AU646852B2 - Connecting means - Google Patents

Description

AUSTRALIb52 ~462 Patents Act COMPLETE SPECIFICATION (OR IGIN AL) Class I t. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: *Go 06 0

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APPLICANT'S REF.: C.A.P. of PJ 9480 Name(s) of Applicant.(s): Address(es) of Applicant(s): CONCRETE CONSTRUCTIONS (AGT) PTY LTD 53 Blackall. Street Barton ACT 2600 Australia Actual Inventor(s): 0 0 Address for Service is: PH-ILLIPS, ORMONDE AND FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne, Australia, 3000 Complexe Specification for the invention entitled: "CONNECTING MEANS" The following statement is a full description of this invention, including the best method of' performing it known to applicant(s): 1119/ 3,H4 CONNECTING MEANS This invention relates to a connecting means. It relates particularly to a means for connecting a membrane such as a foil or a mesh to another member such as another membrane or a rigid sheet.

The invention has particular applicability to the field of electro-magnetic radiation screening, especially in the area of radio frequencies, and the invention will be described with particular reference to that application, although it is to be understood that the invention is not limited to that application.

Telephones, computers and other electrical apparatus emit electro-magnetic radiation during operation. The emitted radiation can be intercepted and used to reconstruct a message such as a telephone conversation or computer data. If a user of electrical communications apparatus S. wishes to be assured that third parties will not listen in to communications using this technique, it is necessary to provide electro-magnetic radiation screening around the communications apparatus. In some installations, such as defence department buildings, electro-magnetic shielding may be required around the whole building.

Electro-magnetic shielding may be effected by means of known materials such as conductive metal sheets and meshes.

Such shields attenuate electro-magnetic signals, rather than completely stopping them, but it is generally considered that a relative attenuation of around 40 dB over the radio frequency spectrum up .o 1 GHz is more than adequate for security purposes.

2 The problem of providing a secure electromagnetic shield around a building is similar to the problem of providing a water-tight container the shield is largely ineffective if radiation leaks can occur at corners and joints. Special care therefore needs to be taken in the construction of joints.

According to known techniques, when a section of flexible shield such as a mesh or a foil is connected to an adjoining section of substantially rigid shield material, such as a metal plate, it is necessary for the two sections to be welded or soldered and riveted together along their connecting edges, or alternatively a substantial overlapping portion of at least about 300 mm must be provided. The amount of labour involved in welding and soldering is extensive and the cost of providing substantial overlaps is high.

According to one aspect of the present invention, there is provided a composite electromagnetic shielding element comprising: a flexible sheet member such as a foil or mesh; a rigid sheet member such as a metal plate; a rib extending along an edge of the rigid sheet member; an edge region of the flexible sheet member, draped over the rib; resilient clamping means placed over the rib and :2 clamping the flexible sheet member to the rib; o the arrangement being such that leakage of electromagnetic radiation between the rigid sheet member and the flexible sheet member is substantially eliminated.

S..The rib may be formed as an integral part of the rigid :az o• 4a a" e -3sheet member. In such an embodiment the rib may be formed by shaping the edge of the rigid sheet member as desired.

Alternatively, the rib may be formed of a separate metal strip and welded to the sheet member as desired, such as by spot welding in the manner outlined in our copending provisional patent specification number PJ 9730. The rib may have any suitable cross-sectional shape including a circular cross-sectional shape. A substantially square cross-sectional shape has been found to be particularly satisfactory in providing at least three firm clamping points at the three corners of the square. It will be appreciated that other shapes such as pentagonal and hexagonal may be employed as desired.

The selection of an appropriate clamping means is Sol* important. Preferably the resilient clamping means is substantially co-extensive with the rib whereby to provide a clamping seal along the length of the rib when fitted thereto although it will be appreciated that a plurality of clamping members may be located along the length of the rib provided that an appropriate seal is achieved.

Preferably the clamping means is provided by an 000.. elongated clamping member which may be made of a resilient material such as a rubber or synthetic rubber composition.

It has been found that ethylene propylene diene monomer **o rubber is an especially suited material. It is durable and has appropriate memory and flexibility characteristics.

The elongated clamping member may be of any suitable cross-section. A circular cross-section has been found to be particularly satisfactory. The elongated clamping member 4 has an elongated rib receiving slot extending therealong.

Preferably the rib receiving slot is of generally circular cross-section. In a particularly preferred example the axis of the rib receiving slot is displaced from the axis of the elongated clamping member so that in cross-section the wall thickness is greatest in the segment opposite the slot opening and at a minimum adjacent the slot opening. With this preferred configuration the elongated member may be provided with a relatively stiff back bone with substantially resilient legs adjacent the slot opening whereby when a strip of material is arched back with the slot extending outwardly the slot opening will be widened to allow the strip to be placed over the rib and when •o o progressively straightened to be clamped thereto.

Preferably the dimensions of the rib receiving slot are smaller than the dimensions of the rib whereby when joined thereto to provide a firm interference fit with the elongated member resiliently urged into firm contact with S the rib.

Accordi-gt-ea-a-nother aspec-t o-ftne-prsetiven there is provided a method for connecting an edge f a flexible sheet member such as a foil or mesh an edge of an adjoining rigid sheet member such a metal or plastic plate. The method comprises the eps of: Providing a rib a) g the edge of the rigid sheet member; Placj the edge of the flexible sheet member over the rib; and -^--e)-Placing-a-resilient-elampingft-ea-ns-ove-r-the-tfirb, 5 According to another aspect of the present invention, there is provided a method of forming a composite electromagnetic shielding element comprising a flexible sheet member connected to a substantially rigid rib, the method comprising the steps of: providing a rib along an edge of the rigid sheet member; placing an edge region of the flexible sheet member over the rig; and placing a resilient clamping means over the rib, clamping the flexible sheet member to the rib and thereby forming a join which substantially prevents leakage of electromagnetic radiation.

In another aspect, the present invention relates to a composite electromagnetic shielding element comprising: a first flexible sheet member such as a foil or mesh; a second flexible sheet member such as a foil or mesh; a substantially rigid rib; an edge region of each of the first and second flexible sheet members, draped over the rib; resilient clamping means placed over the rib and clamping the first and second flexible sheet members to the rib; the arrangement being such that leakage of electromagnetic radiation between the first and second flexible sheet members is substantially eliminated.

999* o .o 9** 9* *a 5a clamping-t-he--fle-xible shee-t-membe-r -to the rib.

In another aspect, the invention relates to appa-fltus for providina a firm connection between an ,ege of a flexible sheet member and an edge of an oining flexible sheet member. The apparatus comprise A rib having a length su tantially equal to that of the edges of the tw olexible sheet members; and Resilient cla ng means; such th in operation, the edges of the flexible s t members are placed over the rib and the resilient clamping means is then placed over the rib, clamping the flexible *shee-embcrs together.

The invention will now be further described with reference to the accompanying drawings. It is to be understood that the drawings are illustrative of an embodiment only, and are not to be construed as limiting the scope of the foregoing disclosure.

Figure 1 is a cross-sectional view of an embodiment of apparatus according to the present invention.

Figure 2 is an exploded view of the apparatus of figure 1.

The apparatus illustrated is for connecting an edge of a flexible sheet, illustrated as mesh 1 to an edge of an adjoining rigid sheet member 2. The apparatus comprises a rib 3 extending along the edge of rigid sheet member 2 and resilient clamping means 4.

In operation, the edge of mesh 1 is placed over rib 3 and resilient clamping means 4 is then placed over rib 3, clamping mesh 1 to rib 3. Rib 3 is shown as being formed 6 from the edge of rigid sheet being folded over into the preferred square cross-sectional configuration. Another suitable cross-sectional configuration is circular. The square cross-sectional configuravion has the advantage that three firm clamping points are achieved at three corners of the square. Similar advantages can be gained by use of triangular, pentagonal, hexagonal and other cross-sectional shapes.

Resilient clamping means 4 is shown with its preferred cross-section as described above.

It will be appreciated that the apparatus can be modified to allow for the clamping together of two flexible

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0: sheet members. In such an application, the two flexible se sheet members would be draped over rib 3 before resilient

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clamping means 4 was applied, clamping the flexible sheet S0 members to each other and to rib 3. Rigid sheet member 2 would of course not be necessary.

In the preferred embodiment illustrated, rigid sheet member 2 is a galvanised sheet having a thickness of about 1 mm. The maximum external cross-sectional diameter of the square rib is about 14 mm and the normal internal diameter of the clamping means is about 10 mm. The normal gap between the legs of the horseshoe is about 3 mm.

Rigid sheet members used in the field of electro-magnetic shielding generally have a pan-shaped configuration, with a turned-up portion on each edge. When this is the case, rib 3 may form the top of a turned-up edge on a pan-shaped rigid sheet 2.

It has been found that the apparatus of the present 7 invention can be safely used in radio frequency electro-magnetic shielding without reducing the attenuation characteristics of the mesh and the metal plate. Thus, for example, when a mesh having an attenuation rating of 70 dB is joined using the present invention to a metal plate having an attenuation rating of 70 dB, the joined mesh-andplate will retain the 70 dB rating.

The apparatus of the present invention has significant advantages over the methods of joining previously known in the field of electro-magnetic shielding. Soldering and welding takes a substantial amount of time, whereas the apparatus of the present invention can be installed very 6:00 quickly. If replacement of components is required, the resilient clamping means of the present invention can be removed rapidly, whereas soldering and welding is very difficult if not impossible to remove satisfactorily.

It is to be understood that various additions, alterations and/or modifications may be incorporated into the parts previously described without departing from the ambit of the present invention.

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Claims (12)

1. A composite electromagnetic shielding element comprising: a flexible sheet member such as a foil or mesh; a rigid sheet member such as a metal plate; a rib extending along an edge of the rigid sheet member; an edge region of the flexible sheet member, draped over the rib; resilient clamping means placed over the rib and clamping the flexible sheet member to the rib; the arrangement being such that leakage of electromagnetic radiation between the rigid sheet member and the flexible sheet member is substantially eliminated.

2. A composite electromagnetic shielding element according to claim 1 wherein the rib is an integral part of the rigid sheet member.

3. A composite electromagnetic shielding element according to claim 1 or claim 2 wherein the rigid sheet member is in a pan configuration with the rib being formed on the top of a turned-up edge of the pan. *t S. S.. S 30 S. S S 5 S 55S555

4. A composite electromagnetic shielding element compris (a) (b) iing: a first flexible sheet member such as a foil or mesh; a second flexible sheet member such as a foil or mesh; a substantially rigid rib; an edge region of each of the first and second flexible sheet members, draped over the rib; resilient clamping means placed over the rib and clamping the first and second flexible sheet members to the rib; the arrangement being such that leakage of electromagnetic radiation between the first and second flexible sheet members is substantially eliminated. 9 A composite electromagnetic shi' Iding element according to any one of claims 1 to 4 wherein the rib is substantially square in cross-section.

6. A composite electromagnetic shielding element according to any one of claims 1 to 4 wherein the rib is substantially circular in cross-section.

7. A composite electromagnetic shielding element according to any one of claims 1 to 6 wherein the resilient clamping means is provided by one or more substantially elongated clamping means.

8. A composite electromagnetic shielding element according to claim 7 wherein the elongated clamping means is substantially co-extensive with the rib.

9. A composite electromagnetic shielding element as claimed in claim 7 or claim 8 wherein said elongated clamping means includes an elongated rib receiving slot extending therealong. A composite electromaganetic shielding element as S claimed in claim 9 wherein the axis of said elongated rib receiving slot is displaced from the axis of said elongated claping means towards tne slot opening whereby to provide a soe wall thickness substantially greater opposite said slot opening.

11. A composite electromagnetic shielding element as claimed in claim 10 wherein said elongated clamping means and said rib receiving slot are each of substantially circular t. cross-section whereby to provide in cross-section a maximum wall thickness opposite said slot opening and a minimum wall ,35 thickness adjacent said slot opening whereby to facilitate connection of said clamping means to said rib. 10

12. A method of forming a composite electromagnetic shielding element comprising a flexible sheet member connected to a substantially rigid rib, the method comprising the steps of: (a) (b) (c) providing a rib along an edge of the rigid sheet member; placing an edge region of the flexible sheet member over the rig; and placing a resilient clamping means over the rib, clamping the flexible sheet member to the rib and thereby forming a join which substantially prevents leakage of electromagnetic radiation.

13. A method as claimed in claim 12 wherein the resilient clamping means is elongated and has a rib receiving slot extending therealong, and wherein said elongated clamping means is arched backwards to increase the opening of the rib receiving slot so that it can be placed over the rib and straightened to allow it to be clamped thereto.

14. A composite electromagnetic shielding element according to claim 1 or claim 4 substantially as hereinbefore described with reference to the drawings. DATED: 29 December 1993 .•c PHILLIPS ORMONDE FITZPATRICK Attorneys for: CONCRETE CONSTRUCTIONS GROUP PTY. ITD. *p p. p p p pp pp p J p ooo• 0c-kS L^< 11