JP2024007140A - Structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure capable of reducing the RCS with a simple configuration without restricting a shape of the structure and increasing cost.

SOLUTION: A structure for reducing the RCS includes a base material that is part of the structure and a radio wave absorber. The radio wave absorber is provided on a surface or inside the base material in a region from a front edge of the base material to only a position separated by predetermined distance along a surface of the base material or in a region from a rear edge of the base material to only a position separated by a predetermined distance along the surface of the base material when a near side of the base material relative to a travel direction of a radio wave is made to be a front side and an advance side of the travel direction is made to be a rear side.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a structure that reduces RCS (Radar Cross Section).

Conventionally, in order to reduce RCS, which is an indicator of the strength of the incoming radio waves emitted from the antenna being reflected in the direction of arrival, the angles of the surfaces and edges that make up the structure are adjusted, or the edges are made into sawtooth shapes, that is, serrations. This processing prevents reflected waves and scattered waves from returning to the direction in which the radio waves arrive (see, for example, Patent Document 1).

Furthermore, it is possible to attach a radio wave absorber to the structure, or process the edges of both the metal structure and the non-metallic structure into serrations, and connect the serrated edges of the metal structure and the non-metallic structure. In this way, RCS is reduced (see, for example, Patent Document 2).

Japanese Unexamined Patent Publication No. 3-139498 Japanese Unexamined Patent Publication No. 4-015195

However, adjusting the angles of the surfaces and edges that make up the structure or creating serrations on the edges of the structure as in the past may impose restrictions on the shape, and the structure to form the serrations may be limited. There was a fear that the complexity would lead to an increase in weight and cost.

Further, a sheet-type or coating-type radio wave absorber using a dielectric loss material or a magnetic loss material may be attached or coated on the entire surface of the structure. However, if the radio wave absorber is attached to the entire surface of the structure, the weight and cost will increase significantly, and if the radio wave absorber is applied to the entire surface of the structure, the precision thickness must be adjusted, the radio wave absorber may deteriorate, and it may fall off. Management such as prevention is required.

Therefore, an object of the present disclosure is to provide a structure that can reduce RCS with a simple configuration without imposing restrictions on the shape of the structure and without increasing cost.

The structure of the present disclosure is a structure for reducing RCS, and includes a base material that is a part of the structure, and a front side of the base material with respect to the traveling direction of radio waves, and a front side of the base material with respect to the traveling direction of radio waves. When the advancing side is the rear side, an area from the front edge of the base material to a position a predetermined distance away along the surface of the base material, or from the rear edge of the base material to the base material A radio wave absorber is provided on or inside the base material in an area up to a predetermined distance away along the surface of the base material.

According to the present disclosure, a radio wave absorber is provided on the surface or inside of the base material in an area extending a predetermined distance from the front edge or the rear edge of the base material along the surface of the base material. It will be done. By providing the radio wave absorber only at the end of the base material in this manner, RCS can be reduced without imposing any major restrictions on the shape of the structure and without increasing cost.

According to the present disclosure, it is possible to provide a structure that can reduce RCS with a simple configuration without imposing restrictions on the shape of the structure and without increasing cost.

FIG. 1 is a perspective view showing a structure including a radio wave absorber according to an embodiment of the present disclosure. FIG. 2 is a perspective view showing a structure including a mushroom structure, which is an example of a metamaterial structure, as a radio wave absorber. 3A is a perspective view showing the mushroom structure of FIG. 2, and FIG. 3B is a side view showing the mushroom structure of FIG. 3A. FIG. 4A is a plan view showing the shape and arrangement of the conductive patch, and FIG. 4B is a plan view showing the shape and arrangement of the conductive patch according to a modification. FIG. 5A is a diagram showing the relationship between the incidence angle of radio waves and the reflection coefficient in the mushroom structure of this embodiment, and FIG. 5B is a diagram showing the relationship between the incidence angle of radio waves and the reflection coefficient in a general radio wave absorber. be. FIG. 6A is a perspective view showing an analysis component in which the mushroom structure is placed at the front end with δ=λ, and FIG. 6B is a perspective view showing the analysis component in which the mushroom structure is placed at the front end with δ=about λ/4. FIG. 6C is a graph showing the analysis results for FIGS. 6A and 6B. FIG. 7A is a perspective view showing an analysis component in which the mushroom structure is placed at the rear end with δ=λ, and FIG. 7B is an analysis component in which the mushroom structure is placed at the rear end with δ=about λ/4. FIG. 7C is a perspective view showing the constituent parts, and FIG. 7C is a graph showing the analysis results for FIGS. 7A and 7B. FIG. 8A is a perspective view showing the analysis component of a perfect conductor, FIG. 8B is a perspective view showing the analysis component in which δ=approximately λ/4 and a mushroom structure is placed at the front end, and FIG. 8C is a 8A and 8B are graphs showing analysis results for FIG. 8A and FIG. 8B. FIG. 9A is a perspective view showing an analysis component of a perfect conductor, FIG. 9B is a perspective view showing an analysis component in which δ=approximately λ/4 and a mushroom structure is placed at the rear end, and FIG. 9B is a graph showing the analysis results for FIGS. 9A and 9B. FIG. 10A is a perspective view showing an analysis component made of a perfect conductor, FIG. 10B is a perspective view showing an analysis component of a perfect conductor having concave serrations, and FIG. 10C is a mushroom structure in the serrations of FIG. 10B. FIG. 2 is a perspective view showing an analysis component provided with a 10A, 10B, and 10C; FIG. FIG. 12A is a perspective view showing an analysis component of a perfect conductor having convex serrations, and FIG. 12B is a perspective view showing an analysis component in which the serrations of FIG. 12A are provided with a mushroom structure. 10A and 12A and 12B. FIG. FIG. 14A is a perspective view showing a modified example of applying the mushroom structure, and FIG. 14B is a perspective view further showing a modified example of applying the mushroom structure.

Hereinafter, a structure 100 according to an embodiment of the present disclosure will be described with reference to the drawings. The structure 100 described below is only one embodiment of the present disclosure. Therefore, the present disclosure is not limited to the following embodiments, and additions, deletions, and changes can be made without departing from the spirit of the present disclosure.

(First embodiment)
FIG. 1 is a perspective view showing a structure 100 including a radio wave absorber 50 according to an embodiment of the present disclosure.

As shown in FIG. 1, a structure 100 according to this embodiment includes a conductive base material 1 and a radio wave absorber 50. The conductive base material 1 is used as a base material constituting a part of, for example, an automobile, a building, a flying object, etc., and is made of a material such as metal or CFRP (Carbon Fiber Reinforced Plastics). The conductive base material 1 corresponds to a base material. The conductive base material 1 has a structure having a predetermined thickness, and may have any shape such as a flat plate shape or a curved shape. Radio wave absorber 50 is provided on conductive base material 1 . Specifically, the radio wave absorber 50 is provided at the front end Tf and the rear end Tr of the conductive base material 1, respectively, as shown in FIG. The front end Tf is the end on the front side when the front side of the conductive base material 1 is the front side with respect to the direction of propagation of radio waves, and the rear side is the back side in the direction of propagation, and the rear end portion Tr is the end on the rear side. Hereinafter, the direction in which the front end Tf is located may be referred to as the front, and the direction in which the rear end Tr is located may be referred to as the rear. However, the radio wave absorber 50 may be provided only on either the front end Tf or the rear end Tr of the conductive base material 1.

In this embodiment, the end portion Tf refers to a region from the front edge ed1 of the conductive base material 1 to a position separated by a predetermined distance δ along the surface of the conductive base material 1. Similarly, the end portion Tr refers to a region from the rear edge ed2 of the conductive base material 1 to a position separated by a predetermined distance δ along the surface of the conductive base material 1. The predetermined distance can also be expressed as depth.

In this embodiment, the edges ed1 and ed2 are, for example, the joints between base materials in a structure such as a flying object including a convex shape or a concave shape as shown in FIG. Includes parts that are not connected to other base materials on the outside, folds of the base material, etc.

The radio wave absorber 50 may be provided on the surface of the conductive base material 1, may be provided inside the conductive base material 1, or may be provided on both the surface and inside of the conductive base material 1. good.

In this way, by applying the radio wave absorber 50 only to the ends Tf and Tr of the conductive base material 1, it is possible to eliminate the need for the conductive material 1 itself to have a complicated shape for reducing RCS. , it becomes possible to reduce RCS without providing a radio wave absorber on the entire surface of the conductive base material as in the conventional case.

Here, as described above, the radio wave absorber 50 is provided in an area up to a predetermined distance δ from the edges ed1 and ed2. In this case, when the wavelength of the incident wave is λ and the angle of incidence is θ, it is desirable that the predetermined distance δ is determined so as to satisfy Expression 1 below. Incidentally, the incident angle θ is an angle between a line related to the direction of incidence of the incident wave and a line perpendicular to the surface of the conductive base material 1.

(Number 1)
δ=(2n+1)×λ/4×1/sinθ [n=0, 1, 2,... (n is an integer greater than or equal to 0)]

Regarding the area where the radio wave absorber 50 is provided, the effects of determining δ using the above relational expression are as follows. By setting the depth of the radio wave absorber 50 to a specific distance in the direction of propagation of radio waves, that is, the above-mentioned distance δ, this occurs in the front and rear of the radio wave absorber 50 including the boundary between the radio wave absorber 50 and the base material. The scattered waves can be caused to interfere so as to cancel each other out in the direction in which RCS is desired to be reduced. Thereby, scattered waves can be suppressed more effectively.

In addition, for the incident angle at which the RCS reduction effect is desired to be maximized, a predetermined distance δ related to the front end Tf and a predetermined distance related to the rear end Tr are set such that the relational expression for the predetermined distance δ described above is satisfied. By setting δ, RCS can be reduced more effectively. For example, if the RCS at the end is required to be small in a region where the angle of incidence of radio waves is large, the angle of incidence is set to 90°, and the predetermined distance δ is specified using the relational expression for the predetermined distance δ described above. By doing so, RCS can be reduced more effectively.

If n is made smaller in the above relational expression, the depth of the radio wave absorber 50 becomes smaller, so the area to which the radio wave absorber 50 is applied becomes narrower, and therefore the effect of suppressing reflected waves in a region where the incident angle is small becomes smaller. However, since the reflection characteristics have a small number of orders, that is, a small number of lobes with respect to changes in the incident angle, fluctuations in the reflection characteristics with respect to changes in the incidence angle can be suppressed to a small level. On the other hand, if n is increased, the depth of the radio wave absorber 50 becomes larger, so the area to which the radio wave absorber 50 is applied also becomes wider, and therefore the effect of suppressing reflected waves in a region where the angle of incidence is small becomes greater. However, since the reflection characteristic has a large order with respect to a change in the incident angle, that is, has a large number of lobes, the fluctuation in the reflection characteristic with respect to a change in the incident angle becomes large.

n in the above calculation formula may be set to be the same for the front end Tf and the rear end Tr, or may be set to be different. θ in the above calculation formula may be set the same for the front end Tf and the rear end Tr, or may be set differently, but it is better to set θ the same for RCS. The reduction effect is high. However, if the incident angle θ at the front end of the radio wave to be reflected is 90°, the RCS reduction effect can be achieved even if θ at the front end Tf and the rear end Tr are not the same. It is played. Furthermore, since the radio wave absorber 50 at the front end Tf absorbs both polarized radio waves, TE waves and TM waves, the incident electric field of the TM wave reaching the rear end Tr is also suppressed. In particular, when the incident angle θ of the radio wave to be reflected on the conductive base material 1 is 90°, the radio wave is not directly irradiated to the rear end Tr, so the radio wave absorber 50 is provided only at the front end Tf. , the RCS reduction effect can also be achieved by absorbing TM waves. In this case, the radio wave absorber 50 may also be provided at the rear end Tr, but the distance δ related to the rear end Tr need not be matched to the distance δ related to the front end Tf.

The radio wave absorber 50 is, for example, a known coating or pasting type radio wave absorber, or a known metamaterial structure.

When a coated or pasted type radio wave absorber is used as the radio wave absorber 50, the radio wave absorber is made of a dielectric loss material such as carbon or a magnetic loss material such as ferrite, and a plastic material such as polyethylene/polypropylene. It is formed by molding it into a sheet type, or by mixing it with a paint such as silicone or polyurethane and coating it on the conductive base material 1. The radio wave absorber 50 is formed into a shape and thickness depending on the wavelength of the frequency of the radio wave to be absorbed.

When employing a metamaterial structure as the radio wave absorber 50, for example, a mushroom structure and an MIM (Metal-Insulator-Metal) structure, which will be described later, can be employed.

As mentioned above, as the radio wave absorber 50, a known coating or pasting type radio wave absorber or a known metamaterial structure can be used, but in order to more effectively reduce RCS, It is preferable to adopt a material structure. Below, a mode in which the mushroom structure 10 is adopted as an example of the metamaterial structure and its effects will be explained. FIG. 2 is a perspective view showing a structure 100 including a mushroom structure 10, which is an example of a metamaterial structure according to an embodiment of the present disclosure. Moreover, FIG. 3A is a perspective view showing the mushroom structure 10 of FIG. 2, and FIG. 3B is a side view showing the mushroom structure 10 of FIG. 3A.

The mushroom structure 10 confines and absorbs incoming radio waves due to its resonance characteristics, and suppresses reflected waves and scattered waves from the surface of the mushroom structure 10. As shown in FIGS. 3A and 3B, the mushroom structure 10 is provided with a lossy dielectric layer 2 having a predetermined thickness, a plurality of conductive pins 3, and a corresponding one of the conductive pins 3. A plurality of conductive patches 4 are provided. The mushroom structure 10 has a plurality of unit cells 10s each including a part of the dielectric layer 2, a conductive pin 3, and a conductive patch 4. The size of the unit cell 10s, that is, the pitch between adjacent conductive patches 4, is the subwavelength size of the radio waves whose reflection is to be prevented. The size of the unit cell 10s is preferably designed to be larger than 1/10 and smaller than 1/2 of the wavelength of the radio wave, and more preferably designed to be larger than 1/10 and smaller than 1/2 of the wavelength of the radio wave. The plurality of conductive patches 4 are made of a good metal conductor such as copper, gold, silver or aluminum. Dielectric layer 2 is provided on conductive base material 1 . The dielectric layer 2 can be made of, for example, FRP (Fiber Reinforced Plastics), which is a resin containing carbon or the like, and in that case, it can be formed at the same time as the conductive base material 1 made of CFRP or the like. It becomes possible. The conductive pins 3 are regularly arranged upright on the conductive base material 1. The conductive patch 4 is formed into a plate shape and is provided at the outer end of the conductive pin 3. Thereby, the conductive base material 1 and the conductive patch 4 are electrically connected by the conductive pin 3.

Such a conductive patch 4 can be formed into, for example, a square shape when viewed from above, as shown in FIG. 4A. The conductive patches 4 are regularly arranged in a square grid. Alternatively, as shown in FIG. 4B, a conductive patch 40 formed in, for example, a regular hexagonal shape in plan view may be employed. In this case, each conductive patch 40 is regularly arranged in a hexagonal lattice. Note that although the illustrations are simplified in FIGS. 4A and 4B, one adjacent conductive patch 4 or conductive patch 40 and the other conductive patch 4 or conductive patch 40 are arranged with an interval from each other. Hereinafter, when the conductive patches 4 and 40 are not distinguished, they will simply be referred to as conductive patches 4.

In the mushroom structure 10, the conductive patch 4 resonates with the electric field component of the incident radio wave in the tangential direction of the dielectric layer 2, that is, mainly the electric field component of the TE wave (Transverse Electromagnetic Wave), thereby causing reflected waves and scattered waves. Performs the function of suppressing waves. Further, the conductive pins 3 act so that the dielectric layer 2 behaves as a thin plate filled with pins, and the electric field component in the vertical direction of the dielectric layer 2, that is, mainly the electric field component of the TM wave (Transverse Magnetic Wave). This causes resonance such that the effective dielectric constant becomes negative with respect to the dielectric constant. Thereby, the TM wave propagating through the dielectric layer 2 is attenuated. By slightly shifting the resonant frequency of the conductive patch 4 and the resonant frequency of the conductive pin 3, the resonant band can be widened. Therefore, absorption in a wider frequency band can be expected for the same incident angle. Further, for the same frequency, absorption can be expected at a wider angle of incidence, that is, in a wider wave number region in the tangential direction. In other words, it is possible to obtain broadband absorption characteristics with little dependence on the incident angle of incoming radio waves and dependence on TE waves and TM waves.Therefore, the radio wave absorber with a metamaterial structure can be used as a coating or pasting type radio wave absorber. It is possible to reduce RCS to a greater extent than in the body.

Generally, when a radio wave is incident from air with an impedance η ₀ to a boundary with a specific impedance Z _inp , the reflectance R is expressed by the following formula 2 and depends on the incident angle θ and the TE wave and TM wave. . Here, Z _inp ^TE is impedance for TE waves, Z _inp ^TM is impedance for TM waves, R ^TE is reflectance for TE waves, and R ^TM is reflectance for TM waves.

In the case of a single layer structure such as a coating or pasting type radio wave absorber, its impedance Z _inp is expressed by the following formula 3, and its characteristics are as follows: incident angle θ, dielectric constant ε _r of the dielectric layer 2, It is characterized by the relative magnetic permeability μ _r of the dielectric layer 2 and the thickness d of the dielectric layer 2 . Note that in Equation 3, k ₀ is the wave number in vacuum.

On the other hand, each impedance due to the conductive patch 4 having a mushroom structure is expressed by Equation 4 below. The characteristics of each impedance are as follows based on the incident angle θ, the relative dielectric constant ε _r of the dielectric layer 2, the thickness d of the dielectric layer 2, the periodic size D of the conductive patches 4, and the interval w between the conductive patches 4. It is characterized by a grid variable α expressed by Equation 5. Here, in Equation 4, μ ₀ is the vacuum permeability, β is the vertical component of the propagation constant of the dielectric layer 2, and k _eff is the effective wave number of the surface of the dielectric layer 2. Further, the period size D in Equation 5 is the sum of the dimension of the conductive patch 4 and the above-mentioned interval w. Note that, since the relative magnetic permeability μ _r of the dielectric layer 2 in the mushroom structure is approximately 1, μ _r is omitted in Equations 4 and 5.

In the mushroom structure, for the electric field component in the vertical direction, the apparent permittivity ε _n and propagation constant β _TM in the vertical direction become conductive due to the resonance of the conductive pin 3, as shown in Equations 6 and 7 below, respectively. The wave number k _p is expressed by the following equation 8, which is characterized by the radius r ₀ of the sex pin 3. Accordingly, the frequency characteristic of the impedance Z _inp ^TM for the TM wave shown in the above equation 4 changes.

FIG. 5A shows the analysis results of radio wave absorption characteristics, and is a diagram showing the relationship between the incident angle of radio waves and the reflection coefficient in the mushroom structure 10 of this embodiment. FIG. 5B shows the analysis results of the radio wave absorption characteristics, FIG. 3 is a diagram showing the relationship between the angle of incidence of radio waves and the reflection coefficient in a radio wave absorber having a general single-layer structure.

FIG. 5A shows the radio wave reflection characteristics of the mushroom structure 10 in which the thickness _d of the dielectric layer is 2 _mm . , are obtained from Equation 2 and Equations 4 to 8 above, assuming a frequency of 10 GHz. Figure 5B shows the radio wave reflection characteristics of a radio wave absorber with a thickness of approximately 1 mm that includes a magnetic material to increase the propagation loss of radio waves. , is obtained from Equation 2 and Equation 3 above with the frequency of the incident wave being 10 GHz. In FIGS. 5A and 5B, the horizontal axis represents the incident angle θ (deg), and the vertical axis represents the reflection coefficient (dB). In FIGS. 5A and 5B, the solid line indicates the analysis result of the TM wave, and the broken line indicates the analysis result of the TE wave.

By slightly shifting the resonance frequency of the conductive patch 4 and the resonance frequency of the conductive pin 3, the reflection characteristics of the mushroom structure 10 in FIG. 5A can be obtained as shown in FIG. 5B even though no magnetic material is used in the TE wave. Compared to the reflection characteristics of radio wave absorbers, the reflection characteristics for large incident angles are improved. In other words, the mushroom structure 10 can reduce the reflection coefficient of the TE wave. On the other hand, for the TM wave in FIG. 5A, there is no sharp decrease in the reflection coefficient compared to FIG. 5B at the specific incident angle where Brewster's angle occurs, that is, around 50° in FIGS. 5A and 5B. Although not, homogeneous reflection characteristics almost similar to TE waves can be confirmed. By improving these reflection characteristics, the mushroom structure 10 can be said to be a good means for uniformly suppressing reflected waves and scattered waves even for radio waves having TE waves and TM waves that are incident at a larger angle of incidence.

The effects when the radio wave absorber 50 has the mushroom structure 10 are as follows. At the end Tf, the dielectric current along the end becomes larger with respect to the incident electric field of the TE wave, so a large scattered wave is generated. In addition, at the end Tr, at a relatively shallow incident angle where the end can be seen directly, a large scattered wave is generated in response to the incident electric field of the TE wave along the end, similar to the front end, and as the incident angle becomes deeper, , a large scattered wave is generated when the incident electric field of the TM wave propagates through the reflective surface connected to the end Tr and reaches the end Tr. Therefore, by applying the mushroom structure 10 to the front end Tf and the rear end Tr, it is possible to suppress the induced current at the ends Tf and Tr due to the incident electric field of the TE wave. Further, since the propagation of the TM wave propagating through the reflective surface can be suppressed to the end Tr, it is possible to suppress scattered waves at both the end Tf and the end Tr.

In this way, by employing the mushroom structure 10 as the radio wave absorber 50, it is possible to obtain broadband absorption characteristics with low incidence angle dependence, TE wave and TM wave dependence. The effect of reducing RCS is greater than that of using a radio wave absorber.

Examples of the first embodiment will be described below. In the example, the effect of reducing RCS by an analytical model including the mushroom structure 10 described above was analyzed.

<First example>
In this example, the predetermined distance δ of the region in which the mushroom structure 10 of this embodiment is provided was variously set, and an analysis was conducted to confirm the effect of reducing RCS. The wavelength of the incident radio wave was λ, and the period size D of the conductive patch 4 was λ/5.

FIG. 6A is a perspective view showing an analysis component 10C in which the mushroom structure 10 is placed at the front end with δ set to λ, and FIG. 6B is a perspective view showing the mushroom structure 10 placed at the front end with δ set to approximately λ/4. 6C is a perspective view showing the analysis component 10D, and FIG. 6C is a graph showing the analysis results when radio waves are incident on the analysis component 10C and the analysis component 10D while changing the incident angle. Further, FIG. 7A is a perspective view showing the analysis component 10E in which the mushroom structure 10 is arranged at the rear end with δ set to λ, and FIG. 7B is a perspective view showing the mushroom structure 10 arranged at the rear end with δ set to approximately λ/4. FIG. 7C is a perspective view showing the analysis component 10F arranged in the analysis component 10E and the analysis component 10F, and FIG. 7C is a graph showing the analysis results when radio waves are incident on the analysis component 10E and the analysis component 10F while changing the incident angle.

FIG. 8A is a perspective view showing a perfect conductor analysis component 1A, and FIG. 8B is a perspective view showing an analysis component 10G in which δ is approximately λ/4 and a mushroom structure 10 is arranged at the front end. 8C is a graph showing the analysis results when radio waves are incident on the analysis component part 1A and the analysis component part 10G while changing the incident angle. Further, FIG. 9A is a perspective view showing a perfect conductor analysis component 1A, and FIG. 9B is a perspective view showing an analysis component 10H in which δ is set to approximately λ/4 and a mushroom structure 10 is arranged at the rear end. 9C is a graph showing the analysis results when radio waves are incident on the analysis component part 1A and the analysis component part 10H while changing the incident angle. 6C, FIG. 7C, FIG. 8C, and FIG. 9C, the horizontal axis shows the incident angle θ of the radio wave, and the vertical axis shows the RCS value (dB).

As shown in FIG. 6C, for TE waves that generate strong scattered waves from the front end, RCS using the analysis component 10D with a small application area of the mushroom structure 10 is better at the incident angle of 55° to 90°. , it can be confirmed that the RCS is smaller than the RCS by the analysis configuration unit 10C, which has a large application area.

Furthermore, as shown in FIG. 7C, for TM waves that generate scattered waves from the rear end, in the range where the incident angle is large up to around 75°, the RCS by the analysis configuration unit 10F is better than the analysis configuration. It can be confirmed that the RCS is generally smaller than the RCS obtained by section 10E.

Further, as shown in FIG. 8C, the effect of reducing RCS can be confirmed for the TE wave at an incident angle of approximately 35° or more, particularly near an incident angle of 90°, which is horizontal incidence. Further, as shown in FIG. 9C, it is possible to confirm the overall RCS reduction effect for the TM wave. From the above, it can be seen that by determining the predetermined distance δ, which is the depth, according to Equation 1, the RCS can be effectively reduced even if the predetermined distance δ is small.

As explained above, according to the present embodiment, from the front end Tf or the rear end Tr of the conductive base material 1 to a position a predetermined distance away along the surface of the conductive base material 1, A radio wave absorber 50 is provided on the surface or inside of the conductive base material 1 in the region. By providing the radio wave absorber 50 only at the ends Tf and Tr of the conductive base material 1 in this way, RCS can be reduced without imposing major restrictions on the shape of the structure 100 and without increasing cost. I can do it.

Furthermore, in this embodiment, it is desired to reduce the RCS of the scattered waves generated at the front end Tf or the rear end Tr by setting the predetermined distance δ at which the radio wave absorber 50 is provided using Equation 1. It is possible to cause interference to cancel each other out in different directions. Thereby, scattered waves can be suppressed more effectively.

Further, in this embodiment, by employing the mushroom structure 10 as the radio wave absorber 50, scattered waves at both the end portion Tf and the end portion Tr can be suppressed, and RCS can be reduced more effectively. The mushroom structure 10 can be molded simultaneously with the conductive substrate 1.

(Second embodiment)
In the first embodiment, the scattered waves generated on the front and rear sides of each radio wave absorber 50 at the front end and the rear end are caused to interfere so as to cancel each other out, thereby returning to the direction of arrival of the incident wave. Suppressed scattered waves. However, with this method, there is a possibility that only the RCS reduction effect can be expected with respect to incidence of radio waves from a specific direction. Therefore, in the second embodiment, from the front edge ed1 or the rear edge ed2 of the structure 100 to a sawtooth-like, that is, serration-like region along the surface of the base material, inside or on the surface of the conductive base material 1. A radio wave absorber 50 is provided. That is, the shape of the boundary 55 (described later) between the conductive base material 1 provided with the radio wave absorber 50 and the conductive base material 1 not provided with the radio wave absorber 50 is made to have a sawtooth shape, that is, a serration shape. A radio wave absorber 50 is provided. The serrated region is a region in which one or more triangular serrated elements are continuously formed. The sawtooth shape is a shape in which the distance in the depth direction from the edge of the conductive base material 1 repeats increasing and decreasing linearly in correspondence with the width direction of the edge of the conductive base material 1. The sawtooth shape is a shape in which the distance from the conductive base material 1 changes periodically or aperiodically in accordance with the width direction of the edge of the conductive base material 1, and the apex of the sawtooth element that is not on the edge. It may be a shape that changes symmetrically or asymmetrically with respect to. That is, the position of the apex of the sawtooth element that is not on the edge can be arbitrarily set in the width direction or the front-back direction (depth direction) of the edge, and the position of the two vertices that are on the edge can be arbitrarily set in the width direction of the edge. For example, when a sawtooth region has two or more sawtooth elements, each sawtooth element may have the same shape, or the distance in the front-rear direction (depth direction) from the edge to the vertex that is not on the edge is The distance between the two vertices on the edge of the sawtooth element may be different for each sawtooth element, and the triangular shape of the sawtooth element itself may be different between the sawtooth elements. In this way, depending on the purpose and structure of the structure to which the serrations are applied (length of sides, presence or absence of curved surfaces, etc.), the depth and width direction of the radio wave absorber 50 may be gradually reduced or increased, for example. An aperiodic shape may also be adopted.

The depth of the radio wave absorber 50, that is, the distance from the front end to the rear end of the radio wave absorber 50, and the length in the width direction are arbitrary, and can be appropriately designed depending on the purpose and the structure of the structure 100. The material of the radio wave absorber 50 of the second embodiment and the effect when the wave absorber 50 has a mushroom structure are the same as those of the first embodiment. In this embodiment, a known radio wave absorber 50 is coated in a periodic shape on a conductive base material 1 having an original shape such as a rectangular plate shape, or a metamaterial structure such as a mushroom structure 10 is coated in a periodic shape. It is molded simultaneously with the conductive base material 1. Thereby, scattered waves generated at the boundary can be suppressed without changing the original shape of the conductive base material 1. In addition, in this embodiment, the radio wave absorber 50 exemplified by the mushroom structure 10 having a shape along a periodic shape corresponds to the second radio wave absorber.

Below, an example of a second embodiment in which a mushroom structure 10 is adopted as the radio wave absorber 50 will be shown. FIG. 10A is a perspective view showing an analysis component 11A made of a perfect conductor as a comparative example, FIG. 10B is a perspective view showing an analysis component 12A of a perfect conductor having serrations 13A, and FIG. It is a perspective view which shows 30 A of analytical structure parts which provided the mushroom structure 10I of serration shape. The serration portion 13A in FIG. 10B is formed in a notch shape, that is, the analysis component portion 12A is formed in a concave shape, and the opening angle, which is the angle of the concave portion, is 60°. Further, the maximum depth of the serration portion 13A, that is, the distance from the front end to the rear end, was 5λ, and the maximum width was 3λ. The mushroom structure 10I is formed in a triangular shape so that the analysis component 30A has an overall rectangular shape in a plan view, and has a similar shape to the serration portion 13A (cutout portion) in FIG. 10B. FIG. 10C is an example of this embodiment. In FIG. 10C, the mushroom structure 10I is formed on the front end Tf, but it may be formed on the rear end Tr, or on both ends.

Further, FIG. 12A is a perspective view showing a perfect conductor analysis structure section 14A having a serration section 15A, and FIG. 12B is a perspective view showing an analysis structure section 31A having a mushroom structure 10J in addition to the serration section 15A of FIG. 12A. It is. The serration portion 15A in FIG. 12A is formed in a convex shape on the front side, that is, the analysis component portion 14A is formed in a convex shape, and the angle of the convex portion is 60°. Further, the maximum value of the distance from the front end to the rear end, which is the depth of the serration portion 15A, was set to 5λ, and the maximum width was set to 3λ. The mushroom structure 10J has serrations 15A so that the analysis component 31A has an overall rectangular shape in plan view, and the boundary 55 with the adjacent structure has a shape similar to the edge of the serrations 15A in FIG. 12A. They are each formed in a triangular shape on both sides in the width direction. FIG. 12B is another example of this embodiment. Although the mushroom structure 10J is formed on the front end Tf in FIG. 12B, it may be formed on the rear end Tr or on both ends.

As described above, according to this embodiment, by combining the radio wave absorber 50, for example the mushroom structure 10, and the serration shape as shown in FIGS. 10C and 12B, the general scattered waves generated at the structure boundaries can be reduced. It is possible to deviate from the direction of arrival. Thereby, the effect of reducing RCS can be further improved than in the first embodiment. In this way, in addition to forming the mushroom structure 10 that can suppress the induced current and surface propagation waves due to TE/TM waves at the front end and the rear end, the structure boundary is periodically This shape makes it possible to suppress reflected waves and scattered waves and to control the direction of the reflected waves and scattered waves, thereby making it possible to more effectively reduce RCS.

<Second example>
Examples of the second embodiment will be described below. FIG. 11 is a graph showing the results of analysis of the RCS of the analysis components shown in FIGS. 10A, 10B, and 10C. Further, FIG. 13 is a graph showing the results of analysis of the RCS of the analysis component shown in FIG. 10A and the RCS of the analysis component shown in FIGS. 12A and 12B. In FIGS. 11 and 13, the horizontal axis indicates the incident angle θ of the radio wave, and the vertical axis indicates the RCS value (dB). In addition, since the mushroom structure 10 is formed at the front end Tf of the analytical structure shown in FIGS. 10C and 12B, in FIGS. 11 and 13, the scattered waves at the front end Tf greatly contribute to the TE wave The RCS is being analyzed.

As shown in FIG. 11, the RCS of the analysis component 30A in FIG. 10C tends to be larger than that of the analysis component 12A in FIG. 10B at some incident angles around about 50 degrees. However, it can be confirmed that the RCS of the analysis component 30A is suppressed to the same level or lower than that of the analysis components 11A and 12A of FIGS. 10A and 10B at all other incident angles.

Further, as shown in FIG. 13, the analysis component 31A in FIG. 12B has a lower RCS than the analysis component 11A in FIG. 10A at all incident angles. Compared to the analysis component 14A of FIG. 12A, the RCS tends to become large at some incident angles around about 30° to 70°. However, it can be confirmed that the RCS of the analysis component 31A is suppressed to the same level or lower than that of the analysis component 14A in FIG. 12A at all other incident angles. For these reasons, in addition to incorporating the mushroom structure 10 into the front end Tf and the rear end Tr, by making the structure boundary into a periodic shape, for example, a serration shape, the RCS can be made more effective. It can be seen that it is possible to reduce the

As described above, according to the second embodiment, it is possible to reduce RCS with a simple configuration without increasing cost, similar to the first embodiment. Further, by providing the radio wave absorber 50 in combination with a periodic shape, it is possible to divert general scattered waves generated at the structural boundary from the direction of arrival. Therefore, it is expected that the RCS reduction effect can be further improved than in the first embodiment.

(Other embodiments)
In addition to the embodiments described above, the present disclosure can be modified in various ways without departing from the spirit thereof.

For structures such as buildings (structures) near radio wave sensors such as radar antennas installed in automobiles, etc., and buildings (structures) near communication equipment that uses radio waves, such as ETC (Electronic Toll Collection System) gates. By applying the present disclosure, even if the present disclosure is applied for the purpose of preventing reflected waves from these structures from being received by radio wave-using devices (radar sensors, Wi-Fi, communication devices with Bluetooth functions, etc.) good. Alternatively, the present disclosure may be applied to a structure aimed at suppressing electro-magnetic interference (EMI), and the present disclosure can be applied generally.

Furthermore, the first embodiment and the second embodiment may be combined.

Further, the shape of the structure adjacent to the mushroom structure 10 (the shape of the boundary between the mushroom structure 10 and the adjacent structure) may be, for example, an edge alignment shape.

Further, in the above embodiment, the radio wave absorber 50 is provided on the conductive base material 1 so as to be the outermost layer, but the present invention is not limited to this, and a surface protective layer may be provided to protect the radio wave absorber 50. In this case, the radio wave absorber 50 does not have to be configured as the outermost layer.

Further, in the embodiment described above, the mushroom structure 10 is employed as an example of a metamaterial structure. However, the metamaterial structure is not limited to the mushroom structure 10. The metamaterial structure is not limited to the mushroom structure 10, as long as it can confine and absorb incoming radio waves and suppress reflected waves and scattered waves. good. This MIM structure includes a conductive base material, a dielectric layer provided on the conductive base material, and a plurality of conductive layers arranged regularly along the surface of the dielectric layer on top of the dielectric layer. Equipped with a patch.

Moreover, from the above analysis results, even when the mushroom structure 10, which is an example of the radio wave absorber 50, is applied only to the front end, there is an effect of reducing RCS for TE waves, and the mushroom structure 10 is applied only to the front end. It was found that even when applied only to the edges, there is an effect of reducing RCS for TM waves. Therefore, even when the incident angle θ is other than 90°, the radio wave absorber 50 may be provided only at either the front end or the rear end.

Further, an outer surface of a structure in which an edge of one conductive base material and an edge of the other conductive base material are connected such that one conductive base material and the other conductive base material have an acute angle, Alternatively, a radio wave absorber 50 may be provided on the inner surface. In this case, edges 56 and 57, which will be described later, in which one conductive base material and the other conductive base material are connected also correspond to edges ed1 and ed2 in the first embodiment or the second embodiment.

In the structure shown in FIG. 14A, the edge of one conductive base material and the edge of the other conductive base material are connected such that one conductive base material 20 and the other conductive base material 21 have an acute angle. It is a struct that has been created. For example, as shown in FIG. 14A, when the connected edge 56 is the front edge ed1, one conductive base material 20 and the other conductive base material 21 are connected along the surface from the connected edge 56. For example, a radio wave absorber 50 such as the mushroom structure 10 may be coated, attached, or molded in the form of serrations on the outer surface. In this case, the mushroom structure 10 may be applied, attached, or molded to each of the conductive substrates 20 and 21 on both sides in the width direction so that the depth at the outermost end in the width direction is maximum.

In the structure of FIG. 14B, the edge of one conductive base material and the edge of the other conductive base material are connected such that one conductive base material 22 and the other conductive base material 23 have an acute angle. It is a structure. As shown in FIG. 14B, when the edge opposite to the connected edge 57 is the front edge ed1, one conductive base material 22 and the other conductive base material are connected along the surface from the front edge ed1. For example, a radio wave absorber 50 such as the mushroom structure 10 may be coated, pasted, or molded on the inner surface of the antenna 23 in the form of serrations. In this case, the mushroom structure 10 may be applied, attached, or molded to each of the conductive substrates 22 and 23 on both sides in the width direction so that the depth at the outermost end in the width direction is maximum.

The structure of the present disclosure is a structure for reducing RCS, and includes a base material that is a part of the structure, and a front side of the base material with respect to the traveling direction of radio waves, and a front side of the base material with respect to the traveling direction of radio waves. When the advancing side is the rear side, an area from the front edge of the base material to a position a predetermined distance away along the surface of the base material, or from the rear edge of the base material to the base material A radio wave absorber is provided on or inside the base material in an area up to a predetermined distance away along the surface of the base material.

According to the present disclosure, a radio wave absorber is provided on the surface or inside of the base material in an area extending from the front edge or rear edge portion of the base material to a position a predetermined distance away along the surface of the base material. provided. By providing the radio wave absorber only at the end of the base material in this manner, RCS can be reduced without imposing any major restrictions on the shape of the structure and without increasing cost.

In the above disclosure, the wavelength of the radio wave to be prevented from being reflected is λ, the angle of incidence of the radio wave is θ, and the distance between the front edge of the base material and the radio wave absorber provided along the surface of the base material , or when the predetermined distance, which is the distance at which the radio wave absorber is provided from the rear edge of the base material along the surface of the base material, is δ, δ=(2n+1)×λ/4×1 /sinθ [n is an integer greater than or equal to 0] may be established.

According to the above disclosure, by setting the depth of the radio wave absorber to a predetermined distance δ with respect to the direction of propagation of radio waves, the scattered waves generated on the front and rear sides of the radio wave absorber cancel each other out in the direction in which RCS is desired to be reduced. can be interfered with. Thereby, scattered waves can be suppressed more effectively.

In the above disclosure, the radio wave absorber may include a metamaterial structure, and the metamaterial structure may have a plurality of subwavelength-sized unit cells. Further, in the above disclosure, the second radio wave absorber may include a metamaterial structure, and the metamaterial structure may have a plurality of unit cells of subwavelength size.

According to the above disclosure, by making the metamaterial structure smaller than the wavelength of the incident radio waves, the refraction of the radio waves can be controlled, thereby increasing the effect of suppressing scattered waves.

The structure of the present disclosure is a structure for reducing RCS, and includes a base material that is a part of the structure, and a front side of the base material with respect to the traveling direction of radio waves, and a front side of the base material with respect to the traveling direction of radio waves. Provided on the surface or inside of the base material in a serrated region along the surface of the base material from the front edge or the rear edge of the base material when the advancing side is the rear side. It is equipped with a radio wave absorber.

According to the present disclosure, it is possible to divert the general scattered waves generated at the structure boundary from the direction of arrival without imposing major restrictions on the shape of the structure and without increasing cost. Thereby, the effect of reducing RCS can be further improved.

In the above disclosure, the base material is conductive, and the metamaterial structure includes a dielectric layer provided on the top of the base material, and a dielectric layer arranged regularly along the surface of the dielectric layer on the top of the dielectric layer. and a part of the base material, the pitch of the conductive patches may be greater than 1/10 and less than 1/2 of the wavelength of the radio wave whose reflection is to be prevented. good.

According to the above disclosure, the refraction of incident radio waves can be controlled, thereby further increasing the effect of suppressing scattered waves.

In the above disclosure, the metamaterial structure may include a plurality of conductive pins respectively connecting the base material and each of the plurality of conductive patches.

According to the above disclosure, the conductive patch has the function of suppressing reflected waves and scattered waves by resonating with the electric field component in the tangential direction of the radio wave incident on the dielectric layer (mainly the electric field component of the TE wave). Fulfill. Further, the conductive pin causes resonance such that the effective dielectric constant becomes negative with respect to the electric field component in the direction perpendicular to the TE wave (mainly the electric field component of the TM wave). This attenuates the TM waves propagating through the dielectric layer.

In the above disclosure, the conductive patch may be formed in a square shape or a regular hexagonal shape.

According to the above disclosure, a plurality of conductive patches can be densely arranged.

1 Conductive base material 2 Dielectric layer 3 Conductive pin 4 Conductive patch 10 Mushroom structure 10s Unit cell 13A, 15A Serration part 20, 21, 22, 23 Base material 100 Structure ed1, ed2 Edge Tf, Tr End part

Claims (8)

A structure for reducing RCS, the structure comprising:
A base material that is part of the structure,
When the front side of the base material is the front side with respect to the direction of propagation of radio waves, and the side of the base material in the propagation direction is the rear side,
A region from the front edge of the base material to a position a predetermined distance along the surface of the base material, or a position a predetermined distance apart from the rear edge of the base material along the surface of the base material. a radio wave absorber provided on or inside the base material in the region up to
Structure. Let λ be the wavelength of the radio wave whose reflection should be prevented,
Let the incident angle of the radio wave be θ,
The distance at which the radio wave absorber is provided from the front edge of the base material along the surface of the base material, or the distance at which the radio wave absorber is provided from the rear edge of the base material along the surface of the base material. When the predetermined distance, which is the provided distance, is δ,
The relational expression δ=(2n+1)×λ/4×1/sinθ [n is an integer greater than or equal to 0] holds,
The structure according to claim 1. The radio wave absorber includes a metamaterial structure, and the metamaterial structure has a plurality of subwavelength-sized unit cells.
The structure according to claim 1. A structure for reducing RCS, the structure comprising:
A base material that is part of the structure;
When the front side of the base material is the front side with respect to the traveling direction of radio waves, and the traveling side in the traveling direction is the rear side,
A radio wave absorber provided on the surface or inside of the base material in a serrated region along the surface of the base material from the front edge or the rear edge of the base material,
Structure. The radio wave absorber includes a metamaterial structure, and the metamaterial structure has a plurality of subwavelength-sized unit cells.
The structure according to claim 4. the base material is electrically conductive;
The metamaterial structure is
a dielectric layer provided on the top of the base material;
a plurality of conductive patches arranged regularly along the surface of the dielectric layer on the top of the dielectric layer;
including a part of the base material,
The pitch of the conductive patch is larger than 1/10 and smaller than 1/2 of the wavelength of the radio wave whose reflection is to be prevented.
The structure according to claim 3. The metamaterial structure includes a plurality of conductive pins respectively connecting the base material and each of the plurality of conductive patches.
The structure according to claim 6. The conductive patch is formed in a square shape or a regular hexagonal shape,
The structure according to claim 6 or 7.

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