A device for reproducing nanotesla to microtesla magnetic fields within a magnetic shield

Abstract

The application discloses a device for reproducing nanotesla to microtesla magnetic field in a magnetic shielding device, which comprises two sets of non-moment coil windings, and the relative size relationship between the two sets of non-moment coil windings is accurately calculated according to the weak magnetic field to be reproduced, so that when the two sets of non-moment coils are reversely connected in series, the most part of the central region can be cancelled, and the central coil constant is reduced to the order of nT / A; an ampere-level large current can generate a nT-level weak magnetic field, and a microampere-level current can generate a pico-tesla-level extremely weak magnetic field. When the two sets of non-moment coils are connected in series in positive direction, the value of the reproduced standard magnetic field can be doubled under the same current. An ampere-level current can generate a maximum magnetic field of 100 muT. Furthermore, through the positive series connection and the reverse series connection, a wide range of magnetic field from nT to muT can be reproduced.

Description

Technical Field

[0001] This invention belongs to the field of magnetic measurement instrument technology, and relates to a device for reproducing nano- to micro-level magnetic fields within a magnetic shielding device. Background Technology

[0002] When calibrating various types of magnetometers, to minimize the impact of external magnetic interference on the calibration process, calibration is typically performed in environments with geomagnetic field interference, such as weak magnetic field laboratories or magnetic shielding devices (including magnetic shielding cylinders and magnetic shielding rooms). This low-interference magnetic field environment, combined with a coil system that reproduces the standard magnetic field, allows for the calibration of parameters such as noise, sensitivity, and indication error of the magnetometer. For high-precision magnetometers with small magnetic field measurement ranges and extremely high sensitivity, such as inductive magnetometers and SERF magnetometers (spin-free exchange relaxation magnetometers), calibration is generally performed within magnetic shielding devices.

[0003] The measurement ranges of different types of magnetometers vary considerably. For example, fluxgate magnetometers typically have a measurement range of 0.1 nT to 100 μT; optically pumped magnetometers and proton magnetometers typically have a range of 20 μT to 100 μT; inductive magnetometers typically have a range of 1 pT to 1 μT; and SERF magnetometers typically have a range of 0.1 pT to 10 nT. Therefore, to meet the measurement range requirements of all these magnetometers, a standard magnetic field of 0.1 pT to 100 μT needs to be reproduced within a magnetically shielded device. The upper and lower limits of the standard magnetic field span nine orders of magnitude. Currently, the reproduction of a standard magnetic field within the range of 100μT within a magnetically shielded device is achieved by using an AC or DC constant current source to power a torqueless coil (the current value is multiplied by a fixed coil constant to obtain the reproduced standard magnetic field value). However, the output current range of the constant current source generally covers a maximum of six orders of magnitude, with typical output ranges of 10μA to 2A and 1μA to 1A. Therefore, to achieve the reproduction of a wide-range standard magnetic field spanning nine orders of magnitude, it is generally necessary to use multiple constant current power supplies with different output current ranges and multiple sets of torqueless coils with different coil constants.

[0004] Furthermore, since the upper limit of the measurement range of the SERF magnetometer is only 10 nT, taking a Helmholtz coil with a relatively small coil constant as an example, the constant of a single-turn Helmholtz coil with a coil diameter of 400 mm is approximately 4.5 μT / A. To reproduce a standard magnetic field in the range of 0.1 pT to 100 μT, the output current range of the constant current source is approximately 22 pA to 2.2 mA. Currently, there are no constant current sources on the market that can output such a small range and a tiny current, and the measurement accuracy and stability of such a weak current in this range cannot meet the requirements for high-precision magnetic field reproduction.

[0005] The calibration apparatus used for calibrating the aforementioned magnetometers generally consists of a magnetic shielding device, a torque-free coil, and a constant current source, each of which is quite expensive. For metrology institutions specializing in magnetic metrology services, or units that develop the aforementioned various magnetometers, equipping themselves with multiple constant current sources and multiple torque-free coils not only significantly increases costs, but also makes it extremely inconvenient to frequently remove and place the torque-free coils from the magnetic shielding device due to their large size and weight. Summary of the Invention

[0006] In view of this, the present invention provides a device for reproducing a magnetic field from nanoter to microter level within a magnetic shielding device, which can achieve magnetic field multiplication or cancellation by adjusting the connection relationship of the torque-free coils, thereby achieving a wide range of magnetic field variations.

[0007] A device for reproducing nano- to micro-level magnetic fields within a magnetic shielding device includes two sets of torque-free coils, each set consisting of an inner non-metallic hollow tube and an outer metallic hollow tube, coaxially placed within a coil frame; it also includes an inner winding and an outer winding of the torque-free coil. The inner winding of the torque-free coil is wound along a helical groove on the inner non-metallic hollow tube, and the diameter of the inner helical tube is D1; ​​the outer winding of the torque-free coil is wound along a helical groove on the outer non-metallic hollow tube, and the diameter of the outer helical tube is D2; the diameter D1 of the inner helical tube is not equal to the diameter D2 of the outer helical tube; and The relationship between the number of turns and diameter of the inner and outer windings is as follows: Where L1 and L2 are the winding lengths of the inner and outer solenoids, respectively; N1 and N2 are the number of turns of the inner and outer solenoid windings, respectively; the current output terminal of the inner winding of the torque-free coil is connected to the output terminal of the outer winding of the torque-free coil; the inner windings and outer windings of the two sets of torque-free coils are the same size;

[0008] Depending on the magnitude of the magnetic field to be reproduced, the magnetic field can be multiplied by connecting two sets of torque-free coils in the forward direction to achieve a micro-level magnetic field; or the magnetic field can be canceled by connecting two sets of torque-free coils in the reverse direction to achieve a nano-level magnetic field.

[0009] Preferably, the forward series connection is as follows: the input terminal of one set of torque-free coils is connected to the output terminal of another set of torque-free coils, and the output terminal of one set of torque-free coils and the input terminal of the other set of torque-free coils are respectively connected to a power supply; the reverse series connection is as follows: the input terminal of one set of torque-free coils is connected to the input terminal of another set of torque-free coils, and the output terminal of one set of torque-free coils and the output terminal of the other set of torque-free coils are respectively connected to a power supply.

[0010] Preferably, the same inner winding size and the same outer winding size of the two sets of torque-free coils mean that the wire diameter, winding length and number of turns of the inner windings of the two sets of torque-free coils are the same; the wire diameter, winding length and number of turns of the outer windings of the two sets of torque-free coils are the same.

[0011] Preferably, continuous spiral grooves are machined on the outer walls of the inner non-metallic hollow tube and the outer metallic hollow tube, respectively. The distance between two adjacent spiral grooves is equal. The width of the spiral groove itself can just wrap around the enameled wire. The groove depth is twice the diameter of the enameled wire, which can vertically and closely arrange two turns of enameled wire windings.

[0012] Preferably, when two sets of torque-free coils are connected in reverse series, the coil constant at the center of the coil is...

[0013]

[0014] When two sets of torque-free coils are connected in positive direction, the coil constant at the center of the coils is...

[0015]

[0016] Where d1 is the center-to-center distance between the enameled wires of the two inner coils, d2 is the center-to-center distance between the enameled wires of the two outer coils, and μ0 is the permeability of free space.

[0017] Beneficial effects

[0018] 1. This invention employs two sets of torque-free coil windings. By precisely calculating the relative dimensional relationship between the two sets of torque-free coil windings to reproduce the required weak magnetic field, when the two sets of torque-free coils are connected in reverse series, most of the central region can be canceled out, reducing the central coil constant to the order of nT / A. A large current in the ampere range can generate a weak magnetic field in the nT range, and a current in the microampere range can generate an extremely weak magnetic field in the femtometer range. Furthermore, when the two sets of torque-free coils are connected in forward series, the reproduced standard magnetic field value can be doubled under the same current. An ampere-level current can generate a maximum magnetic field of 100μT. Therefore, through forward and reverse series connection, a wide range of magnetic field reproduction from nT to μT can be achieved.

[0019] 2. By setting up two non-metallic hollow tubes with different diameters, the magnetic field generated by the two hollow tubes can be deviated, thereby enabling the reproduction of the magnetic field.

[0020] 3. By making the dimensions of corresponding windings of the two sets of torque-free coils as close as possible, magnetic field cancellation can be achieved. This reduces the center coil constant to the order of nT / A, allowing a large current in the ampere range to generate a weak magnetic field in the nT range.

[0021] 4. By designing the wire groove, the inner windings of the two sets of torque-free coils and the outer windings of the two sets of torque-free coils can be tightly attached to each other, thereby minimizing the diameter deviation of the solenoid, i.e. d1 and d2. In this way, the magnetic cancellation error will be smaller and the effect will be better. Attached Figure Description

[0022] Figure 1 This is a parameter diagram of the torque-free coil according to an embodiment of the present invention;

[0023] Figure 2 Cross-sectional views of two sets of torque-free coils Detailed Implementation

[0024] The implementation of the method of the present invention will be described below with reference to the accompanying drawings and embodiments.

[0025] This invention provides a device for reproducing nano- to micro-level magnetic fields within a magnetic shielding device. The main idea is as follows: Figure 1 As shown, two sets of torque-free coil windings are designed within a single coil frame. To accurately calculate the relative dimensional relationship between the two sets of torque-free coil windings, based on the required reproduction of a weak magnetic field, the majority of the central region's magnetic field is canceled out when the two sets of torque-free coils are connected in reverse series. This reduces the central coil constant to the order of nT / A, allowing a large current in the ampere range to generate a weak magnetic field in the nT range, and a current in the microampere range to generate an extremely weak magnetic field in the femtoampere range. When the two sets of torque-free coils are connected in forward series, the same current can double the value of the reproduced standard magnetic field, with a current in the ampere range generating a maximum magnetic field of 100μT. The specific structure of this device is as follows:

[0026] The device of the present invention is provided with two sets of torque-free coils. Each set of torque-free coils is composed of two coaxially symmetrically combined equidistant helical windings of different diameters. Specifically, two non-metallic hollow tubes of different diameters are provided, namely an inner non-metallic hollow tube and an outer metallic hollow tube, which are coaxially placed in a set of coil frames. Continuous helical grooves are processed on the outer walls of the two hollow tubes. The distance between two adjacent helical grooves is equal. The width of the helical groove itself can just wrap around the enameled wire. The groove depth is twice the diameter of the enameled wire, which can vertically and closely arrange two turns of enameled wire windings.

[0027] Specifically, such as Figure 2 As shown, the structure of the first set of torque-free coils is as follows: it consists of an inner winding and an outer winding of a #1 torque-free coil; the inner winding of the #1 torque-free coil is wound along a helical groove on an inner non-metallic hollow tube, the diameter of which is D1; ​​the outer winding of the #1 torque-free coil is wound along a helical groove on an outer non-metallic hollow tube, the diameter of which is D2; the current output terminal of the inner winding of the #1 torque-free coil is connected to the output terminal of the outer winding of the #1 torque-free coil, and their input terminals need to be connected to one end of the second set of torque-free coils and to the power supply.

[0028]

[0029] The number of turns and diameter of the inner and outer windings have the following relationship:

[0030]

[0031] In the formula:

[0032] D1, D2 — Diameters of the inner and outer solenoids;

[0033] L1, L2 — the winding lengths of the inner and outer solenoids;

[0034] N1, N2 — Number of turns in the inner and outer solenoid windings.

[0035] The second set of torque-free coils has the following structure: it consists of an inner winding and an outer winding of a #2 torque-free coil. The inner winding of the #2 coil is wound along the helical groove on the inner non-metallic hollow tube, tightly wrapped around the inner winding of the #1 torque-free coil. The diameter of the inner helical tube is d1+D1. After winding, the two inner windings completely fill the helical groove of the inner non-metallic hollow tube. The outer winding of the #2 coil is wound along the helical groove on the outer non-metallic hollow tube, tightly wrapped around the outer winding of the #1 torque-free coil. The diameter of the outer helical tube is d2+D2. After winding, the two outer windings completely fill the helical groove of the outer non-metallic hollow tube. The current output terminal of the inner winding of the #2 torque-free coil is connected to the output terminal of the outer winding of the #2 torque-free coil. To achieve a wide range of magnetic field variations, the two sets of torque-free coils need to be connected in series in either the forward or reverse direction to achieve magnetic field multiplication or magnetic field cancellation. That is: when connected in forward series, the input terminal of the first set of torque-free coils needs to be connected to the output terminal of the second set of torque-free coils, and the output terminal of the first set of torque-free coils and the input terminal of the second set of torque-free coils are respectively connected to the power supply; or the output terminal of the first set of torque-free coils needs to be connected to the input terminal of the second set of torque-free coils, and the input terminal of the first set of torque-free coils and the output terminal of the second set of torque-free coils are respectively connected to the power supply, and the device is placed inside a magnetic shielding device; when connected in reverse series, the input terminal of the first set of torque-free coils needs to be connected to the input terminal of the second set of torque-free coils, and the output terminal of the first set of torque-free coils and the output terminal of the second set of torque-free coils are respectively connected to the power supply; or the output terminal of the first set of torque-free coils needs to be connected to the output terminal of the second set of torque-free coils, and the input terminal of the first set of torque-free coils and the input terminal of the second set of torque-free coils are respectively connected to the power supply, and the device is placed inside a magnetic shielding device;

[0036] In order to ensure that the magnetic fields at the center of the two sets of torque-free coils largely cancel each other out when they are connected in reverse series, the dimensions of the corresponding windings of the two sets of torque-free coils should be as close as possible. That is, the dimensions of the two internal helices should be as close as possible, and the dimensions of the two external helices should be as close as possible. Therefore, the wire diameter, winding length, and number of turns of the inner winding of the #2 torque-free coil of the second set of torque-free coils are the same as the dimensions of the inner winding of the #1 torque-free coil of the first set of torque-free coils. The wire diameter, winding length, and number of turns of the outer winding of the #2 torque-free coil of the second set of torque-free coils are the same as the dimensions of the outer winding of the #1 torque-free coil of the first set of torque-free coils.

[0037] Based on the above structure, the formula for the coil constant at the center point of the first set of torque-free coils is as follows:

[0038]

[0039] μ0 — Vacuum permeability;

[0040] The second set of torque-free coils differs from the first set only in that D1 and D2 are increased by d1 and d2 respectively. Therefore, the formula for the coil constant at the center point of the second set of torque-free coils is as follows:

[0041]

[0042] Based on the coil constants at the center points of the two sets of torque-free coils, it can be known that when the first and second sets of torque-free coils are connected in reverse series, the magnetic fields generated by the two sets of coils largely cancel each other out. At this time, the coil constant K at the center of the coils is... b =K b1 -K b2 The calculation formula is as follows:

[0043]

[0044] In the formula:

[0045] d1 — Center-to-center distance between the enameled wires of the two inner coils;

[0046] d2 — the center-to-center distance between the enameled wires of the two outer coils.

[0047] Furthermore, when two sets of torque-free coils are connected in positive direction, the superposition of the magnetic fields generated by the two sets of coils can multiply the magnitude of the reproduced magnetic field. At this time, the coil constant K at the center of the coil... b =K b1 +K b2 The calculation formula is as follows:

[0048] Specific implementation examples:

[0050] A magnetic shielding cylinder has an inner diameter of 450mm and an internal length of 1800mm. Based on the above steps, the first set of torque-free coil windings is designed with D1 = 400mm, L1 = 1600mm, N1 = 400 turns, D2 = 180mm, L2 = 1609mm, N2 = 494 turns, and a coil constant K. b1 =25.491μT / A. With the selected enameled wire having a nominal diameter of 0.5mm, the second set of torque-free coil windings has the following parameters: D1 = 401mm, L1 = 1600mm, N1 = 400 turns, D2 = 181mm, L2 = 1609mm, N2 = 494 turns, and the coil constant K... b2 =25.486μT / A.

[0051] At this point, if the two sets of torque-free coils are reversed in series, the coil constant K of the combined coil will be... b =K b1 -K b2=5nT / A, a 2A current can generate a magnetic field of 10nT, and a 10μA current corresponds to a magnetic field of 0.05pT. Therefore, equipping the coil with a constant current source with an output current of 10μA to 2A can cover the measurement range of the SERF magnetometer.

[0052] Using the coil constant K alone b1 When this set of torqueless coils has a current of 25.491μT / A, the constant current source outputs a current in the range of 0.4mA to 2A, which can generate a magnetic field in the range of 10nT to 50μT.

[0053] If two sets of torque-free coils are connected in positive series, then the coil constant K of the combined coil is... b =K b1 +K b2 =50.978μT / A. A constant current source outputting a current in the range of 1mA to 2A can generate a magnetic field in the range of 50nT to 100μT.

[0054] When used in combination with the above three methods, the constant current source can output a current range of 10μA to 2A. When used with a coil, it can generate a magnetic field range of 0.05pT to 100μT. When used in a magnetic shielding device, it can meet the calibration requirements of almost all magnetometers with a measurement range of no more than 100μT.

[0055] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A device for reproducing a wide range of magnetic fields within a magnetic shielding device, characterized in that: It includes two sets of torque-free coils, each set consisting of an inner non-metallic hollow tube and an outer metallic hollow tube, coaxially placed within a coil frame; it also includes an inner winding and an outer winding of the torque-free coil, the inner winding of which is wound along a helical groove on the inner non-metallic hollow tube, the diameter of which is [missing information]. D 1; The outer winding of the torque-free coil is wound along the helical groove on the outer non-metallic hollow tube, and the direct end of the outer solenoid is... D 2; The current output terminal of the inner winding of the torque-free coil is connected to the output terminal of the outer winding of the torque-free coil; Two sets of torque-free coils are connected in series in either forward or reverse directions to achieve magnetic field multiplication or cancellation, depending on the magnitude of the magnetic field to be reproduced. Specifically: when connected in forward direction, the input terminal of one set of torque-free coils needs to be connected to the output terminal of the other set of torque-free coils, and the output terminal of one set of torque-free coils and the input terminal of the other set of torque-free coils are respectively connected to a power supply; when connected in reverse direction, the input terminal of one set of torque-free coils needs to be connected to the input terminal of the other set of torque-free coils, and the output terminal of one set of torque-free coils and the output terminal of the other set of torque-free coils are respectively connected to a power supply.

2. The apparatus as described in claim 1, characterized in that: The diameter of the internal solenoid D 1 is not equal to the diameter of the external solenoid. D 2; and ; The relationship between the number of turns and diameter of the inner and outer windings is as follows: ,in L 1 、L 2 represents the winding lengths of the inner and outer solenoids, respectively; N 1 、N 2 represents the number of turns in the inner and outer solenoid windings, respectively.

3. The apparatus as described in claim 1, characterized in that: The inner windings of the two sets of torque-free coils have the same wire diameter, winding length, and number of turns; the outer windings of the two sets of torque-free coils also have the same wire diameter, winding length, and number of turns.

4. The apparatus as claimed in claim 1, characterized in that: Continuous spiral grooves are machined on the outer walls of the inner non-metallic hollow tube and the outer metallic hollow tube, respectively. The distance between two adjacent spiral grooves is equal. The width of the spiral groove itself can just wrap around the enameled wire. The groove depth is twice the diameter of the enameled wire, and two turns of enameled wire can be arranged vertically and closely.

5. The apparatus as claimed in claim 1, characterized in that: When two sets of torque-free coils are connected in reverse series, the coil constant at the center of the coils is... When two sets of torque-free coils are connected in positive direction, the coil constant at the center of the coil is... ,in, d 1 represents the center-to-center distance between the enameled wires of the two inner coils. d 2 represents the center-to-center distance between the two sets of outer coil enameled wires; L 1 、L 2 represents the winding lengths of the inner and outer solenoids, respectively; N 1 、N 2 represents the number of turns in the inner and outer solenoid windings, respectively, and μ0 represents the permeability of free space.

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