Support pillar system for a magnetic-shielded room

Abstract: The present invention relates to a support pillar system of a magnetic-shielded room. Each support pillar (10) of the support pillar system consists of a nested structure (11,12) composed of a first structure (11) and a second structure (12) there-around. The upper end of the first structure (11) is provided with a threaded part (13) and a member (18) provided with thread and disposed in the threaded part (13). The shield structure (25,26,27) of a magnetic-shielded room has been attached to the second structure (12) of the support pillar (10), whereby the floor (17) of the inner room is supported to the upper end of the first structure (11). When the member (18) provided with thread and disposed in the threaded part (13) is tightened in locking position, the member (18) provided with a thread locks the first structure (11) and the second structure (12) into one and same entity, whereby the vibration of the inner floor (17) is transmitted to the shield structure (25,26, 27) and the shield vibrates substantially in syncronization with the vibration of the floor (17) of the inner room. When the member (18) provided with a thread has been threaded into open position, the locking of the second structure (12) is re-leased, whereby the inner room is allowed to vibrate, irres-pective of the vibration of the other shield structures, and hence, the potential vibration of the inner room is not trans-mitted to the shield structures (25,26,27).

Description: The present invention relates to a magnetic-shielded room, according to the pre-characterizing clause of claim 1. A magnetic-shielded room comprising the features of the pre-characterizing clause of claim 1 is known from document US-A-4 959 504. The support pilar system of the known magnetic-shielded room is formed by a number of fiberglass dowel support pillars which pass through holes in the shield structure. 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 the 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 knife-like 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. 981 to 1471 N (100 to 150 kp.) Document A-B-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 light-weight door structures. Document A-B-73043 discloses a door in a structure to prevent transmission of interference fields, particularly high-frequency 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 plane of the door, 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 toothed wheel 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 on 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 alter-mating 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 magnetometers 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. This processing is called "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 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 an 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 of magnetic field are used in a plurality of applications, not however in general in combi-nation 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 controlled 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 against 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. When someone walks on the inner floor of a magnetic-shielded room or e.g. sits down on a chair, it causes the phenomenon that the inner room vibrates, at least to some extent. Since e.g. highly sensitive measurements are accomplished e.g. on patients in the magnetic-shielded room, the vibration of the inner room is a harmful and undesirable phenomenon. Nowadays there are two different opinions on this matter. The first opinion is that the vibration of the inner room should not be transferred into the shield wall structure surrounding the magnetic-shielded room. The other view is that the vibration of the inner room must be synchronous with the vibration of the shield structure because, in spite of all, the inner room always vibrates to some extent. The object of the present invention is to provide a magnetic-shielded room wherewith it is either possible that the vibration of the inner room cannot be transmitted to the shield structure, or that when desired the shield structure vibrates in synchronization with the vibration of the inner room. This object is achieved by the magnetic-shielded room according to claim 1. Due to the support pillar system of the magnetic-shielded room according to the invention, the vibration of the inner room is directly transmitted e.g. to the bedrock so that the vibration of the inner room is not transmitted to the shield structure surrounding the magnetic-shielded room and would therethrough cause inaccuracy in e.g. sensitive measurements. On the other hand, the support pillar system permits that, when desired, the shield structure around the magnetic-shielded room can be made to vibrate in synchronization with the vibration of the inner room, if this design is considered to be most preferred considering the sensitive measurements. The invention is described in detail, referring to an advantageous embodiment of the invention presented in the figures of the accompanying drawing, whereto the invention is not, however, intended to be exclusively confined. Fig. 1 presents an advantageous embodiment of a support pillar of the support pillar system of the invention in lateral view. Fig. 2 presents the support pillar of Fig. 1 as a lateral view mounted on the bedrock and to the floor of the inner room. Fig. 3 presents an advantageous embodiment of the support pillar system of the invention in top view. In the embodiment of Figs. 1 to 3, a support pillar is in general indicated by reference numeral 10. In said embodiment a support pillar system consists of four separate support pillars. The support pillar 10 consists of a first tubular structure 11, acting as an inner pipe, and of a second tubular structure 12, acting as an outer pipe. The upper end of the inner pipe 11 is provided with a so-called trapezoidal thread 13 and the lower end with a flange 14 to which the inner pipe 11 and the outer pipe 12 have been attached. The support pillar 10 can be mounted on the bedrock 16 e.g. using the mounting system presented in Fig. 2, indicated in general with reference numeral 15. The invention is not, however, in any way critical to the way in which the pillar 10 is mounted to the bedrock 16. The floor 17 of the inner room is supported at the upper end of the inner pipe 11, preferably by means of a flange disposed on the upper end of the inner pipe 11. On the thread 13 a nut 18 is provided. In the embodiment of Fig. 2, the magnetic-shielded room is surrounded by a three-ply shield structure, the first layer whereof being indicated by reference numeral 25, the second by reference numeral 26, and the third, by reference numeral 27. The shield structure 25,26,27 can be any shield structure known as such in the art, and the invention is not critical regarding the shield structure design used. As regards the invention, an essential feature is that the layers 25,26 and 27 are mounted onto the outer pipe 12 of the support pillar 10. When in the embodiment as in Fig. 2, the nut 18 is tightened into locking position, the nut 18 locks the inner pipe 11 and the outer pipe 12 into one and same entity. Now, the vibration of the floor 17 of the inner room is transmitted to the shield structure 25,26,27 and the shield structure vibrates essentially in synchronization with the vibration .of the floor 17 of the inner room. When the locking nut 18 is untightened in open position the locking of the outer pipe 12 is released, whereby the inner room is allowed to vibrate irrespective of the vibration of the other shield structure 25,26,27. Hereby, the potential vibration of the inner room is not directly transmined to the layers 25,26 and 27 of the shield structure. In the embodiment as in Fig. 3, the floor of the inner room is supported by means of four support pillars 10. In this embodiment, on top of the locking nut 18 presented in Fig. 2, a locking/opening member 23 is attached. A locking/opening mechanism 20 comprises a first string or equivalent 21 and a second string or equivalent 22 and the locking/opening member 23 attached to the nut 18. The locking/opening members 23 are connected in pairs with intermediate rods 24 to each other. In the present embodiment, the strings 21 and 22 and the intermediate rods 24 are fastened to the locking/opening members 23 in the right hand side support pillars 10, said members rotating the nuts 18 in the trapezoidal threads 13. When pulling string 21, the pipes 11 and 12 are interlocked. If instead, the other string 22 is pulled, the locking of the pipes 11 and 12 is opened. It can be provided that the first string 21 is e.g. a red string and the other string 22 is e.g. a blue string, so that the locking and opening operations of the pipes 11 and 12 are as clear a possible, so that there is no risk of confusing things when to pull which string. In the foregoing, only one advantageous embodiment of the invention is presented and it is obvious to a person skilled in the art that numerous modifications can be made therein within the scope of the inventive idea presented in the accompanying claims.

Claims: A magnetic-shielded room having an inner room with a floor (17) and a shield structure (25, 26, 27) and a support pillar system for supporting the floor (17), characterized in that each support pillar (10) of the support pillar system consists of a nested structure (11,12) comprising a first structure (11) and a second structure (12) therearound, that the upper end of the first structure (11) is provided with a threaded part (13) and a member (18) provided with a thread disposed on the threaded part (13), that the shield structure (25,26,27) of the magnetic-shielded room is attached to the second structure (12) of the support pillar (10), whereby the floor (17) of the inner room is supported at the upper end of the first structure (11), and that when the member (18) provided with the thread and disposed on the threaded part (13) is tightened in locking position, said member (18) provided with the thread locks the first structure (11) and the second structure (12) into one and the same entity, whereby the vibration of the inner floor (17) is transmitted to the shield structure (25,26,27) and the shield structure vibrates substantially in synchronization with the vibration of the floor (17) of the inner room, and that when the member (18) provided with the thread is untightened in open position, the locking of the second structure (12) is released, whereby the inner room may vibrate, irrespective of the vibration of the shield structure (25, 26,27), and hence, the potential vibration of the inner room is not transmitted to the shield structure (25,26,27). Magnetic-shielded room according to claim 1, characterized in that a locking/opening mechanism (20) of the support pillar (10) is formed by a first string-like member (21) and a second string-like (22) and a locking/opening member (23) attached to the member (18) provided with a thread. Magnetic-shielded room according to claim 2, characterized in that the locking/opening members (23) of plural locking/opening mechanisms (20) are interconnected in pairs by means of intermediate rods (24). Magnetic-shielded room according to any one of claims 1 to 3, characterized in that the first structure (11) and the second structure (12) are tubular structures. Magnetic-shielded room according to claim 4, characterized in that the upper end of the first tubular structure (11) is provided with trapezoidal thread (13) and in that the lower end of the first tubular structure (11) is provided with a flange (14) on which the first tubular structure (11) and the second tubular structure (12) are mounted. Magnetic-shielded room according to any one of claims 1 to 5, characterized in that each support pillar (10) is mounted on a bedrock (16).

Inventors: PERAELAE MARTTI, SOHLSTROEM LASSE, PERAELAE, MARTTI, SOHLSTROEM, LASSE, Perälä, Martti, Sohlström, Lasse
Applicants: EUROSHIELD OY
Application year: 1995
Main classification: E04B1
IPC codes: E04B1, E04H9, H05K9, G12B17