Multifunctional metasurface based on amplitude-phase decoupling modulation

Abstract

The invention discloses a multifunctional metasurface based on amplitude-phase decoupling modulation, and relates to the technical field of antennas. The multifunctional metasurface comprises 1 * 1 metasurface units, each metasurface unit comprises an upper portion, a metal gap layer and a lower portion, and 1 = 2, 3, 4. In the upper part, a rotatable metal circular ring is attached to the upper surface of the first dielectric substrate; four rectangular areas with the same length are arranged on the metal circular ring in the circumferential direction at equal intervals, and a rectangular metal patch is further arranged in the center of the metal circular ring. A rectangular metal patch is arranged between the first dielectric substrate and the second dielectric substrate; the metal gap layer is arranged below the second dielectric substrate, and a rectangular gap is formed in the center of the metal gap layer; in the lower part, a third dielectric substrate, a rectangular metal patch and a fourth dielectric substrate are arranged from top to bottom and are symmetrical with the upper part; wherein the rectangular metal patch is perpendicular to the rectangular gap in length. The multifunctional metasurface can support a plurality of radiation modes and a plurality of polarization modes, and has a high integration level.

Description

Technical Field

[0001] The present invention relates to the technical field of antennas, and particularly to a multifunctional metasurface based on amplitude-phase decoupling modulation. Background Art

[0002] With the in-depth research on metasurface theory and the requirements of modern communication systems for miniaturization, integration, and high speed of devices, electromagnetic devices with a wider range and capable of integrating multiple functions simultaneously have emerged. The multifunctional metasurface technology can greatly improve the transmission efficiency and transmission capacity of communication channels, providing more degrees of freedom for communication systems. Therefore, the research in this field has become a hot topic of concern for researchers. Although fruitful results have been achieved in the design of multifunctional metasurfaces based on phase modulation, amplitude, as an important degree of freedom, still has great potential in metasurface design. To achieve more complex functions and better results, it is often required that the amplitude and phase of the metasurface unit structure can be independently regulated simultaneously. For some complex or high-quality wavefront control, such as the manipulation of diffracted beams, the generation of high-quality holograms, and the synthesis of complex beams, the amplitude and phase (A-P) responses always need to be obtained independently and simultaneously. This amplitude-phase decoupling characteristic can be flexibly applied to multiple fields.

[0003] In 2020, a relevant journal introduced a method of using a multilayer metal cross patch and a slot to form a metasurface unit. By separately regulating the lengths of the patch and the corresponding slot, the co-polarization responses of x and y polarizations can be independently controlled simultaneously. Thus, it is proved that the unit can completely control the transmission response to linearly polarized wave incidence. However, this system can only achieve amplitude-phase decoupling independent regulation of linearly polarized incident waves in the half space, and has poor effect in terms of integration. In 2021, some scholars proposed to realize amplitude-phase decoupling modulation of circularly polarized incident waves by adjusting two orientation angles of superatoms. This design has a better effect through polarization multiplexing and amplitude-phase decoupling, and has a bifocal superlens with transverse and axial foci. That is, the unit can completely control the transmission response to circularly polarized wave incidence. However, this system can only achieve amplitude-phase decoupling regulation of circularly polarized incident waves in the half space, and has poor effect in terms of integration. In 2023, a relevant journal proposed a triple-band multi-channel metasurface. Using frequency multiplexing, it can simultaneously achieve on-demand independent amplitude-phase decoupling modulation of two transmissions and one reflection for circularly polarized incident waves at three different frequencies. This design achieves full-space radiation, but can only be realized for the case of circularly polarized wave incidence, and the unit structure is relatively complex, and the simulation design is difficult.

[0004] It can be seen that the current research on multifunctional amplitude-phase decoupling metasurfaces mostly focuses on the basis of a single polarization mode or a single radiation direction, and there are technical problems such as single radiation mode, single polarization mode, and low integration, which have certain limitations. Summary of the Invention

[0005] To solve the above technical problems existing in the prior art, the present invention provides a multifunctional metasurface based on amplitude-phase decoupling modulation.

[0006] The specific technical solution of the above multifunctional metasurface is as follows: It includes l × l metasurface units, l = 2, 3, 4...; The metasurface unit includes: A first metal ring is attached to the upper surface of the first dielectric substrate; Four equal-length rectangular regions are circumferentially and equally spaced on the first metal ring. The widths of the non-adjacent rectangular regions are equal, forming a first rectangular pair and a second rectangular pair; A rectangular metal patch is also provided at the center of the first metal ring; A rectangular metal patch is provided between the first dielectric substrate and the second dielectric substrate; A metal slit layer is provided between the second dielectric substrate and the third dielectric substrate, and a rectangular slit is provided at the center; the long side of the rectangular slit is perpendicular to the long side of the rectangular metal patch; A rectangular metal patch is provided between the third dielectric substrate and the fourth dielectric substrate; A second metal ring with the same width as the first metal ring is attached to the lower surface of the fourth dielectric substrate; Four equal-length rectangular regions are circumferentially and equally spaced on the second metal ring. The widths of the non-adjacent rectangular regions are equal, forming a third rectangular pair and a fourth rectangular pair; Among different metasurface units: The included angle between the long side of the rectangular metal patch and the diameter where the first rectangular pair is located is different; the included angle between the long side of the rectangular metal patch and the diameter where the third rectangular pair is located is different; The widths of the rectangular regions in the first rectangular pair and the third rectangular pair are both equal to the width of the first metal ring; The widths of the rectangular regions in the second rectangular pair are not equal and are greater than or equal to the width of the first metal ring; The widths of the rectangular regions in the fourth rectangular pair are not equal and are greater than or equal to the width of the first metal ring.

[0007] In the technical solution provided by the present invention, by adjusting the rotation angles of the first metal ring and the second metal ring in different metasurface units, and the widths of the rectangular regions in the second rectangular pair and the fourth rectangular pair, a full-phase and full-amplitude reflection response to the front right-handed circularly polarized incident wave and the back right-handed circularly polarized incident wave can be achieved, such as the reflection reconstruction of a preset pattern; further, by adjusting the lengths of the rectangular metal patches and the metal slot layer in different metasurface units, a full-phase and full-amplitude transmission response to the x-polarized incident wave can be achieved, and the function of a transverse bifocal metalens can be further realized. In addition, by adopting a stacked structure and designing a slotted intermediate layer, it can ensure that the low-frequency circularly polarized wave is directly reflected, the high-frequency linearly polarized wave passes through the slot, and both the linearly polarized wave and the circularly polarized wave can achieve amplitude-phase decoupled modulation, and reduce the mutual influence between multiple functions of the linearly polarized and circularly polarized incident waves, transmission and reflection, significantly improving the integration of the metasurface.

[0008] In short, the technical solution provided by the present invention overcomes the technical problems of the prior art such as single radiation mode, polarization mode, and low integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a schematic structural diagram of a metasurface unit in an embodiment of the present invention.

[0010] Figure 2 It is a schematic layout diagram of the metal rings and rectangular metal patches on the upper surface of the top dielectric substrate of the metasurface unit in an embodiment of the present invention.

[0011] Figure 3 It is a schematic structural diagram of the metal slot layer of the metasurface unit in an embodiment of the present invention.

[0012] Figure 4 It is a schematic layout diagram of the top dielectric substrate when the metasurface units form an array in an embodiment of the present invention.

[0013] Figure 5 It is a schematic layout diagram of the second dielectric substrate when the metasurface units form an array in an embodiment of the present invention.

[0014] Figure 6 It is a schematic layout diagram of the metal slot layer when the metasurface units form an array in an embodiment of the present invention.

[0015] Figure 7 It is a diagram showing the transmission response relationship of the metasurface unit to the x-polarized incident wave in an embodiment of the present invention; among them, (a) is a diagram showing the relationship of the amplitude varying with a 、 Ls varying, and (b) is a diagram showing the relationship of the phase varying with a 、 Ls varying.

[0016] Figure 8The graph showing the relationship between the amplitude of the reflection response of the metasurface unit to the right - hand circularly polarized incident wave and rx , β in an embodiment of the present invention.

[0017] Figure 9 The graph showing the relationship between the phase of the reflection response of the metasurface unit to the right - hand circularly polarized incident wave and rx , β in an embodiment of the present invention.

[0018] Figure 10 The amplitude and phase distribution of each metasurface unit in the corresponding array in an embodiment of the present invention, where (a) is the amplitude distribution and (b) is the phase distribution.

[0019] Figure 11 The x polarized electric field intensity images under different parameters in an embodiment of the present invention, where (a) is the xy plane, focal length z =-150mm, frequency f =14GHz x polarized electric field intensity image, and (b) is the xz plane, at the y direction, taking the center point of the y axis of the metasurface ( y =-5.4mm), frequency f =14GHz x polarized electric field intensity image.

[0020] Figure 12 In an embodiment of the present invention, on the xy plane, taking y =0 (the ordinate of the two foci), a 1 - D curve graph of the relationship between the x axis and the electric field intensity is made.

[0021] Figure 13 The experimental image of the letter "B" with 36×36 pixels in an embodiment of the present invention, where (a) is the grayscale image, (b) is the schematic diagram of the amplitude distribution of each metasurface unit obtained by theoretical calculation, and (c) is the schematic diagram of the phase distribution of each metasurface unit obtained by theoretical calculation.

[0022] Figure 14 The schematic diagram of the full - wave simulation result of the metasurface corresponding to the letter "B" with 36×36 pixels for the backward incident RCP plane wave in an embodiment of the present invention; where (a) is the xy plane z =-140mm RCP wave electric field intensity, and (b) is the xy plane z=-150 mm RCP (Right - hand Circularly Polarized) wave electric field intensity, (c) is xy plane z =-160 mm RCP wave electric field intensity.

[0023] Figure 15 This is the experimental image of the letter "F" with 36×36 pixels in an embodiment of the present invention. Among them, (a) is the grayscale image, (b) is the schematic diagram of the amplitude distribution of each metasurface unit obtained by theoretical calculation, and (c) is the schematic diagram of the phase distribution of each metasurface unit obtained by theoretical calculation.

[0024] Figure 16 This is the schematic diagram of the full - wave simulation result of the metasurface corresponding to the letter "F" with 36×36 pixels in an embodiment of the present invention for the forward - incident RCP plane wave; among them, (a) is xy plane z =-140 mm RCP wave electric field intensity, (b) is xy plane z =-150 mm RCP wave electric field intensity, (c) is xy plane z =-160 mm RCP wave electric field intensity.

[0025] The meanings of each label in the figure are as follows: the first metal ring - 1; the first dielectric substrate - 2; the second dielectric substrate - 3; the metal slit layer - 4; the third dielectric substrate - 5; the fourth dielectric substrate - 6; the second metal ring - 7; the rectangular metal patch - 8. Detailed implementation mode

[0026] Hereinafter, the technical solutions provided by the present invention will be further elaborated in detail in combination with embodiments and drawings.

[0027] Embodiment 1: This embodiment involves the following terms: (1) Amplitude: The amplitude represents the size or intensity of a signal, usually expressed in decibels (dB) or linear values (absolute values). The amplitude of the reflection coefficient S11 represents the voltage reflection coefficient of the port. If the amplitude is - 20 dB, it corresponds to a linear value of 0.1, and the power reflection ratio is 0.01. The smaller the amplitude and the closer it is to negative infinity dB, the weaker the reflection. The amplitude of the transmission coefficient S21 represents the transmission efficiency of the signal from port 1 to port 2. The larger the amplitude and the closer it is to 0 dB, the higher the transmission efficiency.

[0028] (2) Phase: Phase represents the relative delay of a signal in time or space, measured in degrees (°) or radians (rad). The phase difference reflects the difference in the signal propagation path or the nonlinear phase response of a device. The phase of the reflection coefficient S11 represents the phase shift of the reflected signal. The phase of the transmission coefficient S21 represents the phase delay of the transmitted signal. The amplitude and phase together constitute the complex S-parameters.

[0029] (3) Amplitude-phase decoupling: Amplitude-phase decoupling is a key technology in the design of metasurfaces. It means that when designing metasurface units, the amplitude and phase of electromagnetic waves can be independently controlled by adjusting the geometric parameters or material properties of the units. This ability of independent control greatly improves the design flexibility and functional diversity of metasurfaces, making them perform better in applications such as wavefront control, superlenses, and holographic imaging.

[0030] (4) Multifunctional metasurface: It refers to a metasurface material that can simultaneously regulate multiple electromagnetic wave characteristics (such as reflection, transmission, polarization, phase, amplitude, etc.). Through carefully designed sub-wavelength structural units, it can achieve multiple controls of electromagnetic waves, with high flexibility and diverse functions. Compared with traditional single-functional metasurfaces, multifunctional electromagnetic metasurfaces can achieve different types of electromagnetic wave regulation on the same platform, thus meeting more complex application requirements.

[0031] (5) Linearly polarized wave: A linearly polarized wave refers to an electromagnetic wave whose electric field vector remains unchanged along a specific direction during propagation, showing a linear polarization state. A linearly polarized wave includes x polarized wave and y polarized wave. y The polarized wave in the present invention refers to an incident plane wave when the angle between the electric field and the y axis is 0°. x The polarized wave in the present invention refers to an incident plane wave when the angle between the electric field and the y axis is 90°.

[0032] (6) Circularly polarized wave: A circularly polarized wave is a special polarization form of an electromagnetic wave. In this wave, the electric field vector rotates along a helical path at a constant speed over time. Circularly polarized waves are divided into left-handed circularly polarized waves and right-handed circularly polarized waves, and their difference lies in the direction of rotation of the electric field vector. Along the direction of wave propagation, the rotation direction of the electric field vector of a left-handed circularly polarized wave is counterclockwise, and the rotation direction of the electric field vector of a right-handed circularly polarized wave is clockwise.

[0033] (7) Holographic imaging: The basic principle of metasurface holographic imaging is to perform specific arrangements on the units with amplitude-phase control capabilities, enabling the metasurface to form a three-dimensional reconstruction of the target object in space for incident waves with different polarizations and frequencies, and reconstructing the preset holographic image. Metasurface holographic imaging can be used in fields such as 3D display, optical invisibility, and micro-optical devices.

[0034] (8) Multifocal lens: The basic principle of the metasurface multifocal lens is to perform specific arrangements on the units with amplitude-phase control capabilities, enabling the metasurface to simultaneously generate multiple focal points on the same plane for specific incident waves. Each unit can adjust the amplitude and phase of the electromagnetic wave according to the design requirements, changing the propagation direction of the electromagnetic wave. Through precise design of these units, the metasurface can simultaneously generate multiple focal points. The metasurface multifocal lens can be applied in fields such as multifocal imaging systems, optical microscopes, and optical communications.

[0035] Specifically, in this embodiment, a multifunctional amplitude-phase decoupled metasurface unit operating at two frequency points and simultaneously regulating x linearly polarized and circularly polarized incident waves is designed. Through theoretical calculations, different A-P combinations are assigned to each unit, and an array arrangement is carried out to design a 36×36 array. Full-wave simulation of this array is performed to obtain a three-functional metasurface covering the entire space. Among them x the linearly polarized incident wave will form transverse double focal points in the transmission direction, and the circularly polarized waves incident from the front and back will respectively reflect and reconstruct the preset image on the front and back. By separately changing the physical structures of the top and bottom rings of the metasurface unit, the circularly polarized waves incident from the front and back are regulated so that they respectively form holographic images in the reflection direction. By separately changing the lengths of the four layers of patches and the corresponding slits, the x linearly polarized wave incident from the front is regulated so that it forms double focal points in the transmission direction.

[0036] The amplitude-phase decoupled multifunctional metasurface unit adopts a multi-layer dielectric stacking structure, which consists of four dielectric substrates, four layers of patches, and one layer of metal slits. Each layer of metal structure is sandwiched between a layer of dielectric substrate. The role of the middle slit layer is to reflect the circularly polarized incident wave while regulating the linearly polarized incident wave, achieving full-space amplitude-phase decoupled independent regulation of the two polarization modes.

[0037] Specifically, the structure of the amplitude-phase decoupled multifunctional metasurface unit is as Figure 1As shown in the (exploded view of the metasurface unit), it includes the following components arranged from top to bottom: 4 dielectric substrates, including the first dielectric substrate 2, the second dielectric substrate 3, the third dielectric substrate 5, and the fourth dielectric substrate 6; four layers of rectangular metal patches 8, one layer of metal slit layer 4, the first metal ring 1 at the top layer, and the second metal ring 7 at the bottom layer. The first dielectric substrate 2 is located at the top layer, with a rectangular metal patch 8 and the first metal ring 1 above it; the second dielectric substrate 3 is located below the first dielectric substrate 2. A rectangular metal patch 8 is placed above the second dielectric substrate 3, and a metal slit layer 4 is below the second dielectric substrate 3. The third dielectric substrate 5 is located below the metal slit layer 4, and a rectangular metal patch 8 is below the third dielectric substrate 5; the fourth dielectric substrate 6 is located below the rectangular metal patch 8, and the second metal ring 7 and the rectangular metal patch 8 are placed below the fourth dielectric substrate 6 (the bottom surface of the unit structure). The overall metasurface unit uses an F4B board with a dielectric constant of 3.5. The metasurface period p = 10.8 mm, and the thickness h of the dielectric substrate is 1.5 mm.

[0038] The specific structure of the metasurface unit is as shown in Figure 2 and Figure 3 . The metasurface unit consists of four layers of metal patches 8, the first metal ring 1 at the top layer, the second metal ring 7 at the bottom layer, and the metal slit layer 4. By independently setting the lengths of the four layers of rectangular metal patches 8 in a and the length of the metal slit layer 4 in Ls , the amplitude and phase decoupling modulation of the transmitted x polarized wave is jointly completed. Among them, the four layers of rectangular metal patches 8 change synchronously. The width of the rectangular metal patch 8 b = 3 mm, and the length a varies from 2 mm to 5.8 mm. The slit width of the metal slit layer 4 ws = 0.5 mm, and the length Ls varies from 0.5 mm to 6 mm. By independently setting the rotation angles of the first metal ring 1 and the second metal ring 7 and their respective rx widths, reflections are formed with the metal layer of the metal slit layer 4, and the amplitude and phase decoupling modulation of the reflected right-handed circularly polarized wave is jointly completed. Among them, the rotation angles β 1 and β 2 of the first metal ring 1 and the second metal ring 7 can be independently set respectively, taking any value between 0 - 180°. The widths of the rings are all rw = 0.2 mm, the inner radii of the rings are all r = 4.3 mm, the widths of the y axes of the outer rectangles of the rings are all ry = 0.2 mm, and the widths w are all 1.6 mm. The x axis lengths rx 1 of the first metal ring 1 and the second metal ring 7 andrx 2 can be set independently, with a variation range of 0.2 mm - 1.1 mm. Fixed ry while changing rx It can regulate the amplitude of the incident right - hand circularly polarized wave, making it vary from 0 - 1; while changing the rotation angle between the first metal ring 1 and the second metal ring 7 can regulate the phase of the incident right - hand circularly polarized wave, making it cover a range of 0 - 360°.

[0039] According to the principle of different applications, calculate the required A - P combination for each unit, and thus determine the 36×36 metasurface array combination. The layout schematic diagram of the top - layer dielectric substrate when the metasurface units form an array is as Figure 4 shown. The bottom - layer 5 is the same as the first layer except for the different ring structures, and will not be shown separately. The layout schematic diagram of the second - layer dielectric substrate 3 when the metasurface units form an array is as Figure 5 shown. The layout schematic diagram of the metal slot layer 4 when the metasurface units form an array is as Figure 6 shown.

[0040] 1. Working principle of the amplitude - phase decoupled metasurface unit: Mainly apply the method of combining geometric phase and propagation phase to achieve amplitude - phase decoupled modulation of circularly polarized incident waves. Among them, the geometric phase and propagation phase control the phase response and amplitude response of circularly polarized incident waves respectively. The amplitude and phase of the co - polarization reflection coefficient and cross - polarization reflection coefficient of circularly polarized wave incidence can be written as: ; ; ; ; In the formula, the subscripts + and - represent the right - hand circularly polarized wave (RHCP) and left - hand circularly polarized wave (LHCP) respectively. r ++ is the amplitude of the co - polarization reflection coefficient of right - hand circularly polarized wave incidence, is x the phase of the direction, y the phase difference between the phase of the direction and the phase Φ y , represents the phase of the co - polarization and cross - polarization reflection coefficients, r -+ is the amplitude of the cross - polarization reflection coefficient of right - hand circularly polarized wave incidence.

[0041] It can be seen that the amplitudes of the co - polarization and cross - polarization reflection coefficients are only determined by the phase difference between y and Φ It is determined that the phase of the co-polarization reflection coefficient depends on the geometric phase (2 β ), and the propagation phase ( and Φ y ). The phase of the cross-polarization reflection coefficient is determined only by the propagation phase. In this embodiment, a right-handed circularly polarized wave is incident. Therefore, by adjusting the rotation angles of the first metal ring 1 and the second metal ring 7, the phase of the right-handed circularly polarized wave reflection coefficient can be changed; while fixing the width of the rectangular patch in the y direction ry , and adjusting the width of the rectangular patch in the x direction ( rx ), the phase difference and can be changed, thereby regulating the amplitude of the right-handed circularly polarized wave reflection coefficient.

[0042] In this embodiment, the amplitude and phase decoupling modulation of the x polarized incident wave is realized by four layers of synchronously changing metal rectangular patches and a rectangular groove in the middle layer. x The phase and amplitude distributions of the a polarized transmission response are respectively controlled by the length of the rectangular patch a and the length of the rectangular groove perpendicular to the length Ls . Although the amplitude and phase decoupling modulation relationship of the x polarized transmission response is complex and non-linear, by appropriately selecting the lengths of a and Ls, in principle, any A-P combination with an amplitude from 0-1 and a phase from 0-360° can be achieved.

[0043] 2. Arrangement principle of the metasurface array: (1) Multi-focus lenses are of crucial significance for energy harvesting and efficient wireless power transmission. To verify that the designed metasurface unit has the ability to perform amplitude and phase decoupling regulation on the x polarized incident wave, a transverse bifocal metalens is designed on the z = -150 mm, xy plane. The complex amplitude distribution required for the metasurface array can be expressed as: ; In the formula, x , y , z respectively represent the three axes of the three-dimensional coordinate system, A 1, A 2 are respectively the amplitudes of the two foci with focal lengths of f 1, f 2, ( x 1, y 1) and ( x 2, y2) The abscissas of the two foci λ 0 is the wavelength of the working frequency in free space. The amplitudes of both foci are set to 1, and the focal coordinates are respectively set to ( x 1, y 1) = (-75 mm, 0 mm), ( x 2, y 2) = (75 mm, 0 mm). Thus, according to the set specific focal amplitudes, focal lengths and coordinates, the amplitude-phase distribution at the corresponding positions on the metasurface unit can be calculated to form the required metasurface array.

[0044] (2) Holographic imaging also shows great application prospects in the fields of information encoding, near-field communication, data storage and security. To verify that the designed metasurface unit has the ability to decouple the amplitude-phase control for forward RCP and backward RCP incident waves, a metasurface array is designed to reconstruct the preset letters in the z = ±150 mm, xy plane reflection. The Rayleigh-Sommerfeld diffraction theory is used to analyze the A-P combination of the metasurface units required to reconstruct the target image. The A-P distribution of the metasurface unit can be expressed by the following formula: ; ; ; In the formula, represents the coordinates of the hologram plane, represents the coordinates of the imaging plane, and are respectively the electric field distributions of the hologram plane and the imaging plane, λ and k are respectively the working wavelength and the working wave number in free space, n is the serial number of the metasurface unit in the imaging plane, r 1 is the distance between the point on the hologram plane and the point on the imaging plane, S 0 is the imaging area; F is the focal length, that is, in the z axis direction, the distance between the imaging plane and the hologram plane. In this embodiment, F = ±150 mm; is the coordinate of the corresponding metasurface unit in the hologram plane y . The A-P distribution of the metasurface units on the imaging plane is calculated to form the required metasurface array.

[0045] 3. Simulation results and explanations: The metasurface unit forx The relationship between the amplitude of the transmission response of the polarized incident wave and a 、 Ls is shown in (a) of Figure 7 . The relationship between the phase of the transmission response of the metasurface unit to the x polarized incident wave and a 、 Ls is shown in (b) of Figure 7 . It can be seen that when the length of the rectangular metal patch a remains unchanged and the length of the slit in the metal slit layer 4 Ls varies from 0.5 mm to 5.5 mm, the amplitude can vary from 0 to 1; while when the length Ls remains unchanged and the length a varies from 2 mm to 5.5 mm, the phase covers a range of -180° - 180°.

[0046] The relationship between the amplitude of the reflection response of the metasurface unit to the right - hand circularly polarized incident wave and rx 、 β is shown in Figure 8 . The relationship between the phase of the reflection response of the metasurface unit to the right - hand circularly polarized incident wave and rx 、 β is shown in Figure 9 . It can be seen that when Figure 9 β remains unchanged and rx varies from 0.2 mm to 0.9 mm, the amplitude can vary from 0 to 1, while the phase change is small, within 60°. This phase change can be compensated by fine - tuning the rotation angle β . It can be seen from Figure 10 that when rx remains unchanged and β varies from 0 to 180°, the amplitude changes little, while the phase can cover a range of 0 - 360°. Among them, β includes the rotation angle β 1 of the first metal ring 1 and the rotation angle β 2 of the second metal ring 7, which can achieve the response to the right - hand circularly polarized incident wave when it enters from the top or bottom surface.

[0047] For the dual - focus point function of the transmission response of the x polarized incident wave, the complex - amplitude distribution of the metasurface array is calculated and sampled, and then the amplitude and phase of each unit are extracted. The A - P distribution of each metasurface unit in the 36×36 array obtained by theoretical calculation is shown in Figure 10 in (a) and (b).

[0048] The full - wave simulation results in the transmission direction when the metasurface array composed of metasurface units is irradiated by the x polarized wave.Figure 11 In (a), it is the xy plane, focal length z = -150 mm, frequency f = 14 GHz x polarized electric field intensity image. Figure 11 In (b), it is at xz plane, y direction, taking the y axis center point of the metasurface y = -5.4 mm), frequency f = 14 GHz x polarized electric field intensity image. Among them, Ex is x polarization in the xy plane electric field intensity, V / m (volts per meter) is the unit of electric field intensity. From Figure 11 in (a) and (b), clear double focal points can be clearly observed. Figure 12 It is at Figure 11 of (a) xy plane, taking y = 0 (ordinate of the two focal points), making a x axis and the 1D curve graph of the relationship between the electric field intensity. From Figure 12 it can be seen that the amplitudes of the two focal points are both close to 1, and the focal point coordinates are respectively ([[]] x 1, y 1) = (-70 mm, 0 mm), ([[]] x 2, y 2) = (81 mm, 0 mm), which is quite close to the initially set focal point coordinates. The full-wave simulation results of the bifocal metasurface are in good agreement with the theoretical results.

[0049] For the holographic imaging function of the reflection response of the RCP wave incident forward and backward, calculate and sample the complex amplitude distribution of the metasurface imaging plane, so as to extract the specific amplitude and phase distribution of each unit in the array. Figure 13 In (a), it is the grayscale image of the letter "B" with 36×36 pixels. When the RCP wave is incident backward, by manipulating the A-P distribution of the metasurface unit at a lower frequency f = 6 GHz, xy plane, z = -150 mm, reflecting Figure 13 the letter "B" shown in (a). Figure 13 In (b) and (c), it shows the A-P distribution of each metasurface unit in the 36×36 array obtained through theoretical calculation.

[0050] Figure 14 In (a), (b), and (c) are the full-wave simulation results of the metasurface array for the backward incident RCP plane wave. Specifically, they are respectivelyxy Plane, z = -140 mm, z = -150 mm, z The electric field intensity image of the RCP wave at = -160 mm. Among them, ELCP is the electric field intensity of the left-handed circularly polarized wave in the xy plane. It can be seen that obvious letters "B" are displayed at the positions of ±10 mm at the holographic imaging plane z = -150 mm, and the imaging effect is good.

[0051] Figure 15 In (a), it is the grayscale image of the letter "F" with 36×36 pixels. In the case of the incident forward RCP wave, by manipulating the A-P distribution of the metasurface units at a relatively low frequency f = 6 GHz, xy plane, z = 150 mm, the reflected Figure 15 letter "F" shown in (a) in. Figure 15 In (b) and (c) in, the amplitude and phase distributions of each metasurface unit in the array obtained by theoretical calculation are shown.

[0052] Figure 16 In (a), (b), and (c) in, they are the full-wave simulation results of the metasurface array for the forward-incident RCP plane wave. Specifically, they are xy plane, z = 140 mm, z = 150 mm, z The electric field intensity image of the RCP wave at = 160 mm. It can be seen that obvious letters "F" are displayed at the positions of ±10 mm at the holographic imaging plane z = 150 mm, and the imaging effect is good.

[0053] In this embodiment, a 36×36 metasurface array is constructed to obtain better focusing and imaging effects. The F4B with lower cost is selected as the plate material. The multi-layer dielectric substrates are fixed by insulated nylon screws in the PCB manufacturing process, which is easy to manufacture, convenient to install, and has a lower cost. It should be noted that the metasurface provided in this embodiment is a 36×36 array. In practical applications, the array size can be adjusted according to requirements.

[0054] As can be seen from the above embodiments, the technical solution provided by the present invention solves the problem that traditional multifunctional metasurfaces can only operate in the half-space. By adopting a stacked structure and slotting design in the middle layer, it ensures that the low-frequency circularly polarized waves are directly reflected, and the high-frequency linearly polarized waves pass through the slots. Both the linearly polarized waves and the circularly polarized waves can achieve amplitude-phase decoupled modulation. In addition, optimization has been made in terms of integration. By means of structural innovation and change of variable range, the mutual influence among multiple functions such as linearly polarized and circularly polarized incident waves, transmission and reflection is reduced, and the integration of the metasurface is improved. Further, a full-process methodology has been developed for utilizing amplitude-phase decoupled metasurface units. Starting from the actual functions, codes are written for A-P calculation according to different functions, then converted into the physical lengths of the units, and finally the units are transformed into complex arrays by using Matlab-Cst joint automatic modeling, and full-wave simulation analysis is carried out on the arrays.

[0055] In summary, the present invention designs an amplitude-phase decoupled metasurface unit, which can greatly improve the design flexibility and functional diversity of the metasurface. Existing metasurface electromagnetic wave modulation methods are mostly the PO (Phase-Only Modulation) method of only phase modulation, the AO (Amplitude-Only Modulation) method of only amplitude modulation, etc. Due to the omission of important information such as amplitude or phase, the PO and AO methods have high noise and low accuracy. The metasurface using amplitude-phase decoupled modulation can significantly improve the beam control efficiency, making it perform better in applications such as wavefront control, superlens, and holographic imaging. At the same time, based on the amplitude-phase decoupled modulation of the metasurface unit, various combinations and integrations are provided in terms of polarization mode, radiation direction, frequency band, etc., with higher integration.

[0056] It should be noted that the above embodiments present an implementation technique of a specific amplitude-phase decoupled multifunctional metasurface, but the actual technical solution is not limited thereto. For unit design, independent and non-interfering decoupled control of the transmitted linearly polarized waves can be achieved by introducing mutually orthogonal rectangular patches and mutually orthogonal rectangular slots. At the same time, by using the method of combining PG (Propagation phase) phase and PB (Pancharatnam-Berry) phase, an axisymmetric structure can be set to achieve amplitude-phase decoupled control of circularly polarized incident waves. It is also possible to change the resonant points, bandwidth and other indicators of the metasurface operation by changing the size variation range of structures such as patches, rings, slots and the number of stacked layers.

[0057] As can be seen from the above embodiments and the accompanying drawings, in the technical solution provided by the present invention, by adjusting the rotation angles of the first metal ring and the second metal ring in different metasurface units, and the widths of the rectangular regions in the second rectangular pair and the fourth rectangular pair, a full-phase and full-amplitude reflection response to the front right-handed circularly polarized incident wave and the rear right-handed circularly polarized incident wave can be achieved, such as the reflection reconstruction of a preset pattern; further, by adjusting the lengths of the rectangular metal patches and the metal slot layer in different metasurface units, a full-phase and full-amplitude transmission response to the x polarized incident wave can be achieved, and the function of a transverse bifocal metalens can be further realized. In addition, by adopting a stacked structure and designing a slotted intermediate layer, it can ensure that the low-frequency circularly polarized wave is directly reflected, the high-frequency linearly polarized wave passes through the slot, and both the linearly polarized wave and the circularly polarized wave can achieve amplitude-phase decoupled modulation, and reduce the mutual influence between multiple functions of linearly polarized and circularly polarized incident waves, transmission and reflection, significantly improving the integration of the metasurface.

[0058] In short, the technical solution provided by the present invention overcomes the technical problems of the prior art, such as single radiation mode, single polarization mode, and low integration.

Claims

1. A multifunctional metasurface based on amplitude-phase decoupling modulation, characterized in that including l × l metasurface units arranged in an array, l ≥2; The metasurface unit includes: A first metal ring (1) is attached to the upper surface of a first dielectric substrate (2); Four equally long rectangular regions are circumferentially and equally spaced on the first metal ring (1), and the widths of non-adjacent rectangular regions are equal, forming a first rectangular pair and a second rectangular pair; A rectangular metal patch (8) is also provided at the center of the first metal ring (1); A rectangular metal patch (8) is provided between the first dielectric substrate (2) and the second dielectric substrate (3); A metal slot layer (4) is provided between the second dielectric substrate (3) and the third dielectric substrate (5), and a rectangular slot is provided at the center; the long side of the rectangular slot is perpendicular to the long side of the rectangular metal patch (8); A rectangular metal patch (8) is provided between the third dielectric substrate (5) and the fourth dielectric substrate (6); A second metal ring (7) with the same width as the first metal ring (1) is attached to the lower surface of the fourth dielectric substrate (6); Four equally long rectangular regions are circumferentially and equally spaced on the second metal ring (7), and the widths of non-adjacent rectangular regions are equal, forming a third rectangular pair and a fourth rectangular pair; In different metasurface units: The included angle between the long side of the rectangular metal patch (8) and the diameter where the first rectangular pair is located is different; the included angle between the long side of the rectangular metal patch (8) and the diameter where the third rectangular pair is located is different; The widths of the rectangular regions in the first rectangular pair and the third rectangular pair are both equal to the width of the first metal ring (1); The widths of the rectangular regions in the second rectangular pair are not equal, and are greater than or equal to the width of the first metal ring (1); The widths of the rectangular regions in the fourth rectangular pair are not equal, and are greater than or equal to the width of the first metal ring (1).

2. The multifunctional metasurface based on amplitude-phase decoupling modulation according to claim 1, characterized in that, In different metasurface units, the lengths of the rectangular metal patches (8) are not equal, and the lengths of the metal slot layers (4) are not equal.

3. The multifunctional metasurface based on amplitude-phase decoupling modulation according to claim 1, characterized in that It further includes: Taking the plane where the array is located as xy the plane, there is z direction, xy the A-P distribution of the metasurface units in the metasurface that reflects and reconstructs the preset pattern in the plane is as follows: ； ； ； In the formula, represents the coordinates of the hologram plane, represents the coordinates of the imaging plane, and are the electric field distributions of the hologram plane and the imaging plane respectively, i is the imaginary unit, r is the inner radius of the first metal ring, λ and k are the working wavelength and the working wave number in free space respectively, n is the serial number of the metasurface unit in the imaging plane, r 1 is the point on the hologram plane and the distance between the point S 0 is the imaging area, F is the distance between the imaging plane and the hologram plane, is the y coordinates of the corresponding metasurface unit in the hologram plane.

4. The multifunctional metasurface based on amplitude-phase decoupling modulation according to claim 2, wherein, It further includes: Taking the plane where the array is located as xy the plane, there is z a direction, xy the complex amplitude distribution in the metasurface of a transverse bifocal metalens in the plane , and the formula is as follows: ； Among them, x , y , z respectively represent the three axes of a three-dimensional coordinate system, A 1, A 2 are respectively the amplitudes of two foci with focal lengths of f 1, f 2, ([[]] x x 1, y 1) and ([[]] x x 2, y 2) are the lateral coordinates of the two foci, λ 0 is the wavelength of the operating frequency in free space.

5. The multifunctional metasurface based on amplitude-phase decoupling modulation according to claim 4, wherein The z towards, xy transverse bifocal metalens on a plane is specifically z =-150mm, xy transverse bifocal metalens on the surface, ( x 1, y 1)=(-75mm, 0mm), ( x 2, y 2)=(75mm, 0mm), and the amplitudes of both bifocal points are 1.

6. A multifunctional metasurface based on amplitude-phase decoupling modulation according to any one of claims 1 to 5, characterized in that In each metasurface unit, All dielectric substrates are square, with a side length of 10.8 mm and a thickness of 1.5 mm, and the material is F4B with a dielectric constant of 3.5; The metal slot layer (4) is square, with a side length of 10.8 mm; r = 4.3 mm, rw = 0.2 mm, w = 1.6 mm, 0.2 mm ≤ rx 1 ≤ 1.1 mm, 0.2 mm ≤ rx 2 ≤ 1.1 mm; Among them, r and rw are the inner radius and width of all metal rings respectively, ，w is the length of all rectangular areas, rx 1 is the width of the middle rectangular area of the upper second rectangle pair, rx 2 is the width of the middle rectangular area of the fourth rectangle pair; 0° ≤ β 1 ≤ 180°, 0° ≤ β 2 ≤ 180°; wherein, β 1 and β 2 are the rotation angles of the first metal ring (1) and the second metal ring (7), respectively; 2mm ≤ a ≤ 5.8mm, b = 3mm; wherein, a and b are the length and width of the rectangular metal patch (8) respectively; ws = 0.5 mm, 0.5 mm ≤ Ls ≤ 6 mm; wherein, ws and Ls are the width and length of the rectangular slot, respectively.

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