Interference from ELF or AC Magnetic Fields

The most common example of EMI interference caused by an ELF or AC magnetic field is with a computer monitor. Most computer monitors will experience interference when located in an area of with elevated magnetic field levels of 5 to 10 mG present and some graphic monitors can have interference problems in levels as low as 3 mG. Keep in mind that "normal" background ELF magnetic field level in most workplaces typically ranges from 0.3 to 2 mG. The monitor interference, often referred to as "jitter" appears as a rapid horizontal, back-and-forth shifting of the computer screen image.

A large variety of specialized research equipment can experience EMI problems when elevated levels of AC magnetic fields are present. Among the most susceptible, are the newest generations of SEM and TEM electron microscopes. These instruments are extremely sensitive and can exhibit disturbance from external AC fields as little as 0.1 mG !. A variety of laboratory equipment such as a Gas Chromatograph and any device utilizing electron scanning technology is typically sensitive to interference from external magnetic field sources. High precision movement robotic systems can exhibit problems if located in areas with elevated AC magnetic fields present, as can research MRI & NMR imaging systems.

Ultra Sound equipment

Elevated AC magnetic field levels can cause significant EMI problems in broadcasting and entertainment production facilities as they can induce "hum" or objectionable increases in signal/noise in a wide variety of equipment including microphones, musical instrument pickups, recording mixers, etc.

Computer servers

As a precautionary measure, several major industrial and financial services companies have established internal guidelines which recommend that computer equipment including cabling, data-hubs, network controllers, servers, etc. should not be operated in environments where AC magnetic field levels exceed 20 to 30 mG.