A current measurement and stabilization method based on spin-exchange optical pumping nuclear magnetic resonance

Abstract

This invention discloses a current measurement and stabilization method based on spin-switched optically pumped nuclear magnetic resonance (NMR). The measurement method includes: connecting the output terminal of the DC current source to be measured to static magnetic field coils located on both sides of an atomic gas cell; applying a high-frequency carrier signal through a lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell; emitting circularly polarized light in the same direction as the static magnetic field to polarize alkali metal atoms and inert gas atoms; applying an alternating magnetic field to the atomic gas cell and emitting linearly polarized light in the same direction as the alternating magnetic field to induce NMR in the polarized inert gas atoms; obtaining the emitted polarized light passing through the atomic gas cell to determine the Larmor precession frequency of the inert gas atoms; and obtaining the output current value of the DC current source to be measured based on the calibrated coil structure constant and the gyromagnetic ratio of the inert gas atoms. This invention utilizes the Larmor precession frequency of the atomic magnetic moments to achieve DC current measurement, exhibiting high measurement accuracy and stability.

Description

Technical Field

[0001] This invention relates to the field of measurement technology, and in particular to a current measurement and stabilization method based on spin-exchange optically pumped nuclear magnetic resonance. Background Technology

[0002] DC current sources are widely used in scientific research and industrial production. Current DC current sources can achieve an output current accuracy of 0.01% of the output value. However, to meet the high accuracy and stability requirements of some applications, it is necessary to measure the output current of the DC current source. Existing DC current measurement equipment, such as the Agilent 3458A and FLUKE 5720A calibration sources, lacks the measurement resolution and stability suitable for applications requiring high accuracy and stability of the DC current output value. Summary of the Invention

[0003] This invention provides a current measurement and stabilization method based on spin-switched optically pumped nuclear magnetic resonance. Based on the nuclear magnetic resonance system, the method can measure DC current by utilizing the Larmor precession frequency of atomic magnetic moments. It has high measurement accuracy and stability and is suitable for application scenarios that require high precision and stability of DC current output values.

[0004] To address the aforementioned technical problems, a first aspect of this invention provides a current measurement method based on spin-exchange optically pumped nuclear magnetic resonance, comprising the following steps:

[0005] The output terminal of the DC current source to be tested is connected to the static magnetic field coils located on both sides of the atomic gas cell. A high-frequency carrier signal is applied to the static magnetic field coils through a lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell. Circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0006] An alternating magnetic field is applied to the atomic gas cell, and linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell to induce nuclear magnetic resonance in the polarized inert gas atoms, thereby obtaining the outgoing polarized light passing through the atomic gas cell; wherein, the direction of the applied alternating magnetic field is different from the direction of the applied static magnetic field;

[0007] The Larmor precession frequency of the inert gas atoms is determined based on the emitted polarized light, and the output current value of the DC current source under test is obtained based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms, and the Larmor precession frequency.

[0008] As a preferred embodiment, determining the Larmor precession frequency of the inert gas atoms based on the emitted polarized light specifically includes the following steps:

[0009] The emitted polarized light is split into beams by a polarization beam splitter and emitted to a balanced detector;

[0010] The balanced detector converts the optical signal of the split polarized light into an electrical signal and transmits it to the signal processing module.

[0011] The signal processing module determines the Larmor precession frequency of the inert gas atoms based on the electrical signal.

[0012] As a preferred embodiment, the method specifically involves pre-calibrating the coil structure constants through the following steps:

[0013] A DC current source inputs DC current to the static magnetic field coil at several preset current values, and a high-frequency carrier signal is applied to the static magnetic field coil through a lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell. Circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0014] An alternating magnetic field is applied to the atomic gas cell, and linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell to induce nuclear magnetic resonance in the polarized inert gas atoms, thereby obtaining the outgoing polarized light passing through the atomic gas cell under different static magnetic fields.

[0015] Based on the polarized light emitted from the atomic gas chamber under different static magnetic fields, several Larmor precession frequencies of the inert gas atoms are determined. Then, based on several preset current values, the gyromagnetic ratio of the inert gas atoms, and the several Larmor precession frequencies, a linear fit is performed using the following expression to obtain the calibrated coil structure constants:

[0016]

[0017] Where, ω L The value represents the Larmor precession frequency; I represents the preset current value; γ1 represents the gyromagnetic ratio of the inert gas atoms; the static magnetic field is generated by a plurality of coaxial static magnetic field coils located at preset positions. This represents the coil structure constant of the static magnetic field coil at the center position of the i-th preset position.

[0018] As a preferred embodiment, the direction in which the alternating magnetic field is applied differs from the direction in which the static magnetic field is applied, specifically:

[0019] The direction in which the alternating magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied.

[0020] As a preferred embodiment, the axis of the center of the static magnetic field coil coincides with the axis of the center of the atomic gas chamber, and the atomic gas chamber is located at the center between the two static magnetic field coils.

[0021] As a preferred embodiment, the step of emitting circularly polarized light in the same direction as the static magnetic field into the atomic gas chamber specifically includes the following steps:

[0022] A pump light, aligned with the static magnetic field, is emitted into the atomic gas chamber via a laser. In the optical path of the pump light, a linear polarizer adjusts the pump light to linear polarization, and a quarter-wave plate adjusts the linear polarization to circular polarization.

[0023] As a preferred embodiment, the step of emitting linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell specifically includes the following steps:

[0024] A laser emits a probe light that is in the same direction as the alternating magnetic field into the atomic gas chamber, and a linear polarizer is used to adjust the probe light into linearly polarized light in the optical path of the probe light.

[0025] As a preferred embodiment, the method further includes the following steps:

[0026] The atomic gas chamber is heated to a preset target temperature using a non-magnetic heating system.

[0027] The second aspect of the present invention provides a current measurement system based on spin-switched optically pumped nuclear magnetic resonance, which applies the current measurement method based on spin-switched optically pumped nuclear magnetic resonance as described in any of the first aspects, including an atomic gas cell, a static magnetic field coil, a circularly polarized light emission module, an alternating magnetic field coil, a linearly polarized light emission module, and a signal processing component;

[0028] The static magnetic field coils are located on both sides of the atomic gas cell and are used to connect to the output terminals of the DC current source under test and the lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell; the circularly polarized light emission module is used to emit circularly polarized light in the same direction as the static magnetic field into the atomic gas cell to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0029] The alternating magnetic field coil is used to apply an alternating magnetic field to the atomic gas cell; the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell, so as to induce nuclear magnetic resonance in the polarized inert gas atoms; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field;

[0030] The signal processing component is used to acquire the outgoing polarized light passing through the atomic gas cell, determine the Larmor precession frequency of the inert gas atoms based on the outgoing polarized light, and obtain the output current value of the DC current source under test based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms and the Larmor precession frequency.

[0031] The third aspect of the present invention provides a current stabilization method based on spin-switched optically pumped nuclear magnetic resonance, which is based on a current stabilization system including a DC current source, a current stabilization circuit module, a DC current measurement system as described in the second aspect, a lock-in amplifier and a PID control module, and includes the following steps;

[0032] The DC current source transmits the initial output current to the current stabilizing circuit module;

[0033] The current stabilization circuit module performs a current stabilization on the initial output current, generates a preliminary stabilizing current, and transmits it to the DC current measurement system.

[0034] The DC current measurement system measures the received initial stabilized current value, determines the fluctuation of the initial stabilized current based on the current value, and sends it to the lock-in amplifier.

[0035] The lock-in amplifier generates the compensation command based on the fluctuation and sends it to the PID control module;

[0036] The PID control module generates a compensation current according to the compensation command and sends it to the current stabilizing circuit module;

[0037] The current stabilization circuit module performs secondary current stabilization on the initial current stabilization current according to the compensation value corresponding to the compensation current, generates the target output current, and transmits it to the power-consuming equipment.

[0038] Compared with the prior art, the beneficial effect of the embodiments of the present invention is that, based on the nuclear magnetic resonance system, the measurement of DC current can be realized by using the Larmor precession frequency of the atomic magnetic moment, which has high measurement accuracy and measurement stability, and can be applied to application scenarios with high accuracy and high stability requirements for DC current output value. Attached Figure Description

[0039] Figure 1 This is a schematic flowchart of the current measurement method based on spin-exchange optically pumped nuclear magnetic resonance in an embodiment of the present invention.

[0040] Figure 2 This is a schematic diagram of the Helmholtz coil in an embodiment of the present invention;

[0041] Figure 3This is a schematic diagram of the current measurement system based on spin-exchange optically pumped nuclear magnetic resonance in an embodiment of the present invention;

[0042] Figure 4 This is a schematic diagram of the current stabilization system based on spin-exchange optically pumped nuclear magnetic resonance in an embodiment of the present invention;

[0043] Among them, 201 is the Helmholtz coil; 202 is the atomic gas chamber;

[0044] 301. Distributed Bragg reflector laser with a wavelength of 795nm; 302. Beam expander and collimator unit; 303. First half-wave plate; 304. First linear polarizer; 305. Quarter-wave plate; 306. Static magnetic field coil; 307. Alternating magnetic field coil; 308. Distributed Bragg reflector laser with a wavelength of 780nm; 309. Second half-wave plate; 310. Second linear polarizer; 311. Atomic gas cell; 312. Third half-wave plate; 313. Polarization beam splitter; 314. Balanced detector; 315. Signal processing module; 316. Non-magnetic heating system; 317. Magnetic shielding system; 318. Backup alternating magnetic field coil;

[0045] 401. DC current source; 402. Current stabilizing circuit module; 403. DC current measurement system; 404. Lock-in amplifier; 405. PID control module. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] See Figure 1 The first aspect of this invention provides a current measurement method based on spin-exchange optically pumped nuclear magnetic resonance, comprising the following steps S1 to S3:

[0048] Step S1: Connect the output terminal of the DC current source to be tested to the static magnetic field coils located on both sides of the atomic gas cell, and apply a high-frequency carrier signal to the static magnetic field coils through a lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell, and emit circularly polarized light in the same direction as the static magnetic field to the atomic gas cell so as to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0049] Step S2: Apply an alternating magnetic field to the atomic gas cell and emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell, so as to induce nuclear magnetic resonance in the polarized inert gas atoms and obtain the outgoing polarized light passing through the atomic gas cell; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field;

[0050] Step S3: Determine the Larmor precession frequency of the inert gas atoms based on the emitted polarized light, and obtain the output current value of the DC current source under test based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms, and the Larmor precession frequency.

[0051] In step S1, the output terminal of the DC current source under test is connected to the static magnetic field coils located on both sides of the atomic gas cell. The static magnetic field coils generate a static magnetic field due to the current and apply it to the atomic gas cell. A high-frequency carrier signal is applied to the static magnetic field coils through a lock-in amplifier, thereby generating a high-frequency carrier magnetic field which is also applied to the atomic gas cell. It is worth noting that the high-frequency carrier magnetic field is a signal modulation method; high-frequency modulation can avoid the influence of low-frequency flicker noise. The frequency of the high-frequency carrier magnetic field is proportional to the magnitude of the static magnetic field applied in that direction, and the ratio is the gyromagnetic ratio of the alkali metal atoms. Simultaneously, circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell, achieving polarization of the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0052] It is worth noting that nuclear magnetic resonance (NMR) is the physical process by which atomic nuclei with non-zero magnetic moments undergo Zeeman splitting of their spin energy levels under the influence of an external magnetic field, resonating and absorbing radio frequency radiation of a certain frequency. In this embodiment, the atomic gas cell includes alkali metal atoms, inert gas atoms, and other buffer gas atoms. Under the influence of a static magnetic field propagating in a specific direction and circularly polarized light in the same direction as the static magnetic field, the alkali metal atoms are polarized. Then, through spin-exchange optical pumping between the alkali metal atoms and the inert gas atoms, the inert gas atoms are polarized.

[0053] In step S2, this embodiment applies an alternating magnetic field to the atomic gas cell and emits linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell. It is worth noting that the frequency of the alternating magnetic field is close to, or even the same as, the Larmor precession frequency of the inert gas atoms, so as to make the polarized inert gas atoms generate nuclear magnetic resonance; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field.

[0054] It is worth noting that, assuming the axis of the static magnetic field coil is the z-axis, and each nuclear magnetic moment precesses around the z-axis at the Larmor precession frequency, they are out of phase. Therefore, there is no net component in the xy-plane perpendicular to the z-axis. When an alternating magnetic field is applied in a direction different from the applied static magnetic field, such as perpendicular to it, with a frequency equal to or close to the Larmor frequency of the inert gas atomic nuclear magnetic moments, the phase of the Larmor precession of each inert gas atom becomes consistent. Therefore, the macroscopic magnetic moment tilts, moving away from its initial position. Consequently, a component is generated in the xy-plane, which precesses around the z-axis at the Larmor precession frequency of the inert gas atoms, with a Larmor precession frequency of ω. L =1B0, where ω L Let γ1 represent the Larmor precession frequency of the inert gas atoms, γ1 represent the gyromagnetic ratio of the inert gas atoms, and B0 represent the magnetic induction intensity of the static magnetic field. Furthermore, by emitting linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell, the Larmor precession frequency can be detected by acquiring the outgoing polarized light passing through the atomic gas cell.

[0055] In step S3, the Larmor precession frequency of the inert gas atoms is determined based on the emitted polarized light, and the output current value of the DC current source to be measured is obtained based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms, and the Larmor precession frequency.

[0056] Specifically, the static magnetic field coil can be, but is not limited to, a Helmholtz coil, a four-loop coil, or a multi-loop coil. A DC current is provided to the static magnetic field coil through a DC current source to be measured. According to the Biot-Savart law, the formula for calculating the magnetic field generated by the static magnetic field coil at a point x on its central axis is as follows (1):

[0057]

[0058] Where N represents the number of turns of the coil; R represents the coil radius; and μ0 represents the free permeability. Once the radius, number of turns, and current of the coil are determined, the magnetic field generated at any point on its axis depends only on the distance between that point and the center of the static magnetic field coil. This quantity is defined as , and then we have the following equation (2):

[0059]

[0060] When x is a constant, K X This is the coil structure constant at that point. When multiple sets of static magnetic field coils with different radii and turns appear at different positions on the same axis, the total magnetic field generated at point x is a linear superposition of the magnetic fields generated by all the coils. When the coil group is fixed, the total magnetic field at a specific point is shown in equation (3) below:

[0061]

[0062] The static magnetic field is generated by a plurality of coaxial static magnetic field coils located at predetermined positions. Let represent the coil structure constant of the static magnetic field coil at the center position of the i-th preset position. Therefore, the measured Larmor precession frequency of the inert gas atoms is as shown in equation (4):

[0063]

[0064] Since the magnetic induction intensity of the static magnetic field coil is determined only by the coil current, the current value of the DC current source under test and the measurement accuracy of the DC current can be deduced by measuring the Larmor precession frequency and its fluctuation of the inert gas atoms.

[0065] As one alternative embodiment, the alkali metal atoms in the atomic gas chamber are rubidium atoms, and the inert gas atoms are xenon atoms.

[0066] As a preferred embodiment, determining the Larmor precession frequency of the inert gas atoms based on the emitted polarized light specifically includes the following steps:

[0067] The emitted polarized light is split into beams by a polarization beam splitter and emitted to a balanced detector;

[0068] The balanced detector converts the optical signal of the split polarized light into an electrical signal and transmits it to the signal processing module.

[0069] The signal processing module determines the Larmor precession frequency of the inert gas atoms based on the electrical signal.

[0070] As one alternative embodiment, the polarization beam splitter is a Wollaston prism.

[0071] Specifically, in this embodiment, the outgoing polarized light is split by a polarization beam splitter and transmitted to a balanced detector; the balanced detector converts the detection light signal of the split outgoing polarized light into an electrical signal and transmits it to a signal processing module; the signal processing module can determine the Larmor precession frequency of the inert gas atoms based on the received electrical signal, thereby clarifying the fluctuation of the Larmor precession frequency of the inert gas atoms.

[0072] As a preferred embodiment, the method specifically involves pre-calibrating the coil structure constants through the following steps:

[0073] A DC current source inputs DC current to the static magnetic field coil at several preset current values, and a high-frequency carrier signal is applied to the static magnetic field coil through a lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell. Circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell.

[0074] An alternating magnetic field is applied to the atomic gas cell, and linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell to induce nuclear magnetic resonance in the polarized inert gas atoms, thereby obtaining the outgoing polarized light passing through the atomic gas cell under different static magnetic fields.

[0075] Based on the polarized light emitted from the atomic gas chamber under different static magnetic fields, several Larmor precession frequencies of the inert gas atoms are determined. Then, based on several preset current values, the gyromagnetic ratio of the inert gas atoms, and the several Larmor precession frequencies, a linear fit is performed using the following expression to obtain the calibrated coil structure constants:

[0076]

[0077] Where, ω L The value represents the Larmor precession frequency; I represents the preset current value; γ1 represents the gyromagnetic ratio of the inert gas atoms; the static magnetic field is generated by a plurality of coaxial static magnetic field coils located at preset positions. This represents the coil structure constant of the static magnetic field coil at the center position of the i-th preset position.

[0078] It is worth noting that, based on the structure of the static magnetic field coil used, the coil structure constant at the axial center position of the atomic gas chamber is determined, i.e., the ratio constant of the measured Larmor precession frequency to the supply current is obtained. Since the theoretically calculated coil structure constant is affected by errors in manufacturing process and position, the coil structure constant needs to be calibrated before DC current measurement. Specifically, by applying different magnitudes of DC current to the static magnetic field coil through a DC current source, and measuring the Larmor precession frequencies corresponding to different DC currents, linear fitting is performed according to the above formula (4), thereby enabling the calibration of the coil structure constant.

[0079] As a preferred embodiment, the direction in which the alternating magnetic field is applied differs from the direction in which the static magnetic field is applied, specifically:

[0080] The direction in which the alternating magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied.

[0081] Specifically, the direction of the applied alternating magnetic field is perpendicular to the direction of the applied static magnetic field, that is, the axis of the static magnetic field coil that generates the static magnetic field is perpendicular to the axis of the alternating magnetic field coil that generates the alternating magnetic field. In this case, the static magnetic field, the high-frequency carrier magnetic field and the circularly polarized pump light are collinear, and the alternating magnetic field and the linearly polarized probe light are collinear.

[0082] As a preferred embodiment, the axis of the center of the static magnetic field coil coincides with the axis of the center of the atomic gas chamber, and the atomic gas chamber is located at the center between the two static magnetic field coils.

[0083] As one optional embodiment, the static magnetic field in this embodiment is generated by a Helmholtz coil, such as... Figure 2 As shown in the figure, the figure includes a Helmholtz coil 201 and an atomic gas chamber 202 located at the center. The Helmholtz coil 201 consists of two identical current-carrying coils placed parallel to each other and coaxially, with current flowing in the same direction. The magnetic fields generated by the two coils are superimposed and enhanced along the central axis of the two coils. When the distance between the two coils is equal to the coil radius (d = R), an approximately uniform magnetic field will be formed near the axial center point. Under this condition, the relationship between the current I passing through the Helmholtz coil 201 and the magnitude of its magnetic field at the uniform region of the coil (near the axial center point) is shown in the following equation (5):

[0084]

[0085] Where μ0 is the free permeability, with a value of 4π × 10⁻⁶. -7 (·m / ); N is the number of coil turns; R is the coil radius; d is the distance between the two coils; z is the coordinate of a calculation point near the center point of the coil.

[0086] When the nuclear magnetic resonance gyroscope system remains stationary relative to the inertial reference frame, the measured actual precession frequency is given by the following equation (6):

[0087]

[0088] In this embodiment, since the atomic gas chamber 202 is located at the center between the two Helmholtz coils 201, z = 0, that is:

[0089]

[0090] Furthermore, the DC current source under test is connected to the static magnetic field coil, and the nuclear magnetic resonance system is swept at the current output value to obtain the Larmor precession frequency value generated by the corresponding current. Then, the actual output current value and corresponding stability of the DC current source under test can be obtained based on the Larmor precession frequency value.

[0091] As a preferred embodiment, the step of emitting circularly polarized light in the same direction as the static magnetic field into the atomic gas chamber specifically includes the following steps:

[0092] A pump light, aligned with the static magnetic field, is emitted into the atomic gas chamber via a laser. In the optical path of the pump light, a linear polarizer adjusts the pump light to linear polarization, and a quarter-wave plate adjusts the linear polarization to circular polarization.

[0093] As one of the optional embodiments, the laser in this embodiment is a distributed Bragg reflector laser with a laser wavelength of 795nm; the design wavelength of the quarter-wave plate is 795nm.

[0094] As a preferred embodiment, the step of emitting linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell specifically includes the following steps:

[0095] A laser emits a probe light that is in the same direction as the alternating magnetic field into the atomic gas chamber, and a linear polarizer is used to adjust the probe light into linearly polarized light in the optical path of the probe light.

[0096] As one of the optional embodiments, the laser in this embodiment is a distributed Bragg reflector laser with a laser wavelength of 780nm; the half-wave plate is designed with a wavelength of 780nm.

[0097] As a preferred embodiment, the method further includes the following steps:

[0098] The atomic gas chamber is heated to a preset target temperature using a non-magnetic heating system.

[0099] It is worth noting that, before measuring the DC current value, the temperature of the atomic gas chamber is heated to the preset target temperature by a non-magnetic heating system, which can ensure that the atoms in the atomic gas chamber are at a stable atomic number density.

[0100] In one preferred embodiment, a magnetic shielding system is provided outside the atomic gas chamber, the static magnetic field coil, and the alternating magnetic field coil. This effectively avoids magnetic field interference caused by external factors, thereby further improving the accuracy and stability of DC current measurement. Preferably, the magnetic shielding system consists of five layers of permalloy.

[0101] The implementation principle and process of the present invention will be illustrated below through a specific embodiment.

[0102] Assume that the alkali metal atoms in the atomic gas chamber are rubidium atoms, i.e., Rb atoms, and the inert gas atoms are xenon atoms, i.e. Xe atoms; the static magnetic field coil is a Helmholtz coil with a coil radius R = d = 0.2 m and the number of coil turns N = 2. The atomic gas chamber is located at the center position between the two Helmholtz coils, i.e., the corresponding coordinate z = 0.

[0103] When the atomic gas chamber is heated to a preset target temperature using a non-magnetic heating system, the Rb atoms in the chamber undergo spin polarization under the influence of circularly polarized pump light. Under the influence of a static magnetic field, the Rb atoms undergo Larmor precession at a frequency ω = γB0, where γ is the gyromagnetic ratio of the Rb atoms. Simultaneously, spin exchange occurs between the polarized Rb atoms and the inert gas Xe atoms in the atomic gas chamber, ultimately polarizing the Xe atoms as well. Applying an alternating magnetic field perpendicular to the static magnetic field, with the same Larmor precession frequency as the Xe atoms, induces nuclear magnetic resonance (NMR) in the Xe atoms. Because the resonance linewidth of the Xe atoms is very narrow, the Larmor precession frequency of the Xe atoms can be accurately measured by measuring the resonance signal intensity at different frequencies.

[0104] Furthermore, based on the above formula (5), the magnetic induction intensity at the atomic gas cell is determined to be: B≈8.99×10 -6 I(T).

[0105] The actual Larmor precession frequency obtained by measurement is: ω L =1B≈8.99×10 -6 γ1I.

[0106] The relationship between the supplied current and the measured actual Larmor precession frequency can be derived by reverse calculation as follows:

[0107]

[0108] The measurement steps are as follows:

[0109] (1) When the DC current measurement system is stable, apply the output current of the DC current source to be measured to the Helmholtz coil and set the output DC current to 1A.

[0110] (2) Construct a closed-loop magnetic resonance system, 129 Xe forms a spin oscillator and outputs its vibration frequency in real time.

[0111] (3) Based on the above-mentioned relationship between the current and the measured actual Larmor precession frequency, and the vibration frequency of the spin oscillator, the corresponding DC current value is obtained. The scaling factor error of the spin oscillator can be reduced to the order of 1ppm, the signal-to-noise ratio can reach 100dB, and the stability can reach 1E-8 or higher. Therefore, the DC current measurement accuracy of this embodiment can reach the order of 1ppm, and the measurement stability can reach 1E-8, which is suitable for application scenarios with high accuracy and high stability requirements for DC current output values.

[0112] It is worth noting that since the calibration coil structure constant is calibrated using a DC current source, the calibration error is limited by the accuracy of the DC current source used.

[0113] This invention provides a current measurement method based on spin-switched optically pumped nuclear magnetic resonance. Based on the nuclear magnetic resonance system, the method can measure DC current using the Larmor precession frequency of atomic magnetic moments. It has high measurement accuracy and stability and is suitable for application scenarios that require high precision and stability of DC current output values.

[0114] Furthermore, compared to commonly used DC current measuring devices on the market, the cost of embodiments of the present invention is lower.

[0115] See Figure 3 The second aspect of the present invention provides a current measurement system based on spin-switched optical pumping nuclear magnetic resonance, which applies the current measurement method based on spin-switched optical pumping nuclear magnetic resonance as described in any embodiment of the first aspect, including an atomic gas cell 311, a static magnetic field coil 306, a circularly polarized light emission module, an alternating magnetic field coil 307, a linearly polarized light emission module, and a signal processing component.

[0116] The static magnetic field coil 306 is located on both sides of the atomic gas cell 311 and is used to connect to the output terminals of the DC current source to be measured and the lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell 311; the circularly polarized light emission module is used to emit circularly polarized light in the same direction as the static magnetic field into the atomic gas cell 311 so as to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell 311.

[0117] The alternating magnetic field coil 307 is used to apply an alternating magnetic field to the atomic gas chamber 311; the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas chamber 311, so as to cause the polarized inert gas atoms to generate nuclear magnetic resonance; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field;

[0118] The signal processing component is used to acquire the outgoing polarized light passing through the atomic gas cell 311, determine the Larmor precession frequency of the inert gas atoms based on the outgoing polarized light, and obtain the output current value of the DC current source under test based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms and the Larmor precession frequency.

[0119] As a preferred embodiment, the signal processing component includes a polarization beam splitter 313, a balanced detector 314, and a signal processing module 315;

[0120] The signal processing component is used to acquire the emitted polarized light passing through the atomic gas cell 311, determine the Larmor precession frequency of the inert gas atoms based on the emitted polarized light, and obtain the output current value of the DC current source under test based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms, and the Larmor precession frequency. Specifically, this includes:

[0121] The polarization beam splitter 313 is used to acquire the outgoing polarized light that has passed through the atomic gas cell 311, split the outgoing polarized light into beams, and transmit it to the balanced detector 314.

[0122] The balanced detector 314 is used to convert the optical signal of the split polarized light into an electrical signal and transmit it to the signal processing module 315.

[0123] The signal processing module 315 is used to determine the Larmor precession frequency of the inert gas atoms based on the electrical signal, and to obtain the output current value of the DC current source under test based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms and the Larmor precession frequency.

[0124] As a preferred embodiment, the axis of the static magnetic field coil 306 is perpendicular to the axis of the alternating magnetic field coil 307.

[0125] As a preferred embodiment, the axis of the center of the static magnetic field coil 306 coincides with the axis of the center of the atomic gas chamber 311, and the atomic gas chamber 311 is located at the center between the two static magnetic field coils 306.

[0126] As a preferred embodiment, the circularly polarized light emission module includes a distributed Bragg reflector laser 301 with a laser wavelength of 795nm, and a beam expansion and collimation unit 302, a first half-wave plate 303, a first linear polarizer 304, and a quarter-wave plate 305 sequentially disposed between the laser and the static magnetic field coil 306.

[0127] The distributed Bragg reflector laser 301 with a wavelength of 795nm is used to emit pump light in the same direction as the static magnetic field into the atomic gas chamber 311.

[0128] The beam expanding and collimating unit 302 is used to expand and collimate the pump light in the optical path of the pump light;

[0129] The first half-wave plate 303 is used to change the polarization direction of the pump light after beam expansion and collimation to the target polarization direction;

[0130] The first linear polarizer 304 is used to adjust the pump light after changing its polarization direction into linearly polarized light;

[0131] The combined function of the first half-wave plate 303 and the first linear polarizer 304 is to make the laser light after passing through the linear polarizer a linearly polarized light with continuously adjustable power and a certain polarization direction.

[0132] The quarter-wave plate 305 and the first linear polarizer 304 are used to adjust the linearly polarized light into circularly polarized light.

[0133] The combined function of the first half-wave plate 303, the first linear polarizer 304, and the quarter-wave plate 305 is to make the laser light after passing through the quarter-wave plate 305 a circularly polarized light with continuously adjustable power.

[0134] As a preferred embodiment, the linearly polarized light emission module includes a distributed Bragg reflector laser 308 with a laser wavelength of 780nm and a second half-wave plate 309 and a second linear polarizer 310 sequentially disposed between the laser and the alternating magnetic field coil 307.

[0135] The distributed Bragg reflector laser 308 with a wavelength of 780nm is used to emit probe light in the same direction as the alternating magnetic field into the atomic gas chamber 311.

[0136] The second half-wave plate 309 and the second linear polarizer 310 are used to adjust the probe light into linearly polarized light in the optical path of the probe light.

[0137] It is worth noting that the polarized light emitted from the atomic gas chamber 311 is then incident on the signal processing component after passing through the third half-wave plate 312 for signal processing.

[0138] As a preferred embodiment, the system further includes a non-magnetic heating system 316;

[0139] The non-magnetic heating system 316 is used to heat the atomic gas chamber 311 to a preset target temperature.

[0140] As a preferred embodiment, the system further includes a magnetic shielding system 317;

[0141] The magnetic shielding system 317 is composed of five layers of permalloy;

[0142] The magnetic shielding system 317 has a accommodating cavity for housing the atomic gas chamber 311, the static magnetic field coil 306, the alternating magnetic field coil 307, and the non-magnetic heating system 316.

[0143] As a preferred embodiment, the system further includes a backup alternating magnetic field coil 318;

[0144] The axis of the standby alternating magnetic field coil 318 is perpendicular to the axis of the static magnetic field coil 306 and the axis of the alternating magnetic field coil 307, respectively.

[0145] It is understood that the spare alternating magnetic field coil 318 can replace the function of the alternating magnetic field coil 307.

[0146] This invention provides a current measurement system based on spin-switched optically pumped nuclear magnetic resonance. Based on the nuclear magnetic resonance system, the system can measure DC current using the Larmor precession frequency of atomic magnetic moments. It has high measurement accuracy and stability and is suitable for application scenarios that require high precision and stability of DC current output values.

[0147] Furthermore, compared to commonly used DC current measuring devices on the market, the cost of embodiments of the present invention is lower.

[0148] A third aspect of this invention provides a current stabilization method based on spin-switched optically pumped nuclear magnetic resonance, based on a current stabilization system comprising a DC current source 401, a current stabilization circuit module 402, a DC current measurement system 403 as described in the second aspect, a lock-in amplifier 404, and a PID control module 405, comprising the following steps:

[0149] The DC current source 401 transmits the initial output current to the current stabilizing circuit module 402;

[0150] The current stabilizing circuit module 402 performs a current stabilization on the initial output current, generates a preliminary stabilizing current, and transmits it to the DC current measurement system 403.

[0151] The DC current measurement system 403 measures the received initial stabilization current value, determines the fluctuation of the initial stabilization current based on the current value, and sends it to the lock-in amplifier 404.

[0152] The lock-in amplifier 404 generates the compensation command based on the fluctuation and sends it to the PID control module 405;

[0153] The PID adjustment module 405 generates a compensation current according to the compensation command and sends it to the current stabilizing circuit module 402;

[0154] The current stabilization circuit module 402 performs secondary current stabilization on the initial current stabilization current according to the compensation value corresponding to the compensation current, generates the target output current, and transmits it to the electrical equipment.

[0155] The structure of the above current stabilization system is as follows: Figure 4 As shown. It is worth noting that the current stabilizing circuit module 402 transmits the initial stabilizing current to the DC current measurement system 403, specifically: the current stabilizing circuit module 402 outputs the initial stabilizing current to the static magnetic field coil in the DC current measurement system 403.

[0156] Specifically, the principle of generating DC current in this embodiment of the invention is as follows: after the conventional current is stabilized in the first stage by the current stabilization circuit module 402, it supplies power to the static magnetic field coil of the DC current measurement system 403, generating a static magnetic field. The fluctuation of the conventional current can be obtained through the DC current measurement process described in any embodiment of the first aspect. Based on the fluctuation, a PID adjustment module 405 is built to compensate for the fluctuation of the conventional current in real time, thereby achieving the second stage of current stabilization of the conventional current and finally generating a high-precision and high-stability output current.

[0157] It is worth noting that the current stabilization circuit module 402 is used for primary current stabilization of low-precision DC current. Its working principle is to convert current into voltage using Ohm's law, set a reference voltage using a high-precision resistor, and perform PID compensation based on the difference between the converted voltage and the reference voltage. After primary current stabilization by the current stabilization circuit module 402, the DC current is connected to the static magnetic field coil of the DC current measurement system 403. The fluctuation of the connected DC current can be obtained through the DC current measurement process described in any embodiment of the first aspect. The lock-in amplifier 404 and the PID adjustment module 405 can compensate for the fluctuation of the DC current in real time according to the fluctuation, achieving secondary current stabilization of the DC current, and finally outputting a highly stable DC current. This embodiment of the invention can achieve current stabilization and output a highly stable DC current without requiring the current stabilization circuit module 402 to have high compensation accuracy.

[0158] Furthermore, since the magnetometer measures the actual magnetic field value, this magnetic field value can be roughly divided into two parts: the static magnetic field generated by the current source, and the magnetic field composed of the external magnetic field, the residual magnetic field within the magnetic shielding device, and the magnetic field equivalent to fluctuations in experimental parameters. Therefore, the fluctuations in the measured value are not entirely caused by the current; in fact, the fluctuations caused by the current source are lower. Thus, the stability of the DC current generated using the embodiments of this invention has higher accuracy than the actual measured value.

[0159] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A current measurement method based on spin-exchange optically pumped nuclear magnetic resonance, characterized in that, Includes the following steps: The output terminal of the DC current source to be tested is connected to the static magnetic field coils located on both sides of the atomic gas cell. A high-frequency carrier signal is applied to the static magnetic field coils through a lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell. Circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell. An alternating magnetic field is applied to the atomic gas cell, and linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell to induce nuclear magnetic resonance in the polarized inert gas atoms, thereby obtaining the outgoing polarized light passing through the atomic gas cell; wherein, the direction of the applied alternating magnetic field is different from the direction of the applied static magnetic field; The Larmor precession frequency of the inert gas atoms is determined based on the emitted polarized light, and the output current value of the DC current source under test is obtained based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms, and the Larmor precession frequency.

2. The current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in claim 1, characterized in that, The step of determining the Larmor precession frequency of the inert gas atoms based on the emitted polarized light specifically includes the following steps: The emitted polarized light is split into beams by a polarization beam splitter and emitted to a balanced detector. The balanced detector converts the optical signal of the split polarized light into an electrical signal and transmits it to the signal processing module. The signal processing module determines the Larmor precession frequency of the inert gas atoms based on the electrical signal.

3. The current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in claim 1, characterized in that, The method specifically involves pre-calibrating the coil structure constants through the following steps: A DC current source inputs DC current to the static magnetic field coil at several preset current values, and a high-frequency carrier signal is applied to the static magnetic field coil through a lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell. Circularly polarized light in the same direction as the static magnetic field is emitted into the atomic gas cell to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell. An alternating magnetic field is applied to the atomic gas cell, and linearly polarized light in the same direction as the alternating magnetic field is emitted into the atomic gas cell to induce nuclear magnetic resonance in the polarized inert gas atoms, thereby obtaining the outgoing polarized light passing through the atomic gas cell under different static magnetic fields. Based on the polarized light emitted from the atomic gas chamber under different static magnetic fields, several Larmor precession frequencies of the inert gas atoms are determined. Then, based on several preset current values, the gyromagnetic ratio of the inert gas atoms, and the several Larmor precession frequencies, a linear fit is performed using the following expression to obtain the calibrated coil structure constants: Where, ω L The value represents the Larmor precession frequency; I represents the preset current value; γ1 represents the gyromagnetic ratio of the inert gas atoms; the static magnetic field is generated by a plurality of coaxial static magnetic field coils located at preset positions. This represents the coil structure constant of the static magnetic field coil at the center position of the i-th preset position.

4. The current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in claim 1, characterized in that, The direction in which the alternating magnetic field is applied differs from the direction in which the static magnetic field is applied, specifically: The direction in which the alternating magnetic field is applied is perpendicular to the direction in which the static magnetic field is applied.

5. The current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in claim 1, characterized in that, The axis at the center of the static magnetic field coil coincides with the axis at the center of the atomic gas chamber, and the atomic gas chamber is located at the center between the two static magnetic field coils.

6. The current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in claim 1, characterized in that, The step of emitting circularly polarized light in the same direction as the static magnetic field into the atomic gas cell specifically includes the following steps: A pump light, aligned with the static magnetic field, is emitted into the atomic gas chamber via a laser. In the optical path of the pump light, a linear polarizer adjusts the pump light to linear polarization, and a quarter-wave plate adjusts the linear polarization to circular polarization.

7. The current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in claim 1, characterized in that, The step of emitting linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell specifically includes the following steps: A laser emits a probe light that is in the same direction as the alternating magnetic field into the atomic gas chamber, and a linear polarizer is used to adjust the probe light into linearly polarized light in the optical path of the probe light.

8. The current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in claim 1, characterized in that, The method further includes the following steps: The atomic gas chamber is heated to a preset target temperature using a non-magnetic heating system.

9. A current measurement system based on spin-exchange optically pumped nuclear magnetic resonance, employing the current measurement method based on spin-exchange optically pumped nuclear magnetic resonance as described in any one of claims 1 to 8, characterized in that, It includes an atomic gas cell, a static magnetic field coil, a circularly polarized light emission module, an alternating magnetic field coil, a linearly polarized light emission module, and signal processing components; The static magnetic field coils are located on both sides of the atomic gas cell and are used to connect to the output terminals of the DC current source under test and the lock-in amplifier to apply a static magnetic field and a high-frequency carrier magnetic field to the atomic gas cell; the circularly polarized light emission module is used to emit circularly polarized light in the same direction as the static magnetic field into the atomic gas cell to polarize the alkali metal atoms and inert gas atoms in the atomic gas cell. The alternating magnetic field coil is used to apply an alternating magnetic field to the atomic gas cell; the linearly polarized light emission module is used to emit linearly polarized light in the same direction as the alternating magnetic field into the atomic gas cell, so as to induce nuclear magnetic resonance in the polarized inert gas atoms; wherein, the direction of applying the alternating magnetic field is different from the direction of applying the static magnetic field; The signal processing component is used to acquire the outgoing polarized light passing through the atomic gas cell, determine the Larmor precession frequency of the inert gas atoms based on the outgoing polarized light, and obtain the output current value of the DC current source under test based on the pre-calibrated coil structure constant, the gyromagnetic ratio of the inert gas atoms and the Larmor precession frequency.

10. A current stabilization method based on spin-exchange optically pumped nuclear magnetic resonance, characterized in that, A current stabilization system based on a DC current source, a current stabilization circuit module, a DC current measurement system as described in claim 9, a lock-in amplifier, and a PID regulation module includes the following steps; The DC current source transmits the initial output current to the current stabilizing circuit module; The current stabilization circuit module performs a current stabilization on the initial output current, generates a preliminary stabilizing current, and transmits it to the DC current measurement system. The DC current measurement system measures the received initial stabilized current value, determines the fluctuation of the initial stabilized current based on the current value, and sends it to the lock-in amplifier. The lock-in amplifier generates a compensation command based on the fluctuation and sends it to the PID control module; The PID control module generates a compensation current according to the compensation command and sends it to the current stabilizing circuit module; The current stabilization circuit module performs secondary current stabilization on the initial current stabilization current according to the compensation value corresponding to the compensation current, generates the target output current, and transmits it to the power-consuming equipment.

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