WO1994004014A1

WO1994004014A1 - Shielding panel

Info

Publication number: WO1994004014A1
Application number: PCT/US1993/007151
Authority: WO
Inventors: Richard Matthew Cribb
Original assignee: Monsanto Company
Priority date: 1992-08-06
Filing date: 1993-07-29
Publication date: 1994-02-17

Abstract

An air-permeable, electromagnetic radiation-shielding panel comprising metallized textile mounted in a conductive frame for providing electromagnetic radiation shielding of air flow apertures in the walls of an architecturally shielded facility. Preferred metallized textile has an air permeability at a pressure drop of 12.7 mm of water of at least 254 cm3/cm2-sec and exhibits far field shielding of electromagnetic radiation of at least 50 dB over the range of 0.1 to 10 gigahertz. The frame is adapted to be seated in an air flow aperture in a radiation shielding wall covering, comprises a conductive surface, is adapted to secure the edges of the textile and provide electrical contact between the textile and the radiation shielding wall covering.

Description

Disclosed herein are air vents for architectural shielding of electromagnetic interference (EMI) . BACKGROUND OF THE INVENTION

Architectural shielding of buildings or rooms employs a electrically conductive barrier to reflect and/or absorb electromagnetic radiation to protect sensitive equipment from adverse effects of EMI. Such barriers can comprise metal sheet, e.g. copper foil, or metallized textile, e.g. a non-woven fabric. The shielding effectiveness of a facility is typically limited by discontinuity in the integrity of the barrier material, e.g. at doors and utility conduits, e.g. water and drain piping, electrical conduits and air vents. A common method of securing air vents employs one or more layers of metal honeycomb panels where the ratio of length to cross sectional dimension of the honeycomb aperture is at least 4:1. High attenuation of radiation is effected because the honeycomb aperture functions as waveguide below cut-off. One difficulty is that honeycomb panels are difficult to clean, e.g. to remove dust. Thus, with time the honeycomb panels can suffer from reduced air flow.

Attempts to employ other air permeable shielding materials, e.g. metallized fabric, have not proved useful because metallized textiles having a sufficiently high shielding effectiveness typically suffer from undesirably low air permeability. alternatively, metallized textiles having sufficiently high air permeability typically suffer from undesirably low shielding effectiveness.

One object of this invention is to provide a replaceable, air-permeable, electromagnetic radiation- shielding panel adapted to provide radiation shielding in an air flow aperture in radiation shielding wall covering. Another object is to provide an air- permeable, electromagnetic radiation-shielding panel comprising metallized textile which exhibits suffi¬ ciently high air permeability and radiation shielding effectiveness. SUMMARY OF THE INVENTION

This invention provides an air-permeable, electromagnetic radiation-shielding panel comprising metallized textile mounted in a conductive frame. The metallized textile has an air permeability at a pressure drop of 12.7 mm of water of at least 254 cm³/cm²-sec and exhibits far field shielding of electromagnetic radiation of at least 50 dB over the range of 0.1 to 10 gigahertz. This invention also provides an adapter for mounting the air permeable shielding panel in an air flow aperture in a radiation shielding wall covering. The adapter comprises a conductive surface and provides an electrical connection between the air permeable shielding panel and the radiation shielding wall covering. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a partial isometric view of an electromagnetic shielding panel of this invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein the term "air permeability" means air flow through a metallized textile material under a differential pressure of 12.7 mm of water between the two surfaces of the textile material as measured in accordance with ASTM D 737-75: Standard Test Method for Air Permeability of Textile Fabrics; air permeability is expressed in units of "cm³/cm²-sec" or "cm/sec".

As used herein the term shielding effec¬ tiveness means the attenuation of electromagnetic radiation over the range of 0.1 to 10 gigahertz as measured in accordance with MIL-STD-285 and is expressed in units of "decibels" or "dB".

The air-permeable, electromagnetic radiation-shielding panel of this invention comprises metallized textile mounted in a conductive frame. The metallized textile employed in this invention is selected on the basis of two critical characteristics high air permeability and high shielding effectiveness. Preferably the metallized textile is a metallized non-woven fabric, e.g. having a metal coating of copper, nickel, silver, tin and the like. More preferably the fabric is coated with a layer of copper and a corrosion-resistant outer layer of nickel, silver or tin.

Preferably the metallized textile has an air permeability at a pressure drop of 12.7 mm of water (0.5 inch of water) of at least 250 cm³/cm²-sec (about 500 ft³/ft²-min) , more preferably at least 300 cm³/cm²- sec. Preferably the metallized textile exhibits a shielding effectiveness of at least 50 dB over the range of 0.1 to 10 gigahertz, more preferably at least 60 dB or higher, say about 70 dB. Especially preferred metallized textile exhibits a shielding effectiveness of at least 80 dB, even more preferably at least 90 dB. A preferred textile meeting these critical characteristics is a copper-coated, non-woven polyethylene terephthalate (PET) fabric, where the PET fabric has a base weight of at least 33 grams/square meter (g/m²) , e.g. in the range of 33-50 g/m². The fabric preferably comprises at least about 20-30 weight percent metal, e.g copper or copper with a protective layer of nickel, silver or tin. A useful metallized textile is available from Monsanto Company as FLECTRON copper-coated PET non-woven fabric which has a basis weight in the range of 55-65 g/m² typically exhibits far field shielding effectiveness of 80-110 dB in the range of 0.1 to 10 gigahertz and air permeability in the range of 280-345 cm³/cm²-sec. Preferably the frame of the air permeable shielding panel is metal or metal surfaced to provide an electrical connection between the metallized textile and the frame. The metallized textile can be mounted in the conductive frame by a variety of means. For instance, the metallized textile can be secured in the frame by a conductive adhesive, solder or the like. Alternatively, the metallized textile can be secured in the frame by mechanical means, e.g. the edges of the frame can be crimped over the periphery of the textile. Other mechanical fastening means can comprise a flange for securing the textile to the body of the frame by a variety of fasteners. Alternatively, the textile itself can comprise a peripheral ring which can be mounted to the frame by fasteners, clamps, magnets and the like. Regardless of means for mounting the textile to the frame, it should be apparent that the mounting material should encompass the periphery of the textile in the frame to prevent the passage of radiation at the area of mounting.

This invention also provides a conductive filter adapter for mounting the air permeable shielding panel in an aperture in a shielded wall. Such adapter will comprise a flange for overlapping the shielding wall covering and a duct member for extending into the wall for communication with air supply/exhaust ductwork. The adapter is also provides with a seat for mounting the frame of the air permeable shielding panel. The shielding panel can be externally mounted, e.g. on the flange overlapping the shielding wall covering, or can be internally mounted, e.g. in the duct member. In some cases it may be desirable to employ radiation shielding gaskets between the components in the area of mounting, e.g. between the frame and the adapter or between the adapter and the wall. Alternatively, it may be useful to apply a layer of metallized tape over the mounting of the textile to the frame. It is critical that an electrical connection be established between the metallized textile, the frame, the adapter and the shielding wall covering. If the contact between the components does not afford adequate electrical connection it may be useful to employ grounding wires between the components.

Figure 1 illustrates one embodiment of this invention where conductive filter adapter 1 is mounted in an opening in a shielded wall defined by framing members 2. The shielded wall comprises a shielding layer 3, e.g. metal foil or metallized fabric, overlaying wallboard 4. External flange 5 of the conductive filter adapter overlaps the shielding layer by a sufficient amount to reduce radiation penetration via a waveguide effect. The external flange can be secured to the wall by fasteners into the framing members, or by adhesive to the shielding layer. The conductive filter adapter has a duct member 6 for connection to air supply and/or exhaust ductwork. An air-permeable, electromagnetic radiation-shielding panel 7 is mounted on the conductive filter adapter, e.g. on internal flange 8 which can be recessed below the surface of the wall to facilitate mounting of a decorative external vent, not shown. Alternatively, the shielding panel 7 can be mounted on the external flange 5. The shielding panel comprises a metallized textile 9 as described herein secured in a peripheral conductive frame 10 and by reinforcing members 11, e.g. wire mesh, hole-punched metal foil and the like. The shielding panel can be mounted to the conductive filter adapter by a variety of means, e.g. screws, spring clips, adhesive and the like. It may be desirable to cover joints between the conductive filter adapter and the shielding panel and the wall shielding layer with a shielding tape.

While specific embodiments have been described herein, it should be apparent to those skilled in the art that various modifications thereof can be made without departing from the true spirit and scope of the invention. Accordingly, it is intended that the following claims cover all such modifications within the full inventive concept.

Claims

WHAT IS CLAIMED IS:

1. An air-permeable, electromagnetic radiation-shielding panel adapted to provide radiation shielding in an air flow aperture in radiation shielding wall covering, said panel comprising metallized textile mounted in a conductive frame; wherein said metallized textile has an air permeability at a pressure drop of 12.7 mm of water of at least 254 cm³/cm²-sec and exhibits far field shielding of electromagnetic radiation of at least 50 dB over the range of 0.1 to 10 gigahertz.

2. A panel according to claim 1 wherein said textile is a copper coated PET non-woven fabric.

3. A panel according to claim 2 wherein said copper is coated with nickel, silver or tin.

4. An air-permeable, electromagnetic radiation-shielding panel adapter comprising a duct member for extending through a wall, a flange member for extending beyond an aperture in shielded wall to overlay shielding wall covering and means for mounting an air-permeable, electromagnetic radiation-shielding panel.

5. An air-permeable, electromagnetic radiation-shielding wall assembly comprising (a) an air-permeable, electromagnetic radiation-shielding panel comprising metallized textile mounted in a conductive frame, wherein said metallized textile has an air permeability at a pressure drop of 12.7 mm of water of at least 254 cm³/cm²-sec and exhibits far field shielding of electromagnetic radiation of at least 50 dB over the range of 0.1 to 10 gigahertz; and (b) an adapter comprising a duct member for extending through a wall, a flange member for extending beyond an aperture in shielded wall to overlay shielding wall covering and means for mounting said shielding panel.

6. A panel according to claim 5 wherein said textile is a copper coated PET non-woven fabric.

7. A panel according to claim 6 wherein said copper is coated with nickel, silver or tin.