Recording Electrodes SurfaceInserted Microelectrodes Array Electrodes Metal Plate Suction Floating Flexible Needle Wire Solid metal Supported metal Glass micropipette
Surface: Metal Plate Electrodes (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
Surface: Suction Electrodes No straps or adhesives Precordial (chest) ECG Can only be used for short periods
Double-sided Adhesive-tape ring Insulating package Metal disk Electrolyte gel in recess (a)(b) Surface: Floating Electrode
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).
Inserted (Internal) Electrodes (a)Insulated needle, (b)Coaxial needle, (c) Bipolar coaxial, (d) Fine-wire electrode connected to hypodermic needle, before insertion,
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.
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
Electrical Properties of Microelectrodes Metal Microelectrode
Electrical Properties of Glass Intracellular Microelectrodes Glass Micropipette Microelectrode
Electrode Arrays Examples of microfabricated electrode arrays. (a) One-dimensional plunge electrode array, (b) Two-dimensional array, and (c) Three-dimensional array Ag/AgCl electrodes Base Insulated leads (a) Contacts (c) Tines Base Exposed tip
Stimulating Electrodes – 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 Applications of stimulating electrodes 1.Pacing 2.Ablation 3.Defibrillation Features Platinum electrodes: Applications: neural stimulation Steel electrodes for pacemakers and defibrillators
Practical Hints Electrode and lead wire (exposed to the electrolyte) must be of the same material. Electrode and lead wire (exposed to the electrolyte) must be of the same material. Use two similar electrodes when measuring differentials. Use two similar electrodes when measuring differentials. Lead electrode interface failure. Lead electrode interface failure. Electrode insulation material. Electrode insulation material. Input impedance of Amplifier. Input impedance of Amplifier.