An equivalent electromagnetic parameter testing device and inversion method of an electromagnetic structure material

Abstract

The application aims to provide an equivalent electromagnetic parameter testing device and inversion method of electromagnetic structure material, and belongs to the technical field of material electromagnetic performance testing. The device is innovatively provided with a circumferential slide rail, so that the device can realize the acquisition of the reflection coefficient and the transmission coefficient of the electromagnetic structure material under different incidence angle domains, and deduce the equivalent electromagnetic parameter inversion formula under oblique incidence based on the reflection coefficient and the transmission coefficient. Meanwhile, the inversion process is improved based on the device, especially the calibration process is improved, so that the inversion of the equivalent electromagnetic parameter under different incidence angle domains is realized, and the possibility of providing more dimensional electromagnetic performance basic data for the research and application of the electromagnetic structure material is provided.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic property testing technology for materials, specifically relating to a device and inversion method for testing equivalent electromagnetic parameters of electromagnetic structural materials. Background Technology

[0002] Cellular materials, metamaterials, and other electromagnetic structural materials can perform special control and regulation of electromagnetic wave transmission and reflection, and have wide applications in high-speed communication, radar stealth, and sensor design. Equivalent electromagnetic parameters (equivalent complex permittivity and equivalent complex permeability) are fundamental parameters used to characterize the electromagnetic properties of electromagnetic structural materials. Extracting these equivalent electromagnetic parameters plays a fundamental and pioneering role in the study of the macroscopic electromagnetic properties of electromagnetic structural materials. Due to the anisotropy of electromagnetic structural materials, they are highly sensitive to the angle and polarization of electromagnetic wave incidence. Obtaining the angular domain equivalent electromagnetic parameters of electromagnetic structural materials under different polarizations has become an urgent need in the design of next-generation radomes / windows, skins, and other components based on electromagnetic structural materials.

[0003] The acquisition of equivalent electromagnetic parameters of electromagnetic structural materials can be divided into calculation methods and measurement methods. The calculation method is based on the electromagnetic parameters of the matrix components of the electromagnetic structural material and the dimensional parameters of the structural units, and calculates the equivalent electromagnetic parameters of the electromagnetic structural material according to the equivalent medium theory. In the patent "A Method for Extracting Equivalent Electromagnetic Parameters of Gradient Honeycomb Absorbing Material" (Publication No. CN 111259534A), the influence of dimensional parameters such as coating thickness, number of gradient layers, and incremental dimensional parameters between adjacent gradient coatings on the equivalent parameters is considered to extract the equivalent electromagnetic parameters of the gradient honeycomb absorbing material. In the patent "A Method for Extracting Equivalent Electromagnetic Parameters of Irregular Honeycomb Absorbing Structure" (Publication No. CN 112906156A), based on the honeycomb structure's dimensional parameters, physical parameters, and the angle of honeycomb deformation, the equivalent electromagnetic parameter expressions of the irregular honeycomb absorbing structure in different directions are obtained. In the patent "A Training Method for a Neural Network for Inverting the Equivalent Dielectric Constant of a Honeycomb Structure" (Publication No. CN 116306890A), a sample model with honeycomb wall thickness and relative dielectric constant as variables is established by orthogonal method, and the homogeneous method based on HS theory is used to homogeneously equivalence the honeycomb structure to obtain the equivalent dielectric constant. The measurement method involves placing the electromagnetic structural material in a free-space testing system and obtaining the equivalent electromagnetic parameters of the material based on the measured scattering parameters (S-parameters) combined with an inversion algorithm. In the patent CN 106980095A, titled "A Metamaterial Electromagnetic Parameter Inversion Method Based on an Improved KK Algorithm," the free-space method is used to test the electromagnetic parameters of a flat plate metamaterial, and a metamaterial electromagnetic parameter inversion method based on an improved KK algorithm is proposed to address the multi-value problem in the inversion process. In the literature "Analysis of Equivalent Complex Permittivity of a Dielectric Cellular Cell Using the Free-Space Method," the scattering parameters of the cellular cell are extracted using the electromagnetic simulation software HFSS, and its equivalent electromagnetic parameters are calculated based on the free-space method. In the literature "Design, Fabrication, and Testing of Double Negative Metamaterials," the equivalent electromagnetic parameters of metamaterials are extracted based on the free-space method.

[0004] However, the methods mentioned above only extract the equivalent electromagnetic parameters of electromagnetic structural materials under perpendicular electromagnetic wave incidence, and do not address the calculation or inversion methods for equivalent electromagnetic parameters under oblique incidence. Therefore, obtaining the equivalent electromagnetic parameters of electromagnetic structural materials under different incident angles is extremely urgent. Summary of the Invention

[0005] To address the problems existing in the background technology, the present invention aims to provide a device and inversion method for testing the equivalent electromagnetic parameters of electromagnetic structural materials. This device innovatively incorporates a circular slide rail, enabling it to acquire the reflection coefficient and transmission coefficient of electromagnetic structural materials under different incident angle domains. Simultaneously, the inversion process has been adaptively improved based on the device, particularly refining the calibration process, thereby achieving the inversion of equivalent electromagnetic parameters under different incident angle domains.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] An equivalent electromagnetic parameter testing device for electromagnetic structural materials includes a transmitting antenna 1, a receiving antenna 2, a sample holder 3, and a slide rail 4.

[0008] The slide rail is circular, and the transmitting antenna 1 and the receiving antenna 2 can move along the circumference on the slide rail 4. A diameter arm is set inside the circumference of the slide rail 4. The sample holder 3 is rectangular with a hollow center. The electromagnetic structure material or metal plate to be tested is fixed on the surface of the sample holder away from the transmitting antenna. The center of the electromagnetic structure material to be tested or the center of the metal plate is consistent with the center of the sample holder. The sample holder 3 is set at the center of the diameter arm, that is, at the center of the circle. The radiation direction axis 6 of the receiving antenna and the radiation direction axis 5 of the transmitting antenna are symmetrical about the normal 7 at the center of the sample holder plane, or the radiation direction axis 6 of the receiving antenna and the radiation direction axis 5 of the transmitting antenna coincide.

[0009] Furthermore, the sample holder material is a low-loss, microwave-transparent material, preferably plexiglass.

[0010] Furthermore, a groove is provided on the surface of the sample holder facing away from the transmitting antenna 1 for fixing and placing the electromagnetic structure material or metal plate to be tested.

[0011] Furthermore, the center of the electromagnetic structure material under test is located at the focal point of the transmitting antenna and the receiving antenna, and the electromagnetic structure material under test is rectangular; if it is square, the side length L should satisfy L·cosθ greater than 3 times the 3dB focal spot; if it is rectangular, the short side L1 satisfies L1 greater than 3 times the 3dB focal spot, and the long side L2 satisfies L2·cosθ greater than 3 times the 3dB focal spot.

[0012] This invention also provides an inversion method based on the above-mentioned electromagnetic structure material incident angle domain equivalent electromagnetic parameter testing device, comprising the following steps:

[0013] Step 1: Adjust the polarization state of the transmitting antenna 1 according to the required electromagnetic wave incident polarization requirements, and at the same time slide the transmitting antenna along the slide rail 4 so that the angle between the radiation direction axis 5 of the transmitting antenna and the normal 7 at the center of the sample holder plane is equal to the required incident angle θ.

[0014] Step 2: Adjust the polarization state of the receiving antenna 2 to align it with that of the transmitting antenna. Then, slide the receiving antenna along the slide rail 4 to make the radiation direction axis 6 of the receiving antenna symmetrical to the radiation direction axis 5 of the transmitting antenna about the plane normal 7 at the center of the sample holder. Next, extract the reflection coefficient Γ of the electromagnetic structure material under test at the incident angle θ. The specific process is as follows:

[0015] Step 2.1. Without placing any items on sample holder 3, measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0016] Step 2.2. Place a metal plate on sample holder 3 and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0017] Step 2.3. Place the electromagnetic structure material to be tested on the sample holder and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0018] Step 2.4. Calculate the reflection coefficient Γ, the specific formula is as follows:

[0019]

[0020] Step 3: Slide the receiving antenna along the slide rail 4 until the radiation direction axis 6 of the receiving antenna coincides with the radiation direction axis 5 of the transmitting antenna. Then, extract the transmission coefficient T of the electromagnetic structure material under test at the incident angle θ. The specific process is as follows:

[0021] Step 3.1. Without placing any items on sample holder 3, measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0022] Step 3.2. Place a metal plate on sample holder 3 and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0023] Step 3.3. Place the electromagnetic structure material to be tested on the sample holder and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0024] Step 3.4. Calculate the transmission coefficient T, using the following formula:

[0025]

[0026] Where d is the thickness of the electromagnetic structure material to be measured, k0 is the free space wavenumber, k0=2π / λ, λ is the free space wavelength; j is the imaginary number;

[0027] Step 4: Based on the reflection coefficient Γ obtained in Step 2 and the transmission coefficient T obtained in Step 3, calculate the equivalent electromagnetic parameters of the electromagnetic structure material under test at the incident angle θ. The specific formula is as follows:

[0028] When the transmitting antenna is vertically polarized incident, the equivalent permeability μ at the incident angle θ r⊥ and equivalent dielectric constant ε r⊥ They are respectively:

[0029]

[0030]

[0031] When the transmitting antenna is horizontally polarized, the equivalent dielectric constant ε at the incident angle θ is... r∥ and equivalent permeability μ r∥ They are respectively:

[0032]

[0033]

[0034] in:

[0035]

[0036]

[0037]

[0038]

[0039] In the formula, Λ is the transmission coefficient of the electromagnetic structure material under test when it is backed by air at an incident angle θ. The phase change in the propagation direction caused by the sample thickness is denoted as n, which is the phase correction coefficient when the phase is blurred, and n is a natural number.

[0040] Furthermore, the transmitting and receiving antennas are linearly polarized point focusing antennas, and the transmitting and receiving antennas can rotate along the radiation direction axis to switch the incident polarization state.

[0041] Furthermore, incident polarization includes vertical polarization and horizontal polarization.

[0042] Furthermore, in steps 2 and 3, when placing the metal plate and the electromagnetic structure material to be tested on the sample holder, it is necessary to ensure that the distance from the transmitting antenna to the surface of the electromagnetic structure material to be tested near the transmitting antenna is the same as the distance from the transmitting antenna to the surface of the metal plate near the transmitting antenna. The electromagnetic wave travels from the transmitting antenna to the surfaces of the two plates at the same distance, so that the phase at the surfaces of the two plates is consistent.

[0043] Furthermore, in steps 2 and 3, All parameter measurements must undergo time-domain gating.

[0044] Furthermore, in steps 2 and 3, the thickness of the metal plate is consistent with the thickness of the electromagnetic structure material to be tested.

[0045] Furthermore, the transmitting antenna, receiving antenna, and sample holder must be protected from strong scattering objects, and the sample holder must be made of low-loss transparent material.

[0046] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0047] This invention, through the design of a testing device structure, can obtain the reflection coefficient and transmission coefficient of electromagnetic structural materials under different incident angle domains, and derive the equivalent electromagnetic parameter inversion formula under oblique incidence based on the reflection coefficient and transmission coefficient. This extends the existing electromagnetic parameter extraction method based on vertical incident scattering parameter testing to electromagnetic parameter extraction based on arbitrary incident angles, providing more possibilities for the research and development and application of electromagnetic structural materials with more dimensions of basic electromagnetic performance data. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of the overall structure of the equivalent electromagnetic parameter testing device of the present invention.

[0049] Figure 2 This is a schematic diagram showing the positions of the transmitting antenna and the receiving antenna when the reflection coefficient is measured in Embodiment 1 of the present invention.

[0050] Figure 3 This is a schematic diagram showing the positions of the transmitting antenna and the receiving antenna when the transmission coefficient is measured in Embodiment 1 of the present invention.

[0051] Figure 4 The graphs show the equivalent electromagnetic parameters of the cellular flat panel in the 8-12 GHz frequency band in Embodiments 1 and 2 of the present invention.

[0052] Reference numerals in the attached figures: 1 is the transmitting antenna, 2 is the receiving antenna, 3 is the sample holder, 4 is the slide rail, 5 is the axis of the transmitting antenna's radiation direction, 6 is the axis of the receiving antenna's radiation direction, and 7 is the normal to the sample holder's plane. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0054] A schematic diagram of the overall structure of an equivalent electromagnetic parameter testing device for electromagnetic structural materials is shown below. Figure 1 As shown, it includes a transmitting antenna 1, a receiving antenna 2, a sample holder 3, and a slide rail 4;

[0055] The slide rail is circular, and the transmitting antenna 1 and the receiving antenna 2 can move along the circumference of the slide rail 4. Two diameter arms are set inside the circumference of the slide rail 4, and the sample holder 3 is set at the intersection of the two diameter arms, i.e., at the center of the circle. The sample holder 3 is rectangular with a hollow center, so that both surfaces of the sample to be tested are in contact with the air, which is in line with the free space method test. The surface of the sample holder facing away from the transmitting antenna 1 is provided with a groove, and the electromagnetic structure material or metal plate to be tested is fixed in place by screws, so that the distance from the transmitting antenna to the surface of the electromagnetic structure material to be tested near the transmitting antenna is the same as the distance from the transmitting antenna to the surface of the metal plate near the transmitting antenna. The electromagnetic wave travels the same distance from the transmitting antenna to the surfaces of the two plates, so that the phase at the surfaces of the two plates is consistent. The radiation direction axis 6 of the receiving antenna is symmetrical to the radiation direction axis 5 of the transmitting antenna about the normal 7 at the center of the sample holder plane, or the radiation direction axis 6 of the receiving antenna coincides with the radiation direction axis 5 of the transmitting antenna.

[0056] Example 1

[0057] An inversion method based on an electromagnetic structure material incident angle domain equivalent electromagnetic parameter testing device includes the following steps:

[0058] Step 1: According to the required electromagnetic wave incident polarization requirements, adjust the transmitting antenna 1 to a horizontal polarization state, and at the same time slide the transmitting antenna along the slide rail 4 so that the angle θ between the transmitting antenna radiation direction axis 5 and the normal 7 at the center of the sample holder plane is equal to 15°.

[0059] Step 2: Adjust the polarization state of the receiving antenna 2 to align it with that of the transmitting antenna. Then, slide the receiving antenna along the slide rail 4 until the radiation axis 6 of the receiving antenna and the radiation axis 5 of the transmitting antenna are symmetrical about the plane normal 7 at the center of the sample holder. At this point, the positional relationship between the transmitting and receiving antennas is as follows: Figure 2 As shown;

[0060] Next, the reflection coefficient Γ of the electromagnetic structure material under test when it is backed by air at an incident angle θ is extracted. The specific process is as follows:

[0061] Step 2.1. Without placing any items on sample holder 3, measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0062] Step 2.2. Place a metal plate on sample holder 3 and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0063] Step 2.3. Place the cellular flat panel to be tested on the sample holder and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0064] Step 2.4. Calculate the reflection coefficient Γ, the specific formula is as follows:

[0065]

[0066] Step 3: Slide the receiving antenna along slide rail 4 until the radiation direction axis 6 of the receiving antenna coincides with the radiation direction axis 5 of the transmitting antenna. At this time, the positional relationship between the transmitting antenna and the receiving antenna is as follows: Figure 3 As shown;

[0067] Then, the transmission coefficient T of the electromagnetic structure material under test is extracted when it is backed by air at an incident angle θ. The specific process is as follows:

[0068] Step 3.1. Without placing any items on sample holder 3, measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0069] Step 3.2. Place the metal plate from step 2.2 on sample holder 3, and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0070] Step 3.3. Place the electromagnetic structure material to be tested on the sample holder and measure the distance between the transmitting antenna and the receiving antenna. parameter;

[0071] Step 3.4. Calculate the transmission coefficient T, using the following formula:

[0072]

[0073] Where d is the thickness of the electromagnetic structure material to be measured, k0 is the free space wavenumber, k0=2π / λ, λ is the free space wavelength; j is the imaginary number;

[0074] Step 4: Based on the reflection coefficient Γ obtained in Step 2 and the transmission coefficient T obtained in Step 3, calculate the equivalent electromagnetic parameters of the electromagnetic structure material under test at the incident angle θ. The specific formula is as follows:

[0075] When the transmitting antenna is horizontally polarized, the equivalent dielectric constant ε at the incident angle θ is... r∥ and equivalent permeability μ r∥ They are respectively:

[0076]

[0077]

[0078] in:

[0079]

[0080]

[0081]

[0082]

[0083] In the formula, Λ is the transmission coefficient of the electromagnetic structure material under test when it is backed by air at an incident angle θ. The phase change in the propagation direction caused by the sample thickness is denoted as n, which is the phase correction coefficient when the phase is blurred, and n is a natural number.

[0084] Example 2

[0085] The equivalent electromagnetic parameters were inverted according to the steps of Example 1, except that the angle θ between the radiation direction axis 5 of the transmitting antenna and the normal 7 at the center of the sample holder plane in step 1 was adjusted to 30° and 45°, while the other steps remained unchanged.

[0086] Figure 4 These are the equivalent electromagnetic parameter curves of the cellular flat panel in the 8-12 GHz frequency band in Embodiments 1 and 2 of the present invention; wherein, Figure 4 (a) is a graph showing the relative permittivity at different incident angles. Figure 4 (b) shows the loss tangent curves for different incident angles. As can be seen from the figure, at θ = 15°, the relative permittivity is between 1.38 and 1.40, and the loss tangent ranges from 0.66 to 0.90; at θ = 30°, the relative permittivity is between 1.45 and 1.48, and the loss tangent ranges from 0.65 to 0.86; at θ = 45°, the relative permittivity is between 1.54 and 1.60, and the loss tangent ranges from 0.62 to 0.80. This demonstrates that the testing device and inversion method of this invention can extract electromagnetic parameters in different angular domains.

[0087] The above description is merely a specific embodiment of the present invention. Any feature disclosed in this specification may be replaced by other equivalent or similar features unless otherwise specified. All disclosed features, or steps in all methods or processes, may be combined in any way except for mutually exclusive features and / or steps.

Claims

1. An inversion method of equivalent electromagnetic parameters of an electromagnetic structural material, characterized in that, The inversion method is implemented based on the following testing device, which includes a transmitting antenna, a receiving antenna, a sample holder, and a slide rail; The slide rail is circular, and the transmitting and receiving antennas can move along the circumference of the slide rail. A diameter arm is set inside the circumference of the slide rail. The sample holder is rectangular with a hollow center. The electromagnetic structure material or metal plate to be tested is fixed on the surface of the sample holder away from the transmitting antenna. The center of the electromagnetic structure material or metal plate to be tested is aligned with the center of the sample holder. The sample holder is set at the center of the diameter arm. The radiation direction axis of the receiving antenna is symmetrical to the radiation direction axis of the transmitting antenna about the normal of the center of the sample holder plane, or the radiation direction axis of the receiving antenna coincides with the radiation direction axis of the transmitting antenna. The inversion method includes the following steps: Step 1: Adjust the polarization state of the transmitting antenna according to the required electromagnetic wave incident polarization requirements, and slide the transmitting antenna along the slide rail so that the angle between the axis of the transmitting antenna radiation direction and the normal at the center of the sample holder plane is equal to the required incident angle θ. Step 2: Adjust the polarization state of the receiving antenna to match that of the transmitting antenna. Then, slide the receiving antenna along the slide rail until the radiation direction axis of the receiving antenna is symmetrical to the radiation direction axis of the transmitting antenna about the plane normal at the center of the sample holder. Then, extract the reflection coefficient Γ of the electromagnetic structure material under test at the incident angle θ. The specific process is as follows: Step 2.

1. With nothing on the sample holder, measure the distance between the transmitting and receiving antennas parameters; Step 2.

2. Place the metal plate on the sample holder and measure the distance between the transmitting antenna and the receiving antenna parameters; Step 2.

3. Place the electromagnetic structure material to be measured on the sample holder and measure the parameters between the transmitting antenna and the receiving antenna ; Step 2.

4. Calculate the reflection coefficient Γ, using the following formula: (1)； Step 3: Slide the receiving antenna along the slide rail until its radiation direction axis coincides with that of the transmitting antenna. Then, extract the transmission coefficient T of the electromagnetic structure material under test at the incident angle θ. The specific process is as follows: Step 3.

1. With nothing on the sample holder, measure the distance between the transmitting and receiving antennas parameters; Step 3.

2. Place the metal plate on the sample holder and measure the parameters between the transmitting antenna and the receiving antenna ; Step 3.

3. Place the electromagnetic structure material to be tested on the sample holder and measure the distance between the transmitting antenna and the receiving antenna. parameter; Step 3.

4. Calculate the transmission coefficient T, using the following formula: (2) Where d is the thickness of the electromagnetic structure material to be measured, k0 is the free space wavenumber, k0=2π / λ, λ is the free space wavelength; j is the imaginary number; Step 4: Based on the reflection coefficient Γ obtained in Step 2 and the transmission coefficient T obtained in Step 3, calculate the equivalent electromagnetic parameters of the electromagnetic structure material under test at the incident angle θ. The specific formula is as follows: When the transmitting antenna is vertically polarized incident, the equivalent permeability μ at the incident angle θ r⊥ and equivalent dielectric constant ε r⊥ They are respectively: (3) (4) The equivalent permittivity ε and equivalent permeability μ at the incident angle θ when the transmitting antenna is horizontally polarized incident are respectively: r∥ r∥ ​​ (5) (6) in: (7) (8) (9) (10) wherein T(θ) is the transmission coefficient of the electromagnetic structure material to be measured when backed by air at an incident angle θ, , is the phase change in the direction of propagation caused by the thickness of the sample, n is the phase correction coefficient when the phase is ambiguous, and n is a natural number.

2. The equivalent electromagnetic parameter inversion method of claim 1, wherein, The sample holder is made of a low-loss, microwave-transparent material.

3. The equivalent electromagnetic parameter inversion method of claim 1, wherein, The sample holder has grooves on the surface facing away from the transmitting antenna to fix and place the electromagnetic structure material or metal plate to be tested.

4. The equivalent electromagnetic parameter inversion method of claim 1, wherein, The center of the electromagnetic structure material under test is located at the focal point of the transmitting and receiving antennas. The electromagnetic structure material under test is rectangular. If it is square, the side length L should satisfy L·cosθ greater than 3 times the 3dB focal spot. If it is rectangular, the short side L1 should satisfy L1 greater than 3 times the 3dB focal spot, and the long side L2 should satisfy L2·cosθ greater than 3 times the 3dB focal spot.

5. The equivalent electromagnetic parameter inversion method of claim 1, wherein, The transmitting and receiving antennas are linearly polarized point focusing antennas, and they can rotate along the radiation direction axis to switch the incident polarization state.

6. The equivalent electromagnetic parameter inversion method of claim 5, wherein, Incident polarization includes vertical polarization and horizontal polarization.

7. The equivalent electromagnetic parameter inversion method of claim 1, wherein, In steps 2 and 3, when placing the metal plate and the electromagnetic structure material to be tested on the sample holder, it is necessary to ensure that the distance from the transmitting antenna to the side surface of the electromagnetic structure material to be tested near the transmitting antenna is the same as the distance from the transmitting antenna to the side surface of the metal plate near the transmitting antenna.

8. The equivalent electromagnetic parameter inversion method of claim 1, wherein, In step 2 and step 3, , , , Parameter measurement needs time domain gating processing.

9. The equivalent electromagnetic parameter inversion method of claim 1, wherein, In steps 2 and 3, the thickness of the metal plate is consistent with the thickness of the electromagnetic structure material to be tested.

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