A nuclear magnetic resonance magnetometer device for magnetic field measurement at the millitesla level

Abstract

The present invention relates to a nuclear magnetic resonance magnetometer device for measuring magnetic fields at the millitesla level, belonging to the field of magnetic detection technology. The device includes a nuclear magnetic resonance probe, a pre-polarization unit, a water sample transfer unit, and a control circuit part; the control circuit part is electrically connected to the nuclear magnetic resonance probe and the water pump control circuit; the nuclear magnetic resonance probe is used to excite the pre-polarized water sample, and convert the nuclear magnetic resonance electromagnetic wave signal emitted after the water sample resonates into a voltage signal through the probe coil; the control circuit part outputs a pulse signal, which is loaded onto the probe coil to excite the water sample in the glass capillary tube, and collects the free induction decay signal in the water sample after the pulse excitation ends; the spectrum of the signal is obtained by performing a fast Fourier transform on the signal with a computer, the frequency corresponding to the highest peak point of the spectrum is the frequency of the magnetic field to be measured, and the magnetic field strength of the magnetic field to be measured is obtained through the nuclear magnetic resonance gyromagnetic ratio formula. The present invention can achieve accurate measurement of weak magnetic fields from below 40 mT down to 1 mT.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetic detection, and relates to a nuclear magnetic resonance magnetometer device for measuring magnetic fields at the millitesla level. Background Art

[0002] The accurate measurement of spatial magnetic fields is of great value in many fields such as aerospace, industry, medical treatment, and exploration. In recent years, with the discovery of various physical phenomena such as the magnetic force effect, magneto-optical effect, and magnetoelectric effect, and the progress of materials science, electronics, and technology, magnetic field measurement methods based on different physical principles are diverse and are constantly developing towards high accuracy, high stability, high resolution, miniaturization, digitization, and intelligence. The nuclear magnetic resonance magnetometer is a precise magnetic field measurement instrument made using the strict linear correlation between the atomic resonance frequency and the magnetic field strength. It has the characteristics of high precision and wide range, and is widely used in the accurate measurement of medium and high magnetic field environments. However, limited by the low signal-to-noise ratio in weak magnetic field environments, its measurement range is often not less than 40 mT.

[0003] The pre-polarization technique can achieve a multiple increase in low-field nuclear magnetic resonance signals through the pre-polarization treatment of samples at high magnetic field strengths, which provides the possibility for expanding the lower limit of the measurement of nuclear magnetic resonance magnetometers. Based on this, the present invention can design a new nuclear magnetic resonance magnetic field measurement device based on the pre-polarization technique from the perspectives of system structure, excitation method, sample selection, etc. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a nuclear magnetic resonance magnetometer device for measuring magnetic fields at the millitesla level, realizing the accurate measurement of weak magnetic fields from below 40 mT to 1 mT, effectively filling the gap in the high-precision measurement of magnetic fields from 5 mT to 40 mT.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A nuclear magnetic resonance magnetometer device for measuring magnetic fields at the millitesla level includes a nuclear magnetic resonance probe 1, a pre-polarization unit, a water sample transfer unit, and a control circuit part; the nuclear magnetic resonance probe 1 includes a probe coil 101 and a glass capillary 102; the water sample transfer unit includes a water pipe, a water pump, and a water pump control circuit;

[0007] The nuclear magnetic resonance probe 1 and the pre-polarization unit are connected through a water pipe to form a water sample circulation system; the water pump is arranged in the middle of the water pipe to control the flow rate of the water sample in the water sample circulation system;

[0008] The control circuit part is electrically connected to the magnetic resonance probe 1 and the water pump control circuit; the magnetic resonance probe 1 is used to excite the water sample pre-polarized in the pre-polarization unit, and convert the magnetic resonance electromagnetic wave signal emitted after the resonance of the water sample into a voltage signal through the probe coil 101; the control circuit part outputs a pulse signal, which is loaded onto the probe coil 101 to excite the water sample in the glass capillary 102, and collect the free induction decay signal in the water sample after the pulse excitation ends; the computer electrically connected to the control circuit part performs a fast Fourier transform on the signal to obtain the spectrum of the signal, and the frequency corresponding to the highest peak point of the spectrum is the frequency of the magnetic field to be measured, and the magnetic field strength to be measured is calculated through the magnetic resonance gyromagnetic ratio conversion formula.

[0009] Preferably, the pre-polarization unit includes a water tank 202 and a cylindrical polarization magnet 201; the water tank 202 is placed in the polarization magnet 201, so that the water sample in the water tank has a high resultant magnetization vector under the strong magnetic field; the diameter of the water tank needs to meet: the residence time of the water sample under the strong magnetic field established by the polarization magnet 201 is greater than the longitudinal relaxation time T1 of the water sample.

[0010] Preferably, the polarization magnet 201 adopts a Halbach structure (composed of 16 pieces × 6 layers of trapezoidal neodymium iron boron magnets with different magnetization directions to form a ring) or a figure-eight structure.

[0011] Preferably, the magnetic resonance probe 1 further includes a copper shielding case 103 and a rubber soft plug 104; the copper shielding case 103 is wrapped outside the glass capillary 102 and the probe coil 101, and is inserted with the rubber soft plug 104 to shield the interference of external electromagnetic waves on the magnetic resonance probe; a through hole 105 is provided on the rubber soft plug 104, so that the glass capillary 102 passes through the through hole and is connected to the water pipe through a joint 106.

[0012] Preferably, the inside of the glass capillary 102 is hollow, and its outer shape is bent into a U shape or wound into a threaded tubular shape.

[0013] Preferably, the water pipe includes a soft rubber water pipe 303 and a hard water pipe 304; the water pump is close to the water inlet of the water tank 202 in the pre-polarization unit, and the entire water flow path is water tank outlet - probe - water pump - water tank inlet; the water pump adjusts the flow rate of the water sample through a water pump switch or the control circuit part.

[0014] Preferably, the control circuit part includes a magnetic resonance spectrometer (i.e., the digital circuit part) and an analog circuit part; the magnetic resonance spectrometer includes an STM32 single-chip microcomputer, an FPGA, a pulse generation circuit, a low-pass filter circuit, a signal receiving circuit, a VGA circuit, a data storage circuit, and a power supply circuit; the analog part includes a duplexer, a preamplifier, and a radio frequency power amplifier;

[0015] The single-chip microcomputer is connected to the computer; the single-chip microcomputer completes the communication (RS485) between the computer and the water pump control circuit, and in addition, integrates data, coordinates the computer protocol and the communication with the FPGA, controls the data memory to complete data storage, and controls the water pump control circuit; the FPGA is used to realize the control of the pulse generation circuit and complete the control of signal acquisition, demodulate and filter the signals output by the ADC; the pulse generation circuit is controlled by the FPGA to control the DDS to generate sequence waveforms with different frequencies, amplitudes and durations; the free induction relaxation signal is amplified twice by the preamplifier and the VGA circuit, and then the signal is collected by the ADC chip and transmitted to the FPGA for processing; the magnetic resonance probe 1 is connected to the duplexer, and the duplexer is mainly used to switch the working mode of the probe coil, that is, the transmitting state and the receiving state; when the probe coil 101 is in the receiving state, the probe coil 101 receives the magnetic resonance signal through the duplexer. Since the magnetic resonance signal is small, it needs to pass through the preamplifier and then be transmitted to the nuclear magnetic resonance spectrometer; when the probe coil 101 is in the transmitting state, the pulse signal generated by the nuclear magnetic resonance spectrometer passes through the radio frequency power amplifier and acts on the probe coil 101 through the duplexer.

[0016] Preferably, the nuclear magnetic resonance spectrometer emits broadband pulses to excite the water sample.

[0017] Preferably, the device further includes a support structure unit, including a magnet base 5 for supporting the magnet 201 for polarizing the magnet, and a hardware chassis 4 for installing the control circuit part.

[0018] The beneficial effects of the present invention are as follows: The present invention can effectively solve the high-precision measurement blank of the magnetic field measurement device in the magnetic field range of 1-40 mT. Compared with the existing magnetic field measurement devices, the present invention has the following advantages:

[0019] 1) The present invention uses the method of flowing water pre-polarization to broaden the measurement range and improve the signal-to-noise ratio. In the traditional nuclear magnetic resonance gaussmeter, the sample is fixed, and the measurement ability for weak magnetic fields is weak. The present invention solves the limitation of the traditional nuclear magnetic resonance magnetometer in low-field measurement through the method of flowing water pre-polarization.

[0020] 2) The present invention uses the method of pulse waves to collect the free induction relaxation signal and perform Fourier FFT transformation to obtain the highest point of the spectrum to determine the magnetic field intensity, which greatly improves the measurement speed while ensuring the measurement accuracy.

[0021] 3) The design of the present invention mainly focuses on the magnetic field range of 1-40 mT. Compared with other magnetometers such as Hall and fluxgate, the nuclear magnetic resonance magnetometer designed by the present invention has higher accuracy, and the resolution can be as high as 10 nT. It solves the high-precision measurement blank of the magnetic field measurement device in the magnetic field range of 1-40 mT.

[0022] 4) The present invention reduces the volume of the probe by 1 cm through the design of the magnetic resonance probe and the thermal processing and bending of the glass capillary. 3 , which greatly improves the spatial resolution and makes high spatial resolution magnetic field measurement possible.

[0023] 5) The present invention adopts a single coil time-division multiplexing structure and uses a duplexer to switch coil functions to achieve rapid response.

[0024] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0026] Figure 1 is a working principle diagram of a magnetic resonance magnetometer device;

[0027] Figure 2 This is the overall structure diagram of the magnetometer device;

[0028] Figure 3 This is an exploded view of the overall structure of the magnetometer device;

[0029] Figure 4 is a schematic diagram of the structure of a magnetic resonance probe;

[0030] Figure 5 It is an array Halbach magnet structure;

[0031] Figure 6 This is a partial structural diagram of the control circuit.

[0032] Figure numerals: 1-magnetic resonance probe, 101-probe coil, 102-glass tube, 103-copper shielding shell, 104-rubber plug, 105-through hole, 106-connector, 201-polarized magnet, 202-water tank, 203-threaded connector, 204-pagoda head, 205-threaded female head, 301-water pump, 302-water pump flow rate display screen, 303-soft rubber water pipe, 304-hard water pipe, 305-adapter, 4-hardware chassis, 41-universal wheel, 42-heat dissipation and dustproof net, 5-magnet base, 501-power switch, 502-power jack, 503-USB interface, 504-RF SMA interface, 505-expansion interface. DETAILED DESCRIPTION

[0033] The following describes the embodiments of the present invention through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the drawings provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0034] Among them, the drawings are only for illustrative purposes, showing only schematic diagrams, not physical diagrams, and should not be construed as limiting the present invention; in order to better illustrate the embodiments of the present invention, some components in the drawings will be omitted, enlarged or reduced, which do not represent the dimensions of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0035] In the drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "rear", etc. indicating the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0036] Please refer to Figures 1 to 6 , the magnetometer device designed by the present invention mainly includes six parts: a magnetic resonance probe 1, a pre-polarization unit, a water sample transfer unit, a support structure unit, a control circuit part, and a high-resolution fast magnetic field measurement method.

[0037] The magnetic resonance probe 1 includes a copper shielding shell 103, a glass capillary 102, a rubber soft plug 104, a connector (threaded quick-connect head) 106, a probe coil 101, and a printed circuit board placed inside the probe for matching the probe coil. The main function of the magnetic resonance probe 1 is to excite the pre-polarized water sample and convert the magnetic resonance electromagnetic wave signal emitted after the resonance of the water sample into a voltage signal through the magnetic resonance probe coil. The copper shielding shell 103 wraps around the glass capillary 102 and the outer part of the probe coil, and is inserted with the rubber soft plug 104 to shield the interference of external electromagnetic waves on the magnetic resonance probe. The glass capillary is bent by thermal processing and has a U-shaped outer shape. In order to make the water sample stay at the magnetic resonance probe coil for a longer time, it can also be wound into a threaded tubular glass tube. The interior is hollow to provide a passage for the flow of the water sample. The outer diameter of the capillary is less than 3 mm, making the solenoid coil wound on the glass tube smaller in volume. Such a design makes the probe perform better in an inhomogeneous magnetic field and improves the spatial resolution of the measurement. One end of the rubber soft plug has a hole connected to the glass capillary. The surface of the hole is coated with epoxy resin to adhere to the glass and play a waterproof role. The end of the rubber soft plug 104 is connected to the connector (threaded quick-connect head) 106 through threads. The connector (threaded quick-connect head) 106 is in a pagoda shape to better connect with the soft rubber water pipe 303. The female head of the connector passes through the water pipe and is screwed with the male head to better fix and prevent water leakage.

[0038] The pre-polarization unit includes a polarization magnet (1.3T strong permanent magnet) 201, a water tank 202, a threaded connection joint 203, a pagoda head 204, a threaded female head (used to fasten the water pipe) 205, etc. The water tank is placed in the strong permanent magnet so that the water sample in the water tank 202 has a large resultant magnetization vector under the strong magnetic field. The water tank is set with a relatively large diameter so that the water sample stays in the high magnetic field established by the strong permanent magnet for enough time, and the residence time is greater than the longitudinal relaxation time T1 of the water sample. Considering the requirements of the polarization magnet for high magnetic field strength and low uniformity, the polarization magnet is composed of 16 pieces × 6 layers of trapezoidal neodymium iron boron magnets with different magnetization directions to form an annular Halbach magnet. Its overall structure and the magnetization directions of 16 magnets in each layer are as Figure 5 shown.

[0039] The water sample transfer unit includes a water pump 301 with a flow rate display and adjustable flow rate, a soft rubber water pipe 303, a rigid water pipe 304, a connector 305, etc. The function of the connector is to enable water pipes with different diameters to be connected to form a passage. The water pump is connected to the water inlet of the water tank. The flow rate can be adjusted by turning the water pump knob or by the upper computer. The water pump switch is used to control the start and stop of the water pump. The water pump 301 is located at the water inlet of the water tank. The entire water flow path is the water outlet of the water tank - the probe - the water pump - the water inlet of the water tank. The advantage of such a design is that it can avoid the influence of the polarized water sample on the resultant magnetization vector of the sample after passing through the water pump.

[0040] The support structure unit includes a hardware chassis 4, a magnet base (high-strength aluminum alloy support) 5, universal wheels 41, a heat dissipation and dust-proof net 42, and various interfaces (such as a USB interface 503, a radio frequency SMA interface 504, an expansion interface 505, etc.). Since the magnet is heavy, the present invention uses a high-strength aluminum alloy support to support the magnet structure. Below the support is the hardware chassis 4, which is used to place circuit devices including: a power supply, a radio frequency power amplifier, a nuclear magnetic resonance spectrometer, a preamplifier, a duplexer, etc. The power supply is connected to the power switch 501 on the base to control the operation of the entire device; the USB interface 503 is used to connect the spectrometer to a PC, and the radio frequency SMA interface 504 is used to connect the nuclear magnetic resonance probe and the preamplifier. The network cable WLAN interface is used to connect to a local area network to achieve remote data reading.

[0041] The control circuit part is as Figure 6 shown. The computer, as the host computer, mainly sends commands to the slave computer, receives the data uploaded by the slave computer, and organizes, calculates, and displays it. The computer is connected to the nuclear magnetic resonance spectrometer (digital circuit part). The function of the STM32 single-chip microcomputer in the hardware circuit module is to complete the communication between the host computer and the slave computer (RS485). In addition, it integrates the data, coordinates the host computer protocol and the communication with the FPGA, controls the data memory to complete data storage, and controls other peripherals (such as a water pump). The main function of the FPGA is to control the pulse generation circuit and complete the control of signal acquisition, demodulate and filter the signals output by the ADC. The pulse generation circuit is controlled by the FPGA to control the DDS to generate sequence waveforms with different frequencies, amplitudes, and durations. The free induction decay signal is amplified twice by the preamplifier and the VGA circuit, and then the signal is collected by the ADC chip and transmitted to the FPGA for processing. The nuclear magnetic resonance probe is connected to the duplexer. The main function of the duplexer is to switch the working mode of the probe coil, that is, the transmission state and the reception state. When the probe coil is in the reception state, the probe coil receives the nuclear magnetic resonance signal through the duplexer. Since the nuclear magnetic resonance signal is small, it needs to pass through the preamplifier and then be transmitted to the nuclear magnetic resonance spectrometer. When the probe coil is in the transmission state, the pulse signal generated by the nuclear magnetic resonance spectrometer passes through the radio frequency power amplifier and the duplexer acts on the coil.

[0042] In the above magnetometer device, the water tank 202, the water pump 301, the water pipes (303, 304), and the glass capillary 102 form a path for the water sample to flow (i.e., a water circulation system). The wide-caliber water tank is arranged in the cylindrical polarized magnet. The strong magnet adopts a Halbach structure or a figure-eight structure, and the outside of the cylinder has no magnetic field. The water sample obtains a high synthetic magnetization vector in the strong magnetic field of the polarized magnet. Through the water circulation system, the sample is transferred to the nuclear magnetic resonance probe. Then, the nuclear magnetic resonance probe in the low magnetic field can obtain a higher magnetization vector of the water sample, making the voltage signal induced by the coil stronger, increasing the signal-to-noise ratio, and thus significantly improving the resolution of signal measurement.

[0043] The nuclear magnetic resonance spectrometer emits a broadband pulse to excite the water sample, enabling the tester to more quickly find the magnetic field frequency point to be measured and improving the measurement speed. The method of collecting free induction decay signals for Fourier transform spectroscopy is used to determine the magnetic field strength. After the pulse excitation is completed, the free induction decay signal of the water sample is collected by quickly switching the coil function. The free induction decay signal has a faster collection speed compared to other nuclear magnetic resonance signals, and more sampling points can be set, which is very important for improving the resolution of spectral analysis. Then, the free induction decay signal (FID) is Fourier-transformed to obtain the frequency spectrum of the signal. The frequency corresponding to the peak point on the frequency spectrum is the Larmor frequency of the magnetic field to be measured, and the magnitude of the magnetic field strength can be obtained through the conversion of the gyromagnetic ratio formula ω = γB0. The spectral analysis method has higher measurement accuracy, resolution, and faster response speed compared to the continuous wave frequency sweep method. Among them, a broadband radio frequency pulse is used to excite the sample. With a wide excitation frequency band, the signal can be captured earlier and faster, reducing the signal search time. The free induction decay signal (FID) has a shorter sampling time compared to other nuclear magnetic resonance signals such as CPMG, significantly improving the measurement speed. The method of Fourier transform spectroscopy is used to determine the magnetic field strength, which has higher resolution compared to the frequency sweep method.

[0044] Working principle of the magnetometer: The flowing water type nuclear magnetic resonance magnetometer designed in the present invention consists of a single polarized magnet and a probe coil. The entire system mainly includes a polarized magnet 201, a nuclear magnetic resonance probe 1, and a water pump 301. Each part is connected through a pipeline, and the spectrometer circuit is connected to the coil in the nuclear magnetic resonance probe to achieve radio frequency excitation and signal reception. The system structure is as Figure 2 shown. During measurement, water flows through the polarization field and the detection field in sequence, and the physical process of the corresponding nuclear magnetic signal is described in three stages: polarization, excitation, and detection.

[0045] (1) Polarization stage

[0046] The macroscopic magnetization vector is the basis of nuclear magnetic resonance. The process of establishing a macroscopic magnetization vector for hydrogen protons in the sample by applying an external static magnetic field is called polarization. In the flowing water type nuclear magnetic resonance magnetometer, the polarized magnet provides a static polarization magnetic field B with a relatively large field strength for the polarization process of hydrogen protons p .

[0047] In the plane perpendicular to B p , due to the inconsistent precession phases of protons, no transverse magnetization vector is generated. However, in the direction parallel to B p , a macroscopic magnetization vector will be established:

[0048]

[0049] Obviously, B pThe larger it is, the more obvious the energy level splitting is, and the greater the intensity of the macroscopic magnetization vector obtained. The establishment (reaching the Boltzmann equilibrium) of the macroscopic magnetization vector does not occur instantaneously, and this process depends on the longitudinal relaxation time T1 of the sample:

[0050]

[0051] M p is the intensity of the macroscopic magnetization vector when the sample flows out of the polarization field, t p is the time for the sample to flow through the polarization field, and M0 is the maximum longitudinal magnetization vector that can be achieved corresponding to the polarization field strength B p When the sample flows out of the polarization field to the time t of flowing into the detection field, if it is not interfered by resonance, its macroscopic magnetization vector decays according to the T1 law: pd Therefore, to obtain a sufficiently large macroscopic magnetization vector, it should be ensured that the sample stays in the polarization field for enough time and is quickly moved to the detection field for detection.

[0052]

[0053] Therefore, to obtain a sufficiently large macroscopic magnetization vector, it should be ensured that the sample stays in the polarization field for enough time and is quickly moved to the detection field for detection.

[0054] (2) Excitation and detection stage

[0055] The detection field is configured with a time-division multiplexing coil, which generates a radio frequency excitation magnetic field B1 perpendicular to the magnetic field B to be measured under the action of the control circuit. Protons in the lower energy level will absorb radio frequency energy and undergo energy level transitions. When a radio frequency magnetic field B1 consistent with the Larmor frequency is applied on the xoy plane perpendicular to B m , the longitudinal magnetization vector M m will flip to the xoy plane with B1 as the axis. During the measurement process, we apply a π / 2 radio frequency pulse to flip M p by 90°, exactly flipping to the xoy plane. p After the radio frequency excitation is applied, the transverse magnetization vector M

[0056] decoheres due to the spin-spin interaction of the atomic nuclei, and thus the resultant vector gradually decays to zero, satisfying the formula: xy At this time, a free induction decay voltage signal (FID) will be induced at both ends of the coil. At this time, the induced voltage signal satisfies:

[0057]

[0058] At this time, a free induction decay voltage signal (FID) will be induced at both ends of the coil. At this time, the induced voltage signal satisfies:

[0059]

[0060] The voltage signal at both ends of the coil is collected through the acquisition circuit and subjected to Fourier FFT analysis. The peak point of the obtained spectrum is the frequency of the field to be measured. Through the gyromagnetic ratio formula:

[0061] ω = γB0

[0062] The output magnetic induction intensity after conversion is the intensity of the magnetic field to be measured.

[0063] Embodiment 1: The working principle diagram of the nuclear magnetic resonance magnetometer device designed in this embodiment. The entire working area is divided into three parts: a polarization area, a detection area, and a control circuit area. The polarization area consists of a polarization magnet 201 and a water tank 202 with a wide inner diameter. The inside of the water tank 202 is set as a water circuit winding type to increase the residence time of the water sample in the water tank, so that the water sample is fully polarized. The polarization magnet 201 adopts a Halbach magnet structure (as Figure 5 shown). The magnetic field on the outer surface is relatively small, which is beneficial for assembly. The magnetic field strength inside the polarization magnet is 1.3T. The detection area consists of a nuclear magnetic resonance probe 1. The probe matches the Larmor frequency corresponding to the magnetic field in the detection area through a π-type circuit. The probe coil 101 is connected to a nuclear magnetic resonance spectrometer, and the nuclear magnetic resonance spectrometer is connected to a PC host computer (computer). By setting the host computer, radio frequency energy is generated to excite the water sample in the probe coil 101, and the FID signal of the sample relaxation is collected. By performing Fourier analysis on the FID signal, the frequency of the peak point can be obtained. The nuclear magnetic resonance probe 1 and the polarization magnet 201 are connected through a water pipe. The entire system is driven by a water pump 301. The water pump 301 quickly moves the water sample from the polarization magnet 201 to the nuclear magnetic resonance probe 1 for detection at a high speed, so that the water sample still maintains a high magnetization vector when it reaches the detection area.

[0064] Embodiment 2: As Figure 4 shown, the nuclear magnetic resonance magnetic probe 1 includes two parts: a copper shielding shell 103 and an inner plug. The inner plug consists of a glass capillary 102 and a rubber soft plug 104. The copper shielding shell 103 is joined to the inner plug to form a closed whole. The copper shielding shell 103 plays a role in shielding external noise signals. The glass capillary 102 provides a passage for pre-polarized water. The whole probe is enclosed by copper skin. The water inlet and outlet are through holes 105 on the 3D-printed rubber soft plug 104. The through holes 105 have threads to connect with a connector (quick-connect head) 106. The connector (quick-connect head) 106 is connected to a soft rubber water pipe 303 to form a water flow passage. The probe coil 101 is wound in a solenoid type at the top of the glass capillary. The through hole 105 is also used to pass through the radio frequency connection line. The measurement is carried out by moving the front end of the probe to the target area.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the purpose and scope of the present technical solution, and they should all be covered by the scope of the claims of the present invention.

Claims

1. A nuclear magnetic resonance magnetometer device for measuring magnetic fields at the millitesla level, characterized in that, The device includes a magnetic resonance probe (1), a pre-polarization unit, a water sample transfer unit, and a control circuit section; the magnetic resonance probe (1) includes a probe coil (101) and a glass capillary tube (102); the water sample transfer unit includes a water pipe, a water pump, and a water pump control circuit; The magnetic resonance probe (1) and the pre-polarization unit are connected by a water pipe to form a water sample circulation system; the water pump is arranged in the middle of the water pipe to control the flow rate of the water sample in the water sample circulation system; The control circuit section is electrically connected to the magnetic resonance probe (1) and the water pump control circuit; the magnetic resonance probe (1) is used to excite the water sample pre-polarized in the pre-polarization unit, and convert the magnetic resonance electromagnetic wave signal emitted after the water sample resonates into a voltage signal through the probe coil (101); the control circuit section outputs a pulse signal, which is loaded onto the probe coil (101) to excite the water sample in the glass capillary tube (102), and the free induction decay signal in the water sample is collected after the pulse excitation ends; the computer electrically connected to the control circuit section performs a fast Fourier transform on the signal to obtain the spectrum of the signal, and the frequency corresponding to the highest peak point of the spectrum is the frequency of the magnetic field to be measured, and the field strength of the magnetic field to be measured is calculated through the magnetic resonance gyromagnetic ratio formula; The pre-polarization unit includes a water tank (202) and a cylindrical polarization magnet (201); the water tank (202) is placed in the polarization magnet (201) so that the water sample in the water tank has a high resultant magnetization vector under a strong magnetic field; the diameter of the water tank needs to meet the requirement that the residence time of the water sample under the strong magnetic field established by the polarization magnet (201) is greater than the longitudinal relaxation time of the water sample T 1; The magnetic resonance probe (1) further includes a copper shielding case (103) and a rubber soft plug (104); the copper shielding case (103) wraps around the outside of the glass capillary tube (102) and the probe coil (101), and is inserted with the rubber soft plug (104) to shield the interference of external electromagnetic waves to the magnetic resonance probe; a through hole (105) is provided on the rubber soft plug (104), and the glass capillary tube (102) passes through the through hole and is connected to the water pipe by a joint (106); The magnetic resonance probe (1) is connected to a duplexer, and the duplexer is used to switch the working mode of the probe coil, that is, the transmitting state and the receiving state; when the probe coil (101) is in the receiving state, the probe coil (101) receives the magnetic resonance signal, passes through the duplexer, and then is transmitted to the magnetic resonance spectrometer through a preamplifier; when the probe coil (101) is in the transmitting state, the pulse signal generated by the magnetic resonance spectrometer passes through a radio frequency power amplifier, and the duplexer acts on the probe coil (101).

2. The nuclear magnetic resonance magnetometer device according to claim 1, characterized in that The polarization magnet (201) adopts a Halbach structure or a figure-eight structure.

3. The nuclear magnetic resonance magnetometer device according to claim 1, characterized in that The inside of the glass capillary tube (102) is hollow, and its outer shape is bent into a U shape or wound into a threaded tubular shape.

4. The nuclear magnetic resonance magnetometer device according to claim 1, characterized in that, The water pump is close to the water inlet of the water tank (202) in the pre-polarization unit, and the entire water flow path is the water outlet of the water tank - the probe - the water pump - the water inlet of the water tank; the water pump adjusts the flow rate of the water sample through a water pump switch or the control circuit section.

5. The nuclear magnetic resonance magnetometer device according to claim 1, characterized in that The control circuit section includes a magnetic resonance spectrometer and an analog circuit section; the magnetic resonance spectrometer includes a single-chip microcomputer, an FPGA, a pulse generation circuit, a low-pass filter circuit, a signal receiving circuit, a VGA circuit, a data storage circuit, and a power supply circuit; the analog circuit section includes a duplexer, a preamplifier, and a radio frequency power amplifier; The single-chip microcomputer is connected to the computer; the single-chip microcomputer completes the communication between the computer and the water pump control circuit, and in addition, integrates data, coordinates the computer protocol and the communication with the FPGA, controls the data memory to complete data storage, and controls the water pump control circuit; The FPGA is used to implement the control of the pulse generation circuit and the control of signal acquisition, and demodulate and filter the signals output by the ADC; The pulse generation circuit is controlled by the FPGA to control the DDS to generate sequence waveforms with different frequencies, amplitudes, and durations; the free induction decay signal is amplified twice by the preamplifier and the VGA circuit, and then the signal is collected by the ADC chip and transmitted to the FPGA for processing.

6. The nuclear magnetic resonance magnetometer device according to claim 5, characterized in that, The nuclear magnetic resonance spectrometer emits broadband pulses to excite the water sample.

7. The nuclear magnetic resonance magnetometer device according to any one of claims 1 to 5, characterized in that The device further includes a support structure unit, including a magnet base (5) for supporting the magnet to polarize the magnet (201), and a hardware chassis (4) for installing the control circuit part.

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