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Passive VLF Magnetic Remedies

IP.com Disclosure Number: IPCOM000037897D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-30
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Dickerson, JA: AUTHOR [+2]

Abstract

There is a growing concern that very low-frequency (VLF) magnetic fields may have ill effects on human beings. A major source of VLF magnetic fields in display monitors comes from the high- voltage deflection system. In a video display terminal (VDT), the flyback transformer, part of the horizontal deflection and high voltage system that sweeps the electron beam across the face of the CRT, is a source of pulsed VLF magnetic fields. In addition, the deflection yoke and width coil can be significant contributors. Generally, maximum intensity of this field exists on the side or in the rear of the monitor in close proximity to the physical location of the flyback transformer. In some cases, the deflection yoke is the largest contributor. Thus, front- of-screen radiation will be of greater concern.

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Passive VLF Magnetic Remedies

There is a growing concern that very low-frequency (VLF) magnetic fields may have ill effects on human beings. A major source of VLF magnetic fields in display monitors comes from the high- voltage deflection system. In a video display terminal (VDT), the flyback transformer, part of the horizontal deflection and high voltage system that sweeps the electron beam across the face of the CRT, is a source of pulsed VLF magnetic fields. In addition, the deflection yoke and width coil can be significant contributors. Generally, maximum intensity of this field exists on the side or in the rear of the monitor in close proximity to the physical location of the flyback transformer. In some cases, the deflection yoke is the largest contributor. Thus, front- of-screen radiation will be of greater concern. The coils, loops and brackets described in this publication have been used for the reduction of VLF magnetic radiation from both monochrome and color monitors.

With reference to Fig. 1, two shorted-turn conductors of heavy gauge copper criss-cross the bell of the CRT for front- of-screen reduction of magnetic radiation. An elliptical shaped coil (4.5" x 6.0") wound with #18 gauge wire, ends shorted together, is placed above the deflection yoke. This provides a reduction in radiation from the top/front and rear of the monitor. Finally, aluminum plates on top and bottom electrically connected with side brackets attenuate magnetic fields from top...