Composite Materials

Abstract

A composite member (1) according to the present invention is provided with: a matrix part (10) which contains a plurality of inorganic material particles (11) and is formed by bonding the plurality of inorganic material particles (11) with each other; organic particles (20) which are present, in a dispersed state, within the matrix part (10); and a radio wave absorbing material (30) which is present, in a dispersed state, within the matrix part (10). The matrix part (10) contains at least one of a metal oxide and a metal oxide hydroxide.

Description

[Technical field]

[0001] The present invention relates to a composite member. [Background technology]

[0002] Conventionally, dielectric lenses that refract radio waves emitted from an antenna and adjust the direction of travel of the radio waves are known. Patent Document 1 discloses a dielectric lens made of plastic to which an appropriate amount of ferroelectric powder has been added. Patent Document 1 discloses that the dielectric lens is lighter and stronger than a dielectric lens made of ceramics alone, and can be designed to have a higher relative dielectric constant than a dielectric lens made of plastic alone or fiber-reinforced plastic alone. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-101336 A Summary of the Invention

[0004] However, compared to inorganic materials such as ceramics, resins are more susceptible to degradation due to moisture in the air. Therefore, dielectric lenses using a resin matrix may not be sufficiently durable. In addition, because radio waves easily pass through resins, conventional dielectric lenses alone may not be able to control radio wave intensity.

[0005] The present invention has been made in view of the problems associated with the conventional techniques, and an object of the present invention is to provide a composite member which is superior in durability compared to a composite member using a resin matrix and which is capable of controlling radio wave characteristics.

[0006] In order to solve the above problems, a composite material according to an embodiment of the present invention includes a matrix portion containing a plurality of inorganic particles and formed by bonding the plurality of inorganic particles to each other. The composite material includes organic particles present in a dispersed state within the matrix portion, and a radio wave absorbing material present in a dispersed state within the matrix portion. The matrix portion contains at least one of a metal oxide and a metal oxide hydroxide. [Brief description of the drawings]

[0007]

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[0008] Hereinafter, the composite member, the radio wave sensor, and the manufacturing method of the composite member according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for the convenience of explanation and may differ from the actual ratios.

[0009] [Composite material] As shown in Fig. 1, the composite material 1 according to this embodiment includes a transmitting portion 2 and a shielding portion 3. As shown in Fig. 2, the transmitting portion 2 includes a matrix portion 10 and organic particles 20. As shown in Fig. 3, the shielding portion 3 includes a matrix portion 10 and a radio wave absorbing material 30. That is, the composite material 1 according to this embodiment includes the matrix portion 10, the organic particles 20, and the radio wave absorbing material 30.

[0010] The matrix portion 10 of the transmitting portion 2 and the matrix portion 10 of the shielding portion 3 are chemically bonded to each other. This makes it possible to provide a composite member 1 having high mechanical strength overall. In this embodiment, the transmitting portion 2 does not contain the radio wave absorbing material 30, and the shielding portion 3 does not contain the organic particles 20. That is, the volume ratio of the organic particles 20 in the transmitting portion 2 is greater than the volume ratio of the organic particles 20 in the shielding portion 3. In addition, the volume ratio of the radio wave absorbing material 30 in the transmitting portion 2 is smaller than the volume ratio of the radio wave absorbing material 30 in the shielding portion 3. However, the transmitting portion 2 may contain the radio wave absorbing material 30, and the shielding portion 3 may contain the organic particles 20.

[0011] The matrix portion 10 includes a plurality of inorganic particles 11, and is formed by bonding the plurality of inorganic particles 11 to each other. The matrix portion 10 may also include bonding portions 12 that bond the plurality of inorganic particles 11 to each other. By bonding adjacent inorganic particles 11 via the bonding portions 12, the inorganic particles 11 are bonded to each other three-dimensionally, and a composite member 1 having high mechanical strength can be obtained. The plurality of inorganic particles 11 may have a portion where each of the plurality of inorganic particles 11 is directly bonded to each other without the bonding portions 12. The inorganic particles 11 may be in point contact with each other, or may be in surface contact where the surfaces of the inorganic particles 11 are in contact with each other.

[0012] The bonding parts 12 may be present between adjacent inorganic particles 11. The bonding parts 12 may be in direct contact with the inorganic particles 11. The bonding parts 12 may cover at least a portion of the surface of each of the plurality of inorganic particles 11, or may cover the entire surface of each of the plurality of inorganic particles 11. The presence of the bonding parts 12 allows the inorganic particles 11 and the bonding parts 12 to be firmly bonded to each other, thereby making it possible to obtain a composite member 1 having excellent density and mechanical strength.

[0013] The matrix portion 10 contains at least one of a metal oxide and a metal oxide hydroxide. The inorganic substance containing at least one of a metal oxide and a metal oxide hydroxide may be contained in at least one of the inorganic particles 11 and the bonding portions 12. That is, the inorganic substance may be contained in either the inorganic particles 11 or the bonding portions 12, or may be contained in both the inorganic particles 11 and the bonding portions 12.

[0014] At least one of the metal oxide and the metal oxide hydroxide preferably contains at least one metal element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals, and metalloids. In this specification, the alkaline earth metals include calcium, strontium, barium, and radium, as well as beryllium and magnesium. The base metals include aluminum, zinc, gallium, cadmium, indium, tin, mercury, thallium, lead, bismuth, and polonium. The metalloids include boron, silicon, germanium, arsenic, antimony, and tellurium. Among these, it is preferable that the inorganic substance contains at least one metal element selected from the group consisting of zinc, aluminum, and magnesium. The inorganic substance containing these metal elements can easily form the bond 12 derived from the inorganic substance by the pressurized heating method described below.

[0015] The metal oxide may include at least one selected from the group consisting of zinc oxide, magnesium oxide, and a complex of zinc oxide and magnesium oxide. Such a metal oxide can provide a highly durable composite member 1. The oxides of the above-mentioned metal elements may include phosphates, silicates, aluminates, and borates in addition to compounds in which only oxygen is bonded to a metal element. The inorganic material constituting the inorganic material particles 11 may be a complex anion compound containing the above-mentioned metal element. A complex anion compound is a material containing multiple anions in a single compound, and examples of such a compound include oxyfluorides, oxychlorides, and oxynitrides.

[0016] The metal oxide hydroxide may include, for example, aluminum oxide hydroxide. An example of the aluminum oxide hydroxide is boehmite, which is represented by the formula AlOOH. Boehmite is insoluble in water and hardly reacts with acids or alkalis at room temperature, and therefore has high chemical stability. Furthermore, boehmite has a high dehydration temperature of about 500°C, and therefore has excellent heat resistance. In addition, since boehmite has a specific gravity of about 3.07, when the composite material 1 contains boehmite, a composite material 1 that is lightweight and has excellent chemical stability can be obtained.

[0017] When the inorganic material contained in the matrix portion 10 is boehmite, the inorganic material particles 11 may be particles containing only a boehmite phase, or may be particles containing a mixed phase of boehmite and aluminum oxide or aluminum hydroxide other than boehmite. For example, the inorganic material particles 11 may be particles containing a phase containing boehmite and a phase containing gibbsite (Al(OH) 3 ) may be mixed with the phase containing the aluminum oxide and hydroxide oxide. Adjacent inorganic particles 11 are preferably bonded via at least one of an aluminum oxide and hydroxide oxide. That is, it is preferable that the inorganic particles 11 are not bonded via an organic binder containing an organic compound, and are not bonded via an inorganic binder containing an inorganic substance other than the aluminum oxide and hydroxide oxide. When adjacent inorganic particles 11 are bonded via at least one of an aluminum oxide and hydroxide oxide, the aluminum oxide and hydroxide oxide may be crystalline or amorphous.

[0018] When the composite material 1 contains boehmite, the proportion of the boehmite phase is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. By increasing the proportion of the boehmite phase, a composite material 1 that is lightweight and has excellent chemical stability and heat resistance can be obtained. The proportion of the boehmite phase in the composite material 1 can be determined by measuring the X-ray diffraction pattern of the composite material 1 by X-ray diffraction method and then performing Rietveld analysis.

[0019] When the inorganic material contained in the matrix portion 10 is boehmite, the bonding portion 12 may contain a boehmite phase. When the bonding portion 12 contains a boehmite phase, the inorganic material particles 11 may contain aluminum nitride. Aluminum nitride has a high electrical resistance and a high dielectric strength, and furthermore, as a ceramic material, it shows a very high thermal conductivity. The inorganic material particles 11 are not bound by an organic binder containing an organic compound, and may not be bound by an inorganic binder other than the boehmite phase. In addition, as described later, the composite member 1 can be formed by heating a mixture of inorganic material powder and water while applying pressure, and there is no need to use a reaction accelerator or the like. Therefore, the composite member 1 is free of impurities derived from the organic binder, the inorganic binder, and the reaction accelerator, and therefore it is possible to maintain the original properties of aluminum nitride and boehmite.

[0020] It is more preferable that the inorganic substance contained in the matrix portion 10 contains at least one of the oxides and hydroxide oxides of the above-mentioned metal elements as a main component. That is, the inorganic substance preferably contains at least one of the oxides and hydroxide oxides of the above-mentioned metal elements in an amount of 50 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more. In addition, it is preferable that the composite material 1 also contains at least one of the oxides and hydroxide oxides as a main component.

[0021] The inorganic substance contained in the matrix portion 10 is preferably polycrystalline. By using the inorganic substance contained in the matrix portion 10 as a polycrystalline substance, a composite member 1 having high durability can be obtained compared to when the inorganic substance is amorphous. The inorganic substance particles 11 are more preferably crystalline particles containing at least one metal element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals, and metalloids. The inorganic substance particles 11 are more preferably crystalline particles containing at least one of the oxides and hydroxide oxides of the above-mentioned metal elements. The inorganic substance particles 11 are more preferably crystalline particles containing at least one of the oxides and hydroxide oxides of the above-mentioned metal elements as a main component. The inorganic substance particles 11 preferably contain at least one of the oxides and hydroxide oxides of the above-mentioned metal elements in an amount of 80 mol % or more, more preferably 90 mol % or more, and even more preferably 95 mol % or more. The inorganic substance may be single crystal or polycrystalline.

[0022] It is preferable that the inorganic substance contained in the composite member 1 does not contain a hydrate of a calcium compound. The calcium compound referred to here is tricalcium silicate (alite, 3CaO SiO 2 ), dicalcium silicate (Belite, 2CaO SiO 2 ), calcium aluminate (3CaO·Al 2 O 3 ), calcium aluminoferrite (4CaO·Al 2 O 3 Fe 2 O 3 ), calcium sulfate (CaSO 4 2H 2O). When the inorganic substance contained in the composite member 1 contains a hydrate of the calcium compound, the porosity in the cross section of the composite member 1 may exceed 20%, resulting in a decrease in strength. Therefore, it is preferable that the inorganic substance does not contain a hydrate of the calcium compound. It is also preferable that the inorganic substance contained in the composite member 1 does not contain phosphate cement, zinc phosphate cement, or calcium phosphate cement. When the inorganic substance does not contain these cements, the porosity in the cross section of the composite member 1 decreases, thereby increasing the mechanical strength.

[0023] The average particle diameter of the inorganic particles 11 is not particularly limited. The average particle diameter of the inorganic particles 11 is preferably 50 nm or more and 50 μm or less, more preferably 300 nm or more and 30 μm or less, and even more preferably 300 nm or more and 20 μm or less. When the average particle diameter of the inorganic particles 11 is within this range, the inorganic particles 11 are firmly bonded to each other, and the strength of the composite material 1 can be increased. In addition, in this specification, the value of "average particle diameter" is a value calculated as the average particle diameter of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), unless otherwise specified.

[0024] The shape of the inorganic particles 11 is not particularly limited, and may be, for example, spherical. The inorganic particles 11 may be whisker-like (needle-like) particles or scale-like particles. Compared with spherical particles, whisker-like particles or scale-like particles have a higher contact with other particles, and the strength of the composite material 1 is likely to be improved. Therefore, by using particles having such a shape as the inorganic particles 11, it is possible to increase the strength of the composite material 1 as a whole.

[0025] Here, it is preferable that the inorganic substance contained in the composite member 1 does not substantially contain hydrates. In this specification, "the inorganic substance does not substantially contain hydrates" means that hydrates are not intentionally contained in the inorganic substance. Therefore, when hydrates are mixed into the inorganic substance as unavoidable impurities, the condition "the inorganic substance does not substantially contain hydrates" is satisfied. Note that boehmite is a metal oxide hydroxide, and is not included in the hydrates in this specification.

[0026] The bonding portion 12 preferably contains an amorphous inorganic compound. Specifically, the bonding portion 12 may be a portion containing only an amorphous inorganic compound, or a portion in which an amorphous inorganic compound and a crystalline inorganic compound are mixed. The bonding portion 12 may be a portion in which a crystalline inorganic compound is dispersed inside an amorphous inorganic compound. When an amorphous inorganic compound and a crystalline inorganic compound are mixed, the amorphous inorganic compound and the crystalline inorganic compound may have the same chemical composition, or may have different chemical compositions.

[0027] It is preferable that the inorganic particle 11 and the bonding portion 12 contain the same metal element, and the metal element is at least one selected from the group consisting of alkali metals, alkaline earth metals, transition metals, base metals, and metalloids. That is, it is preferable that the inorganic substance contained in the inorganic particle 11 and the amorphous inorganic substance contained in the bonding portion 12 contain at least the same metal element. The inorganic substance contained in the inorganic particle 11 and the amorphous inorganic substance contained in the bonding portion 12 may have the same chemical composition or may have different chemical compositions. Specifically, when the metal element is zinc, the inorganic substance contained in the inorganic particle 11 and the amorphous inorganic substance contained in the bonding portion 12 may both be zinc oxide (ZnO). Alternatively, the inorganic substance contained in the inorganic particle 11 is ZnO, but the amorphous inorganic substance contained in the bonding portion 12 may be a zinc-containing oxide other than ZnO.

[0028] The organic particles 20 are present in a dispersed state inside the matrix portion 10. By dispersing the organic particles 20 inside the matrix portion 10, contact between the organic particles 20 and oxygen and water vapor is suppressed, and deterioration of the organic particles 20 can be suppressed. The organic particles 20 may be disposed between adjacent inorganic particles 11. In addition, the organic particles 20 may be surrounded by the bonding portion 12, or may be surrounded by the inorganic particles 11 and the bonding portion 12. The shape of the organic particles 20 is not particularly limited, and examples thereof include spherical, scale-like, needle-like, fibrous, plate-like, disc-like, and irregular shapes.

[0029] The dielectric constant of the organic particles 20 is different from that of the matrix portion 10. That is, the dielectric constant of the organic particles 20 may be larger than that of the matrix portion 10. Also, the dielectric constant of the organic particles 20 may be smaller than that of the matrix portion 10. Since the dielectric constants of the matrix portion 10 and the organic particles 20 are different, the dielectric constant of the composite member 1 can be changed compared to a member made of the matrix portion 10 that does not contain the organic particles 20. By changing the dielectric constant, it becomes possible to change the radiation angle of the radio waves that penetrate the composite member 1. Therefore, by adjusting the type and amount of the organic particles 20, the radiation angle of the radio waves that penetrate the composite member 1 can be adjusted.

[0030] The organic particles 20 may include at least one of cellulose particles and resin particles. These materials often have a significantly different relative dielectric constant compared to inorganic substances, and therefore can effectively change the relative dielectric constant of the composite material 1. The resin particles may include at least one resin selected from the group consisting of fluororesin, ABS, acrylic resin, polyethylene terephthalate, polypropylene, and polycarbonate. For example, since fluororesin has a small relative dielectric constant, even when a small amount of fluororesin is added, the relative dielectric constant of the composite material 1 can be made smaller than that of the matrix portion 10 alone. The fluororesin may include at least one selected from the group consisting of polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), ethylene-tetrafluoroethylene copolymer (ETFE), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

[0031] The thermal conductivity of the matrix portion 10 may be higher than that of the organic particles 20. This allows heat to be easily dissipated through the matrix portion 10, thereby improving the heat dissipation properties of the composite material 1. Therefore, even when the composite material 1 is continuously irradiated with radio waves, the temperature rise of the composite material 1 can be suppressed. As a result, the radiation characteristics of the composite material 1 can be stabilized. The thermal conductivity of the matrix portion 10 may be greater than 1 W / m·K. The thermal conductivity of the matrix portion 10 may be 5 W / m·K or more. The thermal conductivity of the matrix portion 10 may be 500 W / m·K or less. The thermal conductivity of the organic particles 20 may be 1 W / m·K or less. The thermal conductivity of the organic particles 20 may be 0.01 W / m·K or more. The thermal conductivity of the matrix portion 10 can be measured based on the provisions of JIS R1611:2010. The thermal conductivity of the organic particles 20 can be measured based on the provisions of JIS A1412-2:1999.

[0032] The average particle diameter of the organic particles 20 is not particularly limited. The average particle diameter of the organic particles 20 may be 50 nm or more and 50 μm or less. When the average particle diameter of the organic particles 20 is within this range, the inorganic particles 11 are bonded to each other strongly, so that the strength of the composite material 1 can be increased. The average particle diameter of the organic particles 20 may be 500 nm or more, or may be 1 μm or more. In addition, the average particle diameter of the organic particles 20 may be 30 μm or less, or may be 10 μm or less.

[0033] The radio wave absorbing material 30 exists in a dispersed state inside the matrix portion 10. Dispersion of the radio wave absorbing material 30 inside the matrix portion 10 strengthens the bonds between the inorganic particles 11, thereby improving the strength of the composite material 1. The radio wave absorbing material 30 may be disposed between adjacent inorganic particles 11. The radio wave absorbing material 30 may be surrounded by the bonding portion 12, or may be surrounded by the inorganic particles 11 and the bonding portion 12. The shape of the radio wave absorbing material 30 is not particularly limited, and may be, for example, spherical, scale-like, needle-like, fibrous, plate-like, disk-like, or irregular.

[0034] The radio wave absorbing material 30 is a material that absorbs radio waves. By absorbing radio waves with the radio wave absorbing material 30, it is possible to prevent the radio waves from passing through the shielding portion 3. Therefore, for example, when the composite member 1 is used as a cover for a radio wave sensor, the shielding portion 3 can shield the radio waves to narrow the detection area and prevent erroneous detection outside the detection area. The radio wave absorbing material 30 can absorb radio waves by converting the energy of the radio waves into heat. The radio wave absorbing material 30 may be a dielectric radio wave absorbing material, a magnetic radio wave absorbing material, a conductive radio wave absorbing material, or the like.

[0035] The dielectric electromagnetic wave absorbing material absorbs electromagnetic waves by dielectric loss caused by the polarization reaction of molecules. The dielectric electromagnetic wave absorbing material may include a carbon-containing material in which carbon is dispersed in a dielectric material such as rubber, urethane, or polystyrene.

[0036] The magnetic radio wave absorbing material absorbs radio waves by magnetic loss of the magnetic material. The magnetic radio wave absorbing material may contain at least one material selected from the group consisting of iron, nickel, and ferrite.

[0037] The conductive radio wave absorbing material absorbs radio waves due to resistance loss inside the material. The conductive radio wave absorbing material may contain at least one of a metal and a non-metal. The metal may contain at least one selected from the group consisting of aluminum, copper, nickel, and stainless steel. The non-metal may contain carbon.

[0038] From the viewpoint of suppressing reflection of radio waves, it is preferable that the radio wave absorber 30 contains a non-metal. The radio wave absorber 30 may contain, for example, carbon, or may be carbon itself. Carbon has low reactivity, and therefore can further improve the durability of the composite member 1. The carbon may contain, for example, at least one selected from the group consisting of carbon black, graphite, carbon fiber, carbon nanotubes, and diamond.

[0039] In the composite member 1 according to the present embodiment, the radio wave absorbing material 30 is partially Bias Specifically, the volume ratio of the radio wave absorbing material 30 in the shielding portion 3 is greater than the volume ratio of the radio wave absorbing material 30 in the transmitting portion 2. Therefore, the transmitting portion 2 transmits radio waves easily, while the shielding portion 3 transmits radio waves less easily. Therefore, for example, when the composite member 1 is used in a radio wave sensor, the detection area of ​​the radio wave sensor can be narrowed down to a desired range by adjusting the area of ​​the shielding portion 3. The radio wave absorbing material 30 contains non-metallic material and is partially Bias The non-metallic material suppresses the reflection of radio waves, so that radio waves can be blocked more effectively. Specifically, the radio wave absorbing material 30 contains carbon and is partially Bias It is okay to do so.

[0040] In the composite material 1, the volume ratio of the inorganic particles 11 is preferably 30% or more. In this case, the obtained composite material 1 is a structure that can easily utilize the characteristics of the inorganic particles 11. In the composite material 1, the volume ratio of the multiple inorganic particles 11 is more preferably 40% or more, and even more preferably 50% or more. The volume ratio of the inorganic particles 11 is preferably greater than the volume ratio of the bonding portions 12.

[0041] For the same reasons as above, the volume ratio of the inorganic particles 11 in the transmitting section 2 can be the same as that of the composite material 1 described above. That is, the volume ratio of the inorganic particles 11 in the transmitting section 2 can be 30% or more. Moreover, the volume ratio of the inorganic particles 11 in the shielding section 3 can be the same as that of the composite material 1 described above. That is, the volume ratio of the inorganic particles 11 in the shielding section 3 can be 30% or more.

[0042] The volume ratio of the organic particles 20 in the composite material 1 may be less than 50%. In this embodiment, the volume ratio of the organic particles 20 in the transmission portion 2 may be less than 50%. When the volume ratio of the organic particles 20 is less than 50%, the mechanical properties of the composite material 1 can be improved. The volume ratio of the organic particles 20 may be 0.1% or more. When the volume ratio of the organic particles 20 is 0.1% or more, the relative dielectric constant of the composite material 1 can be changed to be greater than the relative dielectric constant of the matrix portion 10. The volume ratio of the organic particles 20 may be 5% or more, 10% or more, or 20% or more. In addition, the volume ratio of the organic particles 20 may be less than 40%.

[0043] The volume fraction of the radio wave absorber 30 in the composite member 1 may be 20% or more and less than 50%. In this embodiment, the volume fraction of the radio wave absorber 30 in the shielding portion 3 may be 20% or more and less than 50%. When the volume fraction of the radio wave absorber 30 is 20% or more, radio waves can be absorbed more effectively. Furthermore, when the volume fraction of the radio wave absorber 30 is less than 50%, the mechanical properties of the composite member 1 can be improved. The volume fraction of the radio wave absorber 30 may be 25% or more, or may be 30% or more. Furthermore, the volume fraction of the radio wave absorber 30 may be less than 45% or less than 40%.

[0044] The porosity in the cross section of the composite member 1 is preferably 20% or less. In other words, when observing the cross section of the composite member 1, the average ratio of pores per unit area is preferably 20% or less. When the porosity is 20% or less, the occurrence of cracks in the composite member 1 starting from the pores is suppressed, so that the bending strength of the composite member 1 can be increased. The porosity in the cross section of the composite member 1 is preferably 15% or less, more preferably 10% or less, and even more preferably 5% or less. The smaller the porosity in the cross section of the composite member 1, the more cracks starting from the pores are suppressed, so that the strength of the composite member 1 can be increased.

[0045] In this specification, the porosity can be obtained as follows. First, the cross section of the composite material 1 is observed to distinguish between pores and non-pores. Then, the unit area and the area of ​​the pores in the unit area are measured to obtain the ratio of pores per unit area, and this value is taken as the porosity. It is more preferable to obtain the ratio of pores per unit area at multiple points on the cross section of the composite material 1, and then take the average value of the ratio of pores per unit area as the porosity. When observing the cross section of the composite material 1, an optical microscope, a scanning electron microscope (SEM), or a transmission electron microscope (TEM) can be used. The unit area and the area of ​​the pores in the unit area may be measured by binarizing an image observed with a microscope.

[0046] The size of the pores present inside the composite member 1 is not particularly limited, but is preferably as small as possible. Small pore sizes suppress cracks originating from the pores, which increases the strength of the composite member 1 and improves the machinability of the composite member 1. The size of the pores in the composite member 1 is preferably 5 μm or less, more preferably 1 μm or less, and even more preferably 100 nm or less. The size of the pores present inside the composite member 1 can be determined by observing a cross section of the composite member 1 under a microscope, similar to the above-mentioned porosity.

[0047] In the composite material 1, it is preferable that the organic particles 20 do not exist continuously from the surface to the inside of the matrix part 10. The organic particles 20 existing on the surface of the matrix part 10 may deteriorate due to contact with oxygen and water vapor in the air. The organic particles 20 existing continuously from the surface to the inside of the matrix part 10 may also deteriorate due to oxidative deterioration of the organic particles 20 existing on the surface of the matrix part 10. Therefore, from the viewpoint of further suppressing deterioration of the organic particles 20, it is preferable that the organic particles 20 do not exist continuously from the surface to the inside of the matrix part 10. For the same reason, it is preferable that the radio wave absorbing material 30 does not exist continuously from the surface to the inside of the matrix part 10. It is also preferable that the organic particles 20 and the radio wave absorbing material 30 do not exist continuously from the surface to the inside of the matrix part 10.

[0048] The thickness of the composite material 1 is not particularly limited, but may be, for example, 50 μm or more. The composite material 1 of this embodiment is formed by a pressurized and heated method, as described below. Therefore, a thick composite material 1 can be easily obtained. The thickness of the composite material 1 may be 1 mm or more, and may also be 1 cm or more. The upper limit of the thickness of the composite material 1 is not particularly limited, but may be, for example, 50 cm.

[0049] As described above, the composite material 1 according to this embodiment includes a plurality of inorganic particles 11, and is provided with a matrix portion 10 formed by bonding the plurality of inorganic particles 11 to one another. The composite material 1 includes organic particles 20 present in a dispersed state within the matrix portion 10, and a radio wave absorbing material 30 present in a dispersed state within the matrix portion 10. The matrix portion 10 contains at least one of a metal oxide and a metal oxide hydroxide.

[0050] By providing the composite member 1 with the organic particles 20, it is possible to provide the composite member 1 with a relative dielectric constant different from that of the matrix portion 10. As a result, the composite member 1 can achieve a radiation angle different from that of the matrix portion 10. In addition, since the organic particles 20 are dispersed inside the matrix portion 10, they are unlikely to come into direct contact with moisture in the air and are unlikely to deteriorate. Furthermore, since the composite member 1 includes the radio wave absorbing material 30, it is possible to reduce the intensity of radio waves passing through the composite member 1. Therefore, according to the composite member 1 of this embodiment, it is possible to provide excellent durability and control radio wave characteristics compared to the case where a resin matrix is ​​used. As described above, the composite member 1 of this embodiment has excellent durability and can control radio wave characteristics, and therefore can be suitably used, for example, as a cover for a radio wave sensor. Specifically, the composite member 1 can be suitably used as a dielectric lens.

[0051] In the above embodiment, an example has been described in which the composite material 1 includes the transmitting portion 2 and the shielding portion 3. The transmitting portion 2 includes the matrix portion 10 and the organic particles 20, and the shielding portion 3 includes the matrix portion 10 and the radio wave absorbing material 30. However, the composite material 1 according to this embodiment is not limited to this form. For example, the composite material 1 may include three or more portions having different volumetric proportions of the radio wave absorbing material 30.

[0052] The composite material 1 may also include a portion in which the volume ratio of the organic particles 20 gradually decreases from a first end, which is one end of the composite material 1, toward a second end opposite to the first end. The composite material 1 may also include a portion in which the volume ratio of the radio wave absorber 30 gradually decreases, for example, from the second end toward the first end.

[0053] The organic particles 20 may be uniformly dispersed throughout the composite material 1. Since the organic particles 20 are unlikely to impede the radio wave absorbing effect of the radio wave absorber 30, the influence is small even if the organic particles 20 are uniformly dispersed throughout the composite material 1.

[0054] [Radio wave sensor] Next, the radio wave sensor 100 according to this embodiment will be described. As shown in FIG. 4, the radio wave sensor 100 according to this embodiment includes a composite member 1 and a sensor 110. In this embodiment, the composite member 1 is a dielectric lens. The sensor 110 includes a substrate 120, a transmitting section 130, and a receiving section 140. The transmitting section 130 and the receiving section 140 are provided on the substrate 120. The composite member 1 is disposed so as to cover the transmitting section 130 and the receiving section 140. The transmitting section 130 is configured to transmit radio waves. The receiving section 140 is configured to receive reflected waves of the radio waves transmitted from the transmitting section 130.

[0055] The radio waves transmitted from the transmitting unit 130 are electromagnetic waves having a frequency of 3000 GHz or less. The frequency of the radio waves may be 0.03 Hz or more, or may be 3 GHz or more. The frequency of the radio waves may be 300 GHz or less. The frequency of the radio waves may be 24 GHz, 60 GHz, 76 GHz, 79 GHz, 94 GHz, or 140 GHz.

[0056] As described above, the radio wave sensor 100 according to this embodiment includes the composite material 1, the transmitting unit 130, and the receiving unit 140. When a radio wave is transmitted from the transmitting unit 130, the radio wave passes through the composite material 1. The radio wave that passes through the composite material 1 is irradiated to an irradiated object and is reflected from the irradiated object as a reflected wave. The reflected wave passes through the composite material 1 again and is received by the receiving unit 140.

[0057] The composite member 1 is more durable than a resin matrix, and the radio wave characteristics can be controlled. Therefore, the composite member 1 used in the radio wave sensor 100 is also more durable, and the characteristics of the radio waves emitted from the transmitter 130 can be controlled. For example, the radiation angle of the radio waves can be changed by adjusting the composition of the organic particles 20, or the radiation intensity of the radio waves can be changed by adjusting the composition of the radio wave absorber 30, thereby making it possible to easily adjust the radio wave characteristics of the radio wave sensor 100.

[0058] The radio wave sensor 100 may confirm the presence of an irradiated object and obtain position information or speed information of the irradiated object. The radio wave sensor 100 may also obtain information such as a person's breathing, heart rate, and body movement, and estimate or obtain the person's behavior or state. The radio wave sensor 100 may be installed, for example, in a dressing room or a toilet, and may be used, for example, as a monitoring sensor or a human presence sensor.

[0059] [Manufacturing method for composite materials] Next, a method for producing the composite material 1 according to this embodiment will be described.

[0060] First, a method for producing the composite member 1 in which the inorganic substance contained in the composite member 1 is boehmite will be described. The composite member 1 in which the inorganic substance is boehmite can be produced by mixing hydraulic alumina, at least one of the organic particles 20 and the radio wave absorber 30, and a solvent containing water, and then pressurizing and heating the mixture. Hydraulic alumina is an oxide obtained by heat-treating aluminum hydroxide, and contains ρ-alumina. Such hydraulic alumina has the property of bonding and hardening through a hydration reaction. Therefore, by using a pressurized heating method, the hydration reaction of hydraulic alumina progresses, and the hydraulic alumina particles bond to each other while the crystal structure changes to boehmite, whereby the composite member 1 can be formed.

[0061] Specifically, first, a mixture is prepared by mixing hydraulic alumina powder, at least one of the organic particles 20 and the radio wave absorber 30, and a solvent containing water. The solvent containing water is preferably pure water or ion-exchanged water. The solvent containing water may contain an acidic substance or an alkaline substance in addition to water. Furthermore, the solvent containing water may contain water as a main component, and may contain, for example, an organic solvent (e.g., alcohol, etc.).

[0062] The amount of the solvent added to the hydraulic alumina is preferably an amount that allows the hydration reaction of the hydraulic alumina to proceed sufficiently, and is preferably 20 to 200 mass % and more preferably 50 to 150 mass % relative to the hydraulic alumina.

[0063] Next, the inside of the mold is filled with a mixture of hydraulic alumina, at least one of the organic particles 20 and the radio wave absorber 30, and a solvent containing water. After filling the mixture in the mold, the mold may be heated as necessary. Then, pressure is applied to the mixture placed in the mold, and the inside of the mold is put into a high-pressure state. At this time, hydraulic alumina is highly packed, and the hydraulic alumina particles are bonded to each other, thereby increasing the density. Specifically, by adding water to hydraulic alumina, the hydraulic alumina undergoes a hydration reaction, and boehmite and aluminum hydroxide are generated on the surfaces of the hydraulic alumina particles. Then, by applying pressure to the mixture while heating it in the mold, the generated boehmite and aluminum hydroxide diffuse between adjacent hydraulic alumina particles, and the hydraulic alumina particles are gradually bonded to each other. Thereafter, a dehydration reaction proceeds due to heating, and the crystal structure changes from aluminum hydroxide to boehmite. It is assumed that the hydration reaction of hydraulic alumina, the mutual diffusion between hydraulic alumina particles, and the dehydration reaction proceed almost simultaneously. Then, the composite material 1 can be obtained by removing the compact from the inside of the mold.

[0064] The heating and pressurizing conditions of the mixture of hydraulic alumina, at least one of the organic particles 20 and the radio wave absorber 30, and the solvent containing water are not particularly limited as long as the reaction between hydraulic alumina and the solvent proceeds. For example, it is preferable to pressurize the mixture of hydraulic alumina, at least one of the organic particles 20 and the radio wave absorber 30, and the solvent containing water at a pressure of 10 to 600 MPa while heating it to 50 to 300°C. The temperature at which the mixture of hydraulic alumina, at least one of the organic particles 20 and the radio wave absorber 30, and the solvent containing water is heated is more preferably 80 to 250°C, and even more preferably 100 to 200°C. Furthermore, the pressure to be applied to the mixture obtained by mixing hydraulic alumina, at least one of the organic particles 20 and the radio wave absorber 30, and a solvent containing water is more preferably 50 to 600 MPa, and even more preferably 200 to 600 MPa.

[0065] Next, a description will be given of another method for producing the composite material 1 in which the inorganic material contained in the composite material 1 is boehmite. The composite material 1 in which the inorganic material is boehmite can be produced by mixing aluminum nitride powder, at least one of the organic particles 20 and the radio wave absorber 30, and a solvent containing water, and then applying pressure and heating.

[0066] Specifically, first, aluminum nitride powder, at least one of the organic particles 20 and the radio wave absorber 30, and a water-containing solvent are mixed to prepare a mixture. The water-containing solvent is preferably pure water or ion-exchanged water. The water-containing solvent may contain an acidic substance or an alkaline substance in addition to water. Furthermore, the water-containing solvent may contain water as a main component, and may contain, for example, an organic solvent (e.g., alcohol, etc.). Furthermore, the water-containing solvent may contain ammonia.

[0067] The amount of the solvent added to the aluminum nitride is preferably an amount that allows the hydrolysis reaction of the aluminum nitride described below to proceed and produces aluminum hydroxide on the surface of the aluminum nitride. The amount of the solvent added is preferably 5 to 100 mass % and more preferably 20 to 80 mass % based on the aluminum nitride.

[0068] Next, the inside of the mold is filled with a mixture of aluminum nitride, at least one of the organic particles 20 and the radio wave absorber 30, and a solvent containing water. After the mixture is filled in the mold, the mold is heated as necessary. Then, pressure is applied to the mixture placed inside the mold, and the inside of the mold is put into a high-pressure state. At this time, the aluminum nitride is highly packed, and the aluminum nitride particles are bonded to each other, thereby increasing the density. Specifically, by applying pressure while heating the mixture, the aluminum nitride reacts with moisture to generate aluminum hydroxide on the surface of the aluminum nitride. The generated aluminum hydroxide diffuses between adjacent aluminum nitrides, and the aluminum nitrides are gradually bonded to each other. Thereafter, a dehydration reaction proceeds due to heating, and the crystal structure changes from aluminum hydroxide to boehmite. As a result, adjacent aluminum nitride particles are bonded via the boehmite phase containing boehmite. Then, the composite member 1 is obtained by removing the molded body from the inside of the mold.

[0069] The heating and pressurizing conditions for the mixture obtained by mixing aluminum nitride with a solvent containing water are not particularly limited as long as the reaction between aluminum nitride and the solvent and the dehydration reaction of aluminum hydroxide proceed. For example, it is preferable to heat the mixture to 50 to 300°C and pressurize it at a pressure of 10 to 600 MPa. The temperature at which the mixture is heated is more preferably 80 to 250°C, and even more preferably 100 to 200°C. The pressure at which the mixture is pressurized is more preferably 50 to 600 MPa, and even more preferably 200 to 600 MPa.

[0070] Next, a method for manufacturing the composite member 1 in which the inorganic substance contained in the matrix portion 10 is a metal oxide will be described. First, a solvent is added to a mixed powder containing a powder of an inorganic substance and at least one of the organic particles 20 and the radio wave absorber 30. The solvent is not particularly limited, but for example, a solvent capable of dissolving a part of the inorganic substance when the mixed powder is pressurized and heated can be used. In addition, a solvent capable of reacting with the inorganic substance to generate an inorganic substance different from the inorganic substance can be used. As such a solvent, at least one selected from the group consisting of an acidic aqueous solution, an alkaline aqueous solution, water, an alcohol, a ketone, and an ester can be used. As the acidic aqueous solution, an aqueous solution having a pH of 1 to 3 can be used. As the alkaline aqueous solution, an aqueous solution having a pH of 10 to 14 can be used. As the acidic aqueous solution, an aqueous solution of an organic acid is preferably used. As the alcohol, an alcohol having 1 to 12 carbon atoms is preferably used.

[0071] Next, the inside of the mold is filled with a mixture containing the mixed powder and a solvent. After the mixture is filled in the mold, the mold may be heated as necessary. Then, pressure is applied to the mixture placed in the mold, so that the inside of the mold is put into a high-pressure state. At this time, the inorganic material in the mixture is densified, and at the same time, the particles of the inorganic material are bonded to each other.

[0072] Here, when a solvent that dissolves a part of the inorganic substance is used, the inorganic compound contained in the inorganic substance dissolves in the solvent under high pressure. The dissolved inorganic compound penetrates into the gaps between the inorganic substances. Then, by removing the solvent in the mixture under this condition, bonds 12 derived from the inorganic substance are formed between the inorganic substances. When a solvent that reacts with the inorganic substance to produce an inorganic substance different from the inorganic substance is used, the inorganic compound that constitutes the inorganic substance reacts with the solvent under high pressure. Then, the other inorganic substance produced by the reaction fills the gaps between the inorganic substances, and bonds 12 derived from the other inorganic substance are formed.

[0073] The heating and pressurizing conditions of the mixture containing the inorganic substance and the solvent are not particularly limited as long as the dissolution of the surface of the inorganic substance proceeds when a solvent that dissolves a part of the inorganic substance is used. The heating and pressurizing conditions of the mixture are not particularly limited as long as the reaction between the inorganic substance and the solvent proceeds when a solvent that reacts with the inorganic substance to produce an inorganic substance different from the inorganic substance is used. For example, it is preferable to heat the mixture containing the inorganic substance and the solvent to 50 to 300°C, and then pressurize it at a pressure of 10 to 600 MPa. The temperature at which the mixture containing the inorganic substance and the solvent is heated is more preferably 80 to 250°C, and even more preferably 100 to 200°C. The pressure at which the mixture containing the inorganic substance and the solvent is pressed is more preferably 50 to 400 MPa, and even more preferably 50 to 200 MPa. Then, the composite member 1 can be obtained by removing the molded body from inside the mold.

[0074] Here, a sintering method is known as a method for manufacturing an inorganic member containing ceramics. The sintering method is a method for obtaining a sintered body by heating an aggregate of solid powder containing an inorganic substance at a temperature lower than the melting point. However, in the sintering method, the solid powder is heated to, for example, 1000°C or higher. Therefore, even if an attempt is made to obtain a composite member 1 containing an organic substance with low heat resistance using the sintering method, the organic substance will be carbonized by heating at a high temperature. However, in the manufacturing method of the composite member 1 of the present embodiment, the organic substance is less likely to be carbonized because heating is performed at a low temperature of 300°C or less.

[0075] Furthermore, in the manufacturing method of the present embodiment, the powder of the inorganic substance is pressurized while being heated, so that the inorganic substance aggregates to form a dense composite material 1. As a result, the number of pores inside the composite material 1 is reduced, and a composite material 1 having high strength can be obtained.

[0076] As described above, the method for producing the composite member 1 according to this embodiment includes a step of mixing hydraulic alumina, at least one of the organic particles 20 and the radio wave absorber 30, and a solvent containing water to obtain a mixture, and a step of pressurizing and heating the mixture. The heating and pressurizing conditions for the mixture are preferably a temperature of 50 to 300°C and a pressure of 10 to 600 MPa. In this production method, the composite member 1 is molded under low-temperature conditions, and therefore the obtained composite member 1 is mainly composed of a boehmite phase. Therefore, a composite member 1 that is lightweight and has excellent chemical stability can be obtained by a simple method.

[0077] A method for producing a composite member 1 according to another embodiment includes a step of mixing aluminum nitride particles, at least one of organic particles 20 and radio wave absorber 30, and a solvent containing water to obtain a mixture, and a step of pressurizing and heating the mixture. The heating and pressurizing conditions for the mixture are preferably a temperature of 50 to 300°C and a pressure of 10 to 600 MPa. Since the heating temperature is low in the production method of this embodiment, aluminum nitride is bonded via the boehmite phase in the obtained composite member 1. Therefore, it is possible to obtain a composite member 1 having excellent mechanical strength and chemical stability by a simple method.

[0078] A method for producing a composite member 1 according to another embodiment includes a step of mixing a solvent that dissolves an inorganic substance or a solvent that reacts with an inorganic substance, powder of the inorganic substance, and at least one of organic particles 20 and radio wave absorber 30 to obtain a mixture. The method also includes a step of pressurizing and heating the mixture. The heating and pressurizing conditions for the mixture are preferably a temperature of 50 to 300°C and a pressure of 10 to 600 MPa. In the production method of this embodiment, the composite member 1 is molded under such low-temperature conditions, so that changes in physical or chemical properties due to heat can be suppressed. Therefore, a composite member 1 that can be used for various applications can be obtained. EXAMPLES

[0079] The present embodiment will be described in more detail below with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[0080] First, ABS, glass, and aluminum oxide (Al 2 O 3 The relationship between the relative dielectric constant and the radiation angle was analyzed by simulation. r The dielectric constant of glass was set to 5.5 and the dielectric tangent was set to 0.007. The dielectric constant of aluminum oxide was set to 9.8 and the dielectric tangent was set to 0.007. The values ​​of the dielectric constant and the dielectric tangent were taken at a temperature of 25°C and a frequency of 1 MHz.

[0081] (Radiation angle) First, the radiation pattern was analyzed using high-frequency 3D electromagnetic field analysis software Ansys (registered trademark) HFSS. In the analysis, as shown in Figure 5, a sensor was used that included a Tx antenna with four elements arranged in the X direction and an Rx antenna with four elements arranged in the X direction, with the Tx antenna and the Rx antenna arranged in the Y direction. The sensor was made of ABS, glass, or aluminum oxide (Al 2 O 3 ) plate. The radiation pattern was analyzed from the realized gain obtained when the frequency was 24.15GHz, max DeltaS was 0.001%, the analysis time was 15 times, and 1W was fed to the feed line of the Tx antenna at the lumped port. The radiation angle (θ) was set to half the sum of the maximum output angle and the angle with the second highest output among the maximum points in the vertical polarization on the YZ plane shown by the solid lines in Figures 6 to 8. However, in Figure 6, since the second maximum point does not exist in the front (+90 degrees to -90 degrees), the maximum output angle was set to the radiation angle. It has been confirmed that the radiation pattern obtained by the simulation analysis and the radiation pattern obtained by the actual measurement are almost the same.

[0082] Figures 6 to 8 show the radiation patterns of ABS, glass and aluminum oxide, respectively. In the figures, θ indicates the radiation angle. Figure 9 is a graph showing the relationship between the relative dielectric constant and the radiation angle. As shown in Figures 6 to 9, the radiation angle increases as the relative dielectric constant increases, and it was confirmed that the relative dielectric constant and the radiation angle are mutually related.

[0083] Next, the following test samples were prepared, and the relative dielectric constant of each test sample was measured.

[0084] [Sample 1] First, hydraulic alumina BK-112 with a median particle size of 16 μm manufactured by Sumitomo Chemical Co., Ltd. was prepared as an inorganic substance. In addition, polytetrafluoroethylene particles (PTFE fine powder KTL-1N manufactured by Taki Chemical Co., Ltd.) were prepared as organic particles. Then, PTFE was weighed so that it was 40% by volume relative to the total of hydraulic alumina and PTFE, and then the hydraulic alumina and PTFE were mixed using an agate mortar and pestle to obtain a mixed powder. Next, ion-exchanged water was weighed so that it was 80% by mass relative to the hydraulic alumina, and then the mixed powder and the ion-exchanged water were mixed using an agate mortar and pestle to obtain a mixture. Next, the obtained mixture was filled into the inside of a cylindrical molding die (Φ12) having an internal space. Then, the mixture placed inside the die was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to prepare a test sample.

[0085] [Sample 2] A test sample was prepared in the same manner as sample 1, except that the test sample was prepared without the addition of PTFE.

[0086] [Sample 3] First, aluminum nitride powder (purity: 3N) manufactured by Kojundo Chemical Laboratory Co., Ltd. was prepared as an inorganic substance. In addition, polytetrafluoroethylene particles (PTFE fine powder KTL-1N manufactured by Taki Chemical Co., Ltd.) were prepared as organic particles. Then, PTFE was weighed so that it was 40% by volume relative to the total of aluminum nitride and PTFE, and then aluminum nitride and PTFE were mixed using an agate mortar and pestle to obtain a mixed powder. Next, ion-exchanged water was weighed so that it was 80% by mass relative to aluminum nitride, and then the mixed powder and ion-exchanged water were mixed using an agate mortar and pestle to obtain a mixture. Next, the obtained mixture was filled into the inside of a cylindrical molding die (Φ12) having an internal space. Then, the mixture placed inside the die was heated and pressurized under conditions of 400 MPa, 180°C, and 20 minutes to prepare a test sample.

[0087] [Sample 4] A test sample was prepared in the same manner as sample 3, except that the test sample was prepared without the addition of PTFE.

[0088] Next, the following plate-shaped materials were obtained and the relative dielectric constants were measured for reference.

[0089] [Reference example 1] Al 2 O 3 (99.97% purity) [Reference example 2] ABS [Reference Example 3] PMMA (acrylic) [Reference example 4] PTFE

[0090] (Dielectric constant) The relative dielectric constant of each test sample and plate-shaped material was measured using an impedance / material analyzer (Agilent E4991A RF) manufactured by Agilent Technologies, Inc. The measurement temperature was 25° C. and the measurement frequency was 1 GHz.

[0091] [Table 1]

[0092] A comparison between Sample 1 and Sample 2 shows that the addition of PTFE to boehmite reduced the relative dielectric constant. A comparison between Sample 3 and Sample 4 shows that the addition of PTFE to aluminum nitride reduced the relative dielectric constant.

[0093] From these results, it is believed that a composite member with a low dielectric constant can be obtained even when PTFE is added to a matrix portion containing at least one of a metal oxide and a metal hydroxide oxide. Similarly, it is believed that a composite member with a low dielectric constant can be obtained even when organic particles such as ABS or PMMA are added to boehmite or aluminum nitride. In other words, it is believed that the dielectric constant of the resulting composite member can be adjusted by adjusting the type and amount of organic particles added to the inorganic substance particles.

[0094] Next, the radiation patterns of Sample 1 and Sample 2 were measured and the radiation angle was calculated. Specifically, an InnoSenT SMR333 was covered with Sample 1 or 2, and the radiation patterns of the XZ and YZ planes were created from the EIRP (equivalent isotropically radiated power) obtained when the transmission power was 4 dBm (typical) and the frequency was 24.15 GHz. Horizontal For the polarized wave (XZ-plane, Hori.) and the vertically polarized wave (YZ-plane, Vert.) in the radiation pattern of the YZ plane, the angle at which the EIRP was 10 dB lower than the maximum value was measured as the -10 dB angle.

[0095] The radiation pattern in the XZ plane measured for Sample 1 is shown as Pattern 1 in Figure 10. The radiation pattern in the YZ plane measured for Sample 1 is shown as Pattern 2 in Figure 11. The radiation pattern in the XZ plane measured for Sample 2 is shown as Pattern 3 in Figure 12. The radiation pattern in the YZ plane measured for Sample 2 is shown as Pattern 4 in Figure 13. Table 2 also shows the relationship between each sample and the -10 dB angle.

[0096] [Table 2]

[0097] Comparing Pattern 1 with Pattern 3, and Pattern 2 with Pattern 4, it was confirmed that the -10 dB angle was larger for Sample 1 than for Sample 2. This shows that, similar to the simulation results, the radiation angle can be controlled by adding organic particles to the matrix of the inorganic material and changing the relative dielectric constant.

[0098] Next, the effect of shielding radio waves by the radio wave absorber was evaluated. Specifically, as shown in Fig. 14, the radiation pattern when the sensor 210 was covered with a plate 220 made of boehmite was analyzed by simulation in the same manner as above. Also, as shown in Fig. 15, the radiation pattern when the sensor 210 was covered half by the plate 220 made of boehmite and the shielding plate 230 made of carbon was analyzed by simulation in the same manner as above. The radiation pattern when the sensor was not covered with a shielding plate is shown in Fig. 16. Also, the radiation pattern when half of the sensor was covered with a shielding plate is shown in Fig. 17.

[0099] It can be seen that radio wave radiation is suppressed in the area where the sensor is shielded by the shielding plate, as shown in the circle in Figure 17. From this result, it was confirmed that radio waves in a desired area can be partially blocked by the radio wave absorbing material.

[0100] Next, a composite member including a radio wave shielding portion and a radio wave transmitting portion was produced.

[0101] First, hydraulic alumina BK-112 with a median particle size of 16 μm manufactured by Sumitomo Chemical Co., Ltd. was prepared as an inorganic material. In addition, polytetrafluoroethylene particles (PTFE fine powder KTL-1N manufactured by Taki Chemical Co., Ltd.) were prepared as organic particles. Then, PTFE was weighed out so that it was 30% by volume relative to the hydraulic alumina, and then the hydraulic alumina and PTFE were mixed using an agate mortar and pestle to obtain a mixed powder. Next, ion-exchanged water was weighed out so that it was 80% by mass relative to the hydraulic alumina, and then the mixed powder and the ion-exchanged water were mixed using an agate mortar and pestle to obtain a mixture 1.

[0102] In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was prepared as a radio wave absorbing material. Then, graphite was weighed out so that the amount was 30% by volume relative to the hydraulic alumina, and then the hydraulic alumina and graphite were mixed using an agate mortar and pestle to obtain a mixed powder. Next, ion-exchanged water was weighed out so that the amount was 80% by mass relative to the hydraulic alumina, and then the mixed powder and the ion-exchanged water were mixed using an agate mortar and pestle to obtain Mixture 2.

[0103] Next, mixture 1 and mixture 2 were filled approximately evenly on the left and right sides into a cylindrical molding die (Φ50) having an internal space. Then, the mixture placed inside the die was heated and pressurized under conditions of 400 MPa, 180°C, and 20 minutes to prepare a test sample.

[0104] The composite member obtained by the above method is shown in the center of Figure 18. By the above method, a composite member including a carbon-introduced portion (shielding portion) where carbon (graphite) has been introduced and an unintroduced portion (transmitting portion) where no carbon has been introduced could be obtained, as shown in the center of Figure 18. Note that the composite member without carbon introduced made with mixture 1 is shown on the right side of Figure 18, and the composite member with carbon introduced made with mixture 2 is shown on the left side of Figure 18.

[0105] Next, Sample 5 and Sample 6 were prepared, and their porosities were measured.

[0106] [Sample 5] First, hydraulic alumina BK-112 with a median particle size of 16 μm manufactured by Sumitomo Chemical Co., Ltd. was prepared as an inorganic material. In addition, polytetrafluoroethylene particles (PTFE fine powder KTL-1N manufactured by Taki Chemical Co., Ltd.) were prepared as organic particles. Then, these were weighed so that PTFE was 40 volume % relative to the total of hydraulic alumina and PTFE, and then mixed using an agate mortar and pestle to obtain a mixed powder. Next, ion-exchanged water was weighed so that it was 80 mass % relative to hydraulic alumina, and then the mixed powder and ion-exchanged water were mixed using an agate mortar and pestle to obtain a mixture. Next, the obtained mixture was filled inside a cylindrical molding die (Φ12) having an internal space. Then, the mixture placed inside the die was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to prepare a test sample.

[0107] [Sample 6] First, hydraulic alumina BK-112 with a median particle size of 16 μm manufactured by Sumitomo Chemical Co., Ltd. was prepared as an inorganic material. In addition, graphite powder manufactured by Wako Pure Chemical Industries, Ltd. was prepared as an electromagnetic wave absorber. Then, the hydraulic alumina and graphite were weighed so that the graphite was 40 volume % relative to the total of the hydraulic alumina and graphite, and then mixed using an agate mortar and pestle to obtain a mixed powder. Next, ion-exchanged water was weighed so that the hydraulic alumina was 80 mass %. Then, the mixed powder and the ion-exchanged water were mixed using an agate mortar and pestle to obtain a mixture. Next, the obtained mixture was filled into a cylindrical molding die (Φ12) having an internal space. Then, the mixture placed inside the die was heated and pressurized under conditions of 400 MPa, 180° C., and 20 minutes to prepare a test sample.

[0108] (Porosity measurement) First, the cross-section of the cylindrical sample was subjected to cross-section polishing (CP processing). Next, a scanning electron microscope (SEM) was used to observe the backscattered electron images of the cross-section of the sample at a magnification of 5000 times. The backscattered electron images obtained by observing the cross-sections of Sample 5 and Sample 6 are shown in Figures 19 and 20, respectively.

[0109] Next, the SEM images obtained were binarized to clarify the pores. FIG. 21 shows an image in which the backscattered electron image in FIG. 19 was binarized. FIG. 22 shows an image in which the backscattered electron image in FIG. 20 was binarized. In FIG. 21 and FIG. 22, the black parts are pores. Then, the area ratio of the pores was calculated from the binarized images, and the average value was taken as the porosity. From FIG. 21, the porosity of sample 5 was 0.57%. Also, from FIG. 22, the porosity of sample 6 was 0.50%. From the porosity measurement results, it was found that the porosity of these composite members was small. It is considered that the small porosity of the composite members suppresses the occurrence of cracks in the composite members starting from the pores.

[0110] The entire contents of Patent Application No. 2021-208048 (filing date: December 22, 2021) are incorporated herein by reference.

[0111] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment. [Industrial Applicability]

[0112] According to the present disclosure, it is possible to provide a composite member which is superior in durability compared to a case where a resin matrix is ​​used, and which allows control of radio wave characteristics. [Explanation of symbols]

[0113] 1 Composite materials 10 Matrix section 11 Inorganic particles 20 Organic particles 30 Radio wave absorbing material

Claims

1. A matrix portion including a plurality of inorganic particles and formed by bonding the plurality of inorganic particles to each other; Organic particles present in a dispersed state inside the matrix portion; a radio wave absorbing material present in a dispersed state inside the matrix portion; Equipped with The matrix portion of the composite material contains at least one of a metal oxide and a metal oxide hydroxide.

2. 2. The composite member according to claim 1, having a porosity in cross section of 20% or less.

3. 3. The composite material according to claim 1, wherein the organic particles and the radio wave absorbing material are not present continuously from the surface of the matrix portion to the inside thereof.

4. 3. The composite material according to claim 1, wherein the volume ratio of the organic particles is less than 50%.

5. The composite member according to claim 1 or 2, wherein the radio wave absorbing material contains carbon and is unevenly distributed in some areas.

6. The composite material according to claim 1 , wherein the matrix portion has a thermal conductivity higher than that of the organic particles.

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