Overhauser magnetometer for rapid measurement

Abstract

The invention discloses an Overhauser magnetometer for rapid measurement, and belongs to the technical field of magnetic field measurement. The technical problems that an intermittent measurement method is adopted when an existing Overhauser magnetometer is used for measurement, the polarization time is long, and application of the Overhauser magnetometer at the high circulation rate is limited are solved. Rapid measurement of the Overhauser magnetometer is realized by combining continuous radio-frequency polarization excitation and a series of polarization methods of direct-current polarization pulses, the problem of long-time direct-current polarization in traditional intermittent measurement is solved, and the optimized direct-current polarization pulses only need several milliseconds by utilizing a dynamic equation of a proton magnetic moment in an external magnetic field. The circulation rate of the magnetometer is improved, the actual application requirement for the high circulation rate is met, and the sensitivity of output signals is high.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic field measurement, and in particular relates to an Overhauser magnetometer for rapid measurement. Background Art

[0002] Magnetometer is a general term for instruments that measure the strength and direction of magnetic fields. Magnetometers with high precision and high sensitivity are widely used in space magnetic surveys, land magnetic surveys, marine magnetic surveys, military and mineral exploration. Overhauser magnetometers are based on the dynamic nuclear polarization effect of electrons and protons in free radical substances, which significantly improves the polarization intensity of protons, thereby improving the magnetic sensitivity of the instrument. Due to its advantages such as low power consumption, no heading error, no measurement dead zone, long life, high precision and high sensitivity, Overhauser magnetometers are widely used in space magnetic surveys, geomagnetic observations, military and mineral resource exploration.

[0003] At present, most Overhauser magnetometers adopt the traditional intermittent measurement polarization scheme, that is, the RF and DC polarization are turned on first in the measurement cycle, and the polarization source is turned off and the Larmor signal is received after the polarization is completed. For example, a Chinese utility model patent application "A Magnetometer" (CN204945405U) discloses a magnetometer, which turns on RF polarization and DC polarization at the same time to make the free radical solution produce a dynamic nuclear polarization effect, and enhances the magnetization intensity of hydrogen protons along the geomagnetic field and the DC polarization static field. This method belongs to an intermittent measurement, and its advantages are sufficient polarization, strong Larmor signal, high sensitivity, and a sensitivity of 0.01nT can be achieved under a cycle period of 3s. However, the longitudinal relaxation time of protons in liquids is relatively long, resulting in a longer time for the polarization saturation of the hydrogen proton magnetic moment. Therefore, the disadvantage of this method is that it is an intermittent measurement method with a long polarization time, which limits the application of Overhauser magnetometers at high cycle rates.

[0004] Therefore, it is urgent to design a new polarization method to increase the cycle rate of the Overhauser magnetometer to meet the needs of fast measurements while maintaining high sensitivity. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides an Overhauser magnetometer for rapid measurement: The Overhauser magnetometer comprises a radio frequency polarization circuit, a direct current polarization circuit, an Overhauser sensor, a signal conditioning circuit, a shaping circuit, a detection circuit, an FPGA and an embedded controller. The direct current polarization circuit uses a direct current polarization pulse to excite the Overhauser sensor.

[0006] Furthermore, the method for determining the DC polarization pulse is specifically as follows: S1. Establishing proton magnetization The Larmor precession dynamic equation in the external magnetic field, and the Larmor precession dynamic equation is differentiated to obtain the proton magnetization intensity at each moment ; S2. Calculate the pulse polarization field at each moment ; S3. Calculate the geomagnetic field and pulse polarization field at each moment The combined magnetic field ; S4, using polarization saturation factor Characterizing the proton magnetization at the final moment The combined magnetic field of the geomagnetic field and the pulse polarization field at the final moment Angle of deflection efficiency evaluation system is established; S5, through the polarization saturation factor By reverse reasoning, we can obtain the polarization field pulse waveform index corresponding to the optimal DC polarization pulse. , polarization field pulse intensity and the duration of the polarization field pulse .

[0007] Furthermore, the proton magnetization intensity at each moment pass: Obtain, among which, Indicates the current moment, represents the time division scale, represents the proton gyromagnetic ratio constant.

[0008] Furthermore, the pulse polarization field at each moment pass get.

[0009] Furthermore, the geomagnetic field at each moment and the pulse polarization field at each moment The combined magnetic field The Earth's magnetic field and the pulse polarization field at each moment Add to obtain.

[0010] Furthermore, the duration of the polarization field pulse The end is the final moment.

[0011] Furthermore, the polarization saturation factor pass get, Express The modulus length calculation is performed The absolute value of Express The modulus length calculation is performed The absolute value of .

[0012] Furthermore, through the polarization saturation factor By reverse reasoning, we can obtain the polarization field pulse waveform index corresponding to the optimal DC polarization pulse. , polarization field pulse intensity and the duration of the polarization field pulse Specifically: S81, polarization field pulse waveform index Set the polarization field pulse intensity to increase from 0.1 to 10 in steps of 0.1. The duration of the polarization field pulse is set to 5 mT. Set it to 20ms, draw a DC polarization pulse waveform, and take the polarization saturation factor in the drawn waveform. The corresponding waveform function index when it is 0.1° The value is taken as the polarization field pulse waveform index corresponding to the optimal DC polarization pulse ; S82, polarization field pulse intensity Set to increase from 0.05mT to 5mT in steps of 0.05mT, and the polarization field pulse waveform index Set to 3, the duration of the polarization field pulse Set it to 20ms, draw a DC polarization pulse waveform, and take the polarization saturation factor in the drawn waveform. The corresponding polarization field pulse intensity when the polarization field is 0.1° The value is taken as the polarization field pulse intensity corresponding to the optimal DC polarization pulse ; S83, duration of polarization field pulse Set to increase from 0.1ms to 20ms in steps of 0.1ms, polarization field pulse waveform index Set to 3, polarization field pulse intensity Set to 5mT, draw a DC polarization pulse waveform, and take the polarization saturation factor in the drawn waveform. The duration of the polarization field pulse corresponding to 0.1° The value is the duration of the polarization field pulse corresponding to the optimal DC polarization pulse. .

[0013] The beneficial effects of the magnetometer of the present invention are as follows: compared with the prior art, the present invention combines a polarization method of continuous radio frequency polarization excitation with a series of direct current polarization pulses to realize rapid measurement of the Overhauser magnetometer, overcomes the problem of long-term direct current polarization in traditional intermittent measurement, and utilizes the dynamic equation of the proton magnetic moment in the external magnetic field, so that the optimized direct current polarization pulse only takes a few milliseconds. The polarization method of the Overhauser magnetometer of the present invention is simple and more efficient, improves the cycle rate of the magnetometer, meets the practical application requirements of high cycle rates, and has high instrument sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The structure diagram of the Overhauser magnetometer used for rapid measurement in an embodiment of the present invention; Figure 2 This is a timing diagram of an Overhauser magnetometer used for rapid measurement in an embodiment of the present invention; Figure 3 This is a flow chart of obtaining a DC polarization pulse in an embodiment of the present invention; Figure 4 Schematic diagram of the precession process of the proton magnetic moment in an external magnetic field in an embodiment of the present invention; Figure 5 is the pulse waveform index of different polarization fields in the embodiment of the present invention , polarization field pulse intensity and the duration of the polarization field pulse Polarization saturation factor The results of the impact, where Figure (a) shows the pulse waveform index of different polarization fields Polarization saturation factor The results of the impact, Figure (b) shows the different polarization field pulse intensities Polarization saturation factor Figure 2 shows the effect of the polarization field pulses on the pulse duration. Polarization saturation factor Impact results map; Figure 6 This is a diagram of the Larmor signal obtained when the Overhauser sensor (3) is excited using an optimal DC polarization pulse in an embodiment of the present invention. DETAILED DESCRIPTION

[0015] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. 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 protection scope of the present invention.

[0016] This embodiment proposes an Overhauser magnetometer for rapid measurement, which is improved on the basis of traditional intermittent measurement. Since the longitudinal relaxation time of hydrogen protons in the Overhauser magnetometer sensor is long, the required polarization time is usually in the second level, which limits the cycle time of the magnetometer. In order to increase the cycle rate of the Overhauser magnetometer, the present invention uses a short-time DC polarization pulse of millisecond level to replace the long-time DC polarization pulse in the intermittent measurement, thereby realizing the rapid measurement of the Overhauser magnetometer.

[0017] The structure of the Overhauser magnetometer is shown in the figure below. Figure 1 As shown, it includes a radio frequency polarization circuit 1, a DC polarization circuit 2, an Overhauser sensor 3, a signal conditioning circuit 4, a shaping circuit 5, a detection circuit 6, an FPGA 7 and an embedded controller 8.

[0018] The input end of the Overhauser sensor 3 is connected to the RF polarization circuit 1 and the DC polarization circuit 2, the output end of the Overhauser sensor 3 is connected to the signal conditioning circuit 4, the output end of the signal conditioning circuit 4 is connected to the shaping circuit 5 and the detection circuit 6, the output end of the shaping circuit 5 is connected to the FPGA 7, the output end of the detection circuit 6 is connected to the embedded controller 8, the FPGA 7 and the embedded controller 8 are interconnected, and the output end of the FPGA 7 is connected to the RF polarization circuit 1 and the DC polarization circuit 2.

[0019] The functions of each device are as follows: the RF polarization circuit 1 is used to generate a stable RF polarization signal, the DC polarization circuit 2 is used to generate a DC polarization signal, the Overhauser sensor 3 is used to generate and receive the Larmor signal, the signal conditioning circuit 4 is used to amplify and filter the signal, the detection circuit 5 is used to detect the signal envelope, the shaping circuit 6 is used to shape the signal into a square wave signal, the FPGA 7 is used to control the polarization signal and perform digital frequency calculation on the square wave signal, and the embedded controller 8 is used to receive the digital frequency result to calculate the magnetic field value, and receive the envelope signal as a signal quality evaluation and control the FPGA timing.

[0020] The timing diagram of the Overhauser magnetometer for rapid measurement provided by the present invention is as follows: Figure 2 As shown, during the polarization and reception process, the RF polarization field is always turned on; each measurement cycle T Before starting to receive time, use a short time The DC polarization pulse is polarized, and then the Larmor signal is received, where the receiving time is T r .

[0021] The DC polarization circuit 2 uses a DC polarization pulse to excite the Overhauser sensor 3, such as Figure 3 As shown, the method for determining the DC polarization pulse is specifically as follows: S1. Establishing proton magnetization The Larmor precession dynamic equation in the external magnetic field, and the Larmor precession dynamic equation is differentiated to obtain the proton magnetization intensity at each moment ; like Figure 4 As shown in the figure, it is a schematic diagram of the proton magnetic moment precession process in an external magnetic field, where: is the pulse polarization field, is the Earth's magnetic field, is the combined magnetic field of the geomagnetic field and the pulse polarization field, Represents the proton magnetization The combined magnetic field of the Earth's magnetic field and the pulsed polarization field The angle of Represents the proton magnetic moment around the combined magnetic field The precession radius can be deduced based on the relationship in the figure: (1); Proton magnetization The modulus of the time rate of change and the Larmor precession frequency The expression of the relationship is: (2); Larmor precession frequency Combined magnetic field The relationship satisfies: (3); in, represents the proton gyromagnetic ratio constant, because the proton magnetization The direction of motion of the endpoint is perpendicular to the magnetic field Proton magnetization , further, formula (2) can be written in vector form as follows: = (4); Substituting formula (1) and formula (3) into formula (4), we get: (5); Furthermore, in order to study the combined magnetic field Proton magnetization The influence of the endpoint motion trajectory and the analysis of the proton magnetization intensity Trajectory, using the differential method, when the time division scale When the differential form is very small, the formula (5) is written in differential form, and then we have: (6); Furthermore, formula (5) can be expressed as: (7); According to formula (7), as long as the time division scale Set it small enough. The proton magnetization at time The value of and and time The combined magnetic field Decide.

[0022] S2. Calculate the pulse polarization field at each moment , the pulse polarization field at each moment pass: (8); Obtain, among which is the polarization field pulse waveform index corresponding to the DC polarization pulse, is the duration of the polarization field pulse, is the polarization field pulse intensity.

[0023] S3. Calculate the geomagnetic field and pulse polarization field at each moment The combined magnetic field , the geomagnetic field at each moment and the pulse polarization field at each moment The combined magnetic field The Earth's magnetic field and the pulse polarization field at each moment Add to obtain.

[0024] S4, using polarization saturation factor Characterizing the proton magnetization at the final moment The combined magnetic field of the geomagnetic field and the pulse polarization field at the final moment Angle, establish the deflection efficiency evaluation system, the polarization saturation factor pass Obtain the duration of the polarization field pulse The end is the final moment.

[0025] S5, through the polarization saturation factor By reverse reasoning, we can obtain the polarization field pulse waveform index corresponding to the optimal DC polarization pulse. , polarization field pulse intensity and the duration of the polarization field pulse , specifically: S1, polarization field pulse waveform index Set the polarization field pulse intensity to increase from 0.1 to 10 in steps of 0.1. The duration of the polarization field pulse is set to 5 mT. Set it to 20ms, draw a DC polarization pulse waveform, and take the polarization saturation factor in the drawn waveform. The polarization field pulse waveform index corresponding to 0.1° The value is taken as the waveform function index corresponding to the optimal DC polarization pulse ; S2, polarization field pulse intensity Set to increase from 0.05mT to 5mT in steps of 0.05mT, and the polarization field pulse waveform index Set to 3, the duration of the polarization field pulse Set it to 20ms, draw a DC polarization pulse waveform, and take the polarization saturation factor in the drawn waveform. The corresponding polarization field pulse intensity when the polarization field is 0.1° The value is taken as the polarization field pulse intensity corresponding to the optimal DC polarization pulse ; S3, duration of polarization field pulse Set to increase from 0.1ms to 20ms in steps of 0.1ms, polarization field pulse waveform index Set to 3, polarization field pulse intensity Set to 5mT, draw a DC polarization pulse waveform, and take the polarization saturation factor in the drawn waveform. The duration of the polarization field pulse corresponding to 0.1° The value is the duration of the polarization field pulse corresponding to the optimal DC polarization pulse. .

[0026] In this embodiment, by observing Figure 5 Different waveform function indices shown , polarization field pulse intensity and the duration of the polarization field pulse Polarization saturation factor The result diagram of the impact, the polarization field pulse waveform index is finally used 3. Polarization field pulse intensity is 3mT and the duration of the polarization field pulse The optimal DC polarization pulse is 3ms. Figure 6 It can be seen that the DC polarization pulse has a good deflection effect, the overall Larmor signal level is stable, and the signal-to-noise ratio is high.

Claims

1. An Overhauser magnetometer for rapid measurement, the Overhauser magnetometer comprising a radio frequency polarization circuit (1), a direct current polarization circuit (2), an Overhauser sensor (3), a signal conditioning circuit (4), a shaping circuit (5), a detection circuit (6), an FPGA (7) and an embedded controller (8), characterized in that: The DC polarization circuit (2) uses a DC polarization pulse to excite the Overhauser sensor (3).

2. The Overhauser magnetometer for rapid measurement according to claim 1, characterized in that: The method for determining the DC polarization pulse is specifically as follows: S1. Establishing proton magnetization The Larmor precession dynamic equation in the external magnetic field, and the Larmor precession dynamic equation is differentiated to obtain the proton magnetization intensity at each moment ; S2. Calculate the pulse polarization field at each moment ; S3. Calculate the geomagnetic field and pulse polarization field at each moment The combined magnetic field ; S4, using polarization saturation factor Characterizing the proton magnetization at the final moment The combined magnetic field of the geomagnetic field and the pulse polarization field at the final moment Angle of deflection efficiency evaluation system is established; S5, through the polarization saturation factor By reverse reasoning, we can obtain the polarization field pulse waveform index corresponding to the optimal DC polarization pulse. , polarization field pulse intensity and the duration of the polarization field pulse .

3. The Overhauser magnetometer for rapid measurement according to claim 2, characterized in that: The proton magnetization intensity at each moment pass: Obtain, among which, Indicates the current moment, represents the time division scale, represents the proton gyromagnetic ratio constant.

4. The Overhauser magnetometer for rapid measurement according to claim 3, characterized in that: The pulse polarization field at each moment pass get.

5. The Overhauser magnetometer for rapid measurement according to claim 4, characterized in that: The geomagnetic field and pulse polarization field at every moment The combined magnetic field The Earth's magnetic field and the pulse polarization field at each moment Add to obtain.

6. The Overhauser magnetometer for rapid measurement according to claim 5, characterized in that: Duration of the polarization field pulse The end is the final moment.

7. The Overhauser magnetometer for rapid measurement according to claim 6, characterized in that: The polarization saturation factor pass get, Express The modulus length calculation is performed The absolute value of Express The modulus length calculation is performed The absolute value of .

8. The Overhauser magnetometer for rapid measurement according to claim 7, characterized in that: Polarization saturation factor By reverse reasoning, we can obtain the polarization field pulse waveform index corresponding to the optimal DC polarization pulse. , polarization field pulse intensity and the duration of the polarization field pulse Specifically: S81, polarization field pulse waveform index Set the polarization field pulse intensity to increase from 0.1 to 10 in steps of 0.

1. The duration of the polarization field pulse is set to 5 mT. Set it to 20ms, draw a DC polarization pulse waveform, and in the drawn waveform, take the polarization saturation factor The corresponding waveform function index when it is 0.1° The value is taken as the polarization field pulse waveform index corresponding to the optimal DC polarization pulse ; S82, polarization field pulse intensity Set to increase from 0.05mT to 5mT in steps of 0.05mT, and the polarization field pulse waveform index Set to 3, the duration of the polarization field pulse Set it to 20ms, draw a DC polarization pulse waveform, and in the drawn waveform, take the polarization saturation factor The corresponding polarization field pulse intensity when the polarization field is 0.1° The value is taken as the polarization field pulse intensity corresponding to the optimal DC polarization pulse ; S83, duration of polarization field pulse Set to increase from 0.1ms to 20ms in steps of 0.1ms, polarization field pulse waveform index Set to 3, polarization field pulse intensity Set to 5mT, draw a DC polarization pulse waveform, and take the polarization saturation factor in the drawn waveform. The duration of the polarization field pulse corresponding to 0.1° The value is the duration of the polarization field pulse corresponding to the optimal DC polarization pulse. .

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