Metamaterial

Abstract

To provide a metamaterial whose magnetic permeability and permittivity can be controlled independently.SOLUTION: A metamaterial 200 includes a plurality of resonator structures 100 arranged in a spatially distributed manner. The resonator structure 100 includes a pillar-shaped first element 110 and a second element 120 having a circular structure surrounding the first element 110. In each of the plurality of resonator structures 100, the size of the first element 110 and the size of the second element 120 are designed independently.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This disclosure relates to metamaterials. [Background technology]

[0002] In recent years, metamaterials, which exhibit properties not found in nature, have attracted considerable attention. The electromagnetic properties of a material are determined by the combination of its permittivity ε and permeability μ. A typical example is the realization of a negative refractive index by achieving negative permeability and negative permittivity. Metamaterials are expected to have applications such as optical camouflage.

[0003] Metamaterials are realized by controlling the permeability and dielectric constant using structures (called metaatoms) smaller than the target wavelength. To control the permeability μ, a split ring resonator (SRR) is used as a metaatom. An SRR is a metal ring with a gap formed therein, where the gap portion has capacitance C and the metal portion has inductance L, forming an LC resonator. When the magnetic field of an incident electromagnetic field passes through this SRR, an electromotive force is generated by electromagnetic induction, causing a current to flow, and this current generates a magnetic moment. In this way, the SRR exhibits a magnetic response. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-072534 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Conventional metamaterials only controlled either the permeability or dielectric constant of the resonator structure, meaning they could only control the refractive index distribution of one of the two orthogonal polarizations of light. Therefore, when using metamaterials for optical camouflage (invisibility cloaks), there was a problem of reduced transmittance.

[0006] This disclosure is made in such circumstances, and one exemplary objective of a certain aspect thereof is to provide a metamaterial in which permeability and dielectric constant can be controlled independently. [Means for solving the problem]

[0007] Certain aspects of this disclosure relate to a metamaterial. The metamaterial comprises a plurality of spatially distributed and arranged resonator structures. Each resonator structure includes a pillar-like first element and a second element having a circumferential structure surrounding the first element. In each of the plurality of resonator structures, the size of the first element and the size of the second element are designed independently. [Effects of the Invention]

[0008] According to one aspect of this disclosure, the permeability and dielectric constant can be controlled independently. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing the structure of the metamaterial according to the embodiment. [Figure 2] This is a perspective view of the resonator structure according to the embodiment. [Figure 3] This diagram illustrates the design parameters of the first element. [Figure 4] This figure shows the simulation results of the dielectric constant εr when the first element is placed alone. [Figure 5] This figure shows the relationship between the height h of the first element and the dielectric constant εr. [Figure 6] This diagram illustrates the design parameters for the second element. [Figure 7]It is a diagram showing the simulation result of the magnetic permeability μr when the second element is arranged alone. [Figure 8] It is a diagram showing the relationship between the length a of the second element and the magnetic permeability μr. [Figure 9] It is a diagram showing the dielectric constant εr when the design parameter a of the second element is simultaneously changed in addition to the design parameter h of the first element. [Figure 10] It is a diagram obtained by superposing and plotting the dielectric constant εr of FIG. 9 on the plot of FIG. 5. [Figure 11] It is a diagram showing the magnetic permeability μr when the design parameter h of the first element is simultaneously changed in addition to the design parameter a of the second element. [Figure 12] It is a diagram obtained by superposing and plotting the magnetic permeability μr of FIG. 11 on the plot of FIG. 8. [Figure 13] It is a diagram showing a metamaterial sheet according to an embodiment. [Figure 14] It is a diagram for explaining the usage form of the metamaterial sheet of FIG. 13. [Figure 15] It is a diagram showing the distribution of the parameter h for realizing polarization-independent optical camouflage. [Figure 16] It is a diagram showing the distribution of the parameter a for realizing optical camouflage.

Mode for Carrying Out the Invention

[0010] (Overview of the Embodiment) The overview of some exemplary embodiments of the present disclosure will be described. This overview is for the purpose of providing a basic understanding of the embodiments as a prelude to the detailed description to follow, and simplifies and explains some concepts of one or more embodiments. It does not limit the scope of the invention or the disclosure. Also, this overview is not an all-inclusive overview of all possible embodiments and does not limit the essential components of the embodiments. For convenience, "one embodiment" may be used to refer to one embodiment (example or variant) or a plurality of embodiments (examples or variants) disclosed in this specification.

[0011] A metamaterial according to one embodiment comprises a plurality of resonator structures arranged in a spatially distributed manner. Each resonator structure includes a pillar-shaped first element and a second element having a circumferential structure surrounding the first element. In each of the plurality of resonator structures, the size of the first element and the size of the second element are designed independently.

[0012] With this configuration, the dielectric constant can be controlled according to the size of the first element and the permeability can be controlled according to the size of the second element for each resonator structure, thereby forming independent spatial distributions for dielectric constant and permeability.

[0013] In one embodiment, the size of the first element may be its height. By keeping the cross-sectional size of the first element constant while changing its height, the dielectric constant can be easily controlled.

[0014] In one embodiment, the size of the second element may be its circumference. By keeping the size of the cross-section perpendicular to the circumferential direction of the second element constant while changing its length in the circumferential direction, the magnetic permeability can be easily controlled.

[0015] In one embodiment, the second element may have a grid structure.

[0016] In one embodiment, the multiple resonator structures may be formed on a single sheet. By wrapping this sheet around an object multiple times, the multiple resonator structures are distributed three-dimensionally on the surface of the object, forming independent distributions of dielectric constant and magnetic permeability. This makes it possible to achieve highly transparent optical camouflage that utilizes both of the two orthogonal polarization components.

[0017] (Embodiment) The embodiments will be described in detail below with reference to several drawings. In the following description, components having substantially the same function and configuration will be denoted by the same reference numerals, and redundant descriptions will be given only when necessary.

[0018] Preferred embodiments will be described below with reference to the drawings. The same or equivalent components, members, and processes shown in each drawing will be denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. Furthermore, the embodiments are illustrative and not limiting to the disclosure and invention, and not all features or combinations thereof described in the embodiments are necessarily essential to the disclosure and invention.

[0019] Furthermore, the dimensions (thickness, length, width, etc.) of each component shown in the drawing may be enlarged or reduced as appropriate for ease of understanding. Moreover, the dimensions of multiple components do not necessarily represent their relative sizes; even if component A is depicted as thicker than component B in the drawing, component A may actually be thinner than component B.

[0020] Figure 1 is a perspective view showing the structure of a metamaterial 200 according to an embodiment. The metamaterial 200 comprises a plurality of metaatoms 202 distributed in three dimensions (or two dimensions) in space. Each metaatom 202 has controllable permeability μ and permittivity ε, and therefore its refractive index can be controlled. The metaatoms 202 are composed of a resonator structure 100, which will be described later. The metamaterial 200, which is an aggregate of metaatoms 202, has a spatial distribution of arbitrary refractive indices. For example, by forming a negative refractive index distribution in space using the metamaterial 200, optical camouflage and other optical elements can be realized.

[0021] Figure 2 is a perspective view of the resonator structure 100 according to the embodiment. As shown in Figure 1, this resonator structure 100 is used as a metaatom 202 of the metamaterial 200, and its dielectric constant ε and permeability μ are controllable.

[0022] The resonator structure 100 comprises a first element 110 and a second element 120. The first element 110 has a pillar shape. In this example, the first element 110 is a rectangular prism, but it may also be a cylinder or a polygonal prism. The first element 110 is also referred to as an inner bar.

[0023] The second element 120 has a circumferential structure surrounding the first element 110. The second element 120 is also referred to as the outer ring. The first element 110 is configured to form a resonant circuit including an inductor and a capacitor connected in series in the circumferential direction when viewed as an equivalent circuit. In this embodiment, the first element 110 has a grid structure and includes a first wiring pair 122 extending parallel to the first direction and a second wiring pair 124 extending parallel to the second direction, with the first wiring pair 122 and the second wiring pair 124 being formed at different heights.

[0024] The resonator structure 100 has design parameters for the size of the first element 110 and the size of the second element 120, and the dielectric constant ε and permeability μ are controlled by the combination of these parameters.

[0025] Next, I will explain the design parameters.

[0026] Figure 3 illustrates the design parameters of the first element 110. In this example, the first element 110 is a rectangular prism, and its size is defined by its height h and the dimensions w1 and d1 of its rectangular cross-section. Any one or more of these can be used as design parameters for dielectric constant control. However, increasing the number of design parameters exponentially increases the number of combinations, so it is preferable to have fewer design parameters. Therefore, it is preferable to fix w1 and d1 and use height h as the design parameter.

[0027] Figure 4 shows the dielectric constant ε when the first element 110 is placed alone. r This figure shows the simulation results. Here, w1=d1=10nm is fixed, height h is selected as the design parameter, and the height h is varied in 10nm increments within the range of 100nm to 170nm, and the dielectric constant ε r We investigated the changes.

[0028] Figure 5 shows the height h and dielectric constant ε of the first element 110. r This diagram shows the relationship. By using the height h of the first element 110 as a control parameter, the dielectric constant ε r It can be controlled over a wide range from 0 to 1.4.

[0029] FIG. 6 is a diagram for explaining the design parameters of the second element 120. For this second element 120, with respect to the first wiring pair 122, the cross-sectional sizes d1, w1 of the wiring and the distance a1 between the two wirings can be selected as design parameters. Also, with respect to the second wiring pair 124, the cross-sectional sizes d2, w2 of the wiring and the distance a2 between the two wirings can be selected as design parameters. Furthermore, the distance b in the height direction between the first wiring pair 122 and the second wiring pair 124 can be selected as a design parameter.

[0030] Note that although the wiring length l1 of the first wiring pair 122 and the wiring length l2 of the second wiring pair 124 can also be regarded as design parameters, since l2 = a1 + 2×d1 and l1 = a2 + 2×d2, it can be said that l1 and l2 are dependent design parameters.

[0031] Regarding the second element 120 as well, if the number of design parameters is increased, the combinations increase exponentially, so it is preferable that the design parameters be few. Therefore, it is advisable to fix w1, d1, w2, d2, b and, under the constraint condition that a1 = a2 = a, use a as the design parameter. Changing the length a is nothing other than changing the perimeter of the second element 120.

[0032] FIG. 7 is a diagram showing the simulation result of the magnetic permeability μ when the second element 120 is arranged alone. Here, w1 = w2 = 30 nm, d1 = d2 = 30 nm, and b = 60 nm are fixed, the length a is selected as the design parameter, and the length a is changed in 5 nm increments in the range of 50 nm to 90 nm to examine the change in the magnetic permeability μ. r It can be seen that at the oscillation frequency of light of 410.1 THz, the magnetic permeability μ can be changed in the range of 0.05 to 0.44. Note that if the magnetic permeability μ is designed in the negative region, a negative refractive index can be obtained. r at the oscillation frequency of light of 410.1 THz, the magnetic permeability μ r can be changed in the range of 0.05 to 0.44. Note that if the magnetic permeability μ r is designed in the negative region, a negative refractive index can be obtained.

[0033] FIG. 8 shows the length a of the second element 120 and the magnetic permeability μ rThis diagram shows the relationship. By using the length a (i.e., circumference) of the wiring element of the second element 120 as a control parameter, the permeability μ r It can be controlled over a wide range of 0.05 to 0.42.

[0034] Up to this point, we have examined the individual characteristics of the first element 110 and the second element 120. When the first element 110 and the second element 120 are used together, they interact with each other because they are spatially close. Therefore, the dielectric constant ε of the first element 110 alone r This can be controlled, or the permeability μ of the second element 120 alone can be controlled. r Even if we can control it, in those combinations, the dielectric constant ε r and magnetic permeability μ r It's not always possible to control them independently. Therefore, we investigated this concern through simulations.

[0035] Figure 9 shows the dielectric constant ε when the design parameter h of the first element 110 and the design parameter a of the second element 120 are changed simultaneously. r This figure shows the result. Figure 10 shows the dielectric constant ε from Figure 9 plotted on top of Figure 5. r This is a graph plotting the dielectric constant ε. As can be seen from Figure 10, the dielectric constant ε r It can be seen that this is determined by the original design parameter h, with little influence from the design parameter a.

[0036] Figure 11 shows the permeability μ when the design parameter a of the second element 120 and the design parameter h of the first element 110 are changed simultaneously. r This figure shows the plot from Figure 8, with the permeability μ from Figure 11. r This is a figure plotting the values ​​superimposed on each other. As can be seen from Figure 12, the permeability μ r It can be seen that this is determined by the original design parameter a, with little influence from the design parameter h.

[0037] As can be seen from Figures 10 and 12, in the resonator structure 100 of Figure 2, the dielectric constant ε is determined by the height h of the first element 110. rIt can be controlled, and the permeability μ is determined by the length a of the second element 120. r It can be controlled. In other words, the dielectric constant ε r and magnetic permeability μ r It can be seen that these can be controlled independently.

[0038] Figure 13 shows a metamaterial sheet 300 according to one embodiment. This metamaterial sheet 300 has multiple resonator structures 100 formed on a single sheet-like film 302.

[0039] Figure 14 illustrates the usage of the metamaterial sheet 300 shown in Figure 13. The metamaterial sheet 300 is used by wrapping it around an object OBJ. The metamaterial sheet 300 acts as an optical camouflage or invisibility cloak, guiding light directed towards the object OBJ along the metamaterial sheet 300 on the surface of the object OBJ and emitting it from the opposite side of the object OBJ. As a result, to the human eye, the object OBJ appears as if it does not exist.

[0040] Figure 15 shows the distribution of parameter h for achieving polarization-independent optical camouflage. The horizontal axis corresponds to the position along the length of the film in Figure 13. Figure 16 shows the distribution of parameter a for achieving optical camouflage. The horizontal axis corresponds to the position along the length of the film in Figure 13. The calculations were performed assuming a film thickness of 725 nm, 68 turns, a diameter of object OBJ of 50 μm, and a transmission wavelength of 410 THz. Note that parameters h and a satisfy the optical camouflage conditions for both mutually orthogonal polarization components.

[0041] Thus, in this embodiment, optical camouflage can be achieved by optimizing the distribution of two design parameters a and h along the length direction of the sheet. This optical camouflage is polarization-independent, transmitting light for two orthogonal polarization components. In the prior art, the conditions for optical camouflage were met for only one polarization component, but in this embodiment, the conditions for optical camouflage can be met for two polarization components, thereby increasing the transmittance.

[0042] (Variation 1) In this embodiment, only the height h was used as a design parameter for the first element 110 and only the length a was used for the second element 120. However, this disclosure is not limited thereto, and other dimensions may be used as design parameters.

[0043] (Modification 2) In this embodiment, a grid-type resonator was described for the second element 120, but it is not limited to this. For example, a C-shaped resonator structure may be adopted for the second element 120. [Explanation of Symbols]

[0044] 100 resonator structure 110 First element 120 Second element 122 First Wiring Pair 124 Second Wiring Pair 200 Metamaterials 202 metaatoms 300 Metamaterial Sheets

Claims

1. It comprises multiple resonator structures arranged in a spatially distributed manner, The aforementioned resonator structure is A pillar-shaped first element, A second element having a circumferential structure surrounding the first element, Including, The aforementioned second element has a grid structure, A metamaterial characterized in that, in each of the plurality of resonator structures, the size of the first element and the size of the second element are designed independently.

2. The metamaterial according to claim 1, characterized in that the size of the first element is the height of the first element.

3. The metamaterial according to claim 1 or 2, characterized in that the size of the second element is the circumference of the second element.

4. The metamaterial according to claim 1 or 2, characterized in that the plurality of resonator structures are formed on a single sheet.

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