Biopotential Electrodes. Introduction Electrical Contact point Electrical Contact point Transducer...
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Biopotential Biopotential Electrodes Electrodes
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Transcript of Biopotential Electrodes. Introduction Electrical Contact point Electrical Contact point Transducer...
Biopotential Biopotential ElectrodesElectrodes
IntroductionIntroduction
Electrical Contact pointElectrical Contact point Transducer Transducer Biopotential electrodesBiopotential electrodes
– Metal (Al, Cu, Fe, Ag,…..)Metal (Al, Cu, Fe, Ag,…..)– Non-metalNon-metal
metal electrolyte
M+
A-
e -I
Metal Electrolyte Metal Electrolyte InterfaceInterface
To sense a signala current II must flow !
metal electrolyte
M+
A-
e -I
The Interface ProblemThe Interface Problem
To sense a signala current II must flow !
But no electron e- ispassing the interface!?
Metal CationMetal Cation
No current
What’s going on?
leaving into the electrolyte
Metal Cation: Metal Cation: leaving into the leaving into the electrolyteelectrolyte
No current
One atom M out of the metal is oxidized to form one cation M+
and giving off one free electron e- to the metal.
Metal cation: Metal cation: joining the joining the metalmetal
What’s going on?
No current
Metal Cation: Metal Cation: joining joining the metalthe metal
One cation M+ out of the electrolyte becomes one neutral atom M taking off one free electron from the metal.
No current
Half-cell VoltageHalf-cell Voltage
No current
Half-cell VoltageHalf-cell VoltageNo current
metal: Li Al Fe Pb H Ag/AgCl Cu Ag Pt Au
Vh / Volt -3.0 negativ 0 0.223 positiv 1.68
Electrode Double Electrode Double LayerLayer
No current
? ? ?
Electrode Double Electrode Double LayerLayer
No current
? ?
Electrode Double Electrode Double LayerLayer
No current
?
Electrode Double Electrode Double LayerLayer
No current
Oxidation or reduction reactions at the electrode-electrolyte interface lead to a double-charge layer
Contact (Half Cell) Contact (Half Cell) PotentialPotential
•Depends on: • The metal, • Concentration of ions in solution and • Temperature.
• Half cell potential cannot be measured without a second electrode.
•The half cell potential of the standard hydrogen electrode has been arbitrarily set to zero.
Measuring Half Cell Measuring Half Cell PotentialPotential
Note: Electrode material is metal + salt or polymer selective membrane
Half Cell Potential (VHalf Cell Potential (Vhh))
Iron Iron -440 mV -440 mV LeadLead -126 mV-126 mV CopperCopper +337 mV+337 mV Platinum Platinum +1190 mV+1190 mV Compare to electrophysiological Compare to electrophysiological
Signals ???Signals ??? Two Similar electrodes ??? (Ag/Agcl Two Similar electrodes ??? (Ag/Agcl
5 mV and steel 5 mV and steel 100mV)100mV)
Ag/AgCl ElectrodeAg/AgCl Electrode
Fabrication of Ag/AgCl electrodes
1. Electrolytic deposition of AgCl
2. Sintered AgCl: process forming pellet electrodes
Electrolysis ProcessElectrolysis Process
eAgAg
AgClClAg
