A background field large range adjustable ultra-low field nuclear magnetic resonance measuring device and method

Abstract

The application discloses a kind of background field wide-range adjustable ultra-low field nuclear magnetic resonance measuring device, and a kind of background field wide-range adjustable ultra-low field nuclear magnetic resonance measuring method is also disclosed, the present application adopts flat solenoid to realize high background magnetic field requirement and ultra-low ambient magnetic field, flat solenoid can also accommodate more coil and obtain more turns, realize more extensive background field adjustable range;Flat solenoid both ends are stretched outside magnetic shielding module, which can ensure that the magnetic flux line at the end of flat solenoid is connected outside the shielding area, eliminating the problem of background field inhomogeneity generated by ordinary solenoid coil;The present application can eliminate the interference of ambient magnetic field by passive magnetic shielding and active magnetic field compensation, first, the ambient magnetic field is shielded by multiple electromagnetic shielding cylinders, and then the magnetic field opposite to the ambient magnetic field is generated by the shim coil to actively compensate the magnetic field, to offset the interference of ambient magnetic field;The shim coil can also improve the uniformity of the central magnetic field.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of nuclear magnetic resonance measurement, and particularly relates to a super-low-field nuclear magnetic resonance measurement device with a large-range adjustable background field, and also relates to a super-low-field nuclear magnetic resonance measurement method with a large-range adjustable background field, which is suitable for the fields of zero to super-low-field magnetic resonance measurement, nondestructive testing, biomedicine, magnetic resonance imaging, relaxation detection, biological metabolism detection, and magnetic resonance detection of samples containing metals. BACKGROUND

[0002] Nuclear magnetic resonance signals are usually obtained in a background magnetic field (B0 field), and are one of the most important spectral techniques for chemical analysis and structural analysis. However, traditional high-field nuclear magnetic resonance has some disadvantages, such as high-frequency signal distortion caused by 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 super-low magnetic fields by using atomic magnetometers. An atomic magnetometer is a super-high-sensitivity magnetic measurement tool that determines the size of a magnetic field by measuring the Larmor precession frequency of the polarization vector of an atom in an external magnetic field.

[0004] However, due to the limitations of the bandwidth and sensitivity of the atomic magnetometer, it is impossible to measure the Larmor precession information of a sample in a relatively high background magnetic field. In existing near-zero to super-low magnetic field nuclear magnetic resonance experiments, the measurement is carried out without a strong magnetic field, the chemical shift can be ignored, 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, the existing near-zero to super-low magnetic field nuclear magnetic resonance experiments still have some problems. First, the atomic gas chamber of the atomic magnetometer needs to work in a near-zero field (less than 20 nT) environment, and usually uses materials such as multi-layer permalloy to shield the environmental magnetic field. This passive shielding makes the atomic force meter unable to detect the magnetic field outside the shielding layer, and the background field is fixed at the theoretical residual magnetism of the shielding device, and the size of the background field cannot be changed, which seriously limits the application of the atomic magnetometer in the geomagnetic field, deep space magnetic field, underwater magnetic field, etc.

[0006] In recent years, some zero to super-low-field nuclear magnetic resonance measurement devices with adjustable background fields have been developed. For example, after using the MS-1LF four-layer magnetic shielding design, the James Eills team realized a near-zero magnetic field (<2nT) inside the shielding. At the same time, in order to realize the measurement of super-low field, the research team used a hand-wound penetrating solenoid to pass through the magnetic shielding, and applied a local magnetic field at the position of the sample instead of the sensor position, so as to provide a stable and variable magnetic field (0-3.8uT) inside the shielding device, and facilitate the sample to enter and exit the magnetic shielding barrel.

[0007] Although the scheme solves the problem of non-adjustable background field, there are problems of small adjustable range of background field and poor field uniformity at sample. SUMMARY

[0008] The present application aims at the above-mentioned problems existing in the prior art, and provides a super-low-field nuclear magnetic resonance measuring device with a large adjustable range of background field, and a super-low-field nuclear magnetic resonance measuring method with a large adjustable range of background field.

[0009] The above-mentioned purposes of the present application are achieved by the following technical means:

[0010] A super-low-field nuclear magnetic resonance measuring device with a large adjustable range of background field comprises a magnetic shielding module, a flat solenoid, a sample feeding module, an atomic magnetometer, and a radio frequency coil module, the magnetic shielding module comprises a plurality of electromagnetic shielding cylinders fixed in sequence, all the electromagnetic shielding cylinders have a common central axis, the top center and the bottom center of all the electromagnetic shielding cylinders are provided with through holes, the flat solenoid is arranged inside the electromagnetic shielding cylinder with the smallest diameter of circular cross section, the two ends of the flat solenoid respectively extend out of the magnetic shielding module through the through holes in the top center and the bottom center of the four electromagnetic shielding cylinders, the sample feeding module is arranged inside the flat solenoid, the sample feeding module comprises a track, a sample tube, and a sample support, the sample tube is fixedly arranged on the sample support, the sample support is slidingly arranged on the track, the two ends of the track respectively extend out of the two ends of the flat solenoid, the sensor of the atomic magnetometer is fixedly connected with the outer wall of the flat solenoid, the radio frequency coil module is arranged inside the electromagnetic shielding cylinder with the smallest diameter of circular cross section and outside the flat solenoid, and the fixed height of the sensor of the atomic magnetometer is the same as the height at which the center of the radio frequency coil module is located.

[0011] Further comprising a permanent magnet and a pair of shim coils, the permanent magnet is arranged below the magnetic shielding module, the permanent magnet has a common central axis with the electromagnetic shielding cylinders, the pair of shim coils are symmetrically fixed on the inner wall of the electromagnetic shielding cylinder with the smallest diameter of circular cross section about the central axis of the electromagnetic shielding cylinders, and the center of the radio frequency coil module is located in the magnetic field generated by the shim coils.

[0012] The radio frequency coil module includes an X-axis Helmholtz coil, a Y-axis Helmholtz coil and a Z-axis Helmholtz coil, each of which includes a pair of concentric-axis Helmholtz coils, the three pairs of Helmholtz coils have the same diameter, 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 and inside the electromagnetic shielding cylinder with the smallest diameter of the circular cross section, the centers of the three pairs of Helmholtz coils are located in the background magnetic field generated by the flat solenoid and the magnetic field generated by the pair of shim coils, and the three pairs of Helmholtz coils are arranged on the corresponding coil supports, and the coil supports are fixed on the flat solenoid by screws.

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

[0014] The digital control system module 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 with 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 with the shim coil through the shim coil current transmission line, the acquisition module is connected with the atomic magnetometer through the atomic magnetometer data transmission line, and the background field control module is connected with the flat solenoid through the variable field coil current transmission line.

[0015] The top of the magnetic shielding module is provided with a support platform, the support platform is fixedly connected with the top of the electromagnetic shielding cylinder with the largest diameter of the circular cross section through a plurality of support columns, the track includes a center slide rail, an auxiliary slide rail, a rack, an upper pulley and a lower pulley, the center slide rail and the auxiliary slide rail each include a pair of parallel slides, the upper ends of the slides are fixedly connected with the bottom of the support platform, the lower ends of the slides are fixedly connected with the lower pulley, the rack is arranged between the pair of slides of the center slide rail, the two ends of the rack pass through the upper pulley and the lower pulley respectively, and extend into the two slides of the auxiliary slide rail to form a closed loop, the outer periphery of the upper pulley and the lower pulley is provided with teeth engaged with the rack, the rack is engaged with the upper pulley and the lower pulley, the sample holder is fixedly connected with the rack, and the sample holder is also in sliding connection with the pair of slides of the center slide rail, the sample feeding module further includes a motor, a rotating shaft of the motor is connected with a rotating part of the upper pulley, and the digital control system module further includes a sample feeding control module, the sample feeding control module is connected with the motor of the sample feeding module through a motor control line.

[0016] The lower end of the center slide rail passes through the permanent magnet, and the two slide rails of the center slide rail are further provided with a bottom baffle, when the sample support slides to the bottom baffle, the sample tube on the sample support is located at the center of the permanent magnet.

[0017] The shim coil is a patch flexible coil.

[0018] 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 with the variable field coil through a variable field coil current transmission line, when the variable field coil is powered on, the current directions in the variable field coil are all counterclockwise or all clockwise, and the sensor of the atomic magnetometer is fixedly connected with the outer wall of the tube body of the flat solenoid.

[0019] The method comprises the following steps:

[0020] Step one, adjust the current input into the shim coil through the shim coil control module of the digital system control module, so that the shim coil generates a magnetic field opposite to the residual ambient magnetic field to offset the residual ambient magnetic field, and the ambient magnetic field of the electromagnetic shielding cylinder with the smallest circular cross section diameter is a near-zero ultra-low field;

[0021] Step two, fix the sample tube on the sample support, move the sample support to the bottom baffle on the center slide rail through the digital control system module, so that the sample in the sample tube is located at the center of the permanent magnet, and the sample is subjected to thermal polarization;

[0022] Step three, 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 four, start the atomic magnetometer through the digital control system module, and perform zero compensation and correction of the atomic magnetometer;

[0024] Step five, move the sample tube away from the center of the permanent magnet through the digital control system, and reach the center of the three pairs of Helmholtz coils after a set time;

[0025] Step six, excite the sample by inputting pulse current into the X-axis Helmholtz coil, the Y-axis Helmholtz coil and the Z-axis Helmholtz coil through the digital control system module and adjusting the size and duration of the pulse current;

[0026] Step seven, measure and obtain measurement data using the atomic magnetometer, and process the measurement data into magnetic resonance information of the sample.

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

[0028] (1) Compared with the traditional solenoid coil used in zero to ultra-low field nuclear magnetic resonance measurement, the biggest advantage of the flat solenoid used in the present application is the gap between the inner and outer magnetic fields. The traditional solenoid coil cannot usually achieve such a large gap between the inner and outer magnetic fields. The flat solenoid used in the present application can simultaneously meet the requirements of high background magnetic field and ultra-low environmental magnetic field, so that the sample is placed in a strong background magnetic field and the atomic magnetometer is located in an ultra-low environmental magnetic field.

[0029] (2) The flat solenoid can accommodate more coils and obtain more turns, so that a larger current can be used to generate a stronger background magnetic field, thereby realizing a wider range of background field adjustment. Compared with the traditional solenoid, the coils of the flat solenoid are more closely wound, effectively utilizing the space, so that more coils can be accommodated in a limited volume, thereby providing a larger current and a stronger background magnetic field, and further enabling the device to flexibly adjust the strength of the background magnetic field to meet different experimental requirements.

[0030] (3) The two ends of the flat solenoid both extend outside the magnetic shielding module, which can ensure that the magnetic flux lines at the ends of the flat solenoid are connected outside the shielding area, eliminating the problem of non-uniformity of the background field generated by ordinary solenoid coils.

[0031] (4) The present application passively shields the environmental magnetic field and actively compensates for the disturbance of the environmental magnetic field. First, the environmental magnetic field is passively shielded by multiple electromagnetic shielding cylinders, and then actively compensated by the uniform field coil generating a magnetic field opposite to the environmental magnetic field, so as to offset the disturbance of the environmental magnetic field. The uniform field coil can also improve the uniformity of the central magnetic field (i.e. the magnetic field generated by the three pairs of Helmholtz coils).

[0032] (5) The present application uses electrically driven sampling, which controls the motor through the motor control line to control the position of the sample in the device, so that the sample can be quickly and accurately stopped at 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 sampling design, electric sampling has the characteristics of precise parking, automatic control and high repeatability, which improves the experimental efficiency and data accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structural schematic diagram of the device of the present application;

[0034] Reference signs and corresponding component names:

[0035] 1 - permanent magnet; 2 - field variation 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 - shim 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 - shim coil current transmission line; 22 - atomic magnetometer data transmission line; 23 - field variation coil current transmission line. DETAILED DESCRIPTION

[0036] In order to facilitate those skilled in the art to understand and implement the present application, the present application is further described in detail below in conjunction with examples, which are only used to illustrate and explain the present application, and are not a limitation on the present application.

[0037] Example 1:

[0038] A kind of background field wide-range adjustable ultra-low field nuclear magnetic resonance measuring device, including magnetic shielding module 13, adjustable background field module, sample module, atomic magnetometer 3, And radio frequency coil module, magnetic shielding module 13 includes four cylindrical electromagnetic shielding cylinder of fixedly sleeved in turn, four electromagnetic shielding cylinder common central axis, the top center and the bottom center of four electromagnetic shielding cylinder are provided with a through hole respectively, adjustable background field module includes flat solenoid 10, flat solenoid 10 is set in the inside of the electromagnetic shielding cylinder of minimum diameter of circular section, the both ends of flat solenoid 10 respectively pass through the through hole of the top center and the bottom center of four electromagnetic shielding cylinder and extend to the outside of magnetic shielding module 13, i.e. the length of flat solenoid 10 is greater than the length of all electromagnetic shielding cylinder, sample module is set in the inside of flat solenoid 10, sample module includes track, sample tube 8 and sample holder 7, sample tube 8 is fixedly set on sample holder 7, sample tube 8 is used to hold sample, sample holder 7 is slidably set on track, the both ends of track are respectively extended to the both ends of flat solenoid 10, the sensor of atomic magnetometer 3 is fixedly connected with the outer wall of flat solenoid 10, radio frequency coil module is set in the inside of the electromagnetic shielding cylinder of minimum diameter of circular section, and is set in the outside of flat solenoid 10, the fixed height of the sensor of atomic magnetometer 3 is same with the height where the center of radio frequency coil module is located, and makes the sensor of atomic magnetometer 3 opposite to sample tube 8, so that the sensor of atomic magnetometer 3 is closest to sample tube 8.

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

[0040] The flat solenoid 10 is used to generate a stable controllable background magnetic field inside the flat solenoid 10. Compared with the solenoid coil used in traditional zero to ultra-low field nuclear magnetic resonance measurement, the biggest advantage of the flat solenoid 10 used in the present application is the gap between the inner and outer magnetic fields. The traditional solenoid coil usually cannot achieve such a large gap between the inner and outer magnetic fields. The flat solenoid 10 used in the present application can simultaneously meet the requirements of high background magnetic field and ultra-low environmental magnetic field, 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, the two ends of the flat solenoid 10 extend outside the magnetic shielding module 13, which can ensure that the magnetic flux lines at the ends of the flat solenoid 10 are connected outside the shielding area, thereby eliminating the problem of non-uniformity of the background field generated by the ordinary solenoid coil.

[0041] The atomic magnetometer 3 is used for magnetic field measurement and data acquisition. The atomic magnetometer 3 in the present example is an optical magnetometer produced by Quspin Company in the United States, and 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 shimming module. The thermal polarization module includes a permanent magnet 1, which is arranged below the magnetic shielding module 13 and is coaxial with the electromagnetic shielding cylinder. The shimming module includes a pair of shim coils 9, which are symmetrically fixed on the inner wall of the electromagnetic shielding cylinder with the smallest circular cross-section diameter about the center 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 coils 9. The shim coils 9 adopt patch flexible coils.

[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 a pore diameter 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 to the starting end from the other 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 a non-magnetic material. The sensor of the atomic magnetometer 3 is fixedly connected with the outer wall of the tube body of the flat solenoid 10.

[0045] The present application relates to a magnetic resonance imaging system Figure 1 The variable field coil 2 shown is part of the variable field coil 2 wound on the tube body, rather than the complete variable field coil 2.

[0046] As an implementable manner, the tube body of the flat solenoid 10 adopts glass fiber reinforced plastic, the width of the flat solenoid 10 is 80 mm, the height is 16 mm, the variable field coil 2 can adopt oxygen-free pure copper enameled wire (such as enameled wire type AWG28, the resistance size is 126Ω), and the adjustable background field module can generate a controllable and stable background magnetic field of 0-50000 nT.

[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 co-central axis Helmholtz coils, 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 in the adjustable background field module and 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 the magnetic field generated by the pair of shim coils 9, and the three pairs of Helmholtz coils are arranged on corresponding coil supports, and the coil supports are fixed on the flat solenoid 10 by screws.

[0048] When the sample support 7 is moved to the height where the centers of the three pairs of Helmholtz coils are located through the track, the sample tube 8 on the sample support 7 is located at the centers of the three pairs of Helmholtz coils.

[0049] As an implementable manner, the diameters of the three pairs of Helmholtz coils are 115 mm, and the coil supports and the screws used for fixing can be printed by photosensitive resin.

[0050] The shim coil 9 can generate a magnetic field opposite to the environmental magnetic field, so as to offset the interference of the environmental magnetic field; and can also improve the uniformity of the central magnetic field. The shim coil 9 is based on the complete magnetic shielding module 13, performs magnetic field mapping on the central magnetic field, determines the non-uniformity distribution of the central magnetic field based on the measurement data, 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), and can generate a local magnetic field to adjust the non-uniformity of the central magnetic field, so as to realize the adjustment of the central field. In the embodiment, the shim coil 9 adopts a patch flexible coil, the shape of the patch flexible coil is adapted to the shape of the inner wall of the electromagnetic shielding cylinder with the smallest circular cross-section diameter, and after the adjustment of the shim module, the strength of the central magnetic field is 20 nT, and the field uniformity is greatly improved.

[0051] A support platform is arranged above the top of the magnetic shielding module 13, and the support platform is fixedly connected with the top of the electromagnetic shielding cylinder with the largest diameter of circular cross section through a plurality of support columns. The track includes two slide rails 12 (a central slide rail and a secondary slide rail), a rack 11, and two pulleys 14 (an upper pulley and a lower pulley). The central slide rail and the secondary slide rail each include a pair of parallel slide channels, the upper ends of the slide channels are fixedly connected with the bottom of the support platform, the lower ends of the slide channels are fixedly connected with the lower pulley, the rack 11 is arranged between the pair of slide channels of the central slide rail, the two ends of the rack 11 pass around the upper pulley and the lower pulley respectively, and extend into the two slide channels of the secondary slide rail to form a closed loop. The outer periphery of the upper pulley and the lower pulley is provided with teeth engaging with the rack 11. The rack 11 engages with the upper pulley and the lower pulley. The sample holder 7 is fixedly connected with the rack 11 and slidably connected with the pair of slide channels of the central slide rail. The sample feeding module further includes a motor 15, and the rotating shaft of the motor 15 is connected with the rotating part of the upper pulley.

[0052] The lower end of the central slide rail penetrates the permanent magnet 1, and a bottom baffle is further arranged on the two slide channels 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, so as to move to a sample setting position. The sample holder 7 is used to carry the sample tube 8 and load the sample tube 8 to a required position. The sample tube 8 can adopt a standard nuclear magnetic resonance tube. The sample holder 7 and the slide rail 12 are made of non-magnetic material.

[0054] As an implementable mode, the sample tube 8 adopts a Bruker 5mm standard sample tube 8, the sample holder 7 adopts PLA material (poly lactic acid material), and the slide channel adopts a glass steel tube.

[0055] The digital control system module 17 includes a radio frequency control module, a shimming control module, a sample feeding control module, a background field control module, and an acquisition module. The sample feeding control module is connected with the motor 15 of the sample feeding module through the motor control line 16. The radio frequency control module is connected with the X-axis Helmholtz coil 4, the Y-axis Helmholtz coil 6, and the Z-axis Helmholtz coil 5 through the X-axis coil current transmission line 19, the Y-axis coil current transmission line 18, and the Z-axis coil current transmission line 20 respectively. The shimming control module is connected with the shimming coil 9 through the shimming coil current transmission line 21. The acquisition module is connected with the atomic magnetometer 3 through the atomic magnetometer data transmission line 22. The background field control module is connected with the variable field coil 2 of the flat spiral tube 10 through the 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 as to control that the sample tube 8 can be smoothly, quickly and repeatedly stopped 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 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, so as to change the size of the background magnetic field.

[0057] Embodiment 2:

[0058] A kind of background field wide-range adjustable ultra-low field nuclear magnetic resonance measurement method, using the above-mentioned background field wide-range adjustable ultra-low field nuclear magnetic resonance measurement device of embodiment 1, including the following steps:

[0059] Step one, the current input into the shimming coil 9 is adjusted by the shimming control module of the digital system control module, so that the shimming coil 9 generates a magnetic field opposite to the remaining ambient magnetic field (i.e. the ambient magnetic field inside the electromagnetic shielding cylinder with the smallest circular cross-section diameter after shielding by the magnetic shielding module 13), thereby canceling 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 of near zero (<2nT).

[0060] The present application forms a zero to ultra-low field environment in the nuclear magnetic resonance measurement region by the passive magnetic shielding effect of the magnetic shielding module 13 and the active magnetic field compensation of the shimming module, while improving the uniformity of the central magnetic field;

[0061] Step two, the sample tube 8 is fixed on the sample support 7, and the sample support 7 is moved to the bottom stop plate on the center slide rail by the motor 15 controlled by the digital control system module 17, so that the sample in the sample tube 8 is located at the center of the permanent magnet 1, and the sample is polarized;

[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 sample properties);

[0063] Step three, 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 0.1mA is passed through the variable field coil 2, generating a background magnetic field of about 534nT;

[0064] Step four, start the atomic magnetometer 3 through the digital control system module 17, and carry out zero compensation and correction of the atomic magnetometer 3, the optical magnetometer produced by the American Quspin company is used in the embodiment, and the specific zero compensation and correction method can be inquired from the official website of the Quspin company, and will not be described here;

[0065] Step five, 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 100 ms);

[0066] Step six, pulse current is input 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 the size and duration of the pulse current are adjusted, in the embodiment, 100 mA current is input 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 the duration is 20 us, to excite the sample;

[0067] Step seven, measure to obtain measurement data using the atomic magnetometer 3, 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 size of the current in the field-changing coil 2 of the flat solenoid 10 can be changed through the digital control system module 17, so as to adjust the size of the background field, and then steps three to six are repeated to obtain the magnetic resonance information of the sample.

[0069] It should be pointed out that the embodiments described in the present application are only examples of the spirit of the present application. Those skilled in the art of the present application can make various modifications or supplements to the described embodiments or use similar ways to replace them, but will not deviate from the spirit of the present application or exceed the scope defined by the appended claims.

Claims

1. A device for ultra-low field nuclear magnetic resonance measurements with a large range of background field adjustment, comprising a magnetic shielding module (13), a flat solenoid (10), a sample introduction 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 cylinders fixed in sequence. The electromagnetic shielding cylinders share a common central axis. The top center and the bottom center of each electromagnetic shielding cylinder are provided with a through hole. The flat solenoid (10) is arranged inside the electromagnetic shielding cylinder with the smallest diameter of the circular cross section. The two ends of the flat solenoid (10) respectively extend out of the magnetic shielding module (13) through the through holes in the top center and the bottom center of the four electromagnetic shielding cylinders. The sample feeding module is arranged inside the flat solenoid (10). The sample feeding module comprises a track, a sample tube (8) and a sample support (7). The sample tube (8) is fixedly arranged on the sample support (7). The sample support (7) is slidably arranged on the track. 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 cylinder with the smallest diameter of the circular cross section and outside the flat solenoid (10). The fixed height of the sensor of the atomic magnetometer (3) is the same as the height at which the center of the radio frequency coil module is located. The magnetic shielding module (13) comprises a plurality of electromagnetic shielding cylinders fixed in sequence. The electromagnetic shielding cylinders share a common central axis. The top center and the bottom center of each electromagnetic shielding cylinder are provided with a through hole. The flat solenoid (10) is arranged inside the electromagnetic shielding cylinder with the smallest diameter of the circular cross section. The two ends of the flat solenoid (10) respectively extend out of the magnetic shielding module (13) through the through holes in the top center and the bottom center of the four electromagnetic shielding cylinders. The sample feeding module is arranged inside the flat solenoid (10). The sample feeding module comprises a track, a sample tube (8) and a sample support (7). The sample tube (8) is fixedly arranged on the sample support (7). The sample support (7) is slidably arranged on the track. 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 cylinder with the smallest diameter of the circular cross section and outside the flat solenoid (10). The fixed height of the sensor of the atomic magnetometer (3) is the same as the height at which the center of the radio frequency coil module is located.

2. The apparatus according to claim 1, wherein 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 sharing 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 diameter of the circular cross section. The centers of the three pairs of Helmholtz coils are located in the background magnetic field generated by the flat solenoid (10) and the magnetic field generated by the pair of shim coils (9). The three pairs of Helmholtz coils are arranged on corresponding coil supports. The coil supports are fixed to the flat solenoid (10) by screws. When the sample support (7) moves to the height at which the centers of the three pairs of Helmholtz coils are located through the track, the sample tube (8) on the sample support (7) is located at the centers of the three pairs of Helmholtz coils.

3. The apparatus according to claim 2, wherein the background field is set to 0.1 T. The digital control system module (17) 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 with the X-axis Helmholtz coil (4), the Y-axis Helmholtz coil (6) and the Z-axis Helmholtz coil (5) through the X-axis coil current transmission line (19), the Y-axis coil current transmission line (18) and the Z-axis coil current transmission line (20) respectively, the shim control module is connected with the shim coil (9) through the shim coil current transmission line (21), the acquisition module is connected with the atomic magnetometer (3) through the atomic magnetometer data transmission line (22), and the background field control module is connected with the flat solenoid (10) through the variable field coil current transmission line (23).

4. The apparatus according to claim 3, wherein the background field is set to 0.1 T. A support platform is arranged above the top of the magnetic shielding module (13), the support platform is fixedly connected with the top of the electromagnetic shielding cylinder with the largest diameter of circular cross section through a plurality of support columns, the track includes a center slide rail, an auxiliary slide rail, a rack (11), an upper pulley and a lower pulley, the center slide rail and the auxiliary slide rail each include a pair of parallel slides, the upper ends of the slides are fixedly connected with the bottom of the support platform, the lower ends of the slides are fixedly connected with the lower pulley, the rack (11) is arranged between the pair of slides of the center slide rail, the two ends of the rack (11) pass through the upper pulley and the lower pulley respectively, and then extend into the two slides of the auxiliary slide rail to form a closed loop, the outer periphery of the upper pulley and the lower pulley is provided with a gear that meshes with the rack (11), the rack (11) meshes with the upper pulley and the lower pulley, the sample support (7) is fixedly connected with the rack (11), and the sample support (7) is also slidably connected with the pair of slides of the center slide rail, the sample feeding module further includes a motor (15), a rotating shaft of the motor (15) is connected with a rotating part of the upper pulley, and the digital control system module (17) further includes a sample feeding control module, the sample feeding control module is connected with the motor (15) of the sample feeding module through a motor control line (16).

5. The apparatus according to claim 4, wherein the background field is set to 0.1 T. The lower end of the center slide rail penetrates through the permanent magnet (1), and bottom baffles are further arranged on the two slides of the center slide rail, when the sample support (7) slides to the bottom baffles, the sample tube (8) on the sample support (7) is located at the center of the permanent magnet (1).

6. The apparatus according to claim 5, wherein the background field is set to 0.1 T. The shim coil (9) is a patch flexible coil.

7. The apparatus according to claim 6, wherein the background field is set to 0.1 T. 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, the background field control module is connected with the variable field coil (2) through the variable field coil current transmission line (23), when the variable field coil (2) is powered on, the current directions in the variable field coil (2) are all counterclockwise or all clockwise, and a sensor of the atomic magnetometer (3) is fixedly connected with the outer wall of the tube body of the flat solenoid (10).

8. A method for measuring ultra-low field nuclear magnetic resonance with a large range of background field adjustment, using the device for measuring ultra-low field nuclear magnetic resonance with a large range of background field adjustment according to claim 7, characterized in that, The method comprises the following steps: Step one, adjust 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 residual ambient magnetic field to offset the residual ambient magnetic field, so that the ambient magnetic field of the electromagnetic shielding cylinder with the smallest circular cross-section diameter is a near-zero ultra-low field; Step two, fix the sample tube (8) on the sample holder (7), control the motor (15) through the digital control system module (17) to move the sample holder (7) to the bottom stop at the center slide rail, so that the sample in the sample tube (8) is located at the center of the permanent magnet (1), and the sample is heated and polarized; Step three, adjust the current of the variable field coil (2) through the digital control system module (17), so as to adjust the size of the background magnetic field; Step four, start the atomic magnetometer (3) through the digital control system module (17), and carry out zero compensation and correction of the atomic magnetometer (3); Step five, move the sample tube (8) away from the center of the permanent magnet (1) through the digital control system control motor (15), and reach the center of the three pairs of Helmholtz coils after a set time; Step six, excite the sample by inputting pulse current into the X-axis Helmholtz coil (4), Y-axis Helmholtz coil (6) and Z-axis Helmholtz coil (5) and adjusting the size and duration of the pulse current through the digital control system module (17); Step seven, measure the data using the atomic magnetometer (3), and process the data into the magnetic resonance information of the sample.

Images