Strong electromagnetic protective cover

Abstract

A strong electromagnetic protective cover is a cover body with a closed space defined by a specified shell, the specified shell is formed by overlapping at least seven layers of metal materials, and the metal materials sequentially comprise an outer layer of copper, an outer second layer of 1J22, an outer third layer of copper, an outer fourth layer of 1J22, an outer fifth layer of copper, an inner second layer of 1J22 and an inner layer of 1J22 from outside to inside. According to the invention, through computer analogue simulation and sample field actual test, full-frequency-domain protection with the electromagnetic field intensity reaching 6T can be met, and the shielding percentage reaches and exceeds 95%. Reliable theoretical and practical protection is provided for protection of initiating explosive devices and electronic products, and theoretical and practical basis is provided for further deep electromagnetic field protection analysis.

Description

Technical Field

[0001] The invention relates to an electromagnetic protection device, in particular to a strong electromagnetic protection cover. Background Art

[0002] Electromagnetic protection of ammunition is one of the important contents of ammunition support work. With the rapid development of electronic science and technology, various types of civilian and military electromagnetic radiation devices have increased significantly, and the electromagnetic capabilities generated have been continuously enhanced, causing a certain degree of interference to ammunition pyrotechnics and even causing damage. In order to eliminate the influence of the electromagnetic environment and improve the safety and reliability of ammunition pyrotechnics, it is usually adopted to use a single shielding body and magnetic coating to provide electromagnetic protection for ammunition, which can realize the storage and normal use of ammunition in a weak magnetic environment.

[0003] Although simple protective measures can be used to shield weak electromagnetic environments, when faced with strong pulsed magnetic fields, the magnetic field is more penetrating and changes faster, usually reaching a magnetic field strength of several Tesla or even tens of Tesla within a few milliseconds, which can easily cause magnetic saturation or excessive eddy currents in conventional shielding materials, resulting in weakened protective performance and failure. In addition, compared with weak magnetic environments, strong pulsed magnetic fields are more harmful. Due to the instantaneous change of the magnetic field, when acting on ammunition, it will cause the electric pyrotechnics in the internal fuze system of the ammunition to generate induced currents, which may cause the electric pyrotechnics to ignite and cause an explosion. The strong electromagnetic pulses generated by electromagnetic pulse bombs or nuclear explosions can form strong pulsed magnetic fields in a wide area, seriously threatening the safety of ammunition or electronic products.

[0004] Research on the electromagnetic environment safety of ammunition electric pyrotechnics is mainly focused on strong electric fields or high-frequency electromagnetic wave environments, and research on electromagnetic protection technology is also mostly focused on eliminating the impact of long-lasting high-frequency weak magnetic environments. But in fact, strong electric fields and strong magnetic fields are two different concepts, and the strong pulse magnetic field and high-frequency electromagnetic wave environments are not completely the same. At present, the failure mechanism of ammunition electric pyrotechnics safety under strong pulse magnetic fields is still unclear, leaving huge safety risks for the storage, transportation and application of ammunition.

[0005] In order to ensure the safety of EEDs in strong pulsed magnetic field environments, it is necessary to conduct further research on electromagnetic shielding and protection. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a strong electromagnetic protection cover which can meet the full-frequency protection requirements for electromagnetic field strengths up to 6T (Tesla) and achieve a target effect of a shielding percentage of 95%.

[0007] The strong electromagnetic protection shield is characterized in that the core of the strong electromagnetic protection shield is a cover body formed by a designated shell to form a closed space, and the designated shell is composed of only 7 layers of metal materials tightly stacked in sequence, and the metal materials are outer layer: copper, outer second layer: 1J22, outer third layer: copper, outer fourth layer: 1J22, outer fifth layer: copper, inner second layer: 1J22, inner layer: 1J22.

[0008] The thickness of the 7 layers of metal material from the outer layer to the inner layer are: 2mm, 0.1mm, 3mm, 0.1mm, 2mm, 7mm, 2mm, and the thickness tolerance of the metal material is ±20%.

[0009] As an embodiment, the copper is red copper.

[0010] The present invention has been subjected to computer simulation and field testing of samples, and can meet the full-frequency protection of electromagnetic field strength up to 6T, and the shielding percentage reaches and exceeds the index of 95%. The effect of the material arrangement and thickness combination of the present invention has been verified through actual testing, so that the material utilization is optimal and the effect is the best. It provides reliable theoretical and practical protection for the protection of explosives and electronic products, and provides a theoretical and practical basis for further in-depth electromagnetic field protection analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the structure of an embodiment of the present invention.

[0012] Figure 2 It is a schematic diagram of the cross section of the protective cover.

[0013] Figure 3 It is the shielding effectiveness curve of different shielding materials under low-frequency magnetic field.

[0014] Figure 4 It is the shielding percentage curve of different shielding materials under low-frequency magnetic field.

[0015] Figure 5 It is the shielding effectiveness curve of the reference point inside the shielding material under different material combinations.

[0016] Figure 6 It is the shielding percentage curve of the reference point inside the shielding material under different material combinations.

[0017] Figure 7 It is the shielding percentage curve under different layered composite structures.

[0018] Figure 8 It is the shielding effectiveness and shielding percentage curve under the strong magnetic shielding structure.

[0019] Fig. 9 It is the measured magnetization curve of the embodiment of the present invention.

[0020] In the figure: 1-outer layer, 2-outer second layer, 3-outer third layer, 4-outer fourth layer, 5-outer fifth layer, 6-inner second layer, 7-inner layer, 8-specified shell. DETAILED DESCRIPTION

[0021] The present invention is further described below in conjunction with the accompanying drawings and embodiments: Figure 1 The figure shows an example of a protective cover, which is sealed as far as possible in all directions to achieve shielding protection against electromagnetic fields, thereby avoiding sufficient electromagnetic induction inside the electronic product to cause harm.

[0022] After computer simulation and actual measurement, Figure 3 , Figure 4 is the shielding effectiveness and shielding percentage curve under low-frequency magnetic field under different shielding materials, Figure 3 , Figure 4 The results show that the shielding effectiveness of unused shielding materials in single-layer soft magnetic alloy is only 2.3dB at most. The best material tested is Permalloy 1J22, and the shielding percentage is only 23%, which is far below the shielding requirement. The soft magnetic material is only sensitive to magnetic fields. As the thickness of the single-layer shielding material increases, the saturation magnetic induction intensity also changes. However, it is far from meeting the required shielding requirements. For more complex electromagnetic environments, it is necessary to meet the shielding requirements of high-frequency and low-frequency magnetic fields at the same time. It is necessary to use a combination of multiple metal materials and use a multi-layer structure to shield the complex frequency characteristic magnetic field.

[0023] In the experiment, a 2T magnetic flux density modulus was set outside the shielding layer to be equivalent to the strong magnetic field in the external environment, and the frequency domain response of the reference point inside the shielding material was obtained. Figure 5 and Figure 6 It is the shielding effectiveness and shielding percentage curve of the reference point inside the shielding material under three different material combinations. In the frequency band of 1-50Hz, the shielding effectiveness and shielding percentage increase rapidly with the increase of frequency and then tend to a stable state. Compared with single-layer shielding materials, the shielding effectiveness of the multi-layer material combined shielding structure is greatly improved. Since the metal material with low resistivity is added inside the multi-layer shielding structure, the shielding effect of the high-frequency magnetic field is much better than that of the low-frequency magnetic field. The shielding effectiveness and shielding percentage of shielding materials in different combinations have basically the same trend as the frequency increases. In the frequency range above 120Hz, the shielding percentage of the combination of 1J22 and 1J22 is basically greater than 95%, and its protection effect is the best. However, as the frequency continues to increase, the shielding effectiveness and shielding percentage increase slowly and reach the saturation state under this thickness. 1J22 is a high saturation magnetic induction intensity iron-cobalt-vanadium soft magnetic alloy material, often called Permalloy or iron-nickel alloy.

[0024] It can be seen that the magnetic field around the pyrotechnics is greatly attenuated after the layered composite process. Therefore, based on the above characteristics, the use of high magnetic permeability materials and high electrical conductivity materials for multi-layer shielding can greatly reduce the strong magnetic field around the tested pyrotechnics and reduce the impact of the magnetic field on the pyrotechnics. However, due to the reduction in the thickness of the high magnetic permeability material, its shielding effectiveness is much lower than Figure 5 , Figure 6 Therefore, it is necessary to increase the thickness of the high permeability material or continue to increase the number of layers to meet the shielding requirements of strong magnetic environments.

[0025] According to the above test results, the shielding effect of the shielding layer under the three-layer shielding structure at low frequency is still poor when the external interference magnetic field source is large, and certain anti-interference measures need to be taken to improve the shielding effectiveness at the corresponding low frequency. Therefore, according to the characteristics of low-frequency shielding, multi-layer shielding is performed by combining high magnetic permeability materials and high electrical conductivity materials, which can effectively attenuate the magnetic field around the test object and reduce the impact of the magnetic field on the test object. Therefore, by adjusting the thickness of each layer of the layered shielding cover, the size of the magnetic field to which the test object is subjected can be accurately adjusted, providing an effective protection means for electromagnetic interference simulation and electromagnetic protection of the test object.

[0026] From the test results, it can be seen that the shielding effectiveness of the multi-layer shielding structure is not a simple superposition of the single-layer shielding effectiveness. Multi-layer shielding is a re-magnetic shielding of the leakage magnetic flux that passes through the magnetic shielding body for the first time. In comparison, the magnetic lines of force have undergone different changes, and are also affected by the significant increase in the magnetic resistance of the gap between layers under different layering conditions and the induced eddy currents inside each material. Compared with single-layer shielding, the leakage magnetic flux outside the multi-layer shielding body has been significantly reduced, thereby significantly improving the low-frequency magnetic shielding effectiveness.

[0027] When the external magnetic field is strong enough, the high permeability material will quickly reach saturation. At this time, the external magnetic field continues to increase, but the magnetization intensity no longer increases. At this time, the magnetic field intensity increases, while the magnetic induction intensity remains unchanged, which significantly increases the magnetic resistance of the shield (the magnetic resistance of the air in the shield remains unchanged), and the shielding effectiveness decreases significantly.

[0028] When the magnetic field to be shielded is very strong, single-layer shielding materials and simple multi-layer shielding materials cannot meet the requirements. At this time, more effective measures must be taken according to the actual situation to enhance the shielding performance.

[0029] We have summarized the following methods to improve the effectiveness of magnetic field shielding:

[0030] (1) Select appropriate shielding materials, including using high magnetic permeability materials (such as nickel-chromium alloys) as shielding materials, which can effectively guide magnetic field lines around the protected area. These materials can attract magnetic field lines, thereby reducing the magnetic field strength passing through the shielding layer. Secondly, use composite materials and combine multiple materials, such as adding a layer of conductive material outside the metal shielding layer to increase the shielding effect using the principle of electromagnetic induction.

[0031] (2) Designing a multi-layer shielding structure includes using multi-layer shielding: using a multi-layer shielding structure, each layer can be separated by air gaps or other dielectric isolation to reduce the penetration of the magnetic field. Multi-layer shielding can effectively increase the shielding coefficient. At the same time, choose alternating arrangement: when designing a multi-layer shielding, different types of shielding materials can be used alternately to give full play to their respective advantages.

[0032] (3) Improve the geometric design of the shielding box, including the closed structure: Ensure that the shielding body forms a complete closed structure and avoid gaps or gaps, because even a small opening may cause a significant decrease in shielding performance. Shielding layer shape: Optimize the geometric shape of the shielding layer to make it more closely fit the object to be protected and reduce the space between the shielding layer and the object.

[0033] (4) Optimize the thickness of the shielding layer in the shielding configuration: Increasing the thickness of the shielding material can improve the shielding effect, but it is necessary to pay attention to the balance between cost and weight. When designing and implementing the shielding solution, it is necessary to comprehensively consider factors such as shielding effect, cost, and test difficulty, and select the most suitable solution based on the specific application scenario. Finally, under the multi-layer combination of multi-layer high magnetic permeability materials and high conductive materials, the shielding effectiveness and shielding percentage under different layered combinations are demonstrated.

[0034] After repeated calculation and iterative optimization of the layering and layer thickness, the 7-layer composite material structure was finally determined. Figure 2 shown.

[0035] The time domain pulse signal excitation is equivalent to the multi-frequency excitation effect in the frequency domain. The spectrum components of the strong magnetic pulse magnetic field waveform are mainly concentrated in the range of 0-50Hz. Not only is the frequency low, but the main spectrum energy is the DC component, which involves static magnetic shielding. Static magnetic shielding mainly targets static (non-changing) magnetic fields, that is, DC magnetic fields. This type of magnetic field does not change over time, so the shielding method usually depends on the physical properties of the material, especially its magnetic permeability. Common static magnetic shielding materials include high-permeability alloys (such as Permalloy and Iron-Ni alloy), which can guide magnetic field lines around the protected area. The key to static magnetic shielding is to select materials with high magnetic permeability so that the magnetic field lines are concentrated inside such materials, thereby reducing the impact of the magnetic field on the shielded object. Compared with the DC magnetic field, low-frequency magnetic field shielding has a low frequency, an unobvious skin effect, and very small absorption loss. At the same time, the wave impedance is very low and the reflection loss is also very small. Therefore, it is difficult to obtain the required shielding effectiveness simply by absorption and reflection. For low-frequency magnetic fields, shielding is achieved by using high-permeability ferromagnetic materials to provide magnetic bypass. Ferromagnetic materials provide a low-reluctance channel for the magnetic field, concentrating the magnetic field in the shielding material, thereby achieving the required low-frequency magnetic shielding effectiveness. Therefore, while accurately designing a structure that effectively shields the static magnetic field, metal copper with good conductivity is introduced. As the frequency increases, the changing magnetic field produces eddy current effects in the conductive material. These eddy currents further generate their own magnetic fields to offset the effects of the external magnetic field. The complexity of static magnetic shielding is much higher than that of low-frequency magnetic field shielding. Figure 7 It can be seen from the protective plates with different layered composite structures that the low-frequency shielding efficiency meets the requirements and then the shielding effect gradually reaches the optimal level as the frequency increases.

[0036] The strong electromagnetic shield described in the present invention is formed by a designated shell 8 which is tightly enclosed on all sides of the space, and the sealing effect should be achieved as much as possible during the actual production process. Figure 2 As shown, the designated shell 8 is only composed of 7 layers of metal materials tightly stacked in sequence. The 7 layers of metal materials are outer layer 1: copper, outer second layer 2: 1J22, outer third layer 3: copper, outer fourth layer 4: 1J22, outer fifth layer 5: copper, inner second layer 6: 1J22, inner layer 7: 1J22 from outside to inside. After optimization, the thickness of the 7 layers of metal materials, from outer layer 1 to inner layer 7, are: 2mm, 0.1mm, 3mm, 0.1mm, 2mm, 7mm, 2mm. The thickness tolerance is ±20%, and the copper mentioned here is made of red copper with good purity. All materials can be made of existing grades of metal sheets, and no other materials are sandwiched in the arrangement of metal materials, and no other conditions need to be added to achieve the target effect. The enclosure can be provided with a movable door, but it is necessary to ensure that the shell thickness at the weak point in any state is not less than the shell thickness required above.

[0037] from Figure 8From the shielding effectiveness and shielding percentage curves under the strong magnetic shielding structure, it can be seen that multi-layer shielding can significantly improve the shielding effectiveness. It is not a simple superposition of the single-layer shielding effect. Double-layer shielding is to re-magnetically shield the leakage flux that passes through the outer magnetic shielding body for the first time. The direction of the magnetic lines of force will inevitably change, and the interlayer magnetic resistance and the material's own induced eddy current will also participate in the effect. As a result, the leakage flux through the multi-layer shielding body is significantly attenuated. The electromagnetic shielding effectiveness of the multi-layer shielding material structure obtained by design and optimization is greater than 24dB in the low-frequency band, and the low-frequency magnetic shielding performance is excellent. When the external magnetic field to be shielded is very strong, the magnetic shielding material will be saturated. Once magnetic saturation occurs, the shielding effectiveness is greatly reduced. The saturation magnetization intensity and initial relative magnetic permeability of the soft magnetic alloy can be adjusted through the layered composite process to meet different shielding needs. Fig. 9 It is the measured magnetization curve of the embodiment of the present invention. The external magnetic field intensity exceeds 6T, and the saturation magnetic induction intensity reaches about 2.4T. The arrangement of the 7 layers of metal materials and the thickness setting of each layer in the present invention, the combination of the arrangement and thickness values ​​is infinite. Although it cannot be obtained through existing theories and repeated experiments, it is optimized through the unique algorithm deeply set by the inventor team, and verified through actual tests, so that the material utilization is optimal and the effect is the best. The specific implementation method is simple, clear and easy to operate, and there will be no obstacles to implementation. The material and thickness selection arrangement disclosed in the present invention can achieve full-frequency protection under a magnetic field intensity of 6T, and the electromagnetic field shielding percentage exceeds 95%. It is easy to achieve better shielding effect for high-frequency magnetic fields. In order to be more conducive to application in the field of civil electromagnetic protection, this technology is specially disclosed.

[0038] In actual production, the required shielding needs can be met through a layered composite process. For the protective plate, there must be no dirt between the single layers, and the layers must be polished and fit perfectly. The surface of the single-layer plate must be smooth, and the multi-layer plates must fit tightly, which meets the test requirements. Use the above-mentioned composite plate to surround the object to be protected in all directions with gaps. Under normal temperature conditions, when the external magnetic field of electromagnetic protection exceeds 6T, the same high saturation magnetic induction intensity plate is selected inside the electromagnetic protection multi-layer structure to achieve better shielding effectiveness. The shielding effectiveness of the shielding material has reached 24.3dB at 10Hz, and the shielding percentage is greater than 95%, which meets the target effect of shielding requirements. The internal space of the protective cover is shielded, and the internal magnetic induction intensity is greatly reduced, achieving Figure 8 The shielding effectiveness and shielding percentage shown in the figure show that the electromagnetic field shielding percentage above 10 Hz has exceeded 98%.

Claims

1. A strong electromagnetic shield, characterized by: The core of the strong electromagnetic protection shield is a shield body which is enclosed by a designated shell (8) to form a closed space. The designated shell (8) is composed of only 7 layers of metal materials which are closely stacked in sequence. The metal materials are as follows from the outside to the inside: outer layer (1): copper, outer second layer (2): 1J22, outer third layer (3): copper, outer fourth layer (4): 1J22, outer fifth layer (5): copper, inner second layer (6): 1J22, inner layer (7): 1J22.

2. The strong electromagnetic shield according to claim 1 is characterized in that: The thickness of the seven layers of metal material from inner layer (7) to inner layer (7) is: 2mm, 0.1mm, 3mm, 0.1mm, 2mm, 7mm, 2mm, and the thickness tolerance of the metal material is ±20%.

3. The strong electromagnetic shield according to claim 1 is characterized in that: The copper is red copper.

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