• Applied Chemistry for Engineering
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• v.7 no.6
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• pp.1027-1033
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• 1996

Under the Irradiation of the radiofrequency wave, the dipole materials vibrate as microwavic phase change. This causes friction between adjacent molecules and enables an unique charateristics of interior heating of the materials. When dipole gases are adsorbed inside of a solid radiofrequency wave absorber, the gases can be decomposed easily by the microwave energy. The decomposition of sour gases was successfully tested in this manner to develop a sour gas removal process from the combustion flue gas. The standard gas bearing NO and $SO_2$ was passed through and microwave was applied on the calcined char bed as the wave absorber and the gas adsorbent. It was found that more then 95% of NO and 70 % of $SO_2$ was decomposed to the environmentally clean elements during the passage through the 20 gram char bed under the microwave impingement. The surface area and the porosity of char increased because the oxygen radicals produced from decomposed gas attacked carbon in the char capillaries and formed $CO_2$. For a lower concentration of sour gas, general cases in the commercial combustion processes, almost complete decomposion is believed possible and this method is surely expected to be useful for the prevention of air pollutions.

• Journal of the Korea Institute of Military Science and Technology
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• v.27 no.3
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• pp.311-318
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• 2024

In this paper, a design for a radio frequency(RF) and infrared(IR) absorber with metasurfaces is discussed in microwave frequency bands. The RF absorber includes double layers of metasurfaces to operate in S- and X-bands. Effects of sheet resistance of the metasurfaces and thicknesses of dielectric supporting layers on reflection responses are investigated. An IR stealth layer incorporates an array of conductive grids with slits to reflect IR signals but to transmit RF signals and visible rays. Periodicity of the grids and slits is studied for transmission responses in the X-band and a surface area ratio. Reflection responses of the RF/IR multispectral absorber are found to be lower than -10 dB and -16 dB in the S- and X-bands, respectively, from full-wave simulation. Finally, the RF/IR multispectral absorber is fabricated and its reflection responses are measured to verify designed performance.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.06a
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• pp.96-97
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• 2003

• Proceedings of the Korean Magnestics Society Conference
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• 1992.03a
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• pp.52-53
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• 1992

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.4 no.3
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• pp.3-10
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• 1993

As a method to measure the absorbing characteristics of microwave absorber, various microwave measuring method can be used fundamentally. There is, however, a big problem in measuring errors, since the wavelength of microwave such as used for radar is very short. Therefor, this research aimed to design and fabricate a converting adaptor of 20mm .PHI. coaxial tube from a type-N connector to coaxial tube and to use it for evaluating absorption characteristics of microwave absorbor. Furthemore, the measurements of absorbing characteristics and material constants have been perfomed and reviewed, which were carried out by using the coaxial and by using rectangular waveguide, respectively. As a result, the validity of the proposed measuring method has been conformed. In this paper, a preliminary evalua- tion on the characteristics of the electromagnetic wave absorbor for X-band radar designed and fabricated for a laboratory use is performed by reflected power method near to a pratical use. Then for field test by using X-band radar is carried out with real target of $1.2m\times1.2m$ in size. As the result of the above, the usefullness of the designed and fabricated electromagnetic wave absorber in paint type for X-band radar has been confirmed.

• Journal of the Korean Magnetics Society
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• v.19 no.2
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• pp.62-66
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• 2009

The soft magnetic FeSiCr were processed the ball-mill for 30 hours and the shape of FeSiCr particles was changed from sphere to flake type, which was observed using scanning electron microscope. The complex permittivity and permeability spectra and reflection loss of FeSiCr-rubber composite was measured using Network Analyzer in order to investigate the relationship between the microwave absorption and the material constants. The matching frequency shifted toward lower frequency range with microwave absorber thickness, and microwave absorber with FeSiCr-rubber composite showed a maxium reflection loss of -8.3 dB at 1.86 GHz for a 1.3 mm thickness.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.2 s.93
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• pp.228-234
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• 2005

A magnetic composite as noise absorber of quasi-microwave band was developed. The Fe-Si-Al alloy powder were forged by attrition mill to get flaky shape. The magnetic composite sheet was fabricated in which powders are dispersed in polymer and aligned in the direction perpendicular to electromagnetic wave propagation. The permittivity of magnetic composite is increased as forging time increasing, while the permeability is decreased slightly. The maximum attenuation peak of reflection loss is shifted to lower fiequency range as milling time increasing, and the value of maximum attenuation peak is to get smaller gradually. From these result, we could designed a noise absorber sheet (t=1.0 mm) for quasi-microwave band, which is impedance matched at 1.4 GHz with respect to -8.2 dB reflection 1055.

• 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 electromagnetic engineering and science
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• v.16 no.2
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• pp.106-111
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• 2016

A resistive and capacitive (RC) microwave absorber with a layer thickness less than a quarter of a wavelength is investigated based on closed-form design equations, which are derived from the equivalent circuit of the RC absorber. The RC absorber is shown to have a theoretical 90% absorption bandwidth of 93% when the electrical layer thickness is $57^{\circ}$ (about ${\lambda}_0/6$). The trade-offs between the layer thickness and the absorption bandwidth are also elucidated. The presented formulation is validated by a design example at 3 GHz. The RC absorber is realized using a silver nanowire resistive rectangular structure with surrounding gaps. The measured 90% absorption bandwidth with a layer thickness of ${\lambda}_0/8$ is 76% from 2.3 GHz to 5.1 GHz in accordance with the theory and EM simulations. The presented design methodology is scalable to other frequencies.

• Journal of Navigation and Port Research
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• v.27 no.4
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• pp.437-441
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• 2003

In this paper, the 30 W power amplifier for an IMT-2000 repeater was developed a gain flatness and the third IMD (Intermodulation distortion) by microwave absorber. The absorption ability of the absorber is shown up to -10 dB and -4 dB at 3.6 GHz, 2.3 GHz band, respectively. The power amplifier without absorber has the gain over 57 dB, the gain flatness of $\pm$0.33 dB and the third IMD of 27 dBc at 33.3 W output. Otherwise, the power amplifier with absorber has the gain over 58 dB, the gain flatness of less than $\pm$0.9, the third IMD over 29 dBc at the same output power. As a result, the characteristic of the different type shows improvement of 1 dB in gain, 0.3 dB in gain flatness and 1.77 dBc in IMD.