A near-field microwave holographic imaging method, device, electronic device and storage medium

Abstract

The present application provides a near-field microwave holographic imaging method, device, electronic device and storage medium, the method comprising: obtaining a scattering parameter matrix in microwave transmission; obtaining the tangential electric field value corresponding to each grid center position in the imaging plane of the target object to be measured by near-field scanning; determining a measurement matrix based on the tangential electric field value corresponding to each grid center position based on the Fresnel diffraction theory; determining a reflection characteristic matrix based on the scattering parameter matrix and the measurement matrix; reconstructing the image of the target object to be measured based on the reflection characteristic matrix to obtain a reconstructed image. The scheme is based on the Fresnel diffraction theory, the reconstructed image has high precision, and the imaging time is short.

Description

Technical Field

[0001] The present invention belongs to the technical field of microwave imaging, and in particular relates to a near-field microwave holographic imaging method, device, electronic equipment and storage medium. Background Art

[0002] Microwave imaging, as an important research branch in the microwave field, has attracted widespread attention from researchers. Different from traditional optical and infrared imaging methods, microwaves have unique characteristics. Microwave imaging can penetrate non-transparent objects to obtain information such as the position, shape, and electromagnetic properties of metal or dielectric targets. Near-field microwave imaging is essentially an electromagnetic inverse scattering problem. The main principle is to use electromagnetic waves to illuminate the target object, and then reconstruct the object through the scattered electromagnetic wave signals. For existing microwave near-field imaging systems, the focus of imaging quality evaluation is on the construction of the diffraction process between the imaging plane and the antenna aperture. The higher the accuracy of the diffraction process construction, the higher the quality of the reconstructed image.

[0003] For near-field microwave holographic imaging, the existing methods for constructing the diffraction process are still not accurate enough, for example: (1) making equivalent substitutions between the incident field information and the Green's function, making the total field and the incident field information approximately equivalent for weak scatterers, and approximating the square of the incident field information. (2) treating the antenna as a point source, thereby decomposing the imaging plane field information in a plane and solving the calculation in the wave number domain.

[0004] In summary, it can be concluded that the existing microwave near-field imaging reconstruction algorithms have the problem of approximately equivalent substitution for the construction of the diffraction process between the plane where the object to be measured is located and the antenna aperture, and require two diffraction approximate calculations, which cannot obtain as much information as possible from the object's scattering, resulting in the reconstructed image effect being not ideal. At the same time, the calculation process is relatively complicated, which increases the imaging calculation time. The existing calculation methods have the problem of not being accurate enough in the construction of the diffraction process and the low quality of the reconstructed image. Summary of the invention

[0005] The purpose of the embodiments of this specification is to provide a near-field microwave holographic imaging method, device, electronic device and storage medium.

[0006] To solve the above technical problems, the embodiments of the present application are implemented in the following ways:

[0007] In a first aspect, the present application provides a near-field microwave holographic imaging method, the method comprising:

[0008] Obtain the scattering parameter matrix in microwave transmission;

[0009] The tangential electric field value corresponding to each grid center position in the imaging plane of the target object to be measured is obtained by near-field scanning;

[0010] Based on Fresnel diffraction theory, the measurement matrix is ​​determined according to the tangential electric field value corresponding to the center position of each grid;

[0011] Determine the reflection characteristic matrix according to the scattering parameter matrix and the measurement matrix;

[0012] The image of the target object to be measured is reconstructed according to the reflection characteristic matrix to obtain a reconstructed image.

[0013] In one embodiment, obtaining a scattering parameter matrix in microwave transmission includes:

[0014] Acquire a first scattering parameter corresponding to each grid when there is a target object to be measured;

[0015] Acquire a second scattering parameter corresponding to each grid when there is no target object to be measured;

[0016] Determining a scattering parameter according to the corresponding first scattering parameter and second scattering parameter;

[0017] All scattering parameters constitute the scattering parameter matrix.

[0018] In one embodiment, determining the scattering parameter according to the corresponding first scattering parameter and the second scattering parameter includes:

[0019] Calculating the difference between the corresponding first scattering parameter and the second scattering parameter;

[0020] The difference is used as the scattering parameter.

[0021] In one embodiment, based on the Fresnel diffraction theory, the measurement matrix is ​​determined according to the tangential electric field value corresponding to the center position of each grid:

[0022]

[0023] Among them, E (l,i) (x c ,y c ) is the tangential electric field value corresponding to the center position of each grid, H (l,i) It is the measurement representation of the transmitting and receiving antennas at each grid; the measurement representations at all grids constitute a measurement matrix;

[0024]

[0025]

[0026]

[0027]

[0028]

[0029] lx and ly are the sizes of each grid along the x and y directions respectively;

[0030]

[0031]

[0032]

[0033] M is the number of grids in the x direction, and N is the number of grids in the y direction.

[0034] In one embodiment, a reflection characteristic matrix is ​​determined based on a scattering parameter matrix and a measurement matrix:

[0035]

[0036] in, is the scattering parameter matrix, is the measurement matrix;

[0037] Solve the above matrix to get the inverse eigenvalue f at each grid mn , mn=1,2,3...M*N;

[0038] The inverse eigenvalues ​​at all grids constitute the reflected eigenmatrix.

[0039] In one embodiment, the reflection characteristic matrix includes reflection characteristic values ​​at each grid in the imaging plane;

[0040] Reconstructing the image of the target object to be measured according to the reflection feature matrix to obtain a reconstructed image, including:

[0041] All reflection feature values ​​are used as pixel values ​​of the reconstructed image.

[0042] In one embodiment, the reflection characteristic matrix includes reflection characteristic values ​​at each grid in the imaging plane;

[0043] Reconstructing the image of the target object to be measured according to the reflection feature matrix to obtain a reconstructed image, including:

[0044] Normalize all reflection eigenvalues ​​to obtain corresponding normalized eigenvalues;

[0045] All normalized eigenvalues ​​are used as pixel values ​​of the reconstructed image.

[0046] In a second aspect, the present application provides a near-field microwave holographic imaging device, the device comprising:

[0047] A first acquisition module is used to acquire a scattering parameter matrix in microwave transmission;

[0048] The second acquisition module is used to acquire the tangential electric field value corresponding to each grid center position in the imaging plane of the target object to be measured by near-field scanning;

[0049] A first determination module is used to determine a measurement matrix based on the Fresnel diffraction theory and the tangential electric field value corresponding to the center position of each grid;

[0050] A second determination module is used to determine a reflection characteristic matrix according to the scattering parameter matrix and the measurement matrix;

[0051] The reconstruction module is used to reconstruct the image of the target object to be measured according to the reflection characteristic matrix to obtain a reconstructed image.

[0052] In a third aspect, the present application provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the near-field microwave holographic imaging method of the first aspect is implemented.

[0053] In a fourth aspect, the present application provides a readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the near-field microwave holographic imaging method as in the first aspect.

[0054] It can be seen from the technical solution provided in the above embodiments of this specification that the solution: based on the Fresnel diffraction theory, the reconstructed image has high accuracy and the imaging time is short. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0056] Figure 1 An overall schematic diagram of the two-dimensional planar grating scanning near-field imaging system provided in this application;

[0057] Figure 2 A schematic diagram of the process of the near-field microwave holographic imaging method provided in this application;

[0058] Figure 3 This is the radiation field of the narrow slit of the conductor excited by a plane wave, and the schematic diagram of the plane wave spectrum representation;

[0059] Figure 4 This is a schematic diagram of the simulation model for the implementation case of this application;

[0060] Figure 5 (a) and (b) are schematic diagrams showing the comparison of the effects before and after reconstructing an image using the method of the present application; (c) and (d) are schematic diagrams showing the comparison of the effects before and after reconstructing an image using the existing solution 1; (e) and (f) are schematic diagrams showing the comparison of the effects before and after reconstructing an image using the existing solution 2;

[0061] Figure 6 A schematic diagram of the structure of the near-field microwave holographic imaging device provided in this application;

[0062] Figure 7 A schematic diagram of the structure of the electronic device provided in this application. DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this specification will be clearly and completely described below in conjunction with the drawings in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this specification.

[0064] In the following description, specific details such as specific system structures, technologies, etc. are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0065] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present application description without departing from the scope or spirit of the present application. Other embodiments derived from the present application description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0066] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0067] Unless otherwise specified, "parts" in this application are all calculated by mass.

[0068] In the related art, the microwave near-field imaging reconstruction method has the problem of low quality of reconstructed images during the diffraction process, and the calculation process is relatively complicated, which increases the calculation time of imaging.

[0069] Based on the above defects, the present application proposes a near-field microwave holographic imaging method, which is based on the Fresnel diffraction theory and can well characterize the diffraction process of the target plane scattering field, greatly improves the quality of the reconstructed image and reduces the time required for imaging.

[0070] The following is an explanation of the theoretical basis of Fresnel diffraction.

[0071] In geometric optics, diffraction of light is any deviation of light from a straight path that cannot be explained by reflection or refraction. In information optics, diffraction is caused by the limitation of the lateral width of the light wave. When the limitation scale is of the same order of magnitude as the wavelength of the radiation used, the diffraction phenomenon is most significant. There are two theoretical conditions for scalar diffraction of light. One is that the diffraction aperture is much larger than the wavelength; the other is that the observation point cannot be too close to the diffraction aperture. The scalar diffraction theory can be expressed in a framework that is very similar to the linear invariant system theory. If a Fourier analysis is performed on the complex field distribution of monochromatic light disturbances on any plane, then each spatial Fourier component can be regarded as a plane wave propagating away from this plane in different directions. The field amplitude at any other point can be calculated by summing the contributions of these plane waves. At this time, the phase shift that occurs in these plane waves during propagation must be considered. The angular spectrum theory can perform mathematical calculations on the scalar diffraction theory, that is, each contribution value can be solved by angular spectrum calculation. Based on this principle, the diffraction process between the aperture field of the transmitting and receiving antennas and the imaging plane field can be accurately described. After the electromagnetic wave is incident on the imaging plane, the field information of the imaging plane scattering the electromagnetic wave to any position in the space can be obtained. For a raster scanning imaging system with a single antenna transmitting electromagnetic waves and a single antenna receiving, the field information received by the receiving antenna at each receiving position can be obtained, thereby solving the image reconstruction matrix equation.

[0072] Calculation method of Fresnel diffraction:

[0073] The traditional microwave imaging system is based on a linear model system, that is, formula (1).

[0074] g=Hf+n (1)

[0075] Where g is the scattering measurement value, H is called the measurement matrix of the system, f is the reflection characteristic function in the imaging plane area, that is, the unknown quantity to be solved at the end, and n is the system noise. For the microwave grating scanning imaging system, the value of g can be represented by the electric field intensity measured at the corresponding position of each grid. At this time, the electric field intensity measured at each position is also a superposition sum of the spatial electromagnetic waves at that position. The accuracy of f as the solution of the unknown number is closely related to the construction accuracy of the H measurement matrix (or simply referred to as H matrix or H array).

[0076] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0077] Reference Figure 1 , which shows the overall schematic diagram of the two-dimensional planar grating scanning near-field imaging system. Figure 1 In the example, two antennas ( Figure 1 The common horn antennas used in the experiment are placed in a center-aligned manner. One antenna transmits signals and the other receives signals. The plane where the transmitting and receiving antennas are located is the scanning plane, and the plane where the target object to be measured is located is the object plane (also called the imaging plane). For the near-field imaging system, the imaging plane of the target object to be measured is usually decomposed into a pixel point, that is, the plane where the target object to be measured is located is divided into M*N cells (or grids). The distance between the two antennas and the imaging plane is approximately the size of the Fresnel field distance. When moving the two antennas, the centers of the two horn antennas are directly above the center of each grid. During the movement of the antenna, the scattering parameters at each position, namely S 21 Parameters, that is, S 21 1 ,…,S 21 M*N A total of M*N S 21 Parameters, all S 21 The parameter is used as the scattering measurement value g in equation (1). At the same time, during the movement of the antenna, the tangential electric field value E corresponding to the center position of each grid in the imaging plane can be obtained by near-field scanning. (1) (x c ,y c ),…,E (M*N) (x c ,y c ) A total of M*N E(x c ,y c ), it is understandable that each time you move a grid, you get M*N E(x c ,y c ), M*N grids can get M*N×M*N E(x c ,y c ), which can be recorded as E (l,i) (x c ,y c ), where i=1,2,3...M*N, l=1,2,3...M*N.

[0078] Reference Figure 2 , which shows a flow chart of a near-field microwave holographic imaging method applicable to the embodiment of the present application.

[0079] like Figure 2 As shown, the near-field microwave holographic imaging method may include:

[0080] S210, obtaining a scattering parameter matrix in microwave transmission.

[0081] Specifically, the scattering parameter matrix may be composed of scattering parameters recorded by a vector analyzer during the movement of the antenna; or may be obtained after background calibration.

[0082] In one embodiment, S110 obtaining a scattering parameter matrix in microwave transmission may include:

[0083] Acquire a first scattering parameter corresponding to each grid when there is a target object to be measured;

[0084] Acquire a second scattering parameter corresponding to each grid when there is no target object to be measured;

[0085] The scattering parameter is determined according to the corresponding first scattering parameter and the second scattering parameter; optionally, the difference between the corresponding first scattering parameter and the second scattering parameter is calculated, and the difference is used as the scattering parameter.

[0086] All scattering parameters constitute the scattering parameter matrix.

[0087] Exemplarily, the first scattering parameter corresponding to each grid when the target object to be detected exists is obtained, which is recorded as Where l = 1, 2, 3...M*N, obtain the second scattering parameter corresponding to each grid when there is no target object to be measured (i.e., under an empty background) The first scattering parameter of the corresponding grid is subtracted from the second scattering parameter to obtain the scattering parameter at the grid. All scattering parameters constitute the scattering parameter matrix.

[0088] S220, obtaining the tangential electric field value E corresponding to each grid center position in the imaging plane of the target object to be measured by near-field scanning. (l,i) (x c ,y c ), where i=1,2,3...M*N, l=1,2,3...M*N.

[0089] S230. Based on the Fresnel diffraction theory, a measurement matrix is ​​determined according to the tangential electric field value corresponding to the center position of each grid.

[0090] Specifically, Woodward and Lawson proposed in 1948, and Booker and Clemmow in 1950 to apply the plane wave angular spectrum representation method to the analysis and synthesis of antennas. They all used Weyl's two-dimensional plane wave angular spectrum representation method. In 1958, Brown extended the two-dimensional method to three dimensions, and also introduced the reciprocity theorem in antenna analysis to enable the method to be applied to transmission and reception problems. Since then, the concept of angular plane wave spectrum has been used in the analysis of aperture antennas and the measurement of near-field antennas.

[0091] According to Wely's statement, the field diffracted by the slit can be expressed as a superposition of a set of plane waves. The plane wave angular spectrum representation is used to calculate the field at any point p in the plane. The principle diagram is attached. Figure 3 In this representation, θ is the directional variable of a plane wave component that constitutes the angular spectrum. Sinθ is used to represent the plane wave direction. Assuming that a set of plane waves describing the +z direction field is represented by the spectrum equation, the field intensity at point p can be formed by the superposition of this set of plane waves. The intensity of each component is F(sinθ)d(sinθ), and then there is formula (2):

[0092] dE p (x,z)=F(sinθ)d(sinθ)exp(-jk(xsinθ+zcosθ)) (2)

[0093] By integrating and summing formula (2), we can get the electric field intensity at point p, as shown in formula (3):

[0094]

[0095] The field at the gap is defined as formula (4):

[0096] f(x)=E p (x,0) (4)

[0097]

[0098] For f(x) at the gap, the incident field intensity is plane wave E0, and the rest of the area is 0. Substituting it in, we can get the spectrum equation F(sinθ), so that we can get the field intensity at any point p in the plane. Based on this principle, it is extended to three-dimensional space. Assuming that there is a scatterer in the xoy plane, the antenna placed in a plane parallel to it and at a certain distance vertically can be regarded as a point source. Then, the field information at any point in the upper half of the space of the scatterer after the scattering effect of the plane object can also be derived by the expansion of the two-dimensional plane principle described earlier. For the convenience of expression, it is assumed that there is a plane area in the xoy plane, which can be divided into M*N cells (or grids). There is a basic plane wave propagating along the u direction, and its direction is represented by three direction cosines (α, β, γ). p(x, y, z) is any point in space, and the direction vector is represented by r. Assuming that the tangential field on the xoy surface is x-polarized, the angular spectrum function is F x (α, β), then the calculation formula for the electric field intensity in the x direction generated by the plane wave at point p in space is as shown in equations (5), (6) and (7):

[0099]

[0100]

[0101]

[0102] Furthermore, since the plane wave propagates along the u direction, we have Therefore, the components of the electric field are as follows:

[0103]

[0104] Furthermore, the field intensity expression at point p can be obtained as shown in formula (9):

[0105]

[0106] Similarly, if the tangential electric field in the xoy plane is arbitrarily polarized, the electric field value at point p is calculated as shown in formula (10):

[0107]

[0108] Formula (10) is also the Fresnel field expression.

[0109] Furthermore, taking the x-polarization direction as an example to calculate the integral, we can obtain formula (11):

[0110]

[0111] According to Fresnel diffraction theory, we can make an approximation as shown in formula (12):

[0112]

[0113] Substituting formulas (6), (7), and (12) into formula (11), we can obtain formula (13):

[0114]

[0115] Formula (13) can be regarded as the function F x (α, β) and exp[jkz(α 2 +β 2 ) / 2], we can calculate the Fourier integral for each of them and then solve it by convolution. Here, E s (x, y) is recorded as the tangential electric field of the plane, as shown in formula (14):

[0116]

[0117]

[0118] For the two integrals in formula (14), standard integration can be used for calculation. The standard integration formula is as follows:

[0119]

[0120] Combining the above formulas, we can further deduce formula (16):

[0121]

[0122] So far, the field intensity information generated at any point in space based on the Fresnel diffraction theory has been obtained. Next, this theory can be combined with the near-field microwave holographic imaging system to construct a complete near-field microwave holographic imaging system based on the Fresnel diffraction theory.

[0123] As stated before, the plane parallel to the antenna aperture is the imaging plane of the target object to be measured. For the near-field imaging system, the plane of the object to be measured is usually decomposed into a pixel point, that is, the plane where the object to be measured is located is divided into M*N grids. Furthermore, the Fresnel field information calculation formula needs to be integrated into the imaging system. Therefore, formula (16) is discretized, and the size of each grid along the x and y directions is defined as lx and ly (here lx=ly). Furthermore, the coordinates of each grid in the plane can be expressed as formula (17):

[0124]

[0125] Substituting the discretized result into the integral formula (16), we can further obtain:

[0126]

[0127] Where E(x c ,y c ) is the tangential electric field intensity (or tangential electric field value) at each corresponding grid unit, and I(x,y) is calculated as shown in formula (19):

[0128]

[0129] For I(x,y), it can be further organized as:

[0130]

[0131] For the integral of the above formula, the two integrals are in accordance with the Fresnel integral and can be processed as follows:

[0132]

[0133] By simplifying formula (21), we can further obtain:

[0134]

[0135] Similarly, the same calculation method as above can be used to further solve I y :

[0136]

[0137]

[0138] Furthermore, it can be obtained that when the electromagnetic wave is incident on the imaging plane and the electric field intensity at point p (Fresnel region) in space after the action of the scatterer is the superposition field intensity of all regional grids as shown in formula (24):

[0139]

[0140] Similarly, if y-polarized electromagnetic waves are used for irradiation, the electric field strength at each point in the corresponding Fresnel field region can also be calculated.

[0141] From the above expression, the Fresnel diffraction theory can be used to construct the H array of the imaging system:

[0142]

[0143] Among them, E (l,i) (x c ,y c ) is the tangential electric field value corresponding to the center position of each grid obtained in step S220, H (l,i) It is the measurement representation of the transmitting and receiving antennas at each grid; the measurement representations at all grids constitute the measurement matrix.

[0144] S240, determining a reflection characteristic matrix according to the scattering parameter matrix and the measurement matrix:

[0145]

[0146] in, is the scattering parameter matrix, is the measurement matrix;

[0147] Solve the above matrix to get the inverse eigenvalue f at each grid mn , mn=1,2,3...M*N;

[0148] The inverse eigenvalues ​​at all grids constitute the reflected eigenmatrix.

[0149] S250 , reconstructing the image of the target object to be measured according to the reflection characteristic matrix to obtain a reconstructed image.

[0150] In one embodiment, all reflection feature values ​​may be used as pixel values ​​of the reconstructed image.

[0151] In one embodiment, all reflection eigenvalues ​​are normalized to obtain corresponding normalized eigenvalues; all normalized eigenvalues ​​are used as pixel values ​​of the reconstructed image.

[0152] The near-field microwave holographic imaging method provided in the present application is based on the Fresnel diffraction theory, and constructs a relatively accurate measurement matrix, namely the H matrix, in near-field microwave imaging. In the diffraction calculation process between the imaging plane field and the transmitting and receiving antenna aperture field, the reflection characteristic function of the target in the imaging area is solved, and then the contour, shape, electromagnetic parameters and other characteristics of the target to be measured are inverted.

[0153] The near-field microwave holographic imaging method provided in the present application is based on Fresnel diffraction theory and has higher imaging accuracy than the traditional near-field microwave imaging system.

[0154] The near-field microwave holographic imaging method provided in the present application has only one diffraction process, which is the diffraction from the incident field (imaging plane) to the transceiver antenna, and the field information of the plane area to be imaged can be saved in advance, which greatly reduces the time required for imaging and improves the imaging calculation speed.

[0155] Experimental test of the performance of near-field imaging method based on Fresnel diffraction theory:

[0156] The following compares the near-field microwave holographic imaging method provided by the present application with the existing traditional methods.

[0157] In the experiment, a 10GHz dual horn antenna is used, one for transmitting and one for receiving. The centers of the two horn antennas are aligned and placed on both sides of the imaging scanning plane. The vertical distance z between the horn and the imaging scanning plane is set to 250mm, and the size of the imaging scanning plane is set to 450mm*450mm. The imaging plane is gridded into 45*45 grids with a total of 2025 grids. In order to verify the reliability of the entire system, a standard part is designed. Relatively complex scatterers can more reliably verify the system, such as Figure 4 As shown, Figure 4 (a) is a schematic diagram of the target object to be measured. Figure 4 (b) is a schematic diagram of the overall model of the target object to be measured and the two antennas. By comparing with the existing technical solutions (such as compressed sensing methods, direct solution methods, etc.), the quality of the reconstructed image of this application is significantly improved. The comparison of the imaging results with the existing technical solutions can be seen in the attached figure. Figure 5 ,in, Figure 5 (a) is the original image (Fresnel-original) using the method of this application, Figure 5 (b) is the reconstructed image (Fresnel-recovery) after using the method of the present application, Figure 5 (c) is the original image (CS-original) using the existing scheme 1 (compressed sensing method). Figure 5 (d) is the reconstructed image after using the existing solution 1 (CS-recovery). Figure 5 (e) is the original image (Direct-original) using the existing solution 2 (direct solution method). Figure 5 (f) is the reconstructed image (Direct-recovery) after adopting the existing solution 2. The imaging of various technical solutions is calculated using data. The results show that the technical solution proposed in this application is about 4 times higher than the existing solution in imaging quality (see Appendix 1 for data comparison), and the imaging speed is also significantly improved.

[0158] Table 1 Comparison of test results

[0159]

[0160] Reference Figure 6 , which shows a schematic structural diagram of a near-field microwave holographic imaging device described according to an embodiment of the present application.

[0161] like Figure 6 As shown, the near-field microwave holographic imaging device 600 may include:

[0162] A first acquisition module 610 is used to acquire a scattering parameter matrix in microwave transmission;

[0163] The second acquisition module 620 is used to acquire the tangential electric field value corresponding to each grid center position in the imaging plane of the target object to be measured by near-field scanning;

[0164] A first determination module 630 is used to determine a measurement matrix based on the Fresnel diffraction theory and the tangential electric field value corresponding to the center position of each grid;

[0165] A second determination module 640 is used to determine a reflection characteristic matrix according to the scattering parameter matrix and the measurement matrix;

[0166] The reconstruction module 650 is used to reconstruct the image of the target object to be measured according to the reflection characteristic matrix to obtain a reconstructed image.

[0167] Optionally, the first acquisition module 610 is further used for:

[0168] Acquire a first scattering parameter corresponding to each grid when there is a target object to be measured;

[0169] Acquire a second scattering parameter corresponding to each grid when there is no target object to be measured;

[0170] Determining a scattering parameter according to the corresponding first scattering parameter and second scattering parameter;

[0171] All scattering parameters constitute the scattering parameter matrix.

[0172] Optionally, the first acquisition module 610 is further used for:

[0173] Calculating the difference between the corresponding first scattering parameter and the second scattering parameter;

[0174] The difference is used as the scattering parameter.

[0175] Optionally, the first determining module 630 is further configured to:

[0176]

[0177] Among them, E (l,i) (x c ,y c ) is the tangential electric field value corresponding to the center position of each grid, H (l,i) It is the measurement representation of the transmitting and receiving antennas at each grid; the measurement representations at all grids constitute a measurement matrix;

[0178]

[0179]

[0180]

[0181]

[0182]

[0183] lx and ly are the sizes of each grid along the x and y directions respectively;

[0184]

[0185]

[0186]

[0187] M is the number of grids in the x direction, and N is the number of grids in the y direction.

[0188] Optionally, the second determining module 640 is further configured to:

[0189]

[0190] in, is the scattering parameter matrix, is the measurement matrix;

[0191] Solve the above matrix to get the inverse eigenvalue f at each grid mn , mn=1,2,3...M*N;

[0192] The inverse eigenvalues ​​at all grids constitute the reflected eigenmatrix.

[0193] Optionally, the reflection characteristic matrix includes reflection characteristic values ​​at each grid in the imaging plane; the reconstruction module 650 is further used for:

[0194] Reconstructing the image of the target object to be measured according to the reflection feature matrix to obtain a reconstructed image, including:

[0195] All reflection feature values ​​are used as pixel values ​​of the reconstructed image.

[0196] Optionally, the reflection characteristic matrix includes reflection characteristic values ​​at each grid in the imaging plane; the reconstruction module 650 is further used for:

[0197] Normalize all reflection eigenvalues ​​to obtain corresponding normalized eigenvalues;

[0198] All normalized eigenvalues ​​are used as pixel values ​​of the reconstructed image.

[0199] The near-field microwave holographic imaging device provided in this embodiment can execute the embodiment of the above method. Its implementation principle and technical effect are similar and will not be described in detail here.

[0200] Figure 7 FIG. 1 is a schematic diagram of the structure of an electronic device provided by an embodiment of the present invention. Figure 7 As shown, a structural schematic diagram of an electronic device 300 suitable for implementing an embodiment of the present application is shown.

[0201] like Figure 7 As shown, the electronic device 300 includes a central processing unit (CPU) 301, which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM) 302 or a program loaded from a storage part 308 into a random access memory (RAM) 303. In the RAM 303, various programs and data required for the operation of the device 300 are also stored. The CPU 301, the ROM 302, and the RAM 303 are connected to each other via a bus 304. An input / output (I / O) interface 305 is also connected to the bus 304.

[0202] The following components are connected to the I / O interface 305: an input section 306 including a keyboard, a mouse, etc.; an output section 307 including a cathode ray tube (CRT), a liquid crystal display (LCD), etc., and a speaker, etc.; a storage section 308 including a hard disk, etc.; and a communication section 309 including a network interface card such as a LAN card, a modem, etc. The communication section 309 performs communication processing via a network such as the Internet. A drive 310 is also connected to the I / O interface 306 as needed. A removable medium 311, such as a magnetic disk, an optical disk, a magneto-optical disk, a semiconductor memory, etc., is installed on the drive 310 as needed, so that a computer program read therefrom is installed into the storage section 308 as needed.

[0203] In particular, according to the embodiments of the present disclosure, the above reference Figure 1 The described process may be implemented as a computer software program. For example, an embodiment of the present disclosure includes a computer program product including a computer program tangibly contained on a machine-readable medium, the computer program including program code for executing the above-described near-field microwave holographic imaging method. In such an embodiment, the computer program may be downloaded and installed from a network via the communication portion 309, and / or installed from a removable medium 311.

[0204] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present invention. In this regard, each box in the flow chart or block diagram can represent a module, a program segment, or a part of the code, and the aforementioned module, program segment, or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in a different order from the order marked in the accompanying drawings. For example, two boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flow chart, and the combination of the boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs the specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0205] The units or modules involved in the embodiments described in the present application may be implemented by software or hardware. The units or modules described may also be arranged in a processor. The names of these units or modules do not constitute limitations on the units or modules themselves in certain circumstances.

[0206] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions. A typical implementation device is a computer. Specifically, the computer may be, for example, a personal computer, a laptop, a mobile phone, a smart phone, a personal digital assistant, a media player, a navigation device, an email device, a game console, a tablet computer, a wearable device, or a combination of any of these devices.

[0207] As another aspect, the present application further provides a storage medium, which may be the storage medium included in the aforementioned device in the above embodiment; or a storage medium that exists independently and is not assembled into the device. The storage medium stores one or more programs, and the aforementioned programs are used by one or more processors to execute the near-field microwave holographic imaging method described in the present application.

[0208] Storage media include permanent and non-permanent, removable and non-removable media that can be implemented by any method or technology to store information. Information can be computer-readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technology, compact disk read-only memory (CD-ROM), digital versatile disk (DVD) or other optical storage, magnetic cassettes, magnetic tape magnetic disk storage or other magnetic storage devices or any other non-transmission media that can be used to store information that can be accessed by a computing device. As defined herein, computer-readable media does not include temporary computer-readable media (transitory media), such as modulated data signals and carrier waves.

[0209] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0210] Each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

Claims

1. A near-field microwave holographic imaging method, characterized in that: The method comprises: Obtain the scattering parameter matrix in microwave transmission; The tangential electric field value corresponding to each grid center position in the imaging plane of the target object to be measured is obtained by near-field scanning; Based on the Fresnel diffraction theory, a measurement matrix is ​​determined according to the tangential electric field value corresponding to the center position of each grid; Determining a reflection characteristic matrix according to the scattering parameter matrix and the measurement matrix; Reconstructing the image of the target object to be measured according to the reflection characteristic matrix to obtain a reconstructed image; The step of obtaining a scattering parameter matrix in microwave transmission includes: Acquire a first scattering parameter corresponding to each grid when the target object to be measured exists; Acquire a second scattering parameter corresponding to each grid when the target object to be measured does not exist; determining a scattering parameter according to the corresponding first scattering parameter and the second scattering parameter; All the scattering parameters constitute the scattering parameter matrix; Based on the Fresnel diffraction theory, the measurement matrix is ​​determined according to the tangential electric field value corresponding to the center position of each grid: Among them, E (l,i) (x c ,y c ) is the tangential electric field value corresponding to the center position of each grid, H (l,i) The measurement representation of the transceiver antennas at each grid; the measurement representations at all grids constitute the measurement matrix; lx and ly are the sizes of each grid along the x and y directions respectively; M is the number of grids in the x direction, and N is the number of grids in the y direction; Determining a reflection characteristic matrix according to the scattering parameter matrix and the measurement matrix: in, is the scattering parameter matrix, is the measurement matrix; Solve the above matrix to get the inverse eigenvalue f at each grid mn , mn=1,2,3...M*N; The inverse eigenvalues ​​at all grids constitute the reflection eigenmatrix.

2. The method according to claim 1, characterized in that The determining of the scattering parameter according to the corresponding first scattering parameter and the second scattering parameter includes: Calculating a corresponding difference between the first scattering parameter and the second scattering parameter; The difference is used as the scattering parameter.

3. The method according to claim 1, characterized in that The reflection characteristic matrix includes reflection characteristic values ​​at each grid in the imaging plane; The step of reconstructing the image of the target object to be measured according to the reflection feature matrix to obtain a reconstructed image includes: All the reflection feature values ​​are used as pixel values ​​of the reconstructed image.

4. The method according to claim 1, characterized in that: The reflection characteristic matrix includes reflection characteristic values ​​at each grid in the imaging plane; The step of reconstructing the image of the target object to be measured according to the reflection feature matrix to obtain a reconstructed image includes: Normalizing all the reflection eigenvalues ​​to obtain corresponding normalized eigenvalues; All the normalized feature values ​​are used as pixel values ​​of the reconstructed image.

5. A near-field microwave holographic imaging device, characterized in that: The device comprises: A first acquisition module is used to acquire a scattering parameter matrix in microwave transmission; The second acquisition module is used to acquire the tangential electric field value corresponding to each grid center position in the imaging plane of the target object to be measured by near-field scanning; A first determination module is used to determine a measurement matrix based on the Fresnel diffraction theory and according to the tangential electric field value corresponding to the center position of each grid; A second determination module, configured to determine a reflection characteristic matrix according to the scattering parameter matrix and the measurement matrix; A reconstruction module, used to reconstruct the image of the target object to be measured according to the reflection characteristic matrix to obtain a reconstructed image; In the first acquisition module, acquiring a scattering parameter matrix in microwave transmission includes: Acquire a first scattering parameter corresponding to each grid when the target object to be measured exists; Acquire a second scattering parameter corresponding to each grid when the target object to be measured does not exist; determining a scattering parameter according to the corresponding first scattering parameter and the second scattering parameter; All the scattering parameters constitute the scattering parameter matrix; In the first determination module, based on the Fresnel diffraction theory, the measurement matrix is ​​determined according to the tangential electric field value corresponding to the center position of each grid: Among them, E (l,i) (x c ,y c ) is the tangential electric field value corresponding to the center position of each grid, H (l,i) The measurement representation of the transceiver antennas at each grid; the measurement representations at all grids constitute the measurement matrix; lx and ly are the sizes of each grid along the x and y directions respectively; M is the number of grids in the x direction, and N is the number of grids in the y direction; In the second determination module, a reflection characteristic matrix is ​​determined according to the scattering parameter matrix and the measurement matrix: in, is the scattering parameter matrix, is the measurement matrix; Solve the above matrix to get the inverse eigenvalue f at each grid mn , mn=1,2,3...M*N; The inverse eigenvalues ​​at all grids constitute the reflection eigenmatrix.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the near-field microwave holographic imaging method as described in any one of claims 1-4 is implemented.

7. A readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the near-field microwave holographic imaging method as described in any one of claims 1 to 4 is implemented.

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