors can be difficult, time consuming and uncomfortable task for the patient. Moreover the presence of body hair and sweat can be a source of noise and cause signal depletion. This paper proposes a noncontact capacitively coupled electrode based on high impedance input, required to detect weak electrical fields. Noncontact capacitively coupled electrodes rely on reacting to electrical field variations caused by bioelectrical activity, therefore eliminating the need to maintain resistive contact between the skin and the electrode. The sensor high impedance input of 1 teraohms allowed only 0.3 to 1 picoampere input current to flow between the sensor plate and the preamplifier unit. Experiments focused on the recording of electromyogram and electrocardiograms over clothing. Data was collected and compared with data from resistive electrodes. We confirmed that our electrodes are capable of collecting bioelectrical data that can be used for assistive devices interfacing without direct contact with the skin of the subject. Such electrodes can replace currently used resistive contact electrodes improving the reliability of collected signals and increasing user-friendliness of systems that require daily, long term bioelectrical signal monitoring.