• 비파괴검사학회지
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• 제28권1호
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• pp.59-63
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• 2008

Time reversal (TR) of nondispersive body waves has been used in many applications including ultrasonic NDE. However, the study of the TR method for Lamb waves on thin structures is not well established. In this paper, the full reconstruction of the input signal is investigated for dispersive Lamb waves by introducing a time reversal operator based on the Mindlin plate theory. A broadband and a narrowband input waveform are employed to reconstruct the $A_0$ mode of Lamb wave propagations. Due to the frequency dependence of the TR process of Lamb waves, different frequency components of the broadband excitation are scaled differently during the time reversal process and the original input signal cannot be fully restored. This is the primary reason for using a narrowband excitation to enhance the flaw detectability.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1998년도 Proceedings ICPE 98 1998 International Conference on Power Electronics
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• pp.1030-1035
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• 1998

This paper describes a new dc-ac inverter system, which for achieving sinusoidal ac waveform make use of parallel loaded frequency resonant inverter consisting of full bridge. Each one of the pair of switches in the inverter is driven to synchronous output frequency and the other is driven to PWM signal with resonant frequency proportional to magnitude of sine wave. Since current through switches is always zero at its turn-on in proposed inverter, low stress and low switching loss is achieved. The theoretical analysis is proved through the experimental test.

• 대한전기학회논문지
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• 제33권11호
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• pp.425-432
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• 1984

This paper is to propse a new self-excitation method of synchronous generator. Instead of conventional exciter of synchronous generator, the additional winding which is arranged in addition to the armature winding, is used in this generator. The output terminal of the additional winding is connected to a capacitor and to a full wave rectifier in series. In this configuration, one source double excitation which is composed of capacitor-self-excitation by lead urrent and direct current excitation by rectifier, is induced. The result is that` The excetation efficency is improved greatly and output waveform is improved also. In three-phase synchronous generator using the new method of the one source double excitation, voltage element (shunt characteristics) and current element (series characteristics)are compounded in scalar by adapting star-point-open-rectifier system. The result is as following` The effect of load power factor angle on voltage regulation is reduced greatly, compound characteristics is become manifold by controlling capacity of capacitor, and transient response is improved.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.415-419
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• 1997

The left ventricular relaxation rate is used as a golden standard which describes the left ventricular diastolic unction. So far, to get the rate of relaxation one should calculate the data after full recording, that is, off-line method. Therefore one cannot get the rate of relaxation in real-time while changing loading condition or infusing drug. But real time monitoring of the relaxation rate is necessary while changing loading condition or infusing drug to control the mechanics of heart and to get more information. We propose a new criterion to get the left ventricular relaxation rate and a real time algorithm. By comparison, it was turned out that our criterion outperforms others criterion.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2005년도 International Meeting on Information Displayvol.I
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• pp.71-74
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• 2005

There have been various efforts to achieve a better PDP TV, which have low power consumption, high image quality and low price. As the results, the power consumption of LG's new 42 inch HD PDP could be lower than 42 inch LCD under the general movie display load condition. And the address discharge time lag of ${\sim}1\;{\mu}s$ for 42 and 50 inch XGA single scan by which the cost can be reduced and image quality can be improved was achieved by using new MgO material and driving waveform. In addition, we have suggested TCA (Triangular Color pixel Arrangement) cell structure for realizing the full HDTV of 60inch diagonal size, which has $1920{\times}1080$ resolution. The luminous efficiency of the suggested TCA structure has been increased about 40% compared with that of the conventional cell structure.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제51권11호
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• pp.645-651
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• 2002

In this paper, a multilevel PWM inverter employing a cascaded transformer is presented to reduce the harmonics of output voltage and load currents. The proposed PWM inverter consists of two full-bridge modules and their corresponding transformers. The secondarics of each transformer are series-connected. So continuous output voltage levels can be synthesized from the suitable selection of the turns ratio of trasformer. And it appears an integral ratio to input DC source. Because of the cascaded connection of transformers, output filter inductor is not necessary. The operational principles and analysis are explained, and it is compared with a conventional isolated H-bridge PWM inverter. The validity of proposed multilevel inverter is verified through simulated and experimental waveform and their FFT results.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2013년도 전력전자학술대회 논문집
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• pp.337-338
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• 2013

Combination the several type of single phase power conversion utilized simply topology are proposed in this paper. Totally four kind of converter are investigated, they are Boost AC/AC Converter, Buck AC/AC Converter, Boost AC/DC Converter, and Buck DC/AC Converter. Two types action mode are presented to determine the functional of circuit. First is AC chopper action mode, representation of the AC/AC converter. AC chopper action mode offered the sinusoidal current waveform, better power factor, faster dynamics, and smaller input/output filter. They present high robustness, offer safe commutation and have high efficiency. The second is full bridge action mode, determined the transformation AC to DC power and otherwise. Four switching devices and one magnetic contactor will establish the mode operation of circuit and manage the flow of power proceed in proper. The correction and advance of the kind of converter are verified by simulation.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 B
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• pp.1199-1201
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• 2000

This paper proposes a harmonics reducing circuit for fluorescent lamp inverters using hybrid type smoothing circuit with pumping and smoothing capacitors. A waveform of full-wave rectification used as a direct current power supply at fluorescent lamp inverters contains a lot of harmonic wave from inrush current which is generated near the maximum of input voltage with purse shape when voltage smoothing capacitor is charged. Therefore, in order to suppress inrush current which will result in harmonic wave. this paper proposes a method to control abrupt charging current by use of charging voltage at pumping capacitor. The suppression of harmonics generation at lamp current is confirmed through simulations.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2006년도 춘계학술대회 논문집
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• pp.407-409
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• 2006

This paper presents the methods of designing the control circuits for a Class D amplifier to have a peak performance. The proposed approach is based on the three functional components - a carrier generator, a feedback circuit and a dead-time circuit. First the analog signal is applied to the controller, which outputs the 3 level PWM waveform. The controller used for this experiment is made of the operational amplifier and the logic circuit. The experimental results show that the control circuit performs with satisfaction and its output is proportional to input audio signal, providing a satisfactory 3 level PWM pattern. From this design methodology, by implementing a proposed control circuit we can achieve the efficient Class D amplifier using the half-bridge, full-bridge or push-pull topology at the output stage.

• Journal of Power Electronics
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• 제11권3호
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• pp.256-263
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• 2011

This paper utilizes free oscillation and energy injection principles to generate and control the high frequency current in the primary track of a contactless power transfer system. Here the primary power inverter maintains natural resonance while ensuring near constant current magnitude in the primary track as required for multiple independent loads. Such energy injection controllers exhibit low switching frequency and achieve ZCS (Zero Current Switching) by detecting the high frequency current, thus the switching stress, power losses and EMI of the inverter are low. An example full bridge topology is investigated for a contactless power transfer system with multiple pickups. Theoretical analysis, simulation and experimental results show that the proposed system has a fast and smooth start-up transient response. The output track current is fully controllable with a sufficiently good waveform for contactless power transfer applications.