In the previous post we looked the Overcoming the Disadvantages of Electro-oculography (EOG). In this post we will look at how to select the best suitable electrodes for the reliable capturing of EOG signals.
Electrodes are placed above and below the eye for the vertical measurement (red coloured ones) and to the left and right of the eyes for the horizontal measurement (blue coloured ones). A fifth electrode is placed on the user’s forehead to serve as a ground (green colour electrode). The electrodes measure the EOG signal (electrooculographic potential), which corresponds to the angle of the eye balls. The leads from these electrodes are connected to electrophysiological amplifiers. The amplifier outputs are connected to a signal conditioning system.
Selection of Electrodes
The first stage of the design is selecting the electrodes. The basic requirements for wearable body sensors focus very much on convenience of operation, bio-compatibility, and miniaturization. The electrodes must be chosen with the concern of protecting the eyes from hazardous elements. ECG disposable electrodes are easy to find as they are used everywhere. Silver/Silver-Chloride electrodes can be chosen because the half-cell potential is zero. Electrodes with the smallest amount of half-cell potential are desirable because they cause the least amount of offset. By definition, the hydrogen electrode has a zero half-cell potential, but due to the gaseous nature, they cannot be feasibly used. Although lead electrodes have a lower half-cell potential than the Ag/Ag-Cl electrodes, lead is hazardous to the health and thus it is avoided. Ag/Ag-Cl electrodes can simply be held in placed on the skin. Also the selection of electrodes (Ag/Ag-Cl) takes into account cost and proper signal pick-up.