JP2004349431A - Environmental magnetic noise shielding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light magnetic shielding device which has high shielding performance with respect to environmental magnetic noise of DC or AC, especially, unsteady environmental magnetic noise due to movement or vibration of a geomagnetic convergent object which is formed of a high permeability magnetic material and is positioned nearby, is superior in workability, and is provided with lighting property and permeability. <P>SOLUTION: The frame-type environmental magnetic noise shielding device is provided with: a coil 2 constituted in a frame 1; a magnetism detector 3 detecting time change of magnetic flux density orthogonal with a face of the coil 2; a control unit 4 controlling supply of current to the coil 2 based on a signal detected by the magnetism detector 3 and cancel of environmental magnetic noise in the magnetism detector 3; and a movable mechanism 5 adjusting a relative position relation between the frame 1 and the magnetism detection part 3 so that environmental magnetic noise in a prescribed region except for the magnetism detector 3 can be shielded. They are integrated with the frame 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is highly resistant to DC or AC environmental magnetic noise, especially unsteady environmental magnetic noise having a spatial gradient due to the movement or vibration of a nearby geomagnetic convergent made of high permeability magnetic material. The present invention relates to an environmental magnetic shielding device that provides shielding performance and a wide uniform shielding space, is lightweight, has excellent workability, and has lighting and ventilation.
[0002]
[Prior art]
The earth has geomagnetism with a magnetic flux density of about 0.5 Gauss, and constantly fluctuates due to sunspot activity of the sun and the influence of mantle flow inside the earth. Large structures such as automobiles and elevators, which are made of ferromagnetic materials as parts, are geomagnetic convergence points that locally converge geomagnetism due to their high relative magnetic permeability. Moving or vibrating in space is one of the causes of temporal fluctuations and spatial gradients of environmental magnetism. In addition, trains and subways that move while receiving a large current supplied from an overhead wire also change the environmental magnetism in order to move in space while generating a strong magnetic field due to the large current flowing through the pantograph. Even if the generated magnetic field intensity is small, motor devices and electronic devices installed in close places, and power lines that supply power to these devices also change the environmental magnetism. As described above, noise generated by various factors exists in the environmental magnetism, and these are collectively called environmental magnetic noise. The environmental magnetic noise is not constant over time, but is constantly changing.
[0003]
On the other hand, the magnetoencephalogram generated by the electrical activity of the brain is about one-billionth the intensity of geomagnetism, and the electromagnetism generated by the electrical activity of the heart's myocardium is about one millionth of the geomagnetism. Is the size of In such a biomagnetism measurement system that measures a magnetic field generated by a living body, the above-described environmental magnetic noise is a serious obstacle to measurement, and it is necessary to shield the environmental magnetic noise with a high technical shielding factor.
[0004]
Further, there is an electron beam exposure apparatus for directly exposing a silicon wafer by using an electron beam in a process of manufacturing a highly integrated semiconductor such as an VLSI or an application specific integrated circuit (ASIC). When moving at high speed under geomagnetism, the exposure position of the charged particle beam shifts because it is affected by Lorentz force. If the geomagnetism is constant, the shift amount is constant, and accurate drawing should be possible. However, due to the presence of environmental magnetic noise on the earth, the amount of shift of this charged particle beam is also fluctuated over time, which hinders accurate electron beam exposure. Become. In order to improve the electron beam exposure accuracy, it is necessary to shield environmental magnetic noise with a high shielding factor.
[0005]
There are roughly two types of existing technologies for shielding (reducing) environmental magnetic noise. A passive magnetic shield method that surrounds the shielded space using a magnetic material with high magnetic permeability as a magnetic shield material, and an active magnetic shield method (active magnetic canceller or active control method) that generates a magnetic field in phase opposite to environmental magnetic noise in an electronic circuit is there.
[0006]
In the passive magnetic shield system, by forming a box-like space closed with a ferromagnetic material such as permalloy, environmental magnetic noise is affected by the relative permeability of the ferromagnetic material that forms this box-like space. Is drawn into the ferromagnetic material, the magnetic flux in the box-shaped space becomes low density, and a shielding space is formed inside the box-shaped space.
[0007]
The basic principle known as "skin effect" is an important design factor in designing a shielded space with a passive magnetic shield method. It is known that an eddy current flowing in a conductor when a high-frequency magnetic field is externally applied to the conductor has a property that it is large on the surface and decreases exponentially toward the inside of the conductor. The value of the depth at which the reciprocal 1 / e of the natural logarithm base e with respect to the surface current value is called the skin thickness δ, the magnetic permeability of the magnetic material is μ, the conductivity is σ, and the target frequency f [ Hz], the skin depth δ [m] is expressed by using equation (1).
δ = 1 / √ (πfμσ) (1)
Therefore, in order to realize a high shielding ratio in a wide frequency band up to an electromagnetic wave or a low frequency (for example, 0.01 Hz), an electromagnetic shielding material such as copper or aluminum is combined with a high magnetic permeability material such as permalloy. It is necessary to form a shielding space, and the thickness of each material that greatly affects the shielding rate is deeply related to equation (1).
[0008]
On the other hand, as shown in FIG. 2, the active magnetic shield method generally has a square annular cancel magnetic field generating coil corresponding to three axes, one pair for each axis, and detecting by a reference magnetic sensor corresponding to each axis. A canceling magnetic field having a phase opposite to that of the environmental magnetic field is generated based on the generated magnetic field signal, the magnetic noise is canceled at the installation position of the reference magnetic sensor, and the magnetism is shielded (reduced) (Patent Documents 1 to 3). reference).
[0009]
[Patent Document 1] JP-A-2002-257914
[Patent Document 2] JP-A-2002-094280
[Patent Document 3] Japanese Patent Application Laid-Open No. 11-083965
[0010]
[Problems to be solved by the invention]
As described above, the shielding performance of the passive magnetic shielding method is deeply dependent on the skin thickness δ of each shielding material, and the more the shielding space with a better shielding ratio in a wider band is to be realized, the more the shielding material becomes. The thickness increases and the total weight increases in proportion to the cube of the thickness. In addition, the use of a rare ferromagnetic material with high magnetic permeability results in high costs, failure to be installed only underground or on the first floor due to restrictions on the load capacity of the building, and wind and environmental vibration when installed on upper floors As a result of the shaking (structural vibration) of the building, the shielded space itself is the geomagnetic convergence point in the geomagnetism, so there is a problem that environmental magnetic noise is generated in the shielded space due to large structural vibration. .
[0011]
In addition, the passive magnetic shield method uses the magnetic permeability of the shielding material, causing a magnetic gradient in the shielded space depending on the shape of the shielded space. It is difficult to realize such a shielded space.
[0012]
Further, since the ferromagnetic material is large and heavy, there is a problem that workability (transportability) is poor.
[0013]
Furthermore, ferromagnetic materials are opaque. Further, when an opening is provided in a ferromagnetic material, the magnetic shielding performance is reduced, so that it is difficult to provide a large opening in the ferromagnetic material.
[0014]
Due to the above restrictions, when a passive magnetic shield method is adopted for a biomagnetic measurement system, not only a large opening is not provided, but also a feeling of pressure and occlusion is given to the subject, and a problem of poor ventilation is caused. . Generally, SQUIDs (superconducting quantum interference devices) are used as magnetic sensors in biomagnetism measurement systems, and liquid helium is used as a coolant, so that the subject does not fall into a choking state. It becomes necessary to take technical safety measures such as ventilation to prevent or monitoring of oxygen concentration.
[0015]
In the design of the electron beam exposure system, a design has been adopted in which the entire electron beam lithography unit is coated in multiple layers with a high-permeability magnetic shielding material called permalloy, and improvements have been made to reduce the effects of environmental magnetic noise. Was. However, drawing errors due to environmental magnetic noise have become a bottleneck in increasing the integration rate in order to apply the exposure processing under the design rule of 0.15 μm or less. This is because the electron beam exposure system is installed in a clean room, which is a semiconductor manufacturing site with extremely high air cleanliness. Design defects such as difficulty in achieving a high shielding rate due to the necessity of providing a cord insertion port for beam control and power supply are involved.
[0016]
In addition, forklifts and transport devices made of high-permeability materials for transporting members in semiconductor factories, spatial movement of elevators, opening and closing of doors, etc. are triggers of environmental magnetic noise, especially near clean rooms. This is an important issue to be solved because it is impossible to limit the work related to these.
[0017]
In addition, the existing active magnetic shield method can only generate a cancel magnetic field proportional to the magnetic field detected by the reference magnetic sensor, so if the reference magnetic sensor cannot be installed in the magnetic shield space, In addition to a low magnetic shielding effect against environmental magnetic noise having a spatial gradient generated near the magnetic sensor (for example, magnetic noise due to running of a bogie, rotation of a chair, a car running on a road), In some cases, there is a problem that the shielding effect cannot be expected or rather deteriorates.
[0018]
Therefore, when applying the existing active magnetic shield method to the biomagnetic measurement system, the bed on which the subject lies, the biomagnetic sensor, and the supporting table must be housed in the center of the shielded space, and the reference magnetic sensor is shielded. Since it is difficult to arrange in the center of the space, the shielding effect against environmental magnetic noise having a spatial gradient generated in the vicinity of the reference magnetic sensor cannot be expected, or may worsen.
[0019]
Furthermore, since a large coil having substantially the same size as the magnetic shielding space is used, when the shielding space is formed in a large cubic shape, for example, when controlling to cancel magnetic noise in one horizontal direction (x direction), x It is easy for the magnetism from the canceling magnetic field generating coil in the direction to wrap around to a magnetic field component in another horizontal direction (y direction) or a vertical direction (z direction) that is originally unrelated to the control target. Further, if a magnetic material exists in the magnetic shielding space, the magnetic field from the cancel magnetic field generating coil will be drawn due to the influence of the magnetic permeability of the magnetic material. As a result, there is a problem that the magnetic shielding effect is deteriorated.
[0020]
Therefore, when the existing active magnetic shield method is applied to an electron beam exposure apparatus, the canceling magnetic field is drawn in because the entire electron beam drawing unit is coated with a high-permeability magnetic material in multiple layers. Due to the overall shape of the exposure apparatus, a spatial gradient results in the magnetic field distribution inside the apparatus. Therefore, there is a problem that the drawing accuracy is reduced.
[0021]
The present invention has been made in view of the above circumstances, and its object is to provide a small and lightweight, low-cost, excellent workability, a small feeling of pressure and blockage, and excellent environmental magnetic permeability. It is to provide a noise shielding device.
[0022]
Still another object is to provide an environmental magnetic noise shielding device that achieves high shielding performance even for magnetic noise having a spatial gradient generated near a magnetic shielding space.
[0023]
Another object of the present invention is to suppress a decrease in the magnetic shielding rate due to a magnetic field wrapping around from the canceling magnetic field generating coil even if the environmental magnetic shielding space is large.
[0024]
Furthermore, even if there is a device made of a magnetic material in the shielded space, distortion of the canceling magnetic field generated by the canceling magnetic field generating coil is reduced, and the magnetic shielding effect is deteriorated.
Is to suppress.
[0025]
[Means for Solving the Problems]
Among the inventors of the present invention, Tomoaki Ueda has conducted intensive studies in order to achieve the above object.As a result, instead of shielding environmental magnetic noise, all or a part of a closed curved surface surrounding a magnetic shielding space is surrounded by a plurality of coils. It has been found that the above object can be partially solved by canceling the time-dependent change in the magnetic flux density in the normal direction of the coil surface, and the invention on which the present invention is based has been completed.
[0026]
Further, considering the coil as a set of many minute line segments, the magnetic flux density generated by the current flowing through each line segment is obtained by the Biot-Savart rule, and the magnetic field generated by the coil is calculated by the sum of these, as shown in FIG. As a result of simulating the magnetic field distribution generated when the two opposing coils are driven with the same current, the point where the magnetic flux density of the magnetic field synthesized in the center of the shielded space becomes the same It has been found that there are two points on the side, and that a higher magnetic shielding ratio can be obtained by arranging the magnetic detection unit at this point than by arranging it on the coil surface.
[0027]
Further, Kazuhiro Muramatsu among the inventors of the present application conducted a more precise three-dimensional simulation as shown in FIG. 10 and found that the optimal placement position of the magnetic detection unit that can achieve a high shielding efficiency and a uniform shielding performance over almost the entire shielding space. Exist outside the shielded space, and can be calculated based on the shape of the shielded space.
[0028]
In order to solve the above-described problems, the frame-type environmental magnetic noise shielding device according to claim 1 has a frame 1, a coil 2 formed in the frame 1, and a magnetic flux density orthogonal to a surface of the coil 2. A magnetic detector 3 for detecting a time change, and a current is supplied to the coil 2 so that a signal detected by the magnetic detector 3 matches a preset reference value, thereby canceling environmental magnetic noise in the magnetic detector 3. It has a control unit 4 that performs control, and a movable mechanism 5 that can adjust the relative positional relationship between the frame 1 and the magnetic detection unit 3 so as to shield environmental magnetic noise in a predetermined area other than the magnetic detection unit 3. It is characterized by being provided integrally with the frame 1.
[0029]
According to the above configuration, the magnetic detection unit 3 does not need to accurately measure the magnetic intensity with linearity, and can use the MR sensor and the Hall element without using a linearization circuit. It contributes to miniaturization, weight reduction and price reduction.
[0030]
Further, according to the above configuration, a current sufficient to generate a magnetic field for canceling only a temporal change of the magnetic flux density in the normal direction of the coil surface may be supplied to the coil 2 formed in the frame body 1, The control unit 4 requires only a smaller current supply capability than in the case where the environmental magnetism itself is shielded, so that the control unit 4 can be downsized, and the power consumption can be reduced.
[0031]
Further, according to the above configuration, the magnetic detection unit 3 and the control unit 4 can be made sufficiently small in comparison with the size of the frame 1 constituting the coil 2 for generating the cancel magnetic field. An opening having both lighting and ventilation can be provided inside the inside.
[0032]
Furthermore, with the above configuration, the coil 2, the magnetic detection unit 3, the control unit 4, and the movable mechanism 5 can be integrally formed on one frame 1, so that the power is supplied after the frame 1 is fixed in the construction. It is only necessary to perform the wiring described above, and a frame-type environmental magnetic noise shielding device excellent in workability can be configured.
[0033]
Further, since the magnetic detection unit 3 can be fixed at a position different from the coil surface of the coil 2 for generating the cancel magnetic field by the movable mechanism 5, a coil having the same strength as the magnetic detection unit 3 can be generated. The time change of the magnetic flux density of the environmental magnetic field of the component in the normal direction of the coil surface can be completely canceled (zeroed) at opposing positions across the surface. For this reason, it is possible to have an excellent magnetic shielding effect of completely canceling out the component of the environmental magnetic noise in the normal direction of the coil surface without being restricted by the installation location due to the structure.
[0034]
According to a second aspect of the present invention, there is provided a frame type environmental magnetic noise shielding apparatus, wherein the magnetic detection unit is configured to maintain a constant current supplied to the coil in the first aspect of the invention. And a reference value determining means for setting the reference value based on the detected value.
[0035]
With the above configuration, the environmental magnetic noise shielding control can be performed using the state of the environmental magnetic field at an arbitrary time or the average state of the environmental magnetic field within a predetermined time as a reference value. What is necessary is just to supply the coil 2 with a current sufficient to generate a magnetic field for canceling only the time change of the magnetic flux density in the normal direction of the coil surface. Since only a smaller current supply capacity is required, the size can be reduced, and the power consumption can be reduced.
[0036]
Furthermore, with the above configuration, when the current supplied to the coil 2 is set to 0, the reference value can be set to 0, so that control for shielding the environmental magnetism itself can be performed.
[0037]
In order to solve the above-mentioned problems, the environmental magnetic noise shielding device according to claim 3 includes a second frame 6 that forms all or a part of a closed curved surface of an arbitrary shape space, and a plurality of second frames 6. Alternatively, the internal space of the second frame is made uniform by adjusting the movable mechanism 5 configured by the frame type environmental magnetic noise shielding device according to claim 2 and provided in each frame type environmental magnetic noise shielding device. It is characterized by a magnetic shielding space with a high shielding ratio.
[0038]
With the above configuration, a plurality of frame-type environmental magnetic noise shielding devices according to claim 1 or 2 are arranged so as to surround all or a part of the closed curved surface of the arbitrary shape space. In addition, it is possible to provide an environmental magnetic shielding space that is lighter in weight, has better lighting and ventilation, and has less feeling of pressure and occlusion than a passive magnetic shielding method.
[0039]
Furthermore, with the above configuration, even if an environmental magnetic noise source having a relatively large spatial gradient exists near the environmental magnetic noise shielding space, the temporal fluctuation of the environmental magnetic field is canceled for each frame. The inner space of the second frame can be a magnetic shielding space having a uniform and high shielding ratio. This is because a plurality of frame-type environmental magnetic noise shielding devices operate independently, so that even if there is an environmental magnetic noise source with a relatively large spatial gradient, a plurality of coils provided on the same layout surface are generated independently. This is because the magnetic fields that overlap each other and the spatial gradient interpolation processing can be performed, so that the internal space of the second frame can be maintained as a magnetic shielding space with a uniform and high shielding rate.
[0040]
Furthermore, with the above configuration, even when a device using a ferromagnetic material is installed inside the environmental magnetic noise shielding space, the environmental magnetic noise shielding space is surrounded by a large number of small coils to generate a cancel magnetic field. Therefore, the solid angle of the device viewed from each coil can be reduced, so that the phenomenon in which the magnetic field generated by each coil is drawn into the ferromagnetic material of the device can be reduced, and as a result, compared with the prior art. As a result, the deterioration of the shielding performance can be reduced.
[0041]
Furthermore, according to the above configuration, it is possible to carry in or carry out the device by dividing it into a plurality of small frames, so that it is possible to provide an environmental magnetic noise shielding device that is extremely excellent in workability. In the conventional magnetic shield room method, if permalloy is separated, it is almost impossible to disassemble and move it because of the necessity of degaussing, so this effect is particularly noteworthy.
[0042]
Furthermore, according to the above configuration, since the frame 1 and the second frame 6 can be made of a lighter material than the passive magnetic shield method, the weight of the entire apparatus is reduced. The restriction is also relaxed, and when installed on the upper floor of the building, it is possible to cancel the time variation of environmental magnetic noise caused by structural vibration.
[0043]
According to a fourth aspect of the present invention, there is provided an environmental magnetic noise shielding apparatus according to the third aspect of the present invention, wherein one or more shielding rate adjusting magnetic detectors and a shielding rate adjusting magnetic detector are provided. The signal amplitude or the least square sum of the amplitude is calculated based on the signal supplied from the magnetic detection unit 7, and the movable mechanism 5 provided in each frame-type environmental magnetic noise shield device is set so that the calculated value is minimized. It is characterized by having a second control unit 8 for adjusting.
[0044]
With the above configuration, no matter what shape the second frame has, the geomagnetic converging body is located near the installation location, so that environmental magnetic noise with a relatively large spatial gradient exists. Even if a device made of a material having high magnetic permeability exists inside the second frame 6, a large shielding space having a uniform and high shielding performance can be realized.
[0045]
According to a fifth aspect of the present invention, there is provided an environmental electromagnetic noise shielding apparatus according to the third or fourth aspect, wherein the inner surface or the outer surface of the second frame is made of a net-like or foil-like conductor. It is characterized by having an electromagnetic wave shielding material by covering with an electromagnetic wave shielding material.
[0046]
With the above configuration, when covered with a net-shaped electromagnetic wave shielding material, environmental magnetic noise with high air permeability and visibility without impairing lighting or air permeability, without giving a feeling of pressure or blockage. Environmental electromagnetic noise shielding device having a high shielding ability against both the electromagnetic wave noise and the electromagnetic wave noise can be provided. In addition, when covered with an electromagnetic wave shielding material, which is a foil-shaped conductor, the lighting, ventilation, and visibility are impaired, and the problem of giving a feeling of oppression or blockage is not solved, but high electromagnetic wave shielding performance is realized. be able to.
[0047]
BEST MODE FOR CARRYING OUT THE INVENTION
One embodiment of the present invention will be described below.
[0048]
The frame 1 which is a component of the present invention may be made of a non-magnetic material such as wood or resin.
[0049]
Further, the coil 2 for generating the cancel magnetic field, which is formed in the frame 1 which is a component of the present invention, is a coil in which an insulated wire is wound around the frame 1, or a multi-core cable or a flat cable is rotated once. A coil formed by changing the connection position every time, or a coil printed with a conductive material on the surface of an insulating material, or a film made of a conductive material on an insulating material, and then cutting unnecessary parts to create Any of the coils may be used.
[0050]
Further, the magnetic sensor employed in the magnetic detection unit 3 which is a component of the present invention does not need to be a magnetic sensor that detects a magnetic field with linearity in particular. MR: Magnetic Resistance, flux gate, magnetic inductance element (MI), superconducting quantum interference element (SQUID: Superconducting Quantum Interference Devices), DC excitation type amorphous magnetic sensor, etc.
[0051]
The control unit 4, which is a component of the present invention, is a device that performs control to generate a cancel magnetic field by supplying a current to the coil 2 so as to match a predetermined reference value. May be configured. The control method may be any of ordinary negative feedback, PI control, PID control, sigma-delta modulation, and pulse width modulation (PWM).
[0052]
Further, in order to obtain the reference value of the control unit 4 of the present invention, the reference value is determined based on the detection value of the magnetic detection unit 3 when the current supplied to the coil 2 is kept constant before performing the shielding control. Preferably, it is set. For example, it is preferable to measure the detection value of the magnetic detection unit 3 when the current supplied to the coil 2 is kept at 0 for a certain period of time, and to use the average value as a reference value.
[0053]
Examples of uses of the environmental magnetic noise shielding device of the present invention include, for example, an environmental magnetic noise shielding device that shields an environmental magnetic field so that an image on a television or a personal computer is not disturbed by passage of a train, a living body such as a brain magnet or a magnetocardiogram. An environmental magnetic noise shielding device for a system for measuring a magnetic field, or an environmental magnetic noise shielding device for an electron beam exposure device for VLSI manufacturing, and a needle-shaped magnetic marker is driven into the affected part of the cancer, and the position of this marker is determined. Magnetic noise shielding device for a multi-orbit irradiation type radiotherapy system that correctly irradiates the affected part with radiation even if its position changes due to body motion or breathing by magnetically detecting the magnetic field.
[0054]
【Example】
Next, specific examples of the present invention will be described, but the present invention is not limited to these examples.
[0055]
[Example 1]
FIG. 1 illustrates an embodiment of a frame-type environmental magnetic noise shielding device according to claims 1 and 2 of the present invention.
[0056]
The frame-type environmental magnetic noise shielding apparatus according to the first embodiment includes a frame 1, a coil 2 included in the frame 1, a magnetic detection unit 3, a control unit 4, and a movable mechanism 5.
[0057]
The frame 1 is made of a 50 cm square transparent acrylic resin, and a groove having a depth of 2 mm and a width of 5 mm is dug around the frame having a thickness of 1 cm. The groove dug around the frame 1 is for constituting the coil 2. A bridge for traversing the center of the frame and fixing the movable mechanism 5 is provided. The entire frame 1 is made of a transparent acrylic resin including a bridge to ensure visibility, and a sufficient space is provided in the frame to ensure air permeability.
[0058]
The coil 2 is a coil configured by winding 53 turns of an insulated copper wire having a diameter of 0.4 mm.
[0059]
The magnetic flux density B [T] at the center of a circular solenoid coil having a diameter L [m] is given by the following equation (2), where I [A] is the current flowing through the coil and N is the number of turns of the coil.
Given.
[0060]
B = μ0 · N · I / L (2)
Here, μ0 indicates a vacuum magnetic permeability, which is 4π × 10000000.
[0061]
If the coil is square, the strength of the magnetic field is slightly weaker, but the relationship of the following equation (3) is maintained.
[0062]
B = k · μ0 · NI / L (3)
In the case of the coil 2 of the first embodiment, when a current of 400 mA flows, a magnetic field having a magnetic flux density of about 0.5 Gauss can be generated at the center of the frame.
[0063]
The magnetic detector 3 is a bar-shaped magnetic sensor that can be freely slid in the normal direction of the coil surface by a movable mechanism 5 fixed to the center of the frame 1. It can be fixed at a position specified in advance. An MR sensor having a magnetic resolution of 33 μgauss is used for the magnetic detection unit 3, which can detect a magnetic flux density of a component in a normal direction of the coil surface, and outputs an output voltage ± 2 V for ± 20 mGauss. And supplies it to the control unit 4 as a time-series signal.
[0064]
The control unit 4 receives the supply of the voltage signal from the magnetic detection unit 3, passes through a low-pass filter in a frequency band from DC to 12.5 kHz, passes through an integrator, and outputs ± 16 mA for a magnetic field variation of ± 20 mGauss. The current is converted into a current and supplied to the coil 2 so as to form a negative feedback loop.
[0065]
The control unit 4 is a control circuit block for generating a magnetic field for canceling a temporal change of a magnetic flux density in a normal direction of the coil surface of the coil 2 detected by the magnetic detection unit 3 and cancels environmental magnetic noise. A current for generating a magnetic field of opposite phase is supplied to the coil 2.
[0066]
The movable mechanism 5 is a slide mechanism driven by an ultrasonic motor that does not use a magnetic material fixed to the center of the frame body 1 and uses a rod-shaped magnetism detection unit 3 based on an external instruction signal (not shown). Can be slid bidirectionally in the direction of the normal, or fixed at an arbitrary position.
[0067]
The frame type environmental magnetic noise shielding device of the first embodiment has an adjustment (open loop) mode and a shielding (closed loop) mode. In the adjustment mode, the control unit 4 supplies a current of 0 mA to the coil 2, captures environmental magnetic noise detected by the magnetic detection unit 3 for 10 seconds at a rate of 25,000 samples per second, and performs averaging processing. Then, the value obtained as a result of the processing is stored as a reference value. Next, in the shielding mode, the signal supplied from the magnetic detection unit 3 is captured at a rate of 25000 samples per second, a difference from the reference value is obtained, the difference value is integrated, and a current is output based on the integrated value. Then, the negative feedback loop control is realized by supplying the current to the coil 2. Environmental magnetic noise can be shielded. With this negative feedback loop control, not only the time change of the detection direction component of the magnetic flux density at the detection position of the magnetic detection unit 3 can be fixed to 0, but also the coil surface can be used for environmental magnetic noise in which the spatial gradient can be almost ignored. , A shielding effect can be obtained even at a position opposite to the detection position.
[0068]
FIG. 3 is a diagram describing the inside of the control unit 4 of the first embodiment in more detail. A signal supplied from a magnetic detection unit 3 (not shown) is supplied to an averaging processing circuit 41 and a difference calculation circuit 43.
[0069]
In the adjustment mode, the selector 45 selects 0V input and supplies 0V to the voltage / current conversion circuit 46. Thereby, the voltage-current conversion circuit 46 supplies 0 mA to the coil 2 (not shown). The averaging circuit 41 calculates the averaging value of the signal supplied from the magnetic detection unit 3 during the adjustment mode, and supplies the calculated value to the reference value holding circuit 42. When the mode is switched from the adjustment mode to the shielding mode, the reference value holding circuit holds the average value supplied to the input, and starts supplying the average value to the difference calculation circuit 43 as the reference value.
[0070]
When the mode is switched to the shielding mode, the selector 45 selects the output of the integration circuit 44 and supplies the output to the voltage-current conversion circuit 46. The difference calculation circuit 43 performs a difference calculation by subtracting the reference value supplied from the reference value holding circuit 42 from the signal supplied from the magnetic detection unit 3, and supplies the result to the integration circuit 44. Since the connection between the voltage-current conversion circuit 46 and the coil 2 is connected to form a negative feedback loop, a closed loop is formed so that the detection signal component of the magnetic detection unit 3 always matches the reference value.
[0071]
As a result, the magnetic flux density component in the normal direction of the plane where the coil 2 exists is fixed to the reference value, and the magnetic shielding effect is realized.
[Example 2]
FIG. 4 shows an embodiment of the magnetic detection unit 3. The magnetic detection element 31 employs HMC1021S manufactured by Honeywell. The HMC 1021S is a magnetoresistive element (MR sensor) having the input / output characteristics shown in FIG. As can be seen from FIG. 5, the magnetic sensor does not have good linearity. The differential voltage output of the magnetic detection element 31 is
It is supplied to the differential amplifier 32 and is amplified 100 times. The reference input of the differential amplifier 32 receives a voltage of 2.5 V from the active ground circuit 34,
It is designed to have an output fluctuation of ± 500 mV with an input of ± 1 Gauss centering on 2.5V. In order to remove high-frequency noise, the output of the differential amplifier 32 is supplied to a low-pass filter 33 having a cut-off frequency of 800 Hz to perform low-frequency filtering.
[0072]
FIG. 6 shows another embodiment of the control unit 4 in detail. The control unit 4 is a two-channel D / A converter connected by a synchronous serial interface to a one-chip microcomputer 423 having a differential amplifier 421, a low-pass filter 422, a high-speed A / D converter with 12-bit accuracy, and a synchronous serial interface. Since the D / A converters 424 and 425 and the D / A converters 424 and 425 output ± 1 V centering on 2.5 V, they shift the 2.5 V voltage to output ± 1 V centering on 0 V. And a voltage-current conversion circuit 427 for converting a voltage input of ± 1 V into a current of ± 100 mA.
[0073]
In the adjustment mode, the one-chip microcomputer 423 sets 0 to the D / A 425 via the synchronous serial interface. As a result, the D / A 425 outputs 2.5 V and supplies it to the 2.5 V shift circuit 426. The 2.5 V shift circuit 426 receives the input of 2.5 V, performs a downward shift of 2.5 V, and supplies 0 V to the voltage / current conversion circuit 427. The voltage-current conversion circuit 427 supplies 0 mA to the coil 2.
[0074]
The signal detected by the magnetic detection unit 3 in FIG. 4 has a sensitivity of 500 mV with respect to 1 gauss of the environmental magnetic field around 2.5 V by the active ground circuit 34 and is supplied to the positive sign input of the differential amplifier 421. . On the other hand, the negative sign input of the differential amplifier 421 is supplied from the D / A 424, and the output amplified by 100 times by the differential amplifier 421 is subjected to the 800 Hz band limitation by the low-pass filter 422, and then subjected to one-way operation. It is supplied to the input of an A / D converter built in the chip microcomputer 423. The one-chip microcomputer 423 performs a synchronous serial interface so that the A / D conversion result or the average value of the A / D conversion result for a predetermined time is substantially zero while sampling by the built-in A / D converter. , The setting value for the D / A converter 424 is continuously changed, and when the setting value in an optimum state is detected, the setting value for the D / A converter 424 is held as a reference value.
[0075]
When the one-chip microcomputer 423 is switched to the shielding mode, the one-chip microcomputer 423 changes the internal arithmetic processing, and executes the following equation (4) for each sampling using the converted value △ in of the A / D converter and the accumulated value sum.
[0076]
sum ← sum + △ in (4)
Equation (4) is equivalent to the integration process.
[0077]
In order to prevent oscillation, the one-chip microcomputer 423 discards some lower-order bits of the accumulated value sum, performs a right shift process, and then sets the D / A converter 425 via the synchronous serial interface. Thus, a negative feedback loop is configured so that the conversion value △ in of the A / D converter becomes 0.
[0078]
Therefore, also in the second embodiment, the magnetic flux density component in the normal direction of the plane where the coil 2 exists is fixed to the reference value, and the magnetic shielding effect is realized.
[Example 3]
FIG. 7 shows an embodiment of a cubic environmental magnetic noise shielding device. In this embodiment, four frame-type environmental magnetic noise shielding devices are fitted on each plane of the second frame 6 having a cubic shape, and a total of 24 frame-type environmental magnetic noise shielding devices are used to form a 1 m square cube. Of the environmental magnetic noise shielding device, and achieves a shielding performance of about 1/15. The optimal fixing position of the magnetic detection unit 3 was a position where the magnetic detection unit 3 was slid 18 cm outside the second frame 6.
[Example 4]
FIG. 8 shows an embodiment in which a cylindrical environmental magnetic noise shielding device is configured. In the present embodiment, five frame-type environmental magnetic noise shielding devices are fitted on the eight side surfaces of the cylindrical second frame 6, respectively, and a total of approximately 40 frame-type environmental magnetic noise shielding devices are used. Of the environmental magnetic noise shielding device, and achieves a shielding performance of about 1/30. Note that the optimal fixing position of the magnetic detection unit 3 was a position where the magnetic detection unit 3 was slid 23 cm outside the second frame 6.
[0079]
In the present embodiment, the configuration is such that a cylinder circle is approximated by an octagon, and a bed is provided inside the cylindrical frame 6, and the subject lies on the bed in a supine position, and the cardiac magnetic field distribution in the precordial region is measured. It is possible.
[0080]
In the present embodiment, a net-like conductor is attached to the inner surface of the cylindrical frame to provide an electromagnetic wave shielding property.
[0081]
Also, compared to the conventional magnetic shield room method, it has excellent lighting and ventilation, and excellent workability, and it is easy to disassemble it into a frame type environmental magnetic noise shielding device and carry it out and carry it in. There is.
[Example 5]
FIG. 11 shows a cross section of an embodiment in which a cylindrical environmental magnetic noise shielding device approximated by an octagon is configured. In the present embodiment, the shielding ratio adjusting magnetic detector 7 that can measure the three-axis magnetic flux density vectors in the x, y, and z directions inside the second frame 6 and the shielding ratio adjusting magnetic detector 7 Based on the supplied signal, the signal amplitude within a predetermined time is calculated by the least square sum of the amplitudes, and each movable mechanism provided in each frame-type environmental magnetic noise shielding device is set so that the calculated value is minimized. 5 is provided with a second control unit 8 for adjusting the fixed position collectively.
[0082]
In this embodiment, since the cross section is a regular octagon, the fixed position of the magnetic detection unit 3 with respect to each frame can be set to the same distance. If the second control unit 8 performs control to adjust the least square value of the absolute value of the three-axis magnetic flux density vector supplied from the shielding ratio adjustment magnetic detection unit 7 to the minimum, the second frame There is a feature that the inside of 6 is adjusted to a uniform and high shielding rate shielding space.
[0083]
【The invention's effect】
As described above, the frame-type environmental magnetic noise shielding device of the present invention provides the magnetic detection for detecting the time change of the frame 1, the coil 2 formed in the frame 1, and the magnetic flux density orthogonal to the surface of the coil 2. A control unit 4 for supplying a current to the coil 2 so that a signal detected by the magnetic detection unit 3 matches a preset reference value and canceling environmental magnetic noise in the magnetic detection unit 3; A movable mechanism 5 that can adjust the relative positional relationship between the frame 1 and the magnetic detection unit 3 so as to shield environmental magnetic noise in a predetermined area other than the magnetic detection unit 3, and these are integrated with the frame 1. Configuration.
[0084]
Therefore, since only the current supply capability for canceling the temporal variation of the environmental magnetic field is required, the size can be reduced, the weight can be reduced, and the magnetic detection unit 3 and the control unit 4 can be integrated on the surface where the coil 2 is disposed. This has a specific effect that can be provided.
[0085]
In addition, since the magnetic detection unit 3 and the control unit 4 are sufficiently smaller than the coil 2, the frame 1 on which the coil 2 is mounted may be provided with an opening portion having both lighting and air permeability. It has the unique effect of being able to.
[0086]
Further, since the magnetic detection unit 3, the coil 2, and the control unit 4 are integrally formed, a unique effect that the workability is excellent as compared with the conventional magnetic shield room system is achieved.
[0087]
As described above, the frame-type environmental magnetic noise shielding apparatus of the present invention can determine the reference value based on the environmental magnetic noise and the average value of the environmental magnetic noise. As a result, it is possible to operate with lower power consumption.
[0088]
Further, as described above, the frame-type environmental magnetic noise shielding device of the present invention provides a magnetic detection position by setting the relative positional relationship between the frame 1 and the magnetic detection unit 3 by the movable mechanism 5 in advance. This has a specific effect that a portion having a high shielding ratio can be generated at a position opposite to the coil surface.
[0089]
As described above, the environmental magnetic noise shielding device of the present invention is configured by a plurality of the frame-type environmental magnetic noise shielding devices, so that compared to the conventional magnetic shield room system, it has excellent daylighting and air permeability, The workability is also good, and it has a unique effect that it can be easily disassembled into frames and carried out / out.
[0090]
As described above, the environmental magnetic noise shielding apparatus according to the present invention has a signal amplitude or a minimum amplitude of 2 based on the signal supplied from the shielding rate adjusting magnetic detector 7 provided inside the second frame 6. The configuration includes a second control unit 8 that calculates the sum of squares and adjusts the movable mechanism 5 provided in each frame-type environmental magnetic noise shielding device so that the calculated value is minimized.
[0091]
Therefore, regardless of the shape of the second frame 6 and the situation of the surrounding environmental magnetic noise source, a unique effect that it is easy to realize a uniform and wide shielded space while having a high shielding ratio. Play.
[0092]
As described above, the environmental electromagnetic noise shielding device of the present invention has a unique effect of providing electromagnetic wave shielding while maintaining lighting and air permeability.
[Brief description of the drawings]
FIG. 1 is an embodiment of a frame type environmental magnetic noise shielding device of the present invention.
FIG. 2 is an embodiment of a conventional active magnetic shield system.
FIG. 3 is a detailed block diagram of an embodiment of a control unit 4.
FIG. 4 is an embodiment of the magnetic detection unit 3 of the present invention.
FIG. 5 is an example of input / output characteristics of a magnetoresistive (MR) sensor.
FIG. 6 shows an embodiment of the control section 4 of the present invention.
FIG. 7 is an embodiment of a cubic environmental magnetic noise shielding device.
FIG. 8 is an embodiment of an environmental electromagnetic noise shielding device having a cylindrical electromagnetic wave shielding characteristic.
FIG. 9 is a diagram for explaining the existence of a point having a good shielding factor based on the positional relationship between the magnetic detection unit 3 and the coil 2 of two opposing frame-type environmental magnetic noise shielding devices.
FIG. 10 is a diagram for explaining the existence of a point having a good shielding factor based on the positional relationship between the magnetic detection unit 3 and the coil 2 by a three-dimensional simulation.
FIG. 11 is an embodiment of a frame type environmental magnetic noise shielding device of the present invention.
[Explanation of symbols]
1 Frame
2 coils
3 Magnetic detector
6 Second frame
7 Magnetic detection unit for shielding ratio adjustment

Claims (5)

A frame 1, a coil 2 formed in the frame 1, a magnetic detection unit 3 for detecting a time change of a magnetic flux density orthogonal to a surface of the coil 2, and a signal detected by the magnetic detection unit 3 are set in advance. A control unit 4 for supplying a current to the coil 2 so as to match the reference value and performing control for canceling environmental magnetic noise in the magnetic detection unit 3 and environmental magnetic noise in a predetermined area other than the magnetic detection unit 3 can be shielded. A movable mechanism 5 for adjusting the relative positional relationship between the frame 1 and the magnetic detection unit 3, and these are integrated with the frame 1. The invention according to claim 1, further comprising a reference value determining means for setting the reference value based on a detection value of the magnetic detection unit 3 when a current supplied to the coil 2 is kept constant. A frame type environmental magnetic noise shielding device characterized by the above-mentioned. Each of the frame-type environments is constituted by a second frame 6 that constitutes all or a part of a closed curved surface of an arbitrary shape space, and a plurality of frame-type environment magnetic noise shielding devices according to claim 1 or 2. An environmental magnetic noise shielding apparatus characterized in that an internal space of a second frame 6 is made a magnetic shielding space having a uniform and high shielding rate by adjusting a movable mechanism 5 provided in the magnetic noise shielding apparatus. According to the third aspect of the present invention, the signal amplitude or the least square sum of the amplitude is determined based on one or a plurality of shielding ratio adjusting magnetic detectors 7 and a signal supplied from the shielding ratio adjusting magnetic detector 7. An environmental magnetic noise shielding device comprising: a second control unit that calculates and adjusts a movable mechanism provided in each frame-type environmental magnetic noise shielding device so that the calculated value is minimized. In the invention according to claim 3 or 4, the inner or outer surface of the second frame is covered with an electromagnetic wave shielding material which is a net-like or foil-like conductor, so that the second frame has a shielding ability against electromagnetic waves. Environmental electromagnetic noise shielding device.

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