3Recording Electrodes Surface Inserted Solid metal Supported metal Array ElectrodesMicroelectrodesSolid metalSupported metalGlass micropipetteMetal PlateSuctionFloatingFlexibleNeedleWire
4Surface: 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
5Surface: Suction Electrodes No straps or adhesivesPrecordial (chest) ECGCan only be used for short periods
6Surface: Floating Electrode Double-sidedAdhesive-taperingInsulatingpackageMetal diskElectrolyte gelin recess(a)(b)
7Surface: Flexible Electrodes Body contours are often irregularMaterial :(a) Polymer or nylon with silver(b) Carbon filled silicon rubber(Mylar film)(c) Cross-sectional view of the thin-film electrode in (b).
8Inserted (Internal) Electrodes Insulated needle, (b)Coaxial needle, (c) Bipolar coaxial, (d) Fine-wire electrode connected to hypodermic needle, before insertion,
9Fetal ECG ElectrodesElectrodes 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.
10Microelectrodes Measure potential difference across cell membrane RequirementsSmall enough to be placed into cellStrong enough to penetrate cell membraneTypical tip diameter: 0.05 – 10 microns
17Stimulating Electrodes Features– Net current across electrode-electrolyte interface is not zero– The body/electrode has a highly nonlinear response tostimulation– Large currents can cause– Chemical reaction– Cavitation– Cell damage– HeatingPlatinum electrodes:Applications: neural stimulationSteel electrodes for pacemakers and defibrillatorsApplications of stimulating electrodesPacingAblationDefibrillation
18Practical HintsElectrode 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.