Abstract:
Equipment in an enclosure is shielded from affecting, or being affected by, external electromagnetic and magnetic fields. A flooring within the enclosure includes first and second portions. The first portion supports the enclosure walls and provides electromagnetic and magnetic shielding. The second portion is paramagnetic and is disposed inwardly of, and spaced from, the first portion. A third flooring portion disposed between the first and second portions and expansible with heat provides a compatible coupling with the first and second portions. A door in a wall aperture is movable between opened and closed positions. Resilient fingers on the door co-operate with the door jambs to provide an electromagnetic coupling between the door and the walls when the door is closed. A window in another wall aperture provides for a visual inspection of the enclosure and for electromagnetic coupling with the walls. A matrix arrangement of tubes extending through one wall provides for the introduction of air into the enclosure at temperatures different from ambient. The door, the resilient fingers, the window arrangement and the honeycomb of tubes provide a continuity of electromagnetic shielding in combination with the walls. The walls may also be defined by first and second spaced sheets and a material disposed in the space between the sheets anchors the sheets. Wall portions may extend at oblique angles from the opposite wall extremities to define extensions of the flow paths for the magnetic flux and to facilitate the flow of the flux in a closed loop.

Description:
This invention relates to an enclosure for shielding equipment in the enclosure from electromagnetic and magnetic fields outside of the enclosure and for confining within such enclosure any such fields generated by such equipment. The invention is especially adapted to be effective in shielding equipment which is disposed in the enclosure and which is highly sensitive to such fields. 
     In recent years, equipment has been developed and introduced to the market for performing functions not previously available. For example, equipment has been developed, sold and operated for scanning the bodies of patients to detect diseases and body malfunctions in the patients. Such equipment has been of considerable benefit to doctors and hospitals in helping to detect diseases and body malfunctions in patients. Such equipment has been designated as magnetic resonance imagers. 
     Such equipment as magnetic resonance imagers include members which are sensitive to electromagnetic and produce large magnetic fields. Unless the electromagnetic field is limited to a low value, it may affect the operation or performance characteristics of the magnetic image scanners so that the scanners do not operate satisfactorily in detecting diseases and body malfunctions in patients and unless the magnetic field is contained it may adversely affect other equipment in close proximity such as pacemakers and CT scanners. 
     The necessity, or at least desirability, of shielding such equipment as magnetic resonance imagers against electromagnetic and magnetic fields and the containment of such fields has been known for some time. Substantial efforts over a span of at least several decades have been devoted to provide efficient electromagnetic and magnetic shielding of equipment in an enclosure. However, even as of this date, shielding against electromagnetic fields and containment of magnetic fields is still somewhat rudimentary. This is particularly true with respect to shielding electromagnetic and magnetic fields of high strength and also with respect to the shielding of equipment which is sensitive to such fields. 
     This invention provides an enclosure which produces an efficient shielding of electromagnetic and magnetic fields, even when the fields have a high strength. The invention provides such efficient shielding even with the inclusion of doors and windows in the enclosure and equipment for circulating air and other gases through the enclosure or from the enclosure. Although the invention provides an efficient shielding of such fields, the construction of different embodiments of the invention is relatively simple and the cost of such construction is relatively low. 
     In one embodiment of the invention, equipment is shielded in the enclosure from affecting, or being affected by, external electromagnetic and magnetic fields. The enclosure includes walls made from a material providing electromagnetic and magnetic shielding. A flooring within the enclosure includes first and second portions. The first portion supports the walls and provides electromagnetic and magnetic shielding. The second portion is nonmagnetic and is disposed inwardly of, and spaced from, the first portion. A third flooring portion disposed between the first and second portions is expansible with heat and provides a compatible coupling with the first and second portions. 
     A door in an aperture in one of the walls is movable between opened and closed positions. Resilient fingers on the door become engaged with the door jambs to provide electromagnetic coupling between the door and the walls when the door is closed. A window in another aperture in one of the walls g provides for a visual inspection of the enclosure and for electromagnetic coupling with the walls. A matrix arrangement of tubes extending through one of the walls provides for the introduction of air or other gases into or out of the enclosure. The door and the resilient fingers in combination, the window arrangement and the honeycomb of tubes provide a continuity of electromagnetic shielding in combination with the walls. 
     The walls may also be defined by first and second spaced sheets and a material may be disposed in the space between the sheets to anchor the sheets. Wall portions may extend at oblique angles from the opposite extremities of the walls to define extensions of the flow paths for the magnetic flux and to facilitate the flow of the flux in a closed loop. 
    
    
     In the drawings: 
     FIG. 1 is a schematic perspective view of an enclosure for providing electromagnetic and magnetic shielding; 
     FIG. 2 is a sectional view, partially broken away, taken substantially on the line 2--2 of FIG. 1 and illustrates the construction of flooring in the enclosure shown in FIG. 1; 
     FIG. 3 is an enlarged fragmentary sectional view taken substantially on the line 3--3 of FIG. 1 and illustrates further details in the construction of the flooring in the enclosure; 
     FIG. 4 is an enlarged sectional view taken substantially on the line 4--4 of FIG. 1 and illustrates the construction of a window in the enclosure of FIG. 1; 
     FIG. 5 is an enlarged exploded perspective view of certain elements in the window shown in FIG. 4; 
     FIG. 5a is an enlarged fragmentary perspective view illustrating certain details of a mesh screen included in the window assembly shown in FIGS. 4 and 5; 
     FIG. 6 is a fragmentary sectional view taken substantially on the line 6--6 of FIG. 1 and illustrates the construction of a door and a door jamb in the enclosure and of a resilient finger on the door for co-operating with the door jamb to provide electromagnetic coupling between the door and the door jamb when the door is closed; 
     FIG. 7 is an enlarged fragmentary view similar to that shown in FIG. 6 and illustrates the relative disposition of the door and the door jamb, including the resilient fingers on the door, in the closed position of the door; 
     FIG. 8 is a sectional view taken substantially on the line 8--8 of FIG. 1 and illustrates the construction of tubes in the enclosure for circulating air conditioning and heat and gases into and from the enclosure; and 
     FIG. 9 is a sectional view illustrating the construction of an enclosure constituting another embodiment of the invention; 
     FIG. 10 is an enlarged fragmentary sectional view of an arrangement for co-operating with the floor and the walls to prevent refuse from collecting in the intersection between the walls and the floor; 
     FIG. 11 illustrates another embodiment of the door and the door jamb; and 
     FIG. 12 is schematically a preferable method of producing welding seams in the embodiments illustrated in FIGS. 1 through 11. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In one preferred embodiment of the invention, equipment generally indicated at 10 is disposed in an enclosure generally indicated at 12. The equipment may be a magnetic resonance imager such as that manufactured and sold by Diasonics Corporation. Such a magnetic resonance imager provides a crosssectional image of a human body and serves as a tool, through the generation of such image, for detecting diseases and other malfunctions of the human body. The magnetic resonance imager generates large magnetic fields and is sensitive to electromagnetic fields including radio frequency fields. 
     The enclosure 12 is constructed to shield magnetic fields and electromagnetic, such as radio frequency, fields. In this way, electromagnetic and magnetic fields are confined to a satisfactory level within the enclosure 12 and do not affect the operation or performance characteristics of the equipment in the enclosure. Furthermore, electromagnetic and magnetic fields passing from the equipment 10 into the space outside of the enclosure are confined to a satisfactory level. 
     The enclosure 12 may include a plurality of walls 14, 16, 18 and 20 preferably disposed in a perpendicular relationship to provide the enclosure 12 with a rectangular shape. Each of the walls may be made from a magnetically permeable material such as a steel so as to shield electromagnetic and magnetic fields. This prevents any electromagnetic or magnetic fields generated by the equipment 10 from passing out of the enclosure 12 and also prevents any electromagnetic or magnetic fields outside of the enclosure 12 from entering into the enclosure. If desired, the ceiling of the enclosure 12 may also be made from the magnetically permeable material. 
     Beams or support members such as illustrated at 22 in FIG. 3 are disposed under each of the walls 14, 16, 18 and 20 to support the walls and to provide for the attachment of the walls to the flooring of the enclosure. Preferably each of the walls 14, 16, 18 and 20 is disposed at an intermediate position along the length of the associated one of the beams 22 so that the beam or support member will distribute the weight of the adjacent wall along substantially the full horizontal surface of the beam. The beams or support members 22 may be made from a suitable material such as steel so as to shield electromagnetic and magnetic fields. Resilient pads 24 made from a suitable material such as rubber are disposed on a floor 26 under the beams or support members 22. The resilient pads 24 isolate the beams or support members 22 electrically from the floor. A dielectric material 28 such as polyvinyl chloride may be disposed under the resilient pads 24. The polyvinyl material 28 also provides electrical insulation. The polyvinyl material 28 may be suitably adhered to the floor as by an epoxy 29. 
     Flat sheets 30 (FIGS. 2 and 3) of a suitable material such as plywood are disposed on the floor 26 in the interior portion of the enclosure 12. The sheets 30 may be provided with longer lengths than widths and may be disposed on the floor 26 so that, in first layers, the lengths may be disposed in a first direction in the enclosure 12 in first layers and in a perpendicular direction in second layers. This is illustrated in FIG. 2. Sheets 28 of polyvinyl material may be disposed between the plywood sheets 30 and the floor and may be suitably adhered to the floor as by an epoxy. Anchor members 31 made from a suitable material such as nylon extend through the bottom sheets 30 of plywood and the polyvinyl material 28 into the floor to hold such sheets in fixed position on the floor. Nylon is desirable as the material for the anchor members 31 because it is electrically insulating. 
     Sheets 32 (FIG. 3) of a suitably nonmagnetic, but electrically conductive, material such as aluminum are disposed on the plywood sheets 30 to define a sheath. The sheets 32 are preferably overlapped and the overlapped sheets may be secured to the plywood sheets 30 and to each other as by screws 34 and also by a suitable adherent such as epoxy. The sheets 32 may be also suitably attached to one another at the seams by welding. The body portions of wall anchors are preferably covered with a polyvinyl material 36 to provide electrical insulation for the wall anchors, as shown in FIG. 3. 
     Aluminum is preferably used as the material of the sheets 32 because it is relatively light. Aluminum is also desirable as the material of the sheets 32 because the sheets do not have to support the walls 14, 16, 18 and 20. By disposing the plywood sheets 30 under the aluminum sheets 32, a suitable support is provided for the aluminum sheets 32 to prevent warpage of the sheets when the sheets are welded. The combination of the screws 34 and the adherent also inhibits warpage of the aluminum sheets when the aluminum sheets are welded. 
     An expansion member or joint 38 (FIG. 3) is preferably disposed on the sheets 32 at the edge of the sheets closest to the beams 22. The expansion member or joint 38 is attached at one end to the sheets 32 as by welds 40. The expansion member is provided with a substantially V-shaped configuration 41 at the end opposite the welds 40. As a result, the V-shaped portion 41 of the expansion member 38 is expansible with increases in temperature. The expansion member 38 may be made from a suitable material such as aluminum. 
     A bi-metallic strip 42 (FIG. 3) is disposed between the expansion members 38 and the beams 22. One portion of the bi-metallic strip 42 may be made from a suitable material such as aluminum and another portion of the bi-metallic strip may be made from a suitable material such as steel. The aluminum porg tion of the bi-metallic strip 42 abuts the expansion member 38 and the steel portion of the bi-metallic strip abuts the beam 22. In this way, the bi-metallic strip 42 provides a compatible coupling between the expansion member 38 and the beam 22. 
     Sheets 44 (FIG. 3) of a suitable material such as plywood are disposed on the aluminum sheets 32. The plywood sheets may be adhered as by an epoxy 43 to the aluminum sheets 32 and to each other. First layers of the plywood sheets 44 may be arranged with their lengths in one direction and second layers of the plywood sheets may be arranged with their lengths in a second direction perpendicular to the first direction. The sheets 44 tend to level the support surface for the equipment 10 to compensate for the overlaps in the aluminum sheets 32. 
     One of the walls such as the wall 14 is provided with an opening 50 (FIG. 1). The periphery of the opening in the wall 14 defines a door jamb 52, the corners of which are preferably rounded. A door 54 is pivotably attached to the door jamb 52 to be moved between opened and closed positions. The corners of the door 54 are preferably rounded to facilitate the electromagnetic coupling between the door 54 and the door jamb 52. A plurality of resilient fingers generally indicated at 56 (FIGS. 6 and 7) are disposed on the door 54 around the periphery of the door. Each finger 56 is made from a suitable material such as beryllium copper so as to shield electromagnetic fields such as radio frequencies fields. Each finger 56 includes a first arm 58 and a second arm 60 preferably integral with each other. The second arm 60 is bent backwardly on the first arm 58 to define a looped configuration. The first arm 58 is attached to the door 54. Each finger 56 also includes an arm 62 extending from the arm 58 at the end opposite the arm 60. The arm 62 includes a humped portion 64 at an intermediate portion along its length and also includes a flat portion 66 at the end adjacent the arm 60. The flat portion 66 is disposed in the space between the arms 58 and 60. 
     The humped portion 64 of the arm 62 in the finger 56 is disposed to engage the door 50 as the door is closed. This causes the humped portion 64 to become flattened or constrained from the position shown in broken lines in FIG. 7 and in broken lines in FIG. 6 to a position shown in solid lines in FIGS. 6 and 7. In the constrained position of the humped portion 64 as shown in FIG. 6, each finger 56 engages the door jamb 52 and establishes a continuity with the door and the door jamb in providing electromagnetic shielding. 
     As will be appreciated, a number of the fingers 56 may be disposed at spaced positions around the door 54. Actually, more than one set of the fingers 56 may be provided around the door, each set being disposed at a different depth in the door. This is indicated by the sets generally indicated at 68 and 70 in FIG. 6. When more than one set of detents is provided, each set may be disposed in a staggered relationship to the other set as shown in FIG. 6. The electromagnetic coupling between the door 54 and the door jambs 52 through the fingers 56 is facilitated by providing the door with rounded corners. 
     In the embodiment of the door and door jamb shown in FIG. 11, a support member 72 extends from one of the walls such as the wall 14 and has an L-shaped configuration. A door generally indicated at 74 has a body portion 76 which supports fingers such as the fingers 56 in FIGS. 6 and 7. The body portion 76 may be made from a suitable material such as stainless steel. A covering sheet 78 made from a suitable material such as a ferrous material is attached to the body portion 76 to provide magnetic continuity between the door and the supporting wall 14. 
     FIGS. 1, 4, 5 and 5a illustrate an arrangement, generally indicated at 80, which defines a window. The window arrangement 80 is disposed in an aperture 82 in one of the walls such as the wall 14. The window arrangement 80 includes a pair of clamping members 84 and 86 (FIG. 4), the clamping member 84 being suitably attached to the wall 16 as by welds 88. The clamping members 84 and 86 respectively have spaced jaws 89 and 90 for receiving window panes 92, 93 and 94. The clamping members 84 and 86 and the window panes 92 and 94 may be held in a clamped relationship by a nut and bolt arrangement 95. A soft metal gasket 97 may be disposed between the clamping members 84 and 86 to insure electrical continuity between the clamping members. The clamping members may be made from a suitable material such as steel to provide electromagnetic and radio frequency shielding. 
     A pair of mesh screens 96 and 98 are provided, the mesh screen 96 being disposed between the window panes 92 and 93 and the mesh screen 98 being disposed between the window panes 93 and 94. The screens 96 and 98 may be made from a suitable material such as copper so as to provide electromagnetic shielding such as radio frequency shielding. Preferably the mesh in the screen 96 is disposed at an oblique angle relative to the mesh in the screen 98. The mesh in the screens 96 and 98 is sufficiently large so that the equipment 10 in the enclosure 12 may be viewed through the window from a position outside of the enclosure. The screens 96 and 98 provide a continuity with the clamping members 84 and 86 and the wall 14 in producing electromagnetic shielding such as radio frequency shielding. The intersections in the mesh in each of the screens 96 and 98 may be joined as at 99 in FIG. 5a to insure electrical continuity through the screens. 
     FIG. 8 illustrates an arrangement, generally indicated at 100, for circulating air through and from the enclosure 18. The arrangement 100 may be disposed on one of the walls of the enclosure such as the wall 18 in FIG. 1 or it may be provided in the ceiling of the enclosure. The arrangement 100 may provide for air conditioning or heating, or for only a circulation of fresh air into, through and from or for the removal of cryogen gases from the enclosure 18. Such air or gas may be introduced or expulsed to the arrangement through ducts 101 in FIG. 1. 
     The arrangement 100 includes a plurality of tubes 102 disposed in a matrix. Each of the tubes 102 may be attached to the adjacent tubes by an electrically conductive sealant 104 such as a deposited copper. The deposited copper accordingly assures electrical continuity between the tubes. The common point between four contiguous tubes may also be welded to position the tubes and to assure electrical continuity. This is indicated at 105 in FIG. 8. Each of the tubes 102 may be made from a suitable material such as steel to provide magnetic shielding and electromagnetic shielding such as radio frequency shielding. 
     The length of each of the tubes 102 preferably is significantly greater than its width and height. Preferably this ratio is at least 4:1. In this way, the tubes serve as wave guides to trap radio frequency energy and prevent such energy from passing between the interior and exterior of the enclosure 12. Furthermore, the matrix of the tubes 102 provides a continuity of such shielding between the tubes 102 and the adjacent walls. This continuity is also facilitated by the relatively great length of the tubes 102. 
     FIG. 10 illustrates an arrangement which is disposed at the bottom of the walls 14, 16, 18 and 20 to inhibit foreign matter from falling to the floor and inhibiting the electrical isolation of the enclosure 12 from the surrounding structure. The arrangement shown in FIG. 10 includes a cover 140 made from a suitable material such as polyvinyl chloride. The cover 140 is disposed at one end against one of the walls such as the wall 14 and is extended downwardly to the floor and bent under the resilient pad 24. The cover 140 may constitute an extension of the material 28. A resilient clamp 144 made from a suitable material such as steel is attached to the wall 14 and is bent downwardly and inwardly against the top of the cover 140 to retain the cover against the wall. 
     Another embodiment of the invention is generally illustrated at 200 in FIG. 9. The embodiment 200 includes pluralities of abutting sheets 202 made from a suitable material such as steel and defining a wall such as the wall 14 in FIG. 1. An additional sheet 204 of the same material is spaced from the sheets 202. These sheets are supported by a beam or support member 206 corresponding to the beam or support member 22 in the previous embodiment. Abutting sheets 208 and a spaced sheet 210 extend below the support member 206 at positions respectively corresponding to the sheets 202 and the sheet 204. The sheets 208 and 210 may be made from the same material as the sheets 202 and 204. The sheets 208 and 210 are anchored below a floor 212 by concrete 214 or other suitable manner. The sheets 208 may be suitably attached to the support member 206. 
     A plurality of abutting sheets 216 made from the same material as the sheets 202 extend downwardly at an oblique angle relative to the sheets 208 and 210 from a position below, and spaced slightly inwardly from, the sheets 208. Similarly, sheets 218 made from the same material as the sheets 202 extend upwardly at an oblique angle to the sheets 208 and 210 from a position above, and spaced slightly inwardly from, the sheets 208. The sheets 218 are joined at their inner ends by a sheet or sheets 220. 
     The embodiment shown in FIG. 9 may include a door, a window and ducts for the passage of air in a manner similar to that discussed above for the previous embodiment. The embodiment shown in FIG. 9 and described above has certain important advantages. It provides a firm support for the walls and ceiling of the enclosure by anchoring the spaced walls 208 and 210 in the concrete 214 and by providing the concrete between the walls 208 and 210. It also provides the walls in a closed loop approximating the natural path for the flow of the magnetic flux. In this way, leakage of magnetic flux from the flow path is minimized. 
     Preferably all of the seams in the enclosure 12 such as the seams between the walls, roof and flooring are continuously welded, as by arc welding, to provide for an optimal electromagnetic shielding. Preferably, the ground in the welding seam is provided at a position on the wall depending upon the direction in which magnetic flux flows through the wall. Thus, for some walls, the ground for the arc welder is provided at the top of the welding seam. For other walls, the ground for the arc welder is provided at the bottom of the welding seam. By providing grounds for the welding seam in this manner, the flow of flux in a closed loop in the enclosure is facilitated. This results from the fact that the welding seam tends to provide a good conduit for the flow of magnetic flux when the ground for the welding seam is in the proper position. The provision of a ground at the proper position in a seam 222 is schmatically illustrated at 223 in FIG. 12 when an arc welder 224 is used to provide the weld. 
     Although this invention has been disclosed and illustrated with reference to particular embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.