Door structure for a magnetic-shielded room

Abstract: The present invention relates to a door structure (10) of a magnetic-shielded room intended to absorb interference magnetic fields, particularly very low frequency magnetic fields. The door structure (10) has been disposed to move substantially rectilinearly in the direction of the plane of the door leaf (12), and substantially rectilinearly in a direction which is perpendicular to the plane of the door leaf (12). The door leaf (12) has been attached to the structure (11) of the door leaf with a hinge mechanism (16) so that the door leaf (12) is enabled to move perpendicularly to the structure (11) of the door leaf in order to provide a movement in a direction perpendicular to the plane of said door leaf (12). The door structure (10) has been provided with power transmission members (17,17a;17b,18a;18b,19a;19b,20a; 20b,21) which have been arranged to exert such an effect on the press members (22) on the edge areas (12a) of the door leaf (12) that the press members (22) turn around the hinging members (26), whereby the µ metal sheet structure (24) on the edge areas (12a) of the door leaf (12) has been arranged to be pressed tightly against the equivalent µ metal sheet structure of the shield wall structure (30) at an aperture in a wall of the magnetic-shielded room.

Description: The present invention relates to a door structure of a magnetic-shielded room intended for absorbing interference magnetic fields, particularly very low frequency magnetic fields, and which door structure has been arranged to move substantially rectilinearly in the direction of the plane of the door leaf and substantially rectilinearly in a direction which is perpendicular to the plane of the door leaf, see e.g. EP-A-0 224 090 and EP-A-0030529. For providing an interference-shielded space, the function of the structures used can be to prevent penetration of external electromagnetic energy into said shielded space or also to limit the electromagnetic energy within a space surrounded by a structure by preventing leakage of an interfering field into the surroundings. Structures of this type are known in the art and they are generally used for shielding sensitive structures against electromagnetic radiation and for enabling measurements free of radio frequency interferences e.g. in industries employing data transmission and high frequency technology, in research, and e.g. in hospitals. Irrespective of the use of the shielded space, the most poorly absorbing part in the shielding is usually formed by the contact point between a door, window, hatch or equivalent indispensable to be opened for access into the shielded space, and the fixed structure. To avoid the effect deteriorating the shielding properties of the door, the electric contact of the moving part of the door and the door frame, and the redundance path, when shielding against low-frequency magnetic field, is required to be as continous as possible and correspond to the properties of the rest of the structure. The absorption properties of the joint between the door and the frame can be improved, above all at high frequencies, with a labyrinth structure positioned at the point of contact where, for ensuring the contact, the knifelike contact tongues are pressed between the contact springs disposed in a runner running around the aperture. However, in prior art door designs, the performance values achieved in practice have been limited by the fact that especially using a repeated labyrinth structure has not, because of the requisite tight fits, been possible so that the normal convenience of use of the door and the operation properties of a door hinged in a normal way are maintained. When an efficient and complicated labyrinth structure is used, the contact tongues peneterating between the springs tend to, owing to the tight fits, damage the sealing structure by urging the sealing springs off from their locations by means of the swivelling movement of a normally turning door, and on the other hand, closing such door requires enormous press force, e.g. 100 to 150 kp. Finnish patent No. 63992 discloses a door in a structure intended for prevention of transmission of interference fields in which the movement of the door is provided by a rotary movement around an axis determined by the hinge means and by a substantially rectilinear movement producing a contact which prevents transmission of interference fields. It has, however turned out to be that, particularly in large-size door designs, the rotary movement around the axle is not the best possible solution. In such instance, the heavy weight of the door poses high requirements on the hinge means. So, the great forces and torques directed at the rotary hinging of the heavy door structure create more stress in the hinging than in lightweight door structures. Finnish patent No. 73043 discloses a door in a structure preventing transmission of interference fields, particularly highfrequency electromagnetic fields, relative to which the door has been arranged to be moved with hinge means and whereby the door and/or fixed structure has/have been provided with members to have a contact between the door and the fixed structure to prevent transmission of interference fields. The door has been arranged to move with the aid of first hinge means substantially rectilinearly in a direction which is in the direction of the normal to the door plane, and with the aid of second hinge means substantially in the direction of the plane of the door. The first hinge means comprise first coupling means and second coupling means, either of which having been disposed to move while in contact with the cooperative coupling means. The first coupling means consist of a toothed wheel and the second coupling means consist of a pinion rack, whereby the gear has been arranged to move along the teeth of the rack. The second hinge means comprise rollers supported by which the door has been arranged to move in a guide bar. The interferences inhibiting precise magnetic measurements can be classified into two groups: those caused by humans and those cause by nature, such as the magnetic field of the earth. When moving far off from the sphere influenced by the humans an environment is created in which the disturbances caused by humans are insignificant. In general, it is desirable to make measurements in a laboratory environment. Now, powerful interferences are caused, among other things, by lifts, vibrations of the constructional steels, passing vehicles, and electric apparatus. In a magnetic-shielded room endeavours are made to absorb interferences of the laboratory surroundings to the extent that research applying the most sensitive measurement devices is possible in the "inner interiors". Magnetic shielding is implemented utilizing three different methods. These are as follows: passive ferromagnetic shielding, swirl shielding, and active compensation of the interference field. The ferromagnetic shielding consists of one or more nested µ metal shells. Each wall is made of two µ metal layers, the metal strips of which being positioned e.g. crosswise. The µ metal layers have been mounted between two aluminium sheets (thicknesses 2 mm and 5 mm). The 5 mm aluminium sheets serving as the support structure have been joined to each other to form a uniform structure conducting electricity well. In said structure the inducing swirls absorb the alternating current magnetic field which is trying to enter. An active shielding is implemented with coils installed around the magnetic-shielded room, to which the electric current is conducted, the magnetic field generated by which is as great within the magnetic-shielded room but reverse in direction as the external interfering magnetic field trying to enter the room. The active shielding is efficient at low frequencies and its shielding capacity is limited merely by the noise of the magneto-meters and electronic apparatus used. The properties of passive ferromagnetic shielding may be enhanced considerably by superposing a relatively large alternating current magnetic field (H S = 5 A/m, rms) into an interference, whereby the effective permeability of the µ metal increases significantly, thus causing increase in the shielding factor. The English name of this processing is "shaking". It is possible to be shielded against static and slowly varying magnetic fields on a large scale merely by building the walls of the space to be shielded from µ metal or by using active compensation of the magnetic field. A material of high permeability can be thought of acting as a good conductor concerning a magnetic field and shielding the space enclosed therewith by conducting the fields into itself. The shielding factor of the ferromagnetic shell is proportional to the permeability of the material and the thickness of the shell layer. By building a multiplied shield, a higher shielding factor can be obtained with the same quantity of material than by using one single screen of the same weight. Shaking or superposing alternating current magnetic field on the walls of the shield has clearly been found to improve the shielding factor. The effective permeability of the µ metal has been found to be improved with the shaking treatment into twice to seven times greater in 0 to 100 Hz frequency range. The shaking frequency can in practice be varied in the range 3 to 200 Hz. The most useful frequency is in general the 50 Hz mains frequency because the shaking causes a relatively strong interference field in a shielded space. On the mains frequency, the interference level has already been high, and preparations have to be made in any case to absorb the interferences, e.g. using filtering in the measurement apparatus. The shielding factor has been found to be improved both at interference frequencies above and below the shaking frequency. If the walls of the shielded space have been built from a conductive material, the swirls produced in the shielding shell absorb the varying interference field within the room. It goes without saying that the static field is not affected by the swirl shielding at all. The swirls commence to exert their effect at frequencies at which the penetration depth of the interference field is of the order of the thickness of the shielding shell. As the frequency increases, the shielding factor caused by the swirls increases expontentially. The upper limit of the shielding factor is determined by the field entering the room through apertures and joints. Active compensation apparatus for magnetic field is used in a plurality of applications, however, not in general in combination with passive shielding methods. The magnitude of an interference magnetic field is measured at a distance from the target to be shielded, with the purpose that the magnetic field produced by the compensation coil would have no effect on the measurement. The current of the compensation coil is conducted with a precise current generator so that it is directly proportional to the interference field being measured. An interference field may also be measured at a number of points, and the current of the compensation coils can be controlled according to the appropriately weighted mean of the measurement values. If in a magnetic shielding using merely active compensation the interference magnetic field is measured in the proximity of a shielded space or therewithin, also the magnetic field being studied is compensated in addition to the interference field, so that the closed control of the current of the compensation coils is not functional. When active compensation is used in conjunction with passive magnetic shielding, a closed control of the current of the compensation coil is conceivable. The current of the compensation coil is controlled by a closed control circuit which tends to maintain the measured magnetic field constant. After the measured magnetic field is stabilized, also the residual field prevailing in the magnetic-shielded space is constant. In practice, the residual field cannot be turned completely into a constant field because the magnetic field provided by the compensation coil is not homogeneous in the shielded space. When estimating the shielding factor of a magnetic-shielded room, three situations and shielding mechanisms differing from each other can be identified: (a) Shielding caused by a ferromagnetic material to the static field of the earth, that is, the static shielding. (b) Shielding caused by a ferromagnetic material against slowly varying interference fields (f < 1 Hz), that is, so-called quasistatic shielding. (c) Combined effect of swirls and ferromagnetic shielding with increased frequency (f > 1 Hz), that is, dynamic shielding. The above frequency limits are exemplary and dependent on the thickness of the walls of the shield and the materials used. An aperture in a wall of a magnetic-shielded room exerts naturally an effect on the field prevailing within the room. The aperture in the wall impairs the shielding factor, because of which the door structure of a magnetic-shielded room is required to meet extremely high quality requirements if the shielding factor of a magnetic-shielded room is not allowed to be essentially deteriorated. The door designs disclosed in Finnish patents Nos. 63992 and 73043 are appropriate for high frequencies, e.g. for 1 kHz frequencies and higher than that. However, the door structure of a magnetic-shielded door is required to be able to absorb magnetic fields of very low frequencies, whereby the frequency range from 0 Hz upwards varies in general to some 100 Hz. Therefore, the door designs disclosed in the Finnish patents Nos. 63992 and 73043 are not appropriate for use as a door structure of a magnetic-shielded room. The objective of the present invention is to provide a door structure which is particularly appropriate for use as a door structure for an aperture in the wall of a magnetic-shielded room. A more detailed aim of the invention is to produce a door structure wherewith the shielding factor of a magnetic-shielded space will not be greatly impaired. The door structure of a magnetic-shielded room according to the present invention is mainly characterized in that the door leaf has been attached to the structure of the door leaf with a hinge mechanism so that the door leaf is enabled to move perpendicularly to the structure of the door leaf in order to achieve a movement at right angles to the plane of said door leaf, and that the door structure has been provided with power transmission members, adapted to exert such effect on the press members on the edge areas of the door leaf that the press members turn around the hinging members, whereby the µ metal sheet structure on the edge areas of the door leaf has been arranged to be compressed tightly against the µ metal sheet structure corresponding to the shield wall structure at the aperture in a wall of the magnetic-shielded room. The invention is described in detail referring to an advantageous embodiment of the invention presented in the figures of the accompanying drawings, whereto the invention is not, however, intended to be exclusively confined. Fig. 1a presents an advantageous embodiment of a door structure according to the invention in rear view. Fig. 1b presents the door structure of Fig. 1a in top view. Fig. 2 presents the door structure of Fig. 1a in front view. Fig. 3 presents the door structure of the invention applied in a magnetic-shielded room as a schematical elevational view. Fig. 4 presents a detail A of Fig. 2 on enlarged scale, with the press member both in open position and in closed position. The door structure presented in Figs. 1a, 1b and 2 is generally indicated by reference numeral 10. The door structure 10 comprises a structure 11 of the door leaf and the actual door leaf 12. The structure 11 of the door leaf 12 has been disposed at the lower part on a lower guide or a guiding rail 13 with the aid of rollers 14. At the upper part, the structure 11 of the door leaf has been arranged to glide in the upper guide 15. The door leaf 12 has been attached to the structure 11 of the door leaf with a hinge mechanism 16 so that the door leaf 12 is enabled to move perpendicularly to the structure 11 of the door leaf. In the embodiments presented in the figures of the drawings, the door leaf 12 has been attached to the structure 11 of the door leaf at four different points with said hinge mechanism 16. In the essentially central part of the door leaf 12, a centre 17 has been disposed to which handles 17a and 17b have been attached. Handle 17a has been fastened on the side of the door leaf 12 and handle 17b on the side of the structure 11 of the door leaf. On the surface of the centre 17 to the door leaf 12 arms 18a and 18b have been attached, of which a first arm 18a is directed upwards to the centre 19a and the other arm 18b downwards to the centre 19b. To the centres 19a and 19b, arms 20a and 20b have been attached, being directed from the centre 19a and 19b to the sides, towards a joint 21 shown in Fig. 4, this being attached to the press members 22 running on the edges of the door leaf 12. In Fig. 3, the three-ply shield wall structure of a magnetic-shielded room is indicated by reference numerals 30,31 and 32. The wall of the inner room of the magnetic-shielded room is indicated by reference numeral 33. As can be seen best in Fig. 4, the door leaf 12 consists of a laminated structure, comprising a first aluminium sheet 23, the thickness thereof being in general 5 mm, a two-ply aluminium µ metal sheet 24, the overall thickness thereof being in general 2 mm, and a second aluminium sheet 25, in general 5 mm in thickness. The edge areas 12a of the door leaf 12 lack, however, the innermost aluminium sheet 25, and the inner surface of the edge area 12a is formed merely from a two-ply µ metal sheet 24. The arms 20a and 20b exert such an effect on the press members 22 with the aid of joints 21 that the press members 22 rotate around the hinges 26, whereby the µ metal sheet 24 of the edge areas 12a of the door leaf 12 is tightly pressed against the equivalent µ metal sheet of the shield wall structure 30 at an aperture in a wall of the magnetic-shielded room, as can best be seen in Fig. 3. The functioning of the door structure of the invention is as follows. The door structure 10 is moved laterally in the fashion of a conventional sliding door, whereby the structure 11 of the door leaf moves along a lower guide 13 and an upper guide 15, covering the door aperture in the magnetic-shielded room. Thereafter, the door leaf 12 moves moved by a hinged mechanism 16, whereby the door leaf 12 performs a movement perpendicularly to the surface of the door leaf 12 and, at the same time, the door leaf 12 moves, relative to the structure 11 of the door leaf, away therefrom. Thereafter, the handle 17a in the centre 17 is turned, whereby the movement of the arms 18a and 18b is transmitted to the centres 19a and 19b, and further, transmitted by the centres 19a and 19b, to the arms 20a and 20b turning with the aid of joints 21 the press members 22 of the door leaf 12 around the hinged mechanism 26 so that the two-ply µ metal sheet 24 in the edge areas 12a of the door leaf 12 is pressed tightly against the two-ply µ metal sheet 24 of the shield structure 30 on the edge of the door aperture of the magnetic-shielded room. It is to be noted that the shield wall structure 30,31,32 of the magnetic-shielded room otherwise consists of a laminated structure as usual, comprising an outer aluminium sheet 23, being in general 5 mm in thickness, a two-ply µ metal sheet 24, being in general 2 mm in thickness, and an inner aluminium sheet 25, in general 2 mm in thickness, but on the edge of the door aperture, the innermost aluminium sheet 25 is lacking at a distance equivalent to the width of the edge area 12a of the door leaf 12. In the foregoing, merely the principle design of the invention and an advantageous embodiment thereof are presented, and it is obvious to a person skilled in the art that a great number of modifications can be made therein within the scope of the inventive idea presented in the accompanying claims. The present invention relates to a door structure (10) of a magnetic-shielded room intended to absorb interference magnetic fields, particularly very low frequency magnetic fields. The door structure (10) has been disposed to move substantially rectilinearly in the direction of the plane of the door leaf (12), and substantially rectilinearly in a direction which is perpendicular to the plane of the door leaf (12). The door leaf (12) has been attached to the structure (11) of the door leaf with a hinge mechanism (16) so that the door leaf (12) is enabled to move perpendicularly to the structure (11) of the door leaf in order to provide a movement in a direction perpendicular to the plane of said door leaf (12). The door structure (10) has been provided with power transmission members (17,17a;17b,18a;18b,19a;19b,20a; 20b,21) which have been arranged to exert such an effect on the press members (22) on the edge areas (12a) of the door leaf (12) that the press members (22) turn around the hinging members (26), whereby the µ metal sheet structure (24) on the edge areas (12a) of the door leaf (12) has been arranged to be pressed tightly against the equivalent µ metal sheet structure of the shield wall structure (30) at an aperture in a wall of the magnetic-shielded room.

Claims: A door structure (10) of a magnetic-shielded room, intended for absorbing interference magnetic fields, specifically very low-frequency magnetic fields, and said door structure (10) being arranged to move substantially rectilinearly in the direction of the plane of a door leaf (12) and substantially rectilinearly in a direction which is perpendicular to the plane of the door leaf (12), characterized in that the door leaf (12) has been attached to the structure (11) of the door leaf with a hinge mechanism (16) so that the door leaf (12) is enabled to move perpendicularly to the structure (11) of the door leaf, in order to provide a movement in perpendicular direction to the plane of said door leaf (12), and that the door structure (10) is provided with power transmission members (17,17a;17b, 18a;18b, 19a;19b,20a; 20b,21) arranged to exert such an effect on the press members (22) on the edge areas (12a) of the door leaf (12) that the press members (22) rotate around the hinging parts (26), whereby a µ metal sheet structure (24) on the edge areas (12a) of the door leaf (12) has been arranged to be pressed tightly against the corresponding µ metal sheet structure (24) of the shield wall structure (30) at an aperture in a wall of the magnetic-shielded room. Door structure according to claim 1, characterized in that in the substantially central area of the door leaf (12) a centre (17) has been disposed to which handle members (17a, 17b) and arms (18,a, 18b) have been attached, a first arm (18a) whereof being directed upwards to centre (19a) and the other arm (18b) down to centre (19b), and that arms (20a,20b) have been attached to the centres (19a,19b), being directed aside from the centre (19a,19b) towards a joint (21), said joint (21) being attached to the press members (22) in the door leaf (12). Door structure according to claim 1 or 2, characterized in that the press members (22) are located in the immediate proximity of the edge areas (12a) of the door leaf (12). Door structure according to claim 2 or 3, characterized in that the first handle member (17a) has been attached on the side of the door leaf (12) and the second handle member (17b) on the side of the structure (11) of the door leaf. Door structure according to any one of claims 1 to 3, characterized in that the door leaf (12) consists of a laminated structure, comprising a first aluminium sheet (23), a two-ply µ metal sheet (24) and a second aluminium sheet (25), and that the edge areas (12a) of the door sheet (12) are not provided with said second aluminium sheet (25). Door structure according to any one of claims 1 to 5, characterized in that the structure (11) of the door leaf (12) has been arranged at the lower end to be movable to a lower guide (13) and at the upper end, to an upper guide (15) in order to produce a movement in the direction of said door leaf (12).

Inventors: PERAELAE MARTTI, SOHLSTROEM LASSE, PERAELAE, MARTTI, SOHLSTROEM, LASSE, Perälä, Martti, Sohlström, Lasse
Applicants: EUROSHIELD OY
Application year: 1995
Main classification: H05K9
IPC codes: E06B7, H05K9, E05D15, E06B5