1. Electrode theory- Basic electrode, Electrodes for ECG
Need, types of Bio-potential electrodes.
Basic electrode theory
Various Electrodes for ECG.

2. ELECTRODE - ELECTROLYTE & ELECTROLYTE-TISSUE INTERFACE

3. Electric equivalent circuits

4. :

5. Electrode theory- Basic electrode,
Need & Types of Bio-potential electrodes
Surface electrodes
Deep seated electrode
Factors to be consider while measurements:
Careful and suitable selection of electrodes for satisfactory record of bioelectric signal.
Comfortable for the patients to wear over long period
They should not produce any moving artefacts
Convenient in practical applications
Good contact with skin (for low contact impedance)

6. Cont..
The characteristics of a metalic/nonmetalic surface electrodes depends upon-
Condition at metal-electrolyte interface
Electrolyte –skin interface
Quality of electrolytes
Electrode properties
Why electrode jelly is required while measurements of biopotential signals?

7. Cont.. Electrode Potentials
All electrode potentials are measured wrt a ref. Electrodes
Ref. Electrodes-Hydrogen electrode (H absorbed on platinum back
-Calomel electrode
Electrode potentials of few metal electrodes wrt Hydrogen
Metal
Ionic symbol
Electrode Potential(Volt)
Aluminium
Al+++
-1.66
Iron
Fe++
-0.44
Lead
Pb++
-0.12
Hydrogen H+
-0.0
Copper
C++
+0.34
Silver
Ag+
+0.80
Platinum
Pt+
+1.2
gold
Au+
+1.69

8. Cont.. potential between Electrode s in electrolyte Electode Metal
Potential difference between Electrode (mV)
Stainless steel
Saline 10
silver
9.4
Silver-silver chloride
2.5
(11mm disc)
ECG paste
0.47
Silver-silver chloride (sponge)
0.2

9. L6: Electrodes for ECG, EEG, EMG
Electrodes for EEG,
Electrodes for EMG,
Biochemical Electrodes

10. Electrodes for ECG, EEG, EMG
Electrodes are used to pickup the biopotentials from the surface of the body of from inside the cells.
Basic electrodes are classified as:
Skin surface electrodes
Needle electrodes
Microelectrodes

11. Body Surface Recording Electrodes
Electrode metal
Electrolyte
Metal Plate Electrodes (historic)
Suction Electrodes
(historic interest)
Floating Electrodes
Flexible Electrodes

12. Commonly Used Biopotential Electrodes
Metal plate electrodes
Large surface: Ancient, therefore still used, ECG
Metal disk with stainless steel; platinum or gold coated
EMG, EEG
smaller diameters
motion artifacts
Disposable foam-pad: Cheap!
(a) Metal-plate electrode used for application to limbs. (b) Metal-disk electrode applied with surgical tape. (c)Disposable foam-pad electrodes, often used with ECG

13. Commonly Used Biopotential Electrodes
Suction electrodes
No straps or adhesives required
precordial (chest) ECG
can only be used for short periods
Floating electrodes
metal disk is recessed
swimming in the electrolyte gel
not in contact with the skin
reduces motion artifact
Suction Electrode

14. Commonly Used Biopotential Electrodes
Metal disk
Insulating
package
Double-sided
Adhesive-tape
ring
Electrolyte gel
in recess
(a)
(b)
Reusable
Snap coated with Ag-AgCl
External snap
Gel-coated sponge
Disposable
Plastic cup
Plastic disk
Tack
Dead cellular material
Foam pad
Capillary loops
Germinating layer
(c)
Floating Electrodes

15. Commonly Used Biopotential Electrodes
Flexible electrodes
Body contours are often irregular
Regularly shaped rigid electrodes
may not always work.
Special case : infants
Material :
- Polymer or nylon with silver
- Carbon filled silicon rubber
(Mylar film)
(a) Carbon-filled silicone rubber electrode. (b) Flexible thin-film neonatal electrode. (c) Cross-sectional view of the thin-film electrode in (b).

16. Internal Electrodes
Needle and wire electrodes for percutaneous measurement of biopotentials
(a) Insulated needle electrode. (b) Coaxial needle electrode. (c) Bipolar coaxial electrode. (d) Fine-wire electrode connected to hypodermic needle, before being inserted. (e) Cross-sectional view of skin and muscle, showing coiled fine-wire electrode in place.
The latest: BION – implanted electrode for muscle recording/stimulation
Alfred E. Mann Foundation

17. Fetal ECG Electrodes
Electrodes for detecting fetal electrocardiogram during labor, by means of intracutaneous needles (a) Suction electrode. (b) Cross-sectional view of suction electrode in place, showing penetration of probe through epidermis. (c) Helical electrode, which is attached to fetal skin by corkscrew type action.

18. Electrode Arrays
Contacts
Insulated leads
(b)
Base
Ag/AgCl electrodes
Ag/AgCl electrodes
Base
Insulated leads
(a)
Contacts
(c)
Tines
Base
Exposed tip
Examples of microfabricated electrode arrays. (a) One-dimensional plunge electrode array, (b) Two-dimensional array, and (c) Three-dimensional array

19. Microelectrodes Why Measure potential difference across cell membrane
Requirements
Small enough to be placed into cell
Strong enough to penetrate cell membrane
Typical tip diameter: 0.05 – 10 microns
Types
Solid metal -> Tungsten microelectrodes
Supported metal (metal contained within/outside glass needle)
Glass micropipette -> with Ag-AgCl electrode metal
Intracellular
Extracellular

20. Metal Microelectrodes
Microns! R
Extracellular recording – typically in brain where you are interested in recording the firing of neurons (spikes).
Use metal electrode+insulation -> goes to high impedance amplifier…negative capacitance amplifier!

21. Metal Supported Microelectrodes
(a) Metal inside glass (b) Glass inside metal

22. Glass Micropipette heat pull
Ag-AgCl wire+3M KCl has very low junction potential and hence very accurate for dc measurements (e.g. action potential)
heat
pull
A glass micropipet electrode filled with an electrolytic solution (a) Section of fine-bore glass capillary. (b) Capillary narrowed through heating and stretching. (c) Final structure of glass-pipet microelectrode.
Fill with intracellular fluid or 3M KCl
Intracellular recording – typically for recording from cells, such as cardiac myocyte
Need high impedance amplifier…negative capacitance amplifier!

23. Electrical Properties of Microelectrodes
Metal Microelectrode
Metal microelectrode with tip placed within cell
Use metal electrode+insulation -> goes to high impedance amplifier…negative capacitance amplifier!
Equivalent circuits

24. Electrical Properties of Glass Intracellular Microelectrodes
Glass Micropipette Microelectrode

25. Electrodes for ECG, EEG, EMG
Various Electrodes used for the measurement or recording of ECG signal.
Immersion electodes(not used now)
Limb electrodes
Suction cup electrodes
Floating electrodes
Spray –on electrodes
Pregelled disposable electrode
Pasteless (dry) electrodes
Air –jet ECG electrodes

26. ECG Electrodes ECG plate electrode. The electrode is usually
Fastened to the arm
or leg with a perforated
Rubber strap which
keeps it in position
during ECG recording
ECG Electrodes
Light weight floating
Electrode with press Stud
for long term monitoring

27. ECG Electrodes

28. ECG Electrodes Disposable pre-gelled ECG Electrode.
A porous tape overlaying
placed over the electrode
resists perspiration and
Ensures positive placement
Under stress conditions
ECG Electrodes
Air –Jet ECG Electrodes

29. ECG Electrodes Suction cup electrode (Unipolar chest ECG Electrode.)
Floating type skin surface
ECG Electrodes 29

30. Electrodes for ECG, EEG, EMG
Various Electrodes used for the measurement or recording of EEG signal.
Scalp surface electrodes (chlorided silver discs)
Ear-clip electrodes (reference electrode)
Small needle electrodes
Silver ball or pellet electrodes(exposed cortex, high resistance)
Pad electrode(silver ball is belled out at the end and padded with a sponge)
Chlorided silver wire in plastic cup electrodes

31. EEG Electrodes EEG Electrode which can Be applied to the surface
Of the skin by an
adhesive tape.
EEG Electrodes
Ear-clip Electrodes
&
EEG scalp surface Electrodes

32. EEG Electrodes

33. Electrodes for ECG, EEG, EMG
Various Electrodes used for the measurement or recording of EMG signal.
Needle electrodes
Monopolar
Bipolar
Concentric core needle
Multi-element needle electrodes
Biochemical Electrodes
Reference electrode
pH electrodes
Blood Gas electrode

34. EMG Electrodes

35. Micro Electrodes

36. Metal micro-electrodes

37. Biochemical Electrodes
Biochemical Electrodes
Reference electrode
pH electrodes
Blood Gas electrode
pO2 Electrode
pCO2 Electrode

38. L7, L8: Nernst eq. & Skin contact impedance
Nernst equation
Skin contact impedance
Skin contact impedance measurement
Motion artifacts

39. Nernst Equation:
Dept. of Electronics and Telecommunication Engineering

40. SKIN CONTACT IMPEDANCE MEASUREMENT:
Dept. of Electronics and Telecommunication Engineering

41. :
Dept. of Electronics and Telecommunication Engineering