• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.2
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• pp.75-85
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• 2016

A pyrotechnic system consisting of donor/acceptor pair separated by a gap relies on shock attenuation characteristics of the gap material and shock sensitivity of the donor and acceptor charges. Despite of its common use, numerical study of such pyrotechnic train configuration is seldom reported because proper modeling of the full process requires precise capturing of the shock wave attenuation in the gap prior to triggering a full detonation of high explosive and accurate description of the high strain rate dynamics of the explosively loaded inert confinements. We apply a Eulerian level-set based multimaterial hydrocode with reactive flow models for pentolite donor and heavily aluminized RDX as acceptor charge. The complex shock interaction, critical gap thickness, acoustic impedance, and go/no-go characteristics of the gap test are quantitatively investigated.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.6
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• pp.25-29
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• 2017

This paper presents a hetero-integration of electrostatically actuated RF MEMS Switch and step up DC-DC converter on a redistribution layer using commercial PCB process. RF characteristics of Duroid with $56{\Omega}$ impedance GCPW transmission line and that of FR4 with $59{\Omega}$ impedance CPW transmission line were analyzed. From DC to 6GHz, RF characteristics of Duroid were better than that of FR4, insertion loss was 2.08dB lower, return loss was 3.91dB higher, and isolation was 3.33dB higher.

• The Journal of the Acoustical Society of Korea
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• v.31 no.5
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• pp.280-287
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• 2012

This paper presents a study on the experimental analysis of the impedance characteristics according to the rotational direction of the transmission beam of a cylindrical sensor array. Besides, this suggests a real time control technique of the transmitter output for the effective maximum power transmission, in order to drive efficiently the rotational transmission beam of the active sonar transmitter. The output characteristics of the transmitter and the real-time impedance variations of the sensor array are analyzed under the overload conditions. They are caused by electric and acoustic boundary conditions when the rotational transmission beam is operated. From these results, a new output control method of the transmitter is proposed to protect the transmitter and its loads. It can maximize the output power without the transmission pause even if the transient phenomena occur. The proposed technique is verified from the experiment.

• 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.

• Journal of Advanced Navigation Technology
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• v.23 no.2
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• pp.166-171
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• 2019

This paper has designed a current mode class D power amplifier to increase the transmission efficiency of a 6.78 MHz wireless power transfer (WPT) transmitter and to ensure stable characteristics even when the transmitting and receiving coil intervals change. By reducing the loss due to the parasitic capacitor component of the transistor, which limits the theoretical efficiency of the linear amplifier, this research has improved the efficiency of the power amplifier. The circuit design simulator was used to design the high efficiency amplifier, and the power output and efficiency characteristics according to the load impedance change have been simulated and verified. In the simulation, 42.1 dBm output and 95% efficiency was designed at DC bias 30 V. The power amplifier was fabricated and showed 91% efficiency at the output of 42.1 dBm (16 W). The transmitting and receiving coils were fabricated for wireless power transfer of the drone, and the maximum power added efficiency was 88% and the output power was $42.1dBm{\pm}1.7dB$ according to the load change causing from the coil intervals.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.1
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• pp.36-45
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• 2010

In this paper, we propose a new design method to design a wireless power transfer system using loop antennas for consumer electronics. This method can simply design a wireless power transfer system only using measurements of coupling coefficients and simple equations of equivalent circuit model about loop antennas without complicated electromagnetic analysis. Using the proposed design method, a wireless power transfer system with a pair of loop antennas operating at the frequency of 13.56 MHz, which have a dimension of $50{\times}50\;cm^2$, is designed and implemented. The input return loss, coupling coefficient, efficiency, and input impedance variation with respect to a distance between loop antennas were measured. The proposed design method provides good agreements between measured and predicted results. Also, the wireless power transfer system with impedance matching circuits designed by the proposed design method shows two times higher efficiency characteristics than the case with the general $50\;{\Omega}$ impedance matching circuits. Therefore, we verified that our design method could be an effective tool to design a wireless power transfer system.

• Journal of the Korean Electrochemical Society
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• v.10 no.1
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• pp.7-13
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• 2007

We synthesized and investigated $La_{0.75}Sr_{0.25}FeO_3$ by Glycine Nitrate Process(GNP) method used as cathode materials for SOFC(solid oxide fuel cell). Optimized amount of glycine is 3.17 mol. ICP elemental composition analysis indicated that the stoichiometry of the synthesized powders have nearly nominal values. SEM images and XRD patterns reveal that the synthesized powder has uniform size distribution and high degree of crystallinity. The sample powders were isostatically pressed to form a pellet. The green body was sintered at $1200^{\circ}C$ and the relative density of the sintered specimens were measured by Archimedes mettled. We measured electrochemical performance of LSF by AC impedance spectroscopy. Resistance of LSF shows lower value than that of LSM throughout all temperature region. The anode-supported solid oxide fuel cell showed a performance of $342mW/cm^2(0.7V,\;488mA/cm^2)$ at $750^{\circ}C$. The electrochemical characteristics of the single cell were examined by at impedance method.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.140-140
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• 2016

유기전계발광소자 (Organic Light Emitting Diode : OLED)는 보조광원이 필요 없고 천연색 표현이 가능하며, 낮은 소비 전력 및 저전압 구동 등의 장점으로 이상적인 디스플레이 구현이 가능하여 차세대 디스플레이로써 많은 이목을 끌고 있으나 제한된 수명과 안정성의 문제점을 안고 있다. 따라서 OLED의 열화 원인을 분석하고 수명을 연장하기 위한 체계적인 방법과 기술 개발이 중요하다. Impedance Spectroscopy는 이온, 반도체, 절연체 등의 벌크 또는 계면 영역의 전하 이동을 조사하는데 사용될 수 있어, OLED에서도 Impedance Spectroscopy를 이용하여 전하수송과 전자주입 메커니즘 등 폭넓은 전기적 정보를 얻을 수 있다. 본 연구에서는 Impedance Spectroscopy를 이용하여 경과시간에 따른 OLED의 임피던스 특성을 측정하여 열화 메커니즘을 분석하였다. 본 연구에서 OLED는 ITO / 2-TNATA (4,4,4-tris2-naphthylphenyl-aminotriphenylamine) / NPB (N,N'-bis-(1-naphyl)-N, N'-diphenyl-1,1'- biphenyl-4,4'-diamine) / Alq3 (tris(quinolin-8-olato) aluminum) / Liq / Al으로 구성된 녹색 형광 OLED를 제작하였다. OLED의 전계 발광 특성을 측정하기 위한 전원 인가장치로 Keithley 2400을 사용하여 전압과 전류를 인가하였고, 소자에서 발광된 휘도 및 발광 스펙트럼은 Photo Research사의 PR-650 Spectrascan을 사용하여 암실 환경에서 측정하였다. 임피던스 스펙트럼은 컴퓨터 제어 프로그래밍이 가능한 KEYSIGHT사의 E4990A를 사용하여 측정하였다. 임피던스 측정 전압은 0 V부터 2 V 간격으로 8 V까지, 주파수는 20 Hz에서 2 kHz의 범위로 설정하여 측정하였다. I-V-L과 임피던스 특성은 24 시간의 간격을 두고 실온에서 측정하였다. 그림은 경과시간에 따른 녹색 형광 OLED의 인가전압 2 V, 6 V의 Cole-Cole plot을 나타낸 것이다. 문턱전압 미만인 인가전압 2 V에서는 소자를 통하여 전류가 흐르지 않아 큰 반원 형태를 나타내었고, 시간이 경과함에 따라 소자 제작 직후엔 실수 임피던스의 최댓값이 $8982.6{\Omega}$에서 480 시간 경과 후엔 $9840{\Omega}$으로 약간 증가하였다. 문턱전압 이상인 인가전압 6 V에서는 소자 제작 직후 실수 임피던스의 최댓값이 $108.2{\Omega}$으로 작은 반원 형태를 나타내나 시간이 경과함에 따라 방사형으로 증가하는 것을 확인 할 수 있었고, 672 시간 경과 후엔 실수 임피던스의 최댓값이 $9126.9{\Omega}$으로 문턱 전압 미만 일 때와 유사한 결과를 나타내었다. 이러한 임피던스의 증가 현상은 시간이 경과함에 따라 OLED의 열화에 의한 것으로 판단된다.

• Journal of the Korean Electrochemical Society
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• v.3 no.3
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• pp.131-135
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• 2000

In order to investigate the origin of capacity fading with charge/discharge cycling in $LiMn_2O_4$ thin film battery, impedance studies have been performed with increasing cycling in $LiMn_2O_4/1M\;LiClO_4-PC/Li$ cells. The fitted values obtained from impedance data show good agreements with the experimental results. Especially, the element of charge transfer resistance of $LiMn_2O_4/liquid$ electrolyte interface initially increased, and then saturated with increasing the charge/discharge cycles, which could explain the cause of initial abrupt capacity fading of $LiMn_2O_4$ thin film with cycling due to interfacial reaction. The steady capacity fading is caused by the increasing of Warburg resistance. The chemical diffusion coefficient of Li ions decreased from $5.15\times10^{-11}cm^2/sec$ at 1st cycles to $6.3\times10^{-12}cm^2/sec$ at 800th cycles, which attributed to the Jahn-Teller distortion/Mn dissolution which diminishes tetra hedral sites necessary for Li diffusion in $LiMn_2O_4$.

• Journal of Korea Society of Industrial Information Systems
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• v.19 no.5
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• pp.25-31
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• 2014

Bioelectrical Impedance Analysis(BIA) is a widely used method for estimating body composition changes which is a non-invasive, inexpensive, safety and reproductive method. We studied the bioimpedance change and the distinction of blood pressure according to body posture and conducted three kinds of experiments: the real-time bioimpedance measurement, the simulation using equivalent circuit model and the blood pressure measurement. Bioimpedance is measured during 4 minutes at the multi-frequency(1 kHz, 10 kHz, 20 kHz, 50 kHz, 70 kHz, 100 kHz). From the experiment results, the changes in body postures result in changes of resistance and reactance, with an average rapid increase of body impedance when going from standing, sitting to supine. Specially, the laying resistance on average was 16.49% higher than supine resistance at 50 kHz and the laying reactance measurement was also 26.05% higher than sitting reactance at 1 kHz. Blood pressure in standing posture was higher than those in other postures both in maximum($125.14{\pm}12.30$) and in minimum($75.57{\pm}10.31$). The results of BIA and blood pressure in this study will be contributed to the research on acute illness, extreme fat, and body shape abnormalities.