A current sensor based on a solid-state spin system

Abstract

The application discloses a current sensor based on a solid-state spin system. The current sensor comprises four-way probes and a data processing unit. Each way probe comprises a magnetic sensitive unit, a microwave unit, an optical unit, two optical detection units and a lock-in amplifier. The optical unit comprises a laser generator and a lens group for dividing the laser emitted by the laser generator into two optical paths of the main path and the reference path. The magnetic sensitive unit comprises a diamond sample containing NV color centers in four main axis directions. The microwave unit comprises a wave source, a radiation structure, a waveguide structure and a wave source control system. The two optical detection units respectively convert the optical signals on the reference path and the fluorescence into corresponding electrical signals for demodulation by the lock-in amplifier. The application realizes four-axis closed-loop measurement by modifying the microwave frequency, and the directions of the four axes are determined by the crystal direction of the diamond single crystal, so that the current sensor has better stability and orthogonality compared with a three-axis TMR magnetic sensor composed of three TMR magnetic sensors.

Description

Technical Field

[0001] This invention relates to a current sensor in the field of current measurement technology, and more particularly to a current sensor based on a solid-state spin system. Background Technology

[0002] Electric current is one of the seven fundamental physical quantities, and the need for current measurement permeates all aspects of scientific research, production, and daily life. Current sensors can be mainly divided into two categories based on their operating principles. The first category is shunt sensors based on Ohm's law. These sensors can achieve high accuracy and sensitivity, but they introduce energy loss, making them unsuitable for applications such as long-term current monitoring and beam current measurement. Furthermore, in low-current measurement scenarios, these sensors suffer from insufficient dynamic range, hindering their application in applications such as value transfer.

[0003] The second type of current sensor measures the magnetic field generated by the current. These include traditional current transformers, zero-flux current transformers, fiber optic current transformers, magnetic sensor arrays, and Rogowski coils. Each of these current sensors has its limitations: traditional current transformers and Rogowski coils can only be used for AC measurement; zero-flux current transformers have complex installation issues; fiber optic current transformers have low sensitivity, and their complex optical path structure limits their reliability; the use of polarization-maintaining and circularity-maintaining fibers increases their cost. Current sensors based on magnetic sensor arrays offer better flexibility compared to the previous types, enabling non-contact current measurement. However, their technology is currently immature, resulting in insufficient resistance to external interference, and both accuracy when measuring large currents and sensitivity when measuring small currents need improvement. Open-ended Rogowski coils are currently commonly used for online calibration of current transformers. However, open-ended Rogowski coils suffer from insufficient portability, high installation accuracy requirements, and the limitation to AC current measurement. This restricts current online calibration technology to AC, and the calibration process requires manual operation under live voltage, posing a safety hazard. The defects of open-ended Rogowski coils result in insufficient accuracy, versatility, and flexibility in the transfer of values ​​during line calibration.

[0004] In summary, existing current sensors have the following drawbacks: First, online calibration technology cannot calibrate DC current signals, and there are safety risks associated with live operation. Second, their sensitivity for non-contact measurement of small currents is insufficient. Third, current mainstream current sensors for high-voltage DC currents suffer from high cost, complex structure, and low reliability. Fourth, those based on large-resistance shunts have insufficient dynamic range for small current measurements.

[0005] For example, reference 1, "Crosstalk Analysis and Current Measurement Correction in Circular 3D Magnetic Sensor Arrays," uses a triaxial TMR magnetic sensor to simultaneously measure current and eliminate the influence of installation errors and edge currents on the measurement results. However, the triaxial tunnel magnetoresistive (TMR) magnetic sensor used in this technology cannot achieve simultaneous closed-loop measurement of all three axes, thus limiting its measurement range to the hundred-ampere level and its accuracy to within 1%.

[0006] For example, reference 2, "A FluxGate based approach for Ion Beam current measurement in Electron Cyclotron Resonance Ionsources beamline," utilizes a fluxgate magnetometer in conjunction with a special flux focusing system to measure small currents. However, fluxgate magnetometers suffer from the problem of miniaturizing the magnetic sensing element. Even with a specially designed flux focuser, it is still impossible to measure currents of 1 microamp or less when using a fluxgate magnetometer to measure small currents.

[0007] For example, reference 3, "Current sensor based on diamond nitrogen-vacancy colorcenter," utilizes an NV colorcenter ensemble magnetometer, combined with a special flux focusing system, to measure five 10m long wires, achieving current measurements in the range of 1A-10A. However, this flux focusing system cannot achieve the sensitivity superior to other current sensor systems, and it lacks resistance to external interference. Furthermore, its structural flexibility is insufficient, making it difficult to apply in practical scenarios. Summary of the Invention

[0008] To address the shortcomings of current online calibration technologies and to overcome the challenges of non-contact low-current sensors, this invention provides a current sensor based on a solid-state spin system.

[0009] This invention is achieved using the following technical solution: a current sensor based on a solid-state spin system, comprising:

[0010] Four probes are arranged around the object under test for quadriaxial magnetic measurements to obtain sixteen resonant microwave frequencies. Each probe includes a magnetic sensing unit, a microwave unit, an optical unit, two photodetector units, and a lock-in amplifier. The optical unit includes a laser generator and a lens group for splitting the laser emitted by the laser generator into two optical paths: a main path and a reference path. The magnetic sensing unit includes a diamond sample containing NV color centers along the four principal axes. The microwave unit includes a wave source, a radiation structure, a waveguide structure, and a wave source control system. The magnetic sensing unit is placed at the center of the radiation structure, and the wave source control system controls the wave source to modulate four microwaves onto the four resonant microwave frequencies of the diamond sample. The NV color centers along the main axis are individually controlled, and the four microwave paths are kept in resonance with the corresponding NV color centers along the main axis. Under the illumination of the laser on the main path, the corresponding NV color centers emit fluorescence. A waveguide structure is used to collect the fluorescence, and two optical detection units are used to convert the optical signals from the laser on the reference path and the fluorescence into corresponding electrical signals. A lock-in amplifier is used to demodulate the two electrical signals and perform PID processing on the demodulation results to obtain four resonant microwave frequencies for the NV color centers along the four main axis directions. The wave source control system is also used to achieve closed-loop negative feedback of the microwave frequencies while modulating the four microwave paths according to the microwave frequencies.

[0011] The data processing unit is used to perform inverse decomposition on the sixteen resonant microwave frequencies to obtain the current magnitude of the object under test.

[0012] As a further improvement to the above scheme, the four probes are arranged in an array, and the object to be tested passes through the middle of the array.

[0013] As a further improvement to the above scheme, the laser generator is a laser diode or a laser.

[0014] As a further improvement to the above scheme, the lens group includes a beam-splitting lens and a focusing lens; the beam-splitting lens splits the laser beam to form the main path and the reference path laser beam; the focusing lens focuses the laser beam of the main path onto the magnetically sensitive unit.

[0015] Furthermore, the lens group also includes two half-wave plates, both of which are located on the main path and are respectively located in front of and behind the beam splitter.

[0016] As a further improvement to the above scheme, the optical unit also includes a filter located on the main road and between the waveguide structure and the second optical detection unit.

[0017] As a further improvement to the above scheme, each optical detection unit employs a laser diode.

[0018] As a further improvement to the above scheme, the microwave unit also includes a power amplifier. The four microwaves modulated by the wave source are amplified by the power amplifier before they can manipulate the NV color centers in the four principal axis directions of the diamond sample.

[0019] The present invention also provides another current sensor based on a solid-state spin system, which includes:

[0020] The gain unit, which is a magnetic ring, is used to achieve high-sensitivity current measurement of the object under test when the object under test is wrapped around the ring-shaped gain unit in the form of a coil or when it passes through the gain unit in the form of a straight wire / beam.

[0021] A probe, clamped within the gain unit, comprises: a magnetic sensing unit, a microwave unit, an optical unit, a waveguide structure, two photodetector units, and a lock-in amplifier. The magnetic sensing unit includes a diamond sample containing NV color centers along four principal axes. The optical unit includes a laser generator and a lens group for splitting the laser emitted by the laser generator into two optical paths: a main path and a reference path. The microwave unit includes a wave source, a radiation structure, and a wave source control system. The magnetic sensing unit is positioned at the center of the radiation structure, and the wave source control system controls the wave source to modulate at least one microwave path onto at least one NV color center along a principal axis of the diamond sample. The system is manipulated so that the microwave is kept in resonance with the NV color centers in the corresponding principal axis direction, and the corresponding NV color centers emit fluorescence under the illumination of the laser on the principal axis. A waveguide structure is used to collect the fluorescence. Two optical detection units are used to convert the optical signals from the laser on the reference path and the fluorescence into corresponding electrical signals. A lock-in amplifier is used to demodulate the two electrical signals and perform PID processing on the demodulation results to obtain the resonant microwave frequency of at least one NV color center in the principal axis direction. The wave source control system is also used to achieve closed-loop negative feedback of the microwave frequency while modulating the microwave.

[0022] The data processing unit is used to perform inverse decomposition on the four resonant microwave frequencies to obtain the current magnitude of the object under test.

[0023] As a further improvement to the above scheme, the laser generator is a laser diode or a laser.

[0024] As a further improvement to the above scheme, the lens group includes a beam-splitting lens and a focusing lens; the beam-splitting lens splits the laser beam to form the main path and the reference path laser beam; the focusing lens focuses the laser beam of the main path onto the magnetically sensitive unit.

[0025] Furthermore, the lens group also includes two half-wave plates, both of which are located on the main path and are respectively located in front of and behind the beam splitter.

[0026] As a further improvement to the above scheme, the optical unit also includes a filter located on the main road and between the waveguide structure and the second optical detection unit.

[0027] As a further improvement to the above scheme, each optical detection unit employs a laser diode.

[0028] As a further improvement to the above scheme, the microwave unit also includes a power amplifier. The four microwaves modulated by the wave source are amplified by the power amplifier before they can manipulate the NV color centers in the four principal axis directions of the diamond sample.

[0029] The present invention also provides another current sensor based on a solid-state spin system, comprising:

[0030] The gain unit, which is a magnetic ring, is used to achieve high-sensitivity current measurement of the object under test when the object under test is wrapped around the ring-shaped gain unit in the form of a coil or when it passes through the gain unit in the form of a straight wire / beam.

[0031] A probe, clamped within the gain unit, comprises: a magnetic sensing unit, an optical unit, two photodetector units, a waveguide structure, and a data acquisition unit. The magnetic sensing unit includes a diamond sample containing NV color centers along four principal axes. The optical unit includes a laser generator and a lens group for splitting the laser emitted by the laser generator into a main path and a reference path. The laser on the main path illuminates the NV color centers along the four principal axes, causing the corresponding NV color centers to emit fluorescence. The waveguide structure collects the fluorescence. The two photodetector units convert the optical signals from the laser on the reference path and the fluorescence into corresponding electrical signals. The data acquisition unit includes a data acquisition card for differential processing based on the two electrical signals.

[0032] The data processing unit is used to perform inverse decoding on the two differentially processed electrical signals to obtain the current magnitude of the object under test.

[0033] As a further improvement to the above scheme, the laser generator is a laser diode or a laser.

[0034] As a further improvement to the above scheme, the lens group includes a beam-splitting lens and a focusing lens; the beam-splitting lens splits the laser beam to form the main path and the reference path laser beam; the focusing lens focuses the laser beam of the main path onto the magnetically sensitive unit.

[0035] Furthermore, the lens group also includes two half-wave plates, both of which are located on the main path and are respectively located in front of and behind the beam splitter.

[0036] As a further improvement to the above scheme, the optical unit also includes a filter located on the main road and between the waveguide structure and the second optical detection unit.

[0037] As a further improvement to the above scheme, each optical detection unit employs a laser diode.

[0038] Compared with the prior art in the three documents in the background art, the present invention has the following beneficial effects:

[0039] (1) Compared with Reference 1: Compared with this technology, the present invention can achieve four-axis closed-loop measurement by modifying the microwave frequency, and the direction of the four axes is determined by the crystal orientation of the diamond single crystal. Compared with the three-axis TMR magnetic sensor composed of three TMR magnetic sensors, it has better stability and orthogonality. In summary, a non-contact current sensor with a larger range and higher accuracy can be built based on the diamond NV color center system, which can be used in the online calibration of current transformers and other work.

[0040] (2) Compared to Reference 2: Compared to this technology, the carrier of the diamond NV center system is a single diamond crystal, which can be processed to a size much smaller than other magnetic sensors. Therefore, it can be used to realize non-contact measurement of smaller currents. In the future, diamond magnetic sensors can be highly integrated to realize low-energy and simple current sensors, and are expected to be applied to online monitoring of high-voltage currents.

[0041] (3) Compared to Reference 3: Compared to that technology, this invention uses a structure of multiple vector magnetometers to suppress the influence of environmental factors such as installation errors, edge currents, and external magnetic field interference on the measurement results. By using different magnetic ring structures and replacing them with coils to apply the current to be measured, the current sensor can achieve a sensitivity far higher than that of current sensors based on other existing systems. If an all-optical magnetometer is used to build the current sensor, a low-energy-consumption and relatively simple current sensor can be built, which is expected to be applied to the online monitoring of high-voltage currents.

[0042] Therefore, the novel non-contact current sensor based on a solid-state spin system represented by NV color centers of the present invention can, on the one hand, solve the shortcomings of current online calibration technology, and on the other hand, address the challenges of non-contact small current sensors.

[0043] Compared with the prior art, the current sensor based on the solid-state spin system of the present invention has the following advantages:

[0044] (1) Non-contact measurement: In the process of measuring current, the sensor does not need to contact the current to be measured. This invention can build a current sensor that is easier to install and disassemble. It can also be applied in the field of small current measurement to situations where resistance measurement cannot be used, such as ion beam current.

[0045] (2) High sensitivity: In the scheme of the present invention using a magnetic ring, because a smaller sensitive unit can be realized, a magnetic ring with a smaller air gap can be used compared with other magnetic sensors, which can reduce the influence of magnetic flux loss, leakage magnetic field and open stray field, and achieve higher current measurement sensitivity. It can be applied to applications such as the measurement of micro ion beams and the transfer of quantum current values.

[0046] (3) Low cost: The low-cost solution of the present invention eliminates the microwave devices required by the conventional solid spin magnetic measurement method by utilizing the optical properties of solid spin. At the same time, compared with fiber optic transformers, the present invention does not require the use of expensive polarization-maintaining fiber and circular fiber, resulting in low cost and low maintenance cost.

[0047] In contrast, the technical solution of this invention cannot be easily obtained using existing technologies. The specific features of this invention include: utilizing the stable lattice structure of diamond single crystals and the characteristics of a Zeeman effect-based magnetic measurement method to develop a multi-axis closed-loop magnetic sensor for building a current sensor, which can simultaneously achieve easy assembly and disassembly and a large dynamic range. Furthermore, leveraging the miniaturization of magnetic sensing units possible with diamond single crystals, combined with a specially designed magnetic ring, enables high-sensitivity measurement of small currents, achieving non-contact measurement of currents below one microamp. The all-optical magnetic measurement method reduces the power supply requirements of modules such as microwaves, potentially solving the problems of low reliability and high cost of current fiber optic current transformers. Attached Figure Description

[0048] Figure 1 This is a schematic diagram illustrating an application scenario of a current sensor based on a solid-state spin system, as provided in Embodiment 1 of the present invention.

[0049] Figure 2 for Figure 1 Schematic diagram of the frequency modulation principle used in medium current sensors.

[0050] Figure 3 This is a schematic diagram illustrating an application scenario of a current sensor based on a solid-state spin system, as provided in Embodiment 2 of the present invention.

[0051] Figure 4 This is a schematic diagram illustrating an application scenario of a current sensor based on a solid-state spin system, as provided in Embodiment 3 of the present invention. Detailed Implementation

[0052] 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.

[0053] Example 1

[0054] Please see Figure 1 This is a schematic diagram illustrating the application scenario of the current sensor based on a solid-state spin system provided in Embodiment 1 of the present invention. The current sensor can be used for non-contact measurement of small currents at the microampere level and below. The current sensor includes: a four-channel probe 20 and a data processing unit (which is installed on the host computer 11; in other embodiments, it can also be installed on a smart terminal such as a mobile phone, tablet computer, or iPad).

[0055] Four probes 20 are arranged around the object under test 100 to perform quadriaxial magnetic measurements to obtain sixteen resonant microwave frequencies. During measurement, the four probes 20 can be arranged in an array, with the object under test 100 passing through the center of the array. Alternatively, the four probes 20 can be located on the same side of the object under test 100, such as... Figure 1 The dashed line represents the object to be tested.

[0056] Each probe includes a magnetic sensing unit 1, a microwave unit, an optical unit, two optical detection units (such as optical detection unit 1 5 and optical detection unit 2 6), a lock-in amplifier 10, and may also include a power amplifier.

[0057] The magnetically sensitive unit 1 comprises a diamond sample containing NV centers along four principal axes. NV centers, or nitrogen-vacancy centers (NVCs), are point defects in diamond whose ground-state energy levels are sensitive to magnetic fields, making them suitable for magnetic field measurements. They also have the advantage of operating at room temperature and in atmospheric conditions. Furthermore, due to the stability of the diamond lattice structure, this system shows potential in terms of robustness.

[0058] A surface treatment structure can be added to the sensitive unit 1 using a coating process. The surface treatment structure can be a metal film, such as a gold film, silver film, or aluminum film. It can be further protected by a protective film of silicon monoxide, magnesium fluoride, silicon dioxide, or aluminum oxide to further protect the stability of the surface treatment structure.

[0059] As a solid-state spin system, the diamond NV center system possesses a stable lattice structure, offering better orthogonality and higher sensitivity in vector magnetic measurements compared to other magnetic sensors. Furthermore, unlike other vector magnetic sensors based on multiple magnetic sensors, its measured magnetic field direction originates from four fixed crystal orientations, resulting in better stability. By analyzing multiple point vector fields, the magnetic field generated by the current can be decoupled from external magnetic fields and installation errors, enabling more accurate current measurement. Based on the Zeeman splitting magnetic measurement principle, it allows for closed-loop current measurement by adjusting the microwave frequency. Additionally, the system allows for smaller magnetic sensing elements, reducing the negative impact of openings on flux concentration when using a magnetic core, achieving higher amplification and current measurement sensitivity. Moreover, the all-optical magnetic measurement technology based on diamond NV centers can further reduce the high power consumption required for microwave and bias field application, and its simpler structure makes it a promising candidate for online monitoring of high-voltage currents.

[0060] The optical unit includes a laser generator 7 and a lens group 8 for splitting the laser emitted by the laser generator 7 into two optical paths: a main path and a reference path. The laser generator 7 can be a laser diode or a laser, providing the laser required to excite the NV color center. The lens group 8 may include a beam-splitting lens 81, a focusing lens 82, and may also include two half-wave plates 80. The beam-splitting lens 81 splits the laser to form the main path and the reference path, and the focusing lens 82 focuses the laser of the main path onto the magnetic sensing unit 1. The magnetic sensing unit 1 is placed at the center of the radiating structure 2, and the two half-wave plates 80 are both located on the main path and are respectively located in front of and behind the beam-splitting lens 81.

[0061] The microwave unit includes a wave source 9, a radiation structure 2, a waveguide structure 3, and a wave source control system. A magnetic sensing unit 1, positioned at the center of the radiation structure 2, uses four microwave signals generated by the wave source 9 to control the NV color centers along the four principal axes. Electrons in the magnetic sensing unit 1 transition between the ground and excited states, emitting fluorescence signals whose intensity is related to the system's spin population. In other embodiments, the microwave unit may include an oscillator, a radiation structure unit, an optional digital signal synthesis unit, and an optional power amplification unit; furthermore, a microwave frequency closed-loop measurement method can be used to increase the dynamic range of the measurable current.

[0062] The wave source control system controls wave source 9 to modulate four microwaves to manipulate the NV centers in the four principal axis directions of the diamond sample respectively (exciting electrons in the ±1 state of the ground state, increasing measurement contrast and environmental adaptability). The four microwaves are kept in resonance with the corresponding NV centers in the principal axis directions, and the corresponding NV centers emit fluorescence under laser irradiation on the principal axis. Waveguide structure 3 is used to collect the fluorescence; waveguide structure 3 can be a parabolic lens.

[0063] Filter 4 is located on the main path and between waveguide structure 3 and photodetector unit 6. It filters the fluorescence collected by waveguide structure 3 to remove optical noise. The two photodetector units are used to convert the optical signals from the laser and fluorescence on the reference path into corresponding electrical signals, and photodiodes can be used. Photodiodes can convert fluorescence signals into electrical signals, and by applying a bias voltage, they can output a larger saturation current.

[0064] The lock-in amplifier 10 demodulates the two electrical signals and performs PID processing on the demodulation results to obtain four resonant microwave frequencies of the NV color centers in the four principal axis directions. The wave source control system is also used to achieve closed-loop negative feedback of the microwave frequencies while modulating the four microwave signals. In other embodiments, the lock-in amplifier 10 can be integrated with the wave source control system, which can achieve closed-loop negative feedback of the microwave frequencies while modulating the four microwave signals. One probe generates four resonant microwave frequencies, and the current sensor has four probes, thus generating a total of sixteen resonant microwave frequencies.

[0065] The data processing unit is used to perform inverse kinematics on the sixteen resonant microwave frequencies to obtain the current magnitude of the object under test. The data processing unit can be optimized using a neural network; for example, the host computer 11 can use a trained neural network to analyze the data measured by the sensor, which can improve the accuracy of current measurement and its resistance to external interference. This invention can use fiber optic excitation, fluorescence acquisition, and power supply to isolate the current sensor from the host computer 11; simultaneously, it can also improve the sensor's sensitivity and anti-interference capability through excitation light modulation or magnetic field modulation.

[0066] Compared to other types of current sensors, this embodiment can achieve closed-loop current measurement while ensuring non-contact measurement and ease of installation, and boasts a larger dynamic range and greater accuracy. Compared to classical measurement methods, quantum precision measurement utilizes the sensitivity of quantum systems to the environment to achieve precise measurement of physical quantities, exhibiting significant advantages in indicators such as sensitivity.

[0067] The diamond sample has a crystal orientation of

[110] . The NV center consists of a nitrogen atom and a nearby vacancy. When the NV center carries a negative charge, its ground state energy level will form a triplet state. The energy difference between the ground state 3E and the first excited state 3A of the triplet state is 1.945 eV, corresponding to a zero phonon line of 637 nm. Therefore, when the NV center is excited by an excitation light with an energy greater than or equal to 1.945 eV, the electrons in the NV center will be excited to the excited state, and then the electrons will have a high probability of de-excitation and returning to the ground state, thereby emitting fluorescent photons and forming fluorescence. There are two paths in the de-excitation process. The first is direct radiative transition back to the ground state and emission of fluorescent photons, and the other is through two metastable states and non-radiative transition back to the ground state. The probability of an electron returning to the ground state via these two paths depends on its state. When an electron is in the excited state ms = ±1, it has a greater probability of returning to the ground state ms = 0 via a non-radiative transition. Therefore, the population of electrons in each energy level of the ground state can be determined by the fluorescence intensity. When a continuous resonant microwave is applied to the NV center, the population of electrons in each energy level reaches an equilibrium value. At this point, the transition rate from ms = ±1 to ms = 0 is the same as the transition rate from ms = 0 to ms = ±1, and the population tends to stabilize. If the external magnetic field changes at this time, the energy level change will introduce a partial resonance that will disrupt the population equilibrium, macroscopically manifested as a change in fluorescence intensity. Figure 2 As shown, when a frequency modulation is applied to the microwave, the fluorescence receives a modulation signal with the same frequency. Demodulating this modulation yields a spectrum that is the first-order differential spectrum of fluorescence as a function of the microwave frequency. When the manipulating microwave is in perfect resonance with the NV color center, the demodulation result is zero. When a partial resonance exists, the demodulation result changes. Real-time adjustment of the microwave frequency based on the demodulation result ensures the manipulating microwave is always in resonance, thus achieving closed-loop measurement of the magnetic field. Therefore, this invention can obtain sixteen resonant frequencies across four principal axes in four sets for data processing to determine the magnitude of the current to be measured, while simultaneously eliminating interference from external magnetic fields, adjacent currents, and other factors.

[0068] The working process of the current sensor of the present invention is as follows:

[0069] (1) The optical unit provides excitation light to the sensitive unit, causing the electron spin in the magnetic sensitive unit to transition between the ground state and the excited state, emitting a fluorescence signal whose intensity is related to the spin population of the system; the optional optical unit can be a driver plus LD / LED or a laser plus lens group;

[0070] (2) Place the sensitive unit in the magnetic field to be measured, and keep the bias field, excitation light intensity, microwave frequency and microwave power unchanged; under the action of the magnetic field to be measured, the spin population of the spin system in the sensitive unit changes, and the parameters of the emitted fluorescence signal change accordingly. The emitted fluorescence signal contains information such as the frequency of the magnetic field to be measured and the magnetic induction intensity.

[0071] (3) The fluorescence signal containing the magnetic field information to be measured is converted into an electrical signal by the detection unit and recorded as a digital signal by the analog-to-digital converter to complete a magnetic field measurement.

[0072] (4) By processing the magnetic field measurement results and the parameters of the current sensor, the magnitude of the current can be obtained, and the current measurement can be completed.

[0073] The purpose of this invention is to propose a multi-axis magnetometer sensor array scheme to solve the problem of online calibration of large currents, and a magnetic flux focusing scheme to solve the problem of small current value transmission. The current sensor of this invention has the following technical features:

[0074] 1. Quad-axis magnetic measurement is achieved using the stable lattice structure of diamond single crystal, and a current sensor that can eliminate interference factors such as installation errors and adjacent currents is built from this magnetometer array.

[0075] 2. The sensitive unit of the diamond NV color center system is easy to miniaturize. Combined with the magnetic flux focusing method, it enables highly sensitive current measurement.

[0076] 3. By using a multi-axis magnetic sensor array, the magnetic field information at each point can be detected more comprehensively, and the influence of the environment on the measurement results can be reduced while measuring the magnitude of the current.

[0077] 4. The magnetic field generated by the current is amplified by the magnetic flux focusing effect of the ring magnetic core, while also providing a certain shielding effect on the external magnetic field, thus achieving high-sensitivity measurement of the current.

[0078] 5. By utilizing the magnetically sensitive optical properties of diamond NV center ensemble samples and combining them with magnetic flux focusing methods, a fully optical current sensor with low insulation and power supply requirements can be constructed.

[0079] 6. By using all-optical magnetic measurement technology, the energy consumption and structural complexity of magnetic sensors are reduced, making it suitable for measuring high-voltage currents.

[0080] The precision magnetometry technology based on NV color centers in this invention mainly relies on excitation light to polarize NV color centers, and reads out the population of the ground state of NV color centers through the fluorescence at this time. Under the control of microwave field, the population will change with the change of magnetic field, thereby obtaining the strength of external magnetic field.

[0081] This invention mainly utilizes the following four principles.

[0082] 1. Four-axis vector magnetic measurement principle: The magnetic sensing unit of the diamond NV center magnetometer is a single-crystal diamond sample. A single sample has four different crystal orientations, thus containing four NV centers along different principal axes. By applying a bias field, the resonant frequencies of the ground state energy levels of the NV centers along the four principal axes are ensured to be different. If four resonant microwaves with different modulation frequencies are applied simultaneously to manipulate the NV centers along the four principal axes and read out simultaneously using fluorescence, the magnetic field information along the four principal axes can be read out simultaneously, thereby achieving vector magnetic measurement.

[0083] 2. Principle of All-Optical Magnetism Measurement: In a solid-state spin system, when an electron is in an excited state, it can return to the ground state in two ways. The first is through radiative transition, directly returning to the ground state and emitting fluorescent photons; the second is through non-radiative transition via a metastable state, during which no fluorescent photons are emitted. The probability of an electron returning to the ground state via these two paths depends on its energy level state; therefore, fluorescence can be used to determine the electron's state. In the absence of microwaves, when the external magnetic field is zero, the radiative transition process maintains the spin state unchanged. With a transverse magnetic field, spin states overlap, leading to a greater probability that the electron will return to the ground state through a non-radiative transition, macroscopically manifested as a decrease in fluorescence intensity. Therefore, in the absence of microwaves, the fluorescence decreases when a transverse field component is present, allowing for the measurement of changes in the magnetic field strength when the magnetic field direction is constant.

[0084] 3. Magnetic Flux Concentration Principle: In current measurement, high-permeability materials such as iron, cobalt, nickel and their alloys, or ferrites, are often used to create magnetic rings that amplify the magnetic field generated by the current. For current sensors based on magnetic sensors, adding a magnetic ring can also shield against external magnetic fields, improving the sensitivity and accuracy of the current sensor.

[0085] 4. Multi-axis magnetic sensor array current measurement principle: A current generates a magnetic field proportional to its magnitude around it. By measuring the magnetic field at a specific location relative to the current, the magnitude of the current can be measured. Placing several multi-axis magnetic sensors around the current to be measured allows for the acquisition of magnetic field information in multiple directions at that location. Analyzing this information allows for the measurement of the current magnitude while simultaneously eliminating the influence of factors such as adjacent currents and assembly errors.

[0086] Example 2

[0087] Please see Figure 3This is a schematic diagram illustrating an application scenario of the current sensor based on a solid-state spin system provided in Embodiment 2 of the present invention. The current sensor in Embodiment 2 is basically the same as the current sensor in Embodiment 1, and it can achieve the same beneficial effects as the current sensor in Embodiment 1. The difference is that the current sensor in Embodiment 2 also includes a gain unit 13 and a power amplifier 12, and only one probe is needed, although more probes can also be set.

[0088] Gain unit 13 is a magnetic ring used to achieve highly sensitive current measurement of the object under test 100 when it is wrapped around the ring-shaped gain unit 13 in the form of a coil or when it passes through the gain unit 13 as a straight conductor / beam. The magnetic ring can amplify the magnetic field generated by the current and also provides a certain degree of external magnetic field shielding. Gain unit 13 can be a ring structure made of a high-permeability material, such as iron, cobalt, nickel and their alloys, or ferrite.

[0089] If more probes are set up, the magnetic sensing unit 1 of the probe can be placed in each opening of the magnetic ring, and the large surface of the diamond sample is held by the two ends of the opening. It is necessary to apply a specific bias field to ensure that the NV color center resonance frequencies of the diamond sample in each principal axis direction are reasonably separated.

[0090] Wave source 9 modulates at least one microwave signal, which is then amplified by power amplifier 12 before being used to manipulate at least one NV color center in the principal axis direction of the diamond sample. Alternatively, power amplifier 12 can also be used in embodiment 1. Lock-in amplifier 10 demodulates the two electrical signals and performs PID processing on the demodulation result to obtain the resonant microwave frequency of at least one NV color center in the principal axis direction. The wave source control system modulates the microwave signal according to the microwave frequency while simultaneously implementing closed-loop negative feedback on the microwave frequency.

[0091] The sensitive unit of the current sensor in Example 2 is a diamond sample containing NV color centers, which is clamped on a ferromagnetic material ring gain unit 13 with one or more notches (each notch corresponds to a diamond sample). The object to be measured 100 is wrapped around the ring gain unit 13 in the form of a coil or passes through the gain unit 13 in the form of a straight wire, a beam, etc., which can realize high-sensitivity measurement of current. The diamond sample can be of any crystal orientation.

[0092] Example 3

[0093] Please see Figure 4This is a schematic diagram illustrating the application scenario of the current sensor based on a solid-state spin system provided in Embodiment 3 of the present invention. The current sensor in Embodiment 3 is basically the same as the current sensor in Embodiment 2, and the current sensor in Embodiment 2 can achieve the same beneficial effects as the current sensor in Embodiment 2. The difference is that the current sensor in Embodiment 3 does not have a microwave unit and a radiation structure 2, nor does it have a lock-in amplifier, but it does have a data acquisition card 15, i.e., a data acquisition system. The data acquisition card 15 is used to perform differential processing on the two electrical signals, and the data processing unit performs inverse decoding on the two differentially processed electrical signals to obtain the current magnitude of the object under test.

[0094] In the absence of an external magnetic field, the electron population in the laser-irradiated magnetic sensing unit 1 tends to stabilize, and the fluorescence intensity remains constant. When a transverse external magnetic field is present, spin states overlap, and they have a greater probability of returning to the ground state through non-radiative transitions, leading to a decrease in fluorescence intensity. Therefore, the magnitude of the external magnetic field can be quantitatively measured by the magnitude of the fluorescence decrease. The host computer 11 processes the electrical signal transmitted by the photodetector unit to obtain the magnitude of the current to be measured, excluding the influence of factors such as the external magnetic field and installation errors.

[0095] In this embodiment, if high-voltage current measurement is required, the optical unit can be replaced with a combination of a laser and optical fiber. Compared to other types of current sensors, this embodiment has the advantages of simple structure, low cost, low power consumption, all-weather operation, and high sensitivity.

[0096] As can be seen from the above three embodiments, the solid-state spin current sensor of the present invention does not require completely accurate installation. By using the magnetic field information obtained by measuring the NV color centers of the four main axes, the magnetic field generated by the current under test can be decoupled from the equivalent magnetic field generated by interference factors, thereby achieving accurate measurement of the current under test and enhancing the anti-interference capability of the current sensor.

[0097] The solid-state spin current sensor of this invention can measure the current without using any microwave devices. It utilizes the characteristic that solid-state spins in diamond, in the presence of a transverse magnetic field, undergo spin-state overlap, increasing the probability of electrons returning to the ground state via non-radiative transitions, thus reducing fluorescence. Furthermore, this solid-state spin current sensor can maintain a zero magnetic field sensed by the magnetic sensing element by adding a feedback current unit, avoiding the influence of factors such as the nonlinearity of the magnetic permeability of the magnetic ring on the current measurement, and increasing the dynamic range of the measurable current.

[0098] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A current sensor based on a solid-state spin system, characterized in that, It includes: Four probes are arranged around the object under test for quadriaxial magnetic measurement to obtain sixteen resonant microwave frequencies. Each probe includes a magnetic sensing unit (1), a microwave unit, an optical unit, two optical detection units, and a lock-in amplifier (10). The optical unit includes a laser generator (7) and a lens group (8) for splitting the laser emitted by the laser generator (7) into two optical paths: a main path and a reference path. The magnetic sensing unit (1) includes a diamond sample containing NV color centers in four main axis directions. The microwave unit includes a wave source (9), a radiation structure (2), a waveguide structure (3), and a wave source control system. The magnetic sensing unit (1) is placed at the center of the radiation structure (2), and the wave source control system controls the wave source (9) to modulate the microwave frequency. Four microwaves manipulate the NV centers in the four principal axis directions of the diamond sample respectively. The four microwaves are kept in resonance with the NV centers in the corresponding principal axis directions. Under the irradiation of the laser on the principal axis, the corresponding NV centers emit fluorescence. The waveguide structure (3) is used to collect the fluorescence. Two optical detection units are used to convert the optical signals brought by the laser and the fluorescence on the reference path into corresponding electrical signals. The lock-in amplifier (10) is used to demodulate the two electrical signals and perform PID processing on the demodulation results to obtain the four resonant microwave frequencies of the NV centers in the four principal axis directions. The wave source control system is also used to realize closed-loop negative feedback of the microwave frequency while modulating the four microwaves according to the microwave frequency. The data processing unit is used to perform inverse decomposition on the sixteen resonant microwave frequencies to obtain the current magnitude of the object under test.

2. The current sensor based on a solid-state spin system as described in claim 1, characterized in that, The four probes are arranged in an array, and the object to be tested passes through the middle of the array.

3. The current sensor based on a solid-state spin system as described in claim 1, characterized in that, The laser generator (7) is a laser diode or a laser.

4. The current sensor based on a solid-state spin system as described in claim 1, characterized in that, The lens group (8) includes a beam splitter (81) and a focusing lens (82); the beam splitter (81) splits the laser beam to form the main path and the reference path laser; the focusing lens (82) focuses the laser beam of the main path onto the magnetically sensitive unit (1).

5. The current sensor based on a solid-state spin system as described in claim 4, characterized in that, The lens group (8) also includes two half-wave plates (80), which are located on the main path and are located in front of and behind the beam splitter (81), respectively.

6. The current sensor based on a solid-state spin system as described in claim 1, characterized in that, The optical unit also includes a filter (4) located on the main road and between the waveguide structure (3) and the second optical detection unit.

7. The current sensor based on a solid-state spin system as described in claim 1, characterized in that, Each optical detection unit uses a laser diode.

8. The current sensor based on a solid-state spin system as described in claim 1, characterized in that, The microwave unit also includes a power amplifier (12). The four microwaves modulated by the wave source (9) are amplified by the power amplifier (12) before they can manipulate the NV color centers in the four principal axis directions of the diamond sample.

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