Microwave-free zero flux current measurement system based on nitrogen-vacancy color center sensors

Abstract

This application relates to the field of smart grid technology, and in particular to a microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor. The microwave-free zero-flux current measurement system includes a magnetic ring, a nitrogen-vacancy color center sensor, a coil unit, a photoelectric detection module, a modulation / demodulation module, a feedback control module, and an analog-to-digital conversion acquisition module. The magnetic ring is positioned outside the conductor to be measured, and the nitrogen-vacancy color center sensor is located at the opening of the magnetic ring. The coil unit includes a bias coil, a modulation coil, and a secondary feedback coil, which are sequentially wound around the magnetic ring. The microwave-free zero-flux current measurement system completely eliminates microwave power consumption, significantly reduces sensor size, avoids low-frequency noise from the photoelectric detection circuit, and reduces the algorithmic complexity of zero-flux PID or iterative feedback control.

Description

Technical Field

[0001] This application relates to the field of smart grid technology, and in particular to a microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor. Background Technology

[0002] Nitrogen-vacancy centers (NV centers) are quantum systems exhibiting electronic magnetic resonance effects. They produce unique optical responses during magnetic resonance, enabling highly sensitive magnetic resonance detection via photodetectors, thus allowing for precise measurement of magnetic field strength. Current detection methods require laser excitation of NV centers to generate fluorescence, followed by the application of specific frequency microwaves to a diamond sample. Changes in fluorescence intensity are then used to determine the magnetic resonance state and inversely determine the magnetic field strength. Therefore, NV center sensor systems typically integrate a laser source, a microwave source, a photoelectric signal acquisition module, and auxiliary units such as communication and power supply.

[0003] Based on this magnetic measurement principle, researchers have applied NV color centers to current measurement to develop high-precision, high-reliability current sensors. Currently, there are three main technical approaches to magnetic measurement based on NV color centers: an open-loop scheme that directly calculates the magnetic field from fluorescence intensity, which has a simple structure but a small range, poor linearity, and poor long-term consistency, making it difficult to put into practical use; a closed-loop scheme that automatically tracks the microwave resonant frequency, which has the largest range and good long-term stability, but its control is complex and its nonlinearity is significant, limiting its applications; and a closed-loop scheme with magnetic flux balance feedback, which has the best linearity and long-term stability, and excellent overall performance, but it relies on secondary current feedback and is only suitable for current measurement.

[0004] Improvements have been made to the NV color center zero-flux current measurement technology. Existing zero-flux solutions mainly consist of a primary current conductor, a secondary feedback coil, a magnetic ring, and an NV color center sensor. The NV color center acts as a magnetic balance detector, achieving ampere-turn balance by adjusting the secondary current to cancel the magnetic field of the current to be measured. The current to be measured can then be obtained by measuring the secondary current. However, existing zero-flux solutions still require microwave drive, and the microwave system accounts for a very high proportion of power consumption, representing a major source of overall power consumption and a key bottleneck for application and promotion.

[0005] In summary, the technical problems existing in the relevant technologies need to be improved. Summary of the Invention

[0006] The main objective of this application is to propose a microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor, which can completely eliminate microwave power consumption, significantly reduce sensor size, avoid low-frequency noise in the photodetector circuit, and reduce the algorithm difficulty of zero-flux PID or iterative feedback control.

[0007] To achieve the above objectives, one aspect of this application proposes a microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor, comprising: A magnetic ring, wherein the magnetic ring is disposed on the outside of the conductor whose current is to be measured; A nitrogen-vacancy color center sensor is disposed at the opening of the magnetic ring. The nitrogen-vacancy color center sensor is used to sense the magnetic field inside the magnetic ring and output a fluorescence signal. The coil unit includes a bias coil, a modulation coil, and a secondary feedback coil. The bias coil, the modulation coil, and the secondary feedback coil are wound sequentially on the magnetic ring. The bias coil is driven by a fixed current source and is used to generate a steady magnetic field inside the magnetic ring when the current to be measured is zero. The modulation coil is used to receive an alternating modulation signal, and the secondary feedback coil is used to cancel the magnetic field disturbance generated by the current to be measured. A photoelectric detection module is used to receive the fluorescence signal from the nitrogen-vacancy color center sensor and convert the received fluorescence signal into an electrical signal; A modulation and demodulation module is used to synchronously demodulate the electrical signal output by the photoelectric detection module and then output a demodulated voltage. A feedback control module is used to generate and adjust the current of the secondary feedback coil according to the demodulation voltage, so that the measured current and the current of the secondary feedback coil maintain an ampere-turn balance relationship. An analog-to-digital conversion acquisition module is used to acquire the current sensing voltage of the secondary feedback coil circuit and calculate the current to be measured based on the current sensing voltage.

[0008] In some embodiments, the nitrogen-vacancy color center sensor detects a pure optical magnetic field in a reference magnetic field based on the cross-point-free excited state energy level. The range of the reference magnetic field includes a center of 512 Gs and a width of less than or equal to 10 Gs.

[0009] In some embodiments, the bias coil has a winding number of turns greater than or equal to 3000. The bias coil is driven by a fixed DC power supply to obtain the reference magnetic field.

[0010] In some embodiments, the nitrogen-vacancy color center sensor detects the magnetic field offset in the reference magnetic field using a purely optical method based on the quantum property of the excited state energy level crossover-free point. The excited state energy level crossover-free point corresponds to the energy overlap state of the excited state spin 0 and spin -1 energy levels of the nitrogen-vacancy color center sensor. The modulation coil periodically perturbs the reference magnetic field by applying a high-frequency alternating magnetic field, causing the fluorescence intensity of the nitrogen-vacancy color center sensor to alternate synchronously. The modulation and demodulation module performs synchronous demodulation based on a reference signal with the same frequency as the modulation signal.

[0011] In some embodiments, the clamping of the reference magnetic field is always maintained within ±5 Gs around the crossover point of the excited state energy level by closed-loop feedback control; The nitrogen-vacancy color center sensor comprises a spin-1 quantum system. In the absence of an external magnetic field, the intrinsic energy level difference between the spin ±1 state and the spin 0 state of the excited state electronic energy level of the nitrogen-vacancy color center sensor includes a transition frequency of 1.44 GHz. Under the action of an external magnetic field, the spin ±1 state undergoes Zeeman splitting, with a splitting ratio coefficient of 2.8 MHz / Gs.

[0012] In some embodiments, the modulation coil has less than or equal to 10 turns. The frequency of the alternating modulation signal connected to the modulation coil is equal to or greater than 5kHz, and the frequency of the alternating modulation signal connected to the modulation coil is greater than the signal frequency of the current to be measured.

[0013] In some embodiments, the number of turns of the secondary feedback coil is less than or equal to 100 turns; The feedback control module includes a digital-to-analog converter unit, which calculates the current increment based on the demodulation voltage and the proportional coefficient, and iteratively updates the current of the secondary feedback coil based on the current increment. The secondary feedback coil is connected in series with a current-sensing resistor. The voltage across the current-sensing resistor is sampled by the analog-to-digital conversion acquisition module. The current-sensing resistor is used to calculate the secondary feedback current and, based on the ampere-turn balance relationship, to obtain the current to be measured.

[0014] In some embodiments, the feedback control module updates the current of the secondary feedback coil according to an iterative formula, wherein the iterative formula is: ; in, This indicates the current of the secondary feedback coil in the next update. This indicates the current of the secondary feedback coil. Indicates the demodulation voltage. This indicates the preset scaling factor.

[0015] In some embodiments, the formula for calculating the ampere-turn balance relationship is: ; in, This indicates the current to be measured. This refers to the secondary feedback current. This indicates the number of turns of the conductor carrying the current under test through the magnetic ring. This indicates the number of turns of the secondary feedback coil wound on the magnetic ring.

[0016] In some embodiments, the bias coil is driven by the fixed current source to apply DC excitation to the magnetic ring, so that a reference magnetic field is formed inside the magnetic ring, and then the nitrogen-vacancy color center sensor is set at the crossover point of the excited state energy level. The alternating modulation signal is applied to the magnetic field within the magnetic ring via the modulation coil, thereby alternatingly modulating the fluorescence signal of the nitrogen-vacancy color center sensor.

[0017] The embodiments of this application include at least the following beneficial effects: This application provides a microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor. This scheme utilizes the quantum characteristic of the nitrogen-vacancy color center's excited state energy level crossover-free point to achieve pure optical magnetic field detection under a steady reference magnetic field, completely eliminating the high-power microwave drive unit in traditional schemes, significantly reducing the overall power consumption, and breaking through the application bottleneck of nitrogen-vacancy color center sensors; at the same time, it adopts zero-flux closed-loop control, dynamically canceling the magnetic field of the measured current through a secondary feedback coil, so that the nitrogen-vacancy color center always works near the energy level crossover-free point, effectively eliminating the magnetic hysteresis of the magnetic ring and the nitrogen-vacancy color center axis. This significantly improves the accuracy, linearity, and long-term consistency of current measurement by mitigating errors such as deviation and nonlinear response. By applying a high-frequency alternating magnetic field to the modulation coil and cooperating with the modulation and demodulation module, common-mode suppression of low-frequency noise in the photoelectric detection circuit is achieved, further optimizing the measurement signal-to-noise ratio. Compared to traditional frequency tracking schemes that rely on FPGAs and microwave devices, this system only requires a single-chip microcomputer architecture for control, resulting in a simpler structure, lower development and production costs, fewer operating instructions, and higher long-term reliability. It combines the advantages of low power consumption, high precision, high stability, and low cost, providing core technological support for the practical application and industrialization of nitrogen-vacancy color center sensors. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the microwave-free zero flux current measurement system based on a nitrogen-vacancy color center sensor provided in the embodiments of this application; Figure 2 This is a schematic diagram of the energy level cross-point-free quantum structure of the nitrogen-vacancy color center; Figure 3 This is a schematic diagram showing the relationship between fluorescence signal intensity and magnetic field strength; Figure 4 This is a schematic diagram showing the relationship between demodulation voltage intensity and magnetic field intensity. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of apparatuses and methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0020] It is understood that the terms “first,” “second,” etc., used in this application may be used herein to describe various concepts, but unless otherwise stated, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the words “if,” “when,” or “in response to a determination” as used herein may be interpreted as “when…” or “when…” or “in response to a determination.”

[0021] As used in this application, the terms "at least one", "multiple", "each", "any", etc., "at least one" includes one, two or more, "multiple" includes two or more, "each" refers to each of the corresponding multiples, and "any" refers to any one of the multiples.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0023] Before providing a detailed description of the embodiments of this application, some of the nouns and terms involved in the embodiments of this application will be explained first. The nouns and terms involved in the embodiments of this application are subject to the following interpretations.

[0024] A DAC (Digital-to-Analog Converter) is a device that converts digital signals into continuous analog voltages / currents.

[0025] FPGA (Field-Programmable Gate Array) is a hardware programmable logic chip.

[0026] DDS (Direct Digital Synthesizer) is a high-precision frequency generation technology. It generates arbitrary waveforms through table lookup and digital-to-analog conversion, achieving extremely high frequency resolution and fast switching speed.

[0027] A PLL (Phase-Locked Loop) is a type of phase-locked circuit. It is used to lock the frequency and phase of an output signal to a reference signal, providing frequency stabilization and multiplication functions. It is a core component in traditional microwave sources for generating stable frequencies.

[0028] Nitrogen-vacancy color centers (NV centers) are microscopic defect structures in the diamond lattice, consisting of a nitrogen atom and an adjacent vacancy. They are quantum systems with an equivalent spin of 1, emit light when excited by lasers, and are extremely sensitive to external magnetic fields.

[0029] Crossover-free energy levels are special energy level states in quantum systems. Under the influence of an external magnetic field, the energies of adjacent energy levels coincide or are extremely close. This scheme utilizes this point at the 512 Gs excited state of the NV color center to directly sense the magnetic field through optical signals without microwaves, achieving microwave-free measurement.

[0030] Among related technologies, the zero-flux current measurement technology based on nitrogen-vacancy color centers uses a primary current conductor, a secondary feedback coil, a magnetic ring, and a nitrogen-vacancy color center sensor as its core structure. The nitrogen-vacancy color center acts as a magnetic balance detector, regulating the secondary current by detecting changes in the magnetic field to counteract the magnetic field of the current to be measured, thus maintaining an ampere-turn balance between the two. The current to be measured can be obtained by measuring the secondary current. This scheme avoids errors such as axial deviation of the nitrogen-vacancy color center, hysteresis and nonlinear response of the magnetic ring, improving measurement accuracy and consistency. Moreover, it can be controlled using a microcontroller + DAC structure, which is simpler in structure, lower in cost, and has higher long-term operational reliability compared to frequency tracking schemes that require FPGA and microwave devices such as DDS and PLL. However, existing zero-flux nitrogen-vacancy color center current measurement schemes still rely on microwave drive. The microwave system consists of a microwave source and a power amplifier. The microwave source contains two DDS, two PLLs, a temperature-controlled crystal oscillator, a mixer, and other devices, with a power consumption of about 3W. The power amplifier consumes 5W to 60W, which is much higher than the signal acquisition part (about 2W) and the laser drive part (1W to 10W). It is the main source of power consumption of the whole machine and has become a key bottleneck for the promotion and application of nitrogen-vacancy color center sensors.

[0031] In view of this, this application provides a microwave-free zero flux current measurement system based on a nitrogen-vacancy color center sensor. This solution solves the application limitation of nitrogen-vacancy color center sensors due to the high power consumption of microwave systems. By utilizing the energy level crossover-free property of the nitrogen-vacancy color center sensor, a microwave-free zero flux measurement scheme is designed, thereby improving the relevant design.

[0032] like Figure 1 As shown, Figure 1 This is a schematic diagram of the microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor provided in this application embodiment. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor in this application uses a magnetic ring 120 as the core magnetic circuit structure. The magnetic ring is entirely sleeved on the outside of the conductor 110 under test to concentrate the magnetic field generated by the current under test, thereby improving the magnetic field detection sensitivity. The nitrogen-vacancy color center sensor (NV color center sensor) 130 is installed at the opening of the magnetic ring. The nitrogen-vacancy color center sensor outputs a fluorescence signal through a laser driver 150, which can accurately sense the magnetic field changes inside the magnetic ring and output a fluorescence signal corresponding to the magnetic field state based on the quantum optical properties of the nitrogen-vacancy color center, providing a core sensing basis for magnetic field detection.

[0033] The system configuration includes a coil unit comprising a bias coil 141, a modulation coil 142, and a secondary feedback coil 143, all three coils wound sequentially around the magnetic ring body. The bias coil, driven by a fixed current source, provides a stable, constant magnetic field inside the magnetic ring in the initial state where the measured current is zero. This precisely positions the operating point of the nitrogen-vacancy color center sensor near the crossover point of the excited state energy level, establishing a baseline condition for pure optical magnetic field detection without microwave drive. The modulation coil receives a high-frequency alternating modulation signal, applying periodic perturbations to the magnetic field inside the magnetic ring to synchronously alternate the fluorescence signal output by the nitrogen-vacancy color center sensor, providing a basis for subsequent noise suppression and signal demodulation. The secondary feedback coil dynamically cancels out magnetic field disturbances generated by the measured current within the magnetic ring, maintaining the stability of the magnetic field inside the magnetic ring through closed-loop control, ensuring zero-flux detection.

[0034] The photoelectric detection module 161 is set at the fluorescence output terminal of the nitrogen-vacancy color center sensor. It is used to receive the fluorescence signal output by the nitrogen-vacancy color center sensor in real time and convert the optical signal into a processable electrical signal to realize the signal conversion from magneto-optical to electrical. The modulation and demodulation module 162 is connected to the output terminal of the photoelectric detection module. It is used to synchronously demodulate the electrical signal output by the photoelectric detection module and extract the demodulation voltage reflecting the deviation of the magnetic field in the magnetic ring from the reference state, providing the core control basis for closed-loop feedback control. The feedback control module is connected to the output terminal of the modulation and demodulation module and the driving terminal of the secondary feedback coil. It is used to generate and dynamically adjust the driving current of the secondary feedback coil according to the demodulation voltage, so that the current to be measured and the current of the secondary feedback coil always maintain the ampere-turn balance relationship, realizing zero magnetic flux closed-loop control. The analog-to-digital conversion acquisition module 172 is connected in series in the current loop of the secondary feedback coil. It is used to acquire the current detection voltage of the secondary feedback coil loop. By performing analog-to-digital conversion and calculation on the current detection voltage and combining the ampere-turn balance relationship, the magnitude of the current to be measured is finally obtained, and the current measurement is completed.

[0035] In some embodiments, the core of the microwave-free zero-flux current measurement system based on a nitrogen-vacancy center (NV) color center sensor relies on the quantum properties of NV color centers to achieve magnetic field detection. Specifically, the NV color center sensor utilizes the cross-point-free property of its excited-state energy levels to perform purely optical magnetic field detection, eliminating the need for traditional microwave driving methods. Its core reference magnetic field range is set as an interval centered at 512 Gs with a width less than or equal to 10 Gs. Within this interval, the energy level structure of the NV color center exhibits a unique response, allowing direct sensing of magnetic field shifts via optical signals, thus forming the physical basis for microwave-free measurement.

[0036] The bias coil in the system is strictly wound with 3000 turns or more. Driven by a fixed DC power supply, this bias coil can accurately generate and stably maintain the aforementioned reference magnetic field centered at 512 Gs with a width of 10 Gs or less. The high-turn-count winding design effectively reduces the driving current requirement while improving the stability and uniformity of the magnetic field generation. This ensures that the nitrogen-vacancy color center sensor always operates stably in the optimal operating region of the excited state energy level without crossover points, providing the reference magnetic field conditions for subsequent zero-flux measurements.

[0037] The modulation coil performs signal modulation and noise suppression functions in the system. The number of turns in the modulation coil is set to less than or equal to 10 turns, a configuration that balances modulation efficiency and coil loss. The modulation coil needs to be connected to an alternating modulation signal with a frequency equal to or greater than 5kHz, and the frequency of this alternating modulation signal must be greater than the signal frequency of the current being measured. By applying a high-frequency alternating magnetic field, the magnetic field of the nitrogen-vacancy color center can be periodically perturbed, causing the fluorescence signal output by the nitrogen-vacancy color center to alternate synchronously. Subsequently, using same-frequency demodulation technology, the slowly varying magnetic field signal generated by the current being measured can be effectively separated, suppressing low-frequency noise, environmental drift, and other interference factors in the photoelectric detection circuit, ensuring measurement accuracy.

[0038] The secondary feedback coil, serving as the actuator for zero-flux closed-loop control, has a winding count set to less than or equal to 100 turns. Its core function is to dynamically counteract the magnetic field disturbances generated by the measured current within the magnetic ring, achieving ampere-turn balance. The system's feedback control module integrates a digital-to-analog converter unit. This unit receives the demodulated voltage output from the modulation and demodulation module, calculates the current increment based on a preset proportional coefficient, and iteratively updates the drive current of the secondary feedback coil according to this current increment. Through continuous closed-loop adjustment, it ensures that the measured current and the secondary feedback coil current always maintain an ampere-turn balance, keeping the system in a zero-flux operating state.

[0039] In addition, a current-sensing resistor 171 is connected in series in the current loop of the secondary feedback coil. The voltage across the current-sensing resistor is sampled in real time by the analog-to-digital converter (ADC) acquisition module. By acquiring this current-sensing voltage, the ADC acquisition module performs analog-to-digital conversion and numerical calculation to determine the magnitude of the current in the secondary feedback coil. Combined with the ampere-turn balance relationship, the value of the current to be measured is finally calculated accurately, completing the entire microwave-free zero-flux current measurement process. The formula for calculating the ampere-turn balance relationship is: ;in, Indicates the current to be measured. Indicates the secondary feedback current. This indicates the number of turns of the conductor carrying the current under test through the magnetic ring. This indicates the number of turns of the secondary feedback coil wound on the magnetic ring.

[0040] In some embodiments, such as Figure 2 As shown, addressing the technical bottleneck of traditional nitrogen-vacancy color center sensors that rely on microwave actuation, resulting in excessive power consumption and limited applications, this paper innovatively utilizes the cross-point-free quantum properties of nitrogen-vacancy color centers to construct a microwave-free zero-flux current measurement system. The core of this system achieves high-precision current measurement through pure optical magnetic field detection and closed-loop feedback control. Specifically: From the perspective of energy level structure and quantum physics principles, the nitrogen-vacancy color center is equivalent to a spin-1 quantum system, whose electronic energy levels are divided into ground state and excited state, and undergo Zeeman splitting under the influence of an external magnetic field. For example... Figure 2 As shown, the spin-1, spin-0, and spin-+1 energy levels in the ground state initially possess an inherent energy level difference of 2.87 GHz. When an external magnetic field is applied, the spin-+1 and spin--1 states gain an additional energy shift related to the magnetic field strength, with a scaling factor of approximately 2.8 MHz / Gs. Traditional electron magnetic resonance relies on microwave-driven triggering of energy level transitions, requiring the microwave frequency to match a specific energy level difference. The energy level crossover-free point, as a special case, refers to a situation where, when the external magnetic field strength reaches a specific value, adjacent energy levels overlap or approach each other, allowing electrons to undergo energy level transitions without microwave driving. In this application, the nitrogen-vacancy color center excited state possesses an energy level crossover-free point, corresponding to a magnetic field strength of approximately 512 Gs. Within a magnetic field range centered at 512 Gs and with a width not exceeding 10 Gs near this operating point, the nitrogen-vacancy color center exhibits a unique optical response. Magnetic field measurement can be achieved using purely optical methods without microwave driving, which constitutes the core physical basis for microwave-free measurement.

[0041] To achieve the aforementioned microwave-free measurement, a microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor uses a magnetic ring as its core magnetic circuit structure. The nitrogen-vacancy color center sensor is installed at the opening of the magnetic ring, ensuring that the magnetic flux generated by the measured current fully passes through the nitrogen-vacancy color center, enhancing the magnetic field detection sensitivity. A bias coil, a modulation coil, and a secondary feedback coil are sequentially wound on the magnetic ring to form a coil unit. The bias coil is driven by a fixed current source, and its core function is to accurately calibrate the magnetic field inside the magnetic ring to 512 Gs when the measured current is zero, enabling the nitrogen-vacancy color center sensor to operate stably in the optimal region of the excited state energy level without crossover points, thus establishing the reference magnetic field conditions for microwave-free detection. The modulation coil is used to receive the alternating modulation signal. By applying a high-frequency alternating magnetic field to the magnetic ring, the magnetic field of the nitrogen-vacancy color center is periodically perturbed, thereby causing the fluorescence signal output by the nitrogen-vacancy color center to alternate synchronously, laying the foundation for subsequent modulation and demodulation and noise suppression. The secondary feedback coil serves as a closed-loop actuator to dynamically counteract magnetic field disturbances generated by the measured current. Through feedback control, the magnetic field inside the magnetic ring is maintained at 512 Gs, achieving zero magnetic flux measurement.

[0042] In the signal detection and control process, the photoelectric detection module directly receives the fluorescence signal output by the nitrogen-vacancy color center sensor and converts the optical signal into a processable electrical signal. The modulation and demodulation module is connected to the photoelectric detection module and synchronously demodulates the electrical signal, extracting the demodulation voltage that reflects the deviation of the magnetic field from the 512Gs reference value, which serves as the core basis for closed-loop feedback. The feedback control module generates the driving current of the secondary feedback coil based on the demodulation voltage. Specifically, the digital-to-analog converter unit calculates the current increment by combining the demodulation voltage and a preset proportional coefficient, iteratively adjusting the current of the secondary feedback coil to ensure that the measured current and the secondary feedback coil current maintain an ampere-turn balance. At the same time, a current-sensing resistor is connected in series in the current loop of the secondary feedback coil. When the current of the secondary feedback coil flows through the current-sensing resistor, a current-sensing voltage is generated. This voltage is sampled by the analog-to-digital conversion acquisition module. Through analog-to-digital conversion and numerical calculation of the current-sensing voltage, the magnitude of the current of the secondary feedback coil is calculated. Then, combined with the ampere-turn balance relationship, i.e., the product of the measured primary current and the number of primary turns equals the product of the secondary feedback current and the number of secondary turns, the value of the measured current is finally accurately calculated.

[0043] Furthermore, to improve measurement accuracy, an AC drive current is added to the secondary current to form a current-based modulation and demodulation drive circuit. Through high-frequency magnetic field modulation and synchronous demodulation technology, with a modulation frequency no lower than 5kHz and higher than the frequency of the current under test, the slowly varying magnetic field signal generated by the current under test is effectively separated. This suppresses interference factors such as low-frequency noise and environmental magnetic field drift in the photoelectric detection circuit, ensuring the linearity and long-term stability of the current measurement. The overall solution combines the quantum properties of the nitrogen-vacancy color center excited state energy level without crossover points, zero-flux closed-loop feedback control, and current modulation and demodulation technology, achieving low-power, high-precision current measurement without the need for microwave drive.

[0044] In some embodiments, the microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor employs differentiated winding turn designs for the three sets of coils to match different operational requirements and performance indicators, taking into account their functional characteristics. The modulation coil and secondary feedback coil, responsible for dynamic signal processing and closed-loop control, have high requirements for bandwidth response speed; therefore, they use fewer winding turns: the secondary feedback coil is preferably wound with 100 turns, and the modulation coil with 10 turns. Fewer coil turns effectively reduce coil inductance, improve current response speed, ensure that the secondary feedback current can quickly follow changes in the measured current, and simultaneously guarantee the high-frequency transmission characteristics of the modulation signal, meeting the system's dynamic performance requirements. The core function of the bias coil is to generate a stable 512Gs steady-state reference magnetic field. The driving current is DC, and the current amplitude is strictly limited; therefore, a high winding turn design of over 3000 turns is adopted. The high turns design can generate sufficient magnetic field strength at a lower drive current, reducing power supply load, while improving the stability and uniformity of the magnetic field. This ensures that the nitrogen-vacancy color center always operates precisely in the optimal working region of the excited state energy level without crossover points, providing stable reference conditions for microwave-free pure optical measurements.

[0045] The closed-loop current control of the secondary feedback coil is achieved collaboratively by the photoelectric detection system and the modulation / demodulation system, with its core control logic implemented through an iterative algorithm. The specific process is as follows: the photoelectric detection module acquires the fluorescence signal output from the nitrogen-vacancy color center and converts it into an electrical signal. After synchronous demodulation by the modulation / demodulation system, the demodulated voltage of the nth iteration is obtained. Multiply the demodulated voltage by a preset scaling factor. The required current increment for this adjustment is calculated. Then, the current secondary feedback current Adding this to the current increment yields the updated secondary feedback current. This completes one closed-loop feedback control cycle. The entire control process follows an iterative formula. ,in, This indicates the current of the secondary feedback coil in the next update. This indicates the current of the secondary feedback coil. Indicates the demodulation voltage. This represents the preset proportional coefficient. Through iterative adjustments, the secondary feedback current dynamically cancels out the magnetic field disturbance generated by the measured current, maintaining the magnetic field inside the magnetic ring at a stable 512 Gs, thus achieving ampere-turn balance and zero flux state.

[0046] The modulation coil employs a magnetic field modulation technique, its core principle based on the fluorescence absorption peak characteristics of the nitrogen-vacancy color center near the crossover point of the 512 Gs energy level: the closer the magnetic field is to 512 Gs, the weaker the fluorescence intensity of the nitrogen-vacancy color center. The modulation coil applies a high-frequency alternating magnetic field to the magnetic ring, periodically perturbing the reference magnetic field where the nitrogen-vacancy color center is located, causing the fluorescence intensity output by the nitrogen-vacancy color center to change synchronously with the alternating magnetic field, forming an alternating fluorescence signal. The modulation and demodulation system uses a reference signal with the same frequency as the modulation signal to accurately demodulate this alternating fluorescence signal, extracting the output signal reflecting the magnetic field offset. The alternating signal frequency of the modulation coil is set to no less than 5 kHz, much higher than the highest frequency of the current under test (generally not exceeding 1 kHz). Through frequency domain separation, the demodulated output signal reflects only the slowly varying magnetic field component generated by the current under test, effectively filtering out low-frequency noise and environmental magnetic field drift interference in the photoelectric detection circuit, achieving high-precision measurement of magnetic field changes, and significantly improving the system's anti-interference capability.

[0047] In some embodiments, the microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor takes the quantum property of the nitrogen-vacancy color center excited state energy level crossover-free as the core physical basis, and achieves high-precision current measurement under microwave-free conditions through closed-loop feedback control and modulation / demodulation technology.

[0048] Specifically, firstly, a fixed current source applies DC excitation to the magnetic ring through a bias coil, creating a reference magnetic field inside the ring centered at 512 Gs with a width not exceeding 10 Gs. The nitrogen-vacancy color center is then precisely positioned within the working region of the excited-state energy level crossover point. This crossover point corresponds to the energy overlap between the spin-0 and spin-1 excited-state energy levels of the nitrogen-vacancy color center under the 512 Gs magnetic field. As a spin-1 quantum system, the nitrogen-vacancy color center's excited-state electronic energy levels operate in the absence of an external magnetic field. At that time, the intrinsic energy level difference between the spin ±1 state and the spin 0 state is 1.44 GHz. Under the influence of an external magnetic field, the spin ±1 state undergoes Zeeman splitting with a splitting ratio factor of 2.8 MHz / Gs. Based on this, the magnetic field offset is detected using a purely optical method within the reference magnetic field range. Subsequently, a high-frequency alternating modulation signal is applied to the magnetic field within the magnetic ring by a modulation coil. By applying a high-frequency alternating magnetic field, the magnetic field of the nitrogen-vacancy color center is periodically perturbed, causing the fluorescence intensity of the nitrogen-vacancy color center to alternate synchronously. The process begins with alternating modulation of the fluorescence signal. Next, the photodetector receives the fluorescence signal from the nitrogen-vacancy color center, converting it into a corresponding electrical signal. The modulation / demodulation module then demodulates the photodetector signal synchronously with a reference signal of the same frequency as the modulation signal, obtaining a demodulation voltage reflecting the deviation of the magnetic field within the magnetic ring from the 512 Gs reference value. The feedback control module then calculates the current increment using the demodulation voltage and iteratively adjusts the current in the secondary feedback coil according to an iterative formula. This continuous iterative adjustment ensures that the measured current and the secondary feedback current achieve ampere-turn balance and maintain a zero-flux state. Simultaneously, closed-loop feedback control clamps the magnetic field of the nitrogen-vacancy color center within ±5 Gs around the crossover point of the excited state energy level, ensuring measurement stability. Finally, the analog-to-digital conversion acquisition module acquires the current sensing voltage of the secondary feedback coil circuit, calculates the magnitude of the secondary feedback current based on the current sensing voltage, and performs calculations according to the ampere-turn balance formula to obtain the magnitude of the measured current, thus completing the entire microwave-free zero-flux current measurement process.

[0049] In some embodiments, the current measurement process of the microwave-free zero flux current measurement system based on the nitrogen-vacancy color center sensor is divided into three stages: system initialization, closed-loop feedback adjustment, and signal acquisition and output. First, the system is initialized and configured by inputting an initial current into the bias coil to provide a stable magnetic field centered at 512 Gs inside the magnetic ring. At the same time, the laser drive is configured to provide an excitation source for the NV color center magnetic sensor. Then, the modulation signal output function of the modulation and demodulation circuit is turned on to output a high-frequency alternating modulation signal that meets the requirements to the modulation coil, thus completing the initial state calibration and working condition setup of the system. After initialization, the nitrogen-vacancy color center magnetic sensor, under the combined action of the reference magnetic field and the modulation magnetic field, outputs a corresponding fluorescence signal according to the magnetic field state. This fluorescence signal is transmitted to the photodetector, read and converted into an electrical signal, and then synchronously demodulated by the modulation and demodulation circuit to obtain a demodulation result reflecting the magnetic field offset. The demodulation result is used in real time to control the secondary current drive unit, inputting a corresponding feedback current into the secondary feedback coil. When the external magnetic field generated by the current under test changes, the fluorescence intensity of the nitrogen-vacancy color center will change synchronously, thereby dynamically adjusting the demodulation result and the feedback current until the reverse magnetic field generated by the secondary feedback current completely cancels the magnetic field disturbance of the current under test, so that the magnetic field inside the magnetic ring is stably maintained at the 512 Gs energy level crossover-free operating point, achieving an ampere-turn balanced zero flux state. Finally, the feedback current of the secondary feedback coil continues to flow through the current sensing resistor connected in series in the circuit, forming a voltage divider proportional to the feedback current across the current sensing resistor. This voltage signal is sampled in real time by the analog-to-digital conversion acquisition module and output as a current measurement signal to the host computer. The host computer performs calculations based on the ampere-turn balance relationship to finally obtain the accurate value of the current to be measured, thus completing the entire current measurement function.

[0050] In some embodiments, such as Figure 3 and Figure 4 As shown, Figure 3 The core feature is the formation of a distinct fluorescence absorption valley at the 512Gs energy level crossover: when the magnetic field strength is far away from 512Gs, the fluorescence signal intensity of the NV color center remains at a high and stable level; when the magnetic field gradually approaches 512Gs, the fluorescence intensity continues to decrease, reaching its lowest value at 512Gs, and then gradually recovers as the magnetic field continues to increase, eventually returning to a high brightness stable state. Figure 3 Two types of magnetic field components are marked: one is the static magnetic field generated by the current under test, and the other is the high-frequency alternating modulation magnetic field applied by the modulation coil. The alternating magnetic field periodically perturbs the total magnetic field at the NV color center with 512 Gs as the center, causing the originally smooth fluorescence intensity curve to be superimposed with a high-frequency oscillation component with the same frequency as the modulation magnetic field, forming the high-frequency NV color center fluorescence signal shown in the figure. This alternating fluorescence signal is the original physical basis for subsequent modulation and demodulation and extraction of magnetic field offset, and also provides conditions for suppressing low-frequency noise in the photoelectric detection circuit.

[0051] Figure 4 The relationship between demodulation voltage and magnetic field strength is presented intuitively: at the 512Gs energy level crossover, the demodulation voltage is zero, corresponding to a state where the magnetic field perfectly matches the reference operating point; when the magnetic field strength deviates from 512Gs to the left (magnetic field less than 512Gs), the demodulation voltage strength first rises rapidly to its peak value, and then gradually falls back; when the magnetic field deviates to the right (magnetic field greater than 512Gs), the demodulation voltage strength first drops rapidly to its trough value, and then gradually rises back, ultimately forming a symmetrical S-shaped response curve centered on 512Gs. The demodulation voltage signal can accurately reflect the magnitude and direction of the magnetic field deviation relative to the 512Gs reference point, and is the core criterion for closed-loop feedback control: the system adjusts the current of the secondary feedback coil through this signal to counteract the magnetic field disturbance generated by the measured current, ensuring that the NV color center always operates stably near the 512Gs energy level crossover point, achieving high-precision current measurement in a zero-flux state.

[0052] The embodiments described in this application are for the purpose of more clearly illustrating the technical solutions of the embodiments of this application, and do not constitute a limitation on the technical solutions provided by the embodiments of this application. As those skilled in the art will know, with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0053] Those skilled in the art will understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of this application, and may include more or fewer steps than shown, or combine certain steps, or different steps.

[0054] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs.

[0055] Those skilled in the art will understand that all or some of the steps in the methods disclosed above, as well as the functional modules / units in the systems and devices, can be implemented as software, firmware, hardware, or suitable combinations thereof.

[0056] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, such that a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or apparatus.

[0057] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0058] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of the units described above is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or units may be electrical, mechanical, or other forms.

[0059] The units described above as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0060] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0061] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor, characterized in that, include: A magnetic ring, wherein the magnetic ring is disposed on the outside of the conductor whose current is to be measured; A nitrogen-vacancy color center sensor is disposed at the opening of the magnetic ring. The nitrogen-vacancy color center sensor is used to sense the magnetic field inside the magnetic ring and output a fluorescence signal. The coil unit includes a bias coil, a modulation coil, and a secondary feedback coil. The bias coil, the modulation coil, and the secondary feedback coil are wound sequentially on the magnetic ring. The bias coil is driven by a fixed current source and is used to generate a steady magnetic field inside the magnetic ring when the current to be measured is zero. The modulation coil is used to receive an alternating modulation signal, and the secondary feedback coil is used to cancel the magnetic field disturbance generated by the current to be measured. A photoelectric detection module is used to receive the fluorescence signal from the nitrogen-vacancy color center sensor and convert the received fluorescence signal into an electrical signal; A modulation and demodulation module is used to synchronously demodulate the electrical signal output by the photoelectric detection module and then output a demodulated voltage. A feedback control module is used to generate and adjust the current of the secondary feedback coil according to the demodulation voltage, so that the measured current and the current of the secondary feedback coil maintain an ampere-turn balance relationship. An analog-to-digital conversion acquisition module is used to acquire the current sensing voltage of the secondary feedback coil circuit and calculate the current to be measured based on the current sensing voltage.

2. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 1, characterized in that, The nitrogen-vacancy color center sensor detects a pure optical magnetic field in a reference magnetic field based on the excited state energy level without crossover points. The range of the reference magnetic field includes a center of 512 Gs and a width of less than or equal to 10 Gs.

3. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 2, characterized in that, The bias coil has a winding number of 3000 turns or more; The bias coil is driven by a fixed DC power supply to obtain the reference magnetic field.

4. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 2, characterized in that, The nitrogen-vacancy color center sensor detects magnetic field offset in the reference magnetic field through a purely optical method based on the quantum property of the crossover-free excited state energy level. The crossover-free excited state energy level corresponds to the energy overlap state of the excited state spin 0 and spin -1 energy levels of the nitrogen-vacancy color center sensor. The modulation coil periodically perturbs the reference magnetic field by applying a high-frequency alternating magnetic field, causing the fluorescence intensity of the nitrogen-vacancy color center sensor to alternate synchronously. The modulation and demodulation module performs synchronous demodulation based on a reference signal with the same frequency as the modulation signal.

5. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 2, characterized in that, The reference magnetic field is clamped within ±5 Gs around the crossover point of the excited state energy level by closed-loop feedback control. The nitrogen-vacancy color center sensor comprises a spin-1 quantum system. In the absence of an external magnetic field, the intrinsic energy level difference between the spin ±1 state and the spin 0 state of the excited state electronic energy level of the nitrogen-vacancy color center sensor includes a transition frequency of 1.44 GHz. Under the action of an external magnetic field, the spin ±1 state undergoes Zeeman splitting, with a splitting ratio coefficient of 2.8 MHz / Gs.

6. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 1, characterized in that, The modulation coil has 10 or fewer turns. The frequency of the alternating modulation signal connected to the modulation coil is equal to or greater than 5kHz, and the frequency of the alternating modulation signal connected to the modulation coil is greater than the signal frequency of the current to be measured.

7. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 1, characterized in that, The number of turns of the secondary feedback coil is less than or equal to 100 turns; The feedback control module includes a digital-to-analog converter unit, which calculates the current increment based on the demodulation voltage and the proportional coefficient, and iteratively updates the current of the secondary feedback coil based on the current increment. The secondary feedback coil is connected in series with a current-sensing resistor. The voltage across the current-sensing resistor is sampled by the analog-to-digital conversion acquisition module. The current-sensing resistor is used to calculate the secondary feedback current and, based on the ampere-turn balance relationship, to obtain the current to be measured.

8. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 7, characterized in that, The feedback control module updates the current of the secondary feedback coil according to an iterative formula, which is: ； in, This indicates the current of the secondary feedback coil in the next update. This indicates the current of the secondary feedback coil. Indicates the demodulation voltage. This indicates the preset scaling factor.

9. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 7, characterized in that, The formula for calculating the ampere-turn balance relationship is: ； in, This indicates the current to be measured. This refers to the secondary feedback current. This indicates the number of turns of the conductor carrying the current under test through the magnetic ring. This indicates the number of turns of the secondary feedback coil wound on the magnetic ring.

10. The microwave-free zero-flux current measurement system based on a nitrogen-vacancy color center sensor according to claim 1, characterized in that, The bias coil is driven by the fixed current source to apply DC excitation to the magnetic ring, so that a reference magnetic field is formed inside the magnetic ring. Then, the nitrogen-vacancy color center sensor is set at the crossover point of the excited state energy level. The alternating modulation signal is applied to the magnetic field within the magnetic ring via the modulation coil, thereby alternatingly modulating the fluorescence signal of the nitrogen-vacancy color center sensor.

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