Metal Plate electrodes:
It is simplest form, metallic conductor in contact with skin.
An electrolyte soaked pad or gel is used to establish & maintain contact.
The electrode is made up of German silver(Nickel-silver alloy).
Before attaching gel is used.
Fig.(a) Metal plate electrode has lead soldered wire attached at end.
It is made up of Ag & deposited by layer of AgCl and adhesive material used to maintain contact.
They are used in ECG, EMG & EEG systems.
The problem with this kind of electrodes is motion artifact.
Fig.(b) Concerning with economics disposable electrodes with adhesive material is used.
It is most popular electrode consisting of plastic foam material with silver plated on one side.
The lead wire with female portion is snapped into electrodes & used to connected assembly to monitoring apparatus.
- They are frequently used in ECG as precordial leads.
- Hollow cylinders makes contact with skin at base.
- Terminal leads is attached to metal cylinders, rubber suction fits other base.
- Electrolytic gel is placed over contact surface, bulb is squeezed, applies suction against skin holding whole assembly.
- The problem with it is contact area is small, large surface area leads to high source impedance.
- Motion artifact cause disturbance in double layered at electrode-electrolyte interface, so floating electrodes offer suitable technique.
- Here metal disk is recessed in cavity so that it does not come in direct contact with skin.
- The gel doesn’t produce disturbance due to presence of double layer charge.
- They have irregular surface & can change curvature with movements.
- They include woven, stretchable, nylon fabrics with silver particles on one side.
- The carbon particles in silicone makes it electrically conductive.
- Pin is pushed in lead connector hole& used in similar way as metal-plate electrode.
- They can cause skin irritation.
- Flexible lead attached to Mylar by conductive adhesive & silver deposited.