• Journal of the Institute of Electronics Engineers of Korea SD
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• v.39 no.4
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• pp.41-54
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• 2002

In this study, we have analyzed the effects of the membrane layer and the bragg reflector layers on the resonance characteristics through comparing the characteristics of the membrane type FBAR (Film Bulk Acoustic Wave Resonator) and the one type bragg reflector layers with those of the ideal FBAR with top and bottom electrode contacting air by using equivalent circuit technique. It is assumed that ZnO is used for piezoelectric film, $SiO_2$ are used for membrane layer and low acoustic impedance layer, W are used for the high acoustic reflector layer and Al is used for the electrode. Each layer is considered to have a acoustic propagation loss. ABCD parameters are picked out and input impedance is calculated by converting 1-port equivalent circuit to simplified equivalent circuit that ABCD parameters are picked out possible. From the variation of resonance frequency due to the change of thickness of electrode layers, reflector layers and membrane layer it is confirmed that membrane layer and the reflector layer just under the electrode have the greatest effect on the variation of resonance frequency. From the variation of resonance properties, K and electrical Q with the number of layers, K is not much affected by the number of layers but electrical Q increases with the number of layers when the number of layers is less than seven. The electrical Q is saturated when the number of layers is large than six. The electrical Q is dependent of mechanical Q of reflector layers and membrane layer. Both ladder filter and SCF (Stacked Crystal Filters) show higher insertion loss and out-of-band rejection with the increase of the number of resonators. The insertion loss decreases with the increase of the number of reflector layers but the bandwidth is not much affected by the number of reflector layers. Ladder Filter and SCF with membrane layer show the spurious response due to spurious resonance properties. Ladder filter shows better skirt-selectivity characteristics in bandwidth but SCF shows better characteristics in insertion loss.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.1
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• pp.48-55
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• 2014

These Xenon flashlamp power supply for Ultra Violet has converter with high voltage conversion ratio. General model is composed of transformer with high voltage conversion ratio and voltage doubler rectifier circuit. Purpose of power supply leads dielectric breakdown of Xenon flashlamp and passes current rapidly. When passing current, it has to limit current to avoid over-heat, damage of electrode and acceleration of gas oxidation which are cause of performance degradation of lamps. Generally, inductors and resistors, which are called as "Ballast," are used to limit currents. Generally, Transformer has high turn ratio to make high voltages. But we can get high voltages using the transformer with low turn ratio which is driven with self resonance. Also, an advantage of self resonance is to make a circuit simply through impedance of transformer in resonance frequency which filters output voltage. As using an unique impedance of transformer, the circuit does not need other impedance elements like the ballast. So the power supply assures high efficiency of the arc discharge.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.12
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• pp.256-264
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• 2012

The directional algebraic reconstruction technique (DART) using the trigonometric current pattern is one of the image reconstruction algorithms in electrical impedance tomography (EIT). This method needs to compute resistances between electrode pairs as using relation between the injected currents and measured voltages for the reconstruction of the inner image. The delay time is incurred in this process. Therefore this paper proposes modified directional algebraic reconstruction technique (mDART) using the adjacent current pattern instead of the trigonometric current pattern to solve the delay time for initial resistance values. The proposed method uses measured voltages instead of computed resistances in the reconstruction algorithm. Hence this method can eliminate the delay time because it does not use the resistances. In conclusion, the proposed method improves image quality and image reconstruction time by using the adjacent current pattern. To prove performance of the proposed method, we carried on computer simulation of various cases.

• Journal of the Korean Electrochemical Society
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• v.6 no.4
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• pp.255-260
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• 2003

The complex capacitance analysis was performed in order to examine the potential-dependent EDLC characteristics of porous carbon electrodes. The imaginary capacitance profiles $(C_{im}\;vs.\;log\lf)$ were theoretically derived for a cylindrical pore and further extended to multiple pore systems. Two important electrochemical parameters in EDLC can be estimated from the peak-shaped imaginary capacitance plots: total capacitance from the peak area and $\alpha_0$ from the peak position. Using this method, the variation of capacitance and ion conductivity in pores can be traced as a function of electric potential. The electrochemical impedance spectroscopy was recorded on the mesoporous carbon electrode as a function of electric potential and analyzed by complex capacitance method. The capacitance values obtained from the peak area showed a maximum at 0.3V (vs. SCE), which was in accordance with cyclic voltammetry result. The ionic conductivity in pores calculated from the peak position showed a maximum at 0.2 V (vs. SCE), then decreased with an increase in potential. This behavior seems due to the enhanced electrostatic interaction between ion and surface charge that becomes enriched at more positive potentials.

• Korean Journal of Materials Research
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• v.13 no.3
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• pp.160-168
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• 2003

The co-firing processes for the supported type planar solid oxide fuel cell were investigated. A flat cell of $7.7${\times}$10.8\textrm{cm}^2$ was fabricated successfully by the co-firing process, in which green films were co-sintered in the forms of two layers of anode/electrolyte or of three layers of anode/electrolyte/cathode with gas distributor. A co-fired cell of two layers yielded a power of 200 ㎽/$\textrm{cm}^2$ at 608 ㎷. Its performance loss was mainly due to iR drop in the anodic gas distributor, which was attributed to poor contact between anodic gas distributor and current collector. The performance in the co-fired cell of three layers was much lower than that of two layers, which resulted from the large iR drop and activation overvoltage at the cathodic side. In the co-fired cell of two layers, the impedance analysis indicated that the performance decay during cell operation is due to both anode overvoltage and iR drop at anode side. Also the electrode reaction of the co-fired two layers' cell is considered to be controlled by activation overvoltage within the low current of 50 ㎃.

• Transactions on Electrical and Electronic Materials
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• v.17 no.3
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• pp.129-133
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• 2016

Theoretical and graphical analysis of pull-in-voltage and figure of merit for a fixed-fixed capacitive Micro Electromechanical Systems (MEMS) switch is presented in this paper. MEMS switch consists of a thin electrode called bridge suspended over a central line and both ends of the bridge are fixed at the ground planes of a coplanar waveguide (CPW) structure. A thin layer of dielectric material is deposited between the bridge and centre conductor to avoid stiction and provide low impedance path between the electrodes. When an actuation voltage is applied between the electrodes, the metal bridge acquires pull in effect as it crosses one third of distance between them. In this study, we describe behavior of pull-in voltage and figure of merit (or capacitance ratio) of capacitive MEMS switch for five different dielectric materials. The effects of dielectric thicknesses are also considered to calculate the values of pull-in-voltage and capacitance ratio. This work shows that a reduced pull-in-voltage with increase in capacitance ratio can be achieved by using dielectric material of high dielectric constant above the central line of CPW.

• Journal of the Korean Electrochemical Society
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• v.13 no.4
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• pp.235-239
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• 2010

The $Li_4Ti_5O_{12}$/CNT composite is prepared by ultrasound associated sol-gel method. The prepared composite is characterized by SEM, TEM, XRD and TG analysis, and their electrochemical behaviors are investigated by cyclic voltammetry, electrochemical impedance spectroscopy and charge-discharge test in 1M $LiBF_4$/PC electrolyte. From the results, it is identified that the $Li_4Ti_5O_{12}$ nanoparticles coated on CNT surface have regular size with around 10~30 nm and spinel-framework structure. At the current rate of 20C, the discharge capacities of $Li_4Ti_5O_{12}$/CNT composites with CNT contents of 15, 30 and 50 wt% are 57, 63 and $48mAhg^{-1}$, respectively, which have similar value. The improved electrochemical behavior of the $Li_4Ti_5O_{12}$/CNT composite electrode is attributed to the addition of CNT with electronic conductivity.

• Corrosion Science and Technology
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• v.17 no.2
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• pp.54-59
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• 2018

The effect of external DC electric field on atmospheric corrosion behavior of zinc under a thin electrolyte layer (TEL) was investigated by measuring open circuit potential (OCP), cathodic polarization curve, and electrochemical impedance spectroscopy (EIS). Results of OCP vs. time curves indicated that the application of external DC electric field resulted in a negative shift of OCP of zinc. Results of cathodic polarization curves measurement and EIS measurement showed that the reduction current of oxygen increased while charge transfer resistance ($R_{ct}$) decreased under the external DC electric field. Variation of OCP negative shift, reduction current of oxygen, and $R_{ct}$ increase with increasing of external DC electric field strength as well as the effect of external DC electric field on double-layer structure in the electrode/electrolyte interface and ions distribution in thin electrolyte layer were analyzed. All results showed that the external DC electric field could accelerate the corrosion of zinc under a thin electrolyte layer.

• Korean Journal of Materials Research
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• v.26 no.8
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• pp.417-421
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• 2016

We improve the energy conversion efficiency (ECE) of a dye sensitized solar cell (DSSC) by preparing a working electrode (WE) with localized surface plasmon resonance (LSPR) by inducing Au thin films with thickness of 0.0 to 5.0 nm, deposited via sputtering. Field emission scanning electron microscopy and atomic force microscopy were used to characterize the microstructure of the blocking layer (BL) of the Au thin films. Micro-Raman measurement was employed to confirm the LSPR effect, and a solar simulator and potentiostat were used to evaluate the photovoltaic properties, including the impedance and the I-V of the DSSC of the Au thin films. The results of the microstructural analysis confirmed that nano-sized Au agglomerates were present at certain thicknesses. The photovoltaic results show that the ECE reached a value of 5.34% with a 1-nm thick-Au thin film compared to the value of 5.15 % without the Au thin film. This improvement was a result of the increase in the LSPR of the $TiO_2$ layer that resulted from the Au thin film coating. Our results imply that the ECE of a DSSC may be improved by coating with a proper thickness of Au thin film on the BL.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1568-1569
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• 2011

최근 기후변화로 인해 낙뢰의 발생빈도가 크게 증가하고 있으며 이에 따라 피뢰시스템의 중요성이 부각되고 있다. 피뢰시스템의 원활한 기능을 수행하기 위해 접지시스템의 성능이 보장되어야 하며, 접지전극은 뇌격전류를 안전하게 대지로 방류시켜야 한다. 본 논문에서는 피뢰시스템에서 가장 흔하게 사용되는 수직접지전극을 대상으로 서지전류가 인가되었을 때 접지전극이 묻힌 대지저항률, 접지전극의 길이, 서지 전류의 파두시간 등에 따른 규약접지임피던스를 측정하고 그 특성을 분석하였다. 그 결과 대지저항률이 높은 토양과 접지전극의 길이가 짧은 경우 접지임피던스가 감소하는 용량성 특성이 지배적으로 나타나며, 대지저항률이 작고 접지전극의 길이가 긴 경우 접지임피던스가 증가하는 유도성 특성이 지배적으로 나타났다. 따라서 피뢰시스템을 위한 접지시스템 설계 시 대지저항률 및 접지전극의 길이를 고려하여 유도성 특성을 최소화 할 수 있도록 설계해야 한다.