• Title/Summary/Keyword: absorbers

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A Study on the EM Wave Absorber for the Electromagnetic Environment of Indoor Wireless LAN (실내 무선 LAN 전자파 환경 대책용 전파 흡수체에 관한 연구)

  • Yoon, Sang-Gil;Kim, Dong-Il;Lee, Dae-Hee;Choi, Chang-Mook
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.18 no.11
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    • pp.1224-1230
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    • 2007
  • Recently, wireless LAN are often applied in home or office because of its various of convenience. Frequency rage of wireless LAN specified by IEEE 802.11a is at 5.2 GHz and IEEE 802.11b is 2.4 GHz. But in offices with wireless LAN devices, reflection of waves against walls, ceilings, floors and desks made of metal creates multipath problems that reduce communication speed and lose data. These problems can be solved by using EM wave absorber. In this paper, we designed and fabricated EM wave absorbers using MnZn-ferrite, sendust, carbon and CPE(Chlorinated Polyethylene). The EM wave absorber with the ratio of MnZn-Ferrite : sendust : CPE=64 : 16 : 20 wt.% has thickness of 3.7 mm and absorption ability more than 17 dB at 2.4 GHz and the EM wave absorber with the ratio of MnZn-ferrite : carbon : CPE=40 : 15 : 45 wt.% has thickness of 3.8 mm and absorption ability more than 23 dB at 5.2 GHz.

Application Performances of the Simplified Solar Collectors and for the Drying of Red Pepper (간이(簡易) 태양열(太陽熱) 집열기(集熱器)의 유형별(類型別) 분석(分析) 및 고추건조(乾燥)에의 이용(利用))

  • Choi, Boo-Dol;Chun, Jae-Kun
    • Korean Journal of Food Science and Technology
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    • v.18 no.6
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    • pp.479-484
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    • 1986
  • Two different types of solar collector for farm dryer- the flatplate type and the modified tubular type-were constructed and analyzed on their performances. The transparent plastic film, black painted galvanized iron sheet and black vinyl film were used for the cover and absorber of the flat-plate types. The simplified tubular type was constructed with transparent films for the cover and black vinyl films for the absorber Two elliptical iron rings were used to form a tubular shape through which air could pass. No remarkable differences were found in thermal efficiences between the absorbers made with galvanized iron sheet and black vinyl film. The average thermal efficiencies of the solar collectors were 42.8%(max.48.2%, min.38.2%) for flat plate type and 22.971 (max. 25.4%, min. 14.8%)) for tubular one. The empirical equations were proved to be applicable to the prediction of temperature elevation. The tubular solar heat collector was successfully applied to red peppers drying as a practical farm dryer. The drying rate was almost doubled compared to a conventional sun drying.

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Spark plasma sintering of UO2 fuel composite with Gd2O3 integral fuel burnable absorber

  • Papynov, E.K.;Shichalin, O.O.;Belov, A.A.;Portnyagin, A.S.;Buravlev, I.Yu;Mayorov, V.Yu;Sukhorada, A.E.;Gridasova, E.A.;Nomerovskiy, A.D.;Glavinskaya, V.O.;Tananaev, I.G.;Sergienko, V.I.
    • Nuclear Engineering and Technology
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    • v.52 no.8
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    • pp.1756-1763
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    • 2020
  • The paper studies spark plasma sintering (SPS) of industrially used UO2-based fuel containing integral fuel burnable absorber (IFBA) of neutrons Gd2O3. Densification dynamics of pristine UO2 powder and the one added with 2 and 8 wt% of Gd2O3 under ultrasonication in liquid has been studied under SPS conditions at 1050, 1250, and 1450 ℃. Effect of sintering temperature on phase composition as well as on O/U stoichiometry has been investigated for UO2 SPS ceramics. Sintering of uranium dioxide added with Gd2O3 yields solid solution (U,Gd)O2, which is isostructural to UO2. SEM with EDX and metallography were implemented to analyze the microstructure of the obtained UO2 ceramics and composite UO2-Gd2O3 one, particularly, open porosity, defects, and Gd2O3 distribution were studied. Microhardness, compressive strength and density were shown to reduce after addition of Gd2O3. Obtained results prove the hypothesis on formation of stable pores in the system of UO2-Gd2O3 due to Kirkendall effect that reduces sintering efficiency. The paper expands fundamental knowledge on pros and cons of fuel fabrication with IFBA using SPS technology.

Microwave Absorbing Properties of Silver-coated Ni-Zn Ferrite Spheres Prepared by Electroless Plating (무전해 도금법에 의해 제조된 은 피복 Ni-Zn Ferrite Sphere의 전파흡수특성)

  • Kim, Jong-Hyuk;Kim, Jae-Woong;Kim, Sung-Soo
    • 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.

Laboratory and Full-scale Testing to Investigate the Performance of Rock Fall Protection System with Hexagonal Wire Net (육각 낙석방지망의 성능평가를 위한 실내 및 실대형실험)

  • Youn, Ilro;Oh, Sewook;Kwon, Youngcheul
    • Journal of the Korean GEO-environmental Society
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    • v.15 no.9
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    • pp.69-75
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    • 2014
  • Rock fall protection system installed against rock slope is one of the most conventional way to protect nearby infra structures. Despite of wide application of typical rectangular nets, virtually installed to protect rock slope face, several problems have also been pointed out up to date. Rectangular draped nets are vulnerable to a sudden external shock such as rock fall, because it doesn't have any systematical buffers or shock absorbers. Furthermore, it has been widely recognized from the some cases of rock fall accident in Korea that rock fall protection nets cause wide range of failure in the rock slope faces due to insufficient pullout bearing capacity of fixing parts. Therefore, in this study, we tried to make a consideration about the problems of existing standard rock fall protection nets in Korea, and develop a new type of hexagonal net with a shock absorber based on design rock fall energy. In this paper, laboratory and full scale test procedure is described to analysis the performance of newly developed hexagonal rock fall net, and the key results are presented and discussed.

The Scattering and Absorption Effects of Fluorescence Spectroscopy in a Real Time Optical Biopsy (실시간 광학적 생검에서 형광분광법의 산란과 흡수에 대한 영향)

  • Han, Seunghee;Muller, Markus G.;Kang, Seunghee;Kang, Haejin
    • Progress in Medical Physics
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    • v.12 no.1
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    • pp.79-94
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    • 2001
  • The fluorescence emanating from a biological tissue contains information about scattering, absorption and the intrinsic fluorescence (fluorescence only due to fluorophores). Becaue fluorescence spectra of biological tissue are often significantly affected by the presence of tissue absorbers and scatterers, the measured tissue fluorescence cannot be interpreted as a linear combination of intrinsic fluorescence spectra of different tissue biochemical. We conducted experiments to examine the influence of scattering and absorption on the experimentally measured fluorescence of a turbid medium such as biological tissue. Therefore, we acquired fluorescence and reflectance spectra of tissue phantoms with a wide range of scatterer and absorber concentrations. By applying a photon migration model, which uses the scattering and absorption information contained in reflectance spectra to remove their distortion also present in fluorescence spectra, we extract the intrinsic fluorescence of these tissue models. We achieved excellent agreement between modeled and actual intrinsic fluorescence spectra. The motivation for this research is that intrinsic fluorescence spectra are expected to change with progression of disease in human tissue, due to changes in the tissue biochemical composition. It is not possible to distinguish the two tissue types by using only the measured fluorescence, however clear separation can be achieved with the intrinsic fluorescence in real time optical biopsy.

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Microwave Absorbing Properties of M-type Barium Ferrites with BaTi0.5Co0.5Fe11O19 Composition in Ka-band Frequencies (BaTi0.5Co0.5Fe11O19 조성을 갖는 M형 바륨 페라이트의 Ka-밴드 전파흡수특성)

  • Kim, Yong-Jin;Kim, Sung-Soo
    • Journal of the Korean Magnetics Society
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    • v.19 no.6
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    • pp.203-208
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    • 2009
  • Magnetic and Ka-band absorbing properties have been investigated in Ti-Co substituted M-type barium hexaferrites with $BaTi_{0.5}Co_{0.5}Fe_{11}O_{19}$ composition. The ferrite powders were prepared by conventional ceramic processing technique and used as absorbent fillers in ferrite-rubber composites. The magnetic properties were measured by vibrating sample magnetometer. The complex permeability and dielectric constant were measured by using the WR-28 rectangular waveguide and network analyzer in the frequency range 26.5~40 GHz. For the Ti-Co substituted M-hexaferrites, the ferromagnetic resonance is observed at Ka-band (29.4 GHz). The matching frequency and matching thickness are determined by using the solution map of impedance matching. A wide band microwave absorbance is predicted with controlled ferrite volume fraction and absorber thickness.

Development of the EM wave Absorber for Improving the Performance of Hi-Pass System in ITS (ITS에 있어서 Hi-Pass 시스템의 성능 개선을 위한 전파흡수체의 개발)

  • Kim, Dong Il;Kim, Jeong Chang;Joo, Yang Ick
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.18 no.7
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    • pp.1505-1510
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    • 2014
  • High-Pass (ETC ; Electronic Toll Collection) system is one of the basic elements, which adopts a wireless communication method using 5.8 GHz and can realize a part of ITS (Intelligent Traffic System). On the other hand, communication errors occur frequently in Hi-Pass system due to signal erros, multi-path reflection, and/or system-to-system interferences. To solve these problems, an EM (Electro-Magnetic) wave absorber can be used. To solve these Problems, we fabricated some samples in the different composition ratios of Carbon, Sendust, and CPE, and it was confirmed that the optimum composition ratio of Carbon : Sendust : CPE is 10 : 40 : 50 wt.%. The complex relative permittivity and complex relative permeability were derived by using the measured data. In addition, the optimum design parameters for the absorber were determined by simulation. Then the absorption abilities were calculated by changing the thickness of the EM wave absorbers. As a result, the optimum thickness of the developed EM wave absorber was 2.85 mm with absorption ability over 22.4 dB at 5.8 GHz. Futhermore, the EM wave absorber was fabricated based on the simulated and designed values. The measured values agreed well with the simulated ones. Therefore, it was clearly shown that the developed EM wave absorber in this paper is to be applied in actual situations.

A Study on EM Wave Absorber for Electromagnetic Wave Environment of Wireless LAN at 5.2 GHz (5.2 GHz 무선 LAN의 전자파 환경 대책용 전파흡수체에 관한 연구)

  • Yoo, Gun-Suk;Choi, Dong-Soo;Kim, Dong-Il
    • Journal of Navigation and Port Research
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    • v.34 no.1
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    • pp.15-19
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    • 2010
  • Recently, the wireless LAN system is rapidly growing because of its convenience of high speed communication. However, the wireless LAN systems at indoor places occur multi-propagation path by reflected waves from walls, ceilings, floors, and desks. Multipath problems cause transmission errors and degradation of communication speed. These problems can be solved by using EM wave absorbers. In this paper, we analyzed property of Graphite and derived the optimum ratio of Graphite: CPE to develop EM wave absorber for the wireless LAN system. First, we fabricated several samples in different composition ratios of Graphite and CPE, and then measured the reflection coefficient of each samples. Material constants of permittivity and permeability were calculated using the measured data and designed EM wave absorber. Secondly, the EM wave absorber was fabricated and tested on the base of the simulation data. As a result, it showed that the EM wave absorber in 1.7 mm thickness with the ratio of Graphite: CPE=50:50 wt.% has excellent absorption ability more than 27 dB at 5.2 GHz.

Self Assembly and Formation of Bi-continuous Cubic Liquid Crystalline Phase (바이컨티니어스 큐빅상 액정의 생성과 자기조직화)

  • Kim, In-Young;Choi, Hwa-Sook;Lee, So-Ra;Choi, Seong-Ho
    • Journal of the Korean Applied Science and Technology
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    • v.31 no.3
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    • pp.478-485
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    • 2014
  • This study is to form the self assembly of cubic crystalline phase to penetrate into the skin epidermis. The various performance synthesized diglyceryl phytylacetate (DGPA) having hydroxyl group (-OH) and 4 methyl chains with phytyl group was carried out as an amphoteric lipid such as emulsifying power, self assembly. Emulsifying activity of DGPA was very stabilized on only 1% of small content, it could make a W/O emulsion containing high internal phase incorporated with water. Cubic liquid crystal structure with DGPA on three-phase diagram was formed, when mixed DGPA, dimethicone (2CS), and water. Through three-phase diagram forming the cubic liquid crystal area, hexagonal structure zone, and mixing water phase and hexagonal structure area, reversed micelle area were respectively certified. Its structure was proved by the SAXS (small angled x-ray scattering) analysis. As an application, formation of cubosome containing 10% of magnesium ascorbylphosphate and 5% of pyridoxine tris-hexyldecanoate was encapsulated. Occlusive effect of cubosome had above 1.7 times better than reversed micelle. From using poloxamer of dispersing agent, phase structure recovered from W/O emulsion to cubic liquid crystal phase when storage in $33^{\circ}C$ incubator. Therefore, our this study is expected to be as epidermal-dermal skin absorbers in skin care cosmetics and pharmaceuticals industries as raw materials to form a cubic crystal phase through a more in-depth research to DGPA having amphoteric lipid property.