A system for measuring plane vector magnetic field

Abstract

The embodiment of the present application provides a system for measuring a plane vector magnetic field, including: an optical path module with a laser, a fiber circulator, a long-pass filter and a photodetector, a microwave module with a microwave source, a microwave amplifier and a microwave isolator, a signal processing module with a phase-locked amplifier, a magnetic generating device, and an integrated platform device including a diamond NV color center sensor, a microwave antenna and two pairs of magnetic flux concentrators; when working, the laser emits a laser output to the fiber circulator and then incident on the diamond NV color center sensor to excite the diamond NV color center, and at the same time, the microwave source outputs a modulated microwave that is linearly amplified by the microwave amplifier and transmitted again by the microwave isolator to control the electronic spin state of the diamond NV color center, so that the diamond NV color center outputs a microwave-controlled fluorescence, and the fluorescence carries information of the plane vector magnetic field. The system can realize a high-isolation and high-sensitivity plane vector magnetic field measurement method.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of optical fiber magnetic field sensing, and in particular, to a system for measuring a plane vector magnetic field. Background Art

[0002] Magnetic field is a basic and very important physical quantity in nature, and is closely related to human production and life. Traditional vector magnetic field measurement sensors basically require multiple sensors to be applied in three axes for superposition to achieve vector magnetic field measurement. Due to manufacturing and installation defects, the non-orthogonal error of magnetic vector measurement will inevitably increase.

[0003] At present, the magnetic field measurement structure based on nitrogen-vacancy center (NV color center) has insufficient sensitivity and resolution, and cannot directly measure weak geomagnetic field in actual use, and has defects in vector magnetic field measurement. At the same time, the existing magnetic field measurement structure can only achieve magnetic field amplification in a specific direction, and cannot guarantee high detection sensitivity for vector magnetic field in any direction. Therefore, a new magnetic field measurement system is needed that can achieve high detection sensitivity for vector magnetic field in any direction. Summary of the invention

[0004] The embodiment of the present application proposes a system for measuring plane vector magnetic fields, which can realize high-sensitivity plane vector magnetic field measurement with low crosstalk rate in XY axes. The system is simple and easy to use during the test process, has high sensitivity, and can perform real-time detection of plane vector magnetic fields.

[0005] In a first aspect, an embodiment of the present application provides a system for measuring a plane vector magnetic field, comprising: an optical path module, a microwave module, a signal processing module, a magnetic generating device, and an integrated stage device;

[0006] The optical path module includes a laser, an optical fiber circulator, a long-pass filter and a photodetector;

[0007] The microwave module comprises a microwave source, a microwave amplifier and a microwave isolator; the microwave amplifier is used to linearly amplify the microwave signal emitted by the microwave source, and the microwave isolator is arranged between the microwave source and the microwave amplifier to prevent the reflected microwave energy from damaging the microwave source;

[0008] The signal processing module includes a lock-in amplifier and a computer device connected to the lock-in amplifier;

[0009] The magnetic generating device comprises a bias magnetic field generating device and a gradient test magnetic field generating device;

[0010] The integrated platform device includes a diamond NV color center sensor, a microwave antenna, and two pairs of magnetic flux concentrators; the diamond NV color center sensor is made by coupling diamond and plastic optical fiber, and the two pairs of magnetic flux concentrators are respectively placed in the X and Y axes;

[0011] When the system is working, the laser is used to emit a laser with a wavelength of a first value, the laser is output to the target port of the optical fiber circulator through optical fiber coupling, and then incident on the diamond probe of the diamond NV color center sensor to excite the diamond NV color center to generate fluorescence, and at the same time, one end of the microwave source outputs a modulated microwave that is linearly amplified by the microwave amplifier and retransmitted by the microwave isolator, and the modulated microwave is used to regulate the electronic spin state of the diamond NV color center, so that the diamond NV color center outputs fluorescence with microwave regulation, and the fluorescence carries the size and direction of the plane vector magnetic field information; the fluorescence passes through the optical fiber circulator, and is filtered out by a long-pass filter with a cut-off frequency of the second value to remove the optical signal with a wavelength of the first value, and then the photodetector converts the filtered fluorescence into an electrical signal, which is transmitted to the phase-locked amplifier for signal collection and analysis; wherein the other end of the microwave source outputs a reference signal with the same phase as the microwave signal, which is input into the phase-locked amplifier, so that the phase-locked amplifier extracts a valid test signal from the electrical signal transmitted by the photodetector according to the reference signal, and transmits the valid test signal to the computer device for signal processing.

[0012] Optionally, the embodiment of the present application further includes:

[0013] When the system is working, the alignment orientation of the magnetic flux concentrator and the diamond NV color center sensor is optimized so that the NV1 crystal axis and the NV2 crystal axis of the diamond NV color center sensor are in the XOZ plane, the angle between the X axis and the NV1 crystal axis is the same as the angle between the X axis and the NV2 crystal axis, and the NV3 crystal axis and the NV4 crystal axis of the diamond NV color center sensor are in the YOZ plane, and the angle between the Y axis and the NV3 crystal axis is the same as the angle between the Y axis and the NV4 crystal axis;

[0014] The bias magnetic field generating device is used to apply a bias magnetic field to generate two pairs of resonance valleys, and according to the optimized alignment orientation, the two pairs of resonance valleys respond to the X-axis and Y-axis magnetic fields respectively to achieve the isolation measurement of the magnetic components in the X-axis and Y-axis directions;

[0015] The gradient test magnetic field generating device is used to apply the test magnetic field on the X and Y axes respectively, the magnetoelectric conversion coefficient is measured according to the drift of the resonance spectrum line, the 60s signal value is recorded as the voltage noise, and the sensitivity of the X and Y axes is measured.

[0016] Optionally, in the embodiment of the present application, isolation means that when a magnetic field is applied along a certain axis, the corresponding resonant frequency in other axes does not respond; when a magnetic field B is applied in any direction of the X-axis or Y-axis, F V is the resonant frequency drift in the direction parallel to the magnetic field B, F H is the resonant frequency drift in the direction perpendicular to the axis of the magnetic field B; the calculation formula for the isolation degree IS of the magnetic component in the X-axis or Y-axis direction is as follows:

[0017]

[0018] Optionally, in an embodiment of the present application, the method for preparing the diamond NV color center sensor includes:

[0019] Take a plastic optical fiber of a preset length, use optical fiber pliers to peel off the coating layer of the outer layer of the plastic optical fiber, wipe off the remaining debris with cotton soaked in alcohol, and use an optical fiber cutter to cut off the excess optical fiber to obtain a target optical fiber with a flat optical fiber end face;

[0020] 0.5×0.5×0.5mm 3 Place a diamond of the specified specification on a clean glass slide with the polished surface of the diamond facing upwards, and fix it on the stage of the preset microscope system;

[0021] The target optical fiber is dipped in UV glue and fixed on the optical fiber fixture of the microscope system, and the displacement platform of the microscope system is used to move the center of the target optical fiber and the center of the diamond to align and couple the two to obtain a diamond NV color center sensor;

[0022] When it is determined that the ultraviolet lamp irradiates the diamond NV color center sensor for more than a preset time and the UV glue is completely cured, it is determined that the preparation of the diamond NV color center sensor is completed.

[0023] Optionally, in an embodiment of the present application, the direction of the bias magnetic field is in the XOY plane, and the ratio of the magnetic field components of the X-axis to the Y-axis is close to 10:1.

[0024] Optionally, in an embodiment of the present application, the microwave antenna is composed of an SMA radio frequency interface, a 0.2 mm copper wire, and a 50Ω load resistor.

[0025] Optionally, in an embodiment of the present application, the magnetic flux concentrator is a triangular patch with an inner width of 0.25 mm, an outer width of 30 mm, and a height of 0.5 mm.

[0026] Optionally, in an embodiment of the present application, the integrated platform device is provided with a first clamp for adjusting the position of the magnetic flux concentrator, and is also provided with a groove larger than the size of the first clamp, and the groove is used to adjust the distance of the magnetic flux concentrator during the use of the integrated platform device.

[0027] Optionally, in an embodiment of the present application, the integrated platform device is provided with diagonally distributed triangular grooves, and the triangular grooves are used to fix the microwave antenna; the microwave antenna is installed below the sensing area of ​​the magnetic flux concentrator.

[0028] Optionally, in an embodiment of the present application, the integrated stage device is provided with a second fixture and a circular slide rail for adjusting the position of the diamond NV color center sensor.

[0029] Optionally, in an embodiment of the present application, the sensitivity testing method includes:

[0030] Using the gradient test magnetic field generating device to apply five sets of gradient magnetic fields, and respectively record the corresponding phase-locked optical detection magnetic resonance spectra;

[0031] According to the phase-locked light detection magnetic resonance spectrum, five data points are found when the phase-locked signal changes the most with the magnetic field when the microwave frequency is fixed, and a linear fit is performed to obtain the magnetoelectric conversion coefficient, which is a key parameter to characterize the amplification factor of the magnetic flux concentrator;

[0032] The microwave frequency was fixed at the non-resonance point, the sampling rate was set to 1000 Hz, and the 60 s signal value was recorded as the voltage noise;

[0033] Taking the ratio between the voltage noise and the magneto-electric conversion coefficient as a magnetic field noise signal;

[0034] The magnetic field noise signal is subjected to Fourier transform to obtain the magnetic noise spectrum density, and the signal value at 1 Hz is taken as the sensitivity.

[0035] The embodiment of the present application discloses a system for measuring a plane vector magnetic field, which is based on a diamond NV color center enhanced by two pairs of magnetic flux concentrators, and can realize a high-isolation and high-sensitivity plane vector magnetic field measurement method. By optimizing the alignment orientation of the magnetic flux concentrator and the diamond NV color center, high-isolation measurement of the magnetic components in the X and Y directions can be achieved, and the sensitivity is enhanced by the magnetic amplification effect of the magnetic flux concentrator. First, the orientation of the diamond NV color center is calibrated and aligned with the preset target coordinate system to realize a simple, efficient and high-isolation plane vector magnetic field measurement method. Secondly, two pairs of magnetic flux concentrators are introduced in the X and Y axes respectively, and the axial magnetic field enhancement characteristics of the magnetic flux concentrator are used to realize a high-isolation, high-sensitivity plane vector magnetic field measurement. The plane vector magnetic field measurement method that can be performed by the system is simple, efficient, and highly sensitive, and can realize real-time plane vector magnetic field measurement with high isolation. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1A schematic diagram of the structure of a system for measuring a plane vector magnetic field provided by an embodiment of the present invention;

[0037] Figure 2 A schematic diagram of a system for measuring a plane vector magnetic field provided by an embodiment of the present invention;

[0038] Figure 3 Schematic diagram of a plane vector magnetic field test theory provided for an embodiment of the present invention: (a) relative orientation of the NV color center crystal axis and a preset coordinate system, (b) ODMR spectrum line;

[0039] Figure 4 A schematic diagram of a plane vector magnetic field test result provided by an embodiment of the present invention: (a) a phase-locked ODMR spectrum line is measured by applying gradient magnetic fields on the X-axis and Y-axis, (b) a spectrum line of the resonance frequency of the two axes changing with the magnetic field when a gradient magnetic field is applied on the X-axis, (c) a spectrum line of the resonance frequency of the two axes changing with the magnetic field when a gradient magnetic field is applied on the Y-axis;

[0040] Figure 5 A schematic diagram of simulation results of the magnetic field amplification factor of a magnetic flux concentrator provided by an embodiment of the present invention varying with the magnetic field angle;

[0041] Figure 6 A schematic diagram of simulation results of patch flux concentrators of different sizes provided by an embodiment of the present invention;

[0042] Figure 7 Schematic diagram of an integrated stage device provided by an embodiment of the present invention: (a) a design diagram of the integrated stage device, (b) a physical diagram of the integrated stage device loaded with two pairs of magnetic flux concentrators;

[0043] Figure 8 A schematic diagram of the sensitivity test results of an X-axis provided in an embodiment of the present invention: (a) using patch flux concentrators of different sizes, applying a gradient magnetic field to measure the phase-locked ODMR spectrum, (b) the change of the phase-locked signal with the magnetic field, (c) the magnetic noise spectrum density diagram obtained by the test;

[0044] Fig. 9 A schematic diagram of the sensitivity test results of the Y-axis provided in an embodiment of the present invention: (a) using patch flux concentrators of different sizes, applying a gradient magnetic field to measure the phase-locked ODMR spectrum; (b) the change of the phase-locked signal with the change of the magnetic field; (c) the magnetic noise spectrum density diagram obtained by the test. DETAILED DESCRIPTION

[0045] The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. It should also be noted that, for ease of description, only parts related to the present invention, rather than all structures, are shown in the accompanying drawings.

[0046] In the embodiment of the present application, the diamond NV color center can realize the detection of vector magnetic field by a single sensor based on its unique crystal structure. The vector magnetic field sensor based on the diamond NV color center has a natural advantage in measuring vector magnetic field. In addition, as an emerging magnetic field-sensitive quantum system, the diamond NV color center has the advantages of small size, room temperature operation, high sensitivity, etc. Coupling the diamond NV color center with the optical fiber opens up a new way for the realization of miniaturized and highly sensitive vector magnetic field sensors.

[0047] NV color center is the most common point defect structure in diamond. Its structural composition is that a nitrogen atom replaces a carbon atom and forms a carbon vacancy in the adjacent position. NV color center can use ODMR detection method to measure magnetic field based on quantum Zeeman effect. The principle of measuring vector magnetic field of diamond NV color center is based on its internal lattice structure. The crystal axis direction of NV color center is along the

[111] crystal direction. In the NV ensemble, there are four possible NV axis directions:

[111] , [-1-11], [-11-1] and [1-1-1], and the angle between any two axes is 109°. The magnetic field can be measured at NV color center on each axis. Therefore, the vector magnetic field can be projected on four axes to reproduce the measurement of the vector magnetic field.

[0048] Magnetic flux concentrator (MFC) refers to a special material made of some high magnetic permeability alloys, which has an enhanced effect on the magnetic field in the area. This is a very effective way to improve magnetic sensitivity. G is the magnification of the magnetic flux concentrator, which is the ratio of the magnetic field intensity B after the magnetic flux concentrator is amplified to the initial magnetic field intensity B0. The size of the magnetic flux concentrator and the magnetic permeability of the material will affect its magnification.

[0049] Figure 1 A structural schematic diagram of a system for measuring a plane vector magnetic field provided in an embodiment of the present invention. This embodiment is applicable to the situation of real-time measurement of a plane vector magnetic field. The system may include: an optical path module, a microwave module, a signal processing module, a magnetic generating device, and an integrated platform device.

[0050] Among them, the optical path module includes a laser, a fiber circulator, a long-pass filter and a photodetector.

[0051] A microwave module includes a microwave source, a microwave amplifier, and a microwave isolator; the microwave amplifier is connected to the microwave source, and the microwave amplifier is used to linearly amplify the microwave signal emitted by the microwave source; the microwave isolator can be arranged between the microwave source and the microwave amplifier, and is respectively connected to the microwave source and the microwave amplifier to prevent the reflected microwave energy from damaging the microwave source; further, the microwave isolator can include two, one is arranged between the microwave source and the microwave amplifier, and the other can be arranged between the microwave amplifier and the integrated stage device, and is respectively connected to the microwave amplifier and the integrated stage device. In one example, the SMB100A microwave signal generator of Rohde & Schwarz can be used as a microwave source, which can realize amplitude modulation, frequency modulation, phase modulation and pulse modulation; the ZHL-16W-43 power amplifier of MINI-CIRCUITS can be selected as a microwave amplifier.

[0052] The signal processing module includes a lock-in amplifier and a computer device connected to the lock-in amplifier.

[0053] The magnetic generating device comprises a bias magnetic field generating device and a gradient test magnetic field generating device.

[0054] The integrated platform device includes a diamond NV color center sensor, a microwave antenna, and two pairs of magnetic flux concentrators; the diamond NV color center sensor is made by coupling diamond and plastic optical fiber, and the two pairs of magnetic flux concentrators are respectively placed in the X and Y axes.

[0055] When the system is working, the laser is used to emit a laser with a wavelength of a first value, and the laser is output to the target port of the fiber circulator through optical fiber coupling, and then incident on the diamond probe of the diamond NV color center sensor to excite the diamond NV color center to produce fluorescence. At the same time, one end of the microwave source outputs a modulated microwave that is linearly amplified by a microwave amplifier and transmitted again by a microwave isolator. The modulated microwave is used to control the electronic spin state of the diamond NV color center, so that the diamond NV color center outputs microwave-controlled fluorescence, and the fluorescence carries the size and direction information of the plane vector magnetic field; the fluorescence passes through the fiber circulator, and is filtered out by a long-pass filter with a cutoff frequency of a second value to remove the optical signal with a wavelength of the first value, and then the photodetector converts the filtered fluorescence into an electrical signal, which is transmitted to the phase-locked amplifier for signal collection and analysis; wherein, the other end of the microwave source outputs a reference signal with the same phase as the microwave signal, which is input into the phase-locked amplifier, so that the phase-locked amplifier extracts the effective test signal from the electrical signal transmitted by the photodetector according to the reference signal, and transmits the effective test signal to the computer device for signal processing. In a reference example, Figure 2 A schematic diagram of a system for measuring a planar vector magnetic field.

[0056] In one example of the embodiment of the present application, the microwave antenna is composed of an SMA radio frequency interface, a 0.2 mm copper wire, and a 50 Ω load resistor. Due to the two signals generated at both ends of the microwave source, one is the output modulated microwave for regulating the electronic spin state of the diamond NV color center, and the other is the output for directly inputting the reference signal of the phase-locked amplifier; in the transmission path of the output modulated microwave, the microwave signal linearly amplified by the microwave amplifier is transmitted to the copper wire with a diameter of 0.2 mm through the RF radio frequency connecting line and the SMA radio frequency interface, and a 50 Ω load resistor is welded at the end of the copper wire to achieve impedance matching, thereby reducing microwave reflection; wherein, the copper wire can be attached to the surface of the diamond probe of the diamond NV color center sensor to avoid microwave loss during the transmission process.

[0057] In one embodiment, when the system is working, it is necessary to optimize the alignment orientation of the magnetic flux concentrator and the diamond NV color center sensor, so that the NV1 crystal axis and NV2 crystal axis of the diamond NV color center sensor are in the XOZ plane, the angle between the X axis and the NV1 crystal axis is the same as the angle between the X axis and the NV2 crystal axis, the NV3 crystal axis and NV4 crystal axis of the diamond NV color center sensor are in the YOZ plane, and the angle between the Y axis and the NV3 crystal axis is the same as the angle between the Y axis and the NV4 crystal axis; a bias magnetic field generator is used to apply a bias magnetic field to generate two pairs of resonance valleys, and according to the optimized alignment orientation, the two pairs of resonance valleys respond to the X and Y axis magnetic fields respectively to achieve the isolation measurement of the magnetic components in the X and Y axis directions; a gradient test magnetic field generator is used to apply a test magnetic field on the X and Y axes respectively, and the magnetoelectric conversion coefficient is measured according to the drift of the resonance spectrum line, and the 60s signal value is recorded as the voltage noise to measure the sensitivity in the X and Y axis directions. In a specific example, the direction of the bias magnetic field is in the XOY plane, and the ratio of the magnetic field components of the X-axis to the Y-axis is close to 10:1.

[0058] See also Figure 3 As shown, in the specific implementation process of the above embodiment, the NV1 and NV2 crystal axes of the diamond NV color center are placed in the XOZ plane, and the two NV axes are symmetrical about the Z axis, as shown in FIG. Figure 3 As shown in (a), since the Y axis is perpendicular to the XOZ plane, the Y axis magnetic field B Y Perpendicular to the axial direction of NV1 and NV2, based on Hamiltonian theory, it can be known that the drift of the resonance frequency is caused by the axial magnetic field. Therefore, the crystal axis of NV1 and NV2 is perpendicular to B. Y No response. The X-axis has the same angle with the NV1 and NV2 crystal axes, and the X-axis magnetic field B X The magnetic field projection in both crystal axis directions is cos35°·B X , resulting in the same splitting value of the two axial resonance frequencies, overlapping into a resonance valley, which is Figure 3(b) The blue line part shows that the splitting value of the resonance valley is only affected by the X-axis magnetic field. At this time, NV3 and NV4 are in the YOZ plane. Similarly, it can be known that the crystal axes of NV3 and NV4 are close to B. X No response, B Y When the two axis components are the same, they overlap to form a pair of resonance valleys. Figure 3 (b) The red line part shows that the splitting value of the resonance valley is only affected by the Y-axis magnetic field. This realizes a high-isolation planar vector magnetic field measurement method based on diamond NV color centers.

[0059] In the embodiment of the present application, isolation means that when a magnetic field is applied along a certain axis, the corresponding resonant frequency in other axes does not respond; when a magnetic field B is applied in any direction of the X-axis or Y-axis, F V is the resonant frequency drift in the direction parallel to the magnetic field B, F H is the resonant frequency drift in the direction perpendicular to the axis of the magnetic field B; the calculation formula for the isolation degree IS of the magnetic component in the X-axis or Y-axis direction is as follows:

[0060]

[0061] In a specific example of the embodiment of the present application, Figure 4 This is the isolation test result. The test process is as follows:

[0062] The diamond NV color center sensor is fixed in the three-axis coil, and the orientation of the diamond NV crystal axis is adjusted to match the preset theoretical model. A permanent magnet is used to apply a bias magnetic field of about 5mT. In the XOZ plane, the axial magnetic field component of the NV crystal axis is large, resulting in a large splitting value. The NV crystal axes in the YOZ plane are all perpendicular to the magnetic field direction, but there is still a small splitting. The main reason is that the internal stress and the axial direction are not completely aligned, resulting in a certain magnetic field component in the X-axis. Fix the bias magnetic field, and use the three-axis Helmholtz coil to apply gradient test magnetic fields to the X and Y axes respectively. At this time, the two pairs of resonance valleys drift, such as Figure 4 (a) shows that the test magnetic field ΔB is applied on the X-axis. X When the test magnetic field ΔB is applied to the Y axis, the splitting value of the inner resonance valley gradually increases, and the resonance valleys along the Y axis basically overlap, with only a slight amplitude change. Y When , only the Y-axis resonance valley has obvious drift.

[0063] When a 42-212μT (42μT gradient) magnetic field is applied on the X-axis, the resonant frequency drift of the outer spectral line is 46GHz / T, and the resonant frequency drift of the inner spectral line is 0.8GHz / T. Figure 4 As shown in (b), the calculated isolation degree in the X-axis direction is IS X= 98.3%. When a 43-215μT (43μT gradient) magnetic field is applied to the Y axis, the resonant frequency drift of the inner spectrum is 45GHz / T, and the resonant frequency drift of the inner spectrum is 0.6GHz / T. Figure 4 As shown in (c), the isolation IS in the Y-axis direction is calculated. Y =98.7%. Based on the above experimental results, it is verified that the plane vector magnetic field testing method performed by the system provided in the embodiment of the present application can indeed achieve a plane vector magnetic field test with high isolation.

[0064] In another example, to explore the axial isolation of a pair of flux concentrators, Comsol software can be used to perform simulation tests, which may include:

[0065] The magnitude of the magnetic field is fixed, and the direction of the magnetic field is changed to explore the relationship between the magnetic field amplification factor and the rotation angle. The simulation results are as follows: Figure 5 As shown, the X-axis magnetic field B X The magnification factor is in a cosine relationship with the rotation angle, and when the rotation angle is 90°, that is, the magnetic field direction is perpendicular to the magnetic flux concentrator, the magnification factor is approximately 0, which means that the magnetic flux concentrator will only increase the axial magnetic field and has no amplification effect on the vertical axial magnetic field.

[0066] In an embodiment of the present application, the sensitivity testing method may include the following steps:

[0067] Five sets of gradient magnetic fields are applied by using a gradient test magnetic field generator, and the corresponding phase-locked optical detection magnetic resonance spectra are recorded respectively;

[0068] According to the phase-locked optical detection magnetic resonance spectrum (i.e., phase-locked ODMR spectrum), five data points are found when the phase-locked signal changes the most with the magnetic field when the microwave frequency is fixed, and a linear fit is performed to obtain the magnetoelectric conversion coefficient, which is a key parameter to characterize the amplification factor of the magnetic flux concentrator;

[0069] The microwave frequency was fixed at the non-resonance point, the sampling rate was set to 1000 Hz, and the 60 s signal value was recorded as the voltage noise;

[0070] The ratio between the voltage noise and the magneto-electric conversion coefficient is taken as the magnetic field noise signal;

[0071] The magnetic field noise signal is subjected to Fourier transform to obtain the magnetic noise spectral density, and the signal value at 1 Hz is taken as the sensitivity.

[0072] In one embodiment of the present application, Figure 6The simulation results of magnetic flux concentrators of different sizes are shown in Figure 2. As the size of the magnetic flux concentrator increases, its magnification also gradually increases. However, a larger magnetic flux concentrator size will also increase the volume of the sensor. For comprehensive considerations, a magnetic flux concentrator with a maximum size of 30 mm can be selected. When its thickness is 0.5 mm, its magnetic magnification is about 30. Therefore, in a preferred embodiment of the present application, the magnetic flux concentrator can be a triangular patch with an inner width of 0.25 mm, an outer width of 30 mm, and a height (thickness) of 0.5 mm.

[0073] In one embodiment, the integrated stage device is provided with a first fixture for adjusting the position of the magnetic flux concentrator, and is also provided with a groove larger than the first fixture, the groove being used to adjust the distance of the magnetic flux concentrator during use of the integrated stage device.

[0074] In one embodiment, the integrated platform device is provided with diagonally distributed triangular grooves, which are used to fix the microwave antenna; the microwave antenna is installed below the sensing area of ​​the magnetic flux concentrator.

[0075] In one embodiment, the integrated stage apparatus is provided with a second fixture and a circular slide rail for adjusting the position of the diamond NV color center sensor.

[0076] In a reference example, Figure 7 The integrated platform device designed and the physical picture of the double-pair magnetic flux concentrator are shown. In order to facilitate the adjustment of the position of the magnetic flux concentrator, a magnetic flux concentrator fixture is designed, and a groove slightly larger than the fixture size by 1mm is designed on the integrated platform. The distance of the magnetic flux concentrator can be adjusted forward and backward during use to achieve the ideal spacing and obtain the optimal magnetic field enhancement effect. There is a groove slide rail at the tail end of the fixture. After the adjustment is completed, the magnetic flux concentrator can be fixed by tightening the M3 copper screw. A triangular groove with a depth of 3mm is designed on the side diagonal of the platform to facilitate the fixing of the copper wire in the microwave antenna. The two ends can fix the SMA interface and 50Ω load impedance respectively. And at this depth, the microwave antenna is below the sensing area of ​​the magnetic flux concentrator, which is more conducive to the adjustment of the diamond. The other side diagonal of the platform is a diamond sensor fixture. A circular slide rail is set at the connection with the platform, which can realize the horizontal 360° adjustment of the diamond position to achieve axial alignment. A section of optical fiber ferrule extends from the lower end, so that the optical fiber faces vertically downward, which enhances the stability of the optical fiber.

[0077] In any embodiment of the present application, the method for preparing a diamond NV color center sensor includes:

[0078] Take a plastic optical fiber of a preset length, use optical fiber pliers to peel off the outer coating of the plastic optical fiber, wipe off the remaining debris with cotton soaked in alcohol, and use an optical fiber cutter to cut off the excess optical fiber to obtain a target optical fiber with a flat optical fiber end face;

[0079] 0.5×0.5×0.5mm 3 Place a diamond of the specified specification on a clean glass slide with the polished surface of the diamond facing upwards, and fix it on the stage of the preset microscope system;

[0080] The target optical fiber is dipped in UV glue and fixed on the optical fiber fixture of the microscope system. The displacement platform of the microscope system is used to move the center of the target optical fiber and the center of the diamond to align and couple the two to obtain a diamond NV color center sensor.

[0081] When it is determined that the ultraviolet lamp irradiates the diamond NV color center sensor for more than a preset time and the UV glue is completely cured, it is determined that the preparation of the diamond NV color center sensor is completed.

[0082] In a reference example, to evaluate the performance of a diamond NV color center sensor, a sensitivity test was performed as follows:

[0083] Use a three-axis coil to apply five sets of gradient magnetic fields and record the corresponding spectral lines. Find the five data points where the phase-locked signal changes the most with the magnetic field when the microwave frequency is fixed, perform a linear fit on them, and obtain the magnetoelectric conversion coefficient R f The microwave frequency was fixed at the non-resonance point, the sampling rate was set to 1000 Hz, and the 60 s signal value was recorded as the voltage noise S v . Voltage noise S v and magnetoelectric conversion coefficient R f The ratio is the magnetic field noise signal, and the Fourier transform is performed to obtain the magnetic noise spectrum density, and the signal value at 1Hz is taken as the sensitivity. Based on the above sensitivity test method, the sensitivity of sensors using patch flux concentrators of different sizes is tested and compared with those without flux concentrators. Figure 8 The sensitivity test results of the X-axis are as follows: A gradient magnetic field is applied on the X-axis using a three-axis Helmholtz coil, such as Figure 8 As shown in (a), when no flux concentrator is applied, the spectrum line has obvious drift only when the magnetic field gradient is 57.3μT. After the flux concentrator is applied, the spectrum line has obvious drift when the magnetic field gradient is 5.7μT. As the size of the flux concentrator increases, the frequency drift gradually increases. Figure 8 (b) is the magnetoelectric coefficient obtained by fitting. When a 30 mm magnetic flux concentrator is applied, the magnetoelectric coefficient is 776.96 V / T, which is 9.5 times higher than 81.97 V / T without a magnetic flux concentrator. Figure 8 From the sensitivity test results in (c), we can see that the magnetic field sensitivity of the X-axis is increased from 173.39 to 17.28nT / Hz1 / 2@1Hz, which is an order of magnitude improvement. Fig. 9The sensitivity test results of the Y axis are as follows: a gradient magnetic field is applied on the Y axis using a three-axis Helmholtz coil. Fig. 9 (a) shows the spectral line drift after the magnetic flux concentrator is applied, which is close to the situation on the X axis, indicating that the magnetic flux concentrator does amplify the test magnetic field. Fig. 9 (b) It can be seen that when the 30mm magnetic flux concentrator is applied, the magnetoelectric coefficient is 877.09V / T, which is 10.3 times higher than 85.47V / T without the magnetic flux concentrator. The magnetic field sensitivity of the Y axis is increased from 166.34 to 15.31nT / Hz1 / 2@1Hz, as shown in Fig. 9 (c) The magnetic field sensitivity in both XY axes is improved by an order of magnitude.

[0084] It should be noted that, for the sake of simplicity, the method embodiments are described as a series of action combinations, but those skilled in the art should be aware that the embodiments of the present invention are not limited by the order of the actions described, because according to the embodiments of the present invention, certain steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also be aware that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily required by the embodiments of the present invention.

[0085] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A system for measuring a plane vector magnetic field, characterized in that: include: Optical path module, microwave module, signal processing module, magnetic generating device and integrated platform device; The optical path module includes a laser, an optical fiber circulator, a long-pass filter and a photodetector; The microwave module comprises a microwave source, a microwave amplifier and a microwave isolator; the microwave amplifier is used to linearly amplify the microwave signal emitted by the microwave source, and the microwave isolator is arranged between the microwave source and the microwave amplifier to prevent the reflected microwave energy from damaging the microwave source; The signal processing module includes a lock-in amplifier and a computer device connected to the lock-in amplifier; The magnetic generating device comprises a bias magnetic field generating device and a gradient test magnetic field generating device; The integrated platform device includes a diamond NV color center sensor, a microwave antenna, and two pairs of magnetic flux concentrators; the diamond NV color center sensor is made by coupling diamond and plastic optical fiber, and the two pairs of magnetic flux concentrators are respectively placed in the X and Y axes; When the system is working, the alignment orientation of the magnetic flux concentrator and the diamond NV color center sensor is optimized so that the NV1 crystal axis and the NV2 crystal axis of the diamond NV color center sensor are in the XOZ plane, the angle between the X axis and the NV1 crystal axis is the same as the angle between the X axis and the NV2 crystal axis, and the NV3 crystal axis and the NV4 crystal axis of the diamond NV color center sensor are in the YOZ plane, the angle between the Y axis and the NV3 crystal axis is the same as the angle between the Y axis and the NV4 crystal axis; When the system is working, the laser is used to emit a laser with a wavelength of a first value, the laser is output to the target port of the optical fiber circulator through optical fiber coupling, and then incident on the diamond probe of the diamond NV color center sensor to excite the diamond NV color center to generate fluorescence, and at the same time, one end of the microwave source outputs a modulated microwave that is linearly amplified by the microwave amplifier and retransmitted by the microwave isolator, the modulated microwave is used to regulate the electronic spin state of the diamond NV color center, so that the diamond NV color center outputs fluorescence with microwave regulation, and the fluorescence carries the size and direction of the plane vector magnetic field information; the fluorescence passes through the optical fiber circulator, and is filtered out by a long-pass filter with a cut-off frequency of the second value to remove the optical signal with a wavelength of the first value, and then the photodetector converts the filtered fluorescence into an electrical signal, which is transmitted to the phase-locked amplifier for signal collection and analysis; wherein the other end of the microwave source outputs a reference signal with the same phase as the microwave signal, which is input into the phase-locked amplifier, so that the phase-locked amplifier extracts a valid test signal from the electrical signal transmitted by the photodetector according to the reference signal, and transmits the valid test signal to the computer device for signal processing.

2. The system according to claim 1, characterized in that Also includes: When the system is working, the bias magnetic field generating device is used to apply a bias magnetic field to generate two pairs of resonance valleys. According to the optimized alignment orientation, the two pairs of resonance valleys respond to the X-axis and Y-axis magnetic fields respectively to achieve isolation measurement of magnetic components in the X-axis and Y-axis directions. The gradient test magnetic field generating device is used to apply the test magnetic field on the X and Y axes respectively, the magnetoelectric conversion coefficient is measured according to the drift of the resonance spectrum line, the 60s signal value is recorded as the voltage noise, and the sensitivity of the X and Y axes is measured.

3. The system according to claim 1, characterized in that The method for preparing the diamond NV color center sensor comprises: Take a plastic optical fiber of a preset length, use optical fiber pliers to peel off the coating layer of the outer layer of the plastic optical fiber, wipe off the remaining debris with cotton soaked in alcohol, and use an optical fiber cutter to cut off the excess optical fiber to obtain a target optical fiber with a flat optical fiber end face; 0.5×0.5×0.5 mm 3 Place a diamond of the specified specification on a clean glass slide with the polished surface of the diamond facing upwards, and fix it on the stage of the preset microscope system; The target optical fiber is dipped in UV glue and fixed on the optical fiber fixture of the microscope system, and the displacement platform of the microscope system is used to move the center of the target optical fiber and the center of the diamond to align and couple the two to obtain a diamond NV color center sensor; When it is determined that the ultraviolet lamp irradiates the diamond NV color center sensor for more than a preset time and the UV glue is completely cured, it is determined that the preparation of the diamond NV color center sensor is completed.

4. The system according to claim 2, characterized in that The direction of the bias magnetic field is in the XOY plane, and the ratio of the magnetic field components of the X-axis to the Y-axis is close to 10:

1.

5. The system according to claim 1, characterized in that The microwave antenna is composed of an SMA radio frequency interface, a 0.2 mm copper wire, and a 50Ω load resistor.

6. The system according to claim 1, characterized in that The magnetic flux concentrator is a triangular patch with an inner width of 0.25 mm, an outer width of 30 mm, and a height of 0.5 mm.

7. The system according to claim 1, characterized in that The integrated stage device is provided with a first clamp for adjusting the position of the magnetic flux concentrator, and is also provided with a groove larger than the first clamp, wherein the groove is used to adjust the distance of the magnetic flux concentrator during use of the integrated stage device.

8. The system according to claim 1, characterized in that The integrated platform device is provided with diagonally distributed triangular grooves, and the triangular grooves are used to fix the microwave antenna; the microwave antenna is installed below the sensing area of ​​the magnetic flux concentrator.

9. The system according to claim 1, characterized in that The integrated stage device is provided with a second fixture and a circular slide rail for adjusting the position of the diamond NV color center sensor.

10. The system according to claim 2, characterized in that The sensitivity test method includes: Using the gradient test magnetic field generating device to apply five sets of gradient magnetic fields, and respectively record the corresponding phase-locked optical detection magnetic resonance spectra; According to the phase-locked light detection magnetic resonance spectrum, five data points are found when the phase-locked signal changes the most with the magnetic field when the microwave frequency is fixed, and a linear fit is performed to obtain the magnetoelectric conversion coefficient, which is a key parameter to characterize the amplification factor of the magnetic flux concentrator; The microwave frequency was fixed at the non-resonance point, the sampling rate was set to 1000 Hz, and the 60 s signal value was recorded as the voltage noise; Taking the ratio between the voltage noise and the magneto-electric conversion coefficient as a magnetic field noise signal; The magnetic field noise signal is subjected to Fourier transform to obtain the magnetic noise spectrum density, and the signal value at 1 Hz is taken as the sensitivity.

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