Electromagnetic parameter extraction method for profiled fiber reinforced composite material

Abstract

The invention discloses an electromagnetic parameter extraction method for a special-shaped fiber reinforced composite material. The method comprises the specific steps that a multi-layer composite material cabin model is established; based on the flat plate model of the multi-layer composite material, establishing a single-layer composite material homogenization model, and calculating equivalent single-layer electromagnetic parameters; the method comprises the following steps: calculating the internal shielding effectiveness of a composite cabin with a microscopic fine structure and the shielding effectiveness of a homogenized cabin, setting a search step size and a search range, taking equivalent single-layer electromagnetic parameters as initial parameters, continuously changing the electromagnetic parameters of the composite material through the search step size, and further changing the shielding effectiveness of the homogenized cabin. And keeping the internal shielding effectiveness of the composite cabin body with the microscopic fine structure consistent with the shielding effectiveness of the homogenized cabin body, and taking the electromagnetic parameters obtained at the moment as the electromagnetic parameters of the multi-layer composite cabin body model.

Description

Technical Field

[0001] The invention relates to the field of electromagnetic environmental effects, and in particular to a method for extracting electromagnetic parameters of a special-shaped fiber reinforced composite material. Background Art

[0002] Advanced composite materials are gradually replacing metal materials with their unique advantages such as high strength, corrosion resistance, and light weight, and are widely used in aerospace and other industrial fields. my country's domestically produced aerospace vehicles such as satellites, fighter jets, and civil airliners have begun to gradually use composite materials. For example, the use of composite materials in the J-20 is about 27%, and the use of advanced composite materials in the successfully developed C919 large civil aircraft has reached 20%. The use of composite materials has become an important symbol of the advancement of aerospace vehicles.

[0003] Composite materials with carbon fiber as reinforcement are often used for electromagnetic shielding performance of structures such as aircraft and satellites. The electromagnetic parameters of carbon fiber composite materials are the physical basis and key input for analyzing the electromagnetic protection performance of aerospace vehicles. The electromagnetic parameters of composite materials can be obtained by experimental testing methods. The specifications of composite materials involved in aerospace vehicles are various, and it is difficult to obtain complete electromagnetic parameters of composite materials by experimental measurement alone. Theoretical calculations can be used to effectively supplement the electromagnetic parameters of the test. The existing theoretical calculation models for electromagnetic parameter homogenization are all composite flat plate structures, and do not consider the special-shaped cabin structures of multi-layer carbon fiber composite materials with different angles, which are difficult to adapt to the actual application requirements of the dielectric properties of composite materials for aerospace vehicles. Summary of the invention

[0004] The purpose of the present invention is to provide a method for extracting electromagnetic parameters of a special-shaped fiber-reinforced composite material, which takes into account the shape of the cabin and the carbon fiber laying angles of each layer of material in the multi-layer composite material, and solves the problem of extracting electromagnetic parameters of the special-shaped composite cabin.

[0005] In order to achieve the above object, the present invention provides a method for extracting electromagnetic parameters of a special-shaped fiber reinforced composite material, the specific steps of which include:

[0006] Step 1: Establish a multi-layer composite cabin model;

[0007] Step 2: Based on the flat plate model of the multi-layer composite material, a homogenized model of the single-layer composite material is established to calculate the equivalent single-layer electromagnetic parameters;

[0008] Step three, calculate the internal shielding effectiveness of the composite cabin with a microscopic fine structure and the uniform shielding effectiveness of the cabin, and set the search step and search range. Use the equivalent single-layer electromagnetic parameters as the initial parameters, and continuously change the electromagnetic parameters of the composite material through the search step, thereby changing the uniform shielding effectiveness of the cabin, so that the internal shielding effectiveness of the composite cabin with a microscopic fine structure and the uniform shielding effectiveness of the cabin remain consistent, and use the electromagnetic parameters obtained at this time as the electromagnetic parameters of the multi-layer composite cabin model.

[0009] Optionally, in step three, the search step is set according to the dielectric constant value and the calculation time; the search range includes: a search range for relative dielectric constant and a search range for conductivity, the search range for relative dielectric constant is between the relative dielectric constant of the matrix and the relative dielectric constant of the carbon fiber, and the search range for conductivity is between the conductivity of the matrix and the conductivity of the carbon fiber.

[0010] Optionally, in step three, it is determined whether the penalty function value Fc is less than a set accuracy threshold. When the penalty function value Fc is less than the set accuracy threshold, the internal shielding effectiveness of the composite cabin with a microscopic fine structure is consistent with the shielding effectiveness of the homogenized cabin.

[0011] The penalty function is expressed as:

[0012] F c =SE hom (ε(f),σ(f))-SE ori (f) 2 dB

[0013] Where ε(f) is the relative permittivity corresponding to the change of the electromagnetic parameters of the composite material according to the search step size, and σ(f) is the conductivity corresponding to the change of the electromagnetic parameters of the composite material according to the search step size.

[0014] Optionally, the accuracy threshold is 3dB.

[0015] Optionally, in step three, when calculating the internal shielding effectiveness of the composite cabin of a microscopic fine structure, a time domain excitation signal is set according to a required frequency band so that the frequency band and the time domain excitation signal satisfy the Fourier change relationship, and a plane wave irradiation experiment is performed on the multilayer composite cabin model in step one; the time domain transmission coefficient is calculated using a time domain finite integration method; based on the cabin model of the multilayer composite material and the time domain transmission coefficient, a wave algorithm is used to calculate the internal shielding effectiveness of the composite cabin of a microscopic fine structure;

[0016] When calculating the shielding effectiveness of the homogenized cabin, the following conditions must be met:

[0017]

[0018] Where, SE hom is the electric field shielding effectiveness, E s is the field strength value at the field strength monitoring point inside the cabin, E inc is the incident field strength of the external electromagnetic wave.

[0019] Optionally, in step one, the size and quantity of the microstructure units are set and arranged in sequence in the vertical direction to form a composite material surface of the cabin and constitute a multilayer composite material cabin model.

[0020] Optionally, in step 1, the microstructure unit has a circular cross section, and the cabin model of the multilayer composite material is established as a hollow cylinder model having N layers of composite material basic units, and the matrix of each layer of composite material is a hollow cylinder, and the hollow cylinders of each layer of composite material are nested in sequence to form a hollow cylinder of the multilayer composite material;

[0021] The size of the carbon fibers in each layer of the composite material is set to be uniform and the ply angle is set to be the same; the relative dielectric constant and the electrical conductivity of the matrix in each layer of the composite material are set to be the same, and the relative dielectric constant and the electrical conductivity of the carbon fibers in each layer of the composite material are set to be the same.

[0022] Optionally, in step 1, the ply angles include: 0°, 90°, 45°, and -45°;

[0023] When the ply angle is 0°, the ply direction of each carbon fiber in the single-layer composite material is in the vertical direction, perpendicular to the end surface of the substrate, and is evenly arranged along the circumference of the hollow cylinder;

[0024] When the ply angle is 90°, the ply direction of each carbon fiber in the single-layer composite material is in the horizontal direction, and an arc-shaped bend is generated according to the shape of the matrix, so that each carbon fiber forms a horizontally placed circular ring, and a plurality of carbon fibers are evenly arranged along the height direction of the matrix;

[0025] When the ply angle is 45°, each carbon fiber in the single-layer composite material is inclined to the right and forms an angle of 45° with the vertical direction, and along the bending direction of the matrix, each carbon fiber is in a right-hand spiral in the matrix; adjacent carbon fibers in a right-hand spiral shape in the single-layer composite material are connected end to end and spiral upward along the height direction of the matrix;

[0026] When the layup angle is -45°, each carbon fiber in the single-layer composite material is inclined to the left and forms an angle of 45° with the vertical direction, and is laid flat along the bending direction of the matrix, so that each carbon fiber is in a left-hand spiral in the matrix; adjacent carbon fibers in a left-hand spiral shape in the single-layer composite material are connected end to end and spiral upward along the height direction of the matrix.

[0027] Optionally, in step 2, a method for establishing a homogenization model of a single-layer composite material is as follows:

[0028] A flat plate model of N-layer composite materials is established, and the number of layers of the composite materials is consistent with the number of layers of the composite materials in the multi-layer composite cabin model, and the carbon fiber ply angle of each layer of the composite materials is the same as the carbon fiber ply angle of each layer of the composite materials in the cabin model, and the transmission matrix equation of the N-layer composite materials is obtained; an equivalent single-layer uniform material is used to replace the N layers of composite materials to establish a single-layer composite material homogenization model.

[0029] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0030] The present invention establishes a cabin model of multi-layer composite materials and a homogenized model of single-layer composite materials respectively, taking into account the shape of the cabin and the different carbon fiber laying angles of each layer of composite materials; uses a transmission matrix equation to calculate the equivalent single-layer electromagnetic parameters of the homogenized model of the single-layer composite material, and optimizes with the equivalent single-layer electromagnetic parameters as initial values ​​through an optimization algorithm, and uses the shielding effectiveness of the cabin model and the homogenized model as a measurement standard, so that the electromagnetic parameters of the homogenized model can be used as the electromagnetic parameters of the cabin model after optimization, and realizes the solution of the inverse problem of extracting the dielectric properties of the special-shaped composite cabin, which can be used for the electromagnetic protection design and evaluation of new domestic aircraft, satellites, missiles, etc. that support the application of composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic flow chart of the electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material of the present invention.

[0032] Figure 2 It is a schematic diagram of a multilayer composite cabin model in the electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material of the present invention.

[0033] Figure 3 It is a schematic flow chart of the optimization algorithm in the electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material of the present invention.

[0034] Figure 4a It is a schematic diagram of the composite material when the carbon fiber laying angle is 0° in the single-layer composite cabin model of the present invention.

[0035] Figure 4b It is a schematic diagram of the carbon fiber laying direction when the carbon fiber laying angle is 0° in the single-layer composite cabin model of the present invention.

[0036] Figure 5a It is a schematic diagram of the composite material when the carbon fiber laying angle in the single-layer composite cabin model of the present invention is 90°.

[0037] Figure 5bIt is a schematic diagram of the carbon fiber laying direction when the carbon fiber laying angle is 90° in the single-layer composite cabin model of the present invention.

[0038] Figure 6a It is a schematic diagram of the composite material when the carbon fiber laying angle in the single-layer composite cabin model of the present invention is 45°.

[0039] Figure 6b It is a schematic diagram of the carbon fiber laying direction when the carbon fiber laying angle is 45° in the single-layer composite cabin model of the present invention.

[0040] Figure 7a It is a schematic diagram of the composite material when the carbon fiber laying angle is -45° in the single-layer composite cabin model of the present invention.

[0041] Figure 7b It is a schematic diagram of the carbon fiber laying direction when the carbon fiber laying angle is -45° in the single-layer composite cabin model of the present invention.

[0042] Figure 8 It is a schematic diagram of a flat plate model of a multilayer composite material of the present invention.

[0043] Fig. 9 It is a schematic diagram of the homogenization model of a single-layer composite material of the present invention.

[0044] In the figure, 1-carbon fiber, 2-matrix, 21-end face, 3-single-layer composite material. DETAILED DESCRIPTION

[0045] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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.

[0046] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0047] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0048] like Figure 1 As shown, the electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material of the present invention comprises the following specific steps:

[0049] Step 1: Establish a multi-layer composite cabin model.

[0050] like Figure 2 As shown, since the cross-section of the cabin structure is generally regarded as a circle, the circular cross-section is used as the microstructure unit of the special-shaped cabin in the modeling process. By setting the size and number of the microstructure units and arranging them in sequence in the vertical direction, a hollow cylinder is formed. The hollow cylinder is used as the composite material surface of the cabin, and the microstructure units with basic laying angles are used to replace the composite materials of the actual cabin.

[0051] The composite cabin model is composed of multiple layers of composite materials, each layer of which is composed of carbon fibers mixed in a matrix at the same layer angle, and the matrix is ​​usually made of epoxy resin. Since the multi-layer composite cabin model is a hollow cylinder, the matrix 2 of each layer of composite material is also a hollow cylinder, such as Figure 4a , Figure 5a , Figure 6a , Figure 7a As shown, the hollow cylinders of each layer of composite material are nested in sequence to form a hollow cylinder of a multilayer composite material. Since the laying angles of each carbon fiber 1 in an actual single-layer composite material are different, in the multilayer composite cabin model, the carbon fiber 1 is set to a linear cylindrical structure of uniform size, and the microstructure unit of the carbon fiber 1 with the same laying angle is used to replace the single-layer composite material containing carbon fibers with different laying angles in the actual multilayer composite cabin model; since the matrix 2 of each layer of composite material in the multilayer composite cabin model is a hollow cylinder, the carbon fiber 1 in each layer of composite material is bent along the bending direction of the matrix 2, as shown in FIG. Figure 4b , Figure 5b , Figure 6b , Figure 7b The basic ply angles include: 0°, 90°, 45°, and -45°.

[0052] like Figure 4a and Figure 4bAs shown, when the laying angle of the carbon fiber 1 is 0°, the laying direction of each carbon fiber 1 in the single-layer composite material 3 is in the vertical direction, that is, each carbon fiber 1 is perpendicular to the end surface 21 of the matrix 2 and is evenly arranged along the circumference of the hollow cylinder; Figure 5a and Figure 5b As shown in FIG. 1 , when the laying angle of the carbon fiber 1 is 90°, the laying direction of each carbon fiber 1 in the single-layer composite material 3 is in the horizontal direction, and is curved in an arc shape along the shape of the matrix 2 to form a horizontally placed circular ring, that is, a plurality of carbon fibers 1 in the composite material are in the form of circular rings parallel to the end surface of the matrix 2 and are evenly arranged in the matrix 2 along the height direction of the matrix 2; Figure 6a , Figure 6b As shown in FIG. 1 , when the laying angle of the carbon fiber 1 is 45°, each carbon fiber 1 in the single-layer composite material 3 is inclined to the right and is at an angle of 45° to the vertical direction. Since the carbon fiber 1 is bent along the bending direction of the matrix 2, each carbon fiber 1 is in a right spiral in the matrix 2, that is, adjacent carbon fibers 1 in a right spiral shape in the composite material are connected end to end and spiral upward along the height direction of the matrix 2; Figure 7a and Figure 7b As shown, when the laying angle of the carbon fiber 1 is -45°, each carbon fiber in the single-layer composite material 3 is inclined to the left and forms an angle of 45° with the vertical direction. Since the carbon fiber 1 is bent along the bending direction of the matrix 2, each carbon fiber is in a left-hand spiral in the matrix, that is, adjacent carbon fibers 1 in a left-hand spiral shape in the composite material are connected end to end and spiral upward along the height direction of the matrix 2.

[0053] Multiple single-layer composite materials containing carbon fibers with the same layup angles are arranged in sequence to construct a multilayer composite material with a microscopic fine structure of the multilayer composite material, which can reflect the carbon fiber layup angle of each layer of the composite material in the multilayer composite cabin model. Therefore, the electromagnetic performance results obtained by simulating the multilayer composite cabin model based on the multilayer composite cabin model using software are more accurate.

[0054] The cabin model is established using software, and the cabin model is established as a hollow cylindrical model with N layers of composite basic units. The carbon fiber ply angles of each layer of composite material are set to x1, x2, ..., x i , …x N , and x i∈[0°, 90°, 45°, -45°], the diameter of the carbon fiber in each layer of the composite material is a mm, and the total size of the composite material is set to l mm×w mm×h mm, where l is the total thickness of the N layers of composite material, w is the outer diameter of the composite cylinder, and h is the height of the composite material; at the same time, the material properties of the matrix and carbon fiber of each layer of the composite material are set to the same, the relative dielectric constant of the matrix is ​​set to ε1, the conductivity is set to σ1, the relative dielectric constant of the carbon fiber is set to ε2, and the conductivity is set to σ2.

[0055] In a preferred embodiment, the composite cabin model can adopt ellipses with different curvatures as microstructure units of the special-shaped cabin according to actual needs, and the composite cabin model can be designed as a composite cabin model containing openings and holes; the selection range of the layup angle of the fibers in each layer of the composite material constituting the N layers of composite material can be changed according to actual conditions.

[0056] Step 2: Based on the flat plate model of the multi-layer composite material, a homogenized model of the single-layer composite material is established to calculate the equivalent single-layer electromagnetic parameters.

[0057] A flat plate model of N-layer composite materials is established. Each layer of composite materials in the model is a planar structure. The number of layers of the composite materials is consistent with the number of layers of composite materials in the multi-layer composite cabin model, and the carbon fiber ply angle of each layer of composite materials in the model is the same as the carbon fiber ply angle of each layer of composite materials in the cabin model. The electromagnetic parameters of each layer of composite materials in the multi-layer composite materials are extracted using the classical homogenization method, and the transmission matrix model is corrected using the internal microstructure arrangement of the multi-layer composite materials to obtain the equivalent electromagnetic parameters of the multi-layer composite materials.

[0058] like Figure 8 As shown in the figure, when the composite material S of each layer of the N-layer composite plate model is i The relative complex dielectric constant ε i , relative complex permeability μ i and thickness d i When all parameters are known, the transmission matrix equation can be used to solve the reflection coefficient R and transmission coefficient T of the flat plate model surface of the multilayer composite material. The transmission matrix equation of the N-layer composite material is:

[0059]

[0060] In the formula, j is the imaginary unit, j 2 = -1; γ i is the propagation constant of the i-th layer material, R is the reflection coefficient, T is the transmission coefficient, and 1 is the incident electric field amplitude; r i is the reflection coefficient of the i-th layer, and r0 is the boundary condition of the N-layer composite material.

[0061] When the (i+1)th layer and the i-th layer of material are both semi-infinite, the reflection coefficient from the i-th layer to the (i+1) layer can be expressed as:

[0062]

[0063] In the formula, Z i is the normalized wave impedance of the i-th layer material.

[0064] The propagation constant γ in Equation 1 i It can be expressed as:

[0065]

[0066] ”'

[0067] In the formula, γ i is the real part of the propagation constant; γ i is the imaginary part of the propagation constant; k0 is the wave number in vacuum; n i is the refractive index of the i-th layer of material.

[0068]

[0069] D=(1+r0)(1+r1)...(1+r n )(Formula 5)

[0070] Substituting equation 4 and equation 5 into equation 1, simplifying equation 1, we get equation 6. By operating equation 6, we can get the expressions of the reflection coefficient R and transmission coefficient T of the N-layer composite material, as shown in equation 7. Substituting the known parameters of each layer of composite material into equation 7, we get the reflection coefficient R and transmission coefficient T.

[0071]

[0072] like Fig. 9 As shown, a single-layer composite material homogenization model is established on the basis of the N-layer composite material flat plate model, so that an equivalent single-layer uniform material replaces the N-layer composite material. The transmission matrix of the equivalent single-layer uniform material can be expressed as:

[0073]

[0074] Where d is the thickness of the equivalent single-layer uniform material, r0 is the boundary condition of the equivalent single-layer uniform material, r1 is the reflection coefficient of the equivalent single-layer uniform material, and γ is the propagation constant of the equivalent single-layer uniform material.

[0075] Among them, the reflection coefficient r0 of the equivalent single-layer uniform material interacting with the interface of the medium in which it is located and the reflection coefficient r1 of the equivalent single-layer uniform material can be expressed as Equation 9 and Equation 10 respectively. Substituting Equation 9 and Equation 10 into

[0076] In formula 8, further calculation can be obtained:

[0077]

[0078] Where Z is the wave impedance of an equivalent single-layer uniform material.

[0079] By solving the transmission matrix of the equivalent single-layer uniform material, the reflection coefficient R and the transmission coefficient T can be expressed as:

[0080]

[0081] Substituting equation 9 into equation 12 and equation 13, and further processing equation 12 and equation 13, we can obtain:

[0082]

[0083] Substituting equations 16 and 17 into equation 13, we can obtain the wave impedance Z of the equivalent single-layer uniform material:

[0084]

[0085] The propagation constant γ of an equivalent single layer of uniform material is:

[0086]

[0087] Equivalent single-layer electromagnetic parameter ε eff As shown in Equation 20, Equations 18 and 19 can be substituted into Equation 20 to calculate the equivalent single-layer electromagnetic parameter ε eff .

[0088]

[0089] In the formula, μ eff is the equivalent single layer relative complex permeability.

[0090] Step three, calculate the internal shielding effectiveness of the composite cabin with microscopic fine structure and the shielding effectiveness of the homogenized cabin, and use the optimization algorithm to extract the electromagnetic parameters.

[0091] The time domain excitation signal f(t) is set according to the frequency band to be calculated, so that the frequency band and the time domain excitation signal f(t) satisfy the Fourier transform relationship, and a plane wave irradiation test is performed on the multilayer composite cabin model in step 1. The time domain finite integral method calculation algorithm is used to obtain the time domain transmission coefficient S 21 After Fourier transform in time-frequency domain, the composite material transmission coefficient S in this frequency band can be obtained. 21 The amplitude-frequency and phase-frequency characteristics.

[0092] According to the cabin model of multi-layer composite materials and the composite transmission coefficient S of a certain frequency band21 , using the numerical full-wave algorithm to calculate the shielding effectiveness SE of the composite cabin with microscopic fine structure ori ; and calculate the uniform cabin shielding effectiveness SE hom , as shown in Formula 21.

[0093]

[0094] Where, SE hom is the electric field shielding effectiveness, E s is the field strength value at the field strength monitoring point inside the cabin, E inc is the incident field strength value of the external electromagnetic wave, and the field strength value E at the field strength monitoring point inside the cabin s , external electromagnetic wave incident field strength value E inc Affected by the electromagnetic parameters of the composite material.

[0095] like Figure 3 As shown in the figure, the equivalent single-layer electromagnetic parameter ε in the homogenized model of the single-layer composite material is eff Substitute the initial electromagnetic characteristics into equation 21, and optimize and solve the electromagnetic eigenvalues ​​of the N-layer composite cabin model point by point. Set the search step size and search range according to the dielectric constant value and the required calculation time; the search range includes: the search range of relative dielectric constant and the search range of conductivity. The search range of relative dielectric constant is between the relative dielectric constant ε1 of the matrix and the relative dielectric constant ε2 of the carbon fiber, and the search range of conductivity is between the conductivity σ1 of the matrix and the conductivity σ2 of the carbon fiber. The electromagnetic parameters in the homogenized model of the single-layer composite material are continuously changed by the search step size, and the internal shielding effectiveness SE of the composite cabin with a microscopic fine structure is ensured by judging whether the penalty function value Fc is less than the set accuracy threshold. ori and homogenized cabin shielding effectiveness SE hom When the penalty function value Fc is less than the accuracy threshold, the electromagnetic parameters obtained at this time are the electromagnetic parameters in the cabin model of the multilayer composite material.

[0096] F c =SE hom (ε(f),σ(f))-SE ori (f) 2 dB (Formula 22)

[0097] Where ε(f) is the relative permittivity corresponding to the change of the electromagnetic parameters of the composite material according to the search step size, and σ(f) is the conductivity corresponding to the change of the electromagnetic parameters of the composite material according to the search step size.

[0098] Embodiment 1

[0099] Step 1: Establish a multi-layer composite cabin model.

[0100] A hollow cylindrical cabin model with three layers of 0° / 45° / 90° composite materials was established, and the characteristic parameters of the matrix and carbon fiber materials of each layer of composite materials were set to be the same; among them, the relative dielectric constant ε of the matrix material 1r =5, conductivity σ1 = 0Sm, carbon fiber diameter a = 1mm, relative dielectric constant ε 2r =1, conductivity σ2 = 1000Sm; setting the thickness d of the three layers of composite material i =6mm, the outer diameter of the circular cross section of the hollow cylinder R1 =20mm, the inner diameter of the circular cross section of the hollow cylinder R2 =14mm, and the height of the hollow cylinder h =20mm, that is, the total size of the material is 6mm×20mm×20mm.

[0101] Step 2: Based on the flat plate model of the multi-layer composite material, a homogenized model of the single-layer composite material is established to calculate the equivalent single-layer electromagnetic parameters.

[0102] A three-layer composite plate model is established, and the carbon fiber ply angle of each layer of the composite material in the model is the same as the carbon fiber ply angle of each layer of the composite material in the cabin model. i , relative complex permeability μ i and thickness d i When all the parameters are known, the reflection coefficient R and transmission coefficient T of the multilayer material surface are solved using the transmission matrix equation. An equivalent single-layer uniform material is used to replace the three-layer composite material to establish a single-layer composite material homogenization model. By using the obtained wave impedance Z and propagation constant γ of the equivalent single-layer uniform material, its equivalent single-layer electromagnetic parameter ε can be obtained. eff .

[0103] Step three, calculate the internal shielding effectiveness of the composite cabin with microscopic fine structure and the shielding effectiveness of the homogenized cabin, and use the optimization algorithm to extract the electromagnetic parameters.

[0104] Set the plane wave to 1V / m and conduct a plane wave irradiation experiment on the composite cabin model. Set the time domain finite integral method calculation algorithm to obtain the time domain transmission coefficient S 21 After Fourier transform in time-frequency domain, the composite material transmission coefficient S in this frequency band can be obtained. 21 The amplitude-frequency and phase-frequency characteristics.

[0105] Calculation of the shielding effectiveness SE of the interior of a composite cabin with microscopic fine structures ori , uniform cabin shielding effectiveness SE hom . The equivalent single-layer electromagnetic parameter ε calculated in step 2 is effSubstitute the initial value into the optimization algorithm, set the search step, set the relative dielectric constant search range between 1 and 5, and the conductivity search range between 0 and 1000S / m; set the accuracy threshold to 3dB, and the accuracy requirement is met when the penalty function value Fc is less than 3dB. By changing the search step, the electromagnetic parameters in the homogenized model of the single-layer composite material are calculated, thereby changing the shielding effectiveness SE of the homogenized cabin. hom , making the internal shielding effectiveness SE of the microscopic fine structure composite cabin ori , uniform cabin shielding effectiveness SE hom After the penalty function is substituted, the penalty function value Fc is less than 3 dB. When the penalty function value is less than 3 dB, the electromagnetic parameters obtained at this time are the electromagnetic parameters in the cabin model of the multilayer composite material.

[0106] In summary, the present invention establishes a cabin model of a multi-layer composite material and a homogenized model of a single-layer composite material, respectively, taking into account the shape of the cabin and the different carbon fiber laying angles of each layer of composite material; and optimizes the equivalent single-layer electromagnetic parameters as initial values ​​through an optimization algorithm, so that the electromagnetic parameters of the homogenized model can be used as the electromagnetic parameters of the cabin model after optimization, thereby realizing the solution of the inverse problem of extracting the dielectric properties of a special-shaped composite cabin.

[0107] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for extracting electromagnetic parameters of a special-shaped fiber reinforced composite material, characterized in that: The specific steps include: Step 1: Establish a multi-layer composite cabin model; Step 2: Based on the flat plate model of the multi-layer composite material, a homogenized model of the single-layer composite material is established to calculate the equivalent single-layer electromagnetic parameters; Step three, calculate the internal shielding effectiveness of the composite cabin with a microscopic fine structure and the uniform shielding effectiveness of the cabin, and set the search step and search range. Use the equivalent single-layer electromagnetic parameters as the initial parameters, and continuously change the electromagnetic parameters of the composite material through the search step, thereby changing the uniform shielding effectiveness of the cabin, so that the internal shielding effectiveness of the composite cabin with a microscopic fine structure and the uniform shielding effectiveness of the cabin remain consistent, and use the electromagnetic parameters obtained at this time as the electromagnetic parameters of the multi-layer composite cabin model.

2. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 1, characterized in that: In step three, the search step is set according to the dielectric constant value and the calculation time; the search range includes: a search range for relative dielectric constant and a search range for conductivity, the search range for relative dielectric constant is between the relative dielectric constant of the matrix and the relative dielectric constant of the carbon fiber, and the search range for conductivity is between the conductivity of the matrix and the conductivity of the carbon fiber.

3. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 1, characterized in that: In step three, it is determined whether the penalty function value Fc is less than the set accuracy threshold. When the penalty function value Fc is less than the set accuracy threshold, the internal shielding effectiveness of the composite cabin with a microscopic fine structure is consistent with the shielding effectiveness of the homogenized cabin. The penalty function is expressed as: F c =||SE hom (ε(f),σ(f))-SE ori (f)|| 2 dB Where ε(f) is the relative permittivity corresponding to the change of the electromagnetic parameters of the composite material according to the search step size, and σ(f) is the conductivity corresponding to the change of the electromagnetic parameters of the composite material according to the search step size.

4. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 3, characterized in that: The accuracy threshold is 3dB.

5. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 1, characterized in that: In step three, when calculating the internal shielding effectiveness of the composite cabin of a microscopic fine structure, a time domain excitation signal is set according to the required frequency band, so that the frequency band and the time domain excitation signal satisfy the Fourier change relationship, and a plane wave irradiation experiment is performed on the multilayer composite cabin model in step one; the time domain transmission coefficient is calculated using the time domain finite integration method; based on the cabin model of the multilayer composite material and the time domain transmission coefficient, a wave algorithm is used to calculate the internal shielding effectiveness of the composite cabin of a microscopic fine structure; When calculating the shielding effectiveness of the homogenized cabin, the following conditions must be met: In the formula, SE hom is the electric field shielding effectiveness, E s is the field strength value at the field strength monitoring point inside the cabin, E inc is the incident field strength value of the external electromagnetic wave.

6. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 1, characterized in that: In step one, the size and quantity of the microstructure units are set and arranged in sequence in the vertical direction to form a composite material surface of the cabin and construct a multilayer composite material cabin model.

7. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 6, characterized in that: In step 1, the microstructure unit has a circular cross section, and the cabin model of the multilayer composite material is established as a hollow cylinder model with N layers of composite material basic units, and the matrix of each layer of composite material is a hollow cylinder, and the hollow cylinders of each layer of composite material are nested in sequence to form a hollow cylinder of the multilayer composite material; The size of the carbon fibers in each layer of the composite material is set to be uniform and the ply angle is set to be the same; the relative dielectric constant and the electrical conductivity of the matrix in each layer of the composite material are set to be the same, and the relative dielectric constant and the electrical conductivity of the carbon fibers in each layer of the composite material are set to be the same.

8. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 7, characterized in that: In step 1, the ply angles include: 0°, 90°, 45°, and -45°; When the ply angle is 0°, the ply direction of each carbon fiber in the single-layer composite material is in the vertical direction, perpendicular to the end surface of the substrate, and is evenly arranged along the circumference of the hollow cylinder; When the ply angle is 90°, the ply direction of each carbon fiber in the single-layer composite material is in the horizontal direction, and an arc-shaped bend is generated according to the shape of the matrix, so that each carbon fiber forms a horizontally placed circular ring, and a plurality of carbon fibers are evenly arranged along the height direction of the matrix; When the ply angle is 45°, each carbon fiber in the single-layer composite material is inclined to the right and forms an angle of 45° with the vertical direction, and along the bending direction of the matrix, each carbon fiber is in a right-hand spiral in the matrix; adjacent carbon fibers in a right-hand spiral shape in the single-layer composite material are connected end to end and spiral upward along the height direction of the matrix; When the layup angle is -45°, each carbon fiber in the single-layer composite material is inclined to the left and forms an angle of 45° with the vertical direction, and is laid flat along the bending direction of the matrix, so that each carbon fiber is in a left-hand spiral in the matrix; adjacent carbon fibers in a left-hand spiral shape in the single-layer composite material are connected end to end and spiral upward along the height direction of the matrix.

9. The electromagnetic parameter extraction method of the special-shaped fiber reinforced composite material according to claim 1, characterized in that: In step 2, the method of establishing a homogenization model of a single-layer composite material is as follows: A flat plate model of N-layer composite materials is established, and the number of layers of the composite materials is consistent with the number of layers of the composite materials in the multi-layer composite cabin model, and the carbon fiber ply angle of each layer of the composite materials is the same as the carbon fiber ply angle of each layer of the composite materials in the cabin model, and the transmission matrix equation of the N-layer composite materials is obtained; an equivalent single-layer uniform material is used to replace the N layers of composite materials to establish a single-layer composite material homogenization model.

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