• Journal of IKEEE
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• v.22 no.4
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• pp.1006-1011
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• 2018

This paper proposes a three level buck converter utilizing multi-bit flying capacitor voltage control. The conventional three-level buck converter can not control the flying capacitor voltage, so that the operation is unstable or the circuit for controlling the flying capacitor voltage can not be applied to the PWM mode. Also when the load current is increased, an error occurs in the inductor voltage. The proposed structure can control the flying capacitor voltage in PWM mode by using differential difference amplifier and common mode feedback circuit. In addition, this paper proposes a 3bit flying capacitor voltage control circuit to optimize the operation of the three level buck converter depending on the load current, and a triangular wave generation circuit using the schmitt trigger circuit. The proposed 3-level buck converter is designed in $0.18{\mu}m$ CMOS process and has an input voltage range of 2.7V~3.6V and an output voltage range of 0.7V~2.4V. The operating frequency is 2MHz, the load current range is 30mA to 500mA, and the output voltage ripple is measured up to 32.5mV. The measurement results show a maximum power conversion efficiency of 85% at a load current of 130 mA.

• Korean Journal of Optics and Photonics
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• v.30 no.4
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• pp.154-158
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• 2019

We have used a mid-IR (mid-infrared) continuous-wave (cw) optical parametric oscillator (OPO), developed previously and described in Ref. 12, to build a performance-evaluation setup for a mid-IR spectrometer. The used CW OPO had a wavelength tuning range of $ 2.5-3.6{\mu}m$ using a pump laser with a wavelength of 1064 nm and a fan-out MgO-doped periodically poled lithium niobate (MgO:PPLN) nonlinear crystal in a concentric cavity design. The OPO was combined with a near-IR integrating sphere and a Fourier-transform IR optical spectrum analyzer to build a performance-evaluation setup for mid-IR spectrometers. We applied this performance-evaluation setup to evaluating a mid-IR spectrometer developed domestically, and demonstrated the capability of evaluating the performance, such as spectral resolution, signal-to-noise ratio, spectral stray light, and so on, based on this setup.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1552-1554
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• 2004

The modeled resonant frequency and electrical properties of Pb(Zr, Ti)$O_3$ (PZT) film with various thicknesses have been investigated in film bulk acoustic wave resonators (FBARs). PZT films and Pt electrodes were fabricated by rf-magnetron sputtering. Fabrication process of electrodes and PZT were patterned by simple lift-off process and then back side of silicon was etched by 45wt% KOH. The crystal structure of PZT films with 0.5, 1 and 2 ${\mu}m$ thickness was investigated by x-ray deflection (XRD) and scanning electron microscopy (SEM). The dielectric constant and performance characteristics of PZT FBAR strongly depended on the film thickness. The resonant frequency of PZT films decreased with increasing film thickness. These sputtered PZT FBAR with simple lift-off process enable us to fabricate high Q values with resonant frequencies. (0.71 - 1.48 GHz).

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.337-341
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• 2004

Engineering ceramics have superior heat resistance, corrosion resistance, and wear resistance. Consequently, these art significant candidates for hot-section structural components of heat engine and the inner containment of nuclear fusion reactor. Besides, some of them have the ability to heal cracks and great benefit can be anticipated with great benefit the structural engineering field. Especially, law fracture toughness of ceramics supplement with self-healing ability. In the present study, we have been noticed some practically important points for the healing behavior of silicon nitride, alumina, mullite with SiC particle and whisker. The presence of silicon carbide (SiC) in ceramic compound is very important for crack-healing behavior. However, self-healing of SiC has not been investigated well in detail yet. In this study, commercial SiC was selected as sample, which can be anticipated in the excellent crack healing ability. The specimens were produced three-point bending specimen with a critical semi-circular crack of which size that is about $50-700{\mu}m$. Three-point bending test and static fatigue test were performed cracked and healed SiC specimens. A monotonic bending load was applied to cracked specimens by three-point loading at different temperature. The purpose of this paper is to report Strength Properties and Elastic Waves Characteristics of Silicon Carbide with Crack Healing Ability.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.9
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• pp.831-837
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• 2015

Many persons and electronic devices are exposed to electromagnetic (EM) waves generated from magnetic resonance imaging (MRI) equipment, EM pulses (EMPs), and many other kinds of EM wave devices. Finger strips are used to provide shielding from these EM waves. Because of the high thermal conductivity of finger strips, they are used in the design of specialized doors that are installed in shielded rooms. In this study, we perform an accelerated life test using the load acceleration stress, which affects the main failure mode of finger strips. We predict the life of the finger strip under normal usage conditions based on the results of the accelerated life test. We compare the results with those predicted from the life test under normal usage conditions to evaluate the validity of accelerated life testing.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.9
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• pp.25-30
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• 2004

In this Paper, the 0.1 w InGaAs/InAlAs/GaAs Metamorphic HEMT, which is applicable to MIMIC, and a 100 GHz MIMIC amplifier were designed and fabricated. The DC characteristics of MHEMT are 640 mA/mm of drain current density, 653 mS/mm of maximum transconductance. The current gain cut-off frequency(fT) is 173 GHz and the maximum oscillation frequency(fmax) is 271 GHz. A 100 GHz amplifier was designed using 0.1${\mu}{\textrm}{m}$ MHEMT and CPW technology. The measured results from the 100 GHz MIMIC amplifiers show good S21 gain of 10.1 dB and 12.74 dB at 100 GHz and 97.8 GHz, respectively.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.8
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• pp.1248-1256
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• 2008

In this paper, basic characteristics of transmission line employing PPGM (periodically perforated ground metal) were investigated using theoretical and experimental analysis.According to the results, unlike the conventional PBG (photonic band gap) structures, the characteristic impedance of the transmission line employing PPGM structure showed a real value, which exhibited a very small dependency on frequency. The transmission line employing PPGM structure showed a loss (per quarter wave length) higher by $0.1{\sim}0.2\;dB$ than the conventional microstrip line. According to the investigation of the dependency of RF characteristic on ground condition, the RF characteristic of the transmission line employing PPGM structure was hardly affected by the ground condition in the frequency lower than Ku band, but fairly affected in the frequency higher than Ku band, which indicated that coplanar waveguide employing PPGM structure was optimal for RF characteristic and reduction of size. Considering above results, impedance transformer was developed using coplanar waveguide with PPGM structure for the first time, and good RF characteristics were observed from the impedance transformer. In case that {\lambda}/4$ impedance transformer with a center frequency of 9 GHz was fabricated for a impedance transformation from 20 to10 {\Omega}$, the line width and length were 20 and $500\;{\mu}m$, respectively, and its size was only 0.64 % of the impedance transformer fabricated with conventional microstrip lines. Above results indicate that the transmission line employing PPGM is a promising candidate for a development of matching and passive elements on MMIC.

• Korean journal of applied entomology
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• v.16 no.4 s.33
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• pp.235-239
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• 1977

The experiments were contucted to investigate the variability of pathogenesity, growth amount and UV-sensitibity on the streptomycin resistant isolate of the rice bacterial leaf blight pathogen, Xanthomonas oryzae, which selected by the stepwise transfer in 100, 3,000 and 10,000 ug/ml Argepto contained media. And the results obtained were as follows. (1) The SM-resistant isolates were tested the pathogenesity on the differential variety of rice, wase-Aikoku-3, Rant Emas-2, Hwang ok, and Kimmase. And the SM resistant isolate, obtained from 75-6 isolate, showed the reaction of moderately resistant to the differential variety of Hwang ok instead of susceptible reaction with its parental isolate. (2) The growth amount of the SM-resistant isolate was slightly higher than that of parental isolate, on the normal media. And the growth was inhibited on the 100ug/ml Agrepto contained media until 60 hours after transfer, however, its growth exceeded than parental isolate in the normal media, after 70 hours of transfer. (3) It is considered that the resistance factor might be stable character, since the sensitivity to UV irradiation (with 254 mr wave length) of the resistant isolate was the same as that of its parental isolate.

• Journal of Veterinary Clinics
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• v.8 no.1
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• pp.31-45
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• 1991

Present experiment was performed in order to establish the optimal reaction conditions for determination of urinary AAP and GRS activities and to investigate the applicability of urinary AAP and GRS in nephrotoxicity test in rat. The results were as follows ; 1. The optimal pH of phosphate buffer for determination of urinary AAP activity was 7.8. 2. The Michaelis constant of urinary AAP ranged from 0.8 to 1.0mmol/$\ell$ 3. The optimal wave length for determination of urinary GRS activity was 405nm. 4. The optimal pH of acetate buffer for determination of urinary GRS activity was 5.6. 5. The Michaelis constant of urinary GRS ranged from 0.65~0.79mmo1/$\ell$. 6. The AAP activities in gel-filtered samples were significantly higher than those in crude samples. Mean values of AAP activities in gel-filtered samples and crude samples were 29$\pm$20 and 20$\pm$13U/$\ell$, respectively. 7. There was not significant difference between gel-filtered samples and crude samples in urinary GRS activities. Mean values of GRS activities in gel-filtered samples and crude samples were 57$\pm$40 and 56$\pm$39U/$\ell$, respectively. 8. Limits of linearity of urinary AAP and GRS activities were 2.0 and 3.6U/$\ell$, respectively. 9. Within-run imprecisions of the assays, were acceptable, as the coefficients of the AAP activities ranged from 5.5 to 6.3% and those of GRS activities ranged from 1.4 to 6.2%, respectively. 10. Urinary AAP excretion was 675$\pm$227mu/24hrs.kg before administration of potassium dichromate, and increased significantly to 4246$\pm$2567mU/24hrs.kg within 24 hours after administration of potassium dichromate. 11. Urinary GRS excretion did not increase significantly after administration of potassim dichromate. 12. From these findings it is concluded that urinary AAP excretion is early and sensitive Indicator to detect kidney damage in nephrotoxicity experiment.

• Journal of the Korean Geotechnical Society
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• v.21 no.1
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• pp.29-41
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• 2005

The small harbors and fishing ports in Korea have less economic efficiency if the previous construction method of breakwater would be utilized due to bad ground conditions in spite of low design waves. Therefore, it is necessary to develop a new type breakwater economically applicable to the cases with low design wave. In this study, a soldier pile type breakwater, which is found to be economic and can be easily constructed on the ground without any need of treatment of the ground, was newly introduced. The effects of embedded depth, reinforcement methods as well as pile types including saw type and flat type on the lateral behavior of the proposed breakwaters installed in loose sandy soils were investigated from model test. The test results revealed that the lateral resistance increases by increasing the embedded depth and by adopting the reinforcement techniques such as raker and anchor. Furthermore, it was also verified that the saw type breakwater shows better geotechnical performance than the flat type breakwater.