In-situ calibration method of coil constant and non-orthogonal angle based on electron paramagnetic resonance

Abstract

The present invention discloses an in-situ calibration method of coil constants and non-orthogonal angles based on electron paramagnetic resonance, which belongs to the technical field of atomic magnetometer coil calibration. It uses the magnetic resonance curve of a single-beam optically pumped atomic magnetometer to obtain an external bias magnetic field corresponding to different Larmor precession frequencies, considers the non-orthogonal angles between coil axes, establishes an in-situ measurement model, and realizes the synchronous extraction of coil constants and non-orthogonal angles of three-axis coils. The present invention adopts the above-mentioned in-situ calibration method of coil constants and non-orthogonal angles based on electron paramagnetic resonance, which is suitable for the calibration of miniaturized coils, can be directly measured in a geomagnetic environment, avoids the influence of shielding barrel and coil coupling, and realizes more accurate measurement.

Description

Technical Field

[0001] The invention relates to the technical field of atomic magnetometer coil calibration, in particular to an in-situ calibration method for coil constants and non-orthogonal angles based on electron paramagnetic resonance. Background Art

[0002] With the continuous development of quantum precision measurement technology, the accuracy and performance of atomic sensors such as atomic clocks, atomic magnetometers, and atomic gyroscopes have gradually improved and have been widely used in various fields. In recent years, optically pumped atomic magnetometers have continued to develop and can be used directly under the geomagnetic field without being restricted by magnetic shielding and ultra-low temperature environments. They are a magnetic field sensor with great potential. As an important device for generating magnetic fields, the three-axis magnetic coil can not only be used to apply a bias magnetic field, but also to generate the excitation magnetic field required by the optically pumped atomic magnetometer to enable atoms to achieve a magnetic resonance state. The coil constant and non-orthogonal angle affect the size and direction of the magnetic field, especially for the optically pumped atomic magnetometer based on the magnetic resonance principle, which restricts its sensitivity and other performance and affects the accuracy of magnetic field measurement. Therefore, it is crucial to accurately calibrate the coil constant and non-orthogonal angle of the three-axis magnetic coil. Summary of the invention

[0003] The purpose of the present invention is to provide an in-situ calibration method for coil constants and non-orthogonal angles based on electron paramagnetic resonance, which is suitable for the calibration of miniaturized coils and can be measured directly in a geomagnetic environment, avoiding the influence of the coupling between the shielding barrel and the coil, and achieving more accurate measurement.

[0004] To achieve the above object, the present invention provides an in-situ calibration method for coil constants and non-orthogonal angles based on electron paramagnetic resonance, comprising the following steps:

[0005] S1. Start the single-beam optical pump atomic magnetometer system. The pumping laser and the applied AC excitation magnetic field are both along the z-axis direction. A fixed bias magnetic field B is applied along the z-axis of the coil to be measured. z , a bias magnetic field B is also applied along the y-axis y Under the combined effect of the bias magnetic field and the excitation magnetic field, the spin-polarized alkali metal atoms undergo Larmor precession around the direction of the combined magnetic field, and the Larmor precession frequency of the atoms is determined by scanning the excitation magnetic field frequency;

[0006] S2. By changing the magnitude of the current applied on the y-axis, the magnitude of the bias magnetic field applied by the coil on the y-axis is changed multiple times to obtain multiple different magnitudes of yz-axis external bias magnetic fields. The external magnetic field bias is expressed as the product of the coil constant k and the current I passing through the coil. According to the relationship between the Larmor precession frequency and the external bias magnetic field, the coil constants of the y and z axes and the yz-axis non-orthogonal angle are simultaneously fitted:

[0007]

[0008] Among them, ω yz is the frequency of Larmor precession of atoms around the combined magnetic field of the bias magnetic field applied on the yz axis and the residual magnetism in the shielding barrel or the earth's magnetic field; γ is the gyromagnetic ratio of the alkali metal atom; θ yz is the non-orthogonal angle of the yz axis; k y , k z is the coil constant of y and z axis; I y ,I z is the current passing through coils y and z; B x0 , B y0 , B z0 It is the component of the geomagnetic field or the residual magnetism in the shielding barrel along the three-axis direction of the coil to be tested;

[0009] S3, apply an AC excitation magnetic field along the z-axis and a fixed bias magnetic field B along the z-axis of the coil to be tested z , a bias magnetic field is also applied along the x-axis, and the Larmor precession frequency of the atoms is determined by scanning the excitation magnetic field frequency;

[0010] S4. By changing the magnitude of the current applied on the x-axis, the magnitude of the bias magnetic field applied by the coil on the x-axis is changed multiple times to obtain multiple xz-axis external bias combined magnetic fields of different magnitudes; according to the relationship between the Larmor precession frequency and the external bias combined magnetic field, the coil constants of the x- and z-axes and the xz-axis non-orthogonal angle are simultaneously fitted:

[0011]

[0012] Among them, ω xz θ is the frequency of Larmor precession of atoms around the xz axis due to the combined magnetic field of the bias magnetic field applied to them and the residual magnetism in the shielding barrel or the earth's magnetic field; xz is the non-orthogonal angle of the xz axis; k x , k z is the coil constant of the x and z axes, I x ,I z is the current through coils x and z;

[0013] S5. When measuring directly under the geomagnetic field, apply an AC excitation magnetic field along the z-axis and a fixed bias magnetic field B along the y-axis of the coil to be measured. y , a bias magnetic field is also applied along the x-axis, and the Larmor precession frequency of the atoms is determined by scanning the excitation magnetic field frequency; when measuring in the shielding barrel, a fixed bias magnetic field is also applied along the z-axis to ensure that it is away from the dead zone;

[0014] S6. By changing the magnitude of the current applied on the x-axis, the magnitude of the bias magnetic field applied by the coil on the x-axis is changed multiple times to obtain multiple xy-axis external bias combined magnetic fields of different magnitudes; according to the relationship between the Larmor precession frequency and the combined magnetic field, the coil constants of the x- and y-axes and the xy-axis non-orthogonal angle are simultaneously fitted:

[0015]

[0016] Among them, ω xy θ is the frequency of Larmor precession of atoms around the xy axis due to the combined magnetic field of the bias magnetic field applied and the residual magnetism in the shielding barrel or the earth's magnetic field; xy is the non-orthogonal angle of the xy axis; k x , k y is the coil constant of x and y axis, I x ,I y is the current through coils x and y.

[0017] Preferably, in steps S1, S3, and S5, the single-beam optical pump magnetometer response curve is obtained by scanning the excitation magnetic field frequency, and then the Larmor precession frequency is obtained by fitting. The relationship between the response signal output by the lock-in amplifier and the Larmor precession frequency is:

[0018]

[0019] Where I0 is the incident light intensity; n is the measured alkali metal atom density; σ(ν) is the photon absorption cross section at the laser frequency; z is the depth of the gas chamber; S0 is the initial polarization of the atomic ensemble; θ B is the angle between the external bias magnetic field and the pumping light direction; γ is the gyromagnetic ratio of the alkali metal atom; B1 is the excitation magnetic field amplitude; T1 is the longitudinal relaxation time; T2 is the transverse relaxation time; Δω=ω-ω0 is the detuning amount between the Larmor precession frequency and the excitation magnetic field frequency.

[0020] Preferably, the single-beam optically pumped atomic magnetometer system includes an optical path system, which includes a laser, a polarization-maintaining optical fiber with a collimation head, a linear polarizer, a quarter-wave plate, an air chamber, and a photodetector; the pumping light generated by the laser is converted into circularly polarized light after passing through the linear polarizer and the quarter-wave plate in front of the air chamber to polarize the atoms, and after the circularly polarized light passes through the air chamber, the absorption signal is extracted using a photodetector.

[0021] Preferably, a non-magnetic electric heating system is provided on the outside of the gas chamber, and the non-magnetic electric heating system includes an oven and a heating film, which is used to heat the atomic ensemble in the gas chamber and maintain a constant temperature.

[0022] Preferably, a three-axis coil is provided on the outside of the non-magnetic electric heating system, and the three-axis coil is used to provide an external bias magnetic field and an excitation magnetic field.

[0023] Preferably, the single-beam optically pumped atomic magnetometer system further includes a signal processing system, and the signal processing system includes a current source, a phase-locked amplifier, and a transimpedance voltage amplifier.

[0024] Preferably, the input end of the transimpedance voltage amplifier is connected to the photodetector, the output end of the transimpedance voltage amplifier is connected to the input end of the phase-locked amplifier, the output end of the phase-locked amplifier is connected to the excitation magnetic field three-axis coil, and the output end of the current source is connected to the three-axis coil to be measured.

[0025] Therefore, the present invention adopts the above-mentioned in-situ calibration method of coil constant and non-orthogonal angle based on electron paramagnetic resonance, which can be directly measured in the geomagnetic environment, avoiding the problem of inaccurate measurement of coil constant caused by the coupling between the coil and the shielding barrel. At the same time, this method is suitable for miniaturized three-axis coil calibration, and in-situ measurement can be achieved without any auxiliary device.

[0026] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of an embodiment of a method for in-situ calibration of coil constants and non-orthogonal angles based on electron paramagnetic resonance of the present invention;

[0028] Figure 2 It is a schematic diagram of a single-beam optically pumped atomic magnetometer system involved in an in-situ calibration method of coil constants and non-orthogonal angles based on electron paramagnetic resonance of the present invention.

[0029] Reference numerals

[0030] 1. Optical path system; 11. Laser; 12. Polarization-maintaining optical fiber with collimation head; 13. Linear polarizer; 14. Quarter wave plate; 15. Photodetector; 2. Gas chamber; 3. Non-magnetic electric heating system; 4. Three-axis coil to be tested; 5. Three-axis coil with excitation magnetic field; 61. Current source; 62. Phase-locked amplifier; 63. Transimpedance voltage amplifier; In-input terminal; Out-output terminal. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0032] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0033] Embodiment 1

[0034] The present invention provides a method for in-situ calibration of coil constants and non-orthogonal angles based on electron paramagnetic resonance, such as Figure 1 The figure shows a flow chart of the calibration method, which includes the following steps:

[0035] S1. Start the single-beam optical pump atomic magnetometer system. The pumping laser and the applied AC excitation magnetic field are both along the z-axis direction. A fixed bias magnetic field B is applied along the z-axis of the coil to be measured. z , a bias magnetic field B is also applied along the y-axis y Under the combined effect of the bias magnetic field and the excitation magnetic field, the spin-polarized alkali metal atoms undergo Larmor precession around the direction of the combined magnetic field, and the Larmor precession frequency of the atoms is determined by scanning the excitation magnetic field frequency;

[0036] S2. By changing the magnitude of the current applied on the y-axis, the magnitude of the bias magnetic field applied by the coil on the y-axis is changed multiple times to obtain multiple different magnitudes of yz-axis external bias magnetic fields. The external magnetic field bias is expressed as the product of the coil constant k and the current I passing through the coil. According to the relationship between the Larmor precession frequency and the external bias magnetic field, the coil constants of the y and z axes and the yz-axis non-orthogonal angle are simultaneously fitted:

[0037]

[0038] Among them, ω yz is the frequency of Larmor precession of atoms around the combined magnetic field of the bias magnetic field applied on the yz axis and the residual magnetism in the shielding barrel or the earth's magnetic field; γ is the gyromagnetic ratio of the alkali metal atom; θ yz is the non-orthogonal angle of the yz axis; k y , k z is the coil constant of y and z axis; I y ,I z is the current passing through coils y and z; B x0 , B y0 , B z0 It is the component of the geomagnetic field or the residual magnetism in the barrel along the three-axis direction of the coil to be tested;

[0039] S3, applying an AC excitation magnetic field along the z-axis, applying a fixed bias magnetic field along the z-axis of the coil to be tested, and also applying a bias magnetic field along the x-axis, and determining the Larmor precession frequency of the atoms by scanning the excitation magnetic field frequency;

[0040] S4. By changing the magnitude of the current applied on the x-axis, the magnitude of the bias magnetic field applied by the coil on the x-axis is changed multiple times to obtain multiple xz-axis external bias combined magnetic fields of different magnitudes; according to the relationship between the Larmor precession frequency and the external bias combined magnetic field, the coil constants of the x- and z-axes and the xz-axis non-orthogonal angle are simultaneously fitted:

[0041]

[0042] Among them, ω xz θ is the frequency of Larmor precession of atoms around the xz axis due to the combined magnetic field of the bias magnetic field applied to them and the residual magnetism in the shielding barrel or the earth's magnetic field; xz is the non-orthogonal angle of the xz axis; kx , k z is the coil constant of the x and z axes, I x ,I z is the current through coils x and z;

[0043] S5. When measuring directly under the geomagnetic field, apply an AC excitation magnetic field along the z-axis, apply a fixed bias magnetic field along the y-axis of the coil to be measured, and also apply a bias magnetic field along the x-axis. The Larmor precession frequency of the atom is determined by scanning the excitation magnetic field frequency. When measuring in a shielded barrel, a fixed bias magnetic field is also applied along the z-axis to ensure that it is away from the dead zone.

[0044] S6. By changing the magnitude of the current applied on the x-axis, the magnitude of the bias magnetic field applied by the coil on the x-axis is changed multiple times to obtain multiple xy-axis external bias combined magnetic fields of different magnitudes; according to the relationship between the Larmor precession frequency and the combined magnetic field, the coil constants of the x- and y-axes and the xy-axis non-orthogonal angle are simultaneously fitted:

[0045]

[0046] Among them, ω xy θ is the frequency of Larmor precession of atoms around the xy axis due to the combined magnetic field of the bias magnetic field applied and the residual magnetism in the shielding barrel or the earth's magnetic field; xy is the non-orthogonal angle of the xy axis; k x , k y is the coil constant of x and y axis, I x ,I y is the current through coils x and y.

[0047] In steps S1, S3, and S5, the single-beam optical pump magnetometer response curve is obtained by scanning the excitation magnetic field frequency, and then the Larmor precession frequency is obtained by fitting. The relationship between the response signal output by the phase-locked amplifier 62 and the Larmor precession frequency is:

[0048]

[0049] Where I0 is the incident light intensity; n is the measured alkali metal atom density; σ(ν) is the photon absorption cross section at the laser frequency; z is the depth of the gas chamber; S0 is the initial polarization of the atomic ensemble; θ B is the angle between the external bias magnetic field and the pumping light direction; γ is the gyromagnetic ratio of the alkali metal atom; B1 is the excitation magnetic field amplitude; T1 is the longitudinal relaxation time; T2 is the transverse relaxation time; Δω=ω-ω0 is the detuning amount between the Larmor precession frequency and the excitation magnetic field frequency.

[0050] The schematic diagram of the single-beam optically pumped atomic magnetometer system involved in the in-situ calibration method of coil constants and non-orthogonal angles based on electron paramagnetic resonance is shown in Figure 2. Figure 2As shown, the single-beam optical pump atomic magnetometer system includes an optical path system 1, which includes a laser 11, a polarization-maintaining optical fiber 12 with a collimating head, a linear polarizer 13, a quarter-wave plate 14, a gas cell 2, and a photodetector 15. The pumping light generated by the laser 11 is converted into circularly polarized light after passing through the linear polarizer 13 and the quarter-wave plate 14 in front of the gas cell 2, so as to polarize the atoms. After the circularly polarized light passes through the gas cell 2, the absorption signal is extracted by the photodetector 15.

[0051] A non-magnetic electric heating system 3 is provided on the outside of the gas chamber 2. The non-magnetic electric heating system 3 includes an oven and a heating film, which is used to heat the atomic ensemble in the gas chamber 2 and maintain a constant temperature.

[0052] A three-axis coil to be tested 4 and an excitation magnetic field three-axis coil 5 are arranged outside the non-magnetic electric heating system 3. The three-axis coil to be tested 4 is used to provide an external bias magnetic field, and the excitation magnetic field three-axis coil 5 is used to provide an excitation magnetic field.

[0053] The single-beam optically pumped atomic magnetometer system further includes a signal processing system, which includes a current source 61 , a phase-locked amplifier 62 , and a transimpedance voltage amplifier 63 .

[0054] The input terminal In of the transimpedance voltage amplifier 63 is connected to the photodetector 15, the output terminal Out of the transimpedance voltage amplifier 63 is connected to the input terminal In of the phase-locked amplifier 62, the output terminal Out of the phase-locked amplifier 62 is connected to the excitation magnetic field three-axis coil 5, and the output terminal Out of the current source 61 is connected to the three-axis coil to be tested 4. The functions of the three-axis coil to be tested 4 and the three-axis coil to be tested 5 are interchangeable. If the three-axis coil to be tested 4 is used as the coil to be tested, the three-axis coil to be tested 5 is the coil that provides the excitation magnetic field, and vice versa. In this embodiment, the three-axis coil to be tested 4 is used as the coil to be tested.

[0055] Therefore, the present invention adopts the above-mentioned in-situ calibration method of coil constant and non-orthogonal angle based on electron paramagnetic resonance, which is suitable for the calibration of miniaturized coils, can be measured directly in the geomagnetic environment, avoids the influence of the coupling between the shielding barrel and the coil, and achieves more accurate measurement.

[0056] Finally, it should be noted that the contents not described in detail in the specification of the present invention belong to the prior art known to professional and technical personnel in the field. It is pointed out here that the above description is helpful for those skilled in the art to understand the invention, but it does not limit the protection scope of the invention. The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention is described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that they can still modify or replace the technical solution of the present invention, and these modifications or equivalent replacements cannot make the modified technical solution deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for in-situ calibration of coil constants and non-orthogonal angles based on electron paramagnetic resonance, characterized in that: The following steps are involved: S1. Start the single-beam optical pump atomic magnetometer system. The pumping laser and the applied AC excitation magnetic field are both along the z-axis direction. A fixed bias magnetic field B is applied along the z-axis of the coil to be measured. z , a bias magnetic field B is also applied along the y-axis y Under the combined effect of the bias magnetic field and the excitation magnetic field, the spin-polarized alkali metal atoms undergo Larmor precession around the direction of the combined magnetic field, and the Larmor precession frequency of the atoms is determined by scanning the excitation magnetic field frequency; S2. By changing the magnitude of the current applied on the y-axis, the magnitude of the bias magnetic field applied by the coil on the y-axis is changed multiple times to obtain multiple different magnitudes of yz-axis external bias magnetic fields. The external bias magnetic field is expressed as the product of the coil constant k and the current I passing through the coil. According to the relationship between the Larmor precession frequency and the external bias magnetic field, the coil constants of the y and z axes and the yz-axis non-orthogonal angle are simultaneously fitted: Among them, ω yz is the frequency of Larmor precession of atoms around the combined magnetic field of the bias magnetic field applied on the yz axis and the residual magnetism in the shielding barrel or the earth's magnetic field; γ is the gyromagnetic ratio of the alkali metal atom; θ yz is the non-orthogonal angle of the yz axis; k y , k z is the coil constant of y and z axis; I y ,I z is the current passing through coils y and z; B x0 , B y0 , B z0 It is the component of the geomagnetic field or the residual magnetism in the shielding barrel along the three-axis direction of the coil to be tested; S3, apply an AC excitation magnetic field along the z-axis and a fixed bias magnetic field B along the z-axis of the coil to be tested z , a bias magnetic field is also applied along the x-axis, and the Larmor precession frequency of the atoms is determined by scanning the excitation magnetic field frequency; S4. By changing the magnitude of the current applied on the x-axis, the magnitude of the bias magnetic field applied by the coil on the x-axis is changed multiple times to obtain multiple xz-axis external bias combined magnetic fields of different magnitudes; according to the relationship between the Larmor precession frequency and the external bias combined magnetic field, the coil constants of the x- and z-axes and the xz-axis non-orthogonal angle are simultaneously fitted: Among them, ω xz θ is the frequency of Larmor precession of atoms around the xz axis due to the combined magnetic field of the bias magnetic field applied to them and the residual magnetism in the shielding barrel or the earth's magnetic field; xz is the non-orthogonal angle of the xz axis; k x , k z is the coil constant of the x and z axes, I x ,I z is the current through coils x and z; S5. When measuring directly under the geomagnetic field, apply an AC excitation magnetic field along the z-axis and a fixed bias magnetic field B along the y-axis of the coil to be measured. y , a bias magnetic field is also applied along the x-axis, and the Larmor precession frequency of the atoms is determined by scanning the excitation magnetic field frequency; when measuring in the shielding barrel, a fixed bias magnetic field is also applied along the z-axis to ensure that it is away from the dead zone; S6. By changing the magnitude of the current applied on the x-axis, the magnitude of the bias magnetic field applied by the coil on the x-axis is changed multiple times to obtain multiple xy-axis external bias combined magnetic fields of different magnitudes; according to the relationship between the Larmor precession frequency and the combined magnetic field, the coil constants of the x- and y-axes and the xy-axis non-orthogonal angle are simultaneously fitted: Among them, ω xy θ is the frequency of Larmor precession of atoms around the xy axis due to the combined magnetic field of the bias magnetic field applied and the residual magnetism in the shielding barrel or the earth's magnetic field; xy is a non-orthogonal angle to the xy axis.

2. The method for in-situ calibration of coil constant and non-orthogonal angle based on electron paramagnetic resonance according to claim 1, characterized in that: In steps S1, S3, and S5, the response curve of the single-beam optical pump magnetometer is obtained by scanning the excitation magnetic field frequency, and then the Larmor precession frequency is obtained by fitting. The relationship between the response signal output by the lock-in amplifier and the Larmor precession frequency is: Where I0 is the incident light intensity; n is the measured alkali metal atom density; σ(ν) is the photon absorption cross section at the laser frequency; z is the depth of the gas chamber; S0 is the initial polarization of the atomic ensemble; θ B is the angle between the external bias magnetic field and the pumping light direction; γ is the gyromagnetic ratio of the alkali metal atom; B1 is the excitation magnetic field amplitude; T1 is the longitudinal relaxation time; T2 is the transverse relaxation time; Δω=ω-ω0 is the detuning amount between the Larmor precession frequency and the excitation magnetic field frequency.

3. The method for in-situ calibration of coil constant and non-orthogonal angle based on electron paramagnetic resonance according to claim 1, characterized in that: The single-beam optical pump atomic magnetometer system includes an optical path system, which includes a laser, a polarization-maintaining optical fiber with a collimation head, a linear polarizer, a quarter-wave plate, an air chamber, and a photodetector; the pumping light generated by the laser is converted into circularly polarized light after passing through the linear polarizer and the quarter-wave plate in front of the air chamber to polarize the atoms; after the circularly polarized light passes through the air chamber, an absorption signal is extracted using a photodetector.

4. The method for in-situ calibration of coil constant and non-orthogonal angle based on electron paramagnetic resonance according to claim 3, characterized in that: A non-magnetic electric heating system is arranged outside the gas chamber. The non-magnetic electric heating system comprises an oven and a heating film, which is used to heat the atomic ensemble in the gas chamber and maintain a constant temperature.

5. The method for in-situ calibration of coil constant and non-orthogonal angle based on electron paramagnetic resonance according to claim 4, characterized in that: A three-axis coil is arranged outside the non-magnetic electric heating system, and the three-axis coil is used to provide an external bias magnetic field and an excitation magnetic field.

6. The method for in-situ calibration of coil constant and non-orthogonal angle based on electron paramagnetic resonance according to claim 5, characterized in that: The single-beam optically pumped atomic magnetometer system further includes a signal processing system, which includes a current source, a phase-locked amplifier, and a transimpedance voltage amplifier.

7. The method for in-situ calibration of coil constant and non-orthogonal angle based on electron paramagnetic resonance according to claim 6, characterized in that: The input end of the transimpedance voltage amplifier is connected to the photodetector, the output end of the transimpedance voltage amplifier is connected to the input end of the phase-locked amplifier, the output end of the phase-locked amplifier is connected to the excitation magnetic field three-axis coil, and the output end of the current source is connected to the three-axis coil to be tested.

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