Testing and inversion calculation method for equivalent electromagnetic parameters of wave-absorbing structure

Abstract

The invention relates to the field of material electromagnetic performance testing, and particularly discloses a wave-absorbing structure equivalent electromagnetic parameter testing and inversion calculation method, which comprises the following steps of: placing a preset wave-absorbing flat plate on a metal testing platform of an arch method testing device, and testing to obtain vertical reflectivity R0 of the wave-absorbing flat plate at different frequencies f; n covering plates with the same cross section size as the wave-absorbing flat plate are placed on the upper surface of the wave-absorbing flat plate, each covering plate and the wave-absorbing flat plate form an integral structure, N integral structures are obtained, and based on N + 1 groups of test results of vertical reflectivity of the single wave-absorbing flat plate and the N integral structures, the thickness and electromagnetic parameters of the N covering plates are combined to determine the vertical reflectivity of the wave-absorbing flat plate. And carrying out inversion calculation on equivalent electromagnetic parameters of the wave-absorbing flat plate. According to the invention, the problem that other special equipment needs to be adopted to independently test the equivalent electromagnetic parameters is solved, and the requirement on test equipment can be reduced, so that the cost and difficulty of testing the equivalent electromagnetic parameters are reduced.

Description

Technical Field

[0001] The invention relates to a testing and inversion calculation method, in particular to a testing and inversion calculation method for equivalent electromagnetic parameters of an absorbing structure, and belongs to the field of material electromagnetic performance testing. Background Art

[0002] Absorbing structures such as absorbing honeycombs and metamaterials can effectively absorb incident electromagnetic waves within a specific frequency range, and therefore have important application value in many fields such as stealth design of weapons and equipment. By implementing special microstructure design, these absorbing structures can be regarded as homogeneous materials and applied to the design of stealth components. Therefore, accurately determining the equivalent electromagnetic parameters of absorbing structures is of great significance for guiding the design of their microstructures and engineering practice applications.

[0003] Existing technical methods mainly determine the equivalent electromagnetic parameters of absorbing structures from two perspectives: microstructure and macrostructure. The method based on the microstructure perspective focuses on the electromagnetic parameters and distribution of different component materials in the absorbing structure, and then determines the equivalent electromagnetic parameters of the absorbing structure. For example, the Chinese patent with application number 202110170470.2 discloses a method for extracting equivalent electromagnetic parameters of a special-shaped honeycomb absorbing structure. The method divides the honeycomb periodic unit into multiple regions, and determines the equivalent electromagnetic parameters of the overall absorbing structure based on the shape parameters of the honeycomb structure after deformation and the electromagnetic parameters of each component. The Chinese patent with application number 202311800080.4 discloses a precise equivalent method for electromagnetic parameters of absorbing honeycombs. The method is based on the electromagnetic parameters and volume ratio of air, absorbing coating and honeycomb wall, and finally determines the equivalent electromagnetic parameters of the absorbing structure through two-step homogenization equivalence. However, when the electromagnetic parameters and distribution of different component materials are unclear, the method based on the microstructure perspective cannot determine the equivalent electromagnetic parameters of the absorbing structure. Another type of method obtains equivalent electromagnetic parameters from the perspective of macrostructure by inverting and calculating the reflection and transmission parameters of the absorbing structure. Among them, the classic transmission line method has high requirements on the shape of the test structure, which will increase the difficulty of processing. In addition, a variety of test devices and methods based on the free space method have been proposed. Chinese patent application number 202410124879.4 discloses an equivalent electromagnetic parameter test device and inversion method for electromagnetic structural materials. The device can obtain the reflection and transmission parameters of electromagnetic structural materials at different incident angles, and realize the inversion of equivalent electromagnetic parameters under different incident angle domains. Chinese patent application number 202210100369.4 discloses a low-frequency electromagnetic parameter equivalent extraction device and method for composite materials. The device can test the reflection parameters and transmission parameters of the electromagnetic structure respectively, and then invert and calculate the reflection and transmission coefficients and equivalent electromagnetic parameters of the material. The free space method has the advantages of non-contact and non-destructive, and only requires the absorbing plate to have uniform thickness and large size, but requires the use of a dedicated test device.

[0004] As a mature test method, the bow method can be used to measure the reflectivity of the absorbing plate to evaluate its absorbing ability. However, there is currently a lack of methods to use the reflectivity measured by the bow method to invert and calculate the equivalent electromagnetic parameters of the absorbing plate, which results in the need for different test equipment to measure the equivalent electromagnetic parameters of the absorbing plate and test its absorbing performance. Summary of the invention

[0005] In view of the problems in the prior art, the present invention provides a method for testing and inversely calculating equivalent electromagnetic parameters of an absorbing structure.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A method for testing and inversely calculating equivalent electromagnetic parameters of an absorbing structure comprises the following steps:

[0008] Step 1: Place the preset absorbing plate on the metal test platform of the bow method test device, and test and obtain the vertical reflectivity R0 of the absorbing plate at different frequencies f;

[0009] Step 2: Place N cover plates with the same cross-sectional dimensions as the absorbing plate on the upper surface of the absorbing plate. Each cover plate forms an integral structure with the absorbing plate to obtain N integral structures. Test and obtain the vertical reflectivities R1, R2, R3, ..., R of the N integral structures at different frequencies f. N ;

[0010] Step 3: Based on the test results of a single absorbing plate and N overall structures totaling N+1 groups of vertical reflectivity, combined with the thickness and electromagnetic parameters of the N cover plates, the equivalent electromagnetic parameters of the absorbing plate are inverted and calculated.

[0011] Optionally, the equivalent electromagnetic parameters of the absorbing plate include a relative complex permittivity ε0=ε'-jε", and a relative complex magnetic permeability μ0=μ'-jμ", wherein ε' and ε", are respectively the real part and the imaginary part of the relative complex permittivity, μ' and μ", are respectively the real part and the imaginary part of the relative complex magnetic permeability, and j is an imaginary unit; the equivalent electromagnetic parameters of the absorbing plate can be determined by inversely calculating the four equivalent electromagnetic parameters ε', ε", μ' and μ", of the absorbing plate at different frequencies f.

[0012] Optionally, the equivalent electromagnetic parameter inversion calculation method of the absorbing plate is as follows:

[0013] The theoretical input impedance of a single absorbing plate on a total reflection metal test platform is:

[0014]

[0015] Where d0 is the thickness of the absorbing plate, c is the speed of light; the theoretical vertical reflectivity of a single absorbing plate on a total reflection metal test platform is 20log|(Z0-1) / (Z0+1)|, and the deviation from the vertical reflectivity test value R0 is:

[0016]

[0017] For the first integral structure consisting of the absorbing plate and the first covering plate, the theoretical input impedance on the total reflection metal test platform is:

[0018]

[0019] Where d1, ε1 and μ1 are the thickness, relative complex permittivity and relative complex permeability of the first cover plate respectively;

[0020] The theoretical vertical reflectivity value of the first overall structure on the total reflection metal test platform is 20log|(Z1-1) / (Z1+1)|, and its deviation from the vertical reflectivity test value R1 of the first overall structure is:

[0021]

[0022] By analogy, the theoretical input impedance of the Nth overall structure composed of the absorbing plate and the Nth cover plate on the total reflection metal test platform is:

[0023]

[0024] where d N , ε N and μ N are the thickness, relative complex permittivity and relative complex permeability of the Nth cover plate respectively;

[0025] The theoretical vertical reflectivity of the Nth overall structure on the full reflection metal test platform is 20log|(Z N -1) / (Z N +1)|, which is equal to the vertical reflectivity test value R of the Nth overall structure N The deviation is:

[0026]

[0027] Based on N+1 vertical reflectivity deviations, the error function is constructed as:

[0028]

[0029] The nonlinear multivariate function minimization algorithm is used to calculate the four equivalent electromagnetic parameters ε', ε", μ' and μ" that minimize the error function at different frequencies f, and the equivalent electromagnetic parameters of the absorbing plate can be determined.

[0030] Optionally, the thicknesses and electromagnetic parameters of the N cover plates are not completely the same.

[0031] Optionally, in the step 2, if the absorbing plate is made of non-magnetic material, the number of cover plates N≥2; if the absorbing plate is not made of non-magnetic material, the number of cover plates N≥4.

[0032] Optionally, in step 2, after the cover plate is placed on the absorbing plate, the boundaries of the cover plate and the absorbing plate are aligned and there is no gap on the contact surface between the two.

[0033] Optionally, the metal test platform of the bow method test device is a total reflection metal test platform.

[0034] Beneficial effects of the present invention:

[0035] The present application proposes a method for calculating the equivalent electromagnetic parameters of an absorbing plate by inverting the vertical reflectivity measured by the bow method, so that the bow method and its device can not only measure the reflectivity of the structure, but also measure its equivalent electromagnetic parameters. The present invention solves the problem of using other special equipment to test the equivalent electromagnetic parameters separately, and can reduce the requirements for the test equipment, thereby reducing the cost and difficulty of testing the equivalent electromagnetic parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0037] Figure 1 It is a flow chart of the present invention.

[0038] Figure 2 It is a schematic diagram of the structure of the bow method testing device of the present invention.

[0039] Figure 3 It is a schematic diagram of the installation structure of the test platform and the absorbing plate of the present invention.

[0040] Figure 4 It is a schematic diagram of the installation structure of the test platform, the absorbing plate and the cover plate of the present invention.

[0041] Figure 5 This is a schematic diagram of the vertical reflectivity measured in Case 1 of the present invention.

[0042] Figure 6 This is a schematic diagram comparing the equivalent electromagnetic parameters obtained by inversion calculation in Case 1 of the present invention with the equivalent electromagnetic parameters measured by the transmission line method.

[0043] In the figure: 1. bow method test device; 11. horn antenna; 12. bow frame; 13. metal test platform; 14. absorbing background; 2. absorbing flat plate; 3. covering plate. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] See also Figure 1-6 As shown, a method for testing and inversely calculating equivalent electromagnetic parameters of an absorbing structure comprises the following steps:

[0046] Step 1: Place the preset absorbing plate 2 on the metal test platform 13 of the bow method test device 1, and test and obtain the vertical reflectivity R0 of the absorbing plate 2 at different frequencies f; the metal test platform 13 is a total reflection metal test platform 13, and the bow method test device 1 is as follows: Figure 2 shown.

[0047] Step 2: Place N cover plates 3 with the same cross-sectional dimensions as the absorbing plate 2 on the upper surface of the absorbing plate 2, and each cover plate 3 forms an integral structure with the absorbing plate 2 to obtain N integral structures. Test and obtain the vertical reflectivities R1, R2, R3, ..., R of the N integral structures at different frequencies f. N Only one cover plate 3 is placed on the absorbing plate 2 at a time, and N cover plates 3 need to be placed on the absorbing plate 2 for N rotations for testing. After the cover plate 3 is placed on the absorbing plate 2, the boundaries of the cover plate 3 and the absorbing plate 2 are aligned and there is no gap on the contact surface between the two, so that the test result is more accurate.

[0048] Step 3: Based on the test results of the vertical reflectivity of a single absorbing plate 2 and N integral structures (a total of N+1 groups), combined with the thickness and electromagnetic parameters of the N cover plates 3, the equivalent electromagnetic parameters of the absorbing plate 2 are inverted and calculated.

[0049] Specifically, the equivalent electromagnetic parameters of the absorbing plate 2 include a relative complex permittivity ε0=ε'-jε" and a relative complex magnetic permeability μ0=μ'-jμ", wherein ε' and ε" are the real part and the imaginary part of the relative complex permittivity, respectively, μ' and μ" are the real part and the imaginary part of the relative complex magnetic permeability, respectively, and j is an imaginary unit; the equivalent electromagnetic parameters of the absorbing plate 2 can be determined by inversely calculating the four equivalent electromagnetic parameters ε', ε", μ' and μ" of the absorbing plate 2 at different frequencies f.

[0050] Specifically, the inversion calculation method of the equivalent electromagnetic parameters of the absorbing plate 2 is as follows:

[0051] The theoretical input impedance of a single absorbing plate 2 on the total reflection metal test platform 13 is:

[0052]

[0053] Where d0 is the thickness of the absorbing plate 2, c is the speed of light; the theoretical vertical reflectivity of a single absorbing plate 2 on the total reflection metal test platform 13 is 20log|(Z0-1) / (Z0+1)|, and the deviation from the vertical reflectivity test value R0 is:

[0054]

[0055] For the first integral structure composed of the absorbing plate 2 and the first cover plate 3, the theoretical input impedance value on the total reflection metal test platform 13 is:

[0056]

[0057] Where d1, ε1 and μ1 are the thickness, relative complex permittivity and relative complex permeability of the first cover plate 3 respectively;

[0058] The vertical reflectivity theoretical value of the first overall structure on the total reflection metal test platform 13 is 20log|(Z1-1) / (Z1+1)|, and its deviation from the vertical reflectivity test value R1 of the first overall structure is:

[0059]

[0060] By analogy, the theoretical input impedance of the Nth integral structure formed by the absorbing plate 2 and the Nth cover plate 3 on the total reflection metal test platform 13 is:

[0061]

[0062] where d N , ε N and μ N are the thickness, relative complex permittivity and relative complex permeability of the Nth cover plate 3 respectively;

[0063] The theoretical vertical reflectivity of the Nth overall structure on the total reflection metal test platform 13 is 20log|(Z N -1) / (Z N +1)|, which is equal to the vertical reflectivity test value R of the Nth overall structure N The deviation is:

[0064]

[0065] Based on N+1 vertical reflectivity deviations, the error function is constructed as:

[0066]

[0067] By using a nonlinear multivariate function minimization algorithm (such as the fminunc function in Matlab software), four equivalent electromagnetic parameters ε', ε", μ' and μ" that minimize the error function at different frequencies f are calculated, and the equivalent electromagnetic parameters of the absorbing plate 2 can be determined. Since there is an inevitable deviation between the theoretical value and the test value of the vertical reflectivity, the minimum value of the error function is greater than or equal to zero.

[0068] Specifically, the thicknesses and electromagnetic parameters of the N cover plates 3 are not completely the same, so as to avoid the duplication of the test data and make the final result more accurate.

[0069] Specifically, in the step 2, if the absorbing plate 2 is made of non-magnetic material, the number of the covering plates 3 N≥2, and if the absorbing plate 2 is not made of non-magnetic material, the number of the covering plates 3 N≥4.

[0070] In the case of only the absorbing plate 2 and N=3 integral structures with a total of four sets of vertical reflectivity test values, the above error function calculation process may have multiple solutions. Therefore, for the absorbing plate 2 that is not made of non-magnetic materials, N≥4 integral structures are required, that is, the number of cover plates 3 N≥4.

[0071] When the absorbing plate 2 is made of non-magnetic material, its relative complex magnetic permeability satisfies μ0=1, that is, μ'=1 and μ"=0. At this time, the only equivalent electromagnetic parameters to be measured are the real part ε' and the imaginary part ε" of the relative complex dielectric constant. Therefore, it is necessary to measure the vertical reflectivity of a single absorbing plate 2 and N≥2 overall structures, that is, the number of cover plates 3 N≥2. Then, the above calculation method is used to inversely calculate the equivalent electromagnetic parameters ε' and ε" of the absorbing plate 2 at different frequencies.

[0072] Based on the above method, a specific case is given:

[0073] For example, in case 1:

[0074] Taking the absorbing plate 2 made of non-magnetic material with a thickness of d0 = 10mm as an example (μ0 = 1), the test and inversion calculation method of its equivalent electromagnetic parameters are specifically introduced. Prepare the first cover plate 3 with a thickness of d1 = 10mm and the second cover plate 3 with a thickness of d1 = 5mm, and the electromagnetic parameters of the materials constituting them are ε1 = ε2 = 4, μ1 = μ2 = 1. In the test range of 2 to 18GHz, the plane dimensions of the absorbing plate 2 and the first cover plate 3 and the second cover plate 3 are all 300mm×300mm.

[0075] First, the vertical reflectivity R0 of the absorbing plate 2 is obtained by using the bow method. Figure 5 Then, the first cover plate 3 is placed on the upper surface of the absorbing plate 2 to form the first overall structure, ensuring that the boundaries of the first cover plate 3 and the absorbing plate 2 are aligned and there is no gap on the contact surface. The vertical reflectivity R1 of the first overall structure is tested using the bow method as shown in Figure 5 As shown. Next, the first cover plate 3 is replaced with the second cover plate 3 to form the second overall structure, ensuring that the boundary between the second cover plate 3 and the absorbing plate 2 is aligned and there is no gap on the contact surface. The vertical reflectivity R2 of the second overall structure is tested using the bow method as shown in Figure 5 shown.

[0076] Based on the three sets of vertical reflectivity data obtained from the test, the fminunc function in Matlab software is used to optimize the calculation and let the error function e = (e0) 2 +(e1) 2 +(e2) 2 Take the minimum equivalent electromagnetic parameters ε' and ε". The equivalent electromagnetic parameters obtained by inversion calculation are compared with the equivalent electromagnetic parameters measured by the transmission line method. Figure 6 By comparing the test results, it is found that the method proposed in this application has higher accuracy.

[0077] The bow test device 1 used in this application is as follows Figure 1 As shown, it includes a bow frame 12, a horn antenna 11, a metal test platform 13 and an absorbing background 14. The bow method test device 1 in the present application is a mature and commercially available test device on the market, and is also a commonly used test device in the field, and will not be described in detail here.

[0078] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for testing and inverse calculation of equivalent electromagnetic parameters of an absorbing structure, characterized in that: The following steps are involved: Step 1: Place the preset absorbing plate on the metal test platform of the bow method test device, and test and obtain the vertical reflectivity R0 of the absorbing plate at different frequencies f; Step 2: Place N cover plates with the same cross-sectional dimensions as the absorbing plate on the upper surface of the absorbing plate. Each cover plate forms an integral structure with the absorbing plate to obtain N integral structures. Test and obtain the vertical reflectivities R1, R2, R3, ..., R of the N integral structures at different frequencies f. N ; Step 3: Based on the test results of a single absorbing plate and N overall structures totaling N+1 groups of vertical reflectivity, combined with the thickness and electromagnetic parameters of the N cover plates, the equivalent electromagnetic parameters of the absorbing plate are inverted and calculated.

2. The method for testing and inversion calculation of equivalent electromagnetic parameters of an absorbing structure according to claim 1, characterized in that: The equivalent electromagnetic parameters of the absorbing plate include a relative complex permittivity ε0=ε'-jε" and a relative complex magnetic permeability μ0=μ'-jμ", wherein ε' and ε" are the real part and the imaginary part of the relative complex permittivity, μ' and μ" are the real part and the imaginary part of the relative complex magnetic permeability, and j is an imaginary unit; the equivalent electromagnetic parameters of the absorbing plate can be determined by inversely calculating the four equivalent electromagnetic parameters ε', ε", μ' and μ" of the absorbing plate at different frequencies f.

3. The method for testing and inversion calculation of equivalent electromagnetic parameters of an absorbing structure according to claim 2, characterized in that: The inversion calculation method of the equivalent electromagnetic parameters of the absorbing plate is as follows: The theoretical input impedance of a single absorbing plate on a total reflection metal test platform is: Where d0 is the thickness of the absorbing plate, c is the speed of light; the theoretical vertical reflectivity of a single absorbing plate on a total reflection metal test platform is 20log|(Z0-1) / (Z0+1)|, and the deviation from the vertical reflectivity test value R0 is: For the first integral structure consisting of the absorbing plate and the first covering plate, the theoretical input impedance on the total reflection metal test platform is: Where d1, ε1 and μ1 are the thickness, relative complex permittivity and relative complex permeability of the first cover plate respectively; The theoretical vertical reflectivity of the first overall structure on the total reflection metal test platform is 20log|(Z1-1) / (Z1+1)|, and its deviation from the vertical reflectivity test value R1 of the first overall structure is: By analogy, the theoretical input impedance of the Nth overall structure composed of the absorbing plate and the Nth cover plate on the total reflection metal test platform is: where d N , ε N and μ N are the thickness, relative complex permittivity and relative complex permeability of the Nth cover plate respectively; The theoretical vertical reflectivity of the Nth overall structure on the full reflection metal test platform is 20log|(Z N -1) / (Z N +1)|, which is equal to the vertical reflectivity test value R of the Nth overall structure N The deviation is: Based on N+1 vertical reflectivity deviations, the error function is constructed as: The nonlinear multivariate function minimization algorithm is used to calculate the four equivalent electromagnetic parameters ε', ε", μ' and μ" that minimize the error function at different frequencies f, and the equivalent electromagnetic parameters of the absorbing plate can be determined.

4. The method for testing and inverse calculating equivalent electromagnetic parameters of an absorbing structure according to claim 1, characterized in that: The thicknesses and electromagnetic parameters of the N cover plates are not completely the same.

5. The method for testing and inversion calculation of equivalent electromagnetic parameters of an absorbing structure according to claim 1, characterized in that: In the step 2, if the absorbing plate is made of non-magnetic material, the number of covering plates N is greater than or equal to 2; if the absorbing plate is not made of non-magnetic material, the number of covering plates N is greater than or equal to 4.

6. The method for testing and inverse calculating equivalent electromagnetic parameters of an absorbing structure according to claim 1, characterized in that: In the step 2, after the cover plate is placed on the absorbing plate, the boundaries of the cover plate and the absorbing plate are aligned and there is no gap on the contact surface between the two.

7. The method for testing and inversely calculating equivalent electromagnetic parameters of an absorbing structure according to claim 1, characterized in that: The metal test platform of the bow method test device is a total reflection metal test platform.

Images