ECE_3820_lecture_13_2011

ECE_3820_lecture_13_2011 - Biopotential Electrodes(2)...

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Unformatted text preview: Biopotential Electrodes(2) ECE3820: Principles and Practice of Biomedical Engineering Presented by: Huda Asfour • Reference Electrodes • Recording Electrodes • Stimulating Electrodes Usage of electrodes When choosing a reference electrode, think of: – Reproducibility – Stability – Small temperature sensitivity Reference Electrode : an electrode that has a stable and well known electrode potential When using the overpotential equation, we need to make sure that the potential that we measure is only due to the electrochemical reaction One of the ways to accomplish that is by using reference electrodes Overpotential: The difference between the observed half-potential and the standard half potential THINK OF REFERENCE ELECTRODES AS YOUR GROUND! Generally the reference electrode should be chosen that is reversible to one of the ions in solution. However, this is difficult to accomplish all the time The practical approach is to choose a reference electrode that is standard built for some electrolyte conditions Typical reference electrodes – Hydrogen electrode – Calomel electrode (SCE) – Mercury-Mercuric oxide electrode – Mercury-mercurous sulfate electrode – Silver-Silver Chloride electrode Types of Reference Electrodes Recording Electrodes Medical Devices And Systems By Joseph D. Bronzino ECG basics • Amplitude: 1-5 mV • Bandwidth: 0.05-100 Hz • Largest measurement error sources: – Motion artifacts – 50/60 Hz powerline interference • Typical applications: – Diagnosis of ischemia – Arrhythmia – Conduction defects Electrodes for ECG • Limb Electrodes • Floating Electrodes • Pregelled disposable Electrodes • Pasteless Electrodes Limb Electrodes • Shape: – Rectangular or circular • Size: 3x5cm • Material: – German silver, nickle silver or nickle plated steel. • Impedance: 2-5kΩ @10Hz • Used in Surgery • Not suitable for long term recording (long flowing leads are in convenient) • Interference from limb muscles Body-Surface Biopotential Electrodes Figure 5.9- Body-surface biopotential 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 electrocardiographic monitoring apparatus. Metallic Suction Electrode Commonly Used to record the unipolar chest leads. High contact impedance Easily attached to fleshy parts of the body Pregelled Disposable Eelctrodes Helps reducing artefacts and drifts Diameter: 0.5-1.5 cm Electroplated with silver up to the thickness of 10um Surface of Ag layer is partially converted to AgCl Advantages: No risk of infection Smaller size Less time per ECG procedure Electrodes for Detecting Fetal Electrocardiogram Figure 5.14 Electrodes for detecting fetal electrocardiogram during labor, by means of intracutaneous needles. (a) Suction electrode. (b) Cross- sectional view of suction electrode in place, showing penetration of probe through epidermis. (c) Helical electrode, which is attached to fetal skin by corkscrew-type action. corkscrew-type action....
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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_13_2011 - Biopotential Electrodes(2)...

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