A combined shielding method for high-precision electron microscope chamber

Abstract

The invention relates to the field of electromagnetic shielding in an electron microscope room and provides a high-precision combined shielding method for an electron microscope room. The method comprises the following steps: S1, simulating an electron microscope operating experimental environment to perform initial magnetic field measurement, and testing the values ​​of the direct current and alternating current magnetic field environments respectively; S2, using 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 a target value of the magnetic field environment of the electron microscope equipment; S3, after the shielding shell is welded and the shielding door and the waveguide window are installed, a shielding test is performed, and weak points and magnetic leakage points are reinforced, wherein 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 grid; S4, setting an active shielding system, correcting the deviation of the electron microscope experimental magnetic field environment in the actual operating stage, being able to simultaneously meet the requirements of magnetic field and electromagnetic shielding, optimizing the waveguide window structure, and simultaneously meeting the requirements of shielding for low-frequency and high-frequency electromagnetic waves.

Description

Technical Field

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

[0002] The current difficulty in implementing electromagnetic shielding technology in high-precision electron microscope laboratories lies in the fact that the external magnetic field environment values ​​are unknown during the simultaneous construction of the main structure and the electron microscope room. Electron microscope laboratory construction is usually completed after the main project, using on-site measured magnetic field environment values ​​as input parameters. However, since the main construction and electron microscope room construction were carried out simultaneously in this project, the AC magnetic field interference sources such as power distribution lines and electrical equipment around the electron microscope room were not installed and put into operation, and the environmental magnetic field indicators during operation were missing. Currently, only the target values ​​for the magnetic field environment of the electron microscope equipment are known: DC and AC values ​​in the X / Y / Z directions (0.5m, 1.5m, and 2.5m) are required to be less than 20nt, but the external magnetic field environment values ​​during the final operation phase are unknown.

[0003] Furthermore, there are very few examples of shielded rooms with both magnetic and electromagnetic shielding capabilities. Currently, electromagnetic shielding rooms designed to suppress high- and ultra-high-frequency electromagnetic interference are more common in China, while low-frequency magnetic shielding rooms are less common. This makes it more difficult to implement both magnetic and electromagnetic shielding in electron microscope rooms.

[0004] In addition, during implementation, traditional shielding enclosures are usually configured as double-layer separated shielding enclosures, with an insulating frame between the two enclosures as support. A certain distance must be left between the two shielding layers. The outer enclosure is made of copper and aluminum, with magnetic materials + insulating plates for electromagnetic shielding, and the inner enclosure is made of ferromagnetic materials (low-carbon steel plates, silicon steel sheets, etc.) for magnetic shielding. This solution is complex in process, requires a lot of consumables, and affects the usable space of the electron microscope laboratory. Figure 1 As shown, there are also double-layer close-fitting shielding shells, which use high magnetic permeability Permalloy or silicon steel sheets as shielding layers and low-carbon steel plates as base linings. The two shielding layers are set closely together. This approach is difficult to construct and expensive. Figure 2 shown.

[0005] Finally, in order to balance electromagnetic shielding and signal / ventilation requirements and ensure that the high-precision imaging of the electron microscope is not interfered with, a waveguide window needs to be installed in the electron microscope shielding room. The current waveguide window structure usually adopts a hexagonal honeycomb vacuum brazed waveguide window. The waveguide window has a good shielding effect for high-frequency electromagnetic waves. However, since the 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-mentioned 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 chamber, which only uses low-carbon steel as the shielding shell, can simultaneously meet the shielding of magnetic fields and electromagnetics, optimize the waveguide window structure, and simultaneously meet the shielding of low-frequency and high-frequency electromagnetic waves.

[0008] In order to achieve the above objectives, in a first aspect, the present application provides a high-precision electron microscope chamber combined shielding method, comprising the following steps:

[0009] S1. Simulate the electron microscope operating environment to perform initial magnetic field measurements, and test the DC and AC magnetic field environment values ​​in the X / Y / Z directions of the electron microscope shielding control area respectively;

[0010] S2. Use a low-carbon steel plate as the shielding shell, and calculate 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;

[0011] S3. After the shielding shell is welded and the shielding door and waveguide window are installed, a shielding test is performed and weak points and magnetic leakage points are reinforced. The waveguide window includes a magnetic waveguide tube and a waveguide window fixed to the end face of the magnetic waveguide tube. The magnetic waveguide tube includes a shell made of low-carbon steel plate and a grid made of low-carbon steel plate disposed in the shell.

[0012] S4. Set up an active shielding system to correct the deviation of the magnetic field environment of the electron microscope experiment during the actual operation stage.

[0013] Optionally, in step S1, a first test point and a second test point are set respectively, and no electric lines or electrical equipment are configured within 6-8 meters around the first test point, and a distribution box is arranged 2-3 meters around the second test point to simulate a magnetic field interference source.

[0014] 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 tested 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 of the shielding shell t, 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.

[0015] Optionally, in step S3, the shielding door uses low-carbon steel plate composite silicon steel sheet as the door body material, and the connection between the door frame of the shielding door and the shielding shell is seamlessly welded.

[0016] Optionally, beryllium copper spring sheets are provided between the door frame and the door leaf of the shielding door, and between adjacent door leaves.

[0017] 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 a PID algorithm, and outputs a signal to the compensation coil to drive its circuit.

[0018] Optionally, the compensation coil is a three-axis Helmholtz coil.

[0019] Optionally, the compensation coil is embedded in the shielding shell.

[0020] Optionally, the magnetic sensor is a three-axis magnetometer.

[0021] The present invention provides a combined shielding method for a high-precision electron microscope chamber. Compared with the existing technology, its beneficial effect is that low-carbon steel is used as a shielding shell. Compared with the traditional double-layer shielding structure, it not only has a simple structure and low investment cost, but also can meet the requirements of magnetic field and electromagnetic shielding at the same time. In addition, the waveguide window structure is improved to meet the requirements of shielding high-frequency electromagnetic waves and low-frequency electromagnetic waves. Finally, a combination of passive shielding and active shielding is adopted. Passive shielding serves as the basic guarantee, while active shielding responds to sudden changes in the environment. It not only avoids excessive investment but also has good shielding stability. In addition, the waveguide window is combined with a magnetic waveguide tube. The waveguide tube is responsible for low-frequency guidance and the honeycomb window is responsible for high-frequency cutoff to form a composite shielding body covering the entire frequency band. The magnetic waveguide tube uses a low-carbon steel plate shell to provide rigid support and is resistant to impact and vibration. In addition, a grid made of low-carbon steel plate is used to divide the large-section magnetic field into multiple paths, reduce the risk of magnetic saturation, and improve the uniformity of the magnetic field. The grid structure can block some high-frequency eddy current paths, reduce heat generation, and maintain the low-frequency magnetic field guidance capability. At the same time, the grid gap allows air circulation to avoid heat accumulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings that constitute part of this application are used to provide a further understanding of this application and make other features, objects and advantages of this application more apparent. The illustrative embodiment drawings of this application and their descriptions are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0023] Figure 1 It is a traditional double-layer separated shielding shell structure;

[0024] Figure 2 It is a traditional double-layer close-fitting shielding shell structure;

[0025] Figure 3 It is a single-layer shielding shell structure of the present invention;

[0026] Figure 4It is a schematic diagram of the shield door structure;

[0027] Figure 5 It is a schematic diagram of the connection between the shielding door and the shielding shell;

[0028] Figure 6 yes Figure 5 A magnified view of point A;

[0029] Figure 7 It is a schematic diagram of the waveguide window structure.

[0030] Among them: 1. Door frame; 2. Door leaf; 3. Beryllium copper spring sheet; 4. Waveguide window; 5. Shell; 6. Grille structure. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0032] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0033] In this application, terms such as "upper," "lower," "left," "right," "front," "back," "top," "bottom," "inner," "outer," "center," "vertical," "horizontal," "transverse," and "longitudinal" indicate positions or locations based on the positions or locations shown in the accompanying drawings. These terms are primarily intended to better describe this application and its embodiments and are not intended to limit the devices, elements, or components indicated to having a specific orientation, or to being constructed or operated in a specific orientation.

[0034] Furthermore, some of the above terms may be used to express other meanings besides indicating a position or location. For example, the term "on" may also be used to express a dependency or connection in certain circumstances. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0035] Additionally, the term "plurality" shall mean two or more.

[0036] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0037] like Figure 1-Figure 7 As shown, a high-precision electron microscope chamber combined shielding method includes the following steps:

[0038] S1. Simulate the electron microscope operating environment to perform initial magnetic field measurements, and test the DC and AC magnetic field environment values ​​in the X / Y / Z directions of the electron microscope shielding control area respectively;

[0039] S2. Use a low-carbon steel plate as the shielding shell, and calculate 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;

[0040] S3. After the shielding shell is welded and the shielding door and waveguide window 4 are installed, a shielding test is performed and weak points and magnetic leakage points are reinforced. The waveguide window 4 includes a magnetic waveguide tube and a hexagonal honeycomb vacuum brazed 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 disposed in the shell 5.

[0041] S4. Set up an active shielding system to correct the deviation of the magnetic field environment of the electron microscope experiment during the actual operation stage.

[0042] When conducting a simulation test, a first test point and a second test point are set in step S1. No electric lines or electrical equipment are configured within 6-8 meters around the first test point. A distribution box is arranged 2-3 meters around the second test point to simulate a magnetic field interference source. At the first test point, the magnetic field environment is relatively pure. After on-site detection, the maximum magnetic field strength of test point 1 is 29.7nT. At the second test point, due to the setting of magnetic field interference, the maximum magnetic field strength of test point 2 is 168.31nT after on-site detection. This proves that on-site AC power distribution has a great influence on the magnetic field environment. Therefore, the environmental magnetic field value after the laboratory is built is set to 200nT, which is used as the input data for the construction of the shielded room.

[0043] In step S2, the shielding effectiveness SE is first calculated, SE = 20log 10(Hunshielded / Hshielded), where Hshielded is the target value of the magnetic field environment of the electron microscope equipment, and Hunshielded is the maximum value of the tested magnetic field environment. After calculating the shielding effectiveness SE, the shielding shell thickness t is calculated according to the shielding effectiveness formula SE≈20log(1+μrt / D), where μ r is the relative magnetic permeability of the low carbon steel plate, D is the side length of the low carbon steel plate. In this embodiment, after the above simulation test and the setting of the target value of the electron microscope room environment, although the maximum magnetic field intensity of the simulation test is 168.31nT, the set value of 200nT is finally selected when calculating SE. Of course, it is also feasible to calculate using the results of the simulation test. According to the environmental target value of the standard electron microscope room set to <20nt, the shielding effectiveness SE can be calculated. When calculating the thickness, since the shielding shell is made of Q235 low carbon steel plate, its μ r is 4000, and D is set to 1m, thereby calculating the specific thickness of the low-carbon steel plate used. In this embodiment, a 14mm Q235 low-carbon steel plate is finally used as the shielding shell, which can meet the magnetic shielding requirements. As for its electromagnetic shielding performance, according to scientific research data, the electromagnetic shielding performance of a 10mm thick steel plate in a low-frequency environment can reach 38dB (>35dB requirement), which can meet the electromagnetic shielding requirements. Therefore, only one layer of low-carbon steel plate is used as the shielding shell instead of the traditional double-layer shielding structure, which greatly reduces the investment cost.

[0044] Regarding the waveguide window 4, although the existing waveguide window 4 adopts a hexagonal honeycomb vacuum brazed magnetic waveguide window 4, which has a good shielding effect for high-frequency electromagnetic waves, it has a poor effect for low-frequency magnetic fields. In this embodiment, a structural improvement is made on this basis, that is, a magnetic waveguide tube is added, a low-carbon steel plate is used as the shell 5, and a grid plate structure is provided to form a magnetic waveguide tube, thereby forming a good electromagnetic shielding. The waveguide tube is responsible for low-frequency guidance and the honeycomb window is responsible for high-frequency cutoff. In addition, a fractal groove can be provided on the end face of the connecting flange between the magnetic waveguide tube and the waveguide window 4. For example, a 5th-order Hilbert curve can be opened to simultaneously match frequency points such as 18 GHz and 40 GHz. The full-band shielding effectiveness SE from microwave to terahertz TH is improved, with an additional attenuation of 15-30dB, thereby forming a composite shielding body covering the entire frequency band. The low-carbon steel plate shell 5 is used to provide rigid support and 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 and prevents deformation. At the same time, the geometric accuracy of the waveguide path is maintained, and the large-section magnetic field is divided into multiple paths, reducing the risk of magnetic saturation and improving the uniformity of the magnetic field. In addition, the grid structure 6 can block some high-frequency eddy current paths, reduce heat, and maintain the low-frequency magnetic field guidance capability. At the same time, the grid gap allows air circulation to avoid heat accumulation.

[0045] For the shielding door, in step S3, the shielding door uses low-carbon steel plate composite silicon steel sheet as the door body material, the connection between the door frame 1 of the shielding door and the shielding shell is seamlessly welded, and beryllium copper spring sheets 3 are provided between the door frame 1 and the door leaf 2 of the shielding door, and between adjacent door leaves 2. The low-carbon steel plate is an electromagnetic shielding material, and the silicon steel sheet is a magnetic shielding material, thereby achieving simultaneous shielding of electromagnetic and magnetic fields. The thickness of the low-carbon steel plate is 14 mm.

[0046] 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. The compensation coil is a three-axis Helmholtz coil. Preferably, the magnetic sensor is a three-axis magnetometer, a three-axis Helmholtz coil, and three sets of orthogonal coils to independently control each axial magnetic field, and the three-axis magnetometer monitors the electromagnetic interference signal in three-dimensional space (X / Y / Z axis) in real time.

[0047] In order to prevent the supplementary coil from being interfered by external sensors, the compensation coil is embedded in the shielding shell. If a decoration layer is provided on the inner side of the shielding shell, the compensation coil can also be provided between the shielding shell and the decoration layer.

[0048] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A high-precision electron microscope room combined shielding method, characterized in that: The following steps are involved: S1. Simulate the electron microscope operating environment to perform initial magnetic field measurements, and test the DC and AC magnetic field environment values ​​in the X / Y / Z directions of the electron microscope shielding control area respectively; S2. Use a low-carbon steel plate as the shielding shell, and calculate 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 the shielding shell is welded and the shielding door and waveguide window are installed, a shielding test is performed and weak points and magnetic leakage points are reinforced. The waveguide window includes a magnetic waveguide tube and a waveguide window fixed to the end face of the magnetic waveguide tube. The magnetic waveguide tube includes a shell made of low-carbon steel plate and a grid made of low-carbon steel plate disposed in the shell. S4. Set up an active shielding system to correct the deviation of the magnetic field environment of the electron microscope experiment during the actual operation stage.

2. A high-precision electron microscope chamber combined shielding method according to claim 1, characterized in that: In step S1, a first test point and a second test point are set respectively. No electric lines or electrical equipment are configured within 6-8 meters around the first test point. A distribution box is arranged 2-3 meters around the second test point to simulate a magnetic field interference source.

3. A high-precision electron microscope chamber combined shielding method according to claim 1, characterized in that: In step S2, the shielding effectiveness SE is first calculated, 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 tested 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 of the shielding shell t, 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 chamber combined shielding method according to claim 1, characterized in that: In step S3, the shielding door uses low carbon steel plate composite silicon steel sheet as the door body material, and the connection between the door frame of the shielding door and the shielding shell is seamlessly welded.

5. A high-precision electron microscope chamber combined shielding method as claimed in claim 4, characterized in that: Beryllium copper spring sheets are arranged between the door frame and the door leaf of the shielding door and between adjacent door leaves.

6. A high-precision electron microscope chamber combined shielding method 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 electromagnetic interference signals in three-dimensional space. The PID compensation controller converts the interference signal into a digital quantity, extracts the interfering magnetic field vector, calculates the amplitude, phase and direction of the required compensation magnetic field through a PID algorithm, and outputs a signal to the compensation coil to drive its circuit.

7. A high-precision electron microscope chamber combined shielding method according to claim 6, characterized in that: The compensation coil is a three-axis Helmholtz coil.

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

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

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