WO1996019075A1

WO1996019075A1 - Oversize electromagnetic emission shield for video display devices

Info

Publication number: WO1996019075A1
Application number: PCT/US1995/000201
Authority: WO
Inventors: Randall Blair Harmon; Teresa Gushurst Gushurst
Original assignee: Avant Guard Pc Shields, Inc.
Priority date: 1994-12-13
Filing date: 1995-01-04
Publication date: 1996-06-20

Abstract

An electromagnetic emission shield (1) for reducing electromagnetic radiation from a video display device (5) comprising an oversize conductive face plate (2) significantly larger in area than a front surface of said video display device.

Description

OVERSIZE ELECTROMAGNETIC EMISSION SHIELD FOR VIDEO DISPLAY DEVICES

Related Application

This application is a continuation-in-part of United States Patent Application Serial No. 08/181,801 filed January 10, 1994, which is incorporated by reference herein.

Field of the Invention

The present invention relates generally to a device for reducing electromagnetic emissions from electronic equipment, particularly video display terminals. More particularly, the invention relates to an oversize shield for protecting the viewer from electrostatic charges and low frequency radiation which emanate from the front, bottom, top and sides of the video display terminal.

Background of the Invention

Serious questions have been raised about the potentially harmful health effects of electromagnetic emissions from electronic equipment, particularly video display terminals (VDTs) . Although VDTs generate measurable and often substantial amounts of radiation, preliminary reports on the health effects of this radiation are arguably inconclusive. The biological complexity of the human system and the lack of a non-exposed control group complicate the interpretation of data from these studies. Despite these difficulties, researchers suggest that electromagnetic fields may interfere with a cell's ability to process hormonal and enzymatic signals that regulate normal growth. Electromagnetic radiation may also interrupt the flow of calcium ions across cell membranes, which regulates processes such as muscle contraction and cell division.

As scientific evidence increases, a growing number of countries are funding independent investigations into the health effects of electromagnetic fields (EMFs) and implementing regulations to minimize exposure to EMFs. A number of these investigations associate exposure to EMFs with cell mutation, miscarriage, Alzheimer's disease and cancer in humans. In 1992, the Finnish Institute of Occupational Health released a comprehensive study that linked EMFs generated by VDTs with increased miscarriage rates. The study reports that pregnant women exposed to over 3 milligauss (mG) were three times as likely to miscarry as those exposed to less than 1 mG (computer monitors typically emit between 7-20 G at 6 inches) . At least two Swedish studies link exposure to EMFs with increased leukemia risk among children and adult males. As a result of these findings, NUTEK, the Swedish organization that regulates EMF emissions, announced its intent to act on the assumption that EMF exposure causes cancer. The Swedish Institute for Occupational Health now requires that all computer monitors comply with strict emissions standards. Other countries, including the United States, are likely to follow this lead.

In response to increasing health awareness and regulatory pressure, many computer manufacturers now offer computer monitors equipped with internal EMF filters. Several computer accessory manufacturers also offer attachable filters for reducing EMF emissions from existing monitors. For example, U.S. Patent Nos. 4,253,737 and 4,468,702 disclose attachable conductive mesh screens which reduce low frequency radiation emanating from the face of VDTs. These patents also purport to reduce the Moire distortion typically observed with mesh screens, thereby improving clarity. U.S. Patent No. 4,974,935 discloses a mesh shield for use on a color television screen comprising black, anti-reflective conductive filaments. U.S. Patent No. 4,468,702 discloses a nylon screen formed of a plurality of nylon yarns, some of which are electrically conductive. U.S. Patent No. 4,760,456 discloses a conductive screen formed of electrically conductive fibers. U.S. Patent No. 4,839,736 describes a CRT filter comprising a thin conductive film, wherein the film is laminated onto a nonconductive transparent sheet.

Despite the variety of filter devices currently available, a need remains for an EMF shield which enhances the optical properties of the display screen, is sturdy and shatterproof, and effectively eliminates harmful radiation. In particular, none of the available filter devices provide protection against electrostatic charges and low frequency radiation which emanate from the top, bottom and sides of the VDT, and project laterally toward the viewer. Existing shields only reduce radiation from the face of the monitor. Moreover, none of the existing EMF shields can be readily and securely attached to existing terminals, nor are they lightweight and shatterproof. Most existing EMF shields are constructed of glass which is heavy and breakable. Other currently available EMF shields use a woven wire mesh as the conductive component, however woven mesh typically generates wavy interference patterns which compromise the clarity of the displayed image. Moreover, existing EMF shields generally accommodate only one terminal size or a narrow range of terminal sizes. None of the EMF shield devices currently available effectively eliminates harmful radiation, nor do they combine the additional advantages of providing optimal optical qualities while being practical, lightweight and shatterproof.

A need therefore exists for an improved EMF shield which minimizes electromagnetic emissions from electronic equipment by obstructing radiation which emanates from the front, bottom, top and sides of the machine or monitor toward the viewer, is lightweight and shatterproof, provides optimal optical qualities and can be readily and securely affixed to or incorporated into a variety of electronic equipment. It is also an object of this invention to provide an EMF shield comprising a convenient writing surface which extends beyond the perimeter of the video display screen.

Summary of the Invention

The present invention provides an improved electromagnetic emission shield for a variety of electronic equipment, particularly video display terminals (VDT) . This novel design significantly reduces the electrostatic charges and low frequency radiation which emanate from the front, bottom, top and sides of the VDT, the surfaces which emit the highest levels of electromagnetic radiation. The improved electromagnetic emission shield of the present invention comprises an oversize conductive face plate which extends significantly beyond the perimeter of the VDT. The oversize face plate provides additional surface area to attenuate the electrostatic charges and electromagnetic radiation, particularly extremely low frequency (ELF) and very low frequency (VLF) radiation. Also in part because of the oversize design, the electromagnetic emission shield of the present invention can readily accommodate a variety of VDT sizes and shapes.

Another principal object of this invention is to provide an improved electromagnetic emission shield for existing video display terminals, which is lightweight and shatterproof and provides optimal optical qualities for viewing the video display. In accordance with this aspect of the invention, the oversize face plate is a contrast enhancement filter. The contrast enhancement filter may be comprised of any transparent substrate including, without limitation, polycarbonate, acrylic, polyester, polyimide, polyamide or other polymer, copolymers or combinations thereof. The contrast enhancement filter is preferably formed of polycarbonate, such as the polycarbonate substrate sold commercially under the registered trademark "Lexan" (General Electric Co., New York, NY). Contrast enhancement filters enhance image contrast and reduce glare from the screen of the VDT, thus reducing eyestrain and fatigue. Such filters are well known in the art and readily available in commerce. In a preferred embodiment, the oversize face plate is treated with an abrasion-resistant coating such as polysiloxane or an acrylic resin, or other suitable material. Abrasion-resistant coatings are well known in the art and readily available in commerce. The preferred contrast enhancement filter of the present invention comprises an anti-reflective coating on at least one surface. In a particularly preferred embodiment, a polycarbonate substrate is first coated with an abrasion resistant material, and subsequently coated with an electrically-conductive, light- attenuating, antireflection coating. Electrically-conductive, light-attenuating, antireflection coatings are known in the art, including the metallic coatings disclosed in U.S. Patent Number 5,091,244 (Biornard) , incorporated by reference in its entirety herein. The electrically-conductive coating may be applied by chemical vapor deposition, RF or DC sputtering, reactive sputtering, or other suitable means. The preferred electrically- conductive, light-attenuating, antireflection coating is the conductive material sold commercially under the registered trademark "PLASTAR" (Viratec Thin Films, Inc., Faribault, Minn.).

A further object of this invention is to provide an improved electromagnetic emission shield for existing video display terminals, which can be readily and securely attached to the VDT. In accordance with this aspect of the invention, a mounting device is attached to the border on at least two sides of the shield, preferably on opposing sides. In a preferred embodiment, the mounting device is a flap formed from an extension of the opaque border and a resealable adhesive coating, sold commercially under the registered trademark "Dual-Lock" (or 3M Dual-Lock SJ3560 Adhesive) , which is applied to the back of the flap and at a corresponding site on the VDT. Although Dual- Lock™ is the preferred adhesive coating, any substance or combination of substances having suitable adhesive and resealing properties will work. The present invention also contemplates the use of a pair of mating contact strips, for example, the releasable fastener sold commercially under the registered trademark ^MVelcro." Other releasable fasteners suitable for use in the present invention include, without limitation, push-in fasteners, expansion fasteners, panel fasteners, key-hole fasteners, finned fasteners, "arrow-tip" fasteners, bubble snaps, rivet fasteners and poly rivet fasteners. Such fasteners are readily available and well known in the fastening art. In particularly preferred embodiments, the releasable fastener is a one-quarter turn standoff screw fastener or a Nylatch™ push-in fastener, both sold commercially by Hartwell Corporation (Placentia, California) . When the mounting device comprises releasable fasteners, the respective mating members must be placed at appropriate points on the VDT and the emission shield to assure proper positioning of the shield, as will be appreciated by those of skill in the art. The mating members of the releasable fastener may be attached to the VDT and the emission shield by any suitable attachment means including, without limitation, mechanical fastening devices, laminating substances and adhesive materials. Preferably, the male mating member is attached to the emission shield and the corresponding female mating member is attached to the VDT. Depending on the particular releasable fastener, the female mating member may be a pre-punched hole, a bushing, a plastic spacer, a recessed mirror bumper, or any other suitable receiving means. The resealable adhesive coating or releasable fasteners facilitate a secure yet removable connection between the VDT and emission shield. Although resealable adhesives and releasable fasteners are the preferred mounting devices, the present invention contemplates a variety of other attachment means including, for example, suction cups and elastic bands or "bungee" cords.

Yet another object of this invention to provide an improved electromagnetic emission shield for video display terminals which comprises a convenient writing surface. In accordance with this aspect of the invention, the emission shield further comprises an expansive opaque border which serves as a writing surface. The writing surface extends beyond the perimeter of the video display screen, thus providing a convenient surface for writing notes. In a preferred embodiment, the writing surface is formed of a "write-on, wipe-off" material such as a velvet mat-textured polycarbonate. Velvet mat-textured materials are well known in the art and readily available in commerce. Although a velvet mat-texture is the preferred writing surface, any material or combination of materials which provide a suitable writing surface will suffice. The writing surface is laminated onto the outer surface of the conductive face plate and preferably extends from the perimeter of the video display screen to the perimeter of the emission shield. In a particularly preferred embodiment, the border of the emission shield further comprises a clamp-on holder for holding a pencil or a pen with erasable ink, for example, the dry erase pen sold commercially by Sanford Corporation (Bellwood, IL) under the registered trademark "Vis-A-Vis."

Although the border of the electromagnetic emission shield preferably comprises a "write-on, wipe-off" writing surface, the present invention contemplates a variety of functional and/or aesthetic border designs. Suitable border designs include, for example, novelty silk-screen art work, calendars, informative material, charts and tables, customized promotional designs and inspirational messages. Thus, any oversize conductive shielding device which extends significantly beyond the perimeter of the video display terminal is encompassed within the scope of the present invention.

Because of the unique oversize design, the electromagnetic emission shield of the present invention can readily accommodate a wide variety of functional accessories. The expansive border provides a convenient panel to incorporate digital "touch-pads" for such work station accessories as calculators, telephones and telefacsimile machines. The expansive border of the oversize emission shield also provides a convenient attachment site for a variety of accessories including, without limitation, clipboards, pen/pencil holders, paperclip receptacles, calculators, telephones, telefacsimile machines and "rear-view" bubble mirrors. The oversize electromagnetic emission shield can be used with any video display device including, but not limited to, a cathode ray tube (CRT) , digital readout display, liquid crystal display, meter or gauge. The oversize emission shield of the invention is particularly useful where a clear image of the displayed information is required, for example, with computer monitors, instrument panels, television screens, digital clocks, calculators, photocopy machines, microwave oven panels, powered switching devices and automobile dashboards. However, because this shield provides an indiscriminant barrier against electrostatic charges and low frequency radiation, the shield is useful with a wide variety of electronic equipment and apparatuses, for example, junction boxes, circuit breaker boxes, baby incubators, enclosures housing EMF sensitive electronic equipment, and equipment sensitive to radio frequency emissions. The oversize shield can be mounted on any electronic device to provide a transparent electromagnetic shield.

The exact nature of this invention as well as other objects and advantages will be readily apparent from consideration of the specification, including the drawing. Those of skill in the art will appreciate that the invention described herein is susceptible to many modifications and variations without departing from its scope as defined by the appended claims.

Brief Description of the Figures

The accompanying figures illustrate preferred embodiments of the invention, wherein:

FIGURE 1 is a plane view of the inner surface of the oversize electromagnetic emission shield in an embodiment of the present invention.

FIGURE 2 is a perspective view of a video display device showing the oversize electromagnetic emission shield of FIGURE 1 installed thereon. FIGURE 3 is a perspective view of the inner surface of the oversize electromagnetic emission shield in an alternate preferred embodiment of the present invention.

FIGURE 4 is a perspective view of a video display device showing the oversize electromagnetic emission shield of FIGURE 3 installed thereon.

Description of the Preferred Embodiments

Referring now to the drawings, like numbers indicate like features and the same number appearing in more than one figure refers to the same element.

Figures 1-4 illustrate an oversize electromagnetic emission shield 1 comprising an oversize conductive face plate 2 having a central transparent viewing window 3 and an opaque border A . The oversize conductive face plate 2 is a sheet of transparent material cut to the required size. The oversize conductive face plate 2 can be either flat or curved as required for a particular electronic apparatus or video display terminal. The oversize conductive face plate 2 is preferably formed of polycarbonate, but can be any other suitable transparent material. To attenuate electromagnetic emissions in accordance with the present invention, the oversize conductive face plate 2 must further comprise a conductive coating on at least one surface. Examples of conductive coatings include Plastar™, gold, tin oxide, antimony oxide, indium tin oxide, and nitrides of certain transition metals, however any other such coatings well known to those skilled in the art would be suitable.

As illustrated in Figures 2 and 4, the electromagnetic emission shield 1 of the present invention comprises an oversize conductive face plate 2 which extends significantly beyond the perimeter of the video display terminal 5. In other words, the oversize conductive face plate 2 is significantly larger in area than the front surface of the video display device. As used herein, extending "significantly beyond" or being "significantly larger" in area than the front surface of the video display device means that the oversize conductive face plate 2, when centered over the front surface of the video display terminal 5, overlaps the front surface of the display terminal by at least about one inch on each side. The electromagnetic emission shield 1 of the present invention overlaps the video display terminal 5 by at least about one inch, preferably between about 1 to about 8 inches, and most preferably between about 2 to about 4 inches on each side. As exemplified herein, the electromagnetic emission shield 1 of the present invention is at least about 20 percent larger than prior art shields for comparable size monitors. The electromagnetic emission shield 1 of the invention thus provides additional surface area to block radiation which emanates from the top, bottom and sides of the video display device.

In an alternate non-exemplified embodiment, the enhancement of radiation protection obtained by the oversize emission shield 1 may be accomplished by molding the substrate material into a shallow box or cowl, so that the four sides of the shield extend for a distance along the sides of the cabinet to be shielded, forming a removable hood which will obstruct radiation emitted from the top, bottom and sides of the cabinet that might otherwise reach the user. In this non-exemplified embodiment, the emission shield extends beyond the front surface of the video display device and overlaps the top and sides of the device, thereby at least partially enclosing the video display device. Alternatively, the substrate may be molded so as to constitute the cabinet itself and provide complete protection from harmful radiation. In this alternate embodiment, the oversize conductive face plate completely encompasses the electronic equipment or video display device.

In the preferred embodiments illustrated in Figures 1-4, the opaque border 4 functions as a writing surface. The writing surface extends beyond the perimeter of the video display screen 11

(not shown) , thus providing a convenient surface for writing notes. The opaque border 4 is preferably a sheet of "write-on, wipe-off" material, such as a velvet mat-textured polycarbonate, or any other suitable material known in the art. Although the preferred border functions as a writing surface, the opaque border 4 may be any suitable material such as a synthetic or plastic substance. The opaque border 4 is cut to the desired size, then laminated onto the outer surface of the oversize conductive face plate 2 using a suitable adhesive or laminating material, such as "467 mp Adhesive" sold commercially by 3M Corporation (St. Paul, MN) . The laminating material may be any sufficiently tenacious, flexible material capable of performing the necessary lamination and support functions. The laminating material is placed between the oversize conductive face plate 2 and the opaque border 4. In the preferred embodiment, there are no mechanical fastening devices used between the oversize conductive face plate 2 and the opaque border 4. The contact between the two is maintained solely by the laminating or adhesive material. In a preferred embodiment, the opaque border 4 extends from the perimeter of the video display screen (not shown) to the outer perimeter of the oversize conductive face plate 2.

As illustrated in Figures 1-4, the electromagnetic emission shield 1 of the present invention further comprises a mounting device attached to the inner surface of at least two sides of the oversize conductive face plate 2, preferably on opposing sides. In the preferred embodiment illustrated in Figures 1 and 2, the mounting device comprises a pair of flaps 6 and 7 formed from an extension of the opaque border 4 and two mating contact strips 8 and 9, for example, the Velcro™-brand releasable fasteners as exemplified herein. The mating contact strips 8 and 9 are attached to the flaps 6 and 7, respectively, using a suitable adhesive material. The respective mating members for contact strips 8 and 9 are attached at corresponding sites on the video display terminal 5 (not shown) , using a suitable adhesive material. To facilitate proper placement of the electromagnetic emission shield 1 on the video display terminal 5, at least one protective guard (not shown) is inserted between the electromagnetic emission shield 1 and the video display terminal 5. The protective guard(s) may be attached to either the inner surface of the emission shield 1 or the outer surface of the video display terminal 5, using any suitable adhesive material known in the art. In a preferred embodiment, two protective guards are positioned near the center of both the top and bottom sides of the video display terminal 5. Protective guards or pads are typically formed of a resilient synthetic or rubber substance, such as the nylon Bumpon™-brand protector sold commercially by 3M Corporation (St. Paul, MN) . Such protective devices are useful for absorbing shock and preventing damage to the emission shield due to bumping or vibrations. Protective guards and pads are well known in the art and readily available in commerce.

In the alternate preferred embodiment illustrated in Figures 3 and 4, the mounting device comprises a pair of push-in fasteners, for example, the Nylatch™-brand push-in fasteners as exemplified herein. The male mating members 10 and 11 are attached to opposing sides of the electromagnetic emission shield 1. The corresponding female mating members for male mating members 10 and 11 are attached at appropriate sites on the video display terminal 5 (not shown) .

In the preferred embodiment illustrated in Figures 1-2, the electromagnetic emission shield 1 of the present invention further comprises a clamp-on holder 13 and a writing utensil 14, such as the Vis-A-Vis™-brand dry erase pen (Sanford Corporation, Bellwood, IL) exemplified herein.

To complete the electromagnetic enclosure, the oversize conductive face plate 2 must be electrically grounded to a surrounding metallic device or other suitable grounded structure (not shown) . The oversize conductive face plate 2 can be mechanically clamped and electrically connected via a ground leash to the grounded structure, or secured in any suitable fashion which ensures a good electrical ground. Suitable grounding devices and structures are well known in the art and readily available in commerce. The grounding means may vary according to the size and shape of the particular video display device.

Obviously, many modification and variations of the present invention are possible and will be evident to those of ordinary skill in the art. Because of the unique oversize design, the electromagnetic emission shield of the present invention can readily accommodate a wide variety of functional accessories and decorative objects. For example, the border may be modified to incorporate digital "touch-pads" for a variety of accessories including, but not limited to, calculators, telephones and telefacsimile machines. Alternatively, or in addition, the border may be modified to house a variety of accessories including, without limitation, clipboards, pen/pencil holders, paperclip receptacles, picture frames, calculators, telephones, telefacsimile machines and "rear-view" bubble mirrors. Further, while the exemplified embodiments comprise removable fasteners to accommodate existing video display terminals, the emission shield may be custom designed for installation (permanent or removable) onto new display devices. Alternatively, the display device itself may be modified to accommodate the oversize emission shield within the housing. The emission shield may be mounted, for example, within or behind the bezel housing the CRT. Alternatively, the CRT tube itself may formed of the conductive emission shield. Finally, the electromagnetic emission shield may be further modified to include additional safety features such as a light-weight, fiberglass molded hood or a metalized conductive cover. The fiberglass hood or conductive cover may be coated with an electrically-conductive material as described herein to minimize harmful emanations from the top, bottom, sides and back of the video display terminal. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced in ways other than as specifically described herein.

Claims

CLAIMS :

l. An electromagnetic emission shield for reducing electromagnetic radiation from a video display device comprising an oversize conductive face plate significantly larger in area than a front surface of said video display device.

2. The electromagnetic emission shield of claim 1 wherein said oversize conductive face plate comprises a synthetic or plastic substrate.

3. The electromagnetic emission shield of claim 2 wherein said substrate is a polymer or copolymer selected from the group consisting of polycarbonate, acrylic, polyester, polyamide, polyimide, and combinations thereof.

4. The electromagnetic emission shield of claim 2 wherein said substrate is polycarbonate.

5. The electromagnetic emission shield of claim 1 wherein said oversize conductive face plate comprises an electrically conductive, anti-reflective coating on at least one surface.

6. The electromagnetic emission shield of claim 5 wherein said electrically conductive, anti-reflective coating is sold commercially under the registered trademark Plastar™.

7. The electromagnetic emission shield of claim 1 wherein said oversize conductive face plate is a contrast enhancement filter.

8. The electromagnetic emission shield of claim 1 wherein said oversize conductive face plate comprises an abrasion- resistant coating.

9. The electromagnetic emission shield of claim 8 wherein said abrasive-resistant coating is polysiloxane or an acrylic resin.

10. The electromagnetic emission shield of claim 1 wherein said oversize conductive face plate has a removable connection with said video display device.

11. The electromagnetic emission shield of claim 10 wherein said removable connection comprises a resealable adhesive coating.

12. The electromagnetic emission shield of claim 10 wherein said removable connection comprises a releasable fastener.

13. The electromagnetic emission shield of claim 12 wherein said releasable fastener is sold commercially under the registered trademark Velcro™.

14. The electromagnetic emission shield of claim 12 wherein said releasable fastener is selected from the group of fasteners consisting of push-in fasteners, expansion fasteners, panel fasteners, standoff screw fasteners, key- hole fasteners, arrow-tip fasteners, bubble snaps, rivet fasteners and poly rivet fasteners.

15. The electromagnetic emission shield of claim 12 wherein said releasable fastener is a push-in fastener sold commercially under the registered trademark Nylatch™.

16. The electromagnetic emission shield of claim 12 wherein said releasable fastener is a one-quarter turn standoff screw fastener.

17. The electromagnetic emission shield of claim 1 wherein said oversize conductive face plate further comprises an opaque border.

18. The electromagnetic emission shield of claim 17 wherein said opaque border is a writing surface.

19. The electromagnetic emission shield of claim 18 wherein said writing surface comprises a velvet mat-textured polycarbonate.

20. The electromagnetic emission shield of claim 1 wherein said oversize conductive face plate further comprises an accessory selected from the group consisting of a pencil holder, a pen holder, a clipboard, a paperclip receptacle, a calculator, a telephone control panel, a telefacsimile control panel and a rear-view bubble mirror.