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Biopotential ElectrodesBiopotential ElectrodesIIIIII
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ElectrodesElectrodes
Recording Stimulating
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Recording Recording ElectrodesElectrodes
Surface Inserted Microelectrodes
Array Electrodes
• Metal Plate
•Suction
•Floating
•Flexible
•Needle
•Wire
•Solid metal
•Supported metal
•Glass micropipette
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Surface: Metal Plate ElectrodesSurface: 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
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Surface: Suction Electrodes
• No straps or adhesives
• Precordial (chest) ECG
• Can only be used for short periods
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Surface: Floating ElectrodeSurface: Floating Electrode
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Surface: Flexible ElectrodesSurface: 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).
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Inserted (Internal) Inserted (Internal) ElectrodesElectrodes
(a) Insulated needle, (b)Coaxial needle, (c) Bipolar coaxial, (d) Fine-wire electrode connected to hypodermic needle, before insertion,
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Fetal ECG ElectrodesFetal ECG Electrodes
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MicroelectrodesMicroelectrodes
Measure potential difference across cell Measure potential difference across cell membranemembrane
RequirementsRequirements– Small enough to be placed into cellSmall enough to be placed into cell– Strong enough to penetrate cell Strong enough to penetrate cell
membranemembrane– Typical tip diameter: 0.05 – 10 micronsTypical tip diameter: 0.05 – 10 microns
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Metal MicroelectrodeMetal Microelectrode
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Metal Supported Metal Supported MicroelectrodesMicroelectrodes
(a) Metal inside glass (b) Glass inside metal
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Glass MicropipetteGlass Micropipette
Heat and pull
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Electrode ArraysElectrode Arrays
Examples of microfabricated electrode arrays. (a) One-dimensional plunge electrode array, (b) Two-dimensional array, and (c) Three-dimensional array
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Stimulating ElectrodesStimulating 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 – HeatingApplications of stimulating electrodes1. Pacing2. Ablation3. Defibrillation
Features
Platinum electrodes:Applications: neural stimulation
Steel electrodes for pacemakers and defibrillators
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Practical HintsPractical Hints
Electrode and lead wire (exposed to the Electrode and lead wire (exposed to the electrolyte) must be of the same material.electrolyte) must be of the same material.
Use two similar electrodes when Use two similar electrodes when measuring differentials.measuring differentials.
Lead electrode interface failure.Lead electrode interface failure. Electrode insulation material.Electrode insulation material. Input impedance of AmplifierInput impedance of Amplifier..