KR100982163B1 - Radio wave absorbing body - Google Patents

Abstract

The present invention relates to a radio wave absorber comprising a sintered MnZn ferrite, which has 45.0 to 49.0 mol% of iron oxide in terms of Fe ₂ O ₃ , 19.0 to 23.0 mol% of zinc oxide in terms of ZnO, and 28.0 in manganese oxide. It has a main component which consists of -36.0 mol%, and it is comprised so that a predetermined amount may contain cobalt oxide, a silicon oxide, and calcium oxide as a subcomponent with respect to 100 weight part of this main component, and it aims at the remarkable reduction of a manufacturing cost. It also has excellent effects on the temperature characteristic frequency characteristics of the Curie temperature, matching thickness, and radio wave absorption characteristics.

Zn ferrite sintered body, radio wave absorber, iron oxide, zinc oxide, manganese oxide, cobalt oxide, silicon oxide, calcium oxide, reflection attenuation, frequency

Description

Electric wave absorber {RADIO WAVE ABSORBING BODY}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber composed of an MnZn-based ferrite material containing no Ni as a main component, and relates to a radio wave absorber used in a radio wave darkroom, a radio wave absorption wall, or the like.

In recent years, with the development of information and communication technology and the spread of various electric devices, the influence of unnecessary electronic noise on precision device-related devices has become a problem.

The measurement of such electromagnetic noise requires a radio wave dark room (electromagnetic anechoic chamber) without reflection of electromagnetic waves, and a radio wave absorber is used for the inner wall of the radio wave dark room.

Moreover, a radio wave absorber is used for the outer wall of a building, etc. in order to prevent the reception obstacle which a radio wave of a television reflects by a high-rise building etc. is prevented.

Since such a radio wave absorber is used in a large amount in the interior, the outer wall of a radio wave darkroom, etc., a low product cost is calculated | required.

A conventional radio wave absorber, for example, a radio wave absorber having a reflection attenuation amount of 20 dB or more in a frequency band of 40 MHz to 450 MHz, a radio wave absorber obtained by sintering magnesium-zinc ferrite, a radio wave absorber sintered by nickel-zinc ferrite, Manganese-nickel-copper-zinc ferrite.

Among these, the magnesium-zinc ferrite material has a relatively low raw material cost, but the matching thickness of the radio wave absorber is about 8 mm, and there is a limit to reduce the total weight of the radio wave absorber used for the inner wall of the radio dark room or the outer wall of a building. .

On the other hand, ferrite containing nickel as a main component can be said to be an advantageous material in order to obtain desired radio wave absorber characteristics, but the cost is high, which is inconsistent with the purpose of the present invention for the purpose of cost reduction. In addition, in the radio dark room for measuring the electromagnetic noise of the precision equipment-related apparatus, the frequency band for evaluating the electromagnetic noise is standardized, the amount of reflection attenuation in the range of 30 to 1000 MHz is required 20dB or more.

As a prior art considered to be related to this invention, Unexamined-Japanese-Patent No. 2005-179092 is mentioned. This prior art relates to a Mn-Co-Zn-based ferrite similar in composition to the present invention, although its use is not limited to the radio wave absorber. And in this prior art, as a composition of the Example close to the composition range of this invention, the sample number 1-9 of Table 1 mentioned later exists. The composition of Sample No. 1-9 in the prior art is Fe ₂ O ₃ = 45.5 mol%, MnO = 31.5 mol%, ZnO = 21.0 mol%, CoO = 2.0 mol%.

In Sample No. 1-9, when Fe ₂ O ₃ , MnO, and ZnO are the main components, and CoO is regarded as a minor component, and converted to the same indication as the present invention, Sample No. 1-9 is the main component: Fe _2. O ₃ = 46.43 mol%, MnO = 3.314 mol%, ZnO = 21.43 mol%, and the subcomponents: CoO = 13380 weight ppm (0.01338 weight part). The composition range of this prior art does not bring about the desired effect which this invention aims at. This is found by examining the experimental results in the Examples of the present invention described later.

Under these circumstances, the present invention has been devised, and an object thereof is to provide a radio wave absorber in which manufacturing cost can be reduced while maintaining the required characteristic level at a high level. That is, in the low frequency region of 30 MHz, the reflection attenuation at room temperature (25 ° C.) is 20 dB or more, the reflection attenuation at minus 20 ° C. (-20 ° C.) is 15 dB or more, and the matching thickness is 6 mm or less. It is to provide the Mn-Zn type radio wave absorber which has the characteristic, Curie temperature has the characteristic of 80 degreeC or more, and can reduce manufacturing cost.

MEANS TO SOLVE THE PROBLEM In order to solve the said subject, this invention is a radio wave absorber which consists of a MnZn ferrite sintered compact,

Iron oxide in terms of Fe ₂ O ₃ 45.0-49.0 mol%,

Zinc oxide is 19.0 to 23.0 mol% in terms of ZnO, and

Manganese oxide has a main component consisting of 28.0 to 36.0 mol% in terms of MnO,

As a subcomponent with respect to 100 parts by weight of this main component,

1000 to 7000 ppm by weight (0.001 to 0.007 parts by weight) of cobalt oxide in terms of CoO, 10 to 200 ppm by weight (0.00001 to 0.0002 parts by weight) of silicon oxide in terms of SiO _2, and 200 to 2500 parts by weight of calcium oxide in terms of CaO It is configured to contain ppm (0.0002 ~ 0.0025 parts by weight).

Further, as a preferred embodiment of the radio wave absorbent of the present invention, it is configured to be achieved by the niobium oxide as a sub ingredient containing less than 500 ppm by weight (0.0005 parts by weight) in terms of Nb ₂ O _5.

Moreover, as a preferable aspect of the electromagnetic wave absorber of this invention, cobalt oxide is comprised so that 3500-6500 weight ppm (0.0035-0.0065 weight part) may be contained in conversion of CoO.

Moreover, as a preferable aspect of the electromagnetic wave absorber of this invention, the characteristic whose reflection attenuation amount at 25 degreeC is 20 dB or more, the characteristic whose reflection attenuation amount is -15 dB or more at -20 degreeC, and the lower limit frequency which satisfy | fills 20 dB of reflection attenuation at 25 degreeC is 30 MHz. The following characteristics, the upper limit frequency at which the reflection attenuation satisfies 20 dB at 25 DEG C or higher is 300 MHz or higher, the lower limit frequency at which the reflection attenuation satisfies the 15 dB at -20 DEG C is 30 MHz or lower, the matching thickness is 6 mm or lower, and It is comprised so that a Curie temperature may have a characteristic of 80 degreeC or more.

Moreover, as a preferable aspect of the electromagnetic wave absorber of this invention, the characteristic whose sintered density exceeds 4.7 (g / cm <^3> ) and the value of epsilon 'which is a complex dielectric constant real part in frequency 30MHz satisfy | fill the conditions of 10 <ε'<30. Characteristics of the complex permeability real part μ 'at a frequency of 30 MHz satisfy the condition of μ'<80, and a value of μ '' of the complex permeability imaginary part at a frequency of 30 MHz is μ ''> 260. It is configured to have characteristics to meet.

Moreover, as a preferable aspect of this invention, a radio wave absorber is comprised so that it may have a plate-like tile shape.

The electromagnetic wave absorber of the sintered MnZn ferrite of the present invention has iron oxide as 45.0 to 49.0 mol% in terms of Fe ₂ O ₃ , zinc oxide as 19.0 to 23.0 mol% in terms of ZnO, and manganese oxide as 28.0 to 36.0 mol%. It has a main component which consists of, and it is comprised so that a predetermined amount may contain cobalt oxide, a silicon oxide, and calcium oxide as a subcomponent with respect to 100 weight part of this main component, respectively, and it can aim at the remarkable reduction of a manufacturing cost, and Curie It also has an excellent effect on the temperature characteristic frequency characteristics of temperature, matching thickness, and radio wave absorption characteristics.

The present invention provides a radio wave absorber comprising a sintered MnZn ferrite, which is 45.0 to 49.0 mol% of iron oxide in terms of Fe ₂ O ₃ , 19.0 to 23.0 mol% of zinc oxide in terms of ZnO, and manganese oxide in terms of MnO. Since it has a main component which consists of 28.0-36.0 mol%, and it is comprised so that a predetermined amount of cobalt oxide, a silicon oxide, and a calcium oxide may be contained as a subcomponent with respect to 100 weight part of this main component, the reduction of a manufacturing cost is remarkably reduced. It is also possible to achieve an excellent effect on the temperature characteristic frequency characteristics of the Curie temperature, matching thickness, and radio wave absorption characteristics.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described.

(Explanation of main components constituting the radio wave absorber of the present invention)

The radio wave absorber of the present invention comprises a main component composed of iron oxide, zinc oxide, and manganese oxide. Iron oxide is 45.0 to 49.0 mol% in terms of Fe ₂ O ₃ (preferably 46.0 to 48.0 mol%), zinc oxide is 19.0 to 23.0 mol% in terms of ZnO (preferably 20.5 to 22.5 mol%), and manganese oxide 28.0-34.5 mol% is contained in MnO conversion.

In the composition region outside the above range, the frequency characteristic of the complex relative permeability and the frequency characteristic of the complex dielectric constant required for the radio wave absorption characteristics are not satisfied, or the matching thickness of the radio wave absorber exceeds 6.0 mm, or is suitable as a radio wave absorber. Curie point is not obtained.

Here, the radio wave absorption characteristic is expressed by the following equation (1), and when the frequency causing a decrease in the real part (μ ') of the complex permeability becomes high, good radio wave absorption characteristics from the low frequency band cannot be obtained. In addition, when the imaginary part (μ '') of a complex permeability is low, an increase in matching thickness will be caused.

If the real part ε 'of the complex dielectric constant is not an appropriate value, the reflection attenuation amount is lowered.

In addition, when the Curie point is remarkably low, a problem arises in that the temperature of the radio wave absorber itself easily exceeds the Curie point by the converted heat, resulting in loss of magnetism and inability to function as a radio wave absorber.

When the content of the iron oxide is less than 45.0 mol%, the matching thickness becomes 6 mm or more due to the decrease in the imaginary part (μ &quot;) of complex specific permeability, and furthermore, there arises a problem that the Curie temperature becomes 80 ° C. or less. . In addition, when the content of the iron oxide exceeds 49.0 mol%, the frequency causing a decrease in the real part (μ ') of the complex specific permeability is increased, and the amount of reflection attenuation at room temperature (25 ° C) in a low frequency region of 30 MHz is increased. The problem that it becomes less than 20dB arises.

When the content of zinc oxide is less than 19.0 mol%, the frequency causing a decrease in the real part (μ ') of complex specific permeability is increased, and the amount of reflection attenuation at room temperature (25 ° C.) in the low frequency region of 30 MHz is increased. The problem that this becomes 20 dB or less arises. Moreover, when content of the said zinc oxide exceeds 23.0 mol%, the matching thickness will be 6 mm or more, and the problem that a Curie temperature will be 80 degrees C or less arises.

(Description of Subcomponents Added to the Main Ingredient)

(1) Addition of cobalt oxide as a minor component

Cobalt oxide is contained in an amount of 1000 to 7000 ppm by weight (0.001 to 0.007 parts by weight), preferably 3500 to 6500 parts by weight (0.0035 to 0.0065 parts by weight), in terms of CoO, based on 100 parts by weight of the above-mentioned MnZn ferrite main component.

The addition of a suitable cobalt causes the effect of shifting the attenuation of the real part (μ ') of the complex specific permeability to the low frequency side, and when the content of the cobalt oxide is less than 1000 parts by weight (0.001 parts by weight), the real number of complex permeability The frequency causing negative (μ ') degradation becomes high. As a result, there arises a problem that the reflection attenuation at room temperature (25 ° C.) is 20 dB or less in the low frequency region of 30 MHz, and the reflection attenuation at minus 20 ° C. (-20 ° C.) is 15 dB or less.

On the other hand, when the content of cobalt oxide exceeds 7000 ppm by weight (0.007 parts by weight), on the contrary, the frequency causing a decrease in the real part (μ ') of complex specific permeability is increased, and at room temperature (25 ° C) in a low frequency region of 30 MHz ), The reflection attenuation amount becomes 20 dB or less, and the reflection attenuation amount at minus 20 ° C (-2O ° C) becomes 15 dB or less.

(2) Addition of Silicon Oxide (SiO ₂ ) as Subcomponent

Silicon oxide is contained in an amount of 10 to 200 ppm by weight (0.00001 to 0.0002 parts by weight) in terms of SiO ₂ , preferably 30 to 150 ppm by weight (0.00003 to 0.00015 parts by weight), based on 100 parts by weight of the MnZn ferrite main component. . If content of silicon oxide is less than 10 weight ppm (0.00001 weight part), the problem that a sintering density will fall remarkably will arise. Moreover, when content of a silicon oxide exceeds 200 weight ppm (0.0002 weight part), the problem that abnormal grain growth arises arises.

(3) Addition of calcium oxide (CaO) as a minor component

Calcium oxide is contained in an amount of 200 to 3000 ppm by weight (0.0002 to 0.003 parts by weight), preferably 500 to 1500 ppm by weight (0.0005 to 0.0015 parts by weight), in terms of CaO, as a sub ingredient with respect to 100 parts by weight of the above-mentioned MnZn ferrite main component. If the content of calcium oxide is less than 200 ppm by weight (0.0002 parts by weight), the real part (μ ') of the complex specific permeability at the frequency 30 MHz becomes large (the attenuation of the real part (μ') of the complex specific permeability moves toward the high frequency side. A problem arises that the reflection attenuation amount of 20 dB or more cannot be obtained.

Moreover, when content of calcium oxide exceeds 3000 weight ppm (0.003 weight part), the imaginary part (micro ") of the complex specific permeability in frequency 30MHz will become small, and the problem that a matching thickness will become thick will arise.

(4) Addition of niobium oxide (Nb ₂ O ₅ ) as a minor component

In the present invention, niobium oxide (Nb ₂ O ₅ ) is not an essential accessory.

The addition of niobium oxide (Nb ₂ O ₅ ) improves the sintering properties and further improves the characteristics that the attenuation of the real part (μ ') of the complex specific permeability shifts to the low frequency side and the amount of reflection attenuation at 30 MHz is improved. This tends to appear.

However, when the content of niobium oxide exceeds 500 ppm by weight (0.0005 parts by weight), the real part (μ ') of complex specific permeability at frequency 30MHz becomes large (the real part (μ') of complex specific permeability is attenuated. There is a tendency that a problem arises that the reflection attenuation amount of 20 dB or more cannot be obtained.

(5) Other minor ingredients

As other minor components, SnO ₂ , TiO ₂ , NiO, Ta ₂ O ₅ , ZrO ₂ , HfO ₂ , GeO ₂ , MoO ₃ , WO ₃ , Bi ₂ O ₃ , V ₂ O ₅ , In ₂ O ₃ , Cr ₂ O _3, the various subcomponents, such as Al ₂ O ₃ may be contained in a range that does not depart from the effects of the present invention.

The radio wave absorber of the present invention as described above is sintered at a temperature of about 1100 ° C to 1350 ° C after molding a MnZn ferrite material blended so that the composition after sintering is in the above range, for example, in a plate-like tile shape. It is prepared by making. For a more specific manufacturing method, please refer to the experimental example in the Examples below. As the size of the tile shape, a plate-shaped body having a vertical dimension of about 50 to 200 mm, a horizontal dimension of about 50 to 200 mm and a thickness dimension of about 3 to 10 mm can be exemplified.

(Example)

Hereinafter, the present invention will be described in more detail with reference to specific examples.

Each raw material component was weighed and wet-mixed for 16 hours by the steel ball mill so that the composition after baking might become a composition shown in following Table 1.

Next, this mixed powder was plasticized at 900 degreeC in air for 2 hours. The subcomponent was added to the obtained plastic so that the composition after baking might be set to the composition shown in following Table 1, and it wet-pulverized for 16 hours with the steel ball mill.

A 10% by weight polyvinyl alcohol aqueous solution was added to the obtained MnZn ferrite powder, granulated, and molded into a predetermined shape such that a characteristic test of the following radio wave absorber was possible at a pressure of ¹ ton / cm ² .

The molded article thus formed was fired. As the firing conditions, the firing temperature was set at 1300 ° C. (in air to 1300 ° C.), the oxygen partial pressure was controlled to 1000 ° C. in the subsequent cooling zone, and firing was carried out in a nitrogen (N ₂ ) atmosphere at 1000 ° C. or lower.

Thus, with respect to the sample of the radio wave absorber thus obtained, (1) the Curie point, (2) the matching thickness of the radio wave absorber, (3) the frequency characteristics and temperature characteristics of the radio wave absorption characteristics, and (4) the complex specific permeability The real part (μ '), the imaginary part (μ'') of the complex specific permeability, the value of the real part (ε') of the complex dielectric constant, and (5) the sintered density (ρ (g / cm ³ )) were measured, respectively.

(1) Measurement method of Curie point (Tc)

The sample was placed in a high temperature layer and held until sufficiently stable at each temperature, and then the temperature characteristic of the superpermeability (μi) was measured using an LCR meter. The point where the extension line connecting 80% of the maximum value and 20% of the point at the lower portion exceeding the maximum value of the initial permeability intersects the line of μi = 1 was obtained, and was defined as the Curie temperature (Tc). In addition, the measurement frequency was 1 kHz.

In addition, the target value of Curie temperature Tc is 80 degreeC or more.

(2) Matching thickness of the radio wave absorber (d)

As a radio wave absorption characteristic of the radio wave absorber, the reflection coefficient was measured by the network analyzer using the ring-shaped sample processed by the outer diameter of 19.8 mm and the inner diameter of 8.6 mm, and inserted in the coaxial tube. From the obtained measurement results, the amount of reflection attenuation and the normalized impedance of the entire surface of the electromagnetic wave absorber were calculated.

The relationship between the normalized impedance Z and the reflection coefficient S is as follows.

Z = (1 + S) / (1-S)

S = (Z-1) / (Z + 1)

S = (S _sample / S _metal )

-20log ｜ S ｜ = dB

The standardized impedance of each thickness was plotted on the Smith chart, the thickness passing through the center of the Smith chart was calculated | required, and the thickness was made into matching thickness d.

In addition, the target value of the matching thickness d is 6 mm or less.

(3) Frequency characteristics and temperature characteristics of radio wave absorption characteristics

The ring of the matched thickness calculated above was actually produced, and the following items were measured by the coaxial tube method described above.

Lower limit frequency where reflection attenuation satisfies 20 dB or more at 25 ° C: LF ₂₅ (MHz)

Upper limit frequency where reflection attenuation satisfies 20dB or more at 25 ° C: UF ₂₅ (MHz)

Lower limit frequency where reflection attenuation satisfies 15 dB or more at -20 ° C: LF _-20 (MHz)

Reflective attenuation at 25 ° C at frequency 30 MHz: RD ₂₅ (dB)

Reflection attenuation at -20 ° C at frequency 30MHz: RD _-20 (dB)

In addition, the target value of LF ₂₅ is 30 MHz or less.

Further, the target value of the UF ₂₅ is more than 300MHz.

In addition, the target value of LF- ₂₀ is 30 MHz or less.

Further, the target value of the RD _25, is more than 20dB.

In addition, the target value of RD- ₂₀ is 15 dB or more.

(4) Real part (μ ') of complex specific permeability, imaginary part (μ' ') of complex specific permeability, and real part (ε') of complex permittivity

According to the method of (2) above, using a ring-shaped sample processed at an outer diameter of 19.8 mm and an inner diameter of 8.6 mm, the reflection coefficient was measured by a network analyzer in a state of being inserted into a coaxial tube, μ ′, μ ″, and ε ′ were derived.

In addition, the target value of ε 'is in the range of 10 <ε' <30.

In addition, the target value of µ 'is µ' <80.

The target value of μ '' is μ ''> 260.

(5) Sintered Density ρ (g / cm ³ )

It measured by the Archimedes method.

In addition, the target value of sintered density (rho) exceeds 4.7 (g / cm <^3> ).

The measurement results of each of these terms are shown in Table 1 below.

The effect of this invention is clear from the above experiment result. That is, the present invention is a radio wave absorber composed of a sintered MnZn ferrite, which is 45.0 to 49.0 mol% of iron oxide in terms of Fe ₂ O ₃ , 19.0 to 23.0 mol% of zinc oxide in terms of ZnO, and MnO for manganese oxide. Since it has a main component which consists of 28.0-36.0 mol% in conversion, and it is comprised so that a predetermined amount may contain cobalt oxide, a silicon oxide, and calcium oxide as a subcomponent with respect to 100 weight part of this main component, Reduction can be aimed at, and it is excellent also in the temperature characteristic frequency characteristic of a Curie temperature, matching thickness, and a radio wave absorption characteristic.

The manufacturing method of MnZn type ferrite of this invention can be used for various electric parts industry widely.

Claims (6)

As a radio wave absorber composed of MnZn ferrite sintered body, This radio absorber Iron oxide in terms of Fe ₂ O ₃ 45.0-49.0 mol%, Zinc oxide is 19.0 to 23.0 mol% in terms of ZnO, and Manganese oxide has a main component consisting of 28.0 to 36.0 mol% in terms of MnO, As a subcomponent with respect to 100 parts by weight of this main component, 1000 to 7000 ppm by weight (0.001 to 0.007 parts by weight) of cobalt oxide in terms of CoO, 10 to 200 ppm by weight (0.00001 to 0.0002 parts by weight) of silicon oxide in terms of SiO _2, and 200 to 2500 parts by weight of calcium oxide in terms of CaO A radio wave absorber comprising ppm (0.0002 to 0.0025 parts by weight). The radio wave absorber according to claim 1, further comprising less than 500 ppm by weight (0.0005 parts by weight) of niobium oxide in terms of Nb ₂ O ₅ as a minor component. The radio wave absorber according to claim 1, wherein the cobalt oxide is 3500 to 6500 ppm by weight (0.0035 to 0.0065 parts by weight) in terms of CoO. A characteristic according to claim 1, wherein the reflection attenuation at 25 ° C. is 20 dB or more. Characteristic of reflection attenuation at -20 ℃ over 15dB, The characteristic that the lower limit frequency of the reflection attenuation satisfies 20dB at 25 ° C is 30MHz or less, The upper limit frequency where the reflection attenuation satisfies 20dB at 25 ° C is 300MHz or more, The frequency of the lower limit at which the reflection attenuation satisfies 15 dB at -20 ° C is 30 MHz or less,  The matching thickness is 6 mm or less, and The electromagnetic wave absorber characterized by the Curie temperature having a characteristic of 80 ℃ or more. 5. The property of claim 4 wherein the sintered density is greater than 4.7 (g / cm ³ ), The characteristic of ε 'which is a complex dielectric constant part at frequency 30 MHz satisfies the condition of 10 <ε' <30, The property that the value of the complex permeability real part μ 'at the frequency 30 MHz satisfies the condition of μ' <80, and A radio wave absorber characterized in that the value of the complex permeability imaginary part μ '' at a frequency of 30 MHz satisfies the condition of μ ''> 260. The wave absorber according to claim 1, which has a plate-like tile shape.