The brilliant scientist and inventor of the 19th century, Michael Faraday, is known for his active work with electricity, the electromagnetic field and related physical phenomena. One of the most significant discoveries was a protective structure called the Faraday cage. Below we will understand what it is and what practical value the invention represents.
Content
What is a Faraday Cage
A Faraday cage is a box with walls made of a highly conductive metal. The design does not require an external power connection, but, as a rule, is grounded. The physical effect of the cell is manifested under the influence of an external factor, which is electromagnetic radiation.
The first constructs to demonstrate the shielding effect looked like an ordinary cell, which gave the name to this phenomenon.In fact, the wire or perforated walls of the "box" are convenient for visual control of objects or devices located inside a confined space, but they can be easily replaced with solid ones. The main thing is that the material is conductive.
Operating principle
The action of the Faraday cage is based on the fact that the charge, when it enters the conductor, is distributed on its surface, while the inside remains neutral. In fact, the entire cell, consisting of a conductive material, is a single conductor, the "ends" of which acquire the opposite charge. The resulting electric current creates a field that compensates for external influences. The electric field strength in the inner part of such a structure is zero.
Interestingly, if the field is generated inside the cell, then the effect also works. However, in this scenario, the charge will be distributed over the inner surface of the grid or other conductive plane and will not be able to penetrate outside.
In English terminology, CF sounds like “Faraday shield”, that is, “Faraday shield / screen”. This concept well conveys the essence of the device, which, like a shield or a protective screen, reflects the rays that affect its contents.
It should be remembered that the shielding effect only works on an alternating magnetic field. It does not interfere with a constant or slightly variable magnetic effect, for example, the natural magnetic potential of the Earth.
To determine whether the Faraday chamber will reflect high-frequency radiation, it is enough to know the size of the grid cells (if the conductive part is made in the form of a cage) and the wavelength of the acting wave.The construction is effective if the second value is greater than the first.
Spheres of application of the CF effect
The effect discovered by Faraday has not only scientific meaning, but also a fairly wide practical application. The simplest example of a Faraday cage can be found in everyday life, it is present in almost any kitchen - this is a microwave oven. Five walls of its body are made of fairly thick steel plates, and between the two layers of door glass there is a metal layer with perforations for better visibility.
RF cabin
A radio-frequency cabin is a room isolated from the effects of electrical, magnetic and radio emission, usually of a small area. Its walls, floor and ceiling are equipped with highly conductive gratings that form a closed but invisible cage.
MRI rooms
High-precision equipment such as a medical tomograph for magnetic resonance diagnostics requires careful protection from external electromagnetic waves. The slightest outside influence can affect the result of the study, so the room in which the MRI unit is located is completely shielded.
Laboratories
In laboratory research, in order to obtain accurate results, it is important not only to use advanced equipment, but also to reliably protect it from external factors such as magnetic and electric fields.
It should be understood that this refers not only to directional radiation from specific sources, but also to electromagnetic noise that is constantly present in the atmosphere, especially in populated areas and in their vicinity.
For high-quality shielding of equipment with the CF effect, specialized design calculations and professional installation are required.
Protective Suits
For people working in areas with a high probability of electric shock, special suits have been developed. Their upper layer is made of metal-containing fabric and is separated from the body by an insulating material. In the event of residual static or electric current, the charge flows down the outer shell of the kit.
Protective clothing is indispensable when working with high-voltage lines. Even de-energized, they retain a dangerous level of static charge due to many kilometers of electrical wires.
In the world of entertainment
The CF effect, colorfully displayed on the stage, is very spectacular. In this case, not a simple cage is often used, but a seemingly weightless shell made of coarse mesh, or even a specially designed suit that resembles ordinary clothes. In this case, the current is supplied as effectively as possible, for example, using Tesla coils or similar devices that create a charge from an electrostatic generator.
Making a Faraday cage with your own hands
In everyday life, the manufacture of a home-made CF may be necessary to “hide” gadgets from the action of various waves that can cause disturbances in sensitive electronic “stuffing”.
An example of such a design is a plywood box finished in a certain way. Since plywood acts as an insulating layer, it must be perfectly clean and dry. You can assemble the box with your own hands or take it ready - the main thing is that it be assembled without the use of nails or other metal fasteners. Assembly is carried out in several stages:
- Food foil is divided into segments, according to the size of the plywood walls or their blanks.
- The surfaces of the future box are trimmed with foil from the outside. In this case, its shiny side should be turned outward.
- The walls are fastened from the inside with adhesive tape, and a pair of mouse pads is placed on the bottom of the box.
- It is carefully checked that in the closed position of the lid, the foil layer forms a continuous shell, without the slightest gaps and breaks.
The second option assumes that a do-it-yourself metal tank (pan, box, box, etc.) serves as the basis of the Faraday cage, inside which insulation is made of cardboard, the same plywood or other material. The condition of a snug fit of the lid for this design is no less important than for the one described above.
Do I need to do grounding
There is no consensus on the need for grounding the CF. It is mandatory to ground large structures and those that can be affected by a particularly powerful electric discharge.
Grounding, of course, protects against emergency situations when the accumulated strong charge can “break through” the air and hit a nearby object or person.
Testing a Homemade Faraday Cage
To test the principle of the Faraday cage in practice, it is most convenient to use a compact battery-powered radio. It should be turned on at maximum volume and tuned to the most powerful FM channel available. If the cell is working, the radio in it will be silenced.
If the receiver is at least a little, but audible, it means that one hundred percent screening could not be achieved, and gaps in the conductive layer should be looked for.
Suitable for testing self-assembled camera and mobile phone. Once inside, it will stop receiving signals from base stations, that is, when you call it, you will hear the corresponding message from the automatic informant of the mobile operator.
Similar articles:
