Holographic tensor impedance metasurface design method for near-field multi-point focusing

Abstract

The invention relates to the technical field of electromagnetic metasurfaces and near-field electromagnetic imaging, in particular to a holographic tensor impedance metasurface design method for near-field multi-point focusing, which comprises the following steps of: calculating equivalent scalar impedance under periodic boundary and eigenmode solution through full-wave simulation, establishing an equivalent relationship, and establishing a'geometric parameter-impedance tensor 'database; arranging a monopole at the center of the array plane to generate a reference field, and performing normalized linear weighting on a multi-focus expected field according to a surface impedance space change period to obtain a synthetic radiation field; and combining the synthesized radiation field and the reference field to solve a target impedance tensor and an anisotropic main direction, determining unit geometric parameters according to a library to generate a layout, and realizing near-field multi-point focusing at a preset position.

Description

Technical Field

[0001] This invention relates to the fields of electromagnetic metasurfaces and near-field electromagnetic imaging technology, and particularly to a method for designing holographic tensor impedance metasurfaces for near-field multi-point focusing. Background Technology

[0002] Near-field multi-point focusing can spatially reconstruct energy distribution within a finite aperture, which is a key capability for applications such as microwave energy focusing, local heating, near-field sensing, and array emission shaping. To achieve stable surface wave-leakage wave conversion under monopole-excited surface wave conditions at the center of the array, metasurface units with strong anisotropic response and calculable holographic impedance distribution are required.

[0003] Existing technologies have several drawbacks: the traditional method of creating a single slit along the principal axis on a circular or square patch results in weak anisotropy, making it difficult to obtain highly directional leakage waves; multi-point focusing often uses the arithmetic average impedance method for superposition, which makes it difficult to maintain the characteristics of each focus as the number of focuses increases, leading to a decrease in electric field strength and positional deviation. Furthermore, the lack of a usable database of "geometric parameters—impedance tensors" means that there is a lack of quantitative basis for the selection of orientation and geometric degrees of freedom during the design process. Summary of the Invention

[0004] To address the numerous problems existing in the prior art, this invention provides a holographic tensor impedance metasurface design method for near-field multi-point focusing. Under the conditions of periodic boundary and eigenmode solution, this invention performs full-wave simulation of the unit response in different propagation directions, calculates the equivalent scalar impedance, and obtains the surface impedance tensor according to the equivalence relationship, establishing a mapping library between geometric parameters and impedance tensors. Using the reference field generated by the monopole at the center of the array as a reference, the desired multi-focus field is normalized and linearly weighted according to the spatial variation period of the surface impedance to form a synthetic radiation field. This field is then jointly solved with the reference field to determine the target impedance distribution and anisotropic principal directions. Based on the mapping library, a layout is generated, thereby achieving near-field multi-point focusing at a preset position.

[0005] A method for designing holographic tensor impedance metasurfaces for near-field multi-point focusing includes the following steps:

[0006] Full-wave electromagnetic simulation was performed under periodic boundary conditions and intrinsic mode solution configuration. The equivalent scalar impedances of different surface wave propagation directions were calculated and the equivalent relationships were combined to obtain the surface impedance tensor components of the element. A database that associates the element geometric parameters with the surface impedance tensor was constructed.

[0007] A monopole feed is set at the geometric center of the metasurface array to excite surface waves and serve as a reference field, and the spatial coordinates of at least two preset foci are set.

[0008] The periodic weighted shared aperture method is adopted. Based on the periodic change of surface impedance, normalized weights are assigned to each preset focus. The focusing electric field of each focus is linearly weighted at each array unit to obtain the composite radiation electric field.

[0009] The target surface impedance tensor and anisotropic principal directions of the array elements are obtained by jointly solving the synthetic radiated electric field and the reference field, and the corresponding element geometric parameters are determined according to the database to generate the array layout, thereby achieving near-field multi-point focusing at the preset focal point.

[0010] Preferably, the database is established through full-wave electromagnetic simulation, using periodic boundary conditions and the equivalent scalar impedance of the intrinsic mode solver calculation unit under different surface wave propagation directions, and then obtaining the surface impedance tensor components by combining the equivalent relationships and recording them in association with geometric parameters.

[0011] Preferably, the tensor impedance unit is composed of a metal ground, a dielectric substrate and a circular slotted metal patch. The patch has slots along the main anisotropic direction and short slots in a direction orthogonal to the main anisotropic direction to enhance the anisotropic response.

[0012] Preferably, the unit geometric parameters include at least the distance between the circular patch and the unit boundary, the slit width and the main axis slit angle, and are applied to the database entries relative to the surface impedance tensor components.

[0013] Preferably, for the anisotropic principal direction of each unit, the direction in which the main shaft slit angle is equal to the maximum value of the equivalent scalar impedance is used to determine the orientation and parameter selection of the unit.

[0014] Preferably, the reference field is provided by a surface wave generated by a monopole feed located at the center of the array, and is used in conjunction with the synthesized radiated electric field to solve for the surface impedance distribution.

[0015] Preferably, the periodic weighted shared aperture method assigns normalized weights to each preset focal point based on the spatial variation period of surface impedance, and performs linear weighted superposition of the focusing electric fields of each focal point within the aperture range to form a synthetic radiation electric field.

[0016] Preferably, the solution of the surface impedance distribution uses the synthesized radiative electric field and the reference field as inputs to obtain the target surface impedance tensor and its anisotropic principal direction for each array element, and then retrieves matching geometric parameters from the database for layout generation.

[0017] Preferably, the database contains at least the correspondence between patch-boundary distance and the maximum value of equivalent scalar impedance, which is used to guide the determination of unit geometric parameters.

[0018] Preferably, the metasurface is a planar periodic array, and each unit in the array is oriented according to the anisotropic principal direction to generate a layout.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0020] By using a cross-slit tensor unit configuration, a stronger anisotropic response and directional leakage radiation basis are achieved.

[0021] By using the periodic weighted shared aperture method, normalized linear superposition according to periodic weights is achieved within the shared aperture, mitigating the reduction in focal intensity and positional deviation caused by the arithmetic mean method.

[0022] By solving full-wave simulations using periodic boundary conditions and intrinsic modes, and establishing equivalent relationships, the equivalent scalar impedance can be calculated under different propagation directions, and the surface impedance tensor components can be inversely derived. This enables the construction of a "geometric parameter-impedance tensor" database to support layout generation.

[0023] By jointly solving the central monopole reference field and the synthetic radiation field, the target surface impedance tensor and the principal anisotropic direction were determined, and geometric parameters were selected from the database to generate the layout. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the THIM unit topology in this invention;

[0025] Figure 2 Z is the spindle slot angle under different conditions in this invention. e / θ t Schematic diagram of the curve;

[0026] Figure 3 In this invention, Z is the maximum equivalent impedance of the tensor impedance unit. e,max A schematic diagram of the fitting curve with distance g;

[0027] Figures 4(a)-4(b) This is a schematic diagram of the bifocal normalized simulated electric field distribution at different distances using the periodic weighted shared aperture method and the traditional arithmetic average method in this invention.

[0028] Figures 5(a) and 5(b) are schematic diagrams of the simulated electric field distribution at the focal plane using the periodic weight shared aperture method and the traditional arithmetic average method in this invention.

[0029] Figure 6 This is a schematic diagram of the power measurement system in this invention;

[0030] Figures 7(a) and 7(b) are schematic diagrams of the power distribution of the bifocal measurement at the focal plane in the periodic weight shared aperture method and the traditional arithmetic average method of the present invention.

[0031] Figures 8(a) and 8(b) are schematic diagrams of the normalized power distribution measured at two foci along the propagation direction using the periodic weighted shared aperture method and the conventional arithmetic average method in this invention. Detailed Implementation

[0032] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0034] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0035] A method for designing holographic tensor impedance metasurfaces for near-field multi-point focusing includes the following steps:

[0036] Full-wave electromagnetic simulation was performed under periodic boundary conditions and intrinsic mode solution configuration. The equivalent scalar impedances of different surface wave propagation directions were calculated and the equivalent relationships were combined to obtain the surface impedance tensor components of the element. A database that associates the element geometric parameters with the surface impedance tensor was constructed.

[0037] Preferably, the database is established through full-wave electromagnetic simulation, using periodic boundary conditions and the equivalent scalar impedance of the intrinsic mode solver calculation unit under different surface wave propagation directions, and then obtaining the surface impedance tensor components by combining the equivalent relationships and recording them in association with geometric parameters.

[0038] To establish the mapping relationship between element geometric parameters and surface impedance tensors, full-wave electromagnetic simulation was used. Under periodic boundary conditions and eigenmode solver configurations, different surface wave propagation directions θ were set for the elements. t The solution is performed to obtain the corresponding eigenfrequency f, and the equivalent scalar impedance Z is calculated accordingly. e (θ t The subsequent simultaneous equations give the equivalence relation with Z.e (θ t The expression for ) is used to obtain the surface impedance tensor component Z. xx Z xy =Z yx Z yy And obtain Z e With θ t The changing relationship characterizes the anisotropy of the unit; further changing the principal axis slit angle θ k Comparison of different θ k Z under the condition e / θ t The curve determines the direction of the maximum value of the equivalent scalar impedance relative to θ. k The consistency relationship between the circular patch and the boundary spacing g and Z is extracted. e,max The relationship between the geometric parameters g, w, and θ is used to determine the relationship between them. k The values ​​and directions of the tensor components are associated and recorded to form a tensor impedance element database, which is used for parameter selection and generation of subsequent metasurface array layouts.

[0039] Using the equivalent scalar impedance Z e To simplify the analysis, its expression is as follows:

[0040]

[0041] The corresponding eigenfrequency f was obtained, and three different θ values ​​were calculated by substituting them into equation (2). t The corresponding equivalent scalar impedance Z e :

[0042]

[0043] By combining equations (1) and (2), the tensor impedance component Z of this unit can be obtained. xx Z xy =Z yx Z yy Substituting into equation (1) yields Z. e / θ t The curve is as follows Figure 2 As shown.

[0044] Preferably, the tensor impedance unit is composed of a metal ground, a dielectric substrate and a circular slotted metal patch. The patch has slots along the main anisotropic direction and short slots in a direction orthogonal to the main anisotropic direction to enhance the anisotropic response.

[0045] The tensor impedance unit in this embodiment adopts a three-layer structure: the dielectric substrate is made of a dielectric material with a dielectric constant of about 4.4 and a loss tangent of about 0.005, the lower layer is a metal ground, and the upper layer is a circular slotted metal patch; in order to enhance anisotropy, a main slot is set in the main anisotropic direction of the patch, and a short slot is added in the direction orthogonal to this direction to form a cross-slotted configuration, which makes the anisotropy of the unit more obvious and is conducive to converting surface waves into electromagnetic leakage waves with stronger directionality, thereby providing a structural basis for realizing multi-point near-field focusing.

[0046] Preferably, the unit geometric parameters include at least the distance between the circular patch and the unit boundary, the slit width and the main axis slit angle, and are applied to the database entries relative to the surface impedance tensor components.

[0047] Examples of the dimensional parameters of the unit include array period a, substrate thickness h, and arc radius R. s The geometric parameters used for designing degrees of freedom include at least the distance g between the circular patch and the element boundary, the slot width w, and the principal axis slot angle θ. k The aforementioned geometric degrees of freedom and the surface impedance tensor component Z xx Z xy =Z yx Z yy Establish a correspondence to characterize the response to different surface wave propagation directions under different geometric values; record this as an "Geometric Parameter - Tensor Impedance" entry to form a design database.

[0048] Change the spindle slit angle θ k Let them be equal to 45°, 90° and 120° respectively, and we get Z. e / θ t The curve is as follows Figure 2 As shown, θ can be observed t For Z e The maximum value has virtually no impact, and Z e The direction of the maximum value is related to θ t Consistent. And the slit width w is consistent with Z. e The maximum value has little impact, therefore the spindle slot angle θ is set in the design. t The direction θ equal to the maximum value of the equivalent scalar impedance tmax We can obtain the distances g and Z between the circular patch and the boundary. e The relationship of the maximum values ​​is as follows Figure 3 As shown, the design of the tensor impedance element database is now complete.

[0049] Preferably, for the anisotropic principal direction of each unit, the direction in which the main shaft slit angle is equal to the maximum value of the equivalent scalar impedance is used to determine the orientation and parameter selection of the unit.

[0050] Changing the spindle slit angle θk Under the condition, the equivalent scalar impedance Z e The direction of the maximum value is related to θ k Maintain consistency; at the same time, the slit width w should be consistent with Z. e The maximum value has a relatively small impact. Based on this principle, the spindle slot angle θ is set in the design. k The direction θ equal to the maximum value of the equivalent scalar impedance t,max Based on this, g and Z are combined e,max The correspondence is used to determine and select the database and layout parameters.

[0051] A monopole feed is set at the geometric center of the metasurface array to excite surface waves and serve as a reference field, and the spatial coordinates of at least two preset foci are set.

[0052] To establish the design boundary conditions for near-field multi-point focusing, a monopole feed is placed at the geometric center of the metasurface array to excite surface waves on the metasurface and serve as a reference field; during the focusing target determination stage, the spatial coordinates f of at least two preset focal points are set. i =(x i ,y i ,z i ).

[0053] Preferably, the reference field is provided by a surface wave generated by a monopole feed located at the center of the array, and is used in conjunction with the synthesized radiated electric field to solve for the surface impedance distribution.

[0054] The reference field is taken from the surface wave electric field generated by the monopole antenna at the center of the array, denoted as ψ. surf The focusing electric field at each focal point is linearly weighted at the array element using a periodic weighting shared aperture method to obtain the composite radiated electric field ψ. rad (Corresponding to the definitions of equations (4) and (5)). ψ rad With ψ surf Using the combined data as input, the surface impedance distribution of the holographic impedance metasurface is calculated, and the target surface impedance tensor and its anisotropic principal direction for each array element are determined accordingly. Subsequently, the geometric parameters are selected and the layout is generated using an existing database.

[0055] The periodic weighted shared aperture method is adopted. Based on the periodic change of surface impedance, normalized weights are assigned to each preset focus. The focusing electric field of each focus is linearly weighted at each array unit to obtain the composite radiation electric field.

[0056] Preferably, the periodic weighted shared aperture method assigns normalized weights to each preset focal point based on the spatial variation period of surface impedance, and performs linear weighted superposition of the focusing electric fields of each focal point within the aperture range to form a synthetic radiation electric field.

[0057] The surface impedance distribution of the near-field focusing holographic impedance metasurface exhibits a periodically alternating spiral characteristic, varying cosinely along the radial direction. The period d of this variation is related to the wave vector k along the surface wave. t Spatial phase compensation required for each focal point at the corresponding unit The relationship between the distance r from the element to the center of the array is given by equation (3);

[0058]

[0059] Based on this, a periodic weighted shared aperture (PWSA) method is proposed to reconstruct the surface electric field of each element, achieving multi-point focusing. The combined electric field of each element surface is calculated according to equation (4):

[0060]

[0061] ψ radi Let u be the electric field distribution of the focusing electric field at each tensor impedance element for the i-th focus. i Let be the normalized weighting coefficient of the i-th focus in the synthesized electric field, where the normalized weighting coefficient is given by equation (5):

[0062]

[0063] That is, based on the spatial variation period of surface impedance, normalized weights are assigned to each preset focal point, and the focusing electric field of each focal point is linearly weighted and superimposed within the aperture range to form a synthetic radiation electric field.

[0064] Preferably, the solution of the surface impedance distribution uses the synthesized radiative electric field and the reference field as inputs to obtain the target surface impedance tensor and its anisotropic principal direction for each array element, and then retrieves matching geometric parameters from the database for layout generation.

[0065] The combined electric field ψ obtained from equation (4) rad The electric field ψ generated by the monopole antenna at the center of the array surf Using the combined input, the surface impedance distribution of the near-field multi-point focusing holographic impedance metasurface is calculated according to Equation (6); further, the tensor impedance calculated by Equation (6) is substituted into Equation (1) to obtain the maximum equivalent scalar impedance and its direction of each element, and the geometric parameters of each element are determined through the established tensor impedance element database, which is used to realize the design and layout generation of the metasurface array.

[0066]

[0067] Substitute the tensor impedance obtained from equation (6) into equation (1) to calculate the maximum equivalent scalar impedance and its direction for each element. Then, determine the detailed parameters of each element through the established tensor impedance element database to realize the design of the metasurface array.

[0068] Preferably, the database contains at least the correspondence between patch-boundary distance and the maximum value of equivalent scalar impedance, which is used to guide the determination of unit geometric parameters.

[0069] Based on changing the principal spindle slit angle and analyzing the relationship between the equivalent scalar impedance and the surface wave propagation direction, it is determined that the direction of the maximum value of the equivalent scalar refraction is consistent with the principal spindle slit angle. Figure 3 As shown, the distance g between the circular patch and the boundary and the maximum value of the equivalent scalar impedance Z are obtained. e,max The corresponding relationship is used to complete the design of the tensor impedance element database and serve as the basis for selecting geometric parameters.

[0070] The target surface impedance tensor and anisotropic principal directions of the array elements are obtained by jointly solving the synthetic radiated electric field and the reference field, and the corresponding element geometric parameters are determined according to the database to generate the array layout, thereby achieving near-field multi-point focusing at the preset focal point.

[0071] The composite radiative electric field ψ calculated by the periodic weighted shared aperture method rad The reference field ψ generated by the monopole antenna at the center of the array surf Using the combined input, the surface impedance distribution of the near-field multi-point focusing holographic impedance metasurface is calculated according to Equation (6); the tensor impedance obtained from Equation (6) is substituted into Equation (1) to further determine the maximum equivalent scalar impedance and its direction of each array unit, and the matching geometric parameters are retrieved through the existing tensor impedance unit database to generate the array layout, thereby achieving multi-point focusing at the preset coordinates, and the focal position matches the preset position.

[0072] Preferably, the metasurface is a planar periodic array, and each unit in the array is oriented according to the anisotropic principal direction to generate a layout.

[0073] The metasurface is arranged in a planar periodic array (e.g., a two- or three-point focusing prototype with 31×31 elements). Each element is oriented according to its principal anisotropic direction, which is determined by the direction of the maximum value of the equivalent scalar impedance. That is, the principal axis slot angle θ is set in the design. k =θ t,max Based on this, the unit orientation and geometric parameters are selected and the layout is generated.

[0074] The normalized electric field intensity distributions at different distances are shown in Figures 4(a) and 4(b). Figure 4(a) shows the periodic weighted shared aperture method (PWSA), and Figure 4(b) shows the traditional arithmetic average method (AAI). The positions of the two foci are set as f1(-50mm, 0, 200mm) and f2(50mm, 0, 330mm), respectively. It can be seen from the figures that the foci of both methods coincide with the preset positions. Detailed data for each foci are shown in Table 1. The comparison shows that the periodic weighted shared aperture method obtains a stronger electric field intensity at the foci. Compared with the traditional arithmetic average method, using this method increases the electric field intensity at the two foci by 21.0% and 18.2%, respectively.

[0075] Table 1

[0076]

[0077] To verify the effectiveness of the periodic weighted shared aperture method under the condition of increasing focal point number, a simulation was performed on a three-point focusing holographic tensor impedance metasurface with a unit number of 31×31. The three focal points were set at f1(20mm,0,180mm), f2(80mm,35mm,200mm) and f3(80mm,-35mm,220mm), respectively. The electric field intensity distribution at the focusing plane is shown in Figures 5(a)-5(b).

[0078] As shown in Figures 5(a) and 5(b), Figure 5(a) represents the Periodic Weighted Shared Aperture Method (PWSA), and Figure 5(b) represents the Traditional Arithmetic Average Method (AAI). It is easy to see that the three focal points obtained using the PWSA method have higher resolution, while the three focal points obtained using the traditional AAI method are too close together and thus stick together, failing to form a clear focal point at the preset position. Furthermore, due to the more concentrated energy, the PWSA method achieves a higher electric field intensity at the focal position compared to the traditional method, especially at the second and third focal points, where it achieves an improvement of approximately 30%.

[0079] To verify the ability of the designed holographic impedance metasurface to generate multiple focal points under actual working conditions, a two-point focusing holographic impedance metasurface with dimensions of 310×310×1mm³ was fabricated. The test environment was as follows: Figure 6As shown. In the experimental system, the source (Agilent N5181A) is used to generate microwave power, which is amplified by an amplifier operating at a frequency of 5.8 GHz. 6 watts of microwave power is transmitted to a monopole feed to generate a surface wave. When the surface wave passes through the holographic impedance metasurface, it is modulated by tensor impedance units to form a leaky outgoing wave, forming a focal point at a preset location. At the receiving end, a probe is mounted on a slide to measure the received power intensity at different distances, and then the power is transmitted to a power meter (N1913A) and recorded. The measurement results are shown in Figures 7(a)-7(b), where 7(a) is the periodically weighted shared aperture method (PWSA) and 7(b) is the conventional arithmetic average method (AAI); Figures 8(a)-8(b), where Figure 8(a) is a schematic diagram of focal point 1 and Figure 8(b) is a schematic diagram of focal point 2.

[0080] As shown in Figures 7(a) and 7(b), for the holographic impedance metasurface based on the periodic weighted shared aperture method, the maximum power intensity positions of the two focal points are (-45mm, 0, 192mm) and (44mm, 0, 317mm), respectively. In contrast, the focal positions corresponding to the traditional arithmetic averaging method are (-42mm, 0, 191mm) and (42mm, 2mm, 312mm). The angular deviations of focal points 1 and 2 obtained using the periodic weighted shared aperture method in the pitch and azimuth directions are (0.85°, 0°) and (0.72°, 0°), respectively. In comparison, the focal spot shifts of the traditional arithmetic averaging method are larger, at (1.6°, 0°) and (0.94°, 2.73°), respectively.

[0081] The power intensity along the preset focal direction is shown in Figure 8. The focal lengths measured by the periodic weighted shared aperture method are 197 mm and 320 mm, with deviations from the target position of 9.2 mm and 13.7 mm, respectively. In contrast, the focal lengths measured by the traditional arithmetic averaging method are 196 mm and 315 mm, with errors of 10.2 mm and 18.7 mm, respectively. These results show that compared with the traditional arithmetic averaging method, the periodic weighted shared aperture method can obtain a focal point closer to the target position, and the power intensity at the two focal points is improved by 20.3% and 14.8%, respectively, which is consistent with the simulation results. All these simulation and measurement results demonstrate that the periodic weighted shared aperture method has significant advantages in multifocal generation, namely high focusing efficiency and high resolution, and has good application prospects.

[0082] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects.

[0083] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for designing holographic tensor impedance metasurfaces for near-field multi-point focusing, characterized in that, Includes the following steps: Full-wave electromagnetic simulation was performed under periodic boundary conditions and intrinsic mode solution configuration. The equivalent scalar impedances of different surface wave propagation directions were calculated and the equivalent relationships were combined to obtain the surface impedance tensor components of the element. A database that associates the element geometric parameters with the surface impedance tensor was constructed. A monopole feed is set at the geometric center of the metasurface array to excite surface waves and serve as a reference field, and the spatial coordinates of at least two preset foci are set. The periodic weighted shared aperture method is adopted. Based on the periodic change of surface impedance, normalized weights are assigned to each preset focus. The focusing electric field of each focus is linearly weighted at each array unit to obtain the composite radiation electric field. The target surface impedance tensor and anisotropic principal directions of the array elements are obtained by jointly solving the synthetic radiated electric field and the reference field, and the corresponding element geometric parameters are determined according to the database to generate the array layout, thereby achieving near-field multi-point focusing at the preset focal point.

2. The method according to claim 1, characterized in that, The database was established through full-wave electromagnetic simulation. Periodic boundary conditions and equivalent scalar impedances of the intrinsic mode solver calculation unit under different surface wave propagation directions were used. The surface impedance tensor components were obtained by combining the equivalent relationships and then associated with the geometric parameters and recorded.

3. The method according to claim 1, characterized in that, The tensor impedance unit consists of a metal ground, a dielectric substrate, and a circular slotted metal patch. The patch has slots along the main anisotropic direction and short slots in a direction orthogonal to this direction to enhance the anisotropic response.

4. The method according to claim 1, characterized in that, The unit geometry parameters include at least the distance between the circular patch and the unit boundary, the slit width, and the spindle slit angle, and are applied to the database entries relative to the surface impedance tensor components.

5. The method according to claim 4, characterized in that, For each unit's anisotropic principal direction, the direction in which the principal axis slot angle is equal to the maximum value of the equivalent scalar impedance is used to determine the unit's orientation and parameter selection.

6. The method according to claim 1, characterized in that, The reference field is provided by surface waves generated by a monopole feed located at the center of the array, and is used in conjunction with the synthesized radiated electric field to solve for the surface impedance distribution.

7. The method according to claim 1, characterized in that, The periodic weighted shared aperture method assigns normalized weights to each preset focal point based on the spatial variation period of surface impedance, and performs linear weighted superposition of the focusing electric fields of each focal point within the aperture range to form a synthetic radiation electric field.

8. The method according to claim 1, characterized in that, The solution for the surface impedance distribution uses the synthesized radiative electric field and the reference field as inputs to obtain the target surface impedance tensor and its anisotropic principal direction for each array element, and then retrieves matching geometric parameters from the database for layout generation.

9. The method according to claim 1, characterized in that, The database contains at least the correspondence between patch-boundary distance and the maximum value of equivalent scalar impedance, which is used to guide the determination of unit geometric parameters.

10. The method according to claim 1, characterized in that, The metasurface is a planar periodic array, and each unit in the array is oriented according to the anisotropic principal direction to generate a layout.

Images