CN110763219B - Closed-loop magnetic resonance method of nuclear magnetic resonance gyroscope - Google Patents

Closed-loop magnetic resonance method of nuclear magnetic resonance gyroscope Download PDF

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CN110763219B
CN110763219B CN201911126725.4A CN201911126725A CN110763219B CN 110763219 B CN110763219 B CN 110763219B CN 201911126725 A CN201911126725 A CN 201911126725A CN 110763219 B CN110763219 B CN 110763219B
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汪之国
罗晖
张燚
赵洪常
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National University of Defense Technology
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Abstract

The invention provides a closed-loop magnetic resonance method of a nuclear magnetic resonance gyroscope, which realizes phase closed loop by using a self-feedback method and obtains a closed-loop excitation magnetic field with stable amplitude by using an amplification amplitude limiting and filtering method. The method comprises the steps of realizing phase closed loop by adopting a self-feedback method of a spinning precession magnetic moment signal; the amplitude closed loop of the excitation magnetic field is realized by using an amplification amplitude limiting and filtering method; and the phase shifter is utilized to adjust the closed-loop phase to realize accurate closed-loop magnetic resonance. Compared with a phase-locked loop method, the phase-locked loop method has the advantages of simple structure, less required components, large bandwidth, quick response, stable amplitude, good zero bias stability and better application prospect.

Description

Closed-loop magnetic resonance method of nuclear magnetic resonance gyroscope
Technical Field
The invention relates to high-sensitivity measurement based on the interaction of atomic spin angular velocity and even spin with other physical fields, belongs to the field of atomic sensing, and particularly relates to a closed-loop magnetic resonance method of a nuclear magnetic resonance gyroscope.
Background
The accurate measurement of physical quantities such as angular velocity and the like can be realized by utilizing atomic spin (such as alkali metal electron spin and inert gas nuclear spin), and for example, a nuclear magnetic resonance gyroscope based on the atomic spin has the advantages of small volume, high accuracy and the like, and has become an important research direction in the current inertia technical field.
In order for the nmr gyroscope to continuously measure angular velocity, the nmr gyroscope needs to maintain precession of nuclear spins using a closed-loop mr system. A common closed-loop magnetic resonance system is realized by adopting a phase-locked loop, has the advantages of high frequency resolution, stable excitation magnetic field amplitude and the like, and has smaller response speed and bandwidth. Another common closed-loop magnetic resonance system is realized by self-oscillation, has the advantages of fast response, large bandwidth and the like, but has poor amplitude stability, and the zero-offset stability of the nuclear magnetic resonance gyroscope can be influenced by the change of the amplitude.
Disclosure of Invention
The invention provides a closed-loop magnetic resonance method of a nuclear magnetic resonance gyroscope, which realizes phase closed loop by using a self-feedback method similar to self-excitation and obtains a closed-loop excitation magnetic field with stable amplitude by using an amplification amplitude limiting and filtering method.
The technical scheme of the invention is as follows: a closed-loop magnetic resonance method of a nuclear magnetic resonance gyroscope comprises the following specific contents:
1. a self-feedback method of a spinning precession magnetic moment signal is adopted to realize phase closed loop;
2. the amplitude closed loop of the excitation magnetic field is realized by using an amplification amplitude limiting and filtering method;
3. and the phase shifter is utilized to adjust the closed-loop phase to realize accurate closed-loop magnetic resonance.
One sealed glass gas chamber is filled with an excess amount of an alkali metal (at least one of Rb or Cs), an inert gas (one or more of 3He, 21Ne, 83Kr, 129Xe, and 131 Xe), and sometimes a gas such as nitrogen or hydrogen. The glass chamber is heated to a suitable temperature (in the range of 50-200 ℃) to vaporize the alkali metal into a vapor, and then the alkali metal electron spin is polarized using a circularly polarized laser that is in line resonance with the alkali metal atom D1. The circularly polarized laser is generated by the laser, passes through the second polarizer II (3) and the 1/4 wave plate (9), and becomes circularly polarized laser. The heater (11) is used to maintain the glass chamber (15) at a suitable temperature so that the alkali metal remains in a gas state of sufficient density. The alkali metal atoms collide with the inert gas atoms continuously, and the inert gas nuclear spin is polarized through the spin exchange polarization effect. Applying a magnetic field in the z-direction by means of a first coil (14)
Figure DEST_PATH_IMAGE002
Typically, the size is between 1. mu.T and 50. mu.T. The laser (4) outputs laser and alkali metal atoms D1 line near resonance (resonance peak +/-20 GHz), becomes linearly polarized light after passing through the first polarizer I (2), passes through the glass air chamber (15) along the x direction after being reflected, and then is reflected to the polarization beam splitter (6). The laser light transmitted from the polarization beam splitter (6) is received by a balanced photodetector (7) and converted into an electrical signal. The orientation of the polarizing beam splitter (6) is preferably adjusted so that the light intensities of the split light outputs are equal. The electric signal output by the balanced photoelectric detector (7) is sent to a signal processing system (8) and processed to generate a stable magnetic field driving signal and a closed-loop resonance magnetic field driving signal. The steady magnetic field driving signal is converted into current through the first magnetic field driving circuit (10) and then is input into the first coil (14) to generate a steady magnetic field. The closed-loop resonance magnetic field driving signal is converted into current after passing through a second magnetic field driving circuit (12) and is input into a second coil (13) to generate a closed-loop resonance magnetic field. Closed loop resonant magnetic fieldHas the function of generating a magnetic field
Figure DEST_PATH_IMAGE004
At a frequency of
Figure DEST_PATH_IMAGE006
Here, the
Figure DEST_PATH_IMAGE008
Is the gyromagnetic ratio of the inert gas,
Figure DEST_PATH_IMAGE010
is the angular velocity of the carrier. If the nuclear magnetic resonance gyroscope is adopted
Figure DEST_PATH_IMAGE012
(
Figure DEST_PATH_IMAGE014
) The nuclear spin of the inert gas is used as working gas and should be applied in the x direction
Figure DEST_PATH_IMAGE012A
An alternating magnetic field of one frequency and satisfy
Figure DEST_PATH_IMAGE017
，
Figure DEST_PATH_IMAGE019
。
The magnetic shield (1) has the function of attenuating an external magnetic field, so that spins in the glass gas chamber are in a relatively stable magnetic field environment.
Compared with a phase-locked loop method, the phase-locked loop method has the advantages of simple structure, less required components, wide bandwidth, high response speed, stable amplitude, good zero bias stability and better application prospect.
Drawings
FIG. 1 is a diagram showing a nuclear magnetic resonance gyroscope,
fig. 2 is a block diagram of a feedback system.
Detailed description of the preferred embodiments
The following describes the embodiment in detail with reference to fig. 1.
One sealed glass gas chamber (15) is filled with an excess amount of an alkali metal (at least one of Rb and Cs), an inert gas (one or more of 3He, 21Ne, 83Kr, 129Xe, and 131 Xe), and a gas such as nitrogen or hydrogen may be contained. The glass gas cell (15) is heated to a suitable temperature (in the range of 50 ℃ to 200 ℃) to vaporize the alkali metal, and then the alkali metal electron spin is polarized using a circularly polarized laser in linear resonance with the alkali metal atom D1. The circularly polarized laser light is generated by a laser (5), passes through a second polarizer (3) and an 1/4 wave plate (9), and becomes circularly polarized laser light. The heater (11) is used to maintain the glass chamber (15) at a suitable temperature so that the alkali metal remains in a gas state of sufficient density. The alkali metal atoms collide with the inert gas atoms continuously, and the inert gas nuclear spin is polarized through the spin exchange polarization effect. Applying a magnetic field in the z-direction by means of a first coil (14)
Figure DEST_PATH_IMAGE002A
Typically, the size is between 1. mu.T and 50. mu.T. The laser (4) outputs laser which is in line near resonance (resonance peak +/-20 GHz) with alkali metal atoms D1, the laser becomes linearly polarized light after passing through the first polarizer (2), the linearly polarized light passes through the glass air chamber (15) along the x direction after being reflected, and then the linearly polarized light is reflected to the polarization beam splitter (6). The laser light transmitted from the polarization beam splitter (6) is received by a balanced photodetector (7) and converted into an electrical signal. The orientation of the polarizing beam splitter (6) is preferably adjusted so that the light intensities of the split light outputs are equal. The magnetic shield (1) in the figure has the function of attenuating an external magnetic field, so that spins in the glass gas chamber are in a relatively stable magnetic field environment. The electric signal output by the balanced photoelectric detector (7) is sent to a signal processing system (8) and processed to generate a stable magnetic field driving signal and a closed-loop resonance magnetic field driving signal. The steady magnetic field driving signal is converted into current through the first magnetic field driving circuit (10) and then is input into the first coil (14) to generate a steady magnetic field. The closed-loop resonance magnetic field driving signal is converted into current after passing through a second magnetic field driving circuit (12) and is input into a second coil (13) to generate a closed-loop resonance magnetic field. The closed-loop resonant magnetic field has the effect thatGenerating a magnetic field
Figure DEST_PATH_IMAGE004A
At a frequency of
Figure DEST_PATH_IMAGE006A
Here, the
Figure DEST_PATH_IMAGE008A
Is the gyromagnetic ratio of the inert gas,
Figure DEST_PATH_IMAGE010A
is the angular velocity of the carrier. If the nuclear magnetic resonance gyroscope is adopted
Figure DEST_PATH_IMAGE012AA
(
Figure DEST_PATH_IMAGE014A
) The nuclear spin of the inert gas is used as working gas and should be applied in the x direction
Figure DEST_PATH_IMAGE012AAA
An alternating magnetic field of one frequency and satisfy
Figure DEST_PATH_IMAGE017A
，
Figure DEST_PATH_IMAGE019A
。
The generation principle of the closed-loop resonance magnetic field is described by taking the closed-loop magnetic resonance of the nuclear spins of the inert gas as an example. In order to maintain the nuclear spins in magnetic resonance, a feedback system is used to integrate the magnetic field components generated in the y-direction by the nuclear spins
Figure DEST_PATH_IMAGE031
Detecting, amplifying, phase-shifting, voltage-current converting, and sending to magnetic field coil to generate alternating magnetic field
Figure DEST_PATH_IMAGE004AA
。
FIG. 2 shows a signal processing system (8)A specific embodiment. The analog-to-digital converter (20) converts the voltage signal output by the balanced photoelectric detector (7) into a digital signal and sends the digital signal to the lock-in amplifier (21). After being processed by a phase-locked amplifier (21), magnetic field signals generated by nuclear spin in the glass gas chamber are obtained
Figure DEST_PATH_IMAGE034
Here, the
Figure DEST_PATH_IMAGE036
Is the amplitude of the magnetic field and,
Figure DEST_PATH_IMAGE038
in order to be the phase position,
Figure DEST_PATH_IMAGE040
is the angular frequency. Using pairs of limiters (22)
Figure DEST_PATH_IMAGE034A
Performing amplitude limiting to output signal
Figure DEST_PATH_IMAGE043
Here, the
Figure DEST_PATH_IMAGE045
The amplitude is set for the amplitude limiter (22),
Figure DEST_PATH_IMAGE047
which represents a square wave function of the signal,
Figure DEST_PATH_IMAGE049
a phase shift introduced for the limiter (22). The slicer may be implemented using a digital program (e.g., Labview program) by applying a digital signal to the slicer
Figure DEST_PATH_IMAGE034AA
Is judged when
Figure DEST_PATH_IMAGE052
Time output
Figure DEST_PATH_IMAGE045A
Otherwise output
Figure DEST_PATH_IMAGE055
. The output of the limiter (22) is fed to a phase shifter (23) to obtain
Figure DEST_PATH_IMAGE057
Here, the
Figure DEST_PATH_IMAGE059
Is the phase shift caused by the phase shifter and is then input to the filter (24). The phase shifter (23) can be implemented by a digital program, the output of the amplitude limiter is sampled by a high-frequency clock at the frequency of Fs, and then the output is delayed by N cycles through a register, so that the output can be delayed by N/(Fs) time, which is equivalent to phase delay. The filter (24) may be a low pass filter with a cut-off frequency set to a frequency of
Figure DEST_PATH_IMAGE040A
Has a frequency greater than
Figure DEST_PATH_IMAGE062
The composition of (1) is cut off. Since the square wave can be decomposed into
Figure DEST_PATH_IMAGE040AA
The superposition of odd harmonics, the signal passing through the filter can be represented as
Figure DEST_PATH_IMAGE065
，
Figure DEST_PATH_IMAGE067
The phase shift introduced for the filter. The phase of the phase shifter (23) is adjusted to
Figure DEST_PATH_IMAGE069
，
Figure DEST_PATH_IMAGE071
Whether it is + or-is determined according to the gyromagnetic ratio of the nuclear spins. Connecting the output of the filter (24) toAnd a digital-to-analog converter (25) for generating an analog voltage signal, which is input to the second magnetic field driving circuit (12) to drive the second coil (13) to generate a closed-loop magnetic resonance field, wherein the closed-loop magnetic resonance can be maintained by the nuclear spin system.
In order to improve noise immunity, the limiter (22) may be implemented using a hysteresis comparator. The filter (24) may be a band-pass filter with a cut-off frequency set to a frequency of
Figure DEST_PATH_IMAGE040AAA
Has a frequency greater than
Figure DEST_PATH_IMAGE062A
Or a component cut-off of less than 1 Hz. The signal processing system (8) can also be realized by a singlechip, a DSP or an FPGA, and can also be realized by an analog circuit.

Claims (8)

1. A closed-loop magnetic resonance method of a nuclear magnetic resonance gyroscope is characterized in that a self-feedback method is used for realizing phase closed loop, and a closed-loop excitation magnetic field with stable amplitude is obtained by using an amplification amplitude limiting and filtering method, and the method comprises the following steps: (1) a self-feedback method of a spinning precession magnetic moment signal is adopted to realize phase closed loop; (2) the amplitude closed loop of the excitation magnetic field is realized by using an amplification amplitude limiting and filtering method; (3) adjusting the closed-loop phase by using a phase shifter to realize closed-loop magnetic resonance;
the method comprises the following steps: filling alkali metal and inert gas in a closed glass gas chamber, heating the glass gas chamber until the alkali metal becomes steam, and then utilizing circular polarization laser in linear resonance with alkali metal atoms D1 to enable alkali metal electron spin to generate polarization;
the alkali metal atoms and the inert gas atoms collide ceaselessly, and the nuclear spin of the inert gas also generates polarization through the spin exchange polarization effect;
applying a magnetic field B in the z-direction by means of a first coil (14)0The laser output by the laser (4) is in line resonance with alkali metal atoms D1, becomes linearly polarized light after passing through the first polarizer I (2), passes through the glass air chamber (15) along the x direction after being reflected, and then is reflected to the polarization beam splitter (6);
the laser transmitted from the polarization beam splitter (6) is received by a balanced photoelectric detector (7) and converted into an electric signal;
the electric signal output by the balanced photoelectric detector (7) is sent to a signal processing system (8) and processed to generate a stable magnetic field driving signal and a closed-loop resonance magnetic field driving signal;
the stable magnetic field driving signal is converted into current after passing through a first magnetic field driving circuit (10) and is input into a first coil (14) to generate a stable magnetic field; the closed-loop resonance magnetic field driving signal is converted into current after passing through a second magnetic field driving circuit (12) and is input into a second coil (13) to generate a closed-loop resonance magnetic field.
2. The closed-loop magnetic resonance method of the nuclear magnetic resonance gyroscope according to claim 1, characterized in that the closed-loop resonance magnetic field is used for generating a magnetic field BxAt a frequency of ω ═ γ B0+ Ω, γ is the gyromagnetic ratio of the inert gas, and Ω is the carrier angular velocity.
3. The closed-loop magnetic resonance method for the nuclear magnetic resonance gyroscope according to claim 1, characterized in that the circularly polarized laser is generated by a laser and passes through a second polarizer II (3) and an 1/4 wave plate (9) to become the circularly polarized laser.
4. A closed-loop mri method as claimed in claim 1, characterized in that said heater (11) is adapted to maintain the glass gas chamber (15) at a temperature in the range of 50-200 ℃ so as to keep the alkali metal in a gas state of sufficient density.
5. A closed-loop mr method according to claim 1, characterized in that the first coil (14) applies a magnetic field B0Is between 1 muT and 50 muT.
6. A closed-loop mri method as claimed in claim 1, characterized in that the orientation of the polarizing beam splitter (6) is adjusted so that the light intensities of the split outputs are equal.
7. The closed-loop MRI method according to any one of claims 1-6, wherein N inert gas nuclear spins are used as working gas, and an alternating magnetic field with N frequencies is applied in x direction and ω is satisfiedn＝γnB0+Ω，n＝1,2,...,N，N≥1。
8. The closed-loop magnetic resonance method for a nuclear magnetic resonance gyroscope of claim 7, wherein the inert gas is one or more of 3He, 21Ne, 83Kr, 129Xe, and 131 Xe.
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