surfaceelectrode

Surface electrodes are electrical conductors placed on the skin or mucous membranes to record bioelectric signals or to deliver electrical stimulation. They are non-invasive and widely used in clinical, diagnostic, and research settings for monitoring and stimulation.

Construction and types: Surface electrodes come in various forms, including flat disc electrodes, cup electrodes, and flexible patch assemblies. They are broadly categorized as dry electrodes, which require no electrolyte, and wet or gel-based electrodes, which use conductive gel or paste to reduce skin impedance. Some modern designs use hydrogel or dry-contact materials to improve comfort and reduce drying out. Common electrode materials include silver-silver chloride (Ag/AgCl) for low impedance and stable performance, as well as carbon, gold, or platinum. The electrode assembly may include an adhesive cushion and a backing to maintain stable contact.

Applications: They are used to record electroencephalography (EEG), electromyography (EMG), electrocardiography (ECG), and evoked potentials. They are also employed for transcutaneous electrical stimulation, such as transcutaneous electrical nerve stimulation (TENS) or non-invasive muscle or nerve stimulation, and in brain-computer interfaces. In research and clinical practice, surface electrodes enable long-term monitoring and ambulatory measurements.

Considerations and limitations: Impedance, skin preparation, and hair affect signal quality. Motion, sweating, and drying of conductive gel can introduce artifacts or degrade contact. They generally provide lower signal amplitude and spatial resolution than invasive electrodes. They are relatively inexpensive and easy to use but may cause skin irritation in some users. Selection of electrode type, material, gel, and placement depends on the target signal, duration of measurement, and comfort.