WO2004020930A2

WO2004020930A2 - Shielding apparatus

Info

Publication number: WO2004020930A2
Application number: PCT/SG2003/000207
Authority: WO
Inventors: Wee Beng Ng
Original assignee: Dyntek Pte Ltd
Priority date: 2002-09-02
Filing date: 2003-09-01
Publication date: 2004-03-11
Also published as: WO2004020930A3; AU2003265208A1; TW200406523A; AU2003265208A8

Abstract

Shielding apparatus has a number of shielding units 1. Each shielding unit (1) includes two planar sheet members (2, 3). The sheet members (2, 3) are arranged such that a planar surface of one of the sheet members (2) covers a planar surface of the other of the sheet members (3). The planar surfaces of the sheet members (2, 3) are of substantially the same dimensions and the sheet members are mutually offset (6) from each other so that a portion of the planar surface of each sheet member (2) is not covered by the other sheet member (3).

Description

SHIELDING APPARATUS

Field of the Invention

The invention relates to apparatus for shielding a structure.

The term "shielding" as used in this document does not imply a limitation on what the structure is shielded against. In particular, "shielding" may include shielding from magnetic fields and/or electric fields. Alternatively or additionally, the shielding may be shielding from electromagnetic radiation, and/or from other forms of radiation.

Furthermore, the term "shielding a structure" as used here may include reducing the exposure of the structure itself to what it is shielded against (e.g. if the structure is a wall surrounding a room and the shielding is located on the inner surface of the wall, the term "shielding" is used to include preventing the wall from being exposed to fields etc generated within the room). Furthermore, the term "shielding" as used here may include preventing fields etc which penetrate through the structure from passing to any further regions (e.g. if the structure is a wall surrounding a room and the shielding is located on the inner surface of the wall, the term "shielding" is used to include preventing fields etc which pass through the wall from entering the room).

The term "structure" is used broadly to include for example building structures, but also structures which are apparatus such as computer apparatus. In this case, the shielding may be on the exterior of the apparatus to shield the apparatus against some unwanted influence.

Background of the invention

In buildings in which sensitive equipment, such as scientific equipment or medical equipment, is located, it is often necessary to provide shielding around power cables, switching areas and transformers to minimise the risk of magnetic fields generated by the^'power cables and electrical supply equipment interfering with the sensitive equipment.

Conventionally, magnetic shielding has been provided by using steel cladding around the risers in which power cables are located, the switch areas and transformers to minimise the intrusion of magnetic fields into other parts of the building. Typically, in order to provide adequate shielding, the steel cladding has to be a few millimeters thick and is time consuming and difficult to install. In addition, steel cladding is relatively heavy and requires a reinforced supporting structure to adequately support the steel cladding.

Summary of the invention In accordance with a first aspect of the present invention, a shielding apparatus comprises a number of shielding units, each shielding unit comprising two planar sheet members, the sheet members being arranged such that a planar surface of one of the sheet members covers a planar surface of the other of the sheet members, the planar surfaces of the sheet members being of substantially the same dimensions, and the sheet members being mutually offset from each other so that a portion of the planar surface of each sheet member is not covered by the other sheet member.

An advantage of the invention is that by providing shielding apparatus which comprises a number of shielding units, each shielding unit comprising two planar sheet members in which the dimension of the planar surfaces are substantially identical, it is possible to provide a modular shielding apparatus which can be relatively easily assembled.

Indeed, in a further aspect, the invention provides a method of shielding a structure by fastening to it the shielding units of the shielding apparatus.

The partially overlapping arrangement of the sheet members minimises the risk of a gap between the members and therefore, minimises the risk of magnetic fields (for example) penetrating the shielding apparatus.

Preferably, the sheet members are mutually offset so that two adjacent edges of each sheet member are offset from the other sheet member. In this case, the shielding units are preferably fastened to the structure with a shielding member of at least one of the shielding units overlaying a part of one shielding member of at least one of the adjacent shielding units.

Preferably, at least one of the sheet members comprises a mesh structure. Typically, each sheet member may comprise a number of layers arranged on top of each other. This has the advantage that the thickness of each sheet member can be modified to suit a particular shielding application. Preferably, each layer comprises a mesh structure.

In one example of the invention, the mesh structure may be an expanded mesh structure.

Typically, particularly where the shielding is magnetic shielding, the sheet members are manufactured from a material having a high magnetic permeability relative to air. Typically, the relative magnetic permeability is at least 100, preferably at least 500 and most preferably at least 1000. An example of a suitable material is steel. However, any other suitable material or composition of materials, could be used.

Preferably, where the sheet members comprise a mesh structure, the openings of the mesh may have dimensions of a few millimeters. Typically the openings are less than 10mm x 10 mm and preferably, less than 5mm x 5mm.

Typically, the planar sheet members are fixed to each other by bolts, rivets or any other suitable fixing means. The fixing means may be either metallic or non-metallic and may be releasable, for example, for repair purposes. The shielding apparatus preferably further comprises fastening means for fastening the shielding units to the structure which is to be shielded. Preferably, the fastening means permits subsequent removal of the shielding units from the supporting structure, for example for maintenance purposes. The fastening means may comprise bolts, nails, hooks or brackets.

In a preferred form, the fastening means include brackets having a connection portion for connection to the structure which is to be shielded, and a trench portion for receiving at least part of an edge portion of a shielding member of at least one shielding unit. Preferably, the brackets are arranged on the support structure with the trench facing upwardly, and part of the lower edge portions of shielding members of one or more adjacent shielding units are inserted into the trench of the bracket. Preferably lower corner portions of two adjacent shielding units are inserted into the bracket. In this way, the number of brackets required to support all the lower corners of an array of shielding units is only equal to the number of shielding units (neglecting the edges of the array of shielding units).

Preferably, the brackets include a ridge portion, such that when part of a first shielding member of a given shielding unit is fully inserted into the trench, the other shielding member rests on the ridge portion of the bracket.

The bracket may include a folding portion, e.g. which forms part of one wall of the trench, which can be folded down to hold an upper edge portion of another shielding member. When the shielding apparatus is attached to a structure including a surface (preferably a flat surface) such as a wall, the shielding units are distributed across the surface. Preferably, the shielding apparatus further comprises trim units for shielding the structure at a junction between the surface and other surfaces. For example, if the structure to be shielded includes a wall, the shielding units may be arranged in a "tiled" arrangement covering at least part of the wall, and the trim units may be used to cover junctions between the wall and other surfaces such as a floor, a ceiling, or even other walls. The trim units may be structurally similar to the shielding units, for example including two mutually offset laminar trim members. Note that the two members are normally only mutually offset in the direction parallel to the junction. Trim fastening means may be provided for attaching the shielding units to the second surface and/or to the shielding units.

Preferably, the shielding apparatus further comprises means for generating a magnetic field to create an active shield. Thus, the present invention also includes a method of shielding a structure comprising the step of activating the generation means to generate the magnetic field.

Brief Description of the Figures

An embodiment of a shielding apparatus in accordance with the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 shows a shielding unit of the embodiment; Fig. 2, which is composed of Figs. 2(a) to 2(d), shows a bracket of the embodiment;

Figure 3, which is composed of Figs. 3(a) to 3(f), shows the steps of assembling the shielding apparatus; Fig. 4 shows a trim unit of the embodiment;

Fig. 5 is a cross-sectional view of part of the embodiment in use;

Figure 6 is a view of the embodiment in use on a wall having two corners;

Figure 7 is a cross-sectional view of the embodiment attached to a wall and a ceiling; and

Figure 8 shows a preferred form of the bracket of the embodiment viewed from the side;

Figure 9 shows the shielding unit of Figure 1 further comprising a compensating coil for generating a magnetic field.

Detailed description of an embodiment

Referring to Fig. 1 , a shielding unit 1 is shown comprising two planar sheet members 2, 3 which are positioned on top of each other such that they only partially overlap each other. Thus, there is a mutual offset 6 between adjacent edges of the members 2, 3. Each member 2, 3 is formed from a number of layers of steel mesh, which is typically of an expanded mesh structure. Note that each of the members 2, 3 may alternatively be a solid plate. It is possible that the dimensions of the members 2, 3 and of the mesh may be any suitable size. However, an example of sizes which have been found to be useful are for the planar surface of the sheet members to be rectangular with dimensions of 500x1000mm and an offset 6 of 50mm. Each member 2, 3 is formed from a number of layers of expanded steel mesh. Each layer has a nominal thickness of 0.5mm and a mesh opening size of 2mm x 3mm. For a typical magnetic shielding application for power cables, transformers and switch rooms in a normal building, each member 2, 3 has eleven layers of 0.5mm thick mesh. Hence, the total thickness of the units 1 where the members 2, 3 overlap is 11mm.

An advantage of forming each member 2, 3 from a number of layers is that it is possible to fabricate the units 1 to a desired thickness by increasing or decreasing the number of layers appropriately for the particular (e.g. electromagnetic) shielding application.

The layers of mesh in each member 2, 3 may be fixed together by any suitable fixing means, such as by welding, riveting, bolting or adhesive. Similarly, the members 2, 3 may be attached to each other also by any suitable fixing means such as by welding, riveting or by bolts or any other suitable fastening means. In Figure 1 , the members 2, 3 are shown secured to each other by four fasteners 5. It is also possible that the fasteners 5 may be removable to enable detachment of the members 2, 3 from each other, for example, for replacement, repair or maintenance purposes. Figs. 2(a) to 2(c) show the bracket 11 of the embodiment respectively from the side, from the front and in a side perspective view. The bracket includes a connection portion 13, a ridge portion 15 and a trench portion 17. The trench portion 17 includes a rear wall 19, a base 21 and, facing the wall 19, two side portions 23, 27 and a central wall portion 25. The connection portion 13 may be provided with pre-formed apertures (not shown) for connection to the structure which is to be shielded; alternatively the connection portion may be attached to the structure using apertures which are formed at the time (e.g. by nails). The central portion 25 is provided at its lower edge with perforations 29, which weaken the connection between the central portion 25 and the base 21 , so that the central portion can be folded down as shown in Fig. 2(d). Optionally, perforations may be provided outside the central portion, i.e. to allow the side portions 23 and/or 25 to be folded down.

Figs. 3(a) -3(f) show the assembly process of the embodiment, when it is used to shield a wall 31 but not the adjacent floor 33. Firstly, as shown in Fig. 3(a), brackets 11 as shown in Fig. 2 are attached to the wall 31 , using nails 35 (or other fastening means).

After the brackets 11 have been attached to the wall 31 , a first shielding unit 1a is positioned with a first of its shielding members 2 touching the wall, and the second shielding member 3 spaced from the wall. The lower edge corners of the member 3 are inserted into the respective trench portions of two brackets 11 , and the lower edge corners of the members 2 rest on the ridge portions 15 of the two brackets 11.

A second shielding unit 1b is positioned alongside the shielding unit 1a such that one of the offsets 6 of the member 3 of the unit 1 b overlaps the offset 6 of the member 2 of the unit 1a. The lower left corner of the unit 1b is inserted in the same bracket 11 as the lower right corner of the unit 1 a, so that the members 2 of the units 1a, 1b rest on the ridge portion 15 of that bracket, and the members 3 of the units 1a, 1b rest in the trench portion 17

As shown in Fig. 3(c), another bracket 11a is now attached to the wall. The trench portion 17 of the bracket 11a is spaced from the wall 31, so that the upper offset 6 of the shielding members 2 of the shielding units 1a, 1b are between the trench portion 17 of the bracket 11a and the wall 31.

Fig. 3(d) shows how further shielding members 1 and brackets 11, 11a can be arranged to extend the shielding apparatus in the direction parallel to the junction between the wall 31 and floor 33. Fig. 3(e) shows same arrangement also extended vertically up the wall 31. Fig. 3(f) shows a section of shielding apparatus after it is applied to cover a large portion of the wall 31.

Fig. 4 shows a trim unit 40 for attachment to the floor 33 by angle elements 41. Like the shielding units 1 , the trim unit 40 comprises two offset members 42, 43, which may each have the same construction as the members 2, 3 of the shielding units 1. The angle elements 41 each have two portions, 45, 46. Nails (or similar devices) 47 are provided for fixing the angle elements 41 to the floor, and nails (or similar devices) 49 are provided for fixing the angle elements 41 to the trim units 40, and optionally rivets may be used for fixing the members 42, 43 together. The angle between the portions 45, 46 is obtuse, such as 100 degrees, so that the members 42, 43 lean back toward the wall 31. The trim units 40 are attached to the floor 33 and optionally to the shielding apparatus with the offset of the member 43 of each trim unit overlapping the offset of the member 42 of the next adjacent trim unit.

Fig. 5 shows the junction between the wall 31 and the floor 33 in cross section. Preferably, the means for attaching the brackets 11 and the angle elements 41 to the wall 31 and the floor 33 are such that they permit removal of the units 1 , 40 from the wall 33. This may be necessary, for example, for maintenance or repair to ^"either the shielding apparatus or the wall 31 or the floor 33.

Fig. 6 shows the embodiment fastened to a wall having two corners: an "inner corner" 50 and an "outer corner" 51. The construction of the shielding units of this shielding apparatus are as described above, but in addition to the shielding units 1 there are inner and outer corner shielding units 53, 55, each of which flexes in a central portion around the corresponding corner. In addition there are "cut-down" shielding units 57 which are of smaller width than the shielding units 1 and are employed so that the arrays of shielding units 1 (extending for example to the left of Fig. 6 and to the right of Fig. 6) can be joined to the corner shielding units 53, 55 without a vertically extending gap. The "cut-down" shielding units 57 may optionally be pre-formed (whether or not by cutting), or may be produced by cutting the shielding units 1 on-site. The shielding units 57 may be formed of two members which are not fixed to each other.

Note that the centre portions 25 of some of the brackets 11 are folded down (as shown on Fig 2(d)) to press against the shielding units underneath. Particularly, the brackets 11 which support shielding units 57 have the centre portions 25 folded in this way. Thus, these brackets have a dual function.

Fig. 7 shows a cross sectional view oτ a part of the shielding apparatus arranged to shield both a wall 31 and a ceiling 62. An inner corner unit 53 as described above with reference to Fig. 6 is provided at the junction of the wall 31 and the ceiling 62. Again the apparatus comprises "cut-down" shielding units 57 between full-size shielding units 1 and the inner corner units 53. Fastening means 35 (of any of the types described above) may be used to fix the brackets 11 to the wall 31 and/or ceiling 62, and the brackets 11 in turn fix the units 1 , 53, 57 to the wall 31 and/or ceiling 62. Fig. 7 also shows the central portion 25 of a bracket 11 folded down to press against the outer surface of a shielding unit 57 underneath.

Fig. 8 shows an alternative, and preferred, form of a bracket suitable for use in the invention. The reference numerals used in Fig. 2(a) to label portions of the brackets are used in Fig. 8 to label corresponding portions of the preferred bracket. In contrast to the bracket of Fig. 2(a), the bracket of Fig. 8 is angled such that the ridge portion 15 forms an acute angle with each of the wall 19 and connection portion 13. This causes a member resting on the ridge portion to lean towards the connection portion (i.e. towards the wall when the bracket is connected to the wall), thus giving it greater stability. This is particularly useful in the case that the bracket is used to support a shielding unit 57 in which the ridge portion 15 supports a member which is not connected to the member supported by the trench portion 17. Note that the dimensions indicated in Fig. 8 are in millimeters.

Advantages of the invention are that by providing shielding units in modular form, the shielding apparatus is more easily assembled on site than conventional shielding solutions. In addition, there is also the advantage that by using mesh structures for the shielding units and the frame members, the weight of the apparatus 1 can be reduced compared to the conventional steel plates. This has advantages if it is necessary to retrofit shielding to existing buildings as it may reduce the necessity to increase the strength of the existing building structure.

Although the invention has been described above with reference to a single embodiment, many variations are possible within the scope of the invention as will be clear to a skilled reader. For example, the apparatus may further optionally comprise frame members adapted to be fitted onto the structure to be provided with shielding, so that the shielding units can be fitted to the frame structure for assembly of the apparatus. Preferably, in the case that the shielding is magnetic shielding, the frame members comprise a material having a high relative magnetic permeability, and may be manufactured from the same material or materials as the sheet members, e.g. layers of expanded steel mesh.

In addition to the use of the shielding unit 1 as a passive shield as described above, the shielding unit 1 can also be used as an active shield. For example, for shielding low-frequency magnetic noise with frequency range from direct current to around 10Hz, a compensating coil 70, such as that shown in Figure 9, may be incorporated within the sheet members 2,3. The compensating coil 70 generates an antiphase magnetic field to partially cancel or counteract the unwanted noise. Further, a controller (not shown) may be used to control the frequency and level of magnetic field to generate based on measurements provided by a magnetic sensor (not shown) to detect the unwanted magnetic noise. This method of active shielding is described in detail in the Internet publication "Low-Frequency Wave Magnetic Noise Shielded at Low Cost" (www.takenaka.co.jp/takenaka e/techno/n42 actshld/n42 actshld.htm), the contents of which are incorporated herein by reference.

Other active shielding techniques may also be used such as those described in another Internet publication "Power Frequency Magnetic Field Management Using a Combination of Active and Passive Shielding Technology" (www.fms- corp.com/ieee95.htm). the contents of which are also incorporated herein by reference.

Claims

1. A shielding apparatus which comprises a number of shielding units, each shielding unit comprising two planar sheet members, the sheet members being arranged such that a planar surface of one of the sheet members covers a planar surface of the other of the sheet members, the planar surfaces of the sheet members being of substantially the same dimensions, and the sheet members being mutually offset from each other so that a portion of the planar surface of each sheet member is not covered by the other sheet member.

2. A shielding apparatus according to claim 1 , wherein the sheet members are mutually offset so that two adjacent edges of each sheet member are offset from the other sheet member.

3. A shielding apparatus according to claim 1 or claim 2, wherein at least one of the sheet members comprises a mesh structure.

4. A shielding apparatus according to claim 1 or claim 2, wherein each sheet member comprises a number of layers arranged on top of each other.

5. A shielding apparatus according to claim 4, wherein each layer comprises a mesh structure.

6. A shielding apparatus according to claim 3 or claim 5, wherein the mesh structure is an expanded mesh structure.

7. A shielding apparatus according to any of the preceding claims, wherein the sheet members are manufactured from a material having a high magnetic permeability relative to air.

8. A shielding apparatus according to claim 7, wherein the relative magnetic permeability is at least 100.

9. A shielding apparatus according to claim 8, wherein the relative magnetic permeability is at least 500.

10. A shielding apparatus according to claim 9, wherein the relative magnetic permeability is at least 1000.

11. A shielding apparatus according to claim 10, wherein the sheet members comprise steel.

12. A shielding apparatus according to any preceding claim further comprising brackets having a connection portion for connection to the structure which is to be shielded, and a trench portion for receiving at least part of an edge portion of a shielding member of at least one shielding unit.

13. A shielding apparatus according to claim 12 in which each bracket includes a folding portion, for folding to hold an edge portion of another shielding member.

14. A shielding apparatus according to any preceding claim which further comprises trim units for shielding the structure at a junction between the structure and a second surface.

15. A shielding apparatus according to claim 14 in which the trim units include two laminar trim members of substantially the same dimensions arranged overlapping but with an offset, whereby in use a plurality of trim members can be arranged spaced apart along the junction with the offsets of adjacent trim units overlapping.

16. A shielding apparatus according to claim 15 further comprising trim fastening means for attaching the trim units to the second surface and/or to the shielding units.

17. A shielding apparatus according to claim 16 in which the trim fastening means are angle elements for attaching the trim units to the second surface at an angle other than orthogonal thereto.

18. A shielding apparatus according to any one of the preceding claims, further comprising means for generating a magnetic field.

19. A method of shielding a structure comprising the step of activating the generation means of claim 18 to generate a magnetic field.