Method for monitoring the relaxation time of alkali atoms in the operating state of a nuclear magnetic resonance gyroscope

Abstract

The application provides a method for monitoring relaxation time of alkali metal atoms in a running state of a nuclear magnetic resonance gyroscope. The method comprises the following steps: S1: in a closed-loop running state of the nuclear magnetic resonance gyroscope, first-order demodulation signals and second-order demodulation signals of precession of a rare gas nuclear magnetic moment are acquired in real time; S2: a phase difference between the first-order demodulation signals and the second-order demodulation signals is calculated; S3: based on a pre-established relationship model between the phase difference and transverse relaxation time τ2 of the alkali metal atoms, the real-time transverse relaxation time τ2 of the alkali metal atoms is determined according to the phase difference. The method for monitoring relaxation time of alkali metal atoms in a running state of a nuclear magnetic resonance gyroscope has the advantages of fast running speed, low resource consumption, facilitation of analysis and suppression of gyroscope drift, and facilitation of drift compensation in a running process of the gyroscope.

Description

Technical Field

[0001] This invention relates to the field of signal control and quantum device technology, and in particular to a method for monitoring the relaxation time of alkali metal atoms during the operation of a nuclear magnetic resonance gyroscope. Background Technology

[0002] Nuclear magnetic resonance gyroscopes (NMR gyroscopes), as a novel quantum sensor device, possess the potential to achieve high precision while also being small in size, low in power consumption, insensitive to acceleration, and scalable to individual chips. This makes them beneficial for the development of future unmanned and intelligent small-scale transportation devices, and thus they have attracted widespread attention in recent years. The stability of the gyroscope is crucial for its long-term navigation operation. However, the principle of NMR gyroscopes is relatively complex, requiring the simultaneous interaction of multiple physical fields such as light, magnetism, and heat, making it difficult to determine the cause of gyroscope drift and thus hindering the improvement of long-term performance. Monitoring parameters such as atomic relaxation time as much as possible without affecting the normal operation of the gyroscope is of great significance for determining the mechanism and cause of NMR gyroscope drift, thereby contributing to the suppression of gyroscope drift and the improvement of performance.

[0003] However, current domestic and international measurements of relaxation time in NMR gyroscopes mostly employ generalized methods such as the free induction decay method and the inversion recovery method. While these methods provide reliable results, they lack real-time performance. For example, the inversion recovery method for measuring the longitudinal relaxation time of rare gas atoms often consumes a significant amount of time for a single physical parameter measurement. During this time, the gyroscope system state may have already changed, hindering the study of the influence of input parameters on the system state and the establishment of a correspondence between state parameters and gyroscope signals. Furthermore, these generalized measurement methods mostly select relatively simple operating modes for their respective measured parameters, rather than performing measurements in the NMR gyroscope's operating mode. Therefore, after measurement, it is necessary to return to the gyroscope's operating mode and wait for the system to stabilize before obtaining the correspondence with the gyroscope signal, which is still not conducive to accurately studying the correspondence between system state and gyroscope signal. In addition, these methods are mostly based on simplified theoretical models of the measured parameters themselves, and little attention is paid to whether they are affected by interference from other atoms or coupling mechanisms in complex systems like NMR gyroscopes, thus affecting the measurement results.

[0004] Therefore, it is necessary to provide a method for monitoring the relaxation time of alkali metal atoms during the operation of a nuclear magnetic resonance gyroscope to solve the above-mentioned technical problems. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope, which has a fast operating speed, low resource consumption, good real-time performance, is conducive to the analysis and suppression of gyroscope drift, and facilitates the realization of drift compensation during gyroscope operation.

[0006] To solve the above-mentioned technical problems, the present invention provides a method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope, comprising the following steps:

[0007] S1: Under the closed-loop operation of the nuclear magnetic resonance gyroscope, the first-order demodulation signal and the second-order demodulation signal of the precession of the nuclear magnetic moment of rare gas are acquired in real time;

[0008] S2: Calculate the phase difference between the first-order demodulated signal and the second-order demodulated signal.

[0009] S3: Based on a pre-established phase difference The model relating the transverse relaxation time τ2 of alkali metal atoms is based on the phase difference. Determine the real-time transverse relaxation time τ2 of alkali metal atoms;

[0010] The relational model is established through the following steps:

[0011] a) Based on the Bloch equation of the atomic magnetometer embedded in the nuclear magnetic resonance gyroscope, derive the first and second order demodulation signal phase difference of the alkali metal atom transverse relaxation time τ2 with respect to the precession of the nuclear magnetic moment of the rare gas. The parsing expression;

[0012] b) Obtain the inverse function of the analytical expression through numerical fitting or approximation methods.

[0013] c) Calibrate the inverse function in a nuclear magnetic resonance gyroscope simulation or experimental system. The parameters.

[0014] Preferably, in step S1, the first-order demodulated signal is subjected to cos(ω) of the optical detection signal through a closed-loop phase-locked loop. c The second-order demodulated signal is obtained by demodulation of t-θ1); the demodulated signal is obtained by cos(2ω) c After demodulating the optical detection signal (t-θ2), phase detection is performed using the first-order demodulated signal as a reference.

[0015] Preferably, the parsing expression is:

[0016]

[0017] Where A and B are coefficients related to τ2, and C is the system calibration constant, which is determined through calibration experiments.

[0018] Preferably, the expressions for A and B are constructed based on the following parameters:

[0019] gyromagnetic ratio γ of alkali metal atoms Rb Longitudinal magnetic moment M0;

[0020] The amplitude of the transverse excitation magnetic field B1, the longitudinal bias magnetic field B0, and the carrier magnetic field B of the rare gas atoms C ;

[0021] System angular frequency ω c The equivalent precession frequency ω1 of Xe atoms and the transverse relaxation time Γ2;

[0022] Bessel function terms and the denominator terms related to τ2 Where D n± =τ2(γ Rb B0+nω c ±ω1).

[0023] Preferably, the alkali metal atom is rubidium, and the rare gas is xenon.

[0024] Preferably, the relationship model is calibrated while the nuclear magnetic resonance gyroscope is in operation, and the gyroscope is kept in a closed-loop working mode during the calibration process.

[0025] Compared with related technologies, the method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope provided by this invention has the following beneficial effects:

[0026] This invention provides a method for monitoring the relaxation time of alkali metal atoms during the operation of a nuclear magnetic resonance gyroscope. The method operates directly within the gyroscope's running mode, and the results more accurately reflect the actual relaxation characteristics of the atoms inside the gyroscope, which is beneficial for the analysis and suppression of gyroscope drift. It directly uses the phase difference between the first and second-order demodulation signals of the rare gas atom magnetic moment precession to reflect the relaxation time of alkali metal atoms, without adding other interferences that may affect gyroscope performance. This is highly beneficial for achieving drift compensation during gyroscope operation. The method also features high operating speed, low resource consumption, and good real-time performance. Attached Figure Description

[0027] Figure 1 A flowchart of the method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope provided by the present invention;

[0028] Figure 2 The flowchart illustrates the acquisition of the phase difference between the first and second order demodulation signals of rare gas atomic magnetic moment precession in the method for monitoring the relaxation time of alkali metal atoms under the operating state of an alkali metal atom provided by the present invention.

[0029] Figure 3 The simulation experiment verification diagram shows the relationship between the relaxation time of alkali metal atoms and the first and second phase differences in the alkali metal atom relaxation time monitoring method of nuclear magnetic resonance gyroscope under operating conditions provided by the present invention. Detailed Implementation

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Please refer to the following: Figure 1 , Figure 2 and Figure 3 ,in, Figure 1 A flowchart of the method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope provided by the present invention; Figure 2 The flowchart illustrates the acquisition of the phase difference between the first and second order demodulation signals of rare gas atomic magnetic moment precession in the method for monitoring the relaxation time of alkali metal atoms under the operating state of an alkali metal atom provided by the present invention. Figure 3 This invention provides a simulation experiment verification diagram of the relationship between the relaxation time of alkali metal atoms and the first and second-order phase differences in the method for monitoring the relaxation time of alkali metal atoms under the operating state of an NMR gyroscope. The method for monitoring the relaxation time of alkali metal atoms under the operating state of an NMR gyroscope includes the following steps: deriving the relationship between the transverse relaxation time of alkali metal atoms (taking Rb as an example) and the phase difference between the first and second-order demodulation signals of the nuclear magnetic moment precession of rare gas atoms (Xe as an example). Typically, the alkali metal magnetometer embedded in the NMR gyroscope can be described by the Bloch equation:

[0032]

[0033] in, M x M y M z Let B represent the atomic vector magnetic moment and its components in the x, y, and z directions, respectively. x B y B z These represent the magnetic fields sensed by the atom in the x, y, and z directions, respectively. τ1, τ2, τ1, and M0 represent the unit vectors in the x, y, and z directions, respectively, and γ, τ2, τ1, and M0 represent the atomic gyromagnetic ratio, transverse relaxation time, longitudinal relaxation time, and magnetic moment at steady state, respectively.

[0034] On the other hand, when the nuclear magnetic resonance gyroscope is operating stably, the precession of the magnetic moment of the Xe atom satisfies the formula

[0035]

[0036] Where K z K ⊥ K0 represents the longitudinal and transverse magnetic moments and the equilibrium magnetic moment of the Xe atom, respectively; φ represents the phase of the magnetic moment; Γ1 and Γ2 represent the longitudinal and transverse relaxation, respectively; γ Xe B1 represents the gyromagnetic ratio, B1 represents the amplitude of the transverse excitation magnetic field, β represents the difference between the precession phase of the Xe atom and the phase of the transverse excitation magnetic field, and Ω represents the magnetic field strength. zThe equivalent precession frequency of the Xe atomic magnetic moment is represented by K. In equation (2), the Rb-Xe magnetic field coupling coefficient has been absorbed into the Xe magnetic moment K0, that is, K represents the magnetic field generated by the Xe polarization experienced by Rb. Consider the transverse excitation magnetic field -B1sin(φ-β), the longitudinal bias magnetic field B0 and the carrier magnetic field B c cosω c After t, the actual magnetic field in the system can be written as

[0037]

[0038] Substitute (3) into (1) to solve, and use cos(pω) c After demodulation of t-θ, we can obtain

[0039]

[0040] in

[0041]

[0042] Where p = 1, 2 corresponds to the result of equation (4), which is the first and second order demodulated signal mentioned earlier. Therefore, from (4), we know that the phase difference between the first and second order demodulated signals is...

[0043]

[0044] Where C represents the influence of different system filtering characteristics during first- and second-order demodulation, it is generally considered to be a constant and can be determined through system calibration. Furthermore, considering that during actual nuclear magnetic resonance gyroscope debugging, the magnetometer measurement direction will be adjusted to a direction almost unaffected by the coil excitation magnetic field (θ≈0) to avoid self-locking, the terms containing B1 in A and B in equation (5) can be ignored. Therefore, equation (6) can be further simplified to...

[0045]

[0046] in

[0047]

[0048] Observing equation (7), we can find that, except for B0 and γ Rb B c ω c In addition to known parameters such as ω1, it also includes the unknown transverse relaxation time τ2 of alkali metal atoms. In fact, equation (7) can be regarded as a derivation of the relationship between the relaxation time of alkali metal atoms and the phase difference of the first and second order demodulated signals of Xe nuclear magnetic moment precession.

[0049] Next step, utilize relationships Find its inverse function Substitute the phase difference measured in the experiment into the equation. The relaxation time τ2 of alkali metal atoms can then be obtained. However, in actual operation, since equation (7) is relatively complex, it is generally difficult to directly solve it analytically to obtain its inverse function. Therefore, in actual use, it is advisable to numerically fit the inverse function of equation (7) within an appropriate parameter range or use more approximation methods.

[0050] On the other hand, after obtaining the expression Phase difference still needs to be measured in real time in an actual nuclear magnetic resonance gyroscope. Typically, in nuclear magnetic resonance gyroscopes, due to the need for closed-loop operation, cos(ω) has already been used. c The first-order demodulated signal phase of the Xe magnetic moment precession was obtained by demodulation and phase-locked loop (PLL) at t-θ1). In order to obtain phase difference It can be obtained through cos(2ω) c (t-θ2) Demodulate the optical detector signal to obtain a second-order demodulated signal. Then, using the first-order demodulated signal as a reference, perform phase detection processing on the second-order demodulated signal to obtain the desired phase difference. like Figure 2 As shown.

[0051] Finally, the phase difference between the first and second order signals measured in the experiment was... Substitute the relation This allows us to obtain the transverse relaxation time τ2 of the alkali metal magnetometer in the NMR gyroscope system. After obtaining the real-time state of the transverse relaxation time τ2 of the alkali metal magnetometer in the NMR gyroscope, we can directly obtain the first-order signal phase required for gyroscope signal demodulation. The influence of relaxation time variation is subtracted to improve the long-term stability of the gyroscope. On the other hand, the mechanism of gyroscope drift can be further analyzed by using the influence model of temperature, light field and other factors on τ2.

[0052] like Figure 3 As shown, the circles indicate that in the nuclear magnetic resonance gyroscope simulation system, all parameters except τ2 are set to Γ1 = 1 / 20s. -1 Γ2=1 / 10s -1 γ Xe =-2π×11.86rad / μT, B1=1.0nT, B0=2.585μT, β=0rad, γ Rb =-2π×6998.0rad / μT, M0=0.005μT, ω c =2π×17495rad, B c When = 1.357B0, the simulation system passes Figure 2 The phase difference between the first and second order demodulated signals of the precession of the magnetic moments of rare gas atoms obtained by this method The simulation system varies with the alkali metal relaxation time τ2 set in the system. Besides numerically solving the Bloch equation, the simulation system uses a gyroscope control and signal processing module identical to the actual experimental system. Compared to the experimental system, the simulation system can obtain various physical parameters of the system more accurately. The figure shows the phase difference between the first and second order demodulated signals of the rare gas atomic magnetic moment precession. Indeed, it changes significantly with the relaxation time τ2 of alkali metal atoms, therefore... It is effective to characterize the change of τ2.

[0053] also, Figure 3 The solid line in the middle shows the phase difference between the first and second order demodulated signals of the precession of the magnetic moments of rare gas atoms, given by the analytical results of equation (7) under the same system parameters. The variation of the alkali metal atom relaxation time τ2 set in the system shows that, under the same parameters, the result is basically the same as the result of the simulation signal, thus verifying the use of equation (7) and the experimentally measured result. The feasibility of a method to monitor τ2 in nuclear magnetic resonance gyroscopes in real time.

[0054] Compared with related technologies, the method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope provided by this invention has the following beneficial effects:

[0055] This invention provides a method for monitoring the relaxation time of alkali metal atoms during the operation of a nuclear magnetic resonance gyroscope. The method operates directly within the gyroscope's running mode, and the results more accurately reflect the actual relaxation characteristics of the atoms inside the gyroscope, which is beneficial for the analysis and suppression of gyroscope drift. It directly uses the phase difference between the first and second-order demodulation signals of the rare gas atom magnetic moment precession to reflect the relaxation time of alkali metal atoms, without adding other interferences that may affect gyroscope performance. This is highly beneficial for achieving drift compensation during gyroscope operation. The method also features high operating speed, low resource consumption, and good real-time performance.

[0056] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for monitoring the relaxation time of alkali metal atoms during the operation of a nuclear magnetic resonance gyroscope, characterized in that, Includes the following steps: S1: Under the closed-loop operation of the nuclear magnetic resonance gyroscope, the first-order demodulation signal and the second-order demodulation signal of the precession of the nuclear magnetic moment of rare gas are acquired in real time; S2: Calculate the phase difference between the first-order demodulated signal and the second-order demodulated signal. S3: Based on a pre-established phase difference The model relating the transverse relaxation time τ2 of alkali metal atoms is based on the phase difference. Determine the real-time transverse relaxation time τ2 of alkali metal atoms; The relational model is established through the following steps: a) Based on the Bloch equation of the atomic magnetometer embedded in the nuclear magnetic resonance gyroscope, derive the first and second order demodulation signal phase difference of the alkali metal atom transverse relaxation time τ2 with respect to the precession of the nuclear magnetic moment of the rare gas. The parsing expression; b) Obtain the inverse function of the analytical expression through numerical fitting or approximation methods. c) Calibrate the inverse function in a nuclear magnetic resonance gyroscope simulation or experimental system. The parameters.

2. The method for monitoring the relaxation time of alkali metal atoms under the operating state of a nuclear magnetic resonance gyroscope according to claim 1, characterized in that, In step S1, the first-order demodulated signal is processed by a closed-loop phase-locked loop to perform cos(ω) on the optical detection signal. c The second-order demodulated signal is obtained by demodulation of t-θ1); the demodulated signal is obtained by cos(2ω) c After demodulating the optical detection signal (t-θ2), phase detection is performed using the first-order demodulated signal as a reference.

3. The method for monitoring the relaxation time of alkali metal atoms under the operating state of a nuclear magnetic resonance gyroscope according to claim 1, characterized in that, The parsing expression is: Where A and B are coefficients related to τ2, and C is the system calibration constant, which is determined through calibration experiments.

4. The method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope according to claim 3, characterized in that, The expressions for A and B are constructed based on the following parameters: gyromagnetic ratio γ of alkali metal atoms Rb Longitudinal magnetic moment M0; The amplitude of the transverse excitation magnetic field B1, the longitudinal bias magnetic field B0, and the carrier magnetic field B of the rare gas atoms C ; System angular frequency ω c The equivalent precession frequency ω1 of Xe atoms and the transverse relaxation time Γ2; Bessel function terms and the denominator terms related to τ2 Where D n± =τ2(γ Rb B0+nω c ±ω1).

5. The method for monitoring the relaxation time of alkali metal atoms under the operating state of a nuclear magnetic resonance gyroscope according to claim 1, characterized in that, The alkali metal atom is rubidium, and the rare gas is xenon.

6. The method for monitoring the relaxation time of alkali metal atoms in the operating state of a nuclear magnetic resonance gyroscope according to claim 1, characterized in that, The relationship model is calibrated under the operating conditions of the nuclear magnetic resonance gyroscope, and the closed-loop working mode of the gyroscope is maintained during the calibration process.

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