1. Biopotential Electrodes III

2. Electrodes
Recording
Stimulating

3. Recording Electrodes Surface Inserted Solid metal Supported metal
Array Electrodes
Microelectrodes
Solid metal
Supported metal
Glass micropipette
Metal Plate
Suction
Floating
Flexible
Needle
Wire

4. Surface: Metal Plate Electrodes
Metal-plate electrode used for application to limbs.
Metal-disk electrode applied with surgical tape.
)Disposable foam-pad electrodes, often used with ECG

5. Surface: Suction Electrodes
No straps or adhesives
Precordial (chest) ECG
Can only be used for short periods

6. Surface: Floating Electrode
Double-sided
Adhesive-tape
ring
Insulating
package
Metal disk
Electrolyte gel
in recess
(a)
(b)

7. Surface: Flexible Electrodes
Body contours are often irregular
Material :
(a) Polymer or nylon with silver
(b) Carbon filled silicon rubber
(Mylar film)
(c) Cross-sectional view of the thin-film electrode in (b).

8. Inserted (Internal) Electrodes
Insulated needle, (b)Coaxial needle, (c) Bipolar coaxial, (d) Fine-wire electrode connected to hypodermic needle, before insertion,

9. Fetal ECG Electrodes
Electrodes for detecting fetal ECG 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.

10. Microelectrodes 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

11. Metal Microelectrode

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

13. Glass Micropipette
Heat and pull

14. Electrical Properties of Microelectrodes
Metal Microelectrode

15. Electrical Properties of Glass Intracellular Microelectrodes
Glass Micropipette Microelectrode

16. 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

17. Stimulating Electrodes
Features
– Net current across electrode-electrolyte interface is not zero
– The body/electrode has a highly nonlinear response to
stimulation
– Large currents can cause
– Chemical reaction
– Cavitation
– Cell damage
– Heating
Platinum electrodes:
Applications: neural stimulation
Steel electrodes for pacemakers and defibrillators
Applications of stimulating electrodes
Pacing
Ablation
Defibrillation

18. Practical Hints
Electrode and lead wire (exposed to the electrolyte) must be of the same material.
Use two similar electrodes when measuring differentials.
Lead electrode interface failure.
Electrode insulation material.
Input impedance of Amplifier.