ECE_3820_lecture_12_2011

ECE_3820_lecture_12_2011 - Biopotential Electrodes(1)...

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Biopotential Electrodes(1) ECE3820: Principles and Practice of Biomedical Engineering Presented by: Huda Asfour
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Outline • Function of Biopotential Electrodes • Electrode-Electrolyte interface • Electrode Potential • Polarizable vs. Non-Polarizable Electrodes • Electrode Equivalent Circuit • Electrode skin interface • Motion Artifacts
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Functions of Biopotential Electrodes • Interface between body and electronic measuring apparatus. (Electrochemistry) Transducing function: Current in body: Ionic Current in wire: electronic How is the current that flows in the body different than the current flowing in the building wires?
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Electrode-Tissue Interface Tissue Electrolyte-Skin interface Electrolyte Metal-Electrolyte Interface To instrument [Khandpur] Characteristics of surface electrode composed of metal and attached to the body through an electrolyte depend on: •Metal-Electrolyte interface •Electrolyte-Skin interface •Composition of Electrolyte
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Oxidation the loss of electrons by a molecule, atom or ion Reduction the gain of electrons by a molecule, atom or ion red ox A e A Electrode-Electrolyte interface
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http://www.reuk.co.uk/Lemon-Battery.htm Lemon battery Lemon battery is an example of Galvanic cell
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Galvanic Cell Anode Cathode Salt bridge Zn Cu+ 2 ZnS CuS NaCl
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YouTube link: http://youtu.be/A0VUsoeT9aM The galvanic cell
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Electrolytic Cell Anode Cathode Electrolyte
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Silver/Silver chloride Electrode Redox reactions (Reduction/Oxidation Reactions) 1)Ag Ag + +e - 2)Ag + + Cl - AgCl Oxidation reactions dominate Reduction reactions dominate Cell Half Cell
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Electrode-Electrolyte interface C + : Cations A - : Anions e - :electrons Assume electrode is made up of the same material as the cations. Oxidation reactions dominate Half Cell
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Electrode-Electrolyte interface No free electrons in the electrolyte No free cations or anions in the electrode How does current cross the interface? C + : Cations A - : Anions e - :electrons Redox reactions (Reduction/Oxidation Reactions) C C n+ +ne - A m- A + me- n: Valence of C m: Valence of A Assume electrode is made up of the same material as the cations.
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Electrode-Electrolyte interface Rate of oxidation = Rate of reduction => NET CURRENT=0 C + : Cations A - : Anions e - :electrons Redox reactions (Reduction/Oxidation Reactions) C C n+ +ne - A m- A + me- n: Valence of C m: Valence of A Assume electrode is made up of the same material as the cations.
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Electrolyte - - - - - - + + + + + + + + + + + + - - - + + + Electrode material oxidizes Cation moves into Electrolyte i Oxidation reactions dominate C C + e - C C n+ +ne - E hc Half Cell potential of Electrode free of charge concentration gradient normal concentration
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This note was uploaded on 11/14/2011 for the course ECE 3820 taught by Professor Wang during the Fall '11 term at GWU.

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ECE_3820_lecture_12_2011 - Biopotential Electrodes(1)...

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