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bl2408-shielded-enclosures-a

CAUSES OF ELECTROMAGNETIC INTERFERENCE

Electromagnetic interference (EMI) and radio-frequency interference (RFI) can degrade the performance of a circuit or even stop it from functioning. In the case of a data path, the effects can range from an increased error rate to a complete loss of data.

EMI can be caused by electronics such as ignition systems, mobile phone networks, power lines and devices that generate changing electrical currents and voltages. It can also be the result of natural sources such as lightning, solar flares, coronal mass ejections, and the Northern and Southern Lights.

The closer an electronic device is to an EMI source, the more susceptible it is to interference. Devices placed near large motors or radio antennas are more likely to be affected. Equipment that lacks adequate electromagnetic shielding can be more vulnerable to EMI.

Many devices emit signals at multiple frequencies. Interference can occur if these frequencies overlap with those used by other devices. This is particularly relevant in communication systems where multiple signals may be transmitted simultaneously.

WHY INDUSTRIAL WORKPLACES ARE MORE PRONE TO EMI AND RFI

Factories and other industrial buildings tend to have more EMI issues because of the prevalence of heavy machinery, switching devices, variable frequency drives, power lines and high-frequency communications equipment.

This is often exacerbated by the lack of isolation. Various different types of equipment can be grouped close together, increasing the risk of EMI. Furthermore, industrial buildings are often based on large metal structures: the beams, girders and metal walls can reflect and amplify electromagnetic waves.

WAYS TO PREVENT EMI

Effective ways to reduce EMI include proper earthing, filters and maintaining separation between different cables. Increasing the distance between the source of the interference and sensitive equipment can reduce the impact of EMI/RFI. This is often considered in the layout and physical placement of equipment within an environment.

Using twisted pair wiring and designing electronic circuits and layouts to minimise interference (by separating high-frequency components from sensitive areas) can also prevent many potential EMI/RFI issues. But it is wise to specify shielding if EMI and/or RFI are likely to be an issue. Shielding is based on the principle of the Faraday Cage…

HOW THE FARADAY CAGE STOPS EMI/RFI

A Faraday Cage is an enclosure used to block electromagnetic fields. It is named after the English scientist Michael Faraday, who invented it in 1836. The cage works by redistributing an electrical charge over a conductor, neutralizing the effects of external electric fields.

A Faraday Cage can be made from a continuous covering of conductive material (or mesh) such as copper, aluminium or steel. The key is that the material must conduct electricity. When an external electric field hits the Faraday Cage, the free electrons within the conductive material cancel the field’s effect inside the enclosure. Essentially, the external electric field causes these electrons to redistribute themselves in such a way that the internal field is nullified.

For radio frequencies, the Faraday Cage operates by absorbing and reflecting the radio waves. The mesh or solid shell of the cage reflects incoming or outgoing electromagnetic radiation, stopping  it from passing through. The holes in a mesh cage must be significantly smaller than the wavelength of the radio waves they are meant to block. This is why the size of the mesh or gaps in the enclosure is crucial.

RFI/EMI SHIELDING OF PLASTIC ENCLOSURES

Plastic is non-conductive so it does not provide any natural protection against electromagnetic fields. OKW plastic enclosures can be protected with shielding, which is available on request as a custom service.

OKW carries out all shielding in-house to ensure optimum quality and speed of delivery. Plastic parts are vapour-plated with 99.98% pure aluminum. We apply this coating in a high vacuum to achieve a cleaner, more consistent layer of aluminum.

The absence of air and other gases produces a more even coating – minimizing the presence of any contaminants or air molecules that could interfere with the deposition process. The result is a superior coating that also looks better.

Granted, the coating is inside the enclosure – and will therefore not be seen – but if a job is worth doing, it’s worth doing well. Generally, the coating is 2.5 µm thick. But other coating thicknesses are available on request.

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