Vector magnetic field measurement method based on self-excited cesium optical pump magnetometer

Abstract

According to the vector magnetic field measurement method based on the self-excited cesium optical pump magnetometer, a regression equation set of each component of the magnetic field vector to be measured does not need to be constructed by a time sequence of multiple measurements, then the magnetic field vector is calculated, and the method has the technical characteristics of dynamic continuous measurement and large measurement bandwidth. A circular rotating modulation magnetic field is generated in an x-y plane through two paths of sinusoidal signals with the difference of pi / 2 provided by a signal source, two pairs of compensation coils can provide a uniform bias compensation magnetic field in the x-y plane, and a self-excited cesium optical pump magnetometer serves as a sensing unit and is placed in the geometric center of the device. A frequency meter outputs a digital signal of the total magnetic field size, the digital signal is converted into an analog signal through a DAC and then is input into lock amplifiers, two lock amplifiers LIAx and LIAy demodulate measurement signals of the optical pump magnetometer through two paths of modulation reference signals generated by a signal source respectively, after error signals are obtained, output of a current source x and output of a current source y are controlled through two PID, and the optical pump magnetometer is controlled through a current source. And the magnetic field components in x and y directions are measured through closed-loop locking.

Description

Technical Field

[0001] The invention belongs to the technical field of atomic magnetometers, and in particular relates to a vector magnetic field measurement method based on a self-excited cesium optical pump magnetometer. Background Art

[0002] Magnetic field vector measurement is of great significance in the field of magnetic target detection. In the field of scientific research and engineering applications, the current measurement of weak magnetic field vectors mostly uses three-axis fluxgate magnetometers. The three-axis fluxgate sensor has single-axis scale factor error, single-axis zero bias error and three-axis non-orthogonal error, which leads to the measurement error of the total field when measuring the geomagnetic field vector. It may reach hundreds or even thousands of nT. The optically pumped magnetometer is a high-resolution, high-precision and high-stability magnetometer. Taking the Canadian CS-3 cesium optically pumped probe as an example, the sensitivity is Due to its high precision and stable performance, it is widely used in weak magnetic field measurement.

[0003] However, the traditional self-excited cesium optical pump magnetometer is a scalar magnetometer and cannot be used directly to measure the three-axis magnetic field vector. If the optical pump magnetometer can be used to measure the weak magnetic field vector, its accuracy can be improved by 1 to 2 orders of magnitude compared with the fluxgate.

[0004] At present, a common solution is to use an optically pumped magnetometer as the sensitive head, attach an orthogonal three-axis coil, and measure the total magnetic field size when the coil generates different magnetic fields by continuously changing the size and direction of the coil magnetic field, and then establish a set of regression equations for each component of the external magnetic field vector to solve the external magnetic field vector. This three-axis magnetic field vector measurement solution has the limitations of not being able to measure continuously and having a low dynamic response speed in the geomagnetic background. Summary of the invention

[0005] The present invention proposes a vector magnetic field measurement method based on a self-excited cesium optical pump magnetometer, which does not require a time series of multiple measurements to construct a regression equation group of each component of the magnetic field vector to be measured, and then calculate the magnetic field vector. It has the technical characteristics of dynamic continuous measurement and large measurement bandwidth.

[0006] The present invention is achieved through the following technical solutions.

[0007] A method for measuring a vector magnetic field based on a self-excited cesium optical pump magnetometer comprises the following steps:

[0008] Step 1: The signal source generates a sine signal B1 sin(ω1t) and a cosine signal B1cos(ω1t), where B1 and ω1 are the modulation field amplitude and frequency respectively;

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

[0010] Step 3: The frequency meter of the self-excited cesium optical pump magnetometer measures the total magnetic field modulated by the rotating magnetic field in real time. The measured digital signal is converted into an analog signal by DAC, and then phase-locked demodulated with the sine signal B1 sin(ω1t) and the cosine signal B1cos(ω1t) respectively. After low-pass filtering, the differential error signal δB proportional to the magnitude of the components of the magnetic field to be measured in two orthogonal directions is obtained. x ~B x (t) and δB y ~B y (t);

[0011] Step 4: Transform the error signal δB x and δB y The outputs of current source x and current source y are controlled by a PID controller respectively. These two current sources provide a uniform compensation magnetic field B′ through two pairs of compensation coils in the x and y directions respectively. x (t) and B′ y (t) to adjust the error signal to zero; when the system closed loop is locked, the output of the PID control current source corresponds to the magnetic field B′ x (t) and B′ y (t) are the two components of the magnetic field to be measured B x (t) and B y (t);

[0012] Step 5: When the magnetic field in the x and y directions is locked in a closed loop, the actual measurement value of the self-excited cesium optical pump magnetometer is Remove the rotating magnetic field B rot Size is B z ;

[0013] Step 6: After the closed loop is locked, 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] Beneficial effects of the present invention:

[0015] 1. The present invention uses the measurement signal of the self-excited cesium optical pump magnetometer and the rotating field as the reference signal for phase-locked demodulation, and can simultaneously output differential error signals proportional to the magnitudes of the two orthogonal directions of the transverse magnetic field, and then input the error signal into PID, and provide real-time feedback compensation magnetic field through two additional current sources to achieve closed-loop locked measurement;

[0016] 2. The present invention adjusts the uniform compensation magnetic field in the lateral x and y directions to simultaneously lock in a minimum extreme point for closed-loop measurement. If the compensation magnetic field applied in the x and y directions is respectively opposite to the components of the magnetic field to be measured in these two directions, there is a minimum value of the total magnetic field at this position, and the three-axis components of the magnetic field vector can be simultaneously locked in a closed-loop measurement;

[0017] 3. The present invention adopts a closed-loop locking measurement method to realize dynamic continuous measurement of the three-axis magnetic field vector, and the measurement bandwidth is relatively large. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The schematic diagram of the vector magnetic field measurement method based on the self-excited cesium optical pump magnetometer of the present invention;

[0019] Figure 2 This is a principle diagram of the magnetic field rotation modulation method of the present invention;

[0020] Figure 3 This is a schematic diagram of the principle of implementing a transverse magnetic field closed-loop locking measurement by applying a compensation magnetic field through a compensation coil in the present invention. DETAILED DESCRIPTION

[0021] The exemplary embodiments of the present invention are described in detail below with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the accompanying drawings are only exemplary and are intended to illustrate the principles and spirit of the present invention, rather than to limit the scope of the present invention.

[0022] The implementation principle of the present invention: The present invention comprises a pair of x-axis modulation magnetic field coils x mod and a pair of y-axis modulation magnetic field coils y mod , can generate a circular rotating modulated magnetic field B in the xy plane through two sinusoidal signals B1 sin(ω1t) and B1 cos(ω1t) with a phase difference of π / 2 provided by the signal source rot (t). In addition, there are two pairs of compensation coils that can provide a uniform bias compensation magnetic field in the xy plane. A self-excited cesium optical pump magnetometer is placed at the geometric center of the device as a sensitive unit. Its frequency meter outputs a digital signal of the total magnetic field size, which is converted into an analog signal by DAC and then input into the lock-in release. The two lock-ins LIAx and LIAy use the two-way modulation reference signals generated by the signal source to demodulate the optical pump magnetometer measurement signals respectively to obtain the error signal δB x (t) and δB y (t), the outputs of current source x and current source y are controlled by two PIDs, and the closed-loop lock measures the magnetic field components in the x and y directions.

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

[0024] Step 1: The signal source generates a sine signal B1 sin(ω1t) and a cosine signal B1 cos(ω1t), where B1 and ω1 are the modulation field amplitude and frequency respectively;

[0025] Step 2: B 1x =B1 sin(ω1t) applied to a pair of modulation coils x in the x direction mod , B 1y = B1 cos(ω1t) applied to a pair of modulation coils y in the y direction mod The combined field of the two is a rotating magnetic field B around the z direction. rot (t);

[0026] In a 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 3: The frequency meter of the self-excited cesium optical pump magnetometer measures the total magnetic field modulated by the rotating magnetic field in real time. The measured digital signal is converted into an analog signal by DAC, and then phase-locked demodulated with the sine signal B1 sin(ω1t) and the cosine signal B1cos(ω1t) respectively. After low-pass filtering, the differential error signal δB proportional to the magnitude of the components of the magnetic field to be measured in two orthogonal directions is obtained. x ~B x (t) and δB y ~B y (t);

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

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

[0030] Step 4: Transform the error signal δB x and δB y The outputs of current source x and current source y are controlled by a PID controller respectively. These two current sources provide a uniform compensation magnetic field B′ through two pairs of compensation coils in the x and y directions respectively. x (t) and B′ y (t) to adjust the error signal to zero; when the system closed loop is locked, the output of the PID control current source corresponds to the magnetic field B′ x (t) and B′ y (t) are the two components of the magnetic field to be measured B x (t) and B y (t);

[0031] In specific implementation, the error signal is input to the PID, and two additional current sources provide real-time feedback to compensate the magnetic field B′. x (t) and B′ y (t) to close the loop and lock the measurement. x (t) and B y (t) are of the same magnitude but in opposite directions, the transverse magnetic field B x (t) and B y (t) are all compensated to 0, the total field measured will remain stable and its value is the z component of the magnetic field vector to be measured. In this way, closed-loop locking measurement of the three-axis components of the magnetic field vector can be achieved.

[0032] Step 5: When the magnetic field in the x and y directions is locked in a closed loop, the actual measurement value of the self-excited cesium optical pump magnetometer is Remove the rotating magnetic field B rot Size is

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

[0034] Assume that the inclination angle between the measured magnetic field B0(t) and the z-axis is α, and the azimuth angle in the plane perpendicular to z is The component in the z direction is B z (t) = B0cosα, and in the plane perpendicular to the z direction, the components in the x and y directions are and

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

[0036] Step 6: After the closed loop is locked, 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.

[0037] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0038] It is obvious to those skilled in the art that the embodiments of the present invention are not limited to the details of the above exemplary embodiments, and that the embodiments of the present invention can be implemented in other specific forms without departing from the spirit or basic features of the embodiments of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the embodiments of the present invention is limited by the attached claims rather than the above description, so it is intended to include all changes that fall within the meaning and scope of the equivalent elements of the claims in the embodiments of the present invention. Any figure mark in the claims should not be regarded as limiting the claims involved. In addition, it is obvious that the word "comprising" does not exclude other units or steps, and the singular does not exclude the plural. Multiple units, modules or devices stated in the system, device or terminal claims can also be implemented by the same unit, module or device through software or hardware. The words first, second, etc. are used to indicate names, and do not indicate any particular order.

[0039] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the embodiments of the present invention and are not intended to limit them. Although the embodiments of the present invention have been described in detail with reference to the above preferred implementation modes, those skilled in the art should understand that the technical solutions of the embodiments of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring a vector magnetic field based on a self-excited cesium optical pump magnetometer, characterized in that: The following steps are involved: Step 1: The signal source generates a sine signal B1sin(ω1t) and a cosine signal B1cos(ω1t), where B1 and ω1 are the modulation field amplitude and frequency respectively; Step 2: B 1x =B1sin(ω1t) applied to a pair of modulation coils x in the x direction mod , B 1y = B1cos(ω1t) applied to a pair of modulation coils y in the y direction mod The combined field of the two is a rotating magnetic field B around the z direction. rot (t); Step 3: The frequency meter of the self-excited cesium optical pump magnetometer measures the total magnetic field modulated by the rotating magnetic field in real time. The measured digital signal is converted into an analog signal by DAC, and then phase-locked demodulated with the sine signal B1sin(ω1t) and the cosine signal B1cos(ω1t) respectively. After low-pass filtering, the differential error signal δB proportional to the magnitude of the components of the magnetic field to be measured in two orthogonal directions is obtained. x ~B x (t) and δB y ~B y (t); Step 4: Transform the error signal δB x and δB y The outputs of current source x and current source y are controlled by a PID controller respectively. These two current sources provide a uniform compensation magnetic field B′ through two pairs of compensation coils in the x and y directions respectively. x (t) and B′ y (t) to adjust the error signal to zero; When the system closed loop is locked, the output of the PID controlled current source corresponds to the magnetic field B′ x (t) and B′ y (t) are the two components of the magnetic field to be measured B x (t) and B y (t); Step 5: When the magnetic field in the x and y directions is locked in a closed loop, the actual measurement value of the self-excited cesium optical pump magnetometer is Remove the rotating magnetic field B rot Size is B z ; Step 6: After the closed loop is locked, 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.

2. A method for measuring a vector magnetic field based on a self-excited cesium optical pump magnetometer as claimed in claim 1, characterized in that: The error signal is fed into the PID to provide real-time feedback to compensate the magnetic field B via two additional current sources. x ′(t) and B y ′(t) is used to close the loop and lock the measurement. When the two applied compensation magnetic fields are respectively x (t) and B y (t) are of the same magnitude but in opposite directions, the transverse magnetic field B x (t) and B y If (t) is compensated to 0, the total measured field will remain stable and its value is the z component of the magnetic field vector to be measured.

3. A method for measuring a vector magnetic field based on a self-excited cesium optical pump magnetometer as claimed in claim 1 or 2, characterized in that: 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.

4. A method for measuring a vector magnetic field based on a self-excited cesium optical pump magnetometer as claimed in claim 1 or 2, characterized in that: Said 5. A method for measuring a vector magnetic field based on a self-excited cesium optical pump magnetometer as claimed in claim 1 or 2, characterized in that: A self-excited cesium optically pumped magnetometer is used as a high-precision magnetic field scalar measurement sensor.

Images