MULTI-SHELLED SHIELDED ROOM AND METHOD FOR THE PRODUCTION OF A MULTI-SHELLED SHIELDED ROOM

Abstract

A multi-shelled shielded room is provided that has an outer shell with a first soft magnetic alloy having an initial permeability .sub.i1 and a maximum permeability .sub.max1 and an inner shell with a second soft magnetic alloy having an initial permeability .sub.i2 and a maximum permeability .sub.max2. The outer shell encases the inner shell and .sub.max1>.sub.max2 and .sub.i2>.sub.i1.

Claims

1. A multi-shelled shielded room, comprising an outer shell with a first soft magnetic alloy that has an initial permeability .sub.i1 and a maximum permeability .sub.max1; an inner shell with a second soft magnetic alloy that has an initial permeability .sub.i2 and a maximum permeability .sub.max2; wherein the outer shell encases the inner shell and .sub.max1>.sub.max2 and .sub.i2>.sub.i1.

2. A shielded room according to claim 1, wherein .sub.max1>250,000, 100,000.sub.max2350,000, 20,000.sub.i180,000 and .sub.i2>80,000.

3. A shielded room according to claim 1, wherein the first soft magnetic alloy for the outer shell has a B.sub.r/B.sub.s ratio greater than 0.5 and the second soft magnetic alloy for the inner shell has a B.sub.r/B.sub.s ratio less than 0.5.

4. A shielded room according to claim 1, wherein the first soft magnetic alloy and the second soft magnetic alloy are NiFe-based alloys of different compositions, preferably different 80% NiFe alloys.

5. A shielded room according to claim 1, wherein the first soft magnetic alloy for the outer shell contains 76 to 78 wt % nickel, 4.0 to 5.0 wt % copper, 2.8 to 4.5 wt % molybdenum and at least 13 wt % iron, or 79 to 81 wt % nickel, 4.6 to 5.6 wt % molybdenum and at least 13 wt % iron.

6. A shielded room according to claim 1, wherein the second soft magnetic alloy for the inner shell contains 80 to 82 wt % nickel, 5.5 to 6.5 wt % molybdenum and at least 10 wt % iron, or 77 to 79 wt % nickel, 4 to 5 wt % copper, 4 to 5 wt % molybdenum and at least 10 wt % iron.

7. A shielded room according to claim 1, wherein the inner shell and the outer shell each comprise a base plate made of a vibration-damping material and at least one sheet layer made of the first alloy or the second alloy, respectively.

8. A shielded room according to claim 7, wherein the base plate comprises medium-density fibreboard (MDF).

9. A shielded room according to claim 6, wherein the sheet layer is formed from a plurality of sheets arranged side by side on the base plate.

10. A shielded room according to claim 9, wherein at least one of the inner shell and the outer shell comprises at least two sheet layers arranged one above the other, these sheet layers each consisting of a plurality of sheets arranged side by side, and the sheets of adjacent layers running crosswise in relation to one another and being fixed together by means of an adhesive.

11. A shielded room according to claim 10, wherein the adhesive is a silane-modified polymer or polyurethane.

12. A shielded room according to claim 1, wherein the inner shell and the outer shell are each formed from a plurality of panels and at least one of the panels having a linear dimension of greater than 0.8 m.

13. A method for the production of a multi-shelled shielded room, comprising the following: assembling a plurality of first panels in order to produce an outer shell, the first panels being of a first soft magnetic alloy that have an initial permeability .sub.i1 and a maximum permeability .sub.max1, and assembling a plurality of second panels in order to produce an inner shell, the second panels being of a second soft magnetic alloy that have an initial permeability .sub.i2 and a maximum permeability .sub.max2, the outer shell encasing the inner shell and .sub.max1>.sub.max2 and .sub.i2>.sub.i1.

14. A method according to claim 13, wherein a first shielding layer comprising at least one sheet made of the first soft magnetic alloy is fixed to a non-magnetic base plate by an adhesive in order to produce one of the first panels and a second shielding layer comprising at least one sheet made of the second soft magnetic alloy is fixed to a non-magnetic base plate by means of an adhesive in order to produce one of the second panels.

15. A method according to claim 14, wherein the adhesive is a silane-modified polymer (SMP) adhesive or a polyurethane adhesive.

16. A method according to claim 14, wherein a plurality of sheets is fixed side by side on the base plate by the adhesive in order to form a first sheet layer of the first shielding layer.

17. A method according to claim 16, wherein a plurality of sheets is fixed side by side on the first sheet layer by the adhesive in order to form a second sheet layer of the first shielding layer, the sheets of the second sheet layer being laid crosswise in relation to the sheets of the first sheet layer.

18. A method according to claim 14, wherein a plurality of sheets is fixed side by side on the base plate by the adhesive in order to form a first sheet layer of the second shielding layer.

19. A method according to claim 18, wherein a plurality of sheets is fixed side by side on to the first sheet layer by means of the adhesive in order to form a second sheet layer of the second shielding layer, the sheets of the second sheet layer being laid crosswise in relation to the sheets of the first sheet layer.

20. A method according to claim 13, wherein the base plate comprises a vibration-damping material.

21. A method according to claim 13, wherein the base plate comprises medium-density fibreboard (MDF).

22. A method according to claim 13, wherein .sub.max1>250,000, 100,000.sub.max2350,000, 20,000.sub.i180,000 and .sub.i2>80,000.

23. A method according to claim 13, wherein the second soft magnetic alloy for the inner shell has a B.sub.r/B.sub.s ratio of less than 0.5 and the first soft magnetic alloy for the outer shell having a B.sub.r/B.sub.s ratio of greater than 0.5.

24. A method according to claim 13, wherein the first soft magnetic alloy for the outer shell and the second soft magnetic alloy for the inner shell are NiFe-based alloys of different compositions.

25. A method according to claim 13, wherein the first soft magnetic alloy for the outer shell contains 76 to 78 wt % nickel, 4.0 to 5.0 wt % copper, 2.8 to 4.5 wt % molybdenum and at least 13 wt % iron, or 79 to 81 wt % nickel, 4.6 to 5.6 wt % molybdenum and at least 13 wt % iron.

26. A method according to claim 13, wherein the second soft magnetic alloy for the inner shell contains 80 to 82 wt % nickel, 5.5 to 6.5 wt % molybdenum and at least 10 wt % iron, or 77 to 79 wt % nickel, 4 to 5 wt % copper, 4 to 5 wt % molybdenum and at least 10 wt % iron.

27. A method according to claim 13, wherein at least one of the first panels or the second panels has one linear dimension greater than 0.8 m.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Embodiments are explained in greater detail below with reference to the drawings.

[0048] FIG. 1 shows a schematic illustration of a shielded room having two shells.

[0049] FIG. 2 shows hysteresis curves of selected 80% NiFe alloys.

[0050] FIG. 3 shows p(H) curves of elected 80% NiFe alloys.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0051] FIG. 1 shows a schematic view of a multi-shelled shielded room 1 having two shells 2, 3 to illustrate the invention. However, the shielded room 1 is not restricted to two shells 2, 3 and can have more than two, for example six or seven, shells. The Multi-shelled shielded room 1 is a magnetically shielded room with a plurality of shells.

[0052] Each shell 2, 3 of the shielded room 1 is constructed from a floor 4, walls 5 and a ceiling 6 in order to surround and a space completely. The outer shell 2 encases the inner shell 3 completely and so has greater linear dimensions than the inner shell 3. The shells 2, 3 are typically separate of one another. In addition, the shielded room 1 has a door 7 to permit access to the shielded interior 8 of the shielded room.

[0053] The shells 2, 3 each have a base plate 9 on which one or more sheet layers 10 made of a highly permeable soft magnetic material are placed in order to form a shielded room 1. The sheet layers 10 can each have a plurality of sheets 11 arranged side by side. The sheets 11, 11 of adjacent layers 10, 10 can be arranged crosswise in relation to one another. The base plate 9 can be of a vibration-damping material such as medium-density fibreboard (MDF). The sheets 11, 11 can be fixed by means of an adhesive on the base plate 9 or the sheet layer 10 below. In one embodiment the adhesive is a viscoelastic adhesive such as a silane-modified polymer or polyurethane. The shells 2, 3 typically have a plurality of panels, each of which has a base plate 9 with sheet layers 10, that are assembled with connecting pieces in order to form the shell 2, 3.

[0054] According to the invention the highly permeable material of the sheet layers 10,10 and sheets 11, 11 of the shells 2, 3 is selected dependent on the position of the shell in the shielded room 1 in relation to the centre point 12 of the shielded room 1 and so dependent on the magnetic field to which the shell is exposed. As a result, at least one of the shells, e.g. the inner shell 3, has a different composition to the further shells, e.g. the outer shell 2.

[0055] In one embodiment the outer shell 2 has a sheet layer 10 made of a first soft magnetic alloy having an initial permeability .sub.i1 that is lower than the initial permeability .sub.i2 of a second soft magnetic alloy of the sheet layer 10 of the inner shell 3.

[0056] Here the maximum permeability .sub.max1 of the first alloy can be higher than the maximum permeability .sub.max2 of the second alloy. This combination of properties makes it possible to provide a multi-shelled shielded room 1 that has an improved shielding factor and/or a lower residual field in the interior 8.

[0057] The factors to be taken into account in selecting the alloys for the sheet layers 10, 10 and sheets 11, 11 are explained in greater detail below with reference to FIGS. 2 and 3.

[0058] FIG. 2 shows hysteresis curves of selected 80% NiFe alloys. Compared to MUMETALL (solid line), ULTRAVAC 816 (dotted line) has a rounded hysteresis loop. ULTRAVAC 80 (dashed line) has a slightly rounded loop.

[0059] To date MUMETALL has been used for all shells to shield the small modulations required in shielded rooms. One material than can potentially be used for an inner shell in place of MUMETALL, for example, is ULTRAVAC 816 as it has a relatively rounded loop as shown in FIG. 2, i.e. the remanence to saturation ratio is low.

[0060] FIG. 3 shows p(H) curves of selected 80% NiFe alloys. It also shows the modulations for the walls H.sub.1, H.sub.2, H.sub.3 of a theoretical three-shelled room. The p(H) curve in FIG. 3 shows that the permeability of a material is dependent on modulation. The modulation to which the material is exposed in a multi-shelled shielded room is, in turn, dependent on its position in the room since the outer shells shield the inner shells. The exact modulation of the shell is therefore strongly dependent on location. In addition, it depends on the size of the shell and its wall thickness. Consequently, by a position-dependent use of different materials of different permeability, shielded rooms comprising a plurality of shells of different materials can have advantages in terms of their total shielding effect.

[0061] As an example, in the course of testing a finished shielded room a magnetic field is generated from the outside that would measure H.sub.Ext=1.1 A/m in the centre of the room space if no shielded room were present. It is possible to estimate that the outer shell is modulated at H.sub.10.08-0.3 A/m (hatched region H.sub.i in FIG. 3). As illustrated in FIG. 3, at higher modulations MUMETALL of average quality has a higher permeability than the two ULTRAVAC materials shown, from approx. H0.15 A/m for the curves shown. MUMETALL is therefore suitable for the outer shell 2.

[0062] As also shown in FIG. 3, the second shell H.sub.2 is modulated many times more weakly from the outside due to the shielding effect of the outer shell H.sub.1, e.g. H.sub.20.02-0.04 A/m. At this magnitude, in the illustration given in FIG. 3 ULTRAVAC 816 already has the greatest permeability and thus offers better shielding. The inner shell H.sub.3 is modulated even more weakly (H.sub.30.002-0.004 A/m). As a result the modulations of the inner shells are therefore very small for multi-shell rooms. A high initial permeability of the material, in particular, is therefore crucial for these shells.

[0063] As is clear from FIG. 3, the permeability of ULTRAVAC 816 (dotted line) falls only slightly at lower modulations. In contrast, the curve for MUMETALL (solid line) shows that at the smallest measured modulation of H=0.03 A/m initial permeability is lower than for ULTRAVAC 816. Consequently, ULTRAVAC 816 is more suitable for the inner shell or the innermost shell as it has the greatest permeability at this modulation H and so offers better shielding. For the outer shell, on the other hand, a material with higher permeability, i.e. ULTRAVAC 80 or MUMETALL, can still be used at higher frequencies.

[0064] Other materials with similar characteristics, such as ULTRAVAC 816, can also be considered for the inner shell or shells. One example is the alloy ULTRAPERM 91 R. In contrast to ULTRAVAC 816, it is a Cu-containing 80% NiFe alloy but has similar permeability and remanence behaviour.

[0065] Table 1 shows the composition and magnetic properties of some possible examples of suitable 80% NiFe materials.

TABLE-US-00001 TABLE 1 Nominal Material composition .sub.i .sub.max B.sub.s/T B.sub.r/T MUMETALL Fe Ni77 60,000 500,000 0.78 0.45-0.55 Cu4.5 Mo3.3 ULTRAVAC Fe Ni80 70,000 350,000 0.73 0.30-0.40 80 Mo5.0 ULTRAPERM Fe Ni78 100,000 250,000 0.66 0.20-0.40 91 R Cu4.5 Mo4.5 ULTRAVAC Fe Ni81 100,000 200,000 0.65 0.20-0.40 816 Mo6

[0066] The multi-shelled shielded room 1 according to the invention can have n shells, n being a natural number and n2. At least two of the n shells are of a soft magnetic alloy. An inner (in relation to the centre point 12) shell 3 comprises a soft magnetic alloy with a higher initial permeability than the initial permeability of a soft magnetic alloy of an outer (in relation to the centre point 12) shell 2. This outer shell 2 can comprise a soft magnetic alloy with a higher maximum permeability than the maximum permeability of the soft magnetic alloy of the inner shell 3. One or more further shells, each being of a soft magnetic alloy, can be arranged between these outer and inner shells 2, 3. One or more shells can also be arranged outside this outer shell 2 and/or inside this inner shell 3. The multi-shelled shielded room 1 can also have one or more shells of a non-magnetic electrically conductive material, e.g. a metal such as aluminium or an alloy.