• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.992-997
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• 2010

The Propulsion Control Module(PCM) of Hall-thruster Propulsion System(HPS) for Science and Technology Satellite-3 (STSAT-3) has the flow control accuracy of less than ${\pm}$3% and the pressure control accuracy of less than ${\pm}$5%. The pressure controller adjusts pressure around the set point by using a Proportional Flow Control Valve (PFCV) and a high pressure transducer, while the flow controller regulates the flow rate using PFCV and the anode current telemetry of the Hall Thruster. The controllers are chosen as the Proportional and Integral(PI) type, and the PI gains are tuned based on the Matlab simulations. The result of the PCM test had the flow control accuracy of less than ${\pm}$1.87% and the pressure control accuracy of less than ${\pm}$5%. This paper describes the design, realization, and performance test results of the PCM.

• Journal of Energy Engineering
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• v.15 no.1 s.45
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• pp.35-44
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• 2006

This study experimentally investigates effect of boiling heat transfer when ultrasonic vibration was applied. Under the wall temperature condition, temperature distribution in a cavity was measured during the boiling process and heat transfer coefficient of convection, sub-tooled boiling and saturated boiling states were measured with and without ultrasonic vibration, respectively. Also, the profiles of the pressure distribution in acoustic field measured by a hydrophone were compared with the augmentation ratios of heat transfer calculated by local heat transfer coefficient. Result of this study, heat transfer coefficient and augmentation ratio of heat transfer is higher with ultrasonic waves than without one. Especially, augmentation ratio of heat transfer is more increased the convection state than sub-cooled boiling and saturated boiling states. Acoustic pressure is relatively higher near ultrasonic transducer than other points where is no installed it and affects the augmentation ratio of heat transfer.

• The Journal of Korean Physical Therapy
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• v.26 no.5
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• pp.324-330
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• 2014

Purpose: The aim of the current study was to compare the muscle architecture of lower extremity using rehabilitative ultrasound imaging (RUSI) in young adults in Seoul and Hanoi. Methods: The study design was a comparative study of muscle cross-sectional area of lower extremity. Sixty healthy young subjects (Seoul group: 30, Hanoi group: 30) participated in this study. Real-time B-mode RUSI with a 7.5MHz linear transducer was used for measurement of cross-sectional area, pennation angle, and muscle thickness of the rectus femoris, tibialis anterior, and medial gastrocnemius muscles. Independent t-test was used for statistical analysis. Results: Significant difference in cross sectional area of rectus femoris was observed between Korean young adults and Hanoi young adults (p<0.01). Muscle thickness and pennation angle of tibialis anterior in Korean young adults were greater than in Hanoi young adults (p<0.01). In addition, the muscle thickness and pennation angle of the medial part of gastrocnemius muscle were greater in Korean young adults than in Hanoi young adults (p<0.01). In addition, in the results for gender, men had larger muscle architectures than women in both groups (p<0.01). Conclusion: This study, using RUSI, showed significant difference in muscle architectures of lower extremity in a diverse group of young adults RUSI.

• Journal of Biomedical Engineering Research
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• v.35 no.6
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• pp.177-184
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• 2014

Continuous monitoring of heart rates and respiratory rates for newborns or infants is very important since the abnormal breathing and heart problems can threaten the life of newborns or infants. A noncontact baby monitoring system based on a Doppler radar and an air mattress was designed. The Doppler radar was used to acquire respiratory signals and the air mattress was employed to obtain heart rates. The performance of the designed system was evaluated using a commercialized infant simulator ($Simbaby^{TM}$) and a respiration belt transducer was used to measure respiration rates as a reference. Results for respiratory rates revealed that the correlation coefficients between I-and Q-channel and the respiration belt were 0.84 and 0.91 and the mean ${\pm}$ standard deviations of errors between them were $1.66{\pm}1.92$ (bpm) and $0.88{\pm}1.65$ (bpm). Heart rates showed that the correlation coefficient between air mattress and set value of the simulator was 0.73 and the mean ${\pm}$ standard deviation of errors between them was $1.09{\pm}3.45$ (bpm). These results indicate that the designed system holds the potential as an effective monitoring tool for continuous monitoring heart rates and respiratory rates of newborns or infants.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.2
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• pp.92-98
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• 2015

The physical effect induced by acoustic cavitation was investigated to accumulate basic data for the design of ultrasonic soil washing processes using aluminum foil erosion tests. A square aluminum foil was placed on the glass beads in the pyrex vessel submerged in the sonoreactor equipped with a 36 kHz ultrasound transducer module at the bottom. Cavitational erosion of foils was quantitatively analyzed for various glass bead diameter conditions (1, 2, and 4 mm), glass bead height conditions (5, 10, 15, and 20 mm), and water height conditions (5, 10, 15, and 20 mm). It was found that aluminum foil erosion significantly increased as the glass bead diameter increased and water height over the glass bead increased due to less attenuation of ultrasound and the optimization of sound field for cavitation. Moreover mechanical mixing was suggested to move constantly particles to the bottom area where the acoustic cavitation occurs most violently. It was because aluminium foil erosion by ultrasound transmitted through glass beads was relatively too weak.

• Journal of Biomedical Engineering Research
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• v.20 no.4
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• pp.495-502
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• 1999

We propose efficient speech signal processing algorithms and a system for cochlear implant in this paper. The outer and the middle car which perform amplifying, lowpass filtering and AGC, are modeled by an analog system, and the inner ear acting as a time-delayed multi filter and the transducer is implemented by the DSP circuit which enables real-time processing. Especially, the basilar membrane characteristic of the inner ear is modeled by a nonlinear filter bank, and then tonotopy and periodicity of the auditory system is satisfied by using a pitch-synchronous multi-spectra(PSMS) method. Moreover, most of the speech processing is performed by S/W so the system can be easily modified. And as our program is written in C-language, it can be easily transplanted to the system using other processors.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.42 no.1
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• pp.90-97
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• 2014

In this paper, we have designed the antenna for Korea SAT-5 Satellite Communication which can use Ka band in the earth station. The antenna structure consist of the the dual-offset gregorian reflector that has high gain and efficiency, the corrugated horn that has symmetric radiation patterns and low side lobe levels, the iris polarizer that make circular polarization and the OrthoMode Transducer that separate transmitting and receiving signals. The designed antenna gain is more than 45.7dBi in Tx-band which use LHCP and 42.0dBi in Rx-band which use RHCP. The co-polarized and cross-polarized radiation pattern comply with ITU-R S.580-6 and S.731-1 that are recommended by International Telecommunication Union in the geostationary satellite. The Axial ratio is less than 1.0dB in Tx-band and 1.5dB in Rx-band that meet MIL-STD-188-164A.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.4
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• pp.393-400
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• 2014

In this paper, we have designed the transmitter for earth station terminal operating with military geostationary satellite on Ka-band that is complied with MIL-STD-188-164A. The designed antenna of this terminal is dual-offset gregorian reflector which is consist of corrugated horn and iris polarizer, othermode transducer. This antenna meets radiation pattern and transmit EIRP spectral density requirements in this standard. The designed RF systems of this terminal are consist of Block Up Converter(BUC) converting frequency band from IF to Ka band and SSPA having low-power consumption and compact light-weight using the pHEMT MMIC compound devices. This RF systems applied with VSWR, spurious/harmonic suppression, output flatness and phase noise requirement in this standard.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.859-864
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• 2011

An operation temperature of $Pb(Zr,Ti)O_3$ based piezoelectric ultrasonic flowmeter was generally restricted to below 200$^{\circ}C$ due to a low depoling temperature of its ceramic material. Thus, a new designed piezoelectric ultrasonic flowmeter was fabricated in order to protect from the extremely hot fluid. Its structure is optimized by a finite element method to effectively stop heat flowing along a waveguide. Various materials such as Cu, Al, SUS were examined as a multi-plate radiation shield to enhance the performance of piezoelectric ultrasonic flowmeter. The SUS was evaluated as the most effective material to enhance the performance of piezoelectric ultrasonic flowmeter. As the number of plates of the radiation shield increased, the temperature at piezoelectric transducer away from the hot fluid was constantly decreased with a ratio of 3.12$^{\circ}C$ per the plate number.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.48 no.6
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• pp.97-108
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• 2011

Systems for underwater environment monitoring and natural resources can be considered as a part of digital convergence where real-time data transmission is possible with the help of underwater wireless sensor network (UWSN). One of key technologies required for the deployment of the systems is underwater acoustic micro modem. In this work, we design and implement an acoustic modem equipped with a commercial omnidirectional transducer. We also make experiments at the northern Han river for the verification of the developed modem. According to the experiments, the modem supports the working distance of 250 m and the data rate of 200 bps with a negligible bit error rate. It is expected that the acoustic modem can be used for various applications based on UWSN in a near future.