• 한국전기전자재료학회논문지
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• 제13권4호
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• pp.286-293
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• 2000

In this paper we investigated the structural dielectric and piezoelectric properties of 0.03Pb(Sb$\_$1/2//Nb$\_$1/2/)-0.97Pb(Zr$\_$0.495//Ti$\_$0.505/)O$_3$+0.5 wt% excess PbO + wt% MnO(X=0, 0.1, 0.3, 0.5, 0.7) ceramics to develop the high-power piezoelectric transformer. The piezoelectric transformers with dimension of 27.5$\times$27.5$\times$2.5［mm$^3$］were fabricated and their electrical properties were measured. Maxima of piezoelectric properties such as electro-mechanical coupling factor of 0.534 and mechanical quality factor of 1487 were obtained for the PSN-PZT with 0.3wt% MnO. voltage step-up ratios of piezoelectric transformers at 500［Ω］and no load were 0.78, 12.82, respectively. The maximum efficiency of piezoelectric transformer was 98.6% at 800［Ω］. While the 14W fluorescent lamp were driven by the piezoelectric transformer for more than 20［min］, increment of temperature in the piezoelectric transformer was 7［$\^{C}$］.

• Journal of Power Electronics
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• 제18권1호
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• pp.11-22
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• 2018

This paper presents a single switch, high step-up, non-isolated dc-dc converter suitable for renewable energy applications. The proposed converter is composed of a coupled inductor, a passive clamp circuit, a switched capacitor and voltage lift circuits. The passive clamp recovers the leakage inductance energy of the coupled inductor and limits the voltage spike on the switch. The configuration of the passive clamp and switched capacitor circuit increases the voltage gain. A wide continuous conduction mode (CCM) operation range, a low turn ratio for the coupled inductor, low voltage stress on the switch, switch turn on under almost zero current switching (ZCS), low voltage stress on the diodes, leakage inductance energy recovery, high efficiency and a high voltage gain without a large duty cycle are the benefits of this converter. The steady state operation of the converter in the continuous conduction mode (CCM) and discontinuous conduction mode (DCM) is discussed and analyzed. A 200W prototype converter with a 28V input and a 380V output voltage is implemented and tested to verify the theoretical analysis.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2019년도 전력전자학술대회
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• pp.83-85
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• 2019

The use of high voltage gain converters is essential for the distributed power generation systems with renewable energy sources such as the fuel cells and solar cells due to their low voltage characteristics. In this paper, a high voltage gain topology combining cascode Inverting Buck-Boost converter and voltage multiplier structure is introduced. In proposed converter, the input voltage is connected in series at the output, the portion of input power is directly delivered to the load which results in continuous input current. In addition, the voltage multiplier stage stacked in proper manner is not only enhance high step-up voltage gain ratio but also significantly reduce the voltage stress across all semiconductor devices and capacitors. As a result, the high current-low voltage switches can be employed for higher efficiency and lower cost. In order to show the feasibility of the proposed topology, the operation principle is presented and the steady-state characteristic is analyzed in detail. A 380W-40/380V prototype converter was built to validate the effectiveness of proposed converter.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.16-16
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• 2010

The multilayer piezoelectric transformer was manufactured using $Pb(Zn_{1/2}W_{1/2})O_3-Pb(Mn_{1/3}Nb_{2/3})O_3-Pb(Zr_{0.48}Ti_{0.52})O_3$ (abbreviated as PZW-PMN-PZT) ceramics and their electrical properties were investigated. The $k_{eff}$ of the input and the output calculated from the resonant and anti-resonant frequencies were 0.403 and 0.233, respectively. The voltage step-up ratio showed the maximum value in the vicinity of 81kHz. The multilayer piezoelectric transformer showed the temperature rise of about $36^{\circ}C$ at the output power of 12w.

• 한국수소및신에너지학회논문집
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• 제16권4호
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• pp.386-390
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• 2005

Al film(135.5 nm thick) with Pd film(39.6 nm thick) on the top of it was made by thermal evaporation method. Electrical resistance change due to hydrogen absorption and desorption was measured by four point measurement method. The sample was activated by hydrogen absorption and desorption cycling at room temp. Hydrogen was introduced into the film by increasing hydrogen gas pressure step by step up to 640 torr at room temp. The resistance change ratio was decreased to 12 % with increasing hydrogen pressure in contrast to normal metal behavior. This strange tendency was not understood yet. Further study is needed to find out the mechanism of hydrogen absorption in Al in Al/Pd film.

• Geomechanics and Engineering
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• 제7권2호
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• pp.149-164
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• 2014

One of the most advanced classes of techniques for ground response analysis is based on the use of Transfer Functions. They represent the ratio of Fourier spectrum of amplitude motion at the free surface to the corresponding spectrum of the bedrock motion and they are applied in frequency domain usually by FFT method. However, Fourier spectrum only shows the dominant frequency in each time step and is unable to represent all frequency contents in every time step and this drawback leads to inaccurate results. In this research, this process is optimized by decomposing the input motion into different frequency sub-bands using Wavelet Multi-level Decomposition. Each component is then processed with transfer Function relating to the corresponding component frequency. Taking inverse FFT from all components, the ground motion can be recovered by summing up the results. The nonlinear behavior is approximated using an iterative procedure with nonlinear soil properties. The results of this procedure show better accuracy with respect to field observations than does the Conventional method. The proposed method can also be applied to other engineering disciplines with similar procedure.

• Journal of Acupuncture Research
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• 제26권2호
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• pp.171-179
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• 2009

Objectives: The purpose of this study was to investigate the changes of obesity, blood composition and physical ability in obese children on body weight control program. Methods : The body weight control program included exercise, nutrition education and auricular acupuncture was performed 4 times a week during 12 weeks. 32 obese children whose body fat ratio were over 30% participated in this study. Measuring materials were body composition(weight, muscle mass, fat mass, fat ratio, BMI), physical measurement(height, waist circumference, chest circumference, hip circumference), physical ability(grip strength, sit-ups, sitting trunk flexion, sit-down stand-up test, standing long jump, opened eyes foot balance, side step), blood composition(WBC, Hb, ESR, Total Cholesterol, TG, GOT, GPT, BUN, Creatinine, Glucose) and survey(changes of eating habits, changes of living habits, knowledge of obesity, self-confidence, self-esteem). Results : From the results, positive changes were made in BMI, height, waist circumferences, chest circumferences, hip circumferences, sit-ups, sitting trunk flexion, sit-down stand-up test, standing long jump, opened eyes foot balance, side step, Hb, ESR, GOT, GPT and changes of eating habits through the body weight control program. Conclusions : This results suggest that body weight control program including exercise, nutrition education and auricular acupuncture may be effective for helping obese children.

• 전력전자학회논문지
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• 제14권4호
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• pp.315-322
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• 2009

기존의 부스트 컨버터는 출력 전압이 커질수록 스위치와 다이오드의 전압, 전류 스트레스가 커지고 다이오드 역 방향회복에 의한 서지로 인해 실제 사용 가능한 승압비가 제한된다. 본 논문에서는 고승압 응용에 적합한 새로운 비절연 부스트 컨버터를 제안한다. 제안한 컨버터는 듀티비 0.5로 약 6배의 승압비를 가지며 CCM에서도 ZVS 스위칭이 가능하므로 넓은 ZVS 영역을 갖는다. 또한 스위치와 다이오드 전압정격이 출력전압의 1/3로 작고 인터리빙이 가능하여 입출력 수동소자의 정격도 작다. 다이오드도 ZCS 턴오프 동작으로 인해 역방향 회복에 의한 서지가 거의 없다. 제안하는 컨버터의 동작원리를 설명하였고 이론적 해석과 시뮬레이션 및 실험을 통해 타당성을 검증하였다.

• 대한물리의학회지
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• 제9권3호
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• pp.315-324
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• 2014

PURPOSE: This study aimed to determine the correlation of weight bearing ability at the affected side with balance and gait abilities for the development of pressure biofeedback based equipment to stroke patients. METHODS: This study included 35 patients with stroke patient. The tests were conducted to determine the weight bearing ratio while pushing a step forward the affected side, static balance ability using the total length of COP(Center of pressure), sway velocity of COP, COP velocity at the X and Y axis. Functional reaching test (FRT), berg balance scale (BBS) were used to assess the dynamic balance ability and timed up and go test (TUG), 10m walk test (10mWT) were used assess the gait ability respectively. In order to determine the correlation between measured variables, bivariate correlation analysis was conducted. RESULTS: A significant correlation of the weight bearing ratio were shown with COP total length and velocity(r=-.34), Y-axis velocity(r=-.39), FRT(r=.42), BBS(r=.54), TUG (r=-.39), and 10m walking test (r=-.42). CONCLUSION: This study result showed that as patients with stroke had more weight bearing ratio at the affected side, not only their static and dynamic balance abilities increased more but also functional gait ability improved more. These results mean that, to improve stroke patients' static, dynamic balance ability and gait ability, weight bearing training with the affected side foot placed one step forward necessary for gaits are important.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.334-334
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• 2010

In order to fabricate the multilayer piezoelectric transformer by tape casting method, we investigated the effect of $TiO_2$ and PZT powder additions on the Ag/Pd electrode. Meanwhile, effects of $TiO_2$ and PZT powder additives on the microstructure and electrical properties of Ag/Pd electrode were investigated in detail. In addition, the multilayer piezoelectric transformers were fabricated and the characteristics with various load resistance were measured at resonance frequency. The voltage step-up ratio was continuously change with increasing input voltage and load resistance, and then output voltage and powers were increased with increasing input voltage at matching impedance. The temperature rise of multilayer piezoelectric transformers were increased with increasing input voltage and load resistance. Meanwhile, multilayer piezoelectric transformers sintered at $1100^{\circ}C$ show the favorable characteristics with a power of 15 W at $100\;{\Omega}$.