Planar metal metasurface lens with high focusing efficiency

Abstract

The invention relates to a planar metal metasurface lens with high focusing efficiency, and relates to the field of microwave lenses, the planar metal metasurface lens comprises a dielectric layer, two metal layers and split rings, the two metal layers cover the two end faces of the dielectric layer, a plurality of split rings are distributed on the metal layers at intervals, and the split rings are two groups of concentric segmented circular rings which are distributed inside and outside and are provided with symmetrical double openings; and the opening part of the inner ring deflects by an angle greater than 0 degree along the circle center, so that the segmented circular rings in the opening ring are asymmetrically distributed, and the focusing efficiency greater than 60% and the amplification factor of 16 times are realized. And the advantages of high focusing rate and high magnification are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave lenses, and in particular to a planar metal supersurface lens with high focusing efficiency. Background Art

[0002] A metasurface lens is a planar ultrathin lens formed by an array of periodic metal or dielectric metasurfaces with a phase gradient. A metasurface is a planar subwavelength metal or dielectric structure that can flexibly manipulate incident electromagnetic waves through a periodic or quasi-periodic unit array. In recent years, with the proposal of the generalized Snell's law of reflection and refraction, various ultrathin devices based on metasurface technology have been continuously developed. Metasurfaces and superlenses are quasi-two-dimensional ultrathin materials that can not only realize the characteristics of conventional materials, but also have the advantages of thin thickness, low profile, low loss, simple processing, easy plane conformality and low cost.

[0003] In the optical and communication frequency bands, in order to overcome the high loss of metal structures, high numerical aperture metal lenses are generally realized through all-dielectric metasurface structures. For example, in 2015, Arbabi et al. from the California Institute of Technology realized a high numerical aperture metal lens with a high focusing efficiency of 42% through all-dielectric nano-silicon pillars. In the lower terahertz and microwave frequency bands, metasurfaces mostly use periodic metal patches or complementary structures placed on the dielectric substrate or air layer surface, and the incident wave is regulated by the shape, geometric parameters and arrangement of the metal metasurface structure. In the low-frequency band, high focusing efficiency metal lenses have important research value for achieving ultra-compact far-field focusing, and can open up new research ideas for high-resolution imaging, miniaturized projection array antennas and compact lens corner reflectors.

[0004] Currently, most low-frequency high-focusing efficiency metal superlenses are realized by multi-layer metal (greater than 4 layers) supersurface structures. For circularly polarized wave excitation, the device thickness is large, the processing and testing costs are high, and the realization is difficult. The use of single-layer dielectric or double-layer metal supersurface structures can greatly reduce the design cost and realization difficulty of superlenses. The traditional double open resonant ring unit has low transmittance.

[0005] Therefore, in view of the above shortcomings, it is necessary to provide a planar metal metasurface lens with high focusing efficiency. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] The technical problem to be solved by the present invention is to solve the problem that the number of supersurface layers of the current supersurface lens is greater than 4, the unit structure is thick, and the transmittance of the resonant ring unit and the array is low.

[0008] (II) Technical solution

[0009] In order to solve the above technical problems, the present invention provides a planar metal metasurface lens with high focusing efficiency, comprising a dielectric layer, a metal layer and an open ring, wherein two metal layers cover the two end surfaces of the dielectric layer, and a plurality of open rings are distributed at intervals on the metal layer, and the open rings are two groups of concentric segmented circular rings distributed inside and outside and provided with symmetrical double openings, and the opening part of the inner ring is deflected along the center of the circle by an angle greater than 0° so that the segmented circular rings inside the open ring are asymmetrically distributed, so as to achieve a focusing efficiency greater than 60% and a magnification factor of 16 times.

[0010] As a further illustration of the present invention, preferably, each open ring is arranged at fixed period intervals, and the size of the fixed period is smaller than the wavelength of the electromagnetic wave.

[0011] As a further illustration of the present invention, preferably, the phase distribution of the metasurface lens is:

[0012]

[0013] in,

[0014] is the phase distribution of the metasurface lens, i.e., the inner diameter r of the inner ring of the open ring (3);

[0015] f is the frequency of the incident electromagnetic wave;

[0016] x is the horizontal coordinate position of the open ring;

[0017] F is the focal length of the metasurface lens.

[0018] As a further illustration of the present invention, preferably, the metasurface lens aperture is:

[0019] D=n0*sin(θ)

[0020] in

[0021] D is the metasurface lens aperture;

[0022] n0 is the refractive index of the external environment in which the lens is located, which is 1 in air;

[0023] θ is the maximum deflection angle of the incident electromagnetic wave.

[0024] As a further illustration of the present invention, preferably, the maximum deflection angle θ of the incident electromagnetic wave is calculated by the following formula:

[0025]

[0026] in

[0027] D is the metasurface lens aperture;

[0028] F is the focal length of the metasurface lens.

[0029] (III) Beneficial effects

[0030] The above technical solution of the present invention has the following advantages:

[0031] The present invention uses a double open resonant ring structure with a twisted inner ring, combined with a design formula, to enable the metasurface lens array to obtain high efficiency and large numerical aperture focusing spots in the far field, theoretically making the projection efficiency close to 90% and the focusing efficiency greater than 60%. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic diagram of focusing operation of the metasurface lens of the present invention;

[0033] Figure 2 is a top view of the metasurface lens open ring unit of the present invention;

[0034] Figure 3 Schematic diagram of the distribution of the metal layer opening rings of the metasurface lens of the present invention;

[0035] Figure 4 is the focusing energy distribution diagram of the lens of the present invention in the xz plane;

[0036] Figure 5 is a distribution diagram of the focused energy of the present invention on the z-axis;

[0037] Figure 6 is the energy distribution diagram of the focus spot in the xy plane of the present invention;

[0038] Figure 7 is the energy distribution diagram of the incident electromagnetic wave in the xy plane of the present invention;

[0039] Figure 8 It is a normalized energy distribution diagram of the focused wave and the incident electromagnetic wave along the x-axis of the present invention.

[0040] In the figure: 1. dielectric layer; 2. metal layer; 3. open ring. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not 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 are within the scope of protection of the present invention.

[0042] A high-focusing-efficiency planar metal metasurface lens, combined with Figure 1 , Figure 3, including a dielectric layer 1, a metal layer 2 and an open ring 3, two metal layers 2 cover the two end surfaces of the dielectric layer 1, and a plurality of open rings 3 are distributed in an array on the metal layer 2. The dielectric layer 1 is a disc-shaped structure, the thickness of the dielectric layer 1 is t, preferably 2.6 mm, and the designed aperture is D, preferably 175 mm. Conventionally, the equivalent refractive index of the dielectric layer 1 can be increased by increasing its thickness, but the designed aperture D will also increase, resulting in a decrease in focusing efficiency. The present invention adopts a composite structure of a double-layer periodic metal metasurface and a single-layer dielectric structure to achieve an increase in the average transmittance of its gradient structure.

[0043] Combination Figure 2 , Figure 3 , the open ring 3 is composed of two groups of concentric segmented circular rings distributed inside and outside and provided with symmetrical double openings. The open ring 3 is distributed in a periodic p array in the xy plane, and p<λ, where λ is the wavelength of the incident electromagnetic wave. The outer ring part of the open ring 3 is symmetrically distributed on the left and right and has a width of w2, preferably 1mm. The inner diameter of the inner ring is r, and the value is a gradual value, generally 1-2.25mm. The width is w1, preferably 1mm. The interval between the inner ring and the outer ring is g, preferably 1.5mm. The opening part of the inner ring is deflected by an angle α along the center of the circle, and α>0° so that the segmented circular rings in the open ring are not distributed on the left and right, and are misaligned with the opening part of the outer ring. The transmittance within the working frequency bandwidth can be improved by reasonably selecting and optimizing the above data according to the actual incident electromagnetic wave data to be matched.

[0044] Microwave frequency planar superlenses generally use a hybrid sandwich structure of periodic metal patches (or complementary structures) and uniform dielectric layers. In order to simultaneously meet the requirements of high transmittance (greater than 50%) and 360° transmission phase coverage, at least three layers of metal structure are required. By increasing the number of stacked metal layers or the thickness of the dielectric layer, the equivalent refractive index of the unit can be increased, so the transmission amplitude and transmission phase can be improved to a certain extent, but it also brings about the problems of increased device weight, cumbersome design and processing procedures, higher processing costs and greater testing difficulty. The present invention only needs two metal layers 2 and a reasonable distribution of open rings 3 to solve the above problems, where

[0045] The phase distribution of the open ring 3 of the metasurface lens is:

[0046]

[0047] is the phase distribution of the metasurface lens, i.e., the inner diameter r of the inner ring of the open ring (3);

[0048] f is the frequency of the incident electromagnetic wave;

[0049] x is the horizontal coordinate position of the open ring;

[0050] F is the focal length of the metasurface lens, preferably 100 mm.

[0051] The metasurface lens aperture D is:

[0052] D=n0*sin(θ)

[0053] in

[0054] n0 is the refractive index of the external environment in which the lens is located, which is 1 in air;

[0055] θ is the maximum deflection angle of the incident electromagnetic wave, specifically:

[0056]

[0057] in

[0058] D is the metasurface lens aperture;

[0059] F is the focal length of the metasurface lens.

[0060] By changing the radius of the double open resonant ring with a twisted inner ring and designing a phase gradient distribution, a superlens array can obtain a high-efficiency and large numerical aperture focusing spot in the far field. Theoretically, the projection efficiency of the superlens can be close to 90%, and the focusing efficiency can be greater than 60%. The composite structure of a double-layer periodic metal metasurface and a single-layer dielectric structure can achieve an improvement in the average transmittance of its gradient structure.

[0061] Combination Figure 4-Figure 8 The double-layer ultra-thin planar metal superlens of the present invention is based on a phase gradient array designed with a twisted double open resonant ring metasurface unit, which achieves high-efficiency focusing of incident line-polarized electromagnetic waves and can amplify the power intensity of incident plane electromagnetic waves by 16 times. The focused position is 3.3 times the wavelength λ, the half-size width of the lateral focal spot is 0.79 times the wavelength λ, and the longitudinal focusing depth is 2.8 times the wavelength. The designed single-layer metal superlens has a high focusing efficiency of 64.8%, with the least number of metal supersurface layers, thinner thickness, lighter material, simpler processing, and lower cost.

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A planar metal metasurface lens with high focusing efficiency, characterized in that: The invention comprises a dielectric layer (1), a metal layer (2) and an open ring (3), wherein two metal layers cover both end surfaces of the dielectric layer (1), a plurality of open rings (3) are distributed at intervals on the metal layer (2), and the open rings (3) are two groups of concentric segmented circular rings which are distributed inside and outside and have symmetrical double openings, and the opening part of the inner ring is deflected along the center of the circle by an angle greater than 0° so that the inner segmented circular rings of the open ring (3) are distributed asymmetrically, so as to achieve a focusing efficiency greater than 60% and a magnification factor of 16 times.

2. A planar metal metasurface lens with high focusing efficiency according to claim 1, characterized in that: Each open ring (3) is arranged at fixed period intervals, and the size of the fixed period is smaller than the wavelength of the electromagnetic wave.

3. A planar metal metasurface lens with high focusing efficiency according to claim 2, characterized in that: The phase distribution of the metasurface lens is: in, is the phase distribution of the metasurface lens, i.e., the inner diameter r of the inner ring of the open ring (3); f is the frequency of the incident electromagnetic wave; x is the horizontal coordinate position of the open ring; F is the focal length of the metasurface lens.

4. The planar metal metasurface lens with high focusing efficiency according to claim 3, characterized in that: The metasurface lens aperture is: D=n0*sin(θ) in D is the metasurface lens aperture; n0 is the refractive index of the external environment in which the lens is located, which is 1 in air; θ is the maximum deflection angle of the incident electromagnetic wave.

5. The planar metal metasurface lens with high focusing efficiency according to claim 4, characterized in that: The maximum deflection angle θ of the incident electromagnetic wave is calculated by the following formula: in D is the metasurface lens aperture; F is the focal length of the metasurface lens.

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