Orthogonal frequency doubling modulation and demodulation system and method for triaxial SERF atom magnetometer

Abstract

The invention discloses a three-axis SERF atom magnetometer orthogonal frequency doubling modulation and demodulation system and method, and the system employs a signal generation module to generate sine and cosine orthogonal modulation signals with the frequency of fm to drive an X-axis magnetic field generation coil and a Y-axis magnetic field generation coil of an SERF atom magnetometer respectively, and generates sine signals with the frequency of 2nfm to drive a Z-axis coil. Open-loop magnetic field signals of X-axis magnetic field components, Y-axis magnetic field components and Z-axis magnetic field components are obtained through three groups of integral filters for full-period integration, driving current of a three-axis magnetic field coil is controlled through a control module to generate a compensation magnetic field, the open-loop magnetic field signals of the X-axis magnetic field components, the Y-axis magnetic field components and the Z-axis magnetic field components are made to be zero, and at the moment, the magnetic field intensity of the atomic gas chamber is zero. The compensation current output by the control module is the X-axis magnetic field intensity signal, the Y-axis magnetic field intensity signal and the Z-axis magnetic field intensity signal measured by the three-axis SERF atom magnetometer. The system can directly extract a three-axis magnetic field resolving signal from a beam of laser signals, eliminates the cross coupling effect during three-axis magnetic field resolving, improves the measurement range and orthogonality of the SERF atomic magnetometer, and has extremely high engineering application value.

Description

Technical Field

[0001] The invention relates to the field of high-precision vector magnetic field measurement, in particular to an orthogonal double frequency modulation and demodulation system and method for a three-axis SERF atomic magnetometer. Background Art

[0002] The SERF atomic magnetometer is a new type of vector atomic magnetometer with the characteristics of ultra-high precision, small size, and three-axis vector magnetic field measurement. It is expected to be used in space magnetism, ocean magnetism, aviation magnetism, and cardio-cerebral magnetism measurement.

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

[0004] In order to make the atoms enter a state without spin exchange relaxation, it is necessary to ensure that the total magnetic field in the atomic gas chamber is close to zero. The use of a magnetic shielding tube can attenuate the external magnetic field to less than 10nT to achieve the quantum state effect, but the addition of a magnetic shielding tube will reduce the measurement range of the vector magnetometer, and the attenuation coefficient of the magnetic shielding tube cannot be accurately controlled, which will affect the magnetic field measurement accuracy.

[0005] The traditional SERF vector atomic magnetometer is an open-loop mode. Its measurement range is related to the magnetic resonance linewidth of the SERF state signal, which is only 10nT. It can only work in a magnetic shielding room or a magnetic shielding tube, which limits its application in the geomagnetic field environment. In addition, the open-loop modulation mode has a three-axis cross-coupling problem, that is, when the magnetic field of one axis changes, it will affect the measurement results of the other two axes, and the measurement accuracy and precision cannot be guaranteed. Summary of the invention

[0006] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art, to provide an orthogonal double frequency modulation and demodulation system and method for a three-axis SERF atomic magnetometer, to solve the problem of cross-coupling of three-axis solution signals in the prior art modulation and demodulation technology, thereby improving the measurement range and three-axis orthogonality of the SERF atomic magnetometer.

[0007] The technical solution of the present invention is: a three-axis SERF atomic magnetometer orthogonal double frequency modulation and demodulation system, including: a signal generation module, a DA module, a voltage and current conversion module, an AD module, an integral filter module and a control module;

[0008] The signal generation module generates three modulation signals, namely sine signal I, sine signal II and cosine signal; among them, the frequencies of sine signal I and cosine signal are the same, both are f m , the phase difference is 90°, and the frequency of the sine signal II is 2nf m , the initial phase is the same as the phase of the sinusoidal signal I;

[0009] The DA module receives the 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, performs digital-to-analog conversion, and obtains three voltage signals;

[0010] The voltage-current conversion module converts the three voltage signals output by the DA module into current signals, which respectively drive the X, Y and Z axis magnetic field coils of the three-axis SERF atomic magnetometer; thus generating a frequency of f on the X axis magnetic field coil. m The sinusoidally modulated magnetic field signal generates a frequency of f on the Y-axis magnetic field coil. m The cosine modulated magnetic field signal and the frequency generated on the Z-axis magnetic field coil are 2nf m The sinusoidally modulated magnetic field signal changes the laser signal passing through the atomic gas chamber of the three-axis SERF atomic magnetometer, so that the laser signal carries the three-axis magnetic field measurement data;

[0011] AD module, collects the laser signal, performs analog-to-digital conversion, and divides it into three paths: X, Y and Z;

[0012] The integral filter module receives the signals obtained by multiplying the three signals output by the AD module with the sine signal I, cosine signal and sine signal II generated by the signal generation module, performs integral filtering, and obtains the open-loop magnetic field signals of the X, Y and Z axes;

[0013] The control module receives X, Y and Z axis open-loop magnetic field signals, generates X, Y and Z path 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 magnitude to the external magnetic field to be measured and opposite in direction, offsets the external magnetic field to be measured, and makes the magnetic field at the atomic gas chamber zero; the X, Y and Z path 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.

[0014] Further, f m The value range is 10Hz~1kHz, and the value range of n is 1~100.

[0015] Furthermore, the signal generation module uses 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 use three independent devices to realize their respective functions, among which the control module uses three PID controllers to generate X, Y and Z compensation magnetic field signals.

[0016] Furthermore, the integration time of the integral filter 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: set the sampling frequency of the AD module to f s , set the number of integration points of the integral filter module to f s / f m The quotient is rounded.

[0018] The present invention also provides a three-axis SERF atomic magnetometer orthogonal double frequency modulation and demodulation method, comprising the following steps:

[0019] Generate three modulation signals, namely sine signal I, sine signal II and cosine signal; among them, the frequency of sine signal I and cosine signal is the same, both are f m , the phase difference is 90°, and the frequency of the sine signal II is 2nf m , the initial phase is the same as the phase of the sinusoidal signal I;

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

[0021] The three voltage signals are converted into current signals to drive the X, Y and Z axis magnetic field coils of the three-axis SERF atomic magnetometer respectively, and orthogonal double frequency modulation is performed to generate a frequency of f on the X axis magnetic field coil. m The sinusoidally modulated magnetic field signal generates a frequency of f on the Y-axis magnetic field coil. m The cosine modulated magnetic field signal and the frequency generated on the Z-axis magnetic field coil are 2nf m The sinusoidally modulated magnetic field signal changes the laser signal passing through the atomic gas chamber of the three-axis SERF atomic magnetometer, so that the laser signal carries the three-axis magnetic field measurement data;

[0022] The laser signal is collected, and after analog-to-digital conversion, it is divided into three paths: X, Y and Z; then, it is multiplied with the sine signal I, the cosine signal and the sine signal II respectively, and the multiplication results are integrated and filtered respectively to obtain X, Y and Z axis open-loop magnetic field signals;

[0023] Using the X, Y and Z axis open-loop magnetic field signals, generate X, Y and Z path 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 magnitude and opposite in direction to the external magnetic field to be measured, thereby offsetting the external magnetic field to be measured and making the magnetic field at the atomic gas chamber zero;

[0024] The X, Y and Z compensated magnetic field signals are outputted to obtain the X, Y and Z axis magnetic field intensities measured by the three-axis SERF atomic magnetometer.

[0025] Further, f m The value range is 10Hz~1kHz, and the value range of n is 1~100.

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

[0027] Furthermore, let the integration time be 1 / f m The implementation method is: AD sampling frequency is set to f s , set the number of integration points of the integral filter module to f s / f m The quotient is rounded.

[0028] The advantages of the present invention compared with the prior art are:

[0029] (1) The present invention realizes the orthogonal double frequency three-axis digital closed-loop control of the SERF atomic magnetometer, 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 has 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 frequency different from that of the X-axis and Y-axis magnetic field coils is used. In order to increase the system bandwidth in the integration link, the signal frequency is 2n times the frequency of the X-axis and Y-axis modulation signals. In this way, when a multiplier is used for phase-sensitive detection, a high-order harmonic signal with a frequency of n times is generated. It only needs to use the same full-cycle integration filter to filter out the high-order harmonic signal, and then extract the useful Z-axis magnetic field signal, thereby 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 the voltage-controlled constant current source through a PID controller to compensate the ambient magnetic field so that the magnetic field at the atomic gas chamber is zero. At this time, the compensation magnetic field generated by the three-axis magnetic field coil is the external magnetic field to be measured, thereby significantly improving the measurement accuracy, measurement range and orthogonality of the three-axis magnetic field. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the composition of the orthogonal double frequency modulation and demodulation system of the SERF atomic magnetometer of the present invention;

[0033] Figure 2 Schematic diagram of magnetic field measurement principle of the present invention. DETAILED DESCRIPTION

[0034] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. The parts of each structure in the accompanying drawings will be described separately. It is worth noting that the components not shown in the drawings or not described in words are forms known to ordinary technicians in the relevant technical field.

[0035] like Figure 1 , Figure 2 As shown, the orthogonal double frequency modulation and demodulation system of the SERF atomic magnetometer proposed in the present invention includes a signal generation module, a DA module, a voltage-current conversion module, an AD module, an integral filter module and a control module; the SERF atomic magnetometer includes a laser 1, an atomic gas chamber 2, a three-axis 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 modulation signals, namely, sine signal I, sine signal II and cosine signal; wherein, the sine signal I and the cosine signal have the same frequency, both f m , the phase difference is 90°, and the frequency of the sine 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~1kHz, and the value range of n is 1~100.

[0037] The DA module includes three D / A conversion chips 9, which receive the 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, perform digital-to-analog conversion, and obtain three voltage signals;

[0038] The voltage-current conversion module includes three voltage-controlled current sources 10, which convert the three voltage signals output by the DA module into current signals to drive the X-axis, Y-axis and Z-axis magnetic field coils of the three-axis SERF atomic magnetometer respectively; thereby generating a frequency of f on the X-axis magnetic field coil. m The sinusoidally modulated magnetic field signal generates a frequency of f on the Y-axis magnetic field coil. m The cosine modulated magnetic field signal and the frequency generated on the Z-axis magnetic field coil are 2nf m The sinusoidally modulated magnetic field signal changes the laser signal passing through the atomic gas chamber of the three-axis SERF atomic magnetometer, so that the laser signal carries the three-axis magnetic field measurement data;

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

[0040] The integral filter module includes three integral filters 7, which receive the three signals output by the AD module and multiply them with the sine signal I, cosine signal and sine signal II generated by the signal generation module, perform integral filtering, and obtain the open-loop magnetic field signals of the X, Y and Z axes; the integral filter 7 is designed as a full-cycle integral filter, and the integral time is 1 / f m , the implementation method is: set the sampling frequency of the AD module to f s , set the number of integration points of the integral filter module to f s / f m The quotient is rounded to an integer, so that the integration time of the three integrating filters 7 is 1 / f m ;

[0041] The control module includes three PID controllers 8, which receive X-, Y- and Z-axis open-loop magnetic field signals, generate X-, Y- and Z-path 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 magnitude to the external magnetic field to be measured, but opposite in direction, so as to offset the external magnetic field to be measured and make the magnetic field at the atomic gas chamber zero; the X-, Y- and Z-path compensation magnetic field signals generated by the control module are output, so as to obtain the X-, Y- and Z-axis magnetic field strengths measured by the three-axis SERF atomic magnetometer.

[0042] The specific working process of the present invention comprises:

[0043] (1) Laser 1 generates a laser beam, which passes through atomic gas chamber 2, produces a photomagnetic effect with the alkali metal atom rubidium inside atomic gas chamber 2, and is transmitted to detector 3;

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

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

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

[0047] (5) The output signal of the detector 3 is collected by the A / D conversion chip 4, converted into digital form, 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 the 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 coil by the DDS signal generator 6, and the multiplication results are respectively sent to the integral filter 7 for integral filtering to obtain the X, Y, and Z axis open-loop magnetic field signals. The integral filter 7 is designed as a full-cycle integral filter, that is, the current modulation signal frequency is f m , then the integration time of the integrating filter is 1 / f m Since FPGA is used for digital signal processing in this embodiment, the number of integration points m of the integration filter should be equal to the A / D sampling rate f s With the modulation signal frequency f m The quotient of and rounding (rounding up or rounding down) is then the integral filter for the frequency f m Different multiples of sine and cosine signals have good filtering effects. Through this method, the integration time of the integral filter selected by the filter for X-axis, Y-axis and Z-axis magnetic field demodulation can be set to 1 / f m , which can effectively suppress the cross coupling between different axes;

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

[0049] The above process completes the orthogonal double frequency 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 three-axis magnetic field intensity signal measured by the SERF atomic magnetometer.

[0050] It is to be understood that the present invention is described by way of embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and embodiments that can fall within the scope of the claims of this application all fall within the scope protected by the present invention.

[0051] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

Claims

1. A three-axis SERF atomic magnetometer orthogonal double frequency modulation and demodulation system, characterized in that: include: Signal generation module, DA module, voltage-current conversion module, AD module, integral filter module and control module; The signal generation module generates three modulation signals, namely sine signal I, sine signal II and cosine signal; among them, the frequencies of sine signal I and cosine signal are the same, both are f m , the phase difference is 90°, and the frequency of the sine signal II is 2nf m , the initial phase is the same as the phase of the sinusoidal signal I; The DA module receives the 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, performs digital-to-analog conversion, and obtains three voltage signals; The voltage-current conversion module converts the three voltage signals output by the DA module into current signals, which respectively drive the X, Y and Z axis magnetic field coils of the three-axis SERF atomic magnetometer; thus generating a frequency of f on the X axis magnetic field coil. m The sinusoidally modulated magnetic field signal generates a frequency of f on the Y-axis magnetic field coil. m The cosine modulated magnetic field signal and the frequency generated on the Z-axis magnetic field coil are 2nf m The sinusoidally modulated magnetic field signal changes the laser signal passing through the atomic gas chamber of the three-axis SERF atomic magnetometer, so that the laser signal carries the three-axis magnetic field measurement data; AD module, collects the laser signal, performs analog-to-digital conversion, and divides it into three paths: X, Y and Z; The integral filter module receives the signals obtained by multiplying the three signals output by the AD module with the sine signal I, cosine signal and sine signal II generated by the signal generation module, performs integral filtering, and obtains the open-loop magnetic field signals of the X, Y and Z axes; The control module receives X, Y and Z axis open-loop magnetic field signals, generates X, Y and Z path 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 magnitude to the external magnetic field to be measured and opposite in direction, offsets the external magnetic field to be measured, and makes the magnetic field at the atomic gas chamber zero; the X, Y and Z path 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.

2. The orthogonal double frequency modulation and demodulation system of the three-axis SERF atomic magnetometer according to claim 1 is characterized in that: f m The value range is 10Hz~1kHz, and the value range of n is 1~100.

3. The orthogonal double frequency modulation and demodulation system of the three-axis SERF atomic magnetometer according to claim 1 is characterized in that: The signal generation module uses a DDS signal generator to generate three modulation signals; the DA module, voltage-current conversion module, integral filter module and control module all use three independent devices to realize their respective functions, among which the control module uses three PID controllers to generate X, Y and Z compensation magnetic field signals.

4. The orthogonal double frequency modulation and demodulation system of the three-axis SERF atomic magnetometer according to claim 1 is characterized in that: The integration time of the integral filter module is 1 / f m .

5. The orthogonal double frequency modulation and demodulation system of the three-axis SERF atomic magnetometer according to claim 4 is characterized in that: Make the integral time of the integral filter module 1 / f m The implementation method is: set the sampling frequency of the AD module to f s , set the number of integration points of the integral filter module to f s / f m The quotient is rounded.

6. A three-axis SERF atomic magnetometer orthogonal double frequency modulation and demodulation method, characterized in that: The steps include: Generate three modulation signals, namely sine signal I, sine signal II and cosine signal; among them, the frequency of sine signal I and cosine signal is the same, both are f m , the phase difference is 90°, and the frequency of the sine signal II is 2nf m , the initial phase is the same as the phase of the sinusoidal signal I; After respectively adding the sine signal I, cosine signal and sine signal II to the X, Y and Z compensation magnetic field signals, digital-to-analog conversion is performed to obtain three voltage signals; The three voltage signals are converted into current signals to drive the X, Y and Z axis magnetic field coils of the three-axis SERF atomic magnetometer respectively, and orthogonal double frequency modulation is performed to generate a frequency of f on the X axis magnetic field coil. m The sinusoidally modulated magnetic field signal generates a frequency of f on the Y-axis magnetic field coil. m The cosine modulated magnetic field signal and the frequency generated on the Z-axis magnetic field coil are 2nf m The sinusoidally modulated magnetic field signal changes the laser signal passing through the atomic gas chamber of the three-axis SERF atomic magnetometer, so that the laser signal carries the three-axis magnetic field measurement data; The laser signal is collected, and after analog-to-digital conversion, it is divided into three paths: X, Y and Z; then, it is multiplied with the sine signal I, the cosine signal and the sine signal II respectively, and the multiplication results are integrated and filtered respectively to obtain X, Y and Z axis open-loop magnetic field signals; Using the X, Y and Z axis open-loop magnetic field signals, generate X, Y and Z path 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 magnitude and opposite in direction to the external magnetic field to be measured, thereby offsetting the external magnetic field to be measured and making the magnetic field at the atomic gas chamber zero; The X, Y and Z compensated magnetic field signals are outputted to obtain the X, Y and Z axis magnetic field intensities measured by the three-axis SERF atomic magnetometer.

7. The orthogonal double frequency modulation and demodulation method of a three-axis SERF atomic magnetometer according to claim 6, characterized in that: f m The value range is 10Hz~1kHz, and the value range of n is 1~100.

8. The orthogonal double frequency modulation and demodulation method of a three-axis SERF atomic magnetometer according to claim 6, characterized in that: The integration time of the integral filter is 1 / f m .

9. The orthogonal double frequency modulation and demodulation method of a three-axis SERF atomic magnetometer according to claim 8, characterized in that: Let the integration time be 1 / f m The implementation method is: AD sampling frequency is set to f s , set the number of integration points of the integral filter module to f s / f m The quotient is rounded.

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