KR101746338B1 - Apparatus for absorbing electromagnetic wave - Google Patents

Abstract

An electromagnetic wave absorber is disclosed. The electromagnetic wave absorber includes a dielectric substrate and a plurality of unit cells arranged on one surface of the dielectric substrate, the unicell having a patch formed at the center and at least one And a pattern including a circular sector of the pattern.

Description

[0001] Apparatus for absorbing electromagnetic waves [

The present invention relates to an electromagnetic wave absorber.

Electromagnetic (EM) materials (MMs: metamaterials) are artificial materials that are realized to have properties that do not exist in nature. For example, an electromagnetic metamaterial can modulate permittivity or permeability. Further, the electromagnetic meta-material may be realized by periodically arranging sub-wavelength resonators such as a split ring resonator (SPR). Because of these properties, various applications of electromagnetic metamaterials such as super lenses, miniaturized microcomponents and metamaterial electromagnetic wave absorbers have been reported.

In particular, the electromagnetic wave absorber of meta-material was developed in 2008 (Landy, NI, Sajuyigbe, S., Mock, JJ, Smith, DR and Padilla, WJ Perfect metamaterial absorber, Phys. Rev. Lett. )) Have been studied since. The electromagnetic wave absorber of the metamaterial generates electrical and magnetic resonance that independently adjusts the effective permittivity and the permeability. Metamaterial electromagnetic wave absorbers have particular advantages compared to conventional electromagnetic wave absorbers such as ferrite, wedged-tapered absorbers and salisbury screen absorbers. That is, the metamaterial electromagnetic wave absorber can achieve a high absorptivity even on a thin dielectric substrate. In addition, the variable electromagnetic wave absorber can be realized by a device or a material capable of adjusting characteristics such as frequency. Because of these advantages, metamaterial electromagnetic wave absorbers have been studied for various spectral applications from microwave band to optical signals.

Because the metamaterial electromagnetic wave absorber is based on the periodic arrangement of the resonator, it operates at a specific frequency and has a narrow bandwidth. A study on the bandwidth increase of a metamaterial electromagnetic wave absorber has been reported. In general, the absorption rate of a metamaterial electromagnetic wave absorber is influenced by incident angle and polarization. An insensitive metamaterial electromagnetic wave absorber can be achieved by designing a unit cell that is symmetrical in both horizontal and vertical directions. Some metamaterial electromagnetic absorbers that are insensitive to polarization and incident angle have emerged.

The present invention provides a meta-material electromagnetic wave absorber insensitive to incident angle and polarization for X-band application.

According to an aspect of the present invention, an electromagnetic wave absorber using a metamaterial is disclosed.

An electromagnetic wave absorber according to an embodiment of the present invention includes a dielectric substrate and a plurality of unit cells arranged on one surface of the dielectric substrate, And patterned into a shape including at least one circular sector formed around the patch.

The patch is square and the unit cell is formed by superimposing the midpoints of each of the four corners of the square and each of the four sectors so as to be symmetrical in the horizontal and vertical directions.

The resonance frequency is determined according to the length of one side of the square unit cell, the radius of the sector, and the length of one side of the square patch.

The symmetry makes the absorptivity of the electromagnetic wave absorber insensitive to polarization, and the sector makes the absorptivity insensitive to an incident angle.

The sensitivity of the absorption rate to the incident angle is dependent on the angle of the sector, and the angle of the sector is determined according to the sensitivity.

The sensitivity is lowest when the internal angle of the sector is 90 degrees.

The electromagnetic wave absorber according to the embodiment of the present invention can be constituted by a square patch and a unit cell having a sector formed around the square patch, which can be insensitive to polarization by a horizontally and vertically symmetrical structure of the unit cell, It can become insensitive to the incident angle due to the fan shape of the unit cell.

1 is a view showing an electromagnetic wave absorber according to an embodiment of the present invention.
FIG. 2 is a diagram showing a simulation result on the absorption rate of a unit cell according to an embodiment of the present invention. FIG.
3 is a diagram illustrating a simulation result according to a sector angle of a unit cell according to an embodiment of the present invention.
4 is a graph showing a simulation result of absorption rate and normalized complex impedance of an electromagnetic wave absorber according to an embodiment of the present invention.
5 is a view showing a distribution of an electric field scale and a vector current distribution of an electromagnetic wave absorber according to an embodiment of the present invention.
6 is a schematic illustration of an experimental system for measuring the absorption rate of an electromagnetic wave absorber according to an embodiment of the present invention.
7 is a view showing simulation results and measurement results on the absorption rate of the electromagnetic wave absorber according to the embodiment of the present invention.
8 is a graph showing simulation results and measurement results of absorption coefficients according to incident angles of an electromagnetic wave absorber according to an embodiment of the present invention.

As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. In this specification, the terms "comprising ", or" comprising "and the like should not be construed as necessarily including the various elements or steps described in the specification, Or may be further comprised of additional components or steps. Also, the terms "part," " module, "and the like described in the specification mean units for processing at least one function or operation, which may be implemented in hardware or software or a combination of hardware and software .

Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a view showing an electromagnetic wave absorber according to an embodiment of the present invention. More specifically, FIG. 1 (a) shows a conventional cross cell (JC) unit cell, and FIG. 1 (b) shows a unit cell having a sector of an electromagnetic wave absorber according to an embodiment of the present invention. And FIG. 1C is a view showing a sample of the manufacture of the electromagnetic wave absorber according to the embodiment of the present invention.

In order to generate electrical and magnetic resonance, a double layer conductive structure is required. 1 (b), the upper surface of the unit cell of the electromagnetic wave absorber according to the embodiment of the present invention is formed with a square patch 10 at the center, And patterned so as to form four circular sectors 20 in the periphery. At this time, the unit cells may be formed so that the vertexes of the square patches 10 and the midpoints of the sectors 20 overlap each other. The lower surface of the unit cell is completely covered with a conductor.

For example, the unit cell according to the embodiment of the present invention shown in Fig. 1 (b) is based on the structure of the conventional cross resonator shown in Fig. 1 (a).

The conventional cross resonator and the unit cell according to the embodiment of the present invention are both insensitive to polarization due to the symmetrical structure. However, the absorption rate of the cross unit cell varies depending on the incident angle. On the other hand, the sector 20 of the unit cell according to the embodiment of the present invention is insensitive to the incident angle.

For example, this can be demonstrated using electromagnetic simulation, and in order to experimentally show it, as shown in Fig. 1 (c), the electromagnetic wave absorber according to the embodiment of the present invention has a 43 x 43 unit cell Can be fabricated on low cost FR4 dielectric substrates. Here, the FR4 dielectric substrate may have a dielectric constant of 4.4, a dielectric loss of 0.02, and a thickness of 1 mm. The total size of the electromagnetic wave absorber sample shown in FIG. 1 (c) can be 252 mm 252 mm.

When an electromagnetic wave is incident on a metamaterial electromagnetic wave absorber, reflected waves and transmitted waves exist due to the discontinuity of the boundary. The absorption coefficient A can be calculated from the reflection coefficient G and the transmission coefficient T using the following equation.

Therefore, a perfect absorption rate can be achieved when both the reflection coefficient and the transmission coefficient are zero.

Under normal incidence, the reflection coefficient can be given by the following equation.

Here, Z _M (?) And Z ₀ are the impedances of the metamaterial electromagnetic wave absorber and free space, respectively. From Equation (2), it can be seen that when Z _M (?) Coincides with Z ₀ , the reflection coefficient becomes zero. Z _M (?) Can be controlled by tailoring the effective permittivity (? _M ) and the magnetic permeability (占_M ) as shown in the following equation.

Here, ε ₀ and μ ₀ are permittivity and permeability in free space, respectively, and ε _r and μ _r are relative permittivity and permeability, respectively. After impedance matching between the free space and the metamaterial electromagnetic wave absorber, the transmission coefficient can be minimized by destroying the transmission wave with a considerable dielectric loss. The loss factor of the metamaterial electromagnetic wave absorber is large because the imaginary part of the refractive index n is large. Therefore, by designing a meta-material electromagnetic wave absorber having a reflection coefficient and a transmission coefficient of zero, a high absorption rate can be achieved.

However, zero-reflection condition, since the reflection conditions for the vertically polarized wave (Γ _⊥) and parallel polarization (Γ _∥) is given by the following equation, varies with respect to off-axis (oblique incidence).

Even if the metamaterial electromagnetic wave absorber shows a perfect absorption rate under normal incidence, as the incidence angle changes, the absorption rate also changes, as shown in Equations (2), (4) and (5). Therefore, in order to obtain a metamaterial electromagnetic wave absorber insensitive to an incident angle, a unit cell insensitive to an incident angle must be designed.

FIG. 2 is a graph showing a simulation result of the absorption rate of a unit cell according to an embodiment of the present invention.

As shown in Fig. 1 (b), in order to design a unit cell according to an embodiment of the present invention, three parameters a, b, c according to the metric method and one angle parameter? . ≪ / RTI >

For example, a is the length of one side of the square unit cell, b is the radius of the sector 20, c is not only the length of one side of the central square patch 10, but also the distance between each sector, is the inner angle of the sector 20.

In Fig. 2, simulation results are shown for the absorption rates according to the values of the a, b and c parameters. Referring to FIG. 2, when a increases, the resonant frequency increases and the absorption rate slightly increases. The resonance frequency decreases as b becomes larger because the effective permeability is high. When c is larger, the effective permittivity becomes smaller and the resonant frequency increases. Therefore, the parameters a, b, and c can determine the resonant frequency of the electromagnetic wave absorber according to the embodiment of the present invention.

FIG. 3 is a view showing a simulation result according to a sector angle of a unit cell according to an embodiment of the present invention.

, 50

, 60

, 70

, 80

, 90

)을 가지도록 설계되었다. 그리고, 입사각은 0

및 60

로 설정되어 흡수율이 시뮬레이션 되었다. α와 입사각 민감도 사이의 관계를 나타내기 위하여, 입사각 민감도(S_A)는 하기의 수학식으로 정의되었다.A sector of a unit cell according to an embodiment of the present invention is applied for insensitivity to an incident angle. In particular, the internal angle of the sector (?) Affects the incidence angle insensitivity. In order to show this, as shown in Fig. 3 (a), the six unit cells are arranged such that each has a different value 40

, 50

, 60

, 70

, 80

, 90

). The incident angle is 0

And 60

And the absorption rate was simulated. In order to show the relation between? and the incident angle sensitivity, the incident angle sensitivity (S _A ) was defined by the following equation.

, f_0ㅀ)는 입사각 0

와 공진 주파수 f_0ㅀ에서의 흡수율이다.Here, _θ f and f are each _{0 DEG} angle of incidence θ and the resonance frequency at normal incidence, A _(θ, f θ) is the absorption at incident angle θ and the resonance frequency f _θ, A (0

, f _{0 ㅀ} ) is the angle of incidence 0

And the absorption rate at the resonance frequency f ₀ ..

에서 90

로 변할 때의 S_A(60

)를 보여주고 있다. α가 90

일 때, f_60ㅀ와 f_0ㅀ는 각각 10.45GHz 및 10.44GHz이다. 그리고, A(60

, f_60ㅀ)와 A(0

, f_0ㅀ)는 각각 0.99 및 0.91이다. 따라서, α=90

에서 가장 낮은 입사각 민감도가 관찰된다.FIG. 3 (b)

To 90

S (60 < / _RTI &_gt;

). alpha is 90

, F ₆₀ ㅀ and f ₀ ㅀ are 10.45 GHz and 10.44 GHz, respectively. And, A (60

, f _{60 ㅀ} ) and A (0

, f _{0 ㅀ} ) are 0.99 and 0.91, respectively. Therefore,? = 90

The lowest incident angle sensitivity is observed.

4 is a graph showing a simulation result of the absorption rate and the normalized complex impedance of the electromagnetic wave absorber according to the embodiment of the present invention. More specifically, FIG. 4A shows simulation results of the reflection coefficient, the transmission coefficient, and the absorption coefficient of the electromagnetic wave absorber according to the embodiment of the present invention, and FIG. 4B shows the results of simulation according to the embodiment of the present invention And shows that the intrinsic complex impedance of the electromagnetic wave absorber is normalized to the impedance of free space under normal incidence.

에서 70

까지의 입사각에 대하여 흡수율이 90% 보다 더 높아지도록 설계된다.Referring to FIG. 4 (a), it can be seen that the electromagnetic wave absorber according to the embodiment of the present invention exhibits an absorption rate of 91% at 10.44 GHz. Since the real part of the normalized impedance is larger than 1, the absorption rate is not 100%. Even if the absorption rate can be 100% under normal incidence, the unit cell is 0

From 70

The absorption rate is designed to be higher than 90%.

FIG. 5 is a diagram showing the electric field scale distribution and the vector current distribution of the electromagnetic wave absorber according to the embodiment of the present invention. Figure 5 shows (a) the field-scale distribution at 10.44 GHz and (b) the vector current distribution at the top, bottom and sides, for electromagnetic resonance.

Referring to FIG. 5 (a), it can be seen that the electric field is concentrated on the edge of the sector.

Referring to Fig. 5 (b), self resonance from the surface current density is observed. Here, the surface currents flowing through the two metal layers flow in opposite directions to each other.

FIG. 6 is a schematic illustration of an experimental system for measuring the absorption rate of an electromagnetic wave absorber according to an embodiment of the present invention, and FIG. 7 is a graph showing simulation results and measurement results of the absorption rate of the electromagnetic wave absorber according to the embodiment of the present invention FIG.

The designed metamaterial electromagnetic absorber is fabricated on a FR4 dielectric substrate to have a 43 × 43 unit cell. The absorption rate of the manufactured meta-material electromagnetic wave absorber shown in Fig. 1 (c) is measured in free space.

Referring to FIG. 6, two standard-gain horn antennas are used as transmit and receive antennas. This standard gain horn antenna is located 1 meter from the sample of the electromagnetic wave absorber to meet the far-field condition. The S parameter is measured by an Anritsu MS2038C network analyzer and the absorption rate is calculated from this S parameter. To measure only the reflected wave from the electromagnetic wave absorber sample, a wedged-tapered electromagnetic wave absorber is used around the electromagnetic wave absorber sample, as shown in FIG. 6, and the time-gaiting function of the network analyzer is used. Under normal incidence, the absorption rate of the electromagnetic wave absorber according to the embodiment of the present invention is measured at different polarization angles phi.

에서 90

로 변할 때, 본 발명의 실시예에 따른 전자파 흡수기의 흡수율에 대한 시뮬레이션 결과 및 측정 결과가 도시되어 있다.7 (a) and 7 (b), when the polarization angle φ is 0

To 90

The simulation result and the measurement result of the absorption rate of the electromagnetic wave absorber according to the embodiment of the present invention are shown.

Referring to FIG. 7, the measured absorption rate is mostly 100% at 10.44 GHz for all polarizations. The absorption frequency is the same as the simulation result. The measured absorption rate is higher than the simulated absorption rate because the dielectric loss of the FR4 dielectric substrate is higher.

에서 70

사이에서 회전한다. 각 입사각에서, 수신용 혼 안테나는 스넬의 법칙(Snell's law)과 측정된 S 파라미터를 충족하는 각도에 위치된다. TE 모드와 TM 모드에 대한 반사 계수는 다르기 때문에, 경사 입사(oblique incidence)에서의 흡수율은 TE 모드와 TM 모드 둘 다에 대하여 측정된다.Next, the absorption coefficients of the electromagnetic wave absorber according to the embodiment of the present invention were measured at different incident angles?, Respectively. The transmission horn antenna is 0

From 70

. At each incident angle, the receiving horn antenna is located at an angle that meets Snell's law and the measured S parameter. Since the reflection coefficients for the TE mode and the TM mode are different, the absorption rate at oblique incidence is measured for both the TE mode and the TM mode.

FIG. 8 is a graph showing simulation results and measurement results of the absorption rate according to the incident angle of the electromagnetic wave absorber according to the embodiment of the present invention.

에서 70

로 변할 때, 각각 TE 모드 및 TM 모드 각각에 대한 흡수율의 시뮬레이션 결과를 그래프로 나타낸 것이다. 시뮬레이션로 산출된 흡수율은 90%보다 더 높고, 주파수 변화는 70

까지의 입사각에 대하여 0.96%보다 작았다.8 (a) and 8 (b) show a case where the incident angle? Is 0

From 70

, The simulation result of the absorption rate for each of the TE mode and the TM mode is shown in a graph. The absorption rate calculated by simulation is higher than 90%, and the frequency change is 70

Of the incident angle up to 0.96%.

에서 60

로 변할 때, 90%보다 더 높았다. 그리고, 입사각이 70

일 때의 흡수율은 75%로 감소하였다. 흡수율 주파수는 0

에서 70

사이에서 변화가 없었다.Referring to FIG. 8 (c), the absorption rate measured at 10.44 GHz for the TE mode is 0

From 60

, It was higher than 90%. When the incident angle is 70

The absorption rate decreased to 75%. The absorption rate frequency is 0

From 70

There was no change between.

에서 60

로 변할 때, 90%보다 더 높았다. 그리고, 입사각이 70

일 때의 흡수율은 80%로 감소하였다. 흡수율 주파수의 변화는 0

에서 70

사이에서 0.86%이었다.Referring to FIG. 8 (d), the absorption rate measured at 10.44 GHz for the TM mode is 0

From 60

, It was higher than 90%. When the incident angle is 70

The absorption rate decreased to 80%. The change of the absorption rate frequency is 0

From 70

Respectively.

까지의 입사각에 대하여 90%보다 더 높은 흡수율을 달성할 수 있다.Therefore, in the electromagnetic wave absorber according to the embodiment of the present invention, the measured incidence insensitivity was slightly reduced as compared with the simulation result,

A higher absorption rate than 90% can be achieved.

It will be apparent to those skilled in the art that various modifications, additions and substitutions are possible, without departing from the spirit and scope of the invention as defined by the appended claims. Should be regarded as belonging to the following claims.

Claims (6)

In an electromagnetic wave absorber using a metamaterial,
A dielectric substrate; And
And a plurality of unit cells arranged on one surface of the dielectric substrate,
The unit cell includes:
A square patch formed in the center; And
Patterned into a shape including four circular sectors formed around the square patch,
The unit cell is formed by superimposing the midpoints of each of the four corners of the square patch and the vertices of each of the four sectors so as to be symmetrical in the horizontal and vertical directions,
The symmetry causes the absorptivity of the electromagnetic wave absorber to be insensitive to polarization, the sector makes the absorptivity insensitive to an incident angle,
Wherein the sensitivity of the absorption rate to the incident angle is dependent on an internal angle of the sector,
Wherein an internal angle of the sector is determined according to the sensitivity.
delete The method according to claim 1,
Wherein the resonance frequency is determined according to the length of one side of the square unit cell, the radius of the sector, and the length of one side of the square patch.
delete delete The method according to claim 1,
Wherein the sensitivity is lowest when the internal angle of the sector is 90 °.

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