Improvements in and related to zeroing out magnetic fields

Abstract

In an apparatus for zeroing a magnetic field in a zeroing region in an external surrounding magnetic field, a plurality of separate magnetic field generating elements 102 are arranged at respective separate locations surrounding the zeroing region to generate respective zeroing magnetic fields extending into the zeroing region. A plurality of magnetic field sensing elements 103 are arranged at respective separate locations within the zeroing region to sense respective values ​​of the magnetic field in the zeroing region. A feedback control unit 150 controls the value of the respective zeroing magnetic field generated by each of the plurality of magnetic field generating elements by driving the magnetic field generating elements with respective currents that reduce the value of the magnetic field detected by each magnetic field sensing element to a value not exceeding a preset threshold corresponding to a preset zeroing of the magnetic field in the zeroing region in response to the value of the magnetic field sensed by the plurality of magnetic field sensing elements.

Description

[Technical Field]

[0001] This application claims priority under International Application PCT / EP2021 / 080826, filed on 5 November 2021, and the contents and elements of said application are incorporated into this application by reference for all purposes. The present invention relates to a method and apparatus for zeroing out a magnetic field, and more particularly to a method and apparatus for zeroing out a magnetic field in the use of magnetoencephalography (MEG), but is not limited thereto. [Background technology]

[0002] Magnetoencephalography (MEG) is a well-established medical technique for mapping the electrical activity of the brain by recording the magnetic field it generates. The magnetic field produced by the brain is very weak, and detecting it requires an environment where the surrounding magnetic field is virtually absent (or negligible). Many magnetic field detection sensors used in MEG are based on superconducting quantum interference devices (SQUIDs). These devices require cooling with liquid helium, which is very expensive. One alternative sensor technology that does not require cooling and thus reduces the cost of MEG devices is the optically pumped magnetometer (OPM).

[0003] Typically, environments with virtually no (or negligible) ambient magnetic fields (for example, for using MEGs) are created using large, very expensive magnetically shielded rooms (MSRs). These rooms typically have walls, floors, and ceilings made of magnetic shielding materials. Furthermore, MSRs may have limitations that arise from the MSR itself or from the equipment within the room. MSR Some MSRs are equipped with additional systems to counteract any residual magnetic fields present within the system. Because MSRs are extremely expensive, very few facilities can afford to have MEG devices.

[0004] During MEG measurements, the MEG device cannot be moved to the patient along with the MSR (Measuring Sensorineural Restoration), so the patient must come to the MSR. Inside the MSR, preferably only non-magnetic materials should be used to reduce unwanted ambient magnetic fields. Furthermore, the MSR space is very limited and lacks windows. Therefore, the possibility of bringing in tools that can be used for patient interaction, which is important for observing brain responses, is limited. Because the MSR is a fixed structure, it is not possible to examine the patient in a different environment, such as outside the building or in an environment that provides psychological comfort. This is particularly important if the MSR environment is uncomfortable for patients with claustrophobia or frightens children.

[0005] For example, monitoring patients over extended periods, such as during sleep, is extremely difficult within MSR. Furthermore, MSR cannot be combined with other simultaneous measurements that require large equipment for other techniques. For instance, if MSR were no longer necessary, MEG and low-field MRI could be measured simultaneously.

[0006] Furthermore, within the MSR, it is unavoidable that there are some time-varying sources of magnetic fields, such as the beating heart of a patient or the power lines supplying power to the MEG equipment (e.g., computers) within the MSR. Where the MSR itself requires additional compensation for such residual internal magnetic fields, this compensation can be performed using Helmholtz coils or two-plane coils placed within the MSR.

[0007] This invention was made in view of the above matters. [Overview of the project] [Means for solving the problem]

[0008] The inventors have grasped the concepts known from the field of superdiamagnetism. Superdiamagnetism occurs in certain types of superconductors, resulting in the exclusion of the external magnetic field from the internal region, i.e., the internal magnetic field. It is known that superconductors behave as almost perfect diamagnets when placed in an external magnetic field. This is because they exclude the external magnetic field, causing its flux lines to avoid the spatial region occupied by the superconductor. This occurs because the external magnetic field generates an electric current on the surface of the superconductor, and this current, in turn, generates a reverse magnetic field. The external magnetic field and the surface-generated magnetic field cancel each other out.

[0009] The inventors have understood that information about the external magnetic field on a surface is sufficient to cancel out, or reduce to a very small or negligible value, the magnetic field in the three-dimensional space enclosed by that surface. This is supported by Stokes' theorem. Referring to Figure 1, the external magnetic field 1a passes around the diamagnetic material 1b, but does not penetrate it. The reason for this effect lies in Stokes' theorem, which relates the integral of the curl of a vector field over a surface to the line integral of the vector field around the boundary of that surface. In other words, the line integral of a vector field over a loop is equal to the bundle of curls of that vector field passing through the surface enclosed by the loop. Figure 1 schematically shows a loop C enclosing a perfectly conductive two-dimensional surface 1c. This surface is composed of continuous surface elements or facets (ΔS) each defining its own local enclosing loop (a quadrilateral loop in this example). i This can be imagined as having an array of ). Suppose this surface 1c is stretched along a spherical surface (for example, like making a balloon with chewing gum) to create a "bubble" with an opening defined by a boundary loop C, and then the size of the opening C is reduced to a diameter of zero. According to Stokes' theorem, the result is a sphere with no magnetic field inside. The inventors have decided to apply this idea to a conceptual reference plane having an array of adjacent, separate magnetic field generating elements (e.g., conductive loops). Each of the magnetic field generating elements is a surface element or facet (ΔS) of the conceptual reference plane (e.g., the aforementioned spherical bubble) that surrounds or encloses a spatial region where the surrounding magnetic field should be zeroed out. iEach of these corresponds to an individual. This conceptual reference plane can completely enclose the spatial region and can be conceptually divided into a plurality of continuous surface facets that cover the whole or at least a large portion of the conceptual plane, and the separate magnetic field generating elements can be arranged so that each is in or on one of the plurality of continuous surface facets. This results in a structure that approximates part or all of the “bubble” structure consisting of surface 1c in Figure 1.

[0010] In most general terms, the present invention is based on the idea of ​​achieving the cancellation (or zeroing) of magnetic fields in three-dimensional space in a manner similar to the principles that form the basis of super-diamagnetism. By providing an array of magnetic field generating elements surrounding a certain three-dimensional space, these Magnetic field generating By applying feedback control between the magnetic field sensing element array in the three-dimensional space and the magnetic field generating element array, the magnetic field in the three-dimensional space can be substantially canceled out (or "zeroed out") by controlling the current supplied to the magnetic field generating element as needed. In other words, the inventors have found that by achieving the cancellation (or "zeroed out") of the magnetic field in a three-dimensional space in which a magnetic field generating element array is arranged across the entire surface, indirect information about the magnetic field on the surface of the three-dimensional space can be effectively obtained. Once zeroing out is achieved, it means that the magnetic field on the surface of the three-dimensional space is counteracted by the magnetic field generating element array on the surface by an approximately equal amount across the surface.

[0011] The present invention can, for example, eliminate the need for MSR in MEG systems, providing a less expensive and more compact solution. The present invention can be applied to zeroing out / canceling magnetic fields with time-varying magnetic field gradients. The present invention can simultaneously zero out / cancele both the Earth's magnetic field and gradient magnetic fields arising from surrounding magnetic sources as well as time-varying and / or spatially moving magnetic sources.

[0012] In a first embodiment, the present invention is a device for zeroing out a magnetic field in a zeroing region located within an external magnetic field, To generate each zeroing magnetic field extending into the zeroing region, a plurality of separate magnetic field generating elements are arranged at separate locations surrounding the zeroing region, To sense each value of the magnetic field within the zeroing region, a plurality of magnetic field sensing elements are arranged at each of a plurality of separate locations within the zeroing region, A feedback control unit controls the value of each of the zeroed magnetic fields generated by each of the multiple magnetic field sensing elements by driving each of the magnetic field generating elements with a current such that the value of the magnetic field detected by each of the multiple magnetic field sensing elements is reduced to a value that does not exceed a preset threshold corresponding to a preset zeroing of the magnetic field within the zeroing region, in accordance with the value of the magnetic field sensed by the multiple magnetic field sensing elements. We can provide a device that includes the following features.

[0013] The feedback control unit can be designed to determine a set of multiple optimal currents for each of the multiple corresponding magnetic field generating elements by applying an orthogonal projection algorithm. The feedback control unit can be configured to generate a set of basis vectors used to control the value of each zeroing magnetic field generated by each of the multiple magnetic field generating elements by using the respective optimal currents. The feedback control unit can be configured to use the set of basis vectors when calculating the optimal currents for each of the magnetic field generating elements of the device. The set of basis vectors can be based on multiple measurements of the magnetic field generated individually within the zeroing region by each of the multiple magnetic field generating elements (for example, measured separately and by the multiple magnetic field sensing elements) when driven by a preset calibration current. The orthogonal projection algorithm can be designed to generate an orthogonal basis system based on the multiple measurements of the magnetic field generated individually within the zeroing region by each of the multiple magnetic field generating elements when driven by a preset calibration current.

[0014] The inventors have found that orthogonal projection can be extremely efficient and accurate when calculating the appropriate drive current to generate a magnetic field for effective zeroing / cancellation. Surprisingly, this technique requires only one calculation of the drive current value. The calculation of the drive current takes less than 250 μs, for example. This is in contrast to other techniques that require several (sometimes many) iterative calculations to find a better value of the drive current in an iterative optimization process (i.e., iterative improvement of zeroing). These iterative processes have been found to be far slower than orthogonal projection.

[0015] In this way, external magnetic fields (e.g., the Earth's magnetic field) can be zeroed out or canceled out. External gradient magnetic fields can be zeroed out or canceled out, or external time-varying magnetic fields can be zeroed out or canceled out. The present invention provides a system that can create substantially magnetic field-free conditions (or conditions with a magnetic field that can be appropriately ignored) in a large volume relative to the system size. By controlling the magnetic field generating elements with a feedback sensor (e.g., by controlling the current in a coil), the magnetic field in the zeroed-out space can be reduced by several orders of magnitude. The present invention can be applied to zeroed-out regions with complex gradient magnetic fields. Thus, the present invention can be applied to avoid the need to use a magnetic shielding room (MSR) during the use of magnetoencephalography (MEG), and / or to provide additional active zeroing. The relative volume of the zeroed-out space to the three-dimensional space enclosed by the array of magnetic field generating elements can be made larger than with other methods using MSRs or Helmholtz coils. The magnetic field in the zeroed-out region can be reduced to a very low magnetic field level with high magnetic field uniformity. For very low magnetic field levels with high magnetic field uniformity, it has been found that further improvement can be obtained simply by increasing the number of magnetic field generating elements in the array.

[0016] Preferably, the feedback control unit includes input terminals connected to respective output terminals of the magnetic field sensing element (for example, for outputting a magnetic field measurement signal), and one or more signal output terminals connected to input terminals of the associated magnetic field generating element (for example, for outputting a control signal or a drive current). For example, the one or more output terminals of the feedback control unit can be directly connected to respective input terminals of the associated magnetic field generating element. For example, each input terminal of one associated magnetic field generating element can be directly connected to one associated (for example, dedicated) output terminal of the feedback control unit, for example, such that the magnetic field generating element is the only magnetic field generating element connected to the specific output terminal of the feedback control unit. Through this connection between a given output terminal of the feedback control unit and an input terminal of one associated magnetic field generating element, each current directly utilized by the associated magnetic field generating element when generating a magnetic field necessary to reduce the value of the magnetic field detected by each magnetic field sensing element can be transmitted. Alternatively, the one or more output terminals of the feedback control unit can be indirectly connected to respective input terminals of the associated magnetic field generating elements via one or more intermediate current supply units configured to receive a current supply control signal from the feedback control unit and supply a specified current to one or more (or each) specified magnetic field generating elements in response to receiving the current control signal. The specified current and the specified magnetic field generating element can be specified in the current supply control signal.

[0017] Preferably, the feedback control unit is configured to determine, by analyzing each signal from each magnetic field sensing element, how to adjust or regulate the supply current to the associated magnetic field generating element in a direction in which the sensed magnetic field reading value from the magnetic field sensing element decreases.

[0018] The feedback control unit preferably continuously (e.g., without interruption for a given duration or intermittently) monitors the magnetic field values supplied by the magnetic field sensing elements in the null space and continuously controls each supply current to the magnetic field generating elements for correction. In this way, active magnetic field nulling can be provided.

[0019] Preferably, the plurality of magnetic field generating elements includes at least 10 separate magnetic field generating elements, more preferably at least 50 separate magnetic field generating elements, and even more preferably at least 200 separate magnetic field generating elements. Preferably, the plurality of magnetic field generating elements includes at least about 100 elements and up to about 4000 elements or up to about 3000 elements or up to about 2000 elements.

[0020] Preferably, the magnetic field generating element includes a conductive coil adapted to transmit the current. Each magnetic field generating element can be provided with one conductive coil. One coil of one magnetic field generating element can be a circular coil or a coil of other shape, such as a polygonal coil (e.g., hexagonal). One coil of one magnetic field generating element can be substantially flat or planar such that all turns of the coil are in substantially the same plane. The diameter (e.g., the diameter of the loop or turn of the coil) of each coil in the array of magnetic field generating elements can be substantially the same as the diameters of a plurality of other coils in the array of magnetic field generating elements, or the same as the diameters of every other coil in the array of magnetic field generating elements. In the case of a Dual Geodesic Icosahedron lattice, the coils located in the hexagonal parts / facets of the lattice can be made larger than the coils located in the pentagonal parts / facets of the lattice. Preferably, the array of magnetic field generating elements can include a mixture of coils of different diameters. This is preferably applicable when using a geodesic lattice. This helps to achieve a better lattice coverage. When the lattice defining the array of magnetic field generating coils is based on a Platonic solid, a good lattice coverage can be achieved using coils of the same diameter.

[0021] Alternatively, one coil of a magnetic field generating element may be configured such that all of its windings are substantially planar and parallel to the plane, but the continuous windings of the coil are distributed vertically in a direction perpendicular to the plane of the windings, with the windings of the coil arranged in a stacked manner (e.g., a spiral spiral). The degree of vertical distribution is preferably small compared to the spread of the lateral dimension of each coil. In other words, each coil is preferably "thin" to save space. The lateral dimension (e.g., diameter) of the coil windings is at least four times (e.g., four times the width relative to the thickness), more preferably at least five times, even more preferably at least seven times, and even more preferably at least ten times, the vertical dimension of the coil perpendicular to the lateral dimension.

[0022] A single coil may comprise one winding or loop made of conductive wire, track, or strip, or multiple windings or loops made of conductive wire, track, or strip. A single coil may comprise one current input terminal, one current output terminal, and one or more windings or loops electrically connecting these two terminals, wherein the current input via the input terminal flows through the winding or loop and then reaches the current output terminal. Multiple windings or loops of a single coil may share substantially identical shape, dimensions, and orientation by repeating a common loop or winding shape. Alternatively, multiple windings or loops of a single coil may define a spiral shape (e.g., a flat spiral) with a gradually increasing or decreasing spiral radius.

[0023] Preferably, each coil is configured to face toward the center or centroid of the array of magnetic field generating elements. The direction in which a coil "faces" can be considered perpendicular to the plane containing the diameter of the coil. The direction in which a coil "faces" can be considered parallel to the winding axis of the coil (i.e., the central axis around which the coil windings are wound, e.g., the axis of symmetry of the coil). Thus, the direction in which a coil "faces" can determine the direction parallel to the magnetic field generated when the coil is driven by current, passing through its center. The direction of the magnetic field can be controlled by controlling the direction of flow of a given current flowing through the coil. The direction of the current flowing through the coil can be defined, for example, by whether the current flows clockwise or counterclockwise when the coil is viewed toward the center of the array of magnetic field generating elements. For example, a given current in a given coil can be defined as "positive" when viewed from one side of the coil, and "negative" when viewed from the other side (i.e., the direction of viewing is reversed) or when the coil is rotated 180 degrees and the opposite side is presented to a stationary observer (i.e., the "surface" of the coil is reversed).

[0024] The orientation of each coil within the array of separate magnetic field generating elements is most preferably different from that of the other coils in the array, depending on the position of that coil within the array. In other words, the position of the coil within the array also determines the orientation of the coil relative to the center of gravity of the array (i.e., the direction in which the coil "points"). The direction of the current used to drive each individual coil is most preferably different from that of the other coils in the array, depending on the position of that coil within the array. In other words, the position of the coil within the array also determines the direction of the current flowing through that coil. The direction of the current in a coil can be defined with respect to the local coordinate system of that coil. The local coordinate system of each coil can be positioned or rotated with respect to the local coordinate system of the adjacent coils (or all coils) within the array of coils.

[0025] Preferably, each coil in the array of magnetic field generating elements is electrically isolated (e.g., insulated) from any other coil in the array. This allows each coil to be driven independently of any other coil, and provides very flexible control over the array of magnetic field generating elements to achieve zeroing. Adjacent coils in the array of magnetic field generating elements may overlap at least partially, or any coil in the array may be arranged so that it does not overlap with any other adjacent coil in the array.

[0026] Optionally, the coil group of the array of magnetic field generating elements may comprise multiple subgroups, each having three coils facing in three directions perpendicular to one another. For example, each direction that each coil in a subgroup faces may correspond to a local orthogonal triaxial axis (i.e., the xyz coordinate directions with the center in the middle of the subgroup). Preferably, the direction that each coil in the subgroup faces is substantially perpendicular to the direction that each of the other coils in the subgroup faces, so that no two coils in the subgroup face the same direction. This arrangement of the subgroup coils allows for additional control over the vector direction of some of the local magnetic fields within and around the region occupied by each subgroup of coils. One coil in each subgroup of coils may be configured to face toward the center or centroid of the array of magnetic field generating elements.

[0027] Preferably, the plurality of magnetic field generating elements are arranged at their respective separate locations in a first array formed along a three-dimensional reference plane surrounding the zeroing region. Preferably, the plurality of magnetic field sensing elements are arranged at their respective separate locations defining a second array formed along the three-dimensional reference plane. It should be understood that the reference plane may or may not be a physical plane. If the reference plane is a physical plane (i.e., it coincides with a physical plane), it can function as a support plane that constrains and holds the positions of the magnetic field generating elements to conform to a desired array pattern by placing (e.g., mounting) the magnetic field generating elements on it. This support plane may be a continuous plane or a framework, in the latter case, where the magnetic field generating elements are mounted at locations within the framework that coincide with the locations of the conceptual reference plane. For example, the support plane may be a spherical shell surface that coincides with a conceptual spherical reference plane. Alternatively, the support plane may comprise a three-dimensional polyhedral framework where each vertex coincides with each point on the surface of a sphere. The magnetic field generating elements can be attached to each vertex or group of vertices on this support surface, or to the edges of the framework extending between the vertices (for example, the edges of polygons that form the conceptual facets of a polyhedron).

[0028] The support surface (e.g., a continuous surface or framework) can be mounted on a rotatable support assembly that allows rotation of the support surface about at least one spatial axis, or at least two orthogonal spatial axes, or all three orthogonal spatial axes. The rotatable support assembly may include an altazimuth mount that allows independent adjustment of the azimuth and altitude indication positions of the support surface. This allows the support surface (e.g., framework) (along with all the magnetic field generating coils and magnetic field sensing elements on it) to be oriented in the opposite direction to the Earth's magnetic field vector. This helps to achieve better zeroing.

[0029] Preferably, the second arrangement (i.e., the arrangement determined by the plurality of magnetic field sensing elements) is configured to be substantially concentric with the first arrangement (i.e., the arrangement of the magnetic field generating elements). The inventors have found that this arrangement enables particularly precise and effective zeroing within the zeroing region. Each of the distinct locations in the first arrangement can be determined according to a regular grid. These locations can coincide with (or be determined by) conceptual vertices or facets of a polyhedron. Each of the distinct locations in the second arrangement can be determined according to a regular grid. Preferably, the plurality of magnetic field generating elements are arranged at each of the distinct locations that are substantially equidistant from the center of the zeroing region, thereby forming a substantially spherical arrangement surrounding the zeroing region.

[0030] Preferably, the plurality of magnetic field sensing elements are arranged at separate locations approximately equidistant from the center of the zeroing region, thereby establishing a substantially spherical arrangement within the zeroing region.

[0031] Preferably, the diameter of the array of magnetic field sensing elements is at least about 40% of the diameter of the array of magnetic field generating elements. The inventors have found that particularly effective magnetic field zeroing can be achieved when this condition is applied. Preferably, the diameter of the array of magnetic field sensing elements is between about 40% and about 90% of the diameter of the array of magnetic field generating elements. More preferably, the diameter of the array of magnetic field sensing elements is between about 40% and about 80% of the diameter of the array of magnetic field generating elements. Preferably, the diameter of the array of magnetic field sensing elements is between about 40% and about 90% of the diameter of the array of magnetic field generating elements, and the array of magnetic field generating elements comprises at least about 200 elements and no more than about 2000 elements. The inventors have found that particularly effective magnetic field zeroing can be achieved when one or more of these conditions are applied.

[0032] Preferably, the threshold is 5 × 10 -9 Tesla or less, or more preferably 5 x 10 -10 It's inferior to Tesla.

[0033] The magnetic field sensing element may comprise one or more of the following: a Hall effect sensor (e.g., for μT magnetic fields), a magnetic impedance sensor (e.g., to cover the range from μT to nT), a fluxgate sensor (e.g., to cover the range from μT to nT), or an optically pumped magnetometer (OPM) sensor (e.g., to cover the range from nT to fT). Three such sensors can be used as a single sensor feedback group with a wide sensing range.

[0034] The number of magnetic field sensing elements may be less than the number of magnetic field generating elements. The feedback control unit may be configured to generate a magnetic field value associated with one or more locations within the zeroing region by interpolation between multiple magnetic field values ​​sensed by multiple magnetic field sensing elements in an array of magnetic field sensing elements. The control unit may be configured to define a conceptual interpolation sphere determined by the radius from the target point (coordinates) within the zeroing region to which the magnetic field value should be interpolated. The control unit may be configured to determine which of the magnetic field sensing elements are located within the conceptual sphere (and to increase the radius of the sphere until at least two sensors are located within the sphere). The control unit may be configured to calculate the interpolated value of the magnetic field at the target location by three-dimensional interpolation of the magnetic field values ​​received from the multiple sensors within the interpolation sphere.

[0035] The feedback control unit can be configured to generate a set of basis vectors used to control the value of each zeroing magnetic field generated by each of the plurality of magnetic field generating elements. The feedback control unit can be configured to use the set of basis vectors when calculating the current used to drive each of the magnetic field generating elements of the device. The feedback control unit can be configured to supply current to each magnetic field generating element individually in sequence, while all other magnetic field generating elements do not receive current from the control unit. The feedback control unit can be configured to obtain measured values ​​of the magnetic field in the device sensed by each of the magnetic field sensing elements at each fixed location within the zeroing region from the magnetic field sensing elements. The feedback control unit can be configured to use these measured magnetic field values ​​as calibration values ​​to determine the basis vectors corresponding to the magnetic field generating elements to which current is supplied. The control unit can be configured to repeat this process separately for each magnetic field generating element in the coil array, so that each magnetic field generating element separately plays the role of an individual magnetic field generating element to which current is supplied. For each element in the array of m magnetic field generating elements, the control unit can be configured to create a basis vector based on the calibration magnetic field values ​​received from all n sensors. For example, the basis vector corresponding to the first coil is:

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[0036] The arrangement of the m coils and the feedback control unit are based on a basis vector matrix constructed using each basis vector corresponding to all of the m magnetic field generating elements.

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[0037] The feedback control unit, based on these unit vectors, controls each magnetic field occurrenceThe system can be designed to perform active cancellation of the surrounding magnetic field by calculating the value and direction of the drive current to be supplied to the element. The feedback control unit then calculates each measurement of the magnetic field from one magnetic field sensing element while all sensing elements are operating in the active cancellation function.

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[0038] The feedback control unit reduces the magnetic field values ​​measured by the magnetic field sensing elements, either as a whole (for example, as an average among them) or individually, so that they do not exceed a desired preset threshold corresponding to an appropriate level of magnetic field cancellation / zeroing, using the α in the above equation. j The configuration allows for changing the value of the current applied to each magnetic field generating element by changing the value of .

[0039] The feedback control unit calculates the following optimization equation with parameter α j By solving for this, we can determine the current α that must be used to drive each magnetic field generating element. j It can be designed to calculate the value of .

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[0040] The orthogonal projection algorithm directly calculates an appropriate "optimal" drive current for magnetic field cancellation as a result of solving (e.g., inverting) the above equation with respect to parameter α. It should be noted that in this sense, the term "optimization" should be understood to refer to calculating the value of parameter α that is inherently optimal due to the nature of the above equation. This is not the same as the prior art "optimization" techniques that are much less efficient iterative magnetic field minimization techniques and often require many iterations. In other words, compared to that, the orthogonal projection technique discussed in the present application can be considered to obtain what is needed immediately by simply calculating parameter α once, and there is no need to continuously perform "iterative" calculations to find a "better" value of these parameters. Shino For magnetic field cancellation, an appropriate "optimal" drive current can be directly calculated as a result of solving (e.g., inverting) the above equation with respect to parameter α. j It should be noted that it may be possible to directly calculate the appropriate "optimal" drive current for magnetic field cancellation as a result of solving (e.g., inverting) the above equation with respect to parameter α. In this sense, the term "optimization" should be understood to refer to calculating the value of parameter α that is inherently optimal due to the nature of the above equation. This is not the same as the prior art "optimization" techniques that are much less efficient iterative magnetic field minimization techniques and often require many iterations. In other words, compared to that, the orthogonal projection technique discussed in the present application can be considered to obtain what is needed immediately by simply calculating parameter α once, and there is no need to continuously perform "iterative" calculations to find a "better" value of these parameters. j It should be noted that the orthogonal projection algorithm can directly calculate an appropriate "optimal" drive current for magnetic field cancellation as a result of solving (e.g., inverting) the above equation with respect to parameter α. In this sense, the term "optimization" should be understood to refer to calculating the value of parameter α that is inherently optimal due to the nature of the above equation. This is not the same as the prior art "optimization" techniques that are much less efficient iterative magnetic field minimization techniques and often require many iterations. In other words, compared to that, the orthogonal projection technique discussed in the present application can be considered to obtain what is needed immediately by simply calculating parameter α once, and there is no need to continuously perform "iterative" calculations to find a "better" value of these parameters. j The feedback control unit can be designed to use the reading value V from the sensing element. These reading values can be arranged within a reading value matrix by the control unit (e.g., [V1, V2, V3,..., V]). The measured value of the magnetic field can include the measured values (Sx, Sy, Sz) of three orthogonal field components by each of the sensing elements. The feedback control unit can be designed to calculate the dot product of the reading value matrix and the orthogonal basis vectors of the magnetic field generating element as follows.

[0041] The feedback control unit can be designed to use the reading value V from the sensing element. magnetic field The feedback control unit can be designed to use the reading value V from the sensing element. k These reading values can be arranged within a reading value matrix by the control unit (e.g., [V1, V2, V3,..., V]). N The feedback control unit can be designed to use the reading value V from the sensing element. magnetic field The measured value of the magnetic field can include the measured values (Sx, Sy, Sz) of three orthogonal field components by each of the sensing elements. The feedback control unit can be designed to calculate the dot product of the reading value matrix and the orthogonal basis vectors of the magnetic field generating element as follows.

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[0042] In this way, multiple (e.g., three) sensor readings can be generated for each sensor position, and these correspond to multiple orthogonal magnetic field directions (e.g., x, y, z). The elements of the orthogonal basis vector are related to the magnetic field components (e.g., in the three orthogonal component directions of x, y, and z) generated by the magnetic field generating element as follows.

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[0043] The feedback control unit can be designed to invert the optimization equation using the obtained dot product. The control unit has individual values ​​α corresponding to the current used to individually drive the magnetic field generating elements. j It is possible to design a system to generate a matrix that includes [the specified element]. This has proven to be a particularly time-efficient processing method.

[0044] Typically, only a few iterations (usually just once) are required to obtain the best current solution for zeroing / canceling the external magnetic field. The orthogonal basis for the orthogonal projection method is preferably generated during the calibration process described above. This orthogonal basis only needs to be generated once, and thereafter the control unit can use it for all active cancellation / zeroing operations using sensor data received from the magnetic field sensor array during active cancellation / zeroing operations. The calibration process (i.e., determination of the calibration magnetic field, generation of the orthogonal basis) can be performed (e.g., once) in an environment substantially free of ambient or surrounding magnetic fields (i.e., inside a magnetic shielding room (MSR)). This can be done at the time of manufacture of the device or periodically as needed throughout the device's lifespan (i.e., recalibration). Once calibrated, the device can then be used outside the magnetic shielding room (MSR).

[0045] Alternatively, calibration can be performed in a standard environment (i.e., outside the MSR) that includes the Earth's magnetic field and magnetic field gradients from the local environment (e.g., electrical components, electronic equipment, etc.). To perform calibration in such an environment, the instrument should be designed as follows.

[0046] The feedback control unit, (a) When no drive current is supplied to any of the magnetic field generating elements (i.e., the measured value corresponds to the environmental / geomagnetic value), (b) When a preset drive current is supplied to each of the magnetic field generating elements, In either of the above, a correction value is obtained that corresponds to the measured value of the magnetic field within the device sensed by each of the magnetic field sensing elements at each fixed location within the zeroing region, and The correction value is subtracted from the calibration value generated by supplying current to each magnetic field generating element sequentially and individually (as described above), while ensuring that all other magnetic field generating elements do not receive current from the control unit. This allows the system to generate the aforementioned set of basis vectors.

[0047] This yields corrected calibration values ​​used to determine the basis vectors. In this way, the readings of the magnetic field sensing element (feedback sensor) can be effectively set to zero during the calibration process (i.e., the readings are zeroed out with respect to the internal magnetic field).

[0048] The feedback control unit, after the calibration process is completed (i.e., immediately after completion), controls each magnetic field. sensing The device can be configured to stop subtracting the correction value from the measured value generated by the element. This is because of the magnetic field. sensingThis means restoring the current reading of the element to the true reading (i.e., not performing the aforementioned "zeroing"), after which the orthogonal projection process may be performed. As a result, the basis vectors of the orthogonal projection are obtained by intrinsically subtracting the internal magnetic field present under the conditions of (a) or (b) above. The experimental results shown in Figures 27(a), (b) and (c) were generated as a result of calibration performed as described above without using MSR.

[0049] The predetermined drive current (as described in point (b) above) may be the same for each of the magnetic field generating elements, or it may differ between different magnetic field generating elements. The advantage of the predetermined drive current is that it generates a magnetic field around the magnetic field sensing element that can partially zero out the magnetic field to a degree sufficient to reduce the strength of the environmental / earth magnetic field to a value that falls within the dynamic range of the magnetic field sensing element. Note that for some magnetic field sensing elements, the typical strength of the environmental / earth magnetic field far exceeds the dynamic range of the element, and the element will saturate unless a predetermined drive current is used. This allows for the generation (calibration) of basis vectors and subsequent orthogonal projection using magnetic field generating elements with any desired dynamic range.

[0050] Therefore, although it may be advantageous to calibrate the device within the MSR if the MSR is available and convenient, the present invention MSR This provides a means of performing calibration when necessary. In fact, this also means that calibration can be performed each time the device is used. The advantage of this is that mechanical changes in the positioning of the magnetic field generating element and / or magnetic field sensing element are eliminated. Furthermore, temperature changes in the device may affect the performance of the magnetic field sensing element, but this change will also be taken into account by the calibration process.

[0051] In a second embodiment, the present invention is a method for zeroing out a magnetic field in a zeroing region located within an ambient magnetic field (for example, an external one), To generate each zeroing magnetic field extending into the zeroing region, a plurality of separate magnetic field generating elements are provided, each located separately within the zeroing region. To sense each of the magnetic field values ​​within the zeroing region, a plurality of magnetic field sensing elements are provided, each of which is located at a separate location within the zeroing region. In accordance with the magnetic field values ​​sensed by the plurality of magnetic field sensing elements, the magnetic field generating elements are driven with currents such that the value of the magnetic field detected by each magnetic field sensing element is reduced to a value that does not exceed a preset threshold corresponding to a preset zeroing of the magnetic field within the zeroing region, thereby controlling the value of the zeroing magnetic field generated by each of the plurality of magnetic field generating elements. A method can be provided that includes this.

[0052] Preferably, in the present invention, the magnetic field generating element comprises a conductive coil, and the method includes transmitting the current through each of the coils.

[0053] This method may include providing the plurality of magnetic field generating elements as being arranged at their respective separate locations in a first array formed along a three-dimensional reference plane surrounding the zeroing region.

[0054] The present invention may include providing the plurality of magnetic field sensing elements so that they are arranged at each of the separate locations that define a second array formed along a three-dimensional reference plane.

[0055] This method may include arranging the second array so as to be substantially concentric with the first array.

[0056] Preferably, in this method, each of the distinct locations in the first arrangement is determined according to a regular grid. Preferably, in this method, each of the distinct locations in the second arrangement is determined according to a regular grid.

[0057] This method may include arranging the plurality of magnetic field generating elements at separate locations approximately equidistant from the center of the zeroing region, thereby defining a substantially spherical arrangement surrounding the zeroing region.

[0058] This method may include arranging the plurality of magnetic field sensing elements at separate locations approximately equidistant from the center of the zeroing region, thereby establishing a substantially spherical arrangement within the zeroing region.

[0059] Preferably, in this method, the diameter of the array of magnetic field sensing elements is at least 40% of the diameter of the array of magnetic field generating elements.

[0060] This method may include arranging the plurality of magnetic field generating elements to comprise at least 10 separate magnetic field generating elements, more preferably at least 50 separate magnetic field generating elements, and even more preferably at least 200 separate magnetic field generating elements.

[0061] In one method, the feedback control unit may receive an input corresponding to the output from the magnetic field sensing element, and the feedback control unit may supply an output including a control signal that is input to the associated magnetic field generating element.

[0062] Preferably, the threshold is 5 × 10 -9 Tesla or less, or more preferably 5 x 10 -10 It's inferior to Tesla.

[0063] The method may be configured to generate a magnetic field value associated with one or more locations within the zeroing region by interpolation between multiple magnetic field values ​​sensed by multiple magnetic field sensing elements in an array of magnetic field sensing elements. The method may include defining a conceptual interpolation sphere determined by the radius from a target point (coordinate) within the zeroing region where the magnetic field value should be interpolated. The method may include determining which of the magnetic field sensing elements are located within the conceptual sphere (and increasing the radius of the sphere until at least two sensors are located within the sphere). The method may include calculating the interpolated value of the magnetic field at the target location by three-dimensional interpolation of the magnetic field values ​​sensed by the multiple sensors within the interpolation sphere.

[0064] In another embodiment, the present invention can provide a magnetoencephalography (MEG) apparatus comprising one or more magnetoencephalography (MEG) sensors configured to be positioned around a patient's head, and an apparatus according to a first embodiment of the present invention for zeroing out a magnetic field within a zeroing region sized to accommodate the patient's head. The apparatus according to a first embodiment of the present invention can be configured to cancel out ambient magnetic fields (e.g., the Earth's magnetic field and magnetic fields from surrounding objects) within the zeroing region, including the magnetic field sensing element of the apparatus and the patient's head. In a further embodiment, the present invention can provide a medical imaging apparatus comprising the above-described MEG apparatus, and / or a brain activity mapping apparatus comprising the above-described MEG apparatus, and / or a biomagnetic sensing apparatus comprising the above-described MEG apparatus, and / or a neurofeedback apparatus comprising the above-described MEG apparatus, and / or a brain-computer interface apparatus comprising the above-described MEG apparatus.

[0065] For example, when used in an MEG application, magnetic field zeroing using the proposed invention can be performed within the MSR. This method can be used to cancel out residual magnetic fields (e.g., emitted from the device) within the MSR. When used in an MEG application or another medical application, the arrangement of the magnetic field generating elements can be configured to enclose a spatial area (e.g., three-dimensional space) sufficient to accommodate the patient's entire body or body parts other than the patient's head. The arrangement of the magnetic field sensing elements can be configured to be configured in a similar manner.

[0066] In any embodiment, the present invention can provide shielding for electrocardiography (MCG), magnetomyography (MMG), or magnetoneurography (MNG). In any embodiment, the present invention can provide shielding for nerve signal propagation within the lumbar spine for magnetospinography (MSG). In any embodiment, the present invention can provide shielding for cervical spinal cord evoked field (SCEF) measurement. In any embodiment, the present invention can provide shielding for magnetoencephalography-based brain-computer interfaces (BCI).

[0067] In some of these applications, the shielding using the proposed invention can be created to cover the entire body or different body parts of a human or animal.

[0068] In yet another embodiment, the present invention can provide a magnetoencephalography (MEG) method comprising arranging one or more magnetoencephalography (MEG) sensors around a patient's head, and zeroing out a magnetic field within a zeroing region sized to accommodate the patient's head, according to a second aspect of the present invention.

[0069] Any combination of embodiments and preferred features described herein is included in the present invention unless such combination is clearly unacceptable or explicitly avoided. [Brief explanation of the drawing]

[0070] Embodiments and experiments illustrating the principle of the present invention will be discussed below with reference to the attached drawings.

[0071] [Figure 1] A diagram illustrating a schematic representation of the diamagnetic effect in two dimensions and the principle of Stokes' theorem. [Figure 2] (a) and (b) Diagrams showing the elements of the magnetic field zeroing device and a cross-section of the device, respectively. [Figure 3] (a) and (b) Diagrams showing the elements of the magnetic field zeroing device and a cross-section of the device, respectively. [Figure 4] A diagram showing the elements of a magnetic field zeroing device in a cross-sectional view of the device. [Figure 5] (a) and (b) Diagrams showing the elements of the magnetic field zeroing device and a cross-section of the device, respectively. [Figure 6] (a) and (b) are diagrams showing magnetic field lines representing the surrounding external magnetic field, a zeroed-out region generated by a magnetic field zeroing device, and a schematic representation of the diamagnetic effect, respectively. [Figure 7] This figure shows a spatial plot of magnetic field strength representing the surrounding external magnetic field and the zeroed-out region generated by the magnetic field zeroing device. [Figure 8] (a), (b), (c), and (d) Diagrams showing the magnetic field strength within the zeroed region generated by the magnetic field zeroing device. [Figure 9] A figure showing the arrangement of magnetic field generating elements in a magnetic field zeroing device and the zeroed-out region within the arrangement, along with a plot of the current values ​​applied to the magnetic field generating elements of the magnetic field zeroing device to achieve the zeroed-out region. [Figure 10] A figure showing the arrangement of magnetic field generating elements in a magnetic field zeroing device and the zeroed-out region within the arrangement, along with a plot of the current values ​​applied to the magnetic field generating elements of the magnetic field zeroing device to achieve the zeroed-out region. [Figure 11](a)~(d) Figures showing plots of current values ​​applied to the magnetic field generating element of the magnetic field zeroing device in order to achieve a zeroed region. [Figure 12] This figure shows a plot of the magnetic field strength and magnetic field gradient generated within the zeroing region of a magnetic field zeroing device, as a function of the number of magnetic field generating elements provided within the magnetic field zeroing device. [Figure 13] (a)~(d) Figures showing plots of the average magnetic field strength and maximum magnetic field strength, as well as the average magnetic field gradient and maximum magnetic field gradient, generated within the zeroing region of the magnetic field zeroing device by the device, as functions of the number of magnetic field generating elements provided in the magnetic field zeroing device, for different grid types. [Figure 14] (a) and (b) cross-sectional views of the arrangement of magnetic field generating elements of a magnetic field zeroing device, each equipped with one of two different arrangements of magnetic field sensing elements of the magnetic field zeroing device. [Figure 15] (a) A figure showing a plot of the magnetic field gradient realized within the zeroing region of the spherical array of magnetic field generating elements of the magnetic field zeroing device as a function of the diameter of the concentric spherical array of magnetic field sensing elements within the array of magnetic field generating elements, and (b) A figure showing a plot of the optimal diameter of the concentric spherical array of magnetic field sensing elements as a function of the number of magnetic field generating elements within the spherical array of magnetic field generating elements related to Figure 16(a). [Figure 16] (a)~(d) Figures showing plots of the average magnetic field strength and maximum magnetic field strength, as well as the average magnetic field gradient and maximum magnetic field gradient, generated within the zeroing region of the magnetic field zeroing device, as functions of the diameter of the concentric spherical array of magnetic field sensing elements within the array of magnetic field generating elements of the magnetic field zeroing device. [Figure 17] Figures 16(a) to (d) show the plot of the optimal diameter of the concentric spherical array of the magnetic field sensing elements as a function of the number of magnetic field generating elements in the spherical array of magnetic field generating elements. [Figure 18] This diagram schematically illustrates the process of calculating the current applied to the array of magnetic field generating elements using measurements from the array of magnetic field sensing elements. [Figure 19] A schematic diagram showing the components of a magnetic field zeroing device. [Figure 20] A schematic diagram illustrating the process of controlling the components of a magnetic field zeroing device. [Figure 21] (a)~(c) Figures showing plots of the magnetic field zeroing generated by the process in Figure 18. [Figure 22] (a), (b) Diagrams showing a schematic image of a hypothetical array of magnetic field sensing elements generated using the actual lower array of magnetic field sensing elements of a magnetic field zeroing device. [Figure 23] (a), (b), and (c) are diagrams showing magnetic field zeroing devices having different numbers of magnetic field generating elements, along with cross-sectional views of the magnetic field within the zeroing region of the device. [Figure 24] A diagram showing a magnetic field zeroing device. [Figure 25] A diagram showing a magnetic field zeroing device. [Figure 26] A close-up view of a part of the magnetic field zeroing device shown in Figure 24. [Figure 27] (a), (b), and (c) are graphs showing some examples of sensor signals generated by the sensors of the magnetic field zeroing device in Figure 26. [Modes for carrying out the invention]

[0072] Aspects and embodiments of the present invention will be discussed below with reference to the accompanying drawings. Further aspects and embodiments will be obvious to those skilled in the art. All documents referenced herein are incorporated herein by reference.

[0073] Figure 2(a) shows a device for zeroing out a magnetic field within a zeroing region located in an external surrounding magnetic field. Figure 2(b) shows a cross-sectional view of the device. The device comprises a plurality of separate magnetic field generating coil elements 8. Each element has a circular loop with a common diameter and is positioned at separate locations on a first conceptual spherical shell reference plane surrounding the zeroing region to generate its own zeroing magnetic field extending into the zeroing region. Each magnetic field generating coil element 8 is equipped with a current input terminal (not shown) and a current output terminal (not shown) for inputting and outputting drive current to the coil.

[0074] Multiple magnetic field sensing elements 6, such as OPM sensors, are arranged at multiple separate locations within the zeroing region to sense the respective values ​​of the magnetic field within the zeroing region. The magnetic field sensing elements are also arranged at separate locations on a second conceptual spherical shell reference plane surrounding the zeroing region. The first and second spherical shell reference planes are concentric, and the diameter of the first reference spherical shell plane is approximately 2.5 times the diameter of the second reference spherical shell plane.

[0075] The patient's head 2 is positioned within the zeroing region of the spherical shell array of the magnetic field sensing element 6, so as to coincide with the centers of the first and second reference spherical shells.

[0076] The feedback control unit (not shown; see reference numeral 150 in Figure 19) is designed to control the value of each zeroed magnetic field generated by each of the multiple magnetic field generating elements 8 by driving each of the magnetic field generating elements with a current such that the value of the magnetic field detected by each magnetic field sensing element is reduced to a value that does not exceed a preset threshold corresponding to a preset zeroing of the magnetic field within the zeroing region, in accordance with the value of the magnetic field sensed by the multiple magnetic field sensing elements 6.

[0077] Each magnetic field generating coil 8 is configured to face toward the center or centroid of the array of magnetic field generating elements. In other words, each coil "faces" in a direction perpendicular to the plane containing its diameter. The direction in which a coil "faces" is parallel to the winding axis of the coil (i.e., the central axis around which the coil windings are wound, e.g., the axis of symmetry of the coil). Thus, the direction in which a coil "faces" determines the direction parallel to the magnetic field generated when driven by current, passing through the center of the coil. The direction of this magnetic field is controlled by controlling the direction of flow of a given current flowing through the coil.

[0078] Each coil 8 in the array of magnetic field generating elements is electrically isolated and insulated from any other coils in the array, and each coil is driven independently of any other coil. Adjacent coils within the array of magnetic field generating elements are arranged such that no coil in the array overlaps with any other adjacent coil in the array. In other examples, adjacent coils may overlap at least partially.

[0079] In the figure, patient 2 is wearing the MEG sensor cap 4, and in this example, the OPM sensor covers the patient's head. The magnetic field sensor 6 is positioned around the MEG sensor cap 4 at a safe distance. The patient's brain magnetic field cannot be seen by the magnetic field sensor 6. The magnetic field sensor 6 and coil 8 each form a spherical grid with an opening at the bottom for accommodating the patient's head 2. Note that the present invention is flexible in the sense that the range of the grid arrangement of magnetic field generating elements does not need to cover the entire spherical shell reference plane shape, and various conceptual reference plane shapes can be used. For example, the conceptual reference plane may be a spheroid or cylindrical. Since cancellation / zeroing is achieved by electronic control of the current in the magnetic field generating element 8, various arrangements of magnetic field generating elements can be used. This allows for flexible shaping of the arrangement of magnetic field generating elements.

[0080] Figures 3(a) and (b) show a coil array having an opening 11 for inserting a patient's head 2 (e.g., fitted with a magnetoencephalography cap 4 equipped with an OPM sensor). The opening 11 is defined by an opening of a larger auxiliary coil that helps achieve better cancellation by weakening the magnetic flux around the opening. The coil array can perform without such an auxiliary coil. Note that the magnetic field generating coil array includes coil elements of different diameters, from the largest coil diameter 18a to the smallest coil diameter 18b. By using coils of various diameters, the coils can be packed more densely to cover the conceptual reference spherical shell surface.

[0081] Figure 4 is a cross-sectional view of the example in Figure 3(b). The figure shows a plane 22 (generated by calculation / simulation) that defines the boundary of a three-dimensional space in which all points inside have a magnetic field value of less than 5 nT. Therefore, a magnetic field strength of 5 nT exists around the OPM sensor 6 and falls within the dynamic range of the sensor.

[0082] A more complex version of the present invention is shown in Figures 5(a) and (b). Figure 5(b) is a cross-sectional view of Figure 5(a), in which patient 2 is wearing a MEG sensor cap. The magnetic field sensing element 212 (e.g., OPM sensor) is positioned at a sufficiently safe distance so as not to detect the patient's brain magnetic field. In this example, the number of these sensors is reduced because they are associated with the current control of a larger group of magnetic field generating elements 216 and 214. Specifically, the array of magnetic field generating elements (coils) comprises two sets of concentric sub-arrays of magnetic field generating elements, of which the inner sub-array 214 of magnetic field generating elements is concentric with and surrounded by the outer sub-array 216 of magnetic field generating elements. Both the inner and outer sub-arrays are mounted on the surfaces of physical spherical shell support surfaces 218a and 218b, respectively. Both the inner and outer sub-arrays comprise magnetic field generating elements regularly arranged on their respective conceptual spherical shell reference surfaces. Here, each group of coils in each sub-array 214, 216 of magnetic field generating elements comprises a plurality of sub-groups 210. Each subgroup within each subarray comprises three coils, each facing in three directions perpendicular to the others. Each direction that each coil in a subgroup faces corresponds to a local orthogonal triaxial axis (i.e., the xyz coordinate directions centered at the middle of the subgroup). Since the direction that any two coils in a subgroup face is approximately perpendicular to the direction that each of the other coils in the subgroup faces, no two coils in a subgroup face the same direction. Using this arrangement of coils in each subgroup, it is possible to control the vector direction of a portion of the local magnetic field inside and around the region occupied by a given subgroup of coils. One coil in each subgroup of coils is configured to face toward the center or centroid of the subarray of the magnetic field generating elements that it forms part of.

[0083] Figure 6(b) shows the external magnetic field 1a that passes around but does not penetrate the diamagnetic material 1b, as discussed earlier with reference to Figure 1. For comparison, Figure 6(a) shows a cross-sectional view of the external magnetic field 40 (generated by calculation / simulation) that passes around the arrangement of magnetic field generating coils according to an embodiment of the present invention. An exploded view of the magnetic field generated by two magnetic field generating coils in the coil arrangement is shown, in which the two coils face each other in the diametrical direction with respect to the centroid of the coil arrangement. Of the two selected coils, the upper coil is in a positive y-coordinate and has a local coordinate system with a unit vector (a1, b1), while the lower coil is negative It is located at the y-coordinate and has a local coordinate system with unit vectors (a2, b2). The local coordinate system of the lower coil corresponds to the local coordinate system of the upper coil rotated 180 degrees around the z-axis, with a2 = -a1 and b2 = -b1. The direction of the current is indicated for each coil by the symbol (X) (41, 43) indicating the current in the negative z direction (i.e., entering the page surface) and the symbol (+) (42, 44) indicating the current in the positive z direction (i.e., exiting the page surface). In each of the two coil local coordinate systems, the direction of the current closest to the coordinate origin is opposite, indicating that the currents have opposite signs.

[0084] Figure 7 shows a three-dimensional visualization (generated by calculation / simulation) of a similar coil array zeroing operation according to an embodiment of the present invention. In Figure 7, the surface height represents the magnetic flux density. Figure 7 uses a coil array with a diameter of 1 m and 252 coils. A uniform magnetic field of 50 μT was canceled out within the coils, becoming a negligible value. The magnetic field vector was parallel to the Y-axis. In both Figure 6(a) and Figure 7, a cross-section was taken that passes through the center of the coil array and includes the xy-plane at z=0. The zeroed region 53 is clearly visible. The "recess" 51, one of several recesses along the periphery of the zeroed region, corresponds to the location on the surface where the magnetic field generating coil is located. This shows how large the zeroed region is relative to the diameter of the coil array. The surrounding external magnetic field 50 is shown as a surface portion with a turbulent magnetic field strength of 50 μT. The magnetic field depressions 52 aligned along the y-axis on each side of the coil array are a reaction to the cancellation of the effect of a uniform magnetic field also oriented in the positive direction of the y-axis.

[0085] Figures 8(a), (b), (c), and (d) show examples of gradient magnetic field cancellation performance (generated by calculation / simulation) of embodiments of the present invention. The grayscale in Figures 8(a) and (c) is the grayscale in Figures 8(b) and (d) multiplied by 10,000, respectively. The result in Figure 8(a) corresponds to an external magnetic field gradient source with a magnetic field oriented in the positive x-axis direction in the same figure. Figure 8(b) shows the result of zeroing out / canceling the magnetic field in Figure 8(a). The absence of white indicates that the magnetic field from the source has been reduced to less than 1 / 10,000. The result in Figure 8(c) corresponds to an external magnetic field gradient source with a magnetic field oriented in the positive y-axis direction in the same figure. Figure 8(d) shows the result of zeroing out / canceling the magnetic field in Figure 8(c). The absence of white indicates that the magnetic field from the source has been reduced to less than 1 / 10,000.

[0086] Figure 9 shows a magnetic field generating coil array 60 in which the positions of each coil form a Fibonacci lattice. This array consists of 252 coils forming an array with a diameter of 1 m. The three-dimensional shape 61 (generated by calculation / simulation) within the coil array represents a region of magnetic fields less than 5 nT, resulting in a zeroing / cancellation effect against a uniform external surrounding magnetic field (e.g., the Earth's magnetic field) of 50 μT oriented along the y-axis that crosses the figure from left to right. The magnitude and relative direction (positive / negative) of the drive current 62 applied to each coil in this coil array are shown for the y-coordinate value of each coil. Here, the y-axis crosses the figure from left to right, and the coordinate origin corresponds to the center of the coil array.

[0087] Figure 10 shows a magnetic field generating coil array 70 in which the positions of each coil form a double geodesic icosahedron grid. This array consists of 252 coils forming an array with a diameter of 1 m. The three-dimensional shape 71 (generated by calculation / simulation) within the coil array represents a region of magnetic fields less than 5 nT, resulting in a zeroing / cancellation effect against a uniform external surrounding magnetic field (e.g., the Earth's magnetic field) of 50 μT oriented along the y-axis that crosses the figure from left to right. The magnitude and relative direction (positive / negative) of the drive current 72 applied to each coil in this coil array are shown for the y-coordinate value of each coil. Here, the y-axis crosses the figure from left to right, and the coordinate origin corresponds to the center of the coil array. Note that the double geodesic icosahedron grid requires approximately 50% lower current compared to the Fibonacci grid. Table 1 shows a comparison of the performance parameters for these two coil arrays. [Table 1]

[0088] Figures 11(a), (b), (c), and (d) show other examples (generated by calculation / simulation) of the drive current applied to a spherical array of magnetic field generating coils, as a function of the given coil coordinates with respect to the y-axis. In all cases, the coil array grid (81, 83, 85, 88) is a double geodesic icosahedron array with 212 coils. Arrows 82, 84, 86, and 87 represent different magnetic field distributions / sources. The magnetic field vector to be canceled out is parallel to the y-axis. Figure 11(a) corresponds to a uniform magnetic field (three arrows 82). The drive current supplied to each coil in the array to achieve zeroing is almost perfectly linearly proportional to the y-axis position coordinate of the given coil. Figure 11(b) corresponds to a point magnetic field on the negative y-axis (one arrow 84). The linearity between the drive current and the y-coordinate of the coil in Figure 11(a) is now replaced by a curved linearity. Figure 11(c) corresponds to a point magnetic field 86 located on the positive x-axis but oriented parallel to the positive y-axis. Figure 11(d) corresponds to a point magnetic field 87 located on the positive x-coordinate and negative y-coordinate but oriented parallel to the positive y-axis.

[0089] Figure 12 shows typical values ​​(generated by calculation / simulation) of the magnetic field value and magnetic field gradient realized within the zeroing region for each example of the present invention, as a function of the number of magnetic field generating coils in the Fibonacci grid array. Figures 13(a), (b), (c), and (d) show yet another example for a Fibonacci grid (Figure 13(a) shows the magnetic field value, Figure 13(c) shows the magnetic field gradient) and a double geodesic icosahedron grid (Figure 13(b) shows the magnetic field value, Figure 13(d) shows the magnetic field gradient). In all cases, both the maximum and average values ​​of the magnetic field value or magnetic field gradient are shown. These figures show how the performance of the coil array improves as the number of coils increases, and also show that the grid type has a significant influence. The diameter of the coil array was 1 m and acted against a uniform magnetic field of 50 μT. The region evaluated was a sphere with a diameter of 0.35.

[0090] It can be seen that using a double geodesic icosahedron grid provides better performance than using a Fibonacci grid.

[0091] Figures 14(a) and (b) show cross-sections of the spherical shell arrangement of magnetic field generating coils (90, 92) surrounding the spherical shell arrangement of magnetic field sensing elements (91, 94). The former is configured to be approximately concentric with the spherical shell arrangement of magnetic field generating coils surrounding it. The patient's head 2 is located at the center of the arrangement of magnetic field sensing elements. The inventors have found that this concentric arrangement enables particularly accurate and effective zeroing within the zeroing region. Coils of the coil arrangement ( 90 Each of the distinct locations of the 90 and 92) and each of the distinct locations of the sensors within the sensor array (91, 94) is determined by a regular grid, where the locations coincide with (or are determined by) conceptual vertices or facets of a polyhedron or points on a sphere. Two physical polyhedral or spherical support structures (not shown) each support the elements of each array at the said locations. The plurality of magnetic field generating coils (90, 92) are positioned at each of the distinct locations approximately equidistant from the center of the zeroing region, thereby defining a roughly spherical array surrounding the zeroing region. Similarly, the plurality of magnetic field sensing elements (91, 94) are also positioned at each of the distinct locations approximately equidistant from the center of the zeroing region, thereby defining a roughly spherical array within the zeroing region.

[0092] Figure 14(a) shows a cross-sectional view of a device in which the diameter of the array of magnetic field sensing elements 91 (diameter of the spherical array of sensors 0.35 m) is smaller than the diameter of the array of magnetic field sensing elements 94 (diameter of the spherical array of sensors 0.61 m) is smaller than the diameter of the array of magnetic field sensing elements 92 (diameter of the spherical array of coils 1.0 m) shown in Figure 14(b). The inventors have found that there is an optimal position (e.g., the diameter of the array) in which sensors placed within a surrounding coil array can dramatically improve performance. It has been found that this optimal position depends on the diameter of the coil array, the number of coils in the coil array, the type of grid that defines the coil array, and the shape of the coils. For example, in the case of a Fibonacci grid with 1200 coils as shown in Figures 14(a) and (b), it was found that the optimal position of the sensors in the sensor array corresponds to an array with a concentric diameter that is 0.61 times the diameter of the surrounding coil array, as shown in Figure 14(b), when the sensor array is a spherical shell array.

[0093] Generally, the optimal sensor position corresponds to a concentric diameter of the sensor array that is within the range of at least approximately 30% to approximately 90% of the diameter of the surrounding magnetic field generating coil array. Figures 15(a) and (b) show how the value of the magnetic field gradient within the zeroed region of the external surrounding magnetic field (Figure 15(a)) changes as a function of the diameter of the magnetic field sensor array (with the diameter of the coil array fixed), and how the optimal sensor array diameter changes (Figure 15(b)) as a function of the number of coils in the array (with the diameter of the coil array varied), respectively. Here, the coil array is a Fibonacci grid. For example, if 2000 coils are used, and the diameter of the sensor array is approximately 68% of the diameter of the coil array, the zeroed magnetic field is less than 1.6 pT in the zeroed three-dimensional space, and this zeroed magnetic field value is approximately the diameter of the sensor sphere relative to the diameter of the coil array. 81Even when increased to a percentage, the value only rises to 0.95 nT. This example means that if a coil array sphere with a diameter of 1 m is used, the diameter of the sensor array sphere is 0.81 m. Figure 15(b) shows how the optimal diameter of the sensor array sphere changes as a function of the number of magnetic field generating coils used in the spherical Fibonacci arrangement of coils. The relationship is well approximated by quadratic order, and the diameter of the sensor array changes as a quadratic function of the number of coils in the coil array.

[0094] Figures 16(a) and (c) show another example of how the magnetic field value (Figure 16(a)) and magnetic field gradient (Figure 16(c)) within the zeroed region of an array of 200 coils in an external peripheral magnetic field vary as a function of the diameter of the magnetic field sensor array, when the coil array is a Fibonacci grid with a fixed diameter of 1.0 m and the surrounding magnetic field being zeroed is a uniform magnetic field of 50 μT. Both the maximum magnetic field value of 95 and the average value of 96, as well as the maximum magnetic field gradient, are shown. 99 The average value is shown as 100. Figures 16(b) and (d) show another example of how the magnetic field value (Figure 16(b)) and magnetic field gradient (Figure 16(d)) within the zeroed region of an array with 600 coils in an external surrounding magnetic field vary as a function of the diameter of the magnetic field sensor array, when the coil array is a double geodesic icosahedron grid with a fixed diameter of 1.0 m and the surrounding magnetic field being zeroed is a uniform magnetic field of 50 μT. Both the maximum value of 98 and the average value of 97 for the magnetic field, as well as the maximum value of 102 and the average value of 101 for the magnetic field gradient, are shown. In both cases, it is clear that there is an optimal sensor array diameter corresponding to the minimum magnetic field value and magnetic field gradient value. Figure 17 shows how the optimal sensor array sphere diameter values ​​identified from Figures 16(a) to (d) vary as a function of the number of magnetic field generating coils used in the spherical Fibonacci arrangement of coils. This relationship is well approximated by a quadratic function, where the diameter of the sensor array changes as a quadratic function of the number of coils in the coil array.

[0095] As a result, the inventors discovered a strong synergistic effect between the diameter of the array of magnetic field generating elements and the diameter of the array of magnetic field sensing elements necessary to achieve optimal zeroing of the magnetic field within the zeroing region. In other words, by optimally arranging the sensors in the feedback system of the present invention, the optimal feedback value of the magnetic field is supplied to the control system, and the current used to drive the magnetic field generating elements when reducing the magnetic field within the zeroing region is optimally controlled. The diameter of the array of magnetic field sensing elements is preferably between approximately 40% and approximately 80% of the diameter of the array of magnetic field generating elements. For example, the diameter of the array of magnetic field sensing elements may be between approximately 40% and approximately 90% of the diameter of the array of magnetic field generating elements, and the array of magnetic field generating elements may contain at least approximately 200 elements and no more than approximately 2000 elements. The inventors found that particularly effective magnetic field zeroing can be achieved when one or more of these conditions are applied.

[0096] Figure 18 shows the process for determining the value of the current to be supplied to the magnetic field generating coils of a coil array. Figure 19 shows a device for zeroing out a magnetic field in a zeroing region within an external surrounding magnetic field, and includes a plurality of separate magnetic field generating elements 102 arranged at separate locations surrounding the zeroing region in order to generate each zeroing magnetic field that extends into the zeroing region. A plurality of magnetic field sensing elements 103 are arranged at multiple separate locations within the zeroing region in order to sense each value of the magnetic field within the zeroing region. A feedback control unit 150 is configured to control the value of each zeroing magnetic field generated by each of the plurality of magnetic field generating elements in accordance with the magnetic field values ​​sensed by the plurality of magnetic field sensing elements. The feedback control unit is designed to drive the magnetic field generating elements 102 with a current such that the value of the magnetic field detected by each magnetic field sensing element 103 is reduced to a value that does not exceed a preset threshold corresponding to a preset zeroing of the magnetic field within the zeroing region.

[0097] The feedback control unit is designed to calculate an appropriate drive current as follows. Consider the following items. Minimizing the magnetic field readings from each sensor 103 is sufficient to cancel out the magnetic field inside the target zeroing space. The magnetic field reading from one sensor 103 is the sum of the total magnetic fields from all magnetic field generating elements 102 and the external surrounding magnetic field. Each sensor at the coil position is fixed such that this spatial component of the magnetic field equation remains constant. The only variable that is changing is the drive current, which is proportionally dependent on the magnetic field.

[0098] The contribution of each magnetic field generating element 102 (e.g., a coil) to all sensors 103 can be calibrated. When the magnetic fields cancel each other out, the feedback value of the magnetic field sensed by the sensor group for the three-dimensional space enclosed by the sensor group also becomes zero. There is a proportional dependency between the current and the magnetic field. The following equation describes the value of the magnetic field at a given location, which is a fixed position for each sensor expressed in cylindrical coordinates.

number

[0099] In other words, each coil is driven by current independently in sequence, while all other magnetic field generating elements do not receive current from the control unit. The magnetic field generated by an individual coil is sensed by each of the magnetic field sensing elements 103, each located at a fixed position within the zeroing region. These measured electric field values ​​are calibration values ​​and determine the basis vector for the individual coil in question. These values ​​are input from each magnetic field sensing element 103 to the control unit 150, which stores them. The control unit is configured to repeat this process separately for each magnetic field generating element 102 in the coil array, so that each magnetic field generating element 102 acts as an independent magnetic field generating element supplied with current. For each coil 102, the control unit 150 generates a basis vector containing the calibration magnetic field values ​​for all n sensors 103. For the first coil,

number

[0100] The arrangement of m coils ultimately becomes an arrangement of these basis vectors constructed using the respective basis vectors corresponding to all m coils.

number

number

number

number

number

[0101] Typically, only a few iterations (usually just once) are needed to obtain the best current solution for zeroing / canceling the external magnetic field. The orthogonal basis for the orthogonal projection method is generated during the calibration process. The orthogonal basis only needs to be generated once, and thereafter the control unit can use it for all active cancellation / zeroing operations using sensor data received from the magnetic field sensor array during the active cancellation / zeroing operations. This is a very fast and simple process. As a result, any magnetic field distortions resulting from differences and inaccuracies between them are eliminated. Figure 20 summarizes this process, including the following steps. Step 160: The control unit 150 sequentially outputs the drive current to each individual coil 102, while the other coils do not receive any current. Step 161: Measure the magnetic field within the zeroing region using the magnetic field sensing sensor array 103. Step 162: The control unit 150 calculates the individual drive current to be applied to each coil 102 by solving the optimization equation, and then drives each coil with the calculated drive current.

[0102] figure 21(a), (b), and (c) show two very different examples of magnetic sources used as magnetic field generating elements in a regular spherical array 102 with a diameter of 0.5 m, comprising 32 magnetic field generating elements arranged in a double geodesic icosahedron shape surrounding the array of magnetic field feedback sensors 103. 21 The magnetic field within the zeroing region of the array shown in (b) corresponds to the case where each magnetic field generating element is configured to generate its local magnetic field using a circular current (for example, a circular coil with a diameter of 14 cm). In contrast, Figure 21 The magnetic field within the zeroing region of the arrangement shown in (c) corresponds to the case where each magnetic field generating element is configured to generate its local magnetic field as a magnetic dipole field. In both cases, zeroing is achieved over the entire zeroing region with a diameter of 8 cm, and 50 μ An external surrounding magnetic field exceeding T results in an average magnetic field of approximately 0.5 nT and an average magnetic field gradient of 0.027 nT / cm (Figure) 21 (b)) or an average magnetic field of approximately 1.0 nT and an average magnetic field gradient of 0.044 nT / cm (Figure 21 (c)) was reduced to this extent. This reinforces the point that the magnetic field generating element does not have to be a coil, and could instead be, for example, a suitable magnetic field source configured to generate a dipole magnetic field.

[0103] Figure 22 shows an example of how the orthogonal projection method described above can use fewer magnetic field sensing elements (feedback sensors) 103 than the number of magnetic field generating coils 102. Specifically, if the number of sensors 103 is reduced to about 40% of the number of magnetic field generating coils 102, the performance of the method may begin to deteriorate. To overcome this problem, the control unit 150 can be configured to generate a magnetic field calibration value associated with a conceptual "virtual" magnetic field sensor 105 located at any point in the zeroing region by interpolating the calibration magnetic field value actually received by the physical sensors 103 of the sensor array. The control unit 150 can be configured to define a conceptual interpolation sphere 106 (see Figure 22(b)) determined by the radius from the target point (coordinates: x,y,z) in the zeroing region where the virtual sensor calibration magnetic field value should be interpolated. The control unit 150 can determine which real magnetic field sensors 103 are located within the conceptual sphere and increase the radius of the sphere until at least two real sensors are within that sphere. Once the control unit identifies multiple real-world sensors within the interpolation sphere, it calculates a virtual value of the calibration magnetic field at the target location (x,y,z) by 3D interpolation of the real-world calibration magnetic field values ​​received from the multiple real-world sensors within the interpolation sphere. This virtual value is then used in the process described above, with reference to Figure 20. For example, any number of separate target locations (coordinates: x,y,z), such as positions corresponding to some array on the conceptual sphere 108 (see Figure 22(a)), can be selected, and along with them, any number of virtual (i.e., interpolated) calibration magnetic field values ​​can be generated. The interpolation may be as simple as calculating the sum of the calibration magnetic field values ​​supplied by the real-world sensors within the interpolation sphere (i.e., the sum of appropriate x,y, and z components of each field) and dividing the result (for each field component) by the number of real-world sensors within the interpolation sphere. If the difference in the number between coil 102 and feedback sensor 103 is large, the orthogonal projection method can be improved by introducing virtual feedback sensors created using readings from real-world feedback sensors in this way. The heatmap 108 covering the conceptual sphere on which the feedback sensors (virtual and real) are located shows a grayscale map representing the magnitude of the magnetic flux density of the magnetic field.

[0104] Figures 23(a), (b), and (c) show implementation examples of this method. Figure 23(a) shows a device 30 having a coil array with 32 coils and 16 real sensors. The magnetic field zeroing result 31 is shown for a 4cm spherical zeroing region. An average magnetic field of 1.35 nT is obtained with an average gradient of 0.0043 nT / cm. Figure 23(b) shows a device 32 having a coil array with 92 coils, 16 real sensors, and 76 virtual sensors. The magnetic field zeroing result 33 is shown for a 4cm spherical zeroing region. An average magnetic field of 0.04 nT is obtained with an average gradient of 0.001 nT / cm. Figure 23(c) shows a device 34 having a coil array with 212 coils, 16 real sensors, and 196 virtual sensors. The magnetic field zeroing result 35 is shown for a 4cm spherical zeroing region. An average magnetic field of 0.02 nT was obtained with an average gradient of 0.001 nT / cm.

[0105] Figure 24 shows a support frame 110 for supporting the array of magnetic field generating coils 102 and the array of magnetic field sensing elements 103. The distance from the center of the array to the sensor mounting section can be adjusted by pressing with bolts. The support frame has a non-magnetic polyhedral frame. This is just one example of how the coils and feedback sensors can be mounted. The grid type is a 32-faced double geodesic icosahedron. Each feedback sensor 103 is mounted on one of several adjustable mounting rods 111, each having a fixed end at the center of a local facet of the grid on which the feedback sensor is mounted, and a free end within the three-dimensional space enclosed by the grid. Each mounting rod points radially into the three-dimensional space enclosed by the array. To make adjustments for optimal performance, the proximity from a given sensor to the center of the coil grid can be adjusted by adjusting the length of the mounting rod. For example, in this example, each mounting rod has a cylindrical tube containing a cylindrical sensor that can move back and forth along the axis of the mounting rod to extend and retract the length of the mounting rod like a telescope. The grid support frame thus holds the coils and sensors in the correct positions. Each coil can be fixed in place using various methods, such as adhesive, locking systems, or gripping bodies.

[0106] Figure 25 shows another example of the apparatus according to the present invention being used in a magnetoencephalogram (MEG) shielding device using an OPM-based cap. The patient's head 2 is located within a hemispherical arrangement of flat coils 114 mounted on a transparent hemispherical support surface 115 made of a non-magnetic material. For example, each coil wire can be formed by vapor deposition, printing, metal foil etching, etc. A passive magnetic field shield 113, for example, a layer of mu-metal and aluminum, covers the magnetic field generating coil arrangement. Support arms and housings 116 for electrical cables are provided.

[0107] The present invention makes it possible to reduce the cost of sensors used to cancel out / zero out weak magnetic fields and realize a region where the magnetic field is zeroed out in the range of μT to nT or nT to fT.

[0108] Figure 26 shows an example of a magnetic field zeroing device constructed using a support frame according to the design described above, with reference to Figure 24. This device supported an array of magnetic field generating coils 102 and an array of magnetic field sensing elements 103. This device uses 32 magnetic field generating coils 102 and 16 magnetic field sensing elements 103. The magnetic field generating coils were arranged to cover a geodesic icosahedron with a diameter of 0.5 m. The magnetic field sensing elements were positioned appropriately to obtain a spherical zeroing space with a diameter of 8 cm, and the magnetic field zeroing device was designed to obtain a zero magnetic field throughout this zeroing space. This magnetic field zeroing device was installed in a normal building environment exposed to the Earth's magnetic field of approximately 50 μT. In addition, the magnetic field zeroing device was surrounded by magnetic materials including noise from nearby electrical mains power sockets and cables. These magnetic materials combined with the Earth's magnetic field to generate a magnetic field within the spherical zeroing space, which was then substantially neutralized by the action of the magnetic field zeroing device.

[0109] Figure 26 shows a close-up view of the magnetic field zeroing device, and the arrangement of the magnetic field sensing elements 103 inside the zeroing device is visible. magnetic field The sensing element 103 is equipped with three magnetic impedance sensors, each positioned to measure one of the three orthogonal magnetic field components in the x, y, and z axes, namely Sx, Sy, and Sz. A suitable example of a magnetic impedance sensor is the nanotesla sensor manufactured by Aichi Steel Corporation, available under model number MI-CB-1DH. These sensors were modified to operate in DC mode (not AC mode) according to the instructions provided by Aichi Steel Corporation (which are readily available to those skilled in the art). The magnetic impedance sensors were operated in DC mode and calibrated in a low magnetic field environment. A fluxgate type sensor was placed at the center of the array of magnetic field sensing elements. magnetic field A sensing element 123 (manufactured by Bartington Instruments, USA, product name "MAG-13") was added as an additional reference sensor.

[0110] Because the magnetic impedance sensor used in this example has a narrow dynamic range, the Earth's magnetic field was initially canceled out by aligning the arrangement of the magnetic field generating coils 102 and the magnetic field sensing elements 103 of the zeroing device to an appropriate orientation. This was done by orienting the support frame (and the arrangement of the magnetic field generating coils 102 and magnetic field sensing elements 103 mounted thereon) in the opposite direction to the Earth's magnetic field vector, and supplying current to the coils of the arrangement of magnetic field generating coils 102 as described above, referring to the configuration shown in Figure 11(a). As a result, the initial magnetic field in the spherical zeroing space came within the dynamic range of the magnetic impedance sensor.

[0111] Subsequently, the calibration process described above was performed on the magnetic field zeroing device with reference to Figures 18 and 19 to obtain the orthogonal basis matrix as described above. Then, the scalar product was calculated, and the inverse matrix was calculated from that product and saved for use in the active cancellation process.

[0112] The control unit (reference numeral 150 in Figure 19) must use the current α to drive each magnetic field generating coil. j The "negative" value of the following "orthogonal projection" optimization equation

number

[0113] To calculate the "negative" value of the coil current in each active cancellation loop, magnetic field The readings from the sensing elements are [V1, V2, V3, ..., V N The values ​​were placed within the measurement matrix ]. The magnetic field measurement includes the three orthogonal field component measurements (Sx, Sy, Sz) from each of the sensors, which are represented within the elements of the measurement matrix as follows.

number

[0114] The dot product of the aforementioned matrix and the orthogonal basis was calculated as follows.

number

number

[0115] Using the obtained dot product, the control unit is configured to invert the above "orthogonal projection" optimization equation. The result is an individual value α corresponding to the current used to individually drive the coil 102. j It consists of a matrix containing [a specific element].

[0116] In this example, we used a 2.8GHz quad-core controller with product code "PXIe-8861" obtained from National Instruments. magnetic field To read the sensing elements, this product is equipped with two PXI-6349 simultaneous analog-to-digital converters (ADCs). These are product codes "PXI-6349" obtained from National Instruments. To provide a current source to supply the drive current for the magnetic field generating coil, a digital-to-analog converter (DAC) with product code "PXIe-6739," also obtained from National Instruments, is placed. The magnetic field (Sx, Sy, Sz), etc., is measured, and the "negative" current α j The time required to identify these currents and apply them to the coil was less than 250 μs. This process can be easily accelerated by using a field-programmable gate array (FPGA).

[0117] Figure 27(a) shows 16 magnetic fieldThe readings (Sx, Sy, Sz) obtained from the sensing element 103 are shown. These correspond to 48 (i.e., 16 × 3 = 48) individual magnetic impedance magnetic sensors, which are disturbed by the non-uniform magnetic field.

[0118] Figure 27(b) shows the same reading after one calculation of the orthogonal projection (zeroing) algorithm. magnetic field Figure 27(c) shows the readings (Sx, Sy, Sz) from the reference magnetic sensor of the sensing element 123 ("MAG-13"). The vertical axis scale in these figures is measured in volts (V), and a reading of 2.5V corresponds to a measured value of 5μT.

[0119] When active cancellation is performed within the magnetic field zeroing device, the support frame can be rotated to any position relative to the Earth's magnetic field, and it has been found that even with magnetic materials or AC magnetic field sources present, the magnetic field environment within the zeroing region can be approached to zero without quality degradation. Furthermore, it has been found that errors due to changes in the characteristics of the device's electronic components or unacceptable physical dimensions have an effect equivalent to fluctuations in the external magnetic field, but the device responds in a way that cancels out the effects that these errors would otherwise have had on the zeroing of the magnetic field environment.

[0120] Each feature disclosed in the preceding description, the subsequent claims, or the accompanying drawings may be expressed in its specific form, as necessary, or in terms of means for performing the disclosed function or methods or processes for obtaining the disclosed results. These features can be used individually or in any combination to realize the present invention in its various forms.

[0121] While the present invention has been described above in conjunction with exemplary embodiments, many equivalent modifications and variations would be obvious to those skilled in the art if disclosed in this application. Therefore, the exemplary embodiments of the present invention described above should be considered illustrative and not limiting. Various modifications can be made to the above embodiments without departing from the spirit and scope of the invention.

[0122] To avoid any misunderstanding, it should be stated that all theoretical explanations provided herein are intended to enhance the reader's understanding. The inventors do not wish to be bound by any of these theoretical explanations.

[0123] The headings used in this specification are for organizational purposes only and should not be interpreted as limiting the subjects described.

[0124] Throughout this specification, including in the subsequent claims, the words “comprise” and “include,” as well as their variations (comprises, comprising, including, etc.), should be interpreted as including the integer or step or group of integers or steps mentioned, rather than excluding other integers or steps or groups of integers or steps, unless the context requires otherwise.

[0125] In this specification and the attached claims, the singular form includes cases where there are multiple references, unless the context makes it clear otherwise. When a range is expressed herein, a specific starting number and / or another specific ending number may be preceded by "approximately." When a range is expressed in this way, a form in which the aforementioned specific number is precisely the starting point and / or the other specific number is precisely the ending point constitutes a different embodiment. Similarly, when a value is expressed as an approximation by the use of the antecedent "approximately," it should be understood that the particular value constitutes a different embodiment. The relationship between the term "approximately" and a number is arbitrary and may mean, for example, ±10%.

[0126] In this application, when we refer to "diameter," we mean a straight line that passes through the center of a structure, arrangement, body, or figure, in particular a circle or a sphere (but not limited to these).

Claims

1. A device for zeroing out the magnetic field within a zero-out region located within the surrounding magnetic field, To generate each zeroing magnetic field extending into the zeroing region, a plurality of separate magnetic field generating elements are arranged at separate locations surrounding the zeroing region, A plurality of magnetic field sensing elements, each of which is located at a separate location within the zeroing region, for sensing the respective values ​​of the magnetic field within the zeroing region, wherein the diameter of the array of magnetic field sensing elements is at least 30% of the diameter of the array of magnetic field generating elements, A feedback control unit controls the value of each of the zeroed magnetic fields generated by each of the multiple magnetic field sensing elements by driving each of the magnetic field generating elements with a current such that the value of the magnetic field detected by each of the multiple magnetic field sensing elements is reduced to a value that does not exceed a preset threshold corresponding to a preset zeroing of the magnetic field within the zeroing region, in accordance with the value of the magnetic field sensed by the multiple magnetic field sensing elements. A device equipped with the following features.

2. The apparatus according to claim 1, wherein the feedback control unit is designed to determine a set of multiple optimal currents used to drive the corresponding multiple magnetic field generating elements by applying an orthogonal projection algorithm.

3. The apparatus according to claim 1, wherein the magnetic field generating element comprises a conductive coil adapted to transmit the current.

4. The apparatus according to claim 1, wherein the plurality of magnetic field generating elements are arranged at their respective separate locations in a first arrangement formed along a three-dimensional reference plane surrounding the zeroing region.

5. The apparatus according to claim 1, wherein the plurality of magnetic field sensing elements are arranged at each of the separate locations that define a second arrangement formed along a three-dimensional reference plane.

6. The apparatus according to claims 4 and 5, wherein the second arrangement is configured to be substantially concentric with the first arrangement.

7. The apparatus according to claim 4, wherein each of the distinct locations in the first arrangement is determined according to a regular grid.

8. The apparatus according to claim 4, wherein each of the separate locations in the first arrangement is determined according to a geodesic grid.

9. The apparatus according to claim 5, wherein each of the distinct locations in the second arrangement is determined according to a regular grid.

10. The apparatus according to claim 1, wherein the plurality of magnetic field generating elements are arranged at separate locations approximately equidistant from the center of the zeroing region, thereby forming a substantially spherical arrangement surrounding the zeroing region.

11. The apparatus according to claim 1, wherein the plurality of magnetic field sensing elements are arranged at separate locations approximately equidistant from the center of the zeroing region, thereby forming a substantially spherical arrangement within the zeroing region.

12. The apparatus according to claim 1, wherein the diameter of the array of magnetic field sensing elements is within the range of about 30% to about 90% of the diameter of the array of magnetic field generating elements.

13. The apparatus according to claim 1, wherein the diameter of the array of magnetic field sensing elements is between approximately 40% and approximately 90% of the diameter of the array of magnetic field generating elements.

14. The apparatus according to claim 1, wherein the plurality of magnetic field generating elements comprises at least 10 separate magnetic field generating elements.

15. The apparatus according to claim 1, wherein the plurality of magnetic field generating elements comprises at least 50 separate magnetic field generating elements.

16. The apparatus according to claim 1, wherein the plurality of magnetic field generating elements comprises at least 200 separate magnetic field generating elements.

17. The apparatus according to claim 1, wherein the feedback control unit includes an input terminal connected to the output of the magnetic field sensing element, and an output terminal connected to the input terminal of the associated magnetic field generating element.

18. The aforementioned threshold is 5 × 10 －9 The apparatus according to claim 1, which is less than or equal to Tesla.

19. The aforementioned threshold is 5 × 10 －10 The apparatus according to claim 1, which is less than or equal to Tesla.

20. The apparatus according to claim 1, wherein the feedback control unit is designed to control the value of the zeroed magnetic field generated by each of the plurality of magnetic field sensing elements by driving each of the magnetic field generating elements with a current such that the value of the magnetic field detected by each of the plurality of magnetic field sensing elements is reduced to a value corresponding to an average magnetic field gradient not exceeding approximately 10 nT / cm within the zeroed region, in accordance with the value of the magnetic field sensed by the plurality of magnetic field sensing elements.

21. A method for zeroing out the magnetic field within a zero-out region located within the surrounding magnetic field, To generate each zeroing magnetic field extending into the zeroing region, a plurality of separate magnetic field generating elements are provided, each located separately within the zeroing region. To sense each value of the magnetic field within the zeroing region, a plurality of magnetic field sensing elements are provided, each of which is located at a separate location within the zeroing region, wherein the diameter of the array of magnetic field sensing elements is at least 30% of the diameter of the array of magnetic field generating elements. In accordance with the magnetic field values ​​sensed by the plurality of magnetic field sensing elements, the magnetic field generating elements are driven with currents such that the value of the magnetic field detected by each magnetic field sensing element is reduced to a value that does not exceed a preset threshold corresponding to a preset zeroing of the magnetic field within the zeroing region, thereby controlling the value of the zeroing magnetic field generated by each of the plurality of magnetic field generating elements. A method for providing this.

22. The method according to claim 21, wherein a set of multiple optimal currents used to drive a plurality of corresponding magnetic field generating elements is determined by applying an orthogonal projection algorithm.

23. The method according to claim 21, wherein the magnetic field generating element comprises a conductive coil, and the method includes transmitting the current through each of the conductive coils.

24. The method according to claim 21, further comprising providing the plurality of magnetic field generating elements as being arranged at separate locations in a first array formed along a three-dimensional reference plane surrounding the zeroing region.

25. The method according to claim 21, further comprising providing the plurality of magnetic field sensing elements so as to be arranged at each of the separate locations that define a second arrangement formed along a three-dimensional reference plane.

26. The method according to claims 24 and 25, comprising providing the second arrangement substantially concentrically with the first arrangement.

27. The method according to claim 24, wherein each of the distinct locations in the first arrangement is determined according to a regular grid.

28. The method according to claim 24, wherein each of the distinct locations in the first arrangement is determined according to a geodesic grid.

29. The method according to claim 25, wherein each of the distinct locations in the second arrangement is determined according to a regular grid.

30. The method according to claim 21, comprising arranging the plurality of magnetic field generating elements at separate locations approximately equidistant from the center of the zeroing region, thereby defining a substantially spherical arrangement surrounding the zeroing region.

31. The method according to claim 21, comprising providing the plurality of magnetic field sensing elements at separate locations approximately equidistant from the center of the zeroing region, thereby establishing a substantially spherical arrangement within the zeroing region.

32. The method according to claim 21, wherein the diameter of the array of magnetic field sensing elements is within the range of about 30% to about 90% of the diameter of the array of magnetic field generating elements.

33. The method according to claim 21, wherein the diameter of the array of magnetic field sensing elements is between approximately 40% and approximately 90% of the diameter of the array of magnetic field generating elements.

34. The method according to claim 21, further comprising arranging the plurality of magnetic field generating elements to comprise at least 10 separate magnetic field generating elements.

35. The method according to claim 21, wherein the plurality of magnetic field generating elements are provided with at least 50 separate magnetic field generating elements.

36. The method according to claim 21, further comprising arranging the plurality of magnetic field generating elements to comprise at least 200 separate magnetic field generating elements.

37. The method according to claim 21, comprising: receiving an input corresponding to the output from the magnetic field sensing element in a feedback control unit; and supplying an output from the feedback control unit that includes a control signal to be input to an associated magnetic field generating element.

38. The aforementioned threshold is 5 × 10 －9 The method according to claim 21, wherein the result is less than or equal to Tesla.

39. The aforementioned threshold is 5 × 10 －10 The method according to claim 21, wherein the result is less than or equal to Tesla.

40. The method according to claim 21, wherein the value of the zeroed magnetic field generated by each of the plurality of magnetic field sensing elements is controlled by driving each of the magnetic field generating elements with a current such that the value of the magnetic field detected by each of the plurality of magnetic field sensing elements is reduced to a value corresponding to an average magnetic field gradient not exceeding approximately 10 nT / cm within the zeroed region, in accordance with the value of the magnetic field sensed by the plurality of magnetic field sensing elements.

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