High-altitude electromagnetic pulse resistant seal

Abstract

A high altitude electromagnetic pulse closure and seal assembly includes a door frame defining a perimeter and supporting a first portion of a labyrinth seal. The first portion of the labyrinth seal defines one of a channel or a finger protrusion extending from the door frame. A door is moveable relative to the door frame and defines a perimeter. The door perimeter supports a second portion of the labyrinth seal comprising the other one of the channel or finger protrusion extending from the door. The labyrinth seal is configured such that when the door is moved into a closed position relative to the door frame, the first and second portions of the labyrinth seal are brought together. The finger protrusion enters the channel to define a non-contact, free-air labyrinth seal resistant to the intrusion of a high energy electromagnetic pulse radiation.

Description

Attorney Docket No. 63561 -WO- PCTTITLEHIGH-ALTITUDE ELECTROMAGNETIC PULSE RESISTANT SEALCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of United States Provisional Application No. 63 / 771,723, filed March 14, 2025, the disclosure of which is incorporated herein by reference in its entirety.BACKGROUND OF THE INVENTION

[0002] This invention relates in general to access doors and closure mechanisms having electromagnetic pulse resistant closure seals.

[0003] Current techniques and constructions that protect sensitive electrical and electronic equipment from the harmful effects of Electro-Magnetic Interference (EMI) and Radio-Frequency Interference (RFI) typically consist of enclosing the equipment to be protected inside a conductive metallic enclosure which is connected to earth ground. Such a shield acts to attenuate the impinging EMI / RFI radiations by converting them into charges on the outer surface of the shield, which then are drained to earth ground by conventional electrical processes.

[0004] The construction, EMI impermeability, and materials of the enclosure will vary depending upon two factors:a) the frequency of the impinging EMI / RFI, andb) the amplitude of the impinging EMI / RFI.As a general rule, the higher the frequency and the higher the amplitude of the impinging EMI / RFI, the more-complete and thicker the shielding enclosure should be to adequately attenuate the impinging radiation and eliminate its harmful effects on the equipment inside. As either frequency, amplitude, or both increase, penetrationAttorney Docket No. 63561 -WO- PCTpoints, openings, joints and seals in the enclosure become potential weakened entry point to EMI / RFI intrusion. Thus, these susceptible areas need additional safeguards to ensure that the effects of the impinging radiation cannot penetrate to the equipment inside.

[0005] The very-highest levels of EMI / RFI for which protection is required are typically those generally referred to as Electro-Magnetic Pulse (EMP) or High-altitude Electromagnetic Pulse (HEMP) radiations. These are typically the result of extremely high-energy electrical events. Typically, the most extreme events are those generally classified as HEMP events, resulting from a thermo-nuclear explosion at very high altitudes above ground level. Due to a combining effect with the earth’s magnetic field, a HEMP-inducing event produces an extremely short burst of electromagnetic energy (a few microseconds) across a very wide frequency spectrum (from 10 MHz to around 10 GHz) which generates very high electric field strengths (up to 50kV / m) at distances up to hundreds of kilometers from the site of the event. The electromagnetic radiation and the resulting electric fields span the whole range of frequencies used for communications, data transmission and digital processing, and are more-than-powerful enough (if not adequately attenuated), not only to disrupt electrical and electronic equipment, but to permanently destroy it.

[0006] Critical military and infrastructure equipment often needs to be protected from such events. To ensure the survival of mission-critical military communications and intelligence assets from the effects of a HEMP event, the US military applies MIL-STD 188-125 to such assets. This standard requires at least 80dB of attenuation of frequencies from 10MHz to IGhz and beyond, and it is current US military practice in many cases to specify attenuation to ‘MIL-STD 188-125+20’, that is to say, lOOdB of attenuation across the specified frequency ranges.

[0007] To meet such a requirement, HEMP- shielding facilities are typically constructed to be as very-nearly seamless as possible. A typical ‘MIL-STD 188- 125+20’ enclosure will be constructed of continuous steel sheet 1 / 8 - ” (3mm-Attorney Docket No. 63561 -WO- PCT6mm) thick, with all seams and joints continuously- welded inside and out. The most-minute attention is paid to the design to avoid the presence or creation of the slightest opening, hole or break in the solid and seamless construction.

[0008] An exception to the goal of totally- seamless enclosure without any penetration whatsoever is offered by the properties of so-called ‘ waveguides’. Due to the physics of the propagation of electromagnetic waves, it is possible to construct a penetration in an EMI / RFI shield in the form of a conductive tube. If the tube is made long enough relative to its cross section (within limits) then the tube acts as an attenuator to impinging radiation and acts as an effective shield, as effective as a solid, unbroken metal wall would be. As a general rule of thumb, for the frequency ranges under discussion, a tubular waveguide having a cross section with a maximum dimension, ‘d’ of 1-2 inches (25-50mm) has an unbroken length of between 15d-20d to effectively attenuate impinging radiation. This is known as a WaveGuide Beyond Cutoff (WGBC).

[0009] The properties of the WGBC can be further enhanced by suitable shaping of the tube feature where possible. The simplest WGBC is a straight tube having smooth rectilinear walls. This configuration is a common form of fabrication of metallic materials and is readily available at low cost. Many WGBCs are constructed of straight metal tubes having conventional round or square cross-sectional openings. However, if the WGBC can be configured with a sinuous or varying direction and / or cross-section, or walls which are not smooth and continuous in form, or some combination of all these features, the attenuating effect of the WGBC can be enhanced. This feature can then be used to pass any non-conductive material into and out of the shielding enclosure with no loss of attenuation. The physics of WGBCs are understood and have been implemented in many WGBC solutions to allow the passage of air, water, diesel fuel, hydraulic fluid and non-conductive fiber-optic lines into and out of HEMP- shielded enclosures.Attorney Docket No. 63561 -WO- PCT

[0010] One challenge for the designers of HEMP-shielding enclosures is regular access from the outside to the inside of the enclosure, typically for the entry of personnel and equipment. While it is theoretically possible to create a WGBC large enough for a person or equipment to pass through, such a construction is often impractical within the overall requirements of the enclosure. Especially for enclosures which are limited in size or aspect ratio for operational reasons, a WGBC solution for access is not possible. In such cases, the current state-of-the-art is typically to construct a conventional hinged access door which is conductive, and then provide a continuous conductive means around the entire periphery of the door such that when the door is closed, it is continuously electrically connected round the entire periphery to the enclosure walls and forms a continuous part of the enclosure wall.

[0011] Such solutions typically rely upon the use of some form of conformable conductive gasket / seal type material, which engages features on the edges of the door 10 when it closes into the doorjamb 12 to form a continuous conductive seal. A typical construction is shown in Fig. 1. The entire periphery of the enclosure door 10 is fitted with a brass ‘knife-edge’ seal, shown generally at 14. When the door 10 closes, the ‘knife edge’ 14a engages with a seal, shown generally at 16, consisting of a multitude of conductive spring ’fingers’ 16a, which compress against the knife edge 14a to form a conductive connection. Exact details of construction may vary, but this is the general principle which is used to construct the majority of HEMP-shielded doors in use today. The door seal hardware - the ‘knife edge’ 14a, the spring fingers 16a, their mountings and accessories - needs to form part of a continuous, unbroken conductive assembly, both of the moving door and the enclosure wall, in order to block HEMP surges.

[0012] While HEMP-shielding doors of the ‘knife-edge’ type work fine in principle, practical field experience shows that they do not operate well or reliably in normal operation. The single most-common mode of shielding effectiveness failure of HEMP-shielded enclosures with knife edge-type access doors is failure of the doorAttorney Docket No. 63561 -WO- PCTseals, in various forms. Since the knife edge seals are electrical contact seals, damage may be physical or environmental in nature.Damage to the knife edge. The knife edge is an exposed element, making it prone to accidental physical damage and environmental exposure such as corrosion.Damage to the spring fingers. The spring fingers are also exposed to the elements and may be prone to the entry of foreign material, corrosion, and freezing failures, where the door is exposed to the elements.

[0013] Because of their unpredictable nature, these failure modes can be very insidious because they are hard to see and hard to verify. To ensure the continued effectiveness of the door edge shielding, monitoring of EMI / RFI radiation levels may utilize a Shielding Effectiveness Monitor (SEM) device inside the enclosure. The SEM constantly monitors EMI / RFI radiation levels to determine the shielding effectiveness of the enclosure. While an SEM will warn of a failed door seal, the contents of the enclosure are at potential risk until repairs to the door seal can be made, raising concerns with mission-critical assets.

[0014] In addition to the common modes of failure, knife edge-type doors also suffer from some issues intrinsic to their design. These include:• Geometry. In a conventional hinge-type door, the radius of rotation of the vertical edge of the door closest to the hinge is very-much smaller than that of the edge of the door furthest from the hinge. This creates a wiping and rotational action between the knife edge and the spring fingers resulting in accelerated wear through scrubbing contact.• Closure / Insertion force. Most spring fingers in HEMP applications have a relatively-high insertion force requirement for the knife edge to ensure good electrical conductivity. This insertion force may be as high as 2 Ibf per linear inch of seal. This force may result in as much as 500 pounds of force to close the door against the insertion resistance of the springAttorney Docket No. 63561 -WO- PCTfingers. The high insertion force leads in turn to a high extraction force required to open the door. The result is that such doors are fitted with complex and powerful multi-point camming systems to force the door closed against the resistance of the spring fingers against the knife edge, and then to force it open again against the grip of the spring fingers on the knife edge when closed.• Frame rigidity. Due to the high forces described above, the structure of the door and its frame are designed to be very stiff and rigid to accommodate the closure forces and maintain the spatial orientation of contact points so the door properly functions.• Fragile spring fingers. By their nature, the spring fingers employed in a typical knife-edge door are fragile, brittle and prone to breakage. They are typically made from highly-tempered spring materials chosen for their corrosion resistance, to maintain good contact conductivity while still having the necessary spring reaction to conform to the knife edge and create continuous seal. As a result, the spring fingers are generally made from materials such as beryllium copper, and are usually very thin and narrow - typically in a range of 0.010 - 0.15 inches (0.25-0.4 mm) thick and between 0.25 - 0.50 inch (6- 12mm) wide. To mitigate damage effects, knife edge seals may use multiple rows of spring fingers to create redundant pathways of conductivity in the event of failure. These redundancies, in turn, increase insertion and extraction forces and the complexity and cost of the door construction.• Spring finger grounding. Due to the nature of the materials used to make the spring fingers, it can be difficult to obtain a continuous, reliable ground path between the spring fingers and the underlying structure of the door frame. Many solutions rely on surface contact conductivity between the spring fingers and the supporting structure of the door frame. This arrangementAttorney Docket No. 63561 -WO- PCTcan create additional points where conductivity may be compromised by issues such as corrosion or the entry of foreign matter.

[0015] These operating characteristics combine to create a door, frame, hinges and opening / closing mechanism which are typically very heavy and difficult to open / close. The resulting door assembly becomes costly to construct and difficult to use in everyday operations. A typical HEMP-shielded door is shown in Fig. IB may include large hinges, large and complex camming open / close mechanism, and generally-massive construction.

[0016] All these shortcomings of knife edge-type seals lead to doors which are unreliable in the field, require constant and careful operation and maintenance, and which still fail often and unpredictably. What is needed is an improved EMI / RFI seal configured to resist HEMP conditions and be capable of permitting door construction as needed for building structural specifications and provide durable and easy use.SUMMARY OF THE INVENTION

[0017] This invention relates to High-altitude Electromagnetic Pulse (HEMP) shielding facilities, generally. In particular, this invention relates to a door closure system for HEMP facilities that shields high energy EMI / RFI pulses and allows improved ingress / egress of personnel.

[0018] A two-part door and jamb sealing interface encircles the periphery of HEMP- shielding doors against EMI / RFI radiation to create a non-contact seal in the form of a free-air labyrinth. The labyrinth includes a small cross-sectional area and effective length to effectively attenuate impinging HEMP-class radiation while permitting ingress and egress associated with conventional door structures. The door seal labyrinth is formed by the non-contact interlocking of suitably-formed members mounted to the peripheries of the door and door frames. Attenuation effects of labyrinth structures have been described previously; however, these labyrinths are in the form of wall sections with no separability within the structures.Attorney Docket No. 63561 -WO- PCT

[0019] The invention provides a separable labyrinth assembly where analytical shaping of the interlocking blades that form the labyrinth are optimized to create the desired cross-sectional opening when the door is closed. The extending elements, or fingers, are configured to maximize the internal reflections of impinging radiation thereby maximizing the shielding effect. In addition, the mating finger and channels defining the labyrinth have surfaces optimized to maximize the absorption of impinging radiation to further enhance the shielding effect. The separable, labyrinth door sealing system eliminates the need for discrete conductive sealing architectures such as spring fingers. This reduces opening and closing forces and, therefore, reduces the size and weight of doors, hinges, and closing structures. The labyrinth seal can be flanked by a simple dust seal component to enhance the ability to withstand debris intrusion.

[0020] A high altitude electromagnetic pulse closure and seal assembly comprises a door frame defining a perimeter and supporting a first portion of a labyrinth seal. The first portion of the labyrinth seal comprises one of a channel or a finger protrusion extending from the door frame. A door, moveable relative to the door frame, defines a perimeter that is substantially aligned with the door frame perimeter and supports a second portion of the labyrinth seal. The second portion of the labyrinth seal comprises the other one of the channel or finger protrusion extending from the door. The first and second portions of the labyrinth seal are brought together when the door is moved into a closed position relative to the door frame. The finger protrusion enters the channel to define a non-contact, free-air labyrinth seal resistant to the intrusion of a high energy electromagnetic pulse radiation.

[0021] In one aspect of the invention, the high altitude electromagnetic pulse closure and seal assembly includes a door that is rotatably moveable relative to the door frame. The door is supported by at least one hinge defining a radius of rotation relative to the door frame. In one configuration, the channel and finger protrusions are curved such that the finger protrusion enters the channel as the door is rotated into theAttorney Docket No. 63561 -WO- PCTclosed position. In certain configurations, the curved finger protrusions and channels are formed along door and jamb vertical edges. The vertical edges are parallel to the hinge axis of rotation defined by the hinge pin. The horizontal edges, defined as generally perpendicular to the hinge axis of rotation, may be of generally linear construct.

[0022] Alternatively, the high altitude electromagnetic pulse closure and seal assembly may be attached to a door that is slidably moveable relative to the door frame along a first axis. Additionally, the door may be translatable along a second axis that is generally perpendicular to the first axis. The first and second portions of the labyrinth seal are substantially parallel to the second axis such that the finger protrusion enters the channel as the door is translated toward the door frame into the closed position.

[0023]

[0024] Various aspects of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Fig. 1 A is a prior art sealing structure for an electromagnetic pulse door shield.

[0026] Fig. IB is a prior art door assembly.

[0027] Fig. 2A is a prior art structural panel sealing joint for a HEMP enclosure, shown in cross section.

[0028] Fig. 2B is a schematic illustration of a structural panel sealing joint, shown in cross section, for a HEMP enclosure in accordance with the invention.

[0029] Fig. 3A is a door assembly according to the invention as viewed from a “dirty” side.

[0030] Fig. 3B is the door assembly of Fig. 3A as viewed from a “clean” side.Attorney Docket No. 63561 -WO- PCT

[0031] Fig. 4A is a top view of the door and jamb structures of the door assembly of Fig. 3, taken in cross section at line 4A-4A.

[0032] Fig. 4B is an enlarged view of the HEMP sealing structure of Fig. 4A.

[0033] Fig. 5A is a finger section of a HEMP seal assembly in accordance with an embodiment of the invention.

[0034] Fig. 5B is an embodiment of a HEMP seal assembly having the finger section of Fig. 5A positioned in a channel section.

[0035] Fig. 6 is a schematic illustration of another embodiment of a HEMP seal assembly for a hinged door section positioned in a channel section.

[0036] Figs. 7A and 7B illustrate a schematic illustration of a section of a HEMP seal embodiment during and after engagement of a hinged door assembly.

[0037] Figs. 8A and 8B illustrate a section of a HEMP seal embodiment during and after engagement of an axially moved door assembly.

[0038] Figs. 9A-9C are schematic illustrations of a sequence of closing events for a sliding and axially closing HEMP door assembly according to the invention.

[0039] Figs. 10A-10C are schematic illustrations of a sequence of closing events for a double-hinged HEMP door assembly according to the invention.

[0040] Figs. 11A-11C are schematic illustrations2470 of a sequence of closing events for an axially closing HEMP door assembly with hinged HEMP seal member according to the invention.DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0041] Referring now to the drawings, there is illustrated in Figs. 3 A and 3B a HEMP sealed door system in accordance with the invention. In one embodiment, the HEMP seal design permits a door to have a clear opening on the order of 36” wide by 80” tall, though any suitable size may be accommodated with the HEMP seal disclosed herein. Though shown in the context of a hinged door, the inventionAttorney Docket No. 63561 -WO- PCTcontemplates sliding doors, segmented overhead doors, and two-stage door closure configurations. In addition, wall panel attachments are also disclosed.

[0042] As disclosed herein, a protected interior surface and the outer or exterior surface of the door assembly are distinguished respectively as a “clean side” 40 and the “dirty side” 50. This common naming convention describes the side of the door exposed to hazardous radiation as the ‘dirty’ side, and the side of the door facing the protected enclosed shelter volume as the ‘clean’ side. As shown in Figs. 3A and 3B, a HEMP door assembly 100 according to the invention comprises a door structure 102 pivotally supported on a door frame 104 by a plurality of hinges 106. The door 102 and frame 104 are formed from electrically conductive materials, such as metals (e.g., ferrous and non-ferrous), or conductive composite materials. The door 102 includes a portion of a perimeter seal 108, illustrated as a plurality of projecting and concentric seal frames 110. In cross-section, the seal frames 110 resemble “fingers” and are discussed accordingly herein. The door frame 104 includes a plurality of mating perimeter seal channels 112 illustrated as offset projecting and concentric frame fingers defining spaces that interleave with the seal frames 110 of the door. In other embodiments, the perimeter seal 112 may be configured as channels 112a or grooves formed into the seal 112 that define the spaces accepting the concentric seal frames 110.

[0043] In one aspect of the invention, both the hinged door 102 and the frame 104 are constructed from mild steel or aluminum alloys. The frame 104 is illustrated having a continuous, flat, metallic peripheral flange 104a, defining an opening 104b. The peripheral frame 104a allows ready attachment into or onto a suitably-framed opening in the wall of a larger shelter. While illustrated as flat, the peripheral flange may have any geometry to adapt to the structure of the HEMP enclosure. The hinged door 102 is mounted on conventional rotational hinges 106. In the illustrated embodiment, the hinges 106 are mounted in an offset orientation relative to a vertical edge 102a of the door assembly. While the illustrated embodiment of Fig. 3 shows theAttorney Docket No. 63561 -WO- PCThinges 106 mounted to the ‘dirty’ side 40 of the door, other mounting configurations can accommodate the hinges positioned on the clean side 50 and in either handed swing orientations.

[0044] As shown in Figs. 3A and 3B, the HEMP seal 108 is a continuous, metallic construction around the entire periphery of the door 102 and the mating opening 104b in the fixed door frame 104. The door portion of the seal 108 consists of a plurality of concentric and continuous, linear protruding blade-like ‘fingers’ or frames 110 mounted on the door 102. These fingers 110 engage and mesh with enveloping linear ‘channels’ 112a mounted on the door frame 104a. When the door 102 is closed against the frame 104, the ‘fingers’ and ‘channels’ form a continuous peripheral labyrinth around the door / frame opening, creating a structure with the WGBC effect described above to form an effective HEMP seal. The labyrinth defines a gap between the fingers and channels to create the WGBC effect.

[0045] In certain aspects of the invention, the fingers and channels may have a nominal gap dimension, G, of about 1 / 8”, and a gap length, L, (linear distance of the gap between ‘dirty’ side 50 and ‘clean’ side 40) of approximately 18 inches. This configuration forms a WGBC with a length / gap ratio of approximately 144:1. In one aspect of the invention, the HEMP seal 108 may provide an EMI / RFI shield having a frequency range of about 1kHz to about 1GHz. The gap length and width may be altered to attenuate EMI / RFI in a range of 10MHz to IGhz or a range extending beyond those specified in associated MIL specifications. In another aspect of the invention, the sinuous nature of the formed WGBC and the varying cross-sections formed by the various finger and channel designs described herein further enhance and magnify the effect of EMI / RFI pulse attenuation. The labyrinth formed by the mated fingers and channels eliminate mechanical contact and electrical conductivity as components of HEMP attenuation. The seal design permits an easily separable HEMP seal along with a corresponding weight and cost reduction in construction.Attorney Docket No. 63561 -WO- PCTThe HEMP seal is both damage tolerant and resistant debris ingress and corrosion. Additionally, the fingers and channels are easily cleanable and replaceable.

[0046] With conventional HEMP sealing structures, entries are constructed of materials which are both 1) electrically-conductive within themselves to create the attenuating effect required for shielding, and 2) possess very-good surface conductivity so that component contact forms the continuous, conductive shield. This surface conductivity is subject to deterioration during service due to wear of physically mating components, corrosion from weather, and the effects of repeated cycling on surface cleanliness and contact area. Current means to address these limitations utilize a variety of materials and special finishes, such as stainless steel, nickel and chromium-based finishes, and / or brass and bronze alloys. While aluminum alloys would be an attractive alternative, underlying corrosion issues generally inhibit consideration. Another consideration in material selection is how to join materials, particularly dissimilar metals. Fasteners create issues related to the number and additional joint preparations that joining similar materials do not exhibit.

[0047] The HEMP closure seals described herein rely on a gap between the door and jamb structures, which eliminates issues of dissimilar material joining, galvanic reactivity, and electrical contact considerations. While the entry is constructed of conductive materials to obtain the required attenuation, the need to obtain and maintain surface conductivity between its separating parts is obviated. This permits a wider range of materials for consideration based upon their assembled conductivity regardless of surface conductivity characteristics.

[0048] In one aspect of the invention, HEMP seals 108 and the supporting entries 102 may be made from aluminum alloys, allowing for lower cost component manufacturing and assembly methods such as extrusions and welding or conductive adhesive bonding. In a particular aspect, the ‘finger’ and ‘channel’ features are suited to be manufactured in aluminum by a linear-extrusion process. Other seal assembly elements, such as the transitions between the vertical and horizontal seal segments,Attorney Docket No. 63561 -WO- PCTmay be manufactured using such techniques such as die-casting processes and additive manufacturing methods such as three dimensional (3D) printing.

[0049] The meshing of the ‘fingers’ and ‘channels’ during closure are configured to account for rotation of the door about the vertical axis of the hinge pins for conventionally hinged door mountings. In one aspect, the ‘fingers’ and ’channels’ are configured to permit relative movement of the fingers and the channels past each other and separate when the door is opened without contact. As illustrated in Figs. 4A-4B, fingers 208 of door 202 and channels 212 of jamb 204 are formed with tapers that permit meshing during closure and maintain a generally uniform gap over the closed seal. The channels 212 may be wider at an opening 212a of the channel and taper to a closed end 212b. The fingers 208 are configured with a mating profile of a narrow tip 208a and a wide base 208b that mate together to define the desired gap dimension and form the labyrinth seal when the door is closed.

[0050] Figs. 5A-6 illustrate an embodiment of a HEMP closure 300 including a HEMP seal structure showing horizontal and vertical seal sections 308 and 408, respectively. The horizontal seal section 308 of Figs. 5A-5B and vertical seal sections 408 of Fig. 6 are supported on a door 302 and jamb 304 as described above. The horizontal seal sections span the door sections perpendicular to the hinges, typically the upper and lower portions of the door 302 and jamb 304. These sections close together as described in conjunction with the seal 108 described above to form the labyrinth seal. The vertical sections of the seal 408, shown in Fig. 6, illustrate the ‘fingers’ 411 and mating ’channels’ 412 having a curved or arcuate structure formed with regard to the radii of rotation of the hinge axes at the relative distances to each finger and channel. Each section of the seal finger and channel designs form different arced shapes for the vertical segment of the seal closer to the hinge versus the vertical segment of the seal further from the hinge. As shown in Fig. 6, the radii Ri forming the channel shape and R2 forming the finger shape emanate from the hinge centerline of rotation, CLh, and define the profile of the channel and finger. This arcuateAttorney Docket No. 63561 -WO- PCTconfiguration may be advantageous where hinge placement is tight to the door and frame, rather than offset. Corner sections of the seal, not shown, may form a transition from curved finger and channel elements to straight elements. In certain other aspects of the HEMP seal, the linear sections of the interlocking elements may be formed in an arc-shape from one vertical segment to the opposite vertical segment to accommodate doors with generally curved upper and lower sections, such as bulkhead closures or those found on naval vessels.

[0051] Referring now to Figs. 7A-7B and 8A-8B, the mating channels and fingers are configured with a simpler geometry applicable to a wider range of seal applications. As shown in Figs. 7A-7B, the seal geometry is applied to a conventional hinged door, similar to the door assembly 100, above. Fig. 7A illustrates the seal assembly in a closed position where the door 502 is closed against the jamb 504. Fig.7B illustrates the seal 508 separated as the door 502 is opened relative to the jamb 504. The seal assembly 508 includes fingers 510 and channels 512. The fingers 510 have a base 510a that tapers to arounded tip 510b. The channel 512 includes an open end 512 a that tapers toward a rounded closed end 512b. The seal assembly 508 may define a larger gap between the side of the channel 512 and the finger 510. In this instance, the length of the gap will increase in order to provide a length to gap ratio of 144:1. In one configuration, if the gap is increased to inch (6.35 mm), the gap length increases to 36 inches (914.4 mm). This adjustment may be accommodated by additional channel and finger segments and / or an increase in the finger length and channel depth.

[0052] As shown in Figs. 8A-8B, an alternative door closure configuration is configured for linear movement from an open position (Fig. 8B) to a closed position (Fig. 8A). In the illustrated embodiment, the seal channels 512 and fingers 510 are similar to those of Figs. 7A-B and labeled accordingly. It should be appreciated that other finger and channel shapes, such as the straight fingers and channels of Figs. 3A-B or the triangular elements of Figs. 4A and B, can accommodate relative linearAttorney Docket No. 63561 -WO- PCTmovement of the door to the jamb. Since the seal segments are not defined by a hinge axis, they can be brought into correct alignment and engagement for proper sealing in other ways, such as by a simple linear motion. Alternative door closure actuation structures are shown in Figs. 9-11.

[0053] Referring now to Figs. 9A-9C, a schematic illustration of a door system 600 utilizes the linear closure of a HEMP seal 608 on a sliding and linearly moveable door 602 relative to a doorjamb 604 supported on a wall section 604a. The seal 608 is schematically illustrated and may include the embodiments of Figs. 3A-B, 4A-B, 5A-B, or 8A-B, as desired. The door 602 operates to close and engage the seal sections 612 and 612 by a combination of 2 linear motions - axial or tangential relative to the wall (Fig. 9A, Arrow “A”) and linear or perpendicular to the wall (Fig.9B, Arrow “B”), similar to a sliding ‘barn-door’ type application. In the closed position of Fig. 9C, the seal sections 610 and 612 are engaged to form the labyrinth seal. Door stops (not shown) may be mounted on selective points on the door perimeter edge to contact the wall and define the desired gap.

[0054] As shown in Figs. 10A-10C, a schematic illustration of an alternative door closure system is shown generally at 700. A door 702 is pivotally supported by a two-stage hinge 706, as might be advantageous for a recessed ‘plug’ door application. Referring to Fig. 10A, the hinge 706 includes a first pivot 706a supported relative to jamb 704. A second pivot 706b pivotally connects a hinge link 706c and the door 702. As shown in Fig. 10B, a first pivot movement (Arrow “C”) moves the hinge link 706c from a position proximate to a wall 704a through an angle toward the jamb 704. As shown in Fig. 10C, a second pivot movement (Arrow “D”) closes the door 702 and brings a first HEMP seal structure 710 into engagement with a second HEMP seal structure 712 to form a completed HEMP seal 708. The first and second HEMP seal structures may be embodied as any of the finger and channel constructions disclosed herein.Attorney Docket No. 63561 -WO- PCT

[0055] Figs. 11 A-l 1C illustrates another door closure system, shown generally at 800. A door 802 is configured with a first portion of a HEMP seal 810 positioned around a perimeter of the door 802. A wall section 804 defines an access opening 804a with similarly configured HEMP seal section 810 positioned around a perimeter of the access opening 804a. The door 802 may be moveable by any number of structures and is positioned into the opening 804a as shown in Fig. 11 (step 1 IB). A seal ring 820 is pivotally supported by a hinge 806. The seal ring 820 may be a single structure resembling a hoop that supports two mating perimeter HEMP seal second portions 812. Alternatively, the seal ring 820 may be two separately hinged ring halves that overlap at a seam. After the door 802 is moved into the opening, the seal ring 820 is pivoted over the door and wall sections such that the HEMP seal sections 810 and 812 connect to form a labyrinth seal 808 as described previously around the door and opening perimeter.

[0056] In addition to constructing seals for closure devices, such as hinged doors, sliding doors, hatches, and segmented overhead doors, the invention also provides EMI / RFI sealing capabilities for very-large access or structural panels in HEMP-sealed enclosures. These panels may be designed for infrequent access to / removal of a large area of the enclosure. Typically, removal of these large panels would be for access to sizeable equipment inside the enclosure, repair or replacement of damaged panes, or for additions to the existing structure.

[0057] Currently, enclosure panels are typically constructed using a continuous, unbroken and electrically-conductive joint around the entire periphery of the panel at the attachment point to the underlying structure, a typical panel joint for HEMP panels is shown generally at 900 in Fig. 2A. The panel joint 900 includes a first connector leg 902 and a second connector leg 904. The connector legs may be attached to or integrally formed as part of the panels of the HEMP enclosure. The connector legs 902 and 904 are electrically conductive and are provided with large mating surfaces which are made closely-mating and conductive, typically by beingAttorney Docket No. 63561 -WO- PCTfinished flat to a very high standard and then treated with permanent conductive coating or plating surface treatments to ensure a durable, low-resistance connection between the faces. These large mating surfaces are shown as a first contact 902a having a threaded aperture 902b and a second contact 904a having a bore formed therethrough and configured to permit a fastener 906 to access the threaded aperture 902b. In order to ensure electrical connectivity, a conductive gasket 908 is placed between the first and second contacts 902a, 904a. The conductive gasket 908 is typically a flexible and compressible, electrically-conductive gasket material to ensure the electrical connection and account for defects or irregularities between the contacts 902a and 904a.

[0058] Limitations with the prior art connections includes the introduction of threaded fasteners, which tend to create potential leak paths for radiation to penetrate the enclosure. The contacts 902a and 904a are typically configured to have large surface areas and utilize many fasteners 906 to create the compression between the contacts and the gasket. This design creates difficulties in removing and reattaching panels to ensure effective EMI / RFI resistance. In addition, degradation of components over time and environmental exposure creating corrosion and loosening of joints reduces enclosure effectiveness.

[0059] Referring now to Fig. 2B, a HEMP seal assembly 950 is shown as part of HEMP enclosure panels and structural members. The HEMP seal assembly 950 includes mating finger and channel structures as described above. An enclosure wall 952 includes a finger seal 954 at or near the wall edge. A structure panel 956 includes a mating channel seal 958 and a panel connector 960. The panel connector 960 includes a bore 962 and is configured to fasten the enclosure wall 952 to the structural panel 956 with a fastener 964. The mated finger and channel seals 954 and 958 form the labyrinth-type seal as described above. The labyrinth seal 900 is not dependent upon electrically-conductive contact paths and permits separation of the EMI seal function from the mechanical / structural fastenings of the access panel.Attorney Docket No. 63561 -WO- PCT

[0060] The labyrinth seal configuration, as disclosed in the various descriptions herein, can be constructed as an integral part of the enclosure and panel periphery and is not reliant on a separable, conductive joint. The fasteners 964 are only used to secure the panel to the face of the enclosure. The number of fasteners 964 can be reduced based on what is needed to structurally secure the panel.

[0061] The principle and mode of operation of this invention have been explained and illustrated in its preferred embodiment. However, it must be understood that this invention may be practiced otherwise than as specifically explained and illustrated without departing from its spirit or scope.

Claims

Attorney Docket No. 63561 -WO- PCTWhat is claimed is:

1. A high altitude electromagnetic pulse seal assembly comprising:a first portion of a labyrinth seal comprising one of a channel or a finger protrusion;a second portion of the labyrinth seal comprising the other one of the channel or finger protrusion;wherein the first and second portions of the labyrinth seal are brought together such that the finger protrusion enters the channel to define a gap therebetween, the gap forming a non-contact, free-air labyrinth seal resistant to the intrusion of a high energy electromagnetic pulse radiation.

2. The high altitude electromagnetic pulse seal assembly of claim 1 wherein the first and second portions of the labyrinth seal are a plurality of mating channels and finger protrusions defining a gap dimension between surfaces of the first and second portions and a gap length between a dirty side and a clean side.

3. The high altitude electromagnetic pulse seal assembly of claim 2 wherein the gap length and the gap dimension define a ratio, the ratio determining a waveguide before cutoff electromagnetic pulse filter capacity.

4. The high altitude electromagnetic pulse seal assembly of claim 3 wherein the ratio of gap length to gap dimension is 144:1.

5. The high altitude electromagnetic pulse seal assembly of any of claims 1-4 wherein the gap length is determined by a number of the mating channels and the finger protrusions, a length of the finger protrusions, and a depth of the channels.Attorney Docket No. 63561 -WO- PCT6. The high altitude electromagnetic pulse seal assembly of claims 1-5 wherein the first portion of the labyrinth seal is attached to a jamb of a wall section of an enclosure, the jamb defining an opening, and the second portion of the labyrinth seal is attached to a door, wherein closing the door relative to the jamb engages the first and second portions to establish the gap dimension.

7. The high altitude electromagnetic pulse seal assembly of claims 1-5 wherein the first portion of the labyrinth seal is attached to a first wall section of an enclosure and the second portion of the labyrinth seal is attached to an adjacent second wall section, wherein assembling the first and second wall sections overlaps the first and second portions of the labyrinth seal to establish the gap dimension8. A high altitude electromagnetic pulse closure and seal assembly comprising:a door frame defining a perimeter and supporting a first portion of a labyrinth seal comprising one of a channel or a finger protrusion extending from the door frame;a door moveable relative to the door frame, the door defining a perimeter that is substantially aligned with the door frame perimeter and supporting a second portion of the labyrinth seal comprising the other one of the channel or finger protrusion extending from the door;wherein the first and second portions of the labyrinth seal are brought together when the door is moved into a closed position relative to the door frame such that the finger protrusion enters the channel to define a non-contact, free-air labyrinth seal resistant to the intrusion of a high energy electromagnetic pulse radiation.

9. The high altitude electromagnetic pulse closure and seal assembly of claim 8 wherein the door is rotatably moveable relative to the door frame.Attorney Docket No. 63561 -WO- PCT10. The high altitude electromagnetic pulse closure and seal assembly of claim 9 wherein the door is supported by at least one hinge defining a radius of rotation relative to the door frame, the channel and finger protrusions being curved such that the finger protrusion enters the channel as the door is rotated into the closed position.

11. The high altitude electromagnetic pulse closure and seal assembly of claim 8 wherein the door is slidably moveable relative to the door frame along a first axis.

12. The high altitude electromagnetic pulse closure and seal assembly of claim 11 wherein the door is translatable along a second axis that is generally perpendicular to the first axis, the first and second portions of the labyrinth seal being substantially parallel to the second axis such that the finger protrusion enters the channel as the door is translated toward the door frame into the closed position.

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