• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.1
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• pp.1-7
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• 2003

Leaky modes on a circular dielectric rod are investigated from the precisely determined normalized complex propagation constants using Davidenko's complex root finding technique. Below the cutoff frequency of the guided mode, distinct frequency regions that have unique properties are observed, such as nonphysical region, antenna mode region, reactive mode region, and spectral gap region.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.594-606
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• 1999

The electromagnetic scattering characteristics by a periodic strip grating on a grounded dielectric slab for TE polarization case is examined from the viewpoints of both the reflection grating and the leaky wave antenna problems. Numerical results for two kinds of Bragg blazing (resonance type and non-resonance type) phenomena are given and some discussions on the properties such as complex propagation constants, scattering characteristics, and distributions of strip current density are presented.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.12
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• pp.9-14
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• 2000

A numerical method for scattering of electromagnetic waves from a arbitrary shaped grating covered with dielectric slab is considered for TE polarization case from the viewpoints of both reflection grating problem and leaky wave antenna problem. The analysis is based on a periodic Green's function and the method of moments. Numerical results involving some combinations of geometric parameters are presented in terms of relative scattered powers of spectral modes and complex propagation constants.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.21-26
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• 1995

The systematic variation of complex permeability and complex permittivity and their relationship with micro-wave absorbing properties are investigated in sintered Ni-Zn ferrites of non-stoichiometric composition. The specirrens of ${(Ni_{0.5}Zn_{0.5}O)}_{1-x}(Fe_{2}O_{3})_{1+x}$ spinels were prepared by a conventional ceramic processing technique. In the present study. complex permeability and permittivity can be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the spinel lattice. The primary effect of the excess ${\alpha}-Fe_{2}O_{3}$ is to increase the dielectric constant. while the notable decrease of magnetic loss is observed in the iron-deficient ferrites. The results suggest that the matching fre-queocyand matching thickness could be controlled by the variation of ${\alpha}-Fe_{2}O_{3}$ contents in the Ni-Zn ferrite.

• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.2
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• pp.73-82
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• 2003

For measurements and analysis of dielectric characteristics of planar slabs of microwave absorbing materials, I have applied a free-space method in the frequency range of 8~14 GHz. The measurement system for free-space method consists of transmit and receive antennas, mode transitions, precision coaxal cables, the network analyzer, and a computer Special Spot-focused horn lens antenna was used to eliminate diffraction effects. Diffraction effects at the edges of the sample are minimized by satisfying the condition for minimum transverse dimension of the plate and the beamwidth of the antennas at the focus. The time-domain gating feature of the network analyzer and the thru, reflect, and line(TRL) calibration technique were used to eliminate the effects of undesirable multiple reflections. The complex coefficients of reflection and transmission, $S_{11}$ and $S_{21}$, of planar samples were measured for standard materials such as Teflon, Rexolite$\textregistered$ 2200. The results were compared with existing measurement method. And I applied a free-space method for measurement to measure dielectric constants of some electromagnetic absorbing materials. Dielectric properties for the same samples were also measured with a 7mm coxial transmission line method for purposes of comparison with the free-space method.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.4
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• pp.763-770
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• 2021

In this paper, in order to exclude the influence of BAN(Body Area Network) signals operating in the ISM band, the design and optimization process of an on-body microstrip patch antenna operating at 4.567 GHz is presented. The antenna for the monitoring of the lower legs with cancellous osteoporosis is designed to be lightweight and compact with improved return loss and bandwidth. The structure around the applied lower leg consisted of a five-layer dielectric plane. Taking into account losses, the complex dielectric constant of each layer is calculated using multi Cole-Cole model parameters, whereas a unipolar model is used for normal or osteoporotic cancellous bones. The return loss of the coaxial feed antenna on the phantom is -67.26 dB at 4.567 GHz, and in the case of osteoporosis, at the same frequency the return loss difference is 35.88 dB, and the resonance frequency difference is about 7 MHz.

• The Journal of the Korea institute of electronic communication sciences
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• v.16 no.2
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• pp.385-394
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• 2021

In this paper, a new equation of electromagnetic wave transmission matrix was proposed to calculate the reflected power and transmitted power for the multi-layered planar lossy structure. The applied human leg was modeled as a four-layer planar structure of skin, fat, muscle and bone. The complex dielectric constant to consider the loss of each of these layers was calculated using the 4-pole cole-cole model parameter. When electromagnetic waves were incident on the skin surface, total reflected and transmitted power, and human body loss were calculated for a frequency band of 0.1 to 20.0 GHz. And for various muscle thicknesses, the power reflected only from the outermost bone and re-radiated from the skin was calculated. It was confirmed that at the muscle thickness of 3.0 mm and the frequency of 4.6 GHz the return loss was -6.13 dB, which was 3.42 dB lower than the average value.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.4
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• pp.528-536
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• 1999

This work studies the effects of transient reflectance on the thermal responses of a metal(gold) thin-film during ultrashort laser heating. The heating process is calculated using the conventional conduction model (parabolic one-step: POS), parabolic two-step model (PTS) with and without variable properties, hyperbolic two-step model (HTS). Results from the HTS model are very similar to those from the PTS model, since the laser heating time in this study is greater than the electron relaxation time. PTS model with variable properties, however, results in totally different temperature profiles compared to those from POS models or calculation with constant properties. Transient reflectances are estimated from electron temperature distributions and based on the linear relationship between the electron temperature and complex dielectric constants. Reflectance of the front surface can be changed with respect to dielectric constants, while those of the rear surface remain unchanged.

• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.70-72
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• 2003

본 논문에서는 설계민감도 해석법과 위상최적화 기법을 사용하여 산란체의 물질상수 분포를 알기위한 수치해석 알고리즘을 제안하였다. 설계민감도 해석법과 보조변수법을 사용하여 복소 유전율에대한 목적함수의 미분정보를 계산하였고 이 민감도 정보를 통해 물질정보를 최적화 하였다. 최적화 기법으로 최대경사법(Steepest descent Method)을 사용하였으며 이 제안한 해석 기법을 2차원 TMz 모델에 적용함으로써 검증하였다.

• Electrical & Electronic Materials
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• v.9 no.6
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• pp.572-577
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• 1996

Alternating current and direct current of pure, ball milled, and $Al_{2}$O$_{3}$ added ZnO were investigated by means of complex impedance measurement and voltage-current source measurement unit. The electrical conductivity of A1$_{2}$O$_{3}$ added ZnO samples increases when the content of A1$_{2}$O$_{3}$ is used within 1 at% and decreases when it's used more than that. The increase and decrease of electrical conductivity seem to be the donor effect of $Al_{2}$O$_{3}$ and the increase of the number of ZnO grains, respectively. Impedance spectrum seems to be one semircicle. The size of semicircle increase with increasing the A1$_{2}$O$_{3}$ contents. The calculated dielectric constant(at 50.deg. C) were about 70-140 at the peak of the semicircle. The semicircles seem not to be the resistance of ZnO grain as compared to that of 10 for pure ZnO.