CA1254988A - Voltage dividing shielded door seal - Google Patents
Voltage dividing shielded door sealInfo
- Publication number
- CA1254988A CA1254988A CA000485091A CA485091A CA1254988A CA 1254988 A CA1254988 A CA 1254988A CA 000485091 A CA000485091 A CA 000485091A CA 485091 A CA485091 A CA 485091A CA 1254988 A CA1254988 A CA 1254988A
- Authority
- CA
- Canada
- Prior art keywords
- closure
- door
- cavity
- seal member
- seal
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Shielding Devices Or Components To Electric Or Magnetic Fields (AREA)
Abstract
ABSTRACT
Disclosed is an electromagnetic shielded door seal which will block both low frequency electromagnetic waves as well as very high frequency electromagnetic waves. The sealing effectiveness of the door seal which may be used for a shielded enclosure, is improved by introducing a high frequency impedance between the two coacting surfaces of the door seal. The door seal is provided with two cooperating members which move relative to one another. At least one of the members contains a small cavity therein which is filled with a dielectric or lossy material. The periphery surrounding the cavity is closed, with the exception of a small gap ensuring communication between the material provided within the cavity and a sealing surface between the two cooperating members. The combination of this gap and the dielectric material introduces a high frequency impedance between the surfaces of the seal. This impedance results in a voltage dividing action and reduces the voltage across the protected surface of the door seal.
Disclosed is an electromagnetic shielded door seal which will block both low frequency electromagnetic waves as well as very high frequency electromagnetic waves. The sealing effectiveness of the door seal which may be used for a shielded enclosure, is improved by introducing a high frequency impedance between the two coacting surfaces of the door seal. The door seal is provided with two cooperating members which move relative to one another. At least one of the members contains a small cavity therein which is filled with a dielectric or lossy material. The periphery surrounding the cavity is closed, with the exception of a small gap ensuring communication between the material provided within the cavity and a sealing surface between the two cooperating members. The combination of this gap and the dielectric material introduces a high frequency impedance between the surfaces of the seal. This impedance results in a voltage dividing action and reduces the voltage across the protected surface of the door seal.
Description
543~8 A-1623 ¦ BACKGROUND OF THE INVENTION
._~
The prior art is replete with various devices for ensuring that radio frequency or electromagnetic waves do not penetrate into or out of a sealed enclosure. Early prior art devices were designed to try to protect highly sensitive computers by preventing radio fre~uency and electromagnetic waves from entering a sealed enclosure contain.ing the computer equipment. Due to the classified nature of the programs which various computers utilize, and the use to which they are directed, ].ater patents directed to shielding a particular environment were drawn to various methods and devices for preventing electromagnetic or radi.o ~Erequency waves from being transmitted from the shielded enclosure to the outside environment. These devices were important because highly sophisticated methods were being developed to eavesdrop on highly confidential governmental communications and operations.
Rec~ntly, a new problem has presented itself in the form of an extremely high frequency electromagnetic pulse which is produced by the detonation of a nuclear blast high in the atmosphere. This problem is documented in the ~anuary/February 1983 issue of Science magazine (pp. 41-49 wherein the deleterious effects of this electromagnetic pulse are described wi-th respect to the problems which are imposed upon communications systems and shielded enclosures.
These high frequency electromagnetic waves could play havoc with the classified material contained ln compute:rs which is to be protected in the enclosed environment.
~>' I
A-1623 1¦
he majority of prior art devices, which have dealt with ensuring tha-t radio frequency or electromagnetic waves do not p~netrate into or exit from -the sealed environment, generally protect the environment from relatively low frequencies of radiation, but does not afford comparable a-ttenuation levels at microwave frequencies. As the ¦ computational speed o modern digital computers has increased so has the frequency content of electromagnetic emanations from these computers and diyital communica-tions systems.
Therefore, a door seal that is more effective at microwave frequencies is required to protect the classified material being processed within a shielded enclosure.
t has been established -tha-t the voltage drop ¦ across the seal on -the inside surface of all shlelded enclosure or equipment access doors is an important consideration when designing a seal which would protect a shielded enclosure from the egress of very high frequency electromagnetic waves through the shielded door. In this context, all of these doors require extremely good metal-to-me-tal contact around their periphery.
Prior art patents which have dealt with this problem I of providing an adequate door seal employ beryllium copper or phosphor bronze spring fingers within the door seal. Such ¦ prior art door seals are described in U.S. Patents 3,589,070 issued to Hansen and ~,069,618 issued to Geiss Both of these patents describe door seals used in shielded enclosures.
These patents employ a knife edge provided on a first closure member which coopera-tes with spring fingers provided on a second closure member to form a door seal for screen rooms .
.
I
-1~23 ¦ and shielded enclosures. While it has been shown that the door seal configurations shown in the Hansen and Geiss patents are quite effective in forming a good closure at low frequencies, at very hiyh frequencies in excess of .5 GHz, the inductance of the tines of the spring fingers increases and the leakage throuyh the slots formed in the door seal increases, thereby decreasing ~he effectivenessof the door seal.
The patent to Geiss also uses a woven me-tallic RF
gasket in the area of cooperation be-tween the knife edge and the spring fingers. This gasket introduces ano-ther low frequency current path in parallel wi-th the two rows of spring fingers thereby reducing the voltage drop across the door seal. Secondly, the presence of this yasket increases the microwave attenuation of the door seal by acting as ano-ther barrier to the microwave energy. This material does not have the resilience of the beryllium copper spring fingers and ultimately it will l'take a set" and added attenuation of the waves will be los-t.
While differen-t RF absorbing materials can be used between the rows of spring fingers to improve the microwave at-tenuation of the door seal, the limi-ted space ~e~ween ~he spring fingers of approximately one centimeter limits the effectivenessof the door seal.
Consequently, it is seen that there is a continuing need for a more effective door seal which would block both low frequency elec-tromagnetic w~ves as well as very hiyh frequency electromagnetic waves.
, . , ~L2.~
70015-~
SU~ARY OF TH~ INVENTION
The present invention is direc-ted to improving -the sealing effectiveness of a door seal for a shielded enclosure b" introducing a high frequency impedance between the two coacting surfaces of the door seal. The door seal is provided wi-th two cooperating members whish move rela-tive -to one another.
At leas-t one of -the members contains a small cavity ~herein which is filled with a dielectric or lossy ma-terial. The periphery surrounding the cavity is closed, with t~e exception of a small gap ensuring communlca-tion between the material provided within -the cavity and a sealing surface between -the two coopera-ting members. The combina-tion of this gap and the dielectric material introduces a high frequency impedance be-tween -the surfaces of -the seal. This impedance results in a voltage dividing action and reduces the voltage across the protected surface of the door seal, According -to a broad aspect of the inven-tion -there is provided an electromagne-tic shielded door seal utilized wi-th a shielded enclosure adapted for US2 between a door and a door frame, said door seal comprising:
firs-t closure seal member fixedly a-t-tached to said door provided wi-th a pair of firs-t spaced wall members Eorming a flrst slot therebetween;
second closure seal member fixedly attached -to said door frame provided with a pair of second spaced w~ll members forming a second slo-t -therebe-tween, one of said second wall mem-bers adapted to be inser-ted in-to sald first slot and operatively csopera-ting^ wi-th said firs-t clocure seal member -to form an RF elec-tromagnetic frequency resistant seal;
a first cavity provided in said firs-t closure seal member, said cavi-ty filled with an energy absorbent dielectric material, 70015-~32 said first cavi-ty substantially enclosed wi-th the exception of a dis-tinct -First gap providecl in a surrounding periphery of said first cavity, said first gap direct.l.y opening on-to said Eirst slot; and firs-t and seco.nd spring closure members provided respecti-vely on each of said first pair of spaced wall members, said firs-t and second spring closure members resiliently urged agains-t the said second spaced wall member which is inserted in-to said firs-t slo-t.
Alternatively, the closure members can be reversed, i.e. the first closure member can he attached to the door frame and the second slosure member can be a-ttached to the door.
~ccording to another broad aspec-t of the invention there is provided an electromagnetic door seal utilized with a shielded enclosllre adapted fox use be-tween a door and a door frame comprising:
first closure seal member fixedly at-tached to said door;
second closure seal member fixedly attached -to said door,~
frame operatively cooperating w th said first closure seal member to form an RF or electromagne-ti.c frequency resistant seal;
a cavi-ty provided in said first closure seal member filled wi-th an energy absorben-t dielectric ma-te.rial,said cavity substantially enclo~ed with the excep-tion of a dis-tinc-t gap provided in a surrounding periphery of said cavi-ty, said gap provided on -the portio~ of said periphery of said cavity directly facing and opening onto said second clo~ure member; and first and second sprin~ closure members provided on said surrounding periphery of said first closure seal member on either side of said gap.
-4a-Again, the closure members can be reversed.
~ ccording to another broad aspect of the invention there is provided an electrcmagnetic door seal utilized with a shielded enclosure adapted for use between a door and a door frame comprising:
first closure seal member fi~edly attached to said door;
second closure seal member provided wi-th an L-shaped sealing surface, said second closure means fixedly at-tached to said door frame and operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency seal;
a cavity provided in said first closure seal member filled with an energy a~sorbent dielectric material, said cavity substanti.ally enclosed wi-th the exception of a distinct gap provided ln a surrounding periphery of said ca~ity, said gap provided on the portion of said periphery of said cavity directly facing and opening onto said second closure mem~er;
and first spring closure member provided on one of the L shaped legs of said L--shaped sealing surface and a second spring closure member provided on the second leg o~ said L-shaped se~ling surfase.
Again, the closure mem~erscan be reversed.
Other objects, advantages and novel features of the presen-t invention will become apparent from the followi.ng detailed description of the invention when considered in conjunction with the accompanying drawings; wherein like reference numerals identify like parts throughout. !
-~b-BRIEF DESCR~PTION OF THE D~WINGS
Figure l is a front view of the door which is used in a shielded enclosure;
Figure 2 is a cu-taway view of one embodiment of the door seal of the presen-t i.nvention showing t.he relation-ship of -the first and second cloc.ure members;
-4c~
,7 A, ~2 .
A-1623 FIGS. 3, 4 and 5 are cutaway views of different embodiments of the present invention showing the relationship of the first and second closure members; and FIG. 6 is the equivalent circuit for the present invention with respect to the door seal shown in FIG. 2.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a typical door/door frame combination 10 which can be utilized with the door seal described in the present invention. Th~ combination contains a door 12 provided with a door core constructed of virtually any standard door core materials such as wood, aluminum, s~eel or the like. The door core is surrounded by a layer of 26 gauge galvanized steel and can be provided with a color-coordinated decorative veneer or acoustical covering provided on both the inside and outside of the door core.
A plurality oE knuckle ball bearing hinges 14 is provided between the door 12 and door frame 20 to allow opening and closing of the door. Although three knuckle ball bearing hinges are shown in FIG. 1, it is understood that this number iB merely illustrative of the number and positioning of the hinges which are utili2ed. An alignment bearing 16 is provided -to ensure that the door will easily be opened and closed while ensuring that radiation cannot enter or leave the shielded enclosure. A polished chrome door handle 18 is provided to allow access to the interior of the enclosure.
~ ~ .
A similar handle is provided on the inside door in the enclosure. The door frame 20 can be constructed of standard materials which are used to prevent the passage of radiation into a sealed enclosure. The frame can be constructed with a four inch depth tubing frame having shielded lapp joints, but the invention is not to be construed to be limited to such a construction.
FIG. 2 shows a cutaway view of one embodiment of the present invention showing the various components of the door seal in an open position. The door seal is provided with a first closure member 23 secured to the door frame 20 and a second closure member 25 secured to the door 12. The first closure member 23 provided in the door frame 20 contains an L-shaped member having legs 22 and 2~. A second L-shaped member having legs 26 and 28 is also provided. The legs 24 and 28 are opposed to one another and are arranged such -that a slot 30 is provided therein. Although it is not important for this invention, these L-shaped members can be constructed of material such as hot-rolled steel. A ~ap 34 is provided within the slot 30 and between legs 22 and 28 of the two L shaped members. A cavity 36 is provided between the legs 22, 26 and 28 within which is provided a dieleckric or lossy material such as polyurethane. ~dditionally, although it is not imperative to -the operation of the present invention, the dielectric or lossy material can include conductive particles of copper or iron or any other ma-terial used to attenuate RF or electromagnetic waves. Although the exact dimensions of the gap 3~ are not inlportant, it has been found that a dimension of between four and eight millimeters can be ~1 '~ 8 provided. I-t is important to note that the gap 34 must be provided such that there is communication between the slot 30 and the dielectric material within the cavity 36. A
pair of spring fingers 32,33 is provided on the surface of the opposed members 24 and 28, respectively. These spring fingers can be constructed out of beryllium copper or phosphor bronze or any other similar material.
The second closure member 25 is provided on the door 12 and is provided with an L-shaped member 42 directly joined to a knife edge 38. A slot 44 is provided between L-shaped member 42 and the knife edge 38. The door core 40 is provided adjacent to the slot 44 and can be constructed of various materials, as has been indicated ilereinabove.
In operation, the door 12 is swung closed such that knife edge 38 is provided between the resilient spring fingers 32,33 to ensure that an effective seal has been made.
Although the door seal has been described as having a knife edge provided on the door and spring fingers provided on the door frame, the positioning of these elements can be reversed. Additionally, either side of the seal can be outside of the door. Furthermore, both the first and second closure members 23,25 are provided along the entire periphery of the door 12 at the door frame 20.
The operation of this seal can best be explained using the Thevenin equivalent circuit shown in FIG. 6. For illustrative purposes, consider that a plane wave field is incident from the bot-tom of FIG. 2 upward toward the seal.
~ithout any spring fingers in the assembly, a large voltage VOC
would appear between the knife edge 38 and leg 28, as shown in FIGS. 2 and 6. With the spring fingers 32,33 in place, the voltage between the knife edge 38 and the leg 28 is reduced to only the voltage drop across the contacts of the spring fingers. Since the impedance of the spring finger is much lower than the equivalent impedance of the slot Z30, the output voltage VO is much smaller than the voltage VOC. In a shielded doorit isthis reduction that is responsible for the effectiveness of the door seal.
In the present design, the voltage can be reduced further. It is apparent that the voltage between the knife edge 38 and the leg 28 is the sum of the voltages between the knife edge 28 and the leg 24 and the voltage between the leg 24 and the leg 28. According to the equivalent circuit in FIG. 6, the voltage between the knife edge 38 and the leg 28 is applied to the series combination of -the impedance Z32 of the spring finger 32 and the inpedance Z34 across the gap 34.
Since the impedances Z33 and Z32 are small, the impedance Z34 does not have to be very large to reduce -the voltage across the knife edge 38 and leg 24 significantly.
Since this voltage drives the fields inside the enclosures, the improved shield effectiveness is obtained by introducing the gap 34 and the dielectric material wi-thin the cavity 36. Since the dimensions of the cavity, and the electrical conductivity, permittivity and permeability of the material contained in the cavi-ty can be varied, the performance characteristics of the present invention can be changed.
FIG. 3 shows an alternate embodiment of the present invention wherein both the first and second closure members 23 ~2~ 8 and 25 respectively include gaps such that dielectric material provided in each of the closure members can communicate with the door seal. The first closure member 23 is similar to the embodiment shown in FIG. 2 and the same reference numerals are utilized. The second closure member 25 is provided on the door frame 20 and includes an L-shaped member having legs 46 and 48 which are used to substantially enclose a cavity 54 having dielectric material similar to the material contained in cavity 36 provided therein. Similar to the seal shown in FIG. 2, a knife edge 56 is provided which will cooperate with the spring fingers 32 and 33 in the manner which has been described herein-above, and the slot 44 is provided between leg 48 and the knife edge 56. A single spring member 50 is provided on the leg 48 which is to cooperate with the outside surEace oE the leg 24 of the first closure member 23. Additionally, similar to the gap 34 which is provided in the first closure member, a gap 52 is provided between leg 48 and the continuation of the knife edge 56 allowing communication between the door seal and the di-electric material 54. As was true with respect to the embodiment shown in FIG. 2, the reversal of the first and second closure members on the door 12 itself and the door frame 20 is also contemplated.
FIG. 4 shows a third embodiment of the present inven-tion which can be applied to a wiping/compression finger stock door seal having a Eirst closure member 60 provided on door frame 61 and a second closure member 62 provided on door 79. The first closure member 60 is applied to the door frame 61 and sub-stantially encloses a cavity 70 having dielectric material therein. The cavity 70 is surrounded by leg members 64, 66 and 82, except for a small gap 68 provided in leg member 82, ~ 8~ 7~015-32 The second closure member 62 is provided with a leg 74 having a spring finger 76 thereon, and a leg 72 having a spring finger 78 thereon. Conventional door core material is provided at 80.
In operation, the gap 68 would cooperate with a sealing surface to ensure that the voltage dividing effect described herein-above will also be present in this embodiment, As was true with respect to the previous embodiments, the first and second closure members can be reversed with respect to the positioning on the door frame or the door itselE.
Yet another embodiment of the present invention is shown in FIG. 5. This embodiment illustrates the voltage dividing door seal applied to a compression door. The door seal includes a first closure member 82 provided on door frame 83 and a second closure member 84 provided on door 99, The first closure member contains legs 88, 90 and 92 which substantially surround a cavity 86 created therein. The cavity contains dielectric material similar to that whlch has been described with respect to the other embodiments of the present invention.
The leg 92 is provided with a gap 94 such that the dielectric material can communicate with the door seal, As was true with respect to the gap provided in all of the embodiments of the present invention, this gap can be dimensioned between four and eight millimeters. Spring fingers 96 and 98 are each provided on one side of the gap which would cooperate with a sealing surface 102 on the second closure member 84. A door core 100 is provided which is constructed of conventional door core material, As was true ~ 38 with respect to all of the o-ther embodiments of the presen-t invention, the positioning of the firs-t closure member 82 and the second closure member 84 can be reversed with respect to the door frame and the door itself.
Other features, advantages, characteristics, alternatives, modifica-tions and variations of the present invention will be apparent to those skilled in the art, and such may be made by those skilled in the art within the spirit and scope of the present invention.
._~
The prior art is replete with various devices for ensuring that radio frequency or electromagnetic waves do not penetrate into or out of a sealed enclosure. Early prior art devices were designed to try to protect highly sensitive computers by preventing radio fre~uency and electromagnetic waves from entering a sealed enclosure contain.ing the computer equipment. Due to the classified nature of the programs which various computers utilize, and the use to which they are directed, ].ater patents directed to shielding a particular environment were drawn to various methods and devices for preventing electromagnetic or radi.o ~Erequency waves from being transmitted from the shielded enclosure to the outside environment. These devices were important because highly sophisticated methods were being developed to eavesdrop on highly confidential governmental communications and operations.
Rec~ntly, a new problem has presented itself in the form of an extremely high frequency electromagnetic pulse which is produced by the detonation of a nuclear blast high in the atmosphere. This problem is documented in the ~anuary/February 1983 issue of Science magazine (pp. 41-49 wherein the deleterious effects of this electromagnetic pulse are described wi-th respect to the problems which are imposed upon communications systems and shielded enclosures.
These high frequency electromagnetic waves could play havoc with the classified material contained ln compute:rs which is to be protected in the enclosed environment.
~>' I
A-1623 1¦
he majority of prior art devices, which have dealt with ensuring tha-t radio frequency or electromagnetic waves do not p~netrate into or exit from -the sealed environment, generally protect the environment from relatively low frequencies of radiation, but does not afford comparable a-ttenuation levels at microwave frequencies. As the ¦ computational speed o modern digital computers has increased so has the frequency content of electromagnetic emanations from these computers and diyital communica-tions systems.
Therefore, a door seal that is more effective at microwave frequencies is required to protect the classified material being processed within a shielded enclosure.
t has been established -tha-t the voltage drop ¦ across the seal on -the inside surface of all shlelded enclosure or equipment access doors is an important consideration when designing a seal which would protect a shielded enclosure from the egress of very high frequency electromagnetic waves through the shielded door. In this context, all of these doors require extremely good metal-to-me-tal contact around their periphery.
Prior art patents which have dealt with this problem I of providing an adequate door seal employ beryllium copper or phosphor bronze spring fingers within the door seal. Such ¦ prior art door seals are described in U.S. Patents 3,589,070 issued to Hansen and ~,069,618 issued to Geiss Both of these patents describe door seals used in shielded enclosures.
These patents employ a knife edge provided on a first closure member which coopera-tes with spring fingers provided on a second closure member to form a door seal for screen rooms .
.
I
-1~23 ¦ and shielded enclosures. While it has been shown that the door seal configurations shown in the Hansen and Geiss patents are quite effective in forming a good closure at low frequencies, at very hiyh frequencies in excess of .5 GHz, the inductance of the tines of the spring fingers increases and the leakage throuyh the slots formed in the door seal increases, thereby decreasing ~he effectivenessof the door seal.
The patent to Geiss also uses a woven me-tallic RF
gasket in the area of cooperation be-tween the knife edge and the spring fingers. This gasket introduces ano-ther low frequency current path in parallel wi-th the two rows of spring fingers thereby reducing the voltage drop across the door seal. Secondly, the presence of this yasket increases the microwave attenuation of the door seal by acting as ano-ther barrier to the microwave energy. This material does not have the resilience of the beryllium copper spring fingers and ultimately it will l'take a set" and added attenuation of the waves will be los-t.
While differen-t RF absorbing materials can be used between the rows of spring fingers to improve the microwave at-tenuation of the door seal, the limi-ted space ~e~ween ~he spring fingers of approximately one centimeter limits the effectivenessof the door seal.
Consequently, it is seen that there is a continuing need for a more effective door seal which would block both low frequency elec-tromagnetic w~ves as well as very hiyh frequency electromagnetic waves.
, . , ~L2.~
70015-~
SU~ARY OF TH~ INVENTION
The present invention is direc-ted to improving -the sealing effectiveness of a door seal for a shielded enclosure b" introducing a high frequency impedance between the two coacting surfaces of the door seal. The door seal is provided wi-th two cooperating members whish move rela-tive -to one another.
At leas-t one of -the members contains a small cavity ~herein which is filled with a dielectric or lossy ma-terial. The periphery surrounding the cavity is closed, with t~e exception of a small gap ensuring communlca-tion between the material provided within -the cavity and a sealing surface between -the two coopera-ting members. The combina-tion of this gap and the dielectric material introduces a high frequency impedance be-tween -the surfaces of -the seal. This impedance results in a voltage dividing action and reduces the voltage across the protected surface of the door seal, According -to a broad aspect of the inven-tion -there is provided an electromagne-tic shielded door seal utilized wi-th a shielded enclosure adapted for US2 between a door and a door frame, said door seal comprising:
firs-t closure seal member fixedly a-t-tached to said door provided wi-th a pair of firs-t spaced wall members Eorming a flrst slot therebetween;
second closure seal member fixedly attached -to said door frame provided with a pair of second spaced w~ll members forming a second slo-t -therebe-tween, one of said second wall mem-bers adapted to be inser-ted in-to sald first slot and operatively csopera-ting^ wi-th said firs-t clocure seal member -to form an RF elec-tromagnetic frequency resistant seal;
a first cavity provided in said firs-t closure seal member, said cavi-ty filled with an energy absorbent dielectric material, 70015-~32 said first cavi-ty substantially enclosed wi-th the exception of a dis-tinct -First gap providecl in a surrounding periphery of said first cavity, said first gap direct.l.y opening on-to said Eirst slot; and firs-t and seco.nd spring closure members provided respecti-vely on each of said first pair of spaced wall members, said firs-t and second spring closure members resiliently urged agains-t the said second spaced wall member which is inserted in-to said firs-t slo-t.
Alternatively, the closure members can be reversed, i.e. the first closure member can he attached to the door frame and the second slosure member can be a-ttached to the door.
~ccording to another broad aspec-t of the invention there is provided an electromagnetic door seal utilized with a shielded enclosllre adapted fox use be-tween a door and a door frame comprising:
first closure seal member fixedly at-tached to said door;
second closure seal member fixedly attached -to said door,~
frame operatively cooperating w th said first closure seal member to form an RF or electromagne-ti.c frequency resistant seal;
a cavi-ty provided in said first closure seal member filled wi-th an energy absorben-t dielectric ma-te.rial,said cavity substantially enclo~ed with the excep-tion of a dis-tinc-t gap provided in a surrounding periphery of said cavi-ty, said gap provided on -the portio~ of said periphery of said cavity directly facing and opening onto said second clo~ure member; and first and second sprin~ closure members provided on said surrounding periphery of said first closure seal member on either side of said gap.
-4a-Again, the closure members can be reversed.
~ ccording to another broad aspect of the invention there is provided an electrcmagnetic door seal utilized with a shielded enclosure adapted for use between a door and a door frame comprising:
first closure seal member fi~edly attached to said door;
second closure seal member provided wi-th an L-shaped sealing surface, said second closure means fixedly at-tached to said door frame and operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency seal;
a cavity provided in said first closure seal member filled with an energy a~sorbent dielectric material, said cavity substanti.ally enclosed wi-th the exception of a distinct gap provided ln a surrounding periphery of said ca~ity, said gap provided on the portion of said periphery of said cavity directly facing and opening onto said second closure mem~er;
and first spring closure member provided on one of the L shaped legs of said L--shaped sealing surface and a second spring closure member provided on the second leg o~ said L-shaped se~ling surfase.
Again, the closure mem~erscan be reversed.
Other objects, advantages and novel features of the presen-t invention will become apparent from the followi.ng detailed description of the invention when considered in conjunction with the accompanying drawings; wherein like reference numerals identify like parts throughout. !
-~b-BRIEF DESCR~PTION OF THE D~WINGS
Figure l is a front view of the door which is used in a shielded enclosure;
Figure 2 is a cu-taway view of one embodiment of the door seal of the presen-t i.nvention showing t.he relation-ship of -the first and second cloc.ure members;
-4c~
,7 A, ~2 .
A-1623 FIGS. 3, 4 and 5 are cutaway views of different embodiments of the present invention showing the relationship of the first and second closure members; and FIG. 6 is the equivalent circuit for the present invention with respect to the door seal shown in FIG. 2.
DETAILED DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates a typical door/door frame combination 10 which can be utilized with the door seal described in the present invention. Th~ combination contains a door 12 provided with a door core constructed of virtually any standard door core materials such as wood, aluminum, s~eel or the like. The door core is surrounded by a layer of 26 gauge galvanized steel and can be provided with a color-coordinated decorative veneer or acoustical covering provided on both the inside and outside of the door core.
A plurality oE knuckle ball bearing hinges 14 is provided between the door 12 and door frame 20 to allow opening and closing of the door. Although three knuckle ball bearing hinges are shown in FIG. 1, it is understood that this number iB merely illustrative of the number and positioning of the hinges which are utili2ed. An alignment bearing 16 is provided -to ensure that the door will easily be opened and closed while ensuring that radiation cannot enter or leave the shielded enclosure. A polished chrome door handle 18 is provided to allow access to the interior of the enclosure.
~ ~ .
A similar handle is provided on the inside door in the enclosure. The door frame 20 can be constructed of standard materials which are used to prevent the passage of radiation into a sealed enclosure. The frame can be constructed with a four inch depth tubing frame having shielded lapp joints, but the invention is not to be construed to be limited to such a construction.
FIG. 2 shows a cutaway view of one embodiment of the present invention showing the various components of the door seal in an open position. The door seal is provided with a first closure member 23 secured to the door frame 20 and a second closure member 25 secured to the door 12. The first closure member 23 provided in the door frame 20 contains an L-shaped member having legs 22 and 2~. A second L-shaped member having legs 26 and 28 is also provided. The legs 24 and 28 are opposed to one another and are arranged such -that a slot 30 is provided therein. Although it is not important for this invention, these L-shaped members can be constructed of material such as hot-rolled steel. A ~ap 34 is provided within the slot 30 and between legs 22 and 28 of the two L shaped members. A cavity 36 is provided between the legs 22, 26 and 28 within which is provided a dieleckric or lossy material such as polyurethane. ~dditionally, although it is not imperative to -the operation of the present invention, the dielectric or lossy material can include conductive particles of copper or iron or any other ma-terial used to attenuate RF or electromagnetic waves. Although the exact dimensions of the gap 3~ are not inlportant, it has been found that a dimension of between four and eight millimeters can be ~1 '~ 8 provided. I-t is important to note that the gap 34 must be provided such that there is communication between the slot 30 and the dielectric material within the cavity 36. A
pair of spring fingers 32,33 is provided on the surface of the opposed members 24 and 28, respectively. These spring fingers can be constructed out of beryllium copper or phosphor bronze or any other similar material.
The second closure member 25 is provided on the door 12 and is provided with an L-shaped member 42 directly joined to a knife edge 38. A slot 44 is provided between L-shaped member 42 and the knife edge 38. The door core 40 is provided adjacent to the slot 44 and can be constructed of various materials, as has been indicated ilereinabove.
In operation, the door 12 is swung closed such that knife edge 38 is provided between the resilient spring fingers 32,33 to ensure that an effective seal has been made.
Although the door seal has been described as having a knife edge provided on the door and spring fingers provided on the door frame, the positioning of these elements can be reversed. Additionally, either side of the seal can be outside of the door. Furthermore, both the first and second closure members 23,25 are provided along the entire periphery of the door 12 at the door frame 20.
The operation of this seal can best be explained using the Thevenin equivalent circuit shown in FIG. 6. For illustrative purposes, consider that a plane wave field is incident from the bot-tom of FIG. 2 upward toward the seal.
~ithout any spring fingers in the assembly, a large voltage VOC
would appear between the knife edge 38 and leg 28, as shown in FIGS. 2 and 6. With the spring fingers 32,33 in place, the voltage between the knife edge 38 and the leg 28 is reduced to only the voltage drop across the contacts of the spring fingers. Since the impedance of the spring finger is much lower than the equivalent impedance of the slot Z30, the output voltage VO is much smaller than the voltage VOC. In a shielded doorit isthis reduction that is responsible for the effectiveness of the door seal.
In the present design, the voltage can be reduced further. It is apparent that the voltage between the knife edge 38 and the leg 28 is the sum of the voltages between the knife edge 28 and the leg 24 and the voltage between the leg 24 and the leg 28. According to the equivalent circuit in FIG. 6, the voltage between the knife edge 38 and the leg 28 is applied to the series combination of -the impedance Z32 of the spring finger 32 and the inpedance Z34 across the gap 34.
Since the impedances Z33 and Z32 are small, the impedance Z34 does not have to be very large to reduce -the voltage across the knife edge 38 and leg 24 significantly.
Since this voltage drives the fields inside the enclosures, the improved shield effectiveness is obtained by introducing the gap 34 and the dielectric material wi-thin the cavity 36. Since the dimensions of the cavity, and the electrical conductivity, permittivity and permeability of the material contained in the cavi-ty can be varied, the performance characteristics of the present invention can be changed.
FIG. 3 shows an alternate embodiment of the present invention wherein both the first and second closure members 23 ~2~ 8 and 25 respectively include gaps such that dielectric material provided in each of the closure members can communicate with the door seal. The first closure member 23 is similar to the embodiment shown in FIG. 2 and the same reference numerals are utilized. The second closure member 25 is provided on the door frame 20 and includes an L-shaped member having legs 46 and 48 which are used to substantially enclose a cavity 54 having dielectric material similar to the material contained in cavity 36 provided therein. Similar to the seal shown in FIG. 2, a knife edge 56 is provided which will cooperate with the spring fingers 32 and 33 in the manner which has been described herein-above, and the slot 44 is provided between leg 48 and the knife edge 56. A single spring member 50 is provided on the leg 48 which is to cooperate with the outside surEace oE the leg 24 of the first closure member 23. Additionally, similar to the gap 34 which is provided in the first closure member, a gap 52 is provided between leg 48 and the continuation of the knife edge 56 allowing communication between the door seal and the di-electric material 54. As was true with respect to the embodiment shown in FIG. 2, the reversal of the first and second closure members on the door 12 itself and the door frame 20 is also contemplated.
FIG. 4 shows a third embodiment of the present inven-tion which can be applied to a wiping/compression finger stock door seal having a Eirst closure member 60 provided on door frame 61 and a second closure member 62 provided on door 79. The first closure member 60 is applied to the door frame 61 and sub-stantially encloses a cavity 70 having dielectric material therein. The cavity 70 is surrounded by leg members 64, 66 and 82, except for a small gap 68 provided in leg member 82, ~ 8~ 7~015-32 The second closure member 62 is provided with a leg 74 having a spring finger 76 thereon, and a leg 72 having a spring finger 78 thereon. Conventional door core material is provided at 80.
In operation, the gap 68 would cooperate with a sealing surface to ensure that the voltage dividing effect described herein-above will also be present in this embodiment, As was true with respect to the previous embodiments, the first and second closure members can be reversed with respect to the positioning on the door frame or the door itselE.
Yet another embodiment of the present invention is shown in FIG. 5. This embodiment illustrates the voltage dividing door seal applied to a compression door. The door seal includes a first closure member 82 provided on door frame 83 and a second closure member 84 provided on door 99, The first closure member contains legs 88, 90 and 92 which substantially surround a cavity 86 created therein. The cavity contains dielectric material similar to that whlch has been described with respect to the other embodiments of the present invention.
The leg 92 is provided with a gap 94 such that the dielectric material can communicate with the door seal, As was true with respect to the gap provided in all of the embodiments of the present invention, this gap can be dimensioned between four and eight millimeters. Spring fingers 96 and 98 are each provided on one side of the gap which would cooperate with a sealing surface 102 on the second closure member 84. A door core 100 is provided which is constructed of conventional door core material, As was true ~ 38 with respect to all of the o-ther embodiments of the presen-t invention, the positioning of the firs-t closure member 82 and the second closure member 84 can be reversed with respect to the door frame and the door itself.
Other features, advantages, characteristics, alternatives, modifica-tions and variations of the present invention will be apparent to those skilled in the art, and such may be made by those skilled in the art within the spirit and scope of the present invention.
Claims (12)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electromagnetic shielded door seal utilized with a shielded enclosure adapted for use between a door and a door frame, said door seal comprising:
first closure seal member fixedly attached to said door provided with a pair of first spaced wall members forming a first slot therebetween;
second closure seal member fixedly attached to said door frame provided with a pair of second spaced wall members forming a second slot therebetween, one of said second wall members adapted to be inserted into said first slot and operatively cooperating with said first closure seal member to form an RF electromagnetic frequency resistant seal;
a first cavity provided in said first closure seal member, said cavity filled with an energy absorbent dielectric material, said first cavity substantially enclosed with the exception of a distinct first gap provided in a surrounding periphery of said first cavity, said first gap directly opening onto said first slot; and first and second spring closure members provided respectively on each of said first pair of spaced wall members, said first and second spring closure members resiliently urged against the said second spaced wall member which is inserted into said first slot.
first closure seal member fixedly attached to said door provided with a pair of first spaced wall members forming a first slot therebetween;
second closure seal member fixedly attached to said door frame provided with a pair of second spaced wall members forming a second slot therebetween, one of said second wall members adapted to be inserted into said first slot and operatively cooperating with said first closure seal member to form an RF electromagnetic frequency resistant seal;
a first cavity provided in said first closure seal member, said cavity filled with an energy absorbent dielectric material, said first cavity substantially enclosed with the exception of a distinct first gap provided in a surrounding periphery of said first cavity, said first gap directly opening onto said first slot; and first and second spring closure members provided respectively on each of said first pair of spaced wall members, said first and second spring closure members resiliently urged against the said second spaced wall member which is inserted into said first slot.
2. The electromagnetic shielded door seal in accordance with claim 1 further including:
a second cavity provided in said second closure seal member filled with an energy absorbent dielectric material, said second cavity substantially enclosed with the exception of a distinct second gap provided in a surrounding periphery of said second cavity, said second gap directly opening onto said second slot; and third spring closure provided on the said second spaced wall member which is not inserted into said first slot, said third spring closure resiliently urged against one of said spaced wall members when the said second spaced wall member is inserted into said first slot.
a second cavity provided in said second closure seal member filled with an energy absorbent dielectric material, said second cavity substantially enclosed with the exception of a distinct second gap provided in a surrounding periphery of said second cavity, said second gap directly opening onto said second slot; and third spring closure provided on the said second spaced wall member which is not inserted into said first slot, said third spring closure resiliently urged against one of said spaced wall members when the said second spaced wall member is inserted into said first slot.
3. The electromagnetic shielded door in accordance with claim 2 wherein said first and second cavities are completely filled with an energy absorbent dielectric material.
4. An electromagnetic shielded door seal utilized with a shielded enclosure adapted for use between a door and a door frame, said door seal comprising:
first closure seal member fixedly attached to said door frame provided with a pair of first spaced wall members forming a first slot therebetween;
second closure seal member fixedly attached to said door provided with a pair of second spaced wall members forming a second slot therebetween, one of said second wall members adapted to be inserted into said first slot and operatively cooperating with said first closure seal member to form an RF electromagnetic frequency resistant seal;
a first cavity provided in said first closure seal member, said cavity filled with an energy absorbent dielectric material, said first cavity substantially enclosed with the exception of a distinct first gap provided in a surrounding periphery of said first cavity, said first gap directly opening onto said first slot; and first and second spring closure members provided respectivte-ly on each of said first pair of spaced wall members, said first and second spring closure members resiliently urged against the said second spaced wall member which is inserted into said first slot.
first closure seal member fixedly attached to said door frame provided with a pair of first spaced wall members forming a first slot therebetween;
second closure seal member fixedly attached to said door provided with a pair of second spaced wall members forming a second slot therebetween, one of said second wall members adapted to be inserted into said first slot and operatively cooperating with said first closure seal member to form an RF electromagnetic frequency resistant seal;
a first cavity provided in said first closure seal member, said cavity filled with an energy absorbent dielectric material, said first cavity substantially enclosed with the exception of a distinct first gap provided in a surrounding periphery of said first cavity, said first gap directly opening onto said first slot; and first and second spring closure members provided respectivte-ly on each of said first pair of spaced wall members, said first and second spring closure members resiliently urged against the said second spaced wall member which is inserted into said first slot.
5. The electromagnetic shielded door seal in accordance with claim 4 further including:
a second cavity provided in said second closure seal member filled with an energy absorbent dielectric material, said second cavity substantially enclosed with the exception of a distinct second gap provided in a surrounding periphery of said second cavity, said second gap directly opening onto said second slot;
and third spring closure provided on the said second spaced wall member which is not inserted into said first slot, said third spring closure resiliently urged against one of said spaced wall members when the said second spaced wall member is inserted into said first slot.
a second cavity provided in said second closure seal member filled with an energy absorbent dielectric material, said second cavity substantially enclosed with the exception of a distinct second gap provided in a surrounding periphery of said second cavity, said second gap directly opening onto said second slot;
and third spring closure provided on the said second spaced wall member which is not inserted into said first slot, said third spring closure resiliently urged against one of said spaced wall members when the said second spaced wall member is inserted into said first slot.
6. The electromagnetic shielded door in accordance with claim 5 wherein said first and second cavities are completely filled with an energy absorbent dielectric material.
7. An electromagnetic door seal utilized with a shielded enclosure adapted for use between a door and a door frame comprising:
first closure seal member fixedly attached to said door;
second closure seal member fixedly attached to said door frame operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency resistant seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said gap provided on the portion of said periphery of said cavity direct-ly facing and opening onto said closure member; and first and second spring closure members provided on said surrounding periphery of said first closure seal member on either side of said gap.
first closure seal member fixedly attached to said door;
second closure seal member fixedly attached to said door frame operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency resistant seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said gap provided on the portion of said periphery of said cavity direct-ly facing and opening onto said closure member; and first and second spring closure members provided on said surrounding periphery of said first closure seal member on either side of said gap.
8. An electromagnetic door seal utilized with a shielded enclosure adapted for use between a door and a door frame comprising:
first closure seal member fixedly attached to said door;
second closure seal member provided with an L shaped sealing surface, said second closure means fixedly attached to said door frame and operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said gap provided on the portion of said periphery of said cavity directly facing and opening onto said second closure member; and first spring closure member provided on one of the L-shaped legs of said L-shaped sealing surface and a second spring closure member provided on the second leg of said L-shaped sealing surface.
first closure seal member fixedly attached to said door;
second closure seal member provided with an L shaped sealing surface, said second closure means fixedly attached to said door frame and operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said gap provided on the portion of said periphery of said cavity directly facing and opening onto said second closure member; and first spring closure member provided on one of the L-shaped legs of said L-shaped sealing surface and a second spring closure member provided on the second leg of said L-shaped sealing surface.
9. The electromagnetic shielded door in accordance with claim 8 wherein said cavity is completely filled with an energy absorbent dielectric material.
10. An electromagnetic door seal utilized with a shielded enclosure adapted fox use between a door and a door frame comprising:
first closure seal member fixedly attached to said door frame;
second closure seal member fixedly attached to said door operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency resistant seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said yap provided on the portion O r said periphery of said cavity dir-ectly facing and opening onto said second closure member; and first and second spring closure members provided on said surrounding periphery of said first closure seal member on either side of said gap.
first closure seal member fixedly attached to said door frame;
second closure seal member fixedly attached to said door operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency resistant seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said yap provided on the portion O r said periphery of said cavity dir-ectly facing and opening onto said second closure member; and first and second spring closure members provided on said surrounding periphery of said first closure seal member on either side of said gap.
11. The electromagnetic shielded door in accordance with claim 10 wherein said cavity is completely filled with an energy absorbent dielectric material.
12. An electromagnetic door seal utilized with a shielded enclosure adapted for use between a door and a door frame comprising:
first closure seal member fixedly attached to said door frame;
second closure seal member provided with an L-shaped seal-ing surface, said second closure means fixedly attached to said door and operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said gap provided on the portion of said periphery of said cavity directly facing and opening onto said second closure member; and first spring closure member provided on one of the L-shaped legs of said L-shaped sealing surface and a second spring closure member provided on the second leg of said L-shaped sealing surface.
first closure seal member fixedly attached to said door frame;
second closure seal member provided with an L-shaped seal-ing surface, said second closure means fixedly attached to said door and operatively cooperating with said first closure seal member to form an RF or electromagnetic frequency seal;
a cavity provided in said first closure seal member filled with an energy absorbent dielectric material, said cavity substantially enclosed with the exception of a distinct gap provided in a surrounding periphery of said cavity, said gap provided on the portion of said periphery of said cavity directly facing and opening onto said second closure member; and first spring closure member provided on one of the L-shaped legs of said L-shaped sealing surface and a second spring closure member provided on the second leg of said L-shaped sealing surface.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000485091A CA1254988A (en) | 1985-06-25 | 1985-06-25 | Voltage dividing shielded door seal |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000485091A CA1254988A (en) | 1985-06-25 | 1985-06-25 | Voltage dividing shielded door seal |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1254988A true CA1254988A (en) | 1989-05-30 |
Family
ID=4130821
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000485091A Expired CA1254988A (en) | 1985-06-25 | 1985-06-25 | Voltage dividing shielded door seal |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1254988A (en) |
-
1985
- 1985-06-25 CA CA000485091A patent/CA1254988A/en not_active Expired
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| MKEX | Expiry |