• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.2
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• pp.147-154
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• 2017

The impedance approximation has been widely used to model an earth surface such as ocean surface. In calculation of the dyadic Green's function for the impedance half plane, Sommerfeld integral and its partial derivatives are required. It is known that two far-field approximation of the Sommerfeld integral can be represented in terms of Legendre or Laguerre polynomials. Hence, a criterion is required to choose one of two far-field approximations for a given application, which can be expressed in a complex plane of the surface impedance. Also, we approximate the required partial derivatives of Sommerfeld integral and numerically verify the accuracy of the approximation.

• 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.

• Journal of the Korean Ceramic Society
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• v.38 no.8
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• pp.693-697
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• 2001

고상반응법으로 이론 밀도의 약 92%의 소결 밀도를 갖는 입방정계의 새로운 이온전도체 L $a_{2-x}$S $r_{x}$M $o_{2-y}$C $r_{y}$ $O_{9-{\delta}}$(x=0, 0.05, y=0, 0.1)를 제조하였다. 교류 복소임피던스는 3$50^{\circ}C$~90$0^{\circ}C$의 온도범위에서 공기중에서 측정하여, EQUIVCRT 모델링 소프트웨어로 해석하였다. 상 전이온도인 58$0^{\circ}C$ 전.후로 임피던스 스펙트럼에 큰 차이가 있었으며, 전기전도도는 L $a_2$M $o_2$ $O_{9}$ 시편의 경우 7$50^{\circ}C$에서 3$\times$$10^{-2}$ S$cm^{-1}$ /로 우수하였으며, 활성화 에너지는 고온 상 영역에서는 0.89 eV, 저온 상 영역에서는 1.12 eV이었다. 순수한 L $a_2$M $o_2$ $O_{9}$과 비교하여 Cr 치환효과는 크지 않았으나, Sr 치환 시에는 상 전이온도의 감소와 전기전도도의 증가 현상을 보였으며, 전이온도 부근에서의 전기전도도 변화 폭은 작았다.다.

• Journal of the Korean Chemical Society
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• v.30 no.3
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• pp.273-281
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• 1986

This study is focused on the correct measurement of the equations for the determination of the impedance parameters-the differential capacity of the double layer $C_d$, solution resistance $R_Q$, transfer resitance $R_i$, and adsorption pseudcapacity $C_{\phi}$/ The application of only an imaginary part of complex function of ${\omega}$ at the sinusoidal steady state indicates the following equations of total impedance: at low frequency $|Z_{LF}|=1/{\omega}_1\;C_{\phi}\;{\sqrt{1+{{\omega}_1}^2/{\omega}^2}$, at high frequency $|Z_{HF}|={\omega}_2/({\omega}_1{\omega}_3C{\phi})({\omega}^2+{{\omega}_2}^2)\;{\sqrt{{({\omega}^2+{\omega}_2{\omega}_3)}^2+{({\omega}_2{\omega}-{\omega_3{\omega})^2}}$. The values of the total impedance of cell, phase angle, and cell current that are necessary for the calculations of impedance parameters were experimentally measured from 200 to 6000Hz for the following supporting electrolytes, 0.5M $Na_2SO_4$, 1M NaCl, 19.373% sea water, 1M HCl, 1M $KNO_3$ and for $10^{-2}M$ KI and 60mM DBNA (Di-iso-Butylnitrosoamine) in these supporting electrolytes. The derived equations in this study shows that the values of impedance parameters of $C_d,\;C_{\phi},\;R_i\;and\;R_Q\;are\;15{\sim}40\;{\mu}F/cm^2,\;162{\sim}758\;{\mu}F/cm^2\;11.5{\sim}57.6\;ohm{\cdot}cm^2\;and\;0.5{\times}10^{-2}{\sim}4.1{\times}10^{-2}\;ohm{\cdot}cm^2$ respectively.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.60-68
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• 2007

Conventional analysis of spectral induced polarization (SIP) data consists of measuring impedances over a range of frequencies, followed by spectral analysis to estimate spectral parameters. For the quantitative and accurate estimation of subsurface SIP parameter distribution, however, a sophisticated and stable inversion technique is required. In this study, we have developed a two-step inversion approach to obtain the two-dimensional distribution of SIP parameters. In the first inversion step, all the SIP data measured over a range of frequencies are simultaneously inverted, adopting cross regularisation of model complex resistivities at each frequency. The cross regularisation makes it possible to enhance the noise characteristics of the inversion by imposing a strong assumption, that complex resistivities should show similar characteristics over a range of frequencies. In numerical experiments, we could verify that our inversion approach successfully reduced inversion artefacts. As a second step, we have also developed an inversion algorithm to obtain SIP parameters based on the Cole-Cole model, in which frequency-dependent complex resistivities from the first step are inverted to obtain a two-dimensional distribution of SIP parameters. In numerical tests, the SIP parameter images showed a fairly good match with the exact model, which suggests that SIP imaging can provide a very useful subsurface image to complement resistivity.

• Journal of the Microelectronics and Packaging Society
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• v.2 no.2
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• pp.41-48
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• 1995

본 논문에서는 테이프 케스팅법으로 제조한 BaTiO3 계 쉬트형 PTCR 세라믹스의 적기적물성에 대하여 연구하였다. PTCR의 조성은 몰비로 89.9 BaTiO3-0.1Sb2O3-10 CaTiO3-0.05MnO3였고 케스팅용 슬러리의 유기물질은 결합제로 PVB 가소제로는 DBP 용제 로는 에탄올과 톨류엔 그리고 분산제로는 fish oil을 사용하였다. 케스팅하여 얻어진 그린쉬 트를 13$25^{\circ}C$와 135$0^{\circ}C$에서 1시간 소성하여 얻은 쉬트형 PTCR을 온도에 대한 저항 및 복소 임피던스를 측정하고 미세구조를 SEM으로 관찰하여 칩화를 위한 조건들을 검토하였다.

• Journal of the Korean Ceramic Society
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• v.31 no.9
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• pp.1012-1220
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• 1994

BaTiO3 ceramics doped with 0.1 to 4.0 mol% Nb2O5 were prepared by conventional solid stage sintering process, so as to investigate the effect of the amount of Nb2O5 on the dielectric properties and complex impedance patterns of barium titanates. From the measurement of capacitance, we found that the dielectric constant of BaTiO3 samples with 1 mol% or more Nb2O5 remained approximately constant around room temperature with values higher than 2500. In this paper, the effect of impurity content as well as temperature on complex impedance patterns was discussed in detail. In particular, the grain and grain boundary behavior of samples which showed PTCR characteristics was discussed in terms of measuring temperature.

• 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.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.11
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• pp.1223-1232
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• 2008

In this paper, an analytic method is proposed to extract the reference slot admittance required for the design of a non-resonant waveguide edge slot array. A slot and two neighboring transmission line sections of the numerous alternately inclined slots with the identical inclination angle are modelled as a uniform lossy transmission line, and thus, the total ABCD matrix is easily calculated and compared with the simulated or measured one. From this procedure, the complex characteristic impedance and the complex propagation constant of the lossy transmission line are calculated and the normalized slot admittance is analytically obtained. In order to validate the proposed method, the admittance value of a reference slotted waveguide fabricated for designing the X-band edge slot array is extracted and it is compared with the one obtained by the other conventional method.

• Journal of Navigation and Port Research
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• v.32 no.10
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• pp.805-811
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• 2008

This paper presents a design of RFID(Radio Frequency Identification) tag antenna which is available for a vehicle's side mirror and directivity characteristics by mr body. The proposed Tag antenna is designed symmetrical structure to improve the broad bandwidth characteristic and the readable range. A proposed tag antenna($30\;mm{\times}24\;mm{\times}1\;mm$) has resonant frequency at 910 MHz and bandwidth is 780 MHz ($540\;MHz{\sim}1320\;MHz$). The chip impedance is the 16 - $j131\;{\Omega}$ and the complex conjugate impedance of commercial chip has been used for tag antenna design. In order to evaluate effects of tag antenna for side view mirror's permittivity as well as car body(conductor), radiation pattern characteristics and readable range have been calculated and measured. The optimized position for a vehicle's RFID system has been observed in the inside of a side mirror and the calculated results show good agreement with the measured results.