System and method for atomic nucleus spin pointing control and precession signal measurement

Abstract

The invention discloses a system and method for atomic nucleus spinning pointing control and precession signal measurement, and the system comprises a radio frequency generator, a radio frequency amplifier, a single-pole double-throw switch, a nuclear magnetic resonance coil, a signal processing module, a DAQ data collection system, an upper computer, and a time reference module. The time reference module is respectively connected with the DAQ data acquisition system, the signal processing module and the radio frequency generator, the radio frequency generator is connected with the radio frequency amplifier, the radio frequency amplifier, the nuclear magnetic resonance coil and the signal processing module are all connected with the single-pole double-throw switch, the upper computer is connected with the DAQ data acquisition system, the DAQ data acquisition system is connected with the signal processing module, and the signal processing module is connected with the single-pole double-throw switch. The DAQ data acquisition system outputs TTL control signals to the signal processing module, the single-pole double-throw switch and the radio frequency amplifier. The device has the advantages that accurate control of nuclear spin pointing to the 360-degree range is achieved, and integration of signal receiving and transmitting is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of strong current measurement and strong magnetic measurement, and in particular to a system and method for atomic nucleus spin pointing control and precession signal measurement. Background Art

[0002] With the development of quantum science and technology, an ultra-high precision atomic magnetometer based on hyperpolarized atomic nuclear magnetic resonance has been proposed and experimentally verified. Its magnetic field measurement accuracy exceeds that of traditional magnetic field sensors, making it the world's most accurate magnetic field measurement sensor. It can be used to measure the magnetic field generated by ultra-high voltage and strong current in turbines, and to build a quantum large current sensor. Due to the ultra-high precision characteristics of atomic magnetometers, they can be used for magnetic field measurement and calibration, and have many advantages over traditional magnetic field sensors. Due to the principle of hyperpolarized nuclear magnetic resonance, the magnetometer needs to apply a transverse radio frequency magnetic field to deflect the polarization direction of the nuclear spin and collect the nuclear spin free induction decay signal to obtain the magnitude of the magnetic field to be measured. Therefore, it is necessary to develop a system for precise manipulation of the nuclear spin orientation and relaxation signal measurement in magnetic field measurement, so that the transverse radio frequency magnetic field signal can be automatically and periodically applied and the free induction decay signal can be collected when measuring the magnetic field, greatly reducing the measurement time and improving the measurement accuracy.

[0003] However, due to the limitations of radio frequency pulse width and pulse time, the traditional nuclear magnetic resonance technology cannot control the nuclear spin direction 360 degrees. The pulse control between various devices does not have a unified time base, which makes it impossible to accurately control the nuclear spin direction. The various functional components are not modularized, and there are problems such as the lack of integrated signal transmission and reception. For example, the nuclear precession magnetic field detection method and nuclear magnetic resonance gyroscope disclosed in Chinese patent publication number CN116359806A, although the detection of precession signals is achieved, its nuclear spin direction cannot be controlled 360 degrees, and many of the above-mentioned problems still exist. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the existing nuclear magnetic resonance system has the problem that the nuclear spin orientation cannot be accurately controlled within a 360-degree range, and the receiving and transmitting signals are not integrated.

[0005] The present invention solves the above technical problems through the following technical means: a system for controlling the pointing of atomic nuclear spin and measuring precession signals, comprising a radio frequency generator, a radio frequency amplifier, a single-pole double-throw switch, a nuclear magnetic resonance coil, a signal processing module, a DAQ data acquisition system, a host computer and a time reference module, wherein the time reference module is respectively connected to the DAQ data acquisition system, the signal processing module and the radio frequency generator, the radio frequency generator is connected to the radio frequency amplifier, the radio frequency amplifier, the nuclear magnetic resonance coil and the signal processing module are all connected to the single-pole double-throw switch, the host computer is connected to the DAQ data acquisition system, the signal acquisition port of the DAQ data acquisition system is connected to the signal processing module, the DAQ data acquisition system outputs TTL control signals to the signal processing module, the single-pole double-throw switch and the radio frequency amplifier respectively, and the DAQ data acquisition system outputs a clock synchronization signal to the time reference module.

[0006] Furthermore, the time reference module includes a signal generator and a rubidium clock. The signal generator receives a clock synchronization signal output by a DAQ data acquisition system. The signal generator is connected to the rubidium clock, and the rubidium clock is connected to a radio frequency generator.

[0007] Furthermore, the signal processing module includes a single-pole single-throw switch, a bandpass filter, an amplifier, a mixer and a preamplifier connected in sequence, the single-pole single-throw switch is also connected to a single-pole double-throw switch and receives a TTL control signal output by a DAQ data acquisition system, and the preamplifier is connected to a signal acquisition port of the DAQ data acquisition system.

[0008] Furthermore, the signal generator is connected to the mixer, and the signal generator generates a trigger signal as a local oscillator signal input of the mixer.

[0009] The present invention also provides a method for a system for controlling the pointing direction of atomic nuclear spin and measuring precession signals, comprising:

[0010] First, turn on the single-pole double-throw switch to connect the RF amplifier to the nuclear magnetic resonance coil. The RF generator sends an adjustable-frequency RF wave to the RF amplifier for amplification. The output of the RF amplifier is turned on and off by the DAQ data acquisition system. The host computer controls the time of the RF amplifier outputting the pulse signal to generate a pulse of variable length. The pulse signal is loaded onto the nuclear magnetic resonance coil through the single-pole double-throw switch to enable the nuclear magnetic resonance coil to generate a transverse pulse magnetic field perpendicular to the spin direction of the helium-3 atom, stimulating the helium-3 atomic spin to produce transverse precession. When the pulse signal frequency is equal to the precession frequency of the helium-3 nuclear spin, the helium-3 atom absorbs the pulse energy and its spin direction will deflect toward the direction of the pulse magnetic field. The deflection angle is controlled by the pulse time. When the pulse signal loading is completed, the single-pole double-throw switch connects the nuclear magnetic resonance coil and the signal processing module loop, and the helium-3 nuclear spin will relax back to the direction of the magnetic field to be measured. During this process, the nuclear magnetic resonance coil senses a change in magnetic flux, that is, a free decay oscillation signal will be generated in the nuclear magnetic resonance coil. The free induction decay signal is extracted, amplified, and denoised through a bandpass filter, an amplifier, a mixer, and a preamplifier to obtain a FID signal related to the magnetic field strength information to be measured. At the same time, the processed FID signal is recorded and saved by the host computer. In order to improve the signal-to-noise ratio, the above process is repeated to remove additional environmental interference; for each cycle, the emitted pulse time and the time of the entire cycle are controlled by the host computer program, and the external synchronous clock provided by the time reference module is used as a reference. Compared with the prior art, this test method does not need to obtain magnetic field information through optical signals, further reducing the use of lasers, and integrating the signal processing module and the signal loading module into a board card, which is convenient for subsequent integration and synchronization between control signals, and further improves the measurement accuracy.

[0011] Furthermore, the signal processing module includes a single-pole single-throw switch, a bandpass filter, an amplifier, a mixer and a preamplifier connected in sequence. The single-pole single-throw switch is in a closed state during the period when the radio frequency generator transmits a pulse signal. After the pulse signal is loaded, the single-pole double-throw switch is closed and the nuclear magnetic resonance coil probe is connected to the single-pole single-throw switch. At the same time, the single-pole single-throw switch is opened to connect the channel between the nuclear magnetic resonance coil and the signal processing module. The free induction attenuation signal is extracted, amplified and denoised through the bandpass filter, the amplifier, the mixer and the preamplifier.

[0012] Furthermore, during the pulse signal loading and the extraction of the free induction decay signal, the magnetic moment of the nucleus is Where γ is the rotational magnetic ratio, is the angular momentum;

[0013] The equation of motion for the magnetic moment is in, is the magnetic field;

[0014] Define a stationary frame S and a new rotating coordinate frame S'. The coordinate axes of frame S are x, y, and z, and the coordinate axes of frame S' are x', y', and z'. The z' axis coincides with the z axis, and the x'y' plane rotates around the z axis with an angular velocity of Get the rotating coordinate system frame The equation of motion Define the magnetic field in the stationary frame as along z: In magnetic field In the case of existence, In the stationary frame at the Larmor frequency To precess.

[0015] Furthermore, in the process of pulse signal loading and free induction decay signal extraction, in addition to the magnetic field to be measured In addition, another RF field is applied The direction is defined as perpendicular to And rotates at an angular velocity ω in the stationary coordinate system, then Then, in S' which rotates with ω, Direction along If it remains unchanged, the effective field in the rotating coordinate system is:

[0016]

[0017] in, They represent the unit vectors of the x-axis and y-axis in the stationary frame and the unit vectors of the z-axis and x-axis in the new rotating coordinate system. The term is generated by rotating B0 to S';

[0018] Defining ω1=-γB1 as the Larmor frequency associated with B1, where B1 is always positive, the magnitude of the effective field is:

[0019]

[0020] Among them, ω0 is defined as ω0 = γB0; find ω eff =γB eff Indicates the rotation frame with B eff The associated Larmor field, magnetic moment in the stationary frame The precession of is the combination of the angular velocity ω of the rotation between the stationary and rotating coordinate systems.

[0021] Furthermore, the effective field and The angle θ between them is calculated as follows:

[0022]

[0023] When this angle is static, the magnetic moment in the stationary frame The change of the angle α between and B0 over time is:

[0024] cos(α)=cos 2 (θ)+sin 2 (θ)cos(ω eff t).

[0025] Furthermore, by turning on the RF field B1 with a frequency of ω0 for a period of time t, the magnetic moment can be rotated from the z-axis to a certain angle α, at which the magnetic moment rotates around the z-axis, and the angle α is the magnetic moment The angle between B0 and B0 is the nuclear spin pointing angle, so precise control of the nuclear spin pointing angle can be achieved by precisely controlling the RF pulse working time through the host computer.

[0026] The advantages of the present invention are:

[0027] (1) The present invention adds an RF amplifier between the RF generator and the single-pole double-throw switch, thereby greatly enhancing the RF signal applied to the nuclear magnetic resonance coil, greatly improving the rotation angle range of the polarized nuclear spin direction, improving the extraction efficiency of collecting free induction decay signals, improving the superposition efficiency of RF signals, reducing additional hardware equipment, and improving the convenience and compatibility of the system. The RF amplifier is synchronized to the calibrated DAQ data acquisition system through the control port, and the time accuracy and stability are greatly improved, thereby achieving precise control within a range of 360 degrees. In addition, each functional component is modularized, and the transmission and reception of signals are implemented in one system, realizing the integration of the transmission and reception of signals.

[0028] (2) The present invention introduces an additional time reference signal into the data system through the clock reference module, so that the timing control and time control between the various modules of the system are based on the same reference, which greatly improves the stability and time accuracy of the system. The host computer controls the output of TTL signals at each output end of the DAQ data acquisition system to control each module, thereby improving the system integration and convenience.

[0029] (3) The present invention adds a preamplifier after extracting the free induction decay signal, thereby improving the signal-to-noise ratio of the collected signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of a system for controlling the orientation of atomic nuclear spins and measuring precession signals disclosed in an embodiment of the present invention;

[0031] Figure 2A timing diagram of nuclear magnetic resonance pulse control in a system for nuclear spin pointing control and precession signal measurement disclosed in an embodiment of the present invention;

[0032] Figure 3 A diagram of nuclear spin pointing and free induction decay signals at different pulse times in a system for nuclear spin pointing control and precession signal measurement disclosed in an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] like Figure 1 As shown, a system for controlling the direction of atomic nuclear spin and measuring precession signals includes a radio frequency generator, a radio frequency amplifier, a single-pole double-throw switch, a nuclear magnetic resonance coil, a signal processing module, a DAQ data acquisition system, a host computer, and a time reference module.

[0035] The time reference module is used to control the time reference and signal reading and writing speed of each module of the system, and generates a trigger signal for the local oscillator signal input of the mixer. The time reference module includes a signal generator and a rubidium clock. The signal generator receives the clock synchronization signal output by the DAQ data acquisition system. The signal generator is connected to the rubidium clock, and the rubidium clock is connected to the radio frequency generator. The time synchronization reference port is connected to the signal generator synchronized by the rubidium clock to provide the time reference of the system, ensuring the time synchronization of each module of the system, so that the system has ultra-high time accuracy. The radio frequency generator is used to generate a transverse (perpendicular to the z direction) radio frequency signal to deflect the polarized nuclear spin direction. The radio frequency generator is connected to the radio frequency amplifier, and the radio frequency amplifier realizes public power amplification. The radio frequency amplifier, the nuclear magnetic resonance coil and the signal processing module are all connected to the single-pole double-throw switch. The pulse signal amplified by the radio frequency amplifier is output to the single-pole double-throw switch. The host computer is connected to the DAQ data acquisition system, and the pulse width, pulse time and switch control, the radio frequency pulse signal applied to the nuclear magnetic resonance coil and the free induction decay signal acquisition control are realized by the host computer. The signal acquisition port of the DAQ data acquisition system is connected to the signal processing module. The DAQ data acquisition system outputs TTL control signals to the signal processing module, the single-pole double-throw switch and the radio frequency amplifier respectively. The DAQ data acquisition system outputs clock synchronization signals to the time reference module.

[0036] The signal processing module includes a single-pole single-throw switch, a bandpass filter, an amplifier, a mixer and a preamplifier connected in sequence, which complete the filtering, amplification, extraction and further amplification operations of the signal, extract and amplify the free induction decay signal from the collected signal, and improve the signal-to-noise ratio. The single-pole single-throw switch is also connected to the single-pole double-throw switch and receives a TTL control signal output by the DAQ data acquisition system. The preamplifier is connected to the signal acquisition port of the DAQ data acquisition system to realize the digitization of the extracted free induction decay signal and transmit it to the host computer for storage and analysis. The signal generator is connected to the mixer, and the signal generator generates a trigger signal as the local oscillator signal input of the mixer, which further improves the time accuracy and reduces the introduction of additional system hardware.

[0037] The DAQ data acquisition system is used to collect the processed free induction decay signal and digitize it, store it on the host computer, and then output a multi-channel TTL signal to control the timing and working time of each module to avoid signal crosstalk between modules when working. The system is synchronized to a rubidium clock time reference with ultra-high stability, so that the device still has high stability during long-term operation.

[0038] The host computer is used for controlling the timing and sampling frequency of the entire device, as well as the working time control between various modules, the storage of collected signals, and data processing.

[0039] like Figure 2 As shown, the present invention also provides a system for nuclear magnetic resonance pulse generation and free induction decay signal acquisition and recording for atomic nuclear spin pointing control and precession signal measurement as follows:

[0040] First, the single-pole double-throw switch is turned on to connect the RF amplifier to the nuclear magnetic resonance coil. The RF generator sends an adjustable frequency RF wave to the RF amplifier for amplification. The output of the RF amplifier is turned on and off by the DAQ data acquisition system. The time when the RF amplifier outputs the pulse signal is controlled by the host computer to generate a pulse of variable length. The output of the RF amplifier is connected to the single-pole double-throw switch and output to the nuclear magnetic resonance coil through the single-pole double-throw switch to complete the loading of the pulse signal. After the pulse signal is recorded on the nuclear magnetic resonance coil, the nuclear magnetic resonance coil generates a transverse pulse magnetic field in a direction perpendicular to the spin direction of the helium-3 atom, which stimulates the helium-3 atom spin to produce transverse precession. When the pulse signal frequency is equal to the precession frequency of the helium-3 nuclear spin, the helium-3 atom absorbs the pulse energy, and its spin direction will deflect toward the direction of the pulse magnetic field. The deflection angle is controlled by the pulse time. The single-pole single-throw switch is in a closed state during the period when the RF generator transmits a pulse signal. When the pulse signal is loaded, the single-pole double-throw switch is closed, and the nuclear magnetic resonance coil probe is connected to the single-pole single-throw switch. At the same time, the single-pole single-throw switch is opened to connect the channel between the nuclear magnetic resonance coil and the signal processing module. The helium-3 nuclear spin will relax back to the direction of the magnetic field to be measured. During this process, the nuclear magnetic resonance coil senses a change in magnetic flux, that is, a free decay oscillation signal will be generated in the nuclear magnetic resonance coil. The free induction decay signal is extracted, amplified, and denoised through a bandpass filter, an amplifier, a mixer, and a preamplifier to obtain a FID signal related to the magnetic field strength information to be measured. At the same time, the processed FID signal is recorded and saved through the host computer so that the FID signal related to the magnetic field strength information to be measured can be used for data fitting to obtain the magnetic field strength information.

[0041] Furthermore, in order to improve the signal-to-noise ratio, the process of nuclear magnetic resonance pulse generation and free induction decay signal acquisition and recording is repeated multiple times, that is, the above process of nuclear magnetic resonance pulse generation and free induction decay signal acquisition and recording is repeated multiple times to remove additional environmental interference; for each cycle, the emitted pulse time and the time of the entire cycle are controlled by the host computer program, and an external synchronous clock is used as a reference. The read and write data rates can be determined by an external function generator, and all function signals used as triggers in the system are synchronized to the rubidium clock to ensure that all component times are based on the rubidium clock reference.

[0042] The working principle of the above system for nuclear spin pointing control and precession signal measurement is as follows:

[0043] Hyperpolarized NMR techniques are usually performed on atomic gas cell samples with a magnetization intensity of M = ρPμ, where is the magnetic moment of the nucleus. and magnetic moment The nucleus

[0044]

[0045] Where γ is the rotational magnetic ratio. In the case of From Newton's second law, it is equal to the rate of change of angular momentum:

[0046]

[0047] get The equation of motion is:

[0048]

[0049] The NMR form uses the technique of switching to a rotating coordinate system. Define a stationary frame S and a new rotating coordinate frame S', with the z' axis coinciding with the z axis, and the angular velocity of x'y' relative to S is The rotation coordinate system is obtained The equation of motion is:

[0050]

[0051] The equation of motion is In the effective magnetic field The equation of motion in is the Larmor frequency.

[0052] If the magnetic field in the stationary frame is defined along z: Among them, B0 is the amplitude of the magnetic field generated by the current to be measured, is the direction of the magnetic field to be measured, then when Effective magnetic field This is called the Larmor frequency, where The equation of motion in S' reduces to This shows that the magnetic moment does not move in the rotating coordinate system. In the case of existence, In the stationary frame at the Larmor frequency The power of NMR as an experimental technique lies in It can be measured by measuring the Larmor frequency of a sample of nuclei with known gamma.

[0053] In addition to the magnetic field to be measured In addition, another RF pulse magnetic field is applied The direction is defined as perpendicular to And rotates at an angular velocity ω in the stationary coordinate system, where ω is the angle of rotation in the magnetic field to be measured. 3 Larmor precession frequency of He:

[0054]

[0055] Then, in S' which rotates with ω, Direction along constant, is the unit vector of the x' axis in the new rotated coordinate system, They represent the unit vectors of the x-axis and y-axis in the stationary frame respectively.

[0056] Then the effective field in the rotating coordinate system is:

[0057]

[0058] in The term is generated by rotating B0 to S', is the unit vector of the axis z' in the new rotated coordinate system.

[0059] If ω1=-γB1 is defined as the Larmor frequency related to B1 (where B1 is always positive and B1 is the RF pulse magnetic field The magnitude of the effective field is:

[0060]

[0061] It should be noted that here we find ω eff =γB eff Indicates the rotation frame with B eff The associated Larmor precession magnetic field, ω eff is the equivalent motion frequency of the nuclear spin in the rotating coordinate system, B eff It represents the magnitude of the equivalent magnetic field felt by the nuclear spin in the rotating coordinate system and the magnetic moment in the stationary frame. The precession of is the combination of the angular velocity ω of the rotation between the stationary and rotating coordinate systems.

[0062] Effective Field and the magnetic field to be measured The angle θ between them can be calculated as follows:

[0063]

[0064] When this angle is static, the change of the angle between the magnetic moment and B0 in the stationary frame with time is determined by assuming that the magnetic moment and B0 are both at the same angle in the stationary frame at t = 0. Alignment, is the unit vector of the z-axis in the stationary frame.

[0065] cos(α)=cos 2 (θ)+sin 2 (θ)cos(ω eff t)

[0066] Where α is the The angle of nuclear spin pointing under the action, that is, the angle between the nuclear spin and the z direction. In practice, the amplitude of B1 is much smaller than B0, α is very small, and ω0-ω is very small (equivalent to ω1). In other words, the magnetic moment is aligned with B0 along the z-axis. When the frequency ω of the field B1 is close to ω0, that is, the Larmor frequency of B0, this causes resonance, which means that by turning on the field B1 with a frequency close to ω0 for a period of time t, the magnetic moment can be controlled to rotate from the z-axis to a certain angle α, at which time the magnetic moment rotates around the z-axis. Therefore, precise control of the nuclear spin pointing angle α can be achieved by accurately controlling the working time of the RF pulse by the host computer. The relationship between the duration t of the RF pulse signal and the nuclear spin offset angle α is:

[0067] t=α / γB1

[0068] Where γ is the rotating magnetic ratio, B1 is the RF pulse magnetic field The amplitude of , α is the arbitrary nuclear spin deviation angle.

[0069] For example, when the rotation angle is 90°, It is called a π / 2 pulse, with a duration of t 1 / 2 for:

[0070]

[0071] After rotating the precession into the transverse plane using such a π / 2 pulse, the induced current can be picked up from this precession using a pickup coil. The signal from the coil is called the free induction decay (FID) signal, and thus provides a measure of the B0 magnetic field. This process is called pulsed NMR, as Figure 3 The different nuclear spin pointing angles and corresponding free induction decay signal distributions generated by different pulse times are shown, where 3-(a), 3-(b), and 3-(c) represent the free induction decay signal distributions corresponding to nuclear spin pointing angles of 45 degrees, 90 degrees, and 135 degrees, respectively. Figure 3 It can be seen that the present invention can achieve the adjustment of different nuclear spin pointing angles, greatly increasing the rotation angle range of the polarized nuclear spin pointing.

[0072] Through the above technical scheme, the present invention adds an RF amplifier between the RF generator and the single-pole double-throw switch, so that the RF signal applied to the nuclear magnetic resonance coil is greatly enhanced, the rotation angle range of the polarized nuclear spin pointing is greatly improved, the extraction efficiency of collecting free induction decay signals is improved, the superposition efficiency of RF signals is improved, additional hardware equipment is reduced, and the convenience and compatibility of the system are improved. The RF amplifier is synchronized to the calibrated DAQ data acquisition system through the control port, and the time accuracy and stability are greatly improved, thereby realizing precise control within a range of 360 degrees, and each functional component is modularized, and the sending and receiving signals are realized in one system, realizing the integration of sending and receiving signals.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A system for controlling the direction of atomic nuclear spin and measuring precession signals, characterized in that: It includes a radio frequency generator, a radio frequency amplifier, a single-pole double-throw switch, a nuclear magnetic resonance coil, a signal processing module, a DAQ data acquisition system, a host computer and a time reference module. The time reference module is respectively connected to the DAQ data acquisition system, the signal processing module and the radio frequency generator, the radio frequency generator is connected to the radio frequency amplifier, the radio frequency amplifier, the nuclear magnetic resonance coil and the signal processing module are all connected to the single-pole double-throw switch, the host computer is connected to the DAQ data acquisition system, the signal acquisition port of the DAQ data acquisition system is connected to the signal processing module, the DAQ data acquisition system outputs TTL control signals to the signal processing module, the single-pole double-throw switch and the radio frequency amplifier respectively, and the DAQ data acquisition system outputs a clock synchronization signal to the time reference module.

2. A system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 1, characterized in that: The time reference module comprises a signal generator and a rubidium clock. The signal generator receives a clock synchronization signal output by a DAQ data acquisition system. The signal generator is connected to the rubidium clock, and the rubidium clock is connected to a radio frequency generator.

3. A system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 2, characterized in that: The signal processing module includes a single-pole single-throw switch, a bandpass filter, an amplifier, a mixer and a preamplifier connected in sequence. The single-pole single-throw switch is also connected to a single-pole double-throw switch and receives a TTL control signal output by a DAQ data acquisition system. The preamplifier is connected to a signal acquisition port of the DAQ data acquisition system.

4. A system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 3, characterized in that: The signal generator is connected to the mixer, and the signal generator generates a trigger signal as a local oscillator signal input of the mixer.

5. A method for a system for nuclear spin pointing control and precession signal measurement according to any one of claims 1 to 4, characterized in that: include: First, open the single-pole double-throw switch to connect the RF amplifier to the nuclear magnetic resonance coil. The RF generator sends an adjustable frequency RF wave to the RF amplifier for amplification. The output of the RF amplifier is controlled to open and close by the DAQ data acquisition system. The output pulse time of the RF amplifier is controlled by the host computer to generate a pulse of variable length. The output of the RF amplifier is connected to the single-pole double-throw switch and output to the nuclear magnetic resonance coil to complete the loading of the pulse signal. The signal processing module is in a closed state during the RF generator transmitting the pulse signal. After the pulse signal is loaded, the single-pole double-throw switch is closed, and the nuclear magnetic resonance coil probe is connected to the signal processing module. At the same time, the signal processing module is turned on, and the channel between the nuclear magnetic resonance coil and the signal processing module is connected to perform the extraction, amplification, and denoising process of the free induction decay signal. At the same time, the processed FID signal is recorded and saved by the host computer. In order to improve the signal-to-noise ratio, the above process is repeated to remove additional environmental interference. For each cycle, the emitted pulse time and the time of the entire cycle are controlled by the host computer program, and the external synchronous clock provided by the time base module is used as the base.

6. A method for a system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 5, characterized in that: The signal processing module includes a single-pole single-throw switch, a bandpass filter, an amplifier, a mixer and a preamplifier connected in sequence. The single-pole single-throw switch is in a closed state during the period when the radio frequency generator transmits a pulse signal. After the pulse signal is loaded, the single-pole double-throw switch is closed and the nuclear magnetic resonance coil probe is connected to the single-pole single-throw switch. At the same time, the single-pole single-throw switch is opened to connect the channel between the nuclear magnetic resonance coil and the signal processing module. The free induction attenuation signal is extracted, amplified and denoised through the bandpass filter, the amplifier, the mixer and the preamplifier.

7. A method for a system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 5, characterized in that: During the pulse signal loading and free induction decay signal extraction process, the magnetic moment of the nucleus is Where γ is the rotational magnetic ratio, is the angular momentum; The equation of motion for the magnetic moment is in, is the magnetic field; Define a stationary frame S and a new rotating coordinate system frame S'. The coordinate axes of frame S are x, y, and z, and the coordinate axes of frame S' are x', y', and z'. The z' axis and the z axis coincide. The x'y' plane rotates around the z axis, and its angular velocity is Get the rotating coordinate system frame The equation of motion Define the magnetic field in the stationary frame as along z: In magnetic field In the case of existence, In the stationary frame at the Larmor frequency To precess.

8. A method for a system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 7, characterized in that: In the process of pulse signal loading and free induction decay signal extraction, in addition to the magnetic field to be measured In addition, another RF field is applied The direction is defined as perpendicular to And rotates at an angular velocity ω in the stationary coordinate system, then Then, in S' which rotates with ω, Direction along If it remains unchanged, the effective field in the rotating coordinate system is: in, They represent the unit vectors of the x-axis and y-axis in the stationary frame and the unit vectors of the z-axis and x-axis in the new rotating coordinate system. The term is generated by rotating B0 to S'; Defining ω1=-γB1 as the Larmor frequency associated with B1, where B1 is always positive, the magnitude of the effective field is: Among them, ω0 is defined as ω0 = γB0; find ω eff =γB eff Indicates the rotation frame with B eff The associated Larmor field, magnetic moment in the stationary frame The precession of is the combination of the angular velocity ω of the rotation between the stationary and rotating coordinate systems.

9. A method for a system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 8, characterized in that: Effective Field and The angle θ between them is calculated as follows: When this angle is static, the magnetic moment in the stationary frame The change of the angle α between and B0 over time is: cos(α)=cos 2 (θ)+sin 2 (θ)cos(ω eff t).

10. A method for a system for controlling the orientation of atomic nuclear spins and measuring precession signals according to claim 9, characterized in that: By turning on the radio frequency field B1 with a frequency of ω0 for a period of time t, the magnetic moment can be rotated from the z-axis to a certain angle α. At this time, the magnetic moment rotates around the z-axis, and the angle α is the magnetic moment. The angle between B0 and B0 is the nuclear spin pointing angle, so precise control of the nuclear spin pointing angle can be achieved by precisely controlling the RF pulse working time through the host computer.

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