Biopotential ElectrodesBiopotential ElectrodesIIIIII

ElectrodesElectrodes

Recording Stimulating

Recording Recording ElectrodesElectrodes

Surface Inserted Microelectrodes

Array Electrodes

• Metal Plate

•Suction

•Floating

•Flexible

•Needle

•Wire

•Solid metal

•Supported metal

•Glass micropipette

Surface: Metal Plate ElectrodesSurface: Metal Plate Electrodes

(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

Surface: Suction Electrodes

• No straps or adhesives

• Precordial (chest) ECG

• Can only be used for short periods

Surface: Floating ElectrodeSurface: Floating Electrode

Surface: Flexible ElectrodesSurface: Flexible Electrodes

Body contours are often irregular Material : (a) Polymer or nylon with silver (b) Carbon filled silicon rubber (Mylar film) (c) Cross-sectional view of the thin-film electrode in (b).

Inserted (Internal) Inserted (Internal) ElectrodesElectrodes

(a) Insulated needle, (b)Coaxial needle, (c) Bipolar coaxial, (d) Fine-wire electrode connected to hypodermic needle, before insertion,

Fetal ECG ElectrodesFetal ECG Electrodes

MicroelectrodesMicroelectrodes

Measure potential difference across cell Measure potential difference across cell membranemembrane

RequirementsRequirements– Small enough to be placed into cellSmall enough to be placed into cell– Strong enough to penetrate cell Strong enough to penetrate cell

membranemembrane– Typical tip diameter: 0.05 – 10 micronsTypical tip diameter: 0.05 – 10 microns

Metal MicroelectrodeMetal Microelectrode

Metal Supported Metal Supported MicroelectrodesMicroelectrodes

(a) Metal inside glass (b) Glass inside metal

Glass MicropipetteGlass Micropipette

Heat and pull

Electrode ArraysElectrode Arrays

Examples of microfabricated electrode arrays. (a) One-dimensional plunge electrode array, (b) Two-dimensional array, and (c) Three-dimensional array

Stimulating ElectrodesStimulating Electrodes

– Net current across electrode-electrolyte interface is not zero– The body/electrode has a highly nonlinear response to stimulation– Large currents can cause – Chemical reaction – Cavitation – Cell damage – HeatingApplications of stimulating electrodes1. Pacing2. Ablation3. Defibrillation

Features

Platinum electrodes:Applications: neural stimulation

Steel electrodes for pacemakers and defibrillators

Practical HintsPractical Hints

Electrode and lead wire (exposed to the Electrode and lead wire (exposed to the electrolyte) must be of the same material.electrolyte) must be of the same material.

Use two similar electrodes when Use two similar electrodes when measuring differentials.measuring differentials.

Lead electrode interface failure.Lead electrode interface failure. Electrode insulation material.Electrode insulation material. Input impedance of AmplifierInput impedance of Amplifier..