A single-layer coded metasurface unit for four-channel holographic imaging

Abstract

A single-layer coded metasurface unit for four-channel holographic imaging relates to the field of electromagnetic structure technology. The present invention is to solve the problems of high complexity of existing metasurfaces, waste of electromagnetic resources, and only being able to achieve dual functions, which is not conducive to the functional diversification development of electromagnetic equipment. The single-layer coded metasurface unit for four-channel holographic imaging described in the present invention includes a top layer, a dielectric layer, and a bottom layer stacked in sequence. The top layer is a rectangular metal sheet with a circular hole in the center, and two split ring resonators concentrically nested therein are arranged in the circular hole. The bottom layer includes a circular metal sheet and a "C"-shaped metal ring. The circular metal sheet is located in the "C"-shaped metal ring, and the two are concentrically arranged, and the center of the circular metal sheet in the bottom layer and the center of the circular hole in the top layer are opposite to each other. The present invention realizes electromagnetic reconstruction of four different images in the same coded metasurface, which is suitable for multi-channel information processing and multi-functional imaging systems.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic structures, and in particular relates to a coded metasurface. Background Art

[0002] Since the invention of holography, it has become the most promising technology for perfectly reproducing the three-dimensional image of an object with its excellent ability to record and reproduce target information. The emergence of metasurfaces provides a new medium for subwavelength-scale holographic imaging. Multi-channel metasurface holographic technology, which aims at miniaturization and high integration, has also received more and more attention and has become a hot research topic in metasurface holography. In recent years, many multifunctional metasurface holographic technologies have been proposed and have achieved great success. However, most metasurface holographic technologies only realize holographic imaging in reflection mode or transmission mode. For example: a dual-band 2-bit reflective metasurface hologram proposed in 2020 that can provide two different information channels, whose encoding unit includes two layers of rectangular metal resonators, two layers of dielectric substrates and a metal ground layer. The metasurface can simultaneously present two different images of "H" and "V" in the low-frequency and high-frequency working areas. However, the above scheme can only realize dual-channel holographic imaging in the reflection space, which causes a waste of electromagnetic wave resources in the transmission space. Therefore, in order to meet the growing demand for multifunctional and high-speed electromagnetic devices and improve the utilization rate of electromagnetic wave resources, it is necessary and meaningful to integrate the manipulation functions of transmitted and reflected electromagnetic waves into a single device to realize multifunctional metasurface holography in the whole space.

[0003] In 2021, a single-layer polarization-dependent transmission and reflection integrated metasurface was proposed, whose digital encoding unit consists of a cross-shaped dielectric substrate and a pair of metal patches printed on the dielectric substrate. The metasurface can obtain two independent focal points in the transmission and reflection regions respectively in two orthogonal linear polarization states.

[0004] Although multifunctional metasurface holography has made great achievements, there is still a lot of room for development in realizing multifunctional digital coding metasurface holography in the whole space. For example, most reports on full-space metasurface holography can only achieve dual functions, which is not conducive to the functional diversification of electromagnetic devices. Therefore, in order to reduce the complexity of equipment and avoid the waste of electromagnetic resources, it is of great significance to study a high-performance, single-layer, multifunctional (more than two channels) transmission-reflection integrated metasurface. Summary of the invention

[0005] The present invention aims to solve the problems of high complexity of existing metasurfaces, waste of electromagnetic resources, and only being able to achieve dual functions, which is not conducive to the functional diversification development of electromagnetic equipment. A single-layer coded metasurface unit for four-channel holographic imaging is now provided.

[0006] A single-layer coded metasurface unit for four-channel holographic imaging comprises a top layer, a dielectric layer 2 and a bottom layer which are stacked in sequence. The top layer is a rectangular metal sheet 1-1 with a circular hole in the center, in which two split ring resonators 1-2 are nested concentrically with the circular hole. The bottom layer comprises a circular metal sheet 3-1 and a "C"-shaped metal ring 3-2. The circular metal sheet 3-1 is located inside the "C"-shaped metal ring 3-2, and the two are concentrically arranged. The center of the circular metal sheet 3-1 in the bottom layer and the center of the circular hole in the top layer are opposite to each other.

[0007] Furthermore, the split ring resonator 1 - 2 is a circular ring-shaped metal sheet, and two mirror-symmetrical openings are provided on the circular ring-shaped metal sheet, and the central axes of the openings on the two split ring resonators 1 - 2 are perpendicular to each other.

[0008] Furthermore, the dielectric layer 2 is a square dielectric substrate with a side length of 12 mm, and the relative dielectric constant ε of the dielectric layer 2 is r =2.2, the tangent value of the loss angle δ is tanδ=0.001, and the thickness is h=2mm.

[0009] Furthermore, the top layer and the bottom layer are both copper sheets, the thickness of the copper sheet is 0.018 mm, the conductivity is 5.8×10 7 Sm -1 .

[0010] Furthermore, the radius of the circular hole in the center of the top layer is r1=5.7 mm, and the width of the circular ring metal sheet is w=0.5 mm.

[0011] Furthermore, the radius r4 of the circular metal sheet 3 - 1 is 5.1 mm, and the outer diameter r5 of the “C”-shaped metal ring 3 - 2 is 5.7 mm.

[0012] Furthermore, in the reflection mode, when the x-polarized electromagnetic wave vertically irradiates the single-layer coded metasurface unit and the radius r2 of the split ring resonator 1-2 located in the outer circle changes, the reflection amplitude of the single-layer coded metasurface unit at the frequency of 13 GHz is 0.9 and the reflection phase difference is 180°, realizing the reconstruction of a "T"-shaped holographic image with 1-bit phase encoding.

[0013] Furthermore, in the reflection mode, when the y-polarized electromagnetic wave vertically irradiates the single-layer coded metasurface unit and the radius r3 of the split ring resonator 1-2 located in the inner circle changes, the reflection amplitude of the single-layer coded metasurface unit at the frequency of 13 GHz is 0.9 and the reflection phase difference is 300°, realizing single focus reconstruction of 2-bit phase coding.

[0014] Furthermore, in the transmission mode, when the excitation wave of the single-layer coded metasurface unit is a left-handed circularly polarized electromagnetic wave, by adjusting the rotation angle θ1 of the "C"-shaped metal ring 3-2, the transmission amplitude of the single-layer coded metasurface unit is 0.45 and the transmission phase difference is 250° at a frequency of 7.5 GHz, realizing four-focus reconstruction of 2-bit transmission phase coding.

[0015] Furthermore, in the transmission mode, when the excitation wave is a left-hand circularly polarized electromagnetic wave, by adjusting the rotation angle θ of the split ring resonator 1-2, the transmission amplitude of the single-layer coded metasurface unit at a frequency of 10 GHz is 0.4 and the transmission phase difference is 360°, thereby realizing dual-focus reconstruction of 3-bit transmission phase coding.

[0016] The present invention provides a single-layer coded metasurface unit for four-channel holographic imaging, which is composed of two metal layers, and the metal layers are printed on the upper and lower sides of a single dielectric substrate. According to the propagation phase principle, by changing the structural parameters of the top metal, the linear polarized wave can be independently controlled in the reflection mode; by rotating different metal structures on both sides of the dielectric substrate, the circular polarized wave can be independently controlled in the transmission mode. Four different imaging functions of "single focus", "quadruple focus", "dual focus" and "T" are respectively realized at different frequencies, and the polarization state of the electromagnetic wave is controlled to operate in the transmission mode or the reflection mode. The present invention realizes electromagnetic reconstruction of four different images in the same coded metasurface, has advantages in polarization utilization and space resource utilization, and breaks through the technical bottleneck that the full-space metasurface is realized by a multi-layer dielectric cascade structure, which has large volume, high cost, difficult processing, and is not conducive to the integration of electromagnetic devices and systems. It is suitable for multi-channel information processing and multi-functional imaging systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the three-dimensional structure of a single-layer coding metasurface unit;

[0018] Figure 2 Schematic diagram of the top-level structure of a single-layer coding metasurface unit;

[0019] Figure 3 Schematic diagram of the underlying structure of a single-layer coding metasurface unit;

[0020] Figure 4 and Figure 5 They are respectively the reflection amplitude and reflection phase curves of a single-layer coding metasurface unit when r2 changes;

[0021] Figure 6 and Figure 7 They are respectively the reflection amplitude and reflection phase curves of a single-layer coding metasurface unit when r3 changes;

[0022] Figure 8 and Fig. 9 They are the transmission amplitude and transmission phase curves of a single-layer coding metasurface unit when θ1 changes;

[0023] Fig.10 and Fig.11 They are the transmission amplitude and transmission phase curves of a single-layer coding metasurface unit when θ changes;

[0024] Fig.12 and Fig.13 The holographic image simulation diagram of a single-layer coded metasurface unit at 13GHz when excited by x-polarized waves and y-polarized waves respectively;

[0025] Fig.14 and Fig.15 These are the holographic image simulation diagrams of a single-layer coded metasurface unit at 10 GHz and 7.5 GHz when excited by left-hand circularly polarized waves. DETAILED DESCRIPTION

[0026] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0027] Specific implementation method 1: refer to Figure 1 , 2 3 specifically illustrate this embodiment. This embodiment describes a single-layer coded metasurface unit for four-channel holographic imaging, comprising a top layer, a dielectric layer 2 and a bottom layer stacked in sequence.

[0028] The top layer is a rectangular metal sheet 1-1 with a circular hole in the center, and two split ring resonators 1-2 are concentrically nested in the circular hole. Specifically, the split ring resonator 1-2 is a circular ring-shaped metal sheet, and the circular ring-shaped metal sheet is provided with two mirror-symmetrical openings, and the central axes of the openings on the two split ring resonators 1-2 are perpendicular to each other. The relative positions of the two split ring resonators 1-2 remain unchanged, and when working, the two split ring resonators 1-2 rotate as a whole. The initial state of the position of the two split ring resonators 1-2 is as follows Figure 2 As shown, the opening center axes of the two split ring resonators 1-2 coincide with the two center lines of the rectangular metal sheet 1-1 respectively, and they are rotated counterclockwise with this as the starting state, and the rotation angle is represented by θ.

[0029] The bottom layer includes a circular metal sheet 3-1 and a "C"-shaped metal ring 3-2, wherein the circular metal sheet 3-1 is located inside the "C"-shaped metal ring 3-2 and the two are arranged concentrically. The center of the circular metal sheet 3-1 in the bottom layer and the center of the circular hole in the top layer face each other.

[0030] The dielectric layer 2 is a square dielectric substrate with a side length of 12 mm. The relative dielectric constant ε of the dielectric layer 2 is r =2.2, the tangent value of the loss angle δ is tanδ=0.001, and the thickness is h=2mm.

[0031] In practical application, the top and bottom layers of this embodiment are both copper sheets with a thickness of 0.018 mm and a conductivity of 5.8×10 7 Sm -1 The radius of the circular hole in the center of the top layer is r1 = 5.7 mm, and the width of the circular metal sheet is w = 0.5 mm. The radius of the circular metal sheet 3-1 is r4 = 5.1 mm, and the outer diameter of the "C"-shaped metal ring 3-2 is r5 = 5.7 mm.

[0032] Specific implementation method 2: refer to Figures 4 to 11 This embodiment is specifically described, and this embodiment further describes a single-layer coded metasurface unit for four-channel holographic imaging described in Specific Embodiment 1. In this embodiment, the working modes of the single-layer coded metasurface unit for four-channel holographic imaging include a reflection mode and a transmission mode.

[0033] When the single-layer coding metasurface unit is in the reflection mode, when the x-polarized electromagnetic wave vertically irradiates the single-layer coding metasurface unit and the radius r2 of the split ring resonator 1-2 located in the outer circle changes, the amplitude and phase curves of the single-layer coding metasurface unit are as follows: Figure 4 and 5 As shown. It can be seen that the reflection amplitude of the single-layer coded metasurface unit at a frequency of 13GHz is 0.9, and the reflection phase difference is 180°, realizing the reconstruction of a "T"-shaped holographic image with 1-bit phase encoding. Specifically, when r2=3.3mm, the single-layer coded metasurface unit is encoded as the "0" state; when r2=3.6mm, the single-layer coded metasurface unit is encoded as the "1" state.

[0034] When the single-layer coding metasurface unit is in reflection mode, the amplitude and phase curves of the single-layer coding metasurface unit are as follows: Figure 6 and 7As shown. The reflection amplitude of the single-layer coded metasurface unit at a frequency of 13 GHz is 0.9, and the reflection phase difference is 300°, realizing single-focus reconstruction of 2-bit phase encoding. Specifically, when r3=4.4 mm, the reflection amplitude of the single-layer coded metasurface unit is 1, the phase is -400°, and the single-layer coded metasurface unit is encoded as the "00" state; when r3=3.4 mm, the reflection amplitude of the single-layer coded metasurface unit is 0.9, the phase is -483°, and the single-layer coded metasurface unit is encoded as the "01" state; when r3=3.6 mm, the reflection amplitude of the single-layer coded metasurface unit is 1, the phase is -605.7°, and the single-layer coded metasurface unit is encoded as the "10" state; when r3=4 mm, the reflection amplitude of the single-layer coded metasurface unit is 1, the phase is -700°, and the single-layer coded metasurface unit is encoded as the "11" state.

[0035] For the transmission mode, based on the geometric phase principle, when the rotation angle (θ and θ1) of the modulation unit structure is changed, the encoding unit can realize arbitrary electromagnetic wavefront control in the transmission space. The details are as follows:

[0036] When the excitation wave of a single-layer coded metasurface unit is a left-hand circularly polarized electromagnetic wave in transmission mode, Figure 8 and Fig. 9 As shown, by adjusting the rotation angle θ1 of the "C"-shaped metal ring 3-2, the transmission amplitude of the single-layer coded metasurface unit at a frequency of 7.5GHz is 0.45, and the transmission phase difference is 250°, realizing the four-focus reconstruction of 2-bit transmission phase coding. Specifically, when θ1=0°, the transmission phase of the single-layer coded metasurface unit is -251°, and the single-layer coded metasurface unit is encoded as the "01" state; when θ1=36°, the transmission phase of the single-layer coded metasurface unit is -170°, and the single-layer coded metasurface unit is encoded as the "00" state; when θ1=96°, the transmission phase of the single-layer coded metasurface unit is -420°, and the single-layer coded metasurface unit is encoded as the "11" state; when θ1=132°, the transmission phase of the single-layer coded metasurface unit is -342°, and the single-layer coded metasurface unit is encoded as the "10" state.

[0037] When the excitation wave of a single-layer coded metasurface unit is a left-hand circularly polarized electromagnetic wave in transmission mode, Fig.10 and Fig.11As shown, by adjusting the rotation angle θ of the split ring resonator 1-2, the single-layer coded metasurface unit can achieve a transmission amplitude of 0.4 and a transmission phase difference of 360° at a frequency of 10 GHz, realizing dual-focus reconstruction of 3-bit transmission phase coding. Specifically, when θ=168°, the single-layer coded hypersurface unit is encoded as the "110" state; when θ=144°, the single-layer coded hypersurface unit is encoded as the "111" state; when θ=132°, the single-layer coded hypersurface unit is encoded as the "000" state; when θ=108°, the single-layer coded hypersurface unit is encoded as the "001" state; when θ=84°, the single-layer coded hypersurface unit is encoded as the "010" state; when θ=60°, the single-layer coded hypersurface unit is encoded as the "011" state; when θ=36°, the single-layer coded hypersurface unit is encoded as the "100" state; when θ=12°, the single-layer coded hypersurface unit is encoded as the "101" state.

[0038] In summary of the above specific embodiments 1 and 2, the single-layer coded metasurface unit for four-channel holographic imaging described in the present invention utilizes a metasurface structure of two double-split ring metal resonators surrounded by copper. Based on the propagation phase principle and the anisotropic characteristics of the metasurface structure, when excited by x- and y-polarized electromagnetic waves, the metasurface realizes a holographic image "T" based on 1-bit phase coding and a "single focus" based on 2-bit phase coding at a frequency of 13GHz in the reflection working mode. Using a metasurface structure combining double-split ring metal resonators, circular patches and C-shaped metal structures, based on the geometric phase principle and the anisotropic characteristics of the metasurface structure, when excited by left-handed circularly polarized waves, the metasurface realizes a "dual focus" based on 3-bit phase coding at a frequency of 10GHz and a "quadruple focus" based on 2-bit phase coding at 7.5GHz in the transmission working mode.

[0039] Specific implementation method three: refer to Figures 12 to 15 Specifically describing this embodiment, this embodiment is a coded metasurface containing a single-layer coded metasurface unit for four-channel holographic imaging described in Specific Embodiment 1. In this embodiment, one single-layer coded metasurface unit is a period, and multiple single-layer coded metasurface units are closely arranged in a periodic array.

[0040] This embodiment effectively integrates the above-mentioned single-layer coded metasurface units together, and can independently control linear polarization waves in reflection mode and circular polarization waves in transmission mode. When the x-polarization wave is excited, by adjusting the radius r2 of the split ring resonator 1-2 located in the outer circle, the coded metasurface can achieve electromagnetic imaging at a frequency of 13 GHz in the reflection working mode. The simulation results are shown in the attached figure. Fig.12As shown in the figure, it can be seen that the two letters "T" are clearly reconstructed in the near field area. When the y-polarized wave is excited, by adjusting the radius r3 of the split ring resonator 1-2 located in the inner circle, the coding metasurface can achieve a "single focus" at 13GHz in the reflection working mode. The simulation results are shown in the attached Fig.13 When the left-hand circularly polarized wave is excited, by adjusting the rotation angle θ of the split ring resonator 1-2, the coding metasurface can achieve "dual focus" at a transmission working mode of 10 GHz. The simulation results are shown in the attached figure. Fig.14 When the rotation angle θ1 of the “C”-shaped metal ring 3-2 is adjusted, the coding metasurface can achieve “quadruple focus” at a frequency of 7.5 GHz in the transmission working mode. The simulation results are shown in the attached Fig.15 shown.

[0041] The coding metasurface proposed in this embodiment contains a single-layer coding metasurface unit for four-channel holographic imaging, and its top and bottom are double split ring resonator structures and circular and C-shaped metal ground plates using the transmission phase principle and geometric phase principle, respectively. By effectively integrating the single-layer coding metasurface units together, a new single-layer full-space coding metasurface is realized. This embodiment utilizes the polarization and working mode (transmission mode / reflection mode) degrees of freedom, and combines the transmission phase and the geometric phase to realize independent control of the phase of the electromagnetic wave in the whole space, and the four working modes do not interfere with each other, and have good isolation.

[0042] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A single-layer coded metasurface unit for four-channel holographic imaging, comprising a top layer, a dielectric layer (2) and a bottom layer stacked in sequence, characterized in that: The top layer is a rectangular metal sheet (1-1) with a circular hole in the center, and two split ring resonators (1-2) are arranged in the circular hole and are nested concentrically therewith. The bottom layer comprises a circular metal sheet (3-1) and a "C"-shaped metal ring (3-2), wherein the circular metal sheet (3-1) is located inside the "C"-shaped metal ring (3-2), and the two are arranged concentrically. The center of the circular metal sheet (3-1) in the bottom layer and the center of the circular hole in the top layer are opposite to each other; When the single-layer coding metasurface unit is in the reflection mode, when the x-polarized electromagnetic wave vertically irradiates the single-layer coding metasurface unit and the radius r2 of the split ring resonator (1-2) located in the outer circle changes, the reflection amplitude of the single-layer coding metasurface unit at the frequency of 13GHz is 0.9 and the reflection phase difference is 180°, realizing the reconstruction of the "T"-shaped holographic image with 1-bit phase coding; When the single-layer coding metasurface unit is in the reflection mode, when the y-polarized electromagnetic wave vertically irradiates the single-layer coding metasurface unit and the radius r3 of the split ring resonator (1-2) located in the inner circle changes, the reflection amplitude of the single-layer coding metasurface unit at the frequency of 13GHz is 0.9 and the reflection phase difference is 300°, realizing the single focus reconstruction of 2-bit phase coding; When the excitation wave of the single-layer coding metasurface unit is a left-hand circularly polarized electromagnetic wave in the transmission mode, by adjusting the rotation angle θ1 of the "C"-shaped metal ring (3-2), the transmission amplitude of the single-layer coding metasurface unit is 0.45 and the transmission phase difference is 250° at a frequency of 7.5 GHz, thereby realizing four-focus reconstruction of 2-bit transmission phase coding; In the transmission mode, when the excitation wave is a left-hand circularly polarized electromagnetic wave, by adjusting the rotation angle θ of the split ring resonator (1-2), the transmission amplitude of the single-layer coded metasurface unit at a frequency of 10 GHz is 0.4 and the transmission phase difference is 360°, realizing dual-focus reconstruction of 3-bit transmission phase coding.

2. A single-layer coded metasurface unit for four-channel holographic imaging according to claim 1, characterized in that: The split ring resonator (1-2) is a circular ring-shaped metal sheet, on which two mirror-symmetrical openings are arranged, and the central axes of the openings on the two split ring resonators (1-2) are perpendicular to each other.

3. The single-layer coded metasurface unit for four-channel holographic imaging according to claim 2, characterized in that: The dielectric layer (2) is a square dielectric substrate with a side length of 12 mm. The relative dielectric constant ε of the dielectric layer (2) is r =2.2, the tangent value of the loss angle δ is tanδ=0.001, and the thickness is h=2mm.

4. The single-layer coded metasurface unit for four-channel holographic imaging according to claim 2, characterized in that: The top and bottom layers are copper sheets with a thickness of 0.018 mm and a conductivity of 5.8 × 10 7 Sm -1 .

5. The single-layer coded metasurface unit for four-channel holographic imaging according to claim 2, characterized in that: The radius of the circular hole at the center of the top layer is r1=5.7 mm, and the width of the circular metal sheet is w=0.5 mm.

6. A single-layer coded metasurface unit for four-channel holographic imaging according to claim 5, characterized in that: The radius r4 of the circular metal sheet (3-1) is 5.1 mm, and the outer diameter r5 of the "C"-shaped metal ring (3-2) is 5.7 mm.

Images