CN108808257B - Refractive index controllable super surface - Google Patents

Abstract

The invention provides a refractive index controllable metasurface, comprising a first dielectric layer (1) and a porous parallel plate waveguide (5); the porous parallel plate waveguide (5) includes a porous metal layer (2) and a second medium layer (3); the first dielectric layer (1), the porous metal layer (2), and the second dielectric layer (3) are sequentially arranged in the thickness extension direction; the porous metal layer (2) comprises a basic unit with holes (6) ), a plurality of basic units (6) with holes are integrally formed or fastened. When used to fit the occasions where the refractive index changes rapidly, the use of the basic unit with holes with variable size can make the step value of the refractive index smaller; further, the basic unit with holes with variable size proposed by the present invention can be better Fit the required rapidly changing refractive index.

Description

Refractive index controllable metasurface

technical field

The invention relates to the field of metamaterials, in particular to a refractive index controllable metasurface.

Background technique

With the development of metamaterial technology, metamaterials are increasingly used to control the equivalent refractive index, thereby controlling the propagation direction of electromagnetic waves. A graded index profile is required in many microwave lenses (eg planar Lumberg lenses, Maxwell fisheye lenses, Eaton lenses, etc.). Compared with the traditional use of multiple layers of materials with different refractive indices to achieve refractive index gradients, metamaterials provide a new way to achieve this type of lens.

The existing methods that can realize the gradient of refractive index mainly include: multiple layers of materials with different refractive indices; dielectric plates with non-uniform perforations; dielectric plates with varying thicknesses inserted into parallel-plate waveguides, and parallel-plate waveguides with uniformly variable spacing between upper and lower parallel plates. (Wu Xidong et al., published in the journal "IEEE Antennas and Propagation" in 2007, "Sector beam millimeter-wave antenna based on cylindrical Lumberg lens design" provides a detailed summary of the waveguide structure that can realize variable refractive index); above The methods all realize that the refractive index can be changed according to the demand to a certain extent, but put forward relatively high requirements on the material or processing accuracy, which limits its accuracy and application range. In order to improve the precision of refractive index control and reduce the difficulty of processing, metasurfaces have been proposed to achieve controllable refractive index.

The basic principle of metasurface to achieve refractive index gradient is to change the local equivalent refractive index by changing the geometric size of the electric small unit. The equivalent refractive index of the parallel-plate waveguide is controllable. This metasurface structure enables precise control of the refractive index because the electrically small cells of the metasurface can be made very small. However, this method usually works in TM wave or TE wave mode by changing the boundary conditions, so the working bandwidth is limited to a certain extent.

SUMMARY OF THE INVENTION

In view of the defects in the prior art, the purpose of the present invention is to provide a refractive index controllable metasurface.

The refractive index controllable metasurface provided according to the present invention includes a first dielectric layer and a porous parallel plate waveguide; the porous parallel plate waveguide includes a porous metal layer and a second dielectric layer;

The first dielectric layer, the porous metal layer, and the second dielectric layer are sequentially arranged in the thickness extension direction;

The porous metal layer includes a basic unit with holes, and a plurality of basic units with holes are integrally formed or fastened.

Preferably, the basic unit is provided with circular openings; when the size of the holes changes, the hole spacing formed between the circular openings on two adjacent basic units with holes is kept equal;

The inner space of the circular opening forms a first transmission unit, and the solid part of the basic unit with holes other than the circular opening forms a second transmission unit.

Preferably, the first dielectric layer includes a first dielectric plate or a first air layer.

Preferably, the second dielectric layer includes a second dielectric plate or a second air layer.

Preferably, the inner diameter of the circular opening is less than or equal to one tenth of the wavelength of the refracted electromagnetic wave.

Preferably, the dielectric constant of the first dielectric layer is greater than or equal to the dielectric constant of the second dielectric layer.

Preferably, the dielectric constant of the first dielectric layer is greater than or equal to 1 and less than or equal to 10.2.

Preferably, the porous parallel plate waveguide further comprises a floor layer; the first dielectric layer, the porous metal layer, the second dielectric layer and the floor layer are arranged in sequence.

Compared with the prior art, the present invention has the following beneficial effects:

1. The method of controlling the refractive index proposed by the present invention has a simple structure, can be processed and manufactured by using a standard printed circuit process, and is suitable for mass production.

2. The structure proposed by the present invention can realize the gradual change of the refractive index from the minimum value a to the maximum value b. a depends on the dielectric constant of the second dielectric layer, and the minimum value of a is 1. The variable range b-a depends on the dielectric constant of the upper and lower dielectric layers. The difference between the constants and the height of the porous parallel plate waveguide is slightly different, and the variable range of the refractive index can be flexibly controlled by changing the above parameters.

3. The metasurface proposed by the present invention can realize the gradual change of the refractive index with smaller step value. The size of the basic unit used in common metasurfaces is unchanged, and the size of the interior of the basic unit is changed to realize the refractive index of different sizes; and the present invention has holes. The size of the base unit varies with the size of the hole; therefore,

4. When used to fit the occasions where the refractive index changes rapidly, the use of a unit with a variable size of the basic unit with holes can make the step value of the refractive index smaller; therefore,

5. The required continuously changing refractive index can be better fitted by using the variable-sized unit with holes in the basic unit proposed by the present invention.

Description of drawings

Other features, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments with reference to the following drawings:

1 is a schematic diagram of a metasurface structure with a controllable refractive index when the second medium layer is an air layer;

Figure 2 is a schematic diagram of the cross-section of the refractive index controllable metasurface and its electric field distribution;

Figure 3 is a schematic diagram of the upper metal hole punching of the parallel plate waveguide; in the figure r _h is the radius of the circular hole, and g is the hole spacing;

Figure 4 shows the change of the pore size corresponding to the equivalent refractive index when the dielectric constant of the first dielectric layer changes from 1 to 10.2; in the figure, Re is the real part of the refractive index, n _eff is the equivalent refractive index, and ε _r is the first medium Layer dielectric constant.

Detailed ways

The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", The orientation or positional relationship indicated by "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the indicated device. Or elements must have a particular orientation, be constructed and operate in a particular orientation, and therefore should not be construed as limiting the invention.

As shown in FIGS. 1 and 2 , the refractive index controllable metasurface provided by the present invention includes a first dielectric layer 1 and a porous parallel plate waveguide 5 ; the porous parallel plate waveguide 5 includes a porous metal layer 2 and a second dielectric layer 3 and the floor layer 4; the first dielectric layer 1, the porous metal layer 2, the second dielectric layer 3, and the floor layer 4 are sequentially arranged in the thickness extension direction; the porous metal layer 2 includes a basic unit 6 with holes, a plurality of belts The hole base unit 6 is integrally formed or fastened.

The basic unit 6 with holes is provided with circular openings; the hole spacing between the circular openings on two adjacent basic units 6 with holes is equal, as shown in Figure 3, the inner space of the circular openings is formed The first propagation unit (corresponding to unit A), the solid part of the basic unit 6 with holes except for the circular opening forms the second propagation unit (corresponding to unit B). Because the circular holes have rotational symmetry and have the same retardation effect on electromagnetic waves in any direction, circular holes are uniformly opened on the upper surface of the porous parallel plate waveguide 5 , that is, the porous metal layer 2 . When all the holes have the same size and are uniformly arranged, the porous parallel plate waveguide 5 can be regarded as a uniform material with an equivalent refractive index n _eff . When the gradient refractive index distribution is required, the size of the circular hole is changed to keep the distance between the holes constant, thereby changing the filling rate of the basic unit with holes 6 to change the equivalent refractive index of the basic unit with holes 6 . It is worth noting that when the size of the circular hole changes, the hole spacing remains unchanged so that the size of the basic unit 6 with holes changes with the size of the circular hole. When the size of the circular hole is larger, the filling rate is larger and the equivalent refractive index is larger. Specifically in the actual gradient refractive index design, the size of the circular hole can be selected according to the required refractive index, thereby obtaining the required gradient refractive index and realizing the regulation of electromagnetic waves.

The present invention is applied to occasions requiring graded refractive index, such as microwave lenses, energy focusing and the like. The equivalent refractive index is improved by opening holes on the upper surface of the porous parallel plate waveguide 5 to change the path of the current, and the equivalent refractive index is further improved by placing the first dielectric layer 1 on the porous parallel plate waveguide 5, and the processing difficulty is reduced at the same time. Standard printed circuit board processes are sufficient. In practical applications, any one or more of the following parts are processed by standard PCB technology: between the first dielectric plate and the porous parallel-plate waveguide 5 ; the overall structure of the porous parallel-plate waveguide 5 .

Preferably, the first dielectric layer 1 includes a first dielectric plate or a first air layer. Preferably, the second dielectric layer 3 includes a second dielectric plate or a second air layer. As shown in FIG. 2, most of the electric field propagates inside the porous parallel plate waveguide 5, but part of it enters the first dielectric plate. Therefore, the equivalent dielectric constant is further improved. Here, taking the second dielectric layer 3 as an air layer as an example, the verification is performed by simulating the S parameters of the metasurface to calculate the refractive index corresponding to different circular hole sizes. Figure 4 shows the variation of the equivalent refractive index with the radius of the circular hole when the dielectric constants of the first dielectric layer 1 are 1, 2.2, 3.48, 6.15 and 10.2, respectively. It can be seen from the figure: 1. For the same first dielectric plate, the larger the radius of the circular hole in the porous metal layer 2, the larger the equivalent refractive index; 2. For different first dielectric layers 1, the circular hole in the porous metal layer 2 is larger. When the size is the same, the higher the dielectric constant of the first dielectric layer 1, the greater the equivalent refractive index; 3. The higher the dielectric constant of the first dielectric layer 1, the greater the achievable maximum equivalent refractive index. As shown in FIG. 4 , when the first dielectric layer 1 is an air layer, the achievable maximum equivalent refractive index is about 1.4; when the dielectric constant of the first dielectric layer 1 is 6.15, the achievable maximum equivalent refractive index is about 2.

working principle:

As shown in Figures 1 and 2, holes are opened on the upper surface of the porous parallel plate waveguide 5, wherein the hole diameter is less than or approximately one-tenth of the wavelength, and the opening can control the surface current distribution of the porous parallel plate waveguide 5, so that the electromagnetic field is The path length propagating within the porous parallel-plate waveguide 5 is increased. Secondly, placing the first dielectric layer 1 on the upper surface of the porous parallel-plate waveguide 5 can further improve the equivalent refractive index under the condition that the size of the hole remains unchanged. Figure 2 shows the distribution of the electric field perpendicular to the propagation direction of the electromagnetic wave, from which it can be seen that although most of the electric field is still bound in the porous parallel plate waveguide 5, a part of the electric field enters the first dielectric layer 1, and the first dielectric layer 1 The dielectric constant is generally higher than that of the second dielectric layer 3 . Therefore, the refractive index is further increased. At the same time, placing the first dielectric plate on the upper surface of the porous parallel plate waveguide 5 can reduce the processing difficulty. The refractive index controllable metasurface proposed by the present invention can be processed using standard printed board technology. It can be seen from the refractive index distribution corresponding to the hole radius in Fig. 4 that the equivalent refractive index can be conveniently controlled only by controlling the hole radius. And by changing the dielectric constant of the first dielectric layer 1 , the rate of change of the refractive index with the hole radius can be controlled, and the maximum achievable refractive index can also be controlled.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above-mentioned specific embodiments, and those skilled in the art can make various variations or modifications within the scope of the claims, which do not affect the essential content of the present invention. The embodiments of the present application and features in the embodiments may be combined with each other arbitrarily, provided that there is no conflict.

Claims (7)

1. A refractive index controllable super-surface comprising a first dielectric layer (1) and a porous parallel plate waveguide (5); the porous parallel plate waveguide (5) comprises a porous metal layer (2), a second dielectric layer (3) and a floor layer (4); the first dielectric layer (1), the porous metal layer (2), the second dielectric layer (3) and the floor layer (4) are sequentially arranged in the thickness extending direction; the porous metal layer (2) comprises basic units (6) with holes, and a plurality of basic units (6) with holes are integrally formed or fixedly connected;

the hole spacing formed between the circular holes on two adjacent basic units (6) with holes is equal, when the basic units are used for fitting the occasion of gradual change of the refractive index, the hole size of the basic units (6) with holes is changed, the hole spacing is not changed, and the basic units with holes with variable periods are formed.

2. A refractive index controllable super surface according to claim 1, characterized in that the holed elementary units (6) are provided with circular openings; the hole spacing formed between the circular holes on the two adjacent basic units (6) with holes is equal; the inner space of the circular opening forms a first transmission unit, and the solid parts of the basic unit (6) with holes except the circular opening form a second transmission unit.

3. The refractive index controllable super surface according to claim 1, wherein the first dielectric layer (1) comprises a first dielectric sheet or a first layer of air.

4. The refractive index controllable super surface according to claim 1, wherein the second dielectric layer (3) comprises a second dielectric sheet or a second layer of air.

5. The index-controllable metasurface of claim 1, wherein an inner diameter of the circular opening is equal to or less than one tenth of a wavelength of an electromagnetic wave to be refracted.

6. The refractive index controllable meta-surface according to claim 1, characterized in that the dielectric constant of the first dielectric layer (1) is equal to or greater than the dielectric constant of the second dielectric layer (3).

7. The refractive index controllable meta-surface according to claim 1, wherein the first dielectric layer (1) has a dielectric constant of 1 or more and 10.2 or less.

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