• Korean Journal of Optics and Photonics
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• v.13 no.4
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• pp.347-355
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• 2002

We have constructed a high efficiency and broad tunable cw Ti:sapphire laser with a four-mirror symmetric Z-type laser cavity to increase the laser usability. From theoretical analyses and experimental data for a symmetric Z-type laser cavity containing a Kerr medium, the cavity mode size and the Kerr-lens mode-locking (KLM) strength for KLM lasers can be confirmed as function of the position in the cavity, the intracavity laser power, and the stability parameter. As a result, the slope efficiency and the maximum average output power of cw Ti:sapphire laser at 5 W pumping power of Ar-ion laser were 31.3% and 1420 ㎽ respectively. The tunablility was ranged from 730 ㎚ to 908 ㎚ with average output power above 700 ㎽. We obtained the KLM operation easily by self-aperturing effect in the Kerr medium and the slope efficiency and the maximum average output power of KLM Ti:sapphire laser was 16% and 550 ㎽ respectively. The spectral bandwidth was 33 ㎚ at the center wavelength of 807 ㎚ and the pulse width was 27 fs with a repetition rate of 82 ㎒.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.6
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• pp.573-582
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• 2010

In this paper, X-band transceiver for high resolution wideband SAR systems is designed and fabricated. Also as a technique for enhancing the performance, error compensation algorithm is presented. The transceiver for SAR system is composed of transmitter, receiver, switch matrix and frequency generator. The receiver especially has 2 channel mono-pulse structure for ground moving target indication. The transceiver is able to provide the deramping signal for high resolution mode and select the receive bandwidth for receiving according to the operation mode. The transceiver had over 300 MHz bandwidth in X-band and 13.3 dBm output power which is appropriate to drive the T/R module. The receiver gain and noise figure was 39 dB and 3.96 dB respectively. The receive dynamic range was 30 dB and amplitude imbalance and phase imbalance of I/Q channel was ${\pm}$0.38 dBm and ${\pm}$3.47 degree respectively. The transceiver meets the required electrical performances through the individual tests. This paper shows the pulse error term depending on SAR performance was analyzed and range IRF was enhanced by applying the compensation technique.

• The Journal of the Acoustical Society of Korea
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• v.33 no.2
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• pp.102-110
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• 2014

The effect of a bonding layer on the performance of a quarter-wave (${\lambda}/4$) mode PVDF ultrasound transducer having not only a piezoelectric layer but also a non-piezoelectric layer between two electrodes was analyzed. The equivalent circuit of a transmission line model by Kikuchi et al.[Sound of IEICE, 55-A, 331-338 (1981)] was introduced for the analysis. The validity of the model was confirmed by comparison with a KLM model for three postulated adhesion cases of a $80{\mu}m$ thick piezoelectric PVDF film to a copper (Cu) backer. The pulse-echo responses of five PVDF transducers, each fabricated with a different thickness ($5{\mu}m{\sim}20{\mu}m$) of the bonding layer, were measured and the results were compared with those by simulation. The two results were in good agreement with each other and it was noted that the effect of the bonding layer on the performance of the transducer could be analyzed by the Kikuchi model. In detail, the $20{\mu}m$ bonding layer decreased the center frequency and the bandwidth by about 19.7 % and 25.0 %, respectively, and increased the insertion loss by 57.2 %.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.10
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• pp.892-899
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• 2016

In this paper, an X-band 50 W internally matched power amplifier is designed and fabricated using an $80{\times}150{\mu}m$ GaN HEMT that is developed by the $0.25{\mu}m$ GaN HEMT process of ETRI. The optimum source and load impedances are experimentally extracted from the loadpull measurement using impedance-transform-prematching circuits, and the transistor performance is predicted. The power performance of the internally matched power amplifier, whose matching circuits are fabricated on a substrate with ${\varepsilon}_r$ of 10.2, is measured under the pulsed mode of $100{\mu}s$ pulse period and 10 % duty cycle, and the best output power of 47.46 dBm(55.5 W) and the power-added efficiency of 46.6 % are obtained at 9.2 GHz. The output power of 47~47.46 dBm(50~55.7 W) is measured in 9.0~9.5 GHz, and the power-added efficiency is measured to be greater than 43 % in 9.0~9.3 GHz and above 36 % in 9.4~9.5 GHz.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.7
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• pp.1235-1242
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• 2008

In this paper, x-ray image sensor of photon counting type having a $32{\times}32$ pixel array is designed with $0.18{\mu}m$ triple-well CMOS process. Each pixel of the designed image sensor has an area of loot $100{\times}100\;{\mu}m2$ and is composed of about 400 transistors. It has an open pad of an area of $50{\times}50{\mu}m2$ of CSA(charge Sensitive Amplifier) with x-ray detector through a bump bonding. To reduce layout size, self-biased folded cascode CMOS OP amp is used instead of folded cascode OP amp with voltage bias circuit at each single-pixel CSA, and 15-bit LFSR(Linear Feedback Shift Register) counter clock generator is proposed to remove short pulse which occurs from the clock before and after it enters the counting mode. And it is designed that sensor data can be read out of the sensor column by column using a column address decoder to reduce the maximum current of the CMOS x-ray image sensor in the readout mode.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.1
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• pp.15-21
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• 2004

It is possible to detect flaws in pipelines without interruption using all EMAT transducer because it is a non-contact transducer which can transmit ultrasonic waves into specimens without couplant. And it ran easily generate guided waves desired in each specific problem by altering the design of coil and magnet. In the present work, EMAT systems have been fabricated to generate surface waves, and selectively the plate wave of $A_1\;or\;S_1$ mode. The surface wave of 1.5MHz showed a good signal-to-noise ratio without distortion in its propagation along a pipeline, while the $S_1$ mode of 800kHz and the $A_1$ mode of 940kHz were distorted according to their dispersive properties. The wider the excitation pulse becomes, the better the mode selectivity of the plate waves becomes. A pipe of 256mm inner diameter and 5.5m thickness with 5 flaws was used for comparing the flaw detectability among the modes under consideration.

• Journal of Advanced Navigation Technology
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• v.10 no.2
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• pp.173-180
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• 2006

An airborne radar is an essential aviation electronic system of the aircraft to perform various missions in all weather environments. This paper presents the design, development, and test results of the multi-mode pulsed Doppler radar system test model for helicopter-borne flight test. This radar system consists of 4 LRU units, which include ANTU(Antenna Unit), TRU(Tx Rx Unit), RSDU(Radar Signal & Data Processing Unit) and DISU(Display Unit). The developed technologies include the TACCAR processor, planar array antenna, TWTA transmitter, coherent I/Q detector, digital pulse compression, DSP based Doppler FFT filtering, adaptive CFAR, IMU, and tracking capability. The design performance of the developed radar system is verified through various helicopter-borne field tests including MTD (Moving Target Detector) capability for the Doppler compensation due to the moving platform motion.

• The Korean Journal of Physiology and Pharmacology
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• v.8 no.2
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• pp.101-110
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• 2004

Voltage-sensitive release mechanism was pharmacologically dissected from the $Ca^{2+}-induced\;Ca^{2+}\;release$ in the SR $Ca^{2+}$ release in the rat ventricular myocytes patch-clamped in a whole-cell mode. SR $Ca^{2+}$ release process was monitored by using forward-mode $Na^+-Ca^{2+}$ exchange after restriction of the interactions between $Ca^{2+}$ from SR and $Na^+-Ca^{2+}$ exchange within micro-domains with heavy cytosolic $Ca^{2+}$ buffering with 10 mM BAPTA. During stimulation every 10 s with a pulse roughly mimicking action potential, the initial outward current gradually turned into a huge inward current of $-12.9{\pm}0.5\;pA/pF$. From the inward current, two different inward $I_{NCX}s$ were identified. One was $10\;{\mu}M$ ryanodine-sensitive, constituting $14.2{\pm}2.3%$. It was completely blocked by $CdCl_2$ (0.1 mM and 0.5 mM) and by $Na^+-depletion$. The other was identified by 5 mM $NiCl_2$ after suppression of $I_{CaL}$ and ryanodine receptor, constituting $14.8{\pm}1.6%$. This latter was blocked by either 10 mM caffeine-induced SR $Ca^{2+}-depletion$ or 1 mM tetracaine. IV-relationships illustrated that the latter was activated until the peak in $30{\sim}35\;mV$ lower voltages than the former. Overall, it was concluded that the SR $Ca^{2+}$ release process in the rat ventricular myocytes is mediated by the voltage-sensitive release mechanism in addition to the $Ca^{2+}-induced-Ca^{2+}\;release$.

• Journal of Advanced Navigation Technology
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• v.20 no.5
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• pp.462-467
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• 2016

Dispersion management (DM) combining with mid-spans spectral inversion (MSSI) is one of the various techniques compensating for the distorted optical signals. For the flexible implementation of this configured link, the compensation characteristics in the optical link with artificial distribution of the gradually ascending and descending of single mode fiber (SMF)'s lengths and residual dispersion per span (RDPS) as the number of fiber spans are assessed as a function of the control positions of net residual dispersion (NRD). It is confirmed that the best compensation is obtained by distributing gradually ascending or descending of SMF's lengths and RDPS capable to place NRD control position at fiber span, in which optical pulse width is most narrow.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.4
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• pp.346-352
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• 2002

A novel Zero Current Switching(ZCS) Pulse Width Modulation(PWM) boost converter with dual mode for reducing two rectifiers reverse recovery related losses is proposed. The switches of the proposed converter are operating to work alternatively turn-on and turn-off with soft switching condition In the every cycle and the proposed converter reduces the reverse recovery current, which is related switching losses and EMI problems, of the free-wheeling diode$(D_1, D_2)$ by adding the resonant inductor Lr, in series with the switch $S_1$. The switching components$(S_1, S_2, D, D_1)$ in the proposed boost converter are subjected to minimum voltage and current stresses same as those in their PWM counterparts because there are no additional active switches and resonant elements compared with the conventional ZVT PWM $converters^{[2]}$. The operation of the proposed converter, in this paper, is analyzed and to verify the feasibility of the characteristics is built and tested.