Electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage to wave-absorbing coating

Abstract

The application provides an electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage of a wave-absorbing coating, and belongs to the technical field of measurement, and comprises the following steps: microwave heating treatment is performed on a wave-absorbing coating sample with damage, and a surface temperature cloud chart of the sample is obtained through computer processing; a region with a surface temperature of the wave-absorbing coating higher than a test environment temperature is extracted from the surface temperature cloud chart; the extracted region is subjected to triangular face mesh division, and all triangular elements are combined to realize three-dimensional reconstruction of the damage region of the wave-absorbing coating; a surface wave propagation method based on a dispersion equation is constructed; the transmission of surface waves in the three-dimensional reconstruction model of the damage region of the wave-absorbing coating is analyzed by using the dispersion equation, the influence of the thickness of the triangular element and the electromagnetic parameters of the combined model on a surface wave attenuation constant is discussed, and a surface wave attenuation constant model based on three-dimensional reconstruction of damage of the wave-absorbing coating is constructed. The application provides a theoretical basis for damage evaluation of a wave-absorbing coating of an aircraft.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of measurement, and particularly relates to an electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage to a wave-absorbing coating. BACKGROUND

[0002] The radar wave-absorbing coating is widely used as one of the low-probability-of-detection technologies for reducing advanced aircrafts, effectively reducing the probability of the aircrafts being discovered and improving the combat effectiveness of the aircrafts. However, when the aircrafts perform combat tasks or routine training, scratches, scratches, peeling, oxidation and other damages are inevitable. The damage to the wave-absorbing coating will affect the radar stealth performance of the aircrafts and reduce the survivability of the aircrafts. Studies have shown that when the damage thickness of the wave-absorbing coating is 4mm, the RCS (radar cross section) of the target will increase by 3dB when the radar signal with a frequency of 2GHz is tested; when the damage thickness of the wave-absorbing coating is 2mm, the RCS will increase by 15dB when the radar signal with a frequency of 8.75GHz is tested; the reflection coefficient of the stealth target increases by 2dB, and the probability of being discovered increases by 3.5%, so the damage to the wave-absorbing coating will seriously affect the stealth performance of the target.

[0003] At present, the detection methods for the damage to the wave-absorbing coating include ultrasonic technology, eddy current method, ray method and infrared thermal imaging. The ultrasonic method uses ultrasonic waves to act on the coating and extracts damage information according to the echo signal; the eddy current method uses the change of the eddy current after the electromagnetic signal acts on the wave-absorbing coating to extract the damage; the ray method uses the attenuation characteristics of the ray when propagating in the wave-absorbing coating to extract the damage; and the infrared thermal imaging method uses the thermal effect of the infrared signal to extract the damage. These detection methods have their own advantages and disadvantages, but these methods can only detect the existence of the damage to the wave-absorbing coating, or can detect the area and thickness information of the damage to the coating, but cannot evaluate the influence of the detected damage on the stealth performance of the target, so as to give instructions on whether the damage needs to be repaired.

[0004] In order to evaluate the influence of the damage to the coating on the stealth performance of the target, it is necessary to start from the electromagnetic wave transmission mechanism and give the propagation of the electromagnetic wave in the damaged area of the wave-absorbing coating. The surface wave is a kind of electromagnetic wave propagating along the interface, but its amplitude decays exponentially along the direction perpendicular to the interface. The interface is usually composed of two different media, and the media binds the surface wave on the interface without radiating the surface wave energy. When the surface wave encounters the damage to the coating, the damage causes the change of the coating medium, mainly including the thickness of the coating, the electric conductance and the magnetic conductance. These changes affect the transmission characteristics of the electromagnetic surface wave on the wave-absorbing coating, so it is urgent to establish a surface wave transmission method for the wave-absorbing coating with damage. SUMMARY

[0005] To solve the above technical problems, the application provides an electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage to a wave-absorbing coating, which is based on a three-dimensional reconstruction model of damage to the wave-absorbing coating, studies the propagation characteristics of electromagnetic plane waves in the damaged area, reveals the propagation mechanism of plane waves in the wave-absorbing coating with damage, and provides a theoretical basis for damage evaluation of the wave-absorbing coating of an aircraft.

[0006] To achieve the above-mentioned purpose, the application adopts the following technical solution:

[0007] An electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage to a wave-absorbing coating, comprising the following steps:

[0008] Step 1: Microwave heating is performed on the wave-absorbing coating sample with damage, an infrared imaging instrument is used to collect the infrared radiation signals on the surface of the wave-absorbing coating sample, and a surface temperature cloud map of the wave-absorbing coating sample is obtained through computer processing;

[0009] Step 2: The area on the surface of the wave-absorbing coating sample with a surface temperature higher than the test environment temperature is extracted from the surface temperature cloud map;

[0010] Step 3: Triangular face mesh division is performed on the area extracted in Step 2, the divided triangular face mesh is a triangular face element, the temperature information of the center of each triangular face mesh is extracted, the generalized reflectivity of the center of the triangular face mesh is calculated, the thickness of the triangular face element is calculated, a triangular element is constructed, and all triangular elements are combined to form a three-dimensional reconstruction model of the damaged area;

[0011] Step 4: A surface wave propagation method based on a dispersion equation is constructed, the first area composed of free space or air and the second area composed of a dielectric layer are distinguished, and the dispersion equation is derived by using the Maxwell equation set;

[0012] Step 5: The transmission of surface waves in the three-dimensional reconstruction model of the damaged area of the wave-absorbing coating sample is analyzed by using the dispersion equation, the influence of the thickness and electromagnetic parameters of the triangular element on the surface wave attenuation constant is analyzed, and a surface wave attenuation constant model based on three-dimensional reconstruction of damage to the wave-absorbing coating is constructed.

[0013] Beneficial effects:

[0014] After the wave-absorbing coating sample with damage is heated and imaged by using the microwave thermal imaging technology, the area with a higher temperature in the thermal infrared cloud map of the sample is extracted, which corresponds to the damaged area of the sample, the three-dimensional reconstruction is performed on the area with a higher temperature, the three-dimensional reconstruction model is obtained, the surface wave transmission method of any triangular element in the reconstruction model is studied by using the dispersion equation, the transmission law of the surface waves of all triangular elements is obtained, the transmission characteristics of electromagnetic surface waves are studied based on the three-dimensional reconstruction model, the attenuation characteristics of electromagnetic waves at the damage of the wave-absorbing coating can be effectively evaluated, and a theoretical basis for the influence of coating damage on stealth performance is provided. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a flow chart of the electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage to the wave-absorbing coating of the present application.

[0016] Figure 2 is a schematic diagram of a triangular mesh of the damaged area of the wave-absorbing coating sample.

[0017] Figure 3 is a schematic diagram of three-dimensional reconstruction of the damaged area of the wave-absorbing coating sample.

[0018] Figure 4 is a schematic diagram of a surface wave plane model. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0020] As shown in Figure 1 , the electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage to the wave-absorbing coating of the present application comprises the following steps:

[0021] Step S1: microwave thermography processing of the wave-absorbing coating with damage;

[0022] Step S2: extracting the area of the wave-absorbing coating surface where the temperature is higher than the test environment temperature (i.e. Figure 1 extracting the area of the coating surface where the temperature is higher) by the computer;

[0023] Step S3: three-dimensional reconstruction of the area of the wave-absorbing coating with damage to obtain a three-dimensional reconstruction model of the damaged area;

[0024] Step S4: constructing a surface wave propagation method based on a dispersion equation;

[0025] Step S5: obtaining the transmission characteristics of the surface wave in the three-dimensional reconstruction model of the damaged area.

[0026] Preferably, in step S1, the wave-absorbing coating sample with damage is heated by microwaves, the infrared radiation signal of the sample coating surface is collected by an infrared imager, and the sample surface temperature cloud image is obtained by computer processing.

[0027] Preferably, in step S2, the area of the wave-absorbing coating surface where the temperature is higher than the test environment temperature is extracted by the computer through the sample surface temperature cloud image.

[0028] Preferably, in step S3, CAD software is used to perform fine triangular meshing on the area with high temperature on the coating surface, dividing it into several triangular elements.

[0029] Preferably, the temperature information at the center of each triangular mesh is extracted, and the generalized reflectivity at the center of the triangular mesh is calculated using the following formula:

[0030] ;

[0031] in, The generalized reflection coefficient of the absorbing coating. Represents the energy density of electromagnetic waves. The intrinsic impedance (or wave impedance) of free space. Indicates the incident electromagnetic intensity. It represents the reciprocal of the energy density of electromagnetic waves. Emissivity of solid surface, dimensionless. Here is the Boltzmann constant, with a magnitude of , The temperature at the center point of the triangular mesh, i.e. ,in, Let c, d, and e represent the temperatures corresponding to the c-th, d-th, and e-th grid nodes, respectively, where c, d, and e represent the grid node numbers of the triangular mesh. This indicates the ambient temperature during the test.

[0032] According to transmission line theory, for a three-layer structure consisting of a metal substrate, an absorbing coating sample, and an air layer, the relationship between its generalized reflectivity and the thickness of the absorbing coating sample is as follows:

[0033] ;

[0034] Among them, intermediate parameters intermediate parameters , Take 1 and 2 respectively. , , Represented as the first The permeability, dielectric constant, and thickness of the coating layer; among which, Indicates the microwave absorbing coating sample layer, Indicates air layer, Indicates wavelength; Indicates the first The generalized reflectivity of the coating layer. When When the value is 0, The generalized reflectivity of a metallic substrate is usually expressed as... .

[0035] Combining the triangular surface elements and the thickness of the triangular surface elements, a triangular volume element formed by the damaged area of the absorbing coating sample can be obtained. As Figure 3 shown, combining all the triangular volume elements can achieve the three-dimensional reconstruction of the damaged area of the absorbing coating. All the triangular volume elements constitute a three-dimensional reconstruction model of the damaged area.

[0036] Preferably, in the step S4, the absorbing coating sample is divided into a first region and a second region. As Figure 4 shown, the first region is free space or an air layer, and its permittivity and permeability are (that is, Figure 2 in ). The second region is a dielectric layer, that is, the absorbing coating sample layer. The absolute permittivity and absolute permeability of the second region are and respectively, where and are the permittivity and permeability in vacuum, represents the direction perpendicular to the horizontal plane , and represents the thickness of the absorbing coating sample.

[0037] Given the frequency, corresponding electromagnetic parameters, and thickness of the triangular volume elements of the three-dimensional reconstruction model of the damaged area of any absorbing coating, the following dispersion equation is used to analyze the transmission of surface waves in the three-dimensional reconstruction model of the damaged area of the absorbing coating:

[0038] ;

[0039] where, represents the thickness of the th triangular volume element, is the free space wave number, represents the angular frequency, represents the surface wave attenuation coefficient of the th triangular volume element, and j represents the imaginary unit; is the free space wave number.

[0040] Preferably, in the step S5, the influence of the thickness of the triangular volume element on its surface wave attenuation constant and the influence of the different electromagnetic parameters of all the triangular volume elements on their surface wave attenuation constants are discussed respectively. Analyze the variation law of the surface wave attenuation constant of any triangular volume element with the thickness and the surface wave transmission characteristics, and construct a surface wave attenuation constant model based on the three-dimensional reconstruction of the absorbing coating damage.

[0041] Example:

[0042] The embodiment provides an electromagnetic surface wave transmission method based on three-dimensional reconstruction of damage of a wave-absorbing coating, utilizes microwave heating of a wave-absorbing coating sample to obtain a sample surface temperature cloud picture, extracts a higher temperature area, combines heat transfer and electromagnetism, three-dimensionally reconstructs a sample damage area, establishes an electromagnetic surface wave transmission method in the reconstructed model based on a dispersion equation, explores influences of damage area thickness and electromagnetic parameters on a surface wave attenuation constant, and constructs a surface wave attenuation constant model based on three-dimensional reconstruction of damage of the wave-absorbing coating, and specifically includes the following steps:

[0043] Step S1: microwave thermal imaging processing of the wave-absorbing coating with damage.

[0044] In a small microwave darkroom, the wave-absorbing coating sample with damage is heated by a heating antenna, and the sample temperature is detected by using an infrared imager. First, the antenna is moved above the wave-absorbing coating sample to heat, and after the temperature is heated to a constant temperature record, the antenna is removed, and the sample is detected by using the infrared imager.

[0045] Step S2: extracting a wave-absorbing coating surface area with a temperature higher than that of a test environment.

[0046] The infrared cloud picture detected by the infrared thermal imager has certain noise, and image noise reduction and image enhancement are used to pre-process the infrared cloud picture. The noise sources of the infrared image mainly include system noise and environmental noise, wherein the system noise is generated by the system itself and can be reduced by improving the system and devices; the environmental noise mainly includes background noise caused by object self-radiation, impurity interference noise in the air and the like, and can be processed by using typical filtering noise reduction methods such as mean, median and Gaussian. After the infrared detection original image is pre-processed, a relatively clear infrared cloud picture is obtained, wherein the temperature of the damage area is obviously higher than that of other areas, and the contour of the area is extracted.

[0047] Step S3: three-dimensional reconstruction of the wave-absorbing coating area with damage.

[0048] The damage area with a higher temperature in the infrared cloud picture is grid divided, and the CAD software CATIA is used to complete fine division of triangular face grid of the area, to form a triangular face element, as shown in Figure 2 In order to better fit the contour information of the damage area, the number of grids can be appropriately increased, so as to fit the contour of the damage area more accurately.

[0049] The temperature information of the center of each triangular face grid is extracted, and the generalized reflectivity of the center of the triangular face grid is calculated, and the formula is as recorded above.

[0050] The relationship between the generalized reflectivity and the thickness of the wave-absorbing coating is obtained, and the formula is as recorded above.

[0051] The thickness of all the center points of the triangular face elements is solved , q represents the number of triangular facets. Using each triangular facet as a plane and its center point thickness as a reference, triangular prism-shaped triangular elements are constructed; these are the triangular elements representing the damaged area of ​​the absorbing coating. Based on the arrangement of these triangular facets, combining all the triangular elements allows for the three-dimensional reconstruction of the damaged area of ​​the absorbing coating, such as... Figure 3 As shown, the three-dimensional reconstruction model of the damaged area is written as follows:

[0052] ;

[0053] in, Indicates the first The area of ​​each triangular facet.

[0054] Step S4: Surface wave propagation method based on the dispersion equation.

[0055] For lossy radar absorbing materials, Ufimtsev established a planar model for the theoretical study of surface wave transmission characteristics, such as... Figure 4 As shown. Assuming a perfect electrical conductor lies in the xz plane, an absorbing coating sample is applied to the metal plane. The thickness of the absorbing coating sample is... The absolute complex permittivity of the material is The absolute complex permeability of the absorbing coating sample is , actual part Characterizing energy storage, imaginary part Characterized by damage, real part Characterizing magnetic energy storage, imaginary part Characterizes magnetic loss.

[0056] The model with a layer of absorbing material coated on the aforementioned metal plane is divided into region 1 and region 2. Region 1 is free space or air, and its permittivity and permeability are... The second region is the microwave absorbing coating sample layer. The absolute permittivity and absolute permeability of the second region are respectively... and ,in and Let be the permittivity and permeability in vacuum.

[0057] The propagation mechanism of TM (surface wave, transverse magnetic wave) propagating along the z-axis, as known from Maxwell's equations, is as follows: In the first region:

[0058] ;

[0059] In region 2:

[0060] ;

[0061] in, , Indicates the magnetic fields of region 1 and region 2. Axial components, , , , Indicates the electromagnetic fields of region 1 and region 2. axis, Axial components, Indicates the thickness of the microwave absorbing coating sample. and The dielectric constant and magnetic permeability of the absorbing coating sample are respectively. For free space wave impedance, For free space wavenumber, The transverse wavenumber of the absorbing material. The transverse wavenumber in free space. Let be the surface wave propagation constant, j be the imaginary unit, y be the position of the absorbing material sample on the y-axis, and z be the position of the absorbing material sample on the z-axis.

[0062] , , The relationship between the three is as follows: , ;

[0063] From the Helmholtz wave equation, we know that: ;

[0064] Based on the continuity assumption of the boundary conditions, a transcendental equation concerning the wavenumber can be derived:

[0065] ;

[0066] The dispersion equation can be obtained as follows:

[0067] ;

[0068] in, It means that it is always equal to.

[0069] As can be seen from the dispersion equation above, given the frequency, corresponding electromagnetic parameters, and thickness of the absorbing material, the basic characteristics of surface wave propagation in the absorbing material can be analyzed using the dispersion equation.

[0070] Step S5: Transmission characteristics of surface waves in the three-dimensional reconstruction model of the damaged region.

[0071] Given the three-dimensional reconstruction model of the damaged area of ​​an arbitrary absorbing coating, the first... Given the frequency, corresponding electromagnetic parameters, and thickness of the triangular solid element, the dispersion equation is obtained.

[0072] Investigating the thickness of triangular elements The influence of the thickness (0.2 mm, 0.5 mm, 0.75 mm, 1 mm) on the surface wave attenuation constant is analyzed, the attenuation contrast curve of different thicknesses is drawn, and the variation law of the surface wave attenuation with the thickness is analyzed;

[0073] The influence of the electromagnetic parameters (the parameter variation ratio is 0.5 times, 1 times, 1.5 times and 2 times) of all triangular elements constituting the damage area on the surface wave attenuation constant is analyzed, the attenuation contrast curve of different electromagnetic parameters is drawn, and the variation law of the surface wave attenuation with the electromagnetic parameters is analyzed.

[0074] The variation law of the surface wave attenuation constant of the arbitrary triangular element with the thickness is analyzed The surface wave attenuation constant model based on the three-dimensional reconstruction of the damage of the wave-absorbing coating is constructed according to the surface wave transmission characteristics:

[0075] ;

[0076] wherein, represents the plane wave attenuation constant of all triangular elements constituting the damage area, represents the fitting function of the damage thickness and the plane wave attenuation constant of the wave-absorbing coating sample, and the undetermined coefficients of the fitting can be determined by using the least square method.

[0077] The above merely describes the preferred embodiments of the present application but should not be used to limit the present application, and various modifications and changes can be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for electromagnetic surface wave propagation based on three-dimensional reconstruction of absorbing coating damage, characterized in that, Includes the following steps: Step 1: Microwave heating is performed on the damaged microwave absorbing coating sample. Infrared radiation signals from the surface of the microwave absorbing coating sample are collected using an infrared imager and processed by a computer to obtain a surface temperature cloud map of the microwave absorbing coating sample. Step 2: Extract the area from the surface temperature cloud map where the surface temperature of the microwave absorbing coating sample is higher than the test environment temperature; Step 3: Divide the region extracted in Step 2 into triangular meshes. The resulting triangular meshes are triangular elements. Extract the temperature information at the center of each triangular mesh, calculate the generalized reflectivity at the center of the triangular mesh, estimate the thickness of the triangular elements, construct triangular elements, and combine all triangular elements to form a three-dimensional reconstruction model of the damaged area. Step 4: Construct a surface wave propagation method based on the dispersion equation, distinguish between the first region composed of free space or air and the second region composed of a dielectric layer, and derive the dispersion equation using Maxwell's equations. Step 5: Analyze the surface wave transmission in the three-dimensional reconstruction model of the damaged area of ​​the absorbing coating sample using the dispersion equation, analyze the influence of the thickness of the triangular element and electromagnetic parameters on the surface wave attenuation constant, and construct a surface wave attenuation constant model based on the three-dimensional reconstruction of the absorbing coating damage.

2. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 1, microwave heating is carried out in a microwave anechoic chamber. A thermal antenna is used to heat the microwave absorbing coating sample. After heating to a constant temperature, the temperature is recorded. Then, an infrared imager is used to detect the microwave absorbing coating sample.

3. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 2, the surface temperature cloud map is preprocessed with image denoising and image enhancement, and environmental noise is processed by filtering and denoising methods to extract the contour of the damaged area.

4. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 3, the thickness at the center point of all triangular elements is calculated based on the relationship between the generalized reflectivity of the flat plate absorbing material lined with a metal substrate and the thickness of the absorbing coating sample.

5. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 4, the propagation mechanism of surface waves propagating along the z-axis is determined by Maxwell's equations. Based on the continuity assumption of the boundary conditions, a transcendental equation for the wave number is derived, which in turn yields the dispersion equation.

6. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 5, the influence of the thickness of the triangular element being 0.2 mm, 0.5 mm, 0.75 mm, and 1 mm on the surface wave attenuation constant is analyzed, and attenuation comparison curves for different thicknesses are plotted to analyze the law of surface wave attenuation changing with thickness.

7. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 5, the influence of electromagnetic parameter changes of 0.5 times, 1 time, 1.5 times and 2 times on the surface wave attenuation constant of the damaged region composed of all triangular elements is analyzed, and attenuation comparison curves of different electromagnetic parameters are plotted to analyze the law of surface wave attenuation with electromagnetic parameter changes.

8. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 5, the least squares method is used to determine the undetermined coefficients of the fitting function between the damage thickness of the absorbing coating sample and the surface wave attenuation constant, thereby constructing a surface wave attenuation constant model based on three-dimensional reconstruction of the absorbing coating damage.

9. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 1, characterized in that, In step 3, the number of triangular mesh divisions is increased to fit a more accurate contour of the damaged area.

10. The electromagnetic surface wave transmission method based on three-dimensional reconstruction of absorbing coating damage according to claim 2, characterized in that, In step 1, after the microwave heating reaches the constant temperature for recording, the heating antenna used for microwave heating is removed.

Images