WO2016035956A1 - Meta-atoms enabling absorption at mhz and ghz bands and meta-material comprising same - Google Patents

Abstract

The present invention relates to meta-atoms capable of absorbing electromagnetic waves at specific frequency bands of incident electromagnetic waves, and to a metal-material comprising the same. Since the meta-atoms according to the present invention are designed as meta-atoms having a size corresponding to 1/30 of the wavelengths of incident electromagnetic waves, the meta-atoms are very simple to manufacture at low-frequency bands including MHz bands, enable complete absorption, are flexible and thus are easy to install, so that the meta-material comprising the meta-atoms can be used in various fields, such as an absorber or like, capable of completely absorbing electromagnetic waves which are generated by various kinds of electronic devices including a mobile phone and are harmful to the human body. Furthermore, the meta-atoms of the present invention can be manufactured with only conductors and dielectrics, thereby reducing manufacturing costs of the meta-material.

Description

Meta-Atoms Absorbable in the MHz and GHz Regions and Metamaterials Containing the Same

The present invention relates to a meta-atom absorbing electromagnetic waves incident in the MHz and GHz region and a metamaterial including the same. More specifically, the present invention relates to a low frequency including the MHz or GHz region using a very small unit cell. The present invention relates to a meta atom capable of completely absorbing electromagnetic waves in a region and a meta material including the same.

Recently, electronic products including mobile phones can be regarded as essential devices for life. However, since these electronic devices generate electromagnetic waves harmful to the human body, many studies have been conducted to block such electromagnetic waves.

In particular, absorbers using meta-materials have recently been studied by many researchers. Here, meta-material is a generic name for an artificially designed material that does not exist in nature and whose electromagnetic properties are determined by the material structure. Natural materials are composed of atoms or molecules, but metamaterials are composed of artificial meta-atomic structures, which are units having a size smaller than the wavelength of electromagnetic waves incident from the outside. Generally known meta-material absorbers are composed of about 1/3 to 1/5 of the unit cell constituting the meta-material, that is, the size of the meta-atoms compared to the wavelength of the electromagnetic wave incident. The meta-atoms such as absorption occur only when meta-atoms are 1/3 to 1/5 in size. Due to the size problem, it is difficult to make it in the visible region because it is too small, and in the MHz region, which is a relatively low frequency region, the meta-atoms constituting the metamaterial are too large to be manufactured. In recent years, active studies on complete absorbers using metamaterials (usually, absorption rate of 93% or more) have been actively conducted in view of the high harmfulness of electromagnetic waves such as mobile phones to the human body and the communication frequency of mobile phones. It is becoming.

[Preceding technical literature]

[Non-Patent Documents]

(Non-Patent Document 1) N. I. Landy, S. Sajuyigbe, J. J. Mock, D. R. Smith, and W. J. Padilla, Phys. Rev. Lett. 100, 207402 (2008).

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a meta-atom having a small size with flexibility while completely absorbing electromagnetic waves incident in a low frequency region of MHz or GHz. will be.

The present invention also provides a meta-material in which a plurality of meta atoms are arranged on the same plane to form a flat plate structure.

The present invention to achieve the above object, a dielectric substrate; A first flat conductor disposed on one surface of the dielectric substrate and having a unit pattern of at least one zigzag structure; And a second flat conductor disposed on the entire other surface of the dielectric substrate.

The first flat conductor absorbs incident electromagnetic waves,

The magnetic field induced by the induced current generated simultaneously in the first and second plate conductors may be absorbed by magnetic resonance with electromagnetic waves incident on the first plate conductor.

The first flat plate conductor and the second flat plate conductor may be copper or silver.

The meta-atoms are characterized in that the absorption frequency range from 380 MHz to 2.5 GHz.

The width of the line forming the unit pattern of the first flat conductor is 0.1 to 0.6 mm, the height of the curved portion of the ruler in the unit pattern is 0.3 to 2.0 mm, the length of the straight portion not curved in the unit pattern is 2.5 to 31 mm, and the separation distance between unit patterns of the first flat conductor is 0.1 to 0.7 mm.

The width and length of the dielectric substrate are 10 to 32 mm, the thickness is 1.0 to 12.0 mm, and the width and length of the first flat conductor are 9.8 to 31.8 mm, and the thickness is 0.01 to 0.1 mm.

In order to achieve the above object, the present invention provides a meta-material comprising the at least one meta atom and having a flat structure formed by arranging the meta atoms on the same plane.

The metamaterial is characterized in that the frequency range of absorption is from 380 MHz to 2.5 GHz.

The meta-atom according to the present invention is capable of completely absorbing electromagnetic waves in the frequency range of 380 MHz to 2.5 GHz, and includes meta-atoms as small as 1/30 or 1/12 compared to the wavelength of the incident electromagnetic waves. The meta-material may be used in various fields such as an electromagnetic wave absorber which is easy to mount, and may absorb electromagnetic waves harmful to a human body generated from various electronic devices. In addition, since the meta-atom of the present invention can be manufactured using only a conductor and a dielectric, the meta-material manufacturing cost can be reduced.

1 is a perspective view illustrating a meta atom according to a first embodiment of the present invention.

2 is a perspective view illustrating a meta atom according to a second embodiment of the present invention.

3 is a conceptual diagram (a) of a meta-material using a meta atom according to the first embodiment of the present invention (a), the actual appearance (b) and a photo (c) showing its flexibility.

4 is a conceptual diagram of a meta material using meta atoms according to a second embodiment of the present invention.

5a and c are simulation graphs (a) and absorption graphs (c) of the absorption frequency and the absorption rate of the meta-atoms prepared from Preparation Example 1 of the present invention.

5B is a graph showing a Q factor and a resonant frequency measured by varying the length of the pattern formed on the first plate conductor of the meta atom manufactured from Example 1 according to the simulation result.

FIG. 6 is a view showing a distribution diagram of a flow of induced currents simultaneously induced in a first plate conductor and a second plate conductor in a meta atom having a pattern length formed on different first plate conductors prepared in Example 1; FIG. .

FIG. 7 is a graph illustrating the absorption rate according to each frequency after vertically injecting electromagnetic waves having a frequency band of 200 MHz to 600 MHz into the metamaterial prepared in Preparation Example 4. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

If it is mentioned that the layer is on another layer or substrate it may be formed directly on the other layer or substrate or a third layer may be interposed therebetween. In addition, the first and the second are not intended to impose any limitation on the components, but should be understood as terms for distinguishing the components.

1 is a perspective view showing in detail the structure of the meta-atom according to the first embodiment of the present invention, Figure 2 is a perspective view showing the structure of the meta-atom according to a second embodiment of the present invention in more detail.

Meta atom 100 according to the present invention is a dielectric substrate 110; A first flat conductor 120 disposed on one surface of the dielectric substrate 110 and having a unit pattern of at least one zigzag structure; And a second flat plate conductor 130 disposed on the entire other surface of the dielectric substrate 110.

1 and 2, k denotes a traveling direction of electromagnetic waves, E denotes an electric field direction, and H denotes a magnetic field direction. At this time, the direction of the electric field may be parallel to the longitudinal direction of the meta atom 100, the incident electric field is in a state perpendicular to the incident surface.

The dielectric substrate 110 is not limited thereto as long as it is a flexible and flexible dielectric having a predetermined dielectric constant, but the most preferable material satisfying the above characteristics may be teflon. In addition, in order to sufficiently absorb electromagnetic waves, the thickness t, the dielectric constant epsilon, and the permeability μ of the dielectric substrate 110 may be appropriately adjusted. To this end, the thickness of the dielectric substrate 110 may be set after the material is set.

The dielectric substrate 110, the first planar conductor 120, and the second planar conductor 130 may provide complete absorption of electromagnetic waves at a specific frequency band through a structure, a pattern shape, and an optimized characteristic dimension.

In particular, the size of the meta atom 100 and the pattern of the first flat conductor 120 may be adjusted to induce complete absorption of electromagnetic waves in a specific frequency region. In this case, the absorbed electromagnetic wave wavelength is characterized in that the size of 12 to 30 times the size of the first flat conductor 120 meta-atomic.

In addition, the first flat plate conductor 120 and the second flat plate conductor 130 are not particularly limited as long as the material has excellent conductivity, but in the embodiment of the present invention, copper having a conductivity of 5.8 × 10 ⁷ S / m was used. . At this time, the dielectric constant and dielectric loss tangent of Teflon were found to be 2.17 and 0.001, respectively.

Unlike the second flat conductor 130, the first flat conductor 120 has a unit pattern of at least one zigzag structure. Due to this structure, the first flat plate conductor 120 absorbs electromagnetic waves incident vertically, and the induced magnetic field due to the induced current generated simultaneously in the first flat plate conductor 120 and the second flat plate conductor 130 The magnetic resonance with the electromagnetic wave absorbed by the first flat conductor 120 may be completely absorbed by the magnetic resonance in a specific frequency band.

In detail, the first flat conductor 120 has a unit pattern 121 having a long curved shape, that is, a zigzag structure, induces an induced current induced by incident electromagnetic waves to form a line of the unit pattern 121. In order to be able to flow along, the longer the induced current flows along the line of the unit pattern 121, the more the frequency band where absorption occurs moves to a lower frequency region, and repeats the unit pattern 121 Since the number of lines increases as the number of times increases, the size of the meta-atoms can maintain a level of 1/12 to 1/30, which is very small compared to the wavelength of the incident electromagnetic wave.

Specifically, the width and length p of the dielectric substrate 110 are 10 to 32 mm, the thickness t is 1.0 to 12 mm, and the width and length of the first flat conductor 120 are a ) Is 9.8 to 31.8 mm, and the thickness t _c is 0.01 to 0.1 mm, and the absorbed electromagnetic wave is almost completely absorbed without dependence on the polarization of the incident electromagnetic wave in all regions from 380 MHz to 2.5 GHz.

At this time, the width (w) of the line forming the unit pattern 121 of the first flat conductor 120 is 0.1 to 0.6 mm, the height (h) of the bent portion in the unit pattern 121 is 0.3 to 2.0 mm, the length (m) of the straight portion that is not bent in the unit pattern 121 is 2.5 to 31 mm, and the separation distance s between the unit patterns 121 of the first flat conductor is 0.1 to 0.7 mm. Is preferably.

In addition, the thickness t _c in the first flat conductor 120 is 0.01 to 0.1 mm. If the thickness t _c of the unit pattern 121 in the first flat conductor 120 is less than 0.01 mm, there is a risk of short-circuit easily due to surface scratches or bending during meta-atomic formation, post-assembly or operation. This is high. In addition, when the thickness t _c of the unit pattern 121 in the first flat conductor 120 exceeds 0.1 mm, the loss of the electromagnetic wave actually absorbed by the high electrical conductivity is reduced, resulting in the establishment of the electromagnetic wave ( Re-reflection) is undesirable.

Meanwhile, the meta-atom according to the present invention can control the frequency band to be absorbed according to the number of repetitions of the unit pattern of the zigzag structure formed on the first flat conductor 120, that is, the length (m) of the line of the unit pattern. have.

As shown in FIG. 1, the meta-atom having one unit pattern 121 of the first flat conductor has an absorption rate of 95% or more in the frequency range of 1.5 GHz to 2.5 GHz.

Here, the width (w) of the line forming the unit pattern 121 is 0.1 to 0.5 mm, the height h of the bent portion in the unit pattern 121 is 0.3 to 2.0 mm, the unit pattern ( The length m of the uncurved straight portion in 121 may be 5 to 9 mm. In such a structure, when the length (m) of the uncurved straight portion of the unit pattern 121 is less than 5 mm, a problem may occur that the absorption rate is lowered to 90% or less.

In this case, in order to sufficiently absorb the electromagnetic wave, the horizontal and vertical lengths (a, p) and the thickness (t _c , t) of the first flat plate conductor 120 and the dielectric substrate 110 may be adjusted. Specifically, the horizontal and vertical lengths p of the dielectric substrate 110 are 1/10 to 1/15 of the resonance frequency wavelength region (mm unit), and the thickness t of the dielectric substrate 110 is a dielectric substrate ( It may be 1/8 to 1/12 as compared to the horizontal and vertical length p of the 110. Even more preferably, the horizontal and vertical lengths (a) of the first flat plate conductor 120 are 9.8 to 14.8 mm, the thickness t _c is 20 to 40 μm, and the horizontal and vertical lengths of the dielectric substrate 110 are shown. It is preferable that (p) is 10-15 mm, and thickness t is 1.0-2.0 mm.

In addition, as shown in FIG. 2, the wavelength of the electromagnetic wave absorbed by the meta atom 200 having the structure of two or more unit patterns 221 of the first flat conductor 220 is 25 to the size of the meta atom. It is characterized by being 35 times larger, and more specifically has an absorption of 95% or more in the frequency range from 380 MHz to 420 MHz.

Here, the width w of the line forming the unit pattern 221 of the first plate conductor 220 of the meta atom 200 is 0.2 to 0.6 mm, and the unit pattern 221 of the first plate conductor 220. ), The separation distance s is 0.1 to 0.7 mm, and the height h of the bent portion in the unit pattern 221 is 0.5 to 2.0 mm, and the straight portion of the straight portion that is not bent in the unit pattern 221. The length m may be 23 to 31 mm.

In this case, in order to sufficiently absorb the electromagnetic wave, the horizontal and vertical lengths (a, p) and the thickness (t _c, t) of the first flat conductor 220 and the dielectric substrate 210 may be adjusted. Specifically, the horizontal and vertical lengths (a) of the first flat conductor 220 are 22.8 to 31.8 mm, the thickness (t _c ) is 0.01 to 0.1 mm, and the horizontal and vertical lengths (p) of the dielectric substrate 210. ) Is 23 to 32 mm, and the thickness t is preferably 6 to 12 mm.

In addition, the present invention provides a meta-material (300, 400) which is an electromagnetic wave absorber including the meta atoms (100, 200). The meta-material of the present invention includes the at least one meta atom (100, 200), the meta atoms (100, 200) are arranged on the same plane to form a flat structure, excellent flexibility, specific frequency region Absorption rate of the electromagnetic wave at 95% or more can be completely absorbed, and its small size makes it easy to install in various electronic devices, so that it can be applied to various fields.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. However, these examples and the like are intended to explain the present invention in more detail, and it will be apparent to those skilled in the art that the scope of the present invention is not limited thereto.

Preparation Example 1.

The meta atom was constructed as follows. A square Teflon dielectric substrate having a length of 12.2 mm in length and width was prepared. The dielectric substrate had a thickness of 1.27 mm, a dielectric constant of 2.17, and a dielectric loss tangent of 0.001. A first flat conductor having a unit pattern as shown in FIG. 1 is disposed on the top surface of the dielectric substrate. The unit pattern is formed in the center portion of the first flat conductor, has a zigzag structure, the length of the unbending straight portion is 2.5, 3.5, 4.5, 5.5, 6.5, 7.5 mm, the width of the line 0.4 mm, the thickness is 0.035 mm It was arranged to be. The upper and lower rectangles connected to the unit pattern of the first flat plate conductor were arranged so that the horizontal length was 12.2 mm and the vertical length was 5 mm. In addition, as shown in FIG. 1, the second flat plate conductor disposed on the entire other surface of the dielectric substrate has a thickness of 0.035 mm. At this time, the first flat plate conductor and the second flat plate conductor were set to copper.

Preparation Example 2.

The meta atom was constructed as follows. A square Teflon dielectric substrate having a length of 27.2 mm in width and length was prepared. The dielectric substrate had a thickness of 9 mm, a dielectric constant of 2.17, and a dielectric loss tangent of 0.001. The first plate conductor 220 as shown in FIG. 2 is disposed on the top surface of the dielectric substrate 210. The length of the long rounded line disposed at the center portion of the first flat conductor was 27 mm, the width was 0.4 mm, and the thickness was disposed so as to be 0.035 mm. The long curved line was twisted a total of five times, and the line was arranged such that the distance between the lines was 0.4 mm. The horizontal and vertical lengths of the rectangular shape, which are arranged on the upper part and the lower part of the first flat conductor and connect the long curved line, are arranged to be 27 mm and 9.3 mm, respectively. In addition, as shown in FIG. 2, the second flat plate conductor 230 is disposed on the entire surface of the bottom surface of the dielectric substrate 210, and the thickness thereof is 0.035 mm. In addition, the first plate conductor and the second plate conductor are set to copper.

Preparation Example 3.

The meta atoms prepared from Preparation Example 1 were arranged in a plane of 8 horizontally and 12 vertically to form an electromagnetic wave absorber which is a metamaterial. 3 is a perspective view showing the structure of the meta-material according to the present invention.

Preparation Example 4.

The meta atoms prepared from Preparation Example 2 were arranged in a plane of 8 horizontally and 12 vertically to form an electromagnetic wave absorber which is a metamaterial. 4 is a perspective view showing the structure of the meta-material according to the present invention.

Subsequently, after the electromagnetic wave having a frequency band of 200 MHz to 600 MHz was vertically incident on the metamaterial, the absorption rate according to the frequency was obtained as shown in FIG. 7 through simulation.

The Hewlett-Packard E8362B network analyzer was used to measure the absorption of meta-atoms prepared from Example 1 according to the present invention, which is shown in FIG. 5.

5A is a graph showing the absorption frequency and the absorption rate of the meta atom prepared from Example 1 according to the simulation result, and accordingly, the length of the unbended straight portion of the unit pattern formed on the first flat conductor of the meta atom (hereinafter, As the length of the unit pattern decreases, it can be seen that the region of the absorbing frequency shifts toward higher and higher wavelengths. On the other hand, when the length of the unit pattern formed on the first flat conductor of the meta-atom increases, it can be seen that the area of the absorbing frequency moves to a lower wavelength and the absorption rate also increases. Therefore, it was confirmed that the length of the unit pattern formed in the meta atom of the present invention can be adjusted according to the frequency range to be absorbed. However, since the length of the unit pattern formed on the first flat conductor of the meta atom is 7.5 mm to 5.5 mm, the complete absorption rate close to 100% is lower than 90% when the length is smaller than this.

In addition, when the length of the unit pattern formed on the first flat conductor of the meta atom was 7.5 mm, the size of the meta atom was close to λ / 12 (resonant frequency is 2 GHz). That is, when there is one unit pattern in the meta atom, since the meta atom has a periodicity (p) (that is, the width and length of the meta atom, for complete absorption in the frequency domain, It can be seen that the thickness t and the resonant frequency wavelength region (in mm) are preferably 1.63 times, 0.169 times, and 20 times the length m of the unit pattern formed on the first flat conductor, respectively. have.

That is, the width and length of the meta-atom have a ratio of about 10: 1 to the thickness, and if the ratio is satisfied, the meta-atom may be completely absorbed in a specific frequency region regardless of the number of repetitions of the unit pattern. .

Additionally, the ratio between the transverse and longitudinal lengths of the meta atoms and the resonant wavelength region (in mm) is about 1:12, and this ratio represents the size of the meta atoms with respect to the resonant wavelength region.

5B is a graph illustrating a Q factor and a resonant frequency measured by varying a length of a unit pattern formed on a first flat conductor of meta atoms manufactured from Example 1 according to a simulation result, and thus, a first flat plate of meta atoms The graph shifting red according to the length of the unit pattern formed in the conductor may be described as an LC circuit resonance represented by Equation 1 below.

Equation 1

At this time, in Equation 1,

L is inductance and C is capacitance.

The length of the unit pattern formed on the first flat conductor of the meta atom is related to the inductance L, and the separation distance between the unit patterns formed on the first flat conductor of the meta atom is related to the capacitance C.

Therefore, when the length of the unit pattern formed on the first flat conductor of the meta atom is increased, the resonant frequency moves to a lower frequency region. Therefore, the horizontal and vertical lengths of the meta atoms and the thickness of the dielectric substrate are adjusted to the resonant frequency. do.

If the area other than the length of the unit pattern formed on the first flat conductor of the meta atom is reduced, the resonance frequency band of the meta atom is red shifted, which is a unit pattern formed on the first flat conductor of the meta atom. This is because the separation distance between them increases. This result means that as the number of repetitions (length) of the unit patterns formed on the first flat conductor of the meta atom is increased, even a small meta reactor can absorb frequencies in the low region.

In addition, the Q factor gradually decreased from 73.15 to 50.10 according to each resonant frequency. This indicates that the Q factor is proportional to the magnetic induction coefficient L and is inversely proportional to the resonance frequency.

Figure 5c is a graph showing the actual experimental results on the absorption frequency and the absorption rate of the meta atom prepared in Example 1. According to this, it can be seen that the simulation value and the absorption frequency and the absorption rate shown in FIG. 5A are very identical. In particular, when the length of the unit pattern formed on the first flat conductor of the meta-atom is 7.5 mm, 1.99 in experiment and simulation It was confirmed that it absorbs 99.99% of GHz frequency.

However, in actual test results, it was confirmed that, unlike the simulation, the absorption rate did not decrease to about 85% or less as the length of the unit pattern formed on the first flat conductor of the meta atom was reduced. Specifically, 97.8% at 2.07 GHz, 94.5% at 2.19 GHz, 9.14% at 2.31 GHz, 90.9% at 2.53 GHz, and 87% at 2.53 GHz.

FIG. 6 is a view showing a distribution diagram of a flow of induced currents simultaneously induced in a first plate conductor and a second plate conductor in a meta atom having a unit pattern length formed in different first plate conductors prepared in Example 1; FIG. to be.

As shown in FIG. 6A, it can be seen that most of the current is located around the unit pattern of the first flat conductor, and current flows through the unit pattern. In addition, as the length of the unit pattern formed on the first flat conductor decreases, it becomes difficult to flow the current, so that the current density increases around the unit pattern.

6B and 6C illustrate surface energy loss density and magnetic energy density of meta-atoms having a unit pattern of 7.5 mm in length formed in the first flat conductor, wherein magnetic Magnetic energy density represents the magnetic field derived from the meta atom. When an electromagnetic wave that can be absorbed according to the structure of the meta atom is incident, an induced current flows along the first flat conductor unit pattern of the meta atom, and a magnetic resonance is generated due to the induced magnetic field. As a result, complete absorption of electromagnetic waves occurs. That is, it was confirmed that energy loss of electromagnetic waves occurs in the first flat conductor unit pattern.

FIG. 7 is a graph illustrating the absorption rate according to each frequency after vertically injecting electromagnetic waves having a frequency band of 200 MHz to 600 MHz into the metamaterial prepared in Preparation Example 4, and accordingly, manufactured from Preparation Example 4 The meta material was found to have a complete absorption of at least about 99% at 400 MHz.

The present invention provides a small size meta atom having flexibility while completely absorbing electromagnetic waves incident in the low frequency region of the MHz or GHz region.

Claims (8)

1. Dielectric substrates;

   A first flat conductor disposed on one surface of the dielectric substrate and having a unit pattern of at least one zigzag structure; And

   And a second flat plate conductor disposed on the entire other surface of the dielectric substrate.
2. The method of claim 1,

   The first flat conductor absorbs incident electromagnetic waves,

   The meta-atoms of the first flat plate conductor and the second flat plate conductor are induced by the induced current generated at the same time characterized in that the magnetic resonance with the electromagnetic wave incident on the first flat plate conductor.
3. The method of claim 1,

   The first flat conductor and the second flat conductor are meta atoms, characterized in that the copper or silver.
4. The method of claim 1,

   The meta-atoms are meta-atoms, characterized in that the frequency range of absorption from 380 MHz to 2.5 GHz.
5. The method of claim 1,

   The width of the line forming the unit pattern of the first flat conductor is 0.1 to 0.6 mm,

   The height of the bent portion of the letter "c" in the unit pattern is 0.3 to 2.0 mm,

   In the unit pattern, the length of the uncurved straight portion is 5 to 31 mm,

   Meta-atoms, characterized in that the separation distance between the unit pattern of the first plate conductor is 0.1 to 0.7 mm.
6. The method of claim 1,

   The width and length of the dielectric substrate is 10 to 32 mm, the thickness is 1.0 to 12.0 mm,

   The width and length of the first flat conductor is 9.8 to 31.8 mm, the thickness is 0.01 to 0.1 mm meta-atoms, characterized in that.
7. At least one meta atom according to claim 1,

   Meta material, characterized in that the planar structure formed by arranging the meta atoms on the same plane.
8. The method of claim 1,

   The meta-material is meta-material, characterized in that the frequency range is absorbed from 380 MHz to 2.5 GHz.

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