• Journal of Powder Materials
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• v.20 no.2
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• pp.125-128
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• 2013

Magnetic and dielectric properties of rubber composites are controlled by using two kinds of high-permeability metal particles with different electrical conductivity (Sendust, Permalloy), and their effect on microwave absorbance has been investigated, focusing on the quasi-microwave frequency band (0.8-2 GHz). Noise absorbing sheets are composite materials of magnetic flake particles of high aspect ratio dispersed in polymer matrix with various filler amount of 80-90 wt.%. The frequency dispersion and magnitude of complex permeability is almost the same for Sendust and Permalloy composite specimens. However, the complex permittivity of the Permalloy composite (${{\varepsilon}_r}^{\prime}{\simeq}250$, ${{\varepsilon}_r}^{{\prime}{\prime}}{\simeq}50$) is much greater than that of Sendust composite (${{\varepsilon}_r}^{\prime}{\simeq}70$, ${{\varepsilon}_r}^{{\prime}{\prime}}{\simeq}0$). Due to the large dielectric permittivity of Permalloy composite, the absorbing band is shifted to lower frequency region. However, the investigation of impedance matching reveals that the magnetic permeability is still small to satisfy the zero-reflected condition at the quasi-microwave frequency band, resulting in a small microwave absorbance lower than 10 dB.

• Journal of the Korean Ceramic Society
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• v.29 no.4
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• pp.293-297
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• 1992

A proper combination of complex permeability and permittivity is necessary to produce the zero-reflection microwave absorber with an impedance matching. Increasing of dielectric permittivity and development of an impedance matching was investigated in ferrite-rubber composite specimens by addition of conducting materials. Graphite powder of high dielectric constant was added to the composite specimens to increase the permittivity. The precise estimation of graphite content to produce the matched-wave-impedance absorber at a given frequency can be made by using the numerically derived solution map of impedance matching. It was suggested that permittivity adjustment is an effective technique to obtained the microwave absorber with both good absorbing properties and small thickness as well.

• Resources Recycling
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• v.9 no.6
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• pp.31-35
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• 2000

The complex permeability, the complex permittivity and the reflection loss are investigated in the composite microwave absorbers which are mixed with the wasted Mn-Zn ferrite and the industrial cement. The cement has larger the complex permittivity than that of the rubber. The complex permittivity is decreasing with the increment of the mixing ratio of Mn-Zn ferrite to cement (F/C in weight) and the complex permeability is increasing with the increment of F/C. The maximum reflection loss is above -40 dB at all samples. The matching frequency is in the range of 1.3 GHz to 2.9 GHz and is decreasing with the increment of F/C from 1 to 3. The matching thickness is increasing with the increment of F/C. The wasted Mn-Zn ferrite and the cement is very useful material for the composite microwave absorber.

• Journal of the Korean Ceramic Society
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• v.31 no.4
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• pp.415-419
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• 1994

The material constants(the complex permeability and permittivity) of ferrite composite determine its microwave absorbing characteristics. Therefore, in order to improve the microwave absorbing characteristics, it is necessary to control the material constants of the ferrite composite. In this study, the method of improving microwave absorbing characteristics by control of permittivity of ferrite composite which has not satisfying matching condition in C-X band (4 GHz~12.4 GHz) was investigated. It was possible to control the permittivity by adjusting graphite loading ratio in the ferrite composite microwave absorber. It was also concluded that the control of permittivity of ferrite composite is effective method to improve the microwave absorbing characteristics.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.21-26
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• 1995

The systematic variation of complex permeability and complex permittivity and their relationship with micro-wave absorbing properties are investigated in sintered Ni-Zn ferrites of non-stoichiometric composition. The specirrens of ${(Ni_{0.5}Zn_{0.5}O)}_{1-x}(Fe_{2}O_{3})_{1+x}$ spinels were prepared by a conventional ceramic processing technique. In the present study. complex permeability and permittivity can be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the spinel lattice. The primary effect of the excess ${\alpha}-Fe_{2}O_{3}$ is to increase the dielectric constant. while the notable decrease of magnetic loss is observed in the iron-deficient ferrites. The results suggest that the matching fre-queocyand matching thickness could be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the Ni-Zn ferrite.

• Journal of electromagnetic engineering and science
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• v.12 no.1
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• pp.20-25
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• 2012

In this paper, the EM wave absorber for ETC system was designed and fabricated. We fabricated several samples in different composition ratios of flaked sendust and CPE(Chlorinated Polyethylene). Absorption abilities were simulated in accordance with different thicknesses of the prepared absorbers and changed complex relative permittivity and permeability according to composition ratio. The optimized mixing ratio of flaked sendust and CPE was found as 60 : 40 wt.% by experiments and simulation. Then the EM wave absorber was fabricated and tested using the simulated data. As a result, the developed EM wave absorber has the thickness of 2.75 mm and absorption ability was 22.5 dB in the case of normal incidence at 5.8 GHz. Therefore, it was confirmed that the newly developed absorber can be used for ETC system.

• Journal of information and communication convergence engineering
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• v.4 no.3
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• pp.114-117
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• 2006

In this paper, we fabricated the EM wave absorber for 94 GHz radar sensors using Permalloy of magnetic material with chlorinated polyethylene (CPE), and S-parameter was measured. The complex relative permittivity and permeability are calculated by the measured data. Absorption abilities are simulated according to different thickness of the EM wave absorbers, and the EM wave absorber was manufactured based on the simulated design. Simulated and measured results agree very well. As a result, we developed the EM wave absorber with the thickness of 1.15 mm which has an absorption ability of 18 dB at 94 GHz.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.304-309
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• 2001

With the development of electromagnetic communication technology and increased use of electromagnetic wave, the countermeasure of EMI(Electromagnetic Interference) becomes more important socially, and interest for the electromagnetic wave absorber has also increased. In this paper, we have studied characteristics of frequency dependency on complex permittivity and complex permeability according to the changes of composition rate and sintering temperature of NiCuZn ferrite also known as electromagnetic wave absorber and further looked into effect of electromagnetic wave absorption properties. From the measurement where the composition of Fe$_2$O$_3$ and ZnO of NiCuZn ferrite was fixed at 49 and 34 mol% respectively while composition of NiO and CuO has been varied at each test, we found out that initial permeability and permittivity were high and the absorbing ability of electromagnetic wave recorded best with loss tangent(${\mu}$r"/${\mu}$r′) displays more than 1 within the frequency band of 2MHz～9.5MHz when the composition ratio of NiO was ranged around 8.5～9.5 mol% and the sintering temperature was 1,080$^{\circ}C$.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.5
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• pp.994-1000
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• 2001

With the development of electromagnetic communication technology and increased use of electromagnetic wave, the countermeasure of EMI(Electromagnetic Interference) becomes more important socially, and interest for the electromagnetic wave absorber has also increased. In this paper, we have studied characteristics of frequency dependency on complex permittivity and complex permeability according to the changes of composition rate and sintering temperature of NiCuZn ferrite also known as electromagnetic wave absorber and further looked into effect of electromagnetic wave absorption properties. From the measurement where the composition of $Fe_2O_3$ and ZnO of NiCuZn ferrite was fixed at 49 and 34 mol% respectively while composition of NiO and CuO has been varied at each test, we found out that Initial permeability and permittivity were high and the absorbing ability of electromagnetic wave recorded best with $loss tangent(=\mur"/\mur')$ displays more than 1 within the frequency band of 2MHz~9.5MHz when the composition ratio of NiO was ranged around 8.5~9.5 mol% and the sintering temperature was $1080^{\circ}C$.TEX>.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.9
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• pp.1051-1057
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• 2008

In this paper, we analyzed the characteristics of the EM wave absorber which was fabricated by using flake sendust (soft metal magnetic powder). The flake sendust was made of 3 different granularity by attrition mill. First, we have fabricated 3 kind of EM wave absorbers using the flake sendust and CPE(Chlorinated Polyethylene) and measured the S-parameters of the EM wave absorber. The complex relative permittivity and permeability were calculated from the measured data and the variations according to a change of granularity were researched. As a result, it was confirmed that the EM wave absorber using flake sendust with the $140{\mu}m$ average granularity has outstanding absorption ability in high frequency range(C band) for the reduction of eddy current loss(increase of permeability) and the increase of space charge polarization(increase of permittivity).