JP5626678B2 - Magnetic field distribution acquisition device - Google Patents

Description

  The present invention relates to a magnetic field distribution acquisition device that acquires a three-dimensional magnetic field distribution.

  Conventionally, a magnetic field distribution has been obtained using a superconducting quantum interferometer (SQUID) sensor. For example, in Patent Document 1, a number of SQUIDs are used in a helmet-shaped sensor holder. A magnetoencephalograph is disclosed in which a sensor is arranged and fixed along the surface of a subject's head, and a magnetic field generated from various positions in the subject's brain is detected.

  In the method of acquiring a three-dimensional magnetic field distribution in Patent Document 2, a magnetic force gradient distribution on a specific measurement surface is acquired as a two-dimensional magnetic force gradient image using a magnetic force microscope above a sample having a magnetic domain. Is done. Further, an auxiliary magnetic force gradient image is obtained by performing measurement on another measurement surface separated from the measurement surface by a minute distance d, and a magnetic force gradient gradient image is obtained by dividing these differences by the minute distance d. Is done. The magnetic force gradient image and the magnetic force gradient image are Fourier transformed and substituted into a three-dimensional field acquisition equation derived from the general solution of the Laplace equation, and a three-dimensional magnetic force gradient distribution image is acquired with high accuracy.

JP 2010-46350 A International Publication No. 2008/123432 Pamphlet

  By the way, in the magnetoencephalograph of Patent Document 1, since the SQUID sensor is fixed to the helmet-shaped sensor holder, the three-dimensional magnetic field distribution shown in Patent Document 2 cannot be reconstructed, and the strict depth of the brain Magnetic field information cannot be obtained accurately. Since the technique of Patent Document 2 uses an exact solution of the Laplace equation, the magnetic field distribution to the magnetic field generation source can be reconstructed strictly. In addition, the helmet-shaped sensor arrangement method cannot be applied to an LSI process integrated on a wafer, and is not suitable for high-density integration. As a result, the magnetic field in the deep part of the brain cannot be reconstructed with high accuracy, and there is a limit to improving the accuracy of image diagnosis for brain diseases.

  On the other hand, as in Patent Document 2, magnetic force gradient distribution (or a two-dimensional distribution of n-th derivative in a specific direction of a projection component in a specific direction in a magnetic field vector) at two different distances from an object. When acquiring a magnetic force gradient distribution by moving a sensor (for example, a probe of a cantilever of a magnetic force microscope in Patent Document 2) two-dimensionally relative to an object when acquiring the magnetic force gradient distribution, Then, after acquiring the magnetic force gradient distribution by relatively moving the sensor in two dimensions, the same measurement is further performed on another measurement surface that is separated from the measurement surface by a minute distance. Therefore, the measurement requires a long time, and the two magnetisms acquired on the two measurement surfaces due to the thermal expansion of the object due to a change in ambient temperature, the movement of the object when the object is a living thing, etc. In the force gradient distribution, the portions on the object corresponding to the two positions overlapping in the direction perpendicular to the measurement surface are different. In this case, the gradient image of the magnetic force gradient cannot be acquired with high accuracy, and it becomes difficult to acquire the three-dimensional magnetic force gradient distribution easily and with high accuracy. Further, after repeating the approach and withdrawal of the sensor to and from the measurement object, the sensor moves relative to the measurement object by one pixel, and further repeats the approach and withdrawal to the measurement object. Although a method of obtaining a measurement image is also assumed, in this case, the positional deviation in the plane direction of the two images is reduced, but since the measurement time is required as in the above method, the positional deviation of the distance to the measurement object. The effect of.

  The present invention has been made in view of the above-described problems, and performs measurement of a two-dimensional magnetic field distribution at two different distances with a target at high speed and with high accuracy, thereby achieving high-precision three-dimensional magnetic field distribution. The purpose is to get.

The invention according to claim 1 is a magnetic field distribution acquisition device that acquires a three-dimensional magnetic field distribution, wherein a first sensor group that measures the magnetic field distribution is discretely arranged on a first plane facing the object. And a second sensor having a configuration similar to that of the first sensor group on a second plane which is separated from the first plane by a minute distance toward the object and is fixed in parallel to the first plane. A sensor unit in which a group is discretely arranged without overlapping the first sensor group in a normal direction of the first plane, a first measurement value group of the first sensor group, and the second sensor group And a calculation unit for obtaining a three-dimensional magnetic field distribution caused by the object based on the second measurement value group, and a sensor interval of the first sensor group in the first plane, and the first interval in the second plane. a sensor spacing 2 sensor group that matches.

  Invention of Claim 2 is a magnetic field distribution acquisition apparatus of Claim 1, Comprising: The said calculating part is set to the measured value group of one sensor group among the said 1st sensor group and the said 2nd sensor group. An interpolation calculation unit that obtains, as a new measurement value group, a magnetic field at a position overlapping with the other sensor group in the normal direction on one plane on which the one sensor group is arranged And a differential measurement value group for obtaining a differential measurement value group between the new measurement value group and the measurement value group of the other sensor group, and obtaining a differential measurement value group obtained by dividing the differential measurement value group by the minute distance. A generator.

  Invention of Claim 3 is the magnetic field distribution acquisition apparatus of Claim 1, Comprising: In the said sensor part, the arrangement | sequence of a said 1st sensor group and the arrangement | sequence of a said 2nd sensor group are the same, The said The magnetic field distribution acquisition device moves the sensor unit relative to the object in a direction along the first plane, and after performing one measurement with the sensor unit, The relative position on the first plane that overlaps the normal position and the relative position of the second sensor group with respect to the target object when the sensor unit is moved relative to the target object. The second sensor group is disposed at a relative position on the second plane that overlaps the normal position and the relative position of the first sensor group with respect to the object at the time of the one measurement. Place other measurements A control unit, wherein the computing unit is a measurement value group of the first sensor group in the one measurement and the other measurement, and a measurement of the second sensor group in the one measurement and the other measurement. A differential measurement value group generation unit that obtains a differential measurement value group that obtains a differential measurement value group from the value group and that divides the difference measurement value group by the minute distance is provided.

The invention according to claim 4 is the magnetic field distribution acquisition device according to claim 2 or 3, wherein the three-dimensional magnetic field distribution obtained by the arithmetic unit satisfies the Laplace equation and φ (x, y, z (However, the two directions parallel to the first plane and the second plane and perpendicular to each other are the X and Y directions, the normal direction is the Z direction, and x, y, and z are the X, Y, and Z directions. The first plane or the second plane is a measurement plane that satisfies z = 0, and the calculation unit is a measurement value on the measurement plane. Φ (x, y, 0) that is a group and φ _z (x, y, 0) that is the differential measurement value group are subjected to two-dimensional Fourier transform with respect to x and y, respectively, and ψ (k _x , k _y ) and ψ _{z (k x, k y)} ( _{however, k x,} k _y are the X and Y directions The wave number.) And, further, from ψ (k _x , k _y ) and ψ _z (k _x , k _y ), the result of Fourier transform of φ (x, y, z) with respect to x and y , Φ (x, y, z).

The invention described in claim 5 is the magnetic field distribution acquiring apparatus according to claim 4, wherein the calculation unit, φ (x, y, z ) z 1 and z values _in, z _{2, z} 3, ... Φ (x, y, z _n ) and φ (x, y, z _n−i ) (where n is an integer of 2 or more, i is 1 or more and less than n) And a value of z at which the value indicating the difference is equal to or smaller than a predetermined value is specified as a position in the Z direction of the magnetic field generation source.

  A sixth aspect of the present invention is the magnetic field distribution acquisition device according to any one of the first to fifth aspects, wherein each sensor included in the first sensor group and the second sensor group is a thin film element. .

  According to the present invention, it is possible to measure the two-dimensional magnetic field distribution at two different distances from the object at high speed and with high accuracy, and to acquire the three-dimensional magnetic field distribution with high accuracy. it can.

  In the inventions of claims 2 and 3, the differential measurement value group can be obtained with high accuracy, and in the invention of claim 4, the three-dimensional magnetic field distribution can be obtained with higher accuracy. In the invention of claim 5, The position of the magnetic field generation source can be specified with high accuracy.

It is a figure which shows the two-dimensional magnetic field distribution (normal direction direction component of a specific plane) which the electric current path | route installed on the specific plane forms far away. It is a figure which shows the two-dimensional magnetic field distribution (normal direction direction component of a specific plane) which the electric current path | route installed on the specific plane forms far away. FIG. A and FIG. It is a figure which shows the two-dimensional magnetic field distribution reconfigure | reconstructed based on the two-dimensional magnetic field distribution of B. It is a figure which shows the structure of a magnetic field distribution acquisition apparatus. It is a figure which shows a sensor part. It is sectional drawing which shows a sensor part. It is a figure which shows the sensor part in the middle of manufacture. It is a figure which shows the sensor part in the middle of manufacture. It is a figure which shows the sensor part in the middle of manufacture. It is a figure which shows the sensor part in the middle of manufacture. It is a figure which shows the sensor part in the middle of manufacture. It is a block diagram which shows the structure of a computer. It is a block diagram which shows the function structure which a computer implement | achieves. It is a figure which shows the flow of the process in which a magnetic field distribution acquisition apparatus acquires a three-dimensional magnetic field distribution. It is a figure which shows a sensor part. It is a figure which shows the sensor part of a comparative example. It is sectional drawing which shows the sensor part of a comparative example. It is a figure which shows the relationship between the minimum limit value of a level | step difference, the distance of the Y direction between a current path and a sensor, and the maximum value of the resistance change rate of a sensor. It is a figure which shows the relationship between the minimum limit value of a level | step difference, and the distance of the Y direction between an electric current path | route and a sensor. It is a figure which shows the relationship between the minimum limit value of a level | step difference, and the maximum value of the resistance change rate of a sensor. It is a figure which shows the relationship between the minimum limit value of a level | step difference, the distance of the Y direction between a current path and a sensor, and element resistance. It is a figure which shows the relationship between the minimum limit value of a level | step difference, and element resistance. It is a figure which shows the other example of a sensor part. It is a figure for demonstrating the principle of the two-dimensional field distribution acquisition method which concerns on related technology. It is a figure which shows the other example of a sensor part. It is sectional drawing which shows the other example of a sensor part. It is a figure which shows the sensor part of another comparative example. It is sectional drawing which shows the sensor part of another comparative example. It is a figure which shows the other example of a sensor part. It is sectional drawing which shows the other example of a sensor part. It is a figure which shows the other example of a sensor part. It is sectional drawing which shows the other example of a sensor part. It is a figure which shows the sensor part of another comparative example. It is sectional drawing which shows the sensor part of another comparative example. It is a figure which shows the sensor part of another comparative example. It is sectional drawing which shows the sensor part of another comparative example. It is a figure which shows the other example of a sensor part. It is a figure which shows the other example of a magnetic field distribution acquisition apparatus. It is a figure which shows a mode that binocular stereoscopic vision is performed.

  First, the principle of the magnetic field distribution acquisition method according to the present invention will be described. Maxwell's basic equation is expressed by Equation 1, where E is the electric field strength, B is the magnetic flux density, H is the magnetic field strength, D is the electric flux density, i is the current density, ρ is the charge density, and t is the time. .

With σ as the conductivity, i can be expressed as σE, and E = E′e ^jωt , B = B′e ^jωt , H = H′e ^jωt , D = D′ e ^jωt (where E ′, (B ′, H ′, D ′ represent amplitudes, j is an imaginary number, and ω is an angular frequency.), Equation 1 is represented by Equation 2.

  Since D ′ can be expressed as εE ′ where ε is the dielectric constant, the second expression from the top of Expression 2 is expressed by Expression 3, and can be further transformed into Expression 4.

  The magnetic permeability is μ, and B ′ can be expressed as μH ′. Based on B ′ = μH ′ and the uppermost expression of Expression 2, Expression 4 is expressed by Expression 5.

  Here, Equation 6 is established using Nabla and Laplacian Δ.

  Further, divH ′ is 0 from Equation 2 at the bottom of Equation 2, and ∇ · H ′ in Equation 6 is 0, so Equation 5 is expressed by Equation 7.

  When ω is sufficiently small in Equation 7, ΔH ′ is 0, and the magnetic field represented by H ′ satisfies the Laplace equation.

  In this magnetic field distribution acquisition method, an object to be measured is arranged in an orthogonal coordinate system defined by mutually perpendicular X, Y, and Z directions, and H ′ is a component in each of the X, Y, and Z directions. have. In a sensor unit described later, a magnetic field (vector) component in a predetermined direction (which may be a direction approximately along the direction, and hereinafter referred to as “detection direction”) is detected. A three-dimensional distribution (hereinafter also referred to as “three-dimensional magnetic field distribution”) of the detection direction component (hereinafter also simply referred to as “magnetic field”) is defined as a function of the distribution of the field to be measured. y, z) (where x, y, and z indicate coordinate parameters in the X, Y, and Z directions).

  As described above, φ (x, y, z) is expressed by Equation 8 using Laplacian Δ.

  Therefore, an expression relating to acquisition of a three-dimensional magnetic field distribution is derived by a method similar to that of International Publication No. 2008/123432 (Patent Document 2). Specifically, the general solution of equation (8) is expressed by equation (9) as the sum of an exponentially decaying term in the Z direction and an exponentially increasing term in the X, Y, Z Cartesian coordinate system. be able to.

In Equation 9, k _x and k _y are wave numbers in the X direction and Y direction, and A (k) and B (k) are functions represented by k _x and k _y . Furthermore, what differentiated both sides of Formula 9 once by z is expressed by Formula 10. In Expression 10, φ (x, y, z) that is differentiated once by z is expressed as φ _z (x, y, z).

  Here, φ (x, y, z) in a plane parallel to the XY plane that satisfies z = 0, that is, φ (x, y, 0) is expressed by Equation 11.

Similarly, φ _z (x, y, 0) is expressed by Equation 12 by substituting z = 0 into Equation 10.

ψ (k _x , k _y ) and ψ _z (k _x , k _y ) (hereinafter, ψ (k) and ψ (k _x , k _y )) obtained by Fourier transform of φ (x, y, 0) and φ _z (x, y, 0), respectively. ψ _z (k)) is represented by A (k) + B (k) and | k | (A (k) −B (k)), respectively. Accordingly, each of A (k) and B (k) can be expressed using ψ (k) and ψ _z (k), and by substituting these into Equation 9, Equation 13 is derived.

From the above, φ (x, y, 0), which is a Dirichlet type boundary condition, and φ _z (x, which is a Neumann type boundary condition) by measurement on a measurement surface satisfying z = 0 set outside the object. , Y, 0) is obtained by performing a Fourier transform to obtain a result of Fourier transform of φ (x, y, z) with respect to x and y as shown in Equation 13 and performing an inverse Fourier transform. , Φ (x, y, z) can be acquired, and a three-dimensional magnetic field distribution is strictly derived.

  FIG. A and FIG. B is a diagram showing an example of a magnetic field satisfying the Laplace equation, and shows a result of a computer obtaining a magnetic field formed around when a current is passed through a path of a “god” shape. The current path exists on a predetermined plane parallel to the XY plane. A and FIG. B indicates the magnetic field in a plane away from this plane by 4.25 μm (micrometer) and 4.75 μm in the Z direction. FIG. C is the same as FIG. A and FIG. Using the two two-dimensional magnetic field distribution images of B, the three-dimensional magnetic field distribution is reconstructed according to Equation 13, and the two-dimensional magnetic field distribution at coordinates 0.25 μm away from the current path in the Z direction is displayed. . In addition, FIG. In C, the word “God” is marked with a white line for reference.

FIG. As shown in FIG. 1C, the shape of the current path can be determined from the magnetic field in the plane close to the current path. A and FIG. As shown in B, the shape of the current path is not clear on the surface away from the current path. However, for example, FIG. Assuming that the surface of the magnetic field shown in B is a measurement surface satisfying z = 0, the above-described φ (x, y, 0) and φ _z (x, y, 0) are obtained by measurement. By using the magnetic field distribution acquisition method according to the above, it is possible to obtain φ (x, y, z) at an arbitrary z value, and direct measurement is not possible due to the case where a current path is formed in the object. It is possible to reproduce the magnetic field distribution on the possible planes (the plane of the magnetic field shown in FIG. 1.C). The above principle is established within a range where φ (x, y, z) satisfies the Laplace equation, and the magnetic field distribution can be obtained within this range.

  Next, a magnetic field distribution acquisition apparatus using the magnetic field distribution acquisition method will be described. FIG. 2 is a diagram illustrating a configuration of the magnetic field distribution acquisition apparatus 1. The magnetic field distribution acquisition device 1 includes a planar sensor unit 2 having a plurality of sensors that measure a magnetic field distribution derived from an object 9 (for example, a human body), and a moving mechanism 3 that moves the sensor unit 2 along its main surface. And a computer 4 that is a control unit that controls each component of the magnetic field distribution acquisition device 1. Note that the rotation mechanism 3b indicated by a broken-line rectangle in FIG. 2 is used in a processing example described later, and is not used in this processing example.

  FIG. 3 is a diagram illustrating the sensor unit 2 viewed from the object 9 side, and FIG. 4 is a cross-sectional view of the sensor unit 2 at the position of the arrow AA in FIG. As shown in FIG. 4, the sensor unit 2 includes a plate-like base material 20, and a plurality of first sensors 211 that are thin film elements using a tunneling magnetoresistance (TMR) effect are provided on the base material 20. Formed on the main surface. The plurality of first sensors 211 are covered with an insulating material 231, and a plurality of second sensors 221 that are TMR elements similar to the first sensor 211 are formed on the insulating material 231 whose surface is planarized. . Similarly to the first sensor 211, the plurality of second sensors 221 are also covered with an insulating material 232.

  In FIG. 3, the first sensor 211 and the second sensor 221 in the insulating materials 231 and 232 are illustrated by solid lines, and the first sensor 211 is indicated by parallel diagonal lines (see FIGS. 9, 17, and FIG. 19, the same as in FIGS. 23 and 25), the first sensor 211, and the second sensor 221 are alternately arranged in the X direction and the Y direction in FIG. 3 (that is, in a checkered pattern). Further, the distance between the centers in the X direction and the Y direction (hereinafter referred to as “arrangement pitch”) between the first sensor 211 and the second sensor 221 adjacent to each other is constant at P1 and P2, respectively. In the following description, a set of the plurality of first sensors 211 is referred to as a first sensor group 21, and a set of the plurality of second sensors 221 is referred to as a second sensor group 22. In FIG. 3, 144 sensors 211 and 221 are arranged, but in the actual sensor unit 2, a large number of sensors 211 and 221 are arranged.

  Here, the plane including the main surface of the substrate 20 (the main surface on the (+ Z) side in FIG. 4) is the first plane 81, and the main surface of the flattened insulating material 231 (the (+ Z) side in FIG. 4). In FIG. 3 and FIG. 4, in the sensor unit 2, the first sensor group 21 is discrete on the first plane 81 facing the object 9. Ordered. Further, the first sensor group 21 is placed on the second plane 82 which is separated from the first plane 81 by the minute distance d toward the object 9 ((+ Z) side) and is fixed in parallel to the first plane 81. The second sensor group 22 having the same configuration as that of the first sensor group 21 is discretely arranged without overlapping the first sensor group 21 in the normal direction of the first plane 81 (that is, the Z direction). The first plane 81 and the second plane 82 are parallel to the X direction and the Y direction.

  When the sensor unit 2 is manufactured, FIG. As shown in FIG. 5A, a ferromagnetic metal layer 291, an insulator layer 292, and a ferromagnetic metal layer 293 are sequentially formed on the substrate 20, and FIG. As shown in B, a negative type photosensitive material (photoresist) film 299 is formed on these layers 291 to 293. Subsequently, light is irradiated to a region on the film 299 corresponding to the plurality of first sensors 211 of the first sensor group 21 (in the case where the photosensitive material is a positive type, other than the region), and development processing is performed. As shown in FIG. As shown in C, a pattern of photosensitive material corresponding to the plurality of first sensors 211 is formed. Then, after the plasma etching process is performed, the photosensitive material is removed, so that FIG. As shown in D, a plurality of first sensors 211 are formed on the substrate 20.

  An insulating material is applied on the base material 20, and the surface thereof is polished and flattened, whereby FIG. As shown in E, an insulating material (layer) 231 is formed. By repeating the above process on the insulating material 231, the sensor unit 2 of FIG. 4 in which the first sensor group 21, the insulating material 231, the second sensor group 22, and the insulating material 232 are formed is completed. Actually, each of the sensors 211 and 221 is formed with a conductive leader line. One of the ferromagnetic metal layers 291 and 293 is a pinned layer, and the other is a soft layer.

  As shown in FIG. 6, the computer 4 is a general computer system in which a CPU 41 for performing various calculations, a ROM 42 for storing basic programs, and a RAM 43 for storing various information are connected to a bus line. The bus line further includes a fixed disk 44 for storing information, a display 45 for displaying various information, a keyboard 46a and a mouse 46b for accepting input from an operator, an optical disk, a magnetic disk, a magneto-optical disk, and the like. A reading device 47 that reads information from the recording medium 8 and a communication unit 48 that sends a control signal to the moving mechanism 3 and receives a signal from the sensor unit 2 appropriately pass through an interface (I / F). Equally connected.

  The computer 4 reads the program 441 from the recording medium 8 via the reader 47 in advance and stores it in the fixed disk 44. The program 441 is copied to the RAM 43 and the CPU 41 executes arithmetic processing according to the program in the RAM 43 (that is, when the computer 4 executes the program), thereby realizing a function as an arithmetic unit described later. .

  FIG. 7 is a block diagram illustrating a functional configuration realized by the CPU 41, the ROM 42, the RAM 43, the fixed disk 44, and the like by the CPU 41 operating according to the program 441. In FIG. 7, the calculation unit 5 including the interpolation calculation unit 51, the differential measurement value group generation unit 52, and the magnetic field acquisition unit 53 shows functions realized by the CPU 41 and the like. The interpolation calculation unit 51 is a function used in the processing described later. These functions may be realized by a dedicated electrical circuit, or a partially dedicated electrical circuit may be used. Further, it may be realized by a plurality of computers.

  FIG. 8 is a diagram showing a flow of processing in which the magnetic field distribution acquisition device 1 acquires a three-dimensional magnetic field distribution. In the magnetic field distribution acquisition device 1 of FIG. 2, first, an object 9 is arranged at a position facing the sensor unit 2, and the magnetic field distribution is simultaneously performed by the first sensor group 21 and the second sensor group 22 of the sensor unit 2 of FIG. 3. Is measured (step S11). As described above, each of the sensors 211 and 221 has a structure in which an insulator layer is sandwiched between two ferromagnetic metal layers extending along the main surface of the substrate 20. , For example, a magnetic field in the X direction is detected (that is, the detection direction is the X direction). Magnetic fields in the detection direction (hereinafter also simply referred to as “magnetic fields”) acquired by the first sensor group 21 and the second sensor group 22 are output to the computing unit 5.

  Subsequently, after confirming that the sensor unit 2 is moved (step S12), the sensor unit 2 is moved in the X direction by a distance equal to the arrangement pitch P1 (step S13). In FIG. 9, the sensor unit 2 before movement is indicated by a two-dot chain line, and the sensor unit 2 after movement is indicated by a solid line. Since the arrangement of the first sensor group 21 on the first plane 81 and the arrangement of the second sensor group 22 on the second plane 82 are the same, the sensor unit 2 after the movement has the second measurement at the previous measurement. The first sensor group 21 is disposed at a position on the first plane 81 that overlaps with the position of the sensor group 22 in the Z direction, and the second plane 82 that overlaps with the position of the first sensor group 21 at the time of the previous measurement in the Z direction. The second sensor group 22 is disposed at the upper position (except for the plurality of sensors 211 and 221 arranged in the Y direction on the leftmost side ((−X) side) in FIG. 9).

  Then, the first sensor group 21 and the second sensor group 22 simultaneously measure the magnetic fields in the detection direction and output them to the computing unit 5 (step S11). By the twice measurement in step S11 repeated twice, in the sensor unit 2 after movement in FIG. 9, X and X of all the sensors 211 and 221 except for the plurality of sensors 211 and 221 arranged in the Y direction on the leftmost side. At the position in the Y direction, the magnetic field on the first plane 81 and the magnetic field on the second plane 82 are acquired.

  In the differential measurement value group generation unit 52, φ (x, y, 0) is acquired from the measurement value group of the first sensor group 21 in two steps S11 with the first plane 81 as a measurement surface that satisfies z = 0. Is done. In the present embodiment, the value (magnetic field) of φ (x, y, 0) at each position on the measurement surface 81 is converted into a pixel value, and the two-dimensional distribution of the magnetic field on the measurement surface 81 is the first image (exactly). Is acquired as image data). Similarly, the magnetic field distribution (that is, φ (x, y, d)) in the second plane 82 is acquired as the second image from the measurement value group of the second sensor group 22 in step S11 twice.

When the first and second images are prepared, a differential image of these images is obtained, and a differential image obtained by dividing the differential image by a minute distance d (a distance between the first plane 81 and the second plane 82). Is generated. The differential image is an image that substantially shows the Z-direction differential of the magnetic field on the measurement surface 81, that is, the gradient of the magnetic field (step S14). As described above, the first image is represented by φ (x, y, 0). Further, since the gradient of the magnetic field is obtained by differentiating the magnetic field with z, the differential image indicating the gradient of the magnetic field is an image indicating φ _z (x, y, 0).

  When the measurement value group acquired by the first sensor group 21 in the two measurements in step S11 is the first measurement value group, and the measurement value group acquired by the second sensor group 22 is the second measurement value group The processes in steps S11 to S14 acquire a first measurement value group and a second measurement value group that indicate a two-dimensional distribution of magnetic fields (hereinafter also referred to as “magnetic field distribution”). The difference measurement value group with respect to the two measurement value groups is obtained, and the difference measurement value group is further divided by the minute distance d to obtain the differential measurement value group.

Subsequently, in the magnetic field acquisition unit 53, the first image that is φ (x, y, 0) and the differential image that is φ _z (x, y, 0) are two-dimensionally Fourier transformed with respect to x and y, and ψ ( k) and ψ _z (k) (ie, ψ (k _x , k _y ) and ψ _z (k _x , k _y ) (where k _x , k _y are the wave numbers in the X direction and the Y direction)). Is obtained (step S15). Specifically, as the Fourier transform, a two-dimensional discrete Fourier transform is performed. In the Fourier transform, for example, a method of multiplying both images by using a sine function in the range of 0 to π (M is 0 or more) as a window function. Adopted.

When ψ (k) and ψ _z (k) are obtained, the equation shown in Expression 13 (hereinafter referred to as “three-dimensional magnetic field distribution obtaining equation”) is used using ψ (k) and ψ _z (k). Is used to obtain φ (x, y, z) (step S16). When ψ (k) and ψ _z (k) are substituted into the three-dimensional magnetic field distribution acquisition formula and inverse Fourier transform is performed with respect to k, a window function similar to that at the time of Fourier transform is used. By obtaining φ (x, y, z), a three-dimensional magnetic field distribution (three-dimensional magnetic field distribution) is obtained strictly.

Subsequently, while sequentially changing the value of z in φ (x, y, z) to z ₁ , z ₂ , z ₃ ,..., Φ (x, y, z _n ) and φ (x, y, z _n-i ) (where n is an integer of 2 or more and i is an integer of 1 or more and less than n) (hereinafter referred to as “evaluation value”). Desired. In the present embodiment, i is 1, and the sum of differences between φ (x, y, z _n ) and φ (x, y, z _n−1 ) or other values indicating cross-correlation (similarity). May be used as an evaluation value that increases as the difference between the two increases. Then, a value h of z at which the evaluation value is equal to or less than a predetermined value is obtained and specified as a position (approximate position) in the Z direction of the magnetic field generation source. The generation source of the magnetic field is the surface or the inside of the object 9. In the magnetic field distribution acquisition device 1, an image showing φ (x, y, h) is stored in the fixed disk 44 as an image showing the magnetic field distribution in the magnetic field generation source (near) (step S17). Since the magnetic field distribution at the magnetic field source corresponds to the state of the magnetic field source, the above operation causes the state of the magnetic field source even when the magnetic field source is within the object. Can be obtained.

  Here, a measurement of a comparative example in which one sensor is moved in the X direction and the Y direction with respect to an object to acquire a magnetic field distribution will be described. When acquiring the magnetic field using the measurement method of the comparative example, after moving the sensor in the X direction and the Y direction on one measurement surface to acquire the magnetic field distribution, the micro distance from the measurement surface in the Z direction. Since the same measurement is performed on other measurement surfaces that are separated by a long distance, the measurement takes a long time. Therefore, in the two magnetic field distributions acquired on the two measurement surfaces due to the thermal expansion of the object due to a change in the ambient temperature, the movement of the object when the object is a living thing, and the like, 2 overlaps in the Z direction. The site | part on the target object to which one position respond | corresponds will differ. In this case, the differential image cannot be acquired with high accuracy, and it is difficult to acquire the three-dimensional magnetic field with high accuracy. Also, move one sensor in the X and Z directions with respect to the object, acquire magnetic field data at two or more coordinates at different heights, and then change the position of one pixel in the Y direction In the method of repeating the above, it is possible to acquire the same or more data amount as described above. In this case, the position of the XY coordinates of the two pieces of image data is a change with time of the relative position of the sensor and the sample. Even if it is guaranteed, the reliability of the Z coordinate is low.

  In contrast, in the sensor unit 2 of the magnetic field distribution acquisition device 1, the first sensor group 21 is discretely arranged on the first plane 81 facing the object 9, and the object 9 side from the first plane 81. The second sensor group 22 having the same configuration as the first sensor group 21 is arranged on the second plane 82 which is separated by a small distance d and fixed in parallel to the first plane 81. They are arranged discretely without overlapping the first sensor group 21 in the normal direction. Thereby, in the magnetic field distribution acquisition apparatus 1, the measurement of the two-dimensional distribution of the magnetic field in two different distances between the object 9 can be performed at high speed and with high accuracy. As a result, based on the first measurement value group of the first sensor group 21 and the second measurement value group of the second sensor group 22, the three-dimensional magnetic field distribution resulting from the object 9 can be obtained with high accuracy. Realized.

  By the way, as shown in FIG. 10 and FIG. 11, when the sensor part 91 of the other comparative example by which the some sensor 911 is arranged by arrangement pitch P1, P2 in the X direction and the Y direction on the same plane is assumed, In such a sensor unit 91, the distance between the sensors 911 in the X direction and the Y direction becomes narrow, and the manufacture of the sensor unit 91 is not easy. On the other hand, in the sensor unit 2 of FIG. 4, the first sensor group 21 is formed on the first plane 81 and the second sensor group 22 is formed on the second plane 82. In each of the second planes 82, the distance between the sensors in the X direction and the Y direction can be made wider than that of the sensor unit 91 of the comparative example, and the sensor unit 2 can be easily manufactured. In the case of the sensor unit 2 of FIG. 4 manufactured by the same method as the semiconductor manufacturing process, it is possible to easily position the sensors on the first plane 81 and the second plane 82 with high accuracy. .

In the calculation unit 5, φ (x, y, 0), which is a measurement value group on the measurement surface 81, and φ _z (x, y, 0), which is a differential measurement value group, are Fourier-transformed, respectively, ψ (k _x , k _y ) and ψ _z (k _x , k _y ) are obtained, and Φ (x, y, z) is further Fourier transformed from ψ (k _x , k _y ) and ψ _z (k _x , k _y ) To obtain φ (x, y, z). Thereby, the three-dimensional magnetic field distribution can be obtained more accurately.

  Further, in the magnetic field distribution acquisition device 1, after one measurement is performed by the sensor unit 2, the moving mechanism 3 moves the sensor unit 2 in a direction along the first plane 81, so that the one measurement with respect to the Z direction is performed. The first sensor group 21 is arranged at a position on the first plane 81 that overlaps with the position of the second sensor group 22 at the time, and on the second plane 82 that overlaps with the position of the first sensor group 21 at the time of the one measurement. The second sensor group 22 is arranged at the position, and another measurement is performed. Then, a difference measurement value group between the measurement value group of the first sensor group 21 in the one measurement and the other measurement and the measurement value group of the second sensor group 22 in the one measurement and the other measurement is obtained. Then, the differential measurement value group is obtained by dividing the difference measurement value group by the minute distance d. Thereby, the differential measurement value group can be obtained with high accuracy, and the three-dimensional magnetic field distribution can be obtained with higher accuracy.

Further, the arithmetic unit 5 sequentially changes the values of z in φ (x, y, z) to z ₁ , z ₂ , z ₃ ,..., Φ (x, y, z _n ) and φ (x , Y, z _n-1 ) (where n is an integer greater than or equal to 2), an evaluation value is obtained, and the z value at which the evaluation value is less than or equal to a predetermined value is the Z direction of the magnetic field generation source. Is specified as the position. Thereby, the position of the generation source of a magnetic field can be specified accurately.

Here, the minimum limit value of the minute distance d (that is, the step between the first sensor 211 and the second sensor 221) between the first plane 81 and the second plane 82 in the sensor unit 2 will be described. In each of the sensors 211 and 221 which are TMR elements, the minimum limit value D _lim [m] of the step between the first sensor 211 and the second sensor 221 is based on Johnson noise derived from the element resistance as shown in Equation 14: expressed. In Equation 14, it is assumed that there is a current path having a length l _x [m] in the object 9 (a current path extending only in the X direction), and a current value flowing through the current path is I [A]. Also, the distance in the Y direction between the sensor located at the same position as one end of the current path with respect to the X direction and the one end of the current path is denoted by r _a [m], and the distance in the Z direction is denoted by r _b [m]. . Note that μ is the magnetic permeability, A _a is the maximum value [%] of the resistance change rate of the sensor, v ₀ is the applied voltage value [V] to the sensor, and R ₀ is a state in which no magnetic field is acting. Is the element resistance [Ω], k is the Boltzmann constant, B is the noise bandwidth [Hz], and T is the sensor temperature [K]. In addition, when the resistance change rate [%] of the sensor is (A _a / 2) and the slope of the resistance change rate with respect to the magnetic field H is (A _a / H _w ), B _w is obtained as μH _w. .

Figure 12 is a minimum limit value D _lim of the step is a diagram showing the relationship between the distance r _a and the maximum value A _a rate of change in resistance of the sensor in the Y direction between the current path and the sensor. Here, the current value I is 1.0 [μA], the current path length l _x is 10 [nm], and the distance r _{b in} the Z direction between the current path and the sensor (that is, the current path is formed). The distance between the measured surface and the measurement surface is 1.0 [μm], and the element resistance R ₀ is 0.40 [Ω] (here, the resistance per unit area is 0.40 [Ω / μm). ² ], the area of the element is 1 [μm ² ].), H _w is 5.0 × 10 ⁻² [T], and the noise bandwidth B is 1.0 [Hz]. The temperature T of the sensor is 300 [K]. FIG. 13 shows the relationship between the minimum limit value D _lim of the step when the maximum value A _a of the resistance change rate of the sensor is 50 [%] and the distance r _{a in} the Y direction between the current path and the sensor. is a diagram showing a, 14 Y direction distance r _a is 0.32 [[mu] m] steps of the minimum limit value D _lim and the maximum value of the resistance change rate of the sensor when it is between the current path and the sensor is a diagram showing the relationship between a _a.

Figure 15 is a minimum limit value D _lim of the step is a diagram showing the relationship between the Y-direction distance r _a and the element resistance R ₀ between the current path and the sensor. In Figure 15, the maximum value A _a rate of resistance change of the sensor except a 50 [%], the conditions are the same as FIG. 12. Figure 16 is a diagram showing the relationship between the minimum limit value D _lim and element resistance R ₀ of the step when Y direction distance r _a is 0.32 [[mu] m] between the current path and the sensor.

For example, a current value I is 1.0 [.mu.A], a current path length _{l x} is 10 [nm], in the Z-direction distance _{r b} between the current path and the sensor 1.0 [[mu] m] There, the distance _{r a} in the Y direction between the current path and the sensor is the 3.2 [[mu] m], the element resistance _{R 0} of the sensor is 0.40 [Omega], the maximum value _{a a} rate of change of resistance Is 50 [%], H _w is 5.0 × 10 ⁻² [T], noise bandwidth B is 1.0 [Hz], and sensor temperature T is 300 [K]. In this case, the minimum limit value D _lim of the step is 260 [nm]. In addition, about the maximum limit value of a level | step difference, it determines suitably according to the distance between the sensor part 2 and the target object 9, and an electric current value.

Next, another processing example in the magnetic field distribution acquisition apparatus 1 will be described. Here, the pitches in the X direction and Y direction of the first sensor 211 on the first plane 81 are P _X and P _Y, and the pitches in the X direction and Y direction of the second sensor 221 on the second plane 82 are also P _X , P _{As Y} , coordinates in the X direction and Y direction of the first sensor 211 arranged on the first plane 81 are represented as (nP _X , mP _Y ) (where n and m are integers of 0 or more), and the second Assume that the coordinates in the X direction and the Y direction of the second sensor 221 arranged on the plane 82 are represented as ((n + 1/2) P _X , (m + 1/2) P _Y ). In the present processing example, the interpolation calculation unit 51 of FIG. 7 is used.

In the magnetic field distribution acquisition device 1, when the magnetic field is measured by the first sensor group 21 and the second sensor group 22 of the sensor unit 2 (step S11), the gradient of the magnetic field is shown without moving the sensor unit 2. The differential image φ _z (x, y, 0) is acquired (steps S12 and S14).

Specifically, since the coordinates in the X direction and the Y direction of the first sensor 211 arranged on the first plane 81 (measurement surface) are expressed as (nP _X , mP _Y ) as described above, interpolation is performed. In the calculation unit 51, the measurement value group φ (x, y, 0) acquired by the first sensor 211 is expressed by Equation 15.

  Similarly, the measurement value group φ (x, y, d) acquired by the second sensor 221 is expressed by Expression 16.

At this time, the magnetic field value φ (nP _{X at} a position on the second plane 82 that overlaps the first sensor 211 in the Z direction, that is, a position where the coordinates in the X direction and the Y direction are represented as (nP _X , mP _Y ). , MP _Y , d) can be approximated as in Eq.

That is, in Equation 17, interpolation calculation is performed on the measurement value group of the second sensor group 22, and a position facing the plurality of first sensors 211 on the second plane 82 (the second sensors 221 are arranged). A new group of measured values at the coordinates (positions represented by the coordinates (nP _X , mP _Y )) is obtained. In Equation 17, the average value (linear interpolation) of the measurement values of the two adjacent second sensors 221 is calculated, but other types of interpolation calculations may be performed.

In this way, when the measurement values at the positions represented by the coordinates (nP _X , mP _Y ) are obtained on both the first plane 81 and the second plane 82, the differential measurement value group generation unit 52 performs numerical values. As shown in FIG. 18, the difference measurement value group between the new measurement value group and the measurement value group of the first sensor group 21 is divided by the minute distance d between the first plane 81 and the second plane 82. Thus, a differential measurement value group φ _z (x, y, 0) that is a differential image is obtained.

When the differential image φ _z (x, y, 0) is obtained, φ (x, y, 0) and φ _z (x, y, 0) are Fourier-transformed with respect to x and y in the same manner as in the above processing example. Ψ (k _x , k _y ) and ψ _z (k _x , k _y ) (that is, ψ (k) and ψ _z (k)) are obtained (step S15), ψ (k _x , k _y ) and Using φ _z (k _x , k _y ), φ (x, y, z) is obtained by a three-dimensional magnetic field distribution acquisition formula (step S16). Then, by obtaining the evaluation value while sequentially changing the value of z, the position of the magnetic field generation source in the Z direction is specified, and an image showing the magnetic field distribution in the magnetic field generation source is acquired (step S17).

  As described above, in the magnetic field distribution acquisition device 1, Z is performed on the second plane 82 on which the second sensor group 22 is arranged by performing an interpolation operation on the measurement value group of the second sensor group 22. A magnetic field at a position overlapping the first sensor group 21 in the direction is obtained as a new measurement value group. Then, a differential measurement value group between the new measurement value group and the measurement value group of the first sensor group 21 is obtained, and the differential measurement value group is obtained by dividing the differential measurement value group by the minute distance d. . Thereby, in the magnetic field distribution acquisition device 1, it is possible to accurately obtain the differential measurement value group without moving the sensor unit 2, and to obtain the three-dimensional magnetic field distribution resulting from the object 9 with high accuracy. Become.

  The interpolation calculation unit 51 performs interpolation calculation on the measurement value group of the first sensor group 21, so that the first calculation unit 51 in the normal direction of the sensor unit 2 on the first plane 81 on which the first sensor group 21 is arranged. The magnetic field at a position overlapping the two sensor group 22 may be obtained as a new measurement value group. That is, by performing an interpolation operation on the measurement value group of one of the first sensor group 21 and the second sensor group 22, on one plane where the one sensor group is arranged, the sensor unit A magnetic field at a position overlapping with the other sensor group in the normal direction of 2 is obtained as a new measurement value group. Then, a differential measurement value group between the new measurement value group and the measurement value group of the other sensor group is obtained, and the differential measurement value group is divided by the minute distance d to obtain the differential measurement value group. Further, the differential measurement value group may be obtained with high resolution by performing an interpolation operation on the measurement value groups of both the first sensor group 21 and the second sensor group 22.

  The arrangement of the first sensor 211 and the second sensor 221 in the magnetic field distribution acquisition device 1 may be variously changed. For example, as shown in FIG. The sensor rows and the second sensor rows in which the plurality of second sensors 221 are continuously arranged in the Y direction may be alternately arranged in the X direction.

When obtaining φ (x, y, 0) and φ _z (x, y, 0) in the sensor unit 2a of FIG. 17, after performing one measurement (FIG. 8: step S11), the moving mechanism 3, the sensor unit 2 a is slightly moved, and the second sensor group 22 at the time of the one measurement (shown by a solid line in FIG. 17) and the position on the first plane 81 that overlaps in the Z direction. The first sensor group 21 is arranged, and the second sensor group 22 is arranged at a position on the second plane 82 that overlaps the position of the first sensor group 21 and the Z direction at the time of the one measurement (in FIG. 17). (See the sensor unit 2a indicated by a two-dot chain line) (steps S12 and S13). The sensor unit 2a obtains φ (x, y, 0) and φ (x, y, d) by performing the following measurement (step S11), and the differential measurement value group generation unit 52 obtains φ _z (X, y, 0) is obtained (steps S12 and S14). Thereby, the three-dimensional magnetic field distribution resulting from the object 9 can be obtained with high accuracy. Of course, the differential measurement value group may be obtained with high accuracy without moving the sensor unit 2a by performing an interpolation calculation in the sensor unit 2a of FIG.

  Next, the principle of the two-dimensional field distribution acquisition method according to the related technique of the present invention will be described. FIG. 18 is a diagram for explaining the principle of the two-dimensional field distribution acquisition method. FIG. 18 shows an orthogonal coordinate system defined by X, Y, and Z directions perpendicular to each other. The thin film sensor denoted by reference numeral 92 in FIG. 18 extends in a direction parallel to the measurement surface on an arbitrary measurement surface that satisfies z = α (where α is an arbitrary value).

  In the following description, the Y direction is the reference direction, the longitudinal direction of the sensor 92 is the Y ′ direction, the direction perpendicular to the longitudinal direction (Y ′ direction) on the measurement surface is the X ′ direction, and the reference direction and the Y ′ direction are formed. The angle (hereinafter referred to as “sensor angle”) is θ, the coordinate parameters in the X ′ direction and the Y ′ direction are x ′ and y ′ (where the origin in the X ′ direction and the Y ′ direction is on the Z axis, 18 is the same as the origin of the orthogonal coordinate system defined in the X, Y, and Z directions.

  In the two-dimensional field distribution acquisition method according to the related technology, the sensor 92 is moved in the X ′ direction, and a predetermined region on the measurement surface (a region of interest on the object is a region projected on the measurement surface; , Referred to as “measurement target region”). Then, a signal indicating the magnetic field (total sum of magnetic field lines passing through the sensor 92) received by the entire sensor 92 at each position x 'in the X' direction during scanning is generated and acquired as a measurement value. In practice, the sensor angle θ is changed in a plurality of ways within a range of 0 ° or more and less than 180 °, and scanning in the direction perpendicular to the longitudinal direction is repeated on the measurement surface, and the measurement is derived from a three-dimensional field. A function f (x ′, θ) indicating a value (hereinafter simply referred to as “measured value f (x ′, θ)”) is acquired using x ′ and θ as parameters. It is assumed that the Z axis passes through approximately the center of the measurement target region.

  Here, when viewed along the Z direction, the X′Y ′ coordinate system is obtained by rotating the XY coordinate system by the sensor angle θ about the Z axis, and therefore Expression 19 is satisfied.

  Further, as described above, during each scan in which the sensor 92 is moved in the X ′ direction, since the magnetic field received by the entire sensor 92 is acquired, the measured value f (x ′, θ) is expressed by Equation 20. The Note that the sensor 92 is set to be sufficiently longer than the width of the measurement target region with respect to the longitudinal direction (Y ′ direction) of the sensor 92.

Here, ψ (k _x , k _y ) | _{z = α} (hereinafter simply referred to as ψ (k _x , k _y )) obtained by Fourier transform of φ (x, y, α) in the X direction and the Y direction. It is expressed as Equation 21. However, the number _21, k x, _{k y} is the wave number of the X and Y directions.

In Expression 21, when (k _x = k _{x ′} cos θ), (k _y = k _{x ′} sin θ), and (x ′ = x cos θ + ysin θ) are set, Expression 22 is obtained. However, in Expression 22, k _{x ′} and k _{y ′} are wave numbers in the X ′ direction and the Y ′ direction.

  Further, (dxdy) in Expression 22 is expressed by Expression 23.

Therefore, Equation 22 can be transformed into Equation 24 using Equations 19, 20, and 23. In Equation 24, ψ (k _{x ′} cos θ, k _{x ′} sin θ) is expressed as g (k _{x ′} , θ).

On the other hand, φ (x, y, α) can be expressed as in Expression 25. However, (k _x = k _{x ′} cos θ), (k _y = k _{x ′} sin θ), and (x ′ = x cos θ + ysin θ) are set.

By substituting ψ (k _{x ′} cos θ, k _{x ′} sin θ) of _equation 24 into _equation 25, φ (x, y, α) is expressed by equation 26.

As described above, the sensor 92 is scanned on the measurement surface while changing the angle (that is, sensor angle) θ formed by the reference direction and the longitudinal direction of the sensor 92 in a plurality of ways, and the measured value f (x ′, θ) is obtained, and further, g (k _{x ′} , θ) obtained by Fourier-transforming the measured value f (x ′, θ) with respect to x ′ is obtained, thereby obtaining Equation 26 (hereinafter, “two-dimensional field distribution acquisition formula”). Can be used to obtain φ (x, y, α).

  When acquiring a three-dimensional magnetic field distribution using the related technology, the sensor 92 is scanned on the measurement surface while changing the sensor angle θ on the measurement surface satisfying z = 0, and the measurement value is obtained. By obtaining f (x ′, θ), φ (x, y, 0) as the first image is obtained. Subsequently, by changing the sensor angle θ on the measurement surface satisfying z = d in a plurality of ways, the sensor 92 is scanned on the measurement surface to obtain the measurement value f (x ′, θ). Two images φ (x, y, d) are obtained. Then, a three-dimensional magnetic field is acquired based on the first image and the second image.

  Next, a method for acquiring a three-dimensional magnetic field distribution using the related technique in the magnetic field distribution acquisition device 1 will be described. 19 is a diagram showing the sensor unit 2b viewed from the object 9 side, and FIG. 20 is a cross-sectional view of the sensor unit 2b at the position of the arrow BB in FIG. In the sensor unit 2b shown in FIGS. 19 and 20, each first sensor 211b, which is a TMR element, extends in one direction (hereinafter referred to as “longitudinal direction”) on the first plane 81 that satisfies z = 0. The plurality of first sensors 211b are arranged at a constant pitch in the arrangement direction perpendicular to the direction. Similarly, each second sensor 221b extends in parallel to the first sensor 211b on the second plane 82 satisfying z = d, and the plurality of second sensors 221b are arranged at the same pitch in the arrangement direction. In FIG. 19 in plan view of the sensor unit 2b, the first sensor 211b and the second sensor 221b are alternately arranged at a constant arrangement pitch in the arrangement direction. In the magnetic field distribution acquisition apparatus 1 according to the present method, the sensor unit 2b can be rotated about the Z axis by a rotation mechanism 3b indicated by a broken line in FIG. , 221b is the Y ′ direction, the direction perpendicular to the longitudinal direction (Y ′ direction) is the X ′ direction, and the sensor angle formed by the Y direction (reference direction) and the Y ′ direction is θ.

  Next, the flow of processing in which the magnetic field distribution acquisition device 1 having the sensor unit 2b of FIG. 19 acquires a three-dimensional magnetic field distribution will be described with reference to FIG. In the magnetic field distribution acquisition device 1, the first measurement is performed by the sensor unit 2b, and the measurement values are acquired by the sensors 211b and 221b (FIG. 8: step S11). Subsequently, the sensor unit 2b is moved in the X ′ direction by the arrangement pitch by the moving mechanism 3 (steps S12 and S13), and the second sensor group 22b at the time of the first measurement (that is, a set of a plurality of second sensors 221b). The first sensor group 21b (that is, a set of a plurality of first sensors 211) is disposed at a position on the first plane 81 that overlaps the Z direction and the position of the first sensor group 21b at the time of the first measurement. The second sensor group 22 is arranged at a position on the second plane 82 that overlaps the position in the Z direction. Then, measurement values are acquired by the respective sensors 211b and 221b by performing the second measurement (step S11).

  Therefore, by the first and second measurements, the magnetic field received by the entire first sensor 211 at each position x ′ in the X ′ direction perpendicular to the longitudinal direction on the first plane 81 is acquired, and on the second plane 82. The magnetic field received by the entire second sensor 221 is acquired at each position x ′ in the X ′ direction perpendicular to the longitudinal direction.

  When it is confirmed that the next measurement is performed (step S12), the rotation mechanism 3b rotates the sensor unit 2b, so that the reference direction and the longitudinal direction (Y ′ direction) of each of the sensors 211b and 221b are changed. The formed sensor angle θ is changed by a fixed minute angle (for example, an angle of 1 to 15 degrees (preferably an angle of 10 degrees or less, more preferably 5 degrees or less)) (step S13). Similarly to the above, the first measurement (step S11), the movement of the sensor unit 2b (steps S12 and S13), and the second measurement are performed (step S11). In the following description, the first measurement at one sensor angle θ and the second measurement after the movement by the arrangement pitch of the sensor unit 2b are referred to as “measurement before and after the movement of the sensor unit 2b”.

  As described above, in the magnetic field distribution acquisition device 1, the rotation of the rotation mechanism 3b changes the sensor angle θ in a plurality of ways under the control of the computer 4, and the measurement before and after the movement of the sensor unit 2b is repeated. In each of the two planes 82, measurement values f (x ′, θ) using x ′ and θ as parameters are acquired. The plurality of sensor angles θ in the present embodiment are angles at regular intervals within a range of 0 ° or more and less than 180 °.

When the measurement value f (x ′, θ) is acquired in each of the planes 81 and 82 (step S12), the calculation unit 5 performs a Fourier transform on f ′ (x ′, θ) with respect to x ′, thereby obtaining g (k _{x ′} , θ) is acquired. Then, by substituting g (k _{x ′} , θ) into the two-dimensional field distribution acquisition formula (Equation 26), φ (x, y, 0) indicating the two-dimensional field in the first plane 81, and the second Φ (x, y, d) indicating the two-dimensional field in the plane 82 (that is, the first image and the second image) is obtained. Then, a differential image of these images is obtained, and a differential image φ _z (x, y, 0) obtained by dividing the differential image by the minute distance d is generated (step S14).

When the differential image φ _z (x, y, 0) is obtained, φ (x, y, 0) and φ _z (x, y, 0) are Fourier-transformed with respect to x and y in the same manner as in the above processing example. Ψ (k _x , k _y ) and ψ _z (k _x , k _y ) (that is, ψ (k) and ψ _z (k)) are obtained (step S15), ψ (k _x , k _y ) and Using φ _z (k _x , k _y ), φ (x, y, z) is obtained by a three-dimensional magnetic field distribution acquisition formula (step S16). Then, by obtaining the evaluation value while sequentially changing the value of z, the position of the magnetic field generation source in the Z direction is specified, and an image showing the magnetic field distribution in the magnetic field generation source is acquired (step S17).

  As described above, in the magnetic field distribution acquisition device 1 having the sensor unit 2b of FIG. 19, the first sensor groups 21b each having a long length are arranged on the first plane 81 with an interval therebetween, and the first A second sensor group 22b having the same shape as the first sensor group 21b on a second plane 82 that is separated from the plane 81 toward the object 9 by a minute distance d and is fixed in parallel to the first plane 81. Are arranged in the normal direction of the first plane 81 without overlapping the first sensor group 21b. Then, by changing the sensor angle θ in a plurality of ways and performing measurement before and after the movement of the sensor unit 2 b at each sensor angle θ, φ (x, y, 0) and φ (x, y, d) which is the second measurement value group of the second sensor group 22 are acquired. Thereby, in each of the two planes as in the related art, φ (x, y, 0), which is the first measurement value group, compared to the case where the sensor 92 is scanned at each sensor angle θ, and The second measurement value group φ (x, y, d) can be acquired at high speed and with high accuracy. As a result, φ (x, y, 0) and φ (x, y, d) can be obtained. Based on this, a highly accurate three-dimensional magnetic field distribution can be acquired in a short time.

  Here, as shown in FIG. 21 and FIG. 22, when assuming a sensor unit 91b of a comparative example in which a plurality of long sensors 911b are arranged at a constant arrangement pitch on the same plane, all the sensors 911b are Since they are formed on the same plane, the distance between the sensors 911b becomes narrow, and the manufacture of the sensor portion 91b is not easy.

  On the other hand, in the sensor unit 2b, the distance between the sensors in the arrangement direction is longer in each of the first plane 81 and the second plane 82 than the sensor unit 91b of the comparative example. Can be manufactured. In addition, in the sensor unit 2a of FIG. 17, the plurality of first sensors 211 arranged in the Y direction are regarded as one long first sensor, and the plurality of second sensors 221 arranged in the Y direction are one second long sensor. A three-dimensional magnetic field may be obtained by using the same method as described above as a sensor (the same applies to a sensor unit 2c in FIG. 23 described later).

  In the sensor units 2, 2 a, and 2 b, a magnetic field in a direction approximately along the XY plane is detected, but the detection direction of the magnetic field may be another direction. 23 and 24 are diagrams showing another example of the sensor unit. FIG. 23 is a diagram illustrating the sensor unit 2c viewed from the object 9 side, and FIG. 24 is a cross-sectional view of the sensor unit 2c at the position of the arrow CC in FIG.

  In the sensor unit 2c, as shown in FIG. 24, a plurality of first sensors 211c and a plurality of second sensors 221c are arranged on the base material 20 in a zigzag pattern along the X direction. Specifically, one end of each of the plurality of first sensors 211c is arranged on a first plane 81 (indicated by a two-dot chain line in FIG. 24; the same applies to the second plane 82) perpendicular to the Z direction. One end of the second sensor 221c is arranged on a second plane 82 that is separated from the first plane 81 by the minute distance d toward the object 9 and is perpendicular to the Z direction. As shown in FIG. 23, in the sensor unit 2c, the plurality of first sensors 211c and the plurality of second sensors 221c are covered with an insulating material 230, and the surface of the insulating material 230 (on the side opposite to the base material 20). The main surface is flattened. In the sensor unit 2 c, the sensor layer 24 c is formed by the plurality of first sensors 211 c, the plurality of second sensors 221 c, and the insulating material 230.

  In the insulating material 230 of the sensor layer 24c formed on the base material 20, a plurality of first sensors 211c and second sensors 221c are arranged in a staggered manner along the X direction in the same manner as described above. By covering the first sensor 211c and the plurality of second sensors 221c with the insulating material 230, the sensor layer 24c is formed. In the sensor unit 2c, the first sensor group 21c is two-dimensionally arranged on the first plane 81 by laminating a large number of sensor layers 24c, and the second sensor group having the same configuration as the first sensor group 21c. 22c is two-dimensionally arranged on the second plane 82 without overlapping the first sensor group 21c in the Z direction. Each sensor 211c, 221c detects a magnetic field in a direction approximately along the ZX plane.

  In the sensor unit 2c, the resolution in the X direction is determined by the arrangement pitch of the sensors 211c and 221c in the X direction, and the resolution in the Y direction is determined by the thickness of the sensor layer 24c. Since the actual thickness of the sensor layer 24c is extremely thin, the magnetic field distribution acquisition device 1 having the sensor unit 2c measures the two-dimensional distribution of the magnetic field at two different distances from the object 9 at high speed, and It can be performed with high resolution (in particular, high resolution in the stacking direction of the sensor layer 24c). Note that the distance between the one end of the first sensor 211c and the detection surface of the sensor unit 2c (the distance indicated by the arrow labeled G1 in FIG. 24) is preferably made as small as possible.

  25 and 26 are diagrams showing still another example of the sensor unit. FIG. 25 is a diagram illustrating the sensor unit 2d viewed from the object 9 side, and FIG. 26 is a cross-sectional view of the sensor unit 2d at the position of the arrow DD in FIG.

  In the sensor unit 2d, as shown in FIG. 26, one first sensor 211d that is long in the X direction is formed on the base member 20. The first sensor 211d is covered with an insulating material 230. As shown in FIG. 25, the surface of the insulating material 230 (the main surface opposite to the base material 20) is flattened, and the sensor layer 24d is formed by the first sensor 211d and the insulating material 230. The second sensor 221d that is long in the X direction is formed on the insulating material 230 of the sensor layer 24d formed on the base member 20 and is covered with the insulating material 230. Thereby, the sensor layer 24d including the second sensor 221d and the insulating material 230 is formed. Actually, the side surface of the first sensor 211d is disposed on a first plane 81 (indicated by a two-dot chain line in FIG. 26, the same applies to the second plane 82) perpendicular to the Z direction, and the second sensor A side surface of 221d is arranged on a second plane 82 that is separated from the first plane 81 toward the object 9 by a minute distance d and perpendicular to the Z direction. As shown in FIG. 25, in the sensor unit 2d, the sensor layer 24d including the first sensor 211d and the sensor layer 24d including the second sensor 221d are alternately stacked, so that the first sensor group in the first plane 81 is obtained. 21 d are discretely arranged, and the second sensor group 22 d is discretely arranged on the second plane 82.

  In the magnetic field distribution acquisition device having the sensor unit 2d, the three-dimensional magnetic field distribution is acquired in the same manner as the magnetic field distribution acquisition device having the sensor unit 2b of FIG. Thereby, the two-dimensional distribution of the magnetic field at two different distances from the object 9 can be measured at high speed. Further, in the first plane 81 and the second plane 82, the resolution in the X ′ direction perpendicular to the longitudinal direction is determined by the thickness of the sensor layer 24d, so that the magnetic field distribution can be accurately measured with high resolution. it can.

  In addition, like the sensor unit 91c shown in FIGS. 27 and 28 and the sensor unit 91d shown in FIGS. 29 and 30, one end (or side surface) of all the sensors 911c and 911d is arranged on the same plane. As a comparative example, the magnetic field distribution acquisition device having the sensor units 91c and 91d of the comparative example requires a mechanism for moving the sensor units 91c and 91d from the first plane to the second plane. In the magnetic field distribution acquisition apparatus having the sensor units 2c and 2d in FIG. 25, such a mechanism (that is, a mechanism for moving the sensor units 2c and 2d in the Z direction) is unnecessary.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.

  In the above embodiment, a TMR element is used as a sensor, but other types of sensors that measure a magnetic field may be used. For example, in the sensor unit 2e of FIG. 31, a SQUID element (for example, 30 to 50 μm square) Are used as the first sensor 211e and the second sensor 221e. In the sensor unit 2e, the first sensor group 21e is discretely arranged on the first plane facing the object, and is separated from the first plane by a minute distance (for example, 3 to 5 μm) from the object. On the second plane fixed parallel to the first plane, the second sensor group 22e having the same configuration as the first sensor group 21e overlaps the first sensor group 21e in the normal direction of the first plane. Without being arranged discretely. Thereby, the measurement of the magnetic field distribution on two planes can be performed at high speed.

  In the magnetic field distribution acquisition device 1, the second plane may be a measurement surface that satisfies z = 0, and in this case as well, the second plane is generated based on the measurement value group on the first plane and the measurement value group on the second plane. Using the differential measurement value group and the measurement value group in the second plane, a three-dimensional magnetic field caused by the object 9 can be obtained.

In the sensor unit in the above embodiment, two planes (first plane and second plane) in which sensor groups are discretely arranged are set, but in each of three or more planes set parallel to each other. The sensor group may be arranged discretely. In this case, the sensor group arranged in one plane is arranged at a position that does not overlap the sensor group arranged in another plane in a direction perpendicular to the plane. In such a sensor unit, sensor groups on two planes that are actually used for measurement are selected, and the movement of the sensor unit in a direction parallel to the plane and the measurement at the position after the movement are repeated, and each sensor unit is repeated. Measurement values at each position on the plane are acquired (of course, the above-described interpolation calculation may be performed). If the number of planes on which sensor groups are arranged in the sensor unit is N, _N C _two plane combinations can be determined. However, in order to perform high-accuracy measurement at high speed, it is preferable that only two planes are set in the sensor unit, and a sensor group is arranged on each of the two planes.

  In the magnetic field distribution acquisition device 1, if a three-dimensional magnetic field due to the object 9 is obtained based on the first measurement value group of the first sensor group and the second measurement value group of the second sensor group, Calculations other than the above three-dimensional magnetic field distribution acquisition formula may be used.

  The moving mechanism 3 may move the object 9 in a direction along the first plane of the sensor unit. In other words, the moving mechanism only needs to move the sensor unit relative to the object in the direction along the first plane. The sensor unit is moved relative to the object, and the first sensor group is disposed at a relative position on the first plane that overlaps with the relative position of the second sensor group with respect to the object at the time of the one measurement. In addition, it is possible to dispose the second sensor group at a relative position on the second plane that overlaps with the relative position of the first sensor group with respect to the object at the time of the one measurement.

  The magnetic field distribution acquisition device 1 can also be used for profiling an electron beam emitted from an electron beam emitting device, for example. In an apparatus that performs batch exposure using an electron beam, a bundle (electron beam) of a large number of electron beam elements that are turned on or off in accordance with pattern information is emitted from the electron beam emitting device, and the object is transmitted through the electron optical system. The magnetic field distribution acquisition device 1 achieves electron beam profiling by acquiring a three-dimensional magnetic field distribution generated by an electron beam. Further, the magnetic field distribution acquisition device 1 is an MRI (Magnetic) that acquires wiring inspection (including in-line inspection during manufacturing) of various electronic components and semiconductor products, a detector of a hard disk drive, or a cerebral magnetic field of a human body. (Resonance Imaging) apparatus and the like.

  Further, as shown in FIG. 32, the two sensor units 2 based on the present invention are arranged at different positions with respect to the object 9 with the center of the sensor unit 2 away from each other by a certain distance. Different two-dimensional magnetic field distributions in the vicinity of the magnetic field generation source are respectively reconstructed according to Equation 13. The two images obtained by the reconstruction are alternately displayed on the display 45 as shown in FIG. 33, and the right eye and left eye shutters of the glasses 49 are alternately driven in synchronization with the display, so that binocular stereoscopic vision can be obtained. Do. By this method, for example, it is possible to capture magnetic field information in the vicinity of a diseased part three-dimensionally in brain image diagnosis.

  Before imaging a measurement target (object) with the magnetic field distribution acquisition device according to the present invention, a magnetic field is forcibly applied to the measurement target and a three-dimensional magnetic field distribution in the vicinity of the measurement target is acquired in a magnetized state. Good. Thereby, for example, the state of the reinforcing bar inside the concrete in the building structure can be imaged with high resolution. In addition, structural deterioration such as rust in the reinforcing bars can be grasped without destruction, which is effective in road and tunnel inspection.

  The configurations in the above-described embodiments and modifications may be combined as appropriate as long as they do not contradict each other.

DESCRIPTION OF SYMBOLS 1 Magnetic field distribution acquisition apparatus 2,2a-2e Sensor part 3 Movement mechanism 4 Computer 5 Calculation part 9 Target object 21,21b-21e 1st sensor group 22,22b-22e 2nd sensor group 51 Interpolation calculation part 52 Differential measurement value group Generator 81 First plane 82 Second plane 211, 211b to 211e First sensor 221, 221b to 221e Second sensor

Claims (6)

A magnetic field distribution acquisition device for acquiring a three-dimensional magnetic field distribution,
A first sensor group for measuring the magnetic field distribution is discretely arranged on a first plane facing the object, is separated from the first plane by a minute distance toward the object, and is arranged on the first plane. The second sensor group having the same configuration as the first sensor group is discretely formed on the second plane fixed in parallel to the first plane without overlapping the first sensor group in the normal direction of the first plane. An array of sensor units;
A calculation unit for obtaining a three-dimensional magnetic field distribution caused by the object based on a first measurement value group of the first sensor group and a second measurement value group of the second sensor group;
Equipped with a,
Wherein the sensor interval of the first sensor group in the first plane, the magnetic field distribution obtaining unit and the sensor spacing of the second sensor group in the second plane, characterized that you match. The magnetic field distribution acquisition device according to claim 1,
The computing unit is
By performing an interpolation operation on a measurement value group of one of the first sensor group and the second sensor group, the normal direction on one plane on which the one sensor group is arranged An interpolation calculation unit for obtaining a magnetic field at a position overlapping with the other sensor group as a new measurement value group,
A differential measurement value group generation unit that obtains a differential measurement value group between the new measurement value group and the measurement value group of the other sensor group, and obtains a differential measurement value group obtained by dividing the differential measurement value group by the minute distance. When,
A magnetic field distribution acquisition device comprising: The magnetic field distribution acquisition device according to claim 1,
In the sensor unit, the arrangement of the first sensor group and the arrangement of the second sensor group are the same,
The magnetic field distribution acquisition device is
A moving mechanism for moving the sensor unit relative to the object in a direction along the first plane;
After one measurement is performed by the sensor unit, the sensor unit is moved relative to the object by the moving mechanism, and the second sensor group with respect to the object is measured at the time of the one measurement. The first sensor group is disposed at a relative position on the first plane that overlaps the relative position and the normal direction, and the relative position of the first sensor group to the object and the normal line at the time of the one measurement. A control unit that arranges the second sensor group at a relative position on the second plane that overlaps the direction and performs other measurements;
Further comprising
The computing unit is
A difference measurement value group between a measurement value group of the first sensor group in the one measurement and the other measurement and a measurement value group of the second sensor group in the one measurement and the other measurement; A magnetic field distribution acquisition apparatus comprising: a differential measurement value group generation unit that acquires a differential measurement value group obtained by dividing a difference measurement value group by the minute distance. The magnetic field distribution acquisition device according to claim 2 or 3,
The three-dimensional magnetic field distribution obtained by the calculation unit satisfies the Laplace equation and φ (x, y, z) (where X, Y are two directions parallel to the first plane and the second plane and perpendicular to each other). And the normal direction is the Z direction, and x, y, and z are coordinate parameters of an orthogonal coordinate system defined by the X, Y, and Z directions. The second plane is a measurement surface that satisfies z = 0,
The computing unit performs two-dimensional Fourier transform on φ (x, y, 0), which is a measurement value group on the measurement surface, and φ _z (x, y, 0), which is a differential measurement value group, with respect to x and y, respectively. Ψ (k _x , k _y ) and ψ _z (k _x , k _y ) (where k _x , k _y are the wave numbers in the X direction and the Y direction), and ψ (k _x , k It is characterized in that φ (x, y, z) is obtained by deriving a Fourier transform of φ (x, y, z) with respect to x, y from _y ) and ψ _z (k _x , k _y ). Magnetic field distribution acquisition device. The magnetic field distribution acquisition device according to claim 4,
The arithmetic unit sequentially changes the value of z in φ (x, y, z) to z ₁ , z ₂ , z ₃ ,..., Φ (x, y, z _n ) and φ (x, y , Z _n−i ) (where n is an integer greater than or equal to 2, i is an integer greater than or equal to 1 and less than n), and a value indicating the difference is obtained. A magnetic field distribution acquisition apparatus characterized by specifying a value of z that is equal to or less than a predetermined value as a position in a Z direction of a magnetic field generation source. The magnetic field distribution acquisition device according to any one of claims 1 to 5,
Each of the sensors included in the first sensor group and the second sensor group is a thin film element.