Continuous wave backscatter modulator based on passive artificial two-dimensional structures and methods thereof

Abstract

This invention discloses a continuous wave backscattering modulator and its method based on a passive artificial two-dimensional structure, belonging to the field of electromagnetic wave manipulation technology. This invention achieves backscattering manipulation based on a single-layer passive artificial two-dimensional structure, eliminating the need for active devices or multi-layer complex structures. By introducing a decoupling mechanism between the polarization reflection amplitude and phase response, it achieves continuous adjustability of the polarization reflection amplitude within the range of 0 to 1 while simultaneously controlling the binary phase response. Furthermore, by exciting and selectively enhancing higher-order spatial harmonics, it achieves efficient control over the angle and energy distribution of the scattered wave and establishes a mapping relationship between "polarization reflection amplitude and phase response - structural parameters." This invention possesses excellent design versatility and scalability, a simple overall structure, and advantages in broadband bandwidth and multi-functional integration. It has significant application value and broad development prospects in fields such as electromagnetic stealth, information control, and sensor integration.

Description

Technical Field

[0001] This invention relates to electromagnetic wave manipulation technology, specifically to a continuous beam backscattering modulator based on a passive artificial two-dimensional structure and its design method. Background Technology

[0002] A metasurface is a two-dimensional functional structure composed of a large number of subwavelength-scale artificial electromagnetic units. By designing the electromagnetic response characteristics and spatial arrangement of these units, it is possible to precisely control the reflection phase, scattering direction, and energy distribution during electromagnetic wave propagation. Compared to traditional materials or macroscopic reflective structures, metasurfaces have the advantages of thinness, high integration, and a large degree of controllability, demonstrating significant application value in radar scattering control, wireless communication, and electromagnetic countermeasures, and are gradually becoming an important technical means to achieve precise control of electromagnetic waves. In recent years, with the development of design methods and fabrication processes, the potential of metasurfaces in multifunctional integration and broadband control has been continuously explored, but their high degree of controllability in complex electromagnetic environments still needs further improvement.

[0003] Most metasurface-based beamforming methods rely on continuous phase gradients to control the reflection direction, but they still face several key challenges in practical applications: First, traditional methods mainly target single or a few discrete directions for control, making it difficult to achieve flexible control of multi-channel backscattering and continuous angular ranges, thus limiting their application in complex spatial scenarios; second, existing designs typically focus on phase modulation, lacking independent adjustment capabilities for scattering amplitude, resulting in limited energy distribution across channels and difficulty in achieving fine and multi-dimensional energy control; third, to achieve complex functions, multi-layer structures or active devices are often required, increasing system complexity and implementation difficulty, while also reducing system stability and engineering feasibility. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a continuous beam backscattering modulator based on a passive artificial two-dimensional structure and its design method. Based on a simple structure, it can achieve amplitude and phase coordinated control and support multi-channel continuous backscattering, thereby improving the flexibility and practicality of electromagnetic wave spatial control.

[0005] One objective of this invention is to propose a continuous beam backscattering modulator based on a passive artificial two-dimensional structure.

[0006] The passive artificial two-dimensional structure-based continuous beam backscattering modulator of the present invention comprises, from bottom to top: a reflective layer, a high-frequency dielectric substrate, and a resonant structure layer; wherein, the high-frequency dielectric substrate is disposed on the reflective layer, and the resonant structure layer is composed of multiple metasurface units arranged in a two-dimensional array and disposed on the surface of the high-frequency dielectric substrate, forming a passive artificial two-dimensional structure as a continuous beam backscattering modulator; the electromagnetic wave is incident at an arbitrary angle θ. i When incident on an artificial two-dimensional structure, the electromagnetic wave is scattered, generating a scattered wave. The electromagnetic wave excites the artificial two-dimensional structure to generate spatial harmonics of a specific order. Simultaneously, the artificial two-dimensional structure introduces a spatially varying phase response. By adjusting the transverse momentum of the scattered wave through the compensation wave vector of the artificial two-dimensional structure, the transverse phase of the electromagnetic wave is compensated, which is equivalent to reconstructing the electromagnetic wavefront. Under the combined action of the spatial harmonics and the compensation wave vector, the incident wave and the scattered wave satisfy the wave vector conservation relationship, causing the scattered wave to propagate in the opposite direction of the incident direction, thereby achieving backscattering. Furthermore, the spatial harmonics generated by the electromagnetic wave excitation have multiple orders, and the spatial harmonics of different orders correspond to different angles. This allows multiple specific orders of spatial harmonics to excite backscattering. Under the action of spatially symmetrical spatial harmonics, there are multiple different backscattering angles, achieving multi-channel backscattering.

[0007] The reflective layer is used to efficiently reflect incident electromagnetic waves and suppress transmitted components, thereby improving reflection efficiency. The reflective layer is made of a highly conductive metallic material, including but not limited to copper, gold, silver, or aluminum; its thickness is preferably 10 μm to 70 μm. The high-frequency dielectric substrate is used to support the resonant structure layer and to regulate the propagation phase and impedance matching characteristics of electromagnetic waves within the structure. It is made of a high-frequency dielectric material with extremely low high-frequency loss and excellent thermal stability, with a thickness of 0.1 mm to 2.5 mm. The relative permittivity of the high-frequency dielectric substrate is 2.1 to 10.5, and the loss tangent is preferably less than 0.005.

[0008] The artificial two-dimensional structure is located in the xy plane, and the incident electromagnetic wave is located in the xz plane, making an angle θ with the z-axis. iIn the transverse direction (x-direction), scattered waves are generated by the surface of the artificial two-dimensional structure. Each N metasurface units, arranged according to a preset phase logic, constitute a unit cell, where N is an even number ≥ 2. The artificial two-dimensional structure is composed of multiple identical unit cells arranged periodically along the x-direction. In the longitudinal direction (y-direction), the number of metasurface units is a positive integer M. The value of M is determined based on the preset longitudinal width Wy of the artificial two-dimensional structure and the period p of the metasurface units, i.e., Wy = M × p. Each unit cell includes two types of metasurface units with different phase responses. The first N / 2 metasurface units have the same structure and the same phase response to electromagnetic waves, while the latter N / 2 metasurface units have the same structure. There is a phase response gradient of π between the two types of metasurface units. The phase response gradient of two adjacent unit cells in the transverse direction to electromagnetic waves is 2π, where N is an even number ≥ 2. Metasurface units induce resonance between electromagnetic waves and the artificial two-dimensional structure, thereby causing phase and polarization changes in the incident electromagnetic waves. Changing the parameters of the metasurface units induces different resonance responses, leading to different phase response changes in the incident electromagnetic waves and altering their polarization state, as well as the intensity of the scattered waves after the polarization state is changed. Adjusting the structural parameters of the metasurface units alters the phase response and transpolarization reflection amplitude of the incident electromagnetic waves. Simultaneously, by constructing two types of metasurface units with a phase response gradient of approximately π, binary control of the transpolarization reflection phase (i.e., the phase response) is achieved, corresponding to two phase states: 0 and π. Structural changes in the metasurface units cause changes in the phase response and also in the transpolarization reflection amplitude, affecting the scattering intensity of the scattered waves generated by the artificial two-dimensional structure. The transpolarization reflection amplitudes of the N metasurface units in the unit cell are identical.

[0009] Another objective of this invention is to propose a design method for continuous beam backscattering based on a passive artificial two-dimensional structure.

[0010] The design method of the continuous beam backscattering modulator based on a passive artificial two-dimensional structure of the present invention includes the following steps:

[0011] 1) Determine the design objectives and frequency bands:

[0012] Determine the required number of consecutive backscattering channels m and the scattering intensity of the scattered wave in each channel, and determine the center frequency and operating frequency band of the electromagnetic wave;

[0013] 2) Determine the compensated wave vector at the center frequency:

[0014] Based on the period p of the metasurface unit and the number N of metasurface units in a unit cell, where N is an even number ≥ 2, determine the compensation wave vector at the center frequency; and determine the range of the compensation wave vector based on the center frequency f of the electromagnetic wave and the number of channels m.

[0015] 3) Determine the angle of multi-channel backscattering:

[0016] Electromagnetic waves incident on an artificial two-dimensional structure are scattered to generate scattered waves, which in turn excite the artificial two-dimensional structure to generate spatial harmonics. At the same time, the artificial two-dimensional structure provides a compensating wave vector. Under the combined action of the spatial harmonics and the compensating wave vector, the incident wave and the scattered wave satisfy the wave vector conservation relationship. Combined with the backscattering conditions, the backscattering angle is determined.

[0017] 4) Design artificial two-dimensional structures:

[0018] A high-frequency dielectric substrate is placed on the reflective layer, and a resonant structure layer composed of metasurface units arranged in a two-dimensional array is placed on the high-frequency dielectric substrate to form an artificial two-dimensional structure.

[0019] 5) Build the unit library:

[0020] Based on the structural design of metasurface units, a unit library containing various metasurface units is constructed, and a mapping relationship between "repolarization reflection amplitude and phase response - structural parameters" is established.

[0021] 6) Design the unit cell:

[0022] Along the horizontal direction (x), the artificial two-dimensional structure consists of N metasurface units arranged in a sequence according to a preset phase logic, forming a unit cell. Multiple identical unit cells are arranged in a two-dimensional array to form a resonant structure layer. Each unit cell includes two types of metasurface units with different structures. The first N / 2 metasurface units have the same structure and the same phase response to electromagnetic waves, while the last N / 2 metasurface units have the same structure. There is a phase response gradient of π between the two types of metasurface units. The period of the metasurface units is p. The phase response gradient of two adjacent unit cells along the horizontal direction to electromagnetic waves is 2π. The repolarization reflection amplitude of the metasurface units is determined according to the backscattering intensity distribution. According to the mapping relationship in step 5), two types of metasurface units with a phase response gradient of π and a repolarization reflection amplitude that matches the scattering intensity of the scattered wave determined in step 1) are found from the unit library to form unit cells arranged along the horizontal direction. The two-dimensional arrangement of unit cells forms a resonant structure layer. Electromagnetic waves are incident on the artificial two-dimensional structure at a set incident angle, realizing multi-channel backscattering with adjustable scattering intensity.

[0023] In step 1), the electromagnetic wave incident on the artificial two-dimensional structure is backscattered, and each corresponding backscattering angle is a channel. The present invention can realize multi-channel backscattering.

[0024] In step 2), the compensation wave vector satisfy: The range of the compensated wave vector satisfies: Where k0 is the free space wave vector, f is the center frequency of the electromagnetic wave, and c is the propagation speed of the electromagnetic wave in free space.

[0025] In step 3), the electromagnetic wave incident on the artificial two-dimensional structure is periodically modulated to generate a scattered wave, which in turn excites spatial harmonic components. According to the principle of phase discontinuity, the tangential wave vector components at the interface between the incident and scattered waves must satisfy the generalized Snell's Law, meaning that under the combined action of the spatial harmonics and the compensating wave vector provided by the artificial two-dimensional structure, the incident and scattered waves must satisfy a wave vector conservation relationship. By presetting the specific value of the compensating wave vector, the backscattering condition is satisfied, thereby constraining the propagation direction of the scattered wave to the opposite direction of the incident direction (i.e., satisfying the...). Ultimately, this allows for precise control of the backscattering angle; electromagnetic waves can be incident at any angle θ. i When incident on an artificial two-dimensional structure, electromagnetic waves excite the structure to generate spatial harmonics of a specific order. Simultaneously, the artificial two-dimensional structure introduces a spatially varying phase response. By adjusting the transverse momentum of the scattered wave through the compensating wave vector of the artificial two-dimensional structure, transverse phase compensation is achieved for the electromagnetic wave, which is equivalent to reconstructing the electromagnetic wavefront. The incident wave and the scattered wave satisfy the wave vector conservation relationship.

[0026]

[0027] in, To compensate for the wave vector, l is the order of the spatial harmonics, c is the propagation speed of the electromagnetic wave in free space, f is the center frequency of the electromagnetic wave, and θ i Let θ be the angle of incidence of the electromagnetic wave. r The angle of backscattering;

[0028] When electromagnetic waves undergo backscattering, the incident wave and the scattered wave satisfy the backscattering condition. The above relationship becomes:

[0029]

[0030] Based on the number of channels m and the compensation wave vector The angle of backscattering satisfy:

[0031]

[0032] in, Let l be the angle of the l-th backscattering. From the above equation, it can be seen that the angle of backscattering... There are m channels, which realize backscattering of m channels.

[0033] In step 4), the artificial two-dimensional structure is located in the xy plane, and the incident electromagnetic wave is located in the xz plane, making an angle with the z-axis. The reflective layer is made of a highly conductive metallic material with a thickness of 10 μm to 70 μm. The high-frequency dielectric substrate has a relative permittivity of 2.1 to 10.5 and a thickness of 0.1 mm to 2.5 mm.

[0034] In step 5), based on the structural design of the metasurface units, a unit library containing various metasurface units is constructed. The unit library includes two types of metasurface units with different phase responses. The phase response of each type of metasurface unit has a phase response gradient of π, corresponding to different structural parameters. Each type of metasurface unit also includes multiple different structural parameters, corresponding to different transpolarization reflection amplitudes. The transpolarization reflection amplitude forms multiple continuously selectable states within the range of 0 to 1. Structural changes in the metasurface units cause changes in the phase response and also cause changes in the transpolarization reflection amplitude, affecting the scattering intensity of the scattered waves generated by the artificial two-dimensional structure. By establishing a mapping relationship between the structural parameters and phase response of the metasurface units, the coordinated design of transpolarization reflection amplitude and phase response is achieved. A one-to-one correspondence is established between the structural parameters and transpolarization reflection amplitude of the metasurface units. Simultaneously, phase response sets are constructed between different types of metasurface units through fixed phase response gradients. The transpolarization reflection amplitude of the metasurface units is matched with the backscattering intensity distribution to establish a mapping relationship between "transpolarization reflection amplitude and phase response - structural parameters". Through this mapping relationship, the structural parameters and phase state of the metasurface units required at each location can be determined in reverse according to the preset energy (i.e. scattering intensity) requirements of the backscattering angle, thereby achieving coordinated control of the direction and energy distribution of the backscattering beam.

[0035] In step 6), the number of metasurface units arranged in the longitudinal direction (y direction) is a positive integer M; the value of M is determined according to the preset longitudinal width Wy of the artificial two-dimensional structure and the period p of the metasurface unit, that is, Wy = M×p.

[0036] This invention introduces spatial periodic structural features by arranging repeating metasurface units, maintaining phase discretization while enabling the artificial two-dimensional structure to excite high-order spatial harmonic components of a specific order in the spatial frequency domain. Unlike traditional continuous phase response gradients that primarily rely on the fundamental component for beam deflection, this invention enhances specific harmonic components by adjusting the order l of the spatial harmonics introduced by the arrangement period of the repeating metasurface units, thereby achieving a redistribution of electromagnetic wave energy towards the target direction. The period p of the metasurface units and the number N of metasurface units in one cell are adjusted according to the compensation wave vector range determined in step 2), achieving flexible control over the backscattering angle and intensity. The periodicity parameter of the array primarily determines the direction of the scattered beam, while the magnitude of the repolarization reflection amplitude of different units is used to adjust the energy level of the channel, i.e., the scattering intensity of the scattered wave.

[0037] Advantages of this invention:

[0038] This invention offers significant comprehensive advantages over existing technologies. First, it achieves backscattering control based on a single-layer passive artificial two-dimensional structure, eliminating the need for active devices or complex multi-layer structures. This results in a remarkably simple structure, high stability, and ease of engineering implementation. Second, by innovatively introducing a decoupling mechanism between the transpolarization reflection amplitude and phase, it achieves continuous tunability of the transpolarization reflection amplitude within the 0-1 range while simultaneously controlling the binary phase response. This significantly overcomes the technical bottleneck of traditional metasurfaces relying solely on phase control, greatly enhancing the freedom and precision of electromagnetic wave manipulation. Third, this invention replaces the traditional continuous phase response gradient design with repeating units. By exciting and selectively enhancing higher-order spatial harmonics, it achieves efficient control over the angle and energy distribution of scattered waves, reducing design complexity and significantly enhancing the controllability of multi-channel backscattering. Furthermore, by constructing a mapping relationship between "transpolarization reflection amplitude and phase response - structural parameters," it achieves reversible design from macroscopic functional requirements to microscopic structural parameters, exhibiting excellent design versatility and scalability. With its simple overall structure and advantages of broadband and multi-functional integration, it has significant application value and broad development prospects in fields such as electromagnetic stealth, information control and sensing integration. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the electromagnetic wave incident direction of an embodiment of the continuous beam backscattering modulator based on a passive artificial two-dimensional structure of the present invention.

[0040] Figure 2The diagram shows an embodiment of the passive artificial two-dimensional structure-based continuous beam backscattering modulator of the present invention, wherein (a) is a schematic diagram of a resonant structure layer with a repolarization reflection amplitude of 0.5, (b) is a schematic diagram of a resonant structure layer with a repolarization reflection amplitude of 0.8, and (c) is a schematic diagram of a resonant structure layer with a repolarization reflection amplitude of 1.

[0041] Figure 3 A flowchart of the design method of the continuous beam backscattering modulator based on a passive artificial two-dimensional structure according to the present invention;

[0042] Figure 4 This is a schematic diagram of a metasurface unit of an embodiment of the continuous beam backscattering modulator based on a passive artificial two-dimensional structure of the present invention, wherein (a) is a top view, (b) is a front view, and (c) is a side view;

[0043] Figure 5 The image shows the response characteristics of a metasurface unit in the 28-36 GHz frequency band of an embodiment of the passive artificial two-dimensional structure continuous beam backscattering modulator of the present invention. (a) is a curve of amplitude response with frequency, (b) is a curve of phase response with frequency, and (c) and (d) are example diagrams of amplitude and phase at two typical frequency points of 30 GHz and 32 GHz, respectively.

[0044] Figure 6 The radiation patterns of three different backscattering patterns in the 30 GHz range are shown for an embodiment of the continuous beam backscattering modulator based on a passive artificial two-dimensional structure of the present invention. Among them, (a), (b) and (c) are the backscattering radiation patterns corresponding to the rotation angles of the metasurface unit of 45°, 61° and 16°, respectively.

[0045] Figure 7 The radiation patterns of three different backscattering patterns in the 32 GHz range are shown for an embodiment of the passive artificial two-dimensional structure-based continuous beam backscattering modulator of the present invention. (a), (b), and (c) are the backscattering radiation patterns corresponding to the rotation angles of the metasurface unit of 45°, 61°, and 16°, respectively.

[0046] Figure 8 The following are radiation patterns of three different backscattering patterns in the 34 GHz range for an embodiment of the passive artificial two-dimensional structure-based continuous beam backscattering modulator of the present invention. (a), (b), and (c) are the radiation patterns of backscattering corresponding to rotation angles of 45°, 61°, and 16° of the metasurface unit, respectively. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0048] The passive artificial two-dimensional structure-based continuous beam backscattering modulator of this embodiment includes, from bottom to top: a reflective layer, a high-frequency dielectric substrate, and a resonant structure layer; wherein, the high-frequency dielectric substrate is disposed on the reflective layer, and the resonant structure layer is composed of multiple metasurface units arranged in a two-dimensional array and disposed on the surface of the high-frequency dielectric substrate, thus forming a passive artificial two-dimensional structure as a continuous beam backscattering modulator.

[0049] like Figure 1 As shown, the artificial two-dimensional structure is located in the xy plane, and the incident electromagnetic wave is located in the xz plane with an angle θ with the z-axis. i In the transverse direction (x-direction), scattered waves are generated by the artificial two-dimensional structure surface. For example... Figure 2 As shown, each N metasurface units arranged according to a preset phase logic form a unit cell. The resonant structure layer is composed of multiple identical unit cells arranged periodically along the x-direction. In the longitudinal direction (y-direction), the number of metasurface units is a positive integer M. The value of M is determined according to the preset longitudinal width Wy of the artificial two-dimensional structure and the period p of the metasurface units, i.e., Wy = M × p. Each unit cell includes two types of metasurface units with different structures. The first N / 2 metasurface units have the same structure and have the same phase response to electromagnetic waves, while the last N / 2 metasurface units have the same structure. There is a phase response gradient of π between the two types of metasurface units. The phase response gradient of two adjacent unit cells along the transverse direction to electromagnetic waves is 2π.

[0050] In this embodiment, the reflective layer is made of copper with a thickness of 18 μm; the high-frequency dielectric substrate is made of Rogers RO4350B material with extremely low high-frequency loss and excellent thermal stability, with a thickness of 1.52 mm.

[0051] This embodiment presents a design method for continuous beam backscattering control based on a passive artificial two-dimensional structure, such as... Figure 3 As shown, it includes the following steps:

[0052] 1) Design objectives and frequency band determination:

[0053] The required number of consecutive backscattering channels, m=2, is determined, along with the expected scattering intensity of the scattered wave for each channel. The center frequency is determined to be 32 GHz, and the operating frequency band is determined to be 28~36 GHz. The angular range of backscattering is determined according to the target application scenario, and multiple channels are divided within the angular range. Each channel corresponds to backscattering with the same scattering intensity, which is used to realize multi-channel parallel scattering control. In this embodiment, two channels are divided in the angular range of backscattering: 37°~51° and -51°~-37°.

[0054] 2) Determine the compensated wave vector at the center frequency:

[0055] The compensation wave vector is determined based on the period p of the metasurface unit and the number N of metasurface units in a unit cell. : The range of the compensated wave vector satisfies: Where k0 is the free space wave vector, Let f be the center frequency of the electromagnetic wave; first, randomly set the period p of the metasurface unit and the number N of metasurface units in a unit cell. The initial selection range of the period p of the metasurface unit is λ0 / 6 ~ λ0 / 2, where λ0 is the free space wavelength corresponding to the center frequency. The initial selection range of the number N of metasurface units in a unit cell is an even number within 2 to 10; determine the compensation wave vector. If the wave vector compensation range is satisfied... If the period of the metasurface unit and the number of metasurface units in a unit cell are determined, then the period of the metasurface unit and the number of metasurface units in a unit cell are determined; otherwise, they are reset until the wave vector compensation range is met.

[0056] 3) Determine the angle of multi-channel backscattering:

[0057] Electromagnetic waves at any incident angle θ i When incident on an artificial two-dimensional structure, electromagnetic waves excite the structure to generate spatial harmonics of a specific order. Simultaneously, the artificial two-dimensional structure introduces a spatially varying phase response. By adjusting the transverse momentum of the scattered wave through the compensating wave vector of the artificial two-dimensional structure, transverse phase compensation is achieved for the electromagnetic wave, which is equivalent to reconstructing the electromagnetic wavefront. The incident wave and the scattered wave satisfy the wave vector conservation relationship.

[0058]

[0059] in, To compensate for the wave vector, l is the order of the spatial harmonics, c is the propagation speed of the electromagnetic wave in free space, f is the center frequency of the electromagnetic wave, p is the period of the metasurface unit, N is the number of metasurface units in a unit cell, N is an even number ≥ 2, and θ i Let θ be the angle of incidence of the electromagnetic wave. r The angle of backscattering;

[0060] When electromagnetic waves undergo backscattering, the incident wave and the scattered wave satisfy the conditions for backscattering to occur: That is, the incident wave and the scattered wave at the interface of the artificial two-dimensional structure must obey the generalized momentum conservation relation. Specifically, the x-direction momentum of the scattered wave is equal to the sum of the x-direction momentum of the incident wave and the compensation momentum provided by the artificial two-dimensional structure. When the system satisfies the backscattering condition, the compensation momentum provided by the artificial two-dimensional structure exactly cancels out and flips the tangential component of the incident wave, so that the scattering angle and the incident angle satisfy the condition. This allows the electromagnetic wave to return along its original path; the above relationship becomes:

[0061]

[0062] Based on the number of channels m and the compensation wave vector The angle of backscattering satisfy:

[0063]

[0064] The angle at the center frequency is ±42.5°, the angle at 28GHz is ±50.5°, and the angle at 36GHz is ±37°, thus achieving an angle coverage range of 37°~51° and -51°~-37°.

[0065] 4) Design artificial two-dimensional structures:

[0066] A high-frequency dielectric substrate is placed on the reflective layer, and a resonant structure layer composed of metasurface units arranged in a two-dimensional array is placed on the high-frequency dielectric substrate to form an artificial two-dimensional structure; such as Figure 4 As shown, the metasurface unit adopts an open resonant ring structure, consisting of a pair of symmetrical partially arc-shaped elements connected by a connecting rod. The period p of the metasurface unit is 1.73 mm, which can be adjusted by changing its outer diameter D. out Inner diameter D in and the geometric parameters of the opening angle β, D out <p, where the opening angle β is the angle between the openings of a pair of partial arcs, constructing the basic resonant ring structure; based on this, the rotation angle α is introduced as a key control variable, where the rotation angle α is the rotation angle of the connecting rod relative to the y-axis, where α takes 0° and 90° to correspond to the two types of phase responses, 0 and π respectively, thereby achieving phase binary locking; at the same time, by adjusting the rotation angle α within a certain range, the transpolarization reflection amplitude can be continuously varied over a wide frequency range; simulation results show that in the 28 GHz~39 GHz frequency band, by adjusting the rotation angle α, effective coverage of the transpolarization reflection amplitude in the range of 0 to 1 can be achieved; Figure 2(a), (b), and (c) are schematic diagrams of metasurface units with transpolarization reflection amplitudes of 0.5, 0.8, and 1, respectively, corresponding to rotation angles α of 16°, 61°, and 45°. Furthermore, when α takes a positive and negative symmetric value, a phase response gradient of approximately 180° can be introduced while maintaining a basically consistent amplitude, thereby achieving independent control of the transpolarization reflection amplitude and phase response at the physical level, i.e., decoupling design. The transpolarization reflection amplitude varies periodically with the rotation angle α, approximately satisfying the distribution characteristics of a sine function, reaching a peak value near α = ±45°, and reaching a minimum value near α = 0° and ±90°.

[0067] 5) Build the unit library:

[0068] Based on the structural design of metasurface units, a unit library containing various metasurface units is constructed. This library includes two types of metasurface units with different phase responses, 0 and π respectively. Each type of metasurface unit also includes various structural parameters corresponding to different transpolarization reflection amplitudes, which form multiple continuously adjustable states within the range of 0 to 1. A one-to-one correspondence is established between the rotation angle α of the metasurface unit and the transpolarization reflection amplitude (reaching a peak value near α=45° and a minimum value near α=0° and 90°). Simultaneously, phase response sets are constructed between different types of metasurface units through a fixed phase response gradient π. The transpolarization reflection amplitude of the metasurface unit is matched with the backscattering intensity distribution to establish a mapping relationship between "transpolarization reflection amplitude and phase response - structural parameters." Through this mapping relationship, based on the scattering intensity of the scattered wave set in step 1), the structural parameters and phase response of the required metasurface unit at each location are determined in reverse, thereby achieving coordinated control of the backscattering beam direction and energy distribution.

[0069] 6) Design the unit cell:

[0070] Along the horizontal direction (x-axis), the artificial two-dimensional structure consists of N=4 metasurface units arranged in a sequence according to a preset phase logic, forming a unit cell. Multiple identical unit cells are arranged in a two-dimensional array to form a resonant structure layer. The number of unit cells in the horizontal direction is determined by the horizontal length. In the vertical direction (y-axis), the number of metasurface units is a positive integer M. The value of M is determined based on the preset vertical width Wy of the artificial two-dimensional structure and the period p of the metasurface units, i.e., Wy = M × p. Each unit cell includes two types of metasurface units with different structures. The first two metasurface units have the same structure and a phase response of 0 to electromagnetic waves, while the latter two metasurface units have a phase response of π to electromagnetic waves. There is a phase response gradient of π between the two types of metasurface units. The polarization reflection amplitude of the metasurface units is determined based on the scattering intensity of the scattered wave determined in step 1). The structural parameters of the corresponding metasurface units are found in the unit library according to the mapping relationship in step 5). The phase response gradient of two adjacent unit cells along the horizontal direction to electromagnetic waves is 2π. The compensated wave vector is... The period p of the metasurface unit is twice the original. If the number of resonant units in the metasurface unit is too small, the equivalent compensation wave vector will be too large, making it difficult to meet the momentum matching condition for space wave excitation.

[0071] This invention effectively reduces the equivalent compensation wave vector by increasing the cell size within a single supercell (i.e., doubling the number of cells) while maintaining the same phase compensation amount as existing technologies. This design, by increasing phase sampling points in physical space, reduces the abrupt discretization of the phase response gradient, thus making it more conducive to inducing higher-order spatial harmonics and significantly improving the spatial radiation of electromagnetic waves.

[0072] Figure 5 The graphs show the response characteristics of the metasurface unit in the 28–36 GHz frequency band. (a) shows the variation of the transpolarization reflection amplitude with frequency under different structural parameters; (b) shows the variation of the phase response with frequency under the corresponding parameters; (c) and (d) show the mapping relationship between the transpolarization reflection amplitude and phase response with structural parameters in the 30 GHz and 32 GHz frequency bands, respectively. Figure 5 As can be seen, the red transpolarization reflection amplitude curve changes smoothly in the range of 0 to 1, while the blue phase response curve remains relatively stable in the control range. Furthermore, the positive and negative values ​​of α correspond to the state where the transpolarization phase response gradient is π, respectively, which verifies that the structure has good amplitude and phase decoupling control characteristics.

[0073] Figures 6-8 The radiation patterns for three different backscattering frequencies are shown at 30 GHz, 32 GHz, and 34 GHz, respectively. Figures 6-8Figures (a), (b), and (c) show the backscattering corresponding to three different arrays (with metasurface unit rotation angles of 45°, 61°, and 16°), with the intensity decreasing from strong to weak. While maintaining strict beam pointing consistency at all frequencies, the energy intensity of the scattering main lobe was significantly modulated in a dual-channel manner by adjusting the structural parameters of the metasurface unit. The results demonstrate that this artificial two-dimensional structure can independently and precisely control the intensity distribution of the scattered wave while maintaining a stable backscattering angle, verifying the effectiveness of the proposed amplitude-phase coordinated modulation method over a wide frequency band.

[0074] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A continuous beam backscattering modulator based on a passive artificial two-dimensional structure, characterized in that, The backscattering modulator includes a reflective layer, a high-frequency dielectric substrate, and a resonant structure layer. The high-frequency dielectric substrate is disposed on the reflective layer, and the resonant structure layer, composed of multiple metasurface units arranged in a two-dimensional array, is disposed on the high-frequency dielectric substrate, forming a passive artificial two-dimensional structure as a continuous beam backscattering modulator. Electromagnetic waves are incident on the artificial two-dimensional structure at any incident angle, generating scattered waves. The electromagnetic waves excite the artificial two-dimensional structure to generate spatial harmonics of a specific order. Simultaneously, the artificial two-dimensional structure introduces a spatially varying phase response. Lateral phase compensation is performed on the electromagnetic waves through the compensation wave vector of the artificial two-dimensional structure. Under the combined action of the spatial harmonics and the compensation wave vector, the incident wave and the scattered wave satisfy the wave vector conservation relationship, causing the scattered wave to propagate in the reverse direction along the incident direction, thereby achieving backscattering. Furthermore, the scattered wave intensity is adjustable. The spatial harmonics generated by the electromagnetic waves have multiple orders, and different orders of spatial harmonics correspond to different angles, allowing multiple specific orders of spatial harmonics to excite backscattering. Under the action of the spatial harmonics, multiple different backscattering angles are achieved, realizing multi-channel backscattering.

2. The backscattering modulator according to claim 1, characterized in that, Each N metasurface units constitute a unit cell. The resonant structure layer is composed of multiple identical unit cells arranged in a two-dimensional array. Each unit cell includes two types of metasurface units with different phase responses. The first N / 2 metasurface units have the same phase response to electromagnetic waves, and the last N / 2 metasurface units have the same phase response to electromagnetic waves. There is a phase response gradient of π between the two types of metasurface units. The period of the metasurface units is p. The phase change of two adjacent unit cells along the transverse direction to electromagnetic waves is 2π, and N is an even number ≥ 2.

3. The backscattering modulator according to claim 2, characterized in that, By changing the structural parameters of the metasurface unit, different phase responses of the incident electromagnetic wave are induced, and the change in the polarization reflection amplitude of the electromagnetic wave is altered. The polarization reflection amplitude corresponds to the scattering intensity of the scattered wave.

4. The backscattering modulator according to claim 1, characterized in that, The reflective layer is made of a highly conductive metal material with a thickness of 10 μm to 70 μm; the high-frequency dielectric substrate has a thickness of 0.1 mm to 2.5 mm and a relative permittivity of 2.1 to 10.

5.

5. A design method for a continuous beam backscattering modulator based on a passive artificial two-dimensional structure according to any one of claims 1 to 4, characterized in that, The design method includes the following steps: 1) Determine the design objectives and frequency bands: Determine the number m of backscattering channels and the scattering intensity of the scattered wave in each channel, and determine the center frequency f and operating frequency band of the electromagnetic wave; 2) Determine the compensated wave vector at the center frequency: Based on the period p of the metasurface unit and the number N of metasurface units in a unit cell, where N is an even number ≥ 2, determine the compensation wave vector at the center frequency; and determine the range of the compensation wave vector based on the center frequency f of the electromagnetic wave and the number of channels m. 3) Determine the angle of multi-channel backscattering: Electromagnetic waves incident on an artificial two-dimensional structure are scattered to generate scattered waves, which in turn excite the artificial two-dimensional structure to generate spatial harmonics. At the same time, the artificial two-dimensional structure provides a compensating wave vector. Under the combined action of the spatial harmonics and the compensating wave vector, the incident wave and the scattered wave satisfy the wave vector conservation relationship. Combined with the backscattering conditions, the backscattering angle is determined. 4) Design artificial two-dimensional structures: A high-frequency dielectric substrate is disposed on the reflective layer, and a resonant structure layer is disposed on the high-frequency dielectric substrate. The resonant structure layer includes metasurface units arranged in a two-dimensional array to form an artificial two-dimensional structure. 5) Build the unit library: A unit library containing various metasurface units was constructed, and a mapping relationship between "transpolarization reflection amplitude and phase response - structural parameters" was established. 6) Setting the unit cell: Based on the mapping relationship in step 5), two types of metasurface units with a phase response gradient of π and a repolarization reflection amplitude that matches the scattering intensity are found from the unit library to form a unit cell arranged in the transverse direction; electromagnetic waves are incident at a set incident angle to the artificial two-dimensional structure to achieve multi-channel backscattering with adjustable scattering intensity.

6. The design method according to claim 5, characterized in that, In step 2), the compensation wave vector satisfy: The range of the compensated wave vector satisfies: Where k0 is the free space wave vector, f is the center frequency of the electromagnetic wave, and c is the propagation speed of the electromagnetic wave in free space.

7. The design method according to claim 6, characterized in that, In step 3), the electromagnetic wave is incident at an arbitrary angle θ. i When electromagnetic waves are incident on an artificial two-dimensional structure, they excite the structure to generate spatial harmonics. Simultaneously, the artificial two-dimensional structure introduces a spatially varying phase response. The electromagnetic waves undergo transverse phase compensation through the compensating wave vector of the artificial two-dimensional structure. The incident and scattered waves satisfy the wave vector conservation relationship. Where l is the order of the spatial harmonic, θ i Let θ be the angle of incidence of the electromagnetic wave. r The angle of backscattering; When electromagnetic waves undergo backscattering, the incident wave and the scattered wave satisfy the backscattering condition. The above relationship becomes: Based on the number of channels m and the compensation wave vector The angle of backscattering satisfy: in, Let be the angle of the l-th backscattering.

8. The design method according to claim 5, characterized in that, In step 4), the reflective layer is made of a highly conductive metal material with a thickness of 10 μm to 70 μm; the high-frequency dielectric substrate has a relative permittivity of 2.1 to 10.5 and a thickness of 0.1 mm to 2.5 mm.

9. The design method according to claim 5, characterized in that, In step 5), the unit library includes two types of metasurface units with different phase responses. The phase response of the unit of the two types of metasurfaces has a phase response gradient of π, which corresponds to different structural parameters. Each type of metasurface unit with phase response also includes a variety of different structural parameters, which correspond to different repolarization reflection amplitudes. The repolarization reflection amplitude corresponds to the scattering intensity of the scattered wave.

10. The design method according to claim 9, characterized in that, In step 6), every N metasurface units along the transverse direction constitute a unit cell, and multiple identical unit cells are arranged in a two-dimensional array. Each unit cell includes two types of metasurface units with different structures. The first N / 2 metasurface units have the same structure and have the same phase response to electromagnetic waves, while the last N / 2 metasurface units have the same structure. The phase response gradient of two adjacent unit cells along the transverse direction to electromagnetic waves is 2π. The repolarization reflection amplitude of the metasurface unit is determined according to the scattering intensity of the scattered wave determined in step 1).

Images