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Magnetic Shielding Enclosure for Computer VDUs

Computer Screens & Your Health

As the usage of computers becomes increasingly widespread, there has been a growing concern over electromagnetic fields emitted from computer screens or visual display units (VDUs). These fields are generated in the VDU coils that direct electrons onto the screen and are similar to fields emitted by power lines and electrical appliances. Some researchers believe that these fields affect health and base this on findings of epidemiological studies.

Specification & Prices
The effects that have been reported in people include a decrease in hormone production, slowing of heart rate, changes in brain activity and stress, cancerous tumour development and growth, behaviour, biorhythms, and functions of cells and tissues. The fields of concern are at extremely low frequencies (ELFs - up to 1000 Hz).

Jittering & Distortion in Screens

Cathode ray tube (CRT) based computer screens, besides being a source of ELF fields, are, themselves adversely affected by fields in ELF range, in the form of image and colour distortion, waving or jitter. Common sources of such interference include power distribution lines passing near the monitor (e.g. in a first floor office block), electric cables in the walls or floors, power switchboards or substation equipment inside office blocks.

Solving Both Problems

The first practical solution to reducing screens interference came from a team at Victoria's State Electricity Commission, which developed an ELF Compensator. This was found to be effective in offices and domestic environments.

Since 1993, Magshield's R&D has shown that magnetic shielding of VDU protects the user from the ELF fields and, at the same time, prevents jittering and distortions of image caused by external field sources.

Trials with a vast range of materials and designs resulted in a shield design which is light weight, aesthetically pleasing and allows devices, such as a printer, to be perched on top of the shield without affecting the image. This shield is widely used in office environments. The shield has also been very effective in more extreme industrial environments such as intense AC fields of the BHP platinum smelter in Zimbabwe, control rooms of the Western Mining Corporation's nickel extracting and processing plants in Western Australia and intense DC fields in Hong Kong's underground (the M.T.R.C.).

Although reports of harmful effects have only been in the ELF range, the shield is also very effective in the Very Low Frequency (VLF) range.

Technical Details

Magnetic fields occur in nature. Strong magnetic fields can also be created by electric currents. VDU's with cathode ray tubes generate magnetic fields in a very broad spectrum of frequencies. The internationally accepted standard for magnetic fields radiated by VDU's is the Swedish Standard SS 436 14 90, on Computers and Office Machines - Measurement Method for Electric and Magnetic Near Fields (published in November 1995). This document states that magnetic field in ELF range should be below 2.0 milliGauss (mG) at 300 mm in front of the VDU.

CRT-based computer screens are themselves affected both by DC (e.g. from tram and train lines) and AC fields (e.g. from power lines and electrical equipment). Tests reveal that different monitors have different threshold of sensitivity to AC magnetic fields. They also reveal that the larger the monitor, the higher its sensitivity to these fields. It was determined that 10 mG is the threshold sensitivity level for most 14" screens and this level drops to around 7 mG for screens of up to 22" in size.

Magshield is made of special magnetic material, with extremely low magnetic reluctance. Fields are forced into the shield, since it offers much lower magnetic resistance than the air. Magshield is equally effective with both VFL (Very low 1000-2000 Hz) and ELF (Extremely Low) frequency ranges.

How Effective Is It?

The graph shows field mapping around a 14" super VGA colour monitor in the ELF range; black unshielded, red protected by Magshield , and green the Swedish Standard recommendation. The field is mitigated to a level well below that required by the standard.

Magshield is equally effective in protecting monitors against external fields. Our standard design provides excellent, low cost protection against excessive magnetic fields found in some office and light industrial environments. Our special design is unmatchable, in cost and performance, against magnetic fields most commonly found in heavy industrial environments (1000 - 2000 mG).

Who Developed Magshield?

The Technical Director (and inventor) of Magshield, Garry Melik, has worked in the electrical power industry and has dealt with technical issues relating to low frequency electromagnetic fields and electrical induction since 1976. His work has been published in Australia and internationally.

Garry was the principal designer of the ELF Compensator. He is the Australian representative of the Paris based CIGRE International Working Group. He has regularly conducted studies of VDU interference, its effect and its mitigation for corporations, government departments and private companies. He is the author of the first book on this subject which he was commissioned to write by the Electricity Supply Association of Australia (ESAA). The title of the book is "Magnetic Field Mitigation to Reduce VDU Interference". It was published in July 1996 and can be purchased directly from ESAA.

Who Needs It?

  1. Anyone experiencing a problem with VDU in the form of colour distortion and jittering of the screen image.
  2. Anyone concerned with reducing magnetic fields from VDU's in their environment. Until there is definite proof that magnetic fields do (or do not) seriously affect health, a policy of avoidance is recommended. The virtual elimination of these fields from monitors by Magshield makes it the only prudent, practical and cost-effective means of such avoidance.