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ELF Fields Help

By — McGraw-Hill Professional
Updated on Sep 12, 2011

Introduction

Many electrical and electronic devices produce EM fields. Some of these fields have wavelengths much longer than standard broadcast and communications radio signals. The fields have extremely low frequencies (ELFs); this is how the term ELF fields has arisen.

What Elf Is (and Isn’t)

The ELF spectrum begins, technically, at the lowest possible frequencies (less than 1 Hz) and extends upward to approximately 3 kHz. This corresponds to wavelengths longer than 100 km. The most common ELF field in the modern world has a frequency of 60 Hz. These ELF waves are emitted by all live utility wires in the United States and many other countries. (In some countries it is 50 Hz.) In the Great Lakes area of the United States, the military has an ELF installation that is used to communicate with submarines. The ELF waves travel underground and underwater more efficiently than radio waves at higher frequencies.

The term extremely-low-frequency radiation and the media attention it has received have led some people to unreasonably fear this form of EM energy. An ELF field is not like a barrage of x-rays or gamma rays, which can cause sickness and death if received in large doses. Neither does ELF energy resemble UV radiation, which has been linked to skin cancer, or intense IR radiation, which can cause burns. An ELF field will not make anything radioactive. Some scientists suspect, nevertheless, that long-term exposure to high levels of ELF energy is linked to an abnormally high incidence of certain health problems. This is a hotly debated topic and, like any such issue, has become politicized.

Common Sources

One ELF source that has received much publicity is the common cathode-ray tube (CRT) monitor of the sort used in desktop personal computers. (Actually, CRT monitors produce EM energy at higher frequencies, not only at ELF.) Other parts of a computer are not responsible for much EM energy. Laptop and notebook computers produce essentially none.

In the CRT, the characters and images are created as electron beams strike a phosphor coating on the inside of the glass. The electrons change direction constantly as they sweep from left to right and from top to bottom on the screen. The sweeping is caused by deflecting coils that steer the beam across the screen. The coils generate magnetic fields that interact with the negatively charged electrons, forcing them to change direction. The fields thus fluctuate at low frequencies. Because of the positions of the coils and the shapes of the fields surrounding them, there is more EM energy “radiated” from the sides of a CRT monitor cabinet than from the front. If there’s any health hazard with ELF, therefore, it is greatest for someone sitting off to the side of a monitor and least for someone watching the screen from directly in front.

Protection

The best “shielding” from ELF energy is physical distance. This is especially true for people sitting next to (rather than in front of) a desktop computer monitor. The ELF field dies off rapidly with distance from the monitor cabinet. Computer workstations in an office environment should be at least 1.5 m (about 5 ft) apart. You should keep at least 0.5 m (about 18 in) away from the front of your own monitor. A monitor can be shut off when it’s not in use.

Special monitors designed to minimize ELF fields are available. They are rather expensive, but they can offer peace of mind for people concerned about possible long-term health effects from exposure to ELF fields.

You’ll sometimes see devices marketed with claims to eliminate or greatly reduce ELF fields. Some such schemes are effective; others are not. Electrostatic screens that you can place in front of the monitor glass to keep it from attracting dust will not stop ELF fields. Neither will glare filters.

The ELF issue has attracted the attention of fear mongers and quacks, as well as the interest of legitimate scientists. It is best to avoid blowing it out of proportion and not to succumb to unsubstantiated media hype. If you are concerned about ELF radiation in your home or work environment, consult someone whose word you can trust, such as a computer hardware engineer or a wireless communications engineer.

Practice problems of these concepts can be found at: Forms Of Radiation Practice Test

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