• Composites Research
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• v.27 no.5
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• pp.190-195
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• 2014

This paper predicts the complex permittivity of MWNT added epoxy depending on agglomeration by numerical analysis. 1wt% MWNT added epoxy specimen is prepared using 3-roll-mill method and its complex permittivity is measured in X-band (8.2~12.4 GHz) using freespace measurement system. The analytic model is comprised of cube epoxy and perfect sphere agglomeration. The complex permittivity of the agglomeration model is predicted by complex permittivity mixing rule using the measured complex permittivity of epoxy and 1 wt% MWNT added epoxy. Commercial electromagnetic analysis software, CST, is used to obtain S-parameter of the analytic model and MATLAB code is used to calculate complex permittivity from the S-parameter. It is confirmed that the complex permittivity increases when the agglomeration size decreases.

• Composites Research
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• v.22 no.3
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• pp.44-54
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• 2009

In this paper, we proposed a numerical model the complex permittivity for the E-glass fabric/epoxy composite laminate containing electrical conductive carbon black. The model is based on the percolation theory and for the composites over than the percolation threshold and in higher frequency band in that the AC conductivity is fully proportional to the frequency. The measurement for the complex permittivity wasperformed at the frequency band of 0.5 GHz $\sim$ 18.0 GHz using a vector network analyzer with a 7 mm coaxial air line. The proposed model is composed of the numerical equations of the scaling law used in percolation theory and constants obtained from experiments to quantify the model itself. The model describes the complex permittivity as the function of frequency and filler concentration. The model was verified by being compared with the measurements.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.36D no.8
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• pp.19-26
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• 1999

umerical simulations are performed to estimate how strongly the manufacturing error of an open-ended coaxial probe affects its measured complex permittivity of a contacted medium. The reflection coefficients of several dielectric materials contacted with an open-ended coaxial probe are calculated by employing the FDTD method. And then those complex permittivities are reconstructed by applying the calculated reflection coefficients into a new imaginary transmission-line model, which reveals more physically meaningful than the conventional model. It is found that the reconstructed complex permittivities suffer from significant error in spite of a slight imperfection of open-ended coaxial probe.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2001.11a
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• pp.300-303
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• 2001

개방단말 동축선 프로브는 임의의 매질에 접촉하여 복소 유전율을 구하므로 사용이 용이한 측정법이다. 복소 유전율의 측정 과정은 두 단계로 구성된다. 먼저 프로브의 개구면을 미지의 매질에 접촉시켜서 반사계수를 측정한다. 다음에는 반사계수를 환산모델에 대입하여 복소 유전율을 구한다. 그러나 실제 측정시 발생하는 오차들에 대해 취약하다는 단점을 가지고 있다. 정확성을 떨어뜨리는 주요 오차 요인으로는 프로브의 개구면과 측정매질 사이의 공극으로 인한 불완전 접촉오타와 프로브의 제작 한계로 인한 오차를 들 수 있다. 본 논문에서는 이런 오차상황에서 유한 차분 시간영역법으로 반사계수를 계산하고나서 환산모델에 의해 복소 유전율로 환산함으로써 오차에 대한 환산모델들간의 안정성을 살펴보고자 한다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.11
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• pp.9-19
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• 1990

A theoretical analysis and measurement technique to determine the complex permittivity and permeability of cylindrical and ring type dielectric resonators is given. The resonant frequency, unloaded quality factor and physical dimensions of dielectric resonator placed between two parallel conducting plates are used to evaluate the complex permittivity and permeability. This process is repeated for other higher-order modes to expand the evaluation at higher resonant frequencies. The nature of each mode is identified by measuring the variations of field strength along the azimuthal and longitudinal direction. An error analysis taking into account various error sources reveals that $TE_{0np}$ or quasi-TE modes yield the least amount of measurement error, which is less than $0.5{\%}$for the real part, $4{\%}$for the imaginary part of complex permittivity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.9-15
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• 2011

This paper suggested the fast and easy method of the dielectric constant measurement for planar dielectrics using a microstrip line. The complex permittivity and permeability were presented by the first reflection and transmission coefficient which were derived from the scattering parameters. This method was verified by the measurement of a known planar dielectric using a microstrip line. This method can be applied to the dielectric constant measurement of unknown planar dielectric.

• The Journal of Engineering Geology
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• v.15 no.3
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• pp.281-288
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• 2005

To evaluate a property of moisture distribution and volumetric water content on bentonite media the responses of complex dielectric constant were used which are measured by Frequency Domain Reflectometry with Vector Network Analyzer (FDR-V) system. The bentonite is widely used a barrier liner system in the waste disposal site, recently. In case of barrier liner system, generally, the coefficient of permeability should have to less than 10-7cm/sec. According to the results, the complex dielectric constants are increasing with increase the volumetric water content and temperature together. Also the variation of complex dielectric constant due to temperature gradient is confirmed that the moisture movements are increasing with the variations of temperature from high range to low range, which is represented the property of moisture distribution in the bentonite.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2005.04a
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• pp.36-41
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• 2005

복소유전율상수인 실수부(Real part)와 허수부(Imaginary part)를 측정하기 위하여 Frequency Domain Reflectometry with Vector Network Analyzer(FDR-V) 측정 장비로 $1{\sim}18GHz$ 범위 내에서 매질의 기본 구성단위인 공기, 물, 흙입자에 대한 기본적인 유전율 특성을 파악하고, 이들로부터 다공질 매질내 유류 오염물질의 함유 특성을 측정할 수 있다. 또한 제작된 시료에 대한 포화도와 1GHz 범위에 분포하는 실수부 유전율상수와의 관계로부터 매질의 공극내 함유된 물질의 유전율상수 특성에 매우 민감한 반응을 보이므로, 이들로부터 매질의 공극률 내지 유효공극률의 측정이 가능할 것으로 사료된다.

• Composites Research
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• v.24 no.2
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• pp.38-45
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• 2011

In this paper, we present an optimization method for the single Dallenbach-layer type microwave absorbers composed of E-glass fabric/epoxy composite laminates. The composite prepreg containing carbon nanotubes (CNT) was used to control the electrical property of the composites laminates. The design technology using the genetic algorithm was used to get the optimal thicknesses of the laminates and the filler contents at various center frequencies, for which the numerical model of the complex permittivity of the composite laminate was incorporated. In the optimal design results, the content of CNT increased in proportion to the center frequency, but, on the contrary, the thickness of the microwave absorbers decreased. The permittivity and reflection loss are measured using vector network analyzer and 7 mm coaxial airline. The influence of the mismatches in between measurement and prediction of the thickness and the complex permittivity caused the shift of the center frequency, blunting of the peak at the center frequency and the reduction of the absorbing bandwidth.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.9
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• pp.955-960
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• 2003

In this paper, complex permittivities of reference liquids were measured by a sample holder of terminated slotted coaxial line with a movable probe at mobile communications frequencies. The validity of the liquid measurement system was checked by experimental tests with the reference liquids proposed in IEEE Std 1528-200X.