Radio wave absorbers and high-frequency modules

Abstract

To obtain a radio wave absorber that exhibits excellent radio wave absorption performance in the microwave band and can suppress the shedding of metal particles constituting the radio wave absorber compared to conventional materials. [Solution] The radio wave absorber 1 comprises a glass matrix 2 that maintains its shape and soft magnetic metal particles 3 that have radio wave absorption performance in the microwave band due to magnetic loss, and is made of a composite material in which the soft magnetic metal particles 3 are dispersed in the glass matrix 2. The average particle size of the soft magnetic metal particles 3 is 1 μm or more and less than 10 μm. The ratio of the volume of the soft magnetic metal particles 3 to the sum of the volumes of the soft magnetic metal particles 3 and the glass matrix 2 is 0.3 or more and 0.45 or less.

Description

Technical Field

[0001] The present disclosure relates to a radio wave absorber for the gigahertz (GHz) band composed of a composite material containing soft magnetic metal particles and a glass matrix, and a high-frequency module using the same.

Background Art

[0002] In the field of electronic devices, in order to miniaturize and improve the performance of devices, the frequency has been increased and the density has been increased, and countermeasures against electromagnetic noise, which is a cause of malfunction of devices, have become an important issue. In particular, high-frequency devices have a structure in which a high-frequency circuit is housed in a metal case for the purpose of protecting mounted semiconductor elements and circuit conductors and preventing mutual interference with external circuits. For this reason, the high-frequency noise generated inside the metal case may resonate at a specific frequency corresponding to the cavity size inside the metal case, causing problems such as malfunction of the circuit due to electromagnetic interference inside the metal case. As a method for suppressing electromagnetic interference inside these metal cases, a radio wave absorber using a magnetic material is installed inside the metal case, and unnecessary radio waves generated inside the metal case, that is, high-frequency noise, are absorbed by the magnetic loss of the radio wave absorber.

[0003] Generally, as a material for a radio wave absorber using magnetic loss, spinel-type ferrite materials are often used. Spinel-type ferrite materials have a low magnetic permeability on the high-frequency side and are effective for absorbing radio waves in the megahertz (MHz) band, but do not have sufficient absorption performance for radio waves in the gigahertz band and are not suitable as radio wave absorbers for high-frequency devices operating in the gigahertz band. In particular, in the microwave band used for high-frequency communication applications, the high-frequency noise suppression effect as a radio wave absorber cannot be expected.

[0004] Furthermore, general radio wave absorbers often use composite materials in which the above-mentioned ferrite material is dispersed in a resin matrix, which has the disadvantage of having a low heat resistance temperature. For this reason, when used in an airtight cover to protect the semiconductor of a high-frequency module, contamination due to degassing of the resin component can become a problem.

[0005] Therefore, Patent Document 1 proposes a radio wave absorber with excellent heat resistance, in which glass or ceramics are used as the matrix, metal particles are used as the composite phase, and the volume fraction of the composite phase is 2% or more and 40% or less. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-255408 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, while Patent Document 1 discloses a radio wave absorber, its radio wave absorption performance in the microwave band, i.e., the gigahertz band, has not been sufficiently considered. In other words, the radio wave absorber described in Patent Document 1 may not be able to fully exhibit radio wave absorption performance in the microwave band. Furthermore, Patent Document 1 discloses that the volume fraction of the composite phase is 2% to 40%, and the particle size of the metal particles constituting the composite phase is 150 μm or less in the case of spherical particles, and 1 μm to 200 μm in the case of flattened particles. However, when the radio wave absorber shown in Patent Document 1 is installed in a high-frequency module, depending on the combination of the particle size of the metal particles and the volume fraction of the composite phase, there was a problem that the shedding of the metal particles, which are the constituent material of the radio wave absorber, could cause a short circuit failure in the circuit. In other words, the technology described in Patent Document 1 does not take into account the shedding of metal particles, and the relationship between the matrix that suppresses the shedding of metal particles and the particle size of the metal particles is required.

[0008] This disclosure has been made in view of the above, and aims to provide a radio wave absorber that has excellent radio wave absorption performance in the microwave band and can suppress the shedding of metal particles constituting the radio wave absorber compared to conventional materials. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, the radio wave absorber according to this disclosure comprises a glass matrix that maintains its shape and soft magnetic metal particles that have radio wave absorption performance in the microwave band due to magnetic loss, and consists of a composite material in which the soft magnetic metal particles are dispersed in the glass matrix. The average particle size of the soft magnetic metal particles is 1 μm or more and less than 10 μm. The ratio of the volume of the soft magnetic metal particles to the sum of the volumes of the soft magnetic metal particles and the glass matrix, which is 1, is 0.3 or more and 0.45 or less. [Effects of the Invention]

[0010] According to this disclosure, the material exhibits excellent radio wave absorption performance in the microwave band and has the effect of suppressing the shedding of metal particles constituting the radio wave absorber compared to conventional materials. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic cross-sectional view showing an example of the configuration of a radio wave absorber according to Embodiment 1. [Figure 2] This figure schematically shows an example of the shape of soft magnetic metal particles used in the radio wave absorber according to Embodiment 1. [Figure 3] This figure schematically shows an example of the shape of soft magnetic metal particles used in the radio wave absorber according to Embodiment 1. [Figure 4] A schematic diagram illustrating an example of an undesirable shape of soft magnetic metal particles. [Figure 5] A schematic cross-sectional view showing another example of the configuration of the radio wave absorber according to Embodiment 1. [Figure 6] A schematic cross-sectional view showing an example of the configuration of a high-frequency module using a radio wave absorber according to Embodiment 2. [Figure 7]A schematic cross-sectional view showing an example of the configuration of a resonator for evaluating radio wave attenuation. [Modes for carrying out the invention]

[0012] The radio wave absorber and high-frequency module according to embodiments of this disclosure will be described in detail below with reference to the drawings.

[0013] Embodiment 1. Radio wave absorbers using magnetic materials utilize the effect of absorbing radio waves due to magnetic loss. Therefore, radio wave absorbers are required to have a large magnetic loss in the target frequency band, specifically the frequency band of the noise to be absorbed. Furthermore, when using a composite material in which magnetic particles are dispersed in a matrix as the material for the radio wave absorber, it is necessary to sufficiently fix the magnetic particles in the matrix to prevent them from falling out. From this viewpoint, the inventors have conducted diligent research and have found that by using soft magnetic metal particles with adjusted average particle size and shape as the magnetic particles, and by setting the volume ratio of the soft magnetic metal particles to the glass matrix within an appropriate range, a radio wave absorber with superior radio wave absorption performance compared to conventional materials and without the falling out of the soft magnetic metal particles can be obtained. In particular, Fe-Si-Cr alloy with adjusted average particle size and shape is preferred as the soft magnetic metal particles. A radio wave absorber according to Embodiment 1 will be described below with reference to the drawings.

[0014] Figure 1 is a schematic cross-sectional view showing an example of the configuration of a radio wave absorber according to Embodiment 1. In Figure 1, the radio wave absorber 1 comprises a glass matrix 2 for maintaining its shape and soft magnetic metal particles 3 having radio wave absorption properties, and is made of a composite material in which the soft magnetic metal particles 3 are dispersed in the glass matrix 2. Generally, a radio wave absorber 1 containing a magnetic material absorbs radio waves by converting incident radio waves into heat through magnetic loss. The frequency band in which the magnetic loss is maximum becomes the absorption frequency band of the radio wave absorber 1. Here, the soft magnetic metal particles 3 have a large magnetic loss in the microwave band. In other words, the soft magnetic metal particles 3 have the property of having a maximum magnetic loss in the microwave band. The soft magnetic metal particles 3 are soft magnetic materials that are magnetized when an external magnetic field is applied but return to their original state when the external magnetic field is removed, and are made of metal or alloy. An example of soft magnetic metal particles 3 is an Fe-Si-Cr alloy. The average particle size of the soft magnetic metal particles 3 is 1 μm or more and less than 10 μm. By achieving this average particle size, the soft magnetic metal particles 3, which have excellent radio wave absorption performance in the microwave band, can be easily dispersed uniformly in the glass matrix 2. As a result, variations in radio wave absorption performance are less likely to occur, and stable radio wave absorption performance can be obtained. Furthermore, because the soft magnetic metal particles 3 are uniformly dispersed in the glass matrix 2, the glass matrix 2 can more easily fix the soft magnetic metal particles 3, which also has the advantage of improving the mechanical strength of the radio wave absorber 1.

[0015] In addition, in the radio wave absorber 1 according to Embodiment 1, the volume ratio of the soft magnetic metal particles 3 to the glass matrix 2 is appropriately adjusted, and the volume ratio of the soft magnetic metal particles 3 to the glass matrix 2 ranges from 3:7 to 4.5:5.5. In other words, when the sum of the volumes of the soft magnetic metal particles 3 and the glass matrix 2 is taken as 1, the volume ratio of the soft magnetic metal particles 3 is 0.3 or more and 0.45 or less. Alternatively, when the sum of the volumes of the soft magnetic metal particles 3 and the glass matrix 2 is taken as 1, the volume ratio of the glass matrix 2 is 0.55 or more and 0.7 or less. By setting the volume ratio of the glass matrix 2 within such a range with respect to the soft magnetic metal particles 3 having the above average particle size, the radio wave absorber 1 can maintain excellent radio wave absorption performance while the glass matrix 2 can sufficiently cover and immobilize the soft magnetic metal particles 3. As a result, a radio wave absorber 1 having excellent radio wave absorption performance and no occurrence of dropout of the soft magnetic metal particles 3 can be obtained.

[0016] Further details of the soft magnetic metal particles 3 and the glass matrix 2 will be described. The soft magnetic metal particles 3 in the radio wave absorber 1 according to Embodiment 1 are preferably soft magnetic materials excellent in magnetic loss in the microwave band. Such soft magnetic metal particles 3 are made of one or more materials selected from the group of Fe-Si alloys, Fe-Si-Al alloys, Fe-Si-Cr alloys, and Ni-Fe alloys (permalloy). In particular, in the manufacturing process of the radio wave absorber 1, when heat treatment at a relatively high temperature is required, from the viewpoint of suppressing oxidation of the soft magnetic metal particles 3 in the heat treatment process, it is preferable to use an Fe-Si-Cr alloy having excellent oxidation resistance containing Cr. By using an Fe-Si-Cr alloy, deterioration of magnetic properties due to oxidation can be suppressed, and excellent radio wave absorption performance can be obtained.

[0017] Incidentally, as magnetic particles, there is also a method of absorbing radio waves in the microwave band using hard magnetic particles, which are materials that are magnetized by an external magnetic field and retain their magnetism even after the external magnetic field is removed. However, in this case, since radio waves are absorbed by utilizing the ferromagnetic resonance of the hard magnetic particles, there is a drawback that the absorption frequency band becomes very narrow, and it is not suitable. Therefore, in the radio wave absorber 1 according to Embodiment 1, soft magnetic metal particles 3 having a relatively wide absorption frequency band are used.

[0018] The composite material constituting the radio wave absorber 1 according to Embodiment 1 preferably has a large magnetic loss in the microwave band. As an example, the magnetic loss at an arbitrary frequency in the microwave band is preferably 0.8 or more, and more preferably 1 or more. Here, the magnetic loss is obtained by measuring the S parameter of a sample of the composite material processed into a toroidal shape by the coaxial tube method using a vector network analyzer and coaxial tube fixtures, and calculating the imaginary part μ’’ of the relative permeability. The dimensions of the toroidal shape at this time are an outer diameter of 7 mm, an inner diameter of 3.04 mm, and a thickness of 1 mm.

[0019] In the radio wave absorber 1 according to Embodiment 1, the average particle size of the soft magnetic metal particles 3 is preferably 1 μm or more and less than 10 μm, more preferably 3 μm or more and 8 μm or less, and even more preferably 4 μm or more and 6 μm or less. If the average particle size of the soft magnetic metal particles 3 is less than 1 μm, the specific surface area of ​​the soft magnetic metal particles 3 becomes too large. Therefore, in order to immobilize the soft magnetic metal particles 3 with the glass matrix 2, it is necessary to excessively increase the content of the glass matrix 2, which reduces the radio wave absorption performance of the radio wave absorber 1. On the other hand, if the average particle size of the soft magnetic metal particles 3 is 10 μm or more, the dispersibility of the soft magnetic metal particles 3 and the glass matrix 2 deteriorates in the manufacturing process of the radio wave absorber 1. Therefore, it becomes difficult to obtain a radio wave absorber 1 with a uniform composition. The average particle size of the soft magnetic metal particles 3 can be obtained by cutting the radio wave absorber 1, magnifying the cross-section with a scanning electron microscope (SEM) at a magnification of 1500 times in one example, measuring the major axis of at least 20 particles, and averaging these measurements.

[0020] Figures 2 and 3 schematically show examples of the shapes of soft magnetic metal particles used in the radio wave absorber according to Embodiment 1. Figure 2 shows an example of a soft magnetic metal particle 3 with a roughly spherical shape, and Figure 3 shows an example of a soft magnetic metal particle 3 with a shape in which a part of the roughly spherical shape is stretched. Figure 2(a) shows an example in which the soft magnetic metal particle 3 is spherical, (b) shows an example in which the soft magnetic metal particle 3 is ellipsoidal, and (c) shows an example in which the soft magnetic metal particle 3 is a rectangular parallelepiped with rounded corners. The rectangular parallelepiped shape in (c) also includes a cubic shape. Figure 3(a) shows an example in which the soft magnetic metal particle 3 has a shape in which a part of the sphere is stretched in one direction, (b) shows an example in which the soft magnetic metal particle 3 has a shape in which a part of the ellipsoid is missing along the long axis, and (c) shows an example in which the soft magnetic metal particle 3 has a snowman shape as if two spheres were joined together. Note that Figure 3 shows only one example, and the soft magnetic metal particle 3 can have any shape in which a portion is stretched in one direction, in at least one of the following shapes: spherical, ellipsoidal, and rectangular parallelepiped with rounded corners.

[0021] Figure 4 is a schematic diagram illustrating an example of an undesirable shape for soft magnetic metal particles. Figure 4 shows an example where the soft magnetic metal particles 3 are flattened particles. When the soft magnetic metal particles 3 used in the radio wave absorber 1 according to Embodiment 1 are flattened particles as shown in Figure 4, especially flattened particles with an aspect ratio of 10 or more, they are undesirable because they are difficult to disperse in the glass matrix 2. On the other hand, by making the soft magnetic metal particles 3 into the shape shown in Figures 2 and 3, that is, a shape with an aspect ratio of less than 10, the dispersibility in the glass matrix 2 is easily improved, unlike the case of the shape shown in Figure 4. As a result, a composite material with a uniform composition can be obtained. As a result, variations in radio wave absorption performance are less likely to occur, and a radio wave absorber 1 with stable characteristics can be obtained. The aspect ratio is the ratio of the maximum diameter to the minimum diameter when the longest length of the soft magnetic metal particle 3 is defined as the maximum diameter and the smallest length in the direction perpendicular to the direction of the maximum diameter is defined as the minimum diameter.

[0022] In the radio wave absorber 1 according to Embodiment 1, the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is preferably in the range of 3:7 to 4.5:5.5, and more preferably in the range of 3.5:6.5 to 4:6. That is, the ratio of the volume of soft magnetic metal particles 3 when the sum of the volumes of soft magnetic metal particles 3 and glass matrix 2 is taken as 1 is preferably 0.3 to 0.45, and more preferably 0.35 to 0.4. Alternatively, the ratio of the volume of glass matrix 2 when the sum of the volumes of soft magnetic metal particles 3 and glass matrix 2 is taken as 1 is preferably 0.55 to 0.7, and more preferably 0.6 to 0.65.

[0023] By setting the volume ratio of soft magnetic metal particles 3 to glass matrix 2 within this range, it is possible to obtain a radio wave absorber 1 that has excellent radio wave absorption performance and suppresses the occurrence of detachment of soft magnetic metal particles 3. If the volume ratio of glass matrix 2 exceeds 0.7, the content of soft magnetic metal particles 3 in the radio wave absorber 1 is too low, resulting in a decrease in radio wave absorption performance. On the other hand, if the volume ratio of glass matrix 2 is less than 0.55, the number of voids inside the radio wave absorber 1 increases, making it difficult to sufficiently fix the soft magnetic metal particles 3, which have an average particle size of 1 μm or more and less than 10 μm, and detachment of the soft magnetic metal particles 3 becomes more likely. Thus, the preferred range for the volume ratio of soft magnetic metal particles 3 to glass matrix 2 in Embodiment 1 is closely related to the average particle size of the soft magnetic metal particles 3. In other words, a more effective result can be obtained in a combination of the preferred range for the volume ratio of soft magnetic metal particles 3 to glass matrix 2 and the preferred range for the average particle size of the soft magnetic metal particles 3.

[0024] Figure 5 is a schematic cross-sectional view showing another example of the configuration of the radio wave absorber according to Embodiment 1. The radio wave absorber 1 according to Embodiment 1 may have voids 4 inside the radio wave absorber 1, i.e., inside the glass matrix 2, as shown in Figure 5. However, the voids 4 are provided in a range that does not impair the radio wave absorption performance of the radio wave absorber 1 and does not cause the soft magnetic metal particles 3 to fall out. The porosity of the radio wave absorber 1 according to Embodiment 1 is preferably 15% or less, more preferably 12% or less, and even more preferably 10% or less. Here, the "porosity" of the radio wave absorber 1 can be calculated from the following formula (1) using the weight and dimensions, i.e., the length, width, and height, of the radio wave absorber 1 cut into a rectangular parallelepiped shape.

[0025] Porosity={1-[W d / (L×W×T) / ρ t ]} × 100 ···(1)

[0026] (1) In equation, W dρ is the weight (g) of the radio wave absorber 1 after drying at 150°C for 2 hours, L, W, and T are the length, width, and height (cm) of the rectangular radio wave absorber 1, respectively, and ρ t This is the theoretical density (g / cm³) of the radio wave absorber 1. 3 )

[0027] Furthermore, from the viewpoint of maintaining the mechanical strength of the radio wave absorber 1, the average size of the voids 4 is preferably 2 times or less the average particle size of the soft magnetic metal particles 3, and more preferably 1.5 times or less. If the average size of the voids 4 exceeds 2 times the average particle size of the soft magnetic metal particles 3, large defects may form inside the radio wave absorber 1, which may significantly reduce its mechanical strength. Moreover, the presence of areas with significantly reduced mechanical strength may cause the soft magnetic metal particles 3 to fall off. Here, the average size of the voids 4 in the radio wave absorber 1 is obtained by cutting the radio wave absorber 1, magnifying the cross-section by 1500 times in one example using a SEM, measuring the major axis of at least 20 voids 4, and averaging these measurements.

[0028] In the radio wave absorber 1 according to Embodiment 1, it is preferable that the glass matrix 2 is made of glass that melts at a temperature at which the soft magnetic metal particles 3 do not oxidize during the firing process for melting the glass in the manufacturing process of the radio wave absorber 1. By using such a glass matrix 2, it is possible to suppress the deterioration of magnetic properties due to oxidation of the soft magnetic metal particles 3 and to fix the soft magnetic metal particles 3, thereby achieving good radio wave absorption characteristics and preventing the detachment of the soft magnetic metal particles 3.

[0029] In the radio wave absorber 1 according to Embodiment 1, the melting temperature of the glass matrix 2 is preferably 450°C or more and 600°C or less, more preferably 450°C or more and 580°C or less, and even more preferably 450°C or more and 550°C or less. If the melting temperature of the glass matrix 2 exceeds 600°C, the soft magnetic metal particles 3 may oxidize, which may result in deterioration of the magnetic properties. On the other hand, if the melting temperature of the glass matrix 2 is less than 450°C, it becomes approximately the same temperature as the decomposition temperature of the molding resin binder used in the manufacturing process of the radio wave absorber 1. In this case, during the firing process for melting the glass, decomposition gases of the resin binder are generated after the glass has melted, which may cause blistering or defects.

[0030] Furthermore, when used as a radio wave absorber 1 for high-frequency circuits, it is preferable that the dielectric constant of the radio wave absorber 1 be low, from the viewpoint of suppressing distortion of the electrical signal due to the electrical coupling between the electrical signal flowing through the high-frequency circuit and the capacitance of the radio wave absorber 1, i.e., degradation of signal quality. For this reason, it is preferable to select a glass matrix 2 with a relative permittivity of 20 or less at any frequency in the microwave band, and it is even more preferable to select a glass matrix 2 with a relative permittivity of 15 or less. In addition, the relative permittivity of the radio wave absorber 1 using the above-described glass matrix 2 is preferably 40 or less, more preferably 35 or less, and even more preferably 30 or less. If the relative permittivity of the radio wave absorber 1 exceeds 40, the reflection component due to distortion of the electrical signal increases, which may increase the power loss of the high-frequency circuit.

[0031] Furthermore, it is preferable that the glass matrix 2 is substantially free of alkali metal components. The absence of alkali metal components offers the advantage of improved reliability, such as moisture resistance.

[0032] In the radio wave absorber 1 according to Embodiment 1, one or more materials selected from the group consisting of bismuth-based glass, zinc-based glass, and silica-based glass can be used as an example of the glass matrix 2. In particular, bismuth-based glass is suitable as the glass matrix 2 for immobilizing soft magnetic metal particles 3 because it is easy to select an appropriate melting temperature and it easily becomes low viscosity when melted.

[0033] In the radio wave absorber 1 according to Embodiment 1, the difference in specific gravity between the soft magnetic metal particles 3 and the glass matrix 2 is preferably 3 or less, more preferably 2 or less, and even more preferably 1.5 or less. By setting the difference in specific gravity between the soft magnetic metal particles 3 and the glass matrix 2 within the above range, separation due to the difference in specific gravity between the soft magnetic metal particles 3 and the glass powder that is the raw material for the glass matrix 2 becomes less likely when the slurry, which is an intermediate in the manufacturing process of the radio wave absorber 1, is prepared. Therefore, it is possible to obtain a radio wave absorber 1 with a more uniform composition, and the advantage of reducing variations in radio wave absorption performance is obtained. Generally, the specific gravity of glass tends to be lower than that of soft magnetic metal particles 3. Therefore, in order to set the difference in specific gravity between the soft magnetic metal particles 3 and the glass matrix 2 within the above range, it is necessary to select a glass with a relatively high specific gravity. From this viewpoint as well, bismuth-based glass is suitable for the radio wave absorber 1 according to Embodiment 1.

[0034] The radio wave absorber 1 according to Embodiment 1 exhibits excellent radio wave absorption performance in the microwave band. Generally, a radio wave absorber 1 using a magnetic material absorbs radio waves by converting the energy of the radio waves incident on the radio wave absorber 1 into heat due to magnetic loss in the target frequency band. For this reason, a large magnetic loss in the microwave band is preferable. The radio wave absorber 1 according to Embodiment 1 preferably has a magnetic loss of 0.8 or more at any frequency in the microwave band, and more preferably 1 or more. It is also preferable to have a similarly large magnetic loss in frequency bands other than the arbitrary frequency, and it is more preferable to have a broad and large magnetic loss across a wide frequency band in the microwave band. Having a broad and large magnetic loss across a wide frequency band results in a radio wave absorber 1 that can handle a wide range of frequencies.

[0035] According to Embodiment 1, the above configuration provides a radio wave absorber 1 that has excellent radio wave absorption performance in the microwave band and does not lose its soft magnetic metal particles 3.

[0036] The radio wave absorber 1 according to Embodiment 1 can be manufactured using methods known in the art. For example, the radio wave absorber 1 according to Embodiment 1 can be manufactured as follows.

[0037] First, a slurry is prepared by mixing soft magnetic metal particles 3, glass powder, a dispersant, a binder, and water. The average particle size of the soft magnetic metal particles 3 is preferably 1 μm or more and less than 10 μm, more preferably 3 μm or more and 8 μm or less, and even more preferably 4 μm or more and 6 μm or less. In particular, if the average particle size of the soft magnetic metal particles 3 is 10 μm or more, the soft magnetic metal particles 3 tend to settle in the slurry, making it difficult to uniformly mix the soft magnetic metal particles 3 with the glass powder. The average particle size of the glass powder is not particularly limited, but is preferably 0.05 μm or more and 8 μm or less, more preferably 0.1 μm or more and 5 μm or less. In particular, if the average particle size of each of the above raw material powders is less than 0.05 μm, the powder will aggregate strongly, and the aggregate will not break down during mixing and dispersion after compounding, making uniform mixing difficult. On the other hand, if the average particle size of the glass powder exceeds 8 μm, the glass may not melt easily in the firing process for melting the glass.

[0038] At this time, the weight ratio of soft magnetic metal particles 3 to glass powder is determined such that the ratio of the volume of soft magnetic metal particles 3 to the volume of glass powder, which is the raw material for the glass matrix 2, is 0.3 to 0.45 when the sum of the volumes of soft magnetic metal particles 3 and glass powder is taken as 1. By using this volume ratio of soft magnetic metal particles 3 to glass powder, a radio wave absorber 1 is obtained that has excellent radio wave absorption performance in the microwave band and suppresses the shedding of soft magnetic metal particles 3 constituting the radio wave absorber 1 compared to conventional methods.

[0039] The dispersant is not particularly limited as long as it can be used in aqueous slurries, and any known in the art can be used. Examples of dispersants include anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Examples of anionic surfactants include alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts, polycarboxylic acids, alkylbenzene sulfonates, reactive surfactants, fatty acid salts, and naphthalene sulfonate formalin condensates. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkyl betaine and alkylamine oxide. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene fatty acid castor oil, polyoxyethylene alkylamines, and alkyl alkanolamides. These can be used individually or in combination of two or more.

[0040] The binder is not particularly limited, and any known in the art can be used. Examples of binders include acrylic, cellulose, polyvinyl alcohol, polyvinyl acetal, urethane, and vinyl acetate resins. These can be used individually or in combination of two or more.

[0041] The type of water used is not particularly limited; pure water, reverse osmosis (RO) water, deionized water, etc., can be used.

[0042] The mixing method used to prepare the slurry is not particularly limited and can be carried out using methods known in the art. Examples of mixing methods include those using a kneader, ball mill, planetary ball mill, compounding mixer, or bead mill.

[0043] Next, the slurry is granulated to prepare granulated powder. The granulation method is not particularly limited and can be carried out in accordance with methods known in the art. For example, granulated powder can be obtained by spray drying using a spray dryer or the like. The conditions for spray drying can be adjusted as appropriate depending on the equipment used and are not particularly limited.

[0044] Subsequently, the granulated powder is filled into a mold having the desired shape, for example, a rectangular parallelepiped, and a molded body is produced by pressure molding. The pressure molding method is not particularly limited and can be carried out in accordance with methods known in the art. Examples of pressure molding methods include CIP (Cold Isostatic Pressing) molding, WIP (Warm Isostatic Pressing) molding, and uniaxial pressure molding.

[0045] The pressure applied during pressure molding can be adjusted as appropriate depending on the type of granulated powder and the equipment used, and is not particularly limited, but is generally in the range of 30 MPa to 500 MPa.

[0046] Next, the molded body is fired. The firing method is not particularly limited and can be carried out in accordance with methods known in the art. For example, the molded body can be fired in an air atmosphere. At this time, degreasing of the binder contained in the molded body is also carried out simultaneously. The firing temperature must be such that the soft magnetic metal particles 3 do not oxidize and the glass powder melts, preferably between 450°C and 600°C, more preferably between 450°C and 580°C, and even more preferably between 450°C and 550°C. If the firing temperature exceeds 600°C, the soft magnetic metal particles 3 may oxidize, and the magnetic properties may deteriorate.

[0047] To shape the molded body after firing, the surface of the molded body may be ground. The grinding method is not particularly limited and can be carried out in accordance with methods known in the art. Examples of grinding methods include grinding using a diamond cutting tool. In addition, a barrel polishing step for chamfering the molded body may be added to suppress chipping and other breakage in the molded body after firing. The shape of the radio wave absorber 1 is not particularly limited and can be changed as appropriate depending on the application. In particular, when the grounding space is limited, such as when it is attached to the inside of a case cover for a high-density mounted high-frequency circuit, a thin shape is preferable, and the thickness is preferably 0.5 mm to 2 mm, more preferably 0.5 mm to 1.5 mm, and even more preferably 0.5 mm to 1 mm. If the thickness is 0.5 mm or less, the mechanical strength of the radio wave absorber 1 will be low, and the handling performance may be severely reduced. Furthermore, if the thickness is 0.5 mm or less, the radio wave absorption performance may be reduced because the thickness is too thin.

[0048] The radio wave absorber 1 according to Embodiment 1, manufactured as described above, is a radio wave absorber 1 that has excellent radio wave absorption performance in the microwave band and does not have any detachment of soft magnetic metal particles 3.

[0049] Embodiment 2. A high-frequency module according to Embodiment 2 will now be described. Figure 6 is a schematic cross-sectional view showing an example of the configuration of a high-frequency module using a radio wave absorber according to Embodiment 2. As shown in Figure 6, the high-frequency module 10, in one example, includes a ceramic substrate 11, which is a substrate, and a high-frequency circuit case 21. The ceramic substrate 11 is, in one example, a multilayer dielectric substrate on which elements 12 are mounted, including a high-frequency circuit 12a on which a semiconductor bare chip is mounted and a circuit 12b on which a semiconductor chip is mounted. The high-frequency circuits 12a and 12b are electrically connected to a circuit pattern 13 formed on the ceramic substrate 11 via bonding wires 14.

[0050] The high-frequency circuit case 21 comprises a case body 22 and a high-frequency circuit case cover 23. The case body 22 is made of cylindrical metal. The case body 22 is a cylindrical member provided along the outer circumference of the element mounting surface 11a, which is the surface on the ceramic substrate 11 on which the elements 12 are mounted, and is mounted on the ceramic substrate 11. As a result, the elements 12 on the element mounting surface 11a are surrounded by the cylindrical case body 22. In other words, the members constituting the case body 22 are provided perpendicular to the element mounting surface 11a. The high-frequency circuit case cover 23 is made of plate-shaped metal and is provided to close the opening of the cylindrical case body 22 on the side opposite to the ceramic substrate 11. In one example, the high-frequency circuit case cover 23 is attached to the case body 22. In other words, by attaching the high-frequency circuit case cover 23 to close one of the openings of the cylindrical case body 22, a metal high-frequency circuit case 21 is constructed that covers the elements 12 on the element mounting surface 11a of the ceramic substrate 11.

[0051] The high-frequency module 10 further includes solder material 24, a metal layer 25, and a radio wave absorber 1 on the inner surface of the high-frequency circuit case 21, specifically on the inner surface of the high-frequency circuit case cover 23. The solder material 24, metal layer 25, and radio wave absorber 1 are provided on the inner surface of the high-frequency circuit case cover 23 at positions opposite to the high-frequency circuit 12a. In other words, the solder material 24, metal layer 25, and radio wave absorber 1 are provided at positions on the inner surface of the high-frequency circuit case 21 opposite to the position where the high-frequency circuit 12a is located.

[0052] The solder material 24 serves to bond the metal layer 25 to the inner surface of the high-frequency circuit case cover 23. The metal layer 25 is a component for installing the radio wave absorber 1. The radio wave absorber 1 has the configuration described in Embodiment 1. The method of bonding the radio wave absorber 1 to the high-frequency circuit case cover 23 is not particularly limited, and known methods such as bonding with epoxy adhesive, bonding with solder, and bonding with sintered metal can be applied. When bonding with a metal-based bonding material such as the sintered metal described above, a metal layer can be provided in advance on the surface of the radio wave absorber 1 to be bonded by forming a metallized layer in order to improve bonding performance. Also, when bonding with epoxy adhesive, it is not necessary to provide a metal layer on the surface of the radio wave absorber 1 to be bonded.

[0053] The high-frequency module 10 according to Embodiment 2, which has the structure described above, is a high-frequency module 10 that is free from malfunctions due to noise in the microwave band and is also free from short-circuit failures in the circuit due to the detachment of soft magnetic metal particles 3 constituting the radio wave absorber 1. [Examples]

[0054] The details of the radio wave absorber 1 according to Embodiment 1 will be described below with reference to Examples 1 to 9 and Comparative Examples 1 to 4, but the contents of this disclosure are not limited thereto.

[0055] Table 1 shows the material composition and characterization results of the radio wave absorbers for Examples 1 to 9 and Comparative Examples 1 to 4. In Examples 1 to 9 and Comparative Examples 1 to 4, bismuth-based glass powder with an average particle size of 2.5 μm and a specific gravity of 5.7 was used as the raw material for the glass matrix 2.

[0056] [Table 1]

[0057] Table 2 details the soft magnetic metal particles used as raw materials for the radio wave absorbers in Examples 1 to 9 and Comparative Examples 1 to 4. Here, six types of soft magnetic metal particles A to F are used, all of which are Fe-Si-Cr and have different average particle sizes. Specifically, the average particle size of soft magnetic metal particle A is 1 μm, the average particle size of soft magnetic metal particle B is 3 μm, the average particle size of soft magnetic metal particle C is 5 μm, the average particle size of soft magnetic metal particle D is 8 μm, the average particle size of soft magnetic metal particle E is 0.5 μm, and the average particle size of soft magnetic metal particle F is 10 μm. Furthermore, the shape of the soft magnetic metal particles A to F is approximately spherical, or a spherical shape stretched in one direction.

[0058] [Table 2]

[0059] (Example 1) Example 1 involves a volume ratio of 4.5:5.5 between soft magnetic metal particles 3 and glass matrix 2. 100 parts by mass of bismuth-based glass powder and 99.04 parts by mass of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm as shown in Table 1, are mixed to produce a mixed powder. To 100 parts by mass of this mixed powder, 1 part by mass of a polycarboxylic acid-based dispersant, 1 part by mass of polyvinyl alcohol as a binder, and 107.18 parts by mass of water are added. Next, the mixture of powder, dispersant, binder, and water is mixed in a ball mill for approximately 5 hours to produce a slurry. The prepared slurry is spray-dried in a spray dryer to produce granulated powder. The granulated powder is molded using a mold and a uniaxial press to produce a rectangular parallelepiped-shaped molded body. The molded body is heat-treated at 550°C for 30 minutes in an air atmosphere. Then, the fired molded body is ground down to a thickness of 1.5 mm to produce the radio wave absorber 1 for evaluation of Example 1.

[0060] (Example 2) Example 2 involves a volume ratio of 4:6 between soft magnetic metal particles 3 and glass matrix 2. The radio wave absorber 1 for evaluation in Example 2 is prepared in the same manner as in Example 1, except that the amount of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm (as shown in Table 1), is set to 80.70 parts by mass.

[0061] (Example 3) Example 3 involves a volume ratio of 3.5:6.5 between soft magnetic metal particles 3 and glass matrix 2. The radio wave absorber 1 for evaluation in Example 3 is prepared in the same manner as in Example 1, except that the amount of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm as shown in Table 1, is set to 65.18 parts by mass.

[0062] (Example 4) Example 4 involves a volume ratio of 3:7 between soft magnetic metal particles 3 and glass matrix 2. The radio wave absorber 1 for evaluation in Example 4 is prepared in the same manner as in Example 1, except that the amount of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm as shown in Table 1, is set to 51.88 parts by mass.

[0063] (Example 5) Example 5 involves a case where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 4:6. Using soft magnetic metal particles A, which have a specific gravity of 6.9 and an average particle size of 1 μm as shown in Table 1, the radio wave absorber 1 for evaluation in Example 5 is prepared in the same manner as in Example 1, except that the blending amount is 80.70 parts by mass.

[0064] (Example 6) Example 6 involves a case where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 4:6. Using soft magnetic metal particles B, which have a specific gravity of 6.9 and an average particle size of 3 μm as shown in Table 1, the evaluation radio wave absorber 1 for Example 6 is prepared in the same manner as in Example 1, except that the blending amount is 80.70 parts by mass.

[0065] (Example 7) Example 7 involves a case where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 4:6. Using soft magnetic metal particles D, which have a specific gravity of 6.9 and an average particle size of 8 μm as shown in Table 1, the amount of which is 80.70 parts by mass is used to prepare the radio wave absorber 1 for evaluation of Example 7 in the same manner as in Example 1.

[0066] (Example 8) Example 8 involves a case where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 4:6. The radio wave absorber 1 for evaluation in Example 8 is prepared in the same manner as in Example 1, except that the amount of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm as shown in Table 1, is 80.70 parts by mass and is heat-treated at 520°C for 30 minutes.

[0067] (Example 9) Example 9 involves a case where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 4:6. The radio wave absorber 1 for evaluation of Example 9 is prepared in the same manner as in Example 1, except that the amount of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm as shown in Table 1, is 80.70 parts by mass and is heat-treated at 510°C for 30 minutes.

[0068] (Comparative Example 1) Comparative Example 1 is a case where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 4:6. Using soft magnetic metal particles E with a specific gravity of 6.9 and an average particle size of 0.5 μm as shown in Table 1, the radio wave absorber 1 for evaluation of Comparative Example 1 is prepared in the same manner as in Example 1, except that the blending amount is 80.70 parts by mass.

[0069] (Comparative Example 2) Comparative Example 2 involves a volume ratio of 4:6 between soft magnetic metal particles 3 and glass matrix 2. Using soft magnetic metal particles F with a specific gravity of 6.9 and an average particle size of 10 μm as shown in Table 1, the radio wave absorber 1 for evaluation of Comparative Example 2 is prepared in the same manner as in Example 1, except that the blending amount is 80.70 parts by mass.

[0070] (Comparative Example 3) Comparative Example 3 is the case where the volume ratio of soft magnetic metal particles 3 and glass matrix 2 is 5:5. Except that the amount of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm as shown in Table 1, is set to 121.05 parts by mass, a radio wave absorber 1 for evaluation of Comparative Example 3 is prepared in the same manner as in Example 1.

[0071] (Comparative Example 4) Comparative Example 4 is the case where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 2.5:7.5. The radio wave absorber 1 for evaluation of Comparative Example 4 is prepared in the same manner as in Example 1, except that the amount of soft magnetic metal particles C, which have a specific gravity of 6.9 and an average particle size of 5 μm as shown in Table 1, is set to 40.35 parts by mass.

[0072] The radio wave attenuation of the radio wave absorber 1 obtained in Examples 1 to 9 and Comparative Examples 1 to 4 is evaluated as follows. Figure 7 is a schematic cross-sectional view showing an example of the configuration of a resonator for evaluating radio wave attenuation. The resonator 30 for evaluating radio wave attenuation is a resonator for measuring the radio wave attenuation of the radio wave absorber 1. The resonator 30 for evaluating radio wave attenuation has an airtight configuration in which a metal cover 34 is attached to a metal resonator body 31. The resonator 30 for evaluating radio wave attenuation is spatially designed to have a resonance point at any frequency. The radio wave absorber 1, on which a metal layer 36 is formed, is attached to the cover 34 by soldering material 35. In addition, signal pins 32 and 33 are inserted from the outside into the bottom of the resonator body 31. Signal pin 32 is connected to a radio wave transmitter (not shown). Signal pin 33 is connected to a radio wave detector (not shown). Using the resonator 30 for evaluating radio wave attenuation configured as described above, the S-parameters, which are the transmission characteristics of radio waves between signal pin 32 and signal pin 33, are evaluated, and the transmission loss is expressed in dB to evaluate the radio wave attenuation of each radio wave absorber 1.

[0073] Furthermore, the presence or absence of detachment of soft magnetic metal particles 3 in the radio wave absorbers 1 obtained in Examples 1 to 9 and Comparative Examples 1 to 4 will be evaluated as follows. 15 ml of ethanol will be placed in a glass sample bottle with a capacity of 50 ml, and the samples of radio wave absorbers 1 from Examples 1 to 9 and Comparative Examples 1 to 4 will be placed in it. An ultrasonic cleaner will be used to apply 40 kHz ultrasound with an output of 40 W for 20 minutes to the radio wave absorbers 1 in the sample bottle. After the ultrasound application, the radio wave absorbers 1 will be removed from the sample bottle, and the presence or absence of detached particles will be visually checked. Next, the sample of radio wave absorber 1 will be placed in the sample bottle again, and 40 kHz ultrasound with an output of 80 W will be applied for 20 minutes. After the ultrasound application, the radio wave absorbers 1 will be removed from the sample bottle, and the presence or absence of detached particles will be visually checked. Table 1 shows the results, with an "X" indicating cases where the soft magnetic metal particles 3 detached with 40W ultrasonic waves, a circle indicating cases where they did not detach, and a double circle indicating cases where the soft magnetic metal particles 3 did not detach even with 80W ultrasonic waves.

[0074] Furthermore, the porosity of the radio wave absorber 1 obtained in Examples 1 to 9 and Comparative Examples 1 to 4 is calculated using equation (1). Here, W in equation (1) d ρ is the weight (g) of the radio wave absorber 1 dried at 150°C for 2 hours, and L, W, and T are the length, width, and height (cm) of the rectangular radio wave absorber 1, respectively, and measured values ​​are used. t This is the theoretical density (g / cm³) of the radio wave absorber 1. 3 The results of each of the above evaluations are shown in Table 1.

[0075] As shown in Table 1, the radio wave absorbers 1 of Examples 1 to 9 exhibit excellent radio wave absorption performance in radio wave attenuation evaluations using a resonator. Furthermore, no shedding of soft magnetic metal particles 3 occurs. In particular, in Examples 2 and 3, where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is in the range of 4:6 to 3.5:6.5, the radio wave absorber 1 maintains excellent radio wave absorption performance while further reducing the likelihood of shedding of soft magnetic metal particles 3. In other words, by setting the ratio of the volume of soft magnetic metal particles 3 to 0.4 (when the sum of the volumes of soft magnetic metal particles 3 and glass matrix 2 is 1) to 0.35 or more, or by setting the ratio of the volume of glass matrix 2 to 0.65 or more, it is possible to obtain a radio wave absorber 1 that maintains excellent radio wave absorption performance while further reducing the likelihood of shedding of soft magnetic metal particles 3. On the other hand, focusing on the average particle size of the soft magnetic metal particles 3, a radio wave absorber 1 was obtained in which the shedding of soft magnetic metal particles 3 was suppressed while maintaining good radio wave absorption characteristics in the range of 1 μm to less than 10 μm. In particular, in Examples 2, 6, and 7, where the average particle size is in the range of 3 μm to 8 μm, the radio wave absorber 1 was obtained in which the shedding of soft magnetic metal particles 3 was further suppressed while maintaining excellent radio wave absorption performance.

[0076] In contrast, in Comparative Example 1, the radio wave absorber 1 has very fine soft magnetic metal particles 3 with an average particle size of 0.5 μm, resulting in the detachment of soft magnetic metal particles 3. This is thought to be due to insufficient immobilization by the glass matrix 2 because of the large specific surface area of ​​the soft magnetic metal particles 3. Conversely, in Comparative Example 2, where the average particle size of the soft magnetic metal particles 3 is large at 10 μm, sedimentation of the soft magnetic metal particles 3 occurred during slurry preparation, an intermediate in the manufacturing process, making it impossible to produce a radio wave absorber 1 with a uniform composition. Therefore, the evaluation results in Table 1 are blank.

[0077] Furthermore, in Comparative Example 3, where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 5:5, the soft magnetic metal particles 3 fall off because there is too little glass component to fix the soft magnetic metal particles 3. On the other hand, in Comparative Example 4, where the volume ratio of soft magnetic metal particles 3 to glass matrix 2 is 2.5:7.5, the radio wave absorption performance is significantly reduced because the content of soft magnetic metal particles 3 that absorb radio waves is too low.

[0078] As can be seen from the results above, according to Embodiment 1, the radio wave absorber 1 has excellent radio wave absorption performance in the microwave band and does not lose its soft magnetic metal particles 3.

[0079] Furthermore, by using the radio wave absorber 1 according to Embodiment 1, it is possible to realize a high-frequency module 10 that is free from malfunctions due to noise in the microwave band and free from short-circuit failures due to the detachment of soft magnetic metal particles 3.

[0080] The configurations shown in the above embodiments are merely examples, and can be combined with other known technologies. It is also possible to omit or modify parts of the configuration without departing from the gist of the invention.

[0081] The various aspects of this disclosure are summarized below as an appendix.

[0082] [Note 1] A glass matrix that maintains its shape, Soft magnetic metal particles that have microwave band radio wave absorption performance due to magnetic loss, The composite material comprises soft magnetic metal particles dispersed in the glass matrix, The average particle size of the soft magnetic metal particles is 1 μm or more and less than 10 μm. A radio wave absorber characterized in that the ratio of the volume of the soft magnetic metal particles to the volume of the glass matrix, when the sum of the volumes of the soft magnetic metal particles and the glass matrix is ​​taken as 1, is 0.3 or more and 0.45 or less. [Note 2] The radio wave absorber according to Appendix 1, characterized in that the difference in specific gravity between the soft magnetic metal particles and the glass matrix is ​​3 or less. [Note 3] The soft magnetic metal particles consist of one or more materials selected from the group consisting of Fe-Si-Cr alloy, Fe-Si alloy, Fe-Si-Al alloy, and Ni-Fe alloy. The radio wave absorber according to Appendix 1 or 2, characterized in that the glass matrix is ​​one or more materials selected from the group consisting of bismuth-based glass, zinc-based glass, and silica-based glass. [Note 4] The radio wave absorber according to any one of the appendices 1 to 3, characterized in that the soft magnetic metal particles have a spherical shape, an ellipsoidal shape, a rectangular parallelepiped shape with rounded corners, and a shape in which a portion of at least one of the spherical shape, ellipsoidal shape, and rectangular parallelepiped shape with rounded corners is stretched in one direction. [Note 5] It further contains voids with a porosity of 15% or less inside, The radio wave absorber according to any one of the appendices 1 to 4, characterized in that the average size of the void is 2 times or less the average particle size of the soft magnetic metal particles. [Note 6] The radio wave absorber according to any one of the appendices 1 to 5, characterized in that the magnetic loss of the composite material at any frequency in the microwave band is 1 or more. [Note 7] The radio wave absorber according to any one of the appendices 1 to 6, characterized in that the relative permittivity of the glass matrix at any frequency in the microwave band is 20 or less. [Note 8] A substrate on which elements including high-frequency circuits are mounted, A metal high-frequency circuit case is provided on the surface of the substrate on which the element is arranged, so as to cover the element. A radio wave absorber described in any one of the appendices 1 to 7 is provided on the inner surface of the high-frequency circuit case opposite to the position where the high-frequency circuit is arranged, A high-frequency module characterized by comprising the following features. [Explanation of Symbols]

[0083] 1. Radio wave absorber, 2. Glass matrix, 3. Soft magnetic metal particles, 4. Air gap, 10. High-frequency module, 11. Ceramic substrate, 11a. Element mounting surface, 12. Element, 12a. High-frequency circuit, 12b. Circuit, 13. Circuit pattern, 14. Bonding wire, 21. High-frequency circuit case, 22. Case body, 23. Cover for high-frequency circuit case, 24, 35. Solder material, 25, 36. Metal layer, 30. Resonator for radio wave attenuation evaluation, 31. Resonator body, 32, 33. Signal pins, 34. Cover.

Claims

1. A glass matrix that maintains its shape, Soft magnetic metal particles that have microwave band radio wave absorption performance due to magnetic loss, The composite material comprises soft magnetic metal particles dispersed in the glass matrix, The average particle size of the soft magnetic metal particles is 1 μm or more and less than 10 μm. A radio wave absorber characterized in that the ratio of the volume of the soft magnetic metal particles to the volume of the glass matrix, when the sum of the volumes of the soft magnetic metal particles and the glass matrix is ​​taken as 1, is 0.3 or more and 0.45 or less.

2. The radio wave absorber according to claim 1, characterized in that the difference in specific gravity between the soft magnetic metal particles and the glass matrix is ​​3 or less.

3. The soft magnetic metal particles consist of one or more materials selected from the group consisting of Fe-Si-Cr alloy, Fe-Si alloy, Fe-Si-Al alloy, and Ni-Fe alloy. The radio wave absorber according to claim 1, characterized in that the glass matrix is ​​one or more materials selected from the group consisting of bismuth-based glass, zinc-based glass, and silica-based glass.

4. The radio wave absorber according to claim 1, characterized in that the soft magnetic metal particles have a spherical shape, an ellipsoidal shape, a rectangular parallelepiped shape with rounded corners, and a shape in which a portion of at least one of the spherical shape, ellipsoidal shape, and rectangular parallelepiped shape with rounded corners is stretched in one direction.

5. It further contains voids with a porosity of 15% or less inside, The radio wave absorber according to claim 1, characterized in that the average size of the void is 2 times or less the average particle size of the soft magnetic metal particles.

6. The radio wave absorber according to claim 1, characterized in that the magnetic loss of the composite material at any frequency in the microwave band is 1 or more.

7. The radio wave absorber according to claim 1, characterized in that the relative permittivity of the glass matrix at any frequency in the microwave band is 20 or less.

8. A substrate on which elements including high-frequency circuits are mounted, A metal high-frequency circuit case is provided on the surface of the substrate on which the element is arranged, so as to cover the element. A radio wave absorber according to any one of claims 1 to 7, provided on the inner surface of the high-frequency circuit case opposite to the position where the high-frequency circuit is arranged, A high-frequency module characterized by comprising the following features.

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