• Composites Research
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• v.16 no.2
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• pp.48-53
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• 2003

This paper presents a study on the permittivities of the I-glass fabric/epoxy composite laminates containing carbon black dispersions at microwave frequency. Measurements were performed at the frequency band of 5 GHz∼18 GHz. The results showed that the complex permittivities of the composites depend strongly on the natures and concentrations of the carbon black dispersion. A new scheme is proposed to obtain a mixing law for the estimation of the complex permittivities of the composite laminates as a function of concentration of carbon black. Simultaneously, the complex permittivity of carbon black itself was also calculated by the scheme. The experimental values of the complex permittivities of the composites were compared to those calculated.

• 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.

• 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.

• Journal of Powder Materials
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• v.15 no.1
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• pp.18-22
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• 2008

The electromagnetic (EM) wave absorption properties with a variation of crystallization annealing temperature have been investigated in a sheet-type absorber using the $Fe_{73}Si_{16}B_7Nb_3Cu_1$ alloy powder. With increasing the annealing temperature the complex permeability (${\mu}_r$), permittivity (${\varepsilon}_r$) and power absorption changed. The EM wave absorber shows the maximum permeability and permittivity after the annealing at $610^{\circ}C$ for 1 hour, and its calculated power absorption is above 80% of input power in the frequency range over 1.5 GHz.

• Journal of electromagnetic engineering and science
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• v.1 no.2
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• pp.139-145
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• 2001

In this paper, a coaxial sample holder is proposed with its de-embedding and parameter extraction procedure. The S-parameters were measured up to 1 GHz using network analyzer, HP8753D, and N-type connector together with the de-embedding of N-type connector. The proposed de-embedding procedure is performed to extract electrical parameters of blood glucose, which gives the permittivity of blood glucose. We also analyzed the error of extracted parameters, which are caused by instrument error and geometrical error. Using these error analyses, we reduced the error factors of extracted parameters. We extracted electrical parameters of glucose samples through these all extraction procedure and confirmed the possibility of glucose diagnosis system based on microwave system.

• Proceedings of the KIEE Conference
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• 1988.07a
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• pp.446-449
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• 1988

A spectral inverse technique, which was developed by applying the pulse basis moment method procedure on the direct scattering problem in the reverse sequence for the reconstruction of complex permittivity profiles inside inhomogeneous dielectric objects, is modified to be applicable to the moment method with series-expanded basis. By performing numerical simulations for various type of dielectric objects, it is demonstrated that this inverse technique provides close reconstruction of permittivity profiles. Futhermore, compared to the previous scheme of the pulse basis, the presented method is shown to reduce the computation cost, relative error of reconstructed permittivity profiles by averaging in each cell, and the ill-posedness inherent to this inverse scattering problem.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.9
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• pp.565-570
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• 2016

In this work, the complex permittivity of epoxy resins is measured. Epoxy resins, epoxy with micro size fillers and epoxy with micro+nano alumina composites have been evaluated for dielectric properties according to frequency variation. The dielectric spectroscopy measurement and analyses are carried out in the frequency range of $10^{-2}Hz$ to 1MHz and constant to room temperature. The results of dielectric loss suggest that significant improvement in the electrical performance can be expected by using samples containing nano and micro fillers mixture when compared to materials containing only microfillers. As the result, we verified the specific characteristics of dielectric permittivity and dielectric loss namely, relative permittivity become low with improving dispersibility of nano+micro mixture composites and become rise with agglomerate of nano particles.

• Journal of the Korean Chemical Society
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• v.56 no.1
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• pp.20-27
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• 2012

Complex permittivity spectra of Allyl Chloride (AC), 2-Butanone (2-BU) and their binary mixtures over the entire range of concentration were obtained using the Time Domain Reflectometry (TDR) technique in microwave frequency range at various temperatures. Static dielectric constant and relaxation time are obtained from complex permittivity spectra. Density ($\rho$) and refractive index ($n_D$) are also measured. These parameters are used to determine excess dielectric constant, excess inverse relaxation time, excess molar volume, excess molar refraction, polarity, Bruggeman factor and thermodynamic parameters viz. enthalpy of activation and entropy of activation. The values of static dielectric constant and relaxation time increases while density and refractive index decreases with the percentage of 2-Butanone in Allyl Chloride increases. Excess parameters were fitted to a Redlich-Kister equation.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.341-342
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• 2008

A conductivity of soot at microwave frequency is presented using a novel technique for complex permittivity of materials. The method overcomes limitations of conventional methods which are cavity perturbation and transmission/reflection method. Resonant frequencies and Q factors are measured and simulated for the cylindrical cavity, and they are compared to each other. Similar material property of both real material and simulation material produce similar values of resonant frequency and Q factor. The complex permittivity of material can be determined by simulating the cavity to change material property until the simulation results are nearly the same as the measurement results. Cylindrical cavity has been realized for measurement at 880 MHz, and conductivity of soot is measured. A sample was made by depositing the soot on the glass. The proposed method shows that the conductivity of soot is 11 S/m.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.2
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• pp.69-77
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• 1996

We analyzed wideband propagation characteristics of a microstrip transmission line based on FR-4 composite substrate using the wideband complex dielectric constant model and the phenomenological loss equivalence method. The loss calculated by constant relative permittivity and loss tangent is greatly overestimatd compared to that calculated by the frequency-dependent complex relative permittivity. This wideband analysis can be helpful to characterize high-speed and high-density transmission lines associated with the wideband dielectric characteristics and shows that the FR-4 composite substrate has high potential of high frequency circuit applications in terms o fthe propagation loss.