US2831912A - Equalized cell-type shielded enclosure - Google Patents

Description

April 22, 1958 D. WILLIAMS 2,831,912

EQUALIZED CELL-TYPE SHIELDED ENCLOSURE Filed April 18,- 1955 FIG. I.

INVENTOR DENNEY WILLIAMS ATTORNEYS United States Patent 2,831,912 EQUALIZED CELL-TYPE SHIELDED ENCLOSURE I i Denney Williams, Silver Spring, Md. Application April 1a, 1955, Serial No; 502,130 17 Claims (Cl. 174-35 The present invention relates to interference reduction, and is more particularly concerned with a novel shielded enclosure for confining radio interference to a limited area or for maintaining a limited area substantially free of external radio interference. In this respect, the present invention is primarily concerned with a novel enclosure structure comprising a plurality of cell-type panels of screen construction, interconnected with one another in the manner to be described. I

In the past, shielded enclosures have taken one of three standard forms. These have been termed, respectively, single-shielded structures wherein a substantially planar surface is utilized for interference reduction; double-shielded structures wherein a pair of screen surfaces spaced from one another are utilized for interference reduction; and cell-type structures wherein doubleshielded structures are conductively coupled to' one another thereby to form a continuous screen surface having at least two enlarged planar surfaces spaced from one another. The present invention'is. concerned with a modified form of such cell-type structure; and in particular, relates tosuch cell-type structure; incorporating, in addition, a further ungrounded or floating screen interposed between the aforedescribed two planar surfaces thereby to provide increased attenuation of radio interference and improved shielding characteristic for a composite shielded enclosure. In addition, the present invention'rclates to improved panel constructions of the equalized cell-type structure described, including the provision of novel screening material in conjunction with improved fastening and interlockingmeans for providing the enhanced operating characteristics effected.

It is accordingly an object of the .presentinvention to provide an improved shielded enclosure.

A further object of the present invention resides in the t provision of improved shielding means.-

Still another object of the present invention resides in I I the provision of a novel panel construction for use with shielded enclosures whereby greater attenuation of radio frequencies is possible than has been the case heretofore; A still further object of the present inventionresides in the provision of an improved portable and prefabricated shielding enclosure.

Still another object of the present invention resides in the provision of a shielded enclosure which eliminates the necessity of solder connections or high resistance joints. A further object of the present invention resides in the provision of a novel disposition'of screen surfaces whereby more effective and eflicient shielding may be obtained than has been the case heretofore.

In providing for the foregoing objects and advantages of the present invention, a shielded enclosure is efiected comprising a plurality of interchangeable and interconnected shielding panels.

These panels in turn comprise side panels interconnected with one another and including provisions for an access panel or door; and further include a plurality of top and bottom panels, once more r peripheral may be eliminated.

Patented Apr. 22, 1 958 by improved attenuation is realized. The several panels are preferably constructed of selected, straight-grained, knot-free, Northern white pine, air and kiln-dried,with a moisture content not in excess of 10%, upon application of wood preservative. Each side panel is of the same physical size (preferably 40" in width and 8' in height), and universal mounting holes are provided therein whereby the said side panels may be readily disassembled from one another and interchanged with one another upon assembly. The said side panels, as will appear subsequently, are of double-frame construction and utilize mortise-and-tenon corner and cross-member joints thereby to give an extremely strong construction and to provide a desired separation between inner and outer screen surfaces mounted thereon, whereby the attenuation characteristics of the panel are increased. All

construction, and preferably allow a minimum of 3" of contact surface at all joints whereby an overlap of an inner and outer screen at the said edges may be provided.

In addition to theforegoing, all panels have an equalizing screen placed in the, double frame equidistant from the inner and outer screen; and the purpose of this equalizer is to provide an equal potential plane between the said inner and outer screen which will disperse any concentration spot voltage or standing waves throughout its surface, thereby to prevent such concentration from reaching the other screen in concentrated form. The inner and outer screens preferably comprise a composite screening materialincluding a high permeability iron corehaving copper and silver plating thereon, whereby low contact silver-to-silver, or silver-to-silver oxidejoints are effected between the said inner and outer screens, and the said screens are secured to the wooden frames discussed previously by silver plated staples whereby soldering and the possible high resistance joints attendant thereto The center or equalizing screen has a fairly high characteristic impedance thereby to add to the total impedance losses between the inner and outer screens jdescribedyand the said center screen preferably comprises a high permeability iron core, platedwith zinc (galvanized screen), thereby to increase the resistance of the'said center screen and to allow a greater dissipation of any energy induced therein.

The ceiling and floor panels are of substantially the same mechanical and electrical construction as the side panels except that they are of increased length and the said ceiling and floor panels are once more interchangeable as was the case in respect to the several side panels. By providing such a shielded enclosure comprising equalized cell-type panels and by utilizing the special screen materials and non-solder joints of the present invention, an enclosed cubicle having extremely good attenuation characteristics is effected.

The foregoing objects, advantages, construction and n operation of the present invention will become more readilyapparent from the following description and accompanying drawings, in which: I I

Figure 1 is a perspective view of ashielded enclosure constructed in accordance with the present invention.-

. Figure 2 is a representation of an individual panel for use in theshielded enclosure of Figure 1 and constructed in accordance with thepresent invention.

edges of the several panels are of ship-lap *Figure '3 is *a'view-taken on section 3-3 of Figure'2.

Figure 4 is a view taken on section 44 of Figure 2. 1 Figure 5 is 'a view taken on section '5 -'5 :of Fig- '-ure' 1'. s

Figure 6 is a representative 'of views takencnsec- =tiorn6 6'-ofd=igure;1; and

"Figure'fl :is a-greatly-eiilarged representationroft'anzimproved wire-strand for :use in :thezinner. and .outenscreens -ofthe shielded :panelslinz accordance with the present 'invention.

-.+Referring.'now .to ;=Eigure ':1,'1:it-,.will be 5556.611 :that a shielded enclosurezinaccordance with the;present inven- --tion-"may;-comprise a, plurality. 10f side; panels 10 I interzconnectedawith one v another and with aplurality of top spanelsvll and-a plurality of floor. panels (not shown) of thezsarne constructonas the said top panelsll, whereby -a .shielded;enclosure:is provided. .Each ofthe panels 10 :and .-11-.= comprises .a, frame: construction of wood, as .described above, and includes-bracingstrips 12, thereby ,to form 1a. rigid; mechanical. configuration; and :the several panels-10 and 11 (as well as thefloor panels).are of cell- .type-screen mesh construction and. includean equalizing :center --screen dis posed between: the inner and outer .screensthereof, in themanner tobe described. :Inaddi- .tion, :an access .panelor door 13 is provided and the said-.door 13 .is preferably constructed ,of water-proof marinerplywood to decrease the possibility of door sag- ,ging. Theaccesspanel or door 13 closely resembles the several side .panels10, .inasmuch as a certain amount of Itheplywoodjis. cut out from the center thereof to reduce 'the'door weight; and 'the.door oracccss panel13 is preferably boundby ferrous channels which are copper and silver platef'ln addition, thejarnbs of the door 13 are preferably of the same material as the door itself, and

are'jig-bcrd whereby universal fasteners ofthe type to 'beldescribed in respect to the several side'panels," may beem'ployed; and four ball bearing hinges (not shown are mounted .onthe door jamb.

It-has been'found that the use of dogs for securing doors such"as"13is unnecessary insofar as resultant attenuation'is concerned, and the present invention, thereforeppreferably employs adjustable tension, hospital 'roller latches (not shown) disposed adjacent the top-and "bottom-of the'access-panel 13 whereby access to the shielded enclosure is improved.

'Thefloonshielding panelsof the cubicle are protected =-by an overlay of plywood flooring panels of proper dimensions tocompletely cover the'floor cells, and all of the-side, floor and overhead panels preferably employ the equalized cell type structure discussed previously. In addition, one panel 0f the assembled enclosure includes -provision 1 (such as a power entrance cabinet) for the .entrance of-power lines and-filters and the samepanel,

or another panel, may furtherincludeprovision (such .as

c; a: radio frequency access cabinet) for entrance of" radio frequency transmission lines. In practice, thepoweren- @trance cabinet=may include four filtered power line en- ...trances, as follows: one 28 volt D. C.; two 115 volt 60 cycle linespand, one 115 volt.400, cycle line; and, as men- .tioned, each of ttheserlinesnis preferably provided with -filters which are. fully shielded betweenthe input and output of each filter. In this respect, the power line entrances and filters should provide an insertion-loss-of "100 db at all frequencies between 100 kilocycles and 1000 megacycles.

The radio frequency access cabinet maybe of similar construction, and boththe-radio frequency-cabinetsand -:powen entrance ..cabinets mayacomprise known constructions utilizing two bells (similar to transformer end bells), -rwhichtbells.are connected electrically adjacent their:outside; peripheriesby the panel screening material utilized. .Sucnpowerand radiofrequency cabinets are well-. known .to those. skilled in. the artand thefparticular construction ofranynsuchcabinet. does not, per se, comite enclosure for a number-of reasons.

4 prise the present invention inasmuch as many variations are possible.

An individual panel constructed in accordance with the present invention, and comprising one unit of the shielded structure show in Figure 1, may be seen from an examination of Figures 2, 3 and 4. Such a panel may comprise an outer woodenframe 20 having a further inner frame 21 secured thereto by silver plated screws 23. Theperipheral edges of the resulting panel are of ship-lap-construction; and the outer panela21 .is covered by a screen mesh 24 extending around the frame and between the overlap junction between the panels 21 and 22. Similarly, pthe innerypanel 22.-is covered by a further screen mesh 25,, once. more extending around the said frame 22 and into "the overlap between the panels 21 and 22. The screen materials 24 and 25 are secured to their respective frames by silver plated staples and the said outer and inner screens 24 and 25 contact one another, in junction between frames, 21 1 and .22, thereby .to provide acontinuousclectrical cell-type screen .completelysurrounding the composite frame 21 22.

, glnaddition, .a center orequalizing screen 26, serving the purposes .discussed previously, is interposed between .the. frames..21 and ;22,,and may be attached by silver The said screen 25, and is separated from .the said screen surfaces 24 .and 25 in the junction between frames, 21 and 22, whereby ,the said center screen26 floats free electrically from both ofrscreens24 and 25. x

As has been mentioned previously, the inner andouter ,sc'reensf 24,and.25, utilized to form the cell-type screen structure of. thepresent invention, preferably comprise a special screening materialof the type shown, for instance, in Figure 7. Thus, the screen mesh comprising screen surfaces 24 and 25, employ strands of wire having an iron core30 and the said core 30 is coated with a copperplatingjl which is in'turn coated with a silver pl'ating"32. Due to the provision of the external silver coating, and inasmuch as silver and silver oxide have the same electrical characteristicgthe junction between frames '21 and 22, providing electrical continuity between "the outer and inner screen surfaces 24 and 25, is of low resistance. Such structure provides a-substantial improvement over prior constructions wherein soldered 1 joints have beenutilized, inasmuch as suchsoldered joints have been found to-exhibit relatively poorsurface contact and, inaddition; have atendency to corrode with age whereby high resistance contacts result.

*The special mesh2described and. shown in Figure 7'further enhances the shielding characteristics of the.compos- Thus, .the use of the high permeability: iron corematerial 30 provides a low-reluctance path to electromagnetic'waves; and inasmuch as the-severahiron cores forming the. screen mesh-are insulated byanon-ferrousmetal (copper), mag- -netic short-circuits within the mesh of the screen are elirninated, thus achievingzless core loss. In addition, the use of coppenandsilver coatings on. the core provide low etfective' resistance to electrostatic currents whereby low radiationresistance is effected. .Again, as has ,beemmentioned previously, the use of a silver :coating as the outer material of the mesh'resultsin the screen retaining itseeleetricalcharacteristics even ,if the mesh thereof 'should oxidize onaitsi surface.

As a result of the foregoing construction, it has been found that the iron core :givesextremely goodattenuationat all frequencies below 2600.:kilocycles,..with.-particular reference to .the electromagnetic or H.field. :The copper coating, in addition,

.givesi further attenuation for-intermediate frequencies up =towery highrfrequenciesand thesilver coating in turn givesexcellent attenuationin the V. H. F.-U. H. F. and

' microwave ranges.

During actualoperation, within feet=of the; encloof .3 to kilocycles and from megacycles to 1000 megacycles. In this respect, it should be noted that the actual total attenuation provided by the screen structure described, particularly when employing the center or When assembled in the manner described above, the several panels provide a-unitary shielded enclosure, and each of the said panels in turn comprises a cell-type construction having inner and outer screens in electrical conequalizing screen of the present invention, has thus far 5 tact with one another and a centrally disposed equalizing been outside the capacity of available test equipment; bu screen spaced from each of said inner and outer screens. certain obtained results .are as follows: I By such construction, and due to the provision of silver Maximum Minimum Maximum Capability of Attenuation Attenuation Type of Test Frequency of Combined of Silver Grid of Silver Grid Test Test Shielded (Beyond ca- Equipment Enclosure, db pacity of test Used, db equipment) Elgcfit): magnetic (H 200 Kiioeyclesfi. 80 80 Undetermined.

e Electrostatic (E field). ..do 120 120 Do.

,Do 1 Megacycle- 120 120 Do.

Do 18Megacycles 120 120 Do.

Do 400 Megacycles. 120 120 Do.

As mentioned previously, the center screen 26, utilized staples, special mesh materials, and silver plated bolt and in each of the panels of my novel shielded enclosure, is screw members, the overall attenuation of my novel disposed substantially equidistant from the inner and shielded construction is far in excess of that accomplished outer screens and 24, and provides an equal potential heretofore. plane between the said inner and outer screens which 25 While a preferred embodiment of the present invention disperses any concentrated spot voltage or standing waves throughout its surface. The said equalizing screen 26 exhibits a fairly high characteristic impedance and is preferably of galvanized'construction. The screen type construction utilized in element 26 minimizes hysteresis and eddy current losses, which would reduce the efficiency of the shielding and which might occur with the use of solid metal constructions.

As has been discussed, the several panels comprising the sides of my shielded enclosure, and the several panels forming the top and bottomof my shielded enclosure, are respectively interchangeable and provide for ready disassembly whereby a relatively light, portable, and prefabricated enclosure is effected. The side panels as well as the individual top and bottom panels are interconnected with one another in the manner shown in Figure 5. Such interconnection may be effected by interposing a U-shaped channel 27 (preferably copper and silver plated) between adjacent panels, as shown, and by running bolts 28 and 29through the said channel 27 and the sections 21 and 22 of the frame at right angles to one another. In this respect, the frames 21 and 22 are preferably provided with bolt holes (see Figure 2), and the bolts 28 and 29 are preferably captive type hex-head'bolts, whereby the possibility of lost bolts during asembling or dismantling operations, is eliminated. Once more (as was the case with respect to the iron mesh wire, the channel 27, the screen securing staples, and the screws 23), the bolts 28 and 29 are preferably silver plated to reduce losses and avoid high resistance contacts.

It will further be noted from an examination of Figure 5, that by bolting adjoining panels in orthogonal directions the channel 27 provides pressure between adjacent frame members 21, in two right angle directions, thereby to reduce contact resistance therebetween; and While Figure 5 has, for purposes of clarity, shown the said adjacent frame members 21 as slightly'separated from one another, in practice the said adjacent frame will, due to proper choice of channel 27, be in close and forcible contact with one another.

The method of forming a corner joint, such as would occur at the corner of adjacent side panels, or between the top and side or bottom and side panels, has been shown in Figure 6. Due to the ship-lap construction emplayed, such corner constructions are readily effected and adjacent corner panels may once more be tightly held in contact with one another by further captive type hexhead bolts 36 and 3 7 utilizing the same bolt holes as were provided for the colinear panel arrangement shown in Figure 5.

has been described, it must be stressed that many variations thereof will be suggested to those skilled in the art, particularly in respect to the manner of interconnecting the several individual panels, and in respect to the disposition of an equalizing screen or screens within a cell-type panel. The foregoing description is, therefore, meant to be illustrative only and is not limitative of my invention and all such variations as are in accord with the principles discussed are meant to fall within the scope of the appended claims.

Having thus described my invention, I claim:

1. A shield panel structure fora shielded enclosure comprising a frame of insulating material, first and second substantially parallel conductive screen mesh surfaces supported by and spaced from one another on said frame, said first and second surfaces being electrically interconnected with one another adjacent the periphery of said frame thereby to form a substantially unitary cell-type screen defining an enclosed volume between said first and second screen mesh surfaces and said frame, and a third conductive screen mesh surface interposed in the said enclosed volume between said first and second screen mesh surfaces, said third screen mesh surface being supported by said frame in substantially parallel relation to each of said first and second surfaces, said third surface being electrically insulated from each of said first and second surfaces.

2. The structure of claim 1 wherein said third screen mesh surface comprises a material having higher electrical resistance than said first and second surfaces.

3. The structure of claim 1 wherein said third screen mesh surface comprises galvanized iron.

4.The structure of claim 3 wherein said first and second surfaces comprise screen mesh material having strands of iron core material successively coated with layers of copper and silver.

5. A shielded enclosure comprising a plurality of interconnected panels, each of said panels being of screen mesh cell-type construction, and each of said panels including a further equalizing screen surface centrally disposed within the screen mesh cell and electrically insulated from the screen mesh surfaces comprising said cell, said cell-type and equalizing screen mesh surfaces being carried by and supported on a common frame of insulating material with said equalizing surface being supported on said frame in completely spaced relation to said cell-type screen mesh surface.

6. The enclosure of claim 5 wherein said further equal- 'izing screen surface comprises a material having higher electricalresistance than that of the screen mesh comprising said cell. V

7. A shieldingpanelfora' shielded enclosiirecompris ing' first an'd secondisub'stanti'ally rectangular shield surfaces: s aced from one another"and electrically interconnec'te'd to one another? at their peripheral edges thereby to eiie'ct anenclosed cell-type shield, anda th'ird sub stantially rectangular shield surface interposed between said first and second surfaces and electrically insulated from each of said first and second surfaces.

8. The combination of claim 7 wherein each of said first and second shield surfaces comprises a screen mesh surface, each of said mesh surfaces including interwovenstrands of iron core wire having a copper coating thereon, and having a further coating of silver covering said iron core and copper coating.

9. A shielded enclosure comprising a plurality of side panels, a plurality of top panels, and a plurality of bottom panels interconnected with one another to form an-enclosed cubicle, each of said side, top, and bottom panels comprising conductive screen mesh material of cell-type construction, and each of said panels including a conductive equalizing'shield surface disposedwithin-each of said cells and electrically insulated from the screen mesh comprising said cells;

10. Theenclosure of claim 9 whereinsaid equalizing shield surface comprises galvanized iron screen mesh.

11. The enclosure of claim 9 wherein said conductive screen mesh material is silver plated on its exterior surfaces.

12. The enclosure of claim 9 wherein each of said panels'isof ship-lap; construction comprising .non-conductive inner and outerframes fastened to one another, saidscreen mesh material of cell-type construction comprising inner and outer screens respectively supported by said inner an'dou'ter frames and in electrical contact with oneanotherfinthe junction between said inner and outer frames-.- I

13. The enclosure of claim 12 wherein said equalizing shieldsurface' comprises afurther screen' surface supported between said-inner and o'uterframes at the juncrim thereot, said further screen surface beingespaced in saidfranie junction-from the contacting smfaces of said inner andouter screens.

14. The enclosure of claim 9 wherein said conductive screen mesh material comprises interwoven strands of iron core wire having successive coatings of copper and silver on the said strands of wire.

15; A'shieldedencl'osure comprisingla plurality of interconnected screen mesh panels; each of said panels beingof cell-type: construction and comprising screen mesh materialhavi'rig interwoven strands of iron core wire with successive coatings of copperand silve'rthereon, each of saidcell-type panels includes a further shielding surface of galvanized iron screen mesh disposedwith in References Cited in the file'of' this patent UNITED STATES PATENTS 1,091,669 Manna: Au -29, 1911 Howe NOV.- 13, 2,438,428 Birdsall Mar. 23,1948 2,669,695 Bird Feb. 16, 1954 2,704,301 Feketics Mar. 15, 1955

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