CN102890298B - Metamaterials for compressing electromagnetic waves - Google Patents
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Abstract
The invention discloses metamaterials for compressing electromagnetic waves, comprising base materials and a plurality of artificial microstructures, wherein the base materials are divided into a plurality of lattices; one artificial microstructure is arranged in one lattice to form a unit; the metamaterials are divided into a plurality of zones; the refractive index of each zone is gradually reduced; the length of each zone meets the following formula yi=sqrt((lambda+sqrt(y<i-1><2>+s<2>))<2>-s<2>); the refractive index of the unit in the zone meets with following formula ny=n<max>-(n<max>-n<min>)/(c/f) *(sqrt(y<2>+s<2>)-sqrt(y<i-1><2>+s<2>-sqrt(y<i-1><2>+s<2>)): wherein i is the number of the zone and natural number; when i is equal to 1, y0 is equal to 0; S is the linear distance of the starting unit of the first zone on a wave source vertical metamaterial plane and the wave source; f is the frequency of the wave source; c is velocity of light; gamma is wave length; and the starting unit has the greatest refractive index in the first zone. The metamaterials can transform the diffusing electromagnetic waves into parallel waves to be transmitted; and the metamaterials achieves the effect of compressing the electromagnetic waves.
Description
Technical Field
The invention relates to the field of metamaterials, in particular to a metamaterial for compressing electromagnetic waves.
Background
As is well known, a cylindrical mirror, also called a self-focusing lens, changes the refractive index of the lens by a special manufacturing and processing means through a principle similar to an optical fiber, the aperture of the lens is generally very small, approximately about 2mm, the thinnest is also several micrometers, and the lens can be made into a form of P/4, P/2,. et al (where P is an intercept), wherein the focus of the P/4 cylindrical mirror is on the end face, that is: the focal length is P/4.
Generally, the cylindrical lens is mainly divided into a plano-convex cylindrical lens and a plano-concave cylindrical lens, is mainly used for conducting light energy convergence of an optical fiber, has the properties similar to those of common lenses (mainly optical performance parameters, indexes and the like), but has slight difference that the cylindrical lens is an aspheric lens and can effectively reduce optical losses such as spherical aberration, chromatic aberration and the like; the refractive index of the cylindrical mirror is changed along the radial direction, so that the transmission direction of the horizontal incident light can be changed, the transmission direction of the vertical incident light is not changed, and the cylindrical mirror can be applied to occasions where the transmission of the light in one direction is changed and the transmission of the light in the other direction has no requirement, such as the cylindrical mirror is used for refracting and focusing a diffusion type light source into a linear light source.
With the development of society and the demand of energy conservation and economy, finding a material to maintain the refractive focusing property of a cylindrical lens and simultaneously more effectively reduce the optical loss of the lens becomes a new trend and development trend of people research.
Metamaterial (meta) is a material design concept and is attracting more and more attention as a research frontier, so called meta-material refers to artificial composite structures or composite materials with extraordinary physical properties that natural materials do not have, and through structural ordered design on the key physical scale of materials, the meta-material can break through the limits of some apparent natural laws, thereby obtaining ordinary extraordinary material functions beyond the nature.
The "metamaterials" developed to date include: "left-handed material", photonic crystal, "super magnetic material", etc., the properties of the super material are usually not mainly determined by the intrinsic properties of the constituent materials, but by the artificial structure thereof.
The metamaterial is composed of a dielectric substrate and a plurality of artificial structures arranged on the dielectric substrate, and can provide various material characteristics which are possessed or not possessed by common materials. A single artificial structure is typically sized to be less than 1/10 wavelengths and has an electrical and/or magnetic response to an applied electric and/or magnetic field, thereby exhibiting an equivalent permittivity and/or equivalent permeability, or an equivalent refractive index and wave impedance. The equivalent dielectric constant and equivalent permeability (or equivalent refractive index and wave impedance) of the artificial structure are determined by the cell geometric parameters and can be artificially designed and controlled. Furthermore, the artificial structure can have anisotropic electromagnetic parameters which are artificially designed, so that a plurality of novel phenomena are generated, and the influence of electromagnetic waves is possible.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a metamaterial for compressing electromagnetic waves, which maintains the refractive focusing property of a cylindrical lens, effectively reduces the optical loss of the lens, has small volume, is simple, easy to realize and low in cost.
The first technical scheme adopted by the invention for solving the technical problems is as follows: provided is a metamaterial for compressing electromagnetic waves, including: the metamaterial comprises a substrate and a plurality of artificial microstructures, wherein the substrate is divided into a plurality of crystal lattices, one artificial microstructure is arranged in one crystal lattice to form a unit, the metamaterial is divided into a plurality of sections, the refractive index of each section is gradually changed from large to small, and the length of each section satisfies the following formula: <math>
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the unit refractive index of each section satisfies the following formula:
i is the number of the divided sections, the value is a natural number, and when i is 1, y is0＝0；
nmaxThe maximum refractive index of the unit on each section of the metamaterial;
nminthe minimum refractive index of a unit on each section of the metamaterial;
s is the linear distance between the initial unit of the first section on the plane of the metamaterial and the wave source, f is the frequency of the wave source, c is the speed of light, lambda is the wavelength, the initial unit is the unit with the maximum refractive index of the first section, and y is the distance y in the vertical direction of the metamaterial0The distance of (c).
In the metamaterial for compressing the electromagnetic waves, the metamaterial is formed by laminating a plurality of sheet-shaped substrates, each sheet-shaped substrate is composed of a base material and a plurality of artificial microstructures, and all the artificial microstructures form a periodic array in space.
In the metamaterial for compressing electromagnetic waves, all the artificial microstructures are in a uniform periodic array in space.
In the metamaterial for compressing the electromagnetic wave, the refractive index is obtained by changing the pattern and the design size of the artificial microstructures and/or the arrangement of the artificial microstructures in the space under the condition that the substrate is selected.
In the metamaterial for compressing electromagnetic waves, the base material is made of a ceramic material, a high polymer material, a ferroelectric material, a ferrite material or a ferromagnetic material.
In the metamaterial for compressing electromagnetic waves, the artificial microstructures are metal wires with patterns attached to a base material.
In the metamaterial for compressing electromagnetic waves, the metal wire is attached to the base material by etching, electroplating, drilling, photoetching, electronic etching or ion etching.
In the metamaterial for compressing electromagnetic waves, the metal wire is a copper wire or a silver wire.
In the metamaterial for compressing electromagnetic waves, the metal wire is in a two-dimensional snowflake shape and has a first main wire and a second main wire which are perpendicular to each other and in a cross shape, two ends of the first main wire are respectively and vertically provided with a first branch wire, and two ends of the second main wire are respectively and vertically provided with a second branch wire.
In the metamaterial for compressing electromagnetic waves according to the present invention, the first main line and the second main line are bisected by each other, the center of the first branch line is connected to the first main line, and the center of the second branch line is connected to the second main line.
The metamaterial has the following beneficial effects:
1. the volume is small, and excessive space is not occupied;
2. the method is simple, easy to realize and low in cost, maintains the refractive focusing performance of the cylindrical lens, and simultaneously effectively reduces the optical loss of the lens;
3. the divergent electromagnetic wave can be changed into parallel wave to be emitted, thereby compressing the original electromagnetic wave.
Drawings
FIG. 1 is a block diagram of a metamaterial structure for compressing electromagnetic waves according to an embodiment of the present invention;
FIG. 2a is a cross-sectional view of a metamaterial compressing electromagnetic waves according to an embodiment of the present invention;
FIG. 2b is a schematic diagram of the refractive index of the metamaterial for compressing electromagnetic waves according to the embodiment of the invention;
FIG. 3 is a schematic view of an artificial microstructure;
fig. 4 to 6 are derived views of fig. 3.
Detailed Description
In order to explain technical contents, structural features, and objects and effects of the present invention in detail, the following detailed description is given with reference to the accompanying drawings in conjunction with the embodiments.
"metamaterial" refers to some artificial composite structures or composites having extraordinary physical properties not possessed by natural materials. Through the ordered structure design on the key physical scale of the material, the limit of certain apparent natural laws can be broken through, and the extraordinary material function exceeding the inherent common property of the nature can be obtained.
Three important features of the "metamaterial":
(1) "metamaterials" are typically composite materials with novel artificial structures;
(2) "metamaterials" have extraordinary physical properties (often not found in natural materials);
(3) the properties of a "metamaterial" are often not primarily determined by the intrinsic properties of the constituent materials, but rather by the artificial structure therein.
Referring to fig. 1 and 2, in an embodiment of the present invention, a metamaterial 20 for compressing electromagnetic waves, as shown in fig. 1, includes: the metamaterial comprises a base material 1 and a plurality of artificial microstructures 2, wherein the base material 1 and the artificial microstructures 2 form a metamaterial sheet-shaped base plate 11, the base material 1 is divided into a plurality of crystal lattices, one artificial microstructure 2 is arranged in one crystal lattice to form a unit, a metamaterial 20 is divided into a plurality of sections, the refractive index of each section is gradually changed from large to small, and the length of each section satisfies the following formula: <math>
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the refractive index of the unit in the divided section satisfies the following formula:
i is the number of the divided sections, and the value is natural number, yiIs the distance between the end position of the i-th section and the start position of the first section, and when i is 1, y0＝0，
nmaxThe maximum refractive index of the unit on each section of the metamaterial;
nminthe minimum refractive index of a unit on each section of the metamaterial;
f is the frequency of the wave source 10, c is the speed of light, λ is the wavelength, the first segment starting unit is the unit with the largest refractive index of the first segment, and y is the distance y in the vertical direction of the metamaterial0The distance of (c).
As can be seen from fig. 2a and 2b, S is the linear distance from the first segment start unit 201 to the wave source 10, where the wave source 10 is perpendicular to the plane of the metamaterial 20, f is the frequency of the wave source 10, c is the speed of light, and the refractive index of the first unit is the maximum; y is0The starting position of the first section of the metamaterial 20 in the vertical direction (which can be equivalent to the Y axis on the plane), Y0The value is zero, and the metamaterial is divided into a plurality of sections along the vertical direction, namely: the distance range between the unit on the 1 st section and the initial position of the first section is y0To y1(ii) a The distance range between the unit on the second section and the initial position of the first section is y1To y2(ii) a And so on. The division into segments is due to process limitations, such as the process is easy to achieve if the refractive index of the metamaterial 20 has a certain range distribution, and the refractive index of each segment varies from large to small, and the refractive index of each unit of the metamaterial 20 is distributed up and down symmetrically with the first segment starting unit 201.
As can be seen from fig. 1, the electromagnetic wave passing through the bus bar of the metamaterial 20 does not change its original direction, and the electromagnetic wave that does not pass through the bus bar of the metamaterial 20 is changed from a divergent electromagnetic wave (as shown by a dotted line in fig. 1) into a parallel wave (as shown by a solid line in fig. 1) after passing through the metamaterial 20, thereby compressing the electromagnetic wave.
As can be seen from fig. 1, for higher efficiency, three different metamaterial sheet-shaped substrates 11 are laminated to refract electromagnetic waves, which is only an example, in practical application, four, five, six or other metamaterial sheet-shaped substrates 11 can be laminated according to application requirements, and for higher efficiency, the artificial microstructures 2 preferably form a periodic array, especially a uniform periodic array, on the substrate 1.
Fig. 2 is a cross-sectional view of a metamaterial 20 according to an embodiment of the present invention, although a converging effect can be achieved by using only one sheet substrate 11, in practice, for better refraction effect, a metamaterial assembly 20 is usually formed by a plurality of sheet substrates 11 as described above.
The substrate 1 is divided into several crystal lattices, the concept of "lattice" comes from solid physics, where "lattice" refers to the dimensions occupied by each artificial microstructure 2 in the metamaterial. The "lattice" size depends on the refractive index profile to which the artificial microstructure 2 is required to respond, and typically the size of the artificial microstructure 2 is one tenth of the wavelength of the electromagnetic wave to which it is required to respond.
The artificial microstructures 2 are placed in a lattice to form a unit having a refractive index that is obtained by simulation in a manner that changes the pattern, design dimensions, and/or arrangement of the artificial microstructures 2 in space under selected conditions of the substrate 1.
The metamaterial may respond to an electric field or a magnetic field, or both. The response to an electric field depends on the permittivity epsilon of the metamaterial, while the response to a magnetic field depends on the permeability mu of the metamaterial. By accurately controlling the dielectric constant epsilon and the magnetic permeability mu of each point in the metamaterial space, the influence of the metamaterial on electromagnetic waves can be realized.
The uniform or non-uniform distribution of the electromagnetic parameters of the metamaterial in space is one of the important features of the metamaterial 20. The uniform distribution of electromagnetic parameters in space is a special form of non-uniform distribution, but its specific characteristics are still determined by the characteristics of each unit structure arranged in space. Therefore, by designing the characteristics of each structure arranged in the space, the electromagnetic characteristics of the whole metamaterial at each point in the space can be designed, and the electromagnetic material system has a plurality of singular characteristics and can play a special guiding role in the propagation of electromagnetic waves.
In the metamaterial for compressing electromagnetic waves of the present invention, the base material 1 is made of a ceramic material, a polymer material, a ferroelectric material, a ferrite material, or a ferromagnetic material. Preferably, FR4, F4B and polytetrafluoroethylene are selected, which have very good electrical insulation, so that the material does not interfere with the electric field of electromagnetic waves, has excellent chemical stability and corrosion resistance, has long service life, and is a good choice for the substrate 1 to which the artificial microstructure 2 is attached.
In the metamaterial for compressing electromagnetic waves of the present invention, the artificial microstructure 2 is a microstructure
Patterned metal lines attached to the substrate 1.
In the metamaterial for compressing electromagnetic waves according to the present invention, the metal line is attached to the base material 1 by etching, plating, drilling, photolithography, electron lithography, or ion lithography.
In the metamaterial for compressing electromagnetic waves, the metal wire is a copper wire or a silver wire.
As shown in fig. 3, as a specific embodiment, the metal wire is in a two-dimensional snowflake shape, and has a first main wire 21 and a second main wire 22 which are perpendicular to each other and in a cross shape, two first branch wires 23 are perpendicularly disposed at both ends of the first main wire 21, and two second branch wires 24 are perpendicularly disposed at both ends of the first main wire. The first main line 21 and the second main line 22 are bisected each other, the centers of the two first branch lines 23 are connected to the first main line 21, and the centers of the two second branch lines 24 are connected to the second main line 22. In this embodiment, the isotropic case is:
the first main line and the second main line have the same length; the first branch and the second branch are also the same in length;
of course, this is just a simple example, and the pattern of metal lines may be other, as shown in fig. 4-6. FIGS. 4-6 show the derivation of the above-described pattern, i.e., adding two branches to each of the two first branches and the two second branches, and so on, and many other derivation patterns are possible; the present invention is not intended to be exhaustive. The figures are only schematic, and in practice the first main line, the second main line, the first branch line and the second branch line all have a width.
The 4 examples described above are all artificial microstructures 2 that can influence the refractive index profile; there are also many artificial microstructures 2 that can influence the refractive index profile, such as open resonator ring structures, which are used in many documents. In addition, the artificial microstructure 2 may have a plurality of deformation patterns, which the present invention does not address.
In the selected case of the substrate 1, the desired refractive index distribution result can be obtained by designing the pattern, design size and/or arrangement of the artificial microstructures 2 in space (i.e. the formula shown in the first embodiment should be satisfied), or by designing the pattern, design size and/or arrangement of the artificial microstructures 2 in space, the maximum and minimum refractive index of the metamaterial 20 in each section in space can be designed, so as to determine the refractive index of each section, and how to obtain the pattern, design size and/or arrangement of the artificial microstructures in space, this method is various, for example, can be obtained by inverse computer simulation, first we determine the desired refractive index distribution result, and based on this result, design the refractive index distribution result of the metamaterial as a whole, calculating the refractive index distribution result of each point in the space from the whole, selecting the pattern, the design size and/or the arrangement of the artificial microstructure in the space according to the refractive index distribution of each point (a plurality of kinds of artificial microstructure data are stored in a computer in advance), and designing each point by an exhaustion method, for example, firstly selecting an artificial microstructure with a specific pattern, calculating the refractive index distribution result, comparing the obtained result with the desired refractive index, and repeating the comparison for many times until the desired refractive index is found, and if the desired refractive index is found, completing the design parameter selection of the artificial microstructure 2; if not, the above cycle is repeated for a patterned artificial microstructure until the desired refractive index profile is found. If not, the process does not stop. That is, the process will only stop after finding the artificial microstructure that we need the refractive index profile result. Since this process is performed by a computer, it appears to be complex and can be performed quickly.
The metamaterial has the following beneficial effects:
1. the volume is small, and excessive space is not occupied;
2. the method is simple, easy to realize and low in cost, maintains the refractive focusing performance of the cylindrical lens, and simultaneously effectively reduces the optical loss of the lens;
3. the divergent electromagnetic wave can be changed into parallel wave to be emitted, thereby compressing the original electromagnetic wave.
While the present invention has been described with reference to the embodiments shown in the drawings, the present invention is not limited to the embodiments, which are illustrative and not restrictive, and it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (10)
1. A metamaterial for compressing electromagnetic waves, comprising: the metamaterial comprises a substrate and a plurality of artificial microstructures, wherein the substrate is divided into a plurality of crystal lattices, one artificial microstructure is arranged in one crystal lattice to form a unit, the metamaterial is divided into a plurality of sections, the refractive index of each section is gradually changed from large to small, and the length of each section satisfies the following formula: <math>
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the refractive index of the unit in the divided section satisfies the following formula:
i is the number of the divided sections, and the value is natural number, yiIs the distance between the end position of the i-th section and the start position of the first section, and when i is 1, y0＝0,
nmaxThe maximum refractive index of the unit on each section of the metamaterial;
nminthe minimum refractive index of a unit on each section of the metamaterial;
s is the linear distance between a first section starting unit and a wave source, wherein the wave source is vertical to the plane of the metamaterial, f is the frequency of the wave source, c is the speed of light, lambda is the wavelength, the starting unit is the unit with the maximum refractive index of the first section, and y is the distance from the starting position of the first section in the vertical direction of the metamaterial.
2. The metamaterial for compressing electromagnetic waves as claimed in claim 1, wherein the metamaterial is formed by laminating a plurality of sheet-like substrates, each sheet-like substrate is composed of a base material and a plurality of artificial microstructures, and all of the artificial microstructures form a periodic array in space.
3. The metamaterial for compressing electromagnetic waves as claimed in claim 2, wherein all of the artificial microstructures are in a spatially uniform periodic array.
4. The metamaterial for compressing electromagnetic waves as claimed in claim 1, wherein the refractive index is obtained by changing the pattern, design size and/or arrangement of the artificial microstructures in space under the selected condition of the substrate.
5. The metamaterial for compressing electromagnetic waves of claim 1, wherein the substrate is made of a ceramic material, a polymer material, a ferroelectric material, a ferrite material, or a ferromagnetic material.
6. The metamaterial for compressing electromagnetic waves as in claim 1, wherein the artificial microstructures are patterned metal wires attached to a substrate.
7. The electromagnetic wave compressing metamaterial according to claim 6, wherein the metal lines are attached to the substrate by etching, plating, drilling, photolithography, electrolithography, or ion lithography.
8. The metamaterial for compressing electromagnetic waves of claim 6, wherein the metal wire is a copper wire or a silver wire.
9. The metamaterial for compressing electromagnetic waves as claimed in claim 6, wherein the metal wire is in a two-dimensional snowflake shape and has a first main wire and a second main wire which are perpendicular to each other in a cross shape, a first branch wire is vertically disposed at each end of the first main wire, and a second branch wire is vertically disposed at each end of the second main wire.
10. The metamaterial for compressing electromagnetic waves of claim 9, wherein the first and second main lines are bisected by each other, the center of the first branch line is connected to the first main line, and the center of the second branch line is connected to the second main line.
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| CN101389998A (en) * | 2004-07-23 | 2009-03-18 | 加利福尼亚大学董事会 | Metamaterials |
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| WO2010021736A2 (en) * | 2008-08-22 | 2010-02-25 | Duke University | Metamaterials for surfaces and waveguides |
| CN101699659A (en) * | 2009-11-04 | 2010-04-28 | 东南大学 | Lens antenna |
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| US20090160718A1 (en) * | 2007-12-21 | 2009-06-25 | Ta-Jen Yen | Plane focus antenna |
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