Superconducting quantum interference device magnetic plane gradiometer, magnetic field detection method and system

Abstract

The present invention provides a superconducting quantum interference device magnetic plane gradiometer, a magnetic field detection method and system, including: a superconducting closed loop and two SQUIDs; the superconducting closed loop includes a gradient coil and two input coils; the gradient coil is wound by two induction coils of equal size and opposite winding directions, and the two induction coils are symmetrical about a first symmetry axis; the two input coils are equal in size and symmetrically arranged on both sides of the gradient coil along the first symmetry axis, and the two input coils are connected in series with the gradient coil; two SQUIDs are symmetrically arranged on both sides of the superconducting closed loop along the first symmetry axis, and are used to respectively sense the magnetic flux of the corresponding input coils and convert the magnetic flux into voltage. The present invention sets a fully symmetrical magnetic gradiometer, and through the mode switching of single-side independent operation and double-side joint operation, avoids the common mode influence brought by the introduction of an additional superconducting loop, effectively reduces the imbalance of the gradiometer, and improves the overall uniformity of the device.

Description

Technical Field

[0001] The present invention relates to the field of magnetic field detection, and in particular to a superconducting quantum interference device magnetic plane gradiometer, a magnetic field detection method and a system. Background Art

[0002] Superconducting quantum interference devices (SQUID) are often used in weak magnetic limit detection fields such as biomagnetic fields (such as heart magnetism, brain magnetism, fetal magnetism, etc.) and earth magnetic fields (metallic mines, magnetic mines, etc.) due to their extremely high magnetic resolution. Due to the existence of strong background magnetic fields, such as the earth's magnetic field, the measured signal is often covered by the strong background magnetic field. Generally, two methods are used to detect weak magnetic fields. The first is to use shielding devices, such as shielding covers, to shield the external magnetic field to reduce the interference of the external field; the second is to use a specific structure to suppress the external field. This effect is usually achieved by using the principle that the magnetic gradiometer uses a gradient antenna to respond to high-order magnetic field gradients and suppress uniform magnetic fields or low-order magnetic field gradients. Designing a certain connection between the superconducting quantum interference device and the gradient antenna can enable better detection of weak magnetic limit detection.

[0003] At present, the superconducting quantum interference device magnetic gradiometer is divided into hardware gradiometer and software gradiometer. Among them, the hardware gradiometer is divided into axial gradiometer and planar gradiometer according to the different implementation methods of the gradient antenna. The axial gradiometer is usually implemented by hand-wound gradient antenna, with a long baseline but poor balance, and a large response to uniform magnetic field or low-order magnetic field gradient; the planar gradiometer is usually implemented by planar micro-nano processing technology, with the advantage of high balance and the disadvantage of limited baseline and cannot be made too long. Therefore, the superconducting quantum interference device magnetic planar gradiometer itself combines the high resolution of SQUID and the intrinsic high balance of the planar gradient antenna, which can realize the detection of weak signals in complex electromagnetic environments (such as outdoor electromagnetic environments).

[0004] However, the existing superconducting quantum interference device magnetic gradiometer includes three parts: gradient coil, input coil and SQUID. An input coil is set in series on one side of the gradient coil to detect the measured magnetic field, and then the SQUID is coupled with the input coil to realize the conversion of magnetic flux-voltage, and the voltage is obtained by the readout circuit to complete the detection. Since the processing is completed on the same wafer, the asymmetry of the arrangement of the gradient coil, input coil and SQUID on the wafer of this design will affect the overall uniformity of the device. The preparation of SQUID planar gradiometer is generally realized on substrates such as silicon wafers through thin film technology combined with micro-nano processing methods. The wafer size is limited by the processing capacity of the process equipment, and 4 inches to 6 inches are currently the most common. Taking a 4-inch silicon wafer as an example, when the baseline length of the gradiometer exceeds 3 cm, it can accommodate up to 6 chips for integration, which requires very high process uniformity and consistency to ensure a certain chip yield. If the symmetry of the whole is to be maintained, the design of additional redundant SQUIDs can improve the symmetry of the design. However, although the new SQUID is not directly associated with the gradiometer, it may form a superconducting closed loop, causing the magnetic flux quantization to interfere with the gradiometer. In addition, since the gradient antenna occupies most of the size of the gradiometer design (the baseline is usually several centimeters), and the input coil and SQUID are relatively smaller, only a few microns or even sub-microns, it is equivalent to a chip containing a structural integration spanning from microns to centimeters. The imbalance caused by factors such as strict processing technology and asymmetric structure will affect the chip yield.

[0005] Therefore, it is an urgent problem to improve the symmetry of the superconducting quantum interference device magnetic gradiometer while avoiding the interference caused by introducing redundancy and ultimately improving the chip yield.

[0006] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0007] In view of the shortcomings of the prior art described above, the purpose of the present invention is to provide a superconducting quantum interference device magnetic plane gradiometer, a magnetic field detection method and a system, so as to solve the problems in the prior art that the insufficient symmetry of the superconducting quantum interference device magnetic gradiometer affects the uniformity of the entire device, the interference caused by introducing redundancy to improve the symmetry, and the low chip yield.

[0008] To achieve the above-mentioned and other related purposes, the present invention provides a superconducting quantum interference device magnetic plane gradiometer, comprising at least: a superconducting closed loop and two SQUIDs;

[0009] The superconducting closed loop includes a gradient coil and two input coils; the gradient coil is formed by two induction coils of equal size and opposite winding directions, and the two induction coils are symmetrical with respect to a first symmetry axis; the two input coils are equal in size and symmetrically arranged on both sides of the gradient coil along the first symmetry axis, and the two input coils are connected in series with the gradient coil;

[0010] Two SQUIDs are symmetrically arranged on both sides of the superconducting closed loop along the first symmetry axis, and are used to respectively sense the magnetic flux of the corresponding input coil and convert the magnetic flux into voltage.

[0011] Optionally, the inductance of the input coil is equal to half of the inductance of the gradient coil.

[0012] Optionally, the SQUID is configured as a DC superconducting quantum interference device; the DC superconducting quantum interference device is composed of two Josephson junctions connected in parallel.

[0013] Optionally, the SQUID is set to a first-order gradient configuration, including two Josephson junctions and two coils; the two coils are equal in size and wound in opposite directions; and the Josephson junctions are connected in series on the two coils respectively.

[0014] Optionally, the SQUID is set to a second-order gradient configuration, including two Josephson junctions and four coils; the four coils are of equal size and connected in parallel; the two Josephson junctions are connected in series with the four parallel coils; the four coils are respectively located in four areas divided by the first symmetry axis and the second symmetry axis; the first symmetry axis and the second symmetry axis are vertically arranged to form an intersection in the middle; the four coils are symmetrical around the center of the intersection; the two coils located on the same side of the symmetry axis are wound in opposite directions; and the two coils located in the diagonal area are wound in the same direction.

[0015] Optionally, a filter device is arranged in parallel at both ends of the input coil; the filter device is a CRC filter device, including a first capacitor, a resistor and a second capacitor connected in series in sequence.

[0016] The present invention provides a magnetic field detection method, using the above-mentioned superconducting quantum interference device magnetic plane gradiometer, and the magnetic field detection method at least comprises:

[0017] The gradient coil in the superconducting closed loop detects the measured magnetic field to obtain a corresponding magnetic flux signal; the input coil is coupled with the SQUID magnetic flux, and the SQUID device senses the magnetic flux signal; the sensed magnetic flux signal is linearly converted from magnetic flux to voltage to obtain an output voltage.

[0018] Optionally, only one of the SQUIDs at the two ends is in a current biased working state, and the other SQUID is in a power-off non-working state.

[0019] Optionally, the SQUIDs at both ends are in working state at the same time, and the output voltages at both ends are subtracted to eliminate the common mode signal in the output signal, thereby realizing differential mode signal detection.

[0020] The present invention provides a magnetic field detection system, comprising at least: a readout circuit and the above-mentioned superconducting quantum interference device magnetic plane gradiometer;

[0021] The superconducting quantum interference device magnetic plane gradiometer is used to sense the measured magnetic field; the readout circuit reads the output voltage of the superconducting quantum interference device magnetic plane gradiometer to obtain the magnetic field size of the measured magnetic field.

[0022] As described above, the superconducting quantum interference device magnetic plane gradiometer, magnetic field detection method and system of the present invention have the following beneficial effects:

[0023] 1. The superconducting quantum interference device magnetic plane gradiometer, magnetic field detection method and system of the present invention realize a fully symmetrical structure by arranging symmetrical input coils on both sides of the gradient coil and arranging symmetrical SQUIDs on both sides of the input coil, thereby effectively reducing the imbalance of the gradiometer and improving the overall uniformity of the device.

[0024] 2. The superconducting quantum interference device magnetic plane gradiometer, magnetic field detection method and system of the present invention are equipped with a completely symmetrical gradiometer, and through mode switching between single-side independent operation and double-side joint operation, avoids the common-mode influence caused by introducing a new design to form an additional superconducting loop.

[0025] 3. The superconducting quantum interference device magnetic plane gradiometer, magnetic field detection method and system of the present invention can effectively improve the yield rate of manufactured chips and can be applied to production practice on a large scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Shown is a schematic structural diagram of a superconducting quantum interference device magnetic plane gradiometer.

[0027] Figure 2 Shown is a schematic structural diagram of the superconducting quantum interference device magnetic plane gradiometer of the present invention.

[0028] Figure 3 Schematic diagram of the gradiometer showing the SQUID in first-order gradient configuration.

[0029] Figure 4 Schematic diagram of the gradiometer showing a SQUID in second-order gradient configuration.

[0030] Component number description

[0031] 1 Superconducting quantum interference device magnetic plane gradiometer

[0032] 11. First magnetic induction circuit

[0033] 111 First induction coil

[0034] 112 First input coil

[0035] 113 First SQUID

[0036] 114 Filter components

[0037] 115 First-order gradient SQUID

[0038] 12. Second magnetic induction circuit

[0039] 121 Second induction coil

[0040] 122 Second input coil

[0041] 123 Second SQUID DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0043] Please refer to 2~ Figure 4 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0044] like Figure 1As shown, a superconducting quantum interference device magnetic plane gradiometer includes three parts: a gradient coil, an input coil and a SQUID. A series input coil is provided on one side of the gradient coil for detecting the measured magnetic field. The flux-voltage conversion is realized by coupling induction between the SQUID and the input coil, and the voltage is obtained by the readout circuit (not shown in the figure) to complete the detection. The resolution of the superconducting quantum interference device magnetic plane gradiometer can be represented by a gradient value. The gradient value is the maximum value of the directional derivative of a function at this point along the direction, that is, the function changes fastest along the direction at this point and the rate of change is the largest. The gradient value in the magnetic field can reflect the rate of change of the magnetic field intensity with the spatial displacement, such as the average rate of change of a certain component direction of the magnetic field in the X direction expressed by the following formula (1). The larger the magnetic field increment per unit distance, the larger the magnetic field gradient. That is to say, under unit distance, the size of the magnetic field increment can be inferred by the magnetic field gradient. For the SQUID magnetic plane gradiometer, when testing the same magnetic field, if the magnetic field increment detected by a SQUID magnetic plane gradiometer is large and the magnetic field changes too dramatically, many details may be lost, that is, the ability to distinguish the magnetic field is relatively reduced, resulting in insensitivity to the magnetic field detection to a certain extent. In other words, the resolution refers to the minimum value of the magnetic field that the sensor can distinguish. It is expressed by the gradient formula. The smaller the resolution value, the smaller the gradient value, and the better the performance of the SQUID magnetic plane gradiometer. Figure 1 The superconducting quantum interference device magnetic plane gradiometer shown detects the magnetic field in space. The source of the magnetic field in space can be divided into X, Y, and Z direction components according to the coordinate axis. In this embodiment, the X direction is used as the determination direction of the spatial displacement. Then, the average change rate of one direction component of the magnetic field from space (i.e., the average gradient value) is:

[0045]

[0046] Among them, G x It is expressed as the average rate of change of a certain component of the magnetic field in the X direction (ie, the average gradient value). B1 and B2 correspond to the magnetic induction intensity of any two points in the X direction, and X represents the displacement between the two points B1 and B2.

[0047] Formula (1) represents the average rate of change of one directional component of the magnetic field in space with the X direction as the determination direction. Then the average rate of change of the component of the magnetic field in the Z direction with the X direction as the determination direction is:

[0048]

[0049] Among them, Gzx represents the B of the detected magnetic field ZThe average rate of change of the component in the X direction (i.e., the average gradient value), Bz1 and Bz2 correspond to the magnetic induction intensity of the spatial magnetic field in the Z direction component induced by any two points in the X direction. d represents the distance between the centers of the two coils, and also represents the displacement of the two points in the X direction. In this embodiment, Figure 1 As shown, the induction points of Bz1 and Bz2 are set as the centers of the two coils constituting the gradient coil. In fact, when the gradient coil senses the spatial magnetic field or a component of the spatial magnetic field, the position on the coil should be used as the induction point. However, since the two coils constituting the gradient coil should be centrally symmetrical regardless of the shape of the square, ring, etc., and for the convenience of understanding and calculation, the induction point is set as the center of the two coils using the principle of calculus. In this way, the center distance d of the two coils can be directly used to represent the displacement between the two points. In this way, using d to represent the displacement between the induction points of Bz1 and Bz2 is more intuitive and conducive to comparative calculation.

[0050] Specifically, Figure 1 As shown, the gradient coil is directly connected to the input coil to form a closed loop, in which the input coil and the SQUID are coupled by magnetic flux through mutual inductance. Ideally, in order to achieve the best conversion efficiency, it is assumed that the inductance of the gradient coil and the input coil are equal. The SQUID induced voltage through magnetic flux is V0. Using the calculation formula of formula (2), the relationship between the resolution of the gradiometer and the induced voltage output of the SQUID can be obtained as follows:

[0051]

[0052] V0 is the output voltage of SQUID induced by magnetic flux, V Φ is the SQUID flux-to-voltage conversion coefficient, Li is the self-inductance of the input coil, and Mi is the mutual inductance between the input coil and the SQUID. Figure 1 The superconducting quantum interference device magnetic plane gradiometer shown, L i Indicates the self-inductance of the input coil, M i Represents the mutual inductance between the input coil and the SQUID. V is the volume of the gradient coil, which is equal to the product of the area of ​​the gradient coil and the baseline length. In actual use, the gradient coil is relatively large, the input coil is connected in series and the SQUID is relatively small compared to the gradient coil, which is equivalent to parasitic next to the gradient coil. The gradient coil has a parasitic area and is not designed symmetrically. Figure 1 As shown, the two loop holes of the gradient coil cannot ensure equal areas, that is, there is an error area ΔA between the two, which will lead to the resolution error of the gradiometer under the uniform magnetic field, expressed as:

[0053]

[0054] Among them, Bz represents the z-direction component of the magnetic field, ΔA is the error area, V is the volume of the gradient coil, which is equal to the product of the area of ​​the gradient coil and the baseline length, d is the baseline length, and A is the area of ​​the gradient coil. At this time, ΔA / A can be regarded as the imbalance of the gradiometer. The larger ΔA / A is, the greater the imbalance of the gradiometer is, and the greater the impact on the magnetic plane gradiometer is.

[0055] In order to solve the above problems, the present invention provides a superconducting quantum interference device magnetic plane gradiometer, a magnetic field detection method and a system, and the specific scheme is as follows.

[0056] Embodiment 1

[0057] like Figure 2 As shown, this embodiment provides a superconducting quantum interference device magnetic plane gradiometer 1, including: a superconducting closed loop and two SQUIDs.

[0058] like Figure 2 As shown, in this embodiment, the superconducting closed loop includes a gradient coil and two input coils.

[0059] Specifically, the gradient coil is formed by two induction coils of equal size and opposite winding directions. The two induction coils are wound in opposite directions and form an 8-shape on the plane. The shape of the coil can be a square coil, a rectangular coil, a ring coil, etc. In this embodiment, the induction coil is a ring coil. The two induction coils are symmetrical about the first symmetry axis (such as Figure 2 As shown, in this embodiment, the straight line where AA is located is the first symmetry axis). The two input coils are equal in size and are symmetrically arranged on both sides of the gradient coil along the first symmetry axis. Finally, a structure of the first input coil 112-gradient coil-second input coil 122 is formed to form a superconducting closed loop. The superconducting closed loop is a fully symmetrical structure. With the first symmetry axis as the boundary, the first input coil 112-first induction coil 111 or the second input coil 122-second induction coil 121 is used to cooperate with the first SQUID and the second SQUID respectively to form the first magnetic induction circuit 11 and the second magnetic induction circuit 12 to detect the magnetic field. In fact, during operation, the first induction coil 111 and the second induction coil 121 together form a gradient coil to sense the measured magnetic field. Sensing in the gradient coil cannot be simply understood as magnetic induction occurring only in one of the induction coils. However, the concept of the symmetry axis is introduced here to facilitate the understanding that the devices on both sides are completely symmetrical and can work independently.

[0060] Specifically, two SQUIDs are symmetrically arranged on both sides of the two input coils along the first symmetry axis AA, respectively, for converting magnetic flux into voltage. With the first symmetry axis AA as a reference, the coils are arranged outward, and the two sides of the first symmetry axis AA form an induction coil-input coil-SQUID structure from the inside to the outside, that is, a magnetic induction circuit is formed: the magnetic flux is induced by the induction coil and the input coil, and then the SQUID is used to realize the conversion of magnetic flux to voltage, and the voltage is read from the readout circuit (not shown in the figure), and the detection of magnetic flux is completed, and finally the function of magnetic field detection is realized. With the first symmetry axis AA as a reference, in this embodiment, the two sides of the first symmetry axis AA respectively constitute the first magnetic induction circuit 11 and the second magnetic induction circuit 12.

[0061] As an example, the SQUID is set as a DC superconducting quantum interference device. The DC superconducting quantum interference device is composed of two Josephson junctions in parallel. The input coil is subjected to flux coupling induction through the DC quantum interference device. It should be noted that the SQUID is a superconducting quantum interference device, which mainly includes a DC superconducting quantum interference device and a radio frequency quantum interference device. In this embodiment, a DC superconducting quantum interference device is used for processing, and in fact, a radio frequency quantum interference device can also be used. As long as the SQUID can be flux-coupled with the input coil and the SQUID device that realizes flux-voltage conversion should be within the protection scope of this embodiment.

[0062] As an example, to achieve the best conversion efficiency, the inductance of the induction coil on one side is equal to the inductance of the input coil, so the inductance of the gradient coil composed of two induction coils is twice the inductance of the input coil. In fact, ideally, to achieve the best conversion efficiency, the total inductance of the gradient coil is equal to the total inductance of the input coil. That is to say, if there are multiple input coils, in order to achieve a better conversion rate, the sum of the inductances of the multiple input coils should be equal to the total inductance of the gradient coil.

[0063] At this time, the superconducting quantum interference device magnetic plane gradiometer 1 and Figure 1 The values ​​of the coils of the superconducting quantum interference device magnetic plane gradiometer in the embodiment are basically the same, only the inductance values ​​of the input coils on both sides are adjusted, and the rest remain unchanged (i.e., the input coil is half of the input coil of the existing superconducting quantum interference device magnetic plane gradiometer 1, and other parameters are adaptively adjusted. The baseline length d and the flux induced voltage V0 of the magnetic plane gradiometer remain unchanged). According to the calculation formula of the resolution of the gradiometer, the relationship between the resolution of the gradiometer and the induced voltage output of the SQUID is as follows:

[0064]

[0065] V0′ is the output voltage of the SQUID in this embodiment induced by magnetic flux, V Φis the SQUID flux-to-voltage conversion coefficient in this embodiment, L i ' is the self-inductance coefficient of the input coil in this embodiment, M i ' is the mutual inductance between the input coil and the SQUID in this embodiment. The superconducting quantum interference device magnetic plane gradiometer in this embodiment, if L i represents the self-inductance of the first input coil 112, M i represents the mutual inductance between the first input coil 112 and the SQUID 113. V is the volume of the gradient coil, which is equal to the product of the area of ​​the gradient coil and the baseline length.

[0066] Relative to Figure 1 For the superconducting quantum interference device magnetic plane gradiometer, V Φ is a constant, V does not change, the superconducting quantum interference device magnetic plane gradiometer in this embodiment is relative to Figure 1 In the provided superconducting quantum interference device magnetic plane gradiometer, the input inductance and mutual inductance corresponding to the input coil will be reduced. When other parameters remain unchanged, the parasitic area at this time is significantly reduced, and the two loop holes of the gradient coil are basically equal in area, that is, the error area ΔA between the two can be infinitely close to 0 in theory. ΔA / A can be regarded as the imbalance of the gradiometer. The closer ΔA / A is to 0, the greater the balance of the gradiometer. However, the input inductance and mutual inductance corresponding to the input coil will be reduced, that is, Li′ and Mi′ will change accordingly. The other parameters can be adaptively adjusted to obtain the resolution of the gradiometer at this time relative to Figure 1 In terms of resolution, the following relationship exists:

[0067]

[0068] That is to say, the average gradient value (ie, average resolution) of this embodiment is relatively Figure 1 For the average gradient value of the gradiometer, if it increases, the resolution value will be higher. The larger the resolution value, the larger the magnetic field increment detected by the superconducting quantum interference device magnetic plane gradiometer, and the magnetic field changes relatively drastically, which may lose a lot of details, that is, the ability to distinguish the magnetic field is relatively reduced, resulting in insensitivity to the detection of the magnetic field to a certain extent. That is, this embodiment is relative to Figure 1 The performance has been reduced.

[0069] This embodiment also provides a magnetic field detection method, which is implemented based on the above-mentioned superconducting quantum interference device magnetic plane gradiometer 1.

[0070] like Figure 2As shown, based on the gradient coil in the superconducting closed loop to detect the measured magnetic field, a corresponding flux signal is obtained; the input coil is coupled with the SQUID flux, and the SQUID device senses the flux signal; the sensed flux signal is linearly converted from flux to voltage to obtain the output voltage.

[0071] Specifically, only one of the SQUIDs at both ends is in a current biased working state, and the other SQUID is in a power-off non-working state. The left side of the first symmetry axis is set to the first magnetic induction circuit 11, which is set to a current biased working state, that is, an external current is connected to enter the working state. If the first induction coil 111 is used as a reference, the magnetic field to be measured is induced by the gradient coil, the magnetic signal is converted into an electrical signal, and the corresponding current is induced. The induced current flows to the first input coil 112, and the first input coil 112 converts the electrical signal into a magnetic flux signal again. Through the coupling of the first input coil 112 and the SQUID, the characteristic of the SQUID that can sense the magnetic flux and convert it into a voltage is utilized to realize the conversion of the magnetic flux signal into an electrical signal again, and the value of the electrical signal is read to obtain the output voltage, thereby obtaining the value of the magnetic flux and the measured magnetic field. At this time, the other side of the first symmetry axis is set to a power-off non-working state, and does not directly participate in magnetic detection, but only serves as a backup device. The non-working state can be achieved by designs including but not limited to short-circuiting the switch control circuit, floating ground state, etc. The first magnetic induction circuit 11 is replaced when the magnetic field detection fails due to static electricity or other improper use. Since the first magnetic induction circuit 11 and the second magnetic induction circuit 12 can work independently, in actual use, a certain interval of use can be set and used alternately to extend the service life of the magnetic plane gradiometer. In addition, the first magnetic induction circuit 11 and the second magnetic induction circuit 12 can work independently, and the first magnetic induction circuit 11 and the second magnetic induction circuit 12 can be used for the same measured magnetic field, which can be calibrated.

[0072] It should be noted that the functions of the first magnetic induction circuit 11 and the second magnetic induction circuit 12 in this embodiment are exactly the same, and either one can be selected to enter the working state, and the other one is used as a backup device. Compared with other designs of magnetic plane gradiometers that only add a single SUQID on the chip as a redundant device, the two SQUIDs in this embodiment are both used as part of the superconducting quantum interference device magnetic plane gradiometer 1 and can be used.

[0073] This embodiment also provides another magnetic field detection method, which is implemented based on the above-mentioned superconducting quantum interference device magnetic plane gradiometer 1. The difference between a magnetic field detection method of this embodiment and the above-mentioned magnetic field detection method is that the SQUIDs at both ends of the superconducting quantum interference device magnetic plane gradiometer 1 are in working state at the same time, and the output voltages of the readout circuits at both ends are subtracted to eliminate the common mode signal in the output signal, thereby realizing differential mode signal detection.

[0074] Specifically, Figure 2 For example, the first induction coil 111 and the second induction coil 121 are symmetrically distributed and have opposite winding directions. Therefore, the gradient coil as a whole does not respond to the uniform magnetic field, but only responds to the non-uniform magnetic field: under the uniform magnetic field, the two sides of the first symmetry axis AA of the gradient coil can cancel each other out because the magnetic flux of the induction coils is the same in magnitude and flows in opposite directions; under the non-uniform magnetic field, the magnetic flux of the first induction coil 111 and the second induction coil 121 of the gradient coil are not equal in magnitude, and the magnitude of the induced current is also not equal, and finally the differential mode current of the gradient coil is different. The differential mode current flows to the first input coil 112 and the second input coil 122 respectively, and the input coils realize the conversion of electrical signals into magnetic flux signals. The first SQUID 113 and the second SQUID 123 respectively convert the magnetic flux signals coupled to the input coils into electrical signals linearly to obtain output voltages, such as Figure 2 As shown, the first voltage V1 and the second voltage V2 are read out. The first voltage V1 and the second voltage V2 are used for subtraction calculation to realize differential signal detection. In fact, by using the completely symmetrical first magnetic induction circuit 11 and the second magnetic induction circuit 12, the common mode signal in the output signal can be eliminated through the symmetrical coils, including the common mode signal introduced by the magnetic flux generated by the input coil and the coupling magnetic flux generated by the SQUID itself, thereby greatly improving the signal-to-noise ratio.

[0075] This embodiment also provides a magnetic field detection system, including a readout circuit and the above-mentioned superconducting quantum interference device magnetic plane gradiometer 1. The superconducting quantum interference device magnetic plane gradiometer 1 is used to sense the measured magnetic field. The readout circuit reads the output voltage of the SQUID to obtain the magnetic field size of the measured magnetic field.

[0076] Specifically, the superconducting quantum interference device magnetic plane gradiometer 1 is used to sense the measured magnetic field. Its principle, structure and working process have been discussed above and will not be repeated here. The readout circuit reads the output voltage of the SQUID. Through the linear relationship between the magnetic flux and voltage of the SQUID, the magnitude of the magnetic flux coupled by the SQUID induction input coil can be inferred through the input voltage, thereby obtaining the magnitude of the magnetic field of the measured magnetic field. In actual use, the readout circuit can have a built-in calculation formula to directly obtain the magnitude of the measured magnetic field.

[0077] Embodiment 2

[0078] like Figure 3 As shown, this embodiment provides a superconducting quantum interference device magnetic plane gradiometer 1, and the superconducting closed loop part is basically the same as that of the first embodiment, except that the SQUID used is set to a first-order gradient configuration.

[0079] Specifically, the superconducting closed loop part is the same as that in the first embodiment, and its implementation principle is the same, which will not be described one by one here. The SQUID used in this embodiment is set to a first-order gradient configuration, including two Josephson junctions and two coils; the two coils are equal in size and wound in opposite directions; the two coils are connected in series with Josephson junctions. SQUID is a flux-sensitive component. In the first embodiment, the magnetic flux that the SQUID can sense and convert into voltage includes at least two parts: one is generated by the coupling of the input coil in the superconducting closed loop, and the other is obtained by the magnetic field passing directly through the SQUID. In this case, the SQUID itself will introduce interference, that is, common-mode (uniform magnetic field) interference. At this time, in order to avoid the interference caused by the direct induction magnetic field of the SQUID, this embodiment adopts a gradient configuration, and uses a gradient coil formed by two induction coils of equal size and opposite winding directions to suppress common-mode interference. With one side of the first symmetry axis as a reference, the SQUID part is configured as a first-order gradient configuration. At this time, the first magnetic induction circuit 11 is composed of a first-order gradient SQUID115-input coil 112-first induction coil 111. The two induction coils will cause interference because they are SQUID devices themselves, but because the two induction coils have equal areas but are wound in opposite directions, the common-mode currents generated by them can be offset, which means that the common-mode magnetic field caused by the SQUID itself is suppressed macroscopically. At this time, the magnetic field induced by the two induction coils can only come from the coupling of the input coils, that is, the partial induced magnetic field of the first induction coil 111 that constitutes the gradient coil, which couples the magnetic flux to the two induction coils of the first-order gradient SQUID 115 through the input coil 112, and the measured magnetic field is obtained through the SQUID's flux-voltage conversion relationship.

[0080] like Figure 3 As shown, this embodiment also provides a filter device 114 disposed on a superconducting quantum interference device magnetic plane gradiometer 1 of this embodiment, which is used to reduce the coupling resonance between the input coil and the SQUID, and can be used as a low-pass filter structure. The filter device 114 is connected in parallel to the input coils on both sides on the basis of the SUQID being a gradient configuration.

[0081] Specifically, the filter device is a CRC filter device, including a first capacitor, a resistor and a second capacitor connected in series in sequence. That is: the same capacitors are connected in series on both sides of the resistor. Taking one side of the first symmetry axis AA as an example, the first induction coil 111 and the first input coil 112 are coupled to the first SQUID 113 after induction magnetic flux. As the gradient configuration of the SQUID becomes more complex, coupling resonance is easily generated between the first induction coil 111-first input coil 112 configuration and the first SQUID 113, and this coupling resonance will greatly affect the performance of the magnetic gradiometer. A CRC filter device is added in parallel to the first input coil 111 to increase the structural complexity of the first input coil 111. The series resistor plays a damping role, and the resistor consumes the energy of the overvoltage, thereby suppressing the oscillation of the circuit and avoiding the formation of coupling resonance. In addition, the filter device itself is a CRC configuration, which can be a low-pass filter at the same time to improve the performance of the gradiometer.

[0082] The magnetic field detection method and magnetic field detection system provided in this embodiment are basically the same in principle and process as those of the first embodiment, and will not be described in detail here.

[0083] Embodiment 3

[0084] like Figure 4 As shown, this embodiment provides a superconducting quantum interference device magnetic plane gradiometer 1, and the superconducting closed loop part is basically the same as that of the second embodiment, except that the SQUID used is set to a second-order gradient configuration.

[0085] Specifically, the superconducting closed loop part is the same as that in the first embodiment, and its implementation principle and structure are the same, which will not be described in detail here. The SQUID used in this embodiment is set to a second-order gradient configuration. Compared with the first-order gradient configuration provided by the SQUID in the second embodiment, the high-order gradient configuration formed by the difference can effectively suppress the interference of the environmental magnetic field.

[0086] like Figure 4 As shown, the SQUID is set to a second-order gradient configuration, including two Josephson junctions and four coils; the four coils are equal in size and connected in parallel; the two Josephson junctions are connected in series with the four parallel coils; the four coils are respectively located in four areas divided by the first symmetry axis and the second symmetry axis; the first symmetry axis and the second symmetry axis are vertically arranged, forming an intersection in the middle; the four coils are symmetrical based on the center of the intersection; the two coils on the same side of the symmetry axis are wound in opposite directions; the two coils in the diagonal area are wound in the same direction. In this embodiment, Figure 4As shown, four coils are set up on the same plane for detection, and the two symmetry axes are divided into a second symmetry axis BB and a third symmetry axis CC. The winding directions of the areas located on the diagonal of the four coils are the same, and the winding directions of the areas located on the same side of the symmetry axis are opposite. The four coils are connected to the common end in the middle, and two potentials are set at the common end. The two ends of each coil are respectively connected to the two potentials, which is equivalent to the four coils being connected in parallel. Two Josephson junctions are connected in series with the four parallel coils. In this embodiment, two lead wires are set at the common end, one of which is directly connected to one of the potentials of the common end, and the other lead wire is connected to two Josephson junctions in series, and the two ports of the Josephson junctions in series are respectively connected to the two potentials of the common end, which is equivalent to the two Josephson junctions in series with four parallel coils. In this embodiment, as Figure 4 As shown, the lower left corner and upper right corner area are defined as the magnetic field balance area, the upper left corner and lower right corner area are defined as the measured magnetic field area, the magnetic field balance area and the measured magnetic field area are rectangular in shape, and other shapes are applicable to the superconducting magnetic sensor detection coil of the present invention, not limited to this embodiment. The working principle of the second-order gradient coil is the same as that of the first-order gradient coil, which will not be described one by one here.

[0087] It should be noted that the SUQID at this time can also use a higher-order gradient configuration, such as a third-order gradient configuration, as long as the SQUID itself does not introduce its own interference into the gradiometer, it falls within the protection scope of this embodiment. In addition, as the complexity of the SQUID gradient configuration increases, the coupling resonance between the input coil and the SQUID may cause the performance of the gradiometer to deteriorate. The SQUID of the second-order gradient configuration of this embodiment or the SQUID of the higher-order third-order gradient configuration may be equipped with a filter device 114 (such as Figure 2 The implementation principle and structure of the filter element 114 have been described in the second embodiment and will not be described in detail here.

[0088] The magnetic field detection method and magnetic field detection system provided in this embodiment are basically the same in principle and process as those of the first embodiment, and will not be described in detail here.

[0089] It should be noted that, in order to achieve higher uniformity of the superconducting quantum interference device magnetic plane gradiometer 1 of the above-mentioned embodiments 1 to 3, it is necessary to ensure the high symmetry of the superconducting quantum interference device magnetic plane gradiometer 1, and the parameters of the corresponding coils on both sides based on the first symmetry axis, including but not limited to the number of coil turns, coil material, coil shape, etc., should be equal to each other. For example, the parameters of the first input coil 112 and the second input coil 122 corresponding to the other side of the first symmetry axis should be equal. If a filter device 114 is set at the input coil, in addition to the configuration of the first capacitor-resistor-second capacitor in the filter device 114 being completely consistent, the parameters of the corresponding capacitors and the parameters of the corresponding resistors should also be completely consistent.

[0090] In summary, the present invention provides a superconducting quantum interference device magnetic plane gradiometer, a magnetic field detection method and system, including: a superconducting closed loop and two SQUIDs; the superconducting closed loop includes a gradient coil and two input coils; the gradient coil is wound by two induction coils of equal size and opposite winding directions, and the two induction coils are symmetrical about the first symmetry axis; the two input coils are equal in size and symmetrically arranged on both sides of the gradient coil along the first symmetry axis, and the two input coils are connected in series with the gradient coil; two SQUIDs are symmetrically arranged on both sides of the superconducting closed loop along the first symmetry axis, and are used to respectively sense the magnetic flux of the corresponding input coils and convert the magnetic flux into voltage. The present invention sets a fully symmetrical magnetic gradiometer, and through the mode switching of single-side independent operation and double-side joint operation, avoids the common mode influence brought by the introduction of an additional superconducting loop, effectively reduces the imbalance of the gradiometer, and improves the overall uniformity of the device. Therefore, the present invention effectively overcomes the various shortcomings in the prior art and has a high industrial utilization value.

[0091] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A superconducting quantum interference device magnetic plane gradiometer, characterized in that: The superconducting quantum interference device magnetic plane gradiometer at least comprises: a superconducting closed loop and two SQUIDs; The superconducting closed loop includes a gradient coil and two input coils; the gradient coil is formed by two induction coils of equal size and opposite winding directions, and the two induction coils are symmetrical with respect to a first symmetry axis; the two input coils are equal in size and symmetrically arranged on both sides of the gradient coil along the first symmetry axis, and the two input coils are connected in series with the gradient coil; Two SQUIDs are symmetrically arranged on both sides of the superconducting closed loop along the first symmetry axis, and are used to respectively sense the magnetic flux of the corresponding input coil and convert the magnetic flux into voltage.

2. The superconducting quantum interference device magnetic plane gradiometer according to claim 1, characterized in that: The inductance of the input coil is equal to half the inductance of the gradient coil.

3. The superconducting quantum interference device magnetic plane gradiometer according to claim 1, characterized in that: The SQUID is configured as a DC superconducting quantum interference device; the DC superconducting quantum interference device is composed of two Josephson junctions connected in parallel.

4. The superconducting quantum interference device magnetic plane gradiometer according to claim 1, characterized in that: The SQUID is set to a first-order gradient configuration, including two Josephson junctions and two coils; the two coils are equal in size and wound in opposite directions; the Josephson junctions are connected in series on the two coils respectively.

5. The superconducting quantum interference device magnetic plane gradiometer according to claim 1, characterized in that: The SQUID is set to a second-order gradient configuration, including two Josephson junctions and four coils; the four coils are equal in size and connected in parallel; the two Josephson junctions are connected in series with the four parallel coils; the four coils are respectively located in four areas divided by the first symmetry axis and the second symmetry axis; the first symmetry axis and the second symmetry axis are vertically arranged, and an intersection is formed in the middle; The four coils are symmetrical based on the center of the intersection; the two coils located on the same side of the symmetry axis are wound in opposite directions; and the two coils located in the diagonal area are wound in the same direction.

6. The superconducting quantum interference device magnetic plane gradiometer according to claim 4 or 5, characterized in that: Two ends of the input coil are connected in parallel with a filter device; the filter device is a CRC filter device, including a first capacitor, a resistor and a second capacitor connected in series in sequence.

7. A magnetic field detection method, implemented by using the superconducting quantum interference device magnetic plane gradiometer according to any one of claims 1 to 6, characterized in that: The magnetic field detection method at least comprises: The gradient coil in the superconducting closed loop detects the measured magnetic field to obtain a corresponding magnetic flux signal; the input coil is coupled with the SQUID magnetic flux, and the SQUID device senses the magnetic flux signal; the sensed magnetic flux signal is linearly converted from magnetic flux to voltage to obtain an output voltage.

8. The magnetic field detection method according to claim 7, characterized in that: Only one of the SQUIDs at the two ends is in a current biased working state, and the other SQUID is in a power-off non-working state.

9. The magnetic field detection method according to claim 7, characterized in that: The SQUIDs at both ends are in working state at the same time, and the output voltages at both ends are subtracted to eliminate the common mode signal in the output signal, thereby realizing differential mode signal detection.

10. A magnetic field detection system, characterized in that: The magnetic field detection system comprises: A readout circuit and a superconducting quantum interference device magnetic plane gradiometer as claimed in any one of claims 1 to 6; The superconducting quantum interference device magnetic plane gradiometer is used to sense the measured magnetic field; the readout circuit reads the output voltage of the superconducting quantum interference device magnetic plane gradiometer to obtain the magnetic field size of the measured magnetic field.

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