• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1478-1480
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• 1994

In this paper, the microwave absorption properties of two layered absorber were evaluated. The two layer absorber were composed of Ni-Zn ferrite/rubber absorber and Ferroxplana/rubber absorber. The most absorption properties condition were obtained when the transforming layer and absorbing layer were Ferroxplana/robber absorber and Ni -Zn ferrite/rubber absorber. respectivity. The optimal thickness of the transforming and the absorbing layer were 4(mm) and 1(mm), respective1y.

• Proceedings of the Korean Magnestics Society Conference
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• 1991.05a
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• pp.61-62
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• 1991

• Applied Chemistry for Engineering
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• v.19 no.4
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• pp.445-451
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• 2008

In order to regenerate the activated carbon polluted by volatile organic compounds (VOCs) using microwave, adsorption and desorption characteristics of benzene over activated carbon (AC) coated with insulating materials were investigated. Physical characteristics of activated carbon and insulator-coated ACs were investigated by means of $N_2$ gas adsorption and scanning electron microscopy (SEM). The amount of VOC adsorbed showed a positive relationship with the specific surface area of the ACs, and spark discharge over insulator-coated ACs did not occur. Potassium silicate (PS) was the best binder for coating of insulating materials on AC. Amount of benzene desorbed by microwave irradiation was dependent on output power of microwave. Nearly same performance was obtained even though the adsorption-desorption operation under microwave irradiation was repeated 5 times. Finally, it was known that the microwave heating was a very effective mean for regenerating the polluted AC.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05a
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• pp.45-49
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• 2002

In this paper, we have studied about electromagnetic wave absorbing properties of ferrite-rubber composite with a variation of ferrite. Amounts of ferrite in a composite absorber were changed from 52 wt.% to 62 wt.%. As a result, it has been shown that the electromagnetic wave absorbing properties of ferrite-rubber composite are related to the amount of ferrite in composite absorber. As a summary, it could be controled the electromagnetic wave absorbing property of ferrite-rubber composite by changing some kinds of annex A and amount of ferrite.

• Journal of the Korean Magnetics Society
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• v.18 no.3
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• pp.120-125
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• 2008

In this study, NiCoZn ferrites with the variation of sintering temperature and chemical composition were prepared by the coprecipitation. Microstructures Crystal structure of NiCoZn ferrites were analyzed by XRD and their electric magnetic characteristics were analyzed by LCR meter and their morphology observed by SEM. We identified that these powders have a typical NiCoZn spinel structure and nanoparticles average size of 40 nm. The impurity, the initial permeability and the Q factor value are the lowest of sintered NiCoZn ferrite at $1250^{\circ}C$. Also, we measured S-parameter for $(Ni_{0.4}Co_{0.1}Zn_{0.5})Fe_2O_4$ which showed a maximum reflection loss of -3.1 dB at 6 GHz for the 2 mm thick sample. From this result, we found that the NiCoZn ferrite can be used in ferrite microwave-absorbing application at a higher frequency region (> 6 GHz).

• Journal of the Korean Magnetics Society
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• v.3 no.2
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• pp.115-120
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• 1993

The relationship between magnetic parameter and microwave absorbing performance evaluation factor of electomagnetic wave absorber such as matching frequency, matching thickness were investigated for Ni-Zn ferrite composites. It was identified that the maximum value of ${\mu}_{r}$" is shift to low frequency with decrese Ni/Zn ratio and the value of ${\mu}_{r}$" is maximum in the case of Ni/Zn=1. All Ni-Zn ferrite composites in this study have two matching frequencies in 1-12 GHz frequency. It can be suggested that $f_{m1}$ is proportional to resonance frequency and $f_{m2}$ is proportional to the saturation magnetization.

• Journal of the Korean Magnetics Society
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• v.15 no.3
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• pp.202-206
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• 2005

The present investigation provides an electromagnetic radiation absorptive composition which comprises silver-coated ferrite microspheres dispersed in silicon rubber matrix for the aim of thin microwave absorber in GHz frequencies. Ni-Zn ferrite spheres with $50{\mu}m$ size in average were prepared by spray-drying and sintering at $1130^{\circ}C$. Conductive silver layer was plated on ferrite spheres by electroless plating. Conductive Ni-Zn ferrite sphere with uniform silver layer were obtained in the concentration of 10 g/L $AgNO_3$ per 20 g ferrite spheres. For this powder, electrical resistance is reduced as low as $10^{-2}\~10^{-3}\;\Omega$. The most sensitive material parameters with silver plating is real and imaginary parts of complex permittivity. The conductive Ni-Zn ferrite spheres have large values of dielectric constant. Due to this high dielectric constant of microspheres, matching thickness is reduced to as low as 2 mm at the frequency of 7 GHz, which is much thinner than conventional ferrite absorbers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.68-71
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• 2000

In this study, A set-up for measuring a initial permeability of soft-ferrite powder was developed with a differential transformer coil. To measure a initial permeability of magnetic powder is cumbersome since there are not any measuring equipment and method. A magnetic powder is currently used for a magnetic fluid and microwave absorber materials, and the initial permeability of the magnetic powders is very important to be evaluated a powder for some applications.

• Journal of Environmental Science International
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• v.15 no.6
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• pp.579-586
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• 2006

The purposes of this paper were to monitor the temperature rising courses and spark discharge of the modified granular activated carbon (GAC) by microwave (MW) irradiation and to evaluate absorption of benzene. The GAC coated on $SiO_2$, boron, talc, ferrite was named as the modified GAC. Thermal and spark discharge measurement of virgin GAC and modifed GAC has been carried out using a MW device operating at 2450 MHz under various energy conditions. The results of this paper as follows. First, the modified GAC is more efficient than the virgin GAC in temperature control. Temperature gradient of the modified GAC is more lower than that of virgin GAC. The temperature gradient of GAC was observed in the following order : virgin GAC, Mn-Zn ferrite/GAC, Ni-Zn ferrite,/GAC, $SiO_2/GAC$, Boron/GAC, Talc/GAC. Second, the spark discharge of the modified GAC was diminished, compared with that of virgin GAC. Because of its excellent electrical insulating properties, the coating material prevents the spark discharge. Finally, the benzene adsorption capacity of the modified GAC decreased due to diminishing of adsorption site by the coating material. Considering the temperature gradient and spark discharge of GAC, the GAC coated $SiO_2$ would be appropriate absorbent under irradiation of MW.

• Journal of the Korean Magnetics Society
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• v.1 no.2
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• pp.49-54
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• 1991

In this study the correlation between material constants and microwave absorbing characteristics of ferroxplana composite microwave absorber used in X-band was investigated. The real part of permeability(${\mu}_{r}'$) was decreased and the imaginary part of permeability(${\mu}_{r}"$) of ferroxplana composite was increased with increaing ferroxplana loading ratio(F/R). The frequency showing maximum attenuation was shifted to lower frequency with increasing absorber thickness. The absorber 2.6 mm thick showed good band width property and 3.2 mm thick showed good attenuation property. From the apphcation of ferroxplana composite's material constants to the region of material constants which satisfy broad band width, it is found that the absorbing characteristics were estimated quantitatively. Estabhshment of material constants' region which satisfies broad band width can make practical application to design of high performance ferrite microwave absorber.