A self-calibrating three-axis atomic magnetometer for integrated vector and scalar measurement

Abstract

The present application provides a self-calibrating three-axis atomic magnetometer for realizing integrated vector and scalar measurement. The magnetometer includes a sensor probe and an electronics box. A single-beam pump laser generated by a laser generating unit in the electronics box acts on an alkali metal atomic gas cell in the sensor probe. According to the zero-field resonance principle of alkali metal atoms, the pump laser interacts with the alkali metal atoms to generate an optical absorption signal containing environmental magnetic field information. A photoelectric detection unit in the electronics box converts the optical signal into an electrical signal, and a three-axis modulation compensation circuit demodulates the photoelectric signal and generates a compensation signal to achieve precise three-axis measurement of the magnetic field. The present invention can make the magnetometer operate in the Mz mode or the CPT mode to realize scalar measurement of the magnetic field, thereby realizing self-calibration of the three-axis vector of the magnetometer. By switching the measurement range, the present invention can achieve high-sensitivity and long-term accurate three-axis omnidirectional magnetic field measurement at different measurement ranges.

Description

Technical Field

[0001] This application belongs to the technical field of magnetic field measurement and sensing, and particularly relates to a self-calibrating three-axis atomic magnetometer for realizing integrated vector and scalar measurement. Background Technique

[0002] The magnetic field is a basic physical field existing in space. High-precision magnetic field measurement technology can be applied to fields such as biomedicine, geophysics research, and space exploration. For various space magnetic field detection applications, magnetometers should meet requirements such as a large dynamic range, three-axis omnidirectionality, adapting to the requirements of space exploration tasks, and long-term accuracy and sensitivity. Currently, the most widely used magnetometer in space exploration is the fluxgate magnetometer. However, due to the limitations of its measurement principle, the reference and gain of the fluxgate magnetometer will drift over time and with the environment. In space applications, a scalar atomic magnetometer is often used to calibrate it. However, the sensitivity and accuracy indicators of measuring the magnetic field in this way will be limited by the collaborative detection indicators of the two payloads, and due to the distance between the fluxgate and the scalar atomic magnetometer, a gradient effect will occur during the calibration process.

[0003] The three-axis helium atomic vector magnetometer carried on the Pioneer 10 detector launched by NASA in the United States can achieve a sensitivity of 10 pT / Hz in a small range 1 / 2 , and an accuracy of 25 pT. The helium vector magnetometer developed by Bertrand F of the CEA-Leti laboratory in France has achieved a three-axis sensitivity of 170 fT / Hz 1 / 2 , and a large dynamic range of ±70000 nT. The latest commercial three-axis vector atomic magnetometer product of QuSpin Company in the United States, based on a rubidium atomic cell, has achieved a three-axis sensitivity of less than 23 fT / Hz in the range of ±5 nT 1 / 2 , but no indicators have been given for the accuracy of this product.

[0004] Beihang University in China has achieved high-sensitivity measurement of 30 fT / Hz in three axes by using two orthogonal laser beams to pump and detect rubidium atoms 1 / 2 , and the dynamic range is ±150 nT (Yeguang Yan, Jixi Lu, et al., Opt.Express 2022, 30: 18300-18309). The single-beam vector SERF atomic magnetometer proposed by the 13th Institute of the 9th Academy of Aerospace Science and Technology in China has achieved a transverse magnetic field sensitivity of 350 fT / Hz and 3 pT / Hz 1 / 2 in the dynamic range of 60000 nT 1 / 2Longitudinal magnetic field sensitivity (J. Li, Y. Deng, X. Wang, et al., IEEE Sensors Journal, 2021, 21: 23943-23948). The sensitivity of the newly proposed three-axis helium atomic vector magnetometer at Peking University can reach 150 fT / Hz 1 / 2 (Wang BW, Peng X, et al., PHYSICAL REVIEW A, 2022, 106: 063102). The University of Science and Technology of China disclosed a high-sensitivity and high-stability cryogenic vector atomic magnetometer and method for weak magnetism in a Chinese patent with the publication number CN115561682A, which improved the sensitivity of the magnetometer by placing two pairs of mutually perpendicular multi-reflection cavities in the atomic cell.

[0005] Although existing vector atomic magnetometers have been widely used, there is no magnetometer that can be switched to the Mz or CPT scalar measurement mode, nor is there a vector self-calibration function. Summary of the Invention

[0006] The purpose of this application is to provide a large-dynamic-range self-calibrating three-axis atomic magnetometer that realizes integrated vector and scalar measurements, so as to meet the requirements for large dynamic range, high sensitivity, high accuracy, and long-term stable measurement of magnetic field vector information in space magnetic field detection, and can realize in-orbit self-calibration of the magnetometer.

[0007] To achieve the above purpose, this application proposes a self-calibrating three-axis atomic magnetometer that realizes integrated vector and scalar measurements. The atomic magnetometer includes a sensor probe, an electronics box, an input optical fiber, and an output optical fiber; among them,

[0008] The sensor probe includes: a first fiber optic coupler, a polarizer, a quarter-wave plate, an alkali metal atomic cell, and a second fiber optic coupler arranged in sequence; non-magnetic heating components are provided at both ends of the alkali metal atomic cell; XYZ three-axis magnetic field generating coils are arranged around the alkali metal atomic cell;

[0009] The XYZ three-axis magnetic field generating coils include XYZ-axis magnetic field compensation coils, XYZ-axis magnetic field modulation coils, and an X-axis nuclear magnetic resonance modulation coil;

[0010] The electronics box includes: a laser generating unit, a photoelectric detection unit, a temperature control circuit, a three-axis coil driving unit, a signal conditioning unit, a three-axis modulation compensation circuit, and a laser control circuit;

[0011] The laser control circuit controls the laser generating unit to generate a single beam of laser, which enters the sensor probe through the input optical fiber; in the sensor probe, the single beam of laser sequentially passes through the first fiber optic coupler, the polarizer, and the quarter-wave plate, acts on the alkali metal atomic gas cell to resonate with the atoms, and then passes through the second fiber optic coupler and the output optical fiber to reach the photoelectric detection unit;

[0012] The photoelectric detection unit converts the optical signal into an electrical signal, which is filtered and amplified by the signal conditioning unit and then enters the three-axis modulation compensation circuit for phase-locked processing. The error signal is obtained by using the phase-sensitive detection technology, and the compensation signal is generated through PID control. The modulation signal and the compensation signal are respectively applied to the XYZ-axis magnetic field modulation coil and the XYZ-axis magnetic field compensation coil by the three-axis coil driving unit; the three-axis modulation compensation circuit controls the X-axis nuclear magnetic resonance modulation coil to output the nuclear magnetic resonance modulation magnetic field required for the Mz working mode by using the three-axis coil driving unit;

[0013] The temperature control circuit is connected to the non-magnetic heating component in the sensor probe through a shielded wire to achieve stable control of the temperature of the alkali metal atomic gas cell.

[0014] As an improvement of the above atomic magnetometer, the laser generating unit uses a VCSEL semiconductor laser as the light source.

[0015] As an improvement of the above atomic magnetometer, the XYZ-axis magnetic field modulation coil and the XYZ-axis magnetic field compensation coil are used to generate modulation and compensation magnetic fields to achieve three-axis magnetic field vector measurement;

[0016] The X-axis nuclear magnetic resonance modulation coil is used to generate the nuclear magnetic resonance modulation magnetic field in the Mz scalar working mode to achieve magnetic field scalar measurement.

[0017] As an improvement of the above atomic magnetometer, the 3.4 GHz microwave signal in the laser control circuit is used to modulate the laser frequency. By using the CPT effect of the microwave-modulated laser interacting with alkali metal atoms, the alkali metal atoms are trapped in the dark state, and the magnetometer works in the CPT mode to achieve omnidirectional measurement of the scalar magnetic field.

[0018] As an improvement of the above atomic magnetometer, the three-axis modulation compensation circuit is used to control the output of three-axis modulation, compensation signals and X-axis nuclear magnetic resonance modulation signals, so that the magnetometer works in the vector measurement or Mz scalar measurement mode; it is also used to respectively pass current signals through the three-axis coils according to the measurement results of the scalar magnetic field, calculate the corresponding relationship between the magnetic field change value and the current value, and realize the self-calibration of the three-axis vector measurement of the magnetometer.

[0019] As an improvement of the above-mentioned atomic magnetometer, the self-calibration for realizing the three-axis vector measurement of the magnetometer includes: based on the accurate zero-point characteristic of the vector atomic magnetometer, passing positive and negative current signals into the three-axis coils respectively, and calibrating the coil scale factor to realize the self-calibration of the three-axis vector measurement of the magnetometer; the coil scale factor is:

[0020]

[0021] where I is the current value passed into the coil in the corresponding axial direction; B 0 is the total magnetic field value without adding current signal; B 1 is the total magnetic field value when a positive current signal is added axially; B 2 is the total magnetic field value when a negative current signal is added axially.

[0022] As an improvement of the above-mentioned atomic magnetometer, the resistance value of the three-axis coil driving unit includes multiple gears, enabling the atomic magnetometer to work in multiple range modes.

[0023] As an improvement of the above-mentioned atomic magnetometer, the range of the atomic magnetometer includes multiple gears from the μT level to the nT level.

[0024] Compared with the prior art, the advantages of this application are as follows:

[0025] 1. The present invention uses a VCSEL semiconductor laser as the light source and adopts all-fiber transmission, with a single-beam optical system and a single gas cell structure, featuring simplicity, reliability, and long lifespan.

[0026] 2. By applying a modulation magnetic field, the measurement of the three-axis omnidirectional magnetic field is realized, with high sensitivity and high accuracy, enabling stable long-term accurate measurement.

[0027] 3. An additional set of Mz scalar nuclear magnetic resonance modulation coils is provided in the X-axis direction to generate a nuclear magnetic resonance modulation signal, enabling the magnetometer to work in the Mz mode to complete the scalar measurement of the total magnetic field. It can also utilize the interaction between the laser and alkali metal atoms to enable the magnetometer to work in the CPT (Coherent Population Trapping) mode to complete the omnidirectional scalar measurement of the total magnetic field. Utilizing this high-accuracy scalar measurement ability can realize the self-calibration of the three-axis vector measurement of the magnetometer, having potential for space applications.

[0028] 4. By changing the current values passed into the three-axis coils, different range switching can be achieved (from a large range of 10 μT level to multiple gears of a small range of several nT), thereby covering the large dynamic measurement range of the earth's magnetic field and the weak magnetic field intensity in deep space. Description of the Drawings

[0029] Figure 1 The figure shows a schematic diagram of the overall structure of a self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement;

[0030] Figure 2 The figure shows a schematic diagram of the structure of the sensor probe;

[0031] Figure 3 The figure shows an implementation diagram of a self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement;

[0032] Figure 4 The figure shows the resonance curve of the magnetometer in the vector small - range mode of a self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement;

[0033] Figure 5 The figure shows the step - experiment result diagram of the magnetometer in the vector small - range mode of a self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement;

[0034] Figure 6 The figure shows the resonance curve of the magnetometer in the vector large - range mode of a self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement;

[0035] Figure 7 The figure shows the Mz resonance curve of the magnetometer in the scalar mode of a self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement;

[0036] Figure 8 The figure shows a schematic diagram of the time - sharing injection of bipolar symmetric square - wave current signals into the three - axis coil of a self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement;

[0037] Figure 9 The figure shows a schematic diagram of calculating the coil coefficient. Detailed Embodiment

[0038] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings.

[0039] A self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement provided by the present application can switch between scalar and vector measurement modes to realize self - calibration of the three - axis vector of the magnetometer. Using a single magnetometer to replace the aerospace magnetometer payload composed of a flux - gate magnetometer and a scalar atomic magnetometer can eliminate the gradient effect caused by the distance between the vector and scalar magnetometers. The present invention has a large dynamic range, high sensitivity, high accuracy, and can work stably for a long time, having practical significance and good application prospects.

[0040] A self - calibrating three - axis atomic magnetometer for realizing integrated vector and scalar measurement may include a sensor probe 4, an electronics box 1, an input optical fiber 3, and an output optical fiber 14.

[0041] The sensor probe 4 may include a first fiber optic coupling head 5, a second fiber optic coupling head 13, polarizers 7, 1 / 4 wave plates 8, an alkali metal atomic vapor cell 9, a non - magnetic heating component 10, and XYZ three - axis magnetic field generating coils.

[0042] The XYZ three - axis magnetic field generating coils may include XYZ - axis magnetic field compensation coils 26, XYZ - axis magnetic field modulation coils 27, and an X - axis nuclear magnetic resonance modulation coil 28. Among them, the direction of the laser emitted from the first fiber optic coupling head 5 is the Z - axis direction, and the X and Y axes are perpendicular to the Z - axis.

[0043] The electronics box 1 may include a laser generating unit 2, a main control circuit board 21, a photoelectric detection unit 15, a temperature control circuit 11, and a three - axis coil driving unit 25. The main control circuit board 21 may include a laser control circuit 24, a signal conditioning unit 22, and a three - axis modulation and compensation circuit 23.

[0044] The laser generating unit 2 may include a laser 16, a depolarizer 17, and a third fiber optic coupling head 18. Among them, the laser generating unit 2 may use a VCSEL semiconductor laser as a light source to generate a single laser beam 6. The laser control circuit 24 may be connected to the laser 16 in the laser generating unit 2 to control the current input to the laser 16 and the laser temperature, so that the laser 16 generates a single - beam polarized laser with a required stable wavelength. Optionally, a depolarizer 17 may be provided after the laser 16 to eliminate polarization to suppress the change in light intensity after the laser enters the optical fiber. The stable laser generated by the laser 16 may enter the sensor probe 4 through the third fiber optic coupling head 18 and the input optical fiber 3.

[0045] In the sensor probe 4, the laser beam is received by the first fiber optic coupling head 5, becomes circularly polarized light through the polarizer 7 and the 1 / 4 wave plate 8, acts on the alkali metal atomic vapor cell 9 containing alkali metal atomic vapor and buffer quenching gas, and resonates with the alkali metal atoms. The laser beam passing through the alkali metal atomic vapor cell 9 enters the photoelectric detection unit 15 in the electronics box 1 through the second fiber optic coupling head 13 and the output optical fiber 14.

[0046] The photoelectric detection unit 15 may include a fourth fiber optic coupler 19 and a photodiode 20. The laser signal may enter the photodiode 20 through the fourth fiber optic coupler 19 and be converted into an electrical signal and then input into the signal conditioning unit 22. The signal conditioning unit 22 may filter and amplify the electrical signal and then input it into the three-axis modulation compensation circuit 23. The three-axis modulation compensation circuit 23 may perform phase-locked processing on the input electrical signal, obtain an error signal using the phase-sensitive detection technique, and calculate a magnetic field compensation signal according to PID. Meanwhile, the three-axis modulation compensation circuit 23 may apply a modulation magnetic field to the alkali metal atomic gas cell 9 by outputting modulation signals in three axes. The compensation signal and the modulation signal may be respectively applied to the XYZ-axis magnetic field compensation coil 26 and the XYZ-axis magnetic field modulation coil 27 of the three-axis coil in the sensor probe 4 through the three-axis coil driving unit 25, thereby realizing the modulation and compensation of the magnetic field in the gas cell and obtaining the three-axis vector information of the external magnetic field. The function of the three-axis coil driving unit 25 is to convert the voltage signal output by the three-axis modulation compensation circuit 23 into a current signal and apply it to the three-axis coil.

[0047] The three-axis modulation compensation circuit 23 may also control the X-axis nuclear magnetic resonance modulation coil 28 to output the nuclear magnetic resonance modulation magnetic field required for the Mz working mode, realizing high-accuracy scalar measurement of the magnetic field. When a current signal is passed through any other coil, the corresponding relationship between the magnetic field change value and the passed current value may be obtained by calculating the total magnetic field change amount, realizing the calibration of the three-axis vector coil coefficient.

[0048] The temperature control circuit 11 in the electronics box 1 may be connected to the non-magnetic heating component 10 and the thermistor 29 fixed around the alkali metal atomic gas cell 9 through a shielded wire, heat the alkali metal atomic gas cell 9, and stably control the temperature at a set value.

[0049] The present invention is based on the zero-field resonance principle and the magnetic field bias compensation zero-field technology. It uses circularly polarized light to pump alkali metal atoms to achieve the spin polarization of alkali metal atoms. After the atoms are polarized and reach a stable state, when the external magnetic field is zero, the absorption of laser light by the alkali metal atom cell disappears, and the light intensity transmitted through the alkali metal atom cell reaches the maximum. When the external magnetic field is non-zero and near the zero field, the absorption of light by the alkali metal atom cell increases, and the light intensity transmitted through the alkali metal atom cell decreases. Therefore, the magnetic field information to be measured can be obtained by detecting the optical signal transmitted through the alkali metal atom cell. The optical signal carrying the magnetic field information is converted into an electrical signal by the photoelectric detection unit 15, and after passing through the signal conditioning unit 22, it enters the three-axis modulation compensation circuit 23 to calculate and output a compensation signal, which is applied to the three-axis coil through the three-axis coil driving unit 25. The generated compensation magnetic field is superimposed on the external magnetic field to make the magnetic field in the atom cell zero, and the light intensity transmitted through the alkali metal atom cell reaches the maximum. The magnitude and direction of the external magnetic field can be obtained by calculating the magnitudes of the compensation magnetic fields in the three axes. When the resistance value of the three-axis coil driving unit 25 is changed, the modulation and compensation driving current intensities in the three-axis coil change, and different magnetic field intensity sensitive ranges and magnetic compensation closed-loop working ranges can be realized, thereby realizing magnetic measurements with different dynamic ranges. The three-axis modulation compensation circuit 23 can output modulation signals in the three axes to realize the measurement of the three-axis omnidirectional magnetic field vector. By changing the current value applied to the three-axis coil, different range switches can be achieved (from a large range of 10 μT magnitude to multiple small ranges of a few nT), so as to cover the large dynamic measurement range of the earth's magnetic field and the weak magnetic field intensity in deep space.

[0050] Based on the Bloch equation of the spin magnetic moment of alkali metal atoms driven by a radio frequency field, the present invention can make the magnetometer work in the Mz scalar mode by applying an oscillating signal to the magnetic resonance modulation coil on the X axis. In addition, the present invention can also start the 3.4 GHz microwave signal in the laser control circuit 24 to modulate the laser frequency, and utilize the CPT effect (Coherent Population Trapping) of the interaction between the microwave-modulated laser and alkali metal atoms to trap the alkali metal atoms into the dark state, making the magnetometer work in the CPT mode to complete the omnidirectional measurement of the scalar magnetic field. The relationship between the measured total magnetic field change value and the current value passed through the coil in a certain axis can be used to obtain the scale factor of the coil in this axis as follows:

[0051]

[0052] where I is the current value passed through the corresponding axial coil, B0 is the external magnetic field without current; B1 is the total magnetic field when a positive current signal is passed through the axis; B2 is the total magnetic field when a negative current signal is passed through the axis. Similarly, the scale factors of the other two axial coils can be obtained.

[0053] In the method for measuring the current passing through a three-axis coil by quickly switching it, the scale factors of the three-axis coils can be calculated. Since the inherent zero point of the vector atomic magnetometer is accurate and the zero point accuracy does not require on-orbit calibration, the self-calibration of the three-axis vector measurement of the magnetometer is achieved by completing the scale factor calibration.

[0054] Embodiment 1

[0055] As Figure 1 shown is a schematic structural diagram of a self-calibrating three-axis atomic magnetometer for realizing integrated vector and scalar measurement. The laser control unit 24 can control the VCSEL semiconductor laser to generate a single-beam polarized light with a stable wavelength, which enters the sensor probe 4 through the third fiber optic coupler 18 and the input fiber 3. The single-beam polarized light can be converted into circularly polarized light by the linear polarizer 7 and the quarter-wave plate 8 and act on the alkali metal atomic vapor cell 9. The alkali metal atomic vapor cell 9 contains alkali metal atomic vapor and buffer quenching gas. The non-magnetic heating component 10 located outside the cell can perform AC pulse heating on the cell under the control of the temperature control circuit 11. The circularly polarized light resonates with the alkali metal atoms, and the optical signal carrying the external magnetic field information can enter the photoelectric detection unit 15 through the second fiber optic coupler 13 and the output fiber 14. The photoelectric diode 20 converts the optical signal into an electrical signal. The electrical signal can enter the three-axis modulation compensation circuit 23 after passing through the signal conditioning unit 22, and the compensation signal is obtained through PID calculation and output to the three-axis coil driving unit 25, which is converted into a current signal and applied to the three-axis coil outside the alkali metal atomic vapor cell 9 to generate a compensation magnetic field. At the same time, the three-axis modulation compensation circuit 23 can apply a modulation magnetic field to the alkali metal atomic vapor cell 9 through the three-axis output modulation signal. The compensation magnetic field and the external magnetic field are superimposed and cancelled out, so that the magnetometer operates in a zero magnetic field environment. The vector data of the external magnetic field can be obtained by accurately measuring the magnitude of the three-axis compensation magnetic field.

[0056] Figure 2 It is a block diagram of the sensor probe structure of the three-axis vector atomic magnetometer. The sensor probe 4 can include an alkali metal atomic vapor cell 9, XYZ-axis magnetic field compensation coils 26, XYZ-axis magnetic field modulation coils 27, an X-axis nuclear magnetic resonance modulation coil 28, a linear polarizer 7, a quarter-wave plate 8, a first fiber optic coupler 5, and a second fiber optic coupler 13.

[0057] Figure 3 It is a schematic diagram of the implementation of the three-axis vector atomic magnetometer. The three-axis vector atomic magnetometer can include an electronics box 1, a sensor probe 4, an input fiber 3, and an output fiber 14.

[0058] Please refer to Figure 2 、 Figure 3, the temperature control circuit 11 in the electronics box 1 can control the non-magnetic heating component 10 in the sensor probe 4 to heat the alkali metal atomic gas cell 9. The temperature of the alkali metal atomic gas cell 9 can be detected by a non-magnetic thermistor 29, and the obtained voltage analog signal is converted into a digital signal through ADC sampling and enters the FPGA integrated circuit. The output voltage signal is calculated through the PID algorithm to control the non-magnetic heating component 10 to heat the alkali metal atomic gas cell 9 to keep the gas cell temperature constant.

[0059] Furthermore, the laser 16 in the laser generating unit 2 can use a VCSEL semiconductor laser as the light source, and a depolarizer 17 can be selectively used to eliminate polarization. The temperature control loop and current control loop in the laser control unit 24 can control and lock the temperature and drive current of the laser. The laser generating unit 2 can generate a stable single-beam polarized light of 795 nm and enter the sensor probe 4 through the third fiber optic coupler 18 and the input fiber 3.

[0060] The sensor probe 4 can include an alkali metal atomic gas cell 9, a non-magnetic heating component 10, XYZ-axis magnetic field compensation coils 26, XYZ-axis magnetic field modulation coils 27, and an X-axis nuclear magnetic resonance modulation coil 28. In this example, the alkali metal atomic gas cell 9 is filled with 87 Rb atoms, and at the same time, nitrogen, argon, neon, etc. are filled as buffer gases. The first fiber optic coupler 5 receives the laser signal, which is converted into circularly polarized light through the linear polarizer 7 and the quarter-wave plate 8 and resonates with the 87 Rb atoms in the alkali metal atomic gas cell 9. The optical signal carrying the magnetic field information enters the electronics box 1 through the second fiber optic coupler 13 and the output fiber 14.

[0061] Subsequently, the photodiode 20 in the electronics box 1 converts the optical signal into an electrical signal. After being filtered and amplified by the signal conditioning unit 22, it is sampled by ADC and enters the laser control unit 24 and the three-axis modulation compensation circuit 23 based on FPGA, which are respectively used to lock the laser wavelength and calculate and output the compensation magnetic field. Further, the three-axis modulation compensation circuit 23 generates a modulation signal for applying a modulation magnetic field and as a reference signal of the lock-in amplifier to demodulate the input signal. According to the zero-field resonance principle, when the external magnetic field is zero, the optical intensity of the laser signal passing through the gas cell reaches the maximum value. Manually change the external magnetic field and scan near the zero field. The signal passing through the alkali metal atomic gas cell 9 presents a Lorentzian line shape. After modulation and demodulation, a zero-field resonance signal with high signal-to-noise ratio is obtained as Figure 4 shown. The line width of the resonance curve is about 18 nT. The error signal obtained after demodulation is subjected to PID calculation to obtain a compensation signal, which is superimposed on the modulation signal and output. After V-I conversion, it is applied to the XYZ-axis magnetic field modulation coils 27 and XYZ-axis magnetic field compensation coils 26 in the sensor probe to generate modulation and compensation magnetic fields. The test results of the step experiment by manually changing the external magnetic field value are as Figure 5As shown, each time the magnetic field value is changed to 3 nT, the result shows that the output compensated magnetic field value can stably follow the change of the external magnetic field value and compensate for the external magnetic field. By measuring the compensated magnetic field, the present invention can accurately and stably measure the external magnetic field.

[0062] In this embodiment, the three-axis modulation compensation circuit 23 outputs sine modulation signals in three axial directions, which are respectively applied to the XYZ-axis magnetic field modulation coils 27 through the V-I conversion circuit to generate a modulation magnetic field. Using the above zero-field resonance principle and bias compensation zero-field technology, the electrical signal output by the photodiode 20 is demodulated, and the external magnetic field is compensated by the three-axis modulation compensation circuit 23. By accurately measuring the compensated magnetic field generated by the three-axis compensation coils, the magnetic field magnitudes in three axial directions can be obtained.

[0063] Preferably, by changing the magnitudes of the modulation and compensation drive current intensities in the XYZ-axis magnetic field modulation coils 27 and the XYZ-axis magnetic field compensation coils 26, the range switching of the magnetometer can be realized. As Figure 6 is the result of the three-axis zero-field resonance signal obtained by the present invention in the large-range mode. A zero-field resonance signal with a high signal-to-noise ratio can be obtained in a 100,000 nT dynamic range.

[0064] Embodiment 2

[0065] Please refer to Figure 2 、 Figure 3 , the three-axis modulation compensation circuit 23 controls the X-axis nuclear magnetic resonance modulation coil 28 to output a nuclear magnetic resonance modulation magnetic field signal, so that the magnetometer operates in the Mz scalar mode to complete the scalar measurement of the magnetic field. The nuclear magnetic resonance modulation magnetic field is generated by the X-axis nuclear magnetic resonance modulation coil 28, and the external magnetic field is compensated by the Z-axis compensation coil to measure the magnitude of the external total magnetic field. Figure 7 is the high signal-to-noise ratio resonance signal curve obtained by the present invention in the scalar Mz mode, and the line width is 677 Hz. A sine wave or square wave current signal is passed through any axial coil, and the change value of the external total magnetic field is measured by the Mz mode magnetometer. By calculating the proportional relationship between the magnetic field change value and the passed current signal, the coefficient of the selected coil can be calibrated, and the calibration process for other coils is the same. In this embodiment, bipolar symmetric square wave current signals are respectively passed through the three-axis coils, as Figure 8 shown, the coils through which the positive and negative current signals are passed are switched. According to Figure 9 shown, let B x , B y , B z be the projection values of the external magnetic field B0 in three axial directions without current, respectively, then there are:

[0066]

[0067] Let the total magnetic fields when positive and negative current signals are passed through the z-axis be B 1_z 、B2_z When a current signal is passed through the z-axis, the bias magnetic field generated is B off_z Then there is:

[0068]

[0069]

[0070] From the above formula, the scale factor k of the z-axis coil can be obtained z as:

[0071]

[0072] Similarly, the scale factors of the x-axis and y-axis coils can be obtained as follows:

[0073]

[0074]

[0075] The inherent zero point of the vector atomic magnetometer is accurate, and the zero point accuracy does not require on-orbit calibration. Therefore, completing the scale factor calibration realizes the self-calibration of the three-axis vector measurement of the magnetometer.

[0076] It should be noted that the Mz magnetometer has an equatorial dead zone, so it is required that the external magnetic field works under the condition of no dead zone for on-orbit self-calibration. The present invention can also configure the magnetometer in the CPT omnidirectional mode to realize the omnidirectional measurement of the total magnetic field. The self-calibration of the three-axis vector measurement of the magnetometer in the CPT mode is the same as that in the Mz mode.

[0077] By quickly switching the coil through which the current signal is passed, the present invention can complete the rapid calibration of the three-axis vector coil in a slowly changing external magnetic field environment. When the present invention works in a vector large dynamic range mode such as the Earth's magnetic field or the Jupiter system magnetic field, a small sine or square wave signal is selected for self-calibration of the three-axis vector coil. In a weak magnetic field environment such as deep space, it is switched to a small range mode and a large signal is selected for self-calibration of the three-axis vector coil.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit them. Although the present application has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present application does not depart from the spirit and scope of the technical solutions of the present application, and they should all be covered by the scope of the claims of the present application.

Claims

1. A self-calibrating three-axis atomic magnetometer for integrated vector and scalar measurement, characterized in that: The atomic magnetometer comprises a sensor probe, an electronics box, an input optical fiber and an output optical fiber; wherein, The sensor probe comprises: a first optical fiber coupling head, a polarizing plate, a quarter wave plate, an alkali metal atom gas chamber, and a second optical fiber coupling head arranged in sequence; non-magnetic heating components are arranged at both ends of the alkali metal atom gas chamber; an XYZ three-axis magnetic field generating coil is arranged around the alkali metal atom gas chamber; The XYZ three-axis magnetic field generating coil includes an XYZ-axis magnetic field compensation coil, an XYZ-axis magnetic field modulation coil and an X-axis magnetic resonance modulation coil; The electronic box includes: a laser generating unit, a photoelectric detection unit, a temperature control circuit, a three-axis coil driving unit, a signal conditioning unit, a three-axis modulation compensation circuit and a laser control circuit; The laser control circuit controls the laser generating unit to generate a single laser beam which enters the sensor probe through the input optical fiber; in the sensor probe, the single laser beam sequentially passes through the first optical fiber coupling head, polarizing plate and 1 / 4 wave plate to act on the alkali metal atom gas chamber to resonate with the atoms, and then passes through the second optical fiber coupling head and output optical fiber to reach the photoelectric detection unit; The photoelectric detection unit converts the optical signal into an electrical signal, which is filtered and amplified by the signal conditioning unit and then enters the three-axis modulation compensation circuit for phase-locked processing. The error signal is obtained by using the phase-sensitive detection technology, and the compensation signal is generated by PID control. The modulation signal and the compensation signal are respectively applied to the XYZ-axis magnetic field modulation coil and the XYZ-axis magnetic field compensation coil by using the three-axis coil driving unit; the three-axis modulation compensation circuit controls the X-axis magnetic resonance modulation coil to output the magnetic resonance modulation magnetic field required for the Mz working mode by using the three-axis coil driving unit; The temperature control circuit controls the non-magnetic heating component in the sensor probe through a shielded line to achieve stable control of the temperature of the alkali metal atom gas chamber.

2. The self-calibrated three-axis atomic magnetometer for realizing integrated vector and scalar measurement according to claim 1, characterized in that: The laser generating unit uses a VCSEL semiconductor laser as a light source.

3. The self-calibrated three-axis atomic magnetometer for realizing integrated vector and scalar measurement according to claim 1, characterized in that: The XYZ-axis magnetic field modulation coil and the XYZ-axis magnetic field compensation coil are used to generate modulation and compensation magnetic fields to achieve three-axis magnetic field vector measurement; The X-axis magnetic resonance modulation coil is used to generate a magnetic resonance modulation magnetic field in an Mz scalar working mode to achieve scalar magnetic field measurement.

4. The self-calibrated three-axis atomic magnetometer for realizing integrated vector and scalar measurement according to claim 1, characterized in that: The 3.4 GHz microwave signal in the laser control circuit realizes the modulation of the laser frequency, and utilizes the CPT effect of the interaction between the microwave-modulated laser and the alkali metal atoms to trap the alkali metal atoms in the dark state, so that the magnetometer works in the CPT mode to realize the omnidirectional measurement of the scalar magnetic field.

5. The self-calibrated three-axis atomic magnetometer for realizing integrated vector and scalar measurement according to claim 1, characterized in that: The three-axis modulation compensation circuit is used to control the output of three-axis modulation, compensation signals and X-axis magnetic resonance modulation signals, so that the magnetometer works in vector measurement or Mz scalar measurement mode; it is also used to pass current signals into the three-axis coils respectively according to the measurement results of the scalar magnetic field, calculate the corresponding relationship between the magnetic field change value and the current value, and realize the self-calibration of the three-axis vector measurement of the magnetometer.

6. The self-calibrated three-axis atomic magnetometer for realizing integrated vector and scalar measurement according to claim 3, characterized in that: The self-calibration of the three-axis vector measurement of the magnetometer includes: based on the zero point accuracy characteristics of the vector atomic magnetometer, positive and negative current signals are respectively introduced into the three-axis coils, and the calibration of the coil scale factor is completed to realize the self-calibration of the three-axis vector measurement of the magnetometer; the coil scale factor is: ； in, I is the current value flowing into the corresponding axial coil; B 0 is the total magnetic field value when no current signal is added; B 1 The total magnetic field value when a positive current signal is added to the axial direction; B 2 The total magnetic field value when a negative current signal is added to the axial direction.

7. The self-calibrated three-axis atomic magnetometer for realizing integrated vector and scalar measurement according to claim 1, characterized in that: The resistance value of the three-axis coil driving unit includes multiple gears, so that the atomic magnetometer works in multiple range modes.

8. The self-calibrated three-axis atomic magnetometer for realizing integrated vector and scalar measurement according to claim 7, characterized in that: The measurement range of the atomic magnetometer includes multiple gears from μT level to nT level.

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