Active magnetic shielding system and method of generating active magnetic shielding

Abstract

An active magnetic shielding system includes an array of magnetic field sensors arranged to sense local magnetic fields. An array of magnetic field elements is arranged to generate a magnetic field. Each magnetic field element has a cell coil for mounting to a plurality of surfaces arranged in at least three planes to define a closed cancellation volume and to generate a pattern of magnetic field vectors.

Description

Technical Field

[0001] This invention relates to magnetic shielding systems. More specifically, this invention relates to the design, optimization, and operating principles of active magnetic shielding systems. Background Technology

[0002] Magnetic field shielding of sensors and devices is crucial in many applications, including fundamental physics experiments and satellite measurements. This shielding is also important in medical imaging, including magnetoencephalography (MEG) and magnetic resonance imaging (MRI).

[0003] Magnetic shielding is divided into two types: active shielding and passive shielding. Passive shielding is achieved by isolating the shielded space by using a barrier of conductive or magnetic material to block the magnetic field. For static or slowly changing magnetic fields, permalloy or mu-metal high-permeability alloy shielding is used to provide a path for the magnetic shielding wires around the shielded volume.

[0004] Therefore, the most effective shape for magnetic shielding is a closed container surrounding the volume being shielded.

[0005] For shielding exceeding the limits of passive shielding, active shielding can also be used within the passive shielding volume. Active shielding utilizes the magnetic field generated by an electromagnet to counteract the ambient field within the volume by producing a counterfield that matches the geometry of the ambient field.

[0006] The human brain can be thought of as a highly complex circuit containing hundreds of billions of neurons. Just as electric currents flow through electrical wires, the tiny currents flowing through neurons also generate magnetic fields. Measuring these magnetic fields can provide unique insights into brain function with millimeter-level precision, and can be used to identify clinical biomarkers, such as the location of epileptic activity. It can also provide millisecond-level temporal resolution, which can be used to study real-time changes in the brain's state in response to its environment.

[0007] Magnetoencephalography (MEG) uses an array of magnetic field sensors placed on or near the scalp to noninvasively measure the magnetic field generated by the brain.

[0008] In medical and diagnostic settings, magnetic fields can also be measured from the heart (MCG), spine (MSG), intestines (MGG), and muscular system (MMG). This imaging process is also applicable to the imaging and analysis of body parts and isolated nerves. These applications inherently require a similar level of shielding.

[0009] MEG presents a significant engineering challenge because the magnetic field emanating from the brain is more than 100 billion times smaller than the Earth's magnetic field and many orders of magnitude smaller than other external magnetic field interference sources, such as those generated by electronic devices, cars, elevators, and power grids. Therefore, the magnetic signals generated by brain function can be masked by environmental magnetic interference.

[0010] Magnetic fields are typically measured by using a magnetic field sensor to measure the field, where the intensity and direction of the field are calculated based on the effect of the magnetic field on the magnet, coil, and / or electrical components of the magnetic field sensor. It should be noted that the operating range of ground field sensors is from 10 pT to 1 mT.

[0011] Many systems, including MEG systems, electron microscopes, and equipment used in atomic physics experiments, can be shielded from external magnetic interference sources by passive shielding in the form of magnetic shielding rooms (MSRs). Magnetic shielding rooms (MSRs) are typically composed of two or more layers of materials with high magnetic permeability (e.g., nickel-iron alloys such as mu-metal) and one layer of materials with high electrical conductivity (e.g., copper or aluminum).

[0012] Until recently, all MEG systems and similar systems used superconducting quantum interference devices (SQUIDs) to measure the brain's magnetic field. SQUIDs are low-magnetic-field sensors that can detect low magnetic field values ​​on the order of 1 fT (fetates).

[0013] SQUID is one of the most sensitive magnetic field detectors available, but it requires cryogenic cooling with liquid helium at -269°C. Related costs and practical limitations, including the necessary standardized design to avoid scanning participants with small heads (such as infants) and the need for participants to remain still during the scan, significantly limit the use of MEG.

[0014] To make MEG systems easier to use, optically pumped magnetometers (OPMs) have replaced SQUIDs in MEG systems. The miniaturization and commercialization of this magnetic field sensor has enabled the development of wearable systems capable of adapting to many different scanning scenarios. OPM-MEG systems have been used to scan previously unsuitable subjects, including moving adults, young children, and patients with conditions such as Parkinson's disease and Tourette syndrome, to obtain readings that are unavailable from SQUID-MEG systems.

[0015] However, OPM-MEG systems have inherent drawbacks. SQUID and OPM respond significantly differently to static (or DC) magnetic fields that change very slowly over time (typically at frequencies <1 Hz).

[0016] SQUIDs are largely insensitive to static magnetic fields because they measure the variation of a time-varying or alternating magnetic field relative to a constant offset field. In contrast, OPMs operate around a “zero-field resonance” and are sensitive to magnetic fields only within a narrow range of about ±5 nT (nanotesla).

[0017] Readers in this field will understand 5 nT (10-9 T) and 58 μT (10) at latitude 50° -5 The order of magnitude difference between the Earth's magnetic field strength and that of T).

[0018] Existing MSR technology can reduce the magnetic field of the Earth and other interference sources to about 2 nT, leaving a magnetic field that varies with spatial location at a rate of about 2 nT / m. However, even in these reduced magnetic fields, tiny movements of the sensors on the head can produce large magnetic field changes, which can easily exceed the dynamic range of the sensors, resulting in signal loss.

[0019] Traditionally, active shielding systems for all applications rely on simple coil designs, such as orthogonal circular loops (called "Helmholtz cages"), which generate a controlled magnetic field pattern over a fixed volume. A single Helmholtz coil typically consists of two identical circular magnetic coils placed symmetrically along a common axis, one on each side of the shielding volume, spaced apart by a distance equal to the coil radius. Each coil carries an equal current in the same direction. Helmholtz coils can be used to counteract the Earth's magnetic field within passive shields, thereby creating a region with a magnetic field strength very close to zero.

[0020] The scanned object has difficulty physically entering and exiting the enclosure formed by the Helmholtz coils, and the fixed nature of the cancellation device limits the available movement and experimentation. Biplane designs that confine the coil windings to two planes are possible, but these designs require fabricating at least eight layers of complex wiring paths. Furthermore, the fixed cancellation volume makes the system inflexible and unsuitable for unpredictable large movements.

[0021] The interaction between the magnetic field generated by the active shielded coil and the high-permeability material used to construct the MSR causes the generated magnetic field to deform from its intended shape, and leads to a change in the ratio of the generated magnetic field strength to the applied coil current, resulting in poor shielding. Although these interactions can be incorporated into the coil design, the final system remains confined to a fixed cancellation region. Summary of the Invention

[0022] This invention relates to a magnetic field control system arranged to generate a known magnetic field. One embodiment of the invention provides a magnetic shielding system arranged to reduce residual magnetic fields in an MSR and to minimize signal loss during movement of the object under study within the magnetic shielding device.

[0023] Therefore, the present invention provides an active magnetic shielding system comprising: an array of magnetic field sensors arranged to sense a local magnetic field; an array of magnetic field elements arranged to generate a magnetic field of -20 nT to +20 nT, each magnetic field element including a unit coil for mounting to a plurality of surfaces arranged on at least three planes to define a closed cancellation volume, each unit coil including a coil trace path arranged to generate a vector magnetic field pattern; and a current source arranged to provide a controlled current to each unit coil; and a feedback algorithm arranged to control the current source of each unit coil to minimize the sensed local magnetic field.

[0024] The unit coils can be arranged in three planes that define a closed offset volume, but depending on the size and shape of the offset volume, they can be arranged in up to six planes.

[0025] The active magnetic shielding system may further include a passive magnetic shield arranged to support an array of magnetic field elements. This passive magnetic shield may include at least a first layer formed of a high-permeability material and another layer formed of a high-conductivity material. The passive magnetic shield may also include a magnetic shielding chamber (MSR), in which the array of magnetic field elements is placed on or within each wall of the MSR. Preferably, the magnetic field elements are fixed to the inner surface of each wall of the MSR.

[0026] The active magnetic shielding system preferably generates a vector magnetic field pattern with an order of magnitude of 5 nT or less.

[0027] Preferably, each unit coil is a square coil. These square coils can be arranged in a 2x2 grid configuration in each of the three planes.

[0028] Preferably, the magnetic field element array comprises overlapping unit coils.

[0029] Active magnetic shielding systems can be configured for use in magnetoencephalography (MEG) or MRI applications.

[0030] The present invention also provides a method for generating active magnetic shielding. The method includes generating a magnetic field by: providing an array of magnetic field elements, each magnetic field element including a unit coil; specifying a set of coil parameters in each unit coil; applying a current in each unit coil on a grid of target points spanning a target volume; calculating the magnetic field generated per unit current by each unit coil at each target point; mapping the calculated magnetic field per unit current to a target magnetic field; determining an optimal coil current for each unit coil; and comparing the generated magnetic field with the target magnetic field.

[0031] Preferably, the method for generating active magnetic shielding determines the optimal coil current by minimizing the sum of current values ​​and applying a threshold that limits the maximum value of the applied current. The magnetic field per unit current is preferably generated by each coil at each magnetic field sensor, calculated using its known target point location. The magnetic field per unit current generated by each coil at each magnetic field sensor can be measured by sequentially applying a known current to each coil. Preferably, the coil parameters in each unit coil are based on the unit coil geometry and the offset between unit coils.

[0032] The method for generating active magnetic shielding preferably further includes changing the coil parameters in each unit coil based on a comparison between the generated magnetic field and the target magnetic field, and repeating the steps of the method until the generated magnetic field and the target magnetic field match. Attached Figure Description

[0033] Embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:

[0034] Figure 1 is an example of a known two-plane coil system;

[0035] Figure 2A This is a first view of an exemplary active magnetic shielding system according to the present invention;

[0036] Figure 2B yes Figure 2A A second view of an exemplary active magnetic shielding system;

[0037] Figure 2C yes Figure 2A and 2B A first view of a wall panel of an exemplary active magnetic shielding system;

[0038] Figure 2D yes Figure 2A and 2B A second view of a wall panel of an exemplary active magnetic shielding system;

[0039] Figure 3A This is a first plan view of the first coil disk according to the present invention;

[0040] Figure 3B yes Figure 3A A cross-sectional view of the first coil disk;

[0041] Figure 3C yes Figure 3A A partial cross-sectional view of the coil of the first coil disk;

[0042] Figure 3D yes Figure 3A The second plan view of the coil connection of the first coil disk;

[0043] Figure 3E yes Figure 3D A cross-sectional view of the coil connection;

[0044] Figure 4A This is a plan view of the second coil disk according to the present invention;

[0045] Figure 4B yes Figure 4A A cross-sectional view of the second coil disk;

[0046] Figure 4C yes Figure 4A A partial cross-sectional view of the coil arrangement of the second coil disk;

[0047] Figure 4D yes Figure 4A A partial cross-sectional view of the coil connection of the second coil disk;

[0048] Figure 5A This is a plan view of the third coil disk according to the present invention;

[0049] Figure 5B yes Figure 5A A cross-sectional view of the third coil disk;

[0050] Figure 5C yes Figure 5A A partial cross-sectional view of the coil arrangement of the third coil disk;

[0051] Figure 5D yes Figure 5A A partial cross-sectional view of the coil connections of the third coil disk;

[0052] Figure 6A This is a plan view of the fourth coil disk according to the present invention;

[0053] Figure 6B yes Figure 6A A cross-sectional view of the fourth coil disk;

[0054] Figure 6C yes Figure 6A A partial cross-sectional view of the coil arrangement of the fourth coil disk;

[0055] Figure 6D yes Figure 6A A partial cross-sectional view of the coil connections of the fourth coil disk;

[0056] Figure 7A This is a plan view of the fifth coil disk according to the present invention;

[0057] Figure 7B yes Figure 7A A cross-sectional view of the fifth coil disk;

[0058] Figure 7C yes Figure 7AA partial cross-sectional view of the coil arrangement of the fifth coil disk;

[0059] Figure 7D yes Figure 7A A partial cross-sectional view of the coil connections of the fifth coil disk;

[0060] Figure 8A This is a plan view of the sixth coil according to the present invention;

[0061] Figure 8B yes Figure 8A A cross-sectional view of the sixth coil.

[0062] Figure 8C yes Figure 8A A partial cross-sectional view of the coil arrangement of the sixth coil disk;

[0063] Figure 8D yes Figure 8A A partial cross-sectional view of the coil connections of the sixth coil disk;

[0064] Figure 9A This is a plan view of the seventh coil according to the present invention;

[0065] Figure 9B yes Figure 9A A cross-sectional view of the seventh coil.

[0066] Figure 9C yes Figure 9A A partial cross-sectional view of the coil arrangement of the seventh coil disk;

[0067] Figure 9D yes Figure 9A A partial cross-sectional view of the coil connections of the seventh coil disk;

[0068] Figure 10 This is a schematic diagram of an exemplary window coil system according to the present invention;

[0069] Figure 11 This is a schematic diagram of an embodiment of a window coil system with matrix configuration according to the present invention; and

[0070] Figure 12 This is a plan view of a window coil disk with a matrix configuration according to another embodiment of the window coil with a matrix configuration according to the present invention. Detailed Implementation

[0071] Figure 1A known biplane coil system is shown against the backdrop of a magnetically shielded chamber 10. A first set of coil windings 11 is arranged substantially perpendicularly on a first side of a volume 13 to be shielded. A second set of coil windings 12 is arranged substantially perpendicularly on a second side of the volume 13 to be shielded, which is commonly referred to as the canceling volume. The first and second coil windings 11, 12 are constrained in two planes. Each of the first and second coil windings 11, 12 includes multiple layers of interlaced traces. The number of trace layers can be three to eight or more. In this embodiment, the first and second coil windings 11, 12 include at least eight layers. The canceling volume 13 is fixed and constrained by the biplane arrangement of the coils such that when the observed object is enclosed in the volume 13, it must remain stationary, producing only small and predictable movements that can be described using data obtained during processing.

[0072] The magnetic fields generated by the first and second coil windings 11, 12 interact with each other and with the high-permeability material used in constructing the magnetic shielding chamber 10. These interactions cause the generated magnetic fields to deviate from their intended shape and change the ratio of the generated magnetic field strength to the applied coil current, which adversely affects the shielding efficiency. Although these interactions can be incorporated into the coil design, the final system is still limited by the fixed cancellation volume 13 and the tolerable parameters of the observed objects within volume 13.

[0073] Figure 2A This is a first partial view of an exemplary active magnetic shielding device according to the present invention. The illustrated embodiment is an example of a "window coil" system according to an embodiment of the present invention.

[0074] An active magnetic shielding system includes an array of magnetic field sensors arranged to detect localized magnetic fields. An array of magnetic field elements is provided to generate magnetic shielding, each magnetic field element comprising multiple unit coils arranged in a “window” configuration. The magnetic field elements are distinct from and physically displaced from the magnetic field sensors. The unit coils are arranged in at least three planes to eliminate “blind spots” in the space to be shielded. In the case of generating magnetic shielding across an entire cubic space, the unit coils are arranged in six planes.

[0075] Simple unit coil structures include trace paths of various geometries, including rectangular, square, and circular trace paths. The coils can be arranged in any shape and can be selected to fit a surface that offsets the volume. The trace paths can be placed directly on the inner surface of the MSR's walls or embedded therein. Example layouts are shown in Figures 2A through 9D, and an exemplary mounting system is shown in Figure 10.

[0076] Although particularly well-suited for use with MSRs, active magnetic shielding devices can also be used independently.

[0077] Figure 2A The arrangement of coils on the two walls 21, 22 and the uppermost ceiling surface 24 of a magnetically shielded room (MSR) 20 is shown. The MSR 20 is an enclosure with a shell comprising layers of highly permeable metals that are good electrical conductors and can attenuate stray magnetic and electric fields emanating from external sources. The highly permeable metals typically comprise mu-metals, forming a passive shield.

[0078] Passive shielding may comprise a single layer of material with high magnetic permeability, such as mu-metal or another such metal alloy, nickel, or others. Passive shielding may comprise another layer of material with high electrical conductivity, such as copper or aluminum. Alternatively, passive shielding may consist of two or more layers with high magnetic permeability and / or high electrical conductivity.

[0079] In the application of this invention to MRI, the passive shield can be formed of materials including copper, steel or other ferroalloys or aluminum. Such materials contain the magnetic field generated by the MRI equipment.

[0080] To further reduce the residual magnetic field in the MSR 20, a passive shielding system provided by mu-metal complements the "active" shielding system. The active shielding uses electromagnetic coils to generate a magnetic field that is equal to and opposite to the magnetic field in the room, functioning much like active noise cancellation technology in headphones, to "eliminate" and counteract the ambient magnetic field in the space.

[0081] The magnetic field elements are arranged to provide multiple unit coils on each surface of an enclosed space. The unit coils are arranged in three planes. The unit coils cooperate to define a canceling volume. The unit coils are capable of generating a three-dimensional vector magnetic field pattern that can be adjusted or defined as desired.

[0082] The coil routing layout on wall 21 comprises four square coil grids arranged in a 2x2 pattern, each grid having an overall visual appearance of a "window". Each of the four grids on wall 21 is as follows: Figures 3A-3E The coil disk 1 described in the text.

[0083] The coils are arranged to cover most of the wall surface on which they are mounted. Wall surface 22 has two such... Figures 5A-5D The coil disks 3 are further defined and arranged adjacent to each other in a substantially perpendicular 1x2 arrangement. Wall 22 has an opening therein for access to the internal volume 25 of the MSR 20. Doorway 23 includes two coil disks arranged in a substantially perpendicular 1x2 arrangement; therefore, the combined second wall 22 and doorway 23 comprise a 2x2 coil disk arrangement spanning wall 22. The lowermost part of doorway 23 includes... Figures 8A-8D The coil disk 6 is described further. The uppermost part of the facade 23 includes, as shown in the description... Figures 7A-7DThe coil disk 5 is described further.

[0084] In most known MSR designs, features such as door openings, equipment holes, and removable panels are "dead zones" without shielding because using high-permeability metals in these areas is not always feasible or practical, leaving gaps in passive shielding. In this invention, active shielding components can be configured to incorporate room features (e.g., doors, vents, and other openings related to offsetting volume entry and exit, and functionality) into the design process by providing appropriately sized coils, so as not to obstruct these features. Therefore, surfaces that do not contain room features may require fewer coils.

[0085] Five coils are arranged on the ceiling surface 24, extending substantially over the entire ceiling surface 24. Two coils 1 are arranged adjacent to each other, such that one coil 1 is adjacent to the uppermost coil 3 of the wall 22, and the other coil 1 of the ceiling surface 24 is adjacent to the coil 5 of the door 23 on the first side and to the uppermost coil 1 of the wall 21 on the second side. Two additional coils 2 are arranged at the corners of the quadrilateral ceiling surface 24, and additional coils 4 are arranged between the coils 2 to provide more complete coverage of the ceiling surface 24.

[0086] The simple geometric coil design simplifies the production and installation of the array. Positioning of the coil array on the walls or surface of the shielded volume or MSR means the magnetic shielding system does not occupy additional space within the shielded volume. The coils are arranged to provide coverage across the central portion of the walls or surface of the shielded volume.

[0087] Figure 2B It is arranged as Figure 2A The second part of the view shows an exemplary active magnetic shielding system with a "window coil" configuration. When arranged together with the features of FIG2A, the combined features of FIG2A and 2B form a system that covers all surfaces of the magnetic shielding chamber 20, thereby defining a counterbalancing volume 25.

[0088] The floor surface 28 has a window coil arrangement that is substantially the same as that of the wall surface 21. The window coils are arranged in a 2×2 pattern but are formed by four coil disks 7. The coil disks 7 are about Figures 9A-9D Further description.

[0089] Walls 26 and 27 have a window coil layout substantially the same as that of ceiling surface 24, formed by an array of five unit coils to provide uniform coverage across the respective walls. Each of walls 26 and 27 has two coil disks 1 arranged adjacent to and horizontally relative to each other. Coil disks 2 and 4 are arranged adjacent to each other, forming a first upper corner of the quadrilateral of walls 26 and 27. A second coil disk 2 is arranged opposite to coil disk 4 to provide shielding for a second upper corner of the quadrilateral of walls 26 and 27 opposite the first upper corner. The coil disks 4 of walls 26 and 27 are rectangular and arranged such that each of the two longer sides is adjacent to both sides of the coil disk 2 located therebetween. The lowermost of the two shorter sides is adjacent to the coil disk 1 of walls 26 and 27.

[0090] The regular grid pattern described in this embodiment is a simple example, but in practice, any number of coil trace paths can be chosen for the array, and a wider range of parameters can be considered. For example, the coils of each magnetic field element can have arbitrary shapes. Different faces of the MSR can have different coil array layouts, and it is permissible for the coils to overlap or be arranged separately.

[0091] Overlapping coil routing allows for partial control of the magnetic field direction without placing coils on all surfaces.

[0092] Figure 2C Multiple magnetic field elements are shown applied to surfaces 21, 22, 26, 27, 23, 24, and 28 of the MSR 20, which defines a counterbalancing volume of 25. A second plane of the coil disks is shown, obscuring the corresponding coil trace path for each coil disk. Connecting components of the coil trace paths are visible at the corner portions of each coil disk.

[0093] This system is characterized by having numerous coil trace paths, typically 24 to 48 or more in a magnetically shielded chamber. The number of coil trace paths is determined by the shape of the shielding space, which in turn determines the number of surfaces to which the unit coils must be attached. Therefore, for illustrative purposes, this embodiment applies to a standard, generally rectangular, shielded chamber.

[0094] Figure 2D shows the unit coils of the magnetic field elements arranged in an array, obscured in the view of Figure 2C. As shown in Figures 2A and 2B, each type of coil disk is labeled, and the wiring path of each coil disk is visible. Each of the coil disks 1-7 is shown in situ and, when viewed from the first plane side, the coil wiring path is visible. In this embodiment, the magnetic field system includes multiples of each type of coil disk: 10 x coil disk 1, 6 x coil disk 2, 2 x coil disk 3, 3 x coil disk 4, 1 x coil disk 5 and coil disk 6, and 4 x coil disk 7.

[0095] Figure 3A This is a plan view of the first coil disc 1 according to the present invention. The coil disc 1 is shown as an assembly in the plan view. A coil trace path 30 is fixed to a first plane of a support panel 31. The coil trace path 30 extends in a square around the periphery of the plane of the support panel 31 to fit within the surface area of ​​the panel, which in this embodiment is a regular quadrilateral. The coil trace path 30 extends along each substantially equal side length 32 of the panel. The coil trace path 30 is a continuous winding formed by either a single portion or multiple connected portions to form a single trace, which is repeatedly wound to form coils of adjacent portions.

[0096] When placed in situ on a selected surface of the MSR 20, the coil disk 1 is mounted such that the trace path 30 is adjacent to the surface of the MSR 20 and is shielded by the panel 31 when viewed from the offset volume 25. In some embodiments, the trace path 30 is embedded in the surface of the MSR 20. However, the coil disk 1 may also be arranged such that the trace path 30 is exposed and faces the offset volume 25.

[0097] Certain coil parameters are determined; in this embodiment, these parameters are the symmetrical side length 32 of each coil square 30, the regular spacing between coil centers 33, and the distance from the center of each surface of the MSR to the center of the 2x2 grid. For a given set of coil parameters, the magnetic field generated by a unit current applied in each coil within a regular grid spanning the “target point” of interest is calculated. Where relevant or necessary, the magnetic field calculation can incorporate data relating to mu-metal interactions near the surface of the MSR 20.

[0098] Each target point is determined based on user preferences. In a preferred arrangement, the cancellation volume is defined by the arrangement and coverage area of ​​the sensor array. These parameters are used to determine the approximate cubic cancellation volume mapped by the grid of target points. The number of target points is determined based on the desired resolution. In a preferred embodiment, target points can be placed at 5 cm intervals throughout the cubic cancellation volume.

[0099] Then, by identifying the optimal coil current, the calculated magnetic field per unit current generated at the target point is mapped to the target magnetic field. The target magnetic field can be chosen as a magnetic field with the same value at every target point, referred to as a "uniform field". Alternatively, the target magnetic field can be a magnetic field that varies linearly with position, referred to as a "field gradient". Some embodiments of the invention use at least one uniform target magnetic field, while other embodiments use at least one field gradient target magnetic field. Further embodiments may use a mixture of uniform target magnetic fields and field gradient target magnetic fields, or any combination of each.

[0100] Figure 3B yes Figure 3A A cross-sectional view of the first coil disk 1. The coil trace path 30 is shown recessed into the plane of the support panel 31. The support panel 31 is formed of any suitable non-metallic and / or non-magnetic material. However, in some embodiments, the support panel may be formed of a suitable material such that the support panel provides passive shielding.

[0101] The unit coil windings of coil trace path 30 are typically recessed to a depth of 3 mm and remain visible on the first plane of support panel 31. Each successive winding is offset by 2 mm from the previous winding, and the diameter of the conductor in each coil trace path 30 is typically 1.5 mm.

[0102] In some embodiments, the surface of the support panel 31 may be covered to protect or simply cover the unit coil.

[0103] Figure 3C yes Figure 3A A partial cross-sectional view of the coil trace path 30 of the first coil disk 1 shows the coil trace path 30 and associated connections. The coil trace path 30 is formed by individual windings arranged around the periphery of the plane of the support panel 31, such that each successive winding is adjacent to the previous repetition.

[0104] In this embodiment, the coil routing path 30 is formed by 20 windings extending between coil terminals 34 and 36. The magnetic field strength is linearly proportional to B to N1, where I is the current and N is the number of windings. In this embodiment, N=20 is chosen to generate a sufficient magnetic field.

[0105] Based on the known maximum current of the current source and the estimate of the magnetic field inside the MSR, N can be selected to ensure that the system generates a sufficient magnetic field to produce the required magnetic field strength.

[0106] The coil bridging portion 37 extends between the coil terminal 34 and the coil terminal 36. The external connector 35 connects both the coil terminal 36 and the coil bridging portion 37 to an external current source, which is connected via the coil bridging connector 38.

[0107] An external current source is arranged to provide a set of current values, such that the coils in each coil trace path generate arbitrary vector magnetic field patterns according to the current applied to each unit coil. The magnetic field pattern is not limited to magnetic fields in the x, y, or z directions; therefore, the object to be measured can be placed anywhere within the shielding cancellation volume.

[0108] An external current source is configured to apply various current values ​​to the unit coil to alter the resulting magnetic field pattern according to a series of criteria. Based on measurements from a magnetic field sensor or other data related to changes in external disturbances, the magnetic field pattern can be updated to better attenuate local magnetic fields. The magnetic field pattern can also be dynamically updated to track and cancel moving objects within the space.

[0109] The current value can be determined using a feedback algorithm, or by using a predetermined or measured value. When using passive shielding, the current calculation method can be arranged to compensate for the interaction between the magnetic field element and the passive shield.

[0110] Figure 3D yes Figure 3C The second plan view shows the coil connections of the first coil disk 1. Coil terminals 34, 36, coil bridging portions 37, coil bridging connectors 38, and external connectors 35 are located on the second plane of the support panel 31 opposite to the first plane. The coil trace path 30 is located on the first plane, so only components located on the second plane of the support panel 31 are visible and / or accessible. In embodiments where the coil trace path 30 is located on the plane of the support panel 31 visible from within the offset volume 25 of the magnetic shielding chamber 20, the coil terminals 34, 36, coil bridging portions 37, coil bridging connectors 38, and external connectors 35 are located on the same plane as the coil trace path 30.

[0111] Figure 3E This is a cross-sectional view of the external connector 35, showing the recess 39 formed by a standard manufacturing process. The recess may exist to accommodate coil trace paths 30 that are preferably flush with the panel surface profile. The connector recess 39 ensures that the coil return line is flush with the panel surface for easy installation during mounting.

[0112] Figure 4A This is a plan view of the second coil disk 2 according to the present invention. The coil disk 2 is shown as an assembly in the plan view. The coil trace path 40 is fixed to a first plane of the support panel 41. The coil trace path 40 extends in a rectangular shape near the periphery of the plane of the support panel 41 to fit within the surface area of ​​the panel, which in this embodiment is also rectangular. The support panel 41 has a panel side width 42 that is shorter than the panel side length 43. Therefore, the portion of the coil trace path 40 extending adjacent to the panel side length 43 extends a longer length than the portion of the coil trace path 40 extending adjacent to the panel side width 42.

[0113] The coil trace path 40 extends along the first panel side width 42, the first panel side length 43, the second panel side width 42, and the second panel side length 43 to form a rectangular coverage area. The coil trace path 40 is a continuous winding formed by either a single section or multiple sections connected to form a single trace, which is repeatedly wound to form coils of adjacent sections with a selected number of repetitions.

[0114] When placed in situ on a selected surface of the MSR 20, the coil disk 2 is mounted such that the trace path 40 is adjacent to the surface of the MSR 20 and is shielded by the panel 41 when viewed from the offset volume 25. In some embodiments, the trace path 40 is embedded in the surface of the MSR 20. However, the coil disk 2 may also be arranged such that the trace path 40 is exposed and faces the offset volume 25.

[0115] The relevant coil parameters are determined. In this embodiment, these coil parameters are the side width 42 and side length 43 of each coil trace path 40, the regular spacing between the coil center 49 and the centers of adjacent coils, and the distance from the center of each surface of the MSR 20 to the center of the 2x2 grid.

[0116] In a preferred embodiment, the coil parameters are determined by assuming the cancellation volume is a cube within a passive shield without any "holes" or unshielded areas. An arrangement of four coils is applied to each surface. The side lengths, offsets from the center, and height of the arrangement are varied, and the solution value for each component is recorded. The solution value is derived from the square root of the sum of the squared differences between the desired magnetic field at each target point and the magnetic field produced by the coil parameters at each target point. If the coils perfectly reproduce the desired magnetic field, the solution value is zero.

[0117] The parametric data are combined to determine individual parametric factors for each surface. The required parameters for each surface are co-optimized so that they are calculated simultaneously, rather than on a surface-by-surface basis. In this way, the vector magnetic field pattern is optimized.

[0118] For a given set of coil parameters, calculate the magnetic field produced by a unit current applied in each coil across a regular grid spanning a "target point" with a cancellation volume of 25. In relevant cases, the magnetic field calculation can incorporate data related to mu-metal interactions near the MSR 20 surface.

[0119] In most respects, coil 2 is substantially the same as coil 1 in form, structure, and material. The same applies to coils 3, 4, 5, 6, and 7. Therefore, the description of coil 1 applies to all coils in this embodiment, unless otherwise specified in the description of individual plates.

[0120] Figure 4B yes Figure 4A A cross-sectional view of the second coil disc, with the support panel 41 shown in cross-section. The coil trace path 40 is shown recessed into the plane of the support panel 41. The windings of the coil trace path 40 are generally recessed into the surface of the support panel 41 and remain visible on its first plane. In a coil comprising a single layer of windings, each successive winding is offset from the previous winding.

[0121] Figure 4C yes Figure 4A A partial cross-sectional view of the coil trace path 40 of the second coil disk 2 shows the coil trace path 40 and its associated connections. The coil trace path 40 is formed by a single winding arranged around the periphery of the plane of the support panel 41, such that each successive winding is adjacent to the previous winding. In this embodiment, the coil trace path 40 is formed by 20 windings extending between coil terminals 44 and 46.

[0122] A coil bridging portion 47 extends between coil terminals 44 and 46. An external connector 45 connects both coil terminals 46 and coil bridging portion 47 to an external current source. Coil bridging portion 47 is connected to external connector 45 via coil bridging connector 48.

[0123] Figure 4D yes Figure 4C The second plan view shows the coil connections of the second coil disk 2. Coil terminals 44, 46, coil bridging portion 47, coil bridging connector 48, and external connector 45 are located on the second plane of the support panel 41 opposite to the first plane. The coil trace path 40 is located on the first plane, so only the components located on the second plane of the support panel 41 are visible and / or accessible.

[0124] Figure 5A This is a plan view of the third coil disk 3 according to the present invention. The coil disk 3 is shown as an assembly in the plan view. The coil trace path 50 is fixed to a first plane of the support panel 51. The coil trace path 50 extends in a rectangular shape near the periphery of the plane of the support panel 51 to fit within the surface area of ​​the panel, which in this embodiment is also rectangular. The support panel 51 has a panel side width 52 that is longer than the panel side length 53. Therefore, the portion of the coil trace path 50 extending adjacent to the panel side width 52 extends a longer length than the portion of the coil trace path 50 extending adjacent to the panel side length 53.

[0125] The coil trace path 50 extends along the first panel side width 52, the first panel side length 53, the second panel side width 52, and the second panel side length 53 to form a rectangular coverage area. The coil trace path 50 is a continuous winding formed by connecting one or more sections to form a single trace, and the single conductor is repeatedly wound to form coils of adjacent sections.

[0126] The relevant coil parameters are determined. In this embodiment, these coil parameters are the side width 52 and side length 53 of each coil trace path 50, the regular spacing between the coil center 59 and the centers of adjacent coils, and the distance from the center of each surface of the MSR 20 to the center of the 2x2 grid.

[0127] Similar to coil coils 1, 2, 3, 5, 6, and 7, support plate 51 has a cutout in the central portion of the coil coils, defined by the periphery of the coil routing paths 50. The four cutout portions are arranged symmetrically in a 2 x 2 pattern, such that the material of the central portion of support plate 51 is arranged in a cross shape to provide rigidity while also providing access to underlying features, such as small inlet / outlet holes or bolts in a mu-metal panel. Alternatively, each coil routing path 50 can be mounted on a solid square. The horizontal portion of the cross shape is substantially parallel to the panel side width 52, while the vertical portion is substantially parallel to the panel side length 53. The coil center 59 is located at the intersection of the horizontal and vertical portions of the support plate 51 material in the central portion. The horizontal and vertical portions of the central portion of support plate 51 have equal width and depth.

[0128] Figure 5B yes Figure 5A A cross-sectional view of the second coil disc, wherein the support panel 51 is shown in cross-section. The coil trace path 50 is shown as recessed into the plane of the support panel 51. The windings of the coil trace path 50 are generally recessed into the surface of the support panel 51 and remain visible on its first plane.

[0129] Figure 5C yes Figure 5A A partial cross-sectional view of the coil routing path 50 of the third coil disk 3 shows the coil routing path 50 and related connections. The coil routing path 50 is formed by a single winding arranged around the periphery of the plane of the support panel 51, such that each successive winding is adjacent to the previous winding. In this embodiment, the coil routing path 50 is formed by 20 windings extending between coil terminals 54 and 56.

[0130] Figure 5D yes Figure 5C The second plan view shows the coil connections of the third coil disk 3. Coil terminals 54 and 56, coil bridging portion 57, coil bridging connector 58, and external connector 55 are located on the second plane of the support panel 51 opposite to the first plane. The coil trace path 50 is located on the first plane, so only the components located on the second plane of the support panel 51 are visible and / or accessible.

[0131] Figure 6AThis is a plan view of the fourth coil disk 4 according to the present invention. The coil disk 4 is shown as an assembly in the plan view. The coil trace path 60 is fixed to a first plane of the support panel 61. The coil trace path 60 extends in a rectangular shape near the periphery of the plane of the support panel 61 to fit within the surface area of ​​the panel, which in this embodiment is also rectangular. The support panel 61 has a panel side width 62 that is shorter than the panel side length 63. Therefore, the portion of the coil trace path 60 extending near the panel side length 63 extends a greater length than the portion extending near the panel side width 62.

[0132] The support panel 61 includes three cutouts within a central portion defined by the coil trace path 60. A first central member of the support panel 61 extends between panel side lengths 63, such that the coil center 69 falls within the central member. A second central member of the support panel 61 extends from one of the panel side widths 62 to the first central member to form a T-shaped member. The first and second central members of the support panel 61 have approximately the same width. The support panel 61 has a uniform cross-sectional area.

[0133] When placed in situ on a selected surface of the MSR 20, the coil disk 4 is mounted such that the trace path 60 is adjacent to the surface of the MSR 20 and is shielded by the panel 61 when viewed from the offset volume 25. In some embodiments, the trace path 60 is embedded in the surface of the MSR 20. However, the coil disk 4 may also be arranged such that the trace path 60 is exposed and faces the offset volume 25.

[0134] Figure 6B yes Figure 6A A cross-sectional view of the fourth coil disk 4, wherein the support panel 61 is shown in cross-section. The coil trace path 60 is shown as recessed into the plane of the support panel 61. The windings of the coil trace path 60 are generally recessed into the surface of the support panel 61.

[0135] Figure 6C yes Figure 6A A partial cross-sectional view of the coil routing path 60 of the fourth coil disk 4 shows the coil routing path 60 and related connections. The coil routing path 60 is formed by a single winding arranged around the periphery of the plane of the support panel 61, such that each successive winding is positioned adjacent to the previous one. In this embodiment, the coil routing path 60 consists of 20 windings extending between coil terminals 64 and 66.

[0136] Figure 6D yes Figure 6CThe second plan view shows the coil connections of the fourth coil disk 4. Coil terminals 64 and 66, coil bridging portion 67, coil bridging connector 68, and external connector 65 are located on the second plane of the support panel 61 opposite to the first plane. The coil trace path 60 is located on the first plane, so only the components located on the second plane of the support panel 61 are visible and / or accessible.

[0137] Figure 7A This is a plan view of the fifth coil disk 5 according to the present invention. The coil disk 5 is shown in plan view. The coil routing path 70 is fixed to the first plane of the support panel 71. The coil routing path 70 extends in a square around the periphery of the plane of the support panel 71 to be mounted in the surface area of ​​the panel; in this embodiment, it is also a regular quadrilateral. The coil routing path 70 extends along each substantially equal panel side length 72, 73. The coil routing path 70 is a continuous winding formed by connecting one or more portions to form a single wire, which is repeatedly wound to form coils of adjacent portions.

[0138] The coil disk 5 is arranged such that the trace path 70 is adjacent to the surface of the MSR 20 and is shielded by the panel 71 when viewed from the offset volume 25. In some embodiments, the trace path 70 is embedded in the surface of the MSR 20. However, the coil disk 5 may also be arranged such that the trace path 70 is exposed and faces the offset volume 25. In some embodiments, the surface of the support panel 71 may be covered to protect or simply shield the unit coil.

[0139] Certain coil parameters were determined; in this embodiment, these parameters are the symmetrical side lengths 72 and 73 of each coil square 70, the regular spacing between coil centers 79, and the distance from the center of each surface of the MSR to the center of the 2x2 grid. For a given set of coil parameters, the magnetic field generated by a unit applied current in each coil across a regular grid spanning the “target point” of interest was calculated. The magnetic field calculation could incorporate data relating to the interaction of mu-metal near the surface of the MSR 20. Each target point was determined as previously described.

[0140] Figure 7B yes Figure 7A A cross-sectional view of the fifth coil disk 5. The coil trace path 70 is shown recessed into the plane of the support panel 71. The support panel 71 is made of plastic or wood.

[0141] In some embodiments, the support panel may be formed of a suitable material such that the support panel provides passive shielding.

[0142] The unit coil windings of coil trace path 70 are typically recessed to a depth of 3 mm and remain visible on the first plane of support panel 71. Each successive winding is offset 2 mm from the previous winding, and the diameter of each trace in trace path 70 is typically 1.5 mm.

[0143] Figure 7C yes Figure 7A A partial cross-sectional view of the coil routing path 70 of the fifth coil disk 5 shows the coil routing path 70 and its associated connections. The coil routing path 70 is formed by a single winding arranged around the periphery of the plane of the support panel 71, such that each successive winding is adjacent to a previous repetition. In this embodiment, the coil routing path 70 consists of 20 windings extending between coil terminals 74 and 76.

[0144] The coil bridging portion 77 extends between the coil terminal 74 and the coil terminal 76. The external connector 75 connects both the coil terminal 36 and the coil bridging portion 77 to an external current source, which is connected via the coil bridging connector 78.

[0145] An external current source is arranged to provide a set of current values, such that the coils of coil trace path 70 generate arbitrary vector magnetic field patterns according to the current applied to each unit coil.

[0146] Figure 7D yes Figure 7C The second plan view shows the coil connections of the fifth coil disk 5. Coil terminals 74, 76, coil bridging portion 77, coil bridging connector 78, and external connector 75 are located on a second plane of the support panel 71 opposite to the first plane. The coil trace path 70 is located on the first plane, so only components located on the second plane of the support panel 71 are visible and / or accessible. In embodiments where the coil trace path 70 is located on the plane of the support panel 71 visible from within the offset volume 25 of the magnetic shielding chamber 20, the coil terminals 74, 76, coil bridging portion 77, coil bridging connector 78, and external connector 75 are located on the same plane as the coil trace path 70.

[0147] Figure 8A This is a plan view of the sixth coil disk 6 according to the present invention. The coil disk 6 is shown in plan view. The coil trace path 80 is fixed to a first plane of the support panel 81. The coil trace path 80 extends in a rectangular shape near the periphery of the plane of the support panel 81 to fit within the surface area of ​​the panel, which in this embodiment is also rectangular. The support panel 81 has a panel side width 82 that is shorter than the panel side length 83. Therefore, the portion of the coil trace path 80 extending near the panel side length 83 extends a longer length than the portion of the coil trace path 80 extending near the panel side width 82.

[0148] The coil trace path 80 extends along the first panel side width 82, the first panel side length 83, the second panel side width 82, and the second panel side length 83 to form a rectangular coverage area. The coil trace path 80 is either a single part or multiple connected parts forming a continuous winding formed by a single trace, which is repeatedly wound to form coils of adjacent parts.

[0149] The coil disk 6 is mounted such that the trace path 80 is adjacent to the surface of the MSR 20 and is shielded by the panel 81 when viewed from within the offset volume 25. In some embodiments, the trace path 80 is embedded in the surface of the MSR 20. However, the coil disk 6 may also be arranged such that the trace path 80 is exposed and faces the offset volume 25.

[0150] The relevant coil parameters are determined. In this embodiment, the coil parameters are the side width 82 and side length 83 of each coil trace path 80, the regular spacing between the coil center 89 and the centers of adjacent coils, and the distance between the center of the 2x2 grid arranged in three planes and the center of each surface. For a given set of coil parameters, the magnetic field generated by a unit applied current in each coil on the regular grid spanning the "target point" of the offset volume 25 is calculated.

[0151] Figure 8B yes Figure 8A A cross-sectional view of the second coil disc, wherein the support panel 81 is shown in cross-section. The coil trace path 80 is shown as recessed into the plane of the support panel 81. The windings of the coil trace path 80 are generally recessed into the surface of the support panel 81 and remain visible on its first plane. In a coil trace path with a single layer, each successive winding is offset from the previous winding.

[0152] Figure 8C yes Figure 8A A partial cross-sectional view of the coil routing path 80 of the sixth coil disk 6 shows the coil routing path 80 and related connections. The coil routing path 80 is formed by a single winding arranged around the planar periphery of the support panel 81, such that each successive winding is adjacent to the previous one. In this embodiment, the coil routing path 80 consists of 20 windings extending between coil terminals 84 and 86.

[0153] A coil bridging portion 87 extends between coil terminals 84 and 86. An external connector 85 connects both coil terminals 86 and coil bridging portion 87 to an external current source. Coil bridging portion 87 is connected to external connector 85 via coil bridging connector 88.

[0154] Figure 8D yes Figure 8CThe second plan view shows the coil connections of the sixth coil disc, namely coil disc 6. Coil terminals 84 and 86, coil bridging portion 87, coil bridging connector 88, and external connector 85 are located on the second plane of the support panel 81 opposite to the first plane. The coil trace path 80 is located on the first plane, so only the components located on the second plane of the support panel 81 are visible and / or accessible.

[0155] Figure 9A This is a plan view of the seventh coil disk 7 according to the present invention. The coil disk 7 is shown in plan view. The coil trace path 90 is fixed to a first plane of the support panel 91. The coil trace path 90 extends in a square around the periphery of the plane of the support panel 91 to be mounted in the surface area of ​​the panel, which is also a regular quadrilateral in this embodiment. The coil trace path 90 extends along each substantially equal panel side length 92, 93. The coil trace path 90 is either a single part or multiple parts connected to form a continuous winding formed by a single trace, which is repeatedly wound to form coils of adjacent parts.

[0156] The coil disk 7 is arranged such that the trace path 90 is adjacent to the surface of the MSR 20 and is shielded by the panel 91 when viewed from the offset volume 25. In some embodiments, the trace path 90 is embedded in the surface of the MSR 20. However, the coil disk 7 may also be arranged such that the trace path 90 is exposed and faces the offset volume 25. In some embodiments, the surface of the support panel 91 may be covered to protect or simply shield the unit coil.

[0157] Certain coil parameters are determined; in this embodiment, these parameters are the symmetrical side lengths 92 and 93 of each coil square 90, the regular spacing between coil centers 99, and the distance from the center of each MSR surface to the center of the 2x2 grid. For a given set of coil parameters, the magnetic field generated by a unit applied current in each coil across a regular grid spanning the “target point” of interest is calculated. The magnetic field calculation can incorporate data related to mu-metal interactions near the MSR 20 surface.

[0158] Figure 9B yes Figure 9A A cross-sectional view of the seventh coil disk 7. The coil trace path 90 is shown recessed into the plane of the support panel 91. The support panel 91 is formed of a non-metallic material. However, in some embodiments, the support panel may be formed of a suitable material such that the support panel provides passive shielding.

[0159] The unit coil windings of the coil trace path 90 are typically recessed to a depth of 3 mm and remain visible on the first plane of the support panel 91. Each successive winding is offset 2 mm from the previous winding, and each conductor 90 of the trace path is typically 1.5 mm in diameter.

[0160] Figure 9C yes Figure 9A A partial cross-sectional view of the coil routing path 90 of the seventh coil disk 7 shows the coil routing path 90 and associated connections. The coil routing path 90 is formed by a single winding arranged around the planar periphery of the support panel 91, such that each successive winding is adjacent to a previous repetition. In this embodiment, the coil routing path 90 consists of 20 windings extending between coil terminals 94 and 96.

[0161] A coil bridging portion 97 extends between coil terminals 94 and 96. An external connector 95 connects both coil terminals 96 and coil bridging portion 97 to an external current source, which is connected via a coil bridging connector 98.

[0162] An external current source is set to provide a set of current values, such that the coils of coil trace path 90 generate arbitrary vector magnetic field patterns according to the current applied to each unit coil.

[0163] Figure 9D yes Figure 9C The second plan view shows the coil connections of the seventh coil disk 7. Coil terminals 94, 96, coil bridging portions 97, coil bridging connectors 98, and external connectors 95 are located on a second plane of the support panel 91 opposite to the first plane. The coil trace path 90 is located on the first plane, so only components located on the second plane of the support panel 91 are visible and / or accessible. In embodiments where the coil trace path 90 is located on the plane of the support panel 91 visible from within the offset volume 25 of the magnetic shielding chamber 20, the coil terminals 94, 96, coil bridging portions 97, coil bridging connectors 98, and external connectors 95 are located on the same plane as the coil trace path 90.

[0164] Support panel 91 is used for the floor surface of MSR 20. Typically, the subfloor is formed from the building foundation and has a mu-metal and conductive layer. Support panel 91 is usually covered by the finished floor covering. Support panel 91 has recesses therein to receive multiple layers of bolts or other fasteners that can extend through the floor, thereby connecting the finished floor covering to the building foundation.

[0165] Figure 10This is a circuit diagram of an active magnetic shielding system according to the present invention. In the exemplary window coil system 1000, a sensor array 1001 is placed near the unit coil 1007. In this embodiment, the sensor array 1001 includes sensors 1002 and 1003 and is arranged in the center within an enclosure 1008 defining a counteracting volume.

[0166] The sensor can be located anywhere within the coil enclosure because the windowed coil adapts to changes in position. The location will be selected based on the size of the volume to be shielded and the complexity of the measured field. Typically, three or more measurements of the full vector of the magnetic field are required, which can be done by measuring individual components of the magnetic field vector using three triaxial magnetic field detectors or nine magnetic field detectors.

[0167] Sensor array 1001 is arranged to provide magnetic field measurements 1004, which are processed by algorithm 1005 to determine current output from at least one current source 1006. The current output is fed to unit coil 1007 to generate active magnetic shielding in enclosure 1008, which in some embodiments will be formed by passive magnetic shielding.

[0168] Active magnetic shielding is generated by providing an array of magnetic field elements as described herein, each magnetic field element including a unit coil 1007, each unit coil including a wiring path as described herein. A set of coil parameters is specified in each unit coil 1007 to which current is applied by a current source 1006 to correspond to a target point grid spanning a target volume of enclosure 1008. The magnetic field per unit current generated by each unit coil 1007 at each target point is calculated. The calculated magnetic field per unit current is mapped to the target magnetic field, and the optimal coil current for each unit coil is determined.

[0169] In a preferred embodiment, the target magnetic field is derived from the magnetic field measurement value 1004 provided by sensors 1002 and 1003 of the sensor array 1001. The generated magnetic field is compared with the target magnetic field.

[0170] However, the desired target magnetic field can be a predetermined field, or it can be based on sensing data from magnetic field sensors 1002 and 1003.

[0171] In a preferred embodiment, the optimal coil current is determined by minimizing the sum of the current values ​​and applying a threshold to limit the maximum value of the applied current. The magnetic field per unit current generated by each unit coil 1007 in each magnetic field sensor 1002, 1003 is calculated using its known target point location.

[0172] The magnetic field per unit current generated by each unit coil 1007 at each magnetic field sensor 1002, 1003 is measured by sequentially applying a known current to each coil.

[0173] The coil parameters in each unit coil 1007 are based on the unit coil geometry and the offset between unit coils. The coil parameters in each unit coil can be changed according to a comparison between the generated active magnetic field and the target magnetic field.

[0174] If the generated magnetic field is compared with the target magnetic field and the result does not meet the required threshold, the coil parameters can be changed to generate a modified magnetic field, which is then compared with the target magnetic field. If the mismatch between the modified magnetic field and the target magnetic field exceeds the threshold, the process can be repeated until the generated magnetic field matches the target magnetic field and falls within the preferred range or the threshold.

[0175] The goal of coil current optimization is to minimize the total power consumed by the system by keeping the sum of the current values ​​as low as possible. A threshold is set to determine the maximum applied current and ensure that the window coil array operates with a physically feasible power supply.

[0176] Following this constrained optimization, the quality of the solution is evaluated based on the accuracy of the simulation system. In this embodiment, the coil parameters are the side length of the square, the offset between the coil centers, and the offset of the grid center; these parameters are varied until an optimal set of parameters is found based on the desired target magnetic field.

[0177] The goal is to generate many different target magnetic fields at each target point. This optimization is repeated to find a set of coil parameters that produce field components in all areas requiring shielding. In a preferred embodiment, at least eight field components are generated: three uniform fields and five field gradients.

[0178] Traditional coil routing is designed to generate a single, known magnetic field component, i.e., a magnetic field in the x, y, or z direction. In the invention disclosed herein, a set of current values ​​required to generate an arbitrary vector magnetic field pattern within the coil is calculated and applied. The windowed coil system essentially “redesigns” itself to generate different magnetic fields. The flexibility offered by the windowed coil system allows the shielding volume to be located anywhere within the MSR and can be dynamically updated to compensate for changing external disturbances or to “track” participants as they move around the MSR. This is impossible with conventional systems capable of generating fixed field patterns without physically transforming the coils.

[0179] A system based on an optically pumped magnetometer (OPM) array can be used to monitor participants located in the MSR 20, who typically wear the system for anatomical scans of the subject's head. These magnetic field sensors record biomagnetic signals without the need for cryogenic cooling. Each OPM sensor contains a glass unit containing 87Rb vapor heated to approximately 150 °C. Atoms are spin-polarized using a 795 nm laser beam, and the light intensity passing through the unit is detected using a photodiode. Under zero magnetic field conditions, the spin magnetic moments are aligned with the laser beam, maximizing laser transmission. The presence of a magnetic field perpendicular to the beam causes a significant decrease in light transmission, thus requiring additional shielding in the conventional MSR 20. The OPM sensors exhibit noise levels comparable to SQUID and a dynamic range of ±5 nT.

[0180] The operation of the shielding system of this invention requires a magnetic field sensor array, a controllable current source for each coil in the array, and a feedback algorithm to calculate the optimal current. Data collected from the magnetic field sensor array is used to determine the current applied to each magnetic field element to produce the desired magnetic field output.

[0181] In practice, the magnetic field per unit current generated by each coil at each magnetic field element can be calculated using its known location within the MSR, or measured by sequentially applying a known current to each coil. The resulting magnetic field value per unit current can then be used to obtain the coil current that produces the desired response at each magnetic field sensor. Example responses include driving all outputs to zero for magnetic shielding, but the same method can also generate a known magnetic field on the array. This ability to generate a known magnetic field on the array is particularly useful for experiments studying how a system interacts with a magnetic field or in techniques such as magnetic resonance imaging (MRI).

[0182] Current calculation methods can be configured to take into account interference in the form of interaction with passive shielding materials to improve shielding quality. The number, shape, size, and position of the coils can be optimized for each enclosure or space to be shielded to ensure good cancellation within the cancellation volume of the relevant size and shape, unlike traditional systems that can only produce fixed magnetic field patterns.

[0183] The device disclosed herein can reduce the magnetic field in a volume equivalent to the average head size within an MSR from ~5 nT to <0.2 nT, thus providing an ultra-low magnetic field environment suitable for OPM-MEG applications. Therefore, this system increases the reduction of the Earth's magnetic field within a conventional MEGMSR from the usual 10,000-fold to 250,000-fold. This reduction will allow OPM-MEG to be used for neuroscience applications, where multiple subjects can be scanned simultaneously and real-time face-to-face interactions between adults or between parents and children can be tracked, as well as for research on space navigation.

[0184] Clinical applications include, for example, long-term monitoring of epileptic activity, where keeping the subject stationary in traditional systems is impractical and uncomfortable. When a magnetic field sensor rotates or translates, it measures changes in the magnetic field equivalent to the magnitude of the field in which it operates. This data does not contain brain information and is therefore undesirable. The system described in this paper reduces the magnetic field, thus reducing the size of unwanted artifacts in the data and allowing for the movement of larger objects without signal loss.

[0185] Figure 11 Another embodiment of the window coil system according to the present invention is shown, and a schematic diagram of a matrix-configured window coil system is also shown.

[0186] A magnetic shielding chamber 20 is provided to form a passive shield as previously described herein. An active magnetic shield, disposed within the passive shield 20 to make the residual magnetic field within the passive shielding space zero, comprises a plurality of coil disks on which wiring paths are provided, as previously described.

[0187] The first set of coil traces, 1100 and 1110, is placed on wall 26. The second set of coil traces, 1120 and 1130, is placed on wall 21. Wall 21 and wall 26 are arranged opposite and parallel to each other to define the opposite sides of the canceling volume 25. The two sets of coil traces, 1100, 1110, 1120, and 1130, form an active magnetic shield within the passive shielding chamber 20.

[0188] The first group of coil trace paths 1100 includes four rows of four trace paths 1100A, 1100B, 1100C, and 1100D. Each coil trace path in the first group of coil trace paths 1100 is arranged according to a previous embodiment of the window coil described with respect to Figures 2 to 10, wherein the coils are arranged in a grid pattern in a single plane. The coils are arranged to be adjacent to each other in both the vertical and horizontal directions.

[0189] The first set of overlapping coils 1120 includes eight coils arranged such that each of the eight coils covers the central intersection of a 2×2 coil grid fixed to the wall 26 by the first coil trace path 1100. Although the coils are arranged in a biplane arrangement, unlike the Helmholtz coil system, the presence of overlapping coils results in the generation of a magnetic field in the x, y, and z planes.

[0190] Similarly, the second set of coil routing paths 1120 includes four rows of four routing paths 1120A, 1120B, 1120C, and 1120D. Each coil routing path in the second set of coil routing paths 1120 is arranged in a grid pattern in a single plane. The coils are arranged to be adjacent to each other in both the vertical and horizontal directions. The second set of overlapping coils 1130 includes eight coils, which are arranged such that each of the eight coils covers the center intersection of the 2×2 grid of coils of the second coil routing path 1120 fixed to the wall 26.

[0191] The specific arrangement of the active magnetic shielding system in this embodiment is as follows: Figure 11 As shown.

[0192] Data acquisition unit 1170 is arranged to receive sensor data from OPM sensor control unit 1160. Data acquisition unit 1170 typically includes software that allows the measurement and / or control of electrical or physical parameters (e.g., voltage, current, temperature, pressure, and sound) utilized or detected by sensor array 1001. In this embodiment, the data acquisition unit includes a computer processor having programmable software arranged to receive information from sensors, and signal conditioning elements.

[0193] In the preferred embodiments disclosed herein, each OPM sensor is preferably a small integrated unit comprising a heated glass unit containing rubidium atom vapor, a 795 nm wavelength diode laser tuned to the D1 transition of rubidium, and a photodetector. After light pumping, rubidium atoms are insensitive to photons of polarized laser light in a zero magnetic field. Therefore, the intensity of light reaching the photodetector through this unit is maximized. Since photons are absorbed by the atoms, changes in the magnetic field passing through this unit result in a decrease in the measured laser intensity. Therefore, the photodetector signal can be used as a sensitive measurement of the magnetic field. OPM measurements are typically performed on two mutually tangential planes. However, other suitable known vector magnetic field sensors can also be used.

[0194] Data from sensor array 1001 is used to drive the zeroing process of the matrix coil magnetic field before MEG recording begins. Optical tracking records the participant's movement during MEG recording. The positions of the sensor array 1001 at the first set of target points 1140 and the second set of target points 1150 provide data on the position and status of the sensors during measurement. A single cluster of target points can be used, or multiple clusters of target points can be used, each providing a discrete set of measurements related to the object or participant to which they are attached. Data acquisition unit 1170 provides data to control PC 1180 and coil amplifier 1190.

[0195] The data acquisition unit 1170 receives information about stimulus triggering from the stimulation PC 1200, and the stimulation PC 1200 provides data to the participant via auditory instructions transmitted through the speaker 1220.

[0196] The stimulation PC 1200 provides and receives data from the motion capture system 1210, which records the physical movements of the participant within the offset volume 25. The participant can be located anywhere within the offset volume 25. In this embodiment, the "Optitrack" system is used, but other known systems of this kind that capture all types of human motion can also be used. The motion capture system 1210 captures rigid body motion, including subtle and rapid movements. Body motion is captured using visible markers attached to the body, typically at least three in total, visible to the motion capture system 1210. Facial movements, muscle movements, and skeletal movements can be tracked. The location and number of markers will be selected based on the experimental procedure performed and the stimuli chosen.

[0197] Each unit coil 1100, 1110, 1120, 1130 is connected to a single output of a 48-channel low-noise voltage amplifier, as shown in coil amplifier 1190 in Figure 11. The number of channels matches the number of coils present in the array. Coil amplifier 1190 interfaces with a digital-to-analog converter in data acquisition unit 1170.

[0198] In this embodiment, the voltage applied at the amplifier input ranges from ±10 V. The maximum current in each coil is tuned by an additional series resistor, chosen to be 1.2 kΩ, thereby reducing the magnetic field noise generated by the coils below the low noise threshold of the OPM sensor array 1001. The OPM low noise threshold is typically 15 fT / √Hz over the selected frequency range. The coil driver current noise at this resistor is less than 10 nA / √Hz in the 1–100 Hz band, which translates to a field noise of less than 0.1 fT / √Hz, simulated from the sum of the squared vector field components from each coil, substantially centered on the two wall planes 21, 26.

[0199] The MSR 20 of this exemplary experimental setup comprises four layers of mu-metal, one layer of copper, and multiple demagnetizing coils. A typical residual magnetic field and gradient, on the order of 2 nT and 2 nT / m, are located at the center of the magnetically shielded chamber 20.

[0200] A 48-coil dual-plane matrix coil system is provided, wherein 24 coils are formed by a first set of coil trace paths 1100 and a first set of overlapping coils 1110 on wall 21, and another 24 coils are formed by a second set of coil trace paths 1120 and a second set of overlapping coils 1130 on wall 26.

[0201] In an exemplary experimental protocol, the effectiveness of the matrix coil system and its impact on the background magnetic field and the quality of the resulting data are evaluated by performing biomagnetic measurements on two participants playing a simple ball game. In this exemplary protocol, the first and second participants are placed within a counteracting volume 25 between the walls 21 and 26 of a magnetically shielded chamber 20. A first target point array 1140, formed by sensor array 1101, is fixed to one participant, and a second target point array 1150, also formed by sensor array 1101, is fixed to the other participant. Each of the target point arrays 1140 and 1150 comprises an array of twelve OPM sensors arranged to capture magnetoencephalography (MEG) data. The location of the OPMs is selected based on the desired measurement and the basic anatomy of the participants. In other preferred embodiments, each participant may be supported by an array of sixteen OPMs placed on a specific anatomical structure (e.g., the left sensoromotor cortex) or evenly distributed across the entire head. The number and location of the sensors can vary depending on the nature of the data collected and / or the MEG target, as well as the arrangement and size of the observed objects / participants.

[0202] Each participant is equipped with a wearable magnetoencephalography (MEG) device including a sensor array 1001 to record electrophysiological data from the brain. High-precision control of the background magnetic field allows one or more participants to be scanned simultaneously, enabling free movement and individual scanning of each participant within the same cancellation space. Therefore, it eliminates the need to confine two participants in a single machine, or in separate machines connected electronically. Regarding the window coil arrangement described in Figures 2 through 10, the unit coils generate a 3D vector magnetic field pattern that can be adjusted or defined within the cancellation volume according to zeroing requirements. In embodiments where the window coil array is arranged without overlapping coils, the coils need to be placed on all six faces of the cubic cancellation volume. The target point group defined by the sensor array can be located anywhere within the shielding volume 25, allowing the scanned object or participant to move with the shielding space even with more than one observation, thus allowing simultaneous multi-person scans.

[0203] The current in each of the 48 coil traces is individually controlled to generate the required magnetic field to counteract the residual magnetic field inside the MSR20 at the locations of each target sensor array 1140, 1150.

[0204] A current distribution of -8 to +9 mA was used during the exemplary two-person ball game. The strength of the DC field was reported by 48 total magnetic field measurements from sensor arrays 1140 and 1150 arranged for each participant.

[0205] Although OPM sensors typically have an "on-sensor" coil to compensate for local static magnetic fields up to ±50 nT, any subsequent movement of the OPM relative to the background magnetic field will cause a change in the measured magnetic field for data measured relative to this offset within a narrow dynamic range of approximately ±5 nT. This can result in a magnetic field offset greater than 5 nT saturating the sensor output, making data collection impossible; variations in sensor gain can lead to significant inaccuracies in the measurement data; and / or rotating the sensor in the magnetic field or translating the sensor in the magnetic field gradient can cause artifacts that interfere with brain activity measurements.

[0206] When the residual magnetic field is not compensated, due to significant artifacts in the magnetoencephalography data, biomagnetic activity in the sensorimotor regions of each participant is recorded and correlated with stimulation instructions from the stimulation PC 1200 and data from the motion capture system 1210 under active shielding initiated by the coil wiring path.

[0207] During the experiment, a motion capture system 1210 was used to track the participants' movements. This system consisted of two cameras, each with an array of 15 infrared LEDs illuminating infrared reflective markers. The combined coordinates of multiple markers were used for participant body tracking with six degrees of freedom (x, y, and z translation, pitch, yaw, and roll rotation).

[0208] "Hyperscanning" provides a method for simultaneously assessing the brain function of two interacting individuals. Current techniques are severely limited by performance or unnatural scanning environments, but natural hyperscanning is possible by providing an overlapping matrix of window coils as described herein. Unlike previous active magnetic shielding systems (e.g., Helmholtz coil arrangements using two planes to generate a single field vector), this matrix window coil arrangement allows for precise magnetic field control anywhere within the cancellation volume surrounded by the coil array. By positioning two spatially separated zero-field regions on the OPM sensor arrays worn by the interacting subjects, the environment required to collect high-quality MEG data in two-person experiments can be achieved. Using a matrix coil system at the locations of the first sensor array 1140 and the second sensor array 1150 allows for zero residual magnetic field within the cancellation volume.

[0209] Figure 12 This is a plan view of one of two window coil disks arranged in a matrix configuration according to another embodiment of the window coil. According to the arrangement disclosed in Figure 11, the coil paths are arranged on both surfaces of the MSR 20, but arranged to produce a 3D vector pattern.

[0210] The active shielding in this embodiment includes two planes, each containing twenty-five individually controllable square "window" coils, instead of... Figure 11 The embodiment comprises twenty-four coils. Overlapping coils 1110, 1130 are arranged in a 3×3 grid such that each of the overlapping coils 1110, 1130 overlaps with a portion of four window coils 110, 1120, the window coils being substantially as described above. Figure 11 Arranged as described.

[0211] The magnetic fields generated by the coils are superimposed, with each coil carrying an independently controllable current, thus enabling the generation of arbitrary magnetic field variations in a 3D vector pattern within (multiple) selected target volumes. Simply put, overlapping coils can cancel the magnetic field generated by the bottom window coils arranged in a 4x4 matrix. Therefore, finer control over directional cancellation can be achieved in the resulting pattern, specifically the resolution of the magnetic fields generated by the coil trace paths 1100, 1120 and the overlapping trace paths 1110, 1130. This results in a finer resolution. The overlapping coil layout can generate off-axis vector components, making 3D vector cancellation possible.

[0212] In this exemplary embodiment, a small shield is described, wherein each coil has a square side length of 38 cm and is formed of ten turns of copper wire. Non-overlapping window coils are arranged in a regular 4×4 grid, i.e., coil routing paths 1100 and 1120, wound onto each surface 26 and 21, respectively. Overlapping coils 1110 and 1130 are applied to each surface 26 and 21, respectively. The coil planes are spaced 150 cm apart and positioned such that the center of the coil array is 130 cm above the floor, and the array spans a height range of 50 to 210 cm to accommodate a selected range of adult participants.

[0213] An embodiment of overlapping unit coils is provided in MSR 20 (such as...) Figure 11 and 12 In the example shown, it is not necessary to place the coils on all six surfaces of the cubic shielding volume 25. However, providing an overlapping coil array on all six faces of the cuboid MSR 20 can produce more types of magnetic shielding.

[0214] The modular nature of the window coil structure simplifies the design and construction compared to the complex wiring required by distributed coil systems. Whether the window coil structure includes adjacent coils or a combination of adjacent and overlapping coils, the complexity shifts from the coils themselves to the coil amplifier and the magnetic field control system. The data-driven magnetic field cancellation method adapts to any location of the sensor array within the 25-volume cancellation volume, coil layout, and magnetic field distortion caused by the presence of mu-metal in the passive shield. Therefore, the MSR 20 is not limited to a specific shape.

[0215] The residual magnetic field (projected along their vertical and horizontal axes) experienced by each sensor in sensor array 1001 within MSR 20 is measured together with the magnetic field per unit current generated at each of the 48 matrix coils contained in the calibration matrix. The coil current that will optimally make the magnetic field experienced by the OPM array zero is calculated.

[0216] To ensure the residual magnetic field within the MSR is zero during magnetoencephalography (MEG) experiments, the following equation is used. If the magnetic field measured by the nth OPM in an array of N sensors is due to a unit current in the mth coil of a set of M (= 48) matrix coils, it is written as... We can form an (N x M) coil calibration matrix A using all values. Then, the magnetic field zeroing problem can be described using the following matrix equation:

[0217]

[0218]

[0219] The (M x 1) column vector x contains the current applied to each coil, while the (N x 1) column vector b represents the magnetic field to be canceled. b is formed using the DC field value measured at the sensor, and the negative sign is used to ensure that the calculated current makes the magnetic field measured by the array zero.

[0220] By identifying the negative value of the Moore-Penrose pseudo-inverse matrix of A, the optimal coil current required to minimize the sum of squares of the measured magnetic field values ​​can be determined:

[0221] To minimize the system's power consumption and ensure the solution is physically feasible, the matrix can be padded with matrix αI before inversion. Perform regularization, where I is the expression with respect to... α is the regularization parameter:

[0222] To keep the coil current within allowable limits, the latter equation is transformed into a feedforward controller with the required current at each time point i, where i is related to the current applied at the previous time point and the magnetic field measured at the current time point:

[0223]

[0224] The gain factor G is set empirically to steadily reduce the measurement field to zero over a time span of a few seconds.

[0225] The system can therefore adapt to variations in the number and shape of the unit coils and flexibly include multiple sensor arrays 1001, each representing a participant in the offset volume 25.

[0226] The coil calibration data used to fill matrix A can be collected in a variety of ways, depending on the available sensing technology, such as by applying pulses to each coil sequentially or by applying a known sinusoidal current to each coil. Values ​​can also be calculated based on known sensor locations, coil designs, and the geometry of the MSR 20.

[0227] Participants are typically required to remain still during the zeroing process while a 5V (4.16mA) 100ms pulse is applied sequentially to each coil. The zeroing volume can be placed anywhere between the coils, meaning the experiment can be conducted with a single subject standing, sitting, or with multiple subjects. The inventors have found that, for a given participant, zeroing can reduce the average background magnetic field by 6 to 10 times.

[0228] The time required for the calibration process is proportional to the number of coils; for a system with 48 coils, the calibration process takes approximately one minute. The magnetic field value reported by each sensor before calibration is stored along with the coil calibration matrix, the final voltage applied to each coil, and the final magnetic field value.

[0229] This invention can be applied to other applications requiring magnetic shielding or other forms of magnetic field control. Beyond diagnostics and medical imaging, the devices disclosed herein can be combined with scanners for virtual reality experiences.

[0230] It is understood, of course, that many variations can be made to the above embodiments without departing from the scope of the invention. For example, a cylindrical shield can be used instead of the cuboid shape described herein. In this case, a suitable coordinate system will be used instead of the standard 3-plane coordinate system.

Claims

1. An active magnetic shielding system, comprising: An array of magnetic field sensors arranged to sense local magnetic fields. An array of magnetic field elements arranged to generate a magnetic field from -20 nT to +20 nT. Each magnetic field element includes a unit coil for mounting to one of a plurality of surfaces selected from at least three planes. Each unit coil includes coil traces arranged to generate a vector magnetic field pattern. The array of magnetic field elements includes a first set of unit coils and a second set of unit coils, wherein the first set of unit coils is arranged on a first plane, and the second set of unit coils is arranged on a second plane spaced apart from and opposite to the first plane, defining a cancellation volume between the two. The first set of unit coils includes a first plurality of unit coils arranged in a 2×2 grid on the first plane, and at least one further unit coil overlapping the first plurality of unit coils; as well as The second set of unit coils includes a second plurality of unit coils arranged in a 2×2 grid on the second plane, and at least one further unit coil overlapping the second plurality of unit coils; A current source is arranged to provide controlled current to each unit coil, and A processor configured to execute a feedback algorithm to control the current source of each unit coil in order to minimize the sensed local magnetic field; The at least one further unit coil of the first group of unit coils is arranged such that its coils cover the intersection point defined by the 2×2 arrangement of the first plurality of unit coils.

2. The active magnetic shielding system according to claim 1, wherein, The at least one further unit coil of the second group of unit coils is arranged such that its coil covers the intersection point defined by the 2×2 arrangement of the second plurality of unit coils.

3. The active magnetic shielding system according to claim 1, wherein, The unit coils are arranged on 4 to 6 planes to define a closed offset volume.

4. The active magnetic shielding system according to claim 1 further includes a passive magnetic shield, wherein the passive magnetic shield is arranged as an array supporting the magnetic field element.

5. The active magnetic shielding system according to claim 4, wherein, The passive magnetic shielding comprises at least a first layer formed of a high magnetic permeability material and another layer formed of a high electrical conductivity material.

6. The active magnetic shielding system according to claim 4, wherein, The passive magnetic shielding includes a magnetic shielding chamber (MSR), wherein an array of magnetic field elements is placed on or within each wall of the MSR.

7. The active magnetic shielding system according to claim 1, wherein, The vector magnetic field pattern has an order of magnitude of 5nT or smaller.

8. The active magnetic shielding system according to claim 1, wherein, Each unit coil is a square coil.

9. The active magnetic shielding system according to claim 1, used in magnetoencephalography (MEG).

10. The active magnetic shielding system according to claim 1, wherein, The first plurality of unit coils comprises an array of sixteen unit coils, and the at least one further unit coil of the first set of overlapping unit coils comprises up to nine overlapping coils.

11. The active magnetic shielding system according to claim 10, wherein, The second plurality of unit coils comprises an array of sixteen unit coils, and the at least one further unit coil of the second set of unit coils comprising up to nine overlapping coils.

12. The active magnetic shielding system according to claim 1, wherein, The overlapping coils are configured to at least partially cancel the magnetic field generated by the cell coils of the underlying grid, thereby allowing the generation of an off-axis magnetic field component, wherein the axis is defined as a direction perpendicular to the first and second planes.

13. The active magnetic shielding system according to claim 1, wherein, The overlapping coils cover the center intersection defined by the 2×2 arrangement of the lower unit coils.

14. The active magnetic shielding system according to claim 1, wherein, The first plane and the second plane are 150 cm apart.

15. A method for generating active magnetic shielding, the method comprising: A magnetic field is generated in the following ways: An array of magnetic field elements is provided, each magnetic field element including a unit coil, the array including a first set of unit coils and a second set of unit coils, wherein the first set of unit coils is arranged on a first plane, the second set of unit coils is arranged on a second plane spaced apart from and opposite to the first plane, defining a canceling volume between the two, the first set of unit coils including a first plurality of unit coils arranged in at least a 2×2 grid on the first plane, and at least one further unit coil overlapping the first plurality of unit coils; Furthermore, the second set of unit coils includes a second plurality of unit coils arranged in a 2×2 grid on the second plane, and at least one further unit coil overlapping the second plurality of unit coils; Specify a set of coil parameters for each cell coil, and apply current to each cell coil on the target point grid spanning the target volume. Calculate the magnetic field per unit current generated by each unit coil at each target point. Map the calculated magnetic field per unit current to the target magnetic field. Determine the optimal coil current for each unit coil, and The generated magnetic field is compared with the target magnetic field.

16. The method for generating active magnetic shielding according to claim 15, wherein the optimal coil current is determined by minimizing the sum of current values ​​and applying a threshold that defines the maximum value of the applied current.

17. The method for generating active magnetic shielding according to claim 15, wherein, The magnetic field per unit current generated by each coil at each magnetic field sensor is calculated using its known target point location.

18. The method for generating active magnetic shielding according to any one of claims 15, wherein the magnetic field per unit current generated by each coil at each magnetic field sensor is measured by sequentially applying a known current to each coil.

19. The method for generating active magnetic shielding according to claim 15, wherein, The coil parameters in each unit coil are based on the unit coil geometry and the offset between unit coils.

20. The method for generating active magnetic shielding according to claim 15, Also includes: Based on the comparison between the generated magnetic field and the target magnetic field, the coil parameters in each unit coil are changed, and Repeat the steps of claim 15 until the generated magnetic field matches the target magnetic field.

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