KR102335787B1 - electromagnetic wave absorber - Google Patents

Abstract

The present invention provides an electromagnetic wave absorber.
The electromagnetic wave absorber may include a first body having a flat plate shape; a second body having a flat plate shape formed on one surface of the first body; and a conical conical body formed inside the first body.

Description

electromagnetic wave absorber

The present invention relates to an electromagnetic wave absorber.

In order to increase absorption, both reflection and transmission should be small. In terms of reflection, if the intrinsic impedance of the material is the same as the impedance of the free space, the reflection can be canceled and an ideal absorber can be created.

However, since it is impossible to create such a characteristic through the characteristics of a general material, methods for matching the impedance through a technique such as a metamaterial have been proposed.

Methods for fabricating metamaterials of frequency selective surface (FSS) absorbers proposed so far include a method of modifying the shape of a material and a method of making a material having appropriate permittivity and permeability.

The present invention provides an electromagnetic wave absorber.

The present invention provides an electromagnetic wave absorber.

The electromagnetic wave absorber is

a first body in the shape of a flat plate;

a second body having a flat plate shape formed on one surface of the first body;

It is formed inside the first body and includes a conical conical body arranged on a grid,

The thickness of the first body is formed to be thicker than the thickness of the second body,

The thickness of the conical body is formed to be thicker than the thickness of the second body,

The bottom surface of the conical body is disposed on the same line as the bottom surface of the first body,

The conical body is formed in plurality in the interior of the first body,

The vertices of each of the conical bodies formed in plurality have different heights,

At the upper end of the first body, among the conical bodies formed in plurality, fixing blocks for fixing the lower end of the outermost conical body are formed,

Among the conical bodies formed in plurality, the remaining conical bodies except for the outermost conical body are spaced apart from each other at a uniform distance, and are connected to each other so as to be electrically conductive through connection blocks.

In another embodiment, the present invention provides a first body in the form of a flat plate;

a second body having a flat plate shape formed on one surface of the first body;

It is formed inside the first body and includes a paramid-shaped paramid body arranged on a lattice,

The thickness of the first body is formed to be thicker than the thickness of the second body,

The thickness of the pyramid body is formed to be thicker than the thickness of the second body,

The bottom surface of the pyramid body is disposed on the same line as the bottom surface of the first body,

The pyramid body is formed in plurality in the interior of the first body,

The vertices of each of the pyramid bodies formed in plurality have different heights,

At the upper end of the first body, fixing blocks for fixing the lower end of the outermost paramid body among the pyramid bodies formed in plurality are formed,

Among the paramid bodies formed in plurality, the remaining paramid bodies except for the outermost paramid body are spaced apart from each other at uniform intervals, and provide an electromagnetic wave absorber that is connected to each other through connection blocks to enable conduction.

In particular, the connection blocks are formed in a polygonal shape having a predetermined length.

Both ends of the connecting blocks are connected to each other by being fitted on the side of the neighboring pyramid body.

The four pyramid bodies formed in plurality form a group, and the four pyramid bodies are connected to each other by the connecting blocks. The connecting blocks form a right angle.

When the pyramid body consists of 1, 2, and 3 layers, the pyramid bodies constituting the first layer are connected to each other through one connection block,

The pyramid bodies forming the two layers are connected to each other through two connecting blocks,

The three-layer pyramid bodies are arranged close to each other without the connecting block. The pyramidal bodies forming the three layers are the outermost pyramidal bodies.

It is possible to provide a method for measuring absorption characteristics of an absorber and a design method for a plate-type or pyramid-type absorber having high absorption characteristics in a wide frequency band.

1 is a view showing the structure of a flat plate type + cone type + flat plate type (three-layer structure).
FIG. 2 is a graph showing the optimized absorption performance of an absorber having a flat-type + cone-type + flat-type three-layer structure.
3 is a graph showing the optimized absorption performance when the thickness of each layer is changed to 15 mm in FIG. 2 .
FIG. 4 is a graph showing optimized absorption performance according to thickness and medium characteristics in the structure of FIG. 2 .
5 is a graph showing the effect of a cone structure on absorption performance, a change in a (r = a/2).
6 is a graph showing the effect of the cone structure on the absorption performance, the change in r (a = 30 mm).
7 is a graph showing the optimized absorption performance of the planar three-layer structure.
8 is a graph showing the optimized absorption performance of the planar two-layer structure.
9 is a graph showing the optimized absorption performance of a planar one-layer structure.
Fig. 10 is a cross-sectional view of the arrangement and standard (a) overall shape (b) of the five-layer structure.
11 is a graph showing optimized absorption characteristics when the medium V is air in the structure of FIG. 10 .
12 is a graph showing the change in absorption performance with respect to the change of a in the optimized five-layered absorber.
13 is a result of optimization after fixing a to different values in advance.
14 is a graph showing the effect of a on the absorption performance when the medium V is not air.
15 is a cross-sectional view of the arrangement and specification of a four-layer pyramid structure (a) overall shape (b) incident polarization (c).
16 is a graph showing absorption characteristics optimized for the incident polarization direction in the pyramidal four-layered absorber of FIG. 15 (a) Polarized wave 1 (0 degree incident) (b) Polarized wave 2 (45 degree incident)
17 to 20 are perspective views showing the configuration of the electromagnetic wave absorber according to the present invention.

The present invention provides an electromagnetic wave absorber.

The electromagnetic wave absorber includes a first body in the form of a flat plate; a second body having a flat plate shape formed on one surface of the first body; It is formed inside the first body, and includes a conical conical body arranged on a grid.

The thickness of the first body is formed to be thicker than the thickness of the second body, the thickness of the conical body is formed to be thicker than the thickness of the second body, and the bottom surface of the conical body is, the bottom surface of the first body and Arranged on the same line, the conical body is formed in a plurality inside the first body, and the vertices of each of the conical bodies formed in plurality have different heights, and at the upper end of the first body, a plurality of Among the conical bodies formed of They are spaced apart and connected to each other through connection blocks to enable conduction.

In another embodiment, the present invention provides a first body in the form of a flat plate; a second body having a flat plate shape formed on one surface of the first body; It is formed in the interior of the first body and includes a paramid-shaped paramid body arranged on a grid, wherein the thickness of the first body is formed to be thicker than the thickness of the second body, the thickness of the paramid body is formed to be thicker than the thickness of the second body, the bottom surface of the pyramid body is disposed on the same line as the bottom surface of the first body, and the pyramid body is formed in plurality in the interior of the first body and the vertices of each of the pyramid bodies formed in plurality have different heights, and at the upper end of the first body, among the pyramid bodies formed in plurality, the lower end of the outermost pyramid body is fixed Fixed blocks are formed, and among the pyramid bodies formed in plurality, the remaining pyramid bodies except for the outermost pyramid body are spaced apart from each other at uniform intervals, and electromagnetic waves are connected to each other to enable conduction through the connecting blocks. It provides an absorber.

In particular, the connection blocks are formed in a polygonal shape having a predetermined length.

Both ends of the connecting blocks are connected to each other by being fitted on the side of the neighboring pyramid body.

The four pyramid bodies formed in plurality form a group, and the four pyramid bodies are connected to each other by the connecting blocks. The connecting blocks form a right angle.

When the pyramid body consists of 1, 2, and 3 layers, the pyramid bodies constituting the first layer are connected to each other through one connection block,

The pyramid bodies forming the two layers are connected to each other through two connecting blocks,

The three-layer pyramid bodies are arranged close to each other without the connecting block. The pyramidal bodies forming the three layers are the outermost pyramidal bodies.

In more detail, in the present invention, the structure of the plate-type or pyramidal (conical) absorber and absorption performance according to the characteristics of the medium will be described. In this case, the boundary condition for the analysis was the unitcell boundary condition, and the analysis was carried out assuming that there are innumerable structures to be analyzed on the plane.

Characterization of single cone structures

The absorber structure to be considered here is as follows.

- Flat type + conical type + flat type (3-layer structure)

- Flat type + Flat type + Flat type (3-layer structure)

- Flat type + flat panel type (two-layer structure)

- Flat type (one-story structure)

1 is a view showing the structure of a flat plate type + cone type + flat plate type (three-layer structure).

Flat type + cone + flat panel type 3 layer structure layout and specification (a) overall shape (b) central cone structure (c) physical properties and dimensions for each layer

The first structure to be considered is the flat plate + cone + flat plate (three-layer structure) structure shown in Figure 2-21. A conical structure is inserted in the center, and flat plates are placed above and below it.

은 상대 유전율 (실수부),

은 상대 투자율 (실수부),

는 전기 손실 탄젠트,

는 자기 손실 탄젠트이다. 흡수체의 xy 평면상 단면은 한 변의 길이가 a인 정사각형이고, r은 원뿔 구조의 넓은 바닥면의 반경이다.

is the relative permittivity (real part),

is the relative permeability (real part),

is the electric loss tangent,

is the magnetic loss tangent. The xy plane cross section of the absorber is a square with a side length a, and r is the radius of the wide bottom surface of the conical structure.

으로 고정하여 사용하였다.The relative permittivity is

was used to fix it.

FIG. 2 is a graph showing the optimized absorption performance of an absorber having a flat-type + cone-type + flat-type three-layer structure.

[Table 1] Optimized Characteristics 1 (Length: mm) of Flat Type + Conical Type + Flat Type 3 Layer Structure Absorber

2 is a result of optimization for the case where the thickness of each layer is 5 mm, and the optimized medium properties for the change in thickness were again obtained as in FIG. 3 . Fig. 3 shows the absorption performance when only the thickness is changed.

3 shows the parameters used as the optimized absorption performance when the thickness of each layer is changed to 15 mm in FIG. 2 are as follows [Table 2].

[Table 2] Optimized Characteristics 2 (Length: mm) of Flat Type + Conical Type + Flat Type 3 Layer Structure Absorber

Comparing FIGS. 2 and 3 , it can be seen that the maximum absorption rate is very similar at 95% or more, but there is a difference in the absorption rate in the low frequency band. That is, when the thickness is thicker, a higher absorption rate is shown in a lower band, because the absorption characteristic is related to the wavelength. Another difference between the two cases is the characteristics of permittivity and permeability. It can be seen that the required relative permeability and magnetic loss tangent and electrical loss tangent are lower for the thicker case compared to the thinner case. This means that a certain thickness is required to obtain a constant absorption rate.

From the two results, it can be seen that the following conditions are necessary to obtain the same maximum absorption characteristics.

- Thin thickness + high permittivity, permeability and loss tangent

- Thick thickness + relatively low permittivity, permeability and loss tangent

- In order to improve the absorption characteristics of the low frequency band, high values are required for thickness, dielectric constant, magnetic permeability, and loss tangent.

FIG. 4 is a graph showing optimized absorption performance according to thickness and medium characteristics in the structure of FIG. 2 .

[Table 3] Optimized Characteristics 3 (Length: mm) of Flat Type + Conical Type + Flat Type 3 Layer Structure Absorber

4 shows the results calculated by the optimization parameters up to the thickness of each layer. The absorption performance was improved in the low frequency band than in the previous two cases, because as shown in [Table 3], both the magnetic permeability and the electromagnetic loss tangent increased.

Based on these results, it can be understood that the thickness is determined according to the achievable dielectric constant, permeability, loss tangent, and maximum absorption capacity from the standpoint of manufacturing.

Pyramid-type absorbers commonly found in full anechoic chambers have a great influence on absorption performance as well as physical properties and shape. The developed absorber has a flat plate structure and is characterized by having a cone-shaped absorber layer in the middle. Therefore, it is necessary to analyze the effect of the cone structure on the absorption performance. The effect of the length a of one side of the absorber on the absorption performance is shown.

5 is a graph showing the effect of a cone structure on absorption performance, a change in a (r = a/2). 6 is a graph showing the effect of the cone structure on the absorption performance, the change in r (a = 30 mm).

It can be seen that there is almost no difference in the absorption performance even when the volume of the cone changes as a changes. This means that the shape of the cone does not affect the absorption performance.

In order to understand the effect of the cone more accurately, in Fig. 2-26, the absorption performance was calculated by changing only the radius r of the bottom surface of the absorber with the length a of one side of the absorber fixed to 30 mm. As can be seen from the figure, it can be confirmed that the area of the bottom surface of the absorber does not affect the absorption performance. It can be seen from FIGS. 5 and 6 that the structure of the intermediate layer does not significantly affect the absorption performance.

Since the conical structure, which is not easy to manufacture, does not contribute to the improvement of absorption performance, it would be more advantageous in terms of manufacturing to make a three-layer structure in a flat plate type. Figure 2-27 shows the optimized absorption performance of the three-layer planar structure to support this. In Figure 2-21, the cone has been replaced by a plate.

7 is a graph showing the optimized absorption performance of the planar three-layer structure.

[Table 4] Optimized Characteristics of Absorber with Flat Type + Flat Type + Flat Type 3 Layer Structure (Length: mm)

The absorber composed of three layers also has very good absorption performance, which means that it is not necessary to use a structure that is difficult to manufacture as described above.

The conclusions reached so far are summarized as follows.

- The structure of the intermediate layer has little effect on the absorption performance

- For the same permittivity, permeability and loss tangent, the thicker the thickness, the better the absorption performance (same reflection coefficient + lower transmission coefficient)

- For the same thickness, the higher the dielectric constant, the magnetic permeability, and the loss tangent, the better the absorption performance.

From the above conclusion, it can be seen that there is no need to take the absorber layer in multiple layers or to use a special structure such as a cone or pyramid, which is difficult to manufacture. To prove this, the optimization results of the two-layer or one-layer absorber are presented in Figures 2-28 and 2-29, respectively.

8 is a graph showing the optimized absorption performance of the planar two-layer structure. 9 is a graph showing the optimized absorption performance of a planar one-layer structure.

[Table 5] Optimized Characteristics of Flat Plate + Flat Plate Two-Layer Structure Absorber (Length: mm)

[Table 6] Optimized Characteristics of Flat-Type One-Layer Structure Absorber (Length: mm)

As expected, the planar two-layer and one-layer structures also show very high absorption, and it can be confirmed again that the permeability and loss tangent must also increase as the thickness decreases to obtain the same absorption performance.

Characterization of multi-conical structures

The absorber structure to be considered here is as follows.

- Flat type + Conical type 1 + Conical type 2 + Conical type 3 + Flat type (5-layer structure)

There are three types of cones.

Fig. 10 is a cross-sectional view of the arrangement and standard (a) overall shape (b) of the five-layer structure.

11 is an optimized absorption characteristic when the medium V is air in the structure of FIG. 10, and the optimized parameters are given in [Table 7].

[Table 7]

Table 2-9. Optimized parameters of 5-layer absorber (length: mm)

11 , the overall absorption performance is very good. However, the absorption performance is inferior at lower frequency bands than with the top flat surface (medium III).

It was shown that the size a of the unit cell had little effect on the absorption performance when there was a medium III structure with the top flat surface in the three-layer structure. This is because a significant amount of energy has already been absorbed while passing through medium III. However, when there is no medium III structure, that is, when the cone is exposed to air, the size a of the unit cell affects the absorption performance, and the results are shown in FIG. 12 .

12 is a graph showing the change in absorption performance with respect to the change of a in the optimized five-layered absorber.

12 shows changes in absorption performance while changing half a in the optimized structure as shown in [Table 9]. The case where the absorption performance is the best is when a = 33.0 mm, and it can be seen that the low frequency band absorption performance is affected by the change of the remaining a. This result is very different from the result that the change in overall size has little effect on the absorption performance in the case of flat + conical + flat plate in Figure 2-21. Because. In summary, the size of the unit cell including the cone affects the absorption performance only when there is no top plate-like medium.

13 is a result of optimization after fixing a to different values in advance, and shows the optimized absorption performance after fixing a and the thickness of each layer in the five-layer absorber.

[Table 8] Optimized parameters of 5-layer absorber (length: mm)

[Table 9] Normalized radio impedance for each medium (length: mm)

As can be seen from FIG. 13 , the absorption performance of the absorber is very similar after optimization even if different a is used. Looking at Table 2-10, there is a characteristic common to all cases, that the relative permittivity and the relative permeability and the dielectric loss and the investment loss all increase from medium V to medium I. This is because good absorption performance can be obtained by minimizing transmission while minimizing reflection. In addition, Table 2-10 also presents considerations in the manufacture of absorbers. The cross-sectional area of the absorber can be made large or small by adjusting the dielectric constant and permeability, and it can be seen that it is the composition of the material used rather than the cross-sectional area of the absorber that affects the absorption performance. Table 2-11 is the propagation impedance of each medium calculated from the parameters in Table 2-10, and is the value normalized to the free space impedance. Through this, it can be seen that the values in Table 2-10 are not arbitrarily calculated values, but are set to minimize both reflection and transmission.

The last configuration to be considered is the absorption characteristic when the medium V is not air, which is given in FIG. 14 .

14 is a graph showing the effect of a on the absorption performance when the medium V is not air.

[Table 10] Parameters (Length: mm)

14 is a simulation result for examining how the size a of the unit cell affects the absorption performance when the medium V is present in the structure of FIG. 10 . Similar to the result shown in Figure 2-25, this result means that the size a of the unit cell does not affect the absorption performance when the top plate-like medium V exists. This is because, as explained above, a significant amount of energy has already been absorbed from the medium V. However, in order to increase the absorption performance in the low frequency band, it can be said that the selection of the cone structure is necessary.

Characterization of the pyramid structure

The absorber structure to be considered here is as follows.

- Flat type + Pyramid 1 + Pyramid 2 + Pyramid 3 (4-layer structure, the bottom is square)

15 is a cross-sectional view of the arrangement and specification of a four-layer pyramid structure (a) overall shape (b) incident polarization (c).

FIG. 16 is a graph showing absorption characteristics optimized for the incident polarization direction in the pyramidal four-layered absorber of FIG. 15 (a) Polarized wave 1 (0 degree incident) (b) Polarized wave 2 (45 degree incident)

FIG. 16 shows the optimized absorption performance of the four-layer pyramid structure absorber given in FIG. 15 . The direction of the incident polarization was determined to be 0 degrees and 45 degrees, where the performance difference is expected to be the greatest, and the parameters used for optimization are given in [Table 11]. 16 (a) and (b) show absorption performance when the incident polarization is 0 degrees and 45 degrees, respectively, and it can be seen that there is little difference in performance between the two at high frequencies. However, it can be seen that the cell size (a) affects the performance in a low frequency band, that is, between 30 MHz and 500 MHz.

Referring to the enlarged view of FIG. 16 , when the absorption performance is optimal, a is between 30 and 40 mm. Another important fact is that, unlike general scatterers, if dielectric and investment losses are above a certain level, it can be confirmed that it is possible to fabricate an absorber that is hardly affected by the incident polarization direction. This is a very important property that can make the absorber performance evaluation and fabrication easier.

[Table 11] Optimized parameters of the four-layer pyramid structure absorber (length: mm)

In the present invention, in order to measure the accurate absorption characteristics, various analyzes were performed on the conductor plate having the largest reflection coefficient using a simulation tool. As a result, it was confirmed that the edge diffraction component of the conductor plate, multiple reflections between the antenna and the conductor plate, and direct coupling between the antennas have a great influence on the accuracy of the measurement.

Therefore, in the present invention, a new method for calculating an accurate measurement result between the antenna and the conductor plate by removing all of the above unnecessary signals is proposed, and accordingly, the minimum measurement distance can also be calculated.

The proposed method is to replace the antenna with an equivalent source source applying the Huygens principle to eliminate scattering of the antenna. Since the equivalent source source receives the incident wave without reflection or scattering, it is possible to eliminate all multi-reflection phenomena. Direct coupling between antennas can be eliminated in the proposed way after two measurements. The proposed method has great significance in that it can accurately calculate the effect on the distance between the antenna and the conductor plate.

The most important parameters to be considered in the design of a plate-type or pyramid-type absorber are the physical properties of the absorber and the physical size and shape of the absorber. In this service, the effect of these major parameters on the absorption performance was examined closely from various angles.

First, the medium was divided into dielectric (relative permeability = 1, magnetic loss tangent = 0) and magnetic material (relative permittivity = 2, electrical loss tangent = 0), and the absorption performance obtainable from each medium was analyzed. As a result, it was proved that the absorption performance cannot be increased beyond a certain level because there is a limit to control the reflection characteristics only with individual dielectrics and magnetic materials.

These results mean that in order to increase absorption performance, a mixture having both relative permittivity and relative permeability of 1 or more and a high loss tangent value must be used. Based on the various results analyzed in this service, in the case of a flat absorber, it was found that the medium characteristic of the mixture was the most important parameter rather than the structure or shape of a cone or pyramid located inside the absorber. Based on this, some important conclusions about the planar absorber are summarized as follows.

- When the top plate has absorption performance, the physical structure (cone, etc.) of the absorber positioned below it has little effect on absorption performance.

- In order to increase the absorption performance, both the reflection coefficient and the transmission coefficient must be very small.

- In order to lower the reflection coefficient, the impedance of the medium must be equal to the free space, which means that the ratio of permittivity to permeability should be close to 1.

- In order to lower the transmission coefficient, the loss tangent of the medium must be large.

- At the same thickness, the greater the loss tangent, the better the absorption performance. (However, assuming that the reflection coefficients are the same)

- In a medium with the same loss tangent, the higher the thickness, the better the absorption performance. (However, assuming that the reflection coefficients are the same)

- In order to increase the absorption performance in the low frequency band, it is necessary to increase the thickness or increase the loss tangent.

Also, it is a case where there is no planar structure and a pyramid-shaped absorption structure is exposed to the air. In the pyramidal absorber, only the bottom support structure is flat, and the three layers are pyramidal. Although the length of the absorber unit cell affects the absorption performance in the low frequency band, it was possible to obtain very good absorption performance regardless of the direction of the incident polarized wave.

As with the planar absorber discussed above, the above problem from the point of view of fabrication means that the thickness and absorption performance of the absorber are ultimately determined by the achievable loss tangent. However, as shown in the text, it is not easy to create a medium that maintains the same permeability and magnetic loss tangent even at high frequencies. Therefore, it can be said that finding the composition and implementation method of the mixture to obtain the loss tangent value required in actual fabrication is a necessary process for making an absorber with good performance. Based on this, the development of the absorber can be made in a way that calculates the optimal absorption performance within the realizable range.

Claims (2)

a first body in the shape of a flat plate;
a second body having a flat plate shape formed on one surface of the first body;
It is formed inside the first body and includes a conical conical body arranged on a grid,
The thickness of the first body is formed to be thicker than the thickness of the second body,
The thickness of the conical body is formed to be thicker than the thickness of the second body,
The bottom surface of the conical body is disposed on the same line as the bottom surface of the first body,
The conical body is formed in plurality in the interior of the first body,
The vertices of each of the conical bodies formed in plurality have different heights,
At the upper end of the first body, among the conical bodies formed in plurality, fixing blocks for fixing the lower end of the outermost conical body are formed,
Among the conical bodies formed in plurality, the remaining conical bodies excluding the outermost conical body are spaced apart from each other at a uniform distance, and are connected to each other through connection blocks to enable conduction. . a first body in the shape of a flat plate;
a second body having a flat plate shape formed on one surface of the first body;
It is formed inside the first body and includes a paramid-shaped paramid body arranged on a lattice,
The thickness of the first body is formed to be thicker than the thickness of the second body,
The thickness of the pyramid body is formed to be thicker than the thickness of the second body,
The bottom surface of the pyramid body is disposed on the same line as the bottom surface of the first body,
The pyramid body is formed in plurality in the interior of the first body,
The vertices of each of the pyramid bodies formed in plurality have different heights,
At the upper end of the first body, among the pyramid bodies formed in plurality, fixing blocks for fixing the lower end of the outermost pyramid body are formed,
Among the pyramid bodies formed in plurality, the remaining pyramid bodies except for the outermost pyramid body are spaced apart from each other at uniform intervals, characterized in that they are connected to each other through connecting blocks to enable conduction. electromagnetic wave absorber.

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