• 한국정보디스플레이학회:학술대회논문집
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• 2007.08b
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• pp.1108-1111
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• 2007

OLED driving voltage shift can reduce the OLED display lifetime, especially for digitally driven AMOLED. By operating OLED at high frequency, we were able to suppress OLED voltage shift degradation, expecting improved AMOLED lifetime. We describe frequency dependence of voltage shift obtained from bias stress test of OLED.

• Journal of Biomedical Engineering Research
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• v.4 no.1
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• pp.29-36
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• 1983

In this paper, center frequency down slift of ultrasonic echo signals which for the measurements of frequency dependent attenuation in the biological tissue are estimated. Center frequency down shift of echo-signals are estimated after signal spectrum analysis of whole echo-signals. In case of signal spectrums are simple, estimation of down shift frequency is very simple and in case of complicate spectrum, estimation of down shift frequency is depend on spectral shape. In case of unable to estimate, frequency dependence of medium is nonlinear(n) 1), in which upper shift of spectrums are presented. In case of unable to estimate, spectrum analysis are performed at local position. At consquence, we know that spectral dispersions are caused complicately by biological tissue layer.

• Journal of the Optical Society of Korea
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• v.16 no.2
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• pp.181-184
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• 2012

We report, for the first time, operation frequency dependence of current density-voltage ($J_{OLED}-V_{OLED}$) shift for multi-layer organic light-emitting diodes (OLEDs). When the OLEDs were electrically stressed for 21 hours with 50% duty voltage pulses at 60, 120, 240, and 360 Hz, the JOLED-VOLED shifts were suppressed by half for 360 Hz operation compared with 60 Hz operation, but with little change in emission efficiencies. This frequency dependent $J_{OLED}-V_{OLED}$ shift is believed to be commonly observed for typical multi-layer OLEDs and can be used to further improve lifetime of digitally-driven active-matrix OLED displays.

• Journal of Sensor Science and Technology
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• v.17 no.4
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• pp.289-294
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• 2008

The purpose of this study is to materialize the viscosity sensor by using the SH-SAW sensor of which the center frequency is operated at higher than 50 MHz. In order to measure the viscosity, SAW sensor of which the center frequency is operated at 100 MHz is developed. By using the developed sensor, phase shift, delay time, insertion loss, and frequency variation are measured at different viscosity. The result shows that the phase shift difference between the viscosity variations is such that the difference between the distilled water and the 100 % glycerol solution is approximately $45^{\circ}$, the change of the insertion loss is approximately 9 dB, and the difference of frequency variation is approximately 5.9 MHz. Therefore, it is shown that viscosity of unknown solution can be measured with the surface acoustic wave sensor.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.7
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• pp.998-1000
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• 2012

By cascading RHTL (Right-Handed Transmission Line) and LHTL (Left-Handed Transmission Line), we fabricated a BPF (Band Pass Filter) in which the phase propagation at the pass band center frequency is fixed as we want. We utilized a positive phase propagation of a RHTL which is a form of LPF (Low Pass Filter) and negative phase propagation of LHTL which is a form of HPF (High Pass Filter). Therefore, if RHTL and LHTL are cascaded, a BPF can be constructed and the phase propagation inside the passband is decided by the number of RHTLs and LHTLs. In this paper, we provide a detailed theory related to it and proved the theory with an actual experiment. In the experiment, we fabricated two BPFs with similar passband. One with $90^{\circ}$ phase shift and the other with $-90^{\circ}$ phase shift at the center of passband. The result of simulation and actual experiment agrees well. This proves the suggested theory is correct and feasible.

• Proceedings of the KIPE Conference
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• 2003.07a
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• pp.227-230
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• 2003

In this paper, a full bridge edge-resonant zero voltage mode based soft-switching PWM DC-DC power converter with a high frequency center tapped transformer link stage is presented from a practical point of view. The power MOSFETS operating as synchronous rectifier devices are implemented in the rectifier center tapped stage to reduce conduction power losses and also to extend the transformer primary side power MOSFETS ZVS commutation area from the rated to zero-load without a requirement of a magnetizing current. The steady-state operation of this phase-shift PWM controlled power converter is described in comparison with a conventional ZVS phase-shift PWM DC-DC converter using the diodes rectifier. Moreover, the experimental results of the switching power losses analysis are evaluated and discussed in this paper. The practical effectiveness of the ZVS phase-shift PWM DC-DC power converter treated here is actually proved by using 2.5kW-32kHz breadboard circuit. An actual efficiency of this converter is estimated in experiment and is achieved as 97$\%$ at maximum.

• Journal of IKEEE
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• v.16 no.1
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• pp.51-55
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• 2012

In this paper, we propose to employ a ternary sequence as a cyclic code shift keying (CCSK) modulation sequence. And we simulate the performance in a frequency hopping spread spectrum/time division multiple access (FHSS/TDMA) system with CCSK. Wireless channel is modeled as Rayleigh fading channel. From the simulation results, it is demonstrated that the system adopting the ternary sequence as a CCSK sequence has higher performance than that with a random sequence.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.787-789
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• 2000

High temperature superconducting YBCO films have been grown on MgO substrates by pulsed laser deposition (PLD) with Nd:YAG laser Superconducting microwave filter was fabricated by conventional photolithography method. We have designed filter with the center frequency of 14 GHz. We have measured the center frequency of filter at 77 K and its critical temperature 89K. Also we have designed another filter to compare frequency responses. The measured frequency responses will be presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.15 no.2
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• pp.364-370
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• 1995

The purpose of this paper was to develop a nondestructive evaluation method of sintered material by ultrasonic method. The density distribution of sintered material becomes inhomogeneous partially because of the friction between the powder and the die during compaction. The inhomogeneity was investigated by measurement of the energy attenuation coefficient and the shift of the center frequency in the frequency spectrum of the ultrasonic reflection echo. The experimental results showed that the center frequency of reflection wave depended linearly on the density of sintered materials. However, the attenuation coefficient decreased inversely as the density increased. This study shows that the shift of the center frequency in the frequency spectrum of reflection wave can be used to a nondestructive evaluation of sintered materials.

• Journal of Power Electronics
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• v.19 no.6
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• pp.1337-1350
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• 2019

This paper proposes a Phase-Shift Triple Full-Bridge (PSTB) Zero-Voltage Zero-Current-Switching (ZVZCS) converter with a high switching frequency and high efficiency. In the proposed converter, all three bridge legs are shared leading-legs, and all three transformers work in the Discontinuous Conduction Mode (DCM). Thus, all of the switches and diodes in the PSTB ZVZCS can be soft switched. Moreover, since all of the transformers can pass energy from the primary-side to the secondary-side when their primary-side currents are not zero, there is no circulating current. As a result, the PSTB ZVZCS converter can achieve a high efficiency at high operating frequencies. A theoretical analysis and the characteristics of the proposed converter are presented and verified on a 1MHz 200~300V/24V 1.2kW hardware prototype. The proposed converter can reach a peak efficiency of 96.6%.