A revolver-type feed-through for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads pass through a wall of a cabinet or other enclosure comprises a housing having a conical inner surface, the housing being attachable to the wall through a first attachment means; and a plug member having a conical outer surface matching the conical inner surface of the housing, the plug member being attachable to the housing through a second attachment means, wherein the conical inner surface of the housing and/or the conical outer surface of the plug member have recesses forming, when the plug member is attached to the housing, a plurality of waveguides. The first attachment means and the second attachment means being operable by one or more operating members located, with the feed-through in installed position, exclusively on one side of the wall, so that the first attachment means and the second attachment means are exclusively operable from the said one side of the wall.

FIELD OF THE INVENTION

The present inventive concept relates to a revolver-type feed-through for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads pass through a wall of a cabinet or other enclosure.

BACKGROUND OF THE INVENTION

Such a feed-through can be used to prevent emission of electromagnetic waves, for example to avoid electromagnetic interference or the leakage of critical information from electronic equipment, such as a network switch or server, placed in a cabinet or enclosure. For this application, standards, usually referred to using the term “TEMPEST”, are established that require attenuation up to the order of 100 dB at frequencies up to 10 GHz at the feed-through.

To achieve such attenuation characteristics, such a feed-throughs may comprise one or more waveguides operating below cut-off frequency.

Revolver-type feed-throughs, wherein a plurality of waveguides are distributed around the interface between a housing and a plug member pushable into the housing, are known in the prior art. Examples of such feedthroughs are disclosed in documents U.S. Pat. No. 4,849,723 and US20170090120A1.

There is always a need to improve such feed-throughs.

SUMMARY OF THE INVENTION

According to the present inventive concept, and, according to a first aspect, there is provided a revolver-type feed-through for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads pass through a wall of a cabinet or other enclosure, comprising a housing having a conical inner surface, the housing being attachable to the wall through a first attachment means; and a plug member having a conical outer surface matching the conical inner surface of the housing, the plug member being attachable to the housing through a second attachment means, wherein the conical inner surface of the housing and/or the conical outer surface of the plug member have recesses forming, when the plug member is attached to the housing, a plurality of waveguides. Each of the first attachment means and the second attachment means are operable by one or more operating members located, with the feed-through in installed position, exclusively on one side of the wall, so that the first attachment means and the second attachment means are exclusively operable from that one side of the wall.

Typically, the said one side of the wall is the inside of the cabinet of enclosure. In this way, a tamper- and breakin-proof feed-through is provided. Using such a feed-through eliminates or mitigates the need for additional security measures external to the feed-through, saving space and cost.

Preferably, the first attachment means and the second attachment means are removable. This allows for flexibility of installation.

A recess of the conical outer surface may have a slot for a cover, wherein, with the plug member attached to the housing and the cover installed in the slot, the housing covers the slot, preventing the cover from being removed from the slot. In typical use, a waveguide will be covered by a slot if it is unused, i.e., no signal passes through it. This provides additional security and tamper-proofing, since it eliminates the possibility of tampering with the operating members through the waveguides.

The housing may have a non-circular cross-section, which, with the housing in installed position at the wall, may fit into a corresponding non-circular opening in the wall, preventing the housing from rotating with respect to the wall. Alternatively, or additionally, the one or more operating means of the first attachment means may be operable without rotating the housing. This provides additional security and tamper-proofing, since it eliminates the possibility of tampering with or loosening the housing from the wall by rotating it.

The first attachment means may comprise an outer thread on the housing and a nut, comprising the operating member, having an inner thread matching the outer thread of the housing. This provides a simple yet secure mechanism for attaching the housing to the wall.

The second attachment means may, in a first alternative, comprise a bolt provided with an outer thread; a threaded bore in the plug member with an opening located, with the feed-through in installed position, on said one side of said wall, the threaded bore matching the outer thread of the bolt; and an elongated crossbar; wherein the bolt, with the plug member attached to said housing, pulls against said plug member through the threaded bore and pushes against the housing through the crossbar. This provides a simple yet reliable mechanism for attaching the plug member to the housing.

Using an elongated crossbar, which may fit into a pair of slots on the housing, instead of a more elaborate plate structure which must have large recesses matching the waveguides, simplifies manufacturing while still providing a second attachment means with higher strength and reliability that also is easier to install.

In a second alternative, the second attachment means may comprise a transversal slot through the plug member; a pair of openings in the housing, matching the transversal slot; and a locking rod provided with a convex surface, wherein the locking rod, with the plug member attached to the housing, extends through the transversal slot and the pair of openings and at a first end is pivoted at a pivot point fixed in position with respect to the housing and at a second end is pushed so that the convex surface abuts against an inner surface of the transversal slot, pushing the plug member in a direction into the housing.

This provides a mechanism that is easier to install, yet secure, if space behind the feed-through, usually on the inside of the cabinet or enclosure, is tight. Further, the locking rod provides a lever arm which simplifies removal of the second attachment means.

The locking rod may have a second convex surface, opposite the convex surface, where, during removal of the second attachment means, the second convex surface abuts a second inner surface of the transversal slot. This aids removal of the second attachment means using the locking rod as a lever arm.

The pivot point and the pushing may be provided by a frame arrangement mountable around the housing. The frame, in installed position, may abut against a shoulder of the housing.

Alternatively again, the feed-through may comprise second attachment means according to both the first alternative and according to the second alternative above. The alternative actually used at the point of installation may then be selected during installation of the feed-through, increasing flexibility. For example, the components may be provided as a kit.

The feed-through may further comprise a weather seal frame, comprising an upper part and a lower part adapted to fit around the housing; and a plurality of resilient sealing blocks adapted to be compressed between the upper part and the lower part of said weather seal, sealing around the one or more signal leads. Advantages and embodiments are identical to those described below in conjunction with the sixth aspect.

The plurality of waveguides may comprise four waveguides arranged in a rectangular pattern. This allows the waveguides to line up with the resilient blocks of the weather seal, allowing such a seal to be used together with the revolver-type feed-through.

The said plug member may comprise a transversally extending pin matching a transversal slot in the housing. During insertion of the plug member into the housing, the slots will rotationally guide the plug member. Further, with the plug member inserted into and attached to the housing, the slot and pin will prevent the plug member from rotating with respect to the housing. This provides a simple and robust mechanism that simplifies installation, as the plug member is ensured to always have the correct rotational configuration with respect to the housing.

According to a second aspect, there is provided a system, comprising the feed-through according to the first aspect, one or more of signal leads, and a cabinet or enclosure.

Advantages and embodiments of this second aspect are at least the same as and/or compatible with those described above in conjunction with the first aspect.

According to a third aspect, there is provided a method of installing a revolver-type feed-through for TEMPEST-grade electromagnetic shielding through a wall of a cabinet or other enclosure, comprising: attaching a housing to the wall through a first attachment means, the housing having a conical inner surface; pulling one or more non-electric signal leads through the housing; attaching a plug member to the housing through a second attachment means, an outer conical surface of said plug member matching the conical inner surface of the housing, the conical inner surface and/or the conical outer surface having recesses forming a plurality of waveguides enclosing said one or more signal leads; said method being characterized by said first attachment means and said second attachment means being exclusively operated from one side of said wall.

Advantages and embodiments of this third aspect are at least the same as and/or compatible with those described above in conjunction with the first aspect.

According to a fourth aspect, there is provided a revolver-type feed-through for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads pass through a wall of a cabinet or other enclosure, comprising a housing having a conical inner surface, the housing being attachable to the wall through a first attachment means; and a plug member having a conical outer surface matching the conical inner surface of the housing, the plug member being attachable to the housing through a second attachment means, wherein the conical inner surface of the housing and/or the conical outer surface of the plug member have recesses forming, when the plug member is attached to said housing, a plurality of waveguides, the feed-through being characterized by further comprising a weather seal frame comprising an upper part and a lower part adapted to fit around and seal against the housing; and a plurality of resilient sealing blocks adapted to be compressed between the upper part and the lower part of said weather seal, sealing around the one or more signal leads.

With weather seal should be understood a seal sealing against one or more of, but not limited to, weather, moist, dirt, oil, splashing water, which may be fresh or salt water, or similar.

This allows weather sealing to be provided directly by the feed-through, eliminating the need for additional measures to provide weather sealing, for example the need to place the cabinet or enclosure in a weather-sealed room. This saves space. This, for example, is useful in marine applications.

The upper part and the lower part may be identical in design, which simplifies manufacturing and installation.

Advantages and embodiments described above in conjunction with the first aspect are compatible with this fourth aspect.

According to a fifth aspect, there is provided use of a revolver-type feed-through for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads pass through a wall of a cabinet or other enclosure, the feed-through comprising: a housing having a conical inner surface, the housing being attachable to the wall through a first attachment means; and a plug member having a conical outer surface matching the conical inner surface of the housing, the plug member being attachable to the housing through a second attachment means, wherein the conical inner surface of the housing and/or the conical outer surface of the plug member have recesses forming, when the plug member is attached to the housing, a plurality of waveguides, in combination with a weather seal comprising a weather seal frame comprising an upper part and a lower part adapted to fit around and seal against the housing; and a plurality of resilient sealing blocks adapted to be compressed between the upper part and the lower part of the weather seal frame, sealing around the one or more signal leads.

Advantages and embodiments of this fifth aspect are at least the same as and/or compatible with those described above fourth aspect. Advantages and embodiments described above in conjunction with the first aspect are compatible with this fifth aspect.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG.17illustrates a protected cabinet or other enclosure201, which is a context where a feed-through2(cf.FIGS.1aand1b) according to the present disclosure can be used. Such a cabinet or other enclosure can be used in a sensitive environment where processing devices203in the cabinet201, such as servers, electronically process unencrypted or encrypted sensitive information. The cabinet201, made from an electrically conductive material, which may be thick sheet metal, functions as a Faraday cage, containing within its enclosure any electromagnetic radiation from the processing devices203, thereby preventing the leakage of sensitive information. The processing devices203communicate with nodes213outside the cabinet201via non-electric signal leads205, such as optical fibers, which are terminated by means of connectors207,209at each if their ends. The signal-leads must be non-electric in order not to spoil the functioning of the shielding, as an electric signal lead would act as an antenna, spoiling the shielding of the inside of the cabinet or enclosure. The signal leads may convey less sensitive information or the information carried by them may be encrypted. Furthermore, the conveyed optical signals as such usually give negligible leaked radiation, preventing interception of such signals, unless the fibers are tampered with.

The feed-through where the optical fibers extend out of the cabinet201requires special attention so that electromagnetic radiation does not escape the cabinet, risking interception by a third party nearby.

In addition to the shielding situation described above, the feed-through may be useful in other situations where considerable attenuation at a connection into a Faraday cage is needed. For instance, as the effect provided is more or less reciprocal, the feed-through could protect sensitive equipment in a cabinet from external electromagnetic interference, such as electromagnetic pulses with high energy. Further, a shielded room used for sensitive measurements could be protected from external electromagnetic interference, etc.

Additionally, the cabinet or enclosure201may be subject to requirements of weather proofing and/or tamper proofing and/or security against break-in. Normally such feed-throughs do not provide such functionality by themselves, requiring such functionality to be provided external to the cabinet or enclosure201, for example by the cabinet or enclosure being located in a secured and/or weather sealed room. With the present inventive concept, such functionality may be provided directly by the feed-through itself. This is particularly advantageous in environments where space is at a premium.

As is well known per se, an attenuating feed-through can be obtained by means of a waveguide below-cutoff, WBCO, of which one example is schematically illustrated inFIG.16. In this example the waveguide212, made from a conductive material, has a cavity214, open at both ends, with a circular cross section with diameter D and a length1. The waveguide extends through a wall in a Faraday cage201.

Electromagnetic waves can propagate through a waveguide in a number of different modes, corresponding to different solutions to the Maxwell equations. These modes are distinguished by different configurations of the electric and magnetic fields. Each of these modes has a cut-off frequency, below which no substantial propagation in that mode is possible. Below the lowest cut-off frequency of all possible modes, no substantial propagation of electromagnetic waves is possible at all. Instead, signals suffer exponential attenuation. For example, in a circular waveguide, the mode with the lowest cut-off frequency is the TE11(transverse electric) mode. The cut-off frequency fcof that mode can be shown to be, to three significant figures,

where v is the propagation speed of the waveguide dielectric, i.e., the non-conductive material forming the bulk of the waveguide cavity. In air, v is to a good approximation 3×108m/s. Below this cut-off frequency, over a distance l, an electromagnetic wave with frequency f suffers a total attenuation of again to three significant figures,

It can thus be seen that to maximize attenuation of signals of a certain frequency requires as high a cut-off frequency as possible, and thus as narrow a waveguide as possible, as well as a long a waveguide as possible. It can also be seen that the larger the diameter a waveguide has, the longer the waveguide needs to be to achieve target attenuation.

FIGS.1aand1bshow exploded views, from two different angles, of a revolver-type feed-through2providing TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads18(cf.FIG.15) pass through a wall16of a cabinet or enclosure (cf.101,FIG.15), for example in the context described above with reference toFIGS.17and18.

The feed-through2is intended to be attached to the wall16and comprises a housing4intended to be attached to the wall16and a plug member6intended to be attached to the housing4. The wall16has a first side, typically corresponding to the outside of the cabinet or enclosure, towards the housing4and plug member6, as depicted inFIGS.1aand1b, and a second side, typically corresponding to the inside of the cabinet or enclosure, towards the nut24and the bolt38, again as depicted inFIGS.1aand1b.

The housing4has a conical inner surface8matching a conical outer surface12of the plug member6so that a tight fit may be achieved between the conical inner surface8and the conical outer surface12(cf.FIG.5c).

The plug member has a plurality of longitudinal recesses20, so that, with the plug member6inserted into and attached to the housing4, the conical outer surface12of the plug member6meets the conical inner surface8of the housing4, each recess20forming a waveguide22(cf.FIG.5d) through the feed-though2.

In the depicted feed-through2, only the plug member6has recesses20. However, it is equally possible for the wave-guide-forming recesses20to instead be located on the conical inner surface8of the housing4, or on both the conical inner surface8of the housing4and the conical outer surface12of the plug member6.

In order to properly form the respective waveguides22, a tight fit is needed between the housing4and the plug member6. The housing4and the plug member6must thus be formed from material with good electrical conductivity, typically a metal such as steel or brass. Typically, they are made from machined, such as lathed, parts in order to achieve the required tolerances needed for a tight fit between the two parts.

The depicted plug member has four recesses20evenly distributed around the outer surface12so to form a quadratic, i.e., rectangular pattern. Thus, the waveguides22formed when the plug member6is inserted into the housing4will also form a quadratic/rectangular pattern.

Each of the recesses20of the outer conical surface12of the plug member6has a slot28located close to the outer end of the plug member6, in installed position on the first side of the wall. Before the plug member6is inserted into the housing4, a cover30may optionally be inserted into a respective such slot28. With the plug member6then inserted into the housing4, the wall66close to the outer end of the housing4will cover the cover30so that the cover30cannot be removed from the slot, preventing an intruder from gaining access to the opposite, second, side of the wall through the waveguide22located behind the cover30.

The plug member6comprises two transversally extending and diametrically opposite pins68located close to the outer end of the plug member6, matching two respective slots70in the housing4. During insertion of the plug member6into the housing4, the plug member6will be guided rotationally by the slots70. Further, with the plug member6inserted into and attached to the housing4, the slots70and pins68will prevent the plug member6from rotating with respect to the housing4.

The feed-through2further comprises a first attachment means10for attaching the housing4to the wall16of the cabinet or enclosure. The second attachment means is in the form of an outer thread34on the housing4and a nut24with an inner thread36matching the outer thread34of the housing4. Further, a washer62protects the housing4and will, in installed position, be located between the wall16and a shoulder64on the housing4, located next to the outer thread34. The washer62ensures electrical contact between the housing4and the electrically-conducting wall16and is preferably made of a material softer than the housing and/or the wall, such as copper. The nut24acts as an operating member10for the first attachment means10and is, with the housing4in installed position, entirely located on the second side of the wall16. Thus the first attachment means10is only operable from that second side of the wall16. The nut24can be rotated without rotating the housing4with respect to the wall16. Thus, the operating means24of the first attachment means10is operable without rotating the housing4.

The part of the housing4which in installed position extends through the wall16has a non-circular cross-section, as evident by two diametrically opposed flat sections72. This is matched by a corresponding non-circular cross section of the hole32in the wall16, including two straight sections74matching the flat sections72of the housing72. This geometric configuration prevents the housing, in installed position attached to the wall, from rotating with respect to the wall16.

The feed-through2ofFIGS.1aand1bfurther comprises a second attachment means26for attaching the plug member6to the housing4, comprising the following. A bolt38is provided with an outer thread40. The bolt may be inserted into an elongated crossbar46. The thread40matches an inner thread of a threaded bore42(cf.FIG.5c) in the plug member. The threaded bore42has an opening located, with the plug member6inserted into and attached to the housing4, on the inner side of the wall16.

A head26of the bolt38may be rotated by a user to drive the bolt38into the plug member6, thereby pulling the plug member6into the housing4. Thus, the head26acts as an operating member for the second attachment means and is entirely located, in installed position, on the same, second, side of the wall16as the operating member of the first attachment means. Thus the second attachment means14is only operable from that second side of the wall16.

In installed position, the bolt38pulls against the plug member6, keeping it attached to the housing4through the thread of the threaded bore42of the plug member6(cf.FIG.5c), while pushing against the housing though the crossbar46, which abuts two slots76located at the inner end of the housing4.

FIGS.2a,2b;3;4and5a-dshow a typical assembly sequence of the feed-through2.

First, with reference toFIGS.2aand2b, the housing4is pushed from the first side of the wall16into the hole32of the wall16(cf.FIGS.1aand1b), as indicated by an arrow A, the non-circular cross-section of the housing4lining up with the non-circular cross section of the hole32of the wall16, with the washer62located on the first side of the wall16between the wall16and the shoulder64of the housing4.

Then, the first attachment means10(cf.FIGS.1aand1b) is operated, on the second side of the wall16, by operating the operating means, by tightening the nut24by rotating it, as indicated by an arrow B. With the nut24tightened, the housing4is now attached to the wall16through the first attachment means10.

Then, with reference toFIG.3, one or more non-electric signal leads18—typically optical fibers or fiber-optic cables—are pulled through the housing4and thus through the wall16. Covers30may be placed into the slots28corresponding to recesses20/waveguides22(cf.FIGS.1aand1b) not intended to carry signal leads18.

Then, still with reference toFIG.3, the plug member6is pushed into the housing4, from the first side of the wall16, as indicated by an arrow C, the pins68being guided by the slots70. The waveguides22(cf.FIGS.5a,5b) are formed.

Then, still with reference toFIG.3, the bolt38is pushed, from the second side of the wall16, through the hole of the crossbar46and into the opening44(cf.FIG.1b) of the plug member and the crossbar46placed into the two slots76(cf.FIGS.1b,4) of the housing4, as indicated by an arrow D.

Then, with reference toFIG.4, the bolt38is tightened, on the second side of the wall16, by engaging the head26with a suitable tool and rotating the head26, as indicated by an arrow E.

With reference toFIGS.5a,5b,5c, and5d, with the bolt38tightened, the plug member6is now attached to the housing4through the second attachment means14(cf.FIGS.1a,1b). The signal leads18run through waveguides22formed between the housing4and the plug member6, while waveguides having no signal leads are covered and blocked by the covers30placed into the slots28, with the covers30being prevented from being removed from their respective slots28in the plug member6by the wall66of the housing4.

As is best seen inFIG.5c, the threads of the threaded bore42are exclusively located close to the inner end of the threaded bore42. This ensures that the plug member6, when attached to the housing4, is mainly subjected to a compressing force, which makes the arrangement less sensitive to tensions caused by, e.g., temperature variations.

As is best seen inFIG.5d, the waveguides22follow the cone shape of the plug member6, diverging transversally outwards from the second side of the wall to the first side of the wall.

FIGS.6;7;8;9a,9b; and10show assembly of an alternative second attachment means14, based on the plug member6having a transversal slot48(cf.FIGS.1a,1b) extending through the same and the housing having two openings50(cf.FIGS.1a,1b) matching, i.e., lining up with the transversal slot48of the plug member6when the plug member6has been inserted into the housing4. In installed position, a locking rod52extends through the transversal slot48and the openings50, pushing the plug member6in a direction into the housing4, as will be explained below.

With reference toFIG.6, starting with the plug member6pushed into the housing4(cf. the procedure above disclosed in conjunction withFIGS.2a,2b, and3), a frame arrangement58is mounted around the housing4on the second side of the wall16. The frame arrangement comprises a first part58aand a second part58bjoined by bolts78. Both parts58a,58bof the frame arrangement58abut a shoulder65of the housing4.

FIG.7shows the two parts58a,58bof the frame arrangement58thus joined by the bolts78.

Then, with reference toFIG.8, the locking rod52is inserted, as indicated by an arrow F, into the openings50and the transversal slot48(cf.FIG.9b). The locking rod52has an elongate shape and is substantially flat in a vertical direction. At a first end of the locking rod52, a two-prong fork-like structure60is located, extending longitudinally and horizontally from the locking rod52. Further, a convex surface54extends transversally and horizontally close to the middle of the locking rod52along one of its long edges. A slot80is located close to the other, second, end of the locking rod52opposite that of the fork-like structure and on the opposite long edge to that of the convex surface54, the function all of which will be explained in the following. Alternatively, the slot80may be replaced by a shoulder (not depicted) extending all the way to the second end of the locking rod.

FIGS.9aand9bshow the locking rod52thus inserted, extending through the transversal slot48and the pair of openings50. The fork-like structure60surrounds a pin56provided by the frame arrangement58and functioning as a pivot point for the locking rod52. The slot80is aligned with a bolt82provided by the frame arrangement58

The bolt82is then tightened, the locking rod52pivoting around the pin56, which remains fixed in position with respect to the housing4due to the frame arrangement58being supported by the housing4through the shoulder65. Simultaneously, the convex surface54of the locking rod52pushes the inner surface of the transversal slot48, pushing the plug member6into the housing4and fixing it in place.

Thus, with reference toFIG.10, the second attachment means according to the present alternative attaches the plug member6to the housing4. The operating members, the locking rod52and the bolt82, are exclusively operable from the second side of the wall16, i.e., the same side as the operating member of the first attachment means, i.e., the nut24(cf.FIG.2a,2b,3).

FIG.11illustrates removal of the alternative second attachment means14(cf.FIGS.6;7;8;9a,9b; and10). Due to the tight fit between the plug member6and the housing4, some force will be required to separate the two.

Then, a force, such as a “knock”, is applied at the free end of the locking rod52, for example using a hammer, as illustrated by a vertical arrow G. The locking rod52, pivoting around the pin58, acts a lever arm, with a second convex surface55, opposite to the first convex surface54(cf.FIG.9b) abutting a second inner surface of the transversal slot48, pushing the plug member6out of the housing4.

Finally, the locking rod52may be removed from the transversal slot48and the frame58may be removed from the housing4.

The feed-through may be delivered as a kit comprising both the bolt38and the crossbar46(cf.FIG.1a) and the frame arrangement58and the locking rod52, so that the choice of the first or the second alternative for the second attachment means may be made according to need at the point of installation.

FIGS.12,13,14,15,16show assembly of an optional weather seal for use with a revolver-type feedthrough.

Starting with an assembled feed-through as described above in conjunction withFIGS.5a-dorFIG.11, with reference toFIG.12, resilient substantially cube-shaped blocks104are attached to the signal leads outside of the housing4on the first side of the wall16. As depicted, the cube-shaped blocks104may have one or several holes of different sizes to match the outer dimensions of the signal leads. If no signal lead is present, the corresponding block104may have no hole at all (not shown). The blocks104are made from a resilient material, such as natural or synthetic rubber.

Then, with reference toFIG.13, the lower part106aof a frame106(cf.FIG.14) is mounted, as indicated by an upward-pointing arrow H. The lower part106aof the frame has a shape matching the resilient blocks104and the housing4, in particular the cylindrical shape of the housing4, including a cylindrical protrusion. Further, the lower part106acomprises a lower semicircular resilient part108designed to seal around the housing4. A flat section116(not visible but identical to the flat section116visible on the top of the housing4matches a flat protrusion114of the lower part106a, preventing the lower part106afrom rotating around the housing4.

Then, with reference toFIG.14, an upper part106bof the frame106is mounted, as indicated by a downward pointing arrow I. Just like the lower part106a, the upper part106nof the frame106has a shape matching the resilient blocks104and the housing4. Further, the upper part106bcomprises an upper circular-shaped resilient part (not visible) designed to seal around the housing4. The flat section116on the upper part of the housing4matches a flat protrusion114on the upper part106bof the frame (not visible, but identical to the flat section visible on the lower part106a, cf.FIG.13), preventing the upper part106bfrom rotating around the housing4.

The lower part106aand the upper part106bare made from non-resilient material, such as a thermoplastic, such as ABS. They may be identical in design, which simplifies manufacturing and installation.

Then, with reference toFIG.15, two respective U-shaped reinforcement plates110are added to the upper surface of the upper part106band to the lower surface of the lower part106a, by sliding, as indicated by horizontal arrows J. The reinforcement plates110are preferably made of metal, such as steel.

Finally, with reference toFIG.16, the upper part106band the lower part106aare joined by bolts112through both of the reinforcement plates110, holes on the reinforcement plates110lining up with holes in the upper part106band lower part106a, compressing the resilient blocks104, ensuring sealing action of the resilient blocks104around the signal leads18and sealing around the housing4by the semicircular resilient parts. Further resilient parts may seal between the upper part106aand the lower part106b.

The following are examples.

1. A revolver-type feed-through (2) for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads (18) pass through a wall (16) of a cabinet or other enclosure, comprising:a housing (4) having a conical inner surface (8), said housing being attachable to said wall through a first attachment means (10); anda plug member (6) having a conical outer surface (12) matching said conical inner surface (8) of said housing (4), said plug member (6) being attachable to said housing (4) through a second attachment means (14),wherein said conical inner surface (8) of said housing (4) and/or said conical outer surface (12) of said plug member have recesses (20) forming, when said plug member (6) is attached to said housing (4), a plurality of waveguides (22), said feed-through (2) being characterized by each of said first attachment means (10) and said second attachment means (14) being operable by one or more operating members (24,26) located, with said feed-through in installed position, exclusively on one side of said wall (16), so that said first attachment means (10) and said second attachment means (14) are exclusively operable from said one side of said wall (16).

2. The feed-through (2) of example 1, wherein a said recess (20) of said conical outer surface (12) has a slot (28) for a cover (30), wherein, with said plug member (12) attached to said housing (4) and said cover (30) installed in said slot (28), said housing (4) covers said slot (28), preventing said cover (30) from being removed from said slot (28).

3. The feed-through (2) of any one of examples 1-2, wherein said housing (4) has a non-circular cross-section, which, with said housing in installed position at said wall, may fit into a corresponding non-circular opening (32) in said wall (16), preventing said housing (4) from rotating with respect to said wall.

4. The feed-through of any one of examples 1-3, wherein said one or more operating means (24) of said first attachment means (10) is operable without rotating said housing (4).

5. The feed-through (2) of any one of examples 1-4, wherein said first attachment means (10) comprises an outer thread (34) on said housing (4) and a nut (24), comprising said operating member (24), having an inner thread (36) matching said outer thread (34) if said housing (4).

6. The feed-through (2) of any one of examples 1-5, wherein said second attachment means (14) comprises:a bolt (38) provided with an outer thread (40);a threaded bore (42) in said plug member (6) with an opening (44) located, with said feed-through (2) in installed position, on said one side of said wall (16), said threaded bore (42) matching said outer thread (40) of said bolt; andan elongated crossbar (46);wherein said bolt (38), with said plug member (6) attached to said housing (4), pulls against said plug member (6) through said threaded bore (42) and pushes against said housing (4) through said crossbar (46).

7. The feed-through (2) of any one of examples 1-5, wherein said second attachment means (14) comprises:a transversal slot (48) through said plug member (6);a pair of openings (50) in said housing (4), matching said transversal slot (48); anda locking rod (52) provided with a convex surface (54), wherein said locking rod (52), with said plug member (6) attached to said housing (4), extends through said transversal slot (48) and said pair of openings (50) and at a first end pivoted at a pivot point (56) fixed in position with respect to said housing (4) and at a second end is pushed so that said convex surface abuts against an inner surface of said transversal slot (48), pushing said plug member (6) in a direction into said housing (6).

8. The feed-through (2) of example 7, wherein said pivot point (56) and said pushing is provided by a frame arrangement (58) mountable around said housing (4).

9. The feed-through (2) of example 8, wherein said frame arrangement (58), in installed position, abuts against a shoulder (65) of said housing (4).

10. The feed-through (2) of any one of examples 1-5, comprising the second attachment means (14) of example 6 and the second attachment means (14) of any one of examples 7-9, selectable during installation of said feed-through (2).

11. The feed-through (2) of any one of the preceding examples, wherein said plug member (6) a transversally extending pin (68), matching a transversal slot (70) in said housing (4).

12. The feed-through (2) of any one of the preceding examples, further comprising:a weather seal frame (106) comprising an upper part (106b) and a lower part (106a) adapted to fit around said housing; anda plurality of resilient sealing blocks (104) adapted to be compressed between said upper part (106b) and said lower part (106a) of said weather seal frame (106), sealing around said one or more signal leads (18).

13. The feed-through (2) of any one of the preceding examples, wherein said plurality of waveguides comprises four waveguides (22) arranged in a rectangular pattern.

14. A system, comprising the feed-through (2) of any one of the preceding examples, one or more said signal leads, and said cabinet (18) or enclosure.

15. A method of installing a revolver-type feed-through (2) for TEMPEST-grade electromagnetic shielding through a wall (16) of a cabinet or other enclosure, comprising:attaching a housing (4) to said wall (16) through a first attachment means (10), said housing (4) having a conical inner surface (8);pulling one or more non-electric signal leads (18) through said housing (4);attaching a plug member (6) to said housing (4), an outer conical surface (12) of said plug member (6) matching said conical inner surface (8) of said housing (4), said conical inner surface (8) and/or said conical outer surface (12) having recesses forming a plurality of waveguides (22) enclosing said one or more signal leads (18);said method being characterized by said first attachment means (10) and said second attachment (14) means being exclusively operated from one side of said wall (16).

16. A kit, comprising:the feed-through (2) of any one of examples 1-5 or 11-15, comprising the second attachment means of any one of examples 7-9; andan alternative second attachment means (14),
said alternative second attachment means (14) comprising:a bolt (38) provided with an outer thread (40);a threaded bore (42) in said plug member (6) with an opening (44) located, with said feed-through (2) in installed position, on said one side of said wall (16), said threaded bore (42) matching said outer thread (40) of said bolt; andan elongated crossbar (46),
wherein said bolt (38), with said plug member (6) attached to said housing (4), pulls against said plug member (6) through said threaded bore (42) and pushes against said housing (4) through said crossbar (46), and
wherein one of said second attachment means (14) and said alternative second attachment means (14) is selectable during installation of said feed-through (2).

17. A revolver-type feed-through (2) for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads (18) pass through a wall (16) of a cabinet or other enclosure, comprising:a housing (4) having a conical inner surface (8), said housing being attachable to said wall through a first attachment means (10); anda plug member (6) having a conical outer surface (12) matching said conical inner surface (8) of said housing (4), said plug member being attachable to said housing (4) through a second attachment means (14),wherein said conical inner surface (8) of said housing (4) and/or said conical outer surface (12) of said plug member have recesses (20) forming, when said plug member (6) is attached to said housing (4), a plurality of waveguides (22), said feed-through (2) being characterized by further comprising:a weather seal frame (106) comprising an upper part (106b) and a lower part (106a) adapted to fit around and seal against said housing; anda plurality of resilient sealing blocks (104) adapted to be compressed between said upper part (106b) and said lower part (106a) of said weather seal frame (106), sealing around said one or more signal leads (18).

18. The feed-through of example 17, wherein said plurality of waveguides (22) comprises four waveguides (22) arranged in a rectangular pattern.

19. Use of a revolver-type feed-through (2) for TEMPEST-grade electromagnetic shielding where one or more non-electric signal leads (18) pass through a wall (16) of a cabinet or other enclosure, the feed-through comprising:a housing (4) having a conical inner surface (8), said housing being attachable to said wall through a first attachment means (10); anda plug member (6) having a conical outer surface (12) matching said conical inner surface (8) of said housing (4), said plug member being attachable to said housing (4) through a second attachment means (14),wherein said conical inner surface (8) of said housing (4) and/or said conical outer surface (12) of said plug member (6) have recesses (20) forming, when said plug member (6) is attached to said housing (4), a plurality of waveguides (22),
in combination with a weather seal comprising:a weather seal frame (106) comprising an upper part (106b) and a lower part (106a) adapted to fit around and seal against said housing (4); anda plurality of resilient sealing blocks (104) adapted to be compressed between said upper part (106b) and said lower part (106a) of said weather seal frame, sealing around said one or more signal leads (18).