Browse Prior Art Database

Two-Material Shields for the Reduction of Magnetic-Field Emanations in Visual Display Units

IP.com Disclosure Number: IPCOM000036068D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 14K

Publishing Venue

IBM

Related People

Pitts, OD: AUTHOR [+2]

Abstract

Disclosed is a general method for constructing a shielding enclosure to reduce the magnetic-field emanations associated with the electronic operation of a Visual Display Unit (VDU). This shield construction consists of an appropriately ordered layering of two materials, one being a high-conductivity (high-s) material such as copper, and the other being a high-permeability (high-m material such as nickel.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 2

Two-Material Shields for the Reduction of Magnetic-Field Emanations in Visual Display Units

Disclosed is a general method for constructing a shielding enclosure to reduce the magnetic-field emanations associated with the electronic operation of a Visual Display Unit (VDU). This shield construction consists of an appropriately ordered layering of two materials, one being a high-conductivity (high-s) material such as copper, and the other being a high-permeability (high-m material such as nickel.

Recently, a need has arisen to reduce the magnetic-field emanations associated with VDU operation, the frequency range of concern being approximately 1KHz to 400 KHz. Of the possible methods that exist for effecting such a reduction, the most general is to construct a shielding enclosure for the VDU electronics (the horizontal yoke and deflection circuitry, for example).

Fundamentally, there are two different approaches that can be taken to shield, or contain, a magnetic field. One approach, known as a Faraday shield, is to enclose the source of the magnetic field with a high-s material. The source- produced field induces currents in the shielding enclosure, which, in turn, produce a magnetic field of opposite polarity that tends to cancel the source- produced field. The other approach is to enclose the source with a shield made of a high-m material. Much like a transformer core, the high-m shield contains the exterior magnetic field to the very near vicinity of the shield, owing to the difference in permeability between the shield and the surrounding air.

In essence, either approach relies on the ability to manufacture a shielding enclosure of sufficient thickness: in the case of the Faraday shield, a minimum thickness is necessary to obtain the desired conductivity s; in the case of the high-m shield, a minimum thickness is necessary to prevent the high-m material from saturating.

In the case of a VDU, a variety of practicalities limit the ability to produce effective magnetic shields by following either one of the aforementioned approaches exclusively--the requisite thicknesses of either type of material are simply too great to be practical. I...