Atomic magnetic gradient measuring device and measuring method

Abstract

The invention relates to the technical field of magnetic field precision measurement, in particular to an atomic magnetic gradient measurement device and method. Comprising a host which is internally provided with a laser light source and a control circuit thereof, a data acquisition unit and a probe control unit; each probe comprises a polarizer, a collimating and focusing lens, an atomic gas chamber and a photoelectric detector; the laser light source generates frequency-stabilized laser, the laser is divided into a plurality of paths with equal light intensity through the light splitting device, and the plurality of paths of laser enter the plurality of probes through the optical fibers respectively; the magnetometer is provided with a plurality of probes which are completely homologous, laser homology, air chamber excitation homology, clock homology and signal synchronous processing are included, common-mode noise caused by a laser light source, a signal processing circuit and the environment of the magnetometer is reduced in a differential mode, and the magnetic field measurement sensitivity and the system anti-jamming capability are improved; therefore, the influence of geomagnetic diurnal variation and ambient noise on the quality of magnetic field measurement data can be effectively eliminated.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetic field precision measurement, and in particular to an atomic magnetic gradient measurement device and a measurement method. Background Art

[0002] As a ubiquitous field substance, magnetic field is widely used in geological exploration, military applications, biomedicine and other fields. In these fields, accurate measurement of magnetic field is crucial. Among many magnetometers, optical pumping magnetometer is widely used in magnetic field measurement in the above fields due to its high sensitivity, low noise, good accuracy and many other advantages.

[0003] The working principle of the optically pumped magnetometer is based on the Zeeman splitting phenomenon produced by atomic energy levels in a magnetic field, and is made using optical pumping and magnetic resonance technology. This type of magnetometer usually uses alkali metals, helium, etc. as working elements. Through the action of optical pumping, the atoms of each magnetic sub-energy level are completely concentrated on a certain magnetic sub-energy level, thereby realizing the polarization of the atoms. Subsequently, the drive coil generates an alternating radio frequency magnetic field, which undergoes magnetic resonance with the atoms. At this time, the metastable atoms need to reabsorb the detection light, causing the detection light to pass through the atomic gas chamber to become weaker. When the light intensity passing through the gas chamber is the weakest, the corresponding radio frequency field frequency is the magnetic resonance frequency. The size of the measured magnetic field can be inferred from the gyromagnetic ratio of the resonant element.

[0004] However, most traditional laser optically pumped magnetometers measure the total field in a single channel. This measurement method has great limitations because it is easily affected by many factors, including the daily variation of the magnetic field, the effect of ambient temperature changes on magnetic field measurement, and the effect of the magnetometer background noise. These factors may increase the error of the measurement results, thereby reducing the practicality and accuracy of the magnetometer. Summary of the invention

[0005] The present invention provides an atomic magnetic gradient measuring device and a measuring method. The device has a plurality of probes, and the probes have homology, namely, laser homology, gas chamber excitation homology, clock homology and signal synchronization processing. The common mode noise caused by the laser light source, signal processing circuit and environment of the magnetometer itself is reduced by a homology difference method, and the magnetic field measurement sensitivity and the anti-interference ability of the system are improved, so that the influence of the geomagnetic diurnal variation and the surrounding environmental noise on the magnetic field measurement data quality can be effectively eliminated.

[0006] To achieve the above object, the technical solution of the present invention is:

[0007] An atomic magnetic gradient measuring device, comprising:

[0008] A host computer with built-in laser light source and its control circuit, data acquisition unit and probe control unit;

[0009] A plurality of probes, each of which includes a polarizer, a collimating and focusing lens, an atomic gas chamber, and a photodetector;

[0010] The host and the probe are connected via an optoelectronic hybrid cable consisting of a non-magnetic single-mode polarization-maintaining optical fiber and a non-magnetic cable;

[0011] The laser light source generates a frequency-stabilized laser, which is divided into a plurality of paths with equal light intensity by a light splitting device, and enters a plurality of probes respectively through optical fibers;

[0012] The multiple probes measure the total magnetic field and perform differential processing on the measurement results inside the host to remove laser noise and circuit noise, thereby achieving higher sensitivity magnetic field measurement.

[0013] Laser homology, gas chamber excitation homology, clock homology and signal synchronization processing are adopted to reduce the common mode noise caused by the magnetometer's own laser light source, signal processing circuit and environment through differential method.

[0014] Furthermore, the laser light source adjusts the temperature and current parameters of the laser so that the wavelength of the laser output is at the absorption wavelength of the working element of the magnetometer, and stabilizes the laser wavelength at the absorption peak of the working element through amplitude modulation.

[0015] Furthermore, a Larmor coil is provided outside the atomic gas chamber in the probe, and the RF signal generation and signal processing adopt a homologous synchronous method to apply a frequency corresponding to the external magnetic field, calculate the size of the external magnetic field through the gyromagnetic ratio of the element, and realize total field measurement.

[0016] Furthermore, the differential processing is to compare and calculate the total magnetic field information measured by the two probes through the data acquisition unit inside the host to eliminate common mode noise.

[0017] A measuring method comprises the steps of:

[0018] Step 1: Gradient laser magnetometer magnetic field data acquisition;

[0019] Step 2: Data preprocessing;

[0020] Step 3: Differentiate the magnetic field data of different probes;

[0021] Step 4: Acquire magnetic field gradient data.

[0022] Furthermore, in step 1, in a test or practical environment, external magnetic field data is collected, the collection time is t, and the number of collected points is n.

[0023] Furthermore, in step 2,

[0024] Preprocess the data collected by different probes to obtain the magnetic field data sequence of different probes in this time period. 1 Including B 1i , where i=1,2,…N; B 2 Including B 2j , where j=1,2,…N;

[0025] Magnetic field data sequence B obtained by different probes 1 and B 2 contains the real magnetic field value and the magnetic field noise caused by the internal and external interference of the magnetic measurement system. 1i and B 2j It is expressed as follows:

[0026] (1)

[0027] (2)

[0028] Where N 11i and N 21j They represent the magnetic field noise caused by the fluctuation of the light source and signal processing circuit during the test. Since the same light source and signal processing circuit are used for simultaneous measurement, the values ​​of the two are equal, so:

[0029] (3);

[0030] N 12i and N 22j Represents the magnetic field noise caused by external interference during the test. Since the two probes use the same design and measure at the same time, N 12i and N 22j The values ​​of are equal, which is common mode noise, so:

[0031] (4);

[0032] N 13i and N 23j They represent the inconsistency of magnetic field testing caused by the two probes due to process and assembly reasons.

[0033] Furthermore, in step 3,

[0034] The magnetic field gradient is obtained by performing differential calculation on equations (1) and (2). According to the analysis of step (2), the common mode noise caused by the fluctuation of the light source and signal processing circuit and the external interference can be effectively removed during the differential calculation process.

[0035] Subtracting formula (2) from formula (1) yields:

[0036] (5)

[0037] Substituting formula (3) and formula (4) into formula (5), we get:

[0038] (6);

[0039] in is the true magnetic field gradient, is the measured value, The error is caused by process assembly.

[0040] The beneficial effects achieved by the present invention are:

[0041] A method and device for measuring atomic magnetic gradients, which effectively improve the anti-interference ability of the atomic magnetometer to the external environment by adopting a multi-probe distributed differential measurement method, eliminate the influence of platform magnetic interference, environmental magnetic interference and geomagnetic diurnal variation on magnetic field measurement, and make the system have the characteristics of wide use scenarios and strong applicability.

[0042] In order to solve the problem that the system's own noise is difficult to remove in the total magnetic field measurement system, a laser is used to provide light source for multiple atomic gas chambers to ensure the consistency of optical properties such as wavelength, power, and polarization. The common-mode noise caused by the light source can be suppressed through differential processing. The same constant temperature crystal oscillator is used to ensure the consistency of the frequency reference. The RF noise and drift can be reduced through differential processing. The same RF field is used to excite the helium atomic gas chambers of different probes to ensure the consistency of the working state and eliminate the difference in probe signals. Through synchronous detection and feedback of different probe signals, it is ensured that the processed signals are the detection signals at the same time, which effectively removes the common-mode noise between different probes, reduces the system's own noise, and further improves the system sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0044] Figure 1 This is the system block diagram of the atomic magnetic gradient measurement system.

[0045] Figure 2 Schematic diagram of the optical path for measuring atomic magnetic gradient.

[0046] Figure 3 This is the working flow diagram of the atomic magnetic gradient measurement system.

[0047] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back...), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0050] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, if the meaning of "and / or" appearing in the full text is to include three parallel schemes, taking "A and / or B" as an example, it includes scheme A, or scheme B, or a scheme that satisfies both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0051] like Figures 1 to 3 As shown, an atomic magnetic gradient measuring device comprises:

[0052] A host computer has a built-in laser light source and its control circuit, a data acquisition unit and a probe control unit; multiple probes, each of which includes a polarizer, a collimating focusing lens, an atomic gas chamber and a photoelectric detector; the host computer and the probe are connected through an optoelectronic hybrid cable composed of a non-magnetic single-mode polarization-maintaining optical fiber and a non-magnetic cable; the laser light source generates a frequency-stabilized laser, which is divided into a plurality of paths with equal light intensity through a spectrometer, and enters a plurality of probes through optical fibers respectively; the plurality of probes measure the total magnetic field, and perform differential processing on the measurement results inside the host computer to remove laser noise and circuit noise, thereby achieving higher-sensitivity magnetic field measurement.

[0053] The laser light source adjusts the temperature and current parameters of the laser so that the wavelength of the laser output by the laser is within the absorption wavelength of the working element of the magnetometer, and stabilizes the laser wavelength on the absorption peak of the working element through amplitude modulation.

[0054] A Larmor coil is arranged outside the atomic gas chamber in the probe, and the radio frequency signal generation and signal processing adopt a homologous synchronous mode to apply a frequency corresponding to the external magnetic field, calculate the size of the external magnetic field through the gyromagnetic ratio of the element, and realize the total field measurement.

[0055] The differential processing is to perform differential calculation on the total magnetic field information measured by the two probes through the data acquisition unit inside the host to eliminate common mode noise.

[0056] Figure 1 This is the system block diagram of the atomic magnetic gradient measurement system. The atomic magnetic gradient measurement system consists of a host and multiple probes. The host includes a data acquisition unit, a probe control unit, a laser light source and its control circuit; the probe mainly includes a polarizer, a collimating focusing lens, an atomic gas chamber and a photoelectric detector; the probe and the host are connected by an optoelectronic hybrid cable consisting of a non-magnetic single-mode polarization-maintaining optical fiber and a non-magnetic cable. The host is responsible for the drive and signal processing of the probe, completes the digitization of the total magnetic field and gradient information, and has storage and communication functions; the probe is responsible for magnetic field sensitivity and converts the magnetic field size into a photoelectric signal.

[0057] Figure 2 This is a schematic diagram of the optical path for atomic magnetic gradient measurement. The lasers of different probes come from the same laser. The laser and its circuit are placed inside the host. The light from the laser is divided into two beams of the same intensity through a spectroscopic device (splitting fiber or spectroscopic prism), which are transmitted to different probes through non-magnetic optical fibers, and finally focused on the photodetector after passing through a polarizer, collimating lens, atomic gas chamber, and focusing lens. A weak modulation signal is added to the laser, and then the atomic gas chamber absorbs light to achieve frequency stabilization of the laser. After frequency stabilization, the laser enters different probes. When the frequency of the radio frequency field generated by the Larmor coil is equal to the magnetic resonance frequency, the light intensity will be absorbed. The absorption signal is transmitted to the back-end processing circuit for magnetic field locking and tracking. By differentially processing the magnetic fields measured by different probes, common mode noise can be eliminated, and the system sensitivity and anti-interference ability can be improved.

[0058] The specific working process is as follows: ① Magnetic→Optical Conversion: The atomic magnetic gradient measurement system designed in the present invention has an atomic gas chamber in the probe, and the gas chamber contains working elements such as alkali metals or He-4. The element undergoes Zeeman splitting under the action of an external magnetic field, and the degree of splitting is related to the size of the external magnetic field. Laser and radio frequency signals are used as detection tools, and magnetic resonance signals are generated through optical pumping and magnetic resonance. The magnetic field information is collected through a photoelectric detector to convert the total magnetic field information into a light absorption signal; this process is carried out simultaneously in different probes, and the laser and radio frequency signals are derived from the same laser and excitation module to achieve homology and synchronization; ② Optical→Electrical Conversion: The light absorption signal is converted into an electrical signal through a signal processing circuit, AD acquisition, digital demodulation and other processes, and digitized. The signal extraction is achieved through digital phase-locked amplification technology to reduce circuit noise interference and ultimately achieve digital acquisition of the total magnetic field information. This process is carried out in the host, and is synchronously processed by the circuits with the same design. The same constant temperature crystal oscillator is used to ensure the consistency of the frequency reference. The differential processing can reduce the RF noise and drift. The digital signal processing is processed in the same FPGA with consistent timing, so that the consistency and synchronization of the back-end processing can be achieved; ③ Total field → gradient: The total field information of the magnetic field is differentiated to obtain the magnetic field gradient. Since the probes are completely homologous, the same common mode noise exists in the measured magnetic field. The common mode noise can be eliminated through differential processing, further reducing the magnetic field measurement noise, and also eliminating the influence of geomagnetic daily changes and environmental interference on the magnetic field measurement. Since the atomic magnetic gradient measurement system has low noise and strong anti-interference ability, it can achieve extremely weak magnetic signal measurement.

[0059] A measuring method comprises the steps of:

[0060] Step 1: Gradient laser magnetometer magnetic field data acquisition;

[0061] Step 2: Data preprocessing;

[0062] Step 3: Dual-probe magnetic field data differential;

[0063] Step 4: Acquire magnetic field gradient data.

[0064] In step 1, in a test or practical environment, external magnetic field data is collected, the collection time is t, and the number of collected points is n.

[0065] In step 2, the data collected by different probes are preprocessed to obtain the magnetic field data sequence of different probes in this time period. 1 Including B 1i , where i=1,2,…N; B 2 Including B 2j , where j=1,2,…N.

[0066] Magnetic field data sequence B obtained by different probes 1 and B2 contains the real magnetic field value and the magnetic field noise caused by the internal and external interference of the magnetic measurement system. 1i and B 2j It is expressed as follows:

[0067] (1)

[0068] (2)

[0069] Where N 11i and N 21j They represent the magnetic field noise caused by the fluctuation of the light source and signal processing circuit during the test. Since the same light source and signal processing circuit are used for simultaneous measurement, the values ​​of the two are equal, so:

[0070] (3);

[0071] N 12i and N 22j Represents the magnetic field noise caused by external interference during the test. Since the two probes use the same design and measure simultaneously (that is, use the same set of circuits for RF excitation and the same set of clocks for signal synchronization processing), N 12i and N 22j The values ​​of are equal, which is common mode noise, so:

[0072] (4);

[0073] N 13i and N 23j They represent the inconsistency of magnetic field testing caused by the two probes due to process and assembly reasons.

[0074] In step 3, equations (1) and (2) are differentially calculated to obtain the magnetic field gradient. According to the analysis of step (2), during the differential operation, the common mode noise caused by the fluctuation of the light source and signal processing circuit and external interference can be effectively removed. This type of noise is difficult to eliminate in traditional atomic magnetometers, so this solution can effectively reduce system noise and improve the system's anti-interference ability.

[0075] Subtracting formula (2) from formula (1) yields:

[0076] (5)

[0077] Substituting formula (3) and formula (4) into formula (5), we get:

[0078] (6);

[0079] in is the true magnetic field gradient, is the measured value, The error is caused by process assembly.

[0080] The above descriptions are only optional embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly / indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims

1. An atomic magnetic gradient measuring device, characterized in that: include: A host computer with built-in laser light source and its control circuit, data acquisition unit and probe control unit; A plurality of probes, each of which includes a polarizer, a collimating and focusing lens, an atomic gas chamber, and a photodetector; The host and the probe are connected via an optoelectronic hybrid cable consisting of a non-magnetic single-mode polarization-maintaining optical fiber and a non-magnetic cable; The laser light source generates a frequency-stabilized laser, which is divided into a plurality of paths with equal light intensity by a light splitting device, and enters a plurality of probes respectively through optical fibers; Laser homology, gas chamber excitation homology, clock homology and signal synchronization processing are adopted to reduce the common mode noise caused by the magnetometer's own laser light source, signal processing circuit and environment through differential method.

2. The atomic magnetic gradient measuring device according to claim 1, characterized in that: The laser light source adjusts the temperature and current parameters of the laser so that the wavelength of the laser output by the laser is within the absorption wavelength of the working element of the magnetometer, and stabilizes the laser wavelength on the absorption peak of the working element through amplitude modulation.

3. The atomic magnetic gradient measuring device according to claim 1, characterized in that: A Larmor coil is arranged outside the atomic gas chamber in the probe, and the radio frequency signal generation and signal processing adopt a homologous synchronous mode to apply a frequency corresponding to the external magnetic field, calculate the size of the external magnetic field through the gyromagnetic ratio of the element, and realize the total field measurement.

4. The atomic magnetic gradient measuring device according to claim 1, characterized in that: The differential processing is to perform differential calculation on the total magnetic field information measured by different probes through the data acquisition unit inside the host to eliminate common mode noise.

5. A measurement method, characterized in that: The method is based on the device according to any one of claims 1 to 4, comprising the steps of: Step 1: Gradient laser magnetometer magnetic field data acquisition; Step 2: Data preprocessing; Step 3: Differentiate the magnetic field data of different probes; Step 4: Acquire magnetic field gradient data.

6. A measuring method according to claim 5, characterized in that: In step 1, in a test or practical environment, external magnetic field data is collected, the collection time is t, and the number of collected points is n.

7. A measuring method according to claim 6, characterized in that: In step 2, Preprocess the data collected by different probes to obtain the magnetic field data sequence of different probes in this time period. B1 includes B 1i , where i=1,2,…N; B2 includes B 2j , where j=1,2,…N; The magnetic field data sequences B1 and B2 obtained by different probes contain the real magnetic field value and the magnetic field noise caused by the internal and external interference of the magnetic measurement system. 1i and B 2j It is expressed as follows: (1) (2) Where N 11i and N 21j They represent the magnetic field noise caused by the fluctuation of the light source and signal processing circuit during the test. Since the same light source and signal processing circuit are used for simultaneous measurement, the values ​​of the two are equal, so: （3）； N 12i and N 22j Represents the magnetic field noise caused by external interference during the test. Since the two probes use the same design and measure at the same time, N 12i and N 22j The values ​​of are equal, which is common mode noise, so: （4）； N 13i and N 23j They represent the inconsistency of magnetic field testing caused by the two probes due to process and assembly reasons.

8. A measuring method according to claim 7, characterized in that: In step 3, The magnetic field gradient is obtained by performing differential calculation on equations (1) and (2). According to the analysis of step (2), the common mode noise caused by the fluctuation of the light source and signal processing circuit and the external interference can be effectively removed during the differential calculation process. Subtracting formula (2) from formula (1) yields: （5） Substituting formula (3) and formula (4) into formula (5), we get: （6） in is the true magnetic field gradient, is the measured value, The error is caused by process assembly.

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