Electrodes for EEG/ECG/EMG
Last update: June 28, 2019, 4:09 p.m.
Biopotential signals are the result of the electrochemical activity of certain cells of the nervous, muscular or glandular tissue. The average activity of the brain cells can be monitored on the scalp, and this signal is called electroencephalography (EEG). The electric activity of heart cells is monitored by electrocardiography (ECG) and the electrical activity produced by skeletal muscles is called Electromyography (EMG). Monitoring biopotential signals, such as EEG, ECG, and EMG, provides important information about certain health-related conditions of a person, which opens a broad range of applications.
In electrical instruments the signals are based on movement of electrons. Biopotential electrodes are transducers that convert ionic currents to electrical currents at the interface between biological systems and measurement instruments. The most commonly used electrode is silver-silver chloride (Ag-AgCl) surface electrode due to its low and stable half-cell potential, low level of intrinsic noise, a relative non-polarizability, and small metal-electrolyte interface impedance. With increasing attention towards long-term health monitoring, there is a pressing need to create noninvasive sensors that monitor vital bioelectronic signals. Unfortunately, Ag-AgCl electrodes cannot translate to a long-term monitoring setting due to the electrolytic gel of the electrodes drying and causing skin irritation. Dry electrodes require less skin preparation time and could be better than gel-based electrodes for long-term measurement. The use of dry electrodes within and outside the clinical setting would reduce the complexity and time required for sEMG signal acquisition. Dry electrodes have the potential to provide a more convenient system for biopotential data acquisition with respect to wearable mobility monitoring applications.
Our research group in MBTechLab is exploring classes of materials and cost-effective approaches that enable electronic devices with features that would be impossible to achieve using traditional, wafer-based technologies. We have developed an economically novel stretchable PDMS-based dry electrode to realize electrically and mechanically stable metal patterns based on PDMS substrate by employing an intermediate polyimide layer. Our surface biopotential dry electrodes are highly compatible with stretchable electronics components and materials in mechanical, electrical properties and fabrication process, aiding in future integration. This approach can be used to measure ECG and EMG signals and to meet the patient's comfort and anti-motion needs while measuring vital signals.
The fabricated dry electrodes produced biopotential signals that were easily discernable from baseline noise and were similar to the output from Ag/AgCl electrodes that are commonly used in clinical settings. Future works could involve improving our fabrication techniques, optimizing biopotential signals quality, and measuring impedance reduction rates.