Low-Emission Computers

An electrical engineer Harry — who is disabled — designs and develops low-emission computers for use by people with severe electrical sensitivity. Two computers are described here that are one-of-a-kind research and development projects he has worked on over several years in his home workshop.

The first — the "Montana Project" — was designed primarily to reduce low-frequency and radio-frequency emissions up to 200 megahertz. Parts and materials were funded by the Arizona Rehabilitation Services Administration (ARSA). This computer is used by an ARSA client who has severe reactions to conventional computers, but needs computer access in order to work at home part-time. She has used it successfully for three years. The second — the "Brickbat Project" — is a second-generation implementation that Harry is building for his own use.

Montana Project: User's Workstation

Brickbat Project: Rear Projector

Harry has found that reducing emissions to make computers safe for sensitive individuals is a sizable challenge. Computers are among the most troublesome devices for people who are sensitive to electricity, causing symptoms such as headaches, inability to concentrate, memory loss, depression and other mood alterations, itchiness, insomnia, and seizures. Some people's reactions are so severe that they can't be near a conventional computer in a school, hospital, or work setting, let alone at home. This is a particularly unfortunate situation considering that for people with other severe disabilities, computers and Internet access often are enabling and empowering. Using a computer reduces  isolation and sometimes makes work possible.

The job of making computers safe is difficult partly because people react to different frequencies. Consequently, while one person may have severe reactions to some electronic components and not others, another person may react most severely to a different set of components. However, because sensitivities often spread to new frequencies, predisposed individuals generally need to reduce their exposures throughout the electromagnetic spectrum, from extremely low frequencies through radio and microwave frequencies. This can include everything from less than one hertz (one cycle per second) to eight gigahertz (8,000,000,000 hertz).

Also, the job of making computers safe is tough because large reductions in stimuli result in only small perceived reductions. To successfully protect an individual from troublesome emissions, it may be necessary to reduce emissions to a small fraction of the amount allowed by the FCC and other regulatory agencies. While Harry reduced emissions to roughly one-thousandth of commercial levels (60 decibels) in the Montana Project, in the Brickbat Project he expects to achieve reductions to one ten-thousandth (80 decibels). He has found that a 60 decibel reduction typically feels "much better'' to a sensitive person, but that it is not adequate for the lengthy exposures that would occur in a normal work session. Ideally, he would like to reduce emissions  to one-millionth (120 decibels).

The best way to reduce emissions is at the source by redesigning the electrical and mechanical components so that they don't produce emissions in the first place. Usually the most troublesome components are switching power supplies, monitors, cables, and motherboards, but other components cause problems to some degree.

Naturally, replacing components could be done most effectively by computer manufacturers. Short of that kind of help from industry, Harry has found that he can replace some computer components by customizing the computer configuration. For example, he replaces switching power supplies with linear supplies and toroidal transformers. In cases where component substitution isn't feasible, he uses remoting (moving the components away from the user); and shielding (wrapping the components in materials that block emissions). Common shield materials include aluminum foil, galvanized steel, five percent silicon steel, mu metal, copper tape, and copper mesh. Each one is best suited to shielding a specific frequency range.

Harry often uses remoting and shielding together since remoting components results in long cables that re-radiate emissions. To prevent that effect, he places the cables  inside steel conduit.

While shielding cables is often not too hard, shielding other components can be more difficult, expensive, and not too effective. It is hard to maintain the integrity of a shield enclosure, such as a CPU box, when it needs to have openings for air vents, cables, user access, maintenance, and so forth. Harry uses a variety of methods such as gasketing door openings, covering other openings with copper mesh, and putting conductive tape over seams.

The Montana Project

In the Montana Project Harry used all three techniques — component substitution, remoting, and shielding. He reduced emissions by:

Workstation Box and Display Screen

Workstation Box, Keyboard, and Trackball

Harry housed the display in a galvanized steel box and covered the seams of the box with conductive adhesive copper tape to prevent leaks of electromagnetic radiation. The LCD screen is shielded with copper mesh. Outside the copper mesh it is covered with glass that has an anti-reflective coating on one side and a conductive coating on the other. The speaker holes are covered with copper mesh, as is an air inlet located underneath the box.

A KeyTronic keyboard was selected for its membrane key-switch technology. When the user presses a key, the key in turn presses a plastic plunger against the membrane inside the keyboard. The entire key switch membrane is shielded in aluminum foil. The keyboard's microprocessor and the cable leading to the display enclosure are shielded with copper tape and copper mesh.

The rest of the Montana computer is housed in a wooden box located at the opposite end of the house from the user’s workstation. The box is lined with aluminum foil. It has a small door that can be opened to insert and remove floppy disks and CDs and a large door for maintenance. Inside the box is a Dell PC as well as an external power supply for the LCD panel, power supplies for audio amplifiers, and devices that enable the use of extremely long cables for the keyboard, trackball, video, and audio. All power supplies have five percent silicon steel shielding.

Computer Box Showing Drive Access Door

Inside of the Computer Box

The doors have gaskets that provide connectivity where they join the box. The gasketing is essential to enable the box to perform effectively as a shield for RF emissions. It consists of conductive tape over strips of foam.

Two steel pipes run from the workstation box up through the attic and connect to the remote computer box. One carries cables for the video, keyboard, trackball, and audio while the other connects to a sound-insulated blower fan located in the attic. The fan cools the light bulbs and LCD system to prevent overheating inside the workstation box.

Steel Pipes Holding Cables

Remote On-Off Switch

The on-off switch  is located about halfway between the user's workstation and the computer box, at a good distance from the user. Metal clad wiring was used, although its shielding performance is mediocre. Harry considers steel conduit or a fiber-optic switch better choices.

The primary technical limitation of the Montana Project involves the direct-view LCD panel. It puts a limit on the level of emission reduction because of the close proximity of the panel and inverters to the user and because of the gap in shielding caused by the display aperture (six by eight inches). Despite copper mesh shielding and the overlay of conductive glass, it creates a gap that allows emissions to escape.

The Brickbat Project

Armed with the knowledge he gained on the Montana Project and with a somewhat larger budget, Harry is building the Brickbat system to serve as both a computer and a low-emission television set. Harry solved the technical problems of the LCD panel by adopting a rear-projection design. This design allowed him to move the LCD panel to a distance of nearly twelve feet from the user. He also reduced the size of the aperture to a three-inch diameter hole, just large enough for the projector's lens to show through. The lens is recessed several inches into the shield enclosure inside a metal tube. Together with a piece of ten Ohm-per-square-inch Indium-tin oxide ("ITO'') glass that covers the aperture, the tin tube, which is bonded to the housing, helps prevent emissions from the projector shield enclosure.

Rear Projector and Moveable Mirror

Fiber-Optic SVGA Video Link

In addition to the rear-projection technology, two other features are essential in reducing emissions. First, all switching power supplies were replaced with custom toroidal transformer linear power supplies. Second, a line-voltage halogen lamp was used instead of a metal halide lamp (which would ordinarily be used in a rear projector). Metal halide lamps are high emission sources because they have inverters and because they are high-frequency AC arc lamps.

For cooling, a steel duct connects the projector to a quiet blower fan located (remotely) in the attic. To provide continuity of shielding at the projector box, the air inlet and outlet are covered with honey-combed shield vents.

Harry remoted the keyboard and trackball microprocessors to about seven feet away from the user and put them in a shield enclosure with a fiber-optic interface to the remote computer. Also, he developed a custom-designed solution to remove the pulsing digital signals from the keyboard (i.e., matrix scanning for key presses).

While Harry’s projector, keyboard, and trackball are in his house, the computer, satellite receiver, VCR, stereo receiver, and CD carousel are in his garage. It is a steel-sided, steel-roofed building about 75 feet away from the house. Custom fiber-optic cables connect the components in the garage to the components in the house. A custom SVGA video link transmitter allows the computer to be up to 500 feet away from the projector.

Future Directions

Harry's next project — the "Asilo Project'' — is for a new home that has two shield rooms. The shield rooms are entirely lined with sheet metal and have conductive gasketing around the doors and copper-mesh shielding and gasketing on the windows. One shield room is between the user's office and living room. It will house two projectors, one for television in the living room and one for the user's workstation.The shielding of the room will add to the shielding of the projector housings, resulting in a reduction of approximately 120 decibels.

In the second shield room, located at the far end of the house, is the rest of the user's computer. Steel conduit buried outside the house in the yard holds cables that connect components in the two rooms. The computer room's shielding helps prevent the computer's emissions from leaking into the rest of the house, together with the exterior shielded cabling and a military-grade power filter.

After the Asilo Project, Harry hopes to create a rear-projection monitor that would have the advantages of small size and portability. It would be much easier to incorporate into the typical home or workplace than is the current design.

Taking portability and compactness a step further, Harry would like to incorporate laptop electronics, providing a complete computer in one shielded box. He anticipates shielding the disk drive motors and providing a fiber-optic interface to the modem and remote printer (shielded and power-filtered).


If you are familiar with the state of the art in computer shielding technology, you probably find Harry's work encouraging. It provides proof of concept that low-emission computers can be built and successfully used by electrically-sensitive people.

However, if you are disabled and need the empowerment and opportunities a computer could give you, this is likely to be discouraging. The unfortunate truth is that there is no good, near-term solution. Harry's projects are research efforts and each computer he produces is one of a kind. Because they haven't been adapted for mass production, or even for replication, reproducing any one of them would be a major undertaking requiring the efforts of an electrical engineer trained in electromagnetic compatibility work (EMC). Harry plans to begin documenting his work to help bring other engineers up to speed. Meanwhile, recommended reading is included below.

Hopefully, readers will see in these research projects a crucial first step, and look forward to a time when later implementations will be designed for replication and eventually manufacture.

Recommended Reading

The books listed below are recommended for engineers interested in learning about electromagnetic compatibility.

  1. Gerke, Daryl, and B. Kimmel. EDN's Designer's Guide to Electromagnetic Compatibility. Des Plaines, IL: Cahners (800-523-9654).
  2. Mardiguian, Michel. Controlling Radiated Emissions by Design. New York: Chapman & Hall, 1992.
  3. White, R.J., and M. Mardiguian. Volume 3, Electromagnetic Shielding. Gainesville, VA: emf-emi Control, Inc., 1988.


The resources listed below include a source for a gauss meter as well as information about the health effects of electromagnetic fields. They may be of interest to engineers, non-engineers, and people with illnesses related to electricity.

AlphaLab, Inc. sells a gauss meter, the TriField Meter, useful for measuring low frequency electromagnetic fields (below 100 kilohertz). An external probe is available for the meter that increases its sensitivity 100 times. Mailing address: 1280 South 300 West, Salt Lake City, UT 84101.
Phone: 800-769-3754, 801-487-9492
Fax: 801-487-3877
Web: www.trifield.com
Microwave News is a source of information about the health effects of electromagnetic fields, including cancer and other illnesses as well as electrical sensitivity. It is published by Louis Slesin, Ph.D., on a bi-monthly basis. Mailing address: P.O. Box 1799, Grand Central Station, New York, NY 10163
Phone: 212-517-2800
Fax: 212-734-0316
Email: mwn@pobox.com
Web: www.microwavenews.com

Written by Kathleen Hemenway, Ph.D.
Photography by Chris Geanious

For additional information please go to http://www2.nau.edu/aztap-p/

This document was developed for the Arizona Technology Access Program. Funding is provided by the U.S. Department of Education, National Institute on Disability and Rehabilitation Research (NIDRR) Grant #H224A40002. The contents of this publication do not necessarily reflect the views of NIDRR or the U.S. Department of Education, and do not imply endorsement by the U.S. Government.

Created: January 10, 2000
Last Updated: August 21, 2001

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