A magnetic probe measurement system for plasma three-dimensional magnetic reconnection research

Abstract

The application discloses a magnetic probe measurement system for three-dimensional magnetic reconnection research of plasma, which comprises a high-resolution magnetic probe array, a filtering circuit, an integration circuit, an amplification circuit, an acquisition card, a data storage unit and an upper computer. The high-resolution magnetic probe array is used for sensing the magnetic field change in the three-dimensional magnetic reconnection area and acquiring an induced voltage signal. The induced voltage signal is transmitted to the filtering circuit to extract a low-frequency dipole field signal, a high-frequency interplanetary magnetic field signal and a magnetic reconnection signal. The low-frequency dipole field signal, the high-frequency interplanetary magnetic field signal and the magnetic reconnection signal are restored by the integration circuit, amplified by the amplification circuit, collected by the acquisition card in real time and stored in the data storage unit. The upper computer restores and corrects the magnetic field data to restore the change process of the magnetic field in the area and the fluctuation of the magnetic field. The application can measure the change of the magnetic field in the magnetic reconnection area and achieves good time resolution and spatial resolution.

Description

Technical Field

[0001] This invention belongs to the field of plasma physics experimental diagnostics and relates to a magnetic probe measurement system for plasma three-dimensional magnetic reconnection research. Background Technology

[0002] Plasma, known as the "fourth state of matter," is the fourth form of matter, distinct from solids, liquids, and gases. Plasma is ubiquitous in outer space, from the Earth's magnetosphere to the surface of the sun; this vast expanse is filled with sparse plasma. In the realm of plasma, the magnetic field is one of the most important physical quantities. Magnetic fields can form strongly coupled systems with plasma and interact with it. For example, magnetic pressure can exert magnetic stress on plasma, causing adjacent regions within the plasma to interact, forming phenomena such as plasma flow and shock waves; and magnetic eddy currents can cause electric currents to flow around the magnetic field, thereby altering the plasma's motion and the local magnetic field distribution.

[0003] Magnetic reconnection is a crucial process in Earth's magnetospheric activity, referring to the breakage and reconnection of magnetic field lines between two dissimilar magnetic fields, altering their topology. This reconnection often occurs when the Earth's magnetosphere interacts with the interplanetary magnetic field carried by the solar wind. A significant phenomenon in Earth's magnetospheric activity is the subburst, in which the interplanetary magnetic field, carried by the solar wind in its north-south components, undergoes asymmetrical magnetic reconnection with Earth's north-south magnetic field at the Earth's solar magnetopause. During this reconnection, a large amount of magnetic energy stored in the magnetic field is released, injecting energy into the plasma. This process accelerates electrons and ions in the space plasma, generating high-speed plasma flows that increase plasma density and temperature. This magnetic reconnection process plays a vital role in Earth's magnetospheric activity. It not only releases enormous amounts of energy but also transfers energy to Earth's ionosphere. These high-speed plasma flows influence the movement and structure of the ionosphere, including its density distribution, current systems, and auroral generation.

[0004] To study the aforementioned physical processes, a common practice is to simulate the space environment on the ground for repeatable experiments. Many countries have established ground-based space environment simulation facilities, such as the CTX facility at Columbia University's Plasma Laboratory, the LDX facility at MIT, and the RT-1 facility at the University of Tokyo. Harbin Institute of Technology has also designed and built a ground-based space environment simulation facility, whose subsystem, the Near-Earth Space Plasma Environment Simulation System, aims to construct a near-Earth space plasma simulation environment on the ground. This device uses magnetosheath coils and dipole field coils to simulate the interplanetary magnetic field and the Earth's dipole magnetic field induced by solar wind plasma, respectively. During the experiment, a low-frequency magnetic field is first generated by the dipole field coils to simulate the Earth's magnetosphere. During the plateau period of this magnetic field, a high-frequency magnetic field is generated by the discharge of the magnetosheath coils to simulate the interplanetary magnetic field induced by the solar wind. The interplanetary magnetic field triggers a higher-frequency magnetic reconnection process by compressing the dipole field. However, due to the strong dipole field signal, the high-frequency magnetic field signal will be submerged in the dipole field signal, making it impossible to obtain the dipole magnetic field, interplanetary magnetic field, and magnetic reconnection process magnetic field at the same time. Using a single probe cannot meet the needs of diagnosing magnetic fields in larger areas, and the accuracy of diagnosing magnetic reconnection process magnetic fields needs to be improved, which will bring diagnostic difficulties to physical experiments. Summary of the Invention

[0005] The purpose of this invention is to provide a magnetic probe measurement system for three-dimensional magnetic reconnection research in plasma. This system can accurately reproduce the fluctuations of the magnetic field in the region during the three-dimensional magnetic reconnection process of a near-Earth space plasma simulation system at the Earth's magnetic apex. It can also effectively separate the magnetic field signals of the dipole coil, the magnetic sheath coil, and the magnetic reconnection process for physical experimental research, achieving good temporal and spatial resolution.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A magnetic probe measurement system for three-dimensional magnetic reconnection research in plasma includes a high-resolution magnetic probe array, a filtering circuit, an integrating circuit, an amplifying circuit, a data acquisition card, a data storage unit, and a host computer, wherein:

[0008] The high-resolution magnetic probe array consists of several parallel magnetic probes with high temporal and spatial resolution to meet the diagnostic needs of the magnetic reconnection experimental area. In order to achieve good spatial resolution, each magnetic probe is composed of 3N (N≧1) small magnetic probes, and every 3 small magnetic probes form a group to measure the magnetic field in the X, Y, and Z directions respectively. It is responsible for real-time and accurate sensing of the three-dimensional magnetic field distribution and changes, and obtaining the induced voltage signal.

[0009] The filtering circuit includes a high-pass filter circuit and a low-pass filter circuit. The induced voltage signal collected by the high-resolution magnetic probe array is split into two and output to the high-pass filter circuit and the low-pass filter circuit respectively. The high-pass filter circuit extracts the high-frequency interplanetary magnetic field signal and magnetic reconnection signal through circuit filtering, and the low-pass filter circuit extracts the low-frequency dipole field signal through circuit filtering.

[0010] The integrating circuit includes an integrating circuit for a low-pass filter circuit and an integrating circuit for a high-pass filter circuit. The integrating circuit for the low-pass filter circuit is responsible for integrating and restoring the low-frequency dipole field signal extracted by the low-pass filter circuit, and the integrating circuit for the high-frequency interplanetary magnetic field signal and magnetic reconnection signal extracted by the high-pass filter circuit is responsible for integrating and restoring the high-frequency interplanetary magnetic field signal and magnetic reconnection signal extracted by the high-pass filter circuit.

[0011] The amplification circuit includes a low-pass filter circuit and a high-pass filter circuit. The low-pass filter circuit is responsible for amplifying the integrated low-frequency dipole field signal so that the intensity of the low-frequency dipole field signal reaches the measurement range of the data acquisition card. The high-pass filter circuit is responsible for amplifying the integrated high-frequency interplanetary magnetic field signal and magnetic reconnection signal so that the intensity of the high-frequency interplanetary magnetic field signal and magnetic reconnection signal reaches the measurement range of the data acquisition card.

[0012] The acquisition card is responsible for acquiring data from the low-frequency dipole field signal, high-frequency interplanetary magnetic field signal, and magnetic reconnection signal after they have been amplified by the amplifier circuit, and converting the analog signals into digital signals.

[0013] The data storage unit is responsible for storing the magnetic field data collected by the acquisition card;

[0014] The host computer is responsible for restoring and correcting the magnetic field data stored in the data storage unit, restoring the change process and fluctuation of the magnetic field in the region.

[0015] A method for studying three-dimensional magnetic reconnection in plasma using the aforementioned magnetic probe measurement system includes the following steps:

[0016] Step 1: Sensing the magnetic field changes in the three-dimensional magnetic reconnection region using a high-resolution magnetic probe array and acquiring the induced voltage signal;

[0017] Step 2: The induced voltage signal is transmitted to the low-pass filter circuit and the high-pass filter circuit respectively. The low-frequency dipole field signal, the high-frequency interplanetary magnetic field signal and the magnetic reconnection signal are extracted by the circuit filtering.

[0018] Step 3: The low-frequency dipole field signal, high-frequency interplanetary magnetic field signal, and magnetic reconnection signal extracted by the filtering circuit are restored by the integrating circuit and amplified by the amplifying circuit. They are then acquired in real time by the acquisition card and stored in the data storage unit.

[0019] Step 4: The host computer restores and corrects the magnetic field data, restoring the process of magnetic field changes and fluctuations within the region.

[0020] In this invention, multiple magnetic probes are used to sense changes in the magnetic field in a three-dimensional magnetic reconnection region and acquire induced voltage signals. These signals are then transmitted to two parallel low-pass and high-pass filter circuits. The filter circuits extract low-frequency dipole field signals and high-frequency interplanetary magnetic field signals, as well as signals generated during the magnetic reconnection process. Based on Faraday's principle of electromagnetic induction, the signals obtained by the magnetic probes are differential signals. Two different integrator and amplification circuits are designed for different frequencies. The processed signals are acquired in real-time by a data acquisition card and then stored in a dedicated server. Finally, the magnetic field signals are processed and corrected using software. By establishing a model and actually measuring the specific parameters of each channel, the signals are corrected, and the true three-dimensional magnetic field is calculated. The interplanetary magnetic field signal and the magnetic reconnection signal extracted by the high-pass filter circuit are then separated again. These two signals are extracted to obtain independent dipole field signals, interplanetary magnetic field signals, and magnetic reconnection signals for use in physical experimental research.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. This invention can measure the changes in the magnetic field in the magnetic reconnection region and achieve good temporal and spatial resolution. It is sensitive, real-time, and accurate, and can meet the needs of near-Earth space plasma magnetic field reconnection experiments.

[0023] 2. In current traditional diagnostic methods, high-frequency and low-frequency signals are coupled together with significant amplitude differences. The high-frequency signal is submerged in the low-frequency dipole field signal, causing difficulties in diagnosis and physical process analysis. Simply relying on software separation can lead to significant interference, affecting diagnostic accuracy. Therefore, this invention, based on specific experimental requirements, implements a hardware and software coordinated system and method for separating dipole field signals, interplanetary magnetic field signals, and magnetic reconnection signals. This system can separate and extract these three different but interconnected magnetic field signals, improving the signal-to-noise ratio, reducing electromagnetic interference, and effectively reconstructing the magnetic field fluctuation process within the experimental region. It offers advantages such as fast response, accurate measurement, and good real-time performance. Attached Figure Description

[0024] Figure 1 This is a framework diagram of a magnetic probe measurement system used for three-dimensional magnetic reconnection studies in plasma. 1 represents the magnetic sheath coil; 2 represents the interplanetary magnetic field lines; 3 represents the plasma; 4 represents the magnetic reconnection region; 5 represents the geomagnetic field lines; and 6 represents the dipole field coil.

[0025] Figure 2This diagram illustrates the physical process of three-dimensional magnetic reconnection at the Earth's magnetic apex, simulated in a near-Earth space plasma simulation environment using a ground-based space environment simulation device. 1 represents the magnetic probe array; 2 represents the low-pass filter circuit; 3 represents the high-pass filter circuit; 4 represents the integrating circuit of the low-pass filter circuit; 5 represents the integrating circuit of the high-pass filter circuit; 6 represents the amplification circuit of the low-pass filter circuit; 7 represents the amplification circuit of the high-pass filter circuit; 8 represents the data acquisition card; 9 represents the data storage unit; and 10 represents the data post-processing. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0027] First, the conditions for magnetic reconnection to occur are established, by... Figure 1 As shown, the magnetosheath coil and dipole field coil in the near-Earth space plasma simulation system are moved so that they are 3m apart. During the experiment, the dipole field coil and ECR plasma source are first discharged to generate a low-frequency simulated Earth magnetosphere. During the plateau period of the dipole field, the magnetosheath coil is triggered to discharge to generate simulated high-frequency solar wind and intergalactic magnetic fields. The simulated solar wind moves towards the simulated Earth magnetic field under the influence of its own thermal pressure and the magnetic pressure of the interplanetary magnetic field, squeezing the simulated Earth magnetic field and triggering a higher-frequency magnetic reconnection at the magnetic apex of the simulated Earth magnetosphere.

[0028] like Figure 2 As shown, during the magnetic reconnection process, characteristic changes in the magnetic field are generated within the reconnection region. The spacing between each magnetic probe is set to 2 mm, less than the inertial length of an electron, to achieve good spatial resolution. Testing revealed a frequency response of 1 MHz, greater than the ion cyclotron frequency, achieving good temporal resolution.

[0029] High-resolution magnetic probe arrays need to meet the diagnostic requirements of magnetic reconnection experimental regions, requiring an array of multiple magnetic probes to achieve this. Taking eight probes as an example, the high-resolution magnetic probe array consists of eight parallel magnetic probes, each spaced 60 mm apart, for a total length of 480 mm, covering the plasma magnetic reconnection region. To achieve good spatial resolution, each magnetic probe needs to be composed of multiple smaller magnetic probes; taking 30 smaller probes as an example, three probes are grouped together to measure the magnetic field in the X, Y, and Z directions, respectively, responsible for accurately sensing the three-dimensional magnetic field distribution and changes in real time, and acquiring the induced voltage signal.

[0030] When the magnetic flux through the magnetic probe coil changes, the expression for the induced electromotive force ε generated in a single coil is as follows:

[0031]

[0032] In the formula, ε is the induced electromotive force generated by a single magnetic probe; Δt is the infinitesimal change in magnetic flux passing through the magnetic probe; Δt is the infinitesimal change in time.

[0033] When calculating the magnetic flux through the coil, since the effective area of ​​a single magnetic probe is small and the time resolution is relatively high, the magnetic field within the enclosed region can be approximated as uniform. Therefore, the magnetic induction intensity within the enclosed region of each magnetic probe coil can be represented by the magnetic induction intensity B at the center point. ce To represent this, the calculation yields the following expression:

[0034]

[0035] Therefore, it can be obtained

[0036]

[0037] In the formula, S is the area of ​​the region enclosed by the coil; θ is the normal vector of plane S and the magnetic induction intensity B at the center point. ce The angle between them.

[0038] The changes in the magnetic field within a line range are constructed by the sensing signals of 10 sets of three-dimensional probes contained on a single magnetic probe. Then, the magnetic field fluctuations in the magnetic reconnection region can be reconstructed by a high-resolution magnetic probe array composed of 8 magnetic probes.

[0039] In actual physics experiments, the dipole field signal has a high amplitude, while the high-frequency interplanetary magnetic field and the magnetic field and amplitude of the magnetic reconnection process are low. Therefore, the high-frequency signal is easily submerged in the low-frequency dipole field signal, causing problems for experimental research. This invention designs a filtering circuit that separates the low-frequency and high-frequency magnetic fields. This structure can effectively extract the useful signal and filter out the intermediate-frequency interference signal, achieving a high signal-to-noise ratio. Therefore, it is necessary to estimate the frequency of the magnetic field of interest. First, theoretical estimation and modeling are performed, and the frequency of the dipole field signal is calculated to be 400 Hz, the interplanetary magnetic field signal to be 10 kHz, and the magnetic field frequency during the magnetic reconnection process to be 20 kHz.

[0040] This invention employs a passive LC low-pass filter circuit and a passive LC high-pass filter circuit. The inductance L of the low-pass filter circuit is set to 100mH and the capacitance C to 1.5μF; the inductance L of the high-pass filter circuit is set to 10mH and the capacitance C to 27nF. The signal sensed by each magnetic probe in the high-resolution magnetic probe array is split into two, and transmitted to the low-pass filter circuit and the high-pass filter circuit respectively for magnetic field extraction and filtering. Since the frequencies of the high-frequency magnetic field and the low-frequency magnetic field differ significantly, this filtering method is effective and reliable, and it can filter out intermediate frequency interference caused by transmission line effects, thus greatly enhancing the signal-to-noise ratio.

[0041] The filtered differential signal passes through the integrator circuits of both the passive low-pass filter and the high-pass filter. This invention employs a method to correct the incomplete integration of the integrator circuits of the passive low-pass filter and the high-pass filter, transforming the incomplete integration into a complete integration:

[0042]

[0043] In the formula, V out The output signal is the result of the integrator circuit after passing through the passive low-pass filter circuit and the integrator circuit after passing through the high-pass filter circuit; V ideal The incomplete integration is converted into the fully integrated output signal; RC is the time constant of the integrator circuit of the passive low-pass filter circuit and the integrator circuit of the high-pass filter circuit.

[0044] Because high-frequency and low-frequency signals have different frequencies, the requirements for the time constant RC of the integrator circuit are also different. The time constant RC designed for the low-pass filter circuit is 5ms, while the time constant RC designed for the high-pass filter circuit is 0.5ms, so as to prevent stray capacitance and stray inductance from affecting the time resolution of the system and causing distortion of the signal output by the integrator circuit.

[0045] The signal is amplified using an active low-pass filter and a high-pass filter amplification circuit. The low-pass filter amplifies the signal by 220 times, and the high-pass filter amplifies it by 55 times. The amplified signal is then acquired by a data acquisition card, converting the analog signal to a digital signal. This requires 480 independent acquisition channels to simultaneously acquire data from all points on the high-resolution magnetic probe array. The acquired signal is then stored in a data storage unit. The host computer retrieves the stored data and processes it in real time using software. The processing flow is as follows:

[0046] (1) Obtain the transfer function H1 of the magnetic probe circuit. First, model the magnetic probe circuit to obtain the simulation model of the magnetic probe circuit; use an LCR meter to measure the electrical parameters of each magnetic probe, and input the measured parameters of each magnetic probe into the simulation model of the magnetic probe circuit to obtain the transfer function H1.

[0047] (2) Obtain the transfer function H2 of the transmission line circuit, establish a model of the long transmission line, measure the electrical parameters of the transmission line circuit, and obtain the electrical transfer function H2 of the long transmission line.

[0048] (3) The measured low-frequency dipole field signal, high-frequency interplanetary magnetic field signal, and magnetic reconnection signal are corrected by a passive integrator circuit. The incomplete integration effect of the passive integrator circuit is corrected to convert the incomplete integration into a complete integration.

[0049] (4) Perform a Fourier transform on the signal after incomplete integration correction to transform the signal from the time domain to the frequency domain, obtaining the frequency domain signal V. FFT V FFT =FFT(V ideal Then, multiplying this by the transfer functions of the magnetic probe circuit and the long transmission line circuit corrects for the signal amplitude and phase shifts caused by the stray area of ​​the magnetic probe circuit and the long transmission line effect, resulting in the corrected signal V. correct V correct =V FFT *H1*H2.

[0050] (5) Based on the effective area NS value of each magnetic probe calibrated in the calibration experiment, the actual magnetic field signal amplitude B is deduced from the induced magnetic field signal.

[0051] (6) The three-dimensional magnetic field signal in space can be inverted from the data of the three-dimensional magnetic fields in X, Y, and Z. That is, for a point in space, the direction and amplitude of the magnetic field in the three directions of X, Y, and Z are obtained. A three-dimensional rectangular coordinate system can be established from this. The three-dimensional magnetic field in space can be inverted by the vector sum of the magnetic fields in the three directions. For example, if the magnetic field magnitude measured in the X direction is 50G and the direction is +X; if the magnetic field magnitude measured in the Y direction is 60G and the direction is -Y; if the magnetic field magnitude measured in the Z direction is 70G and the direction is +Z, then the magnetic field in space can be expressed in the form of a vector sum as (50, -60, 70).

Claims

1. A magnetic probe measurement system for three-dimensional magnetic reconnection research in plasma, characterized in that... The magnetic probe measurement system includes a high-resolution magnetic probe array, a filtering circuit, an integrating circuit, an amplifying circuit, a data acquisition card, a data storage unit, and a host computer, wherein: The high-resolution magnetic probe array consists of several parallel magnetic probes with high temporal and spatial resolution, which are responsible for sensing the distribution and changes of the three-dimensional magnetic field in real time and obtaining the induced voltage signal. The filtering circuit includes a high-pass filter circuit and a low-pass filter circuit. The induced voltage signal collected by the high-resolution magnetic probe array is split into two and output to the high-pass filter circuit and the low-pass filter circuit respectively. The high-pass filter circuit extracts the high-frequency interplanetary magnetic field signal and magnetic reconnection signal through circuit filtering, and the low-pass filter circuit extracts the low-frequency dipole field signal through circuit filtering. The integrating circuit includes an integrating circuit for a low-pass filter circuit and an integrating circuit for a high-pass filter circuit. The integrating circuit for the low-pass filter circuit is responsible for integrating and restoring the low-frequency dipole field signal extracted by the low-pass filter circuit, and the integrating circuit for the high-frequency interplanetary magnetic field signal and magnetic reconnection signal extracted by the high-pass filter circuit is responsible for integrating and restoring the high-frequency interplanetary magnetic field signal and magnetic reconnection signal extracted by the high-pass filter circuit. The amplification circuit includes a low-pass filter circuit and a high-pass filter circuit. The low-pass filter circuit is responsible for amplifying the integrated low-frequency dipole field signal so that the intensity of the low-frequency dipole field signal reaches the measurement range of the data acquisition card. The high-pass filter circuit is responsible for amplifying the integrated high-frequency interplanetary magnetic field signal and magnetic reconnection signal so that the intensity of the high-frequency interplanetary magnetic field signal and magnetic reconnection signal reaches the measurement range of the data acquisition card. The acquisition card is responsible for acquiring data from the low-frequency dipole field signal, high-frequency interplanetary magnetic field signal, and magnetic reconnection signal after they have been amplified by the amplifier circuit, and converting the analog signals into digital signals. The data storage unit is responsible for storing the magnetic field data collected by the acquisition card; The host computer is responsible for restoring and correcting the magnetic field data stored in the data storage unit, restoring the change process and fluctuation of the magnetic field in the region.

2. The magnetic probe measurement system for three-dimensional magnetic reconnection research in plasma according to claim 1, characterized in that... The magnetic probe consists of 3N small magnetic probes, where N≧1. Each group of three small magnetic probes measures the magnetic field in the X, Y, and Z directions.

3. The magnetic probe measurement system for three-dimensional magnetic reconnection research in plasma according to claim 1, characterized in that... In the integrator circuits of the low-pass filter circuit and the high-pass filter circuit, the following incomplete integration correction method is used to convert the incomplete integration into a complete integration: In the formula, V out The output signal is the result of the integrator circuit after passing through the passive low-pass filter circuit and the integrator circuit after passing through the high-pass filter circuit; V ideal To convert the incomplete integration into the fully integrated output signal; RC is the time constant of the integrator circuit of the passive low-pass filter circuit and the integrator circuit of the high-pass filter circuit.

4. A method for conducting three-dimensional magnetic reconnection studies of plasma using the magnetic probe measurement system according to any one of claims 1-3, characterized in that... The method includes the following steps: Step 1: Sensing the magnetic field changes in the three-dimensional magnetic reconnection region using a high-resolution magnetic probe array and acquiring the induced voltage signal; Step 2: The induced voltage signal is transmitted to the low-pass filter circuit and the high-pass filter circuit respectively. The low-frequency dipole field signal, the high-frequency interplanetary magnetic field signal and the magnetic reconnection signal are extracted by the circuit filtering. Step 3: The low-frequency dipole field signal, high-frequency interplanetary magnetic field signal, and magnetic reconnection signal extracted by the filtering circuit are restored by the integrating circuit and amplified by the amplifying circuit. They are then acquired in real time by the acquisition card and stored in the data storage unit. Step 4: The host computer restores and corrects the magnetic field data, restoring the process of magnetic field changes and fluctuations within the region.

5. The method for studying three-dimensional magnetic reconnection in plasma according to claim 4, characterized in that... The specific steps of step four are as follows: (1) Obtain the transfer function H1 of the magnetic probe circuit: First, model the magnetic probe circuit to obtain the simulation model of the magnetic probe circuit; use an LCR meter to measure the electrical parameters of each magnetic probe, and input the measured parameters of each magnetic probe into the simulation model of the magnetic probe circuit to obtain the transfer function H1. (2) Obtain the transfer function H2 of the transmission line circuit: Establish a model of the long transmission line, measure the electrical parameters of the transmission line circuit, and obtain the electrical transfer function H2 of the long transmission line; (3) The measured low-frequency dipole field signal, high-frequency interplanetary magnetic field signal, and magnetic reconnection signal are corrected by a passive integrator circuit. The incomplete integration effect of the passive integrator circuit is corrected to convert the incomplete integration into a complete integration. (4) Perform a Fourier transform on the signal after incomplete integration correction to transform the signal from the time domain to the frequency domain, obtaining the frequency domain signal V. FFT V FFT =FFT(V ideal The signal is transformed from the time domain to the frequency domain, and then multiplied by the transfer functions of the magnetic probe circuit and the long transmission line circuit to correct the amplitude and phase shifts caused by the stray area of ​​the magnetic probe circuit and the long transmission line effect, thus obtaining the corrected signal V. correct V correct =V FFT *H1*H2; (5) Based on the effective area NS value of each magnetic probe calibrated in the calibration experiment, the actual magnetic field signal amplitude B is deduced from the induced magnetic field signal. (6) The three-dimensional magnetic field signal in space is inverted from the data of the three-dimensional magnetic fields of X, Y and Z.

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