A spatial-frequency multiplexing holographic device and method based on an optically transparent metasurface

Abstract

To address the limitation of existing methods in achieving transparency within the visible spectrum, this invention provides a metasurface unit for full-space millimeter-wave frequency multiplexing holography based on a complex amplitude metasurface. This unit comprises three metal layers and two transparent substrates, arranged from top to bottom as a first metal layer, a first transparent substrate, a second metal layer, a second transparent substrate, and a third metal layer. A full-space millimeter-wave frequency multiplexing holographic device based on a complex amplitude metasurface is also provided. Furthermore, a method for full-space millimeter-wave frequency multiplexing holography based on a complex amplitude metasurface is provided. This invention's method enables efficient and reliable design of frequency multiplexing metasurface holograms.

Description

Technical Field

[0001] This invention relates to the field of full-space frequency reuse holography, and specifically to a space-frequency reuse holographic device and method based on an optically transparent metasurface. Background Technology

[0002] Traditional holographic manipulation devices suffer from drawbacks such as limited field of view, large size, and high loss. In recent years, electromagnetic metasurfaces have attracted considerable attention due to their powerful electromagnetic wave control capabilities, and have been widely researched and applied in communication, signal modulation, holography, stealth, and many other fields. Metasurface-based holographic imaging design not only effectively overcomes the limitations of traditional imaging devices but also injects new vitality into the development of holographic technology. Metasurface holographic imaging has advantages such as low loss, planar structure, and no higher-order diffraction secondary effects, and has achieved preliminary application verification in the terahertz and infrared bands. Pure phase holography has the advantages of high efficiency and ease of implementation. However, ignoring amplitude information may introduce speckle noise and cannot control the phase information of the imaging surface. Pure amplitude modulation results in some energy loss, reducing the energy utilization rate of electromagnetic waves and leading to low diffraction efficiency of amplitude holograms. To fully utilize the information carried by electromagnetic waves, researchers have begun to explore methods combining amplitude and phase modulation to achieve complex amplitude holographic imaging. In 2021, Cheng et al. achieved efficient transmission-type complex amplitude holography by introducing an ohmic loss layer into a Fabry-Perot (FP) resonant cavity structure. The phase was adjusted according to the opening angle and geometric parameters of the resonant ring. The amplitude response could be continuously tuned by changing the ohmic dissipation intensity (Y.Cheng, Y.Li, H.Wang, H.Chen, W.Wan, J.Wang, L.Zheng, J.Zhang, S.Qu, Advanced Optical Materials, vol.9, no.13, pp.2002242, 2021.). However, the designed complex amplitude metasurface hologram could only achieve image reconstruction in a single channel. Frequency (wavelength) multiplexing metasurface holography is an effective method to improve information capacity. In 2020, Iqbal et al. designed a dual-band reflective metasurface hologram that provides two different information channels in the X-band and Ku-band, and the electric field intensity distribution can be manipulated simultaneously and independently (S. Iqbal, H. Rajabalipanah, L. Zhang, X. Qiang, A. Abdolali, TJ Cui, Nanophotonics, vol. 9, no. 3, pp. 703-714, 2020).Most research on frequency-reused metasurface holograms focuses on half-space control. In 2022, Dong et al. designed a 2-bit encoded metasurface. By encoding the phases of reflection and transmission at different frequencies, they obtained a full-space metasurface hologram using the WGS algorithm. However, due to the transmission amplitude being close to 0.4, the transmission holographic imaging efficiency in this paper was only 23.57% (L.Dong, XSLi, L.Zhu, SNBurokur, Q.Wu, XMDing, Annalen der Physik, vol.534, no.10, pp.2200229, 2022). Currently, there is very little literature on designing complex amplitude metasurfaces to achieve full-space frequency-reused holographic imaging. Summary of the Invention

[0003] To address the shortcomings of existing methods that cannot achieve transparency in the visible spectrum, this invention proposes a metasurface unit for full-space millimeter-wave frequency multiplexing holography based on complex amplitude metasurfaces, comprising three metal layers and two transparent substrates, which are arranged from top to bottom as a first metal layer, a first transparent substrate, a second metal layer, a second transparent substrate, and a third metal layer.

[0004] The first transparent substrate is a thin rectangular sheet with rectangular upper and lower surfaces;

[0005] Establish a rectangular coordinate system with the x-axis pointing forward, the y-axis pointing to the right, and the z-axis pointing upward. A metal C-ring pattern is printed on the upper surface of the first transparent substrate. The upper C-ring is constructed as follows: a ring with an outer radius of r1 and an inner radius of r2 is formed, with the center of the ring located at the origin of the coordinate system. Based on this ring, a solid circle with its center at x = (r1 + r2) / 2, y = 0, and radius Ra is subtracted to form the initial C-ring. The initial C-ring is then rotated clockwise by α degrees along the z-axis to form the first metal layer.

[0006] The second transparent substrate is a thin rectangular sheet. The projection of the second transparent substrate on the horizontal plane is completely superimposed on the first transparent substrate. The first and second transparent substrates operate at similar frequency bands. The upper surface of the second transparent substrate is etched with a hollowed-out C-shaped ring structure, which is the same size as the metal pattern of the first layer, and the projections of the two on the horizontal plane are completely superimposed.

[0007] A smaller C-shaped metal ring pattern than the first metal layer is printed on the bottom of the PET media board. The center of the ring is on the axis formed by the centers of the first and second metal layers, forming the third metal layer.

[0008] In one specific embodiment of the present invention, the upper and lower surfaces of the first transparent substrate are square, with dielectric constant ε1 = 5.27 and tanδ1 = 0.003, made of EAGLE XG glass, and a height of h1 = 0.7 mm.

[0009] In another specific embodiment of the present invention, the second transparent substrate is made of polyethylene terephthalate (PET) with a height of h2 = 1.2 mm and a dielectric constant of ε2 = 2.75 and tanδ2 = 0.0057.

[0010] In one embodiment of the present invention, the structural parameters of the metasurface unit are as follows: the unit period P is 3mm to 10mm; the outer radius r1 of the upper C-ring is 1mm to 2mm, the inner radius r2 of the upper C-ring is 0.5mm to 1.8mm; the outer radius r3 of the lower C-ring is 1mm to 2mm, and the inner radius r4 of the lower C-ring is 0.5mm to 1.8mm.

[0011] In another specific embodiment of the present invention, the structural parameters of the metasurface unit are: P = 4 mm, r1 = 1.6 mm, r2 = 1.1 mm, r3 = 1.0 mm, and r4 = 0.8 mm.

[0012] A full-space millimeter-wave frequency multiplexing holographic device based on complex amplitude metasurface is also provided. This device is based on the metasurface unit of the full-space millimeter-wave frequency multiplexing holographic device based on complex amplitude metasurface, and the device is composed of a×a metasurface units.

[0013] Another method is to provide a full-space millimeter-wave frequency multiplexing holographic device based on a complex amplitude metasurface, which is based on the metasurface unit of the above-mentioned full-space millimeter-wave frequency multiplexing holography based on a complex amplitude metasurface. The device is composed of a×b metasurface units.

[0014] Another method is to provide a full-space millimeter-wave frequency multiplexing holographic device based on a complex amplitude metasurface, which is based on the metasurface unit of the above-mentioned full-space millimeter-wave frequency multiplexing holography based on a complex amplitude metasurface, and the device is composed of a circular array of metasurface units.

[0015] In addition, a full-space millimeter-wave frequency reuse holography method based on complex amplitude metasurface is provided. This method is based on the aforementioned full-space millimeter-wave frequency reuse holography device based on complex amplitude metasurface and uses the WGS algorithm to realize metasurface holography.

[0016] This invention enables the efficient and reliable design of frequency-reused metasurface holograms.

[0017] The advantages of this invention are:

[0018] 1. This invention achieves independent phase and amplitude control simultaneously in the 25.8-27.7GHz and 42.8-46.8GHz frequency bands by changing the opening size and rotation angle of C-rings of different sizes, clearly revealing the complex amplitude control mechanism of the designed unit.

[0019] 2. Based on transparent material substrates of glass and polyethylene terephthalate (PET), this invention provides a general full-space metasurface holographic design method based on the WGS algorithm, which effectively improves space utilization and achieves the reconstruction of two high-performance holographic images "HOLO" and "GRAM" through frequency reuse, with signal-to-noise ratios of 14.6dB and 14.4dB, respectively.

[0020] 3. The optically transparent metasurface reused hologram proposed in this invention is fabricated using micro-3D printing micro-nano technology based on electric field driving, which has the characteristics of low cost and broad application prospects. Attached Figure Description

[0021] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood in conjunction with the following description of the embodiments, in which:

[0022] Figure 1 This is a topological diagram of an optically transparent metasurface unit, consisting of three metal patterns and two dielectric layers, from top to bottom. Figure 1 (a) is a larger C-ring and glass dielectric plate. Figure 1 (b) Etching a large-sized C-ring pattern onto a metal plate and a PET substrate. Figure 1 (c) is a smaller C-ring. Figure 1 (d) is a side view of the proposed unit;

[0023] Figure 2 Let be the surface induced current of each unit cell structure under y-polarized incident radiation, where Figure 2 (a) shows the current distribution of the top layer structure. Figure 2 (b) shows the current distribution in the intermediate layer structure. Figure 2 (c) shows the current distribution of the bottom layer structure;

[0024] Figure 3 The simulation results for cross-polarized transmission and reflection coefficients are shown, where Figure 3 (a) shows the effect of aperture size Ra and rotation angle α on transmission amplitude. Figure 3 (b) shows the effect of aperture size Ra and rotation angle α on the transmission phase. Figure 3 (c) Effect of aperture size s and rotation angle β on reflection amplitude Figure 3 (d) The effect of aperture size s and rotation angle β on the reflection phase;

[0025] Figure 4 The effects of different coding state units on amplitude and phase response under oblique incidence from 0° to 50° are investigated. Figure 4 (a) The effect of different incident angles on the transmission amplitude of the unit when s = 0.2 mm and β = 45°. Figure 4 (b) shows the effect of different incident angles on the reflection amplitude of the unit when Ra = 1.5 mm and α = 45°. Figure 4 (c) shows the effect of different incident angles on the transmission phase of the unit cell when s = 0.2 mm and β = 45°. Figure 4 (d) shows the effect of different incident angles on the reflection phase of the unit cell when Ra = 1.5 mm and α = 45°.

[0026] Figure 5 The flowchart of the WGS algorithm for generating complex amplitude metasurface holograms in two frequency bands based on iterative Fourier transform is shown.

[0027] Figure 6 The amplitude and phase distributions of the designed metasurface, as well as the theoretical and simulated near-field electric field intensity distributions, are shown. Figure 6 (a) shows the transmission amplitude distribution of the unit in the lower frequency band. Figure 6 (b) shows the reflection amplitude distribution of the unit in the higher frequency band. Figure 6 (c) shows the transmission phase distribution of the unit in the lower frequency band. Figure 6 (d) shows the reflection phase distribution of the unit in the higher frequency band. Figure 6 (e) shows the results of the holographic theoretical analysis in the transmission region. Figure 6 (f) shows the results of the holographic theoretical analysis in the reflection region. Figure 6 (g) shows the holographic simulation results in the transmission region. Figure 6 (h) shows the holographic simulation results in the reflection region;

[0028] Figure 7 To achieve image reconstruction of varying complexity using metasurface holograms, among which Figure 7 (a) has four foci. Figure 7 (b) is the letter "X". Figure 7 (c) is the letter "S". Figure 7 (d) is an airplane design;

[0029] Figure 8 These are holographic images reproduced by the metasurface at different frequencies, among which... Figure 8 (a) Image reproduction of "HOLO" at different frequencies in the transmission half-space. Figure 8 (b) Image reproduction of "GRAM" at different frequency points in the reflection half-space;

[0030] Figure 9 Testing of optically transparent complex amplitude metasurfaces, in which Figure 9(a) is a fabrication diagram of an optically transparent metasurface. Figure 9 (b) shows the light transmittance test environment and results. Detailed Implementation

[0031] This invention proposes a design method for full-space millimeter-wave frequency reuse holography based on complex amplitude metasurfaces.

[0032] Metasurface units such as Figure 1 As shown, it consists of three metal layers and two transparent substrates, which are arranged from top to bottom as follows: first metal layer, first transparent substrate, second metal layer, second transparent substrate, and third metal layer.

[0033] Figure 1 (a) shows the first metal layer and the first transparent substrate.

[0034] The first transparent substrate is a thin rectangular sheet with rectangular upper and lower surfaces. In one specific embodiment of the present invention, the upper and lower surfaces of the first transparent substrate are square. Its dielectric constant ε1 = 5.27, tanδ1 = 0.003, is made of EAGLE XG glass, and has a height h1 = 0.7 mm.

[0035] Establish a rectangular coordinate system with the x-axis pointing forward, the y-axis pointing to the right, and the z-axis pointing upward, as follows: Figure 1 As shown in (b), a metal C-ring pattern is printed on the upper surface of the first transparent substrate (L. Bao, RYWu, XJFu, Q. Ma, GDBai, J. Mu, RZJiang, IEEE Transactions on Antennas and Propagation, vol. 67, no. 10, pp. 6680-6685, 2019.). The upper C-ring is made as follows: a ring with an outer radius of r1 and an inner radius of r2 is formed, with the center of the ring located at the origin of the coordinate system. Based on this ring, a solid circle with a center at x = (r1 + r2) / 2, y = 0, and radius Ra is subtracted to form the initial C-ring. The initial C-ring is then rotated clockwise by α degrees along the z-axis to form the first metal layer.

[0036] like Figure 1As shown in (b), the second transparent substrate is a thin rectangular sheet made of polyethylene terephthalate (PET) with a height of h2 = 1.2 mm. Its dielectric constant is ε2 = 2.75, tanδ2 = 0.0057. The projection of the second transparent substrate onto the horizontal plane completely overlaps with that of the first transparent substrate. In a specific embodiment of the invention, because the dielectric constant of the first transparent substrate is greater, the thickness of the first layer is thinner than that of the second transparent substrate, thus making the two operating frequency bands closer. A hollowed-out C-shaped ring structure is etched on the upper surface of the second transparent substrate, with the same dimensions as the metal pattern of the first layer, and their projections onto the horizontal plane completely overlap. Its function is to isolate the first metal layer and the third metal layer, achieving independent control throughout the entire space.

[0037] like Figure 1 As shown in (c), a smaller metal C-shaped ring pattern than the first metal layer is printed on the bottom of the PET substrate. The center of the ring is on the axis formed by the centers of the first and second metal layers, forming a third metal layer for the control of high-frequency electromagnetic waves.

[0038] The structural parameters include the unit period P (3mm~10mm), the outer radius r1 (1mm~2mm) of the upper C-ring, the inner radius r2 (0.5mm~1.8mm) of the upper C-ring, the outer radius r3 (1mm~2mm) of the lower C-ring, and the inner radius r4 (0.5mm~1.8mm) of the lower C-ring. The optimized parameter values ​​are as follows: P=4mm, r1=1.6mm, r2=1.1mm, r3=1.0mm, r4=0.8mm.

[0039] A schematic diagram of the three-dimensional structure of the metasurface unit is shown below. Figure 1 As shown in (d), this unit has the characteristic of controlling the amplitude and phase response of the cross-polarization component in two different frequency bands. The working principle is based on polarization conversion. When the y-polarized wave is incident on the unit, it can be decomposed into two orthogonal electric field components. By changing the slot size and rotation angle, the conversion component of the cross-polarized wave and the path of the induced current can be controlled.

[0040] The numerical calculations for this invention were performed using the electromagnetic simulation software CST Studio Suite 2020. The surface current distribution of the three metal layers is as follows: Figure 2As shown in (a)-(c), a comparison reveals that at 44.0 GHz, a strong surface current intensity exists on the C-ring of the third layer, while the current intensity of the first and second layers is very weak. At 26.6 GHz, the induced current concentrates at the edge of the open ring gap in the second layer, generating a strong current intensity. Therefore, the upper two metal layers play a major role in the transmission performance of the unit, while the reflection performance is mainly affected by the bottom C-ring of the third layer. Furthermore, there is good isolation between the different layers. During the optimization design process, the unit can be treated as two independent parts for parameter optimization, achieving amplitude and phase modulation under ideal target conditions in their respective frequency bands.

[0041] Through parameter scanning and optimization, the following was obtained: Figure 3 The amplitude and phase responses shown demonstrate that the amplitude responses of transmission and reflection can be controlled by adjusting the opening sizes Ra and s of the two C-rings, respectively, while the rotation angles α and β of the C-rings around the z-axis determine their transmission and reflection phase responses, respectively. Figure 3 As shown in (a) and (b), the amplitude can be controlled within the transmission half-space from 0.15 to 0.6; at higher frequencies, the reflection amplitude can be adjusted within the range of 0.1 to 0.9. Figure 3 As can be seen from (b) and (d), the appropriate selection of the rotation angle enables the unit cell to obtain a stable 180° phase difference within the broadband range. In this invention, 60 metasurface units corresponding to the reflection amplitude response of a 5-level quantization gradient, the transmission amplitude response of a 3-level quantization gradient, and the 1-bit phase response are selected to construct a full-space metasurface frequency multiplexing holography. Under y-polarized incident light, the transmission amplitude of the unit cell is 0.15, 0.35, and 0.55, and the reflection amplitude is 0.15, 0.3, 0.5, 0.7, and 0.9. The finally determined operating frequency bands of the metasurface are 25.8-27.7 GHz and 42.8-46.8 GHz, respectively.

[0042] Figure 4 Sensitivity analysis of element performance for y-polarized waves at incident angles ranging from 0° to 50°. For ease of interpretation, these elements are encoded according to the decreasing order of amplitude at specific frequencies. Figure 4 (a) and (c) show the effect of different incident angles on the unit transmission coefficient when s = 0.2 mm and β = 45°. It can be observed that as the incident angle θ increases, the transmission amplitude and phase of the unit are basically stable, and the phase difference between adjacent coding states remains at about 180°. Figure 4(b) and (d) show the effect of different incident angles on the unit reflection coefficient when Ra = 1.5 mm and α = 45°. It can be seen that within the incident angle θ range of 0° to 40°, the change in θ has little effect on the reflection coefficient. However, when θ is 50°, the reflection performance decreases, especially since the reflection amplitude no longer meets the amplitude gradient requirement, which will degrade the imaging performance of the metasurface. Overall, within the incident angle θ range of 0° to 40°, the reflection and transmission performance remain stable. When θ is greater than 50°, the reflection performance exhibits a slight distortion relative to other incident angles, making it challenging to maintain the required amplitude and phase accuracy.

[0043] This invention utilizes the WGS algorithm to achieve array arrangement of metasurface holograms. The flowchart of the WGS algorithm based on iterative Fourier transform is shown below. Figure 5 As shown. First, the initial amplitude and phase information on the diffraction plane are set as follows: and in, This refers to the amplitude information of the nth unit in generation 0. This refers to the phase information of the nth unit in generation 0, where N is the total number of units. (Flowchart) Figure 5 Medium weighting factor w i It can adjust the image to make its electric field intensity uniformly distributed, E i Let be the electric field intensity at the i-th pixel. Then, a complex amplitude metasurface hologram is generated using iterative calculations of Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (iFFT). Finally, during continuous iteration, until a pre-set root mean square error (RMSE) δ tolerance is met or the maximum iteration limit algebra is reached, the final amplitude and phase information of the diffraction plane are output. Determining the four values ​​of reflection amplitude, reflection phase, transmission amplitude, and transmission phase determines a unit cell structure.

[0044] The complex amplitude metasurface can be a×a, forming a square array, or it can be a×b, forming a rectangular array, or a circular array. In a specific embodiment of the present invention, such as... Figure 6 As shown, the designed complex amplitude metasurface consists of 64×64 elements, used to generate different target images in different spaces. The letters distributed at the four corners were chosen as the target images because this allows for a better assessment of the metasurface's ability to manipulate energy in the near-field spatial range. The target image consists of 32×32 pixels. Based on parameter optimization, high signal-to-noise ratio holographic images were obtained at distances of D = 18.0λ (122 mm) and D = 10.8λ (122 mm) from the metasurface. Figure 3 (a)-(d) show the amplitude and phase distributions of the desired elements obtained using the WGS algorithm. The theoretical and simulation results at 26.6 GHz and 44.0 GHz under y-polarized electromagnetic wave incidence are as follows: Figure 6As shown in (e)-(h), the signal-to-noise ratios of the reconstructed images are 14.6 dB and 14.4 dB, respectively, and the root mean square errors (RMSE) are 0.021% and 0.029%, respectively.

[0045] To find a universal method to measure holographic imaging capability, we introduce the two-dimensional entropy (2D entropy) metric. 2D entropy not only reflects the amount of information contained in an image but also the combined characteristics of the grayscale information at pixel locations and the grayscale distribution of the pixel's neighborhood. The specific calculation formula is as follows: The gray values ​​of image pixels are grouped into a feature binary set, denoted as (i,j). Here, i represents the gray value of the pixel, and j represents the average gray value of the region. f(i,j) represents the number of times the feature tuple (i,j) appears, N is the image scale, and P... ij The frequency of occurrence of feature tuples is represented. As entropy increases, the image is considered more complex and contains more information. The designed metasurface achieves amplitude modulation from 0.15 to 0.55 in transmission mode and from 0.15 to 0.9 in reflection mode. Therefore, with the same imaging algorithm, holographic imaging in reflection space will have better quality. Figure 7 Four different target images were presented, along with the image reproduction effect of complex amplitude metasurfaces in reflection and transmission spaces. Through comparison, it can be observed that for the same target image (with the same two-dimensional entropy), the reflection space hologram has a higher signal-to-noise ratio and better imaging capability. Specifically, this is reflected in the more focused energy points of the metasurface hologram, such as the four focal points and the image of the letter "X"; it is also reflected in lower background noise, which is particularly evident in the holographic images of the letter "S" and an airplane.

[0046] Figure 8 The simulation results of holographic images of the metasurface at other operating frequencies are shown, where Figure 8 (a) Holographic reconstruction of the letter “HOLO” at a distance of 122 mm from the metasurface in the range of 25.0 GHz to 27.5 GHz. Figure 8 (b) Holographic reconstruction of the letter "GRAM" at a distance of 122 mm from the metasurface in the range of 42.5 GHz to 45.0 GHz. Note that the effective imaging bandwidth is broadened relative to the unit's operating bandwidth, and the designed metasurface maintains good imaging quality over a wide frequency range. Therefore, it exhibits excellent performance in controlling broadband near-field electromagnetic wave energy.

[0047] The feasibility of the proposed full-space frequency multiplexing holography based on an optically transparent complex amplitude metasurface has been verified through theoretical analysis, numerical simulation, and fabrication experiments. The fabrication model of the optically transparent metasurface is as follows: Figure 9As shown, the fabrication process utilizes an electric field-driven micro-3D printing technology to assemble high-precision copper-based flexible transparent circuits. The thickness of each of the three copper-clad layers is 180 nm, with the metal mesh linewidth set to 4.68 μm and the mesh period set to 200 μm to meet the requirements for metasurface optical transparency. Figure 9 (a) The sunflower behind the sample is clearly visible, confirming its high optical transparency. Figure 9 As shown in (b), an LS116 transmittance meter was used to measure the transmittance at wavelengths of 380–760 nm. First, the two test probes needed to be aligned and tightened. After calibration, the object to be tested was placed between the two probes, ensuring they were aligned. The designed complex amplitude metasurface achieved a maximum transmittance of 72.87%, with an average transmittance of 71.37% for the entire metasurface. Therefore, the processed sample exhibited excellent optical transparency, validating the feasibility of the design.

[0048] This paper proposes a metasurface that satisfies optical transparency (OT) and full-space complex amplitude in the millimeter-wave (mmWave) band. Leveraging the advantages of OT properties and full-space complex amplitude metasurface technology, the proposed frequency-reused metasurface hologram has broad application prospects in target sensing, multi-channel data storage, and encryption.

[0049] This invention proposes an optically transparent complex amplitude metasurface for realizing full-space frequency multiplexing holography under the same polarization, wherein glass and PET materials are used as dielectric substrates with high optical transparency. The designed three-layer metasurface unit has the ability to independently control the amplitude and phase of reflection and transmission in two different frequency bands. Using the WGS algorithm, 60 units with different structures are selected to form a millimeter-wave metasurface hologram. This metasurface hologram can present a "HOLO" image in the transmission half-space with a signal-to-noise ratio of 14.6 dB, and a "GRAM" image in the reflection half-space with a signal-to-noise ratio of 14.4 dB. Finally, experiments verify the effectiveness of the design, demonstrating that the designed metasurface has superior holographic imaging capabilities, as well as advantages such as high optical transparency and high space utilization. The effectiveness and reliability of the proposed method enable its successful application in other fields such as holographic display, data encryption and storage, and mimicry camouflage.

Claims

1. A metasurface unit based on a complex amplitude metasurface for full-space millimeter-wave frequency multiplexing holography, characterized in that, It includes three metal layers and two transparent substrates, which are arranged from top to bottom as follows: first metal layer, first transparent substrate, second metal layer, second transparent substrate, and third metal layer; The first transparent substrate is a thin rectangular sheet with rectangular upper and lower surfaces; Establish a rectangular coordinate system with the x-axis pointing forward, the y-axis pointing to the right, and the z-axis pointing upward. A metal C-ring pattern is printed on the upper surface of the first transparent substrate. The upper C-ring is constructed as follows: a ring with an outer radius of r1 and an inner radius of r2 is formed, with the center of the ring located at the origin of the coordinate system. Based on this ring, a solid circle with its center at x = (r1 + r2) / 2, y = 0, and radius Ra is subtracted to form the initial C-ring. The initial C-ring is then rotated clockwise by α degrees along the z-axis to form the first metal layer. The second transparent substrate is a thin rectangular sheet, and its projection on the horizontal plane completely overlaps with that of the first transparent substrate. The first and second transparent substrates operate at similar frequency bands; the upper surface of the second transparent substrate is etched with a hollowed-out C-shaped ring structure, the size of which is the same as the metal pattern of the first layer, and the projections of the two on the horizontal plane completely overlap. A smaller C-shaped metal ring pattern than the first metal layer is printed on the bottom of the PET media board. The center of the ring is on the axis formed by the centers of the first and second metal layers, forming the third metal layer.

2. The metasurface unit based on complex amplitude metasurfaces for full-space millimeter-wave frequency multiplexing holography as described in claim 1, characterized in that, The first transparent substrate has square upper and lower surfaces with dielectric constants ε1 = 5.27 and tanδ1 = 0.

003. It is made of EAGLE XG glass and has a height of h1 = 0.7 mm.

3. The metasurface unit based on complex amplitude metasurfaces for full-space millimeter-wave frequency multiplexing holography as described in claim 1, characterized in that, The second transparent substrate is made of polyethylene terephthalate (PET) with a height of h2 = 1.2 mm; its dielectric constant is ε2 = 2.75, tanδ2 = 0.0057.

4. The metasurface unit based on complex amplitude metasurfaces for full-space millimeter-wave frequency multiplexing holography as described in claim 1, characterized in that, The structural parameters of the metasurface unit are as follows: the unit period P is 3mm to 10mm; the outer radius r1 of the upper C-ring is 1mm to 2mm, the inner radius r2 of the upper C-ring is 0.5mm to 1.8mm; the outer radius r3 of the lower C-ring is 1mm to 2mm, and the inner radius r4 of the lower C-ring is 0.5mm to 1.8mm.

5. The metasurface unit of full-space millimeter-wave frequency multiplexing holography based on complex amplitude metasurface as described in claim 4, characterized in that, The structural parameters of the metasurface unit are: P = 4 mm, r1 = 1.6 mm, r2 = 1.1 mm, r3 = 1.0 mm, r4 = 0.8 mm.

6. A full-space millimeter-wave frequency multiplexing holographic device based on a complex amplitude metasurface, comprising a metasurface unit for full-space millimeter-wave frequency multiplexing holography as described in any one of claims 1 to 5, characterized in that, The device consists of a×a metasurface units.

7. A full-space millimeter-wave frequency multiplexing holographic device based on a complex amplitude metasurface, comprising a metasurface unit for full-space millimeter-wave frequency multiplexing holography as described in any one of claims 1 to 5, characterized in that, The device consists of a×b metasurface units.

8. A full-space millimeter-wave frequency multiplexing holographic device based on a complex amplitude metasurface, comprising a metasurface unit for full-space millimeter-wave frequency multiplexing holography as described in any one of claims 1 to 5, characterized in that, The device consists of a circular array of metasurface units.

9. A full-space millimeter-wave frequency reuse holography method based on a complex amplitude metasurface, comprising a full-space millimeter-wave frequency reuse holography device based on a complex amplitude metasurface as described in any one of claims 6 to 8, characterized in that, Metasurface holography is achieved using the WGS algorithm.

Images