36 results about "Transient field" patented technology

The invention relates to a finite element analysis-based variable-element permanent magnet synchronous motor modeling method which comprises the following steps of constructing a three-dimensional finite element electromagnetic field simulation model of a permanent magnet synchronous motor, and performing transient field road coupling analysis on the three-dimensional finite element electromagnetic field simulation model to obtain a large quantity of characteristic parameters; creating an improved permanent magnet synchronous motor voltage equation and a torque equation; constructing a simulation model of the permanent magnet synchronous motor according to an improved permanent magnet synchronous motor math model; leading all the obtained characteristic parameters into corresponding ports of the simulation model to construct a finite element analysis-based variable-element permanent magnet synchronous motor dynamic simulation model. The permanent magnet synchronous motor model modeled by the method disclosed by the invention comprehensively considers the magnetic field saturation effect, the d-q axis cross coupling effect, the eddy current effect, the hysteresis effect and the like; the instantaneity is considered, and the accuracy of the permanent magnet synchronous motor model is improved; the permanent magnet synchronous motor model is particularly suitable for the research on the dynamic processes such as power failure-bepelt and three-phase sudden short circuit of the permanent magnet synchronous motor.

The invention relates to a method for calculating DC (direct current) magnetic bias dynamic leakage inductance of a transformer. The method is characterized in that: the method comprises a dynamic parameter calculation step based on a transient field-circuit coupling model, and a dynamic leakage inductance calculation step based on transient field-circuit coupling; the method can establish a three-dimensional finite element magnetic field model of the transformer and solve the model to fully reflect the accuracy of magnetic field calculation under nonlinear excitation of the transformer; and the method can calculate dynamic inductance parameters according to the energy perturbation principle, calculate a transient current by combining with four-order Range-Kuttle method, and then calculate the dynamic leakage inductance based on a T-shaped equivalent circuit of the transformer. In comparison with the existing harmonic calculation method, the method provided by the invention can calculate the dynamic leakage inductance by considering the transient changes of equivalent parameters of magnetic field and circuit of the transformer and the relationship between the parameters under different DC perturbations on the basis of field-circuit coupling. Accordingly, the method provided by the invention has higher adaptability, and higher actual application value.

The invention discloses a modeling method of a generating system of a mixed excited synchronous motor. The method comprises the following steps of: establishing a simulation model of a three-dimensional finite element electromagnetic field of the mixed excited synchronous motor; calculating the synchronous reactance value of the mixed excited synchronous motor under different excitations and different load currents according to a phase potential waveform and a vector diagram of the mixed excited synchronous motor, which are acquired through the coupling analysis of a transient field circuit; establishing a body simulation model of the mixed excited synchronous motor according to a voltage equation of the mixed excited synchronous motor; and adding an output voltage detection module, an excitation current feedback module, a load current feedback compensation calculation module and a load current detection part to form a generating system model of the mixed excited synchronous motor on a basis of the body simulation model of the mixed excited synchronous motor. The modeling method of the mixed excited synchronous electric generating system is particularly suitable for the application research of an airplane generating system and a wind generating system of a novel mixed excited synchronous motor and provides a reference for analyzing the steady-state and dynamic performance of the system and designing the parameters.

The invention relates to a prepolarizing magnetic resonance- or relaxation-based measurement system, comprising a prepolarizing coil for producing a prepolarizing field at the target zone, means for pulsing the prepolarizing field according to a first pulsing scheme, and means for measuring magnetization of a target placed in the target zone. According to the invention, the system further comprises a shielding coil for producing a shielding field and means for pulsing the shielding field according to a second pulsing scheme, whereby the shielding coil and the second pulsing scheme are arranged to reduce the formation of unwanted transient fields caused by the coupling of the prepolarizing coil to conducting or magnetic structures in the surroundings of the system. The invention also relates to a corresponding method of measurement and a process of designing the pulsing schemes for the system or process. By means of the invention, the formation of unwanted eddy currents, for example, in the surroundings of the measurement system, can be reduced.

The invention relates to a detection method which is mainly used for coal mine underground detection, in particular to a transient electromagnetic simulated earthquake detection method used for coal mine underground. According to the method, measured data are added for each detection grid, influences caused by environmental factors in a roadway are substantially weakened, the density of detection data passing abnormal bodies is enhanced, and transient field data are converted into virtual wave field data, so that the influence caused by the volume effect of the electromagnetic method is weakened; meanwhile, the advanced fine processing technology of earthquakes is adopted for the method, fine explanation of geological anomalies is facilitated, and the detection accuracy for potential mine water disaster hazards can be remarkably improved.

A method for electrical survey of hydrocarbons deposits under seabed depths up to 1500 m and equipment therefor are provided. The equipment includes a vessel, a generator, an excitation field block, connected with a vertical dipole with coax electrodes, a data registration / processing block, bottom systems with. The lower dipole electrode is situated at maximally 100 m from the seabed, the upper electrode at maximally 200 m from the surface. The operation of the generator and bottom systems is synchronized the dipole is submersed into the sea, and fed with alternating-sign rectangular current pulses, whose on-off time ratio and duration are programmably determined. The bottom systems register reflected signals and electromagnetic field components, when the dipole's current is on and off. Analysis of the signals accounts modifications of primary and secondary fields, transient field changes for determination of the environment resistivity and strata polarization characteristics thereby improving the hydrocarbons deposits prognosis.

A method of calculating far extrapolation of a transient field of electromagnetic scattering through finite difference time domain includes the steps of 1 dividing an area to be calculated into a main field area and a scattering field area according to the connecting boundary; 2 setting an extrapolation boundary in the scattering field area, and extrapolating electric fields and magnetic fields on the extrapolation boundary to obtain a far field; 3 setting transient incident waves, and sequentially updating the electric fields and the magnetic fields at each time step until the electromagnetic field distribution becomes steady; 4 writing the far field into a product of frequency factors and integral factors, and performing inverse Fourier transform on the integral factors to obtain a time domain expression; 5 setting an integral factor far field time domain response array; 6 performing Fourier transform on integral factor far field time domain response to obtain integral factor far field frequency domain response; 7 using far field and incident wave frequency domain response to obtain RCS (Radar Cross Section) changes with frequency. The method of calculating far extrapolation of the transient field of electromagnetic scattering through finite difference time domain writes the far field into the form of the product of the frequency factors and the integral factors due to the fact that the forms of frequency-time transform and time-frequency transform of the integral factors are simple, thereby simplifying the calculation and improving the efficiency.

A method for survey of hydrocarbon deposits in a researched profile of sea-bottom comprises providing a generator generating pulse electric current with a generator frequency in a towable generator line exciting electric field signals measured by sea-bottom stations synchronized with the generator, forming space-domain data arrays for the generator frequency and for higher odd harmonics frequencies nearest thereto, forming time-domain data arrays for selected offsets, inversion of the time-domain and space-domain data, and determining a bottom strata resistivity and polarization characteristics for the researched profile, based the inversion's results. The inversion preferably encompasses synchronizing and adjusting the generator line and electric field signals, dividing them into a frequency branch, including a fast Fourier transform and a robust summation producing the space-domain arrays, and a time-domain branch, including a robust summation producing the time-domain arrays. Embodiments include transient field analysis with spatial derivatives, special towing configurations, generator line types choices, etc.

A method for survey of hydrocarbon deposits in a researched profile of sea-bottom comprises providing a generator generating pulse electric current with a generator frequency in a towable generator line exciting electric field signals measured by sea-bottom stations synchronized with the generator, forming space-domain data arrays for the generator frequency and for higher odd harmonics frequencies nearest thereto, forming time-domain data arrays for selected offsets, inversion of the time-domain and space-domain data, and determining a bottom strata resistivity and polarization characteristics for the researched profile, based the inversion's results. The inversion preferably encompasses synchronizing and adjusting the generator line and electric field signals, dividing them into a frequency branch, including a fast Fourier transform and a robust summation producing the space-domain arrays, and a time-domain branch, including a robust summation producing the time-domain arrays. Embodiments include transient field analysis with spatial derivatives, special towing configurations, generator line types choices, etc.

The invention discloses a sequential coupling analysis method for an adaptive step length. The sequential coupling analysis method comprises the following steps of: (1) constructing a coupled field analysis model, setting iterative step lengths of a first sub step and a second sub step, performing first and second sub step sequential coupling analysis on each coupling state variable, and thus obtaining a coupling state variable value of an iterative node; (2) extracting the coupling state variable values of the current iterative node of each coupling state variable value and the previous two iterative node, obtaining a gradient of the current iterative node of each coupling state variable curve, setting a step length adjustment range of each coupling state variable, and thus obtaining theiterative step length of the next sub step; and (3) taking the minimum value of the iterative step length of the next sub step from all the coupling state variables as a system iterative step length of the next sub step, performing next sub step sequential coupling analysis on each coupling state variable of a transient field coupling system by adopting the iterative step length, obtaining a coupling state variable value of the iterative node of the next sub step, and returning to the step (2) until the system analysis finish time is up.

A method for electrical survey of hydrocarbons deposits under seabed depths up to 1500 m and equipment therefor are provided. The equipment includes a vessel, a generator, an excitation field block, connected with a vertical dipole with coax electrodes, a data registration / processing block, bottom systems with. The lower dipole electrode is situated at maximally 100 m from the seabed, the upper electrode at maximally 200 m from the surface. The operation of the generator and bottom systems is synchronized the dipole is submersed into the sea, and fed with alternating-sign rectangular current pulses, whose on-off time ratio and duration are programmably determined. The bottom systems register reflected signals and electromagnetic field components, when the dipole's current is on and off. Analysis of the signals accounts modifications of primary and secondary fields, transient field changes for determination of the environment resistivity and strata polarization characteristics thereby improving the hydrocarbons deposits prognosis.

The invention relates to a prepolarizing magnetic resonance- or relaxation-based measurement system, comprising a prepolarizing coil for producing a prepolarizing field at the target zone, means for pulsing the prepolarizing field according to a first pulsing scheme, and means for measuring magnetization of a target placed in the target zone. According to the invention, the system further comprises a shielding coil for producing a shielding field and means for pulsing the shielding field according to a second pulsing scheme, whereby the shielding coil and the second pulsing scheme are arranged to reduce the formation of unwanted transient fields caused by the coupling of the prepolarizing coil to conducting or magnetic structures in the surroundings of the system. The invention also relates to a corresponding method of measurement and a process of designing the pulsing schemes for the system or process. By means of the invention, the formation of unwanted eddy currents, for example, in the surroundings of the measurement system, can be reduced.

The invention discloses an electromagnetic transient simulation analysis system of an electric power system. The system can set multiple fault conditions by a fully graphical user operating mode, automatically traverse simulation fault models by taking an ATP (Array Transform Processor) as a tool, and selectively save general standard data, a verification filtering algorithm, protection principle, a ranging algorithm and a user-defined algorithm, so as to achieve multiple functions such as harmonic analysis, sequence component analysis and effective value calculation for transient data. The electromagnetic transient simulation analysis system disclosed by the invention has modular and extensible performance, can be used for single setting, process control and data transfer of mass simulation, the design and verification of the user-defined algorithm, as well as multi-angle analysis of transient data in the electromagnetic transient field.

The invention relates to electromagnetic prospecting and is used for surface and marine electromagnetic sounding by means of controllable electromagnetic field sources and is applied in a package oil and gas prospecting works for searching and outlining oil and gas fields. The inventive method is based on the selection of a response from earth materials which are secondary modified by hydrocarbons migration. The invention makes it possible to ensure a set of processing technologies enabling to layer-by-layer determine an electrical resistivity and process characteristics of a medium induced polarisation: a polarizability coefficient, a time constant and a relaxation spectrum width. The inventive method consists in carrying out a measurement by several receiving lines, wherein the position of two feeding lines of a sounding plant is substantially symmetrical with respect to the receiving lines which are located within a 30 DEG sector from the feeding line extensions, in recording a transient signal by land axial-dipole sounding devices or by marine sounding devices associated with a continuous signal recording during a ship travel and in calculating the population of interpretable parameters P1, Df, UH, Ps using recorded potential difference curves(U(i) is less than 2, and 2 is more than U(i))which are preliminary processed, contracted in the form of time gates and differentiated.

The invention discloses an electric field simulation method for a DC field of a super / ultrahigh-voltage converter station. The electric field simulation method comprises the steps of determining a keypart according to a structure of the DC field of the converter station; building simulation model of the DC field, and performing simplification to obtain a DC field simplification model; constructing a plurality of geometric models according to the DC field simplification model; obtaining a plurality of air model modules of an outer boundary rule; dividing the DC field simplification model to obtain a DC field division model; determining a corresponding relative dielectric constant and electrical conductivity according to a material of each part of the DC field, and applying to each part ofthe DC field simplification model; and obtaining electric field intensity of different moments by employing a full-period transient field calculation method. According to the electric field simulationmethod for the DC field of the super / ultrahigh-voltage converter station, disclosed by the invention, the simulation model can be simplified, and the simulation calculation efficiency is improved. The invention also discloses an electric field simulation device for the DC field of the super / ultrahigh-voltage converter station and a storage medium.

The invention discloses a method for calculating magnetic shielding frame magnetic loss under alternating-current / direct-current hybrid excitation. Under the alternating-current / direct-current hybrid excitation, the method includes: performing simulation on a smoothing reactor model by adopting a transient field and dividing a magnetic shielding frame model into multiple equivalent uniform domains according to the principle of approximately-equal magnetic flux density Bm distribution; calculating all average magnetic field intensities H in one period of the equivalent uniform domains through MagNet software; further calculating direct-current offset magnetic field intensity Hdc in the equivalent uniform domains; reestablishing the smoothing reactor model according to the divided equivalent uniform domains, giving Bm-P loss characteristic curves of the equivalent uniform domains under the corresponding direct-current offset magnetic field intensity Hdc; performing three-dimensional finite element transient simulation on the smoothing reactor model subjected to remodeling; finally calculating magnetic loss of the equivalent uniform domains, and carrying out algebraic addition on magnetic loss of the equivalent uniform domains to acquire the magnetic loss of a magnetic shielding frame. Through the use of the method, calculating amount of work and calculating time are reduced.

The invention relates to a receiving antenna and a signal processing method, belonging to the signal processing field, and specifically relates to an in-hole receiving antenna and signal processing method of a three-component time-domain electromagnetic method. The in-hole receiving antenna of the three-component time-domain electromagnetic method includes a skeleton and a frame, wherein a Z component coil which is used for receiving secondary field signals from the vertical direction is wound on the skeleton; and the frame is vertically arranged at two ends of the skeleton, and an X componentcoil or Y component coil for receiving secondary field signals from the horizontal direction is wound on the frame. The in-hole receiving antenna of the three-component time-domain electromagnetic method has the advantages that the structure is easy to feed into a drill hole for performing in-hole signal reception, thus being able to avoid external interference caused by underground electrical equipment, and at the same time the receiving antenna can receive transient field signals from three directions, thus being able to obtain more real three dimensional detection data, and preferably reflecting the three dimensional information of the detected object.

The invention discloses a calculation method and system of weak magnetic performance of a permanent magnet synchronous motor. The method comprises steps of establishing a transient field simulation model of a motor, and setting a three-phase excitation current of the model; according to a correspondence relationship of an electromagnetic torque, a stator current and a current control angle, performing parametric scanning on the current control angle, so as to obtain a torque control angle curve under a given stator current; selecting a control manner adaptive to condition of the motor for themotor according to motor rotating speed and motor type, so as to acquire an optimal current control angle meeting a constraint of the control manner under different motor rotating speeds; according toa torque control angle curve under the stator current corresponding to any optimal current control angle, acquiring an electromagnetic torque corresponding to the optimal current control angle, so asto obtain a torque-rotating speed correspondence relationship; according to the torque-rotating speed correspondence relationship, determining a highest motor rotating speed, and determining a weak magnetic expansion range of the motor according to a ratio of the highest motor rotating speed to a motor rated rotating speed. The method improves motor design efficiency.

The invention discloses a method for calculating surface field of valve hall fittings. Since the inside of a valve hall is sophisticated in alternating current and direct current and equipment operating voltage harmonic is rich in content, transient field is calculated according to potential waveform from principle analysis. However, ANSYS software is used to perform transient field calculation under the model of the valve hall, multiple hours in calculating each step is needed, calculating quantity is high, and even a high-performance computing platform is hard to realize calculation. The method for calculating the surface field of the valve hall fittings is simple in calculation, high in accuracy, high in efficiency and practicable.

The invention provides a transient field signal synchronous acquisition system. The transient field signal synchronous acquisition system comprises a plurality of sensors, a plurality of LXI conditioning acquisition equipments, a switch, a transmission medium, and a computer; the sensors are used for recording field signals; the LXI conditioning acquisition equipments are connected with the sensors, and are used for conditioning, collecting, and storing signals; the computer is connected with the switch via the transmission medium; and the switch is connected with the LXI conditioning acquisition equipments. The transient field signal synchronous acquisition system is capable of solving a problem of the prior art that signal test success rate of signal synchronous acquisition systems is not high, and avoiding sensor long distance cable laying.

The invention belongs to the technical field of electromagnetic induction, discloses a finite element analysis method of a switched reluctance motor and an external circuit thereof, determines parameters of the motor, performs electromagnetic design, and obtains a 2D / 3D model. The magnetic density profiles of the rotor with static field and 40A voltage at 0 degree, 7.5 degrees, 15 degrees and 22.5degrees were compared. The torque and rotational speed waveform is obtained by adding external circuit into the transient field. By analyzing the waveform and comparing the angular magnetic density distribution under different conditions, the external circuit design method of switched reluctance motor is as follows: through the reasonable design of some parameters of electronic components relatedto the external circuit, and then connect these electronic components to form the external circuit. The invention obtains relevant data in Ansoft Maxwell through finite element analysis and externalcircuit design of the switched reluctance motor, carries out data analysis and comparison, further optimizes and improves the design, and enables the motor to become more efficient and energy-saving.

The invention relates to a transient electromagnetic three-dimensional finite difference forward modeling method and a system thereof, the time step iterations of preset times are carried out on the initial time step, and the time steps at the other moments are controlled and determined by the apparent conductivity of the underground medium in the geoelectric model at the current moment, so that the proper time step can be obtained by self-adaptive adjustment, for a geoelectric model with high conductivity comparison, the total time iteration step number can be obviously reduced, better adaptability is achieved, the volume effect of a transient field is fully utilized, and the calculation efficiency of forward modeling is effectively improved.

The invention relates to a finite element analysis-based variable-element permanent magnet synchronous motor modeling method which comprises the following steps of constructing a three-dimensional finite element electromagnetic field simulation model of a permanent magnet synchronous motor, and performing transient field road coupling analysis on the three-dimensional finite element electromagnetic field simulation model to obtain a large quantity of characteristic parameters; creating an improved permanent magnet synchronous motor voltage equation and a torque equation; constructing a simulation model of the permanent magnet synchronous motor according to an improved permanent magnet synchronous motor math model; leading all the obtained characteristic parameters into corresponding ports of the simulation model to construct a finite element analysis-based variable-element permanent magnet synchronous motor dynamic simulation model. The permanent magnet synchronous motor model modeled by the method disclosed by the invention comprehensively considers the magnetic field saturation effect, the d-q axis cross coupling effect, the eddy current effect, the hysteresis effect and the like; the instantaneity is considered, and the accuracy of the permanent magnet synchronous motor model is improved; the permanent magnet synchronous motor model is particularly suitable for the research on the dynamic processes such as power failure-bepelt and three-phase sudden short circuit of the permanent magnet synchronous motor.

The invention belongs to the field of novel motor transient electromagnet field analysis and design, and discloses a brushless doubly-feed motor transient field simulation analysis system and method.A brushless doubly-feed motor model is established by using Ansoft; a brushless doubly-feed motor finite element is analyzed; and the brushless doubly-feed motor is subjected to comparative analysis.Brushless doubly-feed motor finite element analysis comprises subdivision, magnetic density, magnetic field line and air gap magnetic density distribution, potential and current winding induction, winding magnetic chain and electromagnetic torquing. According to the brushless doubly-feed motor, brushes and slip rings are omitted, reliability is improved, and the cost is reduced. The connection mode and frequency of the control winding are changed, and excellent starting performance and efficient operation performance are achieved.

The invention discloses an experimental device based on an electrostatic discharge transient field intensity measurement system. An electrostatic discharge transient field intensity measurement systemand an experimental device are included. The electrostatic discharge transient field intensity measurement system is composed of a transient electrostatic field intensity sensor, a high-frequency signal processor, an amplifier and a data acquisition unit. The experimental device comprises an experimental device for calibrating the electrostatic discharge transient field intensity measurement system and a measurement experimental device for measuring the electrostatic discharge field intensity through the electrostatic discharge transient field intensity measurement system. The invention further comprises an experiment method based on an electrostatic discharge transient field intensity measurement system. The experiment method comprises a calibration experiment method and an electrostaticdischarge experiment method with different discharge charge transfer amounts and different powder pile heights, the influence of the position and direction of the field intensity sensor is avoided, explosion prevention is easy to realize, and the safety is good. Meanwhile, the electrostatic discharge charge transfer amount can be measured, and the electrostatic discharge energy can be quantitatively calculated.

The present invention belongs to the field of the pulse power technology, and especially relates to a multiplication device of field strength and power of a transient field. The device is provided with a cylindric housing, a straight shell and a conical shell are arranged on the cylindric housing, and the diameter of the cylindric housing is gradually enlarged; and the housing is internally provided with core wire conductors, and the core wire conductors are closed through support columns and are not connected. When a pulse power supply is added on a first-grade core wire conductor and the cylindric housing, and the pulse time is gradually shortened through stage-by-stage transmission, so that the strength and the power of the field are subjected to multiplication. The multiplication device of field strength and power of a transient field is compact in structure and enables to ensure small connecting line induction, high energy conversion efficiency, light weight and small size. A multi-stage serial multistage transient power multiplier is formed by connection in series of multi-stage coaxial transient power multipliers, and the electromagnetic coupling is small between adjacent multi-stage coaxial transient power multipliers. The short pulse high voltage having a nanosecond-magnitude pulse width is obtained and has the amplitude being as many times as the amplitude of voltage outputted by the multi-stage coaxial transient power multipliers.

The invention discloses a modeling method of a generating system of a mixed excited synchronous motor. The method comprises the following steps of: establishing a simulation model of a three-dimensional finite element electromagnetic field of the mixed excited synchronous motor; calculating the synchronous reactance value of the mixed excited synchronous motor under different excitations and different load currents according to a phase potential waveform and a vector diagram of the mixed excited synchronous motor, which are acquired through the coupling analysis of a transient field circuit; establishing a body simulation model of the mixed excited synchronous motor according to a voltage equation of the mixed excited synchronous motor; and adding an output voltage detection module, an excitation current feedback module, a load current feedback compensation calculation module and a load current detection part to form a generating system model of the mixed excited synchronous motor on a basis of the body simulation model of the mixed excited synchronous motor. The modeling method of the mixed excited synchronous electric generating system is particularly suitable for the application research of an airplane generating system and a wind generating system of a novel mixed excited synchronous motor and provides a reference for analyzing the steady-state and dynamic performance of the system and designing the parameters.

The invention relates to electromagnetic prospecting and is used for surface and marine electromagnetic sounding by means of controllable electromagnetic field sources and is applied in a package oil and gas prospecting works for searching and outlining oil and gas fields. The inventive method is based on the selection of a response from earth materials which are secondary modified by hydrocarbons migration. The invention makes it possible to ensure a set of processing technologies enabling to layer-by-layer determine an electrical resistivity and process characteristics of a medium induced polarisation: a polarizability coefficient, a time constant and a relaxation spectrum width. The inventive method consists in carrying out a measurement by several receiving lines, wherein the positionof two feeding lines of a sounding plant is substantially symmetrical with respect to the receiving lines which are located within a 30 DEG sector from the feeding line extensions, in recording a transient signal by land axial-dipole sounding devices or by marine sounding devices associated with a continuous signal recording during a ship travel and in calculating the population of interpretableparameters P1, deltaDphi, UH, Ps using recorded potential difference curves(deltaU(i) is less than 2, and 2 is more than deltaU(i))which are preliminary processed, contracted in the form of time gates and differentiated.

The invention discloses a transient electromagnetic three-component fluxgate probe with a reverse coil, comprising a forward coil, the reverse coil and a three-component fluxgate sensor, wherein the forward coil is disposed on the periphery of the reverse coil, the three-component fluxgate sensor is installed at the center of the reverse coil, a transient field is applied to the forward coil and the reverse coil, and geological information is collected and detected by the three-component fluxgate sensor. According to the transient electromagnetic three-component fluxgate probe disclosed by theinvention, the transient field is applied to the forward coil and the reverse coil, and the geological information is collected and detected by the three-component fluxgate sensor. The transient electromagnetic three-component fluxgate probe disclosed by the invention has a wide detection depth range and further expands the detection depth range to a shallow layer, and the obtained geological information is rich and comprises rich geological information on three XYZ directions.

A transient field far-field extrapolation method for calculating electromagnetic scattering by finite-difference time-domain method. Set the extrapolation boundary, and extrapolate the electric field and magnetic field on the extrapolation boundary to obtain the far field; 3. Set the transient incident wave, and update the electric field and magnetic field in each time step until the electromagnetic field distribution tends to a steady state; 4. Write the far field as the product of the frequency factor and the integral factor, and perform inverse Fourier transform on the integral factor to obtain the time domain expression; 5. Set the far field time domain response array of the integral factor; 6. The far field time domain response of the integral factor is obtained by Fourier transform to obtain its frequency domain response; 7. Using the frequency domain response of the far field and incident wave, the change of RCS with frequency is obtained. This method writes the far field as the product of the frequency factor and the integral factor, and the frequency-time transformation and time-frequency transformation forms of the integral factor are relatively simple, which simplifies the calculation and improves the efficiency.