Indirect test method for shielding effectiveness of multilayer shields

Abstract

The application belongs to the technical field of electromagnetic shielding. The application provides an indirect test method for shielding effectiveness of a multilayer shielding body. The disclosure embodiment adopts a method based on the magnetic dyadic Green function of the shielding body and the Bethe small hole coupling theory to solve the short-circuit field at the hole and the hole leakage field. The superposition correction factor obtained by solving can consider the reflection of the cavity wall to the electromagnetic wave, so that the multilayer shielding effectiveness obtained by correction is closer to the real value. At the same time, the superposition correction factor can handle the case when the relative position of the inner and outer holes is arbitrary, thereby expanding the application range of the scheme.

Description

TECHNICAL FIELD

[0001] The embodiment of the present disclosure relates to the technical field of electromagnetic shielding, in particular to an indirect test method for shielding effectiveness of a multi-layer shielding body. BACKGROUND

[0002] The multi-layer shielding is usually used to realize the ultra-high performance shielding, for example, the electronic system represented by a large radio telescope system, and the shielding effectiveness of the system is usually 140dB-160dB. However, the ultra-high shielding effectiveness of the multi-layer shielding body exceeds the dynamic range limit of the existing shielding effectiveness test system, which brings great difficulty to the shielding effectiveness test of the multi-layer shielding body. Moreover, the existing method directly adds the shielding effectiveness of each layer of the shielding body, and the result is usually greatly different from the actual shielding effectiveness of the multi-layer rectangular shielding body. SUMMARY

[0003] In order to avoid the shortcomings of the prior art, the present application provides an indirect test method for shielding effectiveness of a multi-layer shielding body, which solves the problems of the dynamic range limit of the existing shielding effectiveness test system and large result error in the prior art.

[0004] According to the embodiment of the present disclosure, an indirect test method for shielding effectiveness of a multi-layer shielding body is provided, which comprises:

[0005] obtaining a double-layer distance parameter of the double-layer shielding body; wherein the double-layer shielding body comprises an inner layer shielding body and an outer layer shielding body;

[0006] obtaining an inner layer distance parameter of the inner layer shielding body and an outer layer distance parameter of the outer layer shielding body based on a test standard;

[0007] determining an obtaining method of a magnetic vector Green function of the double-layer shielding body according to the ratio of the size of the inner layer shielding body and the size of the outer layer shielding body, and obtaining the magnetic vector Green function according to the obtaining method;

[0008] 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 vector Green function;

[0009] performing shielding effectiveness test on the inner layer shielding body and the outer layer shielding body respectively based on the test standard, to obtain an inner layer shielding effectiveness of the inner layer shielding body and an outer layer shielding effectiveness of the outer layer shielding body;

[0010] obtaining a double-layer shielding effectiveness according to the inner layer shielding effectiveness, the outer layer shielding effectiveness and the superposition correction factor.

[0011] Further, the inner layer distance parameter comprises:

[0012] Distance from the transmitting antenna to the inner shield Distance from the receiving antenna to the inner shield First distance between the transmitting antenna and the receiving antenna ;

[0013] The outer layer distance parameter comprises:

[0014] Distance from the transmitting antenna to the outer shield Distance from the receiving antenna to the outer shield Second distance between the transmitting antenna and the receiving antenna ;

[0015] The double-layer distance parameter comprises:

[0016] Distance from the transmitting antenna to the inner shield in the double-layer shield Distance from the transmitting antenna to the outer shield in the double-layer shield Third distance between the transmitting antenna and the receiving antenna .

[0017] Further, according to the ratio of the size of the inner shield and the size of the outer shield, the method for obtaining the magnetic dyadic Green's function of the double-layer shield is determined, and in the step of obtaining the magnetic dyadic Green's function according to the method, the step comprises:

[0018] If the ratio of the size of the inner shield and the size of the outer shield is less than a preset threshold value, 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 taken as the magnetic dyadic Green's function of the double-layer shield.

[0019] If the ratio of the size of the inner shield and the size of the outer shield is greater than a preset threshold value, the magnetic dyadic Green's function of the double-layer shield is obtained by using a numerical simulation method.

[0020] Further, in the step of obtaining the magnetic dyadic Green's function of the double-layer shield by using a numerical simulation method, the step comprises:

[0021] The type of the equivalent dipole source of the test antenna is determined; wherein the type of the equivalent dipole source of the test antenna comprises a magnetic dipole and an electric dipole.

[0022] A double-layer shield simulation model is constructed according to the double-layer distance parameter and the type of the equivalent dipole source of the test antenna.

[0023] 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 gap.

[0024] The first electric field at the outer layer aperture of the double-layer shielding body is obtained by using a simulation model of the double-layer shielding body f e and the first magnetic field f n ;

[0025] The first magnetic dyadic Green's function of the double-layer shielding body is obtained according to the first electric field f e and the first magnetic field f n based on the magnetic dyadic Green's function of the outer layer shielding body.

[0026] 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 layer aperture;

[0027] The second electric field at the outer layer aperture of the double-layer shielding body is obtained by using a simulation model of the double-layer shielding body g e and the second magnetic field g n ;

[0028] The second magnetic dyadic Green's function of the double-layer shielding body is obtained according to the second electric field g e and the second magnetic field g n based on the magnetic dyadic Green's function of the outer layer shielding body.

[0029] Further, in 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, the step comprises:

[0030] 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 based on the Bethe small hole coupling theory.

[0031] Further, the superposition correction factor comprises:

[0032] a magnetic field superposition correction factor and an electric field superposition correction factor ; wherein,

[0033] the expression of the magnetic field superposition correction factor is:

[0034]

[0035] In the formula, is the magnetic field superposition correction factor when the test antenna is horizontally polarized, To test the magnetic field superposition correction factor when the antenna is vertically polarized. The element in the first row and first column of the magnetic dextral Green's function of the outer shielding body. The first row and first column element of the first magnetic dyadic Green's function of the double-layer shielding body. Let be the position vector of the equivalent dipole source in the inner shield. This is the position vector of the holes / slots in the inner shield. The position vector of the transmitting antenna is used to test the shielding effectiveness of the inner shielding layer. The element in the third row and third column of the magnetic dextral Green's function of the outer shielding body. The element in the third row and third column of the first magnetic dyadic Green's function of the double-layer shield;

[0036] The electric field superposition correction factor The expression is:

[0037]

[0038] 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, For wave index, The element in the third row and first column of the magnetic dextral Green's function of the outer shielding body. The first row and third column element of the magnetic dyadic Green's function of the outer shielding body.

[0039] Furthermore, based on the aforementioned test standard, the step of conducting shielding effectiveness tests on the inner shielding layer and the outer shielding layer respectively to obtain the inner shielding effectiveness of the inner shielding layer and the outer shielding effectiveness of the outer shielding layer includes:

[0040] Based on the aforementioned test standard, a through-pass calibration test is performed to obtain the inner layer through-pass power level;

[0041] Based on the aforementioned test standard, the test antenna and test instruments are arranged to perform shielding effectiveness tests on the inner shielding body, so as to obtain the power level after inner shielding and acquire the inner layer distance parameters of the inner shielding body.

[0042] The inner layer shielding effectiveness is obtained based on the direct power level and the power level after the inner layer shielding.

[0043] Based on the aforementioned test standard, a pass-through calibration test is performed to obtain the outer layer pass-through power level;

[0044] Based on the test standard, the test antenna and test instrument are arranged, the shielding effectiveness test is performed on the outer shielding body to obtain the outer shielding after power level, and the outer layer distance parameter of the outer shielding body is obtained.

[0045] The outer shielding effectiveness is obtained according to the straight-through power level and the outer shielding after power level.

[0046] The technical scheme provided by the embodiment of the present disclosure can include the following beneficial effects:

[0047] In the embodiment of the present disclosure, by using the above-mentioned multi-layer shielding body shielding effectiveness indirect test method, for the nested shielding body, the method based on the magnetic dyadic Green's function of the shielding body and the Bethe small hole coupling theory is used to solve the short-circuit field at the hole and the hole leakage field, and the superposition correction factor obtained by solving can consider the reflection of the cavity wall to the electromagnetic wave, so that the corrected multi-layer shielding effectiveness is closer to the true value. Meanwhile, the superposition correction factor can handle the case when the inner and outer layer holes are in any relative position, thereby expanding the application scope of the scheme. BRIEF DESCRIPTION OF DRAWINGS

[0048] The drawings incorporated into the specification and forming a part thereof, illustrate embodiments consistent with the present disclosure and, together with the specification, serve to explain the principles of the present disclosure. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained according to these drawings without creative labor for those skilled in the art.

[0049] Figure 1 A step diagram of a multi-layer shielding body shielding effectiveness indirect test method in an exemplary embodiment of the present disclosure is shown;

[0050] Figure 2 A schematic diagram of a double-layer shielding body in an exemplary embodiment of the present disclosure is shown;

[0051] Figure 3 A schematic diagram of inner and outer single-layer shielding effectiveness test in an exemplary embodiment of the present disclosure is shown;

[0052] Figure 4 A double-layer shielding effectiveness test schematic diagram in an exemplary embodiment of the present disclosure is shown;

[0053] Figure 5 A double-layer rectangular cavity shielding cavity schematic diagram in an exemplary embodiment of the present disclosure is shown;

[0054] Figure 6 A flowchart of obtaining a magnetic dyadic Green's function by using a numerical simulation method in an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0055] Example implementations are now described with reference to the drawings. Example implementations can be implemented in any number of manners, and are not limited to the examples described herein. Functionally equivalent processes can be constructed, and combinations of the described implementations can be made without departing from the scope of the disclosure. Features described in the description and / or shown in the figures can be combined in any suitable manner without departing from the scope of the present disclosure.

[0056] In addition, the drawings are merely schematic and are not drawn to scale. It should thus be appreciated that the specifications and details set forth in any

[0057] In the present example implementation, a method for indirectly testing shielding effectiveness of a multi-layer shielding body is provided. As shown in FIG. 1, the method for indirectly testing shielding effectiveness of a multi-layer shielding body can include steps S101-S106. Figure 1

[0058] Step S101: Obtain a double-layer distance parameter of the double-layer shielding body; wherein the double-layer shielding body includes an inner-layer shielding body and an outer-layer shielding body;

[0059] Step S102: Obtain an inner-layer distance parameter of the inner-layer shielding body and an outer-layer distance parameter of the outer-layer shielding body based on a test standard;

[0060] Step S103: Determine an obtaining method of a magnetic Green's dyadic function of the double-layer shielding body according to a ratio of a size of the inner-layer shielding body and a size of the outer-layer shielding body, and obtain the magnetic Green's dyadic function according to the obtaining method;

[0061] Step S104: Obtain 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 Green's dyadic function;

[0062] Step S105: Perform shielding effectiveness tests on the inner-layer shielding body and the outer-layer shielding body respectively based on the test standard, to obtain an inner-layer shielding effectiveness of the inner-layer shielding body and an outer-layer shielding effectiveness of the outer-layer shielding body;

[0063] Step S106: Obtain a double-layer shielding effectiveness according to the inner-layer shielding effectiveness, the outer-layer shielding effectiveness, and the superposition correction factor.

[0064] ​By the above indirect test method of shielding effectiveness of the multi-layer shielding body, for the nested shielding body, the method based on the magnetic dyadic Green's function of the shielding body and the Bethe small hole coupling theory is used to solve the short-circuit field at the hole and the hole leakage field. The superposition correction factor obtained by solving can consider the reflection of the cavity wall to the electromagnetic wave, so that the corrected multi-layer shielding effectiveness is closer to the real value. At the same time, the superposition correction factor can handle the case of any relative position of the inner and outer holes, thereby expanding the scope of application of the scheme.

[0065] In the following, the above-mentioned indirect test method of shielding effectiveness of the multi-layer shielding body in the present example embodiment will be described in more detail. Figures 1 to 6 The above-mentioned indirect test method of shielding effectiveness of the multi-layer shielding body in the present example embodiment will be described in more detail.

[0066] In steps S101 to S102, a double-layer distance parameter of a double-layer shielding body is obtained; wherein the double-layer shielding body includes an inner shielding body and an outer shielding body; based on a test standard, an inner-layer distance parameter of the inner shielding body and an outer-layer distance parameter of the outer shielding body are obtained.

[0067] In steps S103 to S104, the 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 method; and 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.

[0068] Specifically, if the ratio of the size of the inner shielding body to the size of the outer shielding body is less than a preset threshold, the magnetic dyadic Green's function of the outer shielding body is calculated according to the double-layer distance parameter, and the magnetic dyadic Green's function of the outer shielding body is taken as the magnetic dyadic Green's function of the double-layer shielding body;

[0069] If the ratio of the size of the inner shielding body to the size of the outer shielding body is greater than the preset threshold, the numerical simulation method is used to obtain the magnetic dyadic Green's function of the double-layer shielding body. More specifically,

[0070] The type of the equivalent dipole source of the test antenna is determined; wherein the type of the equivalent dipole source of the test antenna includes a magnetic dipole and an electric dipole; and a double-layer shielding body simulation model is constructed according to the double-layer distance parameter and the type of the equivalent dipole source of the test antenna;

[0071] 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; and the first electric field f e and the first magnetic field f n at the simulation outer hole are obtained by using the double-layer shielding body simulation model; and based on the magnetic dyadic Green's function of the outer shielding body, the second electric field fe and the first magnetic field f n The first magnetic dyadic Green's function of the double-layer shield is obtained.

[0072] 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-layer aperture; the second electric field at the outer-layer aperture is simulated 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-layer shield, 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.

[0073] Based on the Bethe small-hole coupling theory, the superposition correction factor of the double-layer shield is obtained according to the magnetic dyadic Green's function of the double-layer shield, the double-layer distance parameter, the inner-layer distance parameter and the outer-layer distance parameter.

[0074] In steps S105 to S106, the shielding effectiveness of the inner-layer shield and the outer-layer shield is tested based on the test standard, so as to obtain the inner-layer shielding effectiveness of the inner-layer shield and the outer-layer shielding effectiveness of the outer-layer shield; and the double-layer shielding effectiveness is obtained according to the inner-layer shielding effectiveness, the outer-layer shielding effectiveness and the superposition correction factor.

[0075] Specifically, the straight-through calibration test is performed based on the test standard, so as to obtain the inner-layer straight-through power level;

[0076] Based on the test standard, the test antenna and other test instruments are arranged to test the shielding effectiveness of the inner-layer shield, so as to obtain the inner-layer shielding power level and obtain the inner-layer distance parameter of the inner-layer shield;

[0077] The inner-layer shielding effectiveness is obtained according to the straight-through power level and the inner-layer shielding power level;

[0078] The straight-through calibration test is performed based on the test standard, so as to obtain the outer-layer straight-through power level;

[0079] Based on the test standard, the test antenna and other test instruments are arranged to test the shielding effectiveness of the outer-layer shield, so as to obtain the outer-layer shielding power level and obtain the outer-layer distance parameter of the outer-layer shield;

[0080] The outer-layer shielding effectiveness is obtained according to the straight-through power level and the outer-layer shielding power level.

[0081] The double-layer shielding effectiveness is obtained according to the inner-layer shielding effectiveness, the outer-layer shielding effectiveness and the superposition correction factor.

[0082] In one specific embodiment, when the test antenna is a loop antenna (equivalent to a magnetic dipole), its test frequency band is 10 kHz-20 MHz, and the receiving antenna is located in the near-field region of the transmitting antenna. In this case, the magnetic field generated by the magnetic dipole at the same position is much larger than the electric field.

[0083] When the test antenna is a symmetrical dipole antenna or a horn antenna (equivalent to an electric dipole), its test frequency band is above 20 MHz, and the receiving antenna is located in the far-field region of the transmitting antenna. In this case, the electric field and the magnetic field generated by the magnetic dipole or the electric dipole at the same position are consistent in strength.

[0084] The scheme is described in detail taking a double-layer rectangular cavity as an example. The double-layer rectangular shielding cavity is shown in FIG. 1. Figure 2

[0085] Figure 2 The size of the inner shielding cavity is shown in FIG. 2, and the size of the outer shielding cavity is shown in FIG. 3. The point is a monitoring point of the leakage field strength outside the cavity.

[0086] As shown in FIG. 4, it is a schematic diagram for testing the shielding effectiveness of the inner and outer single-layer shielding. Figure 3

[0087] As shown in FIG. 5, it is a schematic diagram for testing the shielding effectiveness of the double-layer shielding. Figure 4

[0088] Figure 3 The distance and the meaning of the test result parameters in FIGS. 1-5 are shown in Table 1. Figure 4 Table 1 Shielding effectiveness test parameters of single-layer and double-layer shielding

[0089]

[0090] The magnetic field shielding effectiveness of the inner, outer and double-layer cavities is shown in FIGS. 6-8, respectively.

[0091] The electric field shielding effectiveness of the inner, outer and double-layer cavities is shown in FIGS. 9-11, respectively. The superposition correction factors of the magnetic field and electric field shielding effectiveness are shown in FIGS. 12 and 13, respectively. Therefore, the correction scheme for the magnetic field shielding effectiveness and the electric field shielding effectiveness is shown in the following formula.

[0092]

[0093] The superposition correction factors of the magnetic field and electric field shielding effectiveness are shown in FIGS. 12 and 13, respectively.

[0094] ​​​​​​​​​​​​1. The calculation process is as follows:

[0095] 1.1 Receiving field strength in straight-through state , The calculation.

[0096] The test loop antenna is equivalent to a magnetic dipole with a size of , and the direction is perpendicular to the loop antenna plane. The field strength at the receiving antenna in the straight-through test state is as follows:

[0097]

[0098] wherein is the first straight-through magnetic field strength of the inner shielding body at the receiving antenna in the straight-through test state, is the second straight-through magnetic field strength of the outer shielding body at the receiving antenna in the straight-through test state, is the third straight-through magnetic field strength of the double-layer shielding body at the receiving antenna in the straight-through test state, is the first distance between the transmitting and receiving antennas in the test of the inner shielding body, is the second distance between the transmitting and receiving antennas in the test of the outer shielding body, is the third distance between the transmitting and receiving antennas in the test of the double-layer shielding body, j is the imaginary part of a complex number, is an angular frequency, is the vacuum permeability.

[0099] 1.2 Receiving field strength of single-layer shielding and calculation.

[0100] The leakage field strength generated by the shielding body aperture can be calculated by the Bethe small aperture coupling theory. The principle is that when the aperture size is much smaller than the electromagnetic wave wavelength, the leakage field strength generated by the aperture can be equivalent to the vector superposition of the equivalent normal electric dipole and tangential magnetic dipole radiation fields at the aperture, as shown in Figure 4 .

[0101] wherein the equivalent normal electric dipole and the tangential magnetic dipole are as follows:

[0102]

[0103] is the normal electric field at the aperture, is the tangential magnetic field at the aperture, is the electric polarization, is the magnetic polarization, is the vacuum permittivity. 、 The polarizability formulas of circular and rectangular holes are shown in Table 2.

[0104] Table 2 Polarizability of circular and rectangular holes

[0105]

[0106] Therefore, in order to apply the Bethe small hole coupling theory, the field strength at the opening site needs to be known, so the magnetic Green function is introduced for calculation. The calculation formulas of the electric field and magnetic field of the magnetic dipole at the opening site are as follows:

[0107]

[0108] wherein, is the size of the equivalent magnetic dipole, and are the electric field strength and the magnetic field strength at the opening site, respectively, is the angular frequency, is the vacuum permittivity, and are the electric Green function and the magnetic Green function of the rectangular cavity under the excitation of the magnetic current element, respectively, and are as follows:

[0109]

[0110]

[0111] wherein are the sizes of the rectangular cavity in the x and y directions, respectively; is an integer greater than or equal to 0; ; ; , is the speed of light; ; when , otherwise , the definition is the same as that of , and the rest are similar, wherein is the coordinate of the opening position, is the coordinate of the equivalent test antenna.

[0112] The above is the calculation principle of the leakage field strength of the shielding body opening. The specific calculation process of the received field strength of the single-layer shielding 、 is as follows:

[0113] a. Calculate the tangential magnetic field strength at the opening site

[0114] Let H0is the magnetic field strength at the opening; wherein , , , , , , , , represent the 9 elements of .

[0115]

[0116] b. Calculate the equivalent magnetic dipole of the opening

[0117]

[0118] c. Calculate the magnetic field strength at the receiving antenna

[0119]

[0120]

[0121] wherein, is the component of the first shielded magnetic field strength in the X-axis direction, is the component of the first shielded magnetic field strength in the Z-axis direction, is the component of the second shielded magnetic field strength in the X-axis direction, is the component of the second shielded magnetic field strength in the Z-axis direction, and will be eliminated in the subsequent calculation.

[0122] 1.3 Calculate the receiving field strength of the double-layer shield .

[0123] The double-layer rectangular cavity is shown in Figure 5 .

[0124] 1) Calculate the magnetic field strength at the opening of the inner layer of the double-layer shield

[0125] Let be the magnetic field strength at the opening of the inner layer, be the magnetic Green's function of the inner-layer rectangular cavity, which is calculated as shown in the following formula:

[0126]

[0127] 2) Calculate the equivalent magnetic dipole of the opening of the inner layer of the double-layer shield

[0128] Let the equivalent magnetic dipole of the opening of the inner layer be , according to the Bethe small-hole coupling theory, the calculation formula is as follows.

[0129]

[0130] 3) Calculate the magnetic field strength at the opening in the outer layer of the double-layer shield.

[0131] Calculating the magnetic field strength at the opening in the outer layer requires the magnetic dextral Green's function of the cavity between the inner and outer layers, denoted as . , Since the cavity between the inner and outer layers is not a regular rectangular cavity, there is no analytical expression.

[0132] 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 (e.g., 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.

[0133] When the ratio of the inner and outer cavity dimensions is small enough that the influence of the inner cavity on the magnetic dextral Green's function cannot be ignored, the accurate magnetic dextral Green's function of the outer space is obtained through numerical simulation. Figure 6 The procedure shown uses Feko simulation to obtain the magnetic dyadic Green's function for irregular cavities.

[0134] First, construct a simulation model of a double-layer shield. Establish an electric dipole or magnetic test antenna at the inner layer's opening and set its size to 1. Then, set the field point at the outer layer's opening.

[0135] The uniqueness theorem for sinusoidal steady-state fields states that "in a region V enclosed by a 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 volume V is uniquely determined by Maxwell's equations." Therefore, for deterministic boundary conditions, the magnetic dextral Green's function satisfying these conditions is unique; that is, the magnetic dextral Green's function of irregular cavities obtained through numerical simulation is accurate. Furthermore, due to the flexibility of numerical simulation, this method can solve for the magnetic dextral Green's function for arbitrarily relative positions of the inner and outer cavities and the openings.

[0136] That is, according to Figure 6 The steps shown yield the transfer function of the field from the dipole at the inner layer aperture to the field at the outer layer aperture. Then, by deriving the relationship between the transfer function and the magnetic dextral Green's function, the numerical solution of the magnetic dextral Green's function is obtained. Finally, by combining Bethe's small aperture coupling theory, the short-circuit field generated by the equivalent dipole at the inner layer aperture in the outer cavity is calculated, thereby calculating the shielding effectiveness of the nested double-layer cavity.

[0137] At the same time, based on the perturbation theory, a simplified method for obtaining the magnetic dyadic Green's function is proposed. This method takes into account the influence of the inner and outer cavity sizes on the magnetic dyadic Green's function. That is, when the size ratio of the inner and outer rectangular cavities satisfies the perturbation criterion, the influence of the inner cavity is approximately ignored. For cases that do not satisfy the perturbation criterion, a method for obtaining the magnetic dyadic Green's function by numerical simulation software Feko is proposed. This method greatly simplifies the calculation of the equivalent superposition correction factor while meeting the requirements of correctness and effectiveness.

[0138] 4) Calculate the equivalent test antenna of the double-layer shielded outer layer with openings (i.e., the fourth equivalent test antenna)

[0139] Let the equivalent magnetic dipole of the outer layer with openings be According to the Bethe small hole coupling theory, the calculation formula is as follows:

[0140]

[0141] The field strength at the receiving antenna is The calculation is as follows:

[0142] According to the magnetic dipole radiation field calculation formula, as shown in the following formula.

[0143]

[0144] wherein, is the component of the double-layer shielded receiving field strength in the X-axis direction, is the component of the double-layer shielded receiving field strength in the Z-axis direction.

[0145] The calculation is as follows:

[0146] According to:

[0147]

[0148] Substitute the results derived above into, and we get:

[0149]

[0150] wherein is the position coordinate of the inner rectangular cavity aperture during the shielding effectiveness test of the double-layer shield, is the position coordinate of the transmitting antenna during the shielding effectiveness test of the outer cavity in the same coordinate system.

[0151] 2. The calculation process of is as follows:

[0152] is defined as shown in the following formula.

[0153]

[0154] 2.1 Straight-through state receiving field strength 、 、 Calculation

[0155] The transmitting antenna is equivalent to an electric dipole, and the dipole size is set as The field strength at the receiving antenna in the straight-through test state is as follows.

[0156]

[0157] 2.2 Single-layer shielding receiving field strength 、 Calculation

[0158] The calculation formula of the electric field and the magnetic field of the electric dipole at the opening site is as follows.

[0159]

[0160] wherein is the equivalent electric dipole size, and are the electric field strength and the magnetic field strength at the opening site, respectively, is the angular frequency, is the vacuum permeability, and are the electric dyadic Green's function and the magnetic dyadic Green's function of the rectangular cavity under the excitation of the current element, and are specifically as follows.

[0161]

[0162]

[0163] wherein are the sizes of the rectangular cavity in the direction, respectively; is an integer greater than or equal to 0; , is the speed of light; ; when , otherwise , the definition is the same as that of , and the rest are similar, wherein is the opening position coordinate, is the equivalent test antenna coordinate.

[0164] ​The above is the calculation principle of the shielding body opening leakage field strength, single layer shielding receiving field strength , The specific calculation is as follows.

[0165] a) Tangential magnetic field strength calculation at the opening site

[0166] Let be the magnetic field strength at the opening. For the sake of representation simplicity, use , , , , , , , , to represent the 9 elements of .

[0167]

[0168] b) Opening equivalent magnetic dipole calculation

[0169]

[0170] c) Electric field strength calculation at the receiving antenna

[0171]

[0172]

[0173] wherein, 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.

[0174] 2.3 Double-layer shielding receiving field strength Calculation

[0175] The double-layer rectangular cavity is shown in Figure 5 .

[0176] The calculation steps are as follows.

[0177] a) Inner layer opening site magnetic field strength calculation

[0178] Let be the magnetic field strength at the inner layer opening, be the inner layer rectangular cavity magnetic dyadic Green function, calculated as shown in the following formula.

[0179]

[0180] b)Inner layer aperture equivalent magnetic dipole calculation

[0181] Let the inner layer aperture equivalent magnetic dipole be According to the Bethe small aperture coupling theory, the calculation formula is as follows.

[0182]

[0183] c)Outer layer aperture site magnetic field strength calculation

[0184] The magnetic dyadic Green's function of the cavity between the inner and outer layers is needed to calculate the magnetic field strength at the outer layer aperture site, denoted as Since the cavity between the inner and outer layers is not a regular rectangular cavity, there is no analytical expression.

[0185] For different relative sizes of the inner and outer cavities, when the size ratio of the outer layer cavity to the inner layer cavity is large enough (for example, the length ratio of the outer layer and inner layer cavities is greater than 6), the influence of the inner layer cavity can be approximately ignored.

[0186] When the size ratio of the inner and outer layer cavities is small, the influence of the inner layer cavity on the magnetic dyadic Green's function cannot be ignored. The accurate magnetic dyadic Green's function of the outer layer space is obtained by numerical simulation. According to the flowchart shown in Figure 6 , the magnetic dyadic Green's function of the irregular cavity is obtained by simulation using Feko.

[0187] That is, according to the steps shown in Figure 6 , the transfer function of the inner layer aperture to the outer layer aperture is obtained, and the numerical solution of the magnetic dyadic Green's function is obtained by deducing the relationship between the transfer function and the magnetic dyadic Green's function. Then, the short-circuit field generated by the inner layer aperture equivalent dipole in the outer layer cavity is calculated by combining the Bethe small aperture coupling theory, so as to calculate the shielding effectiveness of the nested double-layer cavity.

[0188] At the same time, based on the perturbation theory, a method for simplifying the calculation of the magnetic dyadic Green's function is proposed. This method analyzes the influence of the size of the inner and outer cavities on the magnetic dyadic Green's function, that is, when the size ratio of the inner and outer rectangular cavities satisfies the perturbation criterion, the influence of the inner layer cavity is approximately ignored. For cases that do not satisfy the perturbation criterion, a method for obtaining the magnetic dyadic Green's function by numerical simulation software Feko is proposed. This method greatly simplifies the calculation of the equivalent superposition correction factor while meeting the correctness and effectiveness of the calculation.

[0189] Let be the magnetic field strength at the outer layer aperture, and the calculation formula is as follows.

[0190]

[0191] d) Outer layer aperture equivalent magnetic dipole calculation

[0192] Let the outer layer aperture equivalent magnetic dipole be According to the Bethe small aperture coupling theory, the calculation formula is as follows:

[0193]

[0194] e) Field strength at receiving antenna Calculation

[0195] According to the electric dipole radiation field calculation formula, As shown in the following formula.

[0196]

[0197] Wherein, is the component of the double-layer shielding receiving field strength in the X-axis direction, is the component of the double-layer shielding receiving field strength in the Z-axis direction.

[0198] Calculation

[0199] From:

[0200]

[0201] Substitute the results of the above derivation into it, and the following can be obtained:

[0202]

[0203] Wherein is the position coordinate of the inner layer rectangular cavity aperture during the shielding effectiveness test of the double-layer shielding body, is the position coordinate of the transmitting antenna during the shielding effectiveness test of the outer layer cavity in the same coordinate system.

[0204] The multi-layer cavity shielding effectiveness obtained by the traditional method of linearly superimposing the shielding effectiveness of each layer of shielding body is fixed, and the influence of the position change of the inner layer cavity in the outer layer cavity and the different positions and relative orientations of the inner and outer cavity apertures on the shielding effectiveness of the multi-layer cavity is not considered. Based on the magnetic dyadic Green function of the rectangular cavity, the relative positions of the inner layer cavity aperture and the outer layer cavity aperture are introduced; based on the Bethe small aperture coupling theory, the relative orientation of the inner layer cavity aperture and the outer layer cavity aperture is introduced. The calculated shielding effectiveness changes with the change of the aperture position and orientation, which is closer to the true value.

[0205] Through the indirect shielding effectiveness test method of the multi-layer shielding body, for the nested shielding body, the short circuit field and the aperture leakage field at the aperture are solved by using the magnetic dyadic Green's function of the shielding body and the Bethe small aperture coupling theory, and the superposition correction factor obtained by solving can consider the reflection of the cavity wall to the electromagnetic wave, so that the multi-layer shielding effectiveness corrected is closer to the real value. At the same time, the superposition correction factor can handle the case when the relative position of the inner and outer apertures is arbitrary, thereby expanding the scope of application of the scheme.

[0206] The present application introduces a superposition correction factor to modify the existing method, so that the calculation result is closer to the real value. For the nested multi-layer shielding body, based on the analysis of the cavity field distribution characteristics and the aperture coupling leakage elements, the short circuit field and the aperture leakage field at the aperture are solved by using the rectangular cavity magnetic dyadic Green's function and the Bethe small aperture coupling theory, and then the superposition correction factor is obtained.

[0207] In addition, the terms "first", "second", "third", etc. are used only for descriptive purposes and are not to be construed as indicating or implying relative importance or an ordered ranking of the indicated technical features. Thus, a feature defined with "first", "second", etc. can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0208] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in the specification.

[0209] Other embodiments of the present disclosure will be apparent to those skilled in the art upon consideration of the specification and practice of the applications disclosed. The present application is intended to cover any variations, uses, or adaptations of the present disclosure following the general principles thereof and including modifications and equivalents of the present disclosure that are obvious to those skilled in the art. The specification and examples are to be regarded as illustrative 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 multilayer shield, characterized in that, The method comprises: 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; obtaining an inner-layer distance parameter of the inner shielding body and an outer-layer distance parameter of the outer shielding body based on a test standard; determining an obtaining method of a magnetic dyadic Green's function of the double-layer shielding body according to a ratio of a size of the inner shielding body to a size of the outer shielding body, and obtaining the magnetic dyadic Green's function according to the obtaining method; specifically comprising: if the ratio of the size of the inner shielding body to the size of the outer shielding body is less than a preset threshold, calculating the magnetic dyadic Green's function of the outer shielding body according to the double-layer distance parameter, and taking the magnetic dyadic Green's function of the outer shielding body as the magnetic dyadic Green's function of the double-layer shielding body; if the ratio of the size of the inner shielding body to the size of the outer shielding body is greater than the preset threshold, obtaining the magnetic dyadic Green's function of the double-layer shielding body by using a numerical simulation method; wherein, the specific steps of obtaining the magnetic dyadic Green's function of the double-layer shielding body by using the numerical simulation method comprise: determining a type of an equivalent dipole source of a test antenna; the type of the equivalent dipole source of the test antenna comprises a magnetic dipole and an electric dipole; constructing a double-layer shielding body 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 layer aperture; the first electric field at the simulated outer layer aperture is obtained by using a double-layer shielding body simulation model f e and the first magnetic field f n ; based on the magnetic dyadic Green's function of the outer layer shielding body, the first magnetic dyadic Green's function of the double-layer shielding body is obtained according to the first electric field f e and the first magnetic field f n ​ 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 layer aperture; a second electric field at the outer layer aperture is obtained by using a double-layer shield simulation model g e and a second magnetic field g n ; based on the magnetic dyadic Green's function of the outer layer shield, a second magnetic dyadic Green's function of the double-layer shield is obtained according to the second electric field g e and the second magnetic field g n ​ 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; wherein the superposition correction factor comprises: Magnetic field superposition correction factor and electric field superposition correction factor ; Magnetic field superposition correction factor The expression for the magnetic field superposition correction factor is: wherein is the magnetic field superposition correction factor for the test antenna when horizontally polarized, is the magnetic field superposition correction factor for the test antenna when vertically polarized, is the first row first column element of the magnetic dyadic Green's function of the outer shield, is the first row first column element of the first magnetic dyadic Green's function of the double shield, is the position vector of the equivalent dipole source in the inner shield, is the position vector of the aperture in the inner shield, is the position vector of the transmitting antenna when testing the shielding effectiveness of the inner shield, is the third row third column element of the magnetic dyadic Green's function of the outer shield, is the third row third column element of the first magnetic dyadic Green's function of the double shield, Electric field superposition correction factor The expression for the electric field superposition correction factor is: Eh, for testing the electric field superposition correction factor for horizontal polarization of the antenna, Evh, for testing the electric field superposition correction factor for vertical polarization of the antenna, n, for the wave index, Gm,3,1, for the third row first column element of the magnetic dyadic Green's function of the outer shield, Gm,1,3, for the first row third column element of the magnetic dyadic Green's function of the outer shield, performing shielding effectiveness tests on the inner shielding body and the outer shielding body respectively based on the test standard, to obtain an inner-layer shielding effectiveness of the inner shielding body and an outer-layer shielding effectiveness of the outer shielding body; obtaining a double-layer shielding effectiveness according to the inner-layer shielding effectiveness, the outer-layer shielding effectiveness and the superposition correction factor.

2. The method for indirectly testing the shielding effectiveness of a multilayer shield according to claim 1, wherein, In the steps of performing the shielding effectiveness tests on the inner shielding body and the outer shielding body respectively based on the test standard, to obtain the inner-layer shielding effectiveness of the inner shielding body and the outer-layer shielding effectiveness of the outer shielding body, the steps comprise: performing a direct-through calibration test based on the test standard, to obtain an inner-layer direct-through power level; arranging a test antenna and a test instrument based on the test standard, to perform the shielding effectiveness test on the inner shielding body, to obtain an inner-layer shielding-after power level, and to obtain the inner-layer distance parameter of the inner shielding body; obtaining the inner-layer shielding effectiveness according to the direct-through power level and the inner-layer shielding-after power level; performing a direct-through calibration test based on the test standard, to obtain an outer-layer direct-through power level; arranging a test antenna and a test instrument based on the test standard, to perform the shielding effectiveness test on the outer shielding body, to obtain an outer-layer shielding-after power level, and to obtain the outer-layer distance parameter of the outer shielding body; obtaining the outer-layer shielding effectiveness according to the direct-through power level and the outer-layer shielding-after power level.

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