A magnetic field noise calibration device and method for an optically pumped magnetometer

Abstract

The present invention provides a magnetic field noise calibration device and method for an optically pumped magnetometer. A moment-free coil A, a moment-free coil B, and an interference magnetic field compensation coil are connected in series, ensuring that the circuit sizes passed by the three coils are always equal during operation. This ensures that the coil constants at the three locations where a standard optically pumped magnetometer, a calibrated optically pumped magnetometer, and a proton magnetometer are equal, the currents passing through them are also equal, and the reproduced offset magnetic fields are also equal. This allows compensation for coil constant differences between the center points of the moment-free coil A, the center points of the moment-free coil B, and the center points of the magnetic field coils. This prevents mutual influence between the standard optically pumped magnetometer and the calibrated optically pumped magnetometer due to their close distance, while eliminating coil constant differences caused by the optical pumping probe exceeding a uniform range. Ultimately, the calibrated optically pumped magnetometer, the standard optically pumped magnetometer, and the proton magnetometer at the center point synchronously achieve interference magnetic field compensation, achieving the same effect after compensation, thereby achieving accurate calibration of the calibrated optically pumped magnetometer.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetometry, and in particular relates to a device and method for calibrating magnetic field noise of an optically pumped magnetometer. Background Art

[0002] A magnetic field noise calibration device for an optically pumped magnetometer is primarily used to calibrate the magnetic field noise parameters of an optically pumped magnetometer. Three methods are currently commonly used to calibrate the magnetic field noise of an optically pumped magnetometer. One is the differential method, which involves placing two identical optically pumped magnetometers to be calibrated in a field with a relatively stable geomagnetic field. The changes in the geomagnetic field are simultaneously measured, and the differential principle is used to eliminate the geomagnetic field noise to obtain the noise of the optically pumped magnetometer being measured. This method can produce a noise of the calibrated optically pumped magnetometer that is one order of magnitude lower than the geomagnetic field noise. Another is the self-compensation method, which uses the calibrated optically pumped magnetometer as a sensor to track and compensate for changes in the ambient magnetic field. The compensated and stabilized magnetic field noise is then obtained, and this noise is considered to be the noise of the calibrated optically pumped magnetometer. Still another is the mutual compensation method, which involves first using a standard optically pumped magnetometer as a sensor to track and compensate for changes in the ambient magnetic field to obtain a stabilized magnetic field after compensating for the ambient magnetic field noise. The stabilized magnetic field is then directly measured with the calibrated optically pumped magnetometer, and the resulting magnetic field noise is considered to be the noise of the calibrated optically pumped magnetometer.

[0003] The first differential method requires a stable geomagnetic field environment, typically in a remote, desolate area free of human activity. The test time is typically evening or midnight, when the geomagnetic field is most stable. This method has drawbacks such as difficulty selecting a test site, a harsh test environment, and susceptibility to external interference.

[0004] The second self-compensation method, on the one hand, is susceptible to circuit noise due to mismatching issues between different optically pumped magnetometers and the compensation circuit, resulting in excessively high magnetic field noise. On the other hand, because the direct parameter obtained by the compensation circuit is the output frequency of the optically pumped magnetometer, not the magnetic field, this can mask changes in the conversion coefficient between frequency and magnetic field during the measurement process, resulting in insufficiently low magnetic field noise.

[0005] Therefore, the third method is currently the most commonly used. The currently established constant weak magnetic field standard device also has certain drawbacks. First, if the probes of the standard optically pumped magnetometer and the probes of the calibrated optically pumped magnetometer are both within the uniformity range of the standard device, the distance between the two probes is small, which can cause the two probes to interfere with each other. Second, if the distance between the probes of the standard optically pumped magnetometer and the probes of the calibrated optically pumped magnetometer exceeds the uniformity range of the standard device, the inconsistency in the coil constants between the two points will lead to inconsistency in the actual compensated magnetic field between the two points. As a result, the difference in compensation effect is introduced into the calibrated optically pumped magnetometer as magnetic field noise. Assuming the external interference magnetic field is 10nT (although the maximum can exceed 100nT), and the difference in the coil constants between the two points is 0.1% (the actual maximum difference can exceed 1%), the difference in compensation effect is 10nT × 0.1% = 10pT. This value exceeds the current compensated magnetic field noise of no more than 2pT and also exceeds the magnetic field noise of 3pT to 5pT of typical optically pumped magnetometers. Summary of the Invention

[0006] To address the issue of differences in magnetic field compensation effects between the probe positions of a standard optically pumped magnetometer and a calibrated optically pumped magnetometer, the present invention provides a magnetic field noise calibration device and method for an optically pumped magnetometer. These methods can avoid the mutual influence between the standard optically pumped magnetometer and the calibrated optically pumped magnetometer due to their close proximity, while eliminating the difference in coil constants caused by the optically pumped probe exceeding the uniformity range, thereby achieving accurate calibration of the calibrated optically pumped magnetometer.

[0007] A magnetic field noise calibration device for an optically pumped magnetometer comprises a moment-free coil A, a moment-free coil B, a proton magnetometer, a standard optically pumped magnetometer, and a standard magnetic field reproduction coil and an interference magnetic field compensation coil having a common frame; wherein the moment-free coil A, the moment-free coil B and the interference magnetic field compensation coil are connected in series to form a combined compensation coil;

[0008] The standard magnetic field reproduction coil is used to compensate for the fixed component of the Earth's magnetic field and to reproduce a standard magnetic field of any intensity within a set range. The proton magnetometer is placed at the center of the standard magnetic field reproduction coil to measure the reproduced standard magnetic field and obtain an accurate value of the standard magnetic field. The moment-free coil A and the moment-free coil B are placed on either side of the center point of the standard magnetic field reproduction coil, and are equidistant from the center point. The standard optically pumped magnetometer and the calibrated optically pumped magnetometer are placed at the center of the moment-free coil A and the moment-free coil B, respectively. The standard optically pumped magnetometer is used to track and measure the interfering magnetic field. The combined compensation coil is used to reproduce a canceling magnetic field that is equal in magnitude and opposite in direction to the interfering magnetic field. The indication of the calibrated optically pumped magnetometer is used to obtain the peak-to-peak value or magnetic field noise power spectral density of the calibrated optically pumped magnetometer, and is also used to compare with the indication of the proton magnetometer to obtain the indication error of the calibrated optically pumped magnetometer.

[0009] Furthermore, the coil constant K of the moment-free coil A isB,1 , coil constant K of moment-free coil B B,2 They are:

[0010] K B,1 =K B,0 -K B,A

[0011] K B,2 =K B,0 -K B,B

[0012] Among them, K B,0 Indicates the coil constant of the interference magnetic field compensation coil at the center point, K B,A K represents the coil constant of the interference magnetic field compensation coil at the center of the moment-free coil A. B,B It represents the coil constant of the interference magnetic field compensation coil at the center of the moment-free coil B.

[0013] Furthermore, the standard magnetic field reproduction coil is used to reproduce a standard magnetic field of any intensity within the range of 20 μT to 100 μT.

[0014] Furthermore, the magnetic axes of the moment-free coil A and the moment-free coil B are both parallel to the interference magnetic field compensation coil.

[0015] A calibration method for a magnetic field noise calibration device comprises the following steps:

[0016] Build a magnetic field noise calibration device, specifically: place the standard magnetic field reproduction coil and the interference magnetic field compensation coil on the same frame; at the same time, connect the moment-free coil A and moment-free coil B in series with the interference magnetic field compensation coil to form a combined compensation coil;

[0017] A standard magnetic field reproduction coil is used to compensate for the fixed component of the Earth's magnetic field and reproduce a standard magnetic field of any strength within a set range. At the same time, a proton magnetometer is placed at the center of the standard magnetic field reproduction coil to measure the reproduced standard magnetic field and obtain the accurate value of the standard magnetic field.

[0018] The moment-free coil A and moment-free coil B are placed on either side of the center point of the standard magnetic field reproduction coil, and are equidistant from the center point. The standard optically pumped magnetometer and the calibrated optically pumped magnetometer are placed at the center of the moment-free coil A and moment-free coil B, respectively. The standard optically pumped magnetometer is then used to track and measure the interfering magnetic field, and a combined compensation coil is used to reproduce a canceling magnetic field that is equal in magnitude and opposite in direction to the interfering magnetic field.

[0019] A set of continuous readings of the calibrated optically pumped magnetometer is recorded, and the peak-to-peak value or power spectral density of the magnetic field noise of the calibrated optically pumped magnetometer is obtained according to the readings. At the same time, the reading error of the calibrated optically pumped magnetometer is obtained by comparing the readings of the calibrated optically pumped magnetometer with those of the proton magnetometer.

[0020] Furthermore, the time length and time interval for recording the indication of the calibrated pump magnetometer are determined according to actual needs.

[0021] Beneficial effects:

[0022] 1. The present invention provides a magnetic field noise calibration device for an optically pumped magnetometer. A moment-free coil A, a moment-free coil B, and an interference magnetic field compensation coil are connected in series to ensure that the currents passing through the three coils are equal during operation. When the coil constants at the three locations where the standard optically pumped magnetometer, the calibrated optically pumped magnetometer, and the proton magnetometer are located are equal and the currents passing through them are also equal, the resulting offset magnetic fields are also equal. By compensating for the differences in coil constants between the center points of moment-free coil A, moment-free coil B, and the magnetic field coil, the device can avoid mutual influence between the standard optically pumped magnetometer and the calibrated optically pumped magnetometer due to their close proximity, while eliminating the coil constant differences caused by the optical pumping probe exceeding the uniformity range. Ultimately, the calibrated optically pumped magnetometer, the standard optically pumped magnetometer, and the proton magnetometer at the center simultaneously achieve interference magnetic field compensation, achieving the same effect after compensation, thereby achieving accurate calibration of the calibrated optically pumped magnetometer.

[0023] 2. The present invention provides a magnetic field noise calibration device for an optically pumped magnetometer. When a moment-free coil is used to reproduce the magnetic field inside a standard magnetic field reproduction coil, the external magnetic field radiated outward can decay as the seventh power of the distance, while the external magnetic field radiated outward by a traditional coil can only decay as the third power of the distance; therefore, at the same distance, the influence of the moment-free coil of the present invention on the proton magnetometer at the center of the calibration device will be greatly reduced.

[0024] 3. The present invention provides a magnetic field noise calibration method for an optically pumped magnetometer. The standard magnetic field reproduction coil can reproduce a standard magnetic field of any intensity within the range of 20μT to 100μT, and has a wide range of applications.

[0025] 4. The present invention provides a magnetic field noise calibration method for an optically pumped magnetometer. The moment-free coil A, moment-free coil B, and interference magnetic field compensation coil are connected in series, which can ensure that the circuit sizes passed by the three are always equal during operation, so that the coil constants at the three positions where the standard optically pumped magnetometer, the calibrated optically pumped magnetometer, and the proton magnetometer are equal, the currents passing through are also equal, and the reproduced offset magnetic fields are also equal. Therefore, the coil constant differences of the interference magnetic field compensation coil between the center point of the moment-free coil A and the center point of the moment-free coil B and the center point of the magnetic field coil can be compensated. This can avoid the mutual influence between the standard optically pumped magnetometer and the calibrated optically pumped magnetometer due to their close distance, and eliminate the coil constant differences caused by the optical pumping probe exceeding the uniform area. Finally, the calibrated optically pumped magnetometer, the standard optically pumped magnetometer, and the proton magnetometer at the center point synchronously realize interference magnetic field compensation, and the effects after compensation are the same, thereby realizing accurate calibration of the calibrated optically pumped magnetometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a structural schematic diagram of a magnetic field noise calibration device for an optically pumped magnetometer provided by the present invention. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0028] like Figure 1 As shown, a magnetic field noise calibration device for an optically pumped magnetometer includes a moment-free coil A, a moment-free coil B, a proton magnetometer, a standard optically pumped magnetometer, and a standard magnetic field reproduction coil and an interference magnetic field compensation coil with a common frame. The moment-free coil A and the moment-free coil B are connected in series with the interference magnetic field compensation coil to form a combined compensation coil, and their magnetic axes are parallel to the interference magnetic field compensation coil.

[0029] The standard magnetic field reproduction coil is used to compensate for the fixed component of the Earth's magnetic field and to reproduce a standard magnetic field of any strength in the range of 20μT to 100μT; the proton magnetometer is placed at the center of the standard magnetic field reproduction coil (equivalent to the center of the interference magnetic field compensation coil) to measure the reproduced standard magnetic field and obtain the accurate value of the standard magnetic field; it should be noted that the accurate value of the standard magnetic field can be used as a magnetic field calibration point for calibrating the magnetic field noise of the calibrated optical pump magnetometer, and can also be used as a standard magnetic field for calibrating the magnetic field indication error of the calibrated optical pump magnetometer.

[0030] The moment-free coil A and moment-free coil B are placed on both sides of the center point of the standard magnetic field reproduction coil, and the distance from the center point is equal, that is, L1=L2. It should be noted that the two sets of moment-free coils are used to compensate for the difference in coil constants between point A and point B (for the standard optically pumped magnetometer and the calibrated optically pumped magnetometer, respectively) and the center point of the proton magnetometer. Assume that the coil constant of the interference magnetic field compensation coil at the center point is K B,0 The coil constants at the center of the moment-free coil A and moment-free coil B are K B,A and K B,B , then the coil constants of the moment-free coil A and moment-free coil B are K B,0 -K B,A and K B,0 -K B,B .

[0031] The standard optical pumping magnetometer and the calibrated optical pumping magnetometer are placed at the center of the moment-free coil A and moment-free coil B respectively. The standard optical pumping magnetometer is used to track and measure the interfering magnetic field. Figure 1The optical pumping probes A and B correspond to the standard optical pumping magnetometer and the calibrated optical pumping magnetometer, respectively. The combined compensation coil is used to reproduce a canceling magnetic field that is equal in magnitude and opposite in direction to the interfering magnetic field. At this time, a stable standard magnetic field is formed at the center of the standard magnetic field reproduction coil, the center of the moment-free coil A, and the center of the moment-free coil B.

[0032] The indication of the calibrated optically pumped magnetometer is used to obtain the peak-to-peak value of the magnetic field noise or the power spectral density of the magnetic field noise of the calibrated optically pumped magnetometer. This is also used to compare the indication with the proton magnetometer to obtain the indication error of the calibrated optically pumped magnetometer. Calculating the peak-to-peak value of the magnetic field noise or the power spectral density of the magnetic field noise of the calibrated optically pumped magnetometer from the indication is a common technique in the art and will not be described in detail in this disclosure.

[0033] It should be noted that any magnetic field coil has a certain degree of magnetic field non-uniformity, that is, after power is applied, the magnitude of the reproduced magnetic field at different positions of the coil is different (caused by the difference in coil constants at different positions of the magnetic field coil). According to the traditional practice (i.e., there is no moment-free coil), in order to make the difference in coil constants at the three points where the standard optical pumping magnetometer is located, the position where the calibrated optical pumping magnetometer is located, and the center point of the magnetic field coil as small as possible, the distance between the three points should be as small as possible. However, the reduction in the distance between the three points will cause the standard optical pumping magnetometer, the calibrated optical pumping magnetometer, and the proton magnetometer to affect each other. After the present invention uses a moment-free coil, the positions of the standard optical pumping magnetometer, the calibrated optical pumping magnetometer, and the proton magnetometer can be appropriately increased to a distance where the three do not affect each other, as follows:

[0034] Assume that the coil constant differences between the center points of moment-free coil A (the location of the standard optically pumped magnetometer), moment-free coil B (the location of the calibrated optically pumped magnetometer), and the magnetic field coil (the location of the proton magnetometer) are 0.1% and -0.1%, respectively. Assume that the external interfering magnetic field is 100 nT. In the absence of moment-free coils A and B, the canceling magnetic fields reproduced by the interfering magnetic field compensation coil at these three locations are 100.0 nT, 100.1 nT, and 99.9 nT, respectively. At this point, after the interfering magnetic field is canceled out, the remaining interfering magnetic fields are 0nT, 0.1nT, and -0.1nT. That is, a stable standard magnetic field has been achieved at the center of moment-free coil A (where the standard optically pumped magnetometer is located). However, interfering magnetic fields of 0.1nT and -0.1nT still exist at the center of moment-free coil B (where the calibrated optically pumped magnetometer is located) and the center of the magnetic field coil (where the proton magnetometer is located), respectively. Since the magnetic field noise of the optically pumped magnetometer can be less than 0.005nT, the remaining interfering magnetic field will make magnetic field noise calibration impossible.

[0035] Based on this, the present invention sets the moment-free coil A, the moment-free coil B and the interference magnetic field compensation coil in series to ensure that the size of the circuit passed by the three is equal during operation. The magnetic field = coil constant × current. After the moment-free coil A, the moment-free coil B and the interference magnetic field compensation coil are connected in series, the coil constants at the three positions where the standard optical pumping magnetometer, the calibrated optical pumping magnetometer and the proton magnetometer are located are equal, and the currents passing through are also equal, so the reproduced offset magnetic fields are also equal. In this way, the coil constant differences of the interference magnetic field compensation coil between the center point of the moment-free coil A (the location of the standard optical pumping magnetometer) and the center point of the moment-free coil B (the location of the calibrated optical pumping magnetometer) and the center point of the magnetic field coil (the location of the proton magnetometer) are compensated, so that the coil constants of the three points are equal, and then the offset magnetic fields reproduced by the interference magnetic field coil are equal, and a stable standard magnetic field is achieved at the same time.

[0036] It can be seen that the present invention can avoid the mutual influence between the standard optical pumping magnetometer and the calibrated optical pumping magnetometer due to their close distance, while eliminating the difference in coil constants caused by the optical pumping probe exceeding the uniform area. Ultimately, the calibrated optical pumping magnetometer, the standard optical pumping magnetometer and the center point (proton magnetometer) can synchronously compensate for the interfering magnetic field, and the effects after compensation are the same.

[0037] Furthermore, the present invention also provides a calibration method for a magnetic field noise calibration device, comprising the following steps:

[0038] Step 1: Build a magnetic field noise calibration device. Specifically, place the standard magnetic field reproduction coil and the interference magnetic field compensation coil on the same frame. At the same time, connect the moment-free coil A and moment-free coil B in series with the interference magnetic field compensation coil to form a combined compensation coil.

[0039] It should be noted that the present invention adopts the moment-free coil A and moment-free coil B for the following reasons:

[0040] Regardless of the coil structure used, coils A and B will radiate a certain magnetic field to the outside while reproducing the magnetic field inside the standard magnetic field reproduction coil. The magnetic field reproduced by coils A and B when working will have an adverse effect on the proton magnetometer at the center of the calibration device, and there is also the problem of mutual influence between coils A and B. However, if a traditional coil is used, the magnetic field radiated to the outside will decay as the cube of the distance, while if a moment-free coil structure is used, the magnetic field radiated to the outside can decay as the seventh power of the distance. It can be seen that at the same distance, the influence of the moment-free coil used in the present invention on the proton magnetometer at the center of the calibration device will be greatly reduced.

[0041] For example, assume that the coil constant of Coil A is 0.1% of the coil constant at the center of the interference magnetic field compensation coil (this value may actually exceed 1%), and the external interference magnetic field is 100 nT (the actual interference magnetic field is typically between 10 nT and 1000 nT, with a maximum value potentially exceeding 3000 nT to 5000 nT). Coil A then needs to reproduce a magnetic field of 100 nT x 1% = 1 nT. Assume that Coil A has an outer diameter of 400 mm (the probe length of an optically pumped magnetometer is typically between 120 mm and 180 mm, requiring an inner dimension of approximately 300 mm for Coil A) and an outer radius of 200 mm. Assume that the center of Coil A is 400 mm from the center of the interference magnetic field compensation coil and 800 mm from the center of Coil B.

[0042] If a normal coil is used, the effect of coil A on the proton magnetometer (center of the interference magnetic field compensation coil) is 1nT×(200 / 400) 3 =125pT, the effect on the calibrated optically pumped magnetometer (center of coil B) is 1nT×(200 / 800) 3 = 0.016nT = 16pT. The peak-to-peak noise of the proton magnetometer's magnetic field generally does not exceed 10pT, and the peak-to-peak noise of the calibrated optically pumped magnetometer generally does not exceed 2pT to 5pT. In other words, the influence caused by Coil A exceeds the inherent performance of both the proton magnetometer and the calibrated optically pumped magnetometer.

[0043] If a moment-free coil is used, the effect of coil A on the proton magnetometer (center of the interference magnetic field compensation coil) is 1nT×(200 / 400) 7 =8pT, ​​the effect on the calibrated optical pump magnetometer (center of coil B) is 1nT×(200 / 800) 7 =0.06pT, and its influence can meet the calibration requirements.

[0044] Step 2: Use a standard magnetic field reproduction coil to compensate for the fixed component of the Earth's magnetic field and reproduce a standard magnetic field of any strength within a set range; at the same time, place a proton magnetometer at the center of the standard magnetic field reproduction coil to measure the reproduced standard magnetic field and obtain the accurate value of the standard magnetic field;

[0045] Step 3: Place moment-free coil A and moment-free coil B on either side of the center point of the standard magnetic field reproduction coil, equidistant from the center point. Place a standard optically pumped magnetometer and a calibrated optically pumped magnetometer at the center of moment-free coil A and moment-free coil B, respectively. Then, use the standard optically pumped magnetometer to track and measure the interfering magnetic field, and use the combined compensation coil to reproduce a canceling magnetic field that is equal in magnitude and opposite in direction to the interfering magnetic field.

[0046] It should be noted that the momentless coil A, momentless coil B and interference magnetic field compensation coil are connected in series, which can ensure that the size of the circuit passed by the three is always equal during operation. Magnetic field = coil constant × current. After the momentless coil A, momentless coil B and interference magnetic field compensation coil are connected in series, the coil constants of the three positions where the standard optical pumping magnetometer, the calibrated optical pumping magnetometer and the proton magnetometer are located are equal, and the currents passing through are also equal, so the reproduced offset magnetic fields are also equal. In other words, the present invention forms a closed loop through the interference magnetic field compensation coil and the momentless coil A and momentless coil B, and the standard optical pumping magnetometer tracks the changes in the interference magnetic field in the measurement environment in real time, and the interference magnetic field compensation coil reproduces a offset magnetic field that is equal in size and opposite in direction to the interference magnetic field, thereby achieving the purpose of eliminating the external interference magnetic field.

[0047] Step 4: Record a set of continuous readings from the calibrated optically pumped magnetometer. Calculate the peak-to-peak value or power spectral density of the magnetic field noise of the calibrated optically pumped magnetometer based on these readings. Compare the readings of the calibrated optically pumped magnetometer with those of the proton magnetometer to determine the reading error of the calibrated optically pumped magnetometer. The length and time interval for recording the readings of the calibrated optically pumped magnetometer are determined based on actual needs.

[0048] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may of course make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A magnetic field noise calibration device for an optically pumped magnetometer, characterized in that: It includes a moment-free coil A, a moment-free coil B, a proton magnetometer, a standard optically pumped magnetometer, and a standard magnetic field reproduction coil and an interference magnetic field compensation coil with a common frame; wherein the moment-free coil A, the moment-free coil B and the interference magnetic field compensation coil are connected in series to form a combined compensation coil; The standard magnetic field reproduction coil is used to compensate for the fixed component of the Earth's magnetic field and to reproduce a standard magnetic field of any intensity within a set range. The proton magnetometer is placed at the center of the standard magnetic field reproduction coil to measure the reproduced standard magnetic field and obtain an accurate value of the standard magnetic field. The moment-free coil A and the moment-free coil B are placed on either side of the center point of the standard magnetic field reproduction coil, and are equidistant from the center point. The standard optically pumped magnetometer and the calibrated optically pumped magnetometer are placed at the center of the moment-free coil A and the moment-free coil B, respectively. The standard optically pumped magnetometer is used to track and measure the interfering magnetic field. The combined compensation coil is used to reproduce a canceling magnetic field that is equal in magnitude and opposite in direction to the interfering magnetic field. The indication of the calibrated optically pumped magnetometer is used to obtain the peak-to-peak value or magnetic field noise power spectral density of the calibrated optically pumped magnetometer, and is also used to compare with the indication of the proton magnetometer to obtain the indication error of the calibrated optically pumped magnetometer.

2. The magnetic field noise calibration device for an optically pumped magnetometer according to claim 1, wherein: Coil constant K of moment-free coil A B,1 , coil constant K of moment-free coil B B,2 They are: K B,1 =K B,0 -K B,A K B,2 =K B,0 -K B,B Among them, K B,0 Indicates the coil constant of the interference magnetic field compensation coil at the center point, K B,A K represents the coil constant of the interference magnetic field compensation coil at the center of the moment-free coil A. B,B It represents the coil constant of the interference magnetic field compensation coil at the center of the moment-free coil B.

3. The magnetic field noise calibration device for an optically pumped magnetometer according to claim 1, wherein: The standard magnetic field reproducing coil is used to reproduce a standard magnetic field of any strength within the range of 20 μT to 100 μT.

4. The magnetic field noise calibration device for an optically pumped magnetometer according to any one of claims 1 to 3, characterized in that: The magnetic axes of the moment-free coil A and the moment-free coil B are both parallel to the interference magnetic field compensation coil.

5. A calibration method for a magnetic field noise calibration device, characterized in that: The following steps are involved: Build a magnetic field noise calibration device, specifically: place the standard magnetic field reproduction coil and the interference magnetic field compensation coil on the same frame; at the same time, connect the moment-free coil A and moment-free coil B in series with the interference magnetic field compensation coil to form a combined compensation coil; A standard magnetic field reproduction coil is used to compensate for the fixed component of the Earth's magnetic field and reproduce a standard magnetic field of any strength within a set range. At the same time, a proton magnetometer is placed at the center of the standard magnetic field reproduction coil to measure the reproduced standard magnetic field and obtain the accurate value of the standard magnetic field. The moment-free coil A and moment-free coil B are placed on either side of the center point of the standard magnetic field reproduction coil, and are equidistant from the center point. The standard optically pumped magnetometer and the calibrated optically pumped magnetometer are placed at the center of the moment-free coil A and moment-free coil B, respectively. The standard optically pumped magnetometer is then used to track and measure the interfering magnetic field, and a combined compensation coil is used to reproduce a canceling magnetic field that is equal in magnitude and opposite in direction to the interfering magnetic field. Record a set of continuous indications of the calibrated optically pumped magnetometer, and obtain the peak-to-peak value or power spectrum density of the magnetic field noise of the calibrated optically pumped magnetometer according to the indications; At the same time, by comparing the indication of the calibrated optical pump magnetometer with the indication of the proton magnetometer, the indication error of the calibrated optical pump magnetometer is obtained.

6. The calibration method of a magnetic field noise calibration device according to claim 5, characterized in that: The time length and time interval for recording the indication of the calibrated pump magnetometer are determined according to actual needs.

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