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Electrode theory- Basic electrode, Electrodes for ECG
Need, types of Bio-potential electrodes. Basic electrode theory Various Electrodes for ECG.
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ELECTRODE - ELECTROLYTE & ELECTROLYTE-TISSUE INTERFACE
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Electric equivalent circuits
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Electrode theory- Basic electrode,
Need & Types of Bio-potential electrodes Surface electrodes Deep seated electrode Factors to be consider while measurements: Careful and suitable selection of electrodes for satisfactory record of bioelectric signal. Comfortable for the patients to wear over long period They should not produce any moving artefacts Convenient in practical applications Good contact with skin (for low contact impedance)
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Cont.. The characteristics of a metalic/nonmetalic surface electrodes depends upon- Condition at metal-electrolyte interface Electrolyte –skin interface Quality of electrolytes Electrode properties Why electrode jelly is required while measurements of biopotential signals?
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Cont.. Electrode Potentials
All electrode potentials are measured wrt a ref. Electrodes Ref. Electrodes-Hydrogen electrode (H absorbed on platinum back -Calomel electrode Electrode potentials of few metal electrodes wrt Hydrogen Metal Ionic symbol Electrode Potential(Volt) Aluminium Al+++ -1.66 Iron Fe++ -0.44 Lead Pb++ -0.12 Hydrogen H+ -0.0 Copper C++ +0.34 Silver Ag+ +0.80 Platinum Pt+ +1.2 gold Au+ +1.69
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Cont.. potential between Electrode s in electrolyte Electode Metal
Potential difference between Electrode (mV) Stainless steel Saline 10 silver 9.4 Silver-silver chloride 2.5 (11mm disc) ECG paste 0.47 Silver-silver chloride (sponge) 0.2
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L6: Electrodes for ECG, EEG, EMG
Electrodes for EEG, Electrodes for EMG, Biochemical Electrodes
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Electrodes for ECG, EEG, EMG
Electrodes are used to pickup the biopotentials from the surface of the body of from inside the cells. Basic electrodes are classified as: Skin surface electrodes Needle electrodes Microelectrodes
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Body Surface Recording Electrodes
Electrode metal Electrolyte Metal Plate Electrodes (historic) Suction Electrodes (historic interest) Floating Electrodes Flexible Electrodes
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Commonly Used Biopotential Electrodes
Metal plate electrodes Large surface: Ancient, therefore still used, ECG Metal disk with stainless steel; platinum or gold coated EMG, EEG smaller diameters motion artifacts Disposable foam-pad: Cheap! (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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Commonly Used Biopotential Electrodes
Suction electrodes No straps or adhesives required precordial (chest) ECG can only be used for short periods Floating electrodes metal disk is recessed swimming in the electrolyte gel not in contact with the skin reduces motion artifact Suction Electrode
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Commonly Used Biopotential Electrodes
Metal disk Insulating package Double-sided Adhesive-tape ring Electrolyte gel in recess (a) (b) Reusable Snap coated with Ag-AgCl External snap Gel-coated sponge Disposable Plastic cup Plastic disk Tack Dead cellular material Foam pad Capillary loops Germinating layer (c) Floating Electrodes
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Commonly Used Biopotential Electrodes
Flexible electrodes Body contours are often irregular Regularly shaped rigid electrodes may not always work. Special case : infants Material : - Polymer or nylon with silver - Carbon filled silicon rubber (Mylar film) (a) Carbon-filled silicone rubber electrode. (b) Flexible thin-film neonatal electrode. (c) Cross-sectional view of the thin-film electrode in (b).
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Internal Electrodes Needle and wire electrodes for percutaneous measurement of biopotentials (a) Insulated needle electrode. (b) Coaxial needle electrode. (c) Bipolar coaxial electrode. (d) Fine-wire electrode connected to hypodermic needle, before being inserted. (e) Cross-sectional view of skin and muscle, showing coiled fine-wire electrode in place. The latest: BION – implanted electrode for muscle recording/stimulation Alfred E. Mann Foundation
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Fetal ECG Electrodes Electrodes for detecting fetal electrocardiogram 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.
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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
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Microelectrodes Why 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 Types Solid metal -> Tungsten microelectrodes Supported metal (metal contained within/outside glass needle) Glass micropipette -> with Ag-AgCl electrode metal Intracellular Extracellular
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Metal Microelectrodes
Microns! R Extracellular recording – typically in brain where you are interested in recording the firing of neurons (spikes). Use metal electrode+insulation -> goes to high impedance amplifier…negative capacitance amplifier!
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Metal Supported Microelectrodes
(a) Metal inside glass (b) Glass inside metal
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Glass Micropipette heat pull
Ag-AgCl wire+3M KCl has very low junction potential and hence very accurate for dc measurements (e.g. action potential) heat pull A glass micropipet electrode filled with an electrolytic solution (a) Section of fine-bore glass capillary. (b) Capillary narrowed through heating and stretching. (c) Final structure of glass-pipet microelectrode. Fill with intracellular fluid or 3M KCl Intracellular recording – typically for recording from cells, such as cardiac myocyte Need high impedance amplifier…negative capacitance amplifier!
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Electrical Properties of Microelectrodes
Metal Microelectrode Metal microelectrode with tip placed within cell Use metal electrode+insulation -> goes to high impedance amplifier…negative capacitance amplifier! Equivalent circuits
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Electrical Properties of Glass Intracellular Microelectrodes
Glass Micropipette Microelectrode
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Electrodes for ECG, EEG, EMG
Various Electrodes used for the measurement or recording of ECG signal. Immersion electodes(not used now) Limb electrodes Suction cup electrodes Floating electrodes Spray –on electrodes Pregelled disposable electrode Pasteless (dry) electrodes Air –jet ECG electrodes
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ECG Electrodes ECG plate electrode. The electrode is usually
Fastened to the arm or leg with a perforated Rubber strap which keeps it in position during ECG recording ECG Electrodes Light weight floating Electrode with press Stud for long term monitoring
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ECG Electrodes
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ECG Electrodes Disposable pre-gelled ECG Electrode.
A porous tape overlaying placed over the electrode resists perspiration and Ensures positive placement Under stress conditions ECG Electrodes Air –Jet ECG Electrodes
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ECG Electrodes Suction cup electrode (Unipolar chest ECG Electrode.)
Floating type skin surface ECG Electrodes 29
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Electrodes for ECG, EEG, EMG
Various Electrodes used for the measurement or recording of EEG signal. Scalp surface electrodes (chlorided silver discs) Ear-clip electrodes (reference electrode) Small needle electrodes Silver ball or pellet electrodes(exposed cortex, high resistance) Pad electrode(silver ball is belled out at the end and padded with a sponge) Chlorided silver wire in plastic cup electrodes
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EEG Electrodes EEG Electrode which can Be applied to the surface
Of the skin by an adhesive tape. EEG Electrodes Ear-clip Electrodes & EEG scalp surface Electrodes
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EEG Electrodes
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Electrodes for ECG, EEG, EMG
Various Electrodes used for the measurement or recording of EMG signal. Needle electrodes Monopolar Bipolar Concentric core needle Multi-element needle electrodes Biochemical Electrodes Reference electrode pH electrodes Blood Gas electrode
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EMG Electrodes
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Micro Electrodes
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Metal micro-electrodes
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Biochemical Electrodes
Biochemical Electrodes Reference electrode pH electrodes Blood Gas electrode pO2 Electrode pCO2 Electrode
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L7, L8: Nernst eq. & Skin contact impedance
Nernst equation Skin contact impedance Skin contact impedance measurement Motion artifacts
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Nernst Equation: Dept. of Electronics and Telecommunication Engineering
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SKIN CONTACT IMPEDANCE MEASUREMENT:
Dept. of Electronics and Telecommunication Engineering
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: Dept. of Electronics and Telecommunication Engineering
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