• Journal of IKEEE
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• v.25 no.3
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• pp.517-527
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• 2021

This paper presents the phase-shift full-bridge DC-DC converter using the one-chip micom. The proposed converter primary is the full-bridge power topology that operates with the unipolar pulse-width modulation (PWM) by the phase-shift method, and the secondary is the full-bridge full-wave rectifier composed of four diodes. The control of proposed converter is performed by the one-chip micom and its MOSFET switches are driven by the bootstrap circuit. Thus the total system of proposed converter is simple. The proposed converter achieves high-efficiency using the resonant circuit and blocking capacitor. In this paper, first, the power-circuit operation of proposed converter is explained according to each operation mode. And the power-circuit design method of proposed converter is shown, and the software control algorithm on the micom and the feedback and switch drive circuits operating the proposed converter are described, briefly. Then, the operation characteristics of proposed converter are validated through the experimental results of a designed and implemented prototype converter by the shown design and implementation method in this paper. The highest efficiency in the results was about 92%.

• Journal of IKEEE
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• v.26 no.4
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• pp.584-589
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• 2022

For DC-AC power conversion from a high-voltage photovoltaic panel to a single-phase grid, the two-stage transformerless inverter with a buck-boost converter followed by a full-bridge inverter is widely used. To avoid an excessive leakage current due to the large parasitic capacitance of the photovoltaic panel, the full-bridge inverter can only adopt the bipolar PWM which results in much higher power loss compared to the unipolar PWM. In order to overcome such a poor efficiency, this paper proposes a new topology in which an IGBT and a diode for circuit isolation are added to the buck-boost converter. The proposed circuit isolation method allows the unipolar PWM in the full-bridge inverter without any increase in the leakage current so that the overall efficiency can be improved. The validity of the proposed solution is verified by computer simulation and power loss calculation.

• Journal of Sensor Science and Technology
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• v.32 no.4
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• pp.238-245
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• 2023

0.75(Bi_1/2Na_1/2)TiO₃-0.25SrTiO₃ (BNT-25ST) ceramics with high densities were successfully prepared at a sintering temperature of 1,000℃ by adding a mixture of 1 mol% CuO and 0.5 mol% Na₂CO₃ or 0.5 mol% CuO and 0.25 mol% Na₂CO₃. Double polarization-electric field (P-E) hysteresis curves and sprout-shaped bipolar strain-electric field (S-E) hysteresis curves with small negative strains were observed in the pristine and CuO-added BNT-25ST ceramics whereas the Na₂CO₃-added sample showed similar P-E and S-E curves to a typical ferroelectric. The pristine BNT-25ST ceramics showed an extremely large strain and a large-signal piezoelectric strain constant (d₃₃^*): 0.287 % at 80 kV/cm and 850 pm/V at 20 kV/cm. Similar values, 0.248 % at 80 kV/cm and 655 pm/V at 20 kV/cm, were obtained in the CuO-added sample. However, the pristine and CuO-added samples showed large hysteresis in unipolar S-E curves at an electric field of less than 20 kV/cm. The Na₂CO₃-added sample showed smaller values of the strain and d₃₃^* but displayed a linear change and small hysteresis in the unipolar S-E curve. The co-added sample with CuO and Na₂CO₃ displayed intermediate P-E and S-E hysteresis curves.

• Korean Journal of Veterinary Research
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• v.33 no.4
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• pp.735-746
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• 1993

Electrocardiographic parameters of amplitude and the shape of waves on the unipolar precordial chest leads in the normal Korean native cattles have been measured with a 3 channel electrocardiograph built in a computed and analysis. The study was conducted on 98 heads of mean age of 17.6 months. The wave forms of P, T and QRS complex wave in all leads showed various types. The parameters of the amplitude in the wave types showed the most frequency in each lead that were analyzed as follow : 1. In P wave, amplitudes of positive type showed a frequency of 92.9% and 93.9% in leads $CV_6LU$ and $CV_6LL$ that were $83.8{\pm}31.0{\mu}V$ and $76.0{\pm}30.7{\mu}V$, and negative type showed a frequency of 97.9% in lead V 10 that were $-80.2{\pm}29.4{\mu}V$, respectively. But the plate type in leads $CV_6RU$ and $CV_6RL$ showed frequency of 48% and 58.3%, respectively. 2. Average amplitude of the QRS complex were in a range of $277.0{\pm}154.0{\mu}V$ to $648.2{\pm}146.2{\mu}V$(mean of $418.8{\pm}139.4{\mu}V$) in all leads that were manifested the Low-Voltage QRS complex(below 1 mV in unipolar precordial leads). Average amplitudes of each wave type in the QRS complex were $-250.0{\pm}139.8{\mu}V$ and $-399.2{\pm}226.8{\mu}V$ in the QS group types that showed a frequency of 50.0% and 82.5% in the leads $CV_6LU$ and $CV_6LL$, respectively. And average amplitudes of the R group types showed a frequency of 85.6%, 56.1% and 75.8% in the $CV_6RU$, $CV_6RL$ and $V_{10}$ that were $321.5{\pm}142.1{\mu}V$, $271.6{\pm}139.9{\mu}V$ and $552.4{\pm}132.7{\mu}V$, respectively. 3. In T waves, Amplitudes of the positive type showed a frequency of 60.2%, 46.9% and 83.7% in leads of $CV_6LL$, $CV_6RU$ and $CV_6RL$ that were respectively $184.7{\pm}93.7{\mu}V$ $103.7{\pm}64.43{\mu}V$ and $111.8{\pm}39.3{\mu}V$, the negative type showed a frequency of 62.2% and 93.7% in leads $CV_6LU$ and $V_{10}$ that were $142.2{\pm}82.1{\mu}V$ and $-280.3{\pm}107.2{\mu}V$, respectively. 4. Average amplitude of ST segment were $3.7{\pm}33.1{\mu}V$, $0.9{\pm}23.1{\mu}V$, $10.9{\pm}28.6{\mu}V$, $5.8{\pm}28.3{\mu}V$ and $-34.7{\pm}48.4{\mu}V$ in leads $CV_6LL$, $CV_6RU$, $CV_6RL$, $CV_6LU$ and $V_{10}$ respectively.

• Journal of Chest Surgery
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• v.13 no.3
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• pp.219-228
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• 1980

The heart block and bradyarrhythmia with or without Stokes-Adams attacks are serious, usually terminal events and the immediate mortality is very high. Stimulation with an artificial pacemaker is now an accepted form of treatment in cases of Stokes-Adams syndrome in which medication in unable to produce any lasting improvement. Permanent pacemaker therapy is indicated in these circumstances. The purpose of this report is to describe the successful use of pacemaker in 3 cases of Stokes-Adams syndromes and a case of sinoatrial block with bradyarrhythmia at the Department of Thoracic and Cardiovascular Surgery, Kyungpook National University School of Medicine. Electrode catheter was passed through the right external jugular vein and attached to the endocardial surface of the right ventricle. In case 1, fixed type generator was used at first and for the case 2, 3, 4, and case 1 at second, demand type generators were used. The bipolar electrode catheters were used for the three cases and unipolar electrode catheter for case 4. The results of immediate and late period were satisfactory.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1874-1875
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• 2004

A high rate deposition sputtering process of magnesium oxide thin film in oxide mode has been developed using a 20 kW unipolar pulsed power supply. The powersupply was operated at a maximum constant voltage of 500 V and a constant current of 40 A. The pulse repetition rate and the duty were changed in the ranges of 10 ${\sim}$ 50 kHz and 10 ${\sim}$ 60 %, respectively. The deposition rate increased with increasing incident power to the target. Maximum incident power to the magnesium target was obtained by the control of frequency, duty and current. The deposition rate of a moving state was 9 nm m/min at the average power of 1.5 kW. This technique is proposed to apply high through-put sputtering system for plasma display panel.

• Proceedings of the IEEK Conference
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• 2004.08c
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• pp.787-791
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• 2004

We investigated field-effect ion-transport devices based on carbon nanotubes by using classical molecular dynamics simulations under applied external force fields, and we present model schematics that car be applied to the nanoscale data storage devices and unipolar ionic field-effect transistors. As the applied external force field is increased, potassium ions rapidly flow through the nanochannel. Under low external force fields, ther nal fluctuations of the nanochannels affect tunneling of the potassium ions whereas the effects of thermal fluctuations are negligible under high external force fields. Since the electric current conductivity increases when potassium ions are inserted into fullerenes or carbon nanotubes, the field effect due to the gate, which can modify the position of the potassium ions, changes the tunneling current between the drain and the source.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.605-611
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• 2001

A numerical technique for simulating the aggregation of charged particles was presented with a Brownian dynamic simulation in the free molecular regime. The Langevin equation was used for tracking each particle making up an aggregate. A periodic boundary condition was used for calculation of the aggregation process in each cell with 500 primary particles of 16 nm in diameter. We considered the thermal force and the electrostatic force for the calculation of the particle motion. The morphological shape of aggregates was described in terms of the fractal dimension. The fractal dimension for the uncharged aggregate was $D_{f}=1.761$. The fractal dimension changed slightly for the various amounts of bipolar charge. However, in case of unipolar charge, the fractal dimension decreased from 1.641 to 1.537 with the increase of the average number of charges on the particles from 0.2 to 0.3 in initial states.

• Proceedings of the KIPE Conference
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• 2011.07a
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• pp.302-303
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• 2011

일반적인 승압 컨버터와 H-bridge 인버터로 구성되는 비절연 계통연계형 태양광 인버터 시스템의 효율을 높이기 위해 H-bridge의 스위칭에 적합한 Unipolar 스위칭 방식을 선정하고, 또 SiC 다이오드를 사용함으로써 전체 효율을 향상시켰으며 이를 시뮬레이션과 실험으로 보여준다.

• 연구논문집
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• s.34
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• pp.21-28
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• 2004

In this study, we report an investigation for the charging and collection of aerosol nanoparticles in an electrostatic precipitator (ESP) according to particle charging and diffusion effects. The competition between charging probability and diffusion effect determines the collection efficiency of nanoparticles in the ESP. In conclusion, collection efficiency continuously decreased with the reduction in the particle size. This indicates that poor partial charging effect of nanoparticles is more dominant than their diffusion effect in the ESP for the nanoparticles in the particle size range of 4-20 nm. Theoretical calculations using a unipolar diffusion charing theory were in good agreement with the experimental data for the nanoparticles less than 20 nm in diameter.