• 제목, 요약, 키워드: Permittivity

검색결과 784건 처리시간 0.046초

Effects of Size and Permittivity of Rat Brain on SAR Values at 900 MHz and 1,800 MHz

  • Hyun Jong-Chul;Oh Yi-Sok
    • Journal of electromagnetic engineering and science
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    • v.6 no.1
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    • pp.47-52
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    • 2006
  • The objective of this study is to evaluate the effects of size and permittivity on the specific absorption rate(SAR) values of rat brains during microwave exposure at mobile phone frequency bands. A finite difference time domain (FDTD) technique with perfect matching layer(PML) absorbing boundaries is used for this evaluation process. A color coded digital image of the Sprague Dawley(SD) rat based on magnetic resonance imaging(MRI) is used in FDTD calculation with appropriate permittivity values corresponding to different tissues for 3, 4, 7, and 10 week old rats. This study is comprised of three major parts. First, the rat model structure is scaled uniformly, i.e., the rat size is increased without change in permittivity. The simulated SAR values are compared with other experimental and numerical results. Second, the effect of permittivity on SAR values is examined by simulating the microwave exposure on rat brains with various permittivity values for a fixed rat size. Finally, the SAR distributions in depth, and the brain-averaged SAR and brain 1 voxel peak SAR values are computed during the microwave exposure on a rat model structure when both size and permittivity have varied corresponding to different ages ranging from 3 to 10 weeks. At 900 MHz, the simulation results show that the brain-averaged SAR values decreased by about 54 % for size variation from the 3 week to the 10 week-old rat model, while the SAR values decreased only by about 16 % for permittivity variation. It is found that the brain averaged SAR values decreased by about 63 % when the variations in size and permittivity are taken together. At 1,800 MHz, the brain-averaged SAR value is decreased by 200 % for size variation, 9.7 % for permittivity variation, and 207 % for both size and permittivity variations.

분말재료의 복소 유전율 및 투자율 측정 (Measurement of Complex Permittivity and Permeability for Powder-type Materials)

  • 박상복;이장수;정용식;천창율
    • 전기학회논문지
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    • v.56 no.12
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    • pp.2196-2201
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    • 2007
  • Materials used at microwave are usually used as a dielectric with a manufacturing purpose of printed circuit boards, etc. Complex permittivity of them can be measured from attenuation constant or propagation constant of a transmission line using a microstrip line with bulk type. But as the technique recently which can manufacture to have complex permittivity and permeability demanded using nonferrous metals for powder-type grows up, we need sensors and methods which can measure characteristics of powder-type materials. So far measuring methods of permittivity and permeability with waveguide or coaxial cable are used but they have faults which have a complex measurement method and are difficult to simultaneously measure permittivity and permeability. In this paper, a simultaneous measuring method of permittivity and permeability with 2-port coaxial cable and a new proposed calculation. The proposed 2-port coaxial cable is designed to be easy to insert materials and to have a wideband. We measure permittivity and permeability of magnetic powder(Ni-Fe-Mo, Ni-Fe) which reveal its characteristic at $0.3{\sim}1.3GHz$ to identify the proposed sensor.

영동산 일라이트의 전자기적 특성 측정 (A Measurement of Electromagnetic Property of Illite found in Young-dong Area)

  • 김진철;이원희;구경완;허정
    • 한국전기전자재료학회:학술대회논문집
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    • pp.267-270
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    • 2000
  • This paper describes measurement of relative permittivity of illite found in young-dong area. A measurement of relative permittivity of illite used to cylindrical cavity resonators with moveable cap. A concentric dielectric-rod inserted cylindrical cavity resonator and an exact field representation of travelling wave mode are introduced for measurement of relative permittivity. The exact electromagnetic fields in cylindrical cavity with concentric dielectric rod is analysed. A relative permittivity of dielectric in cavity is calculated by analyzing the characteristic equation. The characteristic equation is solved by using the ContourPlot graph of Mathematica. We know that the field representation of travelling mode is exact. As a result, relative permittivity of dielectric materials were 7.820 at sample-1 and 7.894 at sample-2.

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주파수, 온도에 따른 전력케이블용 반도전 재료의 유전올 (Permittivity of Semiconductive Shield Materials in Power Cables by Frequency, Temperature)

  • 양훈;박대희
    • 대한전기학회:학술대회논문집
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    • pp.218-219
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    • 2007
  • This paper researched permittivity of carbon nanotube reinforced semiconductive shield materials for power cable in accordance with carbon nanotube content. Permittivity measured 1[Hz], 1[kHz], 1[Mhz] in frequency range, and range of temperature measured to 100$[^{\circ}C]$ from -50$[^{\circ}C]$. It is stable to 100$[^{\circ}C]$ from -50$[^{\circ}C]$ without different gap. But, in case of CNT:CB=100:0, permittivity decreased by temperature increment. Also, in case of CNT:CB=100:0, it shows highest permittivity. Permittivity of change have little no the power of influence by frequency, but in case of 1[Mhz], CNT:CB=100:0 of specimen decreased more than other frequency. This influence thinks phenomenon of induced electricity dispersion.

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TDR을 이용한 극초단파 대역에서 사용 절연유의 유전율과 전파속도 측정 (Measurement on the permittivity and propagation velocity of used insulation oil at UHF Band using time domain reflectometry)

  • 구선근;주형준;박기준;한기선;윤진열
    • 전기학회논문지
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    • v.57 no.11
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    • pp.2011-2014
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    • 2008
  • We measured the permittivity and electromagnetic wave propagation velocity of used insulation oil with wide frequency range including ultra-high frequency by time domain reflectometry. The permittivity or propagation velocity is essential for locating discharge faults of oil filled power transformer. We derived 2.21 as a permittivity and $2.03{\times}10^8 m/s$ as a velocity from the measurement of pulse travelling time along a coaxial line filled with used insulation oil or air. The permittivity measurement system we designed shows high measurement accuracy and the convenience for field use.

가스절연 개폐장치에서 유전율 구배를 갖는 고체 절연물의 형상 최적화 (Shape Optimization of a Permittivity Graded Solid Insulator in a Gas Insulated Switchgear)

  • 주흥진;김동규;고광철
    • 한국전기전자재료학회논문지
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    • v.25 no.6
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    • pp.467-473
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    • 2012
  • A functionally graded material (FGM) spacer, which the distribution of dielectric permittivity inside an insulator changes spatially, can considerably reduce the electric field concentration around a high-voltage electrode and along the gas-insulator interface when compared to a conventional spacer with a uniform permittivity distribution. In this research, we propose the FGM spacer with an elliptical permittivity distribution instead of that with a distribution of dielectric permittivity varying along a radial direction only in order to improve efficiently the insulation capability. The optimal design of the elliptical FGM spacer configuration is performed by using the response surface methodology (RSM) combined with the steepest descent method (SDM).

Electric double layers interactions under condition of variable dielectric permittivity

  • Payam, Amir Farrokh;Fathipour, Morteza
    • Interaction and multiscale mechanics
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    • v.3 no.2
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    • pp.157-171
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    • 2010
  • In this paper, a theoretical method has been developed for the electric double layer interaction under condition of the variable dielectric permittivity of water. Using Poisson-Boltzmann equation (PBE), for one plate and two plates having similar or dissimilar constant charge or constant potential, we have investigated the electric double layer potential, its gradient and the disjoining pressure as well as the effect of variation of dielectric permittivity on these parameters. It has been assumed that plates are separated by a specific distance and contain a liquid solution in between. It is shown that reduction of the dielectric permittivity near the interfaces results in compression of electric double layers and affects the potential and its gradient which leads to a decreased electrostatic repulsion. In addition, it is shown that variation of dielectric permittivity in the case of higher electrolyte concentration, leads to a greater change in potential distribution between two plates.

Effect of Feed Substrate Thickness on the Bandwidth and Radiation Characteristics of an Aperture-Coupled Microstrip Antenna with a High Permittivity Feed Substrate

  • Kim, Jae-Hyun;Kim, Boo-Gyoun
    • Journal of electromagnetic engineering and science
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    • v.18 no.2
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    • pp.101-107
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    • 2018
  • The impedance bandwidth and radiation characteristics of an aperture-coupled microstrip line-fed patch antenna (ACMPA) with a high permittivity (${\varepsilon}_r=10$) feed substrate suitable for integration with a monolithic microwave integrated circuit (MMIC) are investigated for various feed substrate thicknesses through an experiment and computer simulation. The impedance bandwidth of an ACMPA with a high permittivity feed substrate increases as the feed substrate thickness decreases. Furthermore, the front-to-back ratio of an ACMPA with a high permittivity feed substrate increases and the cross-polarization level decreases as the feed substrate thickness decreases. As the impedance bandwidth of an ACMPA with a high permittivity feed substrate increases and its radiation characteristics improve as the feed substrate thickness decreases, the ACMPA configuration becomes suitable for integration with an MMIC.

에폭시 내부의 MWNT 응집 크기에 따른 복소유전율 변화의 해석적 관찰 (Numerical Analysis of the Complex Permittivity of MWNT added Epoxy Depending on Agglomeration Size)

  • 신재환;장홍규;최원호;송태훈;김천곤;이우용
    • Composites Research
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    • v.27 no.5
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    • pp.190-195
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    • 2014
  • 본 연구에서는 MWNT(Multi-walled carbon nanotube)의 응집크기와 복소유전율의 관계를 수치해석적인 방법을 통하여 접근하였다. 이를 위하여 3-roll-mill 장비를 사용하여 1 wt% MWNT가 첨가된 에폭시 시편을 제작하였다. 제작된 시편은 X-band(8.2~12.4 GHz)에서 네트워크 분석기와 자유공간 측정 장비를 이용하여 복소유전율을 측정하였다. 측정된 복소유전율과 복소유전율 혼합 모델을 이용하여 에폭시와 MWNT 응집으로 이루어진 해석모델의 유전율을 결정하였다. 해석 모델은 앞서 말한 것과 같이 에폭시와 MWNT의 응집으로 이루어져 있으며, 정육면체 에폭시 내에 구 형태의 MWNT 응집을 가정하였다. 이에 따라 에폭시와 MWNT의 부피비율은 고정되며, 변수는 응집의 크기로 한정하였다. 수치해석은 상용 전자기 해석프로그램인 CST를 사용하였다. CST로부터 모델의 S-parameter를 얻었고, 복소유전율은 Nicolson 방법을 사용하여 얻었다. MATLAB으로 코드를 만들어 S-parameter 로부터 복소유전율을 얻었다. 수치해석 결과 응집의 크기가 작아질수록 복소유전율 값이 높아지는 모습을 살펴볼 수 있었으며, 이는 나노 입자의 이용에 있어서 분산도는 기계적인 특성뿐 아니라 전자기적 특성인 복소유전율에도 영향을 미친다고 볼 수 있으며, 같은 나노 입자 함량에서 분산도가 좋을수록 높은 복소유전율을 기대할 수 있다.

실효유전율을 이용한 강우감쇠 예측 모델에 관한 연구 (A study on the rain attenuation prediction model using effective permittivity)

  • 김혁제;조삼모
    • 한국전자파학회논문지
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    • v.9 no.1
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    • pp.52-59
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    • 1998
  • 빗방울이 랜덤하게 분포한 대기를 하나의 실효유전율을 가진 단일 매질로 가정하고 그 매질 내에서 전파가 진행시 감쇠량을 계산하였다. 실효유전율은 빗방울의 유전율과 빗방울이 대기 중에 차지하는 체적 동의 함수로 표현되는데, 주파수와 온도에 따라 변하는 빗방울의 유전율을 계산하고 Marshall-Palmer의 빗방울 크기분포를 이용하여 대기 중 빗방울이 차지하는 체적을 계산하였다. 빗방울이 산재한 대기를 단일 매질로 가정하고 실효유전율을 이용하여 강우에 의한 강우감죄량을 예측한 본 모델과 ITU가 권고하는 강우에 의한 전파감쇠모텔과 비교 하였는데 두 모델의 결과값이 비교적 일치하며 50 GHz 이하에서는 실효유전율 모텔이 낮게, 50 GHz 이상의 주 파수대역에서는높게 강우감쇠량을평가하고 있다.

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