• Korean Journal of Optics and Photonics
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• v.10 no.2
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• pp.162-168
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• 1999

A new design of four-pass dye laser amplifier affording a narrow-bandwidth pulsed output is demonstrated to suppress the amplified spontaneous emission(ASE) carried by the amplifier output and reduce the possibility of parasitic oscillation in the amplifier. By the direct pulsed amplification of a cw 100 mW dye laser under a Q-switched doubled Nd:YAG laser pumping with energy of 5.6 mJ/pulse, high-peak-power pulsed output with 1.5-mJ energy in 130-MHz bandwidth is obtained corresponding to a power gain greater than $2{\times}10^6$ and an energy efficiency of 27%. The ASE ratio in the four-pass amplifier output is dramatically reduced by using a diffraction grating in the amplifier. Compared with the results obtained from the normal operation of the amplifier with no frequency-selective device, the ASE ratio is reduced by a factor in excess of 10 to remain under 1.5% of the amplifier output whereas the total output energy is slightly increased by ~4%.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.1
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• pp.15-19
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• 2005

Conventional eddy current testing has been used for the detection of the defect-like fatigue crack in the conductive materials, such as aluminum, which uses a sinusoidal signal with very narrow frequency bandwidth, Whereas, the pulsed eddy current method uses a pulse signal with a broad bandwidth. This can allow multi-frequency eddy current testing, and the penetration depth is greater than that of the conventional eddy current testing. In this work, a pulsed eddy current instrument was developed for evaluating the metal loss. The developed instrument was composed of the pulse generator generating the maximum square pulse voltage of 40V, an amplifier controlled up to 52dB, an A/D converter of 16 bit and the sampling frequency of 20 MHz, and an industrial personal computer operated by the Windows program. A pulsed eddy current probe was designed as a pancake type in which the sensing roil was located inside the driving roil. The output signals of the sensing roil increased rapidly wich the step pulse driving voltage かn off, and the latter part of the sensing coil output voltage decreased exponentially with time. The decrement value of the output signals increased as the thickness of the aluminum test piece increased.

• Journal of IKEEE
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• v.24 no.1
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• pp.161-169
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• 2020

In order to reduce the manufacturing cost of MCU chips used in applications such as wireless chargers and USB-C, compared to DP-EEPROM (Double Poly EEPROM), which requires 3 to 5 additional process masks, it is even more necessary MTP(Multi-Time Programmable), which is less than one additional mask and have smaller unit cell size. In addition, in order to improve endurance characteristics and data retention characteristics of the MTP memory cell due to E/P(Erase / Program) cycling, the distribution of the V_TP(Program Threshold Voltage) and the V_TE(Erase Threshold Voltage) needs to be narrow. In this paper, we proposed a current-type BL S/A(Bit-Line Sense Amplifier) circuit, WM(Write Mask) circuit, BLD(BL Driver) circuit and a algorithm, which can reduce the distribution of program and V_T and erase V_T, through compare the target current by performing the erase and program pulse of the short pulse several times, and if the current specification is satisfied, the program or erase operation is no longer performed. It was confirmed that the 256Kb MTP memory fabricated in the Magnachip semiconductor 0.13㎛ process operates well on the wafer in accordance with the operation mode.

• Journal of Biomedical Engineering Research
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• v.15 no.4
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• pp.489-497
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• 1994

The most serious problems related to the cardiovascular prothesis are thrombosis and hemolysis. It is known that the flow pattern of cardiovascular prostheses is highly correlated with thrombosis and hemolysis. Laser Doppler Anemometry (LDA) is a usual method to get flow pattern, which is difficult to operate and has narrow measure region. Particle Image Velocimetry (PIV) can solve these problems. Because the flow speed of valve is too high to catch particles by CCD camera, high-speed camera (Hyspeed : Holland-Photonics) was used. The estimated maximum flow speed was 5m/sec and maximum trackable length is 0.5 cm, so the shutter speed was determined as 1000 frames per sec. Several image processing techniques (blurring, segmentation, morphology, etc) were used for the preprocessing. Particle tracking algorithm and 2-D interpolation technique which were necessary in making gridrized velocity pronto, were applied to this PIV program. By using Single-Pulse Multi-Frame particle tracking algorithm, some problems of PIV can be solved. To eliminate particles which penetrate the sheeted plane and to determine the direction of particle paths are these solving methods. 1-D relaxation fomula is modified to interpolate 2-D field. Parachute artificial heart valve which was developed by Seoul National University and Bjork-Shiely valve was testified. For each valve, different flow pattern, velocity profile, wall shear stress and mean velocity were obtained.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.11
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• pp.517-527
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• 1997

Magnetic Resonance Spectroscopic Imaging is a methodology combining the imaging and spectroscopy. It can provide the spectrum of each areas of image so that one can easily compare the spectrum of one position to another position of the image. In this study, we developed pulse sequence or the spectroscopic imaging method, RF wave forms or the saturation of water signal, computer simulations to validate our method, and confirmed the methodology with phantom experiment. Then we applied the spectroscopic method to human subject and identified a few important metabolites in in vivo. To develope a water saturating RF waveform, we used Shinnar-Le-Roux algorithm and obtained maximum phase RF waveform. With this RF pulse, it could suppress the water signal to 1:1000. The magnet is shimmed to under 1.0ppm with auto-shimming technique. The saturation bandwidth is 80Hz(2ppm). The water and fat seperation is 3.3ppm(about 140Hz at 1 Tesla magnet), the bandwidth is enough to resolve the difference. But we are more concerned about the narrow window in between the two peaks, in which the small quantity of metabolites reside. We performed the computer simulation and phantom experiments in 8*8 matrix form and showed good agreement in the image and spectrum. Finally we applied spectroscopic imaging to the brain of human subject. Only the lipid signal was shown in the periphery region which agrees with the at distribution in human head surface area. The spectrum inside the brain shows the important metabolites such as NAA, Cr/PCr, Choline. We here have shown the spectroscopic imaging which is normally done above 1.5 Tesla machine can be performed in the 1 Tesla Magnetic Resonance Imaging Unit.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.44 no.1
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• pp.98-105
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• 2007

In this paper, we propose a timing detector using suboptimal maximum likelihood method. The proposed method has an simple reference signal generator. Additionally, timing detector's gain of the proposed method is the same to Early-Late gate and ML method. We reveal that tracking range of time tracker is narrow because of using data-decision, that is, tracking range is ${\pm}0.06ns$ for the 4-order Gaussian monocycle with 0.7ns pulse width. Therefore we can find that searcher must have very accurate acquisition procedure. When estimating a performance of time tracker, we consider a jitter in transmitter and receiver's pulse generation process as well as background noise. By using computer simulation, we propose mean/variance of timing detector and tracking process. Also we consider a mobility in tracking process, i.e., timing error modeled ramp function. In order to propose a performance of time tracker, we consider only one correlation demodulator.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.11 no.6
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• pp.64-73
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• 1997

RPWM(Random Pulse Width Modulation) techniques have been attracting an interest as an excellent reduction method of acoustic noise on the inverter drive system. Using randomly changed switching fre-quency of the inverter, the power spectrum of the electromagnetic acoustic noise can be spread out into the wide-band area. The wide band noise is much more comfortable and less annoying than the narrow-band one. This paper describes an implementationof the triangular carrier frequency modultde RPWM inverter drive system The poweer soedtrum of the noise emittde from the induction motro was measured in the anechoic chamber. The analysis of the sources for the acoustic noise and the effects of the noise reduction are confirmed by the ceasured dpectra of the noise. Real-time RPWM along with the speed control was achieved by high speed DSP(Digital Signal Processor ) TmS320C31, By changing the center frequency and the bandwidth of the carrier, theis real-time RPWM scheme can be used as an efficient switching frequency band acoustic noise reduction method for the inverter system with variant load conditions.

• Science of Emotion and Sensibility
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• v.5 no.2
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• pp.29-34
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• 2002

Our previous studies investigated that narrow field of view (FOV : 50˚) and slow navigation speed decreased the frequency of occurrence and severity of cybersickness during immersion in the virtual reality (VR). It would cause a significant reduction of cybersickness if it were provided cybersickness alleviating virtual environment (CAVE) using biofeedback method whenever subject underwent physiological agitation. For verifying the hypothesis, we constructed a real-time cybersickness detection and feedback system with artificial neural network whose inputs are electrophysiological parameters of blood pulse volume, skin conductance, eye blink, skin temperature, heart period, and EEG. The system temporary provided narrow FOV and decreased speed of navigation as feedback outputs whenever physiological measures signal the occurrence of cybersickness. We examined the frequency and severity of cybersickness from simulator sickness questionnaires and self-report in 36 subjects. All subjects experienced VR two times in CAVE and non-CAVE condition at one-month intervals. The frequency and severity of cybersickness were significantly reduced in CAVE than non-CAVE condition. Virtual environment of narrow FOV and slow navigation provided by electrophysiological features based artificial neural network caused a significant reduction of cybersickness symptoms. These results showed that efficiency of a cybersickness detection system we developed was relatively high and subjects expressed more comfortable in the virtual navigation environment.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.61-68
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• 2008

In this paper, we propose a RF front-end developments for vehicle UWB radar systems. UWB systems have a very narrow pulse width that is below 1ns. Therefore, UWB is designed to have broadband quality of low power several GHz and must coexist with the radio communication system. UWB's advantages include high channel capacity and data rate, because precise resolution for multi-path can easily position estimate and Rake receiver. Also, UWB has low interference because it displays broadband quality of low power. Positioning is made possible by short range accuracy, which can reduce the expense of system design. An RF front-end module is designed using the DCR(Direct ConveRsion) method and is composed in RF for vehicles at a low-cost.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.160-168
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• 2001

The RPWM (Random· Pulse Width Modulation) is a switching technique to spread the voltage and current harmonics over a wide frequency area. By using randomly changing switching frequency of the inverter, the power spectrum of the electromagnetic acoustic noise can be spread to the wide-band area. The wide­band noise is much more comfortable and less annoying than the narrow-band one. So, the RPWM has been attracting interest as an excellent method for the reduction of acoustic noise on the inverter drive system. In this paper a new RPPWM (Random Position Space Vector PWM) is proposed and implemented. Each of three phase pulses is located randomly in each switching interval. Along with the randomization of PWM pulses, the space vector modulation is also executed in the C167 micro-controller. The experimental results show that the voltage and current harmonics are spread to a wide band area and that the audible switching noise is reduced by the proposed RPPWM method.