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Blog - November 2019

How Electromagnetic Shielding Works

You can stop electromagnetic interference (EMI) – or radio frequency interference (RFI) as it is sometimes known – by creating a Faraday Cage inside your enclosure.

A Faraday Cage uses a conductive barrier to block interference. It distributes an electrostatic charge evenly around the outside of the cage – cancelling out the electric charge or radiation inside the enclosure.

For the cage to work, the conductive material must be the right type and thickness in relation to the electromagnetic fields involved.

OKW’s Electromagnetic Compatibility (EMC) Shielding

Unlike metal enclosures, plastic cases have no natural protection against electromagnetic interference. It can’t stop interference from other devices from interfering with your equipment. And it cannot prevent EMI from your electronics from affecting other devices.

Even enclosures that are predominantly metal (and therefore conductive) may still need EMC shielding. One example is our award-winning SYNERGY enclosures which comprise an extruded alumiium (AlMgSi 0.5) main case and a plastic (ASA+PC-FR) top and base.

So as an option we can apply our own Alvacoat® conductive aluminum coating to the interior of any plastic or aluminum/plastic enclosures you specify. We have our own in-house vapour-plating facility to ensure quality and to guarantee short production and delivery times.

We apply the conductive coating in a high vacuum. The aluminium is 99.99 per cent pure. Our standard coating thickness is 2.5 µm but thicker coatings are available on request if required.

Alvacoat® is certified in accordance with the UL 746C standard for polymeric materials.

Complying With The EU Electromagnetic Compatibility Directive

The EU’s 28-page (EMC) Directive 2014/30/EU – is designed to limit EMI emissions from electronic equipment. It came into force on April 20 2016.

The legislation affects most electronic products but there are some exceptions. These are aircraft, communications equipment, medical devices, military equipment, road vehicles and tractors because they are already covered by their own specific regulations.

Furthermore, the directive does not apply to custom-built evaluation kits destined for use by professionals at R&D facilities. We recommend that OEM manufacturers carry out the following best practices to comply with the directive and the regulations:

  • design all the electronics (including the PCB layout) to meet EMC requirements
  • reduce conducted interference and eliminate cable interference radiation
  • partially screen sensitive components or interference radiators
  • reduce the amount of interfering radiation entering (or exiting) through openings
  • increase the screening effect of the enclosure.
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