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Biopotential Electrodes III

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Presentation on theme: "Biopotential Electrodes III"— Presentation transcript:

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.

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