KR101975231B1 - Wing airfoil structure including metal-coated fiber to absorb electromagnetic wave - Google Patents

Abstract

The aircraft wing structure comprises a base structure having a streamlined cross section and a metal coating fiber covering the surface of the base structure and comprising a metal coating layer surrounding the surface of the base fiber, and a first resin substrate impregnated with the metal coating fiber And an electromagnetic wave absorbing layer made of a metal. The aircraft wing structure can have improved electromagnetic wave absorption performance and the degree of freedom in the designing stage can be increased.

Description

FIELD OF THE INVENTION [0001] The present invention relates to an electromagnetic wave absorbing wing structure for aircraft,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aircraft wing structure, and more particularly, to an aircraft wing structure including metal coated fibers so as to have an electromagnetic wave absorbing performance.

Stealth technology is a technology that is used to prevent the enemy's infra-red signage, acoustic signatures, optical signatures, and radar-based electronic signatures from being easily captured. To reduce or control various signals.

When implementing stealth technology on an aircraft, it is important to reduce the radar cross section (RCS) of the radar by absorbing or scattering electromagnetic waves.

라 하고, 대상의 면적을

라고 하면 그 면적에 입사되는 에너지는

가 된다. 이 때 물체의 등방성으로 재 방사 되는 에너지를

고려하면 최종적으로 RCS 는,

로 나타낼 수 있다. 즉 RCS 는 단위 각도 당 전 방향으로 반사된 에너지와 입사된 에너지의 비로 나타낼 수 있다. Radar cross section (RCS) means the incoming power

And the area of the object

The energy incident on the area is

. At this time, the energy that is re-emitted as isotropy of the object

Finally, considering the RCS,

. In other words, RCS can be expressed as a ratio of energy reflected in all directions per unit angle and incident energy.

A method for lowering the RCS can be divided into three techniques: a shape design method in which an electromagnetic wave incident from a radar is scattered in a direction other than a radar direction in an aircraft designing stage, In order to compensate for the weak durability of shape design and RAM, the electromagnetic wave absorbing material itself absorbs the electromagnetic wave and acts as a supporting structure for supporting the load (Radar Absorbing Material, RAM) (Radar Absorbing Structure, RAS).

Typical electromagnetic wave absorbers consist of fiber, matrix and various carbonaceous nano-conductive particles due to their absorption capacity. Various electromagnetic properties can be obtained depending on the contents of various nanoparticle additives such as carbon nanotubes (CNT), carbon black (CB) and carbon nanofibers (CNF). In order to improve the absorption performance, a weight percentage, wt. %) Nanoparticle additives are dispersed in the matrix material to design the electromagnetic wave absorber.

However, the method of designing the electromagnetic wave absorber by dispersing such nano-loss materials on the base is very complicated and increases the uncertainty in the design stage because of the difference in the method of dispersing according to the operator. In addition, since there is a difference in the thickness direction depending on the degree of dispersion of the material, it has non-homogeneity and adversely affects the absorption performance. In addition, when the designed electromagnetic wave absorber is applied to a curved blade for aircraft, excessive resin migration occurs in the thickness direction due to the high viscosity of the nanoparticle additive (Filler) or the composite material deformed due to the viscosity, And thus a limit is imposed on the curved structure of the aircraft.

Patent Document 1 discloses a method of manufacturing a customized electromagnetic wave absorber having a variable electromagnetic characteristic using a single composite material and a related electromagnetic wave absorber. In the method of manufacturing a composite electromagnetic wave absorber according to a molding pressure using a prepreg containing a nanomaterial, Although various electromagnetic wave absorbers have been proposed based on the change of properties, this method is also a method of dispersing the nanoparticles in a matrix material. As a method of dispersing nanoparticles in a matrix material, electromagnetic properties There is a limitation in the degree of freedom and there is a limit in controlling the thickness at the manufacturing stage.

1. Korean Patent No. 10-1578484 (Dec. 11, 2015)

An object of the present invention is to provide an aircraft wing structure which is easy to manufacture and to control the electromagnetic wave absorption performance and has excellent mechanical properties.

It is to be understood, however, that the present invention is not limited to the above-described embodiments and various modifications may be made without departing from the spirit and scope of the invention.

According to an exemplary embodiment of the present invention, there is provided an aircraft wing structure including a base structure having a streamlined cross section and a metal covering the surface of the base structure, And an electromagnetic wave absorbing layer comprising a metal coated fiber including a coating layer and a first water repellent base impregnated with the metal coated fiber.

In one embodiment, the metal coating layer comprises at least one selected from the group consisting of silver (Ag), nickel (Ni), cobalt (Co), and iron (Fe).

In one embodiment, the metal coating layer is formed on the base fiber through electroless plating.

In one embodiment, the aircraft wing structure further includes a support layer disposed between the base structure and the electromagnetic wave absorbing layer, the support layer including a reinforcing fiber impregnated in the second resin base material and the second resin base material.

In one embodiment, the first resin substrate and the second resin substrate include at least one selected from the group consisting of an epoxy resin, a phenol resin, a polyimide resin, an acrylic resin, and a polyester resin.

In one embodiment, the reinforcing fibers comprise glass fibers or aramid fibers.

In one embodiment, the base fibers comprise glass fibers or aramid fibers.

In one embodiment, the aircraft wing structure absorbs electromagnetic waves of 4 to 18 GHz corresponding to the C-Ku-band band.

As described above, according to exemplary embodiments of the present invention, by providing a metal coating layer on a fiber or a fabric containing it, by using it as an electromagnetic wave absorber for an aircraft wing structure, non-surface scattering elements Unevenness, discontinuity, etc.) can be reduced, and the mechanical properties of the electromagnetic wave absorber can be improved. Therefore, the electromagnetic wave absorbing wing structure for an aircraft can have improved electromagnetic wave absorption performance, and the degree of freedom in the designing step can be increased.

1 is a cross-sectional view illustrating an electromagnetic wave absorbing wing structure for an aircraft according to an embodiment of the present invention.
FIG. 2 is an enlarged cross-sectional view of FIG. 1 A. FIG.
3 is an enlarged cross-sectional view of the metal coated fiber shown in Fig.
4 is an enlarged cross-sectional view of an electromagnetic wave absorbing wing structure for an aircraft according to another embodiment of the present invention.
5 is an energy dispersive spectroscopy (EDS) analysis graph of the content of the surface of the nickel-coated glass fiber of the specimen 1 and the specimen 2. Fig.
6 is a graph showing return loss measurement results of the planar electromagnetic wave absorber designed using the test pieces 1 and 2.
FIG. 7 is a graph showing the results of an RCS (Radar cross section) analysis according to the first embodiment. FIG.
8 is a graph showing the results of RCS analysis of the second embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It is to be understood, however, that the invention is not intended to be limited to the particular forms disclosed, but on the contrary, is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. In the accompanying drawings, the dimensions of the structures are enlarged to illustrate the present invention in order to clarify the present invention.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms " comprises ", or " having ", and the like, are intended to specify the presence of stated features, integers, steps, operations, elements, or combinations thereof, , Steps, operations, elements, or combinations thereof, as a matter of principle, without departing from the spirit and scope of the invention.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

1 is a cross-sectional view illustrating an electromagnetic wave absorbing wing structure for an aircraft according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of FIG. 1 A. FIG. 3 is an enlarged cross-sectional view of the metal coated fiber shown in Fig.

1 to 3, an aircraft electromagnetic wave absorbing wing structure 100 has a streamlined cross-section and includes an electromagnetic wave absorbing layer 120 coated on the surface of the base structure 110.

The base structure 110 may include, without limitation, the materials that make up the known aircraft wing structure. For example, the base structure 110 may include metal, carbon, resin, fiber, and the like.

The electromagnetic wave absorbing layer 120 includes a metal coating fiber 122. For example, the electromagnetic wave absorbing layer 120 may be a fabric formed of metal coated fibers 122 that intersect the warp and weft. For example, the warp and weft yarns may be formed by a set or twist of a plurality of metal coated fibers 122, respectively.

The electromagnetic wave absorbing layer 120 can increase dielectric loss or electromagnetic loss in the electromagnetic wave absorbing vane structure.

The metal coated fiber 122 includes a base fiber 122a and a metal coating layer 122b coated on the base fiber 122a.

For example, the base fibers 122a may include glass fibers, aramid (Kevlar) fibers, and the like.

For example, the metal coating layer 122b may include iron (Fe), cobalt (Co), nickel (Ni), silver (Ag), or the like. In one embodiment, the metal coating layer 122b may include a ferromagnetic material such as iron (Fe), cobalt (Co), nickel (Ni), or the like.

In the electromagnetic wave absorptive layer 120, the metal coating fiber 122 may be impregnated in the first resin base material 124. The content ratio of the first resin base material 124 to the metal coating fiber 122 in the electromagnetic wave absorbing layer 120 can be adjusted in order to adjust the permittivity or the permeability according to a desired electromagnetic wave of the electromagnetic wave absorber.

For example, the first resin base material 124 may include a polymer resin such as an epoxy resin, a phenol resin, a polyimide resin, an acrylic resin, and a polyester resin. In one embodiment, the first resin base material 124 may be made of a thermosetting resin such as an epoxy resin.

The electromagnetic wave absorber can be designed by matching the input impedance while changing the thickness of each layer and the material used. In the electromagnetic wave absorber, it can be said that the closer the input impedance designed to the intrinsic impedance of the free space, the better the reflection loss (for example, the electromagnetic wave absorbing ability). For example, in order to optimize the performance of the electromagnetic wave absorber in the target frequency band, the thickness of the electromagnetic wave absorber material may be about 1/4 of the electromagnetic wave wavelength in the material. However, since the permittivity or permeability of a typical insulator has a substantially constant value in the microwave band, the condition of about 1/4 of the electromagnetic wave wavelength is very limited.

However, when the ferromagnetic material is employed as the material of the electromagnetic wave absorber, since the change of the magnetic permeability in the microwave band is large, it is possible to widen the range of the condition of about 1/4 of the electromagnetic wave wavelength in the material and to realize the broadband electromagnetic wave absorber design have.

Further, in order to adjust the permittivity or the permeability according to a desired absorption electromagnetic wave, the thickness or the content of the metal coating layer 122b in the metal coating fiber 122 may be adjusted.

For example, the metal coated fibers 122 may be formed through electroless plating. Specifically, the metal coating layer 122b may be deposited on the surface of the base fiber 122a by immersing a fabric (or base fiber) made of base fibers into the aqueous metal salt solution in the plating bath.

For example, the metal salt aqueous solution may include a metal salt compound and a reducing agent. In one embodiment, a nickel salt compound may be used as the metal salt compound. For example, the nickel salt compound may include nickel sulfate, nickel acetate or nickel chloride. These may be used alone or in combination of two or more.

By including the reducing agent in the metal salt aqueous solution, an auto catalytic plating process can be substantially carried out. The metal coating layer 122b can be formed by the above-mentioned self-catalytic plating process by the chemical energy through the reducing agent and the catalytic action of the metal to be precipitated without supplying any additional electric energy.

Therefore, a uniform plating film can be formed because the problem of uneven current distribution is eliminated. Therefore, it is possible to realize a uniform electromagnetic wave absorbing ability in a desired target frequency region over the entire area of the electromagnetic wave absorber.

In one embodiment, as the reducing agent, a phosphate salt such as sodium hypophosphite or a boron compound such as methylamine boron may be used. As the concentration of the reducing agent increases, the concentration of phosphorus (P) or boron (B) increases, and the plating rate can be increased.

For example, when sodium hypophosphite is used as the reducing agent and nickel plating is performed, the metal coating layer 122b may include a nickel-phosphorus (Ni-P) alloy, and the boron compound Nickel-boron (Ni-B) alloys. As the dopant such as P or B is included in the metal coating layer 122b, mechanical properties such as hardness and abrasion resistance can be improved as compared with a plating layer formed through electroplating, for example.

For example, when nickel sulfate and sodium hypophosphite are used as the metal salt compound and the reducing agent, the autocatalytic plating process according to the following reaction formula can be carried out.

[Reaction Scheme]

_{NiSO 4 + 2NaH 2 PO 2 +} 2HO → Ni + 2NaH 2 PO 3 + H 2 + H 2 SO 4

In one embodiment, the metal salt aqueous solution may further contain a pH adjusting agent. The pH adjuster may maintain the pH of the aqueous metal salt solution in the range of, for example, about 4 to about 6. Examples of the pH adjusting agent include sodium hydroxide and ammonia.

In one embodiment, the metal salt aqueous solution may further include a stabilizer for protecting the plating bath and prevention of uneven deposition, a surfactant, and the like. Examples of the stabilizer include heavy metal salt compounds such as lead (Pb) and cadmium (Cd).

In one embodiment, the metal coated fiber 122 having the metal coating layer 122b formed thereon after the electroless plating coating described above is removed from the plating bath, and a heat treatment process may be further performed. The adhesion between the metal coating layer 122b and the base fiber 122a and the hardness of the metal coating layer 122b can be improved by the heat treatment. The heat treatment may be performed, for example, at a temperature of about 300 캜 to about 500 캜 for about 1 hour to about 2 hours.

For example, the metal coating layer 122b formed of the electroless plating coating may have a thickness of several nanometers to several tens of micrometers, and the thickness thereof is easily adjusted. For example, the thickness of the metal coating layer or the weight fraction of the metal in the metal coating fiber can be controlled by controlling the content of the metal salt in the aqueous metal salt solution.

The electromagnetic wave absorbing layer 120 including the metal coated fiber 122 or the fabric formed therefrom can function as an electromagnetic wave absorber by itself. That is, in one embodiment, the electromagnetic wave absorbing layer 120 provided in the electromagnetic wave absorbing vane structure for an aircraft may have a single layer structure.

4 is an enlarged cross-sectional view of an electromagnetic wave absorbing wing structure for an aircraft according to another embodiment of the present invention.

Referring to FIG. 4, the electromagnetic wave absorbing wing structure for an aircraft has a streamlined cross section and includes an electromagnetic wave absorbing layer 120 and a support layer 130, which are coated on the surface of the base structure 110. The support layer 130 may be disposed between the electromagnetic wave absorbing layer 120 and the base structure 110. The electromagnetic wave absorption layer 120 and the support layer 130 may constitute an electromagnetic wave absorber.

The electromagnetic wave absorbing layer 120 may have the same structure as that described above, and a detailed description thereof will be omitted.

The support layer 130 supports the electromagnetic wave absorbing layer 120 and may control the dielectric constant of the electromagnetic wave absorber.

The support layer 130 may include a second resin matrix 134 and reinforcing fibers 132 impregnated in the second resin base material 134. In order to adjust the permittivity or the permeability of the electromagnetic wave absorber according to a desired electromagnetic wave, the content ratio of the second resin base material and the reinforcing fiber in the support layer 130 may be adjusted.

For example, the second resin base material 134 may include a polymer resin such as an epoxy resin, a phenol resin, a polyimide resin, an acrylic resin, and a polyester resin. In one embodiment, the second resin base material 134 may be made of a thermosetting resin such as an epoxy resin.

According to exemplary embodiments, the reinforcing fibers 132 may comprise glass fibers, aramid (Kevlar) fibers, carbon fibers, and the like, and may preferably be provided in the form of a fabric. In one embodiment, glass fibers may be used as the reinforcing fibers 132.

The thickness of the electromagnetic wave absorber (the thickness of the electromagnetic wave absorption layer in the case of a single structure of the electromagnetic wave absorption layer and the thickness of the two-layer structure in the case of the two-layer structure of the electromagnetic wave absorption layer and the support layer) can be adjusted according to the electromagnetic wave to be absorbed. For example, the thickness of the electromagnetic wave absorber may be 1/4 of the wavelength to be absorbed. For example, for example, the electromagnetic wave absorber may absorb an electromagnetic wave of 8.2 to 12.4 GHz corresponding to the X-band band, and may absorb electromagnetic waves of 4 to 20 GHz corresponding to a wider band, for example, a C- It is possible to absorb electromagnetic waves of 18 GHz. For example, the electromagnetic wave absorber may have a thickness of 1 to 2 mm. For example, the total thickness of the electromagnetic wave absorber and the like can be calculated / optimized by a genetic algorithm.

According to embodiments of the present invention, by providing a metal coating layer on a fiber or a fabric including the fiber and using it as an electromagnetic wave absorber for an aircraft wing structure, non-surface scattering elements (surface irregularities, discontinuities, etc.) And the mechanical properties of the electromagnetic wave absorber can be improved. Therefore, the electromagnetic wave absorbing wing structure for an aircraft can have improved electromagnetic wave absorption performance, and the degree of freedom in the designing step can be increased.

Hereinafter, the structure and effects of the present invention will be described with reference to specific examples and experiments of the present invention.

Example

A glass fiber fabric (1180, Muhan Composite) was subjected to electroless plating to prepare coated fibers including a nickel layer.

5 is an energy dispersive spectroscopy (EDS) analysis graph of the content of the surface of the nickel-coated glass fiber of the specimen 1 and the specimen 2. Fig. (a) shows the analysis result of the specimen 1, and (b) shows the analysis result of the specimen 2.

Referring to FIG. 5, it can be seen that the atomic ratio of nickel is 1.08 to 1.17 at%, and the nickel layer is plated to a thin thickness of several tens nm or less.

6 is a graph showing return loss measurement results of the planar electromagnetic wave absorber designed using the test pieces 1 and 2. In FIG. 6, specimen 1 was used as a single-slab absorber. Specimen 2 was combined with a glass fiber-epoxy composite prepreg and used as a double-slab absorber having a two-layer structure. .

Specifically, the nickel-coated fibers of the specimen 1 were laminated with an adhesive film (AF126 Scotchweld, 3M) and molded in an autoclave device (using a filler, a perforated release film, a breather or a vacuum bag film) , And the adhesive film and the glass fiber-epoxy composite prepreg (GEP 118, Muhan Composite) were placed on the nickel-coated fiber of the specimen 2 and molded in the same manner to produce a two-layered electromagnetic wave absorber .

The thickness of the electromagnetic wave absorber of the single layer structure was 1.88 mm, and it was measured to have a performance of 32.32 db at a target frequency of 10 GHz (complex permittivity at 10 GHz: 16.31-j 4.84). In the electromagnetic wave absorber having the two-layer structure, the thickness of the electromagnetic wave absorbing layer composed of the nickel-coated glass fiber was 0.66 m, the thickness of the support layer composed of the glass fiber-epoxy composite was 1.85 mm and the thickness of the total electromagnetic wave absorber was 2.51 mm, (Complex permittivity of nickel-coated glass fiber at 11 GHz: 11.94-j9.42, complex permittivity of glass fiber-epoxy composite: 4.69-j0.05) at a target frequency of 10 GHz.

FIG. 7 is a graph showing the results of the RCS (Radar cross section) analysis of the first embodiment, and FIG. 8 is a graph showing the results of the RCS analysis of the second embodiment. In Example 1, the electromagnetic wave absorber having a single-layer structure designed using the specimen 1 was laminated on the surface of the aircraft wing structure (NACA 0012). In Example 2, the electromagnetic wave absorber having a two- (NACA 0012). In the aircraft wing structure, both the span and the chord length are 300 mm. The RCS evaluation was carried out in two cases according to the electromagnetic wave polarization for the wing shape. Electromagnetic wave propagates perpendicularly to the electric field and magnetic field. The polarization direction of the electric field with respect to the traveling direction of the electromagnetic wave is referred to as polarization. The TM polarized wave is a polarized wave whose magnetic field is parallel to the leading edge. The electric field is polarized parallel to the front. Due to this polarization, the difference in scattering characteristics arises because the degree of surface current induced by the electric field is different.

Therefore, the RCS measurement was performed with respect to the TM polarized wave and the TE polarized wave, and the oblique incident angle was measured by dividing by 0, 20 and 40 degrees. As a comparative example, the polarization of the perfect electrical conductor (PEC) was measured.

Referring to the RCS analysis results (6-14 GHz) in FIG. 7, RCS reduction effects of up to 10 dB or more and similar RCS fluctuation widths were observed for all the oblique incidence angles with respect to the TE polarized wave. In addition, the RCS reduction effect of 10 dB or more and the variation range of similar RCS were observed, except for the oblique incident angle 40 ° with respect to the TM polarized wave.

Generally, when the TM polarized wave is incident on the wing shape, the induced current on the surface is derived from the leading edge and propagates largely to the tailing edge of the wing. At this time, a part of it is scattered, and it returns to the front direction of the wing and causes a lot of interference. Therefore, as the current induced in the surface increases (the greater the angle of inclination), the current that returns in the forward direction causes a lot of interference, which increases the RCS variation width. On the other hand, when the TE polarized wave is incident on the wing shape, the induced surface current proceeds in the direction of the protrusion, and a relatively large surface current is induced than the TM polarized wave. In addition, since the phase currents are continuously varied in the direction of the protrusion, the surface currents having different phases generate repetitive and destructive interference repeatedly depending on the directions, and the positions of the interference occur depending on the wavelengths. The variation of RCS in TE polarized wave is relatively large.

Referring to the RCS analysis result (4-18 GHz) in FIG. 8, RCS reduction effect of 10 dB at 4-18 GHz except for 40 ° of oblique incident angle can be seen in both TE polarized wave and TM polarized wave like the single layer type electromagnetic wave absorber there was. As a result of the analysis, if the non-specular element can not be suppressed, the specular reflection performance is superior to the mono-static radar like the two-layer type electromagnetic wave absorber. Since the effect is limited, it can be expected that minimizing the non-surface scattering elements at oblique incidence angles or different polarization modes and absorbers with high absorption performance at the target frequency will have a good RCS reduction effect.

The electromagnetic wave absorbing wing structure for aircraft according to the above-described exemplary embodiments can be applied to the aerospace field to which the stealth technique is applied.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the following claims. It can be understood that it is possible.

110: base structure
120: Electromagnetic wave absorbing layer
122: metal coated fiber
130: Support layer

Claims (8)

A base structure having a streamlined cross section; And
An electromagnetic wave absorbing layer comprising a fabric made of metal coated fibers covering a surface of the base structure and including a metal coating layer surrounding the surface of the base fibers and a first resin base impregnated with the fabric,
Further comprising a support layer disposed between the base structure and the electromagnetic wave absorbing layer, the support layer including a reinforcing fiber impregnated into the second resin base material and the second resin base material. The aircraft wing structure according to claim 1, wherein the metal coating layer comprises at least one selected from the group consisting of silver (Ag), nickel (Ni), cobalt (Co), and iron (Fe). The aircraft wing structure according to claim 2, wherein the metal coating layer is formed on the base fiber through electroless plating. delete The method according to claim 1,
Wherein the first resin base material and the second resin base material comprise at least one selected from the group consisting of an epoxy resin, a phenol resin, a polyimide resin, an acrylic resin, and a polyester resin. The aircraft wing structure according to claim 1, wherein the reinforcing fiber comprises glass fiber or aramid fiber. The aircraft wing structure according to claim 1, wherein the base fibers comprise glass fibers or aramid fibers. The aircraft wing structure according to claim 1, wherein the RCS for an electromagnetic wave of 10 GHz is -10 dB or more with respect to a perfect electric conductor at an incident angle of 20 degrees or less.

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