• Journal of Magnetics
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• 제12권1호
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• pp.49-52
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• 2007

We investigated annealing effect of microforged powders on magnetic properties and electromagnetic absorption behaviors for ferromagnetic Fe-Cr metal alloy powder-polymer composites. The coercive properties greatly decreased with annealing temperature and the magnetic permeability had significantly increased after microforging and subsequent annealing treatment, due to a reduction in lattice strain of the microforged powders. The power loss in the far field regime also had greatly increased after microforging and subsequent annealing treatment in frequency range from 50 MHz to 6 GHz. As a result, the electromagnetic absorption of ferromagnetic Fe-Cr alloy metal powder-polymer composites was highly improved because of the relaxation of the internal strain during annealing process.

• 한국분말재료학회지
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• 제15권1호
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• pp.18-22
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• 2008

The electromagnetic (EM) wave absorption properties with a variation of crystallization annealing temperature have been investigated in a sheet-type absorber using the $Fe_{73}Si_{16}B_7Nb_3Cu_1$ alloy powder. With increasing the annealing temperature the complex permeability (${\mu}_r$), permittivity (${\varepsilon}_r$) and power absorption changed. The EM wave absorber shows the maximum permeability and permittivity after the annealing at $610^{\circ}C$ for 1 hour, and its calculated power absorption is above 80% of input power in the frequency range over 1.5 GHz.

• Journal of electromagnetic engineering and science
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• 제4권2호
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• pp.51-55
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• 2004

With the progress of the electronics industry and radio communication technology, certain problems, such as electromagnetic interference(EMI), have arisen due to the increased use of electromagnetic(EM) waves. International organizations such as CISPR, FCC, and ANSI have provided the standards for the EM wave environment and for the countermeasure of the electromagnetic compatibility(EMC). EM wave absorbers are used for constructing an anechoic chamber to test and measure EMI and electromagnetic susceptibility(EMS). In this paper, we have designed an one-body EM(electromagnetic) wave ferrite absorber, based on the equivalent material constants method for both normally and obliquely incident waves, whose absorption abilities are superior to that of the conventional ones. The fabricated absorber has a thickness of 27.68 mm and shows an absorption ability over 20 ㏈ in the frequency from 30 MHz to 6 ㎓.

• 한국재료학회지
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• 제29권6호
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• pp.363-370
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• 2019

The recent development of information and communication technologies brings new changes to automobile traffic systems. The most typical example is the advancement of dedicated short range communication(DSRC). DSRC mainly consists of an intelligent transportation system(ITS), an electronic toll collection system(ETCS) and an advanced traveler information system(ATIS). These wireless communications often cause unnecessary electromagnetic waves, and these electromagnetic waves, in turn, cause frequent system malfunction. To solve this problem, an absorber of electromagnetic waves is suggested. In this research, various materials, such as powdered metal and iron oxides, are used to test the possibility for an effective absorption of the unnecessary electromagnetic waves. The various metal powders are made into a thin sheet form by compositing through processing. The electromagnetic characteristics(complex permittivity, complex permeability) of the fabricated sheet are measured. As a result, we achieve -6.5 dB at 940 MHz(77.6 % absorption rate) with a 1.0 mm-thickness electromagnet wave absorber, and -9.5 dB at 940 MHz(88.8 % absorption rate) with a 2.0 mm-thickness absorber.

• 한국항해항만학회지
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• 제27권1호
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• pp.75-80
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• 2003

천연세라믹, 옻칠, 그리고 고무의 전파흡수능을 조사하였다. 천연세라믹은 2.5GHz~4.5GHz의 주파수 범위에서 2.5dB이상의 전파흡수능을 나타내었으며 옻칠의 전파흡수능이 기존에 전파흡수체의 지지재로 이용되는 고무에 비해 우수한 전파흡수능을 갖고 있음을 확인하였다. 페라이트에 옻칠을 지지재로 이용한 전파흡수체에 대하여 시뮬레이션 한 결과 0.5GHz~10GHz의 주파수 범위에서 16dB 이상의 우수한 전파흡수능을 나타내었다. 따라서 기종에 지지재로 이용하던 고무대신 본 연구에서 새롭게 제안하는 옻칠을 전파흡수체의 지지재로 이용하는 것이 광대역에서 우수한 전파흡수체를 얻을 수 있을 것으로 예상된다.

• 대한금속재료학회지
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• 제47권12호
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• pp.866-872
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• 2009

The effects of magnetic powder thickness on electromagnetic wave absorption characteristics in Fe-6.5Si-0.9Cr (wt%) alloy flakes/polymer composite sheets available for quasi-microwave band have been investigated. The atomized FeSiCr powders were milled by using attritor for 12, 24, and 36 h, powder thickness changed from $40{\mu}m$ to $3{\mu}m$ upon 36 h milling. The composite sheet, including thinned magnetic flakes, exhibited higher power loss in the GHz frequency range as compared with the sheets having thick flakes. Moreover, both the complex permeability and the loss factor increased with the decrease in thickness of the alloy flakes. Therefore, the enhanced power loss property of the sheets containing thin alloy flakes was attributed to the flakes of high complex permeability, especially their imaginary part. Additionally, the complex permittivity was also increased with the reduction of flake thickness, and this behavior was considered to be helpful for improvement of the electromagnetic wave absorption characteristics in the composite sheets, including thin alloy flakes.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2001년도 종합학술발표회 논문집 Vol.11 No.1
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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 electromagnetic engineering and science
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• 제16권3호
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• pp.150-158
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• 2016

This paper reports on a study of LiNiZn-ferrite composite as a radiation absorbent material (RAM). The electromagnetic (EM) wave absorbers are composed of an EM wave absorbing material and a polymeric binder. The surface morphology, chemical composition, weight percent of the ferrite composite of the toroid sample, magnetic properties, and return loss are investigated using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM), and network analyzer. For preparing the absorbing sheet, chlorinated polyethylene (CPE) is used as a polymeric binder. The EM wave absorption properties of the prepared samples were studied at 4 - 8 GHz. We can confirm the effects of the thickness of the samples for absorption properties. An absorption bandwidth of more than a 10-dB return loss shifts toward a lower frequency range along with an increase in the thickness of the absorber.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.622-629
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• 2003

고성능 복합형 전자파 흡수체를 개발하기 위해 종래에는 지지재로서 주로 Silicone 고무나 CPE가 사용되어 왔다. 본 연구에서는 전통 공예에서 사용되어 오던 옻에 대한 전자파 흡수능을 조사하고 이를 지지재로 사용하여 MnZn 페라이트와 배합하여 전자파 흡수체를 제작한 경우의 전자파 흡수능을 조사하고, 흡수체의 두께에 따른 흡수능을 조사하였다. 옻을 지지재로 한 MnZn 페라이트 복합형 전자파 흡수체는 CPE나 Silicone 고무를 지지재로 한 전자파 흡수체에 비하여 우수한 전파흡수특성 나타내었으며, 옻의 두께 변화에 따라 정합주파수와 전파흡수능이 변화함을 알았다.

• 한국분말재료학회지
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• 제14권5호
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• pp.303-308
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• 2007

The oxidation of $Fe_{73}Si_{16}B_7Nb_3Cu_1$ nanocrystalline powder has been conducted to investigate its influence on the electromagnetic wave absorption characteristics of the soft magnetic material. Oxidation occurred primarily on the surface of nanocrystals. Oxidation reduced the real part of complex permeability due to the reduction of the relative volume of the powder, which otherwise contributes to the permeability. Oxidation reduced the absorption efficiency of the sheet at frequencies over 1GHz, indicating that the relative contribution of skin depth increments to the absorption was not significant. The pulverization and milling process lowered the optimum crystallization temperature of the material by $40{\sim}50^{\circ}C$ because of the internal energy accumulated during the fragmentation and powder thinning processes.