• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.1 s.92
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• pp.26-32
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• 2005

Open-ended coaxial probe is used to measure complex permittivities of materials in a wide bandwidth. Complex permittivity measured by a conventional coaxial probe suffers from severe fluctuation due to instrumental uncertainty when the difference between reflection coeffcients of reference and measuring materials is small. In this paper, open-ended coaxial probe with protruding inner conductor is suggested to increase the difference between reflection coefficients of reference and measuring materials. Its validity is assured by FDTD simulation and actual measurement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.2C
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• pp.10-15
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• 2005

In this paper, a simple but fast and reliable technique for the complex dielectric constant measurement of non-magnetic materials is introduced using a measured transmission coefficient (S21) and a genetic algorithm as an inversion process at microwave frequencies. In this experiment, it has been found that the transmission method is less susceptible with the measurement errors than that of the reflection method and the genetic algorithm can be efficiently used as a search technique. The suggested technique is validated with known and unknown conductor-loaded lossy materials and the conductor-loaded PCB at X-band.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.5 no.4
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• pp.40-46
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• 1994

Design and microwave absorbing properties of ferrite plate are investigated for the application to the radiowave absorbers used in anechoic chamber. The required frequency-dependence of complex permeability is determined on the basis of wave-impedance-matching relationship. The plate thickness and matchingfrequency are determined from the complex permeability and dielectric constant, and then compared with the directly measured reflection loss. A systematic variation of material constants and their influence on the microwave absorbing properties are demonstrated.

• Composites Research
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• v.18 no.3
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• pp.14-20
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• 2005

This paper presents a study on the permittivities of the carbon black/epoxy composite at microwave frequency. The measurements were performed at the frequency band of $1\;GHz\~18\;GHz$. The experimental data show that the complex permittivities of composites depend strongly on the natures and concentrations of the carbon black dispersion. The frequency characteristics of dielectric constants and ac conductivities of composites show the good conformity with descriptions of the percolation theory, satisfying the general scaling relation. The measuring frequency band is over the critical frequency, below that the ac conductivities of composites are constant to the frequency. The values of dielectric constants and ac conductivities have consistent relationships with the carbon black concentration. The A new scheme, that is a branch of Lichtenecker-Rother formula, is proposed to obtain a mixing law to describe the complex permittivities of the composites as function frequency and concentration of carbon black.

• Clean Technology
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• v.30 no.3
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• pp.228-238
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• 2024

Electrolytes are one of the essential components of a lithium-ion battery. They determine the battery's lifespan and cell characteristics. The dielectric constant is a key thermophysical property for determining how much salt can be dissociated and solvated in a solution. Hence, fast and reliable dielectric constant measurement is essential when formulating an electrolyte solution. This work implemented an open-ended coaxial probe (OECP) station as a quick and reliable tool to measure the complex permittivity spectra of electrolyte solutions. The capability of the OECP station was tested by measuring the complex permittivity of propylene carbonate (PC), dimethyl carbonate (DMC), and their mixtures from 0.1 to 8 GHz at 288.15, 298.15, and 308.15 K. The obtained dielectric spectra were then interpreted based on dielectric relaxation models and thermodynamic theories. The measured static dielectric constant data agreed well with the data from previous studies. They were also correlated using the Wang-Anderko thermodynamic model, showing approximately a 1% deviation from the experimental data. In addition, the relaxation characteristics, including the relaxation time and the Cole-Davidson exponent, showed that the microstructure of the solution significantly changes at the propylene carbonate mole fraction of 0.4. These results and methodologies are expected to contribute to the further understanding of electrolyte solutions and ultimately lead to the optimization of electrolyte formulation for lithium-ion batteries.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.11
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• pp.14-18
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• 1992

A gradient matrix method in conjunction with the transmission-reflection method to determine the complex permittivity and permeability of a microwave material is presented. This method does not incur the phase ambiguity due to an improper sample length, and is applicable to the measurement of low-loss materials of a half wavelength. A gradient matrix for a coaxial cable sample is derived, and the results are illustrated.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.8
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• pp.60-68
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• 2008

The complex permittivity and permeability of various periodic metamaterial (MTM) cells are extracted by simulating a fictitious rectangular waveguide consisting of PEC and PMC walls. The shapes of the MTM cells include a thin wire (TW), a single split-ring resonator (SSRR), a double SRR (DSRR), a modified SRR, and a combined structure of the TW and the DSRR. The TW falls on a negative-$\varepsilon$/positive-$\mu$ region, the SRRs on a positive-$\varepsilon$/negative-$\mu$ region, and the combined structure on a negative-$\varepsilon$/negative-$\mu$ region. We also investigate how the permeability and permeability are affected by the dimension parameters of the MTM cells. Another extraction technique utilizing time domain signals is developed overcoming some limitations that the waveguide technique can not handle.

• 한국정보통신설비학회:학술대회논문집
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• 2004.08a
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• pp.226-229
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• 2004

본 논문은 초고주파 영역에서 개방 단말 동축선을 대신해서 복소 유전율을 측정할 수 있는 MEMS 프로브와 그 응용예로 MEMS 프로브 어레이를 제안한다. MEMS 프로브는 기존의 동축선 프로브와 달리 커넥터와의 연결이 간단하여 일회용으로 프로브를 사용할 수 있다는 점에서 의료용으로 사용할 수 있는 가능성이 있다. 샘플의 유전율 분포를 구하기 위해서 기존의 센서는 반복 접촉을 요구하고 이로 인한 번거로움과 측정 오차를 줄일 목적으로 MEMS 프로브 어레이를 개발 하였다. MEMS 프로브 어레이는 RF 스위치를 사용하여 다수의 측정 포인트를 한번의 센서 접촉으로 측정할 수 있는 새로운 개념의 프로브이다. 1GHz부터 40GHz까지의 광대역에서 0.9% 식염수의 유전율을 측정하여 MEMS 프로브의 성능을 검증하였다.

• Journal of the Korean Society for Marine Environment & Energy
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• v.15 no.1
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• pp.19-21
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• 2012

The engine oil life of internal combustion engine is shorted by the thermal effect and that causes air pollution. In order to measure the status of engine oil accurately, the exchange of new oil extends the life of combustion engine and reduces environmental pollution. Capacitance probes, such as engine oil and fluids can be used to measure the dielectric constant. In this paper, the degradation of engine oil varies depending on the degree of dielectric properties was analyzed. Depending on the state of the oil, the variant capacitance of the probe was measured by LCR Meter, respectively, and then the permittivity of oil was calculated. In addition, according to the size of the probe by measuring the change in capacitance measurement, accuracy of dielectric constant are presented. According to oil contaminated with the more increase in dielectric constant, we can decide that contaminated oil is available.

• Journal of the Korean Magnetics Society
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• v.14 no.4
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• pp.131-137
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• 2004

For the aim of thin electromagnetic wave absorbers used in mobile telecommunication frequency band (0.8-2.0㎓), we investigate high-frequency magnetic, dielectric and microwave absorbing properties of iron particles dispersed in rubber matrix in this study. The major experimental variables are particle shape (sphere and flake) and initial particle size (in the range 5-70 $\mu\textrm{m}$) of iron powders. High value of magnetic permeability and dielectric permittivity can be obtained in the composites containing thin plate-shape (flake) iron particles (of which thickness is less than skin depth in ㎓frequency), which can be produced by mechanical forging of spherical iron powders using an attrition mill. This result is attributed to the reduction of eddy current loss (increase of permeability) and the increase of space charge polarization (increase of permeability). The optimum initial particle size is found to be about 10 $\mu\textrm{m}$ for the attainment of the material parameters (particularly, real part of complex permeability) satisfying the wave impedance matching. With the iron powders controlled in size and shape as absorbent fillers in rubber matrix, the thickness can be reduced to about 0.7mm with respect to -5㏈ reflection loss (70% power absorption) in mobile telecommunication frequency band.