• Title, Summary, Keyword: Electromagnetic Wave Absorber

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A Study on the Method to Suppress Radiation-Noise with Electromagnetic Wave Absorber in the Rectangular Cavity Resonator (전파 흡수체에 의한 구형 공동 공진기의 방사노이즈 억제 방법에 관한 연구)

  • 김경용;김왕섭
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.28A no.12
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    • pp.19-23
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    • 1991
  • A method for suppressing unwanted resonance modes by attaching an electromagnetic wave absorber onto a metal case was studied to prevent performance deterioration of electronic devices. The electromagnetic wave absorber fabricated for this study had an attenuation characteristics above 20dB in the frequency band from 450MHz, 1150MHz. A rectangular cavity resonator whose resonance frequencies of TE$_{101}$, TE$_{102}$ modes were 900MHz, 1250MHz, respectively, was made to measure attenuation for the electromagnetic wave absorber-metal assembly. The result showed that the resonance mode for high attenuation was sensitive to the location of electromagnetic wave absorber, and the attenuation characteristics above 20dB could be obtained when electromagnetic wave absorber was properly positioned.

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Preparation and Electromagnetic Properties of an Electromagnetic Wave Absorber

  • Sun, Chang;Sun, Kangning;Pang, Laixue;Liu, Jian
    • Journal of Magnetics
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    • v.21 no.1
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    • pp.61-64
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    • 2016
  • In this study, we report the as-prepared MgO-doped $BaFe_{12}O_{19}$, which was prepared by calcination technique and high-energy ball milling process, as an electromagnetic wave absorber. The phase analysis of $BaFe_{12}O_{19}$ and the as-prepared MgO-doped $BaFe_{12}O_{19}$ was detected utilizing X-ray Diffractometer (XRD). The microstructure was characterized using Scanning Electron Microscope (SEM). By means of the transmission/reflection coaxial line method, the electromagnetic properties and microwave absorbing properties of the as-prepared electromagnetic wave absorber were studied. It is found that the electromagnetic wave absorber has a minimum reflection loss value of -41 dB at 4.27 GHz with a matching thickness of 2.6 mm. The experiment results revealed that the as-prepared electromagnetic wave absorber could find potential applications in many military as well as commercial industries.

An Applicable Method of an Electromagnetic Wave Absorber for SAR Reduction in the Human Head Exposed to Electromagnetic Fields Radiated by a Cellular Phone (휴대폰 전자파에 노출된 두부내 SAR 저감을 위한 전자파 흡수체 적용 방법 연구)

  • 이윤경;백락준;홍진옥;육재림;윤현보
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.14 no.8
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    • pp.884-890
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    • 2003
  • In order to reduce the specific absorption rate(SAR) in a human head exposed to electromagnetic fields radiated by a cellular phone, we have analyzed an electromagnetic wave absorber attached to the handset. A manufactured electromagnetic wave absorber was composed of Mn - Zn, which had complex relative permittivity of 7.30-j0.05 and permeability of 2.20-i1.55. The SAR value from the electromagnetic wave absorber attachment was calculated by using the nonuniform finite difference time domain(FDTD) algorithm and measured by phantom model at 835 MHz. The SAR reduction due to the electromagnetic wave absorber are about 18 % at 835 MHz. The V.S.W.R and radiation pattern of antenna are good agreement with the normal antenna. The gain reduction due to the electromagnetic wave absorber are only 0.3 dB at 835 MHz. But the sensitivity of cellular phone generally improves about 1 dB.

A Study on Development of Broad-band Electromagnetic Wave Absorber for EMI/EMC (EMI/EMC 대책용 광대역화 전파흡수체의 개발에 관한 연구)

  • Jun, Sang-Yup;Kim, Dong-Il
    • Journal of the Korean Institute of Navigation
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    • v.15 no.4
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    • pp.13-25
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    • 1991
  • Recently, according to the development of electromagnetic wave technique, more frequent and powerfull wave radiation becomes inevitable and so electromagnetic environments has become worse accordingly. Electromagnetic wave absorber is known the most effective preventive remedy to cope with the EMI/EMC problem. To realize broad-band electromagnetic wave absorber, triple layered structure where an air layer is interposed between a sintered ferrite layer and a ruber ferrite layer was adopted. Computer simulation for optimum design and evaluation of absorption characteristics has been made. The results shows that designed broad-band electromagnetic wave absorber can be useful for EMI/EMC problem, especially reducing TV ghosts in both VHF and UHF bands by additionally an air layer and a thin rubber ferrite layer on the surface of conventional ferrite, without replacing it.

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Design Method of Electromagnetic Wave Absorber with Ultra Wide-Band Frequency Characteristics. (초광대역특성을 가지는 Ferrite 전파흡수체의 설계법)

  • 김동일;정세모;전상엽
    • Journal of the Korean Institute of Navigation
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    • v.18 no.2
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    • pp.151-158
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    • 1994
  • A wide band design method of an electromagnetic wave absorber using exponentially tapered ferrite, which has very wide band frequency characteristics, is proposed and discussed. The wide band electroma-gnetic wave absorber can be designed by the proposed equivalent material constants method for the re-gions varying spatially in the shape of ferrite. Futhermore, the wide band ferrite electromagnetic wave absorber with taper, which have not only exce-llent reflectivity frequency characteristics but also the band width of 30MHz to 2150 or 2450MHz under the tolerance limits of -20dB reflectivity, were designed.

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A Study on Composite EM Absorber's Absorption Characteristics Using Natural Lacquer by Binder (옻을 지지재로 사용한 복합형 전자파 흡수체의 흡수 특성에 관한 연구)

  • Choi, Dong-Han
    • Proceedings of the Korea Electromagnetic Engineering Society Conference
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    • pp.622-629
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    • 2003
  • Generally, a silicone rubber and a chloride polyethylene(CPE) have been used for the development of high-performance composite EM(ElectroMagnetic) wave absorber. In this study, the EM wave absorption abilities for natural lacquer which is newly suggested in this study as a binder for composite EM wave absorber were investigated to develop an improved EM wave absorber In addition, MnZn ferrite composite EM wave absorber mixed with the natural lacquer were prepared and their absorption ability was also investigated. MnZn ferrite composite EM wave absorber which employs the natural lacquer as a binder showed an improved EM wave absorption characteristics in comparison with the conventional binder such as a silicone rubber and a chloride polyethylene(CPE). The matching frequency and the absorption ability of EM wave absorber mixed with natural lacquer can be controled the change of the thickness of them.

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Design of Ferrite Electromagnetic Wave Absorber for Anechoic Chamber (전파무향실용 페라이트 전파흡수체의 설계)

  • 김동일;이창우;김하근;전상엽;정세모
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.3 no.1
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    • pp.43-50
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    • 1999
  • Electromagnetic wave absorbers for anechoic chamber are needed to broaden the useful frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve the above requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the useful frequency bandwidth by the way of forming air layer. Therefore, an air layer is formed absorber between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 450 MHz in frequency band, far narrower than the aimed bandwidth. The purpose of this paper is on the development of a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell, wall material for prevention of TV ghost, etc. Accordingly, in this paper, a broadened electromagnetic wave absorber is designed, which has the reflection characteristics less than -20 dB from 30 MHz to 5,430 or 8,000 MHz in the bandwidth. Then we will design a super broadband electromagnetic wave absorber by inserting square Ferrite Cylinders Type with the thickness less than 23.5 m in three-layed type and with the frequency band from 30 MHz to 5,430-8,000 MHz under the above tolerance limits.

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A Design of Ferrite Electromagnetic Wave Absorber Three Layered Type with Wide-Band Characteristics. (광대역 특성을 갖는 3층형 페라이트 전파흡수체의 설계)

  • 이창우;김동일
    • Journal of the Korean Institute of Navigation
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    • v.22 no.4
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    • pp.51-57
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    • 1998
  • According to the rapid development of the electric industry, the demand of the frequency allocation and the usage of electromagnetic wave are increased due to automation of modem society. Electromagnetic wave absorbers for anechoic chamber are needed to broaden the effective frequency bandwidth, reduce the thickness, and decrease the weight. There are various absorbers proposed for the above conditions, but they could not decisively solve the above requirements. The Electromagnetic wave absorber made by a conventional ferrite tile has, for example, broadened the effective frequency bandwidth by the way of forming air layer(practically in urethane foam, etc.) on the ferrite tile. Therefore, an air layer is formed between a reflection plate and a sintered Ni-Zn ferrite tile of 7 mm in thickness, which has reflectivity less than -20 dB from 30 MHz to 400 MHz in bandwidth. In this paper, a broadband electromagnetic wave absorber are designed, which has the reflection characteristics less than -20 dB from 30 MHz to 8,000 MHz in the bandwidth. A super broadband electromagnetic wave absorber is achieved by inserting square Ferrite Cylinders Type with the thickness less than 23.5 mm and with the frequency band from 30 MHz to 8,000 MHz under the above tolerance limits. The purpose of this research is on the development of a universal anechoic chamber for measuring radiated electromagnetic wave or immunity of electronic equipments, GTEM-cell and also a wall material for preventing TV ghost, etc.

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A Study on Development of EM Wave Absorber Using TiO2 for Automotive Radar in Cars

  • Choi, Chang-Mook;Kim, Dong-Il
    • Journal of electromagnetic engineering and science
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    • v.8 no.3
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    • pp.110-113
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    • 2008
  • In this paper, we designed and fabricated an electromagnetic(EM) wave absorber for automotive radar in cars using $TiO_2$ as a dielectric material and chlorinated polyethylene(CPE) as a binder. First of all, we confirmed that the optimum composition ratio of $TiO_2$ was about 70 wt.%. The complex relative permittivity of a sample containing $TiO_2$: CPE=70:30 wt.% was calculated from S-parameter. The EM wave absorption abilities were simulated for the EM wave absorbers of different thickness using the calculated relative permittivity, and the EM wave absorber was manufactured based on the simulated design. A comparison of simulated and measured results is in good agreement. Measurement shows that a 1.85 mm thick absorber has absorption ability higher than 20 dB in the frequency range of $76{\sim}77$ GHz for automotive radars.

Design of Wideband Electromagnetic Wave Absorber Using Magnetic Materials (자성재료를 이용한 광대역 전자파 흡수체 설계 연구)

  • Kim, Dong Young;Yoon, Seok Soo
    • Journal of the Korean Magnetics Society
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    • v.22 no.6
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    • pp.210-215
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    • 2012
  • The absorption performance of a metal-backed single layered electromagnetic wave absorber is optimized at matching conditions of thickness and frequency indicating the maximum returns loss of incidence electromagnetic wave in the contour map. These matching conditions are obtained by applying the electromagnetic impedance to the transmission line theory, which depend on the complex permeability and complex permittivity of absorber material. The magnetic materials with high permeability can enhance the matching thickness condition to the wide frequency range based on the decrease of permeability with frequency and it can be used as a wideband electromagnetic wave absorber material. Therefore, the magnetic materials with higher saturation magnetization and lower permittivity than NiZn ferrite can be applied to the wideband electromagnetic wave absorber in order to satisfy the newly enforcing the electromagnetic compatibility regulation in the future.