One key source of motion artifact in biopotential electrodes is the disturbance of the double layer of charge at the electrode-electrolyte interface. Employing non-polarizable electrodes like Ag/AgCl electrode can greatly reduce this artifact but it still can be present, and efforts to stabilize the interface mechanically can help to reduce the artifact further. Floating electrodes offer appropriate technique to reduce the artifact.
The figure below shows an example of a floating type electrode:
The principle feature of the floating electrode is that the actual electrode element or metal disk is recessed in a cavity so that it does not come in contact with the skin itself. Instead, the electrode element is surrounded by electrolyte gel in the cavity. The cavity and hence the gel does not move with respect to the metal disk, therefore it does not produce any mechanical disturbance of the double layer of charge.
Related: Types of Bioelectrodes
In practice, the electrode is filled with electrolyte gel and then attached to the skin surface by means of a double-sided adhesive tape ring as shown in figure 1(a). The electrode element can be a disk made of a metal such as silver coated with AgCl. Another often used form of the floating electrode employs a sintered Ag/AgCl pellet instead of a metal disk. These electrodes are quite stable and reusable after proper cleaning between uses.
Related: Types of Transducers used in Biomedical Measurement Applications
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