Method for predicting electromagnetic shielding performance of electronic equipment under corrosion condition of micro gap structure

Abstract

The application relates to a method for predicting the electromagnetic shielding performance of electronic equipment with a micro gap structure under corrosion conditions, and belongs to the field of predicting the electromagnetic shielding performance of electronic equipment.The method comprises the following steps: S1, constructing a calculation formula of equivalent conductivity; S2, building a shielding box body with a micro gap structure and multiple groups of gap structure samples; S3, simulating corrosion conditions, corroding the multiple groups of gap structure samples, and collecting experimental data; and S4, calculating the equivalent conductivity based on the calculation formula of equivalent conductivity constructed in step S1 and predicting the electromagnetic shielding performance of the electronic equipment.The application can realize the calculation of the conductivity parameter of the micro gap structure of the shielding body, can quickly evaluate the electric contact state of the micro structure surface of the shielding box body under the corrosion environment, can further approximately evaluate the electromagnetic shielding efficiency degradation of the shielding box body, and provides an important basis and means for accurately evaluating the service life of the shielding body.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic shielding performance prediction technology for electronic devices, and specifically relates to a method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions. Background Technology

[0002] In corrosive environments, changes in the electrical contact state of structural surfaces such as riveted seams and gasket overlaps in the chassis or shielding are the main factors affecting the shielding effectiveness. These gap structures and microstructures are corrosion-sensitive structures within the shielding. From a microscopic perspective, considering the surface roughness, these microstructures, such as overlap seams, are essentially an irregular array of holes. The degree of electromagnetic field leakage depends on the array of holes formed by the physical contact surfaces and the properties of the added conductive gaskets. The properties of the physical contact surfaces and gaskets vary due to parameters such as the characteristics of the contact edges of the electronic equipment, the type of gasket, the pressure exerted on the gasket, and the spacing of the screw installation; most of these parameters cannot be accurately obtained. Moreover, the overall effect of the interaction between these parameters further complicates the electrical contact state of the microstructure surfaces, and the further changes in the surface state of the micro-gap structures under corrosive environments further increase the difficulty of electromagnetic leakage analysis of the shielding enclosure.

[0003] Based on a review of relevant research findings both domestically and internationally, current methods often involve testing the transfer impedance of gap-filling materials to analyze the electromagnetic shielding performance of shielded enclosures, such as electronic devices, with these micro-gap structures. Furthermore, the fixtures used for testing transfer impedance have strict requirements regarding the shape and size of the gap structure sample, which differs significantly from the actual installation state of the micro-gap structure on the shielded enclosure.

[0004] In summary, there is an urgent need to study a method for calculating the electrical parameters of micro-gap structures under corrosive conditions, which can calculate the structural electrical parameters of micro-gap structures and further predict the degradation of the electromagnetic shielding effectiveness of shielded enclosures. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions. This method can quickly evaluate the electrical contact state of the surface of the micro-structure of the shielding enclosure under corrosive conditions, and can further approximate the degradation of the electromagnetic shielding effectiveness of the shielding enclosure, i.e., the electronic device. It can provide positive design measures for product developers during the shielding design stage, and provide important basis and means for the accurate assessment of the service life of the shielding enclosure.

[0006] To achieve the above objectives, the present invention discloses the following technical solution:

[0007] Specifically, the present invention provides a method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions, which includes the following steps:

[0008] S1. The calculation model for equivalent conductivity is constructed as follows:

[0009]

[0010] In the formula, σ2 is the equivalent conductivity; f is the frequency; μ is the permeability; h1 is the width of the actual microslit structure; h2 is the width of the equivalent microslit structure; n is a constant representing the multiple between the depth through which current flows in the conductor and the trend depth; Z T1 The measured transfer impedance of the micro-slit structure;

[0011] S2. Construct a shielded box with a micro-gap structure and multiple sets of gap structure samples, each set of gap structure samples including at least three gap structure samples.

[0012] S3. Simulate corrosion conditions, corrode multiple groups of crevice structure samples, and collect experimental data to obtain the measured transfer impedance of the micro-crevice structure. This includes the following sub-steps:

[0013] S31. Simulate corrosion conditions and corrode multiple groups of crevice structure samples, specifically including:

[0014] S311. Preparation of acidic salt solution for the experiment: Prepare NaCl solution and stir to dissolve NaCl. Then add glacial acetic acid solution and stir again. Measure the pH value to reach 3.0-3.1. After standing for a period of time, measure the pH value of the solution again. Adjust the solution according to the measurement results to keep the pH value of the solution constant at 3.0.

[0015] S312. Turn on the power to the salt spray test chamber, set the temperature of the salt spray test chamber to 30±5℃, set the temperature of the saturation tank to 40±5℃, add water to the test chamber and the saturation tank, and then add the NaCl solution with pH=3.0 prepared in step S311 to the salt spray test chamber.

[0016] S313. Place multiple sets of crevice structure samples into the salt spray test chamber in sequence. After filling the sealed water tank at the top of the salt spray test chamber with clean water and sealing it, supply air to the salt spray test chamber. At the same time, adjust the air filter pressure on the back of the salt spray test chamber to 1.5±0.1kg. Then turn on the spray switch and adjust the spray pressure to 1.0±0.1kg to start the test. During the test, set a certain time interval for sampling and testing. Sampling and testing are carried out after a certain time interval between each corrosion.

[0017] S314. After taking out a set of crevice structure samples, measure and record the transfer impedance. Put the remaining crevice structure samples back into the salt spray test chamber for the next time interval corrosion test.

[0018] S32. Data collection and processing: The average value of the transfer impedance of multiple samples in each group of slit structure samples is taken as the measured transfer impedance of the micro-slit structure.

[0019] S4. Calculate the equivalent conductivity using the equivalent conductivity calculation model constructed in step S1 and predict the electromagnetic shielding performance of the electronic equipment. The specific steps are as follows:

[0020] S41. Obtain the measured transfer impedance of the micro-crack structure under different corrosion degrees during the corrosion test and calculate multiple sets of equivalent conductivity.

[0021] S42. Plot multiple sets of equivalent conductivity parameters as regular curves, fit the data to derive a performance prediction model for conductivity degradation over corrosion time, and determine the trend of decreased shielding effectiveness due to performance degradation of the micro-gap structure in the shielding enclosure. If the decrease in equivalent conductivity exceeds 50% of the initial value, the shielding function of the enclosure is deemed to have failed. The performance prediction model is obtained by data fitting based on an exponential form, and the expression is:

[0022] y = 71.734e -0.024x

[0023] In the formula, y is the equivalent conductivity and x is the corrosion time;

[0024] Alternatively, multiple sets of equivalent conductivity parameters can be input into the simulation model to predict the shielding performance of the shielded enclosure.

[0025] Preferably, in step S312, when the test chamber is powered on for the first time, if the test low water level light and the saturation tank low water level light are lit, add an appropriate amount of clean water to the test chamber until the test low water level light goes out. Then, add clean water through the manual water inlet of the saturation tank until the saturation tank low water level indicator light goes out.

[0026] Preferably, in step S313, when sampling and testing are performed after each corrosion interval, the sample should be allowed to cool naturally to room temperature. First, the sample should be taken out and rinsed with water to remove the deposited salt on the sample surface. Then, it should be rinsed further with distilled water and the moisture on the sample surface should be blown away with dry compressed air. Finally, it should be left to dry naturally for a certain period of time.

[0027] Preferably, in step S313, the natural drying time is 24h, 36h, or 48h.

[0028] Preferably, the shielding enclosure equivalent micro-gap structure includes a first insulating block, a second insulating block, and a contact structure simulation area. The first insulating block, the second insulating block, and the contact structure simulation area are fixed together by means of fastening bolts. A non-conductive sealing gasket is provided between the first insulating block and the fastening bolts. The contact structure simulation area includes a first metal clip, a second metal clip, and a test gasket. The test gasket is disposed between the first metal clip and the second metal clip.

[0029] Preferably, the specific steps in step S42 of inputting multiple sets of equivalent conductivity parameters into the simulation model to predict the shielding performance of the shielding enclosure are as follows:

[0030] S421. Construct a simulation box model according to the actual experimental dimensions, and set the geometric parameters, including the length, width, height and thickness of the shielding box. The length and width of the shielding box are the same as the external length and width of the equivalent micro gap, and the thickness of the shielding box is the difference between the inner length and outer length of the equivalent micro gap.

[0031] S422. Draw the geometric model and complete the simulation excitation source and boundary condition settings;

[0032] S423. Complete the mesh generation settings. By refining the mesh of the equivalent gap structure, set the maximum mesh size so that there are 3-5 meshes in the width direction of the tiny gap.

[0033] S424. Complete the field monitor settings, set the field monitoring point at the geometric center of the shielded box, and set the solver at the same time;

[0034] S425. Import multiple sets of equivalent conductivity data into the equivalent gap structure, set the model simulation frequency, and set the frequency sweep method to logarithmic sweep. Specify the upper limit frequency and lower limit frequency as the lowest and highest frequency points of the simulation, and specify the total number of frequency points as the total number of frequency points in the simulation.

[0035] S426. Based on the above steps, calculate the electric field strength and magnetic field strength inside the shielding box under different equivalent conductivity, and calculate and output the shielding effectiveness monitoring value of the box according to the electric field strength and magnetic field strength values.

[0036] Preferably, the sampling and testing interval in step S313 is 8h, 16h, 24h, 32h or 48h.

[0037] Preferably, step S1 specifically includes the following sub-steps:

[0038] S11. Construct a shielded box model with a gap structure. The width of the gap structure is h, and the cross-sectional area is S.

[0039] S12. Assuming that width leakage is not considered, the impedance of the equivalent micro-gap structure of the shielded enclosure can be expressed by its volume resistance in the width direction.

[0040] S13. Construct a calculation model for equivalent conductivity.

[0041] Preferably, the specific process for constructing the calculation model for equivalent conductivity is as follows:

[0042] The volume resistance expression for an equivalent micro-slit structure is:

[0043]

[0044] In the formula, h represents the gap width, S represents the gap area, ρ represents the resistivity, and σ represents the gap conductivity.

[0045] Assuming the actual gap width is h1, and the measured transfer impedance is Z T1 The contact area, width, gap length, and conductivity of the equivalent model are S², h², l², and σ², respectively, and its volume impedance is Z. T2 The bulk resistance is R2, and considering the skin depth under high-frequency conditions, we get:

[0046]

[0047] To ensure that the equivalent micro-slot structure model and the actual micro-slot structure model have the same shielding effectiveness, Z T1 and Z T2 The equivalence relation must be satisfied, that is

[0048]

[0049] Further derivation yields the following formula for calculating the equivalent conductivity:

[0050]

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] (1) The method of the present invention can calculate the conductivity parameters of the micro-gap structure of the shield, can quickly evaluate the surface electrical contact state of the micro-structure of the shield under corrosive environment, can further approximate the degradation of the electromagnetic shielding effectiveness of the shield, can provide positive design measures for product developers in the shield design stage, and can provide important basis and means for the accurate assessment of the service life of the shield.

[0053] (2) Compared with traditional transfer impedance evaluation methods, the present invention can more directly and realistically reflect the trend of shielding effectiveness decline due to the deterioration of micro-gap structure in the corrosive environment of the shielding box.

[0054] (3) Compared with traditional test and testing methods, the present invention can more comprehensively reflect the corrosion effect of the shielding box in the actual service environment. The conductivity parameter can more intuitively reflect the failure modes such as the non-conductive corrosion products generated after the micro gap structure of the shielding is corroded, or the hydrolysis and aging of rubber materials leading to the decrease of the current conductivity of the box surface, thus affecting the shielding performance.

[0055] (4) The method proposed in this invention can provide product designers with reference data on product corrosion protection design. It takes into account the corrosion effect of micro gap structure in the early stage of the development of electronic devices with shielding structure, provides technical support for product development and improvement, and can save later maintenance costs, improve product life and extend product service period. Attached Figure Description

[0056] Figure 1 This is a flowchart of the present invention;

[0057] Figures 2a-2c This is a schematic diagram of an equivalent micro-gap model of the shielding enclosure of the present invention, wherein, Figure 2a This is a schematic diagram of a micro-slit structure. Figure 2b This is a schematic diagram representing the width of the micro-slit structure. Figure 2c A schematic diagram representing the cross-sectional area of ​​a micro-slit structure;

[0058] Figure 3 This is a schematic diagram of the equivalent micro-gap structure of the shielding box of the present invention;

[0059] Figure 4 This is a schematic diagram of the transfer impedance of the beryllium bronze metal gasket, a micro-gap structure, in an embodiment of the present invention.

[0060] Figure 5 This is a schematic diagram of the performance prediction model in an embodiment of the present invention;

[0061] Figure 6 This is a schematic diagram of the equivalent simulation model of the shielding box's equivalent micro-gap structure in an embodiment of the present invention;

[0062] Figure 7 This is a schematic diagram of the simulation time-frequency variable data import interface in an embodiment of the present invention;

[0063] Figure 8 This is a schematic diagram illustrating the 80-hour corrosion test conducted on the beryllium bronze metal gasket contact structure shielding effectiveness in an embodiment of the present invention.

[0064] Figure 9 This is a simulation electric field intensity distribution cloud map of the beryllium bronze metal gasket contact structure in an embodiment of the present invention;

[0065] Figure 10This is a simulated magnetic field strength distribution cloud map of the beryllium bronze metal gasket contact structure in an embodiment of the present invention;

[0066] Figure 11 This is a current distribution diagram on the surface of the simulated shielding body of the beryllium bronze metal gasket contact structure in an embodiment of the present invention. Detailed Implementation

[0067] Exemplary embodiments, features, and aspects of the present invention will now be described in detail with reference to the accompanying drawings. The same reference numerals in the drawings denote elements that have the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise.

[0068] This invention provides a method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions, such as... Figure 1 As shown, it includes the following steps:

[0069] S1. Construct a calculation model for the equivalent conductivity. The specific steps are as follows:

[0070] S11. Construct a shielded box model with a gap structure. The width of the gap structure is h, and the cross-sectional area is S.

[0071] S12. Assuming that width leakage is not considered, the impedance of the shielded enclosure's equivalent micro-gap structure can be expressed by its volume resistance in the width direction.

[0072] S13. The calculation process for the conductivity of the equivalent micro-gap structure model is as follows:

[0073] The volume resistance expression for an equivalent micro-slit structure is:

[0074]

[0075] In the formula, h represents the gap width, S represents the gap area, ρ represents the resistivity, and σ represents the gap conductivity.

[0076] Assuming the actual gap width is h1, and the measured transfer impedance is Z T1 The contact area, width, gap length, and conductivity of the equivalent model are S², h², l², and σ², respectively, and its volume impedance is Z. T2 Given a bulk resistance of R2 and considering the skin depth r under high-frequency conditions, we obtain:

[0077]

[0078] To ensure that the equivalent micro-slot structure model and the actual micro-slot structure model have the same shielding effectiveness, Z T1 and Z T2 The equivalence relation must be satisfied, that is

[0079]

[0080] Further derivation yields the following calculation model for equivalent conductivity:

[0081]

[0082] In the formula, σ2 is the equivalent conductivity; f is the frequency; μ is the permeability; h1 is the width of the actual microslit structure; h2 is the width of the equivalent microslit structure; n is a constant representing the multiple between the depth through which current flows in the conductor and the trend depth; Z T1 This is the measured transfer impedance of a micro-slit structure.

[0083] S2. Construct a shielded enclosure with micro-gap structures and multiple sets of gap structure samples for testing the transfer impedance of the gap structures. Each set of gap structure samples includes three gap structure samples. A shielded enclosure generally refers to electronic equipment with shielding capabilities.

[0084] Specifically, such as Figure 3 As shown, the gap structure includes a first insulating block 1, a second insulating block 2, and a contact structure simulation area 3. The first insulating block 1, the second insulating block 2, and the contact structure simulation area 3 are fixed together by means of fastening bolts 4. A non-conductive sealing gasket 5 is provided between the first insulating block 1 and the fastening bolts 4. The contact structure simulation area 3 includes a first metal clip 6, a second metal clip 7, and a test gasket 8. The test gasket 8 is provided between the first metal clip and the second metal clip.

[0085] S3. Simulate corrosion conditions to corrode the crevice structure sample and collect experimental data. This includes the following sub-steps:

[0086] S31. Simulate corrosion conditions to corrode the crevice structure sample, specifically including:

[0087] S311. Preparation of acidic salt solution for the test: Prepare a 5% NaCl solution and stir thoroughly to completely dissolve the NaCl. Then, add glacial acetic acid solution to adjust the pH value of the solution, stir thoroughly again, and measure the pH value to reach 3.0-3.1. After standing for 30 minutes, measure the pH value of the solution again. Make fine adjustments based on the measurement results to keep the pH value of the test solution constant at 3.0.

[0088] S312. Turn on the power to the salt spray test chamber, set the test chamber temperature to 35±5℃ and the saturation tank temperature to 45±5℃, add water to the test chamber and the saturation tank, and add the pre-prepared NaCl solution with pH=3.0 and a mass concentration of 5% to the salt water storage tank.

[0089] In step S312, when the test chamber is powered on for the first time, if the test low water level indicator light and the saturation tank low water level indicator light are lit, add an appropriate amount of clean water to the test chamber laboratory until the laboratory low water level indicator light on the control panel goes out. Then add clean water through the manual water inlet of the saturation tank until the saturation tank low water level indicator light goes out.

[0090] S313. Place the samples in the salt spray test chamber, ensuring no obstruction between them. Pour clean water into the sealed water tank at the top of the chamber, seal it, and supply air to the chamber. Simultaneously, adjust the air filter pressure at the back of the chamber to 1.5±5 kg. Then, turn on the spray switch and adjust the spray pressure on the front panel to 1.0±5 kg to begin the test. During the test, set a certain sampling and testing interval. Sampling and testing are performed after each corrosion cycle at a specific time interval. In a specific embodiment, the sampling and testing interval is set to 8h, 16h, 24h, 32h, or 48h.

[0091] In step S313, when sampling and testing are performed after each corrosion interval, the sample should be allowed to cool naturally to room temperature. First, the sample should be rinsed with tap water for 5 minutes to remove the deposited salt from the sample surface. Then, it should be rinsed further with distilled water and the surface moisture should be blown off with dry compressed air. Next, it should be left to air dry for a certain period of time. The air drying time is 24h, 36h, or 48h.

[0092] S314. After taking out the sample, set up a transfer impedance test system to measure and record the sample. Keep one set of samples and put the rest of the samples back into the test chamber for corrosion test at the next time interval.

[0093] S32. Data collection and processing: The average value of the transfer impedance parameters of every 3 samples under different corrosion levels is taken as the measured transfer impedance of the micro-crack structure.

[0094] S4. Based on the formula for calculating equivalent conductivity established in step S1, calculate the equivalent conductivity and predict the electromagnetic shielding performance of electronic equipment, specifically as follows:

[0095] S41. Obtain the measured transfer impedance of the micro-crack structure under different corrosion degrees during the corrosion test and calculate multiple sets of equivalent conductivity.

[0096] S42. Plot multiple sets of equivalent conductivity parameters as regular curves, fit the data to derive a performance prediction model for conductivity degradation over corrosion time, and determine the trend of decreased shielding effectiveness due to the performance degradation of the micro-gap structure of the shielding enclosure. If the conductivity decreases by more than 50% of the initial value, the shielding function of the enclosure is considered to have failed. The performance prediction model is generally fitted to the data in an exponential form. The fitting formula and R² value are given. An R² value greater than 0.9 indicates a good fit.

[0097] In an embodiment of the present invention, the expression for the performance prediction model is:

[0098] y = 71.734e -0.024x

[0099] In the formula, y is the equivalent conductivity and x is the corrosion time.

[0100] In this embodiment, data fitting is performed based on the degradation degree of average conductivity test data over time, and the fitting result is as follows: Figure 5 As shown, the goodness of fit R 2 The value is greater than 0.9, indicating a good fit. According to the conductivity test results, after 48 hours of corrosion testing, the average conductivity of the micro-gap structure decreased to 14.59 S / m, a decrease exceeding 80% of the initial value. This suggests that corrosion of the micro-gap structure leads to a significant decrease in the shielding effectiveness of the enclosure.

[0101] In the remaining embodiments, step S42 predicts the shielding performance of the shielding enclosure through simulation, and the specific steps are as follows:

[0102] A simulation box model was constructed according to the actual experimental dimensions, and geometric parameters were set, including the length, width, height, and thickness of the shielding box. The length and width of the shielding box were the same as the external length and width of the equivalent point gap, and the thickness of the shielding box was the difference between the inner and outer lengths of the equivalent conductive gap.

[0103] Draw the geometric model and complete the simulation excitation source settings. In this embodiment, a uniform plane wave is preferably used as the radiation excitation source. Set the boundary conditions. In this embodiment, a radiation boundary or an FE-BI boundary is preferably used.

[0104] After completing the mesh generation settings, by refining the mesh of the equivalent gap structure and setting the maximum mesh size to include 3-5 meshes in the gap width direction, higher simulation accuracy can be obtained.

[0105] After completing the field monitor setup, in this embodiment, the field monitoring point is preferably set at the geometric center of the shielding box, and the complex modulus values ​​of the electric field strength and magnetic field strength are detected simultaneously.

[0106] After completing the solver settings, in this embodiment, a value of 0.01 is preferred to meet the requirements.

[0107] After completing the above settings, import multiple sets of equivalent conductivity data into the equivalent gap structure; set the model simulation frequency, the frequency sweep method to logarithmic sweep, the upper limit frequency and lower limit frequency to specify the lowest and highest frequency points of the simulation, and the total number of frequency points to specify the total number of frequency points of the simulation.

[0108] Based on the above steps, the electric field strength and magnetic field strength inside the shielding box under different average equivalent conductivity are calculated, and the shielding effectiveness monitoring value of the box is calculated and output according to the electric field strength and magnetic field strength values. Specific Implementation

[0110] This invention provides a method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions, the specific implementation steps of which are as follows:

[0111] like Figures 2a-2c As shown, a shielding enclosure was designed and manufactured according to the dimensions recommended in SAE ARP1173. The enclosure material is aluminum alloy, and the length, width, and height are designed to be 305mm each. The four panels and the bottom plate of the shielding enclosure are all spliced ​​by welding. A 2mm square groove is cut at the edge of the top cover plate, and the connection between the top cover plate and the four panels is sealed with conductive rubber strips filled with silicone rubber and aluminum alloy rivets.

[0112] Based on the SAE ARP1705 C standard requirements for measuring fixture specimen dimensions, a "sandwich" structure gap structure simulation test specimen was constructed. The two metal clips in the "sandwich" structure are made of the same material as the shielding box: aluminum alloy. The test gaskets are beryllium bronze metal washers. Both the metal clips and the test gaskets have an outer diameter of 20 mm, an inner diameter of 16 mm, and a wire diameter of 2 mm. The appearance of the sample, i.e., the test specimen, is as follows. Figure 3 As shown.

[0113] Then, the test was carried out in accordance with GB / T 10125-2021 Artificial Atmosphere Corrosion Test - Salt Spray Test:

[0114] First, prepare the acidic salt solution for the experiment. Measure 4000 mL of distilled water using a graduated cylinder, add 200 g of pure NaCl (the NaCl content in this reagent should be no less than 99.5%), prepare a 5% (w / w) NaCl solution, and stir thoroughly to ensure the NaCl is completely dissolved.

[0115] Then, add glacial acetic acid solution to adjust the pH value of the solution, stir thoroughly again, and measure the pH value to reach 3.0-3.1. After standing for 30 minutes, measure the pH value of the solution again, and make fine adjustments based on the measurement results to ensure that the pH value of the test solution is constant at 3.0.

[0116] Next, turn on the power to the salt spray test chamber and set the chamber temperature to 35℃ and the saturation tank temperature to 45℃. Upon initial power-on, the low water level indicator on the control panel and the low water level indicator on the saturation tank will light up, indicating a water shortage in these areas. Add an appropriate amount of clean water to the test chamber until the low water level indicator on the control panel goes out. Then, manually add water to the saturation tank through the manual water inlet until the low water level indicator on the saturation tank goes out.

[0117] Next, add the pre-prepared NaCl solution with pH=3.0 and a mass concentration of 5% to the brine storage tank of the salt spray test chamber.

[0118] Finally, 15 test specimens, i.e., gap structure samples, were placed into the chamber, with 3 specimens forming a parallel group to ensure that there was no obstruction between them. Clean water was poured into the sealed water tank at the top of the test chamber, and the lid was closed to seal the chamber. The air compressor was turned on to supply air to the test chamber. During this process, the air filter pressure on the back of the test chamber needed to be adjusted to 1.5 kg. Then, the spray switch was turned on, and the spray pressure value on the front panel was adjusted to 1.0 kg. The timing test then began.

[0119] During the experiment, sampling and testing were conducted every 16 hours of corrosion. After the samples had naturally cooled to room temperature, all test pieces were first removed and rinsed with tap water for 5 minutes to remove any deposited salt from the sample surface. Then, they were further rinsed with distilled water and the surface moisture was blown away with dry compressed air. Next, they were allowed to air dry for 24 hours. Finally, a transfer impedance testing system was set up to measure and record the results. After completing the above procedures, one set of samples (3 parallel samples) was retained, and the remaining samples were returned to the test chamber for the next corrosion test interval.

[0120] After the corrosion test, a total of six sets of data were obtained: initial data, and data at 16h, 32h, 48h, 64h, and 80h. Figure 4 As shown in Table 1.

[0121] Simplifying other factors, assuming the micro-gap structure of the shielding enclosure is a 2mm wide seam on the surface, the conductivity of the micro-gap structure can be calculated using the following formula:

[0122]

[0123] In the formula, σ2 is the equivalent conductivity; f is the frequency; μ is the permeability; h1 is the width of the actual microslit structure; h2 is the width of the equivalent microslit structure; n is a constant representing the multiple between the depth through which current flows in the conductor and the trend depth; Z T1 This is the measured transfer impedance of a micro-slit structure.

[0124] Table 1

[0125] Test duration sample Test frequency range Average equivalent conductivity (S / m) 0h beryllium bronze metal gasket 10kHz–1.2GHz 91.91 16h beryllium bronze metal gasket 10kHz–1.2GHz 42.52 32h beryllium bronze metal gasket 10kHz–1.2GHz 37.85 48h beryllium bronze metal gasket 10kHz–1.2GHz 14.59 64h beryllium bronze metal gasket 10kHz–1.2GHz 14.70 80h beryllium bronze metal gasket 10kHz–1.2GHz 15.02

[0126] The conductivity degradation results of the micro-slit structure on the surface of the shielding box during the corrosion test are as follows:

[0127] According to the conductivity test results, after 48 hours of corrosion testing, the average conductivity of the micro-gap structure decreased to 14.59 S / m, a decrease of more than 80% of the initial value. This indicates that corrosion of the micro-gap structure leads to a significant decrease in the shielding effectiveness of the enclosure.

[0128] Simulation Examples

[0129] A 3D simulation model of the shielding enclosure is established based on its geometric dimensions and material, such as... Figure 6 As shown, using an aerospace-grade aluminum shielding enclosure as an example, the main body of the enclosure is a cube with a side length of 310mm and a wall thickness of 10mm, while the cover plate is a square plate with a side length of 380mm. By opening a square test window with a side length of 200mm on the front cover plate and using a square test pressure plate with a side length of 260mm, the seam between the two square cover plates is the corrosion-sensitive structure of the shielding enclosure. In this simulation model, the green "ring-shaped band" located between the two cover plates is a uniform and isotropic equivalent gap, with a width of h2, which is the distance between the contact surfaces of the two cover plates. To avoid excessive computational resources due to an excessively small h2 value leading to overly fine meshing, h2 generally needs to be on the same order of magnitude as the enclosure thickness.

[0130] Then, the conductivity is imported using the import function in the parameter setting process and assigned to the equivalent gap. Taking the HFSS simulation process as an example, the process of importing and assigning experimental data to the equivalent gap is as follows. First, open the material library interface, select the new material to be assigned the equivalent gap (in this case, the material is named "DUT"), click the edit button to open its editing interface, and open the material properties interface. In this interface, you can set various properties of the material. However, in this embodiment, the conductivity is frequency-varying, so you need to select the "Set Frequency Variation" button in the lower left corner to open the editing interface for setting the frequency-varying material, and select the "Input Points that Change with Frequency" option in the sub-interface. Enter the selection interface to select the material properties that need to be set to be frequency-varying. This article only involves the frequency variation setting of conductivity. After setting it, the calculated frequency variation test input import interface is as follows. Figure 7 As shown.

[0131] In the selection interface, you can also manually input the frequency-varying conductivity point by point in the input field on the left. Alternatively, you can import the data as a ".dat" format data table using the import data button above; the results from both methods are consistent. After importing the frequency-varying data points, you can observe the frequency variation pattern of the imported data in the plotting box on the right. After completing the above import process, confirm and save the settings to assign the frequency-varying experimental data to the gaps, thus completing the data embedding.

[0132] After embedding the experimental data into the simulation model, the solution conditions need to be set, including boundary conditions, excitation sources, and solution frequencies. HFSS has an embedded radiation boundary, suitable for electromagnetic shielding simulations; simply selecting the solution frequency will automatically define the boundary. During simulation, the boundary frequency should be selected as the lower limit frequency. Simulating frequency bands with large variations will result in excessively high mesh density in the high-frequency range, leading to solution failure. A suitable solution frequency band is where the upper limit frequency is 3 to 5 times the lower limit frequency. Beyond this range, it is recommended to use piecewise solutions and then stitch the simulation results together.

[0133] For the excitation source setting, the "3m method" is followed. A plane wave with an amplitude of 1V / m is set as the excitation source at a distance of 3m from the shield in the positive x-axis direction of the simulation model. The solution frequency is set according to actual needs, and in this invention, it is 10kHz to 1.2GHz. The solution accuracy is set as needed; in this invention, it is set to 0.001, meaning the error between two iterations does not exceed 0.001, which ensures good accuracy.

[0134] Finally, the electric field strength at the geometric center point inside the shield is calculated separately with and without shielding, and the shielding effectiveness is then calculated accordingly. According to the properties of plane waves, the electric field strength at the monitoring point is 1 V / m (0 dB) without shielding. After adding a shield, if the electric field strength at the monitoring point is X... se dB, then the shielding effectiveness of the enclosure is |X se |dB, which means that the equivalent simulation of the shielding effectiveness of the shielding body has been completed.

[0135] After the corrosion test, the equivalent conductivity of the gap structure obtained from the test was substituted into the joint structure of the simulation model. Figure 8 The measured and simulated values ​​of the enclosure shielding effectiveness are compared after 80 hours of degradation. The measured and simulated values ​​are 52.59 dB and 51.18 dB, respectively, with an error of 1.41 dB.

[0136] like Figures 9-11As shown in the electric field cloud map, the shielding effectively shields the electric field. Electric field spikes mainly appear at the edges of the shielding box cover and at the seams of the cover – i.e., the tested contact structure. This result indicates that the electric field leaking into the shielding body is primarily caused by leakage at the box seams. The magnetic field distribution cloud map shows that the magnetic field is significantly weakened at the surface of the shielding body, with no obvious spikes even at the gaps. This is because the box material is aluminum, which has high permeability, and the gaps are very narrow, with minimal air gap influence. Therefore, the shielding body can form a closed magnetic circuit, guiding the magnetic field to propagate on the surface of the shielding body without entering its interior, thus achieving good magnetic field shielding effectiveness. Observing the surface current distribution, it can be seen that the surface current is consistent with the electric field distribution, mainly converging at the seams and the edges of the cover. The surface current accumulating at the gaps causes a significant voltage drop when flowing through them. According to relevant research, this voltage drop at the gaps is equivalent to a new electromagnetic wave emission source, which will emit electromagnetic waves into the shielding body, leading to a decrease in the electromagnetic shielding effectiveness of the shielding body. Analysis of the cloud map distribution results shows that the seams of the shielding body are one of the main reasons for the decline in its shielding effectiveness. The corrosion and degradation of the seams will lead to a decrease in the electrical continuity of the seams and an increase in the transfer impedance. This will increase the ability of the gaps to emit electromagnetic waves into the shielding box, resulting in a significant decrease in shielding effectiveness.

[0137] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions, characterized in that: It includes the following steps: S1. The calculation model for equivalent conductivity is constructed as follows: ； In the formula, Equivalent conductivity; For frequency; Permeability; The width of the actual micro-slit structure; The width of the equivalent micro-slit structure; is a constant, representing the multiple between the depth through which current flows in the conductor and the tendency depth; The measured transfer impedance of the micro-slit structure; S2. Construct a shielded box with a micro-gap structure and multiple sets of gap structure samples, each set of gap structure samples including at least three gap structure samples. S3. Simulate corrosion conditions, corrode multiple groups of crevice structure samples, and collect experimental data to obtain the measured transfer impedance of the micro-crevice structure. This includes the following sub-steps: S31. Simulate corrosion conditions and corrode multiple groups of crevice structure samples, specifically including: S311. Preparation of acidic salt solution for the experiment: Prepare NaCl solution and stir to dissolve NaCl. Then add glacial acetic acid solution and stir again. Measure the pH value to reach 3.0~3.

1. After standing for a period of time, measure the pH value of the solution again. Adjust according to the measurement results to make the pH value of the solution constant at 3.

0. S312. Turn on the power to the salt spray test chamber, set the temperature of the salt spray test chamber to 30±5℃, set the temperature of the saturation tank to 40±5℃, add water to the test chamber and the saturation tank, and then add the NaCl solution with pH=3.0 prepared in step S311 to the salt spray test chamber. S313. Place multiple sets of crevice structure samples into the salt spray test chamber in sequence. After filling the sealed water tank at the top of the salt spray test chamber with clean water and sealing it, supply air to the salt spray test chamber. At the same time, adjust the air filter pressure on the back of the salt spray test chamber to 1.5±0.1kg. Then turn on the spray switch and adjust the spray pressure to 1.0±0.1kg to start the test. During the test, set a certain time interval for sampling and testing. Sampling and testing are carried out after a certain time interval between each corrosion. S314. After taking out a set of crevice structure samples, measure and record the transfer impedance. Put the remaining crevice structure samples back into the salt spray test chamber for the next time interval corrosion test. S32. Data collection and processing: The average value of the transfer impedance of multiple samples in each group of slit structure samples is taken as the measured transfer impedance of the micro-slit structure. S4. Calculate the equivalent conductivity using the equivalent conductivity calculation model constructed in step S1 and predict the electromagnetic shielding performance of the electronic equipment. The specific steps are as follows: S41. Obtain the measured transfer impedance of the micro-crack structure under different corrosion degrees during the corrosion test and calculate multiple sets of equivalent conductivity. S42. Plot multiple sets of equivalent conductivity parameters as regular curves, fit the data to derive a performance prediction model for conductivity degradation over corrosion time, and determine the trend of decreased shielding effectiveness due to performance degradation of the micro-gap structure in the shielding enclosure. If the decrease in equivalent conductivity exceeds 50% of the initial value, the shielding function of the enclosure is deemed to have failed. The performance prediction model is obtained by data fitting based on an exponential form, and the expression is: ； In the formula, Equivalent conductivity Corrosion time; Alternatively, multiple sets of equivalent conductivity parameters can be input into the simulation model to predict the shielding performance of the shielded enclosure.

2. The method for predicting the electromagnetic shielding performance of electronic devices with micro-slot structures under corrosive conditions according to claim 1, characterized in that: In step S312, when the test chamber is powered on for the first time, if the test low water level light and the saturation tank low water level light are lit, add an appropriate amount of clean water to the test chamber until the test low water level light goes out. Then add clean water through the manual water inlet of the saturation tank until the saturation tank low water level indicator light goes out.

3. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 1, characterized in that: In step S313, when sampling and testing are performed after each corrosion interval, the sample should be allowed to cool naturally to room temperature. First, the sample should be taken out and rinsed with water to remove the deposited salt on the sample surface. Then, it should be rinsed further with distilled water and the moisture on the sample surface should be blown away with dry compressed air. Finally, it should be left to dry naturally for a certain period of time.

4. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 3, characterized in that: In step S313, the natural drying time is 24h, 36h, or 48h.

5. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 1, characterized in that: In step S311, the NaCl solution has a mass concentration of 5% and is left to stand for 30 minutes.

6. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 1, characterized in that: The gap structure includes a first insulating block, a second insulating block, and a contact structure simulation area. The first insulating block, the second insulating block, and the contact structure simulation area are fixed together by means of fastening bolts. A non-conductive sealing gasket is provided between the first insulating block and the fastening bolts. The contact structure simulation area includes a first metal clip, a second metal clip, and a test gasket. The test gasket is disposed between the first metal clip and the second metal clip.

7. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 1, characterized in that: The specific steps in step S42 to input multiple sets of equivalent conductivity parameters into the simulation model to predict the shielding performance of the shielded enclosure are as follows: S421. Construct a simulation box model according to the actual experimental dimensions, and set the geometric parameters, including the length, width, height and thickness of the shielding box. The length and width of the shielding box are the same as the external length and width of the equivalent micro gap, and the thickness of the shielding box is the difference between the inner length and outer length of the equivalent micro gap. S422. Draw the geometric model and complete the simulation excitation source and boundary condition settings; S423. Complete the mesh generation settings. By refining the mesh of the equivalent micro-slit structure, set the maximum mesh size so that there are 3-5 meshes in the width direction of the micro-slits. S424. Complete the field monitor settings, set the field monitoring point at the geometric center of the shielded box, and set the solver at the same time; S425. Import multiple sets of equivalent conductivity data into the equivalent micro-gap structure, set the model simulation frequency, and set the frequency sweep method to logarithmic sweep. Specify the upper limit frequency and lower limit frequency as the lowest and highest frequency points of the simulation, and specify the total number of frequency points as the total number of frequency points in the simulation. S426. Based on steps S421-S425, solve for the electric and magnetic field strengths inside the shielding box under different equivalent conductivity, and calculate and output the shielding effectiveness monitoring value of the box according to the electric and magnetic field strength values.

8. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 3, characterized in that: In step S313, the sampling and testing interval is 8h, 16h, 24h, 32h or 48h.

9. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 1, characterized in that: Step S1 specifically includes the following sub-steps: S11. Construct a shielded box model with a gap structure. The width of the gap structure is h, and the cross-sectional area is S. S12. Assuming that width leakage is not considered, the impedance of the equivalent micro-gap structure of the shielded enclosure can be expressed by its volume resistance in the width direction. S13. Construct a calculation model for equivalent conductivity.

10. The method for predicting the electromagnetic shielding performance of electronic devices with micro-gap structures under corrosive conditions according to claim 9, characterized in that: The specific process of constructing the calculation model for equivalent conductivity in step S13 is as follows: The volume resistance expression for an equivalent micro-slit structure is: ； ； In the formula, h represents the gap width, and S represents the gap area. Represents resistivity. Indicates the electrical conductivity of the gap; Assuming the actual width of the gap is The transfer impedance obtained from the test is The contact area, width, gap length, and conductivity of the equivalent model are respectively... The equivalent volume impedance of the micro-slit structure is The volume resistance is Considering the skin depth under high-frequency conditions, we get: ； This ensures that the equivalent micro-slot structure model and the actual micro-slot structure model have the same shielding effectiveness. and The equivalence relation must be satisfied, that is ； Further derivation yields the following calculation model for equivalent conductivity: 。

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