Target defect detection method based on vortex electromagnetic waves
By using the OAM-BP algorithm based on vortex electromagnetic waves in material defect detection, the problems of slow detection speed, low sensitivity and non-contactness in the prior art are solved, and accurate and high-resolution imaging of internal defects of the material are achieved.
Patent Information
- Application Number
- CN202510080931.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-20
- Publication Date
- 2025-05-13
AI Technical Summary
The prior art has problems in material defect detection, low sensitivity and difficult to achieve non-contact detection, especially when detecting complex materials and structures.
The target defect detection method based on vortex electromagnetic waves is adopted to generate OAM waves of different modes through a uniform circular array, and the material defect detection is performed in the terahertz band in combination with the back projection algorithm (OAM-BP algorithm).
Accurate resolution and high-resolution imaging of defects at any position inside the material, improving detection speed and sensitivity without contacting objects.
Smart Images
Figure CN119985548A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of three-dimensional radar imaging, and in particular relates to a target defect detection method based on vortex electromagnetic waves. Background Art
[0002] In the modern industrial field, the quality and integrity of materials have a vital impact on the safety and reliability of products. Therefore, it is particularly important to detect material defects efficiently and accurately. Although traditional detection methods such as ultrasonic testing, X-ray testing and microwave testing can meet the detection needs to a certain extent, they still have many limitations in terms of detection speed, sensitivity and non-contact. For example, there are the following disadvantages in ultrasonic testing: 1. The surface of the object to be tested usually needs to be processed to ensure a good coupling effect, which increases the amount of preparation work before testing. 2. For planar defects such as cracks, if their orientation is not perpendicular to the incident beam, it may be difficult to find. Although ultrasonic testing can be used for thick materials, for particularly thick materials, the sensitivity may decrease due to attenuation. X-ray testing involves the use of radioactive sources or X-ray machines, which will cause harm to the health of workers, and usually takes more time to detect than other non-destructive testing methods. At the same time, it may not provide sufficient resolution for accurate evaluation of very small or thin defects. Traditional microwave testing has obvious advantages in detecting surface or near-surface defects, but it also shows certain limitations when facing complex materials and structures. Its imaging resolution is low and is limited to half a wavelength. Summary of the invention
[0003] The purpose of the present invention is to provide a target defect detection method based on vortex electromagnetic waves to solve the above-mentioned technical problems.
[0004] In order to solve the above technical problems, the specific technical solution of the target defect detection method based on vortex electromagnetic waves of the present invention is as follows:
[0005] A target defect detection method based on vortex electromagnetic waves comprises the following steps:
[0006] Step 1, using UCA to generate vortex electromagnetic waves; for a uniform circular array, using an incremental phase modulation excitation method to generate vortex electromagnetic waves;
[0007] Step 2: Background cancellation;
[0008] Step 3: Combining vortex electromagnetic waves with the back-projection algorithm, an improved OAM-BP algorithm is proposed.
[0009] In the terahertz frequency band, a uniform circular array is used to generate OAM waves of different modes to illuminate the object.
[0010] The algorithm is used to image the location of defects inside the Teflon plate.
[0011] Furthermore, the step 1 comprises the following steps:
[0012] Each array element has the same amplitude. The first unit is used as the reference phase. The excitation phases of other units are increased at equal intervals. The excitation phase difference between two adjacent array elements is Δφ=2πl / N. The UCA array consists of N dipole units. The UCA is located in the XOY plane. Let the array radius be a and the azimuth angle of the nth array element be φ n =2πn / N, l represents the number of orbital angular momentum modes, all array elements transmit single-frequency signals of equal amplitude, so the electric field intensity generated at any point r (r, θ, φ) in space is:
[0013]
[0014] Where j is the current density vector of the dipole antenna, d is the length of the electric dipole, φ n =2π(n-1) / N, n=1,2,…, N is the azimuth position of each array element, μ0 is the vacuum permeability, ω and k are the angular frequency and wave vector of the electromagnetic field, respectively. in and Represents the direction unit vectors of the x-axis and y-axis respectively, J l (ka sinθ) represents l th Bessel function of the first kind.
[0015] Furthermore, the step 2 comprises the following steps:
[0016] Take a complete Teflon plate and use plane scanning to collect the total field, which is recorded as S1. Take another identical Teflon plate with defects inside and use plane scanning to collect the total field, which is recorded as S2. Since the total field = incident field + scattered field, subtract S1-S2 to obtain the scattered field S3 of the defect.
[0017] Furthermore, the step 3 comprises the following steps:
[0018] First, the observation area is divided into grids, each pixel is regarded as a potential scattering source, and it is assumed that the signal reflected from this point will arrive at the receiver with a specific time delay. The BP algorithm reconstructs the image by calculating the total contribution of each pixel. The grid coordinate numbered (i, j) in the two-dimensional discrete grid is denoted as P i,j (x i ,y j ,0), the distance to the transmitting antenna at the slow time η is R i,j(η), which is different from the conventional BP algorithm. Due to the introduction of vortex electromagnetic waves, a variable related to the azimuth angle φ needs to be introduced during phase correction, which is denoted as φ in the antenna coordinate system. ij (η), then the result of accumulation according to the BP algorithm is:
[0019]
[0020] where s rd is the reference signal, and l is the mode number.
[0021] The target defect detection method based on vortex electromagnetic waves of the present invention has the following advantages: the present invention proposes a material defect detection algorithm (OAM-BP) by combining vortex electromagnetic waves with a back-projection algorithm. In the terahertz frequency band, a uniform circular array is used to generate OAM waves of different modes to illuminate the object, and the algorithm is used to image the internal defect position of the teflon plate. From the simulation results, it can be seen that this method can accurately distinguish defects at any position inside the object and achieve high-resolution imaging of the defect image. BRIEF DESCRIPTION OF THE DRAWINGS
[0022] Figure 1 is a schematic diagram of a UCA of the present invention;
[0023] Figure 2 It is a schematic diagram of grid division of the present invention;
[0024] Figure 3 Schematic diagram of amplitude distribution and phase distribution of OAM electromagnetic waves when different modes l=1, 3, 5 of the present invention;
[0025] Figure 4 It is a schematic diagram of the FEKO simulation model of the present invention;
[0026] Figure 5 This is the imaging result diagram. DETAILED DESCRIPTION
[0027] In order to better understand the purpose, structure and function of the present invention, the target defect detection method based on vortex electromagnetic waves of the present invention is further described in detail below in conjunction with the accompanying drawings.
[0028] As a carrier of information, the traditional modulation method of electromagnetic waves mainly focuses on the time domain, frequency domain and polarization domain, and mainly relies on the approximation of far-field plane waves. However, the introduction of orbital angular momentum brings a new degree of freedom to electromagnetic wave modulation. By superimposing orbital angular momentum modulation on the basis of plane waves, the propagation isophase surface of electromagnetic waves is distorted from the original planar structure to a unique spatial spiral structure. At the same time, by utilizing the orthogonal characteristics between different integer modes, the targets in the beam can be measured and displayed more precisely, thereby significantly improving the ability to transmit and obtain information. This technology is similar to the multi-angle diversity illumination of the target by a plane wave, which provides a solid physical basis for the resolution of targets in the beam.
[0029] The present invention uses a uniform circular array (UCA) to generate vortex electromagnetic waves, receives scattered field information of an object through a plane scanning technique, and finally images the defects of a target through an improved BP algorithm. Specifically, the target defect detection method based on vortex electromagnetic waves of the present invention comprises the following steps:
[0030] Step 1: Use UCA to generate vortex electromagnetic waves. For uniform circular arrays, an incremental phase modulation excitation method can be used to generate vortex electromagnetic waves. The excitation principle is as follows: the amplitudes of each array element are the same, the first unit is used as the reference phase, and the excitation phases of other units are increased at equal intervals in sequence. The excitation phase difference between two adjacent array elements is Δφ=2πl / N. Figure 1 A schematic diagram of generating vortex electromagnetic waves based on a UCA array is given. The UCA array consists of N dipole units and is located in the XOY plane. Assume that the array radius is a and the azimuth angle of the nth array element is φ n =2πn / N, l represents the number of orbital angular momentum modes, and all array elements transmit single-frequency signals of equal amplitude. Therefore, the electric field intensity generated at any point r (r, θ, φ) in space is:
[0031]
[0032] Where j is the current density vector of the dipole antenna and d is the length of the electric dipole. n =2π(n-1) / N, n=1,2,…,N is the azimuth position of each array element. μ0 is the vacuum permeability, ω and k are the electromagnetic field angular frequency and wave vector respectively. in and Represents the direction unit vector of the x-axis and y-axis respectively. l (kasinθ) represents l th Bessel function of the first kind.
[0033] Step 2, background cancellation, take a complete Teflon plate and use plane scanning to collect the total field recorded as S1, take another identical Teflon plate with internal defects and use plane scanning to collect the total field recorded as S2, because the total field = incident field + scattered field, subtract S1-S2 to obtain the scattered field S3 of the defect.
[0034] Step 3: Combining vortex electromagnetic waves with the back-projection algorithm, an improved OAM-BP algorithm is proposed. In the terahertz frequency band, a uniform circular array is used to generate OAM waves of different modes to illuminate the object. The algorithm is used to image the internal defect position of the teflon plate. First, the observation area is gridded, such as Figure 2 As shown in Figure 1, each pixel is considered as a potential scattering source, and it is assumed that the signal reflected from this point will arrive at the receiver with a specific time delay. The BP algorithm reconstructs the image by calculating the total contribution of each pixel. Figure 2 The grid coordinates numbered (i, j) in the two-dimensional discrete grid in P are i,j (x i ,y j ,0), the distance to the transmitting antenna at the slow time η is R i,j (η), which is different from the conventional BP algorithm. Due to the introduction of vortex electromagnetic waves, a variable related to the azimuth angle φ needs to be introduced during phase correction, which is denoted as φ in the antenna coordinate system. ij (η), then the result of accumulation according to the BP algorithm is:
[0035]
[0036] where s rd is the reference signal, and l is the mode number.
[0037] The center frequency of the radar in the simulation is set to f c = 100 GHz, bandwidth B = 10 GHz, sampling interval 0.5 GHz, the UCA array consisting of 12 y-polarized dipole antennas generates an OAM wave with mode number l = 3, and its phase structure is as follows Figure 3 The array radius a = 3λ, the acquisition plane is at z = 30λ, the size is 30λ × 30λ, and 51 points are uniformly sampled along the x and y directions respectively. The imaging model is as follows Figure 4 As shown in the figure, the imaging target is a teflon plate with a size of 20λ×20λ×1λ, 15λ away from the antenna plane, with a relative dielectric constant of ε=2.08, and three cylindrical holes with a radius of r=0.5λ and a height of h=0.5λ are dug at random positions inside it. The imaging result is shown in Figure 5 The result hides the influence of the plate and only images the internal defects of the object. The location information of the three defects can be clearly seen from the figure, which is in good agreement with the set value.
[0038] It is to be understood that the present invention is described by some embodiments, and it is known to those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the scope of protection of the present invention.
Claims
1. A target defect detection method based on vortex electromagnetic waves, characterized in that: The following steps are involved: Step 1, using UCA to generate vortex electromagnetic waves; for a uniform circular array, using an incremental phase modulation excitation method to generate vortex electromagnetic waves; Step 2: Background cancellation; Step 3: Combining vortex electromagnetic waves with the back-projection algorithm, an improved OAM-BP algorithm is proposed. In the terahertz frequency band, OAM waves of different modes are generated through a uniform circular array to illuminate the object, and the algorithm is used to image the internal defect position of the Teflon plate.
2. The target defect detection method based on vortex electromagnetic waves according to claim 1 is characterized in that: The step 1 comprises the following steps: Each array element has the same amplitude. The first unit is used as the reference phase. The excitation phases of other units are increased at equal intervals. The excitation phase difference between two adjacent array elements is Δφ=2πl / N. The UCA array consists of N dipole units. The UCA is located in the XOY plane. Let the array radius be a and the azimuth angle of the nth array element be φ n =2πn / N, l represents the orbital angular momentum mode number, all array elements transmit single-frequency signals of equal amplitude, so the electric field intensity generated at any point r (r, θ, φ) in space is: Where j is the current density vector of the dipole antenna, d is the length of the electric dipole, φ n =2π(n-1) / N, n=1, 2, ..., N is the azimuth position of each array element, μ0 is the vacuum permeability, ω and k are the angular frequency and wave vector of the electromagnetic field, respectively. in and Represents the direction unit vectors of the x-axis and y-axis respectively, J l (ka sinθ) represents l th Bessel function of the first kind.
3. The target defect detection method based on vortex electromagnetic waves according to claim 1 is characterized in that: The step 2 comprises the following steps: Take a complete Teflon plate and use plane scanning to collect the total field, which is recorded as S1. Take another identical Teflon plate with defects inside and use plane scanning to collect the total field, which is recorded as S2. Since the total field = incident field + scattered field, subtract S1-S2 to obtain the scattered field S3 of the defect.
4. The target defect detection method based on vortex electromagnetic waves according to claim 1 is characterized in that: The step 3 comprises the following steps: First, the observation area is divided into grids, each pixel is regarded as a potential scattering source, and it is assumed that the signal reflected from this point will arrive at the receiver with a specific time delay. The BP algorithm reconstructs the image by calculating the total contribution of each pixel. The grid coordinate numbered (i, j) in the two-dimensional discrete grid is denoted as P i，j (x i ,y j , 0), the distance to the transmitting antenna at the slow time η is R i，j (η), which is different from the conventional BP algorithm. Due to the introduction of vortex electromagnetic waves, a variable related to the azimuth angle φ needs to be introduced during phase correction, which is recorded as φ in the antenna coordinate system. ij (η), then the result of accumulation according to the BP algorithm is: where s rd is the reference signal, and l is the mode number.