Types of External Electrodes

Biomedical Instrumentation
1

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.

    ground-plate-electrode-250x250
    Fig.(a)

  • 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.

  • Disposable_ECG_Electrode
    Fig.(b)

  • 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.

Suction Electrodes:
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  • 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.

Floating Electrodes:

  • EMG-electrodes
  • 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.

Flexible electrodes:

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  • 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.
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