Electromagnetic Shielding

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What are Electromagnetic Fields and why should I care? 



EMF & RF Information

EMF Testing & Shielding

Understanding Shielding Materials

Project Examples

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The abbreviation EMF can be used to describe both 'electromagnetic force' and electromagnetic fields.

Electrical power in Australia is generated at 50 cycles per second (50 Hz). The electro-magnetic fields produced by 50Hz power supplies are classified as extremely low frequency (ELF) fields. Higher frequencies include RF - Radio Frequency, UHF - Ultra High Frequency or VHF - Very High Frequency.

Different electrical frequencies have different effects on their surrounding environment.

EMF radiates out from the source (hence the term electromagnetic radiation), reducing in strength with distance. Building materials such as concrete and brick do little to stop them.

Common sources of EMF in buildings are transformers, switchboards, mains cables, motors and appliances. A sub-station transformer may radiate significant fields over a distance of several metres, whereas fields from a mobile phone charger or a refrigerator motor don't reach even a metre.

Fields can be measured in units of microtesla (µT) or another unit called milligauss (mG)

EMI Shielding deals in the protection of equipment and people from ELF - extremely low frequency electro-magnetic fields only. Shielding of low frequency magnetic fields requires different materials and methods than shielding for RFI radio frequency interference.

The main effects of EMFs are: 

  • interference with specialist electrical and computer equipment
  • interference with CRT (cathode ray tube) computer monitors causing screen shimmer
  • biological effects are not fully understood however, it is known that each frequency is absorbed at a different rate by living tissue and there has been uncertainty about the health effects of exposure to electromagnetic fields.
  • some research has implicated exposure to EMF's in cases of leukemia, neurodegenerative diseases, miscarriage and clinical depression
  • The World Health Organisation, ARPANSA (the Australian Radiation Protection agency) and other international regulatory bodies agree that ELF's are "possibly carcinogenic" and that this effect is likely to be associated with "prolonged exposure".

Given the uncertainty surrounding the effects of EMF's there is no regulatory standard for use in Australia.

The commonly accepted practice is to limit exposure in workspaces to not more than 10mG (milligauss) and in residential facilities to not more than 4mG.

Shielding is only used to protect areas that are at risk from electrical hazard, equipment interference or where people will spend prolonged periods of time eg. offices, workstations, bedrooms, loungerooms etc...

Shielding is not always required for electro-magnetic interference. Other measures are minimisation or prudent avoidance, for example, rectification of electrical anomalies may reduce EMF.

Other EMI mitigation alternatives include repositioning of cabling and/or equipment, careful design of electrical installations and repositioning of furniture etc..

For further information and reading please see our links


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