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EMI effectively can be addressed in very complex terms but for most applications EMI shielding requires a Faraday cage around the equipment requiring protection. Any gap in the cage will allow some leakage and if the case contents are susceptible to that frequency range or if sensitive data can be compromised by the emission of those frequencies, the EMI effectively is inadequate.
Aluminum offers many advantages over typical composite case construction. It can weather extreme temperatures, resist impact without cracking, and will not rust or corrode over time. ZARGES cases are free of ferromagnetism and are an excellent conductor of electricity and heat. Our Mitraset line of aluminum rackmount cases for electronic installations are inherently shielded against EMI.
Aluminum cases can be fabricated with welded or formed seams to eliminate most radiation leakage with little additional cost in manufacturing processes or material content. Plastic and composite materials require some type of conductive supplement to the nonconductive basic materials and these supplements significantly increase material/labor costs. These supplemental materials are difficult to employ in the case manufacture and often easily damaged when the case experiences rough handling environments or temperature extremes.
The Mitraset and K475 cases passed the shielding requirements of 60dB from 150kHz to 18GHz. The tests were performed at Chomerics, Inc. of Woburn MA. The assessment determined that the Mitraset does comply to the certain requirements set forth in IEEE STD 299.
As a custom option, the Mitraset and K475 cases can be fitted with a EMI shielding gasket made from Chomerics CHO-SEAL 1285, which is silver-plated aluminum in silicone and provides additional shielding between 90-110 dB.
Electromagnetic interference (EMI), or radio frequency interference (RFI) when in radio frequency, is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. These effects can range from a simple degradation of data to a total loss of data. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit, the Sun or the Northern Lights.
A Faraday cage is an enclosure formed by conductive material or by a mesh of such material. Such an enclosure blocks external static and non-static electric fields by channeling electricity along and around, but not through, the mesh, providing constant voltage on all sides of the enclosure. Faraday cages are named after the English scientist Michael Faraday, who invented them in 1836.
A Faraday cage operates because an external static electrical field causes the electric charges within the cage’s conducting material to be distributed such that they cancel the field’s effect in the cage’s interior. This phenomenon is used, for example, to protect electronic equipment from lightning strikes and electrostatic discharges.
Faraday cages shield the interior from external electromagnetic radiation if the conductor is thick enough and any holes are significantly smaller than the wavelength of the radiation. The metal layers are grounded to dissipate any electric currents generated from external or internal electromagnetic fields, and thus they block a large amount of the electromagnetic interference. The reception or transmission of radio waves, a form of electromagnetic radiation, to or from an antenna within a Faraday cage is heavily attenuated or blocked by the cage.