1 / 14

Biopotential electrodes

Delve into the fundamentals of biopotential electrodes, the interface problem, instrumentation, measurement, and analysis from 2011-2012. Learn how to sense a signal where no electron flow is passing the interface but metal cations are leaving into the electrolyte. Explore topics like electrode potentials, Nernst equation, overpotential, polarizable and nonpolarizable electrodes, chemical reactions, and equivalent circuits in electrode-electrolyte systems.

craft
Download Presentation

Biopotential electrodes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Biopotential electrodes A complex interface Basics of Instrumentation, Measurement and Analysis 2011, 2012

  2. the interface problem To sense a signala currentImust flow ! But no electron e- ispassing the interface!

  3. metal cation leaving into the electrolyte 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.

  4. metal cation joining the metal No current One cation M+out of the electrolyte becomes one neutral atom M taking off one free electron from the metal.

  5. metal: Li Al Fe Pb H Ag/AgCl Cu Ag Pt Au Vh / Volt -3,0negativ 00,223positiv1,68 half-cell voltage No current, 1M salt concentration, T = 25ºC

  6. Nernst equation For arbitrary concentration and temperature E = RT/(zF)·ln(c/K)E – electrode potential R = 8.314 J /(mol*K) – molar gas constantT – absolute temperature z – valence F = 96485 C/mol – Faraday’s constant c – concentration of metal ion in solution K – “metal solution pressure”, or tendency to dissolve

  7. electrode double layer No current

  8. concentration (change in double layer) ohmic (voltage drop) current influence • withcurrent flowing the half-cell voltage changes • this voltage change is calledoverpotential orpolarization: Vp = Vr + Vc + Va activation, depends on direction of reaction

  9. polarizable electrode • “perfectly” polarizable electrode:- only displacement current, electrode behave like a capacitor • example: noble metals like platinum Pt

  10. nonpolarizable electrode • “perfectly” nonpolarizable electrode:- current passes freely across interface,- no overpotential • examples: - silver/silver chloride (Ag/AgCl),- mercury/mercurous chloride (Hg/Hg2Cl2) (calomel)

  11. chemical reactions silver / silver chloride

  12. electrical behaviour equivalent circuit

  13. equivalent circuit electrode-electrolyte

  14. more precise approximation of double layer – Randles circuit electrode-electrolyte Rct – active charge transfer resistance W – Warburg element reflecting diffusionwith impedance ZW=AW/(jω)0.5 AW – Warburg coefficient

More Related