A triaxial SERF atomic magnetometer orthogonal second harmonic modulation and demodulation system and method

Abstract

The application discloses a kind of triaxial SERF atom magnetometer quadrature double frequency modulation system and method, the system utilizes signal generation module to generate frequency f m The sine quadrature modulation signal of cosine is respectively driven SERF atom magnetometer X and Y axis magnetic field generating coil, and 2nf m Frequency sine signal of driving Z axis coil, through the integral filter of 3 groups of integral period integration, the open-loop magnetic field signal of X axis, Y axis and Z axis magnetic field component is obtained, and through control module, the driving current of three-axis magnetic field coil is controlled to generate compensation magnetic field, so that the open-loop magnetic field signal of X axis, Y axis and Z axis magnetic field component is zero, at this time, the magnetic field intensity of atom chamber is zero, and the compensation current output by control module is the X, Y and Z axis magnetic field intensity signal measured by triaxial SERF atom magnetometer.The system can directly extract triaxial magnetic field calculation signal from a laser signal, and eliminate the cross-coupling effect when triaxial magnetic field is calculated, improve the measurement range and quadrature of SERF atom magnetometer, with very high engineering application value.

Description

Technical Field

[0001] This invention relates to the field of high-precision vector magnetic field measurement, and in particular to a triaxial SERF atomic magnetometer orthogonal second harmonic modulation and demodulation system and method. Background Technology

[0002] The SERF atomic magnetometer is a novel vector atomic magnetometer with features such as ultra-high precision, small size, and triaxial vector magnetic field measurement. It is expected to be applied in fields such as space magnetometry, ocean magnetometry, airborne magnetometry, and heart and brain magnetometry.

[0003] Under conditions of high pressure, high density, and weak magnetic field, collisions between alkali metal atoms are frequent. When the collision frequency is much higher than the Larmor precession frequency of alkali metal atoms, the spin relaxation effect caused by the collision disappears. At this time, the atom is in a spin-exchange-relaxation-free (SERF) state. The spin polarization lifetime of the atom is increased and the spin exchange broadening part in the atomic magnetic resonance linewidth is eliminated, which can realize highly sensitive magnetic field measurement.

[0004] To enable atoms to enter a spin-free exchange relaxation state, the total magnetic field at the atomic gas cell needs to be close to zero. Using a magnetic shield can attenuate the external magnetic field to below 10 nT to achieve quantum state effects. However, increasing the number of magnetic shields reduces the measurement range of the vector magnetometer, and the attenuation coefficient of the magnetic shield cannot be precisely controlled, affecting the accuracy of magnetic field measurements.

[0005] Traditional SERF vector atomic magnetometers operate in open-loop mode, and their measurement range is limited to the magnetic resonance linewidth of the SERF state signal, which is only 10 nT. This limits their application in geomagnetic environments, as they can only operate in magnetically shielded rooms or magnetically shielded cylinders. Furthermore, the open-loop modulation mode suffers from a three-axis cross-coupling problem, meaning that a change in the magnetic field along one axis can affect the measurement results along the other two axes, making it impossible to guarantee measurement accuracy and precision. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art and provide a triaxial SERF atomic magnetometer orthogonal second harmonic modulation and demodulation system and method, which solves the problem of cross-coupling of triaxial demodulation signals in the existing modulation and demodulation technology, thereby improving the measurement range and triaxial orthogonality of the SERF atomic magnetometer.

[0007] The technical solution of this invention is: a triaxial SERF atomic magnetometer orthogonal second harmonic modulation and demodulation system, comprising: a signal generation module, a DA module, a voltage-to-current conversion module, an AD module, an integral filtering module, and a control module;

[0008] The signal generation module generates three modulated signals: sine wave I, sine wave II, and cosine wave. Sine wave I and cosine wave II have the same frequency, f(x). m The phase difference is 90°, and the frequency of the sinusoidal signal II is 2nf. m The initial phase is the same as that of the sinusoidal signal I;

[0009] The DA module receives the signals obtained by adding the sine signal I, cosine signal II, and sine signal II to the X, Y, and Z compensation magnetic field signals output by the control module, respectively, and then performs digital-to-analog conversion to obtain three voltage signals.

[0010] The voltage-to-current conversion module converts the three voltage signals output from the DA module into current signals, which drive the X, Y, and Z axis magnetic field coils of the triaxial SERF atomic magnetometer, respectively; thereby generating a frequency f on the X-axis magnetic field coil. m A sinusoidally modulated magnetic field signal, with a frequency of f generated on the Y-axis magnetic field coil. m The cosine-modulated magnetic field signal and the frequency 2nf generated on the Z-axis magnetic field coil m The sinusoidally modulated magnetic field signal alters the laser signal passing through the atomic gas cell of the triaxial SERF atomic magnetometer, causing the laser signal to carry triaxial magnetic field measurement data.

[0011] The AD module acquires the laser signal, performs analog-to-digital conversion, and then divides it into three channels: X, Y, and Z.

[0012] The integral filtering module receives the three signals output by the AD module and multiplies them by the sine signal I, cosine signal and sine signal II generated by the signal generation module, respectively, and performs integral filtering to obtain the open-loop magnetic field signals of the X, Y and Z axes;

[0013] The control module receives open-loop magnetic field signals from the X, Y, and Z axes and generates X, Y, and Z-channel compensation magnetic field signals. This ensures that the compensation magnetic fields generated by the X, Y, and Z-axis magnetic field coils are always equal in magnitude and opposite in direction to the external magnetic field to be measured, thus canceling out the external magnetic field to be measured and making the magnetic field at the atomic gas cell zero. The control module outputs the X, Y, and Z-channel compensation magnetic field signals, which are then used to obtain the X, Y, and Z-axis magnetic field strengths measured by the triaxial SERF atomic magnetometer.

[0014] Furthermore, f m The value range is 10Hz to 1kHz, and the value of n ranges from 1 to 100.

[0015] Furthermore, the signal generation module uses a DDS signal generator to generate three modulated signals; the DA module, voltage-to-current conversion module, integral filtering module, and control module each use three independent devices to implement their respective functions, with the control module using three PID controllers to generate X, Y, and Z compensation magnetic field signals.

[0016] Furthermore, the integration time of the integral filtering module is 1 / f. m .

[0017] Furthermore, the integration time of the integral filter module is set to 1 / f. m The implementation method is as follows: set the sampling frequency of the AD module to f s Set the number of integration points of the integral filtering module to f. s / f m Round the quotient.

[0018] This invention also provides a method for orthogonal second harmonic modulation and demodulation of a triaxial SERF atomic magnetometer, comprising the following steps:

[0019] Three modulation signals are generated: sine signal I, sine signal II, and cosine signal; among them, sine signal I and cosine signal have the same frequency, f. m The phase difference is 90°, and the frequency of the sinusoidal signal II is 2nf. m The initial phase is the same as that of the sinusoidal signal I;

[0020] After adding the sine signal I, cosine signal and sine signal II to the X, Y and Z compensation magnetic field signals respectively, perform digital-to-analog conversion to obtain three voltage signals;

[0021] The three voltage signals are converted into current signals, which drive the X, Y, and Z axis magnetic field coils of the triaxial SERF atomic magnetometer, respectively, and perform orthogonal second harmonic modulation to generate a frequency f on the X-axis magnetic field coil. m A sinusoidally modulated magnetic field signal, with a frequency of f generated on the Y-axis magnetic field coil. m The cosine-modulated magnetic field signal and the frequency 2nf generated on the Z-axis magnetic field coil m The sinusoidally modulated magnetic field signal alters the laser signal passing through the atomic gas cell of the triaxial SERF atomic magnetometer, causing the laser signal to carry triaxial magnetic field measurement data.

[0022] The laser signal is acquired, converted from analog to digital, and then divided into three paths: X, Y, and Z. It is then multiplied by sine signal I, cosine signal, and sine signal II, respectively. The results of the multiplication are then integrated and filtered to obtain the open-loop magnetic field signals of the X, Y, and Z axes.

[0023] Using the open-loop magnetic field signals of the X, Y and Z axes, X, Y and Z path compensation magnetic field signals are generated, so that the compensation magnetic field generated by the X, Y and Z axis magnetic field coils is always equal in magnitude and opposite in direction to the external magnetic field to be measured, thus canceling the external magnetic field to be measured and making the magnetic field at the atomic gas cell zero.

[0024] By outputting the X, Y, and Z compensated magnetic field signals, the X, Y, and Z axis magnetic field strengths measured by the triaxial SERF atomic magnetometer are obtained.

[0025] Furthermore, f m The value range is 10Hz to 1kHz, and the value of n ranges from 1 to 100.

[0026] Furthermore, the integration time of the integral filter is 1 / f m .

[0027] Furthermore, the integration time is made 1 / f. m The implementation method is as follows: the AD sampling frequency is set to f s Set the number of integration points of the integral filtering module to f. s / f m Round the quotient.

[0028] The advantages of this invention compared to the prior art are:

[0029] (1) This invention realizes the orthogonal second-harmonic three-axis digital closed-loop control of the SERF atomic magnetometer, which can directly extract the three-axis magnetic field solution signal from a laser signal and eliminate the cross-coupling effect during the three-axis magnetic field solution, thereby improving the measurement range and orthogonality of the SERF atomic magnetometer and having extremely high engineering application value.

[0030] (2) The present invention uses mutually orthogonal sine and cosine modulation signals of the same frequency for the X-axis and Y-axis magnetic field coils. During signal demodulation, the sine and cosine signals will not affect each other due to their orthogonality, thereby eliminating the cross-coupling effect between the X-axis and Y-axis magnetic field measurement results and improving the orthogonality between the X-axis and Y-axis. For the Z-axis magnetic field coil, a modulation signal with a different frequency than that of the X-axis and Y-axis magnetic field coils is used. In order to improve the system bandwidth in the integration stage, the signal frequency is 2n times the frequency of the X-axis and Y-axis modulation signals. Thus, when the phase-sensitive detection is performed using a multiplier, a high-order harmonic signal with a frequency of n times will be generated. Only the same integer-cycle integration filter is needed to filter out the high-order harmonic signal, thereby extracting the useful Z-axis magnetic field signal, realizing the measurement of the Z magnetic field strength, and improving the orthogonality between the Z-axis and the X and Y axes.

[0031] (3) The present invention drives the D / A and voltage-controlled constant current source through the PID controller to compensate the ambient magnetic field so that the magnetic field at the atomic gas cell is zero. At this time, the compensated magnetic field generated by the triaxial magnetic field coil is the external magnetic field to be measured, thereby significantly improving the measurement accuracy, measurement range and orthogonality of the triaxial magnetic field. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the orthogonal second harmonic modulation and demodulation system of the SERF atomic magnetometer of the present invention;

[0033] Figure 2 This is a schematic diagram illustrating the magnetic field measurement principle of the present invention. Detailed Implementation

[0034] To better understand the technical solution of the present invention, the embodiments of the present invention will be specifically described below with reference to the accompanying drawings. Parts of each structure in the drawings will be described separately. It is worth noting that elements not shown in the drawings or not described in words are in forms known to those skilled in the art.

[0035] like Figure 1 , Figure 2 As shown, the SERF atomic magnetometer orthogonal second harmonic modulation and demodulation system proposed in this invention includes a signal generation module, a DA module, a voltage-to-current conversion module, an AD module, an integral filtering module, and a control module; the SERF atomic magnetometer includes a laser 1, an atomic gas chamber 2, a triaxial magnetic field coil 5 (X, Y, and Z axes), and a detector 3.

[0036] The signal generation module, namely the DDS signal generator 6, generates three modulated signals: sine signal I, sine signal II, and cosine signal; among them, sine signal I and cosine signal have the same frequency, f. m The phase difference is 90°, and the frequency of the sinusoidal signal II is 2nf. m The initial phase is the same as the phase of the sinusoidal signal I; preferably, f m The value range is 10Hz to 1kHz, and the value of n ranges from 1 to 100.

[0037] The DA module includes three D / A conversion chips 9. It receives the sine signal I, cosine signal and sine signal II and adds them to the X, Y and Z compensation magnetic field signals output by the control module, respectively, and performs digital-to-analog conversion to obtain three voltage signals.

[0038] The voltage-to-current conversion module includes three voltage-controlled current sources 10, which convert the three voltage signals output from the DA module into current signals, respectively driving the X, Y, and Z axis magnetic field coils of the triaxial SERF atomic magnetometer; thereby generating a frequency f on the X-axis magnetic field coil. m A sinusoidally modulated magnetic field signal, with a frequency of f generated on the Y-axis magnetic field coil. m The cosine-modulated magnetic field signal and the frequency 2nf generated on the Z-axis magnetic field coil m The sinusoidally modulated magnetic field signal alters the laser signal passing through the atomic gas cell of the triaxial SERF atomic magnetometer, causing the laser signal to carry triaxial magnetic field measurement data.

[0039] The AD module, namely the A / D conversion chip 4, collects the laser signal, performs analog-to-digital conversion, and divides it into three channels: X, Y, and Z.

[0040] The integral filtering module includes three integral filters 7. These receive the three signals output from the AD module and multiply them by the sine signal I, cosine signal II, and sine signal II generated by the signal generation module, respectively. The resulting signals are then integrated and filtered to obtain the open-loop magnetic field signals for the X, Y, and Z axes. The integral filters 7 are designed as integer-cycle integral filters with an integration time of 1 / f. m The implementation method is as follows: set the sampling frequency of the AD module to f. s Set the number of integration points of the integral filtering module to f. s / f m The quotient is rounded down, so that the integration time of all three integrator filters 7 is 1 / f. m ;

[0041] The control module includes three PID controllers 8, which receive open-loop magnetic field signals from the X, Y, and Z axes, and generate X, Y, and Z-axis compensation magnetic field signals. This ensures that the compensation magnetic fields generated by the X, Y, and Z-axis magnetic field coils are always equal in magnitude and opposite in direction to the external magnetic field to be measured, thus canceling out the external magnetic field to be measured and making the magnetic field at the atomic gas cell zero. The X, Y, and Z-axis compensation magnetic field signals generated by the control module are output, which gives the X, Y, and Z-axis magnetic field strength measured by the triaxial SERF atomic magnetometer.

[0042] The specific working process of this invention includes:

[0043] (1) Laser 1 generates a laser beam, which passes through atomic gas cell 2 and generates a photomagnetic effect with rubidium alkali metal atoms inside atomic gas cell 2, and is transmitted to detector 3.

[0044] (2) After receiving the laser signal, the detector 3 converts the change in laser intensity into a change in voltage signal;

[0045] (3) The DDS signal generator 6 generates a sine signal I and a cosine signal with a frequency of f. m The phase difference is 90°, and a frequency of 2nf is also generated. m The sinusoidal signal II has an initial phase and frequency of f. m The sinusoidal signals are in phase;

[0046] (4) The DDS signal generator 6 generates a sine signal I, a cosine signal, and a sine signal II. After being added by an adder to the three compensation magnetic field signals output by the PID controller 8, the signals are output to three D / A conversion chips 9. The D / A conversion chips 9 drive three voltage-controlled current sources 10 to generate current, which in turn drives the triaxial magnetic field coil 5 to perform quadrature second harmonic modulation. At this time, a frequency of f can be generated on the X-axis magnetic field coil. m A sinusoidally modulated magnetic field signal generates a frequency f on the Y-axis magnetic field coil. m A cosine-modulated magnetic field signal generates a frequency of 2nf on the Z-axis magnetic field coil. mThe sinusoidal modulated magnetic field signal; thus, the modulated magnetic field signal generated by the triaxial magnetic field coil 5 will change the intensity of the laser signal passing through the atomic gas cell 2, so that the laser passing through the atomic gas cell 2 carries the triaxial magnetic field measurement data.

[0047] (5) The output signal of detector 3 is acquired by A / D conversion chip 4, then converted from analog to digital and divided into three paths: X, Y, and Z. The modulation signals of the X, Y, and Z axis coils are used to demodulate their respective open-loop output signals. That is, the three signals output by A / D conversion chip 4 are multiplied by the modulation signals (i.e., sine signal I, cosine signal, and sine signal II) applied to the three-axis magnetic field coils by DDS signal generator 6, and the results of the multiplication are sent to the integrating filter 7 for integration and filtering to obtain the X, Y, and Z axis open-loop magnetic field signals. Among them, the integrating filter 7 is designed as an integer-cycle integrating filter, that is, the current modulation signal frequency is f. m The integration time of the integral filter is 1 / f. m Since this embodiment uses an FPGA for digital signal processing, the number of integration points m of the integrating filter should be equal to the A / D sampling rate f. s With the frequency of the modulated signal f m The quotient is rounded down (either up or down), and the integral filter is then applied to frequency f. m Sine and cosine signals of different multiples all exhibit good filtering effects. Using this method, the integration time of the integral filter selected for X-axis, Y-axis, and Z-axis magnetic field demodulation can all be set to 1 / f. m This can effectively suppress cross-coupling between different axes;

[0048] (6) The open-loop magnetic field signals of the X, Y and Z axes output by the integral filter 7 are sent to the PID controller 8. The PID controller 8 obtains the X, Y and Z compensation magnetic field signals by changing the output, and adjusts the compensation magnetic field of the triaxial magnetic field coil so that the compensation magnetic field generated by the triaxial magnetic field coil is always equal in magnitude and opposite in direction to the external magnetic field to be measured, which can cancel the external magnetic field to be measured and make the magnetic field at the atomic gas cell zero, that is, adjust the open-loop magnetic field signal output by the integral filter 7 to 0.

[0049] The above process completes the orthogonal second-harmonic three-axis digital closed-loop control. At this time, the compensation magnetic field signal generated by each PID controller 8 is the X, Y, and Z axis magnetic field strength signal measured by the SERF atomic magnetometer.

[0050] It is understood that this invention has been described through embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this invention. Furthermore, under the teachings of this invention, these features and embodiments can be modified to adapt to specific circumstances without departing from the spirit and scope of this invention. Therefore, this invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are protected by this invention.

[0051] The contents not described in detail in this specification are common knowledge to those skilled in the art.

Claims

1. A triaxial SERF atomic magnetometer quadrature double frequency modulation demodulation system, characterized in that, The application relates to a three-axis SERF atomic magnetometer, which comprises a signal generating module, a DA module, a voltage-current conversion module, an AD module, an integral filter module and a control module. The DA module receives signals obtained by adding the sine signal I, the cosine signal and the sine signal II to the X, Y and Z compensation magnetic field signals output by the control module, carries out digital-analog conversion, and obtains three voltage signals. The signal generating module generates three modulated signals, namely, a sinusoidal signal I, a sinusoidal signal II and a cosine signal; wherein the sinusoidal signal I and the cosine signal have the same frequency f m , and a phase difference of 90°, and the sinusoidal signal II has a frequency of 2nf m , and an initial phase same as that of the sinusoidal signal I; The AD module collects the laser signals, carries out analog-digital conversion, and divides the signals into three X, Y and Z signals. A voltage-current conversion module converts the three voltage signals output by the DA module into current signals to drive the X, Y and Z axis magnetic field coils of the three-axis SERF atomic magnetometer, so that the X axis magnetic field coil generates a sinusoidal magnetic field signal with a frequency of f m The Y axis magnetic field coil generates a sinusoidal magnetic field signal with a frequency of f m The Z axis magnetic field coil generates a sinusoidal magnetic field signal with a frequency of 2nf m The laser signal passing through the three-axis SERF atomic magnetometer atom cell changes, so that the laser signal carries three-axis magnetic field measurement data; The integral filter module receives signals obtained by multiplying the three signals output by the AD module with the sine signal I, the cosine signal and the sine signal II generated by the signal generating module, carries out integral filtering, and obtains the X, Y and Z axis open-loop magnetic field signals. The control module receives the X, Y and Z axis open-loop magnetic field signals, generates the X, Y and Z compensation magnetic field signals, makes the compensation magnetic field generated by the X, Y and Z axis magnetic field coils always equal in size and opposite in direction to the external magnetic field to be measured, cancels the external magnetic field to be measured, and makes the magnetic field at the atom chamber zero; the X, Y and Z compensation magnetic field signals generated by the control module are output, and the X, Y and Z axis magnetic field strengths measured by the three-axis SERF atomic magnetometer are obtained. The signal generating module adopts a DDS signal generator to generate three modulation signals; the DA module, the voltage-current conversion module, the integral filter module and the control module all adopt three independent devices to realize their respective functions, wherein the control module adopts three PID controllers to generate the X, Y and Z compensation magnetic field signals.

2. The tri-axial SERF atomic magnetometer quadrature double frequency modulation demodulation system of claim 1, wherein: f m The value range of n is 1-100.

3. The tri-axial SERF atomic magnetometer quadrature double frequency modulation demodulation system of claim 1, wherein: The application further discloses a three-axis SERF atomic magnetometer measurement method, which comprises the following steps:

4. The tri-axial SERF atomic magnetometer quadrature double frequency modulation demodulation system of claim 1, wherein: The integration time of the integration filter module is 1 / f m .

5. The tri-axial SERF atomic magnetometer quadrature double frequency modulation demodulation system of claim 4, wherein: The integral time of the integral filter module is set to 1 / f m The implementation is that the sampling frequency of the AD module is set to f s The integral point number of the integral filter module is set to f s / f m rounded.

6. A triaxial SERF atomic magnetometer quadrature double frequency modulation demodulation method, characterized in that, The sine signal I, the cosine signal and the sine signal II are added to the X, Y and Z compensation magnetic field signals respectively, and then digital-analog conversion is carried out to obtain three voltage signals. The three-path modulation signals are generated, which are sinusoidal signal I, sinusoidal signal II and cosine signal respectively; wherein, the sinusoidal signal I and the cosine signal have the same frequency f m , and a phase difference of 90°, and the sinusoidal signal II has a frequency of 2nf m , and an initial phase same as that of the sinusoidal signal I; The laser signals are collected, analog-digital conversion is carried out, and then the signals are divided into three X, Y and Z signals; the three signals are multiplied with the sine signal I, the cosine signal and the sine signal II respectively, and then the multiplied results are subjected to integral filtering to obtain the X, Y and Z axis open-loop magnetic field signals. The three voltage signals are converted into current signals, which drive the X, Y, and Z axis magnetic field coils of the triaxial SERF atomic magnetometer, respectively, and perform orthogonal second harmonic modulation to generate a frequency f on the X-axis magnetic field coil. m A sinusoidally modulated magnetic field signal, with a frequency of f generated on the Y-axis magnetic field coil. m The cosine-modulated magnetic field signal and the frequency 2nf generated on the Z-axis magnetic field coil m The sinusoidally modulated magnetic field signal alters the laser signal passing through the atomic gas cell of the triaxial SERF atomic magnetometer, causing the laser signal to carry triaxial magnetic field measurement data. The X, Y and Z axis open-loop magnetic field signals are used to generate the X, Y and Z compensation magnetic field signals, so that the compensation magnetic field generated by the X, Y and Z axis magnetic field coils is always equal in size and opposite in direction to the external magnetic field to be measured, the external magnetic field to be measured is cancelled, and the magnetic field at the atom chamber is zero. The X, Y and Z compensation magnetic field signals are output, and the X, Y and Z axis magnetic field strengths measured by the three-axis SERF atomic magnetometer are obtained. ​ 7. The tri-axial SERF atomic magnetometer quadrature double frequency modulation demodulation method of claim 6, wherein: f m The value range of n is 1-100.

8. The tri-axial SERF atomic magnetometer quadrature double frequency modulation demodulation method of claim 6, wherein: The integration time of the integration filter is 1 / f m .

9. The tri-axial SERF atomic magnetometer quadrature double frequency modulation demodulation method of claim 8, wherein: The integral time is 1 / f m The implementation is that the AD sampling frequency is set to f s The integral point number of the integral filter module is set to f s / f m The quotient is rounded.

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