They are special electrodes for the transmission of electrical potentials that represent the vital signal. Electrodes vary in terms of their shape, metal quality and dimensions, and the electrical signals to be transmitted to the body are linked and through which vital efforts are quoted from cells, nerves and muscles.
The human body consists of liquid cells containing ions of potassium, sodium and chloride, and as a result of differences in ion concentration, the action potential - it is captured by electrodes When the metal electrode touches a specific electrolytic solution, a simultaneous chemical reaction occurs between the solution and the surface, and the positive and negative ions move on the interface between the metal and the electrolytic solution in opposite directions to form two polar opposite ionic layers called the inter-latency difference.
What are the types of electrodes:
- Biological Electrodes:
They are electrodes that convert biological and physiological phenomena into electric currents or conversely generate a chemical and physiological biological phenomenon from electric currents.
As an example of the first section of the definition, we think about electrodes, ECG. EOG. EEG. EMG As an example of the second section of the definition, we mention the stimulation electrodes used in pacemakers and muscular stimulation.
They are electrodes that convert the ionic density of some dissolved gases in a liquid such as blood into electrical signals, for example electrodes used to measure PH, PO2, PCO2.
The following figure shows the surface between electrode and electrolyte The transient current in the common surface from electrode to electrolyte contains:
- The electron moves in the opposite direction to the direction of current in the electrode.
- A positive C+ ion moves in the same direction as the current in the electrolyte solution.
- Ion A- moves in the opposite direction to the direction of the current in the electrolyte solution.
The current crosses from left to right, the electrode contains metal atoms C, and the electrolyte solution contains positive electrolytes C+ and negative electrolytes A-.
Polarized and non-polarized electrodes:
This classification is based on what happens when the separation between the electrode and the skin is applied:
1. Fully polarized electrodes:
No actual charge is crossed between the boundary between the electrode and the electrolyte and the only current is the displacement current and the electrode and electrolyte act as a condensed suppository on which only changes in the number of charges occur.
2. The electrodes are completely non-polarized:
In this case, the charges pass freely between the electrode and the electrolyte without the need for this transit.
Ideal electrodes, polarized or non-polarized, cannot be manufactured, but electrodes with characteristics approaching one of the two types can be manufactured.
Platinum electrodes are similar to polarized electrodes because they are originally relatively inert and it is difficult for them to oxidize or decompose the current between the electrode and the electrolyte changes the concentration of atoms on the hyphen.
AG-CL electrodes are commonly used electrodes because their performance is similar in characteristics to those of non-polarized electrodes. This electrode contains AG metal with a low-soluble ionic layer compounded of AG metal and negative ion CL- The total composition is immersed in an electrolyte solution containing negative ions CL- The presence of a low-ionic layer AG-CL of low solubility makes these electrodes relatively stable and with very low noise, making them suitable for biomedical applications.
These electrodes have many types that can be divided into four types:
- Cutaneous surface electrodes.
- spherical electrodes.
- Needle electrodes.
- Electrodes used for electrical stimulation of tissues.
1. Cutaneous surface electrodes.
Since these electrodes are applied to the skin in order to measure or record biological signals from the body, the electrolytic form representing the common surface between the electrode and the electrolyte solution must be developed to include the electrodermal layer of the electrode - electrolyte solution and the skin where the first section described as electrode - electrolyte solution The second section of the shape resulting from the presence of the skin and consists of ESE, which is the latency arising through the half membrane We win for the outer layer of the skin resulting from the difference in ionic concentration We have found that the outer dermal layer Electrical impedance behaves as a branching resistance and the inner dermis layer behaves as a morphological resistance.
- Absorbent electrodes:
These electrodes are used with the electrocardiogram, which is a hollow metal cylinder in contact with the skin from its base and has a connecting tip from both ends and a rubber pipette worn to the other base that is attached to the skin by discharging air on the surface of the skin by rubber pipette.
- Float electrodes:
- The first type of hat:
In it, the electrode element is sunken through a cavity so that it is not in direct contact with the skin, but the contact is made through an electrolytic paste that surrounds it and fills the cavity, and so the cavity does not move in relation to the metal disc, and this in turn does not allow the scattering of the double layer of charges, this electrode is fixed by a double-sided adhesive tape
- The second type is the same sheet metal electrode:
Designed to avoid movement noise, especially to monitor premature babies, as it can be formed as we want, which relieves irritation when repeated removal and pasting, and consists of:
- flexible electrodes:
- Silicone rubber electrode stuffed with carbon.
- Thin and flexible embryonic electrode.
- Needle electrodes:
It is used to reduce the impedance of the joint surface and thus the product of movement by penetrating the outer skin layer.
Some of these electrodes contain a very thin metal wire of copper or platinum whose head is in contact with the place where the measurement is to be made, these wires are placed in the appropriate place, either by surgical procedure or by subcutaneous needles, the electrode is left in place when pulling.
The electrode is usually insulated with varnish except for the head area and at a distance of several millimeters from the nozzle.