• Title/Summary/Keyword: Wave Absorbing Characteristics

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A Study on the EM Wave Absorption Characteristics of Amorphous Metal Powder and Sendust Absorbers for RFID System (RFID 시스템용 Amorphous Metal Powder 및 Sendust 흡수체의 전파흡수 특성 연구)

  • Choi, Dong-Soo;Yoo, Gun-Suk;Choi, Dong-Han;Kim, Dong-Il
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2010.04a
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    • pp.159-160
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    • 2010
  • In this paper, we compared the absorption abilities of AMP and Sendust EM wave absorbers for a port logistics RFID system. Firstly, we fabricated EM wave absorber samples by using each absorbing material, AMP or Sendust, and CPE (Chlorinated Polyethylene) with composition ratios 85 : 15 wt. %. Secondly, we designed the optimum EM wave absorber using the calculated material constants found from the measured input impedance of the samples. Therefore, we confirmed that imaginary factor of complex relative permeability influences absorption ability and that AMP is better absorbing material than Sendust at the frequency band of 433 MHz.

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Sound Absorption Characteristics of Finite-Amplitude Acoustic Waves in Poroelastic Materials (탄성다공성 재질에서 유한진폭 입사음파의 흡음 특성)

  • Lee, Soo-Il;Kim, Jin-Seop;Kang, Yeon-June
    • Proceedings of the KSME Conference
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    • 2000.04a
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    • pp.591-595
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    • 2000
  • Sound absorbing characteristics of poroelastic materials is known to be greatly affected by high intensity acoustic waves. However, this effect has not been considered yet. In this study, the extended semilinear model based on Biot's theory for the porous materials and the characteristics of nonlinear waves in poroelastic sound absorbing materials were introduced. The expressions for the finite-amplitude acoustic plane waves were presented. By combining each nonlinear wave with appropriate matching conditions, we could investigate the effects of finite-amplitude acoustic waves on absorption characteristics of poroelastic materials. In the most ideal case considered in this paper, the absorption coefficient was found to become larger than that of linear incident waves. It was shown that the absorption coefficient became greater especially as frequency goes higher and as distance from the source goes larger. These phenomena may be inferred to result from 'dissipation effects due to nonlinearity'. This finding may have important implications for high intensity noise control.

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Transmitted Noise Reduction of Piezoelectric Smart Panels using Passive/Active Method in Wide Range frequency (수동/능동적 방법을 혼용한 압전지능패널의 광대역 전달 소음저감성능)

  • 이중근;박우철
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.2 no.2
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    • pp.73-79
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    • 2001
  • In this paper, the transmitted noise reduction performance of piezoelectric smart panels is experimentally studied. The proposed piezoelectric smart panels are comprised of plate structure on which piezoelectric sensor/actuators are bonded and sound absorbing material is provided. It is a combination of passive and active approaches utilizing a passive effect at high frequencies and an active effect at low frequencies. To prove the concept of piezoelectric smart panels, an acoustic measurement experiment is performed. An acoustic tunnel is designed and its acoustic characteristics are tested. Below 800Hz, the tunnel exhibits a plane wave guide characteristics. When an absorbing material is bonded on a single plate, a remarkable transmitted noise reduction in mid frequency range is observed except the first resonance frequency. By enabling the active control of single smart panel with negative feedback control. about 10dB noise reduction is achieved at the resonance frequencies. The double smart panel got 4dB at the first resonance frequency and has more potential to reduce the transmitted noise in a wide range frequency. Piezoelectric smart panels incorporating passive absorbing material and active piezoelectric devices is a promising technology for noise reduction in a wide range frequency.

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Electromagnetic Characteristics of Carbon Black filled Class-Fabric Composite Sandwich Structure (카본블랙이 첨가된 유리직물 복합재 샌드위치 구조의 전자기적 특성)

  • Park, Ki-Yeon;Lee, Sang-Eui;Kang, Lae-Hyong;Han, Jae-Hung;Kim, Chun-Gong;Lee, In
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2003.10a
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    • pp.234-237
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    • 2003
  • The absorption and the interference shielding of the electromagnetic wave problem have been a very important issue for commercial and military purposes. This study dealt with the simulation reflection loss for electromagnetic absorbing sandwich type structures in X-band(8.2Ghz~12.4GHz). Glass/epoxy composites containing conductive carbon blacks were used for the face sheets and styrofoams were used for the core. Their permittivities in X-band were measured using the transmission line technique. Simulation results of 3-1ayered sandwich type structures showed the reflection loss using the theory about transmission and reflection in a multi-layered medium.

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Design Method for the Electromagnetic Wave Absorber at 9.45 GHz (9.45GHz용 전파흡수체의 설계 방법)

  • 김왕섭;김경용
    • The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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    • v.4 no.2
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    • pp.11-16
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    • 1993
  • A design method for the electromagnetic wave absorber with the attenuation over 20 dB at a frequency was formulated. In addition to the matching boundary which is determined by the theoretical equation, several limiting conditions due to the fabrication process were examined. Based on the study on the effects of the variance of the thickness and permittivity on the electromagnetic wave absorbing characteristics, a mean to exclude such effects was also included in the proposed design method. The ranges of variables were limited as the frequency of 9.45 GHz and .epsilon.' = 5 ~ 30, when the effect of .epsilon. " was not considered.

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A Numerical Study on Stress Wave Propagation from Pile Driving (말뚝항타시 발생하는 응력파의 전파특성에 관한 수치해석적 연구)

  • 이종세;임정진
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 2002.09a
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    • pp.123-130
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    • 2002
  • The ground-borne vibration from pile driving is causing many public discontents. However, because of the fact that the characteristics of wave propagation and attenuation are not well understood, systematic and effective vibration reduction measures can not be taken. This paper attempts to study the propagation of stress waves induced by the pile driving. To simulate the wave propagation in a semi-infinite domain, the so-called absorbing boundaries are incorporated in the finite element method and a series of numerical simulations is performed. Numerical results show that the surface displacement and velocity increase first and then decrease as the pile penetration depth becomes larges.

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An experimental study on motions of a VLCO for wave power generation(1. Simple floating body) (파력발전용 가변수주진동장치의 운동에 대한 실험적 연구(1. 단일 부유체))

  • Lee, Seung-Chul;Goo, Ja-Sam
    • Journal of Power System Engineering
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    • v.17 no.2
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    • pp.103-107
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    • 2013
  • The structure of a variable liquid column oscillator(a VLCO) is analogous to that of the tuned liquid column damper used to suppress oscillatory motion in large structures like tall buildings and cargo ships. The VLCO is a system absorbing high kinetic energy of accelerated motions of multiple floating bodies in the effect of air springs occurred by installation of inner air chambers. Thus, VLCO can improve the efficiency of energy than wave energy converters of the activating object type made in Pelamis Company. In this research, the experiment was performed that a simple floating body was filled with internal fluid of same draft. The characteristics of motions were evaluated in each case of the opening or closing of the upper valves.

A Study on the Electromagnetic Wave Absorption Properties by the Preparing Condition of NiCuZn Ferrite (NiCuZn 페라이트의 제조 조건에 따른 전자파흡수 특성에 관한 연구)

  • 이영구;박찬규;이문수
    • Proceedings of the Korea Electromagnetic Engineering Society Conference
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    • 2001.11a
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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$^{\circ}C$.

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Analysis of the Sound field in a Reverberation Room(II) (잔향실의 음장해석 (II))

  • 임정빈;권영필
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 1997.04a
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    • pp.681-686
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    • 1997
  • Foamed aluminum is well known metallic porous sound absorption material which has excellent properties of light weight and high absorbing performance. For the purpose of finding out the sound field characteristics within a simple closed cubic enclosure with foamed aluminum, analytic and experimental studies are performed. For the first time, the standing wave apparatus is used to measure absorption coefficient and impedance of the foamed aluminum. Next, the sound effects of absorption material in acoustically loaded rectangular enclosure are identified according as the foamed aluminim is to be or not.

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Laminating Rule for Predicting the Dielectric Properties of the E-glass/Epoxy Laminate Composite (유리섬유/에폭시 복합재료 적층판의 유전성질 예측을 위한 적층판 법칙)

  • Chin, Woo-Seok;Lee, Dai-Gil
    • Proceedings of the Korean Society For Composite Materials Conference
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    • 2005.04a
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    • pp.141-145
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    • 2005
  • Since the electromagnetic properties of fiber reinforced polymeric laminate composite can be tailored effectively by adjusting its composition and regulating the stacking sequence, it is plausible material for fabricating the radar absorbing structures (RAS) of desired performance. In order to design the effective electromagnetic wave (EM) absorber with the fiber reinforced polymeric laminate composite, its electromagnetic characteristics should be available and could be regulated easily in the target frequency bands. In this study, dielectric characteristics of the E-glass/epoxy laminate composites were measured by the free space method in the X-band frequency range ($8.2\;{\sim}\;12.4\;GHz$). In order to describe the dielectric behavior of laminate composites of arbitrary stacking sequences, the equivalent circuit model and the laminating equations for estimating dielectric properties were proposed, and experimentally verified. From the comparison of the predicted and measured data, the proposed method predicted well the experimentally measured data.

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