Radome for projectiles

Abstract

The objective is to provide a radome for projectiles that can improve high-temperature strength and radio wave transmission characteristics. [Solution] The radome for a projectile according to the embodiment is a radome for a projectile that covers an antenna for transmitting and receiving radio waves, comprising a dome portion and a heat insulating portion covering the inner surface of the dome portion, wherein the dome portion comprises a composite material layer including a matrix material and a reinforcing member, the matrix material is selected from at least one of mullite and alumina, the reinforcing member is selected from at least one of ceramic fibers and ceramic particles, the ceramic fibers are selected from at least one of mullite fibers and alumina fibers, and the ceramic particles are selected from at least one of mullite particles and alumina particles.

Description

Technical Field

[0001] Embodiments of the present invention relate to a radome for a flying object.

Background Art

[0002] A flying object is provided with an antenna for transmitting and receiving radio waves. A radome is known as a cover that covers such an antenna and protects the antenna. In such a radome for a flying object, it is desired to improve high-temperature strength and radio wave transmission characteristics.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The problem of the present embodiment is to provide a radome for a flying object that can improve high-temperature strength and radio wave transmission characteristics.

Means for Solving the Problems

[0005] The radome for a flying object according to the embodiment is a radome that covers an antenna for transmitting and receiving radio waves. The radome for a flying object includes a dome portion and a heat insulating portion that covers the inner surface of the dome portion. The dome portion includes a composite material layer including a matrix material and a reinforcing member. The matrix material is selected from at least one of mullite and alumina. The reinforcing member is selected from at least one of ceramic fibers and ceramic particles. The ceramic fibers are selected from at least one of mullite fibers and alumina fibers. The ceramic particles are selected from at least one of mullite particles and alumina particles.

Brief Description of the Drawings

[0006] [Figure 1] Figure 1 is a cross-sectional view showing the radome of this embodiment attached to the airframe of a flying vehicle. [Figure 2] Figure 2 is a cross-sectional view showing the dome portion of the radome in the first configuration example. [Figure 3] Figure 3 is a perspective view showing an example of continuous ceramic fibers. [Figure 4] Figure 4 is a cross-sectional view showing the dome portion of the radome in the second configuration example. [Figure 5] Figure 5 is a cross-sectional view showing the dome portion of the radome in the third configuration example. [Figure 6] Figure 6 is a cross-sectional view showing the dome portion of the radome in the fourth configuration example. [Figure 7] Figure 7 is a cross-sectional view showing the dome portion of the radome in the fifth configuration example. [Figure 8] Figure 8 is a cross-sectional view showing an example of ceramic particles. [Modes for carrying out the invention]

[0007] The embodiments of the present invention will be described below with reference to the drawings. Note that the disclosure is merely an example, and modifications that can be easily conceived by those skilled in the art while maintaining the spirit of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the drawings and descriptions, the width, thickness, shape, etc., of each part may be represented schematically compared to the actual appearance, but this is merely an example and does not limit the interpretation of the present invention. Also, in this specification and in each drawing, elements similar to those described above in previously shown drawings are denoted by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0008] The radome for a projectile according to this embodiment will be described in detail below with reference to the drawings. Figure 1 is a cross-sectional view showing the radome 1 for a projectile (hereinafter referred to as radome 1) of this embodiment attached to the airframe 2 of the projectile. In the figure, the X, Y, and Z directions are defined as mutually orthogonal. The X direction corresponds to the axial direction of the radome 1. The Y and Z directions correspond to the width direction of the radome 1.

[0009] As shown in Figure 1, the radome 1 of this embodiment covers and protects the antenna 210 mounted on the front end (nose section 200) of the aircraft's fuselage 2. The antenna 210 is used for transmitting and receiving radio waves. The radome 1 is attached to the nose section 200 of the aircraft's fuselage 2. In the example shown in Figure 1, the nose section 200 has a cylindrical shape extending along the axis C.

[0010] The radome 1 comprises a dome portion 100 and a heat insulating portion 110. As shown in Figure 1, the dome portion 100 has a topped cylindrical shape with its apex on axis C. The dome portion 100 is attached to the nose portion 200 such that the axis of the dome portion 100 coincides with the axis of the nose portion 200. Hereinafter, in the axial direction, the dome portion 100 side may be described as the front side and the nose portion 200 side as the rear side. The dome portion 100 has an externally structured conical shape that tapers towards the front and is open towards the rear.

[0011] The thermal insulation section 110 is housed inside the dome section 100 and covers the inner surface 100a of the dome section 100. The thermal insulation section 110 has an antenna housing section 111 for housing the antenna 210. In the example shown in Figure 1, the antenna housing section 111 has substantially the same shape as the outer shape of the antenna 210. The antenna 210 is housed in the antenna housing section 111. The thermal insulation section 110 is formed from, for example, polycrystalline short fibers containing quilted alumina or nanoparticles containing fumed silica.

[0012] The dome part 100 includes a composite material layer 10, a first ceramic layer 21, and a second ceramic layer 22. The first ceramic layer 21 covers the heat insulation part 110. The composite material layer 10 is disposed between the first ceramic layer 21 and the second ceramic layer 22. The second ceramic layer 22 covers the composite material layer 10 and is exposed to the outside.

[0013] Although not shown, the dome part 100 may not include the first ceramic layer 21 and the second ceramic layer 22. At this time, the inner surface 10a of the composite material layer 10 covers the heat insulation part 110, and the outer surface 10b of the composite material layer 10 is exposed to the outside.

[0014] Hereinafter, a configuration example of the dome part 100 will be described.

[0015] (First Configuration Example) FIG. 2 is a cross-sectional view showing the dome part 100 of the redome 1 of the first configuration example.

[0016] As shown in FIG. 2, the dome part 100 includes a composite material layer 10, a first ceramic layer 21, and a second ceramic layer 22. The composite material layer 10 is disposed between the first ceramic layer 21 and the second ceramic layer 22. Note that the dome part 100 may not include the first ceramic layer 21 and the second ceramic layer 22.

[0017] The composite material layer 10 is formed of a ceramic matrix composite (Ceramic Matrix Composite). Specifically, the composite material layer 10 includes a reinforcing member 30 and a matrix material 40.

[0018] The reinforcing member 30 is selected from at least one of ceramic fibers and ceramic particles. The ceramic fiber is a fiber formed of ceramics and is selected from at least one of mullite fiber and alumina fiber. The ceramic fiber is a continuous fiber or a short fiber. Here, the "continuous fiber" refers to, for example, a thread that is continuously connected from one end to the other end of the composite material layer 10, or a bundle formed by combining such threads, and the "short fiber" refers to, for example, a fiber having a length of several millimeters to several tens of millimeters. The short fiber is formed, for example, by cutting a long fiber to a length of several millimeters to several tens of millimeters. The ceramic particles are particles formed of ceramics and are selected from at least one of mullite particles and alumina particles.

[0019] In the example shown in FIG. 2, the reinforcing member 30 is a continuous fiber made of ceramics, that is, a ceramic continuous fiber 31. The ceramic continuous fiber 31 may be in the state of a fiber cloth woven in plain weave, twill weave or satin weave with the ceramic continuous fiber 31 as warp and weft. In the example shown in FIG. 2, the composite material layer 10 has a plurality of fiber cloths 50 obtained by weaving the ceramic continuous fiber 31 in plain weave. The composite material layer 10 has, for example, about 10 to 20 fiber cloths 50. The composite material layer 10 has a laminated structure in which a plurality of fiber cloths 50 are laminated. In the example shown in FIG. 2, when the orientation direction of the warp 311 included in one fiber cloth 51 is set to 0 degrees, the plurality of fiber cloths 50 are laminated such that the orientation of the warp 311 included in the fiber cloth 52 adjacent to the fiber cloth 51 becomes 90 degrees. Note that the laminated structure of the plurality of fiber cloths 50 is not limited to the illustrated example.

[0020] Figure 3 is a perspective view showing an example of a ceramic continuous fiber 31. The ceramic continuous fiber 31 may further comprise a coating layer 32 covering its surface 31a. The coating layer 32 is at least one selected from the group consisting of magnesia (MgO), zirconia (ZrO2), yttria (Y2O3), ceria (CeO2), and boron nitride (BN). The thickness of the coating layer 32 is, for example, 50 nm or less. In the example shown in Figure 3, the coating layer 32 covers the entire surface 31a of the ceramic continuous fiber 31, but it is not limited to this, and it is sufficient if it covers at least a part of the surface 31a of the ceramic continuous fiber 31. This makes it possible to suppress the decrease in the high-temperature strength of the radome 1 due to sintering or fusion of the ceramic continuous fiber 31 and the matrix material 40 when the radome 1 is used in a high-temperature environment.

[0021] The matrix material 40 is made of ceramics and is selected from at least one of mullite and alumina. The matrix material 40 may contain an additive. The additive is at least one selected from the group consisting of magnesia, zirconia, yttria, and ceria. By adding the additive to the matrix material 40, the high-temperature strength of the radome 1 can be further improved.

[0022] The matrix material 40 is composited with the reinforcing member 30. The composite layer 10 is formed, for example, by impregnating the reinforcing member 30 into a slurry containing the raw materials for the matrix material 40, and then heat-treating it. When the matrix material 40 contained in the composite layer 10 is considered to be 100% by volume, it is preferable that the reinforcing member 30 is contained in the composite layer 10 at a concentration of 50% by volume or more.

[0023] The first ceramic layer 21 is made of ceramics, selected from at least one of mullite and alumina. The second ceramic layer 22 is also made of ceramics, selected from at least one of mullite and alumina. The first ceramic layer 21 and the second ceramic layer 22 may be made of the same material or of different materials. Furthermore, each of the first ceramic layer 21 and the second ceramic layer 22 may be made of the same material as the matrix material 40 or of different materials.

[0024] Each of the first ceramic layer 21 and the second ceramic layer 22 may contain an auxiliary agent. The auxiliary agent is at least one selected from the group consisting of magnesia, zirconia, yttria, and ceria.

[0025] Next, we will describe the radome 1 in other configuration examples. In the other embodiments described below, the same reference numerals are used for parts that are the same as those in the first configuration example described above, and their detailed descriptions are simplified or omitted. The focus will be on explaining the parts that differ from the first configuration example.

[0026] (Second configuration example) Figure 4 is a cross-sectional view showing the dome portion 100 of the radome 1 of the second configuration example. The dome portion 100 of the second configuration example comprises a composite material layer 10, a first ceramic layer 21, and a second ceramic layer 22. The composite material layer 10 comprises a reinforcing member 30 and a matrix material 40. Note that the dome portion 100 does not necessarily have to include the first ceramic layer 21 and the second ceramic layer 22.

[0027] In the example shown in Figure 4, the reinforcing member 30 is a continuous ceramic fiber 31. The composite layer 10 has a plurality of fiber sheets 60, each containing a continuous ceramic fiber 31 oriented in one direction. The composite layer 10 has, for example, about 10 to 20 fiber sheets 60. The composite layer 10 has a laminated structure in which a plurality of fiber sheets 60 are stacked. In the example shown in Figure 4, the plurality of fiber sheets 60 are stacked such that the orientation direction of the continuous ceramic fiber 31 contained in each of the plurality of fiber sheets 60 is isotropic. That is, the plurality of fiber sheets 60 are stacked such that when the orientation direction of the continuous ceramic fiber 31 contained in one fiber sheet 61 is taken as 0 degrees, the orientation direction of the continuous ceramic fiber 31 contained in a fiber sheet 62 adjacent to fiber sheet 61 is 0 degrees or 180 degrees. Note that the laminated structure of the plurality of fiber sheets 60 is not limited to the example shown in Figure 4.

[0028] (Example of configuration 3) Figure 5 is a cross-sectional view showing the dome portion 100 of the radome 1 of the third configuration example. The dome portion 100 of the third configuration example comprises a composite material layer 10, a first ceramic layer 21, and a second ceramic layer 22. The composite material layer 10 comprises a reinforcing member 30 and a matrix material 40. Note that the dome portion 100 does not necessarily have to include the first ceramic layer 21 and the second ceramic layer 22.

[0029] In the example shown in Figure 5, the reinforcing member 30 is a continuous ceramic fiber 31. The composite material layer 10 has a plurality of fiber sheets 60, each containing a continuous ceramic fiber 31 oriented in one direction. The composite material layer 10 has a laminated structure in which a plurality of fiber sheets 60 are stacked. In the example shown in Figure 5, the plurality of fiber sheets 60 are stacked such that the orientation direction of the continuous ceramic fiber 31 contained in each of the plurality of fiber sheets 60 is pseudo-isotropic. Here, "stacked so as to be pseudo-isotropic" means that the plurality of fiber sheets 60 are stacked such that the orientation direction of the continuous ceramic fiber 31 in adjacent fiber sheets 60 changes continuously by a predetermined angle. In the example shown in Figure 5, the plurality of fiber sheets 60 are stacked such that the orientation direction of the continuous ceramic fiber 31 in adjacent fiber sheets 60 changes continuously by 45 degrees. By stacking the plurality of fiber sheets 60 so that the orientation direction of the continuous ceramic fiber 31 is pseudo-isotropic, the high-temperature strength of the radome 1 can be further improved. Note that the laminated structure of the multiple fiber sheets 60 is not limited to the example shown in Figure 5.

[0030] (Example of configuration 4) Figure 6 is a cross-sectional view showing the dome portion 100 of the radome 1 of the fourth configuration example. The dome portion 100 of the third configuration example comprises a composite material layer 10, a first ceramic layer 21, and a second ceramic layer 22. The composite material layer 10 comprises a reinforcing member 30 and a matrix material 40. Note that the dome portion 100 does not necessarily have to include the first ceramic layer 21 and the second ceramic layer 22.

[0031] In the example shown in Figure 6, the reinforcing member 30 is a ceramic short fiber 33. In the example shown in Figure 6, the ceramic short fiber 33 is oriented such that its long axis generally follows the outer shape of the dome portion 100. However, the orientation direction of the ceramic short fiber 33 is not particularly limited.

[0032] Although not shown in the figures, the ceramic short fibers 33 may further have a coating layer covering their surface, similar to the ceramic continuous fibers 31 shown in Figure 3. The coating layer is at least one selected from the group consisting of magnesia (MgO), zirconia (ZrO2), yttria (Y2O3), ceria (CeO2), and boron nitride (BN). The thickness of the coating layer is, for example, 50 nm or less. The coating layer may cover the entire surface of the ceramic short fibers 33, or it may cover at least a portion of the surface of the ceramic short fibers 33. This makes it possible to suppress the decrease in the high-temperature strength of the radome 1 due to sintering or fusion of the ceramic short fibers 33 and the matrix material 40 when the radome 1 is used in a high-temperature environment.

[0033] (Example of configuration 5) Figure 7 is a cross-sectional view showing the dome portion 100 of the radome 1 of the fifth configuration example. The dome portion 100 of the fifth configuration example comprises a composite material layer 10, a first ceramic layer 21, and a second ceramic layer 22. The composite material layer 10 comprises a reinforcing member 30 and a matrix material 40. Note that the dome portion 100 does not necessarily have to include the first ceramic layer 21 and the second ceramic layer 22.

[0034] In the example shown in Figure 7, the reinforcing member 30 is ceramic particles 34. The ceramic particles 34 may or may not be spherical. Also, the shape and size of adjacent ceramic particles 34 may or may not be uniform. The diameter of the ceramic particles 34 is, for example, about 1 μm to 10 μm. The ceramic particles 34 are dispersed in the matrix material 40.

[0035] Figure 8 is a cross-sectional view showing an example of ceramic particles 34. The ceramic particles 34 may further comprise a coating layer 35 covering its surface 34a. The coating layer 35 is at least one selected from the group consisting of magnesia (MgO), zirconia (ZrO2), yttria (Y2O3), ceria (CeO2), and boron nitride (BN). The thickness of the coating layer 35 is, for example, 50 nm or less. In the example shown in Figure 8, the coating layer 35 covers the entire surface 34a of the ceramic particles 34, but it is not limited to this, and it is sufficient if it covers at least a part of the surface 34a of the ceramic particles 34. This makes it possible to suppress the decrease in the high-temperature strength of the radome 1 due to sintering or fusion of the ceramic particles 34 and the matrix material 40 when the radome 1 is used in a high-temperature environment.

[0036] The effects of the projectile radome of this embodiment, as described above, will be explained below.

[0037] Radomes for hypersonic projectiles require high-temperature strength capable of withstanding aerodynamic heating environments exceeding 1000 degrees Celsius, as well as broadband radio wave transmission characteristics. Examples of materials with excellent radio wave transmission properties include oxide-based ceramic materials such as silica, cordierite, and mullite. However, these materials suffer from low high-temperature strength. Examples of materials with excellent high-temperature strength include nitride-based ceramic materials such as silicon nitride and boron nitride. However, silicon nitride has low radio wave transmission properties, and boron nitride is susceptible to evaporation loss due to high-temperature oxidation. Therefore, it has been difficult to simultaneously satisfy both the high-temperature strength and radio wave transmission characteristics required for projectile radomes with materials consisting of a single component and phase.

[0038] The radome for a projectile in this embodiment comprises a composite layer including a matrix material and reinforcing members. The matrix material is selected from at least one of mullite and alumina, and the reinforcing members are selected from at least one of ceramic fibers and ceramic particles. The ceramic fibers are selected from at least one of mullite fibers and alumina fibers, and the ceramic particles are selected from at least one of mullite particles and alumina particles. Such a composite layer has high-temperature strength capable of withstanding temperatures exceeding 1000 degrees, for example, an aerodynamic heating environment of 1200 degrees or more, and broadband radio wave transmission characteristics. Therefore, according to this embodiment, it is possible to provide a radome for a projectile that can improve high-temperature strength and radio wave transmission characteristics.

[0039] <Examples> The present invention will be described in more detail below with reference to examples, but is not limited to these examples.

[0040] (Example 1) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of mullite continuous fibers coated with zirconia were prepared. A slurry containing alumina (high-purity alumina, manufactured by Sumitomo Chemical Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Example 1 was formed by laminating the slurry-impregnated fiber cloths and firing them.

[0041] (Example 2) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 610, manufactured by 3M) composed of continuous alumina fibers coated with zirconia were prepared. A slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Example 2 was formed by laminating the slurry-impregnated fiber cloths and firing them.

[0042] (Example 3) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of zirconia-coated mullite continuous fibers were prepared. A slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Example 3 was formed by laminating the slurry-impregnated fiber cloths and firing them.

[0043] (Example 4) As a reinforcing material, zirconia-coated mullite particles (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) were prepared. Multiple mullite particles were dispersed in a slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material, and the composite material layer of Example 4 was formed by firing.

[0044] (Example 5) As reinforcing members, multiple fiber sheets were prepared, each composed of multiple unidirectionally oriented, zirconia-coated mullite continuous fibers (Nextel® ceramic roving 720, manufactured by 3M). The multiple fiber sheets were impregnated with a slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material. The multiple fiber sheets were stacked so that the orientation direction of the mullite continuous fibers contained in each fiber sheet was isotropic, and the composite material layer of Example 5 was formed by firing at a temperature of 1000°C or less.

[0045] (Example 6) As reinforcing members, multiple zirconia-coated mullite short fibers (Nextel® ceramic roving 720, manufactured by 3M), cut to a length of several millimeters, were prepared. The composite material layer of Example 6 was formed by impregnating the multiple mullite short fibers with a slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material and firing it.

[0046] (Example 7) As reinforcing members, multiple fiber sheets were prepared, each containing multiple mullite continuous fibers (Nextel® ceramic roving 720, manufactured by 3M Corporation) coated with zirconia and oriented in one direction. The multiple fiber sheets were impregnated with a slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material. The multiple fiber sheets were stacked so that the orientation direction of the mullite continuous fibers contained in each fiber sheet was pseudo-isotropic, and the composite material layer of Example 7 was formed by firing at a temperature of 1000°C or less.

[0047] (Example 8) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of mullite continuous fibers coated with zirconia were prepared. A slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material and zirconia as an auxiliary agent was impregnated into the multiple fiber cloths. The composite material layer of Example 8 was formed by laminating the multiple slurry-impregnated fiber cloths and firing them.

[0048] (Example 9) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of zirconia-coated mullite continuous fibers were prepared. The multiple fiber cloths were impregnated with a slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material and magnesia as an auxiliary agent. The composite material layer of Example 9 was formed by laminating the multiple slurry-impregnated fiber cloths and firing them.

[0049] (Example 10) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of zirconia-coated mullite continuous fibers were prepared. The multiple fiber cloths were impregnated with a slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material and yttria as an auxiliary agent. The composite material layer of Example 10 was formed by laminating the multiple slurry-impregnated fiber cloths and firing them.

[0050] (Example 11) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of zirconia-coated mullite continuous fibers were prepared. The multiple fiber cloths were impregnated with a slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.) as a matrix material and ceria as an auxiliary agent. The composite material layer of Example 11 was formed by laminating the multiple slurry-impregnated fiber cloths and firing them.

[0051] (Example 12) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of continuous mullite fibers coated with magnesia were prepared. A slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Example 12 was formed by laminating the slurry-impregnated fiber cloths and firing them.

[0052] (Example 13) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of yttria-coated mullite continuous fibers were prepared. A slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Example 13 was formed by laminating the slurry-impregnated fiber cloths and firing them.

[0053] (Example 14) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of continuous mullite fibers coated with ceria were prepared. A slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Example 14 was formed by laminating the multiple slurry-impregnated fiber cloths and firing them.

[0054] (Example 15) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of continuous mullite fibers coated with boron nitride (BN) were prepared. A slurry containing mullite (high-purity mullite powder KM101, manufactured by Kyoritsu Material Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Example 15 was formed by laminating the multiple slurry-impregnated fiber cloths and firing them.

[0055] (Comparative Example 1) A matrix material of silica (high-purity fused silica glass, manufactured by Ohara Quartz Co., Ltd.) was prepared and used as the composite layer for Comparative Example 1. The composite layer of Comparative Example 1 did not have any reinforcing members.

[0056] (Comparative Example 2) Alumina (manufactured by Nippon Fine Ceramics Co., Ltd.) was prepared as the matrix material and used as the composite layer for Comparative Example 1. The composite layer for Comparative Example 2 did not have any reinforcing members.

[0057] (Comparative Example 3) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of continuous alumina fibers coated with zirconia were prepared. A slurry containing silica (Denka Fused Silica, manufactured by Denka Corporation), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Comparative Example 3 was formed by laminating the multiple slurry-impregnated fiber cloths and firing them.

[0058] (Comparative Example 4) As reinforcing members, multiple fiber cloths (Nextel® Ceramic Cloth 720, manufactured by 3M) composed of continuous alumina fibers coated with zirconia were prepared. A slurry containing alumina (high-purity alumina, manufactured by Sumitomo Chemical Co., Ltd.), which is the matrix material, was impregnated into the multiple fiber cloths. The composite material layer of Comparative Example 4 was formed by laminating the slurry-impregnated fiber cloths and firing them.

[0059] To evaluate the high-temperature strength of the composite material layer, a high-temperature bending strength test was conducted in accordance with JIS R1604. In this evaluation, the three-point bending strength at 1200 degrees Celsius was measured. A three-point bending strength of 50 MPa or higher at 1200 degrees Celsius was judged as good, 30 MPa or higher but less than 50 MPa as acceptable, and less than 30 MPa as poor. The results are shown in Table 1.

[0060] To evaluate the radio wave transparency of the composite material layer, radio wave absorption characteristics were measured in accordance with JIS R1679. A radio wave transmission loss of 10 dB or less in the frequency range of 1 GHz to 100 GHz was judged as good, 10 dB to 20 dB was judged as acceptable, and exceeding 20 dB was judged as poor. The results are shown in Table 1.

[0061] [Table 1]

[0062] The composite layers of Examples 1 to 15 comprise a matrix material and reinforcing members. The matrix material is selected from at least one of mullite and alumina, and the reinforcing members are selected from at least one of ceramic fibers and ceramic particles. The ceramic fibers are selected from at least one of mullite fibers and alumina fibers, and the ceramic particles are selected from at least one of mullite particles and alumina particles. As is clear from Table 1, the composite layers of Examples 1 to 15 having such configurations all exhibit acceptable or good high-temperature strength and radio wave transmission characteristics.

[0063] On the other hand, it can be seen that the composite material layers of Comparative Examples 1 to 4, which do not have the above-described configuration, all have poor high-temperature strength and radio wave transmission characteristics in at least one of them.

[0064] While embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. Multiple embodiments can also be combined as needed. [Explanation of Symbols]

[0065] 1...Radome, 2...Airframe, 10...Composite layer, 21...First ceramic layer, 22...Second ceramic layer, 30...Reinforcement member, 31...Continuous ceramic fiber, 32...Coating layer, 33...Short ceramic fiber, 34...Ceramic particles, 35...Coating layer, 40...Matrix material, 50...Fiber cloth, 60...Fiber sheet, 100...Dome section, 110...Insulation section, 111...Antenna housing section, 200...Nose section, 210...Antenna.

Claims

1. A radome for a flying object that covers an antenna for transmitting and receiving radio waves, It comprises a dome section and an insulating section that covers the inner surface of the dome section, The dome portion comprises a composite material layer including a matrix material and reinforcing members. The matrix material is selected from at least one of mullite and alumina. The reinforcing member is selected from at least one of ceramic fibers and ceramic particles. The ceramic fibers are selected from at least one of mullite fibers and alumina fibers. The ceramic particles are selected from at least one of mullite particles and alumina particles, in a radome for a projectile.

2. The radome for a projectile according to claim 1, wherein the ceramic fiber is a continuous ceramic fiber.

3. The composite material layer has a structure in which a plurality of fiber sheets are laminated, each containing the ceramic continuous fibers oriented in one direction. The radome for a projectile according to claim 2, wherein the plurality of fiber sheets are laminated such that the orientation direction of the ceramic continuous fibers is isotropic or pseudo-isotropic.

4. The radome for projectiles according to claim 2, wherein the composite material layer has a structure in which multiple layers of fiber cloth made of continuous ceramic fibers in plain weave, twill weave, or satin weave are laminated together.

5. The radome for a projectile according to claim 1, wherein the ceramic fiber is a short ceramic fiber.

6. The reinforcing member further comprises a covering layer that covers the surface of the reinforcing member, The radome for a projectile according to claim 1, wherein the coating layer is at least one selected from the group consisting of magnesia, zirconia, yttria, ceria, and boron nitride.

7. The matrix material further contains an auxiliary agent, The radome for projectiles according to claim 1, wherein the auxiliary agent is at least one selected from the group consisting of magnesia, zirconia, yttria, or ceria.

8. The dome portion further comprises a first ceramic layer and a second ceramic layer. The composite material layer is disposed between the first ceramic layer and the second ceramic layer. The radome for a projectile according to claim 1, wherein the second ceramic layer is disposed between the composite material layer and the heat insulating portion.

9. The radome for a projectile according to claim 8, wherein the first ceramic layer and the second ceramic layer are selected from at least one of mullite and alumina.

10. At least one of the first ceramic layer and the second ceramic layer further contains an auxiliary agent, The radome for projectiles according to claim 9, wherein the auxiliary agent is at least one selected from the group consisting of magnesia, zirconia, yttria, or ceria.

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