Ultra-low field nuclear magnetic resonance measurement device and method with background field adjustable in large range

Abstract

The invention discloses an ultra-low field nuclear magnetic resonance measurement device with a large-range adjustable background field, and also discloses an ultra-low field nuclear magnetic resonance measurement method with a large-range adjustable background field. According to the ultra-low field nuclear magnetic resonance measurement device with the large-range adjustable background field, a flat solenoid is adopted to realize a high background magnetic field requirement and an ultra-low environment magnetic field; the flat solenoid can accommodate more coils and obtain more turns, so that a wider background field adjustable range is realized; two ends of the flat solenoid extend out of the magnetic shielding module, so that a magnetic flux line at the tail end of the flat solenoid can be connected to the outside of a shielding area, and the problem of non-uniformity of a background field generated by a common solenoid coil is solved; interference of an environmental magnetic field is eliminated through passive magnetic shielding and active magnetic field compensation, firstly, passive magnetic shielding is performed on the environmental magnetic field through a plurality of electromagnetic shielding cylinders, then a magnetic field opposite to the environmental magnetic field is generated through a shimming coil to perform active magnetic field compensation, and interference of the environmental magnetic field is counteracted; the shimming coil can also improve the uniformity of the central magnetic field.

Description

Technical Field

[0001] The present invention belongs to the field of nuclear magnetic resonance measurement technology, and specifically relates to an ultra-low field nuclear magnetic resonance measurement device with a background field that can be adjusted over a wide range, and also relates to an ultra-low field nuclear magnetic resonance measurement method with a background field that can be adjusted over a wide range, which is suitable for the field of zero to ultra-low field magnetic resonance measurement, non-destructive testing, biomedicine, magnetic resonance imaging, relaxation testing, biological metabolism testing, magnetic resonance testing of samples containing metals, etc. Background Art

[0002] NMR signals are usually acquired in the background magnetic field (B0 field) and are one of the most important spectral techniques for chemical and structural analysis. However, traditional high-field NMR has some disadvantages, such as high-frequency signal distortion caused by the skin effect, and the bulkiness and high cost of high-field magnets.

[0003] With the emergence and development of atomic magnetometers, nuclear magnetic resonance signals can be detected in near-zero to ultra-low magnetic fields. Atomic magnetometers are ultra-sensitive magnetic measurement tools that determine the magnitude of the magnetic field by measuring the Larmor precession frequency of the atomic polarization vector in an external magnetic field.

[0004] However, due to the bandwidth and sensitivity limitations of atomic magnetometers, it is impossible to measure the Larmor precession information of samples under relatively high background magnetic fields. In existing near-zero to ultra-low magnetic field NMR experiments, the measurements are performed without strong magnetic fields, the chemical shift is negligible, and the main nuclear-spin interaction is spin-spin (J) coupling, which is usually on the order of Hz to hundreds of Hz.

[0005] However, there are still some problems with the existing near-zero to ultra-low magnetic field nuclear magnetic resonance experiments. First, the atomic gas chamber of the atomic magnetometer needs to work effectively in a near-zero field (less than 20nT) environment, and usually uses multiple layers of Permalloy and other materials to shield the environmental magnetic field. This passive shielding makes it impossible for the atomic dynamometer to detect the magnetic field outside the shielding layer, and the background field is fixed at the theoretical residual magnetic size of the shielding device, and its background field size cannot be changed, which seriously limits the application of atomic magnetometers in real magnetic fields such as the Earth's magnetic field, deep space magnetic field, underwater anomalies, etc.

[0006] In recent years, some zero-to-ultra-low-field NMR measurement devices with adjustable background fields have been developed. For example, James Eills' team achieved a near-zero magnetic field (<2nT) inside the shield after using the MS-1LF four-layer magnetic shielding design. At the same time, in order to achieve ultra-low field measurements, the research team used a hand-wound puncture solenoid to pass through the magnetic shielding and apply a local magnetic field at the location of the sample rather than the sensor, thereby providing a stable and variable magnetic field (0-3.8uT) within the shielding device and facilitating the sample to enter and exit the magnetic shielding barrel.

[0007] Although this solution solves the problem of unadjustable background field, there are still problems such as small adjustable range of background field and poor field uniformity at the sample. Summary of the invention

[0008] The purpose of the present invention is to provide an ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field, and also to provide an ultra-low field nuclear magnetic resonance measurement method with a wide range of adjustable background field in view of the above problems existing in the prior art.

[0009] The above-mentioned purpose of the present invention is achieved by the following technical means:

[0010] The invention discloses an ultra-low field nuclear magnetic resonance measuring device with a background field adjustable in a wide range, comprising a magnetic shielding module, a flat solenoid, a sampling module, an atomic magnetometer, and a radio frequency coil module. The magnetic shielding module comprises a plurality of electromagnetic shielding tubes which are sleeved and fixed in sequence, all of which share a central axis, and through holes are arranged at the top center and the bottom center of all of which. The flat solenoid is arranged inside the electromagnetic shielding tube with the smallest circular cross-sectional diameter, and two ends of the flat solenoid respectively pass through the through holes at the top center and the bottom center of four electromagnetic shielding tubes and extend out of the magnetic shielding module. The sampling module is arranged inside the flat solenoid, and comprises a track, a sample tube, and a sample holder. The sample tube is fixedly arranged on the sample holder, and the sample holder is slidably arranged on the track, and two ends of the track respectively extend out of two ends of the flat solenoid. A sensor of the atomic magnetometer is fixedly connected to the outer wall of the flat solenoid, and the radio frequency coil module is arranged inside the electromagnetic shielding tube with the smallest circular cross-sectional diameter and outside the flat solenoid. The fixed height of the sensor of the atomic magnetometer is the same as the height of the center of the radio frequency coil module.

[0011] It also includes a permanent magnet and a pair of shim coils. The permanent magnet is arranged below the magnetic shielding module. The permanent magnet and the electromagnetic shielding tube share a central axis. The pair of shim coils are symmetrically fixed on the inner wall of the electromagnetic shielding tube with the smallest circular cross-section diameter about the central axis of the electromagnetic shielding tube, and the center of the radio frequency coil module is located in the magnetic field generated by the shim coil.

[0012] As described above, the radio frequency coil module includes an X-axis Helmholtz coil, a Y-axis Helmholtz coil, and a Z-axis Helmholtz coil, the X-axis Helmholtz coil, the Y-axis Helmholtz coil, and the Z-axis Helmholtz coil each include a pair of Helmholtz coils with a common central axis, the diameters of the three pairs of Helmholtz coils are the same, the central axes of the three pairs of Helmholtz coils are perpendicular to each other, the central axes of the three pairs of Helmholtz coils intersect at the same center, the three pairs of Helmholtz coils are all arranged outside the flat solenoid and inside the electromagnetic shielding cylinder with the smallest circular cross-section diameter, the centers of the three pairs of Helmholtz coils are located in the background magnetic field generated by the flat solenoid and in the magnetic field generated by a pair of shim coils, the three pairs of Helmholtz coils are respectively arranged on corresponding coil brackets, and the coil brackets are fixed to the flat solenoid by screws;

[0013] When the sample holder is moved to the height where the centers of the three pairs of Helmholtz coils are located through the track, the sample tube on the sample holder is located at the center of the three pairs of Helmholtz coils.

[0014] It also includes a digital control system module, which includes a radio frequency control module, a shim control module, a background field control module, and an acquisition module. The radio frequency control module is connected to the X-axis Helmholtz coil, the Y-axis Helmholtz coil, and the Z-axis Helmholtz coil through the X-axis coil current transmission line, the Y-axis coil current transmission line, and the Z-axis coil current transmission line, respectively. The shim control module is connected to the shim coil through the shim coil current transmission line. The acquisition module is connected to the atomic magnetometer through the atomic magnetometer data transmission line. The background field control module is connected to the flat solenoid through the variable field coil current transmission line.

[0015] As described above, a support platform is arranged above the top of the magnetic shielding module, and the support platform is fixedly connected to the top of the electromagnetic shielding tube with the largest circular cross-sectional diameter through a plurality of support columns. The track comprises a central slide rail, an auxiliary slide rail, a rack, an upper pulley, and a lower pulley. The central slide rail and the auxiliary slide rail each comprise a pair of slideways parallel to each other, the upper end of the slideway is fixedly connected to the bottom of the support platform, and the lower end of the slideway is fixedly connected to the lower pulley. The rack is arranged between the pair of slideways of the central slide rail, and the two ends of the rack are respectively passed around the upper pulley and the lower pulley. The upper pulley and the lower pulley are connected to each other to form a closed loop after being extended into the two slideways of the auxiliary slideway. The outer peripheries of the upper pulley and the lower pulley are provided with gear teeth meshed with the rack. The rack meshes with the upper pulley and the lower pulley. The sample holder is fixedly connected to the rack. The sample holder is also slidably connected to a pair of slideways of the central slideway. The injection module also includes a motor. The rotating shaft of the motor is connected to the rotating part of the upper pulley. The digital control system module also includes an injection control module. The injection control module is connected to the motor of the injection module through a motor control line.

[0016] As described above, the lower end of the central slide rail passes through the permanent magnet, and bottom baffles are also provided on the two slideways of the central slide rail. When the sample holder slides to the bottom baffle, the sample tube on the sample holder is located at the center of the permanent magnet.

[0017] As mentioned above, the shim coil is a patch flexible coil.

[0018] As described above, the flat solenoid includes a tube body and a variable field coil. The variable field coil is wound from one end of the flat solenoid to the other end of the flat solenoid, and then wound back from the other end to the starting end. The background field control module is connected to the variable field coil through a variable field coil current transmission line. When the variable field coil is energized, the current direction in the variable field coil is counterclockwise or clockwise. The sensor of the atomic magnetometer is fixedly connected to the outer wall of the tube body of the flat solenoid.

[0019] A method for measuring ultra-low field nuclear magnetic resonance with a background field that is adjustable over a wide range, using the ultra-low field nuclear magnetic resonance measuring device with a background field that is adjustable over a wide range as described above, comprises the following steps:

[0020] Step 1: adjusting the current input into the shim coil by the shim control module of the digital system control module, so that the shim coil generates a magnetic field opposite to the remaining ambient magnetic field to offset the remaining ambient magnetic field, so that the ambient magnetic field of the electromagnetic shielding cylinder with the smallest circular cross-section diameter is an ultra-low field close to zero;

[0021] Step 2: fix the sample tube on the sample holder, and control the motor through the digital control system module to move the sample holder to the bottom baffle on the central slide rail, so that the sample in the sample tube is located at the center of the permanent magnet, and perform thermal polarization of the sample;

[0022] Step 3: Adjust the current of the variable field coil through the digital control system module, so as to adjust the size of the background magnetic field;

[0023] Step 4: start the atomic magnetometer through the digital control system module, and perform zero filling and calibration of the atomic magnetometer;

[0024] Step 5: Control the motor through the digital control system to make the sample tube leave the center of the permanent magnet and reach the center of the three pairs of Helmholtz coils after a set time;

[0025] Step 6: Pass pulse current to the X-axis Helmholtz coil, the Y-axis Helmholtz coil, and the Z-axis Helmholtz coil through the digital control system module and adjust the magnitude and duration of the pulse current to excite the sample;

[0026] Step 7: Use an atomic magnetometer to obtain measurement data, and process the measurement data into magnetic resonance information of the sample.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) Compared with the conventional solenoid coil used in zero to ultra-low field NMR measurement, the biggest advantage of the flat solenoid used in the present invention is the difference between the internal and external magnetic fields. Conventional solenoid coils are usually unable to achieve such a huge difference between the internal and external magnetic fields. The flat solenoid used in the present invention can simultaneously meet the requirements of high background magnetic field and ultra-low ambient magnetic field, so that the sample is placed in a strong background magnetic field and the atomic magnetometer is located in an ultra-low ambient magnetic field.

[0029] (2) Flat solenoids can accommodate more coils and obtain more turns, so they can generate stronger background magnetic fields through larger currents, thereby achieving a wider adjustable range of background fields. Compared with traditional solenoids, the coils of flat solenoids are more tightly wound, which effectively utilizes space, allowing more coils to be accommodated in a limited volume, thereby providing larger currents and stronger background magnetic fields, and thus enabling the device to flexibly adjust the strength of the background magnetic field to meet different experimental needs.

[0030] (3) Both ends of the flat solenoid extend outside the magnetic shielding module to ensure that the magnetic flux lines appearing at the ends of the flat solenoid are connected to the outside of the shielding area, eliminating the problem of background field inhomogeneity generated by ordinary solenoid coils.

[0031] (4) The present invention uses passive magnetic shielding and active magnetic field compensation to offset the interference of the environmental magnetic field. First, the environmental magnetic field is passively shielded by multiple electromagnetic shielding tubes, and then the shim coil is used to generate a magnetic field opposite to the environmental magnetic field to perform active magnetic field compensation, thereby offsetting the interference of the environmental magnetic field. The shim coil can also improve the uniformity of the central magnetic field (i.e., the magnetic field generated by three pairs of Helmholtz coils).

[0032] (5) The present invention uses electric injection, and controls the motor through the motor control line to control the position of the sample in the device, so that the sample can quickly and accurately stay in the center of the permanent magnet for sample polarization, or in the nuclear magnetic resonance measurement area for sample measurement. Compared with the traditional pneumatic injection design, electric injection has the characteristics of precise docking, automatic control and high repeatability, which improves experimental efficiency and data accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the structure of the device of the present invention;

[0034] Reference numerals and corresponding component names:

[0035] 1—permanent magnet; 2—variable field coil; 3—atomic magnetometer; 4—X-axis Helmholtz coil; 5—Z-axis Helmholtz coil; 6—Y-axis Helmholtz coil; 7—sample holder; 8—sample tube; 9—uniform field coil; 10—flat solenoid; 11—rack; 12—slide rail; 13—magnetic shielding module; 14—pulley; 15—motor; 16—motor control line; 17—digital control system module; 18—Y-axis coil current transmission line; 19—X-axis coil current transmission line; 20—Z-axis coil current transmission line; 21—uniform field coil current transmission line; 22—atomic magnetometer data transmission line; 23—variable field coil current transmission line. DETAILED DESCRIPTION

[0036] In order to facilitate those skilled in the art to understand and implement the present invention, the present invention is further described in detail below in conjunction with embodiments. The embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0037] Embodiment 1:

[0038] An ultra-low field nuclear magnetic resonance measuring device with a wide range of adjustable background fields comprises a magnetic shielding module 13, an adjustable background field module, a sampling module, an atomic magnetometer 3, and a radio frequency coil module. The magnetic shielding module 13 comprises four cylindrical electromagnetic shielding tubes which are sleeved and fixed in sequence, the four electromagnetic shielding tubes share a central axis, and a through hole is respectively arranged at the top center and the bottom center of the four electromagnetic shielding tubes. The adjustable background field module comprises a flat solenoid 10, which is arranged inside the electromagnetic shielding tube with the smallest circular cross-sectional diameter, and the two ends of the flat solenoid 10 respectively pass through the through holes at the top center and the bottom center of the four electromagnetic shielding tubes and extend out of the magnetic shielding module 13, that is, the length of the flat solenoid 10 is greater than the length of all electromagnetic shielding tubes. The sampling module is arranged inside the flat solenoid 10, and the sampling module includes a track, a sample tube 8, and a sample holder 7. The sample tube 8 is fixedly arranged on the sample holder 7, and the sample tube 8 is used to hold the sample. The sample holder 7 is slidably arranged on the track, and the two ends of the track extend out of the two ends of the flat solenoid 10 respectively. The sensor of the atomic magnetometer 3 is fixedly connected to the outer wall of the flat solenoid 10, and the radio frequency coil module is arranged inside the electromagnetic shielding tube with the smallest circular cross-section diameter, and is arranged outside the flat solenoid 10. The fixed height of the sensor of the atomic magnetometer 3 is the same as the height of the center of the radio frequency coil module, and the sensor of the atomic magnetometer 3 is opposite to the sample tube 8, so that the distance between the sensor of the atomic magnetometer 3 and the sample tube 8 is the shortest.

[0039] The magnetic shielding module 13 is used for passive shielding, which can passively shield the ambient magnetic field outside the electromagnetic shielding tube, so that the ambient magnetic field intensity inside the electromagnetic shielding tube with the smallest circular cross-sectional diameter is zero or a near-zero ultra-low magnetic field (<2nT). The number of electromagnetic shielding tubes of the magnetic shielding module 13 includes but is not limited to four, and the electromagnetic shielding tube can be made of Permalloy with high magnetic permeability and low coercive force, including but not limited to Permalloy.

[0040] The flat solenoid 10 is used to generate a stable and controllable background magnetic field inside the flat solenoid 10. Compared with the conventional solenoid coil used for zero to ultra-low field nuclear magnetic resonance measurement, the greatest advantage of the flat solenoid 10 used in the present invention is the gap between the internal and external magnetic fields. Conventional solenoid coils are usually unable to achieve such a huge gap between the internal and external magnetic fields. The flat solenoid 10 used in the present invention can simultaneously meet the high background magnetic field requirements and the ultra-low environmental magnetic field conditions, so that the sample is placed in a strong background magnetic field and the atomic magnetometer 3 is located in an ultra-low environmental magnetic field; in addition, both ends of the flat solenoid 10 extend out of the magnetic shielding module 13 to ensure that the magnetic flux lines appearing at the end of the flat solenoid 10 are connected to the outside of the shielding area, eliminating the problem of background field inhomogeneity generated by ordinary solenoid coils.

[0041] The atomic magnetometer 3 is used for magnetic field measurement and data collection. The atomic magnetometer 3 in this example is an optical magnetometer produced by Quspin Corporation of the United States. Its parameter performance can be queried on the official website. The sensor of the atomic magnetometer 3 is 10 mm away from the sample.

[0042] It also includes a thermal polarization module and a shim module. The thermal polarization module includes a permanent magnet 1, which is arranged below the magnetic shielding module 13. The permanent magnet 1 and the electromagnetic shielding tube share a central axis. The shim module includes a pair of shim coils 9. The pair of shim coils 9 are symmetrically fixed on the inner wall of the electromagnetic shielding tube with the smallest circular cross-section diameter about the central axis of the electromagnetic shielding tube, and the center of the radio frequency coil module is located in the magnetic field generated by the shim coil 9. The shim coil 9 adopts a patch flexible coil.

[0043] The permanent magnet 1 is used for thermal polarization of the sample; the permanent magnet 1 can be a neodymium iron boron (NdFeB) magnet with an aperture of 20 mm, which can provide a magnetic field of 2T (T is Tesla, the unit of magnetic field strength).

[0044] The flat solenoid 10 includes a tube body and a variable field coil 2. The variable field coil 2 is wound from one end of the flat solenoid 10 to the other end of the flat solenoid 10, and then wound back from the other end to the starting end. When the variable field coil 2 is energized, the current direction in the variable field coil 2 is counterclockwise or clockwise. The tube body of the flat solenoid 10 is made of non-magnetic material; the sensor of the atomic magnetometer 3 is fixedly connected to the outer wall of the tube body of the flat solenoid 10.

[0045] The present invention Figure 1 The variable field coil 2 shown is a part of the variable field coil 2 wound on the tube, rather than a complete variable field coil 2 .

[0046] As an implementable embodiment, the tube body of the flat solenoid 10 is made of fiberglass, the width of the flat solenoid 10 is 80 mm, the height is 16 mm, the variable field coil 2 can use oxygen-free pure copper enameled wire (such as the enameled wire model is AWG28, the resistance is 126Ω), and the adjustable background field module of this embodiment can generate a controllable and stable background magnetic field of 0-50000nT.

[0047] The radio frequency coil module includes an X-axis Helmholtz coil 4, a Y-axis Helmholtz coil 6, and a Z-axis Helmholtz coil 5, wherein the X-axis Helmholtz coil 4, the Y-axis Helmholtz coil 6, and the Z-axis Helmholtz coil 5 each include a pair of Helmholtz coils with a common central axis, the diameters of the three pairs of Helmholtz coils are the same, the central axes of the three pairs of Helmholtz coils are perpendicular to each other, the central axes of the three pairs of Helmholtz coils intersect at the same center, the three pairs of Helmholtz coils are all arranged outside the flat solenoid 10 in the adjustable background field module, and are located inside the electromagnetic shielding cylinder with the smallest circular cross-section diameter in the magnetic shielding module 13, the centers of the three pairs of Helmholtz coils are located in the background magnetic field generated by the flat solenoid 10 and in the magnetic field generated by a pair of uniform field coils 9, the three pairs of Helmholtz coils are respectively arranged on corresponding coil brackets, and the coil brackets are fixed to the flat solenoid 10 by screws.

[0048] When the sample holder 7 moves to the height where the centers of the three pairs of Helmholtz coils are located via the track, the sample tube 8 on the sample holder 7 is located at the center of the three pairs of Helmholtz coils.

[0049] As an implementable embodiment, the diameter of the three pairs of Helmholtz coils is 115 mm, and the coil brackets and the screws used for fixing can be printed using photosensitive resin.

[0050] The shim coil 9 can generate a magnetic field opposite to the ambient magnetic field, thereby offsetting the interference of the ambient magnetic field; it can also improve the uniformity of the central magnetic field. The shim coil 9 performs magnetic field mapping on the central magnetic field after the magnetic shielding module 13 is completely built, determines the inhomogeneity distribution of the central magnetic field based on the measurement data, and provides a basis for the shape of the shim coil 9 (such as obtaining the shape of the shim coil 9 by the harmonic coefficient method based on the target field method). The shim coil 9 can generate a local magnetic field to adjust the inhomogeneity of the central magnetic field and achieve the adjustment of the magnetic field of the central field. In this embodiment, the shim coil 9 adopts a patch flexible coil, the shape of which is adapted to the inner wall shape of the electromagnetic shielding tube with the smallest circular cross-section diameter. After adjustment by the shim module, the intensity of the central magnetic field is 20nT, and the field uniformity is well improved.

[0051] A support platform is arranged above the top of the magnetic shielding module 13, and the support platform is fixedly connected to the top of the electromagnetic shielding cylinder with the largest circular cross-sectional diameter through a plurality of support columns. The track includes two slide rails 12 (respectively a central slide rail and an auxiliary slide rail), a rack 11, and two pulleys 14 (respectively an upper pulley and a lower pulley). The central slide rail and the auxiliary slide rail each include a pair of slide rails parallel to each other, the upper end of the slide rail is fixedly connected to the bottom of the support platform, and the lower end of the slide rail is fixedly connected to the lower pulley. The rack 11 is arranged in the middle. Between a pair of slideways of the central slideway, two ends of the rack 11 respectively pass around the upper pulley and the lower pulley, and extend into the two slideways of the auxiliary slideway and then connect to form a closed loop. The outer periphery of the upper pulley and the lower pulley are provided with gear teeth meshing with the rack 11. The rack 11 meshes with the upper pulley and the lower pulley. The sample holder 7 is fixedly connected to the rack 11. The sample holder 7 is also slidably connected to a pair of slideways of the central slideway. The injection module also includes a motor 15, and the rotating shaft of the motor 15 is connected to the rotating part of the upper pulley.

[0052] The lower end of the central slide rail passes through the permanent magnet 1 . Bottom baffles are also provided on the two slideways of the central slide rail. When the sample holder 7 slides to the bottom baffle, the sample tube 8 on the sample holder 7 is located at the center of the permanent magnet 1 .

[0053] The motor 15 can drive the upper pulley to rotate, the upper pulley drives the rack 11 to rotate, and the rack 11 drives the sample holder 7 to slide on the central slide rail, thereby moving to the sample setting position; the sample holder 7 is used to carry the sample tube 8 and carry the sample tube 8 to the required position. The sample tube 8 can use a standard nuclear magnetic resonance tube. The sample holder 7 and the slide rail 12 are both made of non-magnetic materials.

[0054] As an implementable embodiment, the sample tube 8 is a Bruker 5 mm standard sample tube 8 , the sample holder 7 is made of PLA material (polylactic acid material), and the slide is made of a glass fiber reinforced plastic tube.

[0055] It also includes a digital control system module 17, which includes a radio frequency control module, a shim control module, a sampling control module, a background field control module, and an acquisition module. The sampling control module is connected to the motor 15 of the sampling module through a motor control line 16, the radio frequency control module is connected to the X-axis Helmholtz coil 4, the Y-axis Helmholtz coil 6, and the Z-axis Helmholtz coil 5 through an X-axis coil current transmission line 19, a Y-axis coil current transmission line 18, and a Z-axis coil current transmission line 20, respectively, the shim control module is connected to the shim coil 9 through a shim coil current transmission line 21, the acquisition module is connected to the atomic magnetometer 3 through an atomic magnetometer data transmission line 22, and the background field control module is connected to the variable field coil 2 of the flat solenoid 10 through a variable field coil current transmission line 23.

[0056] The digital control system module 17 is connected to the digital control system module 17 through the motor control line 16 to control the operation of the motor, so that the sample tube 8 can be controlled to stop smoothly, quickly, and repeatedly at the center of the X-axis Helmholtz coil 4, the Y-axis Helmholtz coil 6, and the Z-axis Helmholtz coil 5 of the radio frequency coil module, or stop at the center of the permanent magnet 1; the background field control module can change the current in the variable field coil 2 of the flat solenoid 10 through the variable field coil current transmission line 23, thereby changing the size of the background magnetic field.

[0057] Embodiment 2:

[0058] A method for measuring ultra-low field nuclear magnetic resonance with a background field adjustable over a wide range, using the ultra-low field nuclear magnetic resonance measuring device with a background field adjustable over a wide range described in the first embodiment, comprises the following steps:

[0059] Step 1. The current input into the shim coil 9 is adjusted through the shim control module of the digital system control module, so that the shim coil 9 generates a magnetic field opposite to the remaining ambient magnetic field (i.e., the ambient magnetic field inside the electromagnetic shielding tube with the smallest circular cross-sectional diameter after being shielded by the magnetic shielding module 13), thereby offsetting the remaining ambient magnetic field and making the ambient magnetic field of the electromagnetic shielding tube with the smallest circular cross-sectional diameter an ultra-low field of near zero (<2nT).

[0060] The present invention forms a zero to ultra-low field environment in the nuclear magnetic resonance measurement area and improves the uniformity of the central magnetic field through the passive magnetic shielding effect of the magnetic shielding module 13 and the active magnetic field compensation performed by the shimming module.

[0061] Step 2: fix the sample tube 8 on the sample holder 7, and control the motor 15 through the digital control system module 17 to move the sample holder 7 to the bottom baffle on the central slide rail, so that the sample in the sample tube 8 is located at the center of the permanent magnet 1, and perform thermal polarization of the sample;

[0062] In this example, the central field strength of the permanent magnet 1 is 2T, and the polarization time is 10s (typically, the central field strength is > 1T, and the polarization time is determined according to the properties of the sample);

[0063] Step 3: The current of the variable field coil 2 of the flat solenoid 10 is adjusted by the digital control system module 17, so as to adjust the size of the background magnetic field. In this example, a current of 0.1 mA is passed through the variable field coil 2 to generate a background magnetic field of about 534 nT.

[0064] Step 4: Start the atomic magnetometer 3 through the digital control system module 17, and perform zero filling and calibration of the atomic magnetometer 3. The atomic magnetometer 3 used in this embodiment is an optical magnetometer produced by Quspin Company of the United States. The specific zero filling and calibration methods can be found on the official website of Quspin Company, which will not be repeated here;

[0065] Step 5: Control the motor 15 through the digital control system to make the sample tube 8 leave the center of the permanent magnet 1 and reach the center of the three pairs of Helmholtz coils after a set time (such as 100ms);

[0066] Step 6: Pass a pulse current into the X-axis Helmholtz coil 4, the Y-axis Helmholtz coil 6, and the Z-axis Helmholtz coil 5 through the digital control system module 17 and adjust the magnitude and duration of the pulse current. In this embodiment, a current of 100 mA is passed into the X-axis Helmholtz coil 4, the Y-axis Helmholtz coil 6, and the Z-axis Helmholtz coil 5 through the digital control system module 17 for a duration of 20 us to excite the sample;

[0067] Step 7: Use the atomic magnetometer 3 to perform measurement to obtain measurement data, and process the measurement data into magnetic resonance information of the sample.

[0068] When it is necessary to measure the magnetic resonance signal under different background fields (B0 field), the digital control system module 17 can be used to change the current in the variable field coil 2 of the flat solenoid 10 to adjust the background field size, and then repeat steps three to six to obtain the magnetic resonance information of the sample.

[0069] It should be noted that the embodiments described in the present invention are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the described embodiments or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the attached claims.

Claims

1. An ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background fields, comprising a magnetic shielding module (13), a flat solenoid (10), a sample injection module, an atomic magnetometer (3), and a radio frequency coil module, characterized in that: The magnetic shielding module (13) comprises a plurality of electromagnetic shielding tubes which are sleeved and fixed in sequence, all of which share a central axis, and through holes are arranged at the top and bottom centers of all of which, the flat solenoid (10) is arranged inside the electromagnetic shielding tube with the smallest circular cross-sectional diameter, and the two ends of the flat solenoid (10) respectively pass through the through holes at the top and bottom centers of the four electromagnetic shielding tubes and extend out of the magnetic shielding module (13), the sampling module is arranged inside the flat solenoid (10), the sampling module comprises a track, a sample tube (8), and a sample holder (7), the sample tube (8) is fixedly arranged on the sample holder (7), the sample holder (7) is slidably arranged on the track, and the two ends of the track respectively extend out of the two ends of the flat solenoid (10), the sensor of the atomic magnetometer (3) is fixedly connected to the outer wall of the flat solenoid (10), the radio frequency coil module is arranged inside the electromagnetic shielding tube with the smallest circular cross-sectional diameter, and is arranged outside the flat solenoid (10), and the fixed height of the sensor of the atomic magnetometer (3) is the same as the height of the center of the radio frequency coil module.

2. The ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field according to claim 1, characterized in that: It also includes a permanent magnet (1) and a pair of shim coils (9), wherein the permanent magnet (1) is arranged below the magnetic shielding module (13), the permanent magnet (1) and the electromagnetic shielding cylinder share a central axis, and the pair of shim coils (9) are symmetrically fixed on the inner wall of the electromagnetic shielding cylinder with the smallest circular cross-section diameter about the central axis of the electromagnetic shielding cylinder, and the center of the radio frequency coil module is located in the magnetic field generated by the shim coil (9).

3. The ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field according to claim 2, characterized in that: The radio frequency coil module comprises an X-axis Helmholtz coil (4), a Y-axis Helmholtz coil (6), and a Z-axis Helmholtz coil (5); the X-axis Helmholtz coil (4), the Y-axis Helmholtz coil (6), and the Z-axis Helmholtz coil (5) each comprise a pair of Helmholtz coils with a common central axis; the diameters of the three pairs of Helmholtz coils are the same; the central axes of the three pairs of Helmholtz coils are perpendicular to each other; the central axes of the three pairs of Helmholtz coils intersect at the same center; the three pairs of Helmholtz coils are arranged outside the flat solenoid (10) and inside the electromagnetic shielding cylinder with the smallest circular cross-section diameter; the centers of the three pairs of Helmholtz coils are located in the background magnetic field generated by the flat solenoid (10) and in the magnetic field generated by a pair of shim coils (9); the three pairs of Helmholtz coils are respectively arranged on corresponding coil supports, and the coil supports are fixed to the flat solenoid (10) by screws; When the sample holder (7) moves to the height where the centers of the three pairs of Helmholtz coils are located via the track, the sample tube (8) on the sample holder (7) is located at the center of the three pairs of Helmholtz coils.

4. The ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field according to claim 3, characterized in that: The invention also comprises a digital control system module (17), wherein the digital control system module (17) comprises a radio frequency control module, a shimming control module, a background field control module, and a collection module. The radio frequency control module is connected to the X-axis Helmholtz coil (4), the Y-axis Helmholtz coil (6), and the Z-axis Helmholtz coil (5) respectively through an X-axis coil current transmission line (19), a Y-axis coil current transmission line (18), and a Z-axis coil current transmission line (20). The shimming control module is connected to the shimming coil (9) through a shimming coil current transmission line (21). The collection module is connected to the atomic magnetometer (3) through an atomic magnetometer data transmission line (22). The background field control module is connected to the flat solenoid (10) through a variable field coil current transmission line (23).

5. The ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field according to claim 4, characterized in that: A support platform is arranged above the top of the magnetic shielding module (13), and the support platform is fixedly connected to the top of the electromagnetic shielding cylinder with the largest circular cross-sectional diameter through a plurality of support columns. The track comprises a central slide rail, an auxiliary slide rail, a rack (11), an upper pulley, and a lower pulley. The central slide rail and the auxiliary slide rail each comprise a pair of slideways parallel to each other, the upper end of the slideway is fixedly connected to the bottom of the support platform, and the lower end of the slideway is fixedly connected to the lower pulley. The rack (11) is arranged between the pair of slideways of the central slide rail, and the two ends of the rack (11) respectively bypass the upper pulley and the lower pulley and extend into the auxiliary slide rail. The two slideways are connected to form a closed loop, the outer peripheries of the upper pulley and the lower pulley are both provided with gear teeth meshing with a rack (11), the rack (11) is meshed with the upper pulley and the lower pulley, the sample holder (7) is fixedly connected to the rack (11), the sample holder (7) is also slidably connected to a pair of slideways of the central slide rail, the injection module also includes a motor (15), the rotating shaft of the motor (15) is connected to the rotating part of the upper pulley, and the digital control system module (17) also includes an injection control module, and the injection control module is connected to the motor (15) of the injection module through a motor control line (16).

6. The ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field according to claim 5, characterized in that: The lower end of the central slide rail passes through the permanent magnet (1), and bottom baffles are also provided on the two slideways of the central slide rail. When the sample holder (7) slides to the bottom baffle, the sample tube (8) on the sample holder (7) is located at the center of the permanent magnet (1).

7. The ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field according to claim 6, characterized in that: The shim coil (9) is a patch flexible coil.

8. The ultra-low field nuclear magnetic resonance measurement device with a wide range of adjustable background field according to claim 7, characterized in that: The flat solenoid (10) comprises a tube body and a variable field coil (2); the variable field coil (2) is wound from one end of the flat solenoid (10) to the other end of the flat solenoid (10), and then wound back from the other end to the starting end; the background field control module is connected to the variable field coil (2) via a variable field coil current transmission line (23); when the variable field coil (2) is energized, the current direction in the variable field coil (2) is counterclockwise or clockwise; and the sensor of the atomic magnetometer (3) is fixedly connected to the outer wall of the tube body of the flat solenoid (10).

9. A method for measuring ultra-low field nuclear magnetic resonance with a background field adjustable over a wide range, using the ultra-low field nuclear magnetic resonance measuring device with a background field adjustable over a wide range as claimed in claim 8, characterized in that: The following steps are involved: Step 1: adjusting the current input into the shim coil (9) through the shim control module of the digital system control module, so that the shim coil (9) generates a magnetic field opposite to the remaining environmental magnetic field to offset the remaining environmental magnetic field, so that the environmental magnetic field of the electromagnetic shielding tube with the smallest circular cross-section diameter is a near-zero ultra-low field; Step 2: fix the sample tube (8) on the sample holder (7), and control the motor (15) through the digital control system module (17) to move the sample holder (7) to the bottom baffle on the central slide rail, so that the sample in the sample tube (8) is located at the center of the permanent magnet (1), and thermal polarization of the sample is performed; Step 3: adjusting the current of the variable field coil (2) through the digital control system module (17), thereby adjusting the size of the background magnetic field; Step 4: starting the atomic magnetometer (3) through the digital control system module (17), and performing zero filling and calibration of the atomic magnetometer (3); Step 5: Control the motor (15) through the digital control system to make the sample tube (8) leave the center of the permanent magnet (1) and reach the center of the three pairs of Helmholtz coils after a set time; Step 6: Passing pulse current to the X-axis Helmholtz coil (4), the Y-axis Helmholtz coil (6), and the Z-axis Helmholtz coil (5) through the digital control system module (17) and adjusting the magnitude and duration of the pulse current to excite the sample; Step 7: Use the atomic magnetometer (3) to measure and obtain measurement data, and process the measurement data into magnetic resonance information of the sample.

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