JP2018154541A - Radiowave absorber, method for producing the same, and high frequency module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radiowave absorber, excellent in radiowave absorption performance in a gigahertz band, showing no anisotropy in the radiowave absorption performance, and capable of absorbing radiowaves incident from various directions.SOLUTION: This invention relates to a radiowave absorber 1, comprising a sintered body of M-type hexagonal ferrite expressed by compositional formula: BaFe(TiCu)O(X is 2.5 to 3.5), wherein: an orientation degree of ferrite crystalline particles measured by Lotgering method is 0.2 or less, preferably, 0.04 to 0.15; and the sintered body has a thickness of 0.5 to 3 mm. This invention further relates to a method for producing the radiowave absorber 1, including: mixing barium carbonate powder, iron oxide powder, titanium oxide powder and copper oxide powder together, to make a mixture; using the mixture, a binder, and water to make a slurry; spray-drying the slurry to make a granulated substance having an average particle diameter of 0.05 to 8 μm; subjecting the granulated substance to compression molding, to obtain a molded body; and calcining the molded body to prepare the sintered body of M-type hexagonal ferrite.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radio wave absorber, a manufacturing method thereof, and a high frequency module.

  In the field of electronic equipment, in order to reduce size and increase performance, higher frequencies and higher densities are advancing, and countermeasures against electromagnetic noise that causes malfunction of the equipment are an important issue. In particular, high-frequency devices employ a structure in which a high-frequency circuit is housed in a metal case for the purpose of protecting the mounted semiconductor elements and circuit conductors and preventing mutual interference with external circuits. For this reason, the high frequency noise generated in the metal case may resonate at a specific frequency corresponding to the cavity size in the metal case, causing problems such as malfunction of the circuit due to electromagnetic interference in the metal case. In order to suppress electromagnetic interference in these metal cases, a radio wave absorber using a magnetic material is installed in the metal case, and unnecessary radio waves (high frequency noise) generated in the metal case due to the magnetic loss of the radio wave absorber. The method of absorbing is taken.

  In general, spinel ferrite materials are often used as radio wave absorber materials. Spinel ferrite material has low permeability on the high-frequency side and has sufficient absorption performance for radio waves in the gigahertz (GHz) band even though it is effective in absorbing radio waves in the megahertz (MHz) band. Not done. Therefore, the spinel type ferrite material is not suitable as a radio wave absorber for a high frequency device operating in the gigahertz band. In particular, in the 20 GHz band used for high-frequency communication applications, spinel ferrite materials cannot be expected to suppress high-frequency noise as a radio wave absorber.

  Therefore, Patent Document 1 proposes magnetoplumbite type hexagonal ferrite as a material of a radio wave absorber corresponding to the gigahertz band. Patent Document 2 proposes a ferrite sintered body having a high permeability in a specific direction and anisotropy in radio wave absorption performance by orienting crystal grains of magnetoplumbite type hexagonal ferrite in one direction. Has been.

JP 11-354972 A JP 2003-55038 A (Patent No. 4025521)

  However, the radio wave absorber using the magnetoplumbite-type hexagonal ferrite proposed in Patent Document 1 does not have a concept regarding a sintered body structure or crystal orientation that affects the radio wave absorption performance. , May not exhibit sufficient radio wave absorption performance. In addition, the magnetoplumbite-type hexagonal ferrite described in Patent Document 2 has anisotropy in radio wave absorption performance by orienting crystal grains in one direction, so that radio waves are reflected in a metal case. In applications where the light is incident on the radio wave absorber from various directions, there is a problem that sufficient radio wave absorption performance may not be exhibited.

The present invention has been made to solve the above problems, and has excellent radio wave absorption performance in the gigahertz band (20 GHz band) and has no anisotropy in radio wave absorption performance, and is incident from various directions. An object of the present invention is to provide a radio wave absorber capable of absorbing a generated radio wave and a method for manufacturing the same.
Another object of the present invention is to provide a high-frequency module capable of preventing malfunctions due to high-frequency noise generated in a metal case.

  A radio wave absorber using a magnetic material utilizes the radio wave absorption effect due to magnetic loss. Therefore, the radio wave absorber is required to have a large magnetic loss in a target frequency band (frequency band of noise to be absorbed). Further, when the radio wave absorber has anisotropy in the radio wave absorption performance, an effect of absorbing radio waves incident from a specific direction is exhibited, but an effect of absorbing radio waves incident from other directions cannot be expected. Therefore, sufficient radio wave absorption performance cannot be exhibited when radio waves are incident from various directions, such as when a radio wave absorber is installed in a metal case of a high frequency module.

  Therefore, as a result of earnest research to solve the above problems, the present inventors have made the electromagnetic wave absorber a magnetoplumbite type (hereinafter abbreviated as M type) hexagonal ferrite having a specific composition, Excellent radio wave absorption performance in the gigahertz band, and excellent radio wave absorption performance for radio waves incident from various directions by sintering crystal grains of M-type hexagonal ferrite without being oriented in a specific direction. The inventors have found out that the present invention can be exhibited and have completed the present invention.

That is, the present invention relates to an M-type hexagonal ferrite having the composition formula: BaFe _12-X (Ti _0.5 Cu _0.5 ) _X O ₁₉ (where X is 2.5 or more and 3.5 or less). A radio wave absorber comprising a sintered body and having an orientation degree of ferrite crystal particles evaluated by a Lottgering method of 0.2 or less.
In addition, the present invention is a high frequency module comprising the above radio wave absorber inside a metal case that houses a high frequency circuit.
Furthermore, this invention mixes raw material barium carbonate powder, iron oxide powder, titanium oxide powder, and copper oxide powder, so that the composition formula: BaFe _12-X (Ti _0.5 Cu _0.5 ) _X A step of preparing a raw material powder mixture in which components are adjusted so that an M type hexagonal ferrite of O ₁₉ (wherein X is 2.5 or more and 3.5 or less) is formed, and the raw material powder mixture together with a binder A step of preparing a granulated product by mixing, a step of pressure-molding the granulated product to prepare a molded body, and a sintered body of M-type hexagonal ferrite by firing the molded body A process for manufacturing a radio wave absorber.

  ADVANTAGE OF THE INVENTION According to this invention, the electromagnetic wave absorber which is excellent in the electromagnetic wave absorption performance in a gigahertz band, has no anisotropy in an electromagnetic wave absorption performance, and can absorb the electromagnetic wave which injected from various directions can be provided. Further, according to the present invention, it is possible to provide a high frequency module that does not cause a malfunction such as a malfunction due to high frequency noise in the gigahertz band. Furthermore, according to the present invention, a radio wave absorber that is excellent in radio wave absorption performance in the gigahertz band, has no anisotropy in radio wave absorption performance, and can absorb radio waves incident from various directions is manufactured with high productivity. A method can be provided.

3 is a schematic cross-sectional view of the radio wave absorber according to Embodiment 1. FIG. 3 is a flowchart of a manufacturing process of the radio wave absorber according to the first embodiment. 6 is a schematic cross-sectional view of a high-frequency module according to Embodiment 2. FIG. It is a schematic cross section which shows the structure of the resonator for measuring a radio wave attenuation. It is a figure which shows the relationship of the orientation degree (f value) of the M-type hexagonal ferrite particle with respect to the electromagnetic wave attenuation of a radio wave absorber. Is a diagram showing the relationship between the composition of the M-type hexagonal ferrite with respect to radio wave attenuation of a radio wave absorber _(the value of x of _{BaFe 12-x (Ti 0.5 Cu} 0.5) x O 19). It is a figure which shows the relationship of the thickness of the sintered compact with respect to the electromagnetic wave attenuation of a radio wave absorber.

Embodiment 1 FIG.
1 is a schematic cross-sectional view of a radio wave absorber according to Embodiment 1. FIG. As shown in FIG. 1, the radio wave absorber 1 according to Embodiment 1 includes plate-like crystal particles 2 having a composition in which part of iron of M-type hexagonal ferrite is replaced with titanium and copper. It consists of a sintered body of M-type hexagonal ferrite sintered in the direction.
Generally, a radio wave absorber made of a magnetic material absorbs radio waves by converting incident radio waves into heat by magnetic loss. At this time, the frequency band having the maximum magnetic loss is the absorption frequency band of the radio wave absorber. The matrix M-type hexagonal ferrite (BaFe ₁₂ O ₁₉ ) theoretically has an absorption frequency band in a high frequency band of 48 GHz band. By substituting a part of iron of this M-type hexagonal ferrite with a transition metal, the absorption frequency band can be controlled. The M-type hexagonal ferrite constituting the radio wave absorber according to Embodiment 1 has an absorption frequency band in the 20 GHz band by replacing part of iron with titanium and copper, and has excellent radio wave absorption performance. have. The M-type hexagonal ferrite has a crystal structure in which atoms of barium (Ba), iron (Fe), and oxygen (O) are arranged in a hexagonal column shape, and the hexagonal plane (C plane) of the crystal structure. It also has the property of having large radio wave absorption performance in the direction perpendicular to Furthermore, it has the property of being easy to grow crystals in the direction parallel to the hexagonal plane (C plane) by firing, and becoming plate-like crystal grains. Therefore, the plate-like crystal particles of M-type hexagonal ferrite have anisotropy in radio wave absorption performance and do not absorb radio waves incident from other than a specific direction when sintered in a state oriented in a specific direction. The radio wave absorber according to Embodiment 1 can absorb radio waves incident from various directions by sintering the plate-like crystal particles of M-type hexagonal ferrite in a state in which they are oriented in random directions. It has become.

The composition of the radio wave absorber according to the first embodiment is expressed by the formula: BaFe _12-X (Ti _0.5 Cu _0.5 ) _X O ₁₉ , and _X in the above formula is 2.5 or more and 3.5 or less. is there. By making the composition such that X in the above formula falls within the above range, the absorption frequency band can be controlled to the 20 GHz band. When X is less than 2.5 and when X is more than 3.5, the absorption frequency band is greatly shifted and there is no absorption effect in the 20 GHz band.

As described above, the radio wave absorber 1 according to the first embodiment is made of a sintered body in which the plate-like crystal particles 2 of M-type hexagonal ferrite are sintered in a random direction. At this time, the orientation of the crystal grains of the M-type hexagonal ferrite can be evaluated by the following Lottgering method using X-ray diffraction. When the crystal orientation plane of the wave absorber in the present invention is the (00l) plane, the degree of orientation (f value) by the Lottgering method is I (hkl) obtained by X-ray diffraction from the plane perpendicular to the thickness direction of the wave absorber. ) Each peak intensity is obtained, and the ratio of I (001) is shown with respect to the sum of these peak intensities, and is calculated by f given by the following equation.
f = (P−P ₀ ) / (1−P ₀ )
Here, P is represented by P = ΣI (001) / ΣI (hkl), and is the peak intensity obtained from the oriented sample. P ₀ is represented by P ₀ = ΣI ₀ (xyz) / ΣI ₀ (hkl), and is a peak intensity obtained from an unoriented sample. For M-type hexagonal ferrite, P ₀ = 0.05 is used. The degree of orientation (f value) of the ferrite crystal particles in the radio wave absorber according to Embodiment 1 is 0.2 or less, indicating that the ferrite crystal particles are sintered relatively randomly. When the ferrite crystal particles are completely random, the degree of orientation (f value) is 0, but it is difficult to make it completely random in actual production. However, if the degree of orientation (f value) is 0.2 or less, the radio wave absorption performance is not deteriorated, and sufficient radio wave absorption performance can be exhibited. On the other hand, the higher the degree of orientation (f value) exceeds 0.2, the more anisotropy occurs in radio wave absorption performance, absorbing only radio waves incident from a specific direction and absorbing radio waves incident from other directions. The nature of not doing becomes stronger. Therefore, a radio wave absorber having an orientation degree (f value) exceeding 0.2 does not exhibit sufficient radio wave absorption performance in applications where radio waves are incident from various directions. From the viewpoint of ease of manufacture and radio wave absorption performance, the orientation degree (f value) of the ferrite crystal particles is preferably 0.04 or more and 0.15 or less.

  What is necessary is just to change the magnitude | size of an electromagnetic wave absorber suitably according to a use. The thickness of the sintered body constituting the radio wave absorber is preferably in the range of 0.5 mm to 3 mm. If the thickness of the sintered body is within the above range, it is preferable because handleability is improved and radio wave absorption performance is further improved.

  The porosity of the sintered body is related to the mechanical strength of the radio wave absorber. That is, when the porosity of the sintered body exceeds 30%, the voids are connected inside the sintered body, and as a result, the mechanical strength of the radio wave absorber is lowered. Therefore, in a radio wave absorber with a porosity of the sintered body exceeding 30%, the radio wave absorber is likely to be cracked or cracked when installed in a high frequency module, and as a result, the radio wave absorber may drop off. There is sex. Therefore, the porosity of the sintered body is preferably 30% or less, more preferably 5% to 29%, from the viewpoint of obtaining desired mechanical strength.

Here, in this specification, the “porosity” of the sintered body constituting the radio wave absorber is obtained by using the measured values of the weight and dimensions (vertical, horizontal, height) of the rectangular parallelepiped sintered body, and the following formula: It can be calculated from
Porosity = {1- [WT _drying / (L × W × H) / ρ _theory ]} × 100
In the above formula, WT _drying is the weight (g) of the sintered body after drying at 150 ° C. for 2 hours, and L, W, and H are the longitudinal (cm) and horizontal of the rectangular parallelepiped shaped sintered body, respectively. (Cm) and height (cm), and the ρ _theory is the theoretical density (g / cm ³ ) of the sintered body.

Next, a method for manufacturing the radio wave absorber according to Embodiment 1 will be described. Hereinafter, an example of a manufacturing process of the radio wave absorber will be described with reference to the flowchart of FIG.
First, a raw material powder, barium carbonate (BaCO ₃ ) powder, iron oxide (Fe ₂ O ₃ ) powder, titanium oxide (TiO ₂ ) powder, and copper oxide (CuO) powder, are mixed to form a composition formula: BaFe ₁₂ A raw material powder mixture in which components were adjusted so that M-type hexagonal ferrite of _-X (Ti _0.5 Cu _0.5 ) _X O ₁₉ (where X is 2.5 or more and 3.5 or less) was produced. Prepare (S1). The mixing method in preparing the raw material powder mixture is not particularly limited, and can be performed according to a method known in the technical field. Examples of the mixing method include a method using a likai machine, a method using a dry attritor, and a method using a dry mixer.

  The average particle size of the raw material powders of barium carbonate powder, iron oxide powder, titanium oxide powder and copper oxide powder is not particularly limited, but is preferably 0.05 μm or more and 8 μm or less, and is 0.1 μm or more and 5 μm or less. It is more preferable. In particular, when the average particle diameter of each of the above raw material powders is less than 0.05 μm, the raw material powders are strongly aggregated, which may make it difficult to uniformly disperse after mixing. On the other hand, when the average particle diameter of each raw material powder is more than 8 μm, the formation reaction of M-type hexagonal ferrite in the firing step may not easily proceed. In the present specification, the average particle diameter of the raw material powder is a value measured by a laser diffraction particle size distribution measuring device.

  Subsequently, the raw material powder mixture obtained in S1, the binder and water are mixed to prepare a slurry (S2). A dispersant may be added to the slurry for the purpose of improving the dispersibility of the raw material powder. The mixing method at the time of preparing the slurry is not particularly limited, and can be performed according to a method known in the technical field. Examples of the mixing method include a method using a kneader, a ball mill, a planetary ball mill, a kneading mixer, a bead mill and the like. The raw material powder may be mixed with the binder and water in the slurry preparation step (S2) without passing through the step (S1) of preparing the raw material powder mixture.

The binder is not particularly limited, and those known in the technical field can be used. Examples of the binder include acrylic, cellulose, polyvinyl alcohol, polyvinyl acetal, urethane, and vinyl acetate resins. These binders may be used alone or in combination of two or more. Although the addition amount of a binder is not specifically limited, It is preferable that they are 0.5 mass part or more and 5 mass parts or less with respect to 100 mass parts of raw material powder mixtures.
It does not specifically limit as water, Pure water, RO water, deionized water, etc. can be used. What is necessary is just to adjust the addition amount of water suitably so that it may become the slurry physical property suitable for the below-mentioned granulation method.

  The dispersant is not particularly limited as long as it can be used for the aqueous slurry, and those known in the technical field can be used. Examples of dispersants include anions such as alkyl sulfates, polyoxyethylene alkyl ether sulfates, polycarboxylic acids, alkylbenzene sulfonates, reactive surfactants, fatty acid salts, and naphthalene sulfonate formalin condensates. Cationic surfactants; alkylamine salts, quaternary ammonium salts, amphoteric surfactants such as alkylbetaines and alkylamine oxides; polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, sorbitan fatty acid esters , Polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene fatty acid castor oil, polyoxyethylene alkyl Amines, nonionic surfactants such as alkyl alkanolamides. These dispersants may be used alone or in combination of two or more.

  Next, a granulated material is prepared from the slurry obtained in S2 (S3). It does not specifically limit as a granulation method, It can carry out according to a well-known method in the said technical field. Examples of the granulation method include a method of spray drying the slurry with a spray dryer or the like. The conditions for spray drying may be adjusted as appropriate according to the equipment to be used, and are not particularly limited. Spray drying is preferable because a granulated product having a relatively sharp particle size distribution can be obtained. The average particle size of the granulated product is not particularly limited, but is preferably 30 μm or more and 150 μm or less, and more preferably 50 μm or more and 100 μm or less. If the average particle diameter of the granulated product is within the above range, the fluidity of the granulated powder is improved, and the moldability during the production of the molded body is improved. In addition, in this specification, the average particle diameter of a granulated material is the value measured with the laser diffraction type particle size distribution measuring apparatus.

  In addition to the method for preparing the granulated product described above, the granulated product can also be prepared by a dry method that does not use water. Specifically, a binder is added in the middle of mixing barium carbonate powder, iron oxide powder, titanium oxide powder, and copper oxide powder, and the granulated product is mixed by mixing and granulating the raw material powder at the same time. Prepare. The addition amount of the binder here is not particularly limited, but is 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass in total of the barium carbonate powder, the iron oxide powder, the titanium oxide powder, and the copper oxide powder. It is preferable that

  Next, the granulated product obtained in S3 is filled into a mold having a desired shape (for example, a rectangular parallelepiped), and pressure-molded to prepare a molded body (S4). The pressure molding method is not particularly limited, and can be performed according to a method known in the technical field. Examples of the pressure molding method include a CIP molding method, a WIP molding method, and a uniaxial pressure molding method. The pressure at the time of pressure molding may be appropriately adjusted according to the type and content of the binder, the average particle diameter of the granulated product, the apparatus to be used, etc., and is not particularly limited, but is generally 30 MPa or more and 500 MPa or less. .

  Next, the molded body obtained in S4 is degreased to remove the binder contained in the molded body (S5). The method of degreasing is not particularly limited, and can be performed according to a method known in the technical field. For example, a degreasing process can be performed by heat-processing a molded object in an air atmosphere. The heating temperature is not particularly limited as long as the binder can be thermally decomposed, and is generally 300 ° C. or higher and 800 ° C. or lower. The heating time is not particularly limited, and may be appropriately adjusted according to the size of the molded body, the binder content, the heating temperature, and the like, and is generally about 10 minutes to 10 hours. When the size of the molded body is small and the binder content is low, the degreasing treatment may be omitted and the molded body may be fired as it is. In such a case, the molded body is not cracked or broken by rapid combustion of the binder.

  Next, a sintered body of M-type hexagonal ferrite is prepared by firing the molded body obtained in S5 (when S5 is omitted, the molded body obtained in S4) (S6). The firing method is not particularly limited, and can be performed according to a method known in the technical field. For example, the molded body may be fired in an air atmosphere, or may be fired in a high concentration oxygen atmosphere. Moreover, although a calcination temperature is not specifically limited, Generally it is 900 degreeC or more and 1200 degrees C or less, Preferably they are 950 degreeC or more and 1150 degrees C or less.

  Conventionally, when producing a sintered body of hexagonal ferrite from raw material powders such as barium carbonate powder and iron oxide powder, it is common to provide a step of calcining the raw material powder mixture. In other words, through the respective steps of mixing each raw material powder, calcining the raw material powder mixture (ferrite formation), pulverization, slurry preparation, granulated product preparation, green body preparation and green body firing (sintered body preparation), A ferrite sintered body is manufactured. However, in this manufacturing method, since the ferrite produced and pulverized by calcining is plate-like crystal particles, the ferrite crystal particles tend to be oriented during the subsequent molding preparation, and the ferrite crystal particles are oriented in a certain direction. The molded body is easy to prepare. Further, even a ferrite sintered body obtained by firing a molded body in which ferrite crystal particles are oriented in a certain direction tends to be a sintered body in which ferrite crystal particles are oriented in a certain direction. On the other hand, in the production method of the present invention, as described above, the granulated product obtained by granulating the raw material powder mixture is formed without providing the calcining step, and the molded body is fired, whereby the M-type hexagonal ferrite is sintered. A process that simultaneously generates and sinters is used. Thereby, a sintered body in which the orientation of the ferrite crystal particles is suppressed can be manufactured.

  Next, in order to adjust the thickness and shape of the sintered body, the surface of the sintered body may be ground as necessary (S7). It does not specifically limit as a grinding method, It can carry out according to a well-known method in the said technical field. Examples of the grinding method include grinding using a diamond tool. Further, in order to prevent chipping and the like, barrel polishing for chamfering may be performed on the sintered body.

  The radio wave absorber according to Embodiment 1 manufactured as described above is excellent in radio wave absorption performance at 20 GHz and has no anisotropy in radio wave absorption performance, so that radio waves can be transmitted from various directions such as a high-frequency module. In the incident application, it has good radio wave absorption performance.

Embodiment 2. FIG.
A high-frequency module according to Embodiment 2 will be described. FIG. 3 is a schematic cross-sectional view of a high-frequency module including the radio wave absorber 1 according to Embodiment 1 inside a metal case that houses a high-frequency circuit. As shown in FIG. 3, the high-frequency module 3 includes, for example, a cylinder on a ceramic substrate 11 constituting a multilayer dielectric substrate on which a high-frequency circuit 10a mounted with a semiconductor bare chip and a circuit 10b mounted with a semiconductor chip are mounted. A case body 7 made of metal is attached. The high-frequency circuit 10 a and the circuit 10 b are electrically connected to a circuit pattern 8 formed on the ceramic substrate 11 via bonding wires 9. A metal high frequency circuit case cover 6 is attached to the case body 7 to constitute a high frequency circuit case. And the electromagnetic wave absorber 1 is installed in the position which opposes the high frequency circuit 10a in the inner surface of the cover 6 for high frequency circuit cases. In FIG. 3, the metal layer 4 provided on the surface of the radio wave absorber 1 and the inner surface of the high-frequency circuit case cover 6 are joined via a solder material 5. The method of joining the radio wave absorber 1 to the high frequency circuit case cover 6 is not particularly limited, and a known method such as joining by solder, joining by sintered metal, joining by epoxy adhesive or the like can be applied. is there. The metal layer 4 is provided in order to improve the bondability when the radio wave absorber 1 and the high frequency circuit case cover 6 are bonded with a metal-based bonding material, and is a bonding material such as an epoxy adhesive. It is not necessary to provide it when joining with.

  The high-frequency module according to the second embodiment having the above-described structure can absorb high-frequency noise generated in the high-frequency circuit case and prevent problems such as malfunction of the circuit.

  Hereinafter, although an Example and a comparative example demonstrate the detail of this invention, this invention is not limited by these.

[Example 1]
BaCO ₃ powder having an average particle diameter of ₂ μm, Fe ₂ O ₃ powder having an average particle diameter of 1 μm, TiO ₂ powder having an average particle diameter of 1 μm, and CuO powder having an average particle diameter of 4 μm are 1: 4.5: 1.5: 1. 50 parts by mass of a raw material powder mixture blended at a molar ratio of 5, 1 part by mass of a polycarboxylic acid-based dispersant, 1 part by mass of polyvinyl alcohol (binder) and 48 parts by mass of water are mixed for about 5 hours by a ball mill to prepare a slurry. did. The obtained slurry was spray-dried with a spray dryer to obtain a granulated product having an average particle size of 70 μm. The granulated product was filled in a metal mold having a square shape, and a compact was obtained by press molding at a pressure of 98 MPa using a uniaxial pressure press. Next, the obtained molded body was degreased by heat treatment at 600 ° C. for 2 hours in an air atmosphere. Subsequently, the degreased molded body was fired at 1050 ° C. for 3 hours in an air atmosphere to obtain a sintered body. The obtained sintered body was ground with a diamond tool to obtain a radio wave absorber made of a sintered body having a thickness of 1 mm.

[Example 2]
The degreased compact was the same as Example 1 except that it was fired at 1000 ° C. for 3 hours in an air atmosphere.

Example 3
The degreased compact was the same as Example 1 except that it was fired at 1030 ° C. for 3 hours in an air atmosphere.

Example 4
The degreased compact was the same as Example 1 except that it was fired at 1100 ° C. for 3 hours in an air atmosphere.

Example 5
BaCO ₃ powder having an average particle diameter of ₂ μm, Fe ₂ O ₃ powder having an average particle diameter of 1 μm, TiO ₂ powder having an average particle diameter of 1 μm, and CuO powder having an average particle diameter of 4 μm are 1: 4.75: 1.25: 1. Example 1 was performed except that a raw material powder mixture blended at a molar ratio of 25 was used.

Example 6
BaCO ₃ powder having an average particle diameter of ₂ μm, Fe ₂ O ₃ powder having an average particle diameter of 1 μm, TiO ₂ powder having an average particle diameter of 1 μm, and CuO powder having an average particle diameter of 4 μm are 1: 4.25: 1.75: 1. Example 1 was performed except that a raw material powder mixture blended at a molar ratio of 75 was used.

Example 7
The sintered body was processed in the same manner as in Example 1 except that the sintered body was ground with a diamond tool and processed to a thickness of 0.5 mm.

Example 8
The sintered body was processed in the same manner as in Example 1 except that the sintered body was ground with a diamond tool and processed to a thickness of 1.5 mm.

Example 9
The sintered body was processed in the same manner as in Example 1 except that the sintered body was ground with a diamond tool and processed to a thickness of 2.0 mm.

Example 10
The sintered body was processed in the same manner as in Example 1 except that the sintered body was ground with a diamond tool and processed to a thickness of 2.5 mm.

Example 11
The sintered body was processed in the same manner as in Example 1 except that the sintered body was ground with a diamond tool and processed to a thickness of 3.0 mm.

Example 12
The sintered body was processed in the same manner as in Example 1 except that the sintered body was ground with a diamond tool and processed to a thickness of 0.3 mm.

[Comparative Example 1]
BaCO ₃ powder having an average particle diameter of ₂ μm, Fe ₂ O ₃ powder having an average particle diameter of 1 μm, TiO ₂ powder having an average particle diameter of 1 μm, and CuO powder having an average particle diameter of 4 μm are 1: 4.5: 1.5: 1. The raw material powder mixture blended at a molar ratio of 5 was calcined at 900 ° C. for 3 hours in an air atmosphere to form M-type hexagonal ferrite. The obtained M-type hexagonal ferrite was pulverized wet for 3 hours using a ball mill, and then dried at 150 ° C. for 10 hours. Next, 50 parts by mass of the dried M-type hexagonal ferrite powder, 1 part by mass of a polycarboxylic acid-based dispersant, 1 part by mass of polyvinyl alcohol (binder) and 48 parts by mass of water were mixed for about 5 hours with a ball mill, and the slurry was mixed. Prepared. The procedure was the same as Example 1 except that this slurry was used.

[Comparative Example 2]
BaCO ₃ powder having an average particle diameter of ₂ μm, Fe ₂ O ₃ powder having an average particle diameter of 1 μm, TiO ₂ powder having an average particle diameter of 1 μm, and CuO powder having an average particle diameter of 4 μm are 1: 4.5: 1.5: 1. The raw material powder mixture blended at a molar ratio of 5 was calcined at 900 ° C. for 3 hours in an air atmosphere to form M-type hexagonal ferrite. The obtained M-type hexagonal ferrite was wet-ground for 1.5 hours using a ball mill and then dried at 150 ° C. for 10 hours. Next, 50 parts by mass of the dried M-type hexagonal ferrite powder, 1 part by mass of a polycarboxylic acid-based dispersant, 1 part by mass of polyvinyl alcohol (binder) and 48 parts by mass of water were mixed for about 5 hours with a ball mill, and the slurry was mixed. Prepared. The procedure was the same as Example 1 except that this slurry was used.

[Comparative Example 3]
Blending BaCO ₃ powder with an average particle size of ₂ μm, Fe ₂ O ₃ powder with an average particle size of 1 μm, TiO ₂ powder with an average particle size of 1 μm and CuO powder with an average particle size of 4 μm in a molar ratio of 1: 5: 1: 1 Example 1 was performed except that the raw material powder mixture was used.

[Comparative Example 4]
Blending BaCO ₃ powder with an average particle size of ₂ μm, Fe ₂ O ₃ powder with an average particle size of 1 μm, TiO ₂ powder with an average particle size of 1 μm and CuO powder with an average particle size of 4 μm in a molar ratio of 1: 4: 2: 2. Example 1 was performed except that the raw material powder mixture was used.

The radio wave absorbers obtained in the above examples and comparative examples were evaluated for radio wave attenuation as follows.
FIG. 4 is a schematic cross-sectional view showing the configuration of a resonator for measuring the radio wave attenuation of the radio wave absorber. The radio wave attenuation evaluation resonator 12 has an airtight structure in which a metal cover 14 is attached to a metal resonator body 13. The radio wave attenuation evaluation resonator 12 has a spatial design having a resonance point at 20 GHz. The metal layer 4 provided on the surface of the radio wave absorber 1 and the cover 14 are joined via a solder material 5. A signal pin 15 and a signal pin 16 are inserted into the bottom of the resonator body 13 from the outside. The signal pin 15 is connected to the radio wave transmitter. The signal pin 16 is connected to the radio wave detector. Using the radio wave attenuation evaluation resonator 12 having the above-described configuration, the S parameter S21, which is the transmission characteristic of the radio signal between the signal pin 15 and the signal pin 16, is evaluated, and the amount of passage loss is expressed in dB. Thus, the radio wave attenuation of each radio wave absorber was evaluated.

The above evaluation results are shown in Table 1. Further, FIG. 5 shows the relationship of the degree of orientation (f value) of the M-type hexagonal ferrite particles with respect to the radio wave attenuation of the radio wave absorber, and the composition of the M-type hexagonal ferrite with respect to the radio wave attenuation of the radio wave absorber (BaFe ₁₂₋ the relationship between the _x value of x _{(Ti 0.5 Cu 0.5) x O} 19) shown in FIG. 6 shows a relationship between the thickness of the sintered body for an electric wave attenuation amount of the wave absorber in FIG.

  As shown in Table 1, the radio wave absorbers of Examples 1 to 12 had excellent radio wave absorption performance in radio wave attenuation evaluation using a resonator. In contrast, the radio wave absorbers of Comparative Examples 1 and 2 have a large orientation of the M-type hexagonal ferrite particles, so the effect of absorbing radio waves incident from various directions is weak, and the radio wave attenuation is not improved. . Further, in the radio wave absorbers of Comparative Examples 3 and 4, the composition of the M-type hexagonal ferrite (the amount of titanium and copper replacing iron) deviates from the composition range necessary for adjusting the absorption frequency band to the 20 GHz band. Therefore, sufficient radio wave absorption effect could not be obtained.

  As can be seen from the above results, according to the present invention, the radio wave absorption is excellent in the radio wave absorption performance in the gigahertz band (20 GHz) and has no anisotropy in the radio wave absorption performance and can absorb radio waves incident from various directions. The body can be provided. Further, according to the present invention, it is possible to provide a high frequency module that does not cause a malfunction such as a malfunction due to high frequency noise in the gigahertz band. Furthermore, according to the present invention, a radio wave absorber that is excellent in radio wave absorption performance in the gigahertz band, has no anisotropy in radio wave absorption performance, and can absorb radio waves incident from various directions is manufactured with high productivity. A method can be provided.

  DESCRIPTION OF SYMBOLS 1 Radio wave absorber 2, Plate-shaped crystal particle, 3 High frequency module, 4 Metal layer, 5 Solder material, 6 Cover for high frequency circuit cases, 7 Case main body, 8 Circuit pattern, 9 Bonding wire, 10a High frequency circuit, 10b circuit, DESCRIPTION OF SYMBOLS 11 Ceramic substrate, 12 Radio wave attenuation amount evaluation resonator, 13 Resonator body, 14 Cover, 15 Signal pin, 16 Signal pin.

Claims (7)

It consists of a sintered body of M-type hexagonal ferrite having the composition formula: BaFe _12-X (Ti _0.5 Cu _0.5 ) _X O ₁₉ (where X is 2.5 or more and 3.5 or less), A radio wave absorber, wherein the degree of orientation of ferrite crystal particles evaluated by the Lottgering method is 0.2 or less.   The radio wave absorber according to claim 1, wherein the sintered body has a thickness of 0.5 mm to 3 mm.   The radio wave absorber according to claim 1 or 2, wherein the degree of orientation is 0.04 or more and 0.15 or less.   A radio frequency module comprising the radio wave absorber according to any one of claims 1 to 3 inside a metal case that houses a radio frequency circuit. By mixing raw material powder of barium carbonate powder, iron oxide powder, titanium oxide powder and copper oxide powder, the composition formula: BaFe _12-X (Ti _0.5 Cu _0.5 ) _X O ₁₉ (where, A step of preparing a raw material powder mixture in which components are adjusted so that M type hexagonal ferrite of X is from 2.5 to 3.5), and
Mixing the raw material powder mixture with a binder to prepare a granulated product;
A step of pressure-molding the granulated material to prepare a molded body;
And a step of preparing an M-type hexagonal ferrite sintered body by firing the molded body.   6. The method of manufacturing a radio wave absorber according to claim 5, wherein an average particle size of the raw material powder is 0.05 μm or more and 8 μm or less.   The method for producing a radio wave absorber according to claim 5 or 6, wherein the granulated product is obtained by spray drying a slurry containing the raw material powder mixture, the binder, and water.

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