WO1996006520A1

WO1996006520A1 - A see-through radiation shielded assembly

Info

Publication number: WO1996006520A1
Application number: PCT/US1994/011681
Authority: WO
Inventors: Craig D. Lack; Robert L. Sowell, Iii; Kyle K. Whittaker
Original assignee: W. L. Gore & Associates, Inc.
Priority date: 1994-08-19
Filing date: 1994-10-17
Publication date: 1996-02-29
Also published as: AU7979394A

Abstract

A transparent radiation shielded assembly is provided for use with visual display panels having a conductive screen with a planar surface and a polymeric-conductive gasket which is attached to the perimeter of the screen by a layer of conductive adhesive. An assembly with a visual display window is also provided.

Description

TITLE OF THE INVENTION

A SEE-THROUGH RADIATION SHIELDED ASSEMBLY

FIELD OF THE INVENTION

This invention relates to a radiation shielded assembly for use with visual display panels.

BACKGROUND OF THE INVENTION

Many electronic equipment enclosures and housings provide visual display panels for operators to observe read-out data and other information. The visual displays are covered by windows that must be treated to prevent exposure to and from electromagnetic (EMI) and radio frequency (RFI) radiation generated by equipment. Those visual displays are found on equipment such as cathode ray tubes, electroluminescent displays, plasma displays, vacuum fluorescent displays, liquid crystal displays (LCD), light- emitting diodes (LED), control panel fronts, and architectural windows. Many types of windows or optical substrates and laminates used for electronic equipment are commercially available from manufacturers such as Homalite™, Division of Whitco, Inc., of Wilmington, DE and Dontech, Inc. of Doylestown, PA. Such windows include acrylics or polymethymethacrylates (PMMA), polycarbonates (PC), glass, allyl diglycol carbonates (ADC), and thermosetting polyesters. Many of these windows are further treated to reduce the emission of radiation to the environment.

Traditional methods of treatment to minimize exposure to radiation include use of fine wire meshes sandwiched between layers or imbedded within a layer of the windows or use of vapor deposited conductive coatings over the exterior surface or within a layer of the window.

The treated window must also be terminated to a ground plane to create an effective EMI/RFI enclosure. This often requires extending the mesh beyond the surface of the windows so that there is direct contact with the termination surface or painting with a conductive coating the exterior edges of the windows and mesh or providing a conductive tape or bus around the exterior of the windows and mesh so that there is a conductive contact between the windows with mesh and the termination surface. The edge coating termination is difficult to achieve repeatedly and often results in shield reliability problems.

Typical shielded windows employing these traditional piece-meal methods of termination are prone to improper installation and are only marginally effective in attenuating the radiation emitting from the visual display. There is a need for an improved assembly that provides a more effective, reproducible, shield against electromagnetic and radio frequency radiation and facilitates easier and more reliable installation for visual display panels.

SUMMARY OF THE INVENTION

A radiation shielded assembly for use with visual display panels is provided. The assembly is effective in reducing the electromagnetic and radio frequency interference that is generated to and from the display panel of various sorts of electronic equipment.

The assembly is constructed with a conductive screen having a planar surface area, a polymeric conductive gasket that surrounds the perimeter of the conductive screen and overlaps the screen in an area proximate the perimeter, and at least one layer of a conductive adhesive wherein the conductive adhesive is affixed to the surface of the conductive gasket so as to adhere and conductively connect the gasket to the conductive screen thereby forming a shielded assembly having all components conductively connected and provide shielding from electromagnetic and radio frequency radiation. The conductive screen may include a conductive mesh, film or conductive coating and the conductive gasket may include elastomers filled with conductive particles, metal wires, or graphite or expanded polytetrafluoroethylene impregnated or filled with conductive particles. A second layer of adhesive may also be applied adjacent the conductive layer of adhesive for attachment to a window. The second layer of adhesive may optionally be conductive as well.

The shielded assembly may also include a panel window to which the screen and gasket are applied. Means of attaching the components to the window as well as the assembly to an electronic unit are also provided. The assembly of either embodiment may also be provided with a third layer of adhesive located on the other side of the conductive gasket As used herein, conductive means electrically conductive. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is an exploded view of the shielded assembly.

Figure 1a is a front view of the outside surface of the assembly shown in Figure 1.

Figure 1b is a cross-sectional view taken through line A-A' of Figure 1a.

Figure 2 is a front view of the outside surface of the assembly having a circular shape.

Figure 3 is an exploded view of the shielded assembly with visual control panel.

Figure 3a is a cross-sectional view of the assembly shown in Figure 3.

Figures 4a, 4b and 4c are cross-sectional views showing other means of attaching the shielded assembly to a window.

Figure 5 shows a front perspective view of an electronic unit with visual display panel.

Figure 5a is a side view of the electronic unit with shielded assembly attached thereto by bolting means 15.

DETAILED DESCRIPTION OF THE INVENTION

A shielded assembly is provided for use with an electronic unit. The assembly requires the use of only a single window layer as shown in Figures 5 and 5a and does not require that it be sandwiched between multiple layers of windows or plates. In addition, this shielded assembly provides the necessary transparency and visibility to enable one to view the data displayed on the panel.

The shielded assembly is best understood with reference to the drawings.

Figure 1 shows an exploded view of the assembly 1. When assembled, the components form a layered article having contiguous conductively connected layers comprising a conductive screen 4 that has a planar surface and perimeter, a conductive gasket 2 that surrounds the entire perimeter of the screen 4 and overlaps an area of the conductive screen 4 proximate the perimeter. This can best be seen in Figure 1a. The two components are bonded together by a layer of conductive adhesive 6 such that the adhesive layer is sandwiched between the screen and gasket as shown in Figure 1b. The components are essentially flat or planar (i.e. lengths and widths are much greater than thicknesses). When applied to a visual display panel, the assembly maintains this essentially flat and planar configuration. An optional layer of an adhesive 8 may be used to mount the assembly to a window panel of the electronic equipment. This optional adhesive layer need not be but preferably is conductive. A means of aiding the shielded assembly in the form of a non-conductive adhesive layer 9 may also optionally be provided. This additional adhesive layer 9 provided to the side of the gasket 2 that does not have the other adhesive layers as shown in Figure 1b.

The conductive gasket 2 may be made of any material having suitable conductivity, scalability, and chemical resistance. Commercially available conductive gasket materials include elastomers filled or impregnated with conductive particles, metal wire filings, expanded graphite and other conductive materials. A preferred material for the conductive gasket 2 is expanded polytetrafluoroethylene filled or impregnated with conductive particles such as carbon. A conductive gasket, GORE-SHIELD® electrically conductive gasketing commercially available from W. L. Gore & Associates, Inc. of Elkton, MD, is particularly suitable. This conductive gasket 2 when assembled with the screen and panel is subsequently grounded to the electronic unit by contact. The conductive screen 4 is comprised of either a conductive woven mesh or film. Conductive meshes are made from a plurality of woven wires such as stainless steel, copper, phosphor bronze, silver, tin, and conductive polymeric fibers such as metal plated or metal sputtered polymeric fibers or fibers made conductive by impregnating or filling them with conductive materials. The wires may further be coated with other materials such as black oxides. The polymeric fibers may be made from the same materials as identified below for the polymeric films.

Conductive films may include polymeric nonwoven films that are rendered conductive by metal plating, vapor deposition, impregnating, sputter coating or other conventional methods so as to render them conductive.

Polymeric materials may include but are not limited to polyamides, polyesters, polyolefins, polyurethanes, and fluoropolymers. Regardless of the material, the conductive screen 4 must be substantially transparent and be capable of substantially reflecting, intercepting, or otherwise attenuating electromagnetic and/or radio frequency radiation.

The layer of conductive adhesive 6 is used to bond together the conductive gasket 2 and conductive screen 4. Here, the adhesive 6 is positioned on a surface of the gasket that is in contact with and overlaps an area of the outer surface around the perimeter of the conductive screen 4 as can be seen in Figure 1b.

The electrically-conductive adhesive is commercially available from many manufacturers. Suitable adhesives include but are not limited to the classes of thermoplastic, thermosetting, or reaction curing polymers to which conductive particles have been added as fillers to make them conductive. Suitable conductive filler particles include metal particles such as silver, gold, nickel, and stainless steel, silver coated ceramics or highly conductive carbon particles. The conductive adhesive may be applied to the desired surface by conventional means such as by printing, coating, or as a preformed sheet or web. Other conventional methods are also suitable. The conductive adhesive may be applied as a continuous layer so that there are no gaps or spaces within the layer or as a non-continuous coating such as a printed dot pattern. Preferably, the conductive adhesive layer 6 is a pressure-sensitive polymer film containing conductive carbon particles and has an electrical volume resistivity of at least 10 ohm-cm. such as a conductive acrylic resin-based transfer adhesive, containing carbon particles, commercially available from Adhesives Research Corp. of Glen Rock, Pennsylvania.

An optional second layer of adhesive 8 may also be provided adjacent the first conductive adhesive layer 6 on the same side of the gasket 2. This second layer of adhesive can be made from the same materials as described above for the conductive adhesive 6 and may be conductive as well but may also be non-conductive, Pressure-sensitive non-conductive adhesives are also commercially available from Adhesives Research Corp. of Glen Rock, PA. This second adhesive layer 8 is used to mount the conductive gasket 2 with screen 4 attached to a separate window or directly onto a display panel provided on the electronic equipment. The assembly 1 is positioned so that the conductive screen 4 is in direct contact with the window and the adhesive layer 8 bonds the conductive gasket 2 to the window to help hold the screen in place. Although not clear from Figure 3a, the gasket and adhesive layers 6 and 8 are conformable so that they bend slightly to come in contact with window 12. Also, the screen 4 is not as thick as shown in the figures.

A third layer of adhesive 9, also optional may be provided on the surface of the gasket 2 opposite the surface having the two adjacent adhesive layers 6 and 8 as shown in Figure 1 b. This third layer of adhesive 9 aids in positioning the assembly 1 to the electronic device. This adhesive layer 9 need not be conductive provided that the conductive gasket 2 has a ground path to the unit. Other means of attachment 15 such as nuts and bolts, snaps or clamps are also suitable to connect the assembly to the visual display or window as shown in Figures 4a, 4b and 4c, respectively. These means may be used to both attach the assembly components to the window or panel as well as to attach the entire assembly to the electronic unit as shown in Figure 5a.

The assembly may have the shape of the window to which it is attached which is generally but not limited to being rectangular (as in Figure 1) or circular as shown in Figure 2.

A second embodiment is also provided and shown in Figure 3 and 3a. Here the assembly also includes a single visual display panel window 12 to which the shielded assembly is bonded via the layer of adhesive 8' which adheres gasket 21 and screen 4' to the window 12 in a planar configuration so that there is no space between the adhesive layer 8' and window 12. Windows are commercially available, from manufacturers such as Homalite™ of Wilmington, DE and Dontech, Inc. of Doylestown, PA and may be made of acrylics or polymethymethacrylates, polycarbonates, glass, ally) diglycol carbonates, and thermosetting polyesters. As described previously, shield 1' that fits onto this window is not required to be sandwiched between other windows or panels. The window with shield are then applied directly onto a display panel.

EXAMPLES

Woven Mesh Assembly - Example 1 A see-through or transparent radiation shielded assembly was constructed from a GORE-SHIELD® gasket commercially available from W. L. Gore & Associates of Elkton, MD, and a mesh of stainless steel wires that had been chemically-blackened to reduce light reflection off the mesh, commercially available from Adtec, Co., of Lawrence, MA. The gasket and mesh were rectangular in shape.

The mesh had wires with diameters of 0.0012 inches (3.05 mm) with a mesh count of 50 count per inch (20 count per cm) which was substantially transparent so that data from a visual panel could be observed. The gasket comprised four strips of GORE-SHIELD® tape that were each one inch (2.54 cm) wide and 20 mils (0.51 mm) thick. A layer of conductive adhesive was located on one full surface of each of these strips.

The rectangular mesh (7.5 in.) by 7.5 in (19.2 x 19.2 sq. cm) was first placed on a thermoplastic transparent window commercially available from Homalite® of Wilmington, DE and centered. Two strips of GORE-SHIELD® both 8 in (20.3 cm) long were placed on opposite sides of the mesh so that half of the width of each strip was covered with the mesh and the other half of the width of GORE-SHIELD®. Two strips of GORE-SHIELD® both 6 inches (15.2 cm) long were placed on the other two sides of the mesh that had not been covered in the same way as the previous two. The final construction is shown in Figures 3 and 3a.

The window assembly was then bolted to a 1/16 inch (0.16 cm) thick aluminum panel to simulate attachment to a visual display panel of an electronic device and tested using a modified military specification test MIL-

285.

The bolted assembly was placed in a test chamber with an antenna and receiver commercially available from Electro-mechanics Co. of Austin, TX. Test results were as follows:

SHIELDING EFFECTIVENESS ATTENUATION TEST

Frequency of Radiation Attenuation (dBϊ

200 MHz - 1 GHz greater than 40 1-3 GHz greater than 45

Optimal shielding results were between 1 and 3 GHz with an attenuation of greater than 40 dB.

Metallized Film Assembly - Example 2 A see-through or transparent radiation shielded assembly was constructed similar to that described in Example 1 except that the mesh of stainless steel was substituted with a polyester substrate film that was treated with an indium-tin oxide (ITO) vapor, commercially available from Sheldahl of Northfield, MN. The resistivity of the film was determined to be 22 ohms/sq in (3.41 ohms/sq cm), light transmission of 87% to 89%.

Similar construction and test methods as described in Example 1 were used.

Test results were as follows:

Frequency of Radiation Attenuation (dB) 200 MHz - 1 GHz nominally 15

1-3 GHz greater than 20

Optimal shielding results were between 1 and 3 GHz with an attenuation of greater than 20 dB.

Claims

CLAIMS:

1. A transparent radiation shielded assembly for use with visual display panels comprising: (a) a conductive screen having a planar surface and perimeter,

(b) a polymeric conductive gasket that surrounds the perimeter of the conductive screen and overlaps the screen surface in an area proximate the perimeter; and

(c) at least one layer of a conductive adhesive wherein the conductive adhesive is affixed to the conductive gasket in the area of overlap with the conductive screen so as to adhere and conductively connect the gasket to the screen.

2. A transparent radiation shielded assembly as described in Claim 1 wherein the conductive screen is a conductive mesh comprised of a plurality of woven conductive wires.

3. A transparent radiation shielded assembly as described in Claim 2 wherein the conductive wires are selected from the group including stainless steel, copper, phosphorus bronze, silver, tin, and conductive polymeric fibers.

4. A transparent radiation shielded assembly as described in Claim 1 wherein the conductive screen is a conductive nonwoven film.

5. A transparent radiation shielded assembly as described in Claim 4 wherein the conductive nonwoven film is selected from the group including polyamidβs, polyesters, polyolefins, polyurethanes, and fluoropolymers that have been rendered conductive.

6. A transparent radiation shielded assembly as described in Claim 1 wherein the conductive gasket is selected from the group of elastomers impregnated with conductive particles, metal wires, and graphite.

7. A transparent radiation shielded assembly as described in Claim 1 wherein the conductive gasket is comprised of expanded porous polytetrafluoroethylene impregnated with conductive particles.

8. A transparent radiation shielded assembly as described in Claim 1 wherein the conductive adhesive is a pressure-sensitive acrylic-resin- based adhesive that contains carbon particles.

9. A transparent radiation shielded assembly as described in Claim 1 further comprising a means to connect the assembly to a display panel window.

10. A transparent radiation shielded assembly as described in Claim 9 wherein the means to connect are selected from the group including nuts, and bolts, snaps and clamps.

11. A transparent radiation shielded assembly as described in Claim 9 wherein the means to connect include a second layer of adhesive which is optionally conductive and is located on the gasket adjacent the first layer of conductive adhesive.

12. A transparent radiation shielded assembly as described in Claim 1 further comprising an optionally conductive layer of adhesive located on the polymeric conductive gasket on a surface opposite the one with the conductive adhesive layer(s).

13. A transparent radiation shielded assembly as described in Claim 1 wherein the shielded assembly is circular in cross-section.

14. A transparent radiation shielded window assembly comprising: (a) a conductive screen having a planar surface and perimeter;

(b) a polymeric conductive gasket that surrounds the perimeter of the conductive screen and overlaps the screen surface in an area proximate the perimeter;

(c) a first layer of a conductive adhesive wherein the conductive adhesive is affixed to the conductive gasket in the area of overlap with the conductive screen so as to adhere and conductively connect the gasket to the screen;

(d) a control panel window located so that the conductive screen is positioned between the conductive gasket and control panel window; and

(e) a second layer of a conductive adhesive located adjacent the first layer of conductive adhesive and between the conductive gasket and control panel window so as to form an attachment thereby forming an assembly that provides shielding from radiation.

15. A transparent radiation shielded assembly as described in Claim 14 wherein the conductive screen is a conductive mesh comprised of a plurality of woven conductive wires.

16. A transparent radiation shielded assembly as described in Claim 15 wherein the conductive wires are selected from the group including stainless steel, copper, phosphorus bronze, silver, tin, and conductive polymeric fibers.

17. A transparent radiation shielded assembly as described in Claim 14 wherein the conductive screen is a conductive nonwoven film.

18. A transparent radiation shielded assembly as described in Claim 17 wherein the conductive nonwoven film is selected from the group including polyamides, polyesters, polyolefins, polyurethanes, and fluoropolymers that have been rendered conductive.

19. A transparent radiation shielded assembly as described in Claim 14 wherein the conductive gasket is selected from the group of elastomers impregnated with conductive particles, metal wires, and graphite.

20. A transparent radiation shielded assembly as described in Claim 14 wherein the conductive gasket is comprised of expanded porous polytetrafluoroethylene impregnated with conductive particles.

21. A transparent radiation shielded assembly as described in Claim 14 wherein the conductive adhesive is a pressure-sensitive acrylic-resin- based adhesive that contains carbon particles.

22. A transparent radiation shielded assembly as described in Claim 14 further comprising an optionally conductive layer of adhesive located on the polymeric conductive gasket on a surface opposite the one with the conductive adhesive layer(s).

23. A transparent radiation shielded assembly as described in Claim 14 wherein the shielded assembly is circular in cross-section.