Combined shielding method for high-precision electron microscope chamber

Abstract

The invention relates to the field of electron microscope chamber electromagnetic shielding, and provides a high-precision electron microscope chamber combined shielding method, which comprises the following steps: S1, simulating an electron microscope operation experiment environment to carry out initial state magnetic field measurement, and respectively testing direct current and alternating current magnetic field environment values; s2, adopting a low-carbon steel plate as a shielding shell, and calculating the thickness of the shielding shell based on the tested magnetic field environment value and the target value of the magnetic field environment of the electron microscope equipment; s3, after welding of the shielding shell and installation of the shielding door and the waveguide window are completed, shielding testing is carried out, reinforcing treatment is carried out on weak points and magnetic leakage points, the waveguide window comprises a magnetic waveguide tube and a hexagonal honeycomb vacuum brazing waveguide window, and the magnetic waveguide tube comprises a shell and a grating; and S4, setting an active shielding system, correcting an electron microscope experiment magnetic field environment deviation in an actual operation stage, simultaneously satisfying magnetic field and electromagnetic shielding, optimizing a waveguide window structure, and simultaneously satisfying low-frequency and high-frequency electromagnetic wave shielding.

Description

Technical Field

[0001] The present invention relates to the field of electromagnetic shielding for electron microscope rooms, and more specifically, to a high-precision combined shielding method for electron microscope rooms. Background Art

[0002] Currently, the difficulties in implementing electromagnetic shielding technology in high-precision electron microscope rooms are as follows: during the main construction and the construction of the electron microscope room, the external magnetic field environment value is unknown. Usually, the construction of an electron microscope laboratory is carried out after the completion of the main project, using the measured value of the on-site magnetic field environment as the input parameter. Since the main construction of this project is carried out simultaneously with the construction of the electron microscope room, and the AC magnetic field interference sources such as the distribution lines and electrical equipment around the electron microscope room are not installed in place and put into operation, the environmental magnetic field index during use is lacking. Currently, only the target value of the magnetic field environment of the electron microscope equipment is known, requiring that in the X / Y / Z directions, DC and AC (at 0.5m, 1.5m, and 2.5m) < 20 nT, while the external magnetic field environment value in the final operation stage is unknown.

[0003] In addition, there are too few completed cases of shielding rooms with both magnetic and electromagnetic shielding functions: Currently, electromagnetic shielding rooms for suppressing high-frequency and ultra-high-frequency electromagnetic wave interference are relatively common in China, while low-frequency magnetic shielding rooms are less. It is difficult to implement when the electron microscope room requires both magnetic shielding and electromagnetic shielding performance.

[0004] In addition, during implementation, traditional shielding shells usually adopt a double-layer separated shielding shell. The two layers of shells are supported by an insulating frame, and a certain distance needs to be left between the two shielding layers. The outer shell is made of copper-aluminum materials, and a magnetic material + insulating board is used for electromagnetic shielding. The inner shell uses ferromagnetic materials (such as low-carbon steel plates and silicon steel sheets) as magnetic shielding. This solution has complex processes, consumes a lot of materials, and affects the usable space of the electron microscope laboratory, as specifically shown in Figure 1 shown. In addition, there is also a double-layer closely attached shielding shell, which uses permalloy or silicon steel sheets with high magnetic permeability as the shielding layer and low-carbon steel plates as the base lining board. The two shielding layers are closely attached. This method has high construction difficulty and high cost, as shown in Figure 2 shown.

[0005] Finally, currently, in order to balance electromagnetic shielding and signal / ventilation requirements in the electron microscope shielding room and ensure that the high-precision imaging of the electron microscope is not interfered, waveguide windows need to be set up. Currently, the waveguide window structure usually adopts a hexagonal honeycomb vacuum brazing waveguide window, which has a good shielding effect on high-frequency electromagnetic waves. However, since an electron microscope with extremely high requirements for the magnetic field environment is installed in the electron microscope shielding room, it cannot meet the shielding requirements for low-frequency electromagnetic waves.

[0006] In view of this, it is necessary to improve the existing shielding structure and shielding method of the electron microscope room to overcome the above defects. Summary of the Invention

[0007] The main purpose of this application is to provide a combined shielding method for a high-precision electron microscope room. By only using low-carbon steel as the shielding housing, it can simultaneously meet the shielding requirements for both magnetic fields and electromagnetic fields. The waveguide window structure is optimized to simultaneously meet the shielding requirements for low-frequency and high-frequency electromagnetic waves.

[0008] To achieve the above object, in a first aspect, this application provides a combined shielding method for a high-precision electron microscope room, including the following steps: S1. Simulate the initial magnetic field measurement in the electron microscope operation experimental environment, and respectively test the magnetic field environment values of direct current and alternating current in the X / Y / Z directions in the shielding control area of the electron microscope room. S2. Use low-carbon steel plates as the shielding housing, and calculate the thickness of the shielding housing based on the measured magnetic field environment values and the target values of the magnetic field environment of the electron microscope equipment. S3. After the shielding housing is welded and the shielding door and waveguide window are installed, conduct shielding tests, and reinforce the weak points and magnetic leakage points. The waveguide window includes a magnetic waveguide and a waveguide window fixed to the end face of the magnetic waveguide. The magnetic waveguide includes a housing made of low-carbon steel plate and a grille made of low-carbon steel plate arranged inside the housing. S4. Set up an active shielding system to correct the deviation of the magnetic field environment in the electron microscope experiment during the actual operation stage.

[0009] Optionally, in step S1, a first test point and a second test point are respectively set. There are no electrical circuits and electrical equipment within 6 - 8 meters around the first test point, and a distribution box is arranged 2 - 3 meters around the test point to simulate a magnetic field interference source.

[0010] Optionally, in step S2, first calculate the shielding effectiveness SE, SE = 20log 10 (H unshielded / H shielded), where H shielded is the target value of the magnetic field environment of the electron microscope equipment, and H unshielded is the maximum value of the measured magnetic field environment. After calculating the shielding effectiveness SE, calculate the thickness t of the shielding housing according to the shielding effectiveness formula SE ≈ 20log(1 + μ r t / D), where μ r is the relative magnetic permeability of the low-carbon steel plate, and D is the side length of the low-carbon steel plate.

[0011] Optionally, in step S3, the shielding door uses a composite material of low-carbon steel plate and silicon steel sheet as the door body material, and the connection between the door frame of the shielding door and the shielding housing is welded seamlessly.

[0012] Optionally, beryllium copper spring sheets are arranged between the door frame and the door leaf of the shielding door, and between adjacent door leaves.

[0013] Optionally, the active shielding system includes a compensation coil, a magnetic sensor, and a PID compensation controller. The magnetic sensor is used to detect electromagnetic interference signals in three-dimensional space. The PID compensation controller converts the interference signal into a digital quantity, extracts the interference magnetic field vector, calculates the amplitude, phase, and direction of the required compensation magnetic field through the PID algorithm, and outputs a signal to the compensation coil to drive its circuit.

[0014] Optionally, the compensation coil is a three-axis Helmholtz coil.

[0015] Optionally, the compensation coil is embedded in the shielding housing.

[0016] Optionally, the magnetic sensor is a three-axis magnetometer.

[0017] A high-precision electron microscope room combined shielding method provided by the present invention, compared with the prior art, has the beneficial effects that low-carbon steel is used as the shielding housing. Compared with the traditional double-layer shielding structure, it not only has a simple structure and low investment cost, but also can meet both magnetic field and electromagnetic shielding at the same time. In addition, the waveguide window structure is improved to meet the shielding of high-frequency electromagnetic waves and low-frequency electromagnetic waves at the same time. Finally, a combination of passive shielding and active shielding is adopted. Passive shielding is used as the basic guarantee, and active shielding is used to cope with environmental mutations. This not only avoids excessive investment, but also has good shielding stability. In addition, the waveguide window combines a magnetic waveguide. The waveguide is responsible for low-frequency guidance + the honeycomb window for high-frequency cutoff, forming a composite shielding body with full-frequency coverage. This magnetic waveguide uses a low-carbon steel plate housing to provide rigid support, resistance to impact and vibration. In addition, a grille made of low-carbon steel plate is used to divide the large-section magnetic field into multiple paths, reducing the risk of magnetic saturation, improving the magnetic field uniformity. Moreover, the grille structure can block part of the high-frequency eddy current path, reduce heat generation, while maintaining the low-frequency magnetic field guiding ability. At the same time, the grille gap allows air circulation to avoid heat accumulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of this application are used to provide a further understanding of this application, making other features, objectives, and advantages of this application more obvious. The schematic embodiments and descriptions of the drawings of this application are used to explain this application and do not constitute an improper limitation of this application. In the drawings: Figure 1 is the structure of a traditional double-layer separated shielding housing; Figure 2 is the structure of a traditional double-layer closely attached shielding housing; Figure 3 is the single-layer shielding housing structure of the present invention; Figure 4 is a schematic diagram of the shielding door structure; Figure 5 is a schematic diagram of the connection between the shielding door and the shielding housing; Figure 6 is Figure 5 The enlarged view of part A of Figure 7 It is a schematic diagram of the waveguide window structure.

[0019] Wherein: 1. Door frame; 2. Door leaf; 3. Beryllium copper spring piece; 4. Waveguide window; 5. Shell; 6. Grille structure. Specific implementation manners

[0020] In order to enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts shall fall within the protection scope of this application.

[0021] It should be noted that the terms "first", "second", etc. in the description and claims of this application and the above-mentioned drawings are used to distinguish similar objects, and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances, so as to describe the embodiments of this application here. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those clearly listed steps or units, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0022] In this application, the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe this application and its embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation, or be constructed and operated in a specific orientation.

[0023] And, in addition to being able to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0024] In addition, the meaning of the term "plural" should be two or more.

[0025] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The following will detail the present application with reference to the accompanying drawings and in conjunction with the embodiments.

[0026] As Figures 1-7 shown, a combined shielding method for a high-precision electron microscope chamber includes the following steps: S1. Simulate the initial magnetic field measurement in the experimental environment of the electron microscope operation, and respectively test the magnetic field environment values of direct current and alternating current in the X / Y / Z directions in the shielding control area of the electron microscope chamber; S2. Use low-carbon steel plates as the shielding shell, and calculate the thickness of the shielding shell based on the measured magnetic field environment values and the target values of the magnetic field environment of the electron microscope equipment; S3. After the shielding shell is welded and the shielding door and waveguide window 4 are installed, conduct a shielding test, and reinforce the weak points and magnetic leakage points. The waveguide window 4 includes a magnetic waveguide tube and a hexagonal honeycomb vacuum brazing waveguide window 4 fixed to the end face of the magnetic waveguide tube. The magnetic waveguide tube includes a shell 5 made of low-carbon steel plate and a grid structure 6 made of low-carbon steel plate arranged in the shell 5; S4. Set up an active shielding system to correct the deviation of the magnetic field environment in the electron microscope experiment during the actual operation stage.

[0027] During the simulation test, in step S1, a first test point and a second test point are respectively set. There are no electrical circuits and electrical equipment configured within 6 - 8 meters around the first test point. Distribution boxes are arranged 2 - 3 meters away from the test point to simulate magnetic field interference sources. For the first test point, the magnetic field environment is relatively pure. After on-site detection, the maximum magnetic field intensity at test point 1 is 29.7 nT. For the second test point, due to the setting of magnetic field interference, after on-site detection, the maximum magnetic field intensity at test point 2 is 168.31 nT. This proves that the on-site AC power distribution has a great impact on the magnetic field environment. Therefore, the environmental magnetic field value after the laboratory is built is set to 200 nT, which is used as the input data for the shielding room construction at one time.

[0028] In step S2, first calculate the shielding effectiveness SE, SE = 20log 10 (H unshielded / H shielded), where H shielded is the target value of the magnetic field environment of the electron microscope equipment, and H unshielded is the maximum value of the measured magnetic field environment. After calculating the shielding effectiveness SE, according to the shielding effectiveness formula SE ≈ 20log(1 + μrt / D), calculate the thickness t of the shielding shell, where μ rμ is the relative permeability of the low-carbon steel plate, and D is the side length of the low-carbon steel plate. In this embodiment, after the above-mentioned simulation tests and the setting of the environmental target values in the electron microscopy room, although the maximum magnetic field strength in the simulation test is 168.31 nT, when calculating SE, the final value selected is 200 nT after setting. Of course, it is also feasible to calculate using the results of the simulation test. According to the environmental target values of the standard electron microscopy room, it is set to <20 nT. From this, the shielding effectiveness SE can be calculated. When calculating the thickness, since the shielding shell uses Q235 low-carbon steel plate, its μ r is 4000, and D is set to 1 m. From this, the specific thickness of the low-carbon steel plate used is calculated. In this embodiment, finally, a 14-mm Q235 low-carbon steel plate is used as the shielding shell, which can meet the magnetic shielding requirements. Regarding its electromagnetic shielding performance, according to scientific research data, the electromagnetic shielding performance of a 10-mm-thick steel plate in a low-frequency environment can reach 38 dB (>35 dB requirement), which can meet the electromagnetic shielding requirements. Therefore, only one layer of low-carbon steel plate is used as the shielding shell to replace the traditional double-layer shielding structure, greatly reducing the investment cost.

[0029] Regarding the waveguide window 4, although the existing waveguide window 4 uses a hexagonal honeycomb vacuum brazed magnetic waveguide window 4, which has a good shielding effect against high-frequency electromagnetic waves, its effect on low-frequency magnetic fields is poor. In this embodiment, a structural improvement is made on this basis, that is, a magnetic waveguide tube is added. The low-carbon steel plate is used as the shell 5, and a grid plate structure is set, thus forming a magnetic waveguide tube, forming a good electromagnetic shielding. The waveguide tube is responsible for low-frequency guidance + high-frequency cutoff of the honeycomb window. In addition, a fractal groove can be set on the end face of the connecting flange between the magnetic waveguide tube and the waveguide window 4, such as opening a 5th-order Hilbert curve, which can simultaneously match frequency points such as 18 GHz and 40 GHz, realizing an improvement in the shielding effectiveness SE of the full frequency band from microwave to terahertz TH, reaching an additional attenuation of 15 - 30 dB. Thus, a composite shielding body covering the full frequency band is formed. Moreover, the low-carbon steel plate shell 5 provides rigid support, resistance to impact and vibration. In addition, a grid made of low-carbon steel plate is used, and the internal grid structure 6 further improves the overall strength, prevents deformation, and at the same time maintains the geometric accuracy of the waveguide path, divides the large-section magnetic field into multiple paths, reduces the risk of magnetic saturation, and improves the magnetic field uniformity. Moreover, the grid structure 6 can block part of the high-frequency eddy current path, reduce heat generation, and at the same time maintain the low-frequency magnetic field guiding ability. At the same time, the grid gap allows air circulation to avoid heat accumulation.

[0030] For the platform screen door, in step S3, the platform screen door uses low-carbon steel plate composite silicon steel sheet as the door body material. The connection between the door frame 1 of the platform screen door and the shielding shell is welded seamlessly. Between the door frame 1 and the door leaf 2 of the platform screen door, and between adjacent door leaves 2, beryllium copper spring sheets 3 are provided. Among them, the low-carbon steel plate is an electromagnetic shielding material, and the silicon steel sheet is a magnetic shielding material. Thus, the simultaneous shielding of electromagnetic and magnetic fields is achieved. The thickness of the low-carbon steel plate is 14 mm.

[0031] The active shielding system includes a compensation coil, a magnetic sensor, and a PID compensation controller. The magnetic sensor is used to detect the electromagnetic interference signal in the three-dimensional space. The PID compensation controller converts the interference signal into a digital quantity, extracts the interference magnetic field vector, calculates the amplitude, phase, and direction of the required compensation magnetic field through the PID algorithm, and outputs a signal to the compensation coil to drive its circuit. The compensation coil is a three-axis Helmholtz coil. Preferably, the magnetic sensor is a three-axis magnetometer, the three-axis Helmholtz coil, and three groups of orthogonal coils independently control the magnetic field in each axis, while the three-axis magnetometer real-time monitors the electromagnetic interference signal in the three-dimensional space (X / Y / Z axes).

[0032] In order to prevent the compensation coil from being interfered by external sensors, the compensation coil is embedded in the shielding shell. If there is a decorative layer on the inner side of the shielding shell, the compensation coil can also be arranged between the shielding shell and the decorative layer.

[0033] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A combined shielding method for a high-precision electron microscope room, characterized in that, It includes the following steps: S1. Simulate the operating experimental environment of the electron microscope to measure the initial magnetic field, and respectively test the DC and AC magnetic field environment values in the X / Y / Z directions of the shielding control area in the electron microscope room; S2. Use low-carbon steel plates as the shielding shell, and calculate the thickness of the shielding shell based on the measured magnetic field environment values and the target values of the magnetic field environment of the electron microscope equipment; S3. After the shielding shell is welded and the shielding door and waveguide window are installed, conduct shielding tests, and reinforce the weak points and magnetic leakage points. The waveguide window includes a magnetic waveguide and a waveguide window fixed to the end face of the magnetic waveguide. The magnetic waveguide includes a shell made of low-carbon steel plate and a grid made of low-carbon steel plate arranged inside the shell; S4. Set up an active shielding system to correct the deviation of the magnetic field environment in the electron microscope experiment during the actual operation stage.

2. The combined shielding method for a high-precision electron microscope room according to claim 1, wherein: In step S1, a first test point and a second test point are respectively set. There are no electrical circuits and electrical equipment configured within 6-8 meters around the first test point, and a distribution box is arranged 2-3 meters around the test point to simulate a magnetic field interference source.

3. A high-precision electron microscope room combined shielding method according to claim 1, characterized in that: In step S2, first calculate the shielding effectiveness SE, where SE = 20log 10 (H unshielded / H after shielding), where H after shielding is the target value of the magnetic field environment of the electron microscope equipment, and H unshielded is the maximum value of the measured magnetic field environment. After calculating the shielding effectiveness SE, according to the shielding effectiveness formula SE ≈ 20log(1 + μ r t / D), calculate the thickness t of the shielding shell, where μ r is the relative magnetic permeability of the low-carbon steel plate, and D is the side length of the low-carbon steel plate.

4. A high-precision electron microscope room combined shielding method according to claim 1, characterized in that: In step S3, the shielding door uses a composite of low-carbon steel plate and silicon steel sheet as the door body material, and the connection between the door frame of the shielding door and the shielding shell is welded seamlessly.

5. A high-precision electron microscope room combined shielding method according to claim 4, characterized in that: Between the door frame and the door leaf of the shielding door, and between adjacent door leaves, beryllium copper spring sheets are provided.

6. The combined shielding method for a high-precision electron microscope room according to claim 1, characterized in that: The active shielding system includes a compensation coil, a magnetic sensor, and a PID compensation controller. The magnetic sensor is used to detect three-dimensional space electromagnetic interference signals. The PID compensation controller converts the interference signals into digital quantities, extracts the interference magnetic field vector, calculates the amplitude, phase, and direction of the required compensation magnetic field through the PID algorithm, and outputs signals to drive the circuit of the compensation coil.

7. The combination shielding method for a high-precision electron microscope room according to claim 6, wherein: The compensation coil is a three-axis Helmholtz coil.

8. A high-precision electron microscope room combined shielding method according to claim 7, characterized in that: The compensation coil is embedded in the shielding shell.

9. The high-precision electron microscope room combined shielding method according to claim 7, characterized in that: The magnetic sensor is a three-axis magnetometer.

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