A vector magnetic field measurement method based on a self-excited cesium optical pumping magnetometer

Abstract

The application provides a vector magnetic field measurement method based on a self-excitation cesium optical pumping magnetometer, which does not need time series of multiple measurements to construct a regression equation set of each component of a to-be-measured magnetic field vector, and then calculates the magnetic field vector, and has the technical features of dynamic continuous measurement and large measurement bandwidth. Two sinusoidal signals with a phase difference of pi / 2 provided by a signal source generate a circular rotating modulation magnetic field in an x-y plane, two pairs of compensation coils can provide a uniform bias compensation magnetic field in the x-y plane, a self-excitation cesium optical pumping magnetometer is placed at the geometric center of the device as a sensitive unit, the frequency meter outputs a digital signal of the size of the total magnetic field, and the digital signal is converted into an analog signal by a DAC and then input into a lock-in amplifier, two lock-in amplifiers LIAx and LIAy use two modulation reference signals generated by the signal source to demodulate the optical pumping magnetometer measurement signals respectively, and then the error signals are input into two PIDs to control the output of a current source x and a current source y, and the magnetic field components in the x and y directions are locked and measured in a closed loop.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of atomic magnetometer, and particularly relates to a vector magnetic field measurement method based on a self-excitation cesium optical pumping magnetometer. BACKGROUND

[0002] Magnetic field vector measurement has important significance in the field of magnetic target detection. In the field of scientific research and engineering application, the three-axis fluxgate magnetometer is mostly used for measuring weak magnetic field vector. The three-axis fluxgate sensor has single-axis scale factor error, single-axis zero offset error and three-axis non-orthogonal error, which leads to the measurement error of total field to be possibly hundreds or even thousands of nT when measuring the geomagnetic field vector. The optical pumping magnetometer is a kind of magnetometer with high resolution, high precision and high stability. Taking the CS-3 cesium optical pumping probe produced in Canada as an example, the sensitivity is Due to high precision and stable performance, the optical pumping magnetometer is widely used for weak magnetic field measurement.

[0003] However, the traditional self-excitation cesium optical pumping magnetometer is a scalar magnetometer and cannot be directly used for measuring three-axis magnetic field vector. If the optical pumping magnetometer can be used for weak magnetic field vector measurement, the precision can be improved by 1-2 orders of magnitude compared with the fluxgate.

[0004] A common solution is to use the optical pumping magnetometer as a sensitive head and add a three-axis orthogonal coil. The size and direction of the coil magnetic field are continuously changed, the total magnetic field size when the coil generates different magnetic fields is measured, and the regression equation set about each component of the external magnetic field vector is established to solve the external magnetic field vector. This three-axis magnetic field vector measurement scheme has the limitation of low dynamic response speed and cannot be continuously measured in the geomagnetic background. SUMMARY

[0005] The application provides a vector magnetic field measurement method based on a self-excitation cesium optical pumping magnetometer, which does not need a time sequence of multiple measurements to construct the regression equation set of each component of the measured magnetic field vector, and has the technical features of dynamic continuous measurement and large measurement bandwidth.

[0006] The application is implemented by the following technical scheme.

[0007] A vector magnetic field measurement method based on a self-excitation cesium optical pumping magnetometer comprises the following steps:

[0008] Step 1: a signal source generates a sine signal B1 sin(ω1t) and a cosine signal B1 cos(ω1t), and B1 and ω1 are the modulation field amplitude and frequency respectively;

[0009] Step 2: B 1x =B1sin(ω1t) is applied to a pair of x-direction modulation coils x mod , and B1y = B1 cos (ω1t) is applied to a pair of y-direction modulation coils y mod , and the resultant field is a rotating magnetic field B rot (t) around the z direction.

[0010] Step three: the frequency meter of the self-excited cesium optical pumping magnetometer measures the total magnetic field modulated by the rotating magnetic field in real time, and the measured digital signal is converted into an analog signal by a DAC, and then is subjected to phase-locked demodulation with a sine signal B1 sin (ω1t) and a cosine signal B1 cos (ω1t) respectively, and a differential error signal δB x ~ B x (t) and δB y ~ B y (t) proportional to the magnitudes of the two orthogonal components of the magnetic field to be measured are obtained after low-pass filtering.

[0011] Step four: the error signals δB x and δB y are respectively input to the outputs of a PID control current source x and a current source y, and the two current sources respectively provide a uniform compensation magnetic field B' x (t) and B' y (t) through two pairs of compensation coils in the x and y directions to adjust the error signals to be equal to zero; when the system is locked in a closed loop, the magnetic fields B' x (t) and B' y (t) corresponding to the outputs of the PID control current sources are the two components B x (t) and B y (t) of the magnetic field to be measured.

[0012] Step five: when the magnetic fields in the x and y directions are locked in a closed loop, the actual measurement value of the self-excited cesium optical pumping magnetometer minus the rotating magnetic field B rot is B z .

[0013] Step six: after being locked in a closed loop, the magnitude of the three-axis magnetic field vector to be measured is: The spatial angle of the magnetic field vector can be obtained through the three-component relationship.

[0014] Advantages of the present application:

[0015] 1. The present application can simultaneously output differential error signals proportional to the magnitudes of the two orthogonal directions of the horizontal magnetic field and the transverse magnetic field by phase-locked demodulation of the measurement signal of the self-excited cesium optical pumping magnetometer and the rotating field as a reference signal, and then input the error signals to a PID to provide real-time feedback compensation magnetic fields through two additional current sources to realize closed-loop locking measurement.

[0016] 2、The application adjusts the uniform compensation magnetic field in the transverse x and y directions to simultaneously lock around a minimum extreme point to perform closed-loop measurement. If the compensation magnetic field applied in the x and y directions respectively equals the components of the measured magnetic field in the two directions, then there is a minimum value of the total magnetic field at the position, and the three-axis components of the magnetic field vector can be simultaneously measured in closed-loop locking.

[0017] 3、The application uses the closed-loop locking measurement method to realize dynamic and continuous measurement of the three-axis magnetic field vector, and the measurement bandwidth is larger. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a vector magnetic field measurement principle diagram based on the self-excitation cesium optical pumping magnetometer of the application;

[0019] Figure 2 It is a magnetic field rotation modulation method principle diagram of the application;

[0020] Figure 3 It is a principle diagram for realizing transverse magnetic field closed-loop locking measurement by the compensation magnetic field applied by the two current sources through the compensation coil in the application. DETAILED DESCRIPTION

[0021] The exemplary embodiments of the application will be described in detail below with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the drawings are only exemplary, and are intended to illustrate the principles and spirits of the application, and not to limit the scope of the application.

[0022] The implementation principle of the application: the application includes a pair of x-axis modulation magnetic field coils x mod and a pair of y-axis modulation magnetic field coils y mod , which can generate a circular rotating modulation magnetic field B rot (t) in the x-y plane through two-way sinusoidal signals B1 sin(ω1t) and B1 cos(ω1t) provided by a signal source with a phase difference of π / 2. In addition, two pairs of compensation coils can provide uniform bias compensation magnetic fields in the x-y plane. A self-excitation cesium optical pumping magnetometer as a sensitive unit is placed at the geometric center of the device, and the frequency meter outputs a digital signal of the total magnetic field size, which is converted into an analog signal after DAC conversion and then input into a lock-in amplifier. Two lock-in amplifiers LIAx and LIAy use two-way modulation reference signals generated by the signal source to demodulate the optical pumping magnetometer measurement signal to obtain error signals δB x (t) and δB y (t), and then control the output of the current source x and the current source y through two PIDs to perform closed-loop locking measurement of the magnetic field components in the x and y directions.

[0023] As Figure 1As shown, based on the above principle, a vector magnetic field measurement method based on the self-excited cesium optical pumping magnetometer of the application, specifically includes the following steps:

[0024] Step one: the signal source generates a sine signal B1 sin(ω1t) and a cosine signal B1 cos(ω1t), B1 and ω1 are the modulation field amplitude and frequency respectively;

[0025] Step two: B 1x =B1 sin(ω1t) is applied to a pair of x-direction modulation coils x mod , and B 1y =B1 cos(ω1t) is applied to a pair of y-direction modulation coils y mod , the combined field of the two is a rotating magnetic field B rot (t) around the z direction;

[0026] In specific implementation, two pairs of modulation magnetic field coils are used to generate a rotating magnetic field, and two pairs of compensation magnetic field coils are used to generate a compensation feedback magnetic field.

[0027] Step three: the frequency meter of the self-excited cesium optical pumping magnetometer measures the total magnetic field after the rotating magnetic field modulation in real time, and after the measurement digital signal is converted into an analog signal by the DAC, it is respectively phase-locked demodulated with the sine signal B1 sin(ω1t) and the cosine signal B1 cos(ω1t), and after low-pass filtering, the differential error signals δB x ~B x (t) and δB y ~B y (t) proportional to the size of the magnetic field to be measured in two orthogonal directions are obtained.

[0028] As Figure 2 shown, the magnetic field rotating modulation method is used in this step, and the principle is as follows:

[0029] If the total field B0(t) is along the z direction, then a rotating magnetic field B rot (t) is applied in the plane perpendicular to the total field. Then the output of the self-excited cesium optical pumping magnetometer measuring the total field size does not change with time, and the size always remains As Figure 2 (a) shown. When B0(t) and the z axis have an angle α, there are components B z (t)=B0 cosα and B ⊥ (t)=B0 sinα in the z direction and the vertical plane, then the maximum value of the total field measurement is and the minimum value is The total field measurement output oscillates between the maximum value and the minimum value, and the amplitude is ΔB tot =(B max -Bmin ) / 2, as Figure 2 (b) shows, the frequency is the same as that of the rotating field, and the phase is determined by the direction of the transverse magnetic field B ⊥ (t), which is equivalent to the total field measurement being modulated by the rotating field, with a modulation frequency equal to the rotating field frequency. By phase-locked demodulation of the reference sinusoidal signals B1 sin(ω1t) and B1 cos(ω1t), respectively, the differential error signals δB x ~B x (t) and δB y ~B y (t) can be simultaneously output, which are proportional to the magnitudes of the transverse magnetic field in the two orthogonal directions, respectively.

[0030] Step four: the error signals δB x and δB y are respectively passed through a PID control current source x and a current source y, and the two current sources respectively provide a uniform compensation magnetic field B' x (t) and B' y (t) through two pairs of compensation coils in the x and y directions to adjust the error signals to be equal to zero; when the system is closed-loop locked, the magnetic fields B' x (t) and B' y (t) corresponding to the outputs of the PID control current sources are the two components B x (t) and B y (t) of the magnetic field to be measured.

[0031] In specific implementation, the error signals are input to a PID, and real-time feedback compensation magnetic fields B' x (t) and B' y (t) are provided by two additional current sources to close-loop lock the measurement. When the two compensation magnetic fields applied are equal in size to B x (t) and B y (t) but opposite in direction, the transverse magnetic fields B x (t) and B y (t) are both compensated to 0, and the total field measurement will remain stable and unchanged, with a value equal to the size of the z component of the magnetic field vector to be measured. In this way, closed-loop lock measurement of the three-axis components of the magnetic field vector can be achieved.

[0032] Step five: when the magnetic fields in the x and y directions are closed-loop locked, the actual measurement value of the self-excited cesium optical pumping magnetometer, excluding the rotating magnetic field B rot , is

[0033] As shown in Figure 3 , two current sources apply compensation magnetic fields through compensation coils to achieve closed-loop lock measurement of the transverse magnetic field. Taking the x direction as an example for analysis:

[0034] Assuming the tilt angle of the measured magnetic field B0(t) and the z-axis is α, the azimuth angle in the plane perpendicular to z is , then the component in the z direction is B z (t) = B0cosα, while in the plane perpendicular to the z direction, the components in the x and y directions are and

[0035] If a compensation magnetic field B′ x (t) = -B x (t) is applied in the x direction, the y direction is not processed, then the measurement signal after the rotation magnetic field modulation is demodulated by the sinusoidal signal B1 sin(ω1t), the influence of B rot is removed, and the measured value of B0(t) changes with the compensation B′ x (t) and has a minimum extreme point: As shown in Figure 3 (b), closed loop locking can be performed, and the differential feedback signal is as shown in Figure 3 (c). Similarly, the analysis of the y direction also has similar results, and there is also a minimum extreme value of B0(t) measurement: When the x and y directions are simultaneously locked at the respective minimum extreme positions, the system closed loop locking point is a global minimum position of the two-dimensional parameter interval (B′ x (t), B′ y (t)): That is, the z direction component of the measured total field B0(t).

[0036] Step six: after closed loop locking, the size of the measured three-axis magnetic field vector is: The spatial angle of the magnetic field vector can be obtained through the three component relationships.

[0037] In summary, the above is only a preferred embodiment of the present application, and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

[0038] It is apparent for a person skilled in the art that the embodiments of the present application are not limited to the details of the above-described exemplary embodiments but can be carried out in other embodiments without departing from the spirit or essential characteristics of the embodiments of the present application. The embodiments should therefore be considered in all respects as illustrative and not restrictive, the scope of the embodiments of the present application being indicated by the appended claims rather than by the above description, and all changes which come within the meaning and range of equivalents of the claims are therefore intended to be embraced therein. Any reference signs in the claims should not be construed as limiting the claims concerned. The word "comprising" does not exclude other elements or steps not mentioned in the claims. The singular never excludes the plural and vice versa. Units, modules, or apparatuses as set forth in the claims are to be understood to be capable of being implemented by one unit, module or apparatus by means of software or hardware. The words "first", "second" and the like do not imply any particular order but are used to distinguish one element from another. They are also used to distinguish a certain element from at least one other element with a similar or same name.

[0039] Finally, it should be noted that the above implementations are merely used to describe the technical solutions of the embodiments of the present application, rather than limit them. Although the embodiments of the present application are described in detail with reference to the above preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the embodiments of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A vector magnetic field measurement method based on a self-excited cesium optical pumping magnetometer, characterized by, The method comprises the following steps: Step 1: a signal source generates a sine signal B1sin(ω1t) and a cosine signal B1cos(ω1t), wherein B1 and ω1 are the modulation field amplitude and frequency respectively; Step two: B 1x = B1 sin(ω1t) is applied to a pair of x-direction modulation coils x mod , and B 1y = B1 cos(ω1t) is applied to a pair of y-direction modulation coils y mod , the resultant of which is a rotating magnetic field B rot (t) around the z-direction. Step three: the frequency meter of the self-excited cesium optical pumping magnetometer measures the total magnetic field modulated by the rotating magnetic field in real time. After the measurement digital signal is converted into analog signal by DAC, it is respectively phase-locked demodulated with the sine signal B1sin(ω1t) and the cosine signal B1cos(ω1t), and the low-pass filtered differential error signal δB proportional to the size of the magnetic field to be measured in two orthogonal directions is obtained x ~B x (t) and δB y ~B y (t) Step four: the error signal δB x and δB y are respectively fed through a PID control current source x and a current source y, which provide a uniform compensation magnetic field B' x (t) and B' y (t) through two pairs of compensation coils in the x and y directions, respectively, to adjust the error signal to be equal to zero; When the system is closed-loop locked, the output of the PID control current source corresponds to the magnetic field B' x (t) and B' y (t) are two components of the magnetic field to be measured x (t) and B y (t) Step five: When the magnetic fields in x and y directions are locked by the closed loop, the actual measurement value of the self-excited cesium optical pumping magnetometer Remove the rotating magnetic field B rot The size is B z ; Step six: after the closed loop is locked, the size of the measured three-axis magnetic field vector is: The spatial angle of the magnetic field vector is obtained through three component relationships.

2. A vector magnetic field measurement method based on a self-excited cesium optical pumping magnetometer according to claim 1, characterized in that, The error signal input PID provides real-time feedback compensation magnetic field B through two additional current sources x (t) and B y (t) to close-loop lock the measurement, when the two applied compensation magnetic fields are respectively equal in magnitude but opposite in direction to B x (t) and B y (t) are equal in magnitude but opposite in direction, the transverse magnetic field B x (t) and B y (t) are both compensated to 0, the measured total field will remain stable and unchanged, and its value is the magnitude of the z-component of the measured magnetic field vector.

3. A vector magnetic field measurement method based on a self-excited cesium optical pumping magnetometer according to claim 1 or 2, characterized in that, Two pairs of modulation field coils are used to generate a rotating magnetic field, and two pairs of compensation field coils are used to generate a compensation feedback magnetic field.

4. The vector magnetic field measurement method based on the self-excited cesium optical pumping magnetometer according to claim 1 or 2, characterized in that, The 5. The vector magnetic field measurement method based on the self-excited cesium optical pumping magnetometer according to claim 1 or 2, characterized in that, A self-excitation cesium optical pumping magnetometer is used as a high-precision magnetic field scalar measurement sensor.

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