阅读说明：本技术 一种基于多组异形闭环超导线圈的磁场屏蔽系统 (Magnetic field shielding system based on multi-group special-shaped closed-loop superconducting coils ) 是由 池长鑫 蔡传兵 池长昀 于 2020-06-17 设计创作，主要内容包括：本发明属于超导电工学的技术领域,公开了一种基于多组异形闭环超导线圈的磁场屏蔽系统,包括共轴设置的至少两个超导线圈组,它们彼此绝缘且间隔设置,每个所述超导线圈组所在平面相互平行,均多匝闭合串联在一起的内线圈和外线圈,所述内线圈和外线圈同轴共面设置,其通过对单根超导带材或者堆叠在一起的多根超导带材进行横向和纵向切割形成异形闭合线径,再将部分的异形闭合线径撑开形成串联在一起的多匝的内线圈和外线圈。本发明通过在z方向同轴排列多个超导线圈组,不仅可以解决偏平线圈z方向的屏蔽效率衰减明显的问题,还可以增加z方向的屏蔽范围,从而增加整个磁场屏蔽系统的屏蔽范围,扩大其应用范围。(The invention belongs to the technical field of superconducting electrotechnics, and discloses a magnetic field shielding system based on a plurality of groups of special-shaped closed-loop superconducting coils, which comprises at least two superconducting coil groups which are coaxially arranged, wherein the superconducting coil groups are insulated and arranged at intervals, the planes of the superconducting coil groups are parallel to each other, and a plurality of turns of inner coils and outer coils which are connected in series are closed. According to the invention, the plurality of superconducting coil groups are coaxially arranged in the z direction, so that the problem of obvious attenuation of the shielding efficiency of the flat coil in the z direction can be solved, and the shielding range in the z direction can be increased, thereby increasing the shielding range of the whole magnetic field shielding system and expanding the application range of the magnetic field shielding system.)

1. A magnetic field shielding system based on a plurality of groups of special-shaped closed-loop superconducting coils is characterized in that: the superconducting coil comprises at least two superconducting coil groups which are coaxially arranged, wherein the superconducting coil groups are insulated and arranged at intervals, the planes of the superconducting coil groups are parallel to each other, the superconducting coil groups comprise an inner coil and an outer coil which are closed and connected in series, the inner coil and the outer coil are coaxially and coplanarly arranged, a single superconducting strip or a plurality of stacked superconducting strips are transversely and longitudinally cut to form a special-shaped closed wire diameter, and then part of the special-shaped closed wire diameter is unfolded to form the inner coil and the outer coil which are connected in series.

2. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 1, wherein: the larger the number of groups of the coaxial superconducting coil groups, the larger the spacing from each other, which is in direct proportion to the shielding factor.

3. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 2, wherein: the turns of the inner coil and the outer coil of each superconducting coil group are the same, the turns of the inner coil and the turns of the outer coil of each superconducting coil group are the same, the radiuses of the inner coils are the same, and the radiuses of the outer coils are the same.

4. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 1, wherein: the method comprises the steps of transversely cutting the single superconducting strip at equal intervals along the length direction from the lower end to the upper end of the single superconducting strip to form a plurality of transverse paths with different lengths, longitudinally cutting the single superconducting strip at equal intervals along the width direction from the right end to the left end of the single superconducting strip, and connecting the transverse paths at different positions, so that the cut superconducting strip forms a special-shaped closed line diameter comprising a plurality of parallel transverse narrow bands and longitudinal narrow bands.

5. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 4, wherein: recording the sum of the turns of the inner coil and the outer coil as N, wherein N is a natural number, the number of the transverse narrow bands is 2N, the transverse narrow bands at odd number positions and the transverse narrow bands at even number positions are oppositely spread from the lower end to the upper end of the single superconducting strip,

if the number of turns of the inner coil and the outer coil is N/2, correspondingly spreading the transverse narrow bands from the 1 st position to the N/2 nd position, and from the (3N/2) +1 st position to the 2N nd position to form the outer coil; spreading the transverse narrow bands from the (N/2) +1 to the (3N/2) positions to form an inner coil;

if the number of turns of the inner coil is a, the number of turns of the outer coil is b, and a + b is equal to N, correspondingly spreading the transverse narrow bands from the 1 st bit to the b th bit and from the 2a + b +1 st bit to the 2N th bit to form the outer coil; and correspondingly spreading the transverse narrow bands from the b +1 th bit to the 2a + b th bit to form an inner coil.

6. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 5, wherein: the inner coil and the outer coil are round, oval, rectangular, square or regular polygon in shape.

7. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 5, wherein: note that the width of the longitudinal narrow band is T_zdThe interval width between adjacent longitudinal narrow bands is set by T_zlIf the total number of turns of the inner and outer coils is N, N ═ a + b, then 2N-1 transverse paths are required,

wherein, the distance between the right end of the 1 st and 2N-1 st transverse paths and the right end of the single superconducting tape is T_zdThe distance between the right end of the 2 nd and 2N-2 nd transverse paths and the right end of the single superconducting strip is T_zd+(T_zd+T_zl) And so on, the distance between the right end of the nth transverse path and the right end of the (2N-N) th transverse path and the right end of the single superconducting strip is T_zd+(T_zd+T_zl) (N-1), wherein N is a natural number not greater than N;

in the transverse paths greater than N and less than 2N, the distance between the left end of the (N + 2), the (N + 4), the (2N-2) th transverse paths and the left end of the single superconducting tape is T_zd+(T_zd+T_zl) In the transverse paths less than or equal to N, the distance between the left end of the 2 nd transverse path, the 4 th transverse path and the left end of the single superconducting tape is zero, and the distance between the left end of each of the other transverse paths and the left end of the single superconducting tape is T_zd。

8. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 7, wherein: the 1 st longitudinal path counted from the right end to the left end of the single superconducting strip is connected with the 1 st and the (2N-1) th transverse paths, the 2 nd longitudinal path is connected with the 2 nd and the (2N-2) th transverse paths, and so on, the N-1 st longitudinal kerf is connected with the N-1 st and the N +1 st transverse paths,

when N is greater than 2, T is located at the left end of the single superconducting tape_zdA longitudinal path is arranged to connect the (N + 1) th and the (2N-1) th transverse paths.

9. The magnetic field shielding system based on multiple sets of shaped closed-loop superconducting coils of claim 1, wherein: the plurality of superconducting tapes stacked together are insulated from each other, and when the number of turns of the inner coil and the outer coil is 1, the number of the superconducting tapes stacked together is not more than four.

Technical Field

The invention relates to the technical field of superconducting electrotechnics, in particular to a magnetic field shielding system based on a plurality of groups of special-shaped closed-loop superconducting coils.

Background

With the development of the electronic industry, precision electronic instruments are in scienceThe method is widely applied in research, wherein the sensors of some precision instruments are very sensitive to the change of a tiny magnetic field, such as fluxgate sensors, superconducting quantum interferometers, optical pump magnetometers, magnetic resonance imaging atomic magnetometers and the like, and the magnetic sensitivity can even reach fT Hz^-1/2A rank. Therefore, it is necessary to remove the interference of the background noise to the sensor by using the magnetic shielding technology.

Coil-based magnetic field shielding systems can be divided into active shielding and passive shielding. For a passive magnetic field shielding system, reducing the resistance of the shielding coil is beneficial to improving the magnetic shielding efficiency, especially in the environment of low magnetic field strength and low magnetic field frequency. In principle, because the magnetic shielding conductor has resistance, the lower the change rate of an interference magnetic field is, the lower the magnetic shielding efficiency is, and the conventional conductor coil is suitable for shielding medium-frequency and high-frequency magnetic fields. It is known that the resistance of a superconducting material in a superconducting state is zero, and the university of qinghua has reported that two Bi2223(Bi2Sr2Ca2Cu3Ox) superconducting coils with different radii are concentrically wound and connected through a RE123 (rare earth elements such as REBa2Cu3Ox, RE ═ Y, Gd) superconducting tape to form a composite magnetic field shielding coil with an inner coil and an outer coil connected in series. However, when a high-temperature superconducting wire/strip is wound into a closed coil, a coil joint needs to be welded, and at present, even when a superconducting welding technology is adopted, a small resistance still exists. When the change rate of the interference magnetic field is more than mu T Hz^-1/2In the process, the tiny resistance of the superconducting coil has little influence on the magnetic shielding efficiency, but the sensor precision of some precise instruments reaches nT Hz^-1/2And fT Hz^-1/2A rank. In this case, in order to achieve a sufficiently high shielding efficiency, it is necessary to eliminate the minute resistance of the superconducting coil as much as possible. In recent years, a RE123 coil design without joint resistance has appeared, in which a closed loop coil is formed by cutting a sufficiently long gap from the middle of a RE123 (rare earth element such as REBa2Cu3Ox, RE Y, Gd, etc.) high temperature superconducting tape and then spreading the gap, and since there is no joint in this coil, there is no joint resistance, but the magnetic field shielding efficiency of a single-turn loop coil is very low, and even if a plurality of loop coils are stacked, since they are mutually stackedIndependent of each other, the accumulated magnetic shielding efficiency still cannot meet the requirement of a precise instrument. There is therefore a need for a new coil design that connects the turns of the coil in series with each other while ensuring that there is no joint resistance.

Disclosure of Invention

The invention provides a magnetic field shielding system based on a plurality of groups of special-shaped closed-loop superconducting coils, which solves the problems that the existing superconducting coils have joint resistance, so that the shielding efficiency of a low-frequency magnetic field is low, the requirements of precision instruments cannot be met, and the like.

The invention can be realized by the following technical scheme:

a magnetic field shielding system based on a plurality of groups of special-shaped closed-loop superconducting coils comprises at least two superconducting coil groups which are coaxially arranged, wherein the superconducting coil groups are insulated and arranged at intervals, planes of the superconducting coil groups are parallel to each other, and an inner coil and an outer coil which are connected in series are closed in a multi-turn mode.

Further, the larger the number of sets of the coaxial superconducting coil sets, the larger the interval between them, which is in direct proportion to the shielding factor.

Furthermore, the turns of the inner coil and the outer coil of each superconducting coil set are the same, the turns of the inner coil and the turns of the outer coil of each superconducting coil set are the same, the radiuses of the inner coils are the same, and the radiuses of the outer coils are the same.

Further, the single superconducting tape is transversely cut at equal intervals along the length direction from the lower end to the upper end of the single superconducting tape to form a plurality of transverse paths with different lengths, and the single superconducting tape is longitudinally cut at equal intervals along the width direction from the right end to the left end of the single superconducting tape to connect the transverse paths at different positions, so that the cut superconducting tape forms a special-shaped closed line diameter comprising a plurality of parallel transverse narrow bands and longitudinal narrow bands.

Further, the sum of the turns of the inner coil and the outer coil is recorded as N, wherein N is a natural number, the number of the transverse narrow bands is 2N, the transverse narrow bands at odd number positions and the transverse narrow bands at even number positions are oppositely spread from the lower end to the upper end of the single superconducting strip,

if the number of turns of the inner coil and the outer coil is N/2, correspondingly spreading the transverse narrow bands from the 1 st position to the N/2 nd position, and from the (3N/2) +1 st position to the 2N nd position to form the outer coil; spreading the transverse narrow bands from the (N/2) +1 to the (3N/2) positions to form an inner coil;

if the number of turns of the inner coil is a, the number of turns of the outer coil is b, and a + b is equal to N, correspondingly spreading the transverse narrow bands from the 1 st bit to the b th bit and from the 2a + b +1 st bit to the 2N th bit to form the outer coil; and correspondingly spreading the transverse narrow bands from the b +1 th bit to the 2a + b th bit to form an inner coil.

Further, the inner coil and the outer coil are arranged in a shape of a circle, an ellipse, a rectangle, a square or a regular polygon.

Further, let the width of the longitudinal narrow band be T_zdThe spacing width between adjacent longitudinal narrow bands is set Tzl, if the sum of the number of turns of the inner coil and the outer coil is N, 2N-1 transverse paths are needed,

wherein, the distance between the right end of the 1 st and 2N-1 st transverse paths and the right end of the single superconducting tape is T_zdThe distance between the right end of the 2 nd and 2N-2 nd transverse paths and the right end of the single superconducting strip is T_zd+(T_zd+T_zl) And so on, the distance between the right end of the nth transverse path and the right end of the (2N-N) th transverse path and the right end of the single superconducting strip is T_zd+(T_zd+T_zl) (N-1), wherein N is a natural number not greater than N;

in the transverse paths greater than N and less than 2N, the distance between the left end of the (N + 2), the (N + 4), the (2N-2) th transverse paths and the left end of the single superconducting tape is T_zd+(T_zd+T_zl) In the transverse paths less than or equal to N, the distance between the left end of the 2 nd, 4 th andis a distance T between_zd。

Furthermore, the 1 st longitudinal path counted from the right end to the left end of the single superconducting tape is connected with the 1 st and the (2N-1) th transverse paths, the 2 nd longitudinal path is connected with the 2 nd and the (2N-2) th transverse paths, and so on, the N-1 st longitudinal kerf is connected with the N-1 st and the N +1 st transverse paths,

when N is greater than 2, a longitudinal path is arranged at a position Tzd away from the left end of the single superconducting tape to connect the (N + 1) th and the (2N-1) th transverse paths.

Further, a plurality of the superconducting tapes stacked together are insulated from each other, and when the number of turns of the inner coil and the outer coil is 1, not more than four superconducting tapes are stacked together.

The beneficial technical effects of the invention are as follows:

by coaxially arranging a plurality of superconducting coil groups in the z direction, the problem that the shielding efficiency of the flat coil in the z direction is obviously attenuated can be solved, and the shielding range in the z direction can be increased, so that the shielding range of the whole magnetic field shielding system is increased, and the application range of the magnetic field shielding system is expanded. Meanwhile, because the series connection between the inner coil and the outer coil of the invention has no extra connecting wire, but a part of the special-shaped closed wire diameter formed by cutting a single superconducting strip or a plurality of stacked superconducting strips, the invention has no joint resistance, so that the resistance of the inner coil and the outer coil is only the resistance of the superconducting strips, and then, the special-shaped closed wire diameter is partially unfolded to form a plurality of turns of the inner coil and the outer coil which are connected together in series, thereby improving the magnetic field shielding efficiency, realizing the passive shielding in the environment with low magnetic field intensity and low magnetic field frequency, and simultaneously realizing the effective shielding of high and medium frequency magnetic fields.

Drawings

The invention and its features, aspects and advantages will become more apparent from reading the following detailed description of non-limiting embodiments with reference to the accompanying drawings. Like reference symbols in the various drawings indicate like elements. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a schematic diagram of the distribution of shielding coefficients in a three-dimensional spherical space range with a radius of 25mm, in which the center of a Coil3-3 model of the invention is the center of a sphere;

FIG. 2 is a schematic structural view of a plurality of superconducting coil sets of the present invention arranged coaxially, wherein FIG. 2(a) shows coil set 2-2AB, and FIG. 2(B) shows coil set 3-3A 'B';

FIG. 3 is a diagram showing the variation of the shielding coefficient of a single superconducting Coil assembly and a conventional shielding Coil structure at different magnetic field frequencies, and FIG. 3(a) is a diagram showing the comparison of the magnetic shielding coefficients of a conventional superconducting shielding Coil and Coil2-2 AB, with an external field intensity of 10 μ T; FIG. 3(b) is a graph showing a comparison of the change in magnetic shielding coefficient of individual superconducting Coil sets Coil2-2 AB under the interference magnetic fields of 1mT and 1 nT.

FIG. 4 is a schematic diagram showing the shielding coefficient variation of the center points of Coil groups Coil 2-2A and Coil3-3A 'B' of the superconducting Coil of the present invention at different pitches;

FIG. 5 is a schematic diagram showing the distribution of the shielding coefficients of the magnetic field in a spherical space with a radius of 35mm in the central region of the superconducting Coil assembly Coil2-2 AB according to the present invention;

fig. 6 is a view of the present invention and a prior art shield coil structure, wherein fig. 6(a) shows that the prior art concentric inner and outer coils are independent of each other; FIG. 6(b) is a view showing that the inner coil and the outer coil are connected in series by a cutting path of a single superconducting tape using the present invention;

FIG. 7 is a special-shaped closed loop RE123 magnetic shield coil of the present invention, FIG. 7(a) shows the number of turns is 2+2 turns, and FIG. 7(b) shows the number of turns is 3+3 turns;

fig. 8 shows the interference magnetic field variation process of the present invention, the center point shielding effect of different coils, fig. 8(a) shows the magnetic field shielding process of different coils, and fig. 8(b) shows the shielding coefficient values corresponding to different coils;

FIG. 9 is a schematic diagram of the center point shielding coefficient variation of Coil1-1 of the present invention under different outer Coil radii.

Detailed Description

The following detailed description of the preferred embodiments will be made with reference to the accompanying drawings.

In practical applications, the sensor generating the disturbing magnetic field has a certain volume, and therefore, the magnetic shielding coefficient distribution in a certain spatial region needs to be studied. Taking Coil3-3 as an example for analysis, fig. 1 is a shielding coefficient distribution diagram of a three-dimensional spherical space range with a radius of 25mm and a Coil3-3 model with a center position as a spherical center, wherein it can be seen that the shielding coefficient of the center point is 0.2%, is closest to zero, and gradually increases to 13.5% from zero to plus and minus 25mm along the z-axis direction, and gradually increases to 6.5% from zero to plus and minus 25mm along the x-axis direction, so that although the shielding efficiency of the center point of Coil3-3 is better, the shielding efficiency is obviously attenuated in the axial direction due to the flat structure of the Coil. It is worth mentioning that a negative shielding coefficient occurs in the shielding region, and a negative value means that an excessive shielding state exists in a partial space region, that is, the reverse induction magnetic field is larger than the interference magnetic field, and it is expected that if the number of turns of the coil is further increased, the excessive shielding effect is aggravated. The shielding effect is evaluated based on whether the absolute value of the shielding coefficient is close to zero, and an excessively large negative shielding coefficient, like an excessively large positive shielding coefficient, is not favorable for suppressing the interference magnetic field.

Because the shielding coil is a flat structure, the shielding efficiency attenuation in the x and y directions is small, the shielding efficiency attenuation in the z direction is obvious, and in order to improve the shielding efficiency in the z direction, as shown in fig. 2, the invention provides a magnetic field shielding system based on a plurality of groups of special-shaped closed loop superconducting coils, which comprises at least two superconducting coil groups which are coaxially arranged, are insulated and arranged at intervals, the planes of the superconducting coil groups are mutually parallel, and a plurality of turns of inner coils and outer coils which are connected in series are closed and connected together in series, the inner coils and the outer coils are coaxially arranged in a coplanar manner, a single superconducting strip or a plurality of stacked superconducting strips are transversely and longitudinally cut to form special-shaped closed wire diameters, and then part of the special-shaped closed wire diameters are spread to form the plurality of turns of inner coils and outer coils which are connected in series. Therefore, the problem that the shielding efficiency of the flat coil in the z direction is obviously attenuated can be solved by coaxially arranging the plurality of superconducting coil groups in the z direction, and the shielding range in the z direction can be increased, so that the shielding range of the whole magnetic field shielding system is increased, and the application range of the magnetic field shielding system is expanded. Meanwhile, because the series connection between the inner coil and the outer coil of the invention has no extra connecting wire, but a part of the special-shaped closed wire diameter formed by cutting a single superconducting strip or a plurality of stacked superconducting strips, the invention has no joint resistance, so that the resistance of the inner coil and the outer coil is only the resistance of the superconducting strips, and then, the part of the special-shaped closed wire diameter is spread to form the multi-turn inner coil and the outer coil which are connected together in series, thereby improving the magnetic field shielding efficiency and realizing the passive shielding in the environment with low magnetic field intensity and low magnetic field frequency.

The shielding coefficient of a magnetic field shielding system formed by a plurality of coaxially arranged superconducting coil groups is zero, the radius size and the number of turns of an inner coil and an outer coil of each superconducting coil group can be different from each other or the same as each other, and the shielding coefficient of the whole magnetic field shielding system is ensured to be close to zero by adjusting the interval between the adjacent superconducting coil groups.

In order to verify the shielding effect of the shielding system of the present invention, a series of comparative tests were performed, specifically as follows:

the working process of the superconducting magnetic shielding coil comprises the steps of firstly cooling the RE123 superconducting coil to a 77K liquid nitrogen temperature region in a zero field environment, entering a superconducting state, starting a passive magnetic shielding working state, and generating a reverse induction magnetic field by the shielding coil when a changed external magnetic field appears, so as to partially offset the external magnetic field, thereby realizing the magnetic field shielding effect.

The indexes for measuring the magnetic shielding effect are the shielding efficiency SH and the shielding coefficient SF. The shielding effectiveness, i.e., the shielding efficiency SH, can be expressed by equation 1, where H0 is the magnetic field strength without shielding, H1 is the magnetic field strength after shielding, and SH is the magnetic field shielding efficiency in dB.

S_H＝20Lg(H₀/H₁) (1)

In order to describe the magnetic field shielding effect more intuitively, the invention introduces the concept of the shielding coefficient SF. SF can be described by equation 2, where B0 is the magnetic field strength without shielding and Br is the magnetic field strength after shielding. It can be seen that the closer the SF value is to zero, the better the shielding effect. That is, the lower the absolute value of the masking coefficient, the better the masking effect.

SF＝(B_r/B₀)×100％ (2)

The shielding factor of the coil is affected by the interfering magnetic field frequency and the resistance of the coil. For a traditional coil, due to the existence of resistance, the shielding efficiency of the coil is obviously attenuated under the lower frequency of an interference magnetic field, for a superconducting coil, although a superconducting material has no resistance, a welding joint of the coil still has very small resistance, and under the low-frequency interference magnetic field, the attenuation of the shielding efficiency still exists. The RE123 superconducting coil group related by the invention is a topological structure without joint resistance, and the manufacture of a single RE123 superconducting coil group is explained in detail below, so that the coil resistance can be eliminated theoretically, and the stable magnetic field shielding efficiency can still be kept under a low-frequency magnetic field.

FIG. 3(a) compares the center point magnetic shielding coefficient of Coil2-2 AB without joint resistance and a conventional superconducting magnetic shielding Coil (with resistance) at different magnetic field frequencies, with a disturbing magnetic field amplitude of 10 μ T. It can be seen that the shielding coefficient of the connector Coil is gradually increased when the frequency of the interference magnetic field is less than 1Hz, the shielding coefficient of the connector Coil is increased to 8% when the frequency is 0.01Hz, and the shielding coefficient of the Coil group Coil2-2 AB is stably maintained at a level of about 0.01% in the frequency range of the interference magnetic field of 0.01Hz to 1000Hz, from which it can be seen that the resistance-free design can greatly improve the shielding efficiency of the Coil in the low-frequency environment.

FIG. 3(b) compares the shielding coefficients of Coil set Coil2-2 AB at different magnetic field frequencies under a 1mT magnetic interference field and a 1nT magnetic interference field. Due to the non-resistance characteristic of the coil, the stable magnetic field shielding efficiency is still maintained under the low-frequency environment of the interference magnetic field with 1nT change, and under the interference magnetic field with 1mT change, the induced current intensity of the coil with the width of the superconducting strip being 1mm is close to the critical current of 40A, and weak resistance begins to be generated, so that the shielding efficiency under the low-frequency environment is attenuated, namely, the shielding coefficient is gradually increased to 0.46 percent as the frequency is reduced from 10Hz to 0.00001 Hz. If shielding of stronger magnetic field is required, this can be achieved by increasing the critical current of the superconducting tape, such as lowering the temperature, increasing the width of the superconducting tape, multiple sets of coils, etc.

In the following, the change of the shielding coefficients at different distances d is studied by taking as an example that the turns of the inner coil and the outer coil of each superconducting coil set are the same, the turns of the inner coil and the turns of the outer coil of all the superconducting coil sets are the same, the radii of the inner coils are the same, and the radii of the outer coils are the same.

In order to achieve the best shielding efficiency and avoid excessive shielding, the distance d between two independent coil sets needs to be calculated and optimized according to the shielding coefficient. Fig. 4 shows the shielding coefficients of the center points of Coil groups Coil2-2 AB and Coil groups Coil3-3A 'B' at different distances d, and it can be seen that the shielding coefficients are approximately linear with the spacing between adjacent superconducting Coil groups, and too close distances result in excessive shielding, resulting in negative magnetic fields, and too far distances reduce the shielding efficiency. Due to the fact that the number of turns of the superconducting Coil assembly Coil3-3A 'B' is too large, the shielding coefficient of the center point is negative within the distance range of 70mm-115 mm.

For Coil2-2 AB, the shielding factor reached-1% to 1% in the range of d 83.8mm to 87.7mm, and calculations showed that the shielding factor was 0.01% at a distance of 85.78mm, achieving the optimum effect. In order to reduce the volume of equipment and save the cost of the used strip, the design of the Coil2-2 AB is more economical and effective than the design of the Coil3-3A 'B'.

In addition, experiments prove that when the superconducting Coil assembly Coil2-2 is arranged axially in three groups, in order to avoid the occurrence of excessive negative shielding and simultaneously increase the axial shielding area, the distance between the Coil assemblies needs to be increased properly, such as from 85.78mm to 116 mm; when the superconducting Coil assembly Coil2-2 is arranged in four axial groups, the distance between the Coil assemblies needs to be further increased, for example, the distance is increased from 116mm to 123mm, and the axial shielding area is further increased. The axial arrangement of the Coil group Coil3-3 needs to increase the Coil distance properly and further relative to the Coil group Coil2-2 turns, so as to realize the central zero field and increase the axial shielding area.

When the superconducting Coil group Coil1-1 is axially arranged, four groups are closely arranged, so that a central zero field can be realized, and less than four groups cannot realize the central zero field. If more sets are used, the spacing of the coil sets needs to be increased appropriately to avoid negative shielding.

Selecting Coil group Coil2-2 AB, d being 85.78mm as the distance between Coil a and Coil B, calculating the shielding coefficient distribution of a spherical ball space with a central area radius of 35mm, as shown in fig. 5, it can be seen that the shielding coefficient of the central point is 0.01%, is closest to zero, and varies from zero to plus or minus 35mm along the z-axis direction, and the shielding coefficient gradually increases from 0 to 3.4% from zero to plus or minus 35mm along the x-axis direction, compared with Coil group Coil3-3, the shielding efficiency of Coil group Coil2-2 AB is significantly improved, and the attenuation of the shielding efficiency in the z-direction is greatly improved, obviously, Coil2-2 AB based on the helmholtz Coil structure can increase the volume of the central area with high shielding efficiency.

The single RE123 superconducting coil assembly may be manufactured by a single superconducting tape or a plurality of stacked superconducting tapes according to a special cutting and spreading manner, and the cutting method and the corresponding spreading manner are described in detail below by taking the single superconducting tape as an example.

The cutting method can adopt that a plurality of transverse paths with different lengths are formed by performing transverse cutting at equal intervals along the length direction of a single superconducting strip from the lower end to the upper end of the single superconducting strip, and a plurality of transverse paths with different lengths are formed by performing longitudinal cutting at equal intervals along the width direction of the single superconducting strip, so that the cut superconducting strip forms a special-shaped closed wire diameter comprising a plurality of parallel transverse narrow bands and longitudinal narrow bands, and the preparation is made for forming a plurality of turns of inner coils and outer coils subsequently.

Specifically, when performing the transverse cutting, assuming that the sum of the number of turns of the inner coil and the outer coil is N, where N is a natural number, 2N transverse narrow bands and 2N-1 transverse paths are required.

Note that the width of the longitudinal narrow band is T_zdThe interval width between adjacent longitudinal narrow bands is set by T_zlThen the right end of the 1 st, 2N-1 st transverse path and the sheetThe distance between the right ends of the superconducting tapes is T_zdThe distance between the right end of the 2 nd and 2N-2 nd transverse paths and the right end of the single superconducting strip is T_zd+(T_zd+T_zl) And so on, the distance between the right end of the nth transverse path and the right end of the (2N-N) th transverse path and the right end of the single superconducting strip is T_zd+(T_zd+T_zl) (N-1), wherein N is a natural number not greater than N;

in the transverse paths greater than N and less than 2N, the distance between the left end of the (N + 2), the (N + 4), the (2N-2) th transverse paths and the left end of the single superconducting tape is T_zd+(T_zd+T_zl) In the transverse paths less than or equal to N, the distance between the left end of the 2 nd transverse path, the 4 th transverse path and the left end of the single superconducting tape is zero, and the distance between the left end of each of the other transverse paths and the left end of the single superconducting tape is T_zd。

As for the width of the transverse path and the transverse narrow strip, which may be determined according to the specific situation of the superconducting tape, the width of the superconducting tape is generally not more than several tens of mm, so that the width of the transverse path may be set to 0.5 mm or 1mm, and the width of the transverse narrow strip may be set to 1 mm.

When the longitudinal cutting is carried out, the 1 st longitudinal path from the right end to the left end of the single superconducting tape is connected with the 1 st and the (2N-1) th transverse paths, the 2 nd longitudinal path is connected with the 2 nd and the (2N-2) th transverse paths, and the like, the N-1 st longitudinal cutting seam is connected with the N-1 st and the (N + 1) th transverse paths,

when N is greater than 2, T is located at the left end of the single superconducting tape_zdA longitudinal path is arranged to connect the (N + 1) th and the (2N-1) th transverse paths.

The method comprises the steps of cutting a superconducting strip by using the cutting method to obtain a special-shaped closed wire diameter, oppositely strutting odd-number transverse narrow bands and even-number transverse narrow bands from the lower end to the upper end of a single superconducting strip, correspondingly strutting 1 st to N/2 nd transverse narrow bands and (3N/2) +1 nd to 2N nd transverse narrow bands to form an outer coil if the turns of an inner coil and an outer coil are both N/2, and strutting (N/2) +1 nd to (3N/2) th transverse narrow bands to form an inner coil; if the number of turns of the inner coil is a, the number of turns of the outer coil is b, and a + b is equal to N, correspondingly spreading the transverse narrow bands from the 1 st bit to the b th bit and from the 2a + b +1 st bit to the 2N th bit to form the outer coil; and correspondingly spreading the transverse narrow bands from the b +1 th bit to the 2a + b th bit to form an inner coil.

The turns of the inner coil and the outer coil can be the same or different, and the inner coil and the outer coil can be unfolded in different ways. As for the whole of the inner coil and the outer coil having regular geometric shapes, such as circular, oval, rectangular, square, regular polygon and the like, the whole shapes of the two may be the same or different.

Considering the general width of the superconducting tapes, the turns of the inner coil and the outer coil which are manufactured aiming at the cutting and the expanding of a single superconducting tape are limited, and the interference resisting treatment of the interference magnetic field with high magnetic field intensity in reality is difficult to carry out, therefore, a plurality of superconducting tapes can be stacked together and are insulated from each other, the same cutting method is adopted to cut the plurality of superconducting tapes stacked together to form a special-shaped closed wire diameter, the same expanding method is adopted to obtain more turns of the inner coil and the outer coil, so that the superconducting tapes can bear larger current, generate a reverse magnetic field with higher magnetic field intensity, and fully offset the interference magnetic field, thereby achieving higher magnetic field shielding efficiency. However, the number of the stacked superconducting tapes cannot be excessive, otherwise, the reverse magnetic field generated by the induction of the inner coil is larger than the interference magnetic field, and the excessive shielding phenomenon can be generated.

In order to verify the shielding effect of the magnetic field shielding system of a single superconducting coil set, the invention carries out a series of comparative tests, which are as follows:

firstly, a new structure of jointless resistance magnetic shielding coil based on RE123 superconducting tape is designed, and the magnetic field shielding efficiency of the new structure is compared and analyzed. The critical current per mm width superconducting tape at 77K temperature and self-field is 40A, which is a basic independent stacked Coil model, as shown in fig. 6(a), Coil 1/1(Coil 1/1) is composed of two concentric coils, and it can be seen that the inner Coil and the outer Coil are independent from each other, the radius of the inner Coil is r 1-70 mm, the number of turns is n 1-1, the radius of the outer Coil is r 2-180 mm, and the number of turns is n 2-1.

Correspondingly, Coil1-1 (Coil 1-1) shown in fig. 6(b) realizes the jointless series connection of the inner Coil and the outer Coil by the specific tape slit cutting path of the present invention, wherein the radius of the inner Coil is r 1-70 mm, the radius of the outer Coil is n 1-1, the radius of the outer Coil is r 2-180 mm, and the radius of the outer Coil is n 2-1. Theoretically, because the magnetic flux induction area of the outer coil is large, large induced electromotive force can be obtained under the condition of changing the outer magnetic field, the inner coil connected with the outer coil in series is pushed to generate large induced current, and because the inner coil is close to the central magnetic shielding area, the reverse induced magnetic field can offset the outer magnetic field more efficiently.

In order to improve the magnetic field shielding efficiency, a 4-turn series coil and a 6-turn series coil are designed, as shown in fig. 7. The radius of an inner Coil of the Coil2-2 (Coil 2-2) is r 1-70 mm, and the number of turns is n 1-2; the radius of the outer coil is r 2-180 mm, and the number of turns is n 2-2; the radius of an inner Coil of the Coil3-3 (Coil 3-3) is r 1-70 mm, and the number of turns is n 1-3; the radius of the outer coil is r 2-180 mm, and the number of turns is n 2-3.

Then, the present invention sets an amplitude of 10 μ T and a frequency of 10^-5Hz, and verifies the shielding effect of the different coils on the interfering magnetic field at the central location.

Fig. 8(a) shows the magnetic shielding process of Coil 1/1, Coil1-1, Coil2-2, and Coil3-3, from which it can be seen that the magnetic field intensity after shielding is in an equal ratio relation with the interference field intensity during the interference magnetic field variation process, and the more intuitive shielding coefficient value is shown in fig. 8 (b). Comparing Coil 1/1 with Coil1-1, it can be seen that the shielding coils connected in series have better shielding effect than independent coils under the similar Coil structure; comparing Coil1-1, Coil2-2 and Coil3-3, it can be seen that the shielding Coil connected in series has the better shielding effect when the number of turns is larger, and the shielding coefficient of the central point of Coil3-3 reaches 0.2%, but if the number of turns is further increased to 4+4 turns, the excessive shielding state may be reached, and the negative residual magnetic field is obtained.

Finally, in order to verify the relation between the radius ratio of the outer Coil and the inner Coil and the shielding efficiency, on the basis of the model Coil1-1, the shielding coefficients under the condition that the inner Coil is fixed to be 70mm and the outer coils with different radii are designed.

In the shielding coil set, the outer coil has a larger area and contains more magnetic flux, so that the outer coil provides most of the induced electric potential required by the inner coil to generate the reverse shielding magnetic field. Theoretically, the larger the area of the outer coil is, the larger the whole induced electromotive force of the shielding coil is, and the larger the current supplied to the inner coil is, so that a better reverse magnetic field is obtained. The intensity of the environmental disturbance magnetic field is set to be 10 mu T, and the frequency is set to be 0.00001 Hz. As shown in fig. 9, the outer coil radius r2 ranges from 100mm to 400mm, and the shielding factor continues to decrease as r2 increases. When r2 is greater than 300mm, the shielding coefficient decreases to a negative number, which means an overshield state, that is, a reverse induction magnetic field greater than an external magnetic field, and therefore, the overshield state should also be avoided. Compared with the coil1-1, although the shielding coefficient close to 0 can be achieved when r2 is 300mm, the coil with a large radius occupies too much space, the volume of the shielding device is increased, therefore, r2 which occupies a smaller volume can be selected to be 180mm, and the shielding efficiency is improved by increasing the number of turns of the coil. As can be seen from the foregoing, two or three turns can achieve better shielding efficiency and save space.

The invention designs a magnetic shielding Coil capable of stably inhibiting the interference of high, medium and low frequency magnetic fields based on a special-shaped closed loop RE123 superconducting tape, wherein the magnetic shielding coefficient of the central area of a Coil group Coil2-2 AB after structure optimization reaches 0.01 percent, the shielding coefficient is kept to be lower than 1 percent in a spherical space with the radius of 20mm, and the shielding coefficient is kept to be lower than 3.5 percent in a spherical space with the radius of 35 mm. Because of the zero resistance characteristic of the superconducting coils without joints connected in series, the superconducting coils can still keep stable magnetic field shielding efficiency under the environment with extremely low magnetic field intensity and extremely low magnetic field change rate, and can shield fT-Hz theoretically^-1/2A small disturbing magnetic field of the order of magnitude. The magnetic field shielding system can obviously eliminate interference fields on the sensors of precise instruments such as a fluxgate magnetometer, a reluctance magnetometer, a SQUID gradiometer, an optical pump magnetometer and the like, and in addition, the shielding coil has a simple structure and only needs one or more than oneA plurality of specially tailored RE123 superconducting tapes are stacked, and by flexibly adjusting the coil radius, a magnetic field shielding device with a large space range can be built at low cost, and a magnetic field shielding space is created for larger instruments such as clinical medical equipment.

The above description is of the preferred embodiment of the invention. It is to be understood that the invention is not limited to the particular embodiments described above, in that devices and structures not described in detail are understood to be implemented in a manner common in the art; those skilled in the art can make many possible variations and modifications to the disclosed embodiments, or modify equivalent embodiments to equivalent variations, without departing from the spirit of the invention, using the methods and techniques disclosed above. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.