Reverse scattering microwave imaging method based on unconventional incident field

Abstract

The invention discloses a reverse scattering microwave imaging method based on an unconventional incident field. The microwave imaging system collects scattered field data of a target scatterer in a random irradiation mode and processes the scattered field data to obtain a preliminary imaging result; further determining a target area, performing system modulation to form a focusing incident field, and dividing the target area into a plurality of sub-areas according to the focusing incident field and the geometric center position of the initial imaging result of the target scatterer; adjusting the focus point to the center of each sub-region in sequence by adjusting the phase difference of the antenna, and acquiring scattered field data of the target scatterer in different sub-regions; and then quantitative inversion is carried out to obtain the numerical value and spatial distribution of the dielectric constant of the target scatterer, so that a target scatterer image is constructed. According to the method, the scattering effect of a specific area can be enhanced, the multiple scattering effects of other areas can be inhibited, the nonlinearity of the inverse scattering problem is reduced, the imaging precision is improved, and the method has huge application potential in multiple fields of medical imaging, industrial detection, geological exploration and the like.

Description

Technical Field

[0001] The invention relates to an inverse scattering microwave imaging method, in particular to a high-precision microwave imaging method for an unconventional incident field. Background Art

[0002] Electromagnetic inverse scattering imaging (EBI) is an important method for inverting the electromagnetic properties of a target object by utilizing the scattered field data generated by the interaction of electromagnetic waves with the target. It is widely used in fields such as medical diagnosis, nondestructive testing, geological exploration, and target identification. Traditional methods are mainly divided into weak scattering approximation and nonlinear optimization methods. Although the weak scattering approximation is computationally simple and efficient, it is only applicable to weak scatterers and has a limited scope of application. Nonlinear optimization methods (such as Born iteration and contrast source inversion (CSI)) offer high imaging accuracy but are computationally intensive, prone to falling into local optimal solutions, and sensitive to the choice of initial values. While existing technologies each have their advantages, they still have certain shortcomings. The weak scattering approximation has a narrow scope of application, while the nonlinear optimization method is computationally complex. Focusing technology can significantly reduce the nonlinearity of the inverse scattering problem by adjusting the phase of the transmitting source to focus the incident field on the target area. However, the fixed focusing method lacks flexibility and is difficult to adapt to complex or multi-target scenarios. Summary of the Invention

[0003] In order to solve the problems existing in the background technology, the technical problem to be solved by the present invention is to provide a microwave imaging method based on an unconventional incident field.

[0004] The technical solution of the present invention is:

[0005] The present invention comprises the following steps:

[0006] S1. The microwave imaging system collects the scattering field data of the target scatterer by random irradiation and processes the scattering field data by linear sampling method to obtain the preliminary imaging results of the target scatterer;

[0007] S2. Determine the target area based on the preliminary imaging results of the target scatterer. The microwave imaging system forms a focused incident field through phase modulation, and then divides the target area into several sub-areas based on the geometric center positions of the focused incident field and the preliminary imaging results of the target scatterer.

[0008] S3. The microwave imaging system moves the focus point of the incident field by adjusting the phase difference of the antenna, adjusts the focus point to the center of each sub-region in turn, and collects the scattered field data of the target scatterer in different sub-regions;

[0009] S4. Quantitative inversion is performed based on the scattering field data of the target scatterer in different sub-regions to obtain the numerical value and spatial distribution of the dielectric constant of the target scatterer, thereby constructing an image of the target scatterer.

[0010] The method adopts a microwave imaging system, which includes several antennas with phase modulation function and working in time division duplex mode. The antennas are evenly spaced around the target scatterer. In the transmitting mode, the antennas emit electromagnetic waves at a set frequency toward the target scatterer. The electromagnetic waves interact with the target scatterer to form a scattering field. Each antenna receives the scattered field signal in turn in the receiving mode to obtain the scattering field data.

[0011] The random irradiation method in S1 is specifically: the phase distribution of the electromagnetic waves emitted by the antenna array in the transmission mode follows Gaussian distribution.

[0012] The preliminary imaging result of the target scatterer is obtained by processing according to the following formula:

[0013] F[φ]=∫ Ω E scat (r)φ(r′)dr′=G(r,r′)

[0014] Where G(r,r′) is the field generated by the point source at position r at position r′, Ω represents the imaging area, r′ is the position coordinate of the receiving point, r is the position coordinate of the transmitting point, φ(r′) is the indicator function used to indicate whether there is a target scatterer (3) at position r′, and E scat (r) represents the scattered field data measured at position r.

[0015] The S2 is specifically:

[0016] S2.1. Determine, based on the preliminary imaging results of the target scatterers, a rectangular area that includes all target scatterers and has a predetermined redundancy range at its boundaries as the target area;

[0017] S2.2, the microwave imaging system forms a focused incident field through phase modulation;

[0018] S2.3. Divide the target area into N*N rectangular sub-areas of equal size according to the geometric center positions of the focused incident field and the preliminary imaging results of the target scatterer, so that the geometric center position of the preliminary imaging results of the target scatterer is located at the center position of any sub-area, and the length and width of each sub-area are set according to the size of the effective focusing area of ​​the focused incident field.

[0019] The phase difference of the antenna is adjusted in S3 according to the following formula:

[0020] θ t =Arg(G1)-Arg(G t ),t=2,3,…,m

[0021]

[0022] Among them, Arg(.) represents the principal value angle of the complex number, θ t is the phase adjustment of the tth emission source, G1 and G t They represent the Hankel function values ​​of the first and tth emission sources at the focal point x, m represents the total number of emission sources, H0 (1) represents the first kind of zero-order Hankel function, k b represents the beam of the background medium, k b |xy(t)| represents the normalized distance, and |xy(t)| represents the physical distance from the emission source to the focal point.

[0023] The S4 is specifically as follows: first, quantitative inversion is performed on the first sub-region, and the initial guess value of the inversion of the first sub-region adopts the dielectric constant of the background medium to obtain the inversion result of the first sub-region; then, quantitative inversion is performed on the remaining sub-regions in turn, and the initial guess value of the inversion of each remaining sub-region adopts the inversion result of the previous sub-region, and finally the inversion results of all sub-regions are obtained, and the inversion results of all sub-regions are spliced ​​to obtain the numerical value and spatial distribution of the dielectric constant of the target scatterer (3).

[0024] The quantitative inversion is performed according to the following formula:

[0025]

[0026] Among them, ε n (r′) represents the dielectric constant distribution to be inverted under the nth focusing, ε0 represents the dielectric constant of the background medium, and u inc (r′; z n ) represents the focused incident field of the nth sub-region, Represents the measured scattered field data collected at the receiving point r, with the focus point Z n .G s (r, r′) is the free space Green’s function of the receiving area, G Ω (r′, r′) is the free-space Green’s function of the imaging region. λ is the regularization parameter used to suppress noise and pathology, and ▽ε(r′) represents the spatial gradient of the dielectric constant distribution.

[0027] The target scatterer is one or more non-overlapping and discretely distributed dielectric scatterers.

[0028] The beneficial effects of the present invention are:

[0029] 1. Introducing unconventional incident fields: A random incident field with random irradiation characteristics and a focused incident field with focused irradiation characteristics are constructed. A linear sampling method is used to obtain the initial position and outline of the object, quickly determining the approximate area of ​​the target, reducing the computational space, and providing a more accurate initial positioning for the focusing technology. Rapid imaging using the linear sampling method can initially screen out the target area, and combined with focusing technology, further improves imaging accuracy and efficiency. This method not only increases imaging speed but also significantly improves imaging quality, especially when processing high-contrast targets, enabling more accurate inversion of the target's electromagnetic properties.

[0030] 2. The present method uses phase modulation to focus the incident field in the target area, reducing multiple scattering effects outside the target area. This reduces the nonlinearity of microwave imaging and improves imaging quality. It features simple implementation and high-precision imaging. This invention combines the rapid imaging of linear sampling with the high-precision imaging advantages of focusing to achieve efficient and high-precision electromagnetic inverse scattering imaging. It was developed to overcome existing technological bottlenecks and provide an innovative solution.

[0031] 3. A functional partitioning mechanism and spatial alignment criteria for unconventional incident fields were established: the center of the imaged object, the center of the focused incident field beam, and the center of the sub-region must coincide. This partitioning method ensures spatial consistency between coarse positioning results and high-resolution focused inversion, enhancing inversion stability and physical constraints.

[0032] 4. Adopt a unified reconfigurable hardware architecture: Utilizing an antenna array with phase modulation and duplexing capabilities, flexible switching between random incidence and focused incidence can be achieved through dynamic configuration. The overall structure of the system is simple, and only one set of equipment is required to complete the entire imaging process, reducing system complexity and hardware costs.

[0033] Different from the traditional microwave imaging method in the background art that can only obtain rough imaging results, the present invention combines the linear sampling method with the focusing technology to effectively reduce the nonlinearity of the inverse scattering problem and significantly improve the imaging accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of a microwave imaging system of the present invention;

[0035] Figure 2 is an image of a target scatterer according to an embodiment of the present invention, wherein (a) represents a real image of the target scatterer, and (b) represents a preliminary imaging result of the target scatterer obtained by a linear sampling method;

[0036] Figure 3 Schematic diagram of the inversion result of an embodiment of the present invention, wherein (a) represents a reconstructed image in which the focus point is not at the geometric center of the object, Figure 3(b) Reconstructed image showing the focus point at the geometric center of the object;

[0037] In the figure: antenna 1, target area 2, target scatterer 3. DETAILED DESCRIPTION

[0038] The implementation process of the present invention is described in detail below with reference to the accompanying drawings in the embodiments of the present invention.

[0039] The present invention is specifically implemented as follows:

[0040] The unconventional incident field includes a random incident field with a random irradiation function and a focused incident field with a focused irradiation function.

[0041] The method of this embodiment includes the following steps:

[0042] S1. The microwave imaging system collects scattered field data of the target scatterer 3 by random irradiation, and processes the scattered field data by linear sampling method to obtain preliminary imaging results of the target scatterer 3;

[0043] The preliminary imaging result includes preliminary position and contour information of the target scatterer 3 .

[0044] S2. Determine target region 2 based on preliminary imaging results of target scatterer 3. The microwave imaging system forms a focused incident field through phase modulation, and then divides target region 2 into a plurality of subregions based on the geometric center positions of the focused incident field and the preliminary imaging results of target scatterer 3.

[0045] In this embodiment, the target area 2 is set as a square area with a side length of 2λ, and is divided into discrete grids according to imaging resolution requirements.

[0046] S2.1. Determine, based on the position distribution of target scatterers 3 in the preliminary imaging results of target scatterers 3, a rectangular area that includes all target scatterers 3 and has a predetermined redundant range at its boundaries as target area 2;

[0047] S2.2, the microwave imaging system forms a focused incident field through phase modulation;

[0048] S2.3. Divide the target area 2 into N*N rectangular sub-areas of equal size according to the geometric center positions of the focused incident field and the preliminary imaging results of the target scatterer 3, so that the geometric center position of the preliminary imaging results of the target scatterer 3 is located at the center position of any sub-area, and the length and width of each sub-area are set according to the size of the effective focusing area of ​​the focused incident field. In this embodiment, the length and width of each sub-area are equal to the size of the effective focusing area of ​​the focused incident field.

[0049] The effective focusing area is specifically the area with the maximum field intensity concentration formed within the imaging area by the phase-modulated electromagnetic waves emitted by antenna 1. In this embodiment, the size of the effective focusing area is the diameter of the -3dB area of ​​the field intensity amplitude at the focus point.

[0050] S3. The microwave imaging system sequentially scans the incident field by adjusting the phase difference of antenna 1, moving the focal point row by row and column by column. The focal point is then adjusted to the center of each subregion, collecting scattered field data from target scatterer 3 in each subregion. Specifically, by adjusting the phase difference of transmitting antenna 1, the spatial position of the focal point is sequentially scanned across the entire imaging area. Sequential scanning is implemented by dividing the imaging area into several subregions based on the geometric center of the scatterer. The focal point is then moved row by row and column, sequentially adjusting the focal point to the center of each subregion to ensure full coverage of the imaging area.

[0051] The phase difference of antenna 1 is adjusted according to the following formula:

[0052] θ t =Arg(G1)-Arg(G t ),t=2,3,…,m

[0053]

[0054] Among them, Arg(.) represents the principal value angle of the complex number, θ t is the phase adjustment of the tth emission source, G1 and G t They represent the Hankel function values ​​of the first and tth emission sources at the focal point x, m represents the total number of emission sources, H0 (1) represents the first kind of zero-order Hankel function, k b represents the beam of the background medium, k b |xy(t)| represents the normalized distance, and |xy(t)| represents the physical distance from the emission source to the focal point.

[0055] S4. Perform quantitative inversion based on the scattered field data of the target scatterer 3 in different sub-regions to obtain the numerical value and spatial distribution of the dielectric constant of the target scatterer 3, thereby constructing an image of the target scatterer 3.

[0056] The focus point is specifically: by adjusting the phase difference of each transmitting antenna 1, the electromagnetic waves emitted by multiple antennas 1 are coherently superimposed at a target spatial position within the imaging area, forming an area of ​​concentrated and enhanced electromagnetic energy. The center of this energy enhancement area is the focus point. That is, the spatial position with the strongest electromagnetic energy in the focused incident field is the focus point.

[0057] This is to provide richer information for quantitative inversion and make quantitative inversion more accurate. The general steps for quantitative inversion are as follows: Receive antenna 1 receives electromagnetic field data scattered by the target object. After obtaining the preliminary position and outline of the target object, the focus position of the incident field is adjusted multiple times to ensure that the focus coincides with the geometric center of the object obtained by the linear sampling method. The number of focusing cycles is rationally divided, and scattered field data obtained from different focusing positions is collected to provide richer information for quantitative inversion. The scattered field obtained by focusing is combined with the focused incident field to perform quantitative inversion of the target.

[0058] like Figure 1 As shown, the method adopts a microwave imaging system, which includes a plurality of antennas 1 with phase modulation function and working in time division duplex mode. The antennas 1 are evenly spaced around the target scatterer 3. In the transmitting mode, the antennas 1 emit electromagnetic waves at a set frequency toward the target scatterer 3. The electromagnetic waves interact with the target scatterer 3 to form a scattering field. Each antenna 1 receives the scattered field signal in turn in the receiving mode to obtain the scattering field data.

[0059] The microwave imaging system is constructed, comprising a discretely distributed target to be measured and multiple antennas 1 with phase modulation capabilities operating in duplex mode, evenly distributed around the target to form a surrounding arrangement. The transmitting antenna 1 has a phase modulation capability, which can generate an unconventional incident field within the imaging area through phase modulation.

[0060] Antenna 1 works in a duplex mode of simultaneous transmission and reception. When multiple antennas 1 work in the transmission mode, they form a phased array and transmit signals at the same time to form an unconventional incident field. When multiple antennas 1 work in the reception mode, each antenna 1 works independently to receive scattered field data in turn.

[0061] In general, multiple antennas 1 equipped with phase modulation capabilities and operating in duplex mode are arranged outside the imaging area. Phase modulation is used to generate two unconventional incident fields within the imaging area: a random incident field and a focused incident field. Multiple transmitting antennas 1 transmit simultaneously to form the random incident field. Antennas 1 operating in receiving mode acquire scattered field data, which is then used to invert the preliminary position and outline of the scatterer. Antennas 1 then transmit simultaneously to form a focused incident field. The focused incident field is then used to sequentially scan the entire imaging area. The resulting scattered field and the focused incident field are combined to achieve quantitative inversion of the target.

[0062] The random irradiation method in S1 is specifically as follows: the phase distribution of the electromagnetic waves emitted by the antenna array 1 toward the target scatterer 3 in the transmission mode follows a Gaussian distribution.

[0063] The phase distribution of transmitting antenna 1 follows a Gaussian distribution, forming a random incident field in the imaging area. Specifically, in transmit mode, antenna 1 uses random irradiation to illuminate the imaging area where the target is located, forming a random incident field. The target interacts with the incident field, generating an induced current within the target. The induced current in the target acts as a secondary source, generating a scattered field that is ultimately received by antenna 1.

[0064] The preliminary imaging results of target scatterer 3 are obtained by processing according to the following formula:

[0065] F[φ]=∫ Ω E scat (r)φ(r′)dr′=G(r,r′)

[0066] Where G(r,r′) is the free space Green’s function, i.e., the field generated by a point source at position r at position r′, Ω represents the imaging area, r′ is the position coordinate of the receiving point, r is the position coordinate of the transmitting point, φ(r′) is the indicator function to be solved for indicating whether there is a target scatterer (3) at position r′, and the non-zero area is the area where the scatterer is located, E scat (r) represents the scattered field data measured at position r. By solving the least squares solution of this equation, the preliminary position and outline of the target object can be quickly determined.

[0067] The principle of focusing technology is to focus the incident field within a specific area by adjusting the phase of the excitation source, thereby enhancing the field intensity within that area. This method can effectively suppress the multi-scattering effect within the entire area to be measured, reduce the nonlinearity of the problem, and thus improve the accuracy and stability of reconstruction. The condition for achieving a focused incident field is to use phase modulation to make the phase of all transmitting antennas 1 at the focal point the same, thereby forming a focused incident field in the imaging area. That is, a transmitting source is selected as a reference, and its phase is the reference phase. The coordinate position of the center of the target area 2 is determined based on the position of the target object. By calculating the phase difference between each transmitting source and the target area 2, the phase of the transmitting source is adjusted to focus the incident field on the target area 2.

[0068] The focus position of the incident field is adjusted multiple times to ensure that the focus coincides with the geometric center of the object obtained by the linear sampling method. The scattered field data required for quantitative inversion are obtained by sequential scanning, and the focus point is required to coincide with the geometric center of the scatterer obtained by the preliminary inversion.

[0069] To more conveniently align the focus point with the geometric center of the object obtained by the linear sampling method, the number of focusing passes is rationally divided. The focused incident field is then used to scan the entire imaging area, collecting scattered field data from different focus positions, providing rich information for quantitative inversion. Finally, the scattered field obtained by focusing is combined with the focused incident field for quantitative inversion of the target.

[0070] The quantitative inversion is performed according to the following formula:

[0071]

[0072] Among them, ε n (r′) represents the dielectric constant distribution to be inverted under the nth focusing, ε0 represents the dielectric constant of the background medium, and u inc (r′; z n ) represents the focused incident field of the nth sub-region, Represents the measured scattered field data collected at the receiving point r, with the focus point Z n .G s (r, r′) is the free space Green’s function of the receiving area, G Ω (r′, r′) is the free-space Green’s function of the imaging region. λ is the regularization parameter used to suppress noise and pathology, and ▽ε(r′) represents the spatial gradient of the dielectric constant distribution.

[0073] The results of the focus scan are used to construct the initial guess for the iterative method. Specifically, the initial guess for the first focus point is the background medium (zero contrast), and the initial guesses for subsequent focus points are provided by the reconstruction results of the previous focus scan, forming an iterative optimization process. The regularization term is used to constrain the smoothness of the solution.

[0074] The S4 is specifically as follows: first, quantitative inversion is performed on the first sub-region, and the dielectric constant of the background medium is used as the initial guess value of the inversion of the first sub-region to obtain the inversion result of the first sub-region; then, quantitative inversion is performed on the remaining sub-regions in turn, and the inversion initial guess value of each remaining sub-region is used as the inversion result of the previous sub-region to obtain the inversion results of each remaining sub-region respectively, and finally the inversion results of all sub-regions are obtained, and the inversion results of all sub-regions are spliced ​​to obtain the numerical value and spatial distribution of the dielectric constant of the target scatterer (3).

[0075] Specifically, the quantitative inversion is performed in the following steps:

[0076] 1) Divide the target area (2) into n independent sub-areas according to prior information, and focus and invert each sub-area in a predetermined order;

[0077] 2) For the focusing of the first sub-region (n=1), the initial guess value ε0 of ε(r') in the inversion solution is set to the dielectric constant of the background medium;

[0078] 3) For the subsequent focusing of the nth (n>1) sub-region, the reconstruction result obtained by the focusing inversion of the n-1th sub-region is used as the initial guess value ε(r') in this inversion n-1 ;

[0079] 4) Iterate the inversion problem until convergence is achieved. The dielectric constant distribution obtained after convergence is used as the initial guess for the next (n+1) sub-region focused inversion.

[0080] 5) After completing the scanning, focusing, and inversion of all n sub-regions, the dielectric constant distribution finally obtained is the final imaging result of the target scatterer (3).

[0081] One sub-region is focused once, so n represents the number of focuses, and also represents the number of sub-region sequences.

[0082] In this embodiment, the sub-region sequence numbers are sorted from left to right and from top to bottom.

[0083] The target scatterer 3 is one or more dielectric scatterers that do not overlap and are discretely distributed. A dielectric scatterer refers to an object made of dielectric material that causes scattering when irradiated by electromagnetic waves.

[0084] Phase modulation is achieved in two ways:

[0085] (a) Random phase modulation: By providing a random phase following a Gaussian distribution to the transmitting antenna 1, an incident field with random irradiance characteristics is generated, which is used to quickly obtain the preliminary profile of the target.

[0086] (b) Focused phase modulation: Based on the target geometric center position provided by the linear sampling method, the phase difference between each transmitting antenna 1 and the focal point is calculated, and the phase is adjusted so that all transmitted signals are superimposed in phase at the focal point, forming a high-intensity focused incident field.

[0087] The scattered field data used in the linear sampling method for qualitative inversion is obtained through random irradiation. The linear sampling method quickly obtains scattered field data through random phase irradiation, which can provide preliminary position and contour information of the target object in a short time, significantly reducing the complexity of subsequent calculations. Figure 2 (a) represents the real image of the target to be measured, such as Figure 2 (b) The initial position and outline of the object obtained by the linear sampling method can determine the geometric center position of the object.

[0088] The scattered field data used for quantitative target inversion is obtained through sequential scanning. By accurately calculating the phase difference between each transmitting antenna 1 and the target area 2, the phase of transmitting antenna 1 is adjusted to focus the incident field on the target area 2. To provide richer information for quantitative inversion, the focused incident field must fully cover the target imaging area.

[0089] Depend on Figure 3 (a) with Figure 3 The comparison results in (b) show that whether the focus point coincides with the object geometry has a significant impact on the inversion results.

[0090] As can be seen from the above examples, the microwave imaging method based on unconventional incident fields proposed by the present invention effectively reduces the nonlinearity of the inverse scattering problem and improves imaging accuracy by combining linear sampling with focusing technology. It has outstanding technical benefits such as low cost, simple implementation, high imaging accuracy, and high computational efficiency.

[0091] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for inverse scattered microwave imaging based on unconventional incident fields, characterized in that: The method comprises the following steps: S1. The microwave imaging system collects scattering field data of the target scatterer (3) by random irradiation, and processes the scattering field data by a linear sampling method to obtain a preliminary imaging result of the target scatterer (3); S2. determining a target region (2) based on a preliminary imaging result of the target scatterer (3), forming a focused incident field by a microwave imaging system through phase modulation, and then dividing the target region (2) into a plurality of sub-regions based on a geometric center position of the focused incident field and the preliminary imaging result of the target scatterer (3); S3, the microwave imaging system moves the focus point position of the focused incident field by adjusting the phase difference of the antenna (1), adjusts the focus point to the center of each sub-region in turn, and collects the scattered field data of the target scatterer (3) in different sub-regions; S4. Quantitative inversion is performed based on the scattering field data of the target scatterer (3) in different sub-regions to obtain the numerical value and spatial distribution of the dielectric constant of the target scatterer (3), thereby constructing an image of the target scatterer (3).

2. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 1, characterized in that: The method adopts a microwave imaging system, which includes a plurality of antennas (1) with phase modulation function and working in time division duplex mode. The antennas (1) are evenly spaced around a target scatterer (3). In the transmitting mode, the antennas (1) emit electromagnetic waves at a set frequency toward the target scatterer (3). The electromagnetic waves interact with the target scatterer (3) to form a scattering field. Each antenna (1) receives the scattering field signal in turn in the receiving mode to obtain scattering field data.

3. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 2, characterized in that: The random irradiation method in S1 is specifically as follows: the phase distribution of the electromagnetic waves emitted by the antenna (1) array in the transmission mode follows the Gaussian distribution.

4. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 1, characterized in that: The preliminary imaging result of the target scatterer (3) is obtained by processing according to the following formula: F[φ]=∫ Ω E scat (r)φ(r′)dr′=G(r,r′) Where G(r,r′) is the field generated by the point source at position r at position r′, Ω represents the imaging area, r′ is the position coordinate of the receiving point, r is the position coordinate of the transmitting point, φ(r′) is the indicator function used to indicate whether there is a target scatterer (3) at position r′, and E scat (r) represents the scattered field data measured at position r.

5. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 1, characterized in that: The S2 is specifically: S2.

1. Determine, based on the preliminary imaging result of the target scatterer (3), a rectangular area that includes all target scatterers (3) and has a preset redundant range at the boundary as the target area (2); S2.2, the microwave imaging system forms a focused incident field through phase modulation; S2.

3. Divide the target area (2) into N*N rectangular sub-areas of equal size according to the geometric center positions of the focused incident field and the preliminary imaging results of the target scatterer (3), so that the geometric center position of the preliminary imaging results of the target scatterer (3) is located at the center position of any sub-area, and the length and width of each sub-area are set according to the size of the effective focusing area of ​​the focused incident field.

6. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 1, characterized in that: The phase difference of the antenna (1) is adjusted in S3 according to the following formula: θ t NArg(G1)-Arg(G). t ),tD2,3,...,m Among them, Arg(.) represents the principal value angle of the complex number, θ t is the phase adjustment of the tth emission source, G1 and G t They represent the Hankel function values ​​of the first and tth emission sources at the focal point x, m represents the total number of emission sources, H0 (1) represents the zero-order Hankel function of the first kind, k b represents the beam of the background medium, k b |xy(t)| represents the normalized distance, and |xy(t)| represents the physical distance from the emission source to the focal point.

7. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 1, characterized in that: The S4 is specifically as follows: first, quantitative inversion is performed on the first sub-region, and the initial guess value of the inversion of the first sub-region adopts the dielectric constant of the background medium to obtain the inversion result of the first sub-region; then, quantitative inversion is performed on the remaining sub-regions in turn, and the initial guess value of the inversion of each remaining sub-region adopts the inversion result of the previous sub-region, and finally the inversion results of all sub-regions are obtained, and the inversion results of all sub-regions are spliced ​​to obtain the numerical value and spatial distribution of the dielectric constant of the target scatterer (3).

8. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 1, characterized in that: The quantitative inversion is performed according to the following formula: Among them, ε n (r′) represents the dielectric constant distribution to be inverted under the nth focusing, ε0 represents the dielectric constant of the background medium, and u inc (r′; z n ) represents the focused incident field of the nth sub-region, Represents the measured scattered field data collected at the receiving point r, with the focus point Z n , G s (r, r′) is the free space Green’s function of the receiving area, G Ω (r′, r′) is the free-space Green’s function of the imaging region, λ is the regularization parameter used to suppress noise and pathology, Represents the spatial gradient of the dielectric constant distribution.

9. The inverse scattered microwave imaging method based on an unconventional incident field according to claim 1, characterized in that: The target scatterer (3) is one or more non-overlapping and discretely distributed dielectric scatterers.

Images