1 / 18

Biopotential electrodes

Biopotential electrodes. A complex interface. Summer School Timisoara 2002 R. Hinz. the interface problem . To sense a signal a current I must flow !. But no electron e - is passing the interface!. metal cation. leaving into the electrolyte. No current.

crescent
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 Summer School Timisoara 2002R. Hinz

  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

  6. electrode double layer No current

  7. 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

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

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

  10. chemical reactions silver / silver chloride

  11. electrical behaviour equivalent circuit

  12. equivalent circuit electrode-electrolyte

  13. again el. behaviour the skin: an additional interface!

  14. total equivalent circuit simplified

  15. results • high impedance ZE:... • changing half-cell voltage Vh*:...

  16. high impedance • interference with main power-lines (!!) • potential devider with Rinput • frequency dependant. c

  17. changing half-cell voltage • influenced by local concentration • saturation of amplifier • motion artefacts by changing the the gel-skin potential (Vep). simulation:

  18. body-surface electrode half-cell voltage drift simulated

More Related