This document discusses different types of electrodes used in biomedical instrumentation. Electrodes are used to pick up electric signals from the body by converting ionic current into electronic current. Common types of electrodes include surface electrodes like metal plate electrodes and suction cup electrodes, needle electrodes, microelectrodes, depth electrodes, and chemical electrodes. The interface between the electrode and electrolyte allows measurement and recording of body potentials by providing a connection between the body and electronic measuring devices. Key characteristics of this interface include the transfer of electrons and ions across the barrier.

1. OMD551- BASICS OF BIOMEDICAL
INSTRUMENTATION
TYPES OF ELECTRODES

2. ELECTRODES
• Electrodes are used to pickup the electric signals of the
body.
• Electrodes serve as a transducer to convert ionic current
into electronic current.
• Devices that converts ionic potential into electronic
potential are called as electrodes.
• Used to measure the potentials from ECG,EEG,EMG

3. PURPOSE OF ELCTROLYTES
Outer skin is non conductive
Conductivity of the skin directly
proportional to moisture of the skin
represents the body fluid containing ions

4. ELECTROLYTE INTERFACE
• To Measure and record the potentials,
necessary to provide interface between body
and electronic measuring apparatus.
• Electrolyte interface is used to examine the
electric current from body to an electrode

5. ELECTROLYTE INTERFACE
• The net current that crosses the interface, passing from electrode to
electrolyte , consists of
• Electrons moving in the direction opposite to that of the current in the
electrode.
• Cations (C+) moving same direction of current
• Anions (A-) moving opposite direction of current

6. ELECTRODES &ELECTRODE POTENTIAL
• Devices that convert ionic potential into electronic potential are
called electrodes.
• The interface of metallic ions in solution with their associated
metals in an electrical potential is called electrode potential.

7. Half cell potentials
• voltage developed at an electrode- electrolyte
interface is called half cell potential

8. ELECTROLYTE CHARACTERISTICS
Perfect polarized electrode
charges not transfer across metal electrolyte
interface.
Perfect non-polarized electrode
infinite charges transfer across metal electrolyte
interface.
Artifacts
non-polarized electrode will create variable noise
termed as artifacts

10. Types of elctrodes

11. TYPES OF ELECTRODES
Surface Electrode
Needle Electrode
Micro Electrode
Depth Electrode
Chemical Electrode

12. SURFACE ELECTRODE
Surface electrodes are used to measure the potential
available from surface of skin and to sense potential
from heart and brain.

13. Metal plate electrode

14. Metal plate electrode
• One of most frequently used bio potential
electrode
• Consists of metallic conductor in contact with
skin
• Electrolyte gel is used to establish and
maintain connection between skin and
electrode
• This electrode is made of German silver(nickel
silver alloy)

15. Suction cup elctrode –Flat surface of
body

16. Suction cup electrode –Flat surface of
body
• Modification of metal plate electrode
• Does not require straps or adhesives for
holding in a place
• Used in ECG
• Used for short period of time and quite large
• Suction and pressure of contact surface
against skin causes irritation.

17. Adhesive tape
- metallic screen backed by a pad
- holds the electrodes in place
- Delays the evaporation of electrolyte

20. Used for any environmental conditions

21. Flexible Electrodes

23. • R- Gas constant
• T- Absolute temperature in kelvin
• n – valence of ions
• F-Faradays constant
• C1,C2- Concentration of selected ion on two sides of
membrane
• F1,f2-Activity co-efficient of ions on two sides of
membrane