Electromagnetic shielding, and check out Electromagnetic shielding on Wikipedia, Youtube, Google News, Google Books, and Twitter on Digplanet. Electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. The shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields.
Typical materials used for electromagnetic shielding include sheet metal, metal screen, and metal foam. Another commonly used shielding method, especially with electronic goods housed in plastic enclosures, is to coat the inside of the enclosure with a metallic ink or similar material. One example is a shielded cable, which has electromagnetic shielding in the form of a wire mesh surrounding an inner core conductor. RF shielding is also used to protect medical and laboratory equipment to provide protection against interfering signals, including AM, FM, TV, emergency services, dispatch, pagers, ESMR, cellular, and PCS. Similarly, varying magnetic fields generate eddy currents that act to cancel the applied magnetic field. In the case of high-frequency electromagnetic radiation, the above-mentioned adjustments take a non-negligible amount of time, yet any such radiation energy, as far as it is not reflected, is absorbed by the skin (unless it is extremely thin), so in this case there is no electromagnetic field inside either. Suppose that we have a spherical shell of a (linear and isotropic) diamagnetic material with permeability , with inner radius and outer radius . This coefficient describes the effectiveness of this material in shielding the external magnetic field from the cavity that it surrounds. Your use of this website constitutes acknowledgement and acceptance of our Terms & Conditions. We’ve built an international reputation on trust and integrity with some of the largest and most prestigious companies and institutions around the world.
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Shielding is typically applied to enclosures to isolate electrical devices from the 'outside world', and to cables to isolate wires from the environment through which the cable runs.


Any holes in the shield or mesh must be significantly smaller than the wavelength of the radiation that is being kept out, or the enclosure will not effectively approximate an unbroken conducting surface. The ink consists of a carrier material loaded with a suitable metal, typically copper or nickel, in the form of very small particulates. Copper is used for radio frequency (RF) shielding because it absorbs radio and magnetic waves. The shielding impedes the escape of any signal from the core conductor, and also prevents signals from being added to the core conductor.
From the perspective of microwaves (with wavelengths of 12 cm) this screen finishes a Faraday cage formed by the oven's metal housing. One is that, due to the electrical resistance of the conductor, the excited field does not completely cancel the incident field.
For static or slowly varying magnetic fields (below about 100 kHz) the Faraday shielding described above is ineffective. Electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as RF shielding. The amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic field. It is sprayed on to the enclosure and, once dry, produces a continuous conductive layer of metal, which can be electrically connected to the chassis ground of the equipment, thus providing effective shielding. Some cables have two separate coaxial screens, one connected at both ends, the other at one end only, to maximize shielding of both electromagnetic and electrostatic fields. As soon as an electric field is applied to the surface of an ideal conductor, it induces a current that causes displacement of charge inside the conductor that cancels the applied field inside, at which point the current stops. Also, most conductors exhibit a ferromagnetic response to low-frequency magnetic fields, so that such fields are not fully attenuated by the conductor. A measure of the depth to which radiation can penetrate the shield is the so-called skin depth.
In these cases shields made of high magnetic permeability metal alloys can be used, such as sheets of Permalloy and Mu-Metal,[5] or with nanocrystalline grain structure ferromagnetic metal coatings.[6] These materials don't block the magnetic field, as with electric shielding, but rather draw the field into themselves, providing a path for the magnetic field lines around the shielded volume.


Any holes in the shield force current to flow around them, so that fields passing through the holes do not excite opposing electromagnetic fields. The best shape for magnetic shields is thus a closed container surrounding the shielded volume. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction. The effectiveness of this type of shielding depends on the material's permeability, which generally drops off at both very low magnetic field strengths and at high field strengths where the material becomes saturated. It can also affect cell phone, FM radio and television reception, although to a lesser extent.
So to achieve low residual fields, magnetic shields often consist of several enclosures one inside the other, each of which successively reduces the field inside it. The electric field is produced by stationary charges, and the magnetic field by moving charges (currents); these two are often described as the sources of the field.
Simulation is also used when the real system cannot be engaged, because it may not be accessible, or it may be dangerous or unacceptable to engage, or it is being designed but not yet built, or it may simply not exist. Industrially, the electron microscope is often used for quality control and failure analysis. For static or slowly varying magnetic fields (below about 100 kHz) Faraday shielding is ineffective.
The technique is widely used in hospitals for medical diagnosis, staging of disease and for follow-up without exposure to ionizing radiation.



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