High-accuracy Magnetic Shielding Room Simulation and Evaluation Method

Abstract

The present invention discloses a high-accuracy simulation and evaluation method for a magnetic shielding chamber. Based on finite element simulation, the present invention can construct a high-accuracy magnetic shielding chamber environment field in a real environment field; the present invention conducts simulation analysis on a magnetic shielding chamber with a door gap added with an active compensation system, improves the accuracy of the simulation results of the magnetic shielding chamber, so as to conduct high-accuracy simulation on the performance of the designed magnetic shielding chamber before construction, and evaluate the shielding effect of the designed magnetic shielding chamber on environmental noise; the present invention can also evaluate the shielding effect of the magnetic shielding chamber on environmental noise during the construction process, so as to optimize the design scheme of the magnetic shielding chamber in a targeted manner during the construction process to meet the requirements.

Description

Technical Field

[0001] The present invention belongs to the field of finite element simulation and construction methods, and particularly relates to a high-accuracy magnetic shielding chamber simulation and evaluation method. Background Art

[0002] The intensity of the geomagnetic field is about 50 μT, and the environmental noise, including transportation, etc., has an amplitude between μT and nT. For research in frontier science, bioelectromagnetics, and basic physics, etc., it needs to be carried out in a near-zero magnetic environment. It is extremely difficult to reduce the environmental noise to a near-zero magnetic environment. A magnetic shielding chamber is the most effective passive shielding method for reducing environmental noise, mainly composed of high-permeability materials and high-conductivity materials. Due to the extremely high construction cost of the magnetic shielding chamber, the design of the magnetic shielding chamber and the performance evaluation of the designed magnetic shielding chamber are very important. The traditional evaluation method is to establish a simple cube model for simulation and then directly construct it, which has a large difference from the effect of the planned magnetic shielding chamber.

[0003] The environmental magnetic field is an alternating magnetic field, divided into low-frequency and high-frequency. The materials used in the magnetic shielding chamber can shield the environmental field components of each frequency in different ways. The magnetic circuit shunt effect of the high-permeability material can shield the low-frequency magnetic field, and the induced eddy current effect of the high-conductivity material can shield the high-frequency magnetic field. Generally speaking, it is easier for the shielding coefficient of the high-frequency magnetic field to reach a higher value, while it is more difficult to improve the shielding coefficients of the static magnetic field and the low-frequency magnetic field. Therefore, we propose to add an active compensation system outside the magnetic shielding chamber to improve the comprehensive shielding effect of the magnetic shielding chamber. Adding an active compensation system to the magnetic shielding chamber can achieve the improvement of the performance of the magnetic shielding chamber at low cost. The active compensation system uses coils to generate a magnetic field opposite to the environmental field to cancel the environmental magnetic field. The main process is that highly sensitive sensors detect the magnetic field in the coils and feedback it to the upper computer, and the upper computer adjusts the current input to the coils through algorithms to achieve precise compensation. Therefore, the effect evaluation of the magnetic shielding chamber after adding the active compensation system is also crucial. Summary of the Invention

[0004] The technical problem to be solved by the present invention is, in view of the deficiencies of the prior art, to provide a high-accuracy magnetic shielding chamber simulation and evaluation method, which can construct a high-accuracy magnetic shielding chamber environmental field in the real environmental field, perform high-accuracy simulation on the performance of the designed magnetic shielding chamber before construction to evaluate the shielding effect of the designed magnetic shielding chamber on environmental noise, and evaluate the shielding effect of the magnetic shielding chamber on environmental noise during the construction process, so as to optimize the design scheme of the magnetic shielding chamber targeted during the construction process to meet the requirements.

[0005] The technical solution adopted by the present invention to solve the above technical problems is: a high-accuracy magnetic shielding chamber simulation and evaluation method, including the following steps:

[0006] S1 environment field construction:

[0007] S1.1 Establish a magnetic field model in finite element simulation software, the background domain outside the magnetic field model is uniform, and a shielding room model is established in the background domain;

[0008] S1.2 Use fluxgate sensors to measure the three-axis time-domain magnetic field data in the x-axis, y-axis, and z-axis directions in the real environment field, and convert the measured three-axis time-domain magnetic field data into an interpolation function of the finite element simulation software;

[0009] S1.3 The interpolation function is converted into the environmental magnetic field parameters by the formula B=μ0H, where B is the magnetic induction intensity, μ0 is the vacuum magnetic permeability, and H is the magnetic field intensity;

[0010] S1.4 Load the converted environmental magnetic field parameters in the background domain to establish a real environmental magnetic field model.

[0011] The performance evaluation of the magnetic shielding room mainly focuses on its shielding effect on the environmental field. The construction of the environmental field in the simulation is the primary and key point of the present invention. The most common method for constructing the environmental field in the simulation of the prior art is to use a three-axis Helmholtz coil. This method not only requires accurate calculation of the coil current corresponding to the amplitude of the real environmental field, but also is affected by the construction of the grid in the simulation, which is not conducive to the accuracy of the simulation results. Different from the prior art, the present invention uses the "magnetic field" option of the finite element simulation software to establish a uniform magnetic field model in the background domain, uses a fluxgate sensor to measure the three-axis time domain magnetic field data in the x-axis, y-axis, and z-axis directions in the real environmental field, and converts the three-axis time domain magnetic field data into the interpolation function of the finite element simulation software, and converts the interpolation function into the environmental magnetic field parameter by the formula B=μ0H, so as to generate a simulated background field consistent with the real environmental field.

[0012] Preferably, the interpolation function in step S1.2 includes a time dimension variable, and can simulate the time-varying characteristics of the magnetic field.

[0013] S2 evaluates the shielding effect of a magnetically shielded room with a door gap on environmental noise:

[0014] S2.1 Use finite element simulation software to establish a three-dimensional model of the magnetic shielding room including the door gap in the x-axis direction, and use the differential method to construct the door frame structure of the three-dimensional model of the magnetic shielding room;

[0015] S2.2 Add a square Helmholtz coil to the outside of the constructed three-dimensional model of the magnetic shielding room as an active compensation system, and use the plane stretching method to construct the three-dimensional coil geometry structure;

[0016] S2.3 Apply the environmental magnetic field parameters constructed in S1 to the three-dimensional model of the magnetic shielding room, pass currents of different frequencies into the coil, compare the magnetic fields inside and outside the three-dimensional model of the magnetic shielding room, and calculate the shielding coefficient SF=20×log(B0 / B in ), using the time domain signal, magnetic field spectrum and triaxial component changes as evaluation criteria, the shielding effect of the three-dimensional model of the magnetic shielding room on environmental noise is evaluated, where B0 is the environmental magnetic field intensity, B in It is the residual magnetism inside the 3D model of the magnetic shielding room.

[0017] Traditional magnetic shielding room performance simulation and evaluation methods generally only focus on the number of layers of the magnetic shielding room, the spacing between the shielding layers, and the thickness of the shielding material that affect the shielding effect. The effects of these parameters on the shielding effect of the magnetic shielding room have already yielded very applicable results, that is, the more shielding layers there are, the greater the spacing between the layers, and the greater the thickness of the material, the better the shielding effect of the magnetic shielding room. However, traditional magnetic shielding room performance simulation and evaluation methods lack very accurate analysis of the effects of door gaps and the real environment on the magnetic shielding room. Therefore, when the present invention uses finite element simulation software to establish a three-dimensional model of the magnetic shielding room, a door gap is added to the closed model, and then a method for measuring the shielding effect of the magnetic shielding room against magnetic fields of different frequencies in a simulated real environment field is used. A square Helmholtz coil is added to the outside of the constructed three-dimensional model of the magnetic shielding room as an active compensation system, and currents of different frequencies are passed through the coil. The magnetic fields inside and outside the three-dimensional model of the magnetic shielding room are compared, and the formula SF=20×log(B0 / B in )Evaluate the shielding effect of the magnetic shielding room on environmental noise and ensure the accuracy of the simulation results.

[0018] In actual use, the active compensation system is generally a three-axis square Helmholtz coil, while the coil model provided in the finite element simulation software is generally circular, which is inconsistent with our actual application. Therefore, we use the plane stretching method in the present invention to construct a three-dimensional coil geometry structure by stretching the two-dimensional square Helmholtz coil into a three-dimensional coil.

[0019] Preferably, in step S2.2, a two-dimensional plane stretching method is used to construct a three-dimensional coil geometry structure, and a current excitation surface is established by a domain segmentation method.

[0020] Preferably, in step S2.3, currents of different frequencies are passed through the current excitation surface to generate a magnetic field opposite to the ambient magnetic field to compensate for the earth's magnetic field. The magnitude of the current is determined by using Biot-Savart's law to deduce the current, and the magnitude of the current is inferred by determining the amplitude of the ambient magnetic field and the number of coil turns.

[0021] Preferably, the frequency range of the frequency magnetic field in step S2.3 is 0 Hz to 10 kHz.

[0022] S3 Evaluate the shielding effect of the magnetic shielding room with a door gap on environmental noise during the construction process:

[0023] S3.1 Layer by layer, construct the shielding layer of the magnetic shielding room with a door gap, and perform magnetic field measurement after each layer of the shielding layer is completed;

[0024] S3.2 Feed the magnetic field measurement data back into the three-dimensional model of the constructed magnetic shielding room, and use the method in step S2.3 to verify the shielding effect of the currently constructed magnetic shielding room on environmental noise;

[0025] S3.3 Dynamically adjust the parameters of the next layer of the shielding layer to be constructed according to the verification results;

[0026] S3.4 Repeat steps S3.1 to S3.3 until the construction of all shielding layers is completed.

[0027] The design scheme of the magnetic shielding room after simulation evaluation theoretically meets the requirements, but various factors during the actual construction process will still affect the performance of the constructed magnetic shielding room. Therefore, the evaluation during the construction of the magnetic shielding room is also crucial. The present invention proposes a method for evaluating the construction of a high-accuracy magnetic shielding room, layer by layer constructing the shielding layer of the magnetic shielding room, performing magnetic field measurement after each layer of the shielding layer is completed, feeding the measurement results back into the three-dimensional model of the magnetic shielding room constructed by the high-accuracy magnetic shielding room simulation evaluation method for verification. If the verification results do not meet the overall requirements, the parameters of the shielding layer to be constructed later can be dynamically adjusted again through simulation to meet the construction requirements, ensuring that the constructed magnetic shielding room meets the requirements.

[0028] Preferably, in step S3.1, the objects of magnetic field measurement include the time-domain magnetic field intensity in the x-axis, y-axis, and z-axis directions and the shielding factor in the frequency band of 0 Hz to 10 kHz.

[0029] Preferably, in step S3.3, the objects of dynamic parameter adjustment include the adjustment of the layer spacing of the shielding layer within a range of ±10% or the correction of the material thickness of the shielding layer within a range of ±5%.

[0030] Preferably, in step S3.2, the verification process includes the superposition simulation analysis of the effect of the active compensation system.

[0031] Compared with the prior art, the present invention has the following advantages: Based on finite element simulation, the present invention proposes a high-accuracy magnetic shielding chamber simulation and evaluation method, which can construct a high-accuracy magnetic shielding chamber environmental field in a real environmental field; the present invention conducts simulation analysis on a magnetic shielding chamber with a door gap and an active compensation system, improves the accuracy of the simulation results of the magnetic shielding chamber, and thus conducts high-accuracy simulation on the performance of the designed magnetic shielding chamber before construction, and evaluates the shielding effect of the designed magnetic shielding chamber on environmental noise; the present invention can also evaluate the shielding effect of the magnetic shielding chamber on environmental noise during the construction process, so as to optimize the design scheme of the magnetic shielding chamber in a targeted manner during the construction process to meet the requirements. Description of the Drawings

[0032] Figure 1 A three-dimensional perspective view of a complete simulation model of a magnetic shielding chamber with a door gap;

[0033] Figure 2 A transverse cross-sectional view of a complete simulation model of a magnetic shielding chamber with a door gap;

[0034] Figure 3 The magnetic field cloud map inside the magnetic shielding chamber and the variation of the magnetic field intensity in three axes;

[0035] Figure 4 A magnetic field map in the time domain inside the magnetic shielding chamber in a real environment;

[0036] Figure 5 A frequency spectrum map in the frequency domain inside the magnetic shielding chamber in a real environment;

[0037] Figure 6 and Figure 7 The shielding effect of the magnetic shielding chamber on magnetic fields of different frequencies;

[0038] Figure 8 A three-dimensional perspective view of a complete simulation model of a magnetic shielding chamber with an active compensation system;

[0039] Figure 9 The shielding effect of the magnetic shielding chamber with an active compensation system. Detailed Embodiment

[0040] The present invention will be further described in detail below in conjunction with the embodiments of the drawings.

[0041] In a real environmental field, the implementation of the present invention is exemplified by the simulation of a magnetic shielding chamber with two layers of permalloy and one layer of aluminum. Since there are already applicable results on the influence trend of the thickness and layer spacing of the shielding layer on the performance of the magnetic shielding chamber, this embodiment mainly studies the performance of a magnetic shielding chamber with a door gap in a real environmental field, the effect after adding an active compensation system, and evaluates the shielding effect of the magnetic shielding chamber with a door gap on environmental noise.

[0042] The construction process of the magnetic shielding room model with door gap is as follows:

[0043] 1) Through the "magnetic field" option provided by the finite element simulation software, a magnetic field model is established in the finite element simulation software. The background domain outside the magnetic field model is uniform. A three-layer magnetic shielding room model is established in the background domain, that is, a magnetic shielding room model with two layers of permalloy and one layer of aluminum. A commercial fluxgate sensor is used to measure the three-axis time domain magnetic field data in the x-axis, y-axis, and z-axis directions in the real environment field for 30 s, and the measured three-axis time domain magnetic field data is converted into the interpolation function of the finite element simulation software. The interpolation function is converted into the environmental magnetic field parameters through the formula B=μ0H, where B is the magnetic induction intensity, μ0 is the vacuum magnetic permeability, and H is the magnetic field intensity. The converted environmental magnetic field parameters are loaded in the background domain to establish a real environmental magnetic field model.

[0044] 2) In the established three-layer magnetic shielding room model, the differential method is used to construct the door frame of the magnetic shielding room. Then, according to the actual situation, the door model is added in the x-axis direction to obtain Figure 1 and Figure 2 A complete simulation model of a magnetically shielded room with a door gap is shown. Figure 1 and Figure 2 In the figure, 1 is the inner layer of Permalloy, 2 is the aluminum layer, 3 is the outer layer of Permalloy, and 4 is the door.

[0045] First, observe the magnetic field strength in the x-axis, y-axis, and z-axis directions in the magnetic shielding room at a certain time point. The magnetic field cloud diagram inside the magnetic shielding room and the changes in the magnetic field strength in the three axes are shown in the figure. Figure 3 As shown in the figure, it can be seen that the magnetic field strength in the x-axis direction decreases from one end of the door, and the maximum can reach 250.2 nT@DC, and the shielding effect is 58.8 dB@DC. This is due to the leakage magnetic flux in the door gap. The magnetic field diagram in the time domain inside the magnetic shielding room in the real environment is as follows Figure 4 As shown, the spectrum in the frequency domain is as follows Figure 5 As shown, it can be seen that there are some low-frequency fluctuations in the magnetic field inside the magnetic shielding room, while the high-frequency suppression effect is better. According to the actual modeling test, the shielding effect of the magnetic shielding room on magnetic fields of different frequencies is tested. The coil is placed 30 cm outside the magnetic shielding room and 1.3 m high. Currents of different frequencies are added to the coil. The shielding effect of the magnetic shielding room on magnetic fields of different frequencies is shown in the figure. Figure 6 and Figure 7 As shown. Figure 6 and Figure 7 It can be seen that as the frequency increases, the shielding effect of the magnetic shielding room becomes better, which is consistent with the waveform in the time domain. This is because for low-frequency magnetic fields, high magnetic permeability materials play a dominant role, and as the frequency increases, high conductivity materials have better and better shielding effects on high-frequency magnetic fields.

[0046] According to the actual situation, a square Helmholtz coil is added outside the constructed magnetic shielding room model with a door gap as an active compensation system. The three-dimensional coil geometric structure is constructed by the two-dimensional plane stretching method, and the current excitation surface is established by the domain division method. The three-dimensional perspective view of the complete simulation model of the magnetic shielding room after adding the active compensation system is as Figure 8 shown, Figure 8 in which the blue part outside the magnetic shielding room is the active compensation system. Then, the environmental magnetic field parameters obtained in step 1) above are applied to the constructed magnetic shielding room model with a door gap, and currents of different frequencies are passed into the current excitation surface. The method for determining the current magnitude: The current is derived using the Biot-Savart law, and the magnitude of the current is inversely deduced by determining the amplitude of the environmental magnetic field and the number of coil turns. After passing currents of different frequencies into the current excitation surface, a magnetic field opposite to the environmental magnetic field is generated to compensate for the earth's magnetic field, thereby improving the comprehensive shielding effect of the shielding room. The shielding effect of the magnetic shielding room after adding the active compensation system is as Figure 9 shown. Finally, the shielding coefficient SF = 20×log(B0 / B in ) of the three-dimensional model of the magnetic shielding room under magnetic fields of different frequencies is calculated. Using the time-domain signal, magnetic field spectrum, and changes in the three-axis components as the evaluation criteria, the shielding effect of the three-dimensional model of the magnetic shielding room on environmental noise can be evaluated, where B0 is the environmental magnetic field strength and B in is the residual magnetic field inside the three-dimensional model of the magnetic shielding room. According to Figure 9 and the calculation results, although the active compensation system does not change the trend of the magnetic field distribution inside the magnetic shielding room, it significantly reduces the residual magnetic field inside the magnetic shielding room, with a minimum of 4 nT@DC (i.e., the residual magnetic field is 4 nT at static), and the comprehensive shielding effect reaches 68.94 dB@DC (i.e., the shielding effect is 68.94 dB at static).

[0047] The design scheme of the three-layer magnetic shielding room after the above simulation evaluation theoretically meets the requirements. However, various factors in the actual construction process will still affect the performance of the constructed magnetic shielding room. Therefore, during the subsequent construction of the three-layer magnetic shielding room designed by the above simulation, when building the shielding layer of the magnetic shielding room layer by layer, magnetic field measurements are carried out every time a shielding layer is completed. The objects of magnetic field measurement include the time-domain magnetic field strength in the x-axis, y-axis, and z-axis directions and the shielding factor in the frequency band of 0 Hz to 10 kHz. Then, the measurement results are fed back to the constructed magnetic shielding room model with a door gap for verification, and the verification process includes the superposition simulation analysis of the effect of the active compensation system. If the verification results do not meet the overall requirements, the parameters of the shielding layer to be built later can be dynamically adjusted again through simulation to meet the construction requirements. The objects of parameter dynamic adjustment include the adjustment of the layer spacing of the shielding layer within the range of ±10% or the correction of the material thickness of the shielding layer within the range of ±5%, ensuring that the constructed magnetic shielding room meets the requirements.

Claims

1. A high-accuracy magnetic shielding chamber simulation and evaluation method, characterized in that, It includes the following steps: S1 Environmental field construction: S1.1 Establish a magnetic field model in finite element simulation software. The background domain outside the magnetic field model is uniform, and a shielding chamber model is established in the background domain; S1.2 Use a fluxgate sensor to measure the three-axis time-domain magnetic field data in the x-axis, y-axis, and z-axis directions in the real environmental field, and convert the measured three-axis time-domain magnetic field data into an interpolation function of the finite element simulation software; S1.3 Convert the interpolation function into environmental magnetic field parameters through the formula B = μ0H, where B is the magnetic induction intensity, μ0 is the vacuum permeability, and H is the magnetic field intensity; S1.4 Load the converted environmental magnetic field parameters in the background domain to establish a real environmental magnetic field model; S2 Evaluate the shielding effect of the magnetic shielding chamber with a door gap on environmental noise: S2.1 Use finite element simulation software to establish a three-dimensional model of the magnetic shielding chamber with a door gap in the x-axis direction, and use the difference method to construct the door frame structure of the three-dimensional model of the magnetic shielding chamber; S2.2 Add a square Helmholtz coil as an active compensation system outside the constructed three-dimensional model of the magnetic shielding chamber, and use the plane stretching method to construct the three-dimensional coil geometric structure; S2.3 Apply the constructed environmental magnetic field parameters to the three-dimensional model of the magnetic shielding chamber, pass currents of different frequencies through the coil, compare the magnetic fields inside and outside the three-dimensional model of the magnetic shielding chamber, and calculate the shielding coefficient SF = 20×log(B0 / B in ), using the time-domain signal, magnetic field spectrum, and the changes in the three-axis components as the evaluation criteria to evaluate the shielding effect of the three-dimensional model of the magnetic shielding chamber on environmental noise, where B0 is the environmental magnetic field strength and B in is the residual magnetism inside the three-dimensional model of the magnetic shielding chamber; S3 Evaluate the shielding effect of the magnetic shielding chamber with a door gap on environmental noise during the construction process: S3.1 Layer by layer build the shielding layer of the magnetic shielding chamber with a door gap, and perform magnetic field measurement after each shielding layer is built; S3.2 Feed the magnetic field measurement data back into the constructed three-dimensional model of the magnetic shielding chamber, and use the method in step S2.3 to verify the shielding effect of the currently built magnetic shielding chamber on environmental noise; S3.3 Dynamically adjust the parameters of the next shielding layer to be built according to the verification results; S3.4 Repeat steps S3.1 to S3.3 until the construction of all shielding layers is completed.

2. The high-accuracy magnetic shielding chamber simulation and evaluation method according to claim 1, characterized in that The interpolation function in step S1.2 includes a time dimension variable.

3. The high-accuracy magnetic shielding chamber simulation and evaluation method according to claim 1, wherein In step S2.2, use the two-dimensional plane stretching method to construct the three-dimensional coil geometric structure, and establish a current excitation surface by the method of dividing the domain.

4. The high-accuracy magnetic shielding chamber simulation and evaluation method according to claim 3, wherein In step S2.3, pass currents with different frequencies into the current excitation surface to generate a magnetic field opposite to the environmental magnetic field to compensate for the earth's magnetic field. The method for determining the magnitude of the current: Use the Biot-Savart law to deduce the current, and inversely calculate the magnitude of the current by determining the amplitude of the environmental magnetic field and the number of coil turns.

5. The high-accuracy magnetic shielding chamber simulation and evaluation method according to claim 1, characterized in that The frequency band of the frequency magnetic field in step S2.3 is 0 Hz to 10 kHz.

6. The high-accuracy magnetic shielding chamber simulation and evaluation method according to claim 1, wherein In step S3.1, the objects of magnetic field measurement include the time-domain magnetic field intensity in the x-axis, y-axis, and z-axis directions and the shielding factor in the frequency band of 0 Hz to 10 kHz.

7. The high-accuracy magnetic shielding chamber simulation and evaluation method according to claim 1, wherein In step S3.3, the objects of parameter dynamic adjustment include the adjustment within the range of ±10% of the layer spacing of the shielding layer or the correction within the range of ±5% of the material thickness of the shielding layer.

8. The high-accuracy magnetic shielding chamber simulation and evaluation method according to claim 1, wherein, In step S3.2, the verification process includes the superposition simulation analysis of the effect of the active compensation system.

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