High-speed and large dynamic range magnetic field measurement system

Abstract

The present invention provides a high-speed and large dynamic range magnetic field measurement system, including: an agile radio frequency source, which generates an intermediate frequency signal based on a frequency control word; a mixer that connects the intermediate frequency signal and the local oscillator signal and outputs a radio frequency signal; a magnetic field detection module, which detects the magnetic field to generate a fluorescence signal and a corresponding digital electrical signal; a phase-locked demodulation module, which outputs a fluorescence demodulation signal; a closed-loop frequency locking module, which tracks and calculates the microwave frequency movement and magnetic field size change of the current cycle relative to the previous cycle based on the fluorescence demodulation signal, obtains the microwave center frequency and magnetic field size of the current cycle, and converts the microwave frequency movement into a frequency control word to update the frequency of the intermediate frequency signal. The present invention expands the paramagnetic resonance sensor from the traditional small magnetic field measurement to a large dynamic range; through fast feedback tracking, the magnetic measurement speed is improved, and the adaptability of magnetic measurement under different field strengths is enhanced.

Description

Technical Field

[0001] The invention relates to the field of sensor technology, and in particular to a high-speed and large dynamic range magnetic field measurement system. Background Art

[0002] In today's scientific and technological development, accurate measurement of magnetic fields plays a vital role in many fields; the development of high-precision and high-stability magnetic measurement instruments is of great significance to the development of many scientific and technological fields.

[0003] At present, the main methods for detecting weak magnetic signals include superconducting quantum interference device (SQUID), Hall magnetometer, fluxgate magnetometer, optical pump magnetometer, proton magnetometer, etc. SQUID can be divided into high-temperature superconducting SQUID and low-temperature superconducting SQUID according to the material. SQUID is the most sensitive magnetometer so far. Its disadvantages are low spatial resolution and the need to work in a low-temperature environment. The complex and expensive cooling equipment and large size greatly limit the breadth of its application. The sensitivity of the Hall magnetometer is poor and is easily affected by temperature. The proton magnetometer is the most accurate instrument for measuring the total intensity of the Earth's magnetic field so far. Since the recovery frequency of the proton precession magnetometer is in the order of several Hz, the low time accuracy limits its application.

[0004] In the past decade, with the continuous development of quantum technology, magnetometers based on solid-state spin NV centers (Nitrogen-Vacancy Center) have attracted widespread attention from scientists due to their excellent magnetic sensitivity and high spatial resolution, making them one of the most promising quantum devices in contemporary times. The magnetic sensing capability of diamond NV centers is based on the Zeeman effect of electron spin in a magnetic field. The angular momentum of electrons in space is quantized, and the angular momentum characteristics of electrons are called spins. The spin magnetic moment causes the electrons to move in energy levels under a magnetic field, which manifests as energy level splitting in microwave-fluorescence spectroscopy, which is called the Zeeman effect. The size of the Zeeman splitting is proportional to the size of the magnetic field, so the Zeeman splitting in electron spins can be used for magnetic field detection.

[0005] Optically detected magnetic resonance (ODMR) sensing technology based on diamond NV color centers obtains information about changes in the external magnetic field through the resonance point position of the Zeeman splitting energy level of the NV color center. However, the current traditional magnetic detection method based on ODMR has the following disadvantages, making it difficult to adapt to complex working conditions:

[0006] 1. Small dynamic range. Limited by the width of the resonance peak, the maximum dynamic range of magnetic measurement is only a few hundred μT (micro Tesla). If the magnetic field changes beyond the resonance peak, it exceeds the range.

[0007] 2. Pulse sequence method The magnetic field measurement is repeated many times. The magnetic measurement based on complex microwave pulse sequence requires 10 5 —10 6 Repeated measurements, although the measurement accuracy is high, but the duration is long and not suitable for actual working conditions;

[0008] 3. The continuous method magnetic measurement has a low refresh rate and does not meet the requirements of large dynamic range, high refresh rate and high precision measurement.

[0009] Therefore, how to solve the problems of small dynamic range, low time resolution and low precision of NV color center-based optical detection magnetic resonance sensing technology has become one of the urgent issues to be solved by technicians in this field. Summary of the invention

[0010] In view of the shortcomings of the prior art mentioned above, an object of the present invention is to provide a high-speed and large dynamic range magnetic field measurement system to solve the problems of small dynamic range, low refresh rate, low precision and low slew rate in the prior art optical detection magnetic resonance sensing technology based on NV color centers.

[0011] To achieve the above-mentioned and other related purposes, the present invention provides a high-speed and large dynamic range magnetic field measurement system, the high-speed and large dynamic range magnetic field measurement system at least comprising:

[0012] Agile RF source, mixer, magnetic field detection module, phase-locked demodulation module and closed-loop frequency locking module;

[0013] The agile RF source is connected to the output end of the closed-loop frequency locking module, and generates a corresponding intermediate frequency signal based on the frequency control word output by the closed-loop frequency locking module;

[0014] The intermediate frequency signal input end of the mixer is connected to the output end of the agile RF source, the local oscillator signal input end is connected to the local oscillator signal, and the mixer outputs a RF signal;

[0015] The magnetic field detection module is connected to the output end of the mixer, detects the magnetic field based on the radio frequency signal and the laser signal to generate a corresponding fluorescent signal, and outputs a digital electrical signal corresponding to the fluorescent signal;

[0016] The phase-locked demodulation module is connected to the output end of the magnetic field detection module, demodulates the output signal of the magnetic field detection module based on a reference signal, adjusts the phase of the reference signal so that the output signal of the magnetic field detection module is phase-locked with the reference signal, and outputs a fluorescence demodulation signal;

[0017] The closed-loop frequency locking module is connected to the output end of the phase-locked demodulation module, and based on the fluorescence demodulation signal, tracks and calculates the microwave frequency movement and magnetic field size change of the current cycle relative to the previous cycle, obtains the microwave center frequency and magnetic field size of the current cycle, and converts the microwave frequency movement into a frequency control word to update the frequency of the intermediate frequency signal;

[0018] Wherein, the modulation frequency of the local oscillator signal is the same as that of the reference signal.

[0019] Optionally, the magnetic field detection module includes a magnetic sensor, a first photodetector and a first analog-to-digital converter;

[0020] The magnetic sensor detects the magnetic field and generates a corresponding fluorescent signal;

[0021] The first photodetector is connected to the output end of the magnetic sensor to convert the fluorescence signal into an electrical signal;

[0022] The first analog-to-digital converter is connected to the output end of the first photodetector, and converts the analog signal output by the first photodetector into a digital signal.

[0023] More optionally, the magnetic sensor is a paramagnetic resonance sensor.

[0024] More optionally, the magnetic sensor is a diamond NV color center magnetic sensor probe.

[0025] More optionally, the magnetic field detection module further includes a first low-noise preamplifier, and the first low-noise preamplifier is connected between the first photodetector and the first analog-to-digital converter.

[0026] More optionally, the magnetic field detection module further includes a first bandpass filter, and the first bandpass filter is connected between the first photodetector and the first analog-to-digital converter.

[0027] Optionally, the high-speed and large dynamic range magnetic field measurement system further includes a local oscillator signal generating module, and the local oscillator signal generating module performs frequency modulation based on a same-frequency signal of the reference signal to obtain the local oscillator signal.

[0028] More optionally, the high-speed large dynamic range magnetic field measurement system also includes a digital-to-analog converter, which is connected to the reference signal and converts the reference signal into an analog signal to provide the local oscillator signal generating module with a same frequency signal as the reference signal.

[0029] Optionally, the high-speed large dynamic range magnetic field measurement system further includes a display, which is connected to the output end of the closed-loop frequency locking module and is used to display the magnitude of the magnetic field calculated by the closed-loop frequency locking module.

[0030] Optionally, the phase-locked demodulation module includes a first multiplier, a second multiplier, a first low-pass filter, a second low-pass filter, a phase detector and a direct digital frequency synthesizer;

[0031] The first input end of the first multiplier is connected to the output end of the magnetic field detection module, and the second input end is connected to the output end of the direct digital frequency synthesizer, and the output signal of the magnetic field detection module is multiplied by the orthogonal reference signal;

[0032] The first low-pass filter is connected to the output end of the first multiplier to filter out high-frequency components in the output signal of the first multiplier to obtain an orthogonal demodulation signal;

[0033] The first input end of the second multiplier is connected to the output end of the magnetic field detection module, and the second input end is connected to the output end of the direct digital frequency synthesizer, and multiplies the output signal of the magnetic field detection module with the in-phase reference signal;

[0034] The second low-pass filter is connected to the output end of the second multiplier to filter out the high-frequency component in the output signal of the second multiplier to obtain an in-phase demodulation signal; the in-phase demodulation signal is output as a fluorescence demodulation signal;

[0035] The phase detector is connected to the output ends of the first low-pass filter and the second low-pass filter to obtain the phase difference between the output signal of the magnetic field detection module and the in-phase reference signal;

[0036] The direct digital frequency synthesizer is connected to the output end of the phase detector, and adjusts the phases of the quadrature reference signal and the in-phase reference signal based on the phase difference.

[0037] More optionally, the phase detector performs an inverse tangent function operation on the orthogonal demodulation signal and the in-phase demodulation signal.

[0038] More optionally, the phase-locked demodulation module and the closed-loop frequency locking module are implemented using a field programmable logic gate array.

[0039] More optionally, the high-speed and large dynamic range magnetic field measurement system also includes a laser background demodulation signal generating module, which obtains a laser background demodulation signal based on a reference laser signal, and inputs the signal into the closed-loop frequency locking module after differentiating the signal with the output signal of the phase-locked demodulation module.

[0040] More optionally, the laser background demodulation signal generating module comprises: a second photodetector, a second analog-to-digital converter, a third multiplier and a third low-pass filter;

[0041] The second photodetector converts the reference laser signal into an electrical signal;

[0042] The second analog-to-digital converter is connected to the output end of the second photodetector, and converts the analog signal output by the second photodetector into a digital signal;

[0043] The first input end of the third multiplier is connected to the output end of the second analog-to-digital converter, and the second input end is connected to the orthogonal reference signal, and the output signal of the second analog-to-digital converter is multiplied by the orthogonal reference signal;

[0044] The third low-pass filter is connected to the output end of the third multiplier to filter out the high-frequency component in the output signal of the third multiplier to obtain the laser background demodulation signal.

[0045] More optionally, the laser background demodulation signal generating module further includes a second low-noise preamplifier, and the second low-noise preamplifier is connected between the second photodetector and the second analog-to-digital converter.

[0046] More optionally, the laser background demodulation signal generating module further includes a second bandpass filter, and the second bandpass filter is connected between the second photodetector and the second analog-to-digital converter.

[0047] As described above, the high-speed and large dynamic range magnetic field measurement system of the present invention has the following beneficial effects:

[0048] 1. The present invention provides a hardware system for magnetic measurement based on the principle of electron paramagnetic resonance light detection, and expands the measurement dynamic range by using the resonance frequency tracking method. Compared with the measurement dynamic range of hundreds of μT of the traditional ODMR magnetic measurement technology, the measurement dynamic range of the present invention is theoretically unlimited and is only determined by the bandwidth Δω of the agile RF source; when measuring in a single channel, the maximum change in the projected magnetic field intensity is Corresponding magnetic field range

[0049] 2. The high-speed and large dynamic range magnetic field measurement system of the present invention has a high measurement refresh rate, a fast hardware trigger response speed, and a refresh rate of more than 10kHz.

[0050] 3. In the high-speed, large dynamic range magnetic field measurement system of the present invention, the microwave signal is generated by mixing an agile signal source with a local oscillator signal source. The local oscillator source can be replaced according to different application scenarios. It has high flexibility and a wide range of applicable scenarios. It can perform precise magnetic measurements under high background fields and low background fields.

[0051] 4. In the high-speed, large dynamic range magnetic field measurement system of the present invention, the main control unit adopts an FPGA chip. The FPGA chip is programmable and can modify the measurement circuit parameters according to different scenarios (such as changing the reference frequency, etc.), or expand or delete the measurement circuit functions (for example, when using temperature drift suppression and vector measurement, the measurement channel can be flexibly expanded as needed to meet different measurement requirements), and has strong scalability. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Shown is a schematic structural diagram of the high-speed and large dynamic range magnetic field measurement system of the present invention.

[0053] Figure 2 It is a schematic diagram showing the method of realizing large dynamic range magnetic field measurement according to the present invention.

[0054] Figure 3 It is a schematic diagram showing the working principle of the closed-loop frequency locking module of the present invention.

[0055] Figure 4 It is a frequency-amplitude schematic diagram of the magnetic field to be measured according to the present invention.

[0056] Figure 5 Shown is a schematic diagram of experimental data measured in real time by the high-speed and large dynamic range magnetic field measurement system of the present invention.

[0057] Component number description

[0058] 1 High-speed and large dynamic range magnetic field measurement system 10 Agile RF source

[0059] 11 Mixer 12 Magnetic field detection module

[0060] 121 magnetic sensor 122 first photodetector

[0061] 123 first analog-to-digital converter 124 first low-noise preamplifier

[0062] 125 first bandpass filter 13 phase-locked demodulation module

[0063] 131 first multiplier 132 second multiplier

[0064] 133 first low pass filter 134 second low pass filter

[0065] 135 Phase detector 136 Direct digital frequency synthesizer

[0066] 14 Closed-loop frequency locking module 15 Local oscillator signal generation module

[0067] 16 Digital-to-analog converter 17 Laser background demodulation signal generation module

[0068] 171 second photodetector 172 second analog-to-digital converter

[0069] 173 third multiplier 174 third low pass filter

[0070] 175 Second low noise preamplifier 176 Second band pass filter

[0071] 18 Display 19 Field Programmable Gate Array DETAILED DESCRIPTION

[0072] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0073] See also Figure 1 to Figure 5 It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0074] like Figure 1 As shown, this embodiment provides a high-speed large dynamic range magnetic field measurement system 1, and the high-speed large dynamic range magnetic field measurement system 1 includes:

[0075] An agile RF source 10 , a mixer 11 , a magnetic field detection module 12 , a phase-locked demodulation module 13 and a closed-loop frequency locking module 14 .

[0076] like Figure 1 As shown, the agile RF source 10 is connected to the output end of the closed-loop frequency locking module 14 , and generates a corresponding intermediate frequency signal IF based on the frequency control word output by the closed-loop frequency locking module 14 .

[0077] Specifically, the agile RF source 10 provides a sideband offset signal for the mixer 11, receives the frequency control word, and quickly changes the output signal frequency based on the frequency control word (as an example, the switching speed is less than 1us and can be up to the order of ns), obtains the corresponding intermediate frequency signal IF, and provides the sideband offset signal for the mixer 11. The circuit structure of the agile RF source is not limited, and any structure that can obtain the corresponding intermediate frequency signal based on the frequency control word is applicable to the present invention, which will not be described one by one here.

[0078] like Figure 1As shown, the intermediate frequency signal input end of the mixer 11 is connected to the output end of the agile RF source 10, and the local oscillator signal input end is connected to the local oscillator signal LO, and the RF signal RF is output. The modulation frequency of the local oscillator signal LO is the same as the reference signal in the phase-locked demodulation module 13.

[0079] Specifically, the structure of the mixer 11 is not limited, including but not limited to a single sideband mixer or an IQ mixer, and any circuit structure that can achieve a mixing function is applicable to the present invention. The single sideband dynamic range output by the mixer 11 can completely cover the frequency shift interval caused by the four pairs of optical detection magnetic resonance peaks and the magnetic field to be measured.

[0080] like Figure 1 As shown, as another implementation of the present invention, the high-speed large dynamic range magnetic field measurement system 1 also includes a local oscillator signal generating module 15, and the local oscillator signal generating module 15 performs frequency modulation based on the same frequency signal of the reference signal (the modulation frequency is f mod , the modulation depth is f deu ), the modulation frequency is provided by the same frequency signal of the reference signal, as an example, the frequency modulation range is set to 100Hz-100kHz, the lower limit of the modulation frequency is determined by the magnetic field refresh rate, and finally the local oscillation signal LO is obtained. Further, as an example, the high-speed large dynamic range magnetic field measurement system 1 also includes a digital-to-analog converter 16, the digital-to-analog converter 16 is connected to the reference signal, converts the reference signal into an analog signal, and provides the same frequency signal of the reference signal to the local oscillation signal generating module 15.

[0081] It should be noted that, in this embodiment, the co-frequency signal of the reference signal is the reference signal itself; in actual use, a signal with the same frequency as the reference signal may be set as needed, which is not limited to this embodiment.

[0082] like Figure 1 As shown, the magnetic field detection module 12 is connected to the output end of the mixer 11, detects the magnetic field based on the radio frequency signal RF and the laser signal to generate a corresponding fluorescent signal, and outputs a digital electrical signal corresponding to the fluorescent signal.

[0083] Specifically, the magnetic field detection module 12 detects the magnetic field based on the principle of electron paramagnetic resonance light detection, and outputs a corresponding electrical signal, which is a digital signal. In this embodiment, the magnetic field detection module 12 includes a magnetic sensor 121, a first photodetector 122 and a first analog-to-digital converter 123; the magnetic sensor 121 is in the magnetic field environment to be measured, including a high-frequency microwave input interface and an optical output interface, the high-frequency microwave input interface is connected to the radio frequency signal RF, and a fluorescent signal is generated under the joint action of the radio frequency signal RF (microwave) and the laser signal on the magnetic sensor 121, and is output from the optical output interface; as an example, the magnetic sensor 121 is a paramagnetic resonance sensor, including but not limited to a magnetic sensor based on NV color center, such as a magnetic sensor of diamond NV color center. The first photodetector 122 is connected to the output end of the magnetic sensor 121 to convert the fluorescent signal into an electrical signal; as an example, the first photodetector 122 includes but is not limited to a photodiode. The first analog-to-digital converter 123 is connected to the output end of the first photodetector 122, and converts the analog signal output by the first photodetector 122 into a digital signal to sample the output signal of the first photodetector 122; wherein the sampling rate of the first photodetector 122 is greater than 5 times the modulation frequency.

[0084] Specifically, as an implementation of the present invention, the magnetic field detection module 12 further includes a first low-noise preamplifier 124, which is connected between the first photodetector 122 and the first analog-to-digital converter 123, and performs low-noise preamplification on the output signal of the first photodetector 122. As another implementation of the present invention, the magnetic field detection module 12 further includes a first bandpass filter 125, which is connected between the first photodetector 122 and the first analog-to-digital converter 123, and is used to extract the frequency modulation signal selected in the frequency modulation mode. In this embodiment, the first low-noise preamplifier 124 and the first bandpass filter 125 are both used. At this time, the first low-noise preamplifier 124 is connected to the output end of the first photodetector 122, the first bandpass filter 125 is connected to the output end of the first low-noise preamplifier 124, and the first analog-to-digital converter 123 is connected to the output end of the first bandpass filter 125.

[0085] like Figure 1 As shown, the phase-locked demodulation module 13 is connected to the output end of the magnetic field detection module 12, demodulates the output signal of the magnetic field detection module 12 based on the reference signal, adjusts the phase of the reference signal so that the output signal of the magnetic field detection module 12 is phase-locked with the reference signal, and outputs a fluorescence demodulation signal.

[0086] Specifically, in this embodiment, the phase-locked demodulation module 13 uses a two-phase demodulation method to compensate for the phase difference between the reference signal and the output signal of the magnetic field detection module 12, and includes a first multiplier 131, a second multiplier 132, a first low-pass filter 133, a second low-pass filter 134, a phase detector 135 and a direct digital frequency synthesizer (Direct Digital Synthesizer, DDS) 136. The first input end of the first multiplier 131 is connected to the output end of the magnetic field detection module 12, and the second input end is connected to the output end of the direct digital frequency synthesizer 136, and the output signal of the magnetic field detection module 12 is multiplied by the orthogonal reference signal. The first low-pass filter 133 is connected to the output end of the first multiplier 131. The first low-pass filter 133 is a digital filter, which filters out the high-frequency component in the output signal of the first multiplier 131 to obtain the orthogonal demodulation signal Y (DC signal). The first input end of the second multiplier 132 is connected to the output end of the magnetic field detection module 12, and the second input end is connected to the output end of the direct digital frequency synthesizer 136, and the output signal of the magnetic field detection module 12 is multiplied by the in-phase reference signal. The second low-pass filter 134 is connected to the output end of the second multiplier 132. The second low-pass filter 134 is a digital filter, which filters out the high-frequency component in the output signal of the second multiplier 132 to obtain the in-phase demodulation signal X (DC signal); the in-phase demodulation signal X is output as a fluorescence demodulation signal. The phase detector 135 is connected to the output ends of the first low-pass filter 133 and the second low-pass filter 134 to obtain the phase difference between the output signal of the magnetic field detection module 12 and the in-phase reference signal; as an example, the phase detector 135 performs an inverse tangent function operation on the orthogonal demodulation signal Y and the in-phase demodulation signal X to obtain the phase difference, and the phase difference satisfies In actual use, the phase detection method can be set as needed. The direct digital frequency synthesizer 136 is connected to the output end of the phase detector 135, and adjusts the phase of the orthogonal reference signal and the in-phase reference signal based on the phase difference, so that the phase difference between the in-phase reference signal and the output signal of the magnetic field detection module 12 is zero.

[0087] It should be noted that the cutoff frequencies of the first low-pass filter 133 and the second low-pass filter 134 are selected in relation to the time constant and can be adjusted according to the refresh rate and the signal-to-noise ratio, which will not be elaborated herein.

[0088] like Figure 1As shown, the closed-loop frequency locking module 14 is connected to the output end of the phase-locked demodulation module 13, and based on the fluorescence demodulation signal tracking, calculates the microwave frequency movement Δf and the magnetic field size change ΔB of the current cycle relative to the previous cycle, obtains the microwave center frequency and magnetic field size of the current cycle, and converts the microwave frequency movement Δf into a frequency control word to update the frequency of the intermediate frequency signal IF.

[0089] Specifically, the closed-loop frequency locking module 14 includes a list initialization frequency sweep mode and a real-time measurement mode. The relative zero point is determined in the initialization frequency sweep mode, and the magnetic field is tracked and measured based on the relative zero point in the real-time measurement mode.

[0090] More specifically, in the initialization frequency sweep mode, the closed-loop frequency locking module 14 generates a series of frequency control words within a preset frequency range, controls the agile RF source 10 to sweep at equal intervals, and stores the microwave frequency and the demodulated signal in a two-dimensional array to obtain the microwave-demodulated signal spectrum of the resonance peak (the number of the microwave-demodulated signal spectrum of the resonance peak is determined by the material of the magnetic sensor. In this embodiment, diamond is used, so 4 pairs of microwave-demodulated signal spectrum of the resonance peak can be obtained), and the resonance peak is fitted to obtain the slope k of the linear region. i and microwave resonance frequency ∫ i ,according to (2.87 GHz is the energy level difference of diamond, and the material of the magnetic sensor is different and is adjusted accordingly, not limited to the present embodiment) the initialization parameter magnetic field size B0 and the corresponding microwave frequency f0 are calculated, wherein the gyromagnetic ratio γ≈28 GHz / T (the gyromagnetic ratio is determined by the material of the magnetic sensor, not limited to the present embodiment), and i corresponds to different resonance peaks; thereby determining the relative zero point and obtaining the measurement initialization parameters.

[0091] More specifically, in the real-time measurement mode, the closed-loop frequency locking module 14 starts real-time measurement based on the initialization parameters. In each measurement cycle, the microwave frequency shift ∧f and the magnetic field magnitude change ∧R are calculated by the difference between the output signal of the phase-locked demodulation module 13 and the previous cycle, and then the microwave center frequency and magnetic field magnitude of the current cycle are obtained. In this embodiment, a resonance peak is selected for magnetic field measurement, such as Figure 2 The figure shows the process of the closed-loop frequency locking module 14 realizing the large dynamic range measurement of the magnetic field. The change of the external magnetic field causes the resonance peak to move, and the demodulation signal V input to the closed-loop frequency locking module 14 deviates from the zero point. The closed-loop frequency locking module 14 calculates the microwave frequency movement Δf and the magnetic field size change ΔB, where and k is the slope, that is, the NV axial projection magnetic field size B of this cycle is obtained j =B j-1 +ΔB and microwave center frequency f j =fj-1 +Δf, where B j-1 and f j-1 They are respectively the magnetic field size and microwave center frequency obtained in the previous cycle. Figure 3 The figure shows the working principle of the closed-loop frequency locking module 14. The resonance peak frequency position is demodulated through the closed-loop frequency locking technology, and the frequency shift and the corresponding magnetic field change are calculated within a closed-loop cycle. After the microwave center frequency is moved to the resonance peak position, the next measurement cycle is entered.

[0092] More specifically, the microwave frequency shift Δf of each cycle is encoded to generate a frequency control word. As an example, the closed-loop frequency locking module 14 includes a 48-bit parallel interface, through which the frequency control word is transmitted to the agile RF source 10 for tracking frequency hopping, so that the sideband frequency of the RF signal RF is always maintained at the diamond NV color center resonance frequency, achieving the effect of real-time tracking and measuring changes in the external magnetic field. In actual use, the number of transmission data bits of the parallel interface can be set as needed.

[0093] It should be noted that this embodiment only shows the process of closed-loop tracking and measuring one resonance peak. Those skilled in the art can flexibly select the number of resonance peaks for closed-loop tracking to eliminate temperature drift or achieve vector measurement. As an example, temperature drift is manifested as an overall frequency shift in the same direction of two resonance peaks of spin ±1 of the same NV axis, that is, the relative position of the two resonance peaks remains unchanged, they move in phase and the same amount of movement, and the movement reflects the temperature change, thereby achieving temperature compensation; when compensating for temperature drift, at least one pair of resonance peaks of spin ±1 of the same NV axis must be selected for initialization, the system tracks the two resonance peaks of the spin ±1 energy level respectively, and measures the resonance frequency difference ΔF of the spin ±1 energy level. The frequency shift corresponding to the true magnetic field change is half of the resonance peak frequency difference of the spin ±1 energy level, and the frequency shift difference isolates the temperature drift. As another example, during vector measurement, the initialization process requires that the direction of the magnetic field of known polarity be calibrated in the set Cartesian coordinate system; during the real-time measurement process, it is required to perform frequency-locked tracking on four pairs (at least two pairs) of resonance peaks respectively, obtain four pairs of frequency shifts Δf and slopes k, and according to the gyromagnetic ratio γ, run a projection operation in the closed-loop frequency locking module 14 to obtain the size of the spatial vector projection magnetic field based on the projection on each coordinate; the coordinate transformation sign in the determination algorithm of the magnetic field direction initialization calibration is used to quickly obtain the vector direction.

[0094] like Figure 1 As shown, as another implementation of the present invention, the high-speed large dynamic range magnetic field measurement system 1 further includes a display 18, and the display 18 is connected to the output end of the closed-loop frequency locking module 14, and is used to display the magnetic field magnitude calculated by the closed-loop frequency locking module 14. As an example, the magnetic field magnitude is transmitted to the display 18 via a USB bus.

[0095] like Figure 1 As shown, as another implementation of the present invention, the high-speed large dynamic range magnetic field measurement system 1 also includes a laser background demodulation signal generating module 17, which obtains a laser background demodulation signal based on a reference laser signal, and inputs the laser background demodulation signal into the closed-loop frequency locking module 14 after being differentiated from the output signal of the phase-locked demodulation module, so as to reduce the influence of the laser background noise on the magnetic field demodulation signal.

[0096] Specifically, in this embodiment, the laser background demodulation signal generating module 17 includes: a second photodetector 171, a second analog-to-digital converter 172, a third multiplier 173 and a third low-pass filter 174. The second photodetector 171 converts the reference laser signal into an electrical signal. The second analog-to-digital converter 172 is connected to the output end of the second photodetector 171, and converts the analog signal output by the second photodetector 171 into a digital signal. The first input end of the third multiplier 173 is connected to the output end of the second analog-to-digital converter 172, and the second input end is connected to the orthogonal reference signal, and the output signal of the second analog-to-digital converter 172 is multiplied by the orthogonal reference signal. The third low-pass filter 174 is connected to the output end of the third multiplier 173, and filters out the high-frequency component in the output signal of the third multiplier 173 to obtain the laser background demodulation signal. As an example, the laser background demodulation signal generating module 17 further includes a second low-noise preamplifier 175, and the second low-noise preamplifier 175 is connected between the second photodetector 171 and the second analog-to-digital converter 172. As another example, the laser background demodulation signal generating module 17 further includes a second bandpass filter 176, and the second bandpass filter 176 is connected between the second photodetector 171 and the second analog-to-digital converter 172. In this embodiment, the second low-noise preamplifier 175 and the second bandpass filter 176 are both used. At this time, the second low-noise preamplifier 175 is connected to the output end of the second photodetector 171, the second bandpass filter 176 is connected to the output end of the second low-noise preamplifier 175, and the second analog-to-digital converter 172 is connected to the output end of the second bandpass filter 176. More specifically, the reference laser signal and the fluorescence signal are processed as consistent as possible to minimize the impact of laser background noise; as an example, the working wavelengths of the first photodetector 122 and the second photodetector 171 both cover 637nm-800nm, and the working bandwidth is much larger than the modulation frequency; the electronic noise and dark current of the detector are much smaller than the fluorescence signal conversion current, and the saturation power is greater than the maximum fluorescence signal power. The passband center frequency of the first bandpass filter 125 and the second bandpass filter 176 is the microwave modulation frequency, and the frequency modulation signal selected in the frequency modulation mode is extracted, and the passband width is adjusted according to the measurement refresh rate.

[0097] It should be noted that, when the laser background demodulation signal generating module 17 is added, the signal processed by the closed-loop frequency locking module 14 is the differential signal between the fluorescence demodulation signal and the laser background demodulation signal. The processing process is the same as above and will not be repeated here.

[0098] like Figure 1As shown, in this embodiment, the phase-locked demodulation module 13, the closed-loop frequency-locked module 14, and the third multiplier 173 and the third low-pass filter 174 in the laser background demodulation signal generating module 17 are implemented by a field programmable gate array (FPGA) 19 to improve scalability. In actual use, the corresponding functions can be implemented by FPGA as needed, which is not limited to this embodiment.

[0099] like Figure 4 and Figure 5 As shown, the magnetic field to be measured is set to a magnetic field modulated by a 50Hz sine wave, and the magnetic field strength varies in the range of (-2mT to 1.5mT); the measurement results verify the magnetic field variation range and the AC magnetic field frequency. It can be seen that the high-speed and large dynamic range magnetic field measurement system of the present invention can still track the magnetic field when the speed reaches (552±5)mT / s.

[0100] In summary, the present invention provides a high-speed and large dynamic range magnetic field measurement system, including: an agile RF source, a mixer, a magnetic field detection module, a phase-locked demodulation module and a closed-loop frequency locking module; the agile RF source is connected to the output end of the closed-loop frequency locking module, and generates a corresponding intermediate frequency signal based on the frequency control word output by the closed-loop frequency locking module; the intermediate frequency signal input end of the mixer is connected to the output end of the agile RF source, and the local oscillator signal input end is connected to the local oscillator signal, and outputs a RF signal; the magnetic field detection module is connected to the output end of the mixer, detects the magnetic field based on the RF signal and the laser signal to generate a corresponding fluorescent signal, and outputs a digital electrical signal corresponding to the fluorescent signal; the phase-locked demodulation module The modulation module is connected to the output end of the magnetic field detection module, demodulates the output signal of the magnetic field detection module based on a reference signal, adjusts the phase of the reference signal so that the output signal of the magnetic field detection module is phase-locked with the reference signal, and outputs a fluorescence demodulation signal; the closed-loop frequency locking module is connected to the output end of the phase-locked demodulation module, tracks and calculates the microwave frequency movement and magnetic field size change of the current cycle relative to the previous cycle based on the fluorescence demodulation signal, obtains the microwave center frequency and magnetic field size of the current cycle, and converts the microwave frequency movement into a frequency control word to update the frequency of the intermediate frequency signal; wherein the modulation frequency of the local oscillator signal is the same frequency as the reference signal. The high-speed large dynamic range magnetic field measurement system of the present invention adopts high-speed feedback and closed-loop tracking technology to track and measure the peak position of the optically detected magnetic resonance (ODMR) spectrum. The system keeps the microwave frequency and the magnetic response resonance peak synchronous through the microwave frequency tracking method, and can work in a large magnetic field dynamic range, expanding the paramagnetic resonance sensor from the traditional small magnetic field measurement to a large dynamic range; and based on the FPGA main control module, analog-to-digital conversion module, digital-to-analog conversion module, phase-locked demodulation module, closed-loop frequency-locked algorithm module and agile signal source, the rapid feedback tracking of the microwave frequency is realized, the magnetic measurement speed is improved, and the adaptability of magnetic measurement under different field strengths is enhanced. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0101] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A high-speed and large dynamic range magnetic field measurement system, characterized in that: The high-speed and large dynamic range magnetic field measurement system at least comprises: Agile RF source, mixer, magnetic field detection module, phase-locked demodulation module and closed-loop frequency locking module; The agile RF source is connected to the output end of the closed-loop frequency locking module, and generates a corresponding intermediate frequency signal based on the frequency control word output by the closed-loop frequency locking module; The intermediate frequency signal input end of the mixer is connected to the output end of the agile RF source, the local oscillator signal input end is connected to the local oscillator signal, and the mixer outputs a RF signal; The magnetic field detection module is connected to the output end of the mixer, detects the magnetic field based on the radio frequency signal and the laser signal to generate a corresponding fluorescent signal, and outputs a digital electrical signal corresponding to the fluorescent signal; The phase-locked demodulation module is connected to the output end of the magnetic field detection module, demodulates the output signal of the magnetic field detection module based on a reference signal, adjusts the phase of the reference signal so that the output signal of the magnetic field detection module is phase-locked with the reference signal, and outputs a fluorescence demodulation signal; The closed-loop frequency locking module is connected to the output end of the phase-locked demodulation module, and based on the fluorescence demodulation signal, tracks and calculates the microwave frequency movement and magnetic field size change of the current cycle relative to the previous cycle, obtains the microwave center frequency and magnetic field size of the current cycle, and converts the microwave frequency movement into a frequency control word to update the frequency of the intermediate frequency signal; Wherein, the modulation frequency of the local oscillator signal is the same as that of the reference signal.

2. The high-speed and large dynamic range magnetic field measurement system according to claim 1, characterized in that: The magnetic field detection module includes a magnetic sensor, a first photodetector and a first analog-to-digital converter; The magnetic sensor detects the magnetic field and generates a corresponding fluorescent signal; The first photodetector is connected to the output end of the magnetic sensor to convert the fluorescence signal into an electrical signal; The first analog-to-digital converter is connected to the output end of the first photodetector, and converts the analog signal output by the first photodetector into a digital signal.

3. The high-speed and large dynamic range magnetic field measurement system according to claim 2, characterized in that: The magnetic sensor is a paramagnetic resonance sensor.

4. The high-speed and large dynamic range magnetic field measurement system according to claim 2, characterized in that: The magnetic sensor is a diamond NV color center magnetic sensor.

5. The high-speed and large dynamic range magnetic field measurement system according to claim 2, characterized in that: The magnetic field detection module further includes a first low-noise preamplifier connected between the first photodetector and the first analog-to-digital converter.

6. The high-speed and large dynamic range magnetic field measurement system according to claim 2, characterized in that: The magnetic field detection module further includes a first bandpass filter connected between the first photodetector and the first analog-to-digital converter.

7. The high-speed and large dynamic range magnetic field measurement system according to claim 1, characterized in that: The high-speed and large dynamic range magnetic field measurement system further includes a local oscillator signal generating module, and the local oscillator signal generating module performs frequency modulation based on a same-frequency signal of the reference signal to obtain the local oscillator signal.

8. The high-speed and large dynamic range magnetic field measurement system according to claim 7, characterized in that: The high-speed large dynamic range magnetic field measurement system also includes a digital-to-analog converter, which is connected to the reference signal and converts the reference signal into an analog signal to provide the local oscillator signal generating module with a same-frequency signal as the reference signal.

9. The high-speed and large dynamic range magnetic field measurement system according to claim 1, characterized in that: The high-speed large dynamic range magnetic field measurement system also includes a display, which is connected to the output end of the closed-loop frequency locking module and is used to display the magnetic field size calculated by the closed-loop frequency locking module.

10. The high-speed and large dynamic range magnetic field measurement system according to claim 1, characterized in that: The phase-locked demodulation module includes a first multiplier, a second multiplier, a first low-pass filter, a second low-pass filter, a phase detector and a direct digital frequency synthesizer; The first input end of the first multiplier is connected to the output end of the magnetic field detection module, and the second input end is connected to the output end of the direct digital frequency synthesizer, and the output signal of the magnetic field detection module is multiplied by the orthogonal reference signal; The first low-pass filter is connected to the output end of the first multiplier to filter out high-frequency components in the output signal of the first multiplier to obtain an orthogonal demodulation signal; The first input end of the second multiplier is connected to the output end of the magnetic field detection module, and the second input end is connected to the output end of the direct digital frequency synthesizer, and multiplies the output signal of the magnetic field detection module with the in-phase reference signal; The second low-pass filter is connected to the output end of the second multiplier to filter out the high-frequency component in the output signal of the second multiplier to obtain an in-phase demodulation signal; the in-phase demodulation signal is output as a fluorescence demodulation signal; The phase detector is connected to the output ends of the first low-pass filter and the second low-pass filter to obtain the phase difference between the output signal of the magnetic field detection module and the in-phase reference signal; The direct digital frequency synthesizer is connected to the output end of the phase detector, and adjusts the phases of the quadrature reference signal and the in-phase reference signal based on the phase difference.

11. The high-speed and large dynamic range magnetic field measurement system according to claim 10, characterized in that: The phase detector performs an inverse tangent function operation on the quadrature demodulation signal and the in-phase demodulation signal.

12. The high-speed and large dynamic range magnetic field measurement system according to any one of claims 1 to 11, characterized in that: The phase-locked demodulation module and the closed-loop frequency-locked module are implemented using a field programmable logic gate array.

13. The high-speed and large dynamic range magnetic field measurement system according to any one of claims 1 to 11, characterized in that: The high-speed large dynamic range magnetic field measurement system also includes a laser background demodulation signal generating module, which obtains a laser background demodulation signal based on a reference laser signal, and inputs the laser background demodulation signal into the closed-loop frequency locking module after being differentiated from the output signal of the phase-locked demodulation module.

14. The high-speed and large dynamic range magnetic field measurement system according to claim 13, characterized in that: The laser background demodulation signal generating module comprises: a second photodetector, a second analog-to-digital converter, a third multiplier and a third low-pass filter; The second photodetector converts the reference laser signal into an electrical signal; The second analog-to-digital converter is connected to the output end of the second photodetector, and converts the analog signal output by the second photodetector into a digital signal; The first input end of the third multiplier is connected to the output end of the second analog-to-digital converter, and the second input end is connected to the orthogonal reference signal, and the output signal of the second analog-to-digital converter is multiplied by the orthogonal reference signal; The third low-pass filter is connected to the output end of the third multiplier to filter out the high-frequency component in the output signal of the third multiplier to obtain the laser background demodulation signal.

15. The high-speed and large dynamic range magnetic field measurement system according to claim 14, characterized in that: The laser background demodulation signal generating module further includes a second low-noise preamplifier, and the second low-noise preamplifier is connected between the second photodetector and the second analog-to-digital converter.

16. The high-speed and large dynamic range magnetic field measurement system according to claim 14, characterized in that: The laser background demodulation signal generating module further includes a second bandpass filter, and the second bandpass filter is connected between the second photodetector and the second analog-to-digital converter.

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