This invention relates to a door providing radio frequency (“RF”) shielding against high-altitude electromagnetic pulses (HEMP).
RF shielding and RF shielded rooms/shelters for military and other government uses have been in use for some time. The United States military provides specifications for such shelters at Mil-Std-188-125-1 and Mil-Std-188-125-2 (HEMP Shelters), which are incorporated herein by reference (see web site http://www.everyspec.com/MIL-STD/MIL-STD+(0100+−+0299)/MIL-STD-188—125—1−1—4470/ and http://www.everyspec.com/MIL-STD/MIL-STD+(0100+−+0299)/MIL-STD-188-125-2(NOTICE—1)—4473/).
Historically, these government specifications have been met exclusively through use of a so-called “knife edge” door, i.e., a door design in which an RF seal is created where the door joins the door frame by a brass knife edge on the door enters a channel on the door frame. An example of this type of door is shown at http://www.etslindgren.com/pdf/iSKE.pdf; http://www.jaycor.com.
This knife-edge door design has numerous disadvantages, however. Because the knife and channel are made of brass, corrosion occurs and creates non conductive zinc and copper oxides. This oxidation in turn decreases the RF shielding effectiveness of the door seal.
In addition, the channel traps water dirt and contaminants, whereby shielding performance degrades exponentially. Also, the channel is extremely difficult to clean. Typically, cleaning requires removal of the fingerstock in the channel (that is, brass receiving “fingers” that help create an electrical seal with the knife edge in the channel. The fingerstock, when removed, often gets damaged and cannot be reused. Also, all corrosion has to be removed from channel and knife edge surfaces, which is difficult. A conductive lubricant can be used on the brass surfaces to slow corrosion. However, the silicone lubricant traps and holds dirt and dust particles reducing shielding effectiveness.
In addition, water freezes in channel rendering the door inoperable in cold climates. Moreover, the knife edge can wear below serviceable limits in dry sandy environments requiring replacement of entire door within 5 years. In this event, the HEMP enclosure has to be removed from service until repaired
The knife edge design also presents disadvantages because the doors using this design cannot be opened or closed without mechanical assistance. Large lever and cam mechanisms are required to open and close the knife edge door. Appreciable wear on the fingerstock and knife edge occurs because of this mechanical opening action. There are two conditions that make the door difficult to operate: 1—the beryllium copper fingerstock are heat treated, or tempered, to make them springy. This process also hardens them. When the surface of the fingerstock begins to wear and become microscopically abraded, it digs in and grabs the softer brass knife edge requiring more and more effort to operate the lever mechanism. This can be visually confirmed by the grooves that each of the fingers eventually wears into the brass knife edge; 2—the lever mechanism only unseats the knife edge on the strike side of the door requiring the operator to manually pull the door's knife edge completely out of the channel and fingerstock at the top, bottom and hinge side and to push the door in until the lever mechanism can be engaged.
Very high maintenance is required for the knife edge door design. In particular, weekly flushing of the channel with solvents is required to remove loose dirt. In addition, weekly lubrication with conductive lubricant of the fingerstock in the channel is recommended. For the reasons discussed above, monthly or quarterly replacement of fingerstock occurs—with associated down time—based upon usage of the knife edge door. Fingerstock replacement requires special tools and takes approximately 1 hour. Moreover, monthly or quarterly lubrication of the mechanical operating mechanism is required based upon usage. Other repair needs include repair and replacement of worn beyond limits parts in the operating mechanism. Finally, the operating mechanism shaft seal needs periodic replacement to maintain shielding effectiveness.
Additional problems with the knife edge design arise because the brass knife edge can be bent causing misalignment—which makes the door difficult if not impossible to operate and causes a loss of shielding effectiveness. Similarly, the knife edge at the sill cannot be stepped on as damage will occur. The sill must be protected by a steel plate or wood ramp of sufficient strength if furniture, fixtures or supplies need to be wheeled or carted through the door. The knife edge design does not meet ADA door sill height requirements of less than ½″, and commonly requires a 2-3″ step over.
The present invention satisfies that military specifications for a HEMP shelter, but avoids the disadvantages of the knife edge design by using a novel air seal and hinge design. In particular, the present invention, by way of example but not limitation uses an all 304 stainless steel construction for the door and frame which exceeds all shielding performance requirements of Mil-Std-188-125-1 and Mil-Std-188-125-2 The present invention further employs tin plated air seal gasket material that avoids the corrosion problems associated with the knife edge door design because tin oxides are as conductive as tin or similar non-corroding materials such as stainless steel or monel. As a result, shielding effectiveness remains constant.
In addition, the air seals which are attached to the door hinge leaf assembly of the present invention retract significantly or completely when deflated, having little or no surface contact with the inside of the door frame assembly. When the air seals are inflated they expand, pushing the outer metallic woven or braided material of the air seal firmly against both the outer perimeter of the door hinge leaf and the inner perimeter of the door frame creating a continuous electrically conductive path between the two assemblies. When the air seals are deflated, they contract to reduce or eliminate frictional loading between the door and the door frame assembly for ease of opening the door. Since the air seals are attached to the outer perimeter of the door hinge leaf of the door, they move away from the inner perimeter of the door frame assembly when deflated. This creates a “zero friction” or “near zero friction” condition enabling the door to swing opened or closed as freely as any standard commercial door. No mechanical assist through levers or cams is required to open or close the invention as is required by the currently available ‘knife-edge’ type door. Further advantages of the design of the present invention include, inter alia: (i) the sill of door frame meets ADA height requirements of less than ½″; (ii) cleaning only requires wiping mating surfaces with a dry cloth, (iii) if damaged, the air seal can be replaced within 15 min without any tools, and (iv) the typical size man door weighs less than 200 lbs.
The air supply mechanism to the primary and secondary seals, in addition to helping obviate the disadvantages of the knife edge door, provides the additional advantage of a protected and inaccessible air supply. More directly, because the air supply is internal and integral to the door frame, frame hinge leaf, door hinge leaf and door frame, this assembly cannot be accessed or tampered (such as cannot cut the fluid lines) with from the outside when the door is closed. The benefits of this inaccessibility can be enhanced by providing internal attachments, such as screws, between the door hinge leaf and the door hinge leaf. In a preferred embodiment, all seals and gaskets can be protected against outside access with cover plates.
The present invention is illustratively shown and described in reference to the accompanying drawings, in which:
In general, the invention utilizes a fluid system to activate the sealing and shielding of the door entry from radio frequency (“RF”) shielding against high-altitude electromagnetic pulses (HEMP). Though the illustrations and examples are of a pneumatic system, similar or same components can be employed in a hydraulic system depending on the fluid response time requirements. “Fluid” is a substance, such as a liquid or gas, that can flow, has no fixed shape, and offers little resistance to an external stress. The terms “fluid” and “air” are used interchangeably in this application.
One embodiment of the present invention includes a pneumatic door system of fluid lines, valves, switches, and sensors integrated into hinge mechanisms, a door frame, and a door connected to a air pressurization system to inflate and deflate one or more air seals attached to an outer perimeter of the door adjacent to the inner perimeter of the door frame to close a gap between the outer perimeter of the door and inner perimeter of the door frame to provide radio frequency shielding against, for example, high-altitude electromagnetic pulse. The air seal creates a substantially impermeable barrier against radio frequency transmission, as well as air infiltration, when fully inflated. The separate fluid channels in each component interconnect to act as one fluid line or network when the door is closed. The pneumatic door system can be fluidly connected to a conventional air pressurization system, such as a compressor, and in communication with a programmable logic controller to respond to user input or automatic commands with system overrides to react to system air pressure and air flow conditions. The system can operate manually or automatically.
As discussed above, one embodiment of the present invention initiates the air flow actuation to seals 32, 34 by pushing door 4 in direction A toward door frame 42 (
In addition to pin travel distance 10, limit switch 14 can be in direct communication 47 (
In addition to controlling the timing of the start of air pressurization system 36, PLC 46 monitors system pressure 50 (for example air pressure gauge manufactured by Wilkerson, part number 5WZ07) and air flow monitoring 52 (for example air solenoid manufactured by Ingersoll-Rand/ARO, part number 35A-SAC-DDAA-1BA). PLC 46 can start and stop pressurization system 36 with air pressure regulator 54 (for example, manufactured by Wilkerson, part number R08-02-F000) when either the pressure or flow exceeds acceptable parameters. System 2 can continuously monitor pressure and air when door 4 is opened or closed.
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One embodiment of the present invention comprises seals 62 to assure adequate sealing at interface of fluid channels 18, 20 with repeated openings and closings of door 4. Seals 62 can be made of resilient material having elastic, compressive characteristics such that adequate sealing at the interface of fluid channels 18, 20 can occur when the door angular position θ is greater than, for example, zero degrees and fluid channels 18, 20 are not perfectly aligned adjacent to each other. Seals 62 can compress slightly as the door transitions from a predetermined angular position θ degrees to about zero degrees. In this embodiment, seals 62 form a part of the single fluid circuit since fluid channels 18, 20 are not in direct contact (see
Fluid outlet 66 of door hinge leaf integral fluid channel 22 is in sealed fluid communication with inlet 68 of integral fluid channel 64 in door 4. “Integral fluid channel” means the fluid channel is part of or internal to the component by machining, drilling, casting or molding the channel into the component to form a solid, single part and not an assembly of the channel onto the component. The door frame 42 and door 4 can be made of 304 stainless steel, which provides protection against corrosion.
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Air seals 32, 34 of the present invention can be made of pneumatic tubing such as EPDM rubber or a silicone based compound, include an outer braided or woven metallic covering, and an air stem.
With regards to air seals 32, 34 being made of a rubber material, that material can be EPDM rubber or a silicone based compound. EPDM rubber (ethylene propylene diene Monomer (M-class) rubber), a type of synthetic rubber, is an elastomer which is characterized by wide range of applications. M-class refers to its classification in ASTM standard D-1418. The “M” class includes rubbers having a saturated chain of the polymethylene type. The diene(s) currently used in the manufacture of EPDM rubbers are DCPD (dicyclopentadiene), ENB (ethylidene norbornene) and VNB (vinyl norbornene). The choice of materials is based upon the capability of withstanding repeated pressure cycles and expected temperature extremes that the individual invention would be exposed to with EPDM rubber being the most commonly used of the two. EPDM rubber is designed to operate at maximum air temperatures of about 120° C. to minimum are temperatures of about −54° C.
With regards to air seals 32, 34 including an outer braided or woven metallic covering, the covering is the primary factor of creating the Electromagnetic Interference (EMI) seal between the door frame assembly and the door hinge leaf assembly. This woven or braided metallic material is comprised of fine tin plated/copper wires or stainless steel wires, or monel wires, or any conductive metallic wire based upon environmental conditions such as extreme cold or salt water spray.
With regards to air seals 32, 34 further including an air stem that allows air to enter the air seal 32, 34 from the door 4, the stem creates a tight seal with air channel 64 of door 4.
Secondary RF seal 34 can alternatively be an environmental seal, which is a seal intended to protect the shielded enclosure from weather conditions, as well as redundant shielding if air seal 32 fails.
Installation of seals 32, 34 on to door 4 begins be inserting seal inlets 80, 82 into channel outlets 84, 86 (
Though this application illustrates two (2) air seals, alternative systems can operate with only one (1) air seal or a plurality of air seals depending on the size of the door and performance requirements of the user.
One embodiment of system 2 includes redundant fluid networks 18 by incorporating two (2) hinges 19 as illustrated in
Another feature of the present invention are the security screw holes 229 in door hinge leaf 24 (
While the disclosure has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the embodiments. Thus, it is intended that the present disclosure cover the modifications and variations of this disclosure provided they come within the scope of the appended claims and their equivalents.
This application is a Divisional Application of U.S. Non-Provisional application Ser. No. 13/091,448, titled DOOR AND SYSTEM PROVIDING RADIO FREQUENCY SHIELDING AGAINST HIGH-ALTITUDE ELECTROMAGNETIC PULSE, filed on Apr. 21, 2011, which is a Non-provisional Application of U.S. Provisional Application No. 61/327,174, titled DOOR AND SYSTEM PROVIDING RADIO FREQUENCY SHIELDING AGAINST HIGH-ALTITUDE ELECTROMAGNETIC PULSE, filed on Apr. 23, 2010, both herein incorporated by reference.
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Number | Date | Country | |
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20140069020 A1 | Mar 2014 | US |
Number | Date | Country | |
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61327174 | Apr 2010 | US |
Number | Date | Country | |
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Parent | 13091448 | Apr 2011 | US |
Child | 14077318 | US |