Indirect testing method for shielding effectiveness of multi-layer shielding body

Abstract

The invention belongs to the technical field of electromagnetic shielding. The invention provides a method for indirectly testing the shielding effectiveness of a multi-layer shielding body. According to the embodiment of the invention, the short-circuit field and the aperture leakage field at the aperture are solved by adopting a method based on the magnetic covector Green function of the shield and the Bethe aperture coupling theory, and the solved superposition correction factor can consider the reflection effect of the wall surface of the cavity on the electromagnetic wave, so that the multilayer shielding effectiveness obtained by correction is closer to a true value; and meanwhile, the condition of any relative position of the inner and outer layer apertures can be processed by superposing the correction factors, so that the application range of the scheme is expanded.

Description

Technical Field

[0001] The disclosed embodiments relate to the field of electromagnetic shielding technology, and more particularly to an indirect testing method for the shielding effectiveness of a multi-layer shielding body. Background Art

[0002] Ultra-high performance shielding is often achieved by multi-layer shielding. For example, electronic systems, such as large radio telescope systems, usually achieve a shielding effectiveness of 140dB to 160dB. However, the ultra-high shielding effectiveness of multi-layer shields exceeds the dynamic range limit of existing shielding effectiveness test systems, which brings great difficulties to the shielding effectiveness test of multi-layer shields. In addition, the existing method directly adds the shielding effectiveness of each layer of shields, and the results obtained are often quite different from the actual shielding effectiveness of multi-layer rectangular shields. Summary of the invention

[0003] In order to avoid the shortcomings of the prior art, the present application provides an indirect testing method for the shielding effectiveness of a multi-layer shield, so as to solve the problems in the prior art that the existing shielding effectiveness testing system has a limited dynamic range and large result errors.

[0004] According to an embodiment of the present disclosure, a method for indirect testing of shielding effectiveness of a multi-layer shield is provided, the method comprising: Obtaining a double-layer distance parameter of the double-layer shielding body; wherein the double-layer shielding body comprises an inner shielding body and an outer shielding body; Based on the test standard, obtaining the inner distance parameter of the inner shield and the outer distance parameter of the outer shield; Determine a method for obtaining a magnetic dyadic Green's function of the double-layer shield according to a ratio of a size of the inner shield to a size of the outer shield, and obtain the magnetic dyadic Green's function according to the obtaining method; Obtaining a superposition correction factor of the double-layer shielding body according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function; Based on the test standard, respectively performing shielding effectiveness tests on the inner shielding body and the outer shielding body to obtain the inner shielding effectiveness of the inner shielding body and the outer shielding effectiveness of the outer shielding body; The double-layer shielding effectiveness is obtained according to the inner-layer shielding effectiveness, the outer-layer shielding effectiveness and the superposition correction factor.

[0005] Furthermore, the inner distance parameters include: Distance from transmitting antenna to inner shield , the distance from the receiving antenna to the inner shield The first distance between the transmitting and receiving antennas ; The outer distance parameters include: Distance from transmitting antenna to outer shield , the distance from the receiving antenna to the outer shield The second distance between the transmitting and receiving antennas ; The double-layer distance parameters include: Distance from the transmitting antenna to the inner shield of the double shield , the distance from the transmitting antenna to the outer shield in the double shield The third distance between the transmitting and receiving antennas .

[0006] Further, according to the ratio of the size of the inner shielding body to the size of the outer shielding body, a method for obtaining the magnetic dyadic Green's function of the double-layer shielding body is determined, and the step of obtaining the magnetic dyadic Green's function according to the acquisition method includes: If the ratio of the size of the inner shield to the size of the outer shield is less than a preset threshold, the magnetic dyadic Green's function of the outer shield is calculated according to the double-layer distance parameter, and the magnetic dyadic Green's function of the outer shield is used as the magnetic dyadic Green's function of the double-layer shield; If the ratio of the size of the inner shielding body to the size of the outer shielding body is greater than a preset threshold, a numerical simulation method is used to obtain the magnetic dyadic Green's function of the double-layer shielding body.

[0007] Furthermore, the step of obtaining the magnetic dyadic Green's function of the double-layer shielding body by using a numerical simulation method includes: Determine the type of the equivalent dipole source of the test antenna; wherein the type of the equivalent dipole source of the test antenna includes a magnetic dipole and an electric dipole; Constructing a double-layer shielding simulation model according to the double-layer distance parameter and the type of the equivalent dipole source of the test antenna; If the type of the equivalent dipole source of the test antenna is the magnetic dipole, a tangential magnetic dipole is placed at the inner hole; The first electric field at the outer hole is obtained by using the double-layer shield simulation model. f e and the first magnetic field f n ; Based on the magnetic dyadic Green's function of the outer shield, according to the first electric field f e and the first magnetic field f n A first magnetic dyadic Green's function of the double-layer shield is obtained.

[0008] Further, if the type of the equivalent dipole source of the test antenna is the electric dipole, a tangential magnetic dipole is placed at the inner hole; The second electric field at the outer hole is obtained by using the double-layer shield simulation model. g e and the second magnetic field g n ; Based on the magnetic dyadic Green's function of the outer shield, according to the second electric field g e and the second magnetic field g n A second magnetic dyadic Green's function of the double-layer shield is obtained.

[0009] Furthermore, the step of obtaining the superposition correction factor of the double-layer shielding body according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function includes: Based on Bethe's small hole coupling theory, the superposition correction factor of the double-layer shielding body is obtained according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function of the double-layer shielding body.

[0010] Furthermore, the superposition correction factor includes: Magnetic field superposition correction factor and electric field superposition correction factor ;in, The magnetic field superposition correction factor The expression is:

[0011] In the formula, To test the magnetic field superposition correction factor when the antenna is horizontally polarized, To test the magnetic field superposition correction factor when the antenna is vertically polarized, is the first row and first column element of the magnetic dyadic Green's function of the outer shield, is the first row and first column element of the first magnetic dyadic Green's function of the double-layer shield, is the position vector of the equivalent dipole source in the inner shield, is the position vector of the inner shield hole, When testing the shielding effectiveness of the inner shield, the position vector of the transmitting antenna is is the third row and third column element of the magnetic dyadic Green's function of the outer shield, is the third row and third column element of the first magnetic dyadic Green's function of the double-layer shield; The electric field superposition correction factor The expression is:

[0012] To test the electric field superposition correction factor when the antenna is horizontally polarized, To test the electric field superposition correction factor when the antenna is vertically polarized, is the wave index, is the third row and first column element of the magnetic dyadic Green's function of the outer shield, It is the first row and third column element of the magnetic dyadic Green's function of the outer shield.

[0013] Further, based on the test standard, the steps of respectively testing the shielding effectiveness of the inner shield and the outer shield to obtain the inner shielding effectiveness of the inner shield and the outer shielding effectiveness of the outer shield include: Based on the test standard, a through calibration test is performed to obtain an inner layer through power level; Based on the test standard, the test antenna and the test instrument are arranged to perform a shielding effectiveness test on the inner shielding body to obtain the power level after the inner shielding and the inner distance parameter of the inner shielding body; Obtaining the inner shielding effectiveness according to the through power level and the inner shielding power level; Based on the test standard, a through calibration test is performed to obtain an outer layer through power level; Based on the test standard, the test antenna and the test instrument are arranged to perform a shielding effectiveness test on the outer shielding body to obtain the power level after the outer shielding and obtain the outer distance parameter of the outer shielding body; The outer shielding effectiveness is obtained according to the through power level and the outer shielding power level.

[0014] The technical solution provided by the embodiments of the present disclosure may have the following beneficial effects: In the embodiment of the present disclosure, through the above-mentioned indirect test method for the shielding effectiveness of the multi-layer shield, for the nested shield, the method based on the magnetic dyadic Green's function of the shield and Bethe's small hole coupling theory is used to solve the short-circuit field and the leakage field at the aperture, and the obtained superposition correction factor can take into account the reflection effect of the cavity wall on the electromagnetic wave, so that the corrected multi-layer shielding effectiveness is closer to the true value. At the same time, the superposition correction factor can handle the situation when the inner and outer layer apertures are in any relative position, thereby expanding the scope of application of the scheme. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present disclosure, and together with the specification are used to explain the principles of the present disclosure. Obviously, the accompanying drawings described below are only some embodiments of the present disclosure, and for ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without creative work.

[0016] Figure 1 A step diagram showing a method for indirectly testing the shielding effectiveness of a multi-layer shield in an exemplary embodiment of the present disclosure; Figure 2 A schematic diagram showing a double-layer shielding body in an exemplary embodiment of the present disclosure; Figure 3 A schematic diagram showing the inner and outer single-layer shielding effectiveness test in an exemplary embodiment of the present disclosure; Figure 4 A schematic diagram of a double-layer shielding effectiveness test in an exemplary embodiment of the present disclosure is shown; Figure 5 A schematic diagram of a double-layer rectangular cavity shielding cavity in an exemplary embodiment of the present disclosure is shown; Figure 6 A flow chart of obtaining the magnetic dyadic Green's function by using a numerical simulation method in an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0017] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that the disclosure will be more comprehensive and complete and to fully convey the concepts of the example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0018] In addition, the accompanying drawings are only schematic illustrations of the embodiments of the present disclosure and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and their repeated descriptions will be omitted. Some of the block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0019] This exemplary embodiment provides an indirect test method for the shielding effectiveness of a multi-layer shield. Figure 1 As shown in , the indirect testing method for the shielding effectiveness of a multi-layer shield may include: steps S101 to S106.

[0020] Step S101: obtaining a double-layer distance parameter of the double-layer shielding body; wherein the double-layer shielding body comprises an inner shielding body and an outer shielding body; Step S102: based on the test standard, obtaining the inner distance parameter of the inner shield and the outer distance parameter of the outer shield; Step S103: determining a method for obtaining a magnetic dyadic Green's function of the double-layer shield according to a ratio of a size of the inner shield to a size of the outer shield, and obtaining the magnetic dyadic Green's function according to the obtaining method; Step S104: obtaining a superposition correction factor of the double-layer shield according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function; Step S105: Based on the test standard, respectively perform shielding effectiveness tests on the inner shielding body and the outer shielding body to obtain the inner shielding effectiveness of the inner shielding body and the outer shielding effectiveness of the outer shielding body; Step S106: Obtaining double-layer shielding effectiveness according to the inner-layer shielding effectiveness, the outer-layer shielding effectiveness and the superposition correction factor.

[0021] Through the above-mentioned indirect test method of the shielding effectiveness of multi-layer shields, for nested shields, the short-circuit field and leakage field at the apertures are solved by using the method based on the magnetic dyadic Green's function of the shield and Bethe's small hole coupling theory. The obtained superposition correction factor can take into account the reflection effect of the cavity wall on the electromagnetic wave, making the corrected multi-layer shielding effectiveness closer to the true value. At the same time, the superposition correction factor can handle the situation when the inner and outer apertures are in any relative position, thereby expanding the scope of application of the scheme.

[0022] Next, we will refer to Figures 1 to 6 Each part of the above-mentioned indirect testing method of the shielding effectiveness of the multi-layer shield in this exemplary embodiment is described in more detail.

[0023] In step S101 to step S102, double-layer distance parameters of a double-layer shield are obtained; wherein the double-layer shield includes an inner shield and an outer shield; based on the test standard, inner distance parameters of the inner shield and outer distance parameters of the outer shield are obtained.

[0024] In step S103 to step S104, a method for obtaining the magnetic dyadic Green's function of the double-layer shielding body is determined according to the ratio of the size of the inner shielding body to the size of the outer shielding body, and the magnetic dyadic Green's function is obtained according to the acquisition method; a superposition correction factor of the double-layer shielding body is obtained according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function.

[0025] Specifically, if the ratio of the size of the inner shield to the size of the outer shield is less than a preset threshold, the magnetic dyadic Green's function of the outer shield is calculated according to the double-layer distance parameter, and the magnetic dyadic Green's function of the outer shield is used as the magnetic dyadic Green's function of the double-layer shield; If the ratio of the size of the inner shield to the size of the outer shield is greater than a preset threshold, a numerical simulation method is used to obtain the magnetic dyadic Green's function of the double shield. More specifically, Determine the type of the equivalent dipole source of the test antenna; wherein the type of the equivalent dipole source of the test antenna includes a magnetic dipole and an electric dipole; construct a double-layer shielding simulation model according to the double-layer distance parameter and the type of the equivalent dipole source of the test antenna; If the type of the equivalent dipole source of the test antenna is a magnetic dipole, a tangential magnetic dipole is placed at the inner hole; the first electric field at the outer hole is obtained by using the double-layer shielding simulation model. f e and the first magnetic field f n Based on the magnetic dyadic Green's function of the outer shield, according to the first electric field f e and the first magnetic field f n The first magnetic dyadic Green's function of the double-layer shield is obtained.

[0026] If the type of the equivalent dipole source of the test antenna is an electric dipole, a tangential magnetic dipole is placed at the inner hole; the second electric field at the outer hole is obtained by using the double-layer shielding simulation model. g e and the second magnetic field g n Based on the magnetic dyadic Green's function of the outer shield, according to the second electric field g e and the second magnetic field g n The second magnetic dyadic Green's function of the double-layer shield is obtained.

[0027] Based on Bethe's small hole coupling theory, the superposition correction factor of the double-layer shielding body is obtained according to the magnetic dyadic Green's function of the double-layer shielding body with double-layer distance parameter, inner layer distance parameter and outer layer distance parameter.

[0028] In step S105 to step S106, based on the test standard, the shielding effectiveness of the inner shielding body and the outer shielding body are tested respectively to obtain the inner shielding effectiveness of the inner shielding body and the outer shielding effectiveness of the outer shielding body; the double-layer shielding effectiveness is obtained according to the inner shielding effectiveness, the outer shielding effectiveness and the superposition correction factor.

[0029] Specifically, based on the test standard, a through calibration test is performed to obtain an inner layer through power level; Based on the test standard, test instruments such as test antennas are arranged to test the shielding effectiveness of the inner shielding body to obtain the power level after the inner shielding and the inner distance parameters of the inner shielding body; The inner shielding effectiveness is obtained according to the through power level and the power level after the inner shielding; Based on the test standard, a through calibration test is performed to obtain the outer through power level; Based on the test standard, test antennas and other test instruments are arranged to test the shielding effectiveness of the outer shielding body to obtain the power level after the outer shielding and the outer distance parameters of the outer shielding body; The outer shielding effectiveness is obtained based on the direct power level and the power level behind the outer shielding.

[0030] The double-layer shielding effectiveness is obtained based on the inner shielding effectiveness, outer shielding effectiveness and superposition correction factor.

[0031] In a specific embodiment, when the test antenna is a loop antenna (equivalent to a magnetic dipole), the test frequency band is 10kHz-20MHz, and the receiving antenna is located in the near field of the transmitting antenna. At this time, the magnetic field generated by the magnetic dipole at the same position is much larger than the electric field.

[0032] When the test antenna is a symmetrical oscillator antenna or a horn antenna (equivalent to an electric dipole), the test frequency band is above 20MHz, and the receiving antenna is located in the far field of the transmitting antenna. At this time, the electric field and magnetic field strengths generated by the magnetic dipole or electric dipole at the same position are consistent.

[0033] The scheme is described in detail using a double-layer rectangular cavity as an example. Figure 2 shown.

[0034] Figure 2 The size of the inner shielding cavity is , the outer shielding cavity size is ; Point is the leakage field strength monitoring point outside the cavity.

[0035] like Figure 3 The figure shows the schematic diagram of the inner and outer single-layer shielding effectiveness test.

[0036] like Figure 4 The figure shows a schematic diagram of double-layer shielding effectiveness test.

[0037] Figure 3 and Figure 4 The meanings of the distance and test result parameters are shown in Table 1.

[0038] Table 1 Single-layer and double-layer shielding effectiveness test parameters

[0039] The magnetic field shielding effectiveness of the inner, outer and double-layer cavities is , , , the electric field shielding effectiveness is , , The superposition correction factors of magnetic field and electric field shielding effectiveness are , , then the correction scheme for magnetic field shielding effectiveness and electric field shielding effectiveness is shown in the following formula.

[0040]

[0041] Superposition correction factors for magnetic field and electric field shielding effectiveness respectively , Perform calculations.

[0042] 1. The specific calculation process is: 1.1 Receiving field strength in direct-through state , of calculate.

[0043] The test loop antenna is equivalent to a magnetic dipole, the direction of which is perpendicular to the plane of the loop antenna. The dipole size is , the field strength at the receiving antenna in the through test state is as follows:

[0044] in, is the first through-field magnetic field strength of the inner shield at the receiving antenna in the through-field test state, is the second through-field magnetic field strength of the outer shield at the receiving antenna in the through-field test state, is the third through-field magnetic field strength of the double-layer shield at the receiving antenna in the through-field test state, is the first distance between the transmitting and receiving antennas in the inner shield test, is the second distance between the transmitting and receiving antennas in the outer shield test, The third distance between the transmitting and receiving antennas in the double shield test. j is the imaginary part of the complex number, is the angular frequency, is the magnetic permeability of vacuum.

[0045] 1.2 Single-layer shielding receiving field strength and Calculation.

[0046] The leakage field intensity generated by the opening of the shield can be calculated by Bethe's small hole coupling theory. The principle is that when the hole size is much smaller than the wavelength of the electromagnetic wave, the leakage field intensity generated by the opening can be equivalent to the vector superposition of the equivalent normal electric dipole and tangential magnetic dipole radiation field at the opening, such as Figure 4 shown.

[0047] The equivalent normal electric dipole and tangential magnetic dipole As shown below:

[0048] is the normal electric field at the opening, is the tangential magnetic field at the opening, is the electric susceptibility, is the magnetic polarizability, is the dielectric constant of vacuum. , The polarizability formulas for circular and rectangular holes are related to the hole shape and are shown in Table 2.

[0049] Table 2 Polarization ratio of circular and rectangular openings

[0050] Therefore, in order to apply Bethe's small hole coupling theory, the field strength at the opening must be known, so the magnetic dyadic Green's function is introduced for calculation. The calculation formulas for the electric and magnetic fields of the magnetic dipole at the opening are shown below:

[0051] in, is the equivalent magnetic dipole size, and are the electric field intensity and magnetic field intensity at the opening, respectively. is the angular frequency, is the dielectric constant of vacuum, and are the electric dyadic Green's function and magnetic dyadic Green's function of the rectangular cavity under the excitation of the magnetic flux element, as shown in the following formula:

[0052]

[0053] in Respectively, the rectangular cavity Dimensions in direction; The value is an integer greater than or equal to 0; ; , is the speed of light; ;when hour, ,otherwise , The definition is the same as; , , and so on, among which is the coordinate of the opening position, are the equivalent test antenna coordinates.

[0054] The above is the calculation principle of the shield opening leakage field strength. The single-layer shield receiving field strength , The specific calculation process is: a. Calculate the tangential magnetic field strength at the opening set up is the magnetic field strength at the opening; , , , , , , , , To express The 9 elements.

[0055]

[0056] b. Calculate the equivalent magnetic dipole of the opening

[0057] c. Calculate the magnetic field strength at the receiving antenna

[0058]

[0059] in, is the component of the first shielding magnetic field strength in the X-axis direction, is the component of the first shielding magnetic field strength in the Z-axis direction, is the component of the second shielding magnetic field strength in the X-axis direction, is the component of the second shielding magnetic field strength in the Z-axis direction, and It will be eliminated as a whole in subsequent calculations.

[0060] 1.3 Calculation of double-layer shielding receiving field strength .

[0061] Double-layer rectangular cavity Figure 5 shown.

[0062] 1) Calculate the magnetic field strength at the opening of the inner layer of the double-layer shield set up is the magnetic field strength at the inner opening, is the magnetic dyadic Green's function of the inner rectangular cavity, and the calculation is shown in the following formula:

[0063] 2) Calculate the equivalent magnetic dipole of the inner opening of the double-layer shield Assume that the equivalent magnetic dipole of the inner hole is , according to Bethe's small hole coupling theory, the calculation formula is as follows.

[0064]

[0065] 3) Calculate the magnetic field strength at the opening of the outer layer of the double-layer shield The calculation of the magnetic field intensity at the outer opening requires the magnetic dyadic Green's function of the cavity between the inner and outer layers, which is expressed as , Since the cavity between the inner and outer layers is not a regular rectangular cavity, there is no analytical expression.

[0066] For inner and outer cavities of different relative sizes, when the ratio of the size of the outer cavity to the inner cavity is large enough (for example, when the ratio of the side lengths of the outer and inner cavities is greater than 6), the influence of the inner cavity can be approximately ignored.

[0067] When the size ratio of the inner and outer cavities is small and the influence of the inner cavity on the magnetic dyadic Green's function cannot be ignored, the accurate magnetic dyadic Green's function of the outer space is obtained by numerical simulation. Figure 6 In the process shown, Feko simulation is used to obtain the magnetic dyadic Green's function of the irregular cavity.

[0068] First, construct a double-layer shield simulation model, establish an electric dipole or magnetic test antenna at the inner hole, set their size to 1, and then set the field point at the outer shield hole.

[0069] The uniqueness theorem of the sinusoidal steady-state field states that "in the region V enclosed by the closed surface S, when the tangential component of the electric field intensity or the tangential component of the magnetic field intensity on the boundary surface S is given, the electromagnetic field at any point in the volume V is uniquely determined by the Maxwell equations". Therefore, for a certain boundary condition, the magnetic dyadic Green's function that satisfies the boundary condition is unique, that is, the magnetic dyadic Green's function of the irregular cavity obtained by the numerical simulation method is accurate. At the same time, due to the flexibility of numerical simulation, this method can solve the magnetic dyadic Green's function of the inner and outer cavities and the apertures in arbitrary relative positions.

[0070] That is, according to Figure 6The steps shown are used to obtain the transfer function from the dipole at the inner hole to the field at the outer hole, and then the numerical solution of the magnetic dyadic Green's function is obtained by deriving the relationship between the transfer function and the magnetic dyadic Green's function. Then, the short-circuit field generated by the equivalent dipole of the inner hole in the outer cavity is calculated in combination with the Bethe small hole coupling theory, thereby calculating the shielding effectiveness of the nested double-layer cavity.

[0071] At the same time, a simplified method for obtaining the magnetic dyadic Green's function is proposed based on the perturbation theory. This method analyzes and considers the influence of the inner and outer cavity sizes on the magnetic dyadic Green's function, that is, when the ratio of the inner and outer rectangular cavity sizes meets the perturbation criterion, the influence of the inner cavity is approximately ignored. For the case that does not meet the perturbation criterion, a method for obtaining its magnetic dyadic Green's function through numerical simulation software Feko simulation is proposed. This method greatly simplifies the calculation of the equivalent superposition correction factor while meeting the calculation correctness and effectiveness.

[0072] 4) Calculate the equivalent test antenna of the double-layer shielding outer opening (i.e. the fourth equivalent test antenna) Assume that the equivalent magnetic dipole of the outer hole is , according to Bethe's small hole coupling theory, the calculation formula is as follows:

[0073] Field strength at receiving antenna calculate: According to the calculation formula of magnetic dipole radiation field, As shown in the following formula.

[0074]

[0075] in, is the component of the double-shielding receiving field strength in the X-axis direction, It is the component of the double-layer shielding receiving field strength in the Z-axis direction.

[0076] calculate: Depend on:

[0077] Substituting the above derived results into it, we can get:

[0078] in is the position coordinate of the hole in the inner rectangular cavity during the shielding effectiveness test of the double-layer shield. It is the position coordinates of the transmitting antenna when the shielding effectiveness test of the outer cavity is performed in the same coordinate system.

[0079] 2. The specific calculation process is: The definition is shown in the following formula.

[0080]

[0081] 2.1 Receiving field strength in direct-through state , , calculate The transmitting antenna is equivalent to an electric dipole, and the dipole size is , the field strength at the receiving antenna in the through test state is shown as follows.

[0082]

[0083] 2.2 Single-layer shielding receiving field strength , calculate The calculation formulas for the electric field and magnetic field of an electric dipole at the opening are shown below.

[0084]

[0085] in is the equivalent electric dipole size, and are the electric field intensity and magnetic field intensity at the opening, respectively. is the angular frequency, is the vacuum permeability, and They are respectively the electric dyadic Green's function and the magnetic dyadic Green's function of the rectangular cavity under the excitation of the current element, as shown in the following formulas.

[0086]

[0087]

[0088] in Respectively, the rectangular cavity Dimensions in direction; The value is an integer greater than or equal to 0; ; , is the speed of light; ;when hour, ,otherwise , The definition is the same as; , , and so on, among which is the coordinate of the opening position, are the equivalent test antenna coordinates.

[0089] The above is the calculation principle of the shield opening leakage field strength. The single-layer shield receiving field strength , The specific calculation of is as follows.

[0090] a) Calculation of tangential magnetic field intensity at the opening set up is the magnetic field strength at the opening. , , , , , , , , To express The 9 elements.

[0091]

[0092] b) Calculation of equivalent magnetic dipole of opening

[0093] c) Calculation of electric field strength at the receiving antenna

[0094]

[0095] in, is the component of the first shielding electric field strength in the X-axis direction, is the component of the first shielding electric field strength in the Z-axis direction, is the component of the second shielding electric field strength in the X-axis direction, is the component of the second shielding electric field strength in the Z-axis direction.

[0096] 2.3 Double-layer shielding receiving field strength calculate Double-layer rectangular cavity Figure 5 shown.

[0097] The calculation steps are as follows.

[0098] a) Calculation of magnetic field strength at the inner opening set up is the magnetic field strength at the inner opening, is the magnetic dyadic Green’s function of the inner rectangular cavity, and the calculation is shown in the following formula.

[0099]

[0100] b) Calculation of equivalent magnetic dipole of inner opening Assume that the equivalent magnetic dipole of the inner hole is , according to Bethe's small hole coupling theory, the calculation formula is as follows.

[0101]

[0102] c) Calculation of magnetic field strength at the outer opening The calculation of the magnetic field intensity at the outer opening requires the magnetic dyadic Green's function of the cavity between the inner and outer layers, which is expressed as , since the cavity between the inner and outer layers is not a regular rectangular cavity, there is no analytical expression.

[0103] For inner and outer cavities of different relative sizes, when the ratio of the size of the outer cavity to the inner cavity is large enough (for example, when the ratio of the side lengths of the outer and inner cavities is greater than 6), the influence of the inner cavity can be approximately ignored.

[0104] When the size ratio of the inner and outer cavities is small and the influence of the inner cavity on the magnetic dyadic Green's function cannot be ignored, the accurate magnetic dyadic Green's function of the outer space is obtained by numerical simulation. Figure 6 In the process shown, Feko simulation is used to obtain the magnetic dyadic Green's function of the irregular cavity.

[0105] That is, according to Figure 6 The steps shown are used to obtain the transfer function from the dipole at the inner hole to the field at the outer hole, and then the numerical solution of the magnetic dyadic Green's function is obtained by deriving the relationship between the transfer function and the magnetic dyadic Green's function. Then, the short-circuit field generated by the equivalent dipole of the inner hole in the outer cavity is calculated in combination with the Bethe small hole coupling theory, thereby calculating the shielding effectiveness of the nested double-layer cavity.

[0106] At the same time, a simplified method for obtaining the magnetic dyadic Green's function is proposed based on the perturbation theory. This method analyzes and considers the influence of the inner and outer cavity sizes on the magnetic dyadic Green's function, that is, when the ratio of the inner and outer rectangular cavity sizes meets the perturbation criterion, the influence of the inner cavity is approximately ignored. For the case that does not meet the perturbation criterion, a method for obtaining its magnetic dyadic Green's function through numerical simulation software Feko simulation is proposed. This method greatly simplifies the calculation of the equivalent superposition correction factor while meeting the calculation correctness and effectiveness.

[0107] set up is the magnetic field intensity at the outer opening, and its calculation formula is as follows.

[0108]

[0109] d) Calculation of equivalent magnetic dipole of outer opening Assume that the equivalent magnetic dipole of the outer hole is , according to Bethe's small hole coupling theory, the calculation formula is as follows:

[0110] e) Field strength at the receiving antenna calculate According to the electric dipole radiation field calculation formula, As shown in the following formula.

[0111]

[0112] in, is the component of the double-shielding receiving field strength in the X-axis direction, It is the component of the double-layer shielding receiving field strength in the Z-axis direction.

[0113] calculate Depend on:

[0114] Substituting the above derived results into it, we can get:

[0115] in is the position coordinate of the hole in the inner rectangular cavity during the shielding effectiveness test of the double-layer shield. It is the position coordinates of the transmitting antenna when the shielding effectiveness test of the outer cavity is performed in the same coordinate system.

[0116] The traditional method of linearly superimposing the shielding effectiveness of each layer of shielding body to obtain a fixed shielding effectiveness of the multi-layer cavity, without considering the change in the position of the inner cavity in the outer cavity and the difference in the position and relative orientation of the holes in the inner and outer cavities on the shielding effectiveness of the multi-layer cavity. This application introduces the relative position of the holes in the inner cavity and the holes in the outer cavity based on the magnetic dyadic Green's function of the rectangular cavity; based on the Bethe small hole coupling theory, the relative orientation of the holes in the inner cavity and the holes in the outer cavity is introduced. The calculated shielding effectiveness changes with the change of the position and orientation of the holes, which is closer to the true value.

[0117] Through the above-mentioned indirect test method of the shielding effectiveness of multi-layer shields, for nested shields, the short-circuit field and leakage field at the apertures are solved by using the method based on the magnetic dyadic Green's function of the shield and Bethe's small hole coupling theory. The obtained superposition correction factor can take into account the reflection effect of the cavity wall on the electromagnetic wave, making the corrected multi-layer shielding effectiveness closer to the true value. At the same time, the superposition correction factor can handle the situation when the inner and outer apertures are in any relative position, thereby expanding the scope of application of the scheme.

[0118] This application introduces a superposition correction factor to correct the existing method, making the calculation result closer to the true value. For the nested multi-layer shield, based on the analysis of the cavity field distribution characteristics and the aperture coupling leakage factors, the rectangular cavity magnetic dyadic Green's function and Bethe small hole coupling theory are used to solve the short-circuit field and aperture leakage field at the aperture, and then the superposition correction factor is solved.

[0119] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0120] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0121] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the specification and practicing the invention disclosed herein. This application is intended to cover any modification, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the appended claims.

Claims

1. An indirect test method for the shielding effectiveness of a multi-layer shield, characterized in that: The method includes: Obtaining a double-layer distance parameter of the double-layer shielding body; wherein the double-layer shielding body comprises an inner shielding body and an outer shielding body; Based on the test standard, obtaining the inner distance parameter of the inner shield and the outer distance parameter of the outer shield; Determine a method for obtaining a magnetic dyadic Green's function of the double-layer shield according to a ratio of a size of the inner shield to a size of the outer shield, and obtain the magnetic dyadic Green's function according to the obtaining method; Obtaining a superposition correction factor of the double-layer shielding body according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function; Based on the test standard, respectively performing shielding effectiveness tests on the inner shielding body and the outer shielding body to obtain the inner shielding effectiveness of the inner shielding body and the outer shielding effectiveness of the outer shielding body; The double-layer shielding effectiveness is obtained according to the inner-layer shielding effectiveness, the outer-layer shielding effectiveness and the superposition correction factor.

2. The indirect testing method for shielding effectiveness of a multi-layer shield according to claim 1, characterized in that: The inner distance parameters include: Distance from transmitting antenna to inner shield , the distance from the receiving antenna to the inner shield The first distance between the transmitting and receiving antennas ; The outer distance parameters include: Distance from transmitting antenna to outer shield , the distance from the receiving antenna to the outer shield The second distance between the transmitting and receiving antennas ; The double-layer distance parameters include: Distance from the transmitting antenna to the inner shield of the double shield , the distance from the transmitting antenna to the outer shield in the double shield The third distance between the transmitting and receiving antennas .

3. The indirect testing method for shielding effectiveness of a multi-layer shield according to claim 2, characterized in that: According to the ratio of the size of the inner shielding body to the size of the outer shielding body, a method for obtaining the magnetic dyadic Green's function of the double-layer shielding body is determined, and the step of obtaining the magnetic dyadic Green's function according to the obtaining method includes: If the ratio of the size of the inner shield to the size of the outer shield is less than a preset threshold, the magnetic dyadic Green's function of the outer shield is calculated according to the double-layer distance parameter, and the magnetic dyadic Green's function of the outer shield is used as the magnetic dyadic Green's function of the double-layer shield; If the ratio of the size of the inner shielding body to the size of the outer shielding body is greater than a preset threshold, a numerical simulation method is used to obtain the magnetic dyadic Green's function of the double-layer shielding body.

4. The indirect testing method for shielding effectiveness of a multi-layer shield according to claim 3 is characterized in that: The step of obtaining the magnetic dyadic Green's function of the double-layer shielding body by using a numerical simulation method comprises: Determine the type of the equivalent dipole source of the test antenna; wherein the type of the equivalent dipole source of the test antenna includes a magnetic dipole and an electric dipole; Constructing a double-layer shielding simulation model according to the double-layer distance parameter and the type of the equivalent dipole source of the test antenna; If the type of the equivalent dipole source of the test antenna is the magnetic dipole, a tangential magnetic dipole is placed at the inner hole; The first electric field at the outer hole is obtained by using the double-layer shield simulation model. f e and the first magnetic field f n ; Based on the magnetic dyadic Green's function of the outer shield, according to the first electric field f e and the first magnetic field f n A first magnetic dyadic Green's function of the double-layer shield is obtained.

5. The indirect testing method for shielding effectiveness of a multi-layer shield according to claim 4 is characterized in that: If the type of the equivalent dipole source of the test antenna is the electric dipole, a tangential magnetic dipole is placed at the inner hole; The second electric field at the outer hole is obtained by using the double-layer shield simulation model. g e and the second magnetic field g n ; Based on the magnetic dyadic Green's function of the outer shield, according to the second electric field g e and the second magnetic field g n A second magnetic dyadic Green's function of the double-layer shield is obtained.

6. The indirect testing method for the shielding effectiveness of a multi-layer shield according to claim 5 is characterized in that: The step of obtaining the superposition correction factor of the double-layer shielding body according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function comprises: Based on Bethe's small hole coupling theory, the superposition correction factor of the double-layer shielding body is obtained according to the double-layer distance parameter, the inner layer distance parameter, the outer layer distance parameter and the magnetic dyadic Green's function of the double-layer shielding body.

7. The indirect testing method for shielding effectiveness of a multi-layer shield according to claim 6, characterized in that: The stacking correction factors include: Magnetic field superposition correction factor and electric field superposition correction factor ;in, The magnetic field superposition correction factor The expression is: In the formula, To test the magnetic field superposition correction factor when the antenna is horizontally polarized, To test the magnetic field superposition correction factor when the antenna is vertically polarized, is the first row and first column element of the magnetic dyadic Green's function of the outer shield, is the first row and first column element of the first magnetic dyadic Green's function of the double-layer shield, is the position vector of the equivalent dipole source in the inner shield, is the position vector of the inner shield hole, When testing the shielding effectiveness of the inner shield, the position vector of the transmitting antenna is is the third row and third column element of the magnetic dyadic Green's function of the outer shield, is the third row and third column element of the first magnetic dyadic Green's function of the double-layer shield; The electric field superposition correction factor The expression is: To test the electric field superposition correction factor when the antenna is horizontally polarized, To test the electric field superposition correction factor when the antenna is vertically polarized, is the wave index, is the third row and first column element of the magnetic dyadic Green's function of the outer shield, It is the first row and third column element of the magnetic dyadic Green's function of the outer shield.

8. The indirect testing method for shielding effectiveness of a multi-layer shield according to claim 7, characterized in that: Based on the test standard, the step of respectively testing the shielding effectiveness of the inner shield and the outer shield to obtain the inner shielding effectiveness of the inner shield and the outer shielding effectiveness of the outer shield comprises: Based on the test standard, a through calibration test is performed to obtain an inner layer through power level; Based on the test standard, the test antenna and the test instrument are arranged to perform a shielding effectiveness test on the inner shielding body to obtain the power level after the inner shielding and the inner distance parameter of the inner shielding body; Obtaining the inner shielding effectiveness according to the through power level and the inner shielding power level; Based on the test standard, a through calibration test is performed to obtain an outer layer through power level; Based on the test standard, the test antenna and the test instrument are arranged to perform a shielding effectiveness test on the outer shielding body to obtain the power level after the outer shielding and obtain the outer distance parameter of the outer shielding body; The outer shielding effectiveness is obtained according to the through power level and the outer shielding power level.

Images