JP2005347485A - Ferrite radio wave absorbing material and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ferrite system radio wave absorbing material and its manufacturing method, wherein in a ferrite system material composed of compositions which are easily available as a material, an upper limit frequency of a radio wave absorbing characteristic is high, and in the case of being monolithically used as a sintered body, as well as a radio wave absorber which is formed as a composite material, it is easy to be made in a wide band and be thinned easily, and when the ferrite system material per se is manufactured also, a process control is easy and a producibility is excellent. <P>SOLUTION: In a c-axis anisotropic W-type hexagonal ferrite material composed of a specific composition, a bivalent composition of ferrite is adjusted, whereby a magnetic resonant frequency caused by a crystalline magnetic anisotropy can be changed by frequencies of a wide range and the radio wave absorbing characteristic also can be obtained in a wide frequency range, and a manufacturing process which is stably established as a ferrite permanent magnet can be utilized. Compounds such as Bi, Cl, B and F are added to accelerate a crystal particles growth, resulting in raising the imaginary part μ" of a complex permeability, and as a result, a matching thickness in the magnetic resonant frequency can be further thinned. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a ferrite radio wave absorbing material that can constitute a radio wave absorber by forming a mixture with a resin powder or the like, and a W type hexagonal ferrite radio wave having a c-axis anisotropy that can obtain a thin radio wave absorber for GHz band. The present invention relates to an absorbent material and a manufacturing method thereof.

  Radio wave absorbing materials that absorb radio waves from electronic devices can be used at high frequencies such as the millimeter wave band as the frequency of use expands from the MHz band to the GHz band due to recent diversification of radio wave usage. It is demanded.

  Conventionally, spinel type ferrite and soft magnetic hexagonal ferrite sintered bodies are used as they are for the electromagnetic wave absorber in the MHz band and several GHz, and there is no composite magnetic body by kneading ferrite powder into resin etc. It is effective to install this on a conductor plate and use it as an impedance matching type radio wave absorber.

  As the wave absorber for the millimeter wave band, a wave absorber using a resistance film or a wave absorber using a conductive material such as carbon is used. A film using a resistance film is excellent in absorption performance, but needs a certain thickness. For example, it is difficult to reduce the thickness to several hundred μm and to make a paint.

  Also, millimeter wave radio wave absorbers using conductive materials such as carbon can be made thinner and more paintable. However, in order to reduce the thickness, it is necessary to increase the dielectric constant of the absorbent material. The band having radio wave absorption performance is narrowed, and high accuracy is required for the thickness of the absorbent material, which has a great problem in practical use.

  On the other hand, as an electromagnetic wave absorbing material having a high permeability in a higher frequency region, an electromagnetic wave absorber comprising a mixture of magnetic particles and a resin material, a ceramic material, or a low melting point metal material, A configuration has been proposed in which the surface of a magnetic material having magnetic anisotropy is coated with a magnetic material having a saturation magnetization of 1 T or more (Patent Document 1).

As a ferrite material with excellent mass productivity, Z is a composition in which a part of Co is mostly substituted with Fe (Ba ₃ Co _2-x Fe _x Fe ₂₄ O ₄₁ ). Type single-phase barium ferrite can be easily prepared, and a hexagonal ferrite material that has the same permeability and electromagnetic wave absorption performance as a material created in oxygen (Ba ₃ Co ₂ Fe ₂₄ O ₄₁ ) is proposed (Patent Document 2) )

  As a magnetoplumbite type hexagonal ferrite that has good electromagnetic wave absorption performance in the high frequency region, is thin and easy to attach to steel plates, etc., a part of Fe is replaced with a specific metal, and the frequency band of the GHz band A configuration has been proposed (Patent Document 3) in which impedance matching is performed within a certain range and its radio wave absorption performance is exhibited.

It is assumed that a wide range of electromagnetic wave absorption characteristics can be obtained by stacking ferrite sintered bodies of different compositions. To achieve this with a single composition, the M-type structure represented by BaFe ₁₂ O ₁₉ is used in a specific composition. A hexagonal ferrite sintered body has been proposed (Patent Document 4) in which the ratio of the phase of the Z-type structure represented by Ba ₃ Co ₂ Fe ₂₄ O ₄₁ is 3: 7 to 7: 3.
JP2001-60791 JP2000-331816 JP-A-11-354972 JP 10-335132 A

  An electromagnetic wave absorber using spinel ferrite has a low magnetic resonance frequency, and the upper limit frequency of absorption characteristics that can obtain an absorption attenuation of 20 dB or more is only several GHz.

  On the other hand, radio wave absorbers using ferro-planar hexagonal ferrites such as Z-type barium ferrite have a high absorption frequency upper limit of 20 GHz, but in the millimeter wave band, the absorption performance is similar to that of spinel ferrite. Strict management of the manufacturing process is required, such as the property of deteriorating, high manufacturing cost, and control of the atmosphere required for firing during manufacturing.

  In addition, in the case of a radio wave absorber that takes the form of a composite magnetic material in which ferrite powder, carbonyl iron powder, etc. are kneaded in a resin or the like, the frequency characteristics cannot be arbitrarily determined when setting the radio wave absorption characteristics because the materials are combined. In addition, it is difficult to increase the bandwidth and reduce the thickness, and the uniformity of the particle size and filling rate, which are controllable parameters, greatly affect the characteristics, and strict management of the manufacturing process is necessary.

  The present invention has a high upper limit frequency of radio wave absorption characteristics in ferrite-based materials consisting of components that are easily available as raw materials, and has a wider band and thinner thickness when used as a composite radio wave absorber as well as a sintered body alone It is an object of the present invention to provide a ferrite-based radio wave absorbing material and a method for manufacturing the same.

  The inventor has conducted intensive studies on the composition and crystal structure of hexagonal ferrite having uniaxial anisotropy for the purpose of a ferrite material capable of exhibiting characteristics with a magnetic resonance frequency of several tens of GHz. In a material having a c-axis anisotropic compound with a ferrite crystal structure, a magnetic resonance phenomenon occurs due to magnetocrystalline anisotropy, and an imaginary part μ ”of its complex permeability is present at a ferromagnetic resonance frequency in a range of 1 GHz to 35 GHz. We have found that it has the maximum characteristics, and it is possible to reduce the bandwidth and thickness by absorbing the electromagnetic wave using the magnetic loss effect.

  In addition, the inventor can change the magnetic resonance frequency in a wide range of frequencies by adjusting the divalent composition of ferrite in the c-axis anisotropic W-type hexagonal ferrite material having a specific composition. It was also found that radio wave absorption characteristics can be obtained in a wide frequency range.

  Furthermore, the inventors have found that the uniaxially anisotropic W-type hexagonal ferrite material having a specific composition and containing 80% or more of the c-axis anisotropic compound having a W-type crystal structure can be fired in the air and has excellent productivity. In addition, the elements Bi, Cl, B, and F generate a melt in the material to promote crystal grain growth, so that the imaginary part μ ″ can be increased, and as a result, the matching thickness at the magnetic resonance frequency can be increased. As a result, the present invention was completed.

That is, the present invention has a c-axis anisotropic compound having a crystal structure of W-type hexagonal ferrite, whose composition formula (1) is AMe ₂ Fe ₁₆ O ₂₇ , and A in the composition formula is Ca, Ba, Sr , One or more of Pb, and Me having a total amount of 2 moles, Co contains 0.8 mole or less, and includes one or more of Mg, Mn, Fe, Ni, Cu, Zn, or Bi 1 mol% or less as Bi ₂ O ₃ , Cl as 1 mol% or less as one or more of SrCl ₂ , BaCl ₂ , CaCl ₂ , F as 1 mol% as one or more of SrF ₂ , BaF ₂ , CaF ₂ The ferrite-based radio wave absorbing material is characterized in that it contains any additive of 0.5 mol% or less where B is B ₂ O ₃ .

Further, the present invention is a composition formula (2) is AO: 8~10mol%, MeO: 17~19mol %, Fe 2 O 3: c of the crystal structure of the W-type hexagonal ferrite represented by 71～75Mol% Jikukoto And A is one or more of Ca, Ba, Sr, and Pb, MeO is 7 mol% or less of CoO, and one or two of MgO, MnO, FeO, NiO, CuO, and ZnO. containing more species, or even, 1 mol% or less of Bi as Bi ₂ O _3, Cl and SrCl _2, BaCl _2, 1mol% as CaCl ₂ for one or two or more or less, SrF ₂ and F, BaF _2, CaF ₂ 1 or 2 or more, and B or B ₂ O ₃ and 0.5 mol% or less of any additive is included.

The present invention also includes a step of obtaining a calcined powder by calcining a raw material powder prepared by weighing and mixing to a composition represented by the composition formula (1) or (2) in the air, Bi is Bi ₂ O ₃ 1 mol% or less as, Cl and SrCl _2, BaCl _2, 1mol% as CaCl ₂ for one or two or more or less, F and SrF _2, BaF _2, 1mol% as CaF ₂ of one or two or more or less, the B B A ferrite system comprising a step of mixing with the calcined powder so as to contain any additive of 0.5 mol% or less as ₂ O ₃ to obtain a mixed powder, and a step of sintering the mixed powder. This is a method of manufacturing a radio wave absorbing material.

  The present invention also includes a step of obtaining a calcined powder by calcining a raw material powder prepared by weighing and mixing the composition formula (1) or (2) and an additive in the air, and calcining powder. Pulverizing and granulating, and using the obtained granulated powder to produce a mixture with another resin material, ceramic material or low melting point metal material to obtain a radio wave absorbing material of the required shape. This is a method for producing a featured ferrite-based electromagnetic wave absorbing material.

  The c-axis anisotropic W-type hexagonal ferrite material according to the present invention is composed of components whose raw materials are easy to obtain, and can be easily fired and fired in the atmosphere without high sintering temperature and process management is easy and excellent in productivity. The range in which radio wave absorption using the magnetic loss effect can be absorbed is as wide as 1 GHz to 40 GHz, and the magnetic resonance frequency can be changed in a wide range of frequencies by adjusting the divalent composition of ferrite.

  According to the present invention, a composition having a characteristic with a magnetic resonance frequency of several tens of GHz can be easily set, the upper limit frequency of the radio wave absorption characteristic is high, and when used as a composite radio wave absorber as well as a sintered body alone. Even in such a case, it is possible to provide a ferrite-based radio wave absorbing material that can be widened and can be easily made thinner at the same resonance frequency.

  The c-axis anisotropic W-type hexagonal ferrite material according to the present invention can be fired in the atmosphere and has excellent manufacturability. In addition, by using a compound of each element of Bi, Cl, B, F as an additive, firing Since the melt is sometimes generated to promote crystal grain growth, the imaginary part μ ″ can be increased, and as a result, the matching thickness at the magnetic resonance frequency can be further reduced.

  The c-axis anisotropic W-type hexagonal ferrite material according to the present invention is characterized by the composition represented by the composition formula (1) or (2). In particular, a configuration containing 80% or more of the c-axis anisotropic compound having the crystal structure of the W-type hexagonal ferrite represented by the composition formula (1) or (2) is desirable. That is, if it is less than 80%, it is difficult to obtain good radio wave absorption performance, and 80% or more is required to effectively exhibit radio wave absorption performance in various configurations of radio wave absorption materials.

A in the composition formula is an element necessary for reacting with iron oxide to form the hexagonal ferrite of the present invention, and at least one of Ca, Ba, Sr, and Pb is required, preferably Ba. Or Sr. A is the composition formula (1) generated by the c-axis anisotropic W-type hexagonal ferrite material, and requires an amount in the range represented by AMe ₂ Fe ₁₆ O _{27. The} oxide represented by the composition formula (2) In the case of 8 to 10 mol%.

  As Me, the magnetocrystalline anisotropy constant Ku> 0, that is, the condition of uniaxial anisotropy is required, and in the composition formula (1), out of the total amount of 2 mol, Co which is an element that negatively shifts Ku is added. 0.8 mol or less is contained, and the remaining 1.2 mol requires at least one of Mg, Mn, Fe, Ni, Cu, and Zn.

  In the case of the oxide represented by the composition formula (2), Me is required to be 17 to 19 mol%, CoO that negatively shifts Ku contains 7 mol% or less, and the remaining 10 to 12 mol% includes MgO, MnO, At least one selected from FeO, NiO, CuO, and ZnO is selected, and these elements are elements in which Ku is positive when MeO is single.

The c-axis anisotropic W-type hexagonal ferrite material according to the present invention occupies the remainder of A and Me, and in the case of the oxide represented by the composition formula (2), Fe ₂ O ₃ is 71 to It is in the range of 75 mol%.

In the c-axis anisotropic W-type hexagonal ferrite material according to the present invention, there is Cu as an element Me that plays a role in promoting the crystal grain growth, but Bi is also Bi ₂ O ₃ and Cl is SrCl ₂ , BaCl ₂ , CaCl ₂ as one or more types, F as SrF ₂ , BaF ₂ , CaF ₂ as one or more types, and B as B ₂ O ₃ , resulting in a melt during firing Thus, the growth of crystal grains can be promoted and the imaginary part μ ″ can be increased. B is 0.5 mol% or less, and Bi, Cl, and F are each 1 mol% or less.

  As a method for producing a c-axis anisotropic W-type hexagonal ferrite material according to the present invention, a known method for producing a ferrite magnet material can be adopted.For example, water and a dispersant are added to a weighed raw material and mixed in a ball mill, The raw material powder is obtained by filtration, this raw material powder is calcined at 850 ° C to 1350 ° C, pulverized with a ball mill to obtain a calcined powder, and granulated powder granulated with a spray dryer or the like These powders can be formed into a required shape, and a process such as sintering in the air at 1000 ° C. to 1350 ° C. can be appropriately employed.

  The radio wave absorbing material according to the present invention can be used in the state of a sintered body of a required shape, or can be used by attaching a sintered body of a required shape to a conductive plate. The powder obtained by pulverizing the calcined powder is used by forming it into a required shape using a binder or the like, or a mixture obtained by mixing a known resin material, ceramic material or low-melting-point metal material with the powder to form a binder, etc. Various wave absorbers can be formed by molding or sintering to a required shape using

  In the radio wave absorbing material according to the present invention, compounds of each element of Bi, Cl, B, and F are used as additives in order to promote the growth of crystal grains. When the step of sintering the calcined powder can be obtained, the grain growth can be promoted by mixing the compound with the calcined powder and then sintering. .

Example 1
As starting materials, BaO, SrO, PbO, Fe ₂ O ₃ , CoO, ZnO, CuO, NiO, MgO, MnO, TiO ₂ were weighed to have the composition shown in Table 1, and several hours using an iron ball mill Mixing was performed in pure water. Pre-baking was performed in air at 1300 ° C. for 3 hours, and then pulverized to an average particle size of 1 μm and granulated with a spray dryer to obtain a powder for sintering.

  This was molded into a ring shape using powders for sintering of various compositions shown in Table 1, and sintered at 1300 ° C for 3 hours in the atmosphere. A ring sample with an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 2 mm A sintered body was obtained. The obtained sample was investigated for absorption characteristics at frequencies from 1 GHz to 40 GHz. Table 1 shows the relationship between composition, resonance frequency, and matching thickness.

  For compositions No. 1 and No. 4 in Table 1, the frequency characteristics of radio wave absorption from 1 GHz to 20 GHz are shown in FIGS. 1A and 1B. It can be seen that each ring sintered body has an attenuation of 20 dB or more.

  Further, the comparative examples of compositions No. 13 and No. 14 in Table 1 are M-type hexagonal ferrite materials, which were produced in the same manufacturing process. As is clear from the relationship between the resonance frequency and the matching thickness in Table 1, the matching thickness indicating the radio wave absorption performance is smaller in the matching thickness of the embodiment of the present invention when comparing the matching frequencies at substantially the same frequency. Understand.

Example 2
Based on the powder of composition No. 3 in Table 1, each additive of Bi ₂ O ₃ , BaF ₂ , BaCl ₂ , B ₂ O ₃ was weighed so as to have the composition shown in Table 2, and Example 1 A ring sample sintered body was obtained in the same process.

  The obtained sample was investigated for absorption characteristics at frequencies from 1 GHz to 10 GHz. Table 2 shows the relationship between composition, resonance frequency, and matching thickness. It can be seen that the matching thickness is reduced by the additive.

Example 3
Using a sintering powder of composition No. 3 and composition No. 4 in Table 1, this and polycarbonate resin were made into a weight ratio of 75:25 to produce a composite wave absorber, lined with a metal plate, Produced. The absorption characteristics of this radio wave absorber were measured in the range of 5 GHz to 20 GHz by the free space method. The measurement results are shown in FIG.

As can be seen from FIG. 2, an absorption characteristic of 20 dB or more was obtained in the band of 8 GHz to 18 GHz, and an absorption characteristic having a specific frequency bandwidth of 70% or more was obtained.

  According to the present invention, compared to a conventional wave absorber using a ferrite material, the material cost is low, for example, a stable manufacturing process established as a ferrite permanent magnet can be used, and a thin and broadband wave absorption characteristic can be obtained. Excellent electromagnetic absorption characteristics even in the millimeter wave band. In addition, when the composition is selected, the obtained ferrite radio wave absorber material is a magnetic wave absorber that can be attached very easily without using an adhesive or the like on the magnetic metal wall by magnetizing itself. Can be configured.

4 is a graph showing the relationship between a frequency indicating radio wave absorption performance and a reflection coefficient, where A is the composition No. 1 in Table 1 and B is the composition No. 4 in Table 1. 6 is a graph showing the relationship between the frequency and the reflection coefficient indicating the radio wave absorption performance of the composite radio wave absorber according to Example 3.

Claims (6)

It has a c-axis anisotropic compound with a crystal structure of W-type hexagonal ferrite represented by the composition formula AMe ₂ Fe ₁₆ O ₂₇ , and A in the composition formula is one or more of Ca, Ba, Sr, and Pb. A total of 2 mol of Me is a ferrite radio wave absorbing material containing Co of 0.8 mol or less and Mg, Mn, Fe, Ni, Cu, Zn, or one or more of them. AO: 8~10mol%, MeO: 17~19mol %, Fe 2 O 3: has a c-axis anisotropy compound of the crystal structure of the W-type hexagonal ferrite represented by 71~75mol%, wherein A is Ca, Ferrite electromagnetic wave absorbing material that is one or more of Ba, Sr, and Pb, MeO contains CoO at 7 mol% or less, and MgO, MnO, FeO, NiO, CuO, or ZnO. Furthermore, Bi is 1 mol% or less as Bi ₂ O ₃ , Cl is 1 mol% or less as one or more of SrCl ₂ , BaCl ₂ , CaCl ₂ , F is one or more of SrF ₂ , BaF ₂ , CaF _{2 3.} The ferrite radio wave absorbing material according to claim 1 or 2, which contains any additive of 1 mol% or less as B and 0.5 mol% or less as B as B ₂ O ₃ . 3. The ferrite radio wave absorbing material according to claim 1, comprising 80% or more of a c-axis anisotropic compound. Composition formula AO: 8~10mol%, MeO: 17~19mol %, Fe 2 O 3: has a c-axis anisotropy compound of the crystal structure of the W-type hexagonal ferrite represented by 71~75mol%, the A Is one or more of Ca, Ba, Sr, and Pb, MeO is a ferrite material containing 7 mol% or less of CoO and one or more of MgO, MnO, FeO, NiO, CuO, ZnO in the atmosphere. The process of obtaining calcined powder by calcination with Bi, Bi ₂ O ₃ as 1 mol% or less, Cl as SrCl ₂ , BaCl ₂ , CaCl ₂ as one or two or less, 1 mol% or less, F as SrF ₂ , BaF ₂ , a step of obtaining a mixed powder by mixing with the calcined powder so as to contain one or two or more of CaF ₂ and 1 mol% or less, and B as B ₂ O ₃ and 0.5 mol% or less, the mixed powder And a method for producing a ferrite-based electromagnetic wave absorbing material.
Composition formula AO: 8~10mol%, MeO: 17~19mol %, Fe 2 O 3: has a c-axis anisotropy compound of the crystal structure of the W-type hexagonal ferrite represented by 71~75mol%, the A Is one or more of Ca, Ba, Sr, and Pb, MeO contains 7 mol% or less of CoO and one or more of MgO, MnO, FeO, NiO, CuO, ZnO, Bi is Bi ₂ 1 mol% or less as O ₃ , Cl as 1 mol% or less as one or more of SrCl ₂ , BaCl ₂ , CaCl ₂ , F as 1 mol% or less as one or more of SrF ₂ , BaF ₂ , CaF ₂ , B step a to obtain a calcined powder of ferrite material and calcined in air containing B ₂ O ₃ as 0.5 mol% or less of any additives, the step of calcining the powder was ground granulated, obtained granulated A method for producing a ferrite-based radio wave absorption material, comprising: using a powder to produce a mixture of another resin material, a ceramic material, or a low melting point metal material to obtain a radio wave absorption material of a required shape.

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