GB2064629A

GB2064629A - Electromagnetically and Acoustically Shielded Window

Info

Publication number: GB2064629A
Application number: GB8036413A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-11-17
Filing date: 1980-11-13
Publication date: 1981-06-17
Also published as: NO152761C; BE886120A; IT8012720A0; DK481180A; ATA558380A; NO803395L; DE2946519C2; FI803541L; FR2471120A1; IT1133544B; DE2946519A1; GB2064629B; CA1136252A; DK152554C; FR2471120B1; LU82937A1; DK152554B; CH654371A5; NO152761B; JPS5696900A

Abstract

In an electromagnetically shielded wall of a room, an electromagnetically and acoustically shielded window comprises a first pane having a gold vapour deposit 22 and, inside thereof, at least one further pane covered with a wire mesh 24, the deposit and the mesh being conductively connected to the shielding in the wall.

Description

SPECIFICATION Electromagnetically and Accoustically Shielded Window Field of Invention The invention relates to an electromagnetically and acoustically shielded window for insertion in an electromagnetically shielded wall to achieve a bugging-proof room, comprising a first pane having a gold vapour deposit on the inside.

Background to the Invention In industry, research institutes, embassies and like establishments, there is an increasing need for electromagnetically and acoustically shielded rooms. Industrial and commercial espionage are on the increase. There is a need for rooms in which one can converse and hold conferences at ordinary talking volumes without the danger of the discussions being overhead. Unauthorised listeners can direct highly sensitive passive and active directional microphones onto the window.

Further, they could smuggle a miniature transmitter (a so-called bug) into such a room and secrete it. Electromagnetic shielding is also required for rooms in which electronic data processors, computers, electrical controls for industrial installations etc. are accommodated.

Such electronic data processors, computers, controls, etc., could under certain circumstances radiate electromagnetic oscillations of considerable field strength. They constitute disturbing fields in the surroundings. They not only affect the reception of broadcasts but could also lead to incorrect control if they act on other circuits by way of induction. The radiation of such disruptive fields must, therefore, be avoided.

The electromagnetic shielding of rooms is known. For this purpose one covers the wall with a metal foil, a metal wire fabric or the like and connects same to earth. This converts the room to a Faraday cage. This is an electromagnetically closed chamber. Electromagnetic radiation can neither leave nor enter. Miniature transmitters smuggled into such a room thereby become ineffective. This known electromagnetic shielding of rooms is, however, restricted to rooms without windows. It is not possible to extend over the window area the metal foil, metal wire fabric or the like which is used for screening and which is disposed under the wallpaper or paint. In addition to affecting the aesthetic appearance of the room and preventing the window from being opened and closed, there is the further disadvantage that the unauthorised listener will notice the electromagnetic shielding of the room.On the other hand, it is desired that the unauthorised listener should be led to believe as long as possible that the room is unprotected and that he is able to follow the discussions therein by way of the miniature transmitter.

Based on these considerations, it is an object of the present invention to provide such rooms with a window which offers electromagnetic screening and can therefor be adapted to and close the electromagnetic shielding of the wall surfaces of the room. It is a supplementary object to provide a window which is acoustically shielded to prevent listening by way of directional microphones.

The Invention Window panes having a gold vapour deposit on one side are known. They are generally employed to damp long-wave thermal radiation.

By using such a pane with a gold vapour deposit, the object of the invention can be achieved by a window comprising a first pane with a gold vapour deposit on the inside and a further pane covered with a conductive wire mesh which is placed over the inside of the first pane having the gold vapour deposit, and the gold vapour deposit and the wire mesh are connected by an electrically conductive connection to the electromagnetic shielding of the wall. This closes the electromagnetic shielding in the wall surfaces of the room without affecting the function of the window. The gold vapour deposit has no marked effect on the transparency of the window. The same can apply to the conductive wire mesh if it is chosen carefully.This thickness of the wire can be selected to be so small and the mesh width so large that one achieves the necessary electromagnetic shielding properties without detrimentally influencing the optical transparency.

By conductively connecting the gold vapour deposit and the wire mesh to the electromagnetic shielding of the wall that is already provided, the latter is closed and a sealed Faraday cage is produced.

Several embodiments are possible within the scope of this basic concept. They primarily depend on the frequency and strength of transmission of the miniature transmitter that may be expected, at what distance the associated receiver is likely to be installed etc. Several possible embodiments will be mentioned hereinafter and are made the subject of subsidiary claims.

In a first embodiment which considerably increases the mechanical strength and permanence, the first further pane consists of two individual panes and the conductive wire mesh is held or clamped therebetween. The wire mesh can be enclosed or moulded into a plastics film or, stated in other words, we are here concerned with a transparent plastics film containing an embedded conductive wire mesh. The wire mesh is conductively connected to the electromagnetic shielding of the wall.

In a further embodiment, a pane consisting solely of glass or plastics material is disposed between the first and first further pane or placed over the inside of the pane having the gold vapour deposit. This pane does not have the function of electromagnetic shielding. Its mass alone causes damping of acoustic oscillations and thereby shields the room acoustically.

In a further desirable embodiment employed when very highpowered miniature transmitters are expected, a second further pane consisting of a laminate of two individual panes and a conductive wire mesh therebetween is placed over the inside of the first further pane. Here, again, the wire mesh is metallically connected to the shielding of the room. The spacing between the two wire meshes the mesh width and whether the mesh widths of the two meshes are the same or different, etc., depends on each particular case, i.e. the expected frequency range of the miniature transmitter.

The conductive connection of the gold vapour deposit to the shielding of the room is desirably such that a strip of metal foil lies over a margin of the inside of the first pane having the gold vapour deposit and is located under the gold vapour deposit (for example applied before vaporisation), turned over, lies on the narrow sides of this pane and is soldered to the shielding of the wall. A similar procedure is recommended for the electrica! connection of the wire mesh in that a strip of metal foil is in electrically conductive contact therewith, turned over the edge of the respective pane and soldered to the shielding of the wall.

It has been mentioned that a pane solely of glass or plastics material is provided to serve acoustic damping. This damping is increased if this pane solely of glass or plastics material is in a further embodiment held at a spacing from and thereby separated on both sides by air cushions between the first and first further panes.

No special requirements are placed on the physical nature of the wire mesh. However, it is advisable to make the wire mesh of metal wire having a high electrical conductivity and a nonreflective surface. It has already been stated that the mesh width of the wire mesh can fluctuate within wide limits and would be calculated for each particular case. A mesh width of 2 mm may be mentioned as an indication of the size.

Illustrated Embodiment The invention will now be described by way of example with reference to and as illustrated in the accompanying drawing, wherein:~ Fig. 1 is a diagrammatic cross-section through the window and, Fig. 2 an exploded perspective view of the individual panes.

On the outside of the window there is disposed the first pane 12. The first further pane 14 and the second further pane 16 are on the inside. They consist of the individual panes 18 and 20. The inside of the first pane 12 carries the gold vapour deposit 22. A metal wire fabric 24 is disposed between the individual panes 18 and 20. The wire mesh 24 is moulded into a plastics film 26. The pane 28 which is solely of glass or transparent plastics material is disposed between two spacers 30. consequently, air cushions 39 are formed at both sides thereof. Strips 34 of metal foil contact the gold vapour deposit 22 and the metal wire fabrics 24. They may be soldered thereto. They are turned over the ends of the associated panes.

They are electrically connected to the shielding of the wall in a manner not shown, for example soldered thereto. The shielding of the wall itself is diagrammatically represented by an earth connection 36.

It will be evident from Figs. 1 and 2 that radiation from a transmitter on the inside of the window cannot penetrate same. The radiation is intercepted by the two metal wire fabrics 24 and the gold vapour deposit 22 and dissipated by way of the earth connection 36. Acoustic oscillations are dumped by the individual panes and particularly by the pane 28.

The illustrated construction of Figs. 1 and 2 is not to be regarded as limitative for the individual panes. The panes and air cushions may have different thicknesses. In particular, an exaggerated thickness is shown for the plastics foils 26. Similarly, one can omit one metal wire fabric 24 with the panes 18 and 20 enclosing same or provide an additional one. The sequence of the panes can also be changed. The pane 28 can be disposed on the very inside or between the two further panes 14 and 16.

Claims

1. An electromagnetically and acoustically shielded window for insertion in an electromagnetically shielded wall to achieve a sound-proof room, comprising a first pane with a gold vapour deposit on the side, and a further pane covered with a conductive mesh which is placed over the inside of the first pane the gold vapour deposit and the conductive wire mesh being connected by an electrically conductive connection to the electromagnetic shielding of the wall.

2. A window as claimed in claim 1, in which said further pane consists of a laminate of two panes with the conductive wire mesh sandwiched therebetween.

3. establishing a conductive connection between the mesh and the electromagnetic shielding in the wall containing the window.

3. A window as claimed in claim 2, in which the conductive element of the wire mesh is enclosed in a plastics film.

4. A window as claimed in any of claims 1 to 3, in which a pane of glass or plastics material is disposed between the first and said further pane.

5. A window as claimed in any of claims 1 to 4, in which a second further pane consisting of a laminate of two individual panes and a conductive wire mesh sandwiched therebetween is placed over the inside of the first mentioned further pane.

6. A window as claimed in any of claims 1 to 5, in which a strip of metal foil lies over a margin of the inside of the first pane having the gold vapour deposit and is located below the gold vapour deposit, turned over, lies on the narrow sides of the first pane and is soldered to the shielding of the wall.

7. A window as claimed in any of claims 1 to 6, in which a strip of metal foil is in electrically conductive contact with the conductive element of the wire mesh is turned over the edge of the pane and soldered to the shielding of the wall.

8. A window as claimed in any of claims 5 to 7 and claim 4 in which the pane of glass or plastics is spaced from the first and the said further panes and is thereby separated on both sides by air cusions.

9. A window as claimed in any of claims 1 to 8 in which the conductive wire mesh consists of metal wire having a high electrical conductivity and a non-reflective surface.

10. A window as claimed in any of claims 1 to 9 in which the conductive wire mesh has a mesh width of 2 mm.

1 A window as claimed in any of claims 1 to 10 in which the mesh is in the form of a fabric.

12. A method of electromagnetically and acoustically shielding a room having electromagnetically shielded walls but having an aperture in which a glazed window is located which window includes a first pane having a gold vapour deposite in the inside comprising the steps of:

1. locating a second pane over the inside of the first pane, the second pane having a conductive wire mesh covering,

2. establishing a conductive connection between the mesh and the gold vapour deposit on the first pane and