Single-layer full-space metasurface unit and coded metasurface based on 2-bit phase coding

Abstract

A single-layer full-space metasurface unit and a coded metasurface based on 2-bit phase encoding relate to the field of electromagnetic structure technology. The present invention is to solve the problem that the traditional coded metasurface can only realize half-space holographic imaging when performing holographic imaging, while the metasurface that can realize full-space holographic imaging has many layers and a large volume. The present invention includes a top layer, a dielectric layer and a bottom layer stacked in sequence, the top layer includes a "π"-shaped metal patch and a rectangular frame metal patch, and a gap is left in the middle of each line of the "π"-shaped metal patch. The bottom layer is a rectangular grounding metal sheet, and two right-angle gaps are opened on the bottom layer. The two right-angle gaps are axially symmetrically arranged with a diagonal line of the bottom layer as the symmetry axis, and the openings are opposite, and the corners of the two right-angle gaps are respectively opposite to the two opposite corners of the bottom layer. The present invention avoids the waste of electromagnetic resources and meets the needs of miniaturization and high integration of metasurface holographic imaging.

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] The first step of holographic technology is to use the principle of interference to record the light wave information of the object, and the second step is to use the principle of diffraction to reproduce the light wave information of the object. After the emergence of holographic technology, it quickly attracted the attention of researchers from various countries, and it has made great achievements in the fields of data storage, security and anti-counterfeiting. However, traditional holographic imaging equipment is bulky, heavy, and has a diffraction limit, which leads to problems such as low resolution and small viewing angle of holograms. These problems have greatly limited the development of holographic imaging technology. However, the emergence of metasurfaces provides a new method for realizing holographic imaging in the subwavelength scale.

[0003] Nowadays, metasurfaces are developing in the direction of multifunctionality and high integration, and holographic imaging technology that relies on metasurfaces is no exception. So far, most metasurface holographic imaging can only work in half space, that is, either in the transmission space or in the reflection space. For example, in 2020, a single-layer polarization multiplexing metasurface hologram was proposed, which realized the reconstruction of "square" and "diamond" electromagnetic images in the transmission space. However, this design only regulates the electromagnetic wavefront in the transmission space, and the reflection space is not used, which results in a waste of electromagnetic resources.

[0004] In order to improve the utilization rate of electromagnetic resources, the perspective of holographic imaging is gradually shifted from half-space to full-space, and a transmission-reflection integrated metasurface is proposed. This metasurface can realize independent modulation of reflected and transmitted electromagnetic waves in the whole space, but the metasurface is a double-layer dielectric structure, which leads to the disadvantages of large size and high cost, which does not conform to the development direction of miniaturization and integration of modern electronic systems. Therefore, it is necessary and meaningful to realize holographic imaging in the whole space based on a single-layer metasurface. Summary of the invention

[0005] The present invention aims to solve the problem that traditional coded metasurfaces can only achieve half-space holographic imaging when performing holographic imaging, while metasurfaces that can achieve full-space holographic imaging have many layers and are large in size. A single-layer full-space metasurface unit and a coded metasurface based on 2-bit phase encoding are provided, which can achieve reconstruction of electromagnetic images in full space.

[0006] A single-layer full-space metasurface unit based on 2-bit phase encoding includes a top layer 1, a dielectric layer 2 and a bottom layer 3 stacked in sequence. The top layer 1 includes a "π"-shaped metal patch and a rectangular frame metal patch. A gap is left in the middle of each line of the "π"-shaped metal patch. The bottom layer 3 is a rectangular grounding metal sheet. Two right-angle gaps are opened on the bottom layer 3. The two right-angle gaps are axially symmetrically arranged with a diagonal line of the bottom layer 3 as the symmetry axis, and the openings are opposite to each other. The corners of the two right-angle gaps are respectively opposite to the two opposite corners of the bottom layer 3.

[0007] Furthermore, the thickness of the dielectric layer 2 is h=2 mm, and the relative dielectric constant ε r =2.2, loss tangent tanδ=0.001.

[0008] Furthermore, the materials of the top layer 1 and the bottom layer 3 are both copper.

[0009] Furthermore, the thickness of the top layer 1 and the bottom layer 3 are both 0.018 mm.

[0010] Furthermore, the rectangular metal patch is a square with a side length P=10 mm, and the frame width of the rectangular metal patch is 0.3 mm.

[0011] Furthermore, the above-mentioned "π"-shaped metal patch includes a horizontal metal strip and two vertical metal strips, the two vertical metal strips are vertically connected to the horizontal metal strip, the horizontal metal strip is parallel to any side of the rectangular frame metal patch, and strip-shaped gaps are left in the middle seams of the horizontal metal strip and the vertical metal strips, and the gaps at the junction of the horizontal metal strip and the vertical metal strip are also connected to each other; the length of the horizontal metal strip is l = 4mm, the width of the gap in the middle of the vertical metal strip is w1 = 0.3mm, and the width of the metal strips on both sides of the gap is w2 = 0.35mm.

[0012] Furthermore, the width of the right-angle gap is w3 = 0.6 mm.

[0013] Furthermore, when an x-polarized electromagnetic wave is irradiated onto the single-layer full-space metasurface unit, under the co-polarization component, the single-layer full-space metasurface unit operates in the reflection mode and can achieve image reconstruction of the L-shaped character at 15 GHz.

[0014] Furthermore, when an x-polarized electromagnetic wave is irradiated onto the single-layer full-space metasurface unit, under the cross-polarization component, the single-layer full-space metasurface unit operates in the transmission mode and can achieve image reconstruction of the V-shaped character at 14 GHz.

[0015] The coded metasurface containing the above-mentioned single-layer full-space metasurface unit based on 2-bit phase encoding includes multiple single-layer full-space metasurface units based on 2-bit phase encoding, and the multiple single-layer full-space metasurface units are densely arranged in a periodic array with one unit as a period.

[0016] The coding metasurface proposed in the present invention can work in transmission mode and reflection mode when excited by x-polarized waves. For cross-polarized components, the metasurface works in transmission mode; for co-polarized components, the metasurface works in reflection mode. The present invention makes full use of the co-polarized components of x-polarization, and only uses the polarization mode of a single electromagnetic wave to achieve full-space control of electromagnetic waves, effectively avoiding the problem of waste of electromagnetic resources. Secondly, the present invention constructs a 2-bit phase-coded metasurface with the help of a single-layer dielectric substrate clad with copper on both sides, which realizes the reconstruction of different holographic images in the transmission space and the reflection space, and improves the spatial resource utilization of the metasurface. A new type of single-layer metasurface is used to realize full-space holographic imaging, making full use of the co-polarized components of a single-polarized electromagnetic wave, effectively avoiding the waste of electromagnetic resources, and meeting the development needs of metasurface holographic imaging in miniaturization and high integration. The present invention proposes a single-layer coding metasurface that can achieve the reconstruction of different images in the transmission space and the reflection space when excited by a single-polarized electromagnetic wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A three-dimensional schematic diagram of a single-layer full-space metasurface unit based on 2-bit phase encoding of the present invention;

[0018] Figure 2 It is a front view of the top layer of a single-layer full-space metasurface unit;

[0019] Figure 3 It is a front view of the bottom layer of a single-layer full-space metasurface unit;

[0020] Figure 4 The reflection amplitude curve of a single-layer full-space metasurface unit when l1 changes;

[0021] Figure 5 The reflection phase curve of a single-layer full-space metasurface unit when l1 changes;

[0022] Figure 6 Transmission amplitude curve of a single-layer full-space metasurface unit when l2 and θ change;

[0023] Figure 7 Transmission phase curve of a single-layer full-space metasurface unit when l2 and θ change;

[0024] Figure 8 The phase mask image is V;

[0025] Fig. 9 The phase mask image is L;

[0026] Fig.10 It is the numerical simulation result diagram of letter V;

[0027] Fig.11This is the numerical simulation result diagram of the letter L. DETAILED DESCRIPTION

[0028] 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.

[0029] Specific implementation method 1: refer to Figures 1 to 3 Specifically describing this embodiment, the single-layer full-space metasurface unit based on 2-bit phase encoding described in this embodiment includes a top layer 1, a dielectric layer 2 and a bottom layer 3 stacked in sequence, and the top layer 1 and the bottom layer 3 are both copper metal layers with a thickness of 0.018 mm.

[0030] The top layer 1 includes a "π"-shaped metal patch and a rectangular frame metal patch. The "π"-shaped metal patch includes a horizontal metal strip and two vertical metal strips, the two vertical metal strips are vertically connected to the horizontal metal strip, and the horizontal metal strip is parallel to any side of the rectangular frame metal patch; a strip-shaped gap is left at the middle seam of the horizontal metal strip and the vertical metal strip, and the gaps at the junction of the horizontal metal strip and the vertical metal strip are also connected to each other.

[0031] The length of the horizontal metal strip is l=4 mm, the width of the strip gap is w1=0.3 mm, and the width of the metal strips on both sides of the strip gap is w2=0.35 mm. The rectangular metal patch is a square with a side length of P=10 mm, and the frame width of the rectangular metal patch is 0.3 mm.

[0032] The bottom layer 3 is a rectangular grounding metal sheet, and two right-angled slits are opened on the bottom layer 3. The two right-angled slits are arranged axially symmetrically with one diagonal line of the bottom layer 3 as the symmetry axis, and the openings are opposite to each other, and the corners of the two right-angled slits are respectively opposite to the two opposite corners of the bottom layer 3. The width w3 of the right-angled slit is 0.6 mm.

[0033] The thickness of dielectric layer 2 is h = 2 mm, and the relative dielectric constant ε r =2.2, loss tangent tanδ=0.001.

[0034] For the single-layer full-space metasurface unit based on 2-bit phase encoding described in this embodiment, for a vertically incident x-polarized electromagnetic wave, when the length l1 of the vertical metal strip in the top layer 1 changes, the reflection amplitude and reflection phase responses of the co-polarized component of the x-polarized wave are respectively as follows: Figure 4 and Figure 5 As shown. Figure 4 and Figure 5 It can be seen that when l1 takes the value of 2.1mm, 2.3mm, 2.4mm, and 3.6mm respectively, the metasurface unit can achieve a 270° phase difference at 15GHz, and the phase difference between the metasurface units in the four working states is about 90°. At the same time, the reflection coefficient at 15GHz is greater than 0.7. In the transmission mode, when the side length l2 and θ of the right-angle slot in the bottom layer 3 change, the transmission amplitude and transmission phase response of the cross-polarization component of the x-polarized wave are respectively as follows: Figure 6 and Figure 7 As shown. When the underlying parameters l2 and θ are 4.5 mm and 0°, 7.2 mm and 0°, 4.5 mm and 90°, and 7.2 mm and 90°, respectively, at 14 GHz, the metasurface unit can achieve a phase difference of 270°, and the transmission coefficient reaches 0.4. Among them, θ is the clockwise rotation angle of the underlying structural unit with the origin of the coordinate axis as the center.

[0035] In summary, using the "π"-shaped structure and based on the propagation phase principle, when an x-polarized electromagnetic wave irradiates the single-layer full-space metasurface unit, under the co-polarization component, the single-layer full-space metasurface unit works in the reflection mode and can realize the image reconstruction of the L-shaped character at 15 GHz, such as Fig.10 As shown. Using the right-angle slot structure, based on the propagation phase principle and the geometric phase principle, when an x-polarized electromagnetic wave irradiates the single-layer full-space metasurface unit, under the cross-polarization component, the single-layer full-space metasurface unit works in the transmission mode and can achieve V-shaped character image reconstruction at 14GHz, as shown in Fig.11 In this embodiment, the metasurface unit can effectively control the amplitude and phase of the electromagnetic waves in the reflection space and the transmission space.

[0036] At the same time, this embodiment uses an image reconstruction algorithm to calculate the phase mask required for holographic imaging. The calculated phase mask is as follows: Figure 8 and Fig. 9 Attached Figure 8 This is the phase mask diagram of the transmission space V-shaped character, attached Fig. 9 The phase mask diagram of the L-shaped character in the reflection space. 11, 10, 01 and 00 in the phase mask represent the four coding elements of the transmission mode (reflection mode) respectively. For the reflection mode, the four metasurface units corresponding to l1=3.6mm, 2.1mm, 2.3mm and 2.4mm are used to represent the four phase coding states (11, 10, 01 and 00) of the reconstructed V-shaped character; for the transmission mode, the four coding elements with l2 and θ of 7.2mm and 90°, 4.5mm and 0°, 7.2mm and 0°, and 4.5mm and 90° are used to represent the four phase coding states (11, 10, 01 and 00) of the reconstructed L-shaped character.

[0037] This embodiment utilizes the designed metasurface unit in combination with the calculated phase mask to complete the arrangement of the metasurface array and realize the reconstruction of different holographic images in the whole space.

[0038] Specific embodiment 2: The coded metasurface described in this embodiment contains the single-layer full-space metasurface unit based on 2-bit phase coding as described in the above-mentioned specific embodiment 1, including: multiple single-layer full-space metasurface units based on 2-bit phase coding, and the multiple single-layer full-space metasurface units are closely arranged in a periodic array with one unit as a period.

[0039] The top metal of the coded metasurface described in this embodiment is composed of a "π"-shaped structure embedded in a rectangular frame using transmission phase encoding, and works in reflection mode; the bottom metal is a right-angle slot structure using transmission phase encoding and geometric phase encoding, and works in transmission mode. The phase mask is calculated by an image reconstruction algorithm, and then the above-mentioned units are arranged according to the calculated phase mask to realize a single-layer full-space 2-bit coded metasurface hologram. This embodiment utilizes the co-polarization component of a single polarization and the working mode (transmission mode / reflection mode) degree of freedom to achieve independent control of the functions of the two holograms, and the holograms do not interfere with each other, with good isolation.

[0040] 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 full-space metasurface unit based on 2-bit phase encoding, comprising a top layer (1), a dielectric layer (2) and a bottom layer (3) stacked in sequence, characterized in that: The top layer (1) includes a "π"-shaped metal patch and a rectangular frame metal patch. A gap is left in the middle of each line of the "π"-shaped metal patch. The bottom layer (3) is a rectangular grounding metal sheet, and two right-angled slits are opened on the bottom layer (3). The two right-angled slits are axially symmetrically arranged with a diagonal line of the bottom layer (3) as a symmetry axis, and the openings are opposite to each other, and the corners of the two right-angled slits are respectively opposite to the two opposite corners of the bottom layer (3); When an x-polarized electromagnetic wave irradiates the single-layer full-space metasurface unit, under the co-polarization component, the single-layer full-space metasurface unit works in the reflection mode and can achieve image reconstruction of the L-shaped character at 15GHz; When an x-polarized electromagnetic wave is irradiated onto the single-layer full-space metasurface unit, under the cross-polarization component, the single-layer full-space metasurface unit works in the transmission mode and can achieve image reconstruction of V-shaped characters at 14 GHz.

2. The single-layer full-space metasurface unit based on 2-bit phase encoding according to claim 1 is characterized in that: The thickness of the dielectric layer (2) is h = 2 mm, and the relative dielectric constant ε r =2.2, loss tangent tanδ=0.

001.

3. The single-layer full-space metasurface unit based on 2-bit phase encoding according to claim 1 or 2, characterized in that: The materials of the top layer (1) and the bottom layer (3) are both copper.

4. The single-layer full-space metasurface unit based on 2-bit phase encoding according to claim 3 is characterized in that: The thickness of the top layer (1) and the bottom layer (3) is 0.018 mm.

5. The single-layer full-space metasurface unit based on 2-bit phase encoding according to claim 4 is characterized in that: The rectangular metal patch is a square with a side length P=10 mm, and the frame width of the rectangular metal patch is 0.3 mm.

6. The single-layer full-space metasurface unit based on 2-bit phase encoding according to claim 5, characterized in that: The "π"-shaped metal patch includes a horizontal metal strip and two vertical metal strips, the two vertical metal strips are vertically connected to the horizontal metal strip, the horizontal metal strip is parallel to any side of the rectangular metal patch, a strip-shaped gap is left at the middle seam of the horizontal metal strip and the vertical metal strip, and the gaps at the junction of the horizontal metal strip and the vertical metal strip are also connected to each other; The length of the horizontal metal strip is l=4 mm, the width of the strip-shaped gap in the vertical metal strip is w1=0.3 mm, and the width of the metal strips on both sides of the gap is w2=0.35 mm.

7. The single-layer full-space metasurface unit based on 2-bit phase encoding according to claim 1, 2, 4, 5 or 6, characterized in that: The width of the right-angle gap w3 = 0.6 mm.

8. A coding metasurface comprising a single-layer full-space metasurface unit based on 2-bit phase coding according to claim 1, 2, 4, 5 or 6, characterized in that: include: Multiple single-layer full-space metasurface units based on 2-bit phase encoding, and multiple single-layer full-space metasurface units are closely arranged in a periodic array with one unit as a period.

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