Abstract:
An electromagnetically shielded enclosure that is portable and lightweight with a double perimeter entry seal. The electromagnetically shielded enclosure can be used for applications such as testing and security and can be scaled from a bench top unit to a large field deployed enclosure. The electromagnetically shielded enclosure has a novel entry seal that eliminates the electromagnetic leakage that is common around the entry areas of such enclosures. The entry seal of the electromagnetically shielded enclosure is made up of a door having a first perimeter closure material and a second perimeter closure material and an enclosure opening having a first perimeter closure and a second perimeter closure where the first perimeter closure material aligns with the first perimeter closure and the second perimeter closure material aligns with the second perimeter closure. This double perimeter entry seal provides for electromagnetic isolation within the electromagnetically shielded enclosure.

Description:
CROSS REFERENCE TO RELATED PATENT APPLICATIONS 
       [0001]    This application claims priority to U.S. Patent Application Ser. No. 61/577,570 filed Dec. 19, 2011 entitled “Electromagnetically Shielded Enclosure And Double Perimeter Entry Seal” by Gary William Winch of Naples, N.Y. and Brian Donald Smith of Keuka Park, N.Y., the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates generally to electromagnetic shielding, and more specifically to an electromagnetically shielded enclosure having a double perimeter entry seal. 
         [0004]    2. Description of Related Art 
         [0005]    As the proliferation of radiofrequency generating devices continues at a rapid pace, there is an ongoing and growing need to shield from unwanted electromagnetic radiation for various purposes. For example, certain electronic equipment requires an electromagnetically “quiet” environment to function properly. Such equipment includes, for example, some medical diagnostic and imaging equipment. In addition, testing of electronic equipment often requires a similar electromagnetically “quiet” environment. 
         [0006]    In some situations, there is also the need to prevent radiofrequencies from leaving a confined physical area. Such situations include, for example, the use of computer and military electronics where there is the risk of unwanted detection, of a radiated radiofrequency signal or unwanted detection, of the associated harmonics and signature of radiofrequency activity. 
         [0007]    Further, testing such as EMI/EMC testing requires the monitoring of electromagnetic energy released from a device under test in a controlled environment where there are little or no outside sources of electromagnetic radiation that could interfere with the monitoring of the device under test. Such testing may also include subjecting a device under test to external electromagnetic energy and monitoring the impact of this external electromagnetic energy on the proper functioning of the device under test. 
         [0008]    With the various requirements for electromagnetically shielded enclosures, there exists a need to make these enclosures portable. Lightweight, rapidly deplorable, temporary, and relatively low cost. With the advent of metalized fabrics and textiles, shielded tents and portable enclosures are available today. These enclosures are essentially a Faraday Cage where electromagnetic signals should not pass. Such enclosures come in many shapes and sizes, and. are available from various manufacturers. While such enclosures are available, their shielding effectiveness may not always be adequate due to radiofrequency leakage at seams and ingress/egress points such as doors. As such, the overall construction of a portable electromagnetically shielded, enclosure is a vital part of the performance of the shielded enclosure. 
         [0009]    The shielding effectiveness of a portable electromagnetic enclosure is controlled by several variables, including the type of metalized fabric used and the overall construct of the portable electromagnetic enclosure. Stitching, fasteners, ventilation, and ingress/egress panels all must be properly designed to limit the amount of electromagnetic leakage. Most portable electromagnetic enclosures have an ingress/egress section such as a door or removable panel. Such doors and panels are prone to electromagnetic leakage, particularly where the door or panel meets the side of the electromagnetic enclosure. 
         [0010]    It is thus an object of the present invention to provide an electromagnetic enclosure that is portable, lightweight, rapidly deployable, temporary, and relatively low cost. It is another object of the present invention to provide an electromagnetic enclosure with an entry seal that is not prone to electromagnetic leakage, it is another object of the present invention to provide an entry seal for an electromagnetic enclosure that is has a double perimeter seal that is not prone to electromagnetic leakage. It is another object of the present invention to provide an electromagnetic enclosure that Is portable and easily adjustable. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    In accordance with the present invention, there is provided an electromagnetically shielded enclosure having an entry seal where the entry seal comprises a door having a first perimeter closure material and a second perimeter closure material and an enclosure opening having a first perimeter closure and a second perimeter closure where the first perimeter closure material aligns with the first perimeter closure and the second perimeter closure material aligns with the second, perimeter closure to provide for electromagnetic isolation within the electromagnetically shielded enclosure. 
         [0012]    The foregoing paragraph has been provided by way of introduction, and is not Intended to limit the scope of the invention as described in this specification, claims, and the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The invention will be described by reference to the following drawings, in which like numerals refer to like elements, and in which: 
           [0014]      FIG. 1  is a perspective view of an electromagnetically shielded enclosure and double perimeter entry seal in use; 
           [0015]      FIG. 2  is a perspective view of an electromagnetically shielded enclosure and double perimeter entry seal; 
           [0016]      FIG. 3  is a plan view of a feedthrough side of an electromagnetically shielded enclosure 
           [0017]    of the present invention; 
           [0018]      FIG. 4  is a plan view of an entry side of an electromagnetically shielded enclosure and double perimeter entry seal: 
           [0019]      FIG. 5  is a top plan view of an electromagnetically shielded enclosure of the present invention; 
           [0020]      FIG. 6  is a partially cutaway view of an entry side of an electromagnetically shielded enclosure and double perimeter entry seal; 
           [0021]      FIG. 7  is a close-up view of the enclosure to frame retention assembly: 
           [0022]      FIG. 8  is a close-up view of the enclosure to frame retention assembly with a quick release buckle in the open position; 
           [0023]      FIG. 9  is a cross sectional view of the fabric construction for the window seal of the electromagnetically shielded enclosure; 
           [0024]      FIG. 10  is a fabric fold diagram of the accordion bias depicted in  FIG. 9 ; and 
           [0025]      FIG. 11  is an exploded diagrammatic view of the double perimeter seal of the present invention. 
       
    
    
       [0026]    The present invention will be described in connection with a preferred embodiment however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by this specification, claims, and the attached drawings. 
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    There are various techniques for the design and construction of an electromagnetically shielded enclosure. The shape, size and materials selected for an electromagnetically shielded enclosure may vary based on the intended application. The present invention and the various embodiments depicted and envisioned herein do not rely on specific geometries, materials, or structural designs, but rather, the entry seal of the present invention may be adapted and modified to fit a wide range of electromagnetically shielded enclosures. Such adaptations and modifications will become evident to one skilled in the art after reading this specification and claims, and viewing the attached drawings. 
         [0028]    For a general understanding of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. 
         [0029]      FIG. 1  is a perspective view of an electromagnetically shielded enclosure and double perimeter entry seal in use. The electromagnetically shielded enclosure  100  depicted in  FIG. 1  uses a frame  101  for support; such external frames are readily available in various configurations by various manufacturers. An example of a manufacturer of frames is Rose and Krieger of Frederick, Md. Frames may be made from aluminum, fiberglass, or other suitable structurally sufficient material. Various manufacturers and frame designs may be used without departing from the spirit and scope of the present invention and its various embodiments depicted, described, illustrated or envisioned herein. The entry seal of the present invention may also be used with an electromagnetically shielded enclosure that is frameless, or uses an internal frame, an inflatable structure, or the like. 
         [0030]    The electromagnetically shielded enclosure  100  includes a novel magnetic sealing arrangement that provides for electromagnetic shielding and reduces the electromagnetic “leaks” common in the door and entry areas of many electromagnetically shielded enclosures. The electromagnetically shielded enclosure  100  has an entry seal where the entry seal comprises a door having a first perimeter closure material and a second perimeter closure material and an enclosure opening having a first perimeter closure and a second perimeter closure where the first perimeter closure material aligns with the first perimeter closure and the second perimeter closure material aligns with the second perimeter closure to provide for electromagnetic isolation within the electromagnetically shielded enclosure. The closure material may be a conductive hook and loop fastening material, a rigid flap, a weight strip, conductive foam, a radiofrequency absorber material, a conductive zipper, a magnet, a magnetic strip, or the like. In one preferred embodiment of the present invention, the electromagnetically shielded enclosure  100  has an entry seal where the entry seal comprises a door having a first perimeter door magnet and a second perimeter door magnet and an enclosure opening having a first perimeter enclosure magnet and a second perimeter enclosure magnet where the first perimeter door magnet aligns with the first perimeter enclosure magnet and the second perimeter door magnet aligns with the second perimeter enclosure magnet to provide for electromagnetic isolation within the electromagnetically shielded enclosure. The manufacture and use of the entry seal of the present invention and its various embodiments will become evident upon further review of this specification, claims and drawings. 
         [0031]    The electromagnetically shielded enclosure  100 , as depicted in  FIG. 1 , is supported by the frame  101  by way of retaining straps  103 , bungee cords, quick release buckles and fasteners, or similar retention devices. These retention devices are commonly made from nylon, polyester, and the like and may include additional hardware. The electromagnetically shielded enclosure  100  has sides  105 , as well as top and bottom, that are made from a conductive material such as, for example, a metalized woven textile, a mesh, a metal, a non-woven textile or metal, and the like. Other materials may also be included in the electromagnetically shielded enclosure. In addition, the materials may be layered or compositely structured to accomplish additional shielding effectiveness, weather resistance, structural, integrity, and the like. An. example of such a metalized woven textile Is a silver plated woven nylon ripstop fabric sold under the tradename ProTex Ag by Carolina Silver Technologies of Maiden, N.C. In some embodiments of the present invention, the fabric may be fire retardant or be treated with a fire retardant coating or impregnation. An example of a flame retardant coating is a dispersion of halogenated hydrocarbons and antimony, such as, for example, APEX BACKOTE #7245 by Apexical, Inc. of Spartanburg, S.C. Other coatings, such as waterproofing or weatherproofing coatings may also be applied in some embodiments of the present invention. The electromagnetically shielded enclosure  100  has a door assembly that reduces or eliminates electromagnetic leakage around the entry area. Shown in  FIG. 1  is a door  107  that is made from a conductive material such as a metalized woven textile, and may, in some embodiments of the present invention, be the same material used for the sides of the enclosure  100 . The door  107  has an edge  109  that may be attached along one side of the door to the enclosure body by way of stitching, fasteners, or being a piece of material continuous between the door and the enclosure body. The door  107  may, in some embodiments of the present invention, be detachable, The door  107  is depicted with a threshold below it to facilitate proper electromagnetic sealing. The height, of the threshold may vary. The threshold may further be removable or detachable to allow tor ease of passage through the entryway. In some embodiments of the present invention, the threshold may be eliminated or replaced by a suitable retention structure such as a flap or the like. The electromagnetically shielded enclosure  100  may also have an outer protective covering; the protective covering, for example, may cover the bottom of the enclosure, and may be made from, for example, reinforced vinyl. Other parts of the electromagnetically shielded enclosure may also have an outer protective covering for various purposes, such as, for example, increased water resistance, ultraviolet protection, and the like. 
         [0032]    The door  107  may also have an alignment loop  111  or a series of alignment loops to facilitate opening and closing the door. The alignment loop  111  may he made from a material such as, for example, a woven nylon or polyester strap. The alignment loop  111  may also have a similar structure on the enclosure body to facilitate proper alignment of the door with the opening. Proper alignment of the door with the opening allows for proper shielding such that the enclosure maintains electromagnetic shielding in use. The door  107  may also have a viewing window  113  to allow for the viewing of electronic devices under test or operation within the enclosure. The window  113  may be made from a fine metal mesh that may also, in some embodiments of the present invention, be sandwiched between one or more pieces of transparent material such as vinyl or the like. In some embodiments of the present invention, the window  113  may be made from a woven or a non-woven metal or metalized fabric or cording, and may for example be made from a fabric suitable for shielding such as a metalized fabric. An. example of a suitable moralized fabric is the silver plated nylon warp knitted fabric manufactured by Carolina Silver Technologies, LLC of Valdese, N.C. and sold as Salem Antibacterial Fabric under style number 53951348. The window  113  may also, in some embodiments of the present invention, he placed in a side of the electromagnetically shielded enclosure. The window  113  may also have a suitable radiofrequency seal such as that which will be described further by way of  FIG. 4 . In one embodiment of the present invention, the entry seal of the electromagnetically shielded enclosure uses magnets to facilitate proper shielding. The door  107  has a first perimeter door magnet  119  and a second perimeter door magnet  121  where each of the perimeter magnets are fastened to the door  107  with stitching, adhesive, fasteners, or the like. Magnets used in the construction of the entry seal are preferably long strips of magnetic material that can be easily sewn, encased in fabric or other material, or otherwise fastened to the perimeter of each entry and door. An example of such a magnet is the Reance SF™ Neodymium Iron Boron magnet manufactured by The Electrodyne Company of Batavia, Ohio, and further disclosed in U.S. Pat. No. 6,707,361, the entire disclosure of which is incorporated herein by reference. Magnets may also be reinforced with material such as, for example, an adhesive foam or fabric, to increase their durability. Not shown in  FIG. 1 , but visible in the cutaway view of  FIG. 6 , are two perimeter enclosure magnets that are fastened to the perimeter of the enclosure opening such that they align with the perimeter door magnets, creating a radiofrequency shielded seal in use. The first perimeter enclosure magnet  601  and the second perimeter enclosure magnet  603  are preferably long strips of magnetic material that can be easily sewn, encased in fabric or other material or otherwise fastened to the perimeter of each entry and door. An example of such a magnet is the Reance SF™ Neodymium Iron Boron magnet manufactured by The Electrodyne Company of Batavia, Ohio, and further disclosed in U.S. Pat. No. 6,707,361, the entire disclosure of which is incorporated herein by reference. The first perimeter enclosure magnet  601  and the second perimeter enclosure magnet  603  are stitched to the enclosure, or otherwise adhered to the fabric of the enclosure using an adhesive, fasteners, or the like. 
         [0033]    In using the electromagnetically shielded enclosure  100 , an electronic device may be placed within the electromagnetically shielded enclosure. In some uses, the electronic device may be connected by way of cables that pass from the shielded environment inside the electromagnetically shielded enclosure to the outside environment. In such uses, a feedthrough  115  can be seen that is a metal plate ohmically connected to the side  105  of the enclosure. The feedthrough  115  contains connectors that pass through the metal plate to allow the electronic device within the electromagnetically shielded enclosure to be connected to equipment in the outside environment. In some embodiments of the present invention, a support  117  is mechanically connected to the feedthrough  115  to alleviate weight related problems such as fabric tearing, or the like. The support may be, for example, a horizontally oriented plate that is attached to the feedthrough  115  at a generally right angle toward the bottom of the feedthrough  115 . Further, in some embodiments of the present invention, a feedthrough is not present. 
         [0034]    Now turning to  FIG. 2 , a perspective view of an electromagnetically shielded enclosure and double perimeter entry seal is depicted. As in  FIG. 1 , the enclosure is depicted in the closed position. The door  107  can be seen, aligned with the enclosure body using alignment loops  111  that are present in some embodiments of the present invention on both the door and the enclosure body to ensure that the door is properly closed and electromagnetically and mechanically sealed through alignment and closure of the first perimeter door magnet  119  with the first perimeter enclosure magnet  601  (see  FIG. 6 ) and corresponding alignment and closure of the second perimeter door magnet  121  with the second perimeter enclosure magnet  603 . The door  107  may roll inward or outward or merely be moved clear of the opening during use, In some embodiments of the present invention, the door  107  may be detached from the enclosure, and may employ a similar double perimeter seal using magnets or other conductive closure material. In  FIG. 2  the feedthrough  115  can be seen without cables and related connectors installed. The connectors depicted are exemplary, and not limiting. As one skilled in the art will appreciate and understand, the feedthrough  115  may contain a variety of connector, filters, and related hardware depending upon, the specific application of the enclosure. Various connectors and related hardware may he placed in the feedthrough by way of stamping, drilling, machining or otherwise creating an appropriate sized opening for the connector or related hardware to fit. Although the figures depict a window  113 , the electromagnetically shielded enclosure  100  may, in some embodiments, contain a window of a different size, shape, geometry, placement, or overall construction. The electromagnetically shielded enclosure  100  may also have no window in some embodiments. For clarity, stitching or other fastening techniques and. materials are not shown in the drawings, but the placement, of such fasteners or stitches will be clear to one skilled in the art after reviewing this specification with the attached drawings. 
         [0035]      FIG. 3  is a plan view of a feedthrough side of an electromagnetically shielded enclosure of the present invention. The feedthrough  115  can be clearly seen with an exemplary set of connectors and related hardware. Other connectors and hardware may be used as dictated by the application of the electromagnetically shielded enclosure. A support  117  may also be seen in  FIG. 3  that transfers weight from the feedthrough, connectors and related cables to a surface that, the enclosure is placed upon. The support  117  may have a bend, feet or related supports to ensure stability. The support  117  may be made from a metal such as aluminum, steel, brass, or the like. The support  117  may also be made from a plastic such as polypropylene, polyethylene, or fiberglass, or the like. Other sides of the electromagnetically shielded enclosure are similar in construction but may not have a feedthrough or support, but in some embodiments of the present invention may have additional features such as radiofrequency shielded viewing windows, access panels, feedthroughs, and the like. 
         [0036]      FIG. 4  is a plan view of an entry side of an electromagnetically shielded enclosure and double perimeter entry seal. The door  107  can be seen with a window  113 . The door in some embodiments is made from the same or a similar material as the enclosure body. The door  107  may be made from a conductive material such as, for example, a metalized woven textile, a mesh, a metal, and the like. Other materials may also be included in the door  107 , such as a metal or metalized fabric mesh for the window  113 . A suitable metalized fabric is the silver plated nylon warp knitted fabric manufactured by Carolina Silver Technologies, LLC of Vaidese, N.C. and sold as Salem Antibacterial Fabric under style number 53951348. In addition, the materials may be layered or compositely structured to accomplish additional shielding effectiveness, weather resistance, structural integrity, and the like. An example of such a metalized woven textile is a silver plated woven nylon ripstop fabric sold under the tradename ProTex Ag by Carolina Silver Technologies of Maiden, N.C. In some embodiments of the present invention, the fabric may be fire retardant or be treated with a fire retardant coating or impregnation. An example of a flame retardant coating is a dispersion of halogenated hydrocarbons and antimony, such as, for example, APEX BACKOTE #7245 by Apexical, Inc. of Spartanburg, S.C. Other coatings, such as waterproofing or weatherproofing coatings may also be applied in some embodiments of the present invention. 
         [0037]      FIG. 5  is a top plan view of an electromagnetically shielded enclosure of the present invention where the enclosure top  501  can be seen along with a frame  101  and related retaining straps  103 . The enclosure top  501  is also made from a conductive material such as, for example, a metalized woven textile, a mesh, a metal, a non-woven textile or metal, and the like, similar to that of the sides of the electromagnetically shielded enclosure. In addition, the materials may be layered or compositely structured to accomplish additional shielding effectiveness, weather resistance, structural integrity, and the like. An example of such a metalized woven textile is a silver plated woven nylon ripstop fabric sold, under the tradename ProTex Ag by Carolina Silver Technologies of Maiden, N.C. In some embodiments of the present invention, the fabric may be fire retardant or be treated with a fire retardant coating or impregnation. An example of a flame retardant coating is a dispersion of halogenated hydrocarbons and antimony, such as, for example, APEX BACKOTE #7245 by Apexical, Inc. of Spartanburg, S.C. Other coatings, such as waterproofing or weatherproofing coatings may also be applied in some embodiments of the present invention. 
         [0038]    To further understand the entry seal, of the present invention,  FIG. 6  depicts a partially cutaway view of an entry side of an electromagnetically shielded enclosure and double perimeter entry seal. The door  107  can be seen cutaway, revealing the enclosure opening  605 . The perimeter of the enclosure opening  605  contains closure material such as, for example, magnetic material to facilitate an electromagnetically tight seal. In the example depicted by way of  FIG. 6 , a first perimeter enclosure magnet  601  and a second perimeter enclosure magnet  603  can be seen. The strips of magnetic material that comprise the first perimeter enclosure magnet  601  and the second perimeter enclosure magnet  603  are sewn into the enclosure or otherwise fastened or encased thereupon. Various width magnetic strips and respective spacings may be used as well without departing from the spirit and scope of the present invention. The door  107 , as previously described, contains magnetic material on the perimeter of the door. The strips of magnetic material are sewn proximate the edge of the door or otherwise fastened or encased thereupon. The door  107  can be seen with a first perimeter door magnet  119  and a second perimeter door magnet  121 . Various width magnetic strips and respective spacings may be used as well without departing from the spirit and scope of the present invention. The magnetic perimeter door magnets, in use, mate with the magnetic perimeter enclosure magnets, where the first perimeter door magnet  119  mates with the first perimeter enclosure magnet and the second perimeter door magnet mates with the second perimeter enclosure magnet, thus forming an electromagnetically tight seal. The first perimeter door magnet  119  is placed along an outer perimeter of the door  107  with respect to the second perimeter door magnet  121 . The second perimeter door magnet  121  is thus placed along an inner perimeter of the door  107  with respect to the first perimeter door magnet  119 . In one embodiment of the present invention, the first perimeter door magnet  119  and the second perimeter door magnet  121  are generally parallel to each other. In a similar manner, the first perimeter enclosure magnet  601  is placed along an outer perimeter of the enclosure opening  605  with respect to the second perimeter enclosure magnet  603 . The second perimeter enclosure magnet  603  is thus placed along an inner perimeter of the enclosure opening  605  with respect to the first perimeter enclosure magnet  601 . In one embodiment, of the present invention, the first perimeter enclosure magnet  601  and the second perimeter enclosure magnet  603  are generally parallel to each other. The door  107  and the corresponding enclosure opening  605  also may, in some embodiments of the present invention, comprise a bias to ensure that the edge of the metalized fabric is not exposed in a way that would allow it to unravel or otherwise deteriorate with use. 
         [0039]    Turning to  FIGS. 7 and 8 , a close-up view of the enclosure to frame retention assembly with a quick release buckle in the closed and open position respectively, is shown. As previously depicted in  FIG. 1  and previously described herein, a portion of the enclosure  705  may be stitched in such as way that a cord retainer  701  travels along and is retained by the enclosure portion  705 . The cord retainer  701  may be a rope such as woven polypropylene, nylon, or a metal or synthetic stranded or single strand cord. As can be seen in  FIG. 7 , the cord  701  protrudes from the material to allow a retaining strap  103  to be placed through the protruding cord and also placed around the frame  101  as shown in  FIGS. 7 and 8  and in a way that allows the enclosure to be retained and held up by the frame  101 . Should the enclosure be frameless, an internal frame, inflatable, or otherwise not require the frame  101 , this enclosure to frame retention assembly may be omitted or modified. This enclosure to frame retention assembly may also be used with portable enclosures that are not RF shielded enclosures. Other techniques for fastening the enclosure to a supporting frame include grommets, hook and loop fasteners, snaps, ties, cords, wires, and the like. 
         [0040]    Throughout the construction of the electromagnetically shielded enclosure and double perimeter entry seal, various techniques may be used to fasten the conductive pieces, sides, top and bottom together. Such techniques may include stitching, gluing, heat bonding, and the like. One exemplary construction technique for fastening, for example, an electromagnetically shielded window to the door of the present invention, can be seen in  FIG. 9  where an exemplary window seal construction  900  can be seen. The conductive material is folded into an accordion bias  901 , The conductive material may be, for example, a metalized woven textile, a mesh, a metal, and the like, similar to that of the sides of the electromagnetically shielded enclosure. In addition, the materials may be layered or compositely structured to accomplish additional shielding effectiveness, weather resistance, structural integrity, and the like. An example of such a metalized woven textile is a silver plated woven nylon ripstop fabric sold under the tradename ProTex Ag by Carolina Silver Technologies of Maiden, N.C., in some embodiments of the present invention, the fabric may be fire retardant or be treated with a tire retardant coating or impregnation. An example of a flame retardant coating is a dispersion of halogenated hydrocarbons and antimony, such as, for example, APEX BACKOTE #7245 by Apexical, Inc. of Spartanburg, S.C. Other coatings, such as waterproofing or weatherproofing coatings may also be applied in some embodiments of the present Invention. The accordion bias  901  surrounds the window material  903  and the enclosure material  905 . The window material  903  may be a conductive mesh or a similar material that provides electromagnetic shielding as well as transparency. The enclosure material  905  may be a material such as the material used for the accordion bias  901  and previously described herein.  FIG. 10  is a fabric fold diagram of the accordion bias depicted in  FIG. 9 . The folds can be clearly seen along with their orientation in the accordion bias fold diagram  1000  that is shown in  FIG. 10 . 
         [0041]    Lastly,  FIG. 11  is an exemplary exploded diagrammatic view of the double perimeter seal of the present invention. In the example depicted, in  FIG. 11 , the first perimeter enclosure magnet and the second perimeter enclosure magnet that surround the enclosure opening and the first perimeter door magnet and the second perimeter door magnet that surround the door, as seen in  FIG. 6 , may be constructed in a similar manner to that shown in  FIG. 11 . The door electromagnetic seal detail  1100  can be seen along with the enclosure electromagnetic seal detail  1180 . Turning first to the door electromagnetic seal detail  1100 , the door fabric  1101 , as has been previously described herein, can be seen along with a door bias  1103  to prevent fraying, provide structure integrity, and the like. A first perimeter door magnet  1109  can be seen, wrapped in an outer perimeter door magnet fabric  1113  to make up a first or outer door seal assembly  1105 . A. second perimeter door magnet  1111  can also be seen wrapped in an inner perimeter door magnet fabric  1115  to make up a second or inner door seal assembly  1107 . The second or inner door seal assembly  1107  and the first or outer door seal assembly  1105  are then stitched or otherwise fastened to the door fabric  1101  at the perimeter of the door in such as way that the first perimeter door magnet aligns with the first perimeter enclosure magnet and the second perimeter door magnet aligns with the second perimeter enclosure magnet. Turning next to the enclosure electromagnetic seal detail  1180 , the enclosure fabric  1121 , as has been previously described herein, can be seen along with an enclosure bias  1123  to prevent fraying, provide structure integrity, and the like. A first perimeter enclosure magnet  1129  can be seen wrapped in an outer perimeter enclosure magnet fabric  1133  to make up a first or outer enclosure seal assembly  1125 . A second perimeter enclosure magnet  1131  can also be seen wrapped In an inner perimeter enclosure magnet fabric  1135  to make up a second or inner enclosure seal assembly  1127 . The second or inner enclosure seal assembly  1127  and the first or outer enclosure seal assembly  1125  are then stitched or otherwise fastened to the enclosure fabric  1121  at the perimeter of the enclosure in such a way that the first perimeter door magnet aligns with the first perimeter enclosure magnet and the second perimeter door magnet aligns with the second perimeter enclosure magnet. In some embodiments of the present invention, magnets are present on three of the four sides of the door and enclosure opening, and a fourth side of the door is attached and electromagnetically continuous to, a fourth side of the enclosure opening. Various geometries of doors and enclosure openings may also be used with the double perimeter entry seal of the present invention. For clarity, stitching or other fastening techniques and materials are not shown in the drawings, but the placement of such fasteners or stitches will be clear to one skilled in the art after reviewing this specification with the attached drawings. The magnets are preferably long strips of magnetic material that can be easily sewn, encased in fabric or other material, or otherwise fastened, to the perimeter of each entry and door. An example of such a magnet is the Reane SF™ Neodymium Iron Boron magnet manufactured by The Electrodyne Company of Batavia, Ohio, and further disclosed in U.S. Pat. No. 6,707,361, the entire disclosure of which is incorporated herein by reference. The door fabric  1101  that may be used for both the enclosure body and the door of the electromagnetically shielded enclosure is a conductive material such as, for example, a metalized woven textile, a mesh, a metal, a non-woven metalized textile or metal, and the like. Other materials may also be included, such as a metal mesh for the window  113 . In addition, the materials may be layered or compositely structured to accomplish additional shielding effectiveness, weather resistance, structural integrity, and the like. An example of such a metalized woven textile is a silver plated woven nylon ripstop fabric sold under the tradename ProTex Ag by Carolina Silver Technologies of Maiden, N.C. In some embodiments of the present invention, the fabric may be lire retardant or be treated with a fire retardant coating or impregnation. An example of a flame retardant coating is a dispersion of halogenated hydrocarbons and antimony, such as, for example, APEX BACKOTE #7245 by Apexical, Inc. of Spartanburg, S.C. Other coatings, such as waterproofing or weatherproofing coatings may also be applied in some embodiments of the present invention. 
         [0042]    The electromagnetically shielded enclosure and entry seal can be constructed using standard stitching, and may also, in some embodiments, be constructed using adhesives or other fabric fastening techniques known to those skilled in the art. Thread, may be conductive metalized thread or standard non-conductive thread. The electromagnetically shielded enclosure may also be made from a single layer of fabric, or, in some embodiments of the present invention, may be made from multiple layers of fabric, or a combination thereof. For example, the front (entry side) of the electromagnetically shielded enclosure may be made from a double layer of metalized fabric, while the remainder of the enclosure may be made from a single layer of metalized fabric. The remainder of the enclosure may also be made from a double layer of metalized fabric, or further layers. 
         [0043]    It is, therefore, apparent that there has been provided, in accordance with the various objects of the present invention, an electromagnetically shielded enclosure and double perimeter entry seal. While the various objects of this invention have been described in conjunction with preferred embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled In the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of this specification, claims and the attached drawings.