Biomedical Instrumentation Lab Lab Experiments

Study of Different types of Electrodes Lab Experiment

Nov 24 2023

Aim

To study the different types of electrodes.

Theory:

Biopotential electrodes is a transducer that convert the body ionic current in the body into the traditional electronic current flowing in the electrode. Biopotential electrode should be able to conduct small current across the interface between the body and the electronic measuring circuit. We will get to know Electrical characteristics of biopotential electrodes, Different type of biopotential electrodes, Electrodes used for ECG, EEG, EMG, and intracellular electrodes.

Microelectrodes: Electrodes use to measure bioelectric potential near or within a single cell .
Skin surface electrodes: Electrodes used to measure ECG , EMG , EEG potential from the surface of the skin.
Needle electrodes: Electrodes are used to penetrate the skin to record EEG potential from a local region of the brain or EMG potential from gray.

Micro electrodes:

There are electrodes with tip sufficiently small to penetrate a single cell in order to obtain reading from the cell . They have tip diameters ranging from approx 0.05 to10 microns. They can be formed from solid metal needles.

Types of Microelectrodes:

Metal microelectrodes:

They are formed by electrolytic ethching the tip of a fine tungsten or stainless steel wire with a desired size then the wire is coated at most to the tip with an insulating material.

Micropipette microelectrode: This type is a glass with tip drawn out to desired size it is fitted with an electrolyte compatible with cellular fluids . It has dual interface.

Metal wire in contact with electrolyte solution inside micropipette.
Electrode inside the pipette and fluids inside or immediately outside the cell.

Body surface electrodes:

Electrodes used to obtain bioelectric potential from the surface of the body are called as body surface electrodes.

Types of body surface electrodes:

I. Metal plate electrodes: It consist of a flat metal plate that has bent into a cylindrical segment. A terminal is placed on its outside surface near 1 end. This terminal is attached to the lead wire to the EEG.

II. Metal disk electrode: This electrode which has a lead wire welded to the back surface made up of several different material. It is coated with electrolyte gel and then passed against patients chest wall.

III. Disposable foam pad electrode: It consist of relatively large disk of plastic foam material with a silver disk on one side attached to the silver plated snap similar to that of lead wire with female portion is then snapped on electrode.

IV. Suction cup electrode: This electrodes are frequently used in ECG at pre-cardiac levels because they can be placed at particular location and used to take a recording that consist of a hollow metallic cylindrical electrode that makes contact with skin at its base. In appropriate technical form the lead wire is attached to metal cylinder and rubber suction bulb it fits over its oyher base. Electrolyte gel is placed over the contacting surface of electrodes.

Floating electrode: The principle feature of this electrode is that the actual electrode element is released in cavity so that it does not come in contact with skin itself. Instead the element is surrounded by electrolyte gel in cavity.

Insulated needle electrode:

The basic needle electrode consist of solid needle usually made up of stainless steel with a sharp point insulated with a coating such as insulating varnish and its tip is exposed.

Types of needle electrodes:

I. Co-axial needle electrode: It consist of a small gauge hypodermic needle that is modified by running an insulated fine wire down the centre of its lumen and filling remainder of its lumen with an electrode material.

II. Bipolar co-axial electrode: The two wires are placed within lumen of an needle can be connected differentially so as to be sensitive to electrical activity only in immediate vicinity of the electrode tip.