• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.304-309
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• 2004

As it is difficult to construct a micro-fluidic system composed of micro-mixers, micro-channels and/or micro-chambers in a single process, an assembly process is typically used. The assembling and bonding of micro-parts, however, introduces other problems. In this work, a virtual assembly process was developed that can be used to design various micro-fluidic systems before actual fabrication commences. In the process, the information required for the micro-stereolithography process is generated automatically. Consequently, complex micro-fluidic systems can be fabricated in a single process, thereby avoiding the need for additional assembly or bonding processes. Using the developed process, several examples were fabricated.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1249-1253
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• 2007

Experimental studies on the fabrication of sub-30 nm nanofibers using weakly two-photon induced photopolymerized region have been carried out. For the generation of nanofibers inside or outside microstructures, an over-polymerizing method involving a long exposure technique (LET) was proposed. Such nanofibers can find meaningful applications as bio-filters, mixers, and many other uses in diverse research field. A multitude of nanofibers with a notably high resolution (about 22 nm) in two-photon polymerization was achieved using the LET. Furthermore, it was demonstrated that the LET can be employed for the direct fabrication of various embossing patterns by controlling the exposure duration and the interval between voxels. Thin interconnecting networks are formed regularly in the boundary of the over-polymerized region, which allows for the creation of various pattern shapes. Overall of this work, some patterns including nanofibers are fabricated by the LET.

• Journal of the Korean Applied Science and Technology
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• v.19 no.4
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• pp.327-334
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• 2002

Transesterfication of vegetable oils and methanol with alkaline catalyst was carried out to produce biodiesel fuel by continuous process. The process consists of two static mixers, one tubular reactor and two coolers and gave $96{\sim}99$% of methyl ester yield from soybean oil and rapeseed oil. Experimental variables were the molar ratios of methanol to vegetable oil, alkaline catalyst contents, flow rates, mixer element number. The optimum ranges of operating variables were as follows; reaction temperature of $70^{\circ}C$, l:6 of molar ratio of methanol to oil, O.4%(w/w) sodium hydroxide based on oil, static mixer elements number of 24 and 4 min. residence time.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.3
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• pp.20-26
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• 2010

In ultrashort-pulse reflectometry (USPR), a chirped waveform transformed from the USPR source impulse signal via waveguide makes it possible to employ millimeter-wave mixers for the frequency up-conversion process. Consequently, the frequency bandwidth of the USPR system is sufficiently wide to cover a large portion of the electron density profile of the plasma. Some physical aspects of the chirped waveform, such as maximum amplitude and length, are critical factors to determine the performance of the system. In this paper, the propagation of the USPR impulse signal through a rectangular waveguide is numerically studied to derive the chirped waveform using the impulse response of the waveguide. The results of numerical computation show that the chirped waveform significantly depends on the waveguide cutoff frequency as well as the waveguide length.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.30A no.10
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• pp.12-19
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• 1993

Because of their high sensitivity and moderate bandwidth, superconducting receivers with SIS (Superconductor Insulator Superconductor) tunnel junction mixer are now widely used for millimeter wave radio astronomy. In this paper we have introduced how to determine the parameters of SIS tunnel junction which have to be optimized to achieve a good mixer performance. From these results of optimized junction parameters determined by this methods, SIS junctions which consist of a series array of four Nb/Al-AlOx/Nb junctions with each area 3.4${\mu}m^{2}$ have been fabricated by SNEP (Selective Niobium Etching Process) and RIE (Reactive Ion Eching). Also we have tested their DC current-voltage characteristics. These SIS junctions will be used as a mixer for 100GHz band cosmic waves receiver.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.59.2-59.2
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• 2016

As an enhancement to increase mapping speed of the current ALMA TP array, development of a focal plane array system working at ultra wide frequency range of 275-500 GHz with GPU-based software spectrometers has been carried out since 2015. Major progresses on such component development as wideband DSB mixers, a profiled corrugated horn, receiver optics, LO system and GPU-based spectrometer are reviewed with brief introduction to implication of ALMA 2030 for technical implementation.

• Proceedings of the IEEK Conference
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• 2008.06a
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• pp.421-422
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• 2008

In this paper, CMOS RF front-end circuits for an L1/L5 dual-band global positioning system (GPS)/Galileo receiver are designed in $0.13\;{\mu}m$ CMOS technology. The RF front-end circuits are composed of an RF single-to-differential low noise amplifier, an RF polyphase filter, two down-conversion mixers, two transimpedance amplifiers, a IF polyphase filter, four de-coupling capacitors. The CMOS RF front-end circuits provide gains of 43 dB and 44 dB, noise figures of 4 dB and 3 dB and consume 3.6 mW and 4.8 mW from 1.2 V supply voltage for L1 and L5, respectively.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.4
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• pp.1-8
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• 1998

An MMIC single-balanced upconverting mixer for PCS application has been successfully developed using an MMIC process employed by 1 .mu. ion implanted GaAs MESFET and passive lumped elements consisting of spiral inductor, Si3N4 MIM capacitors and NiCr resistors. The configuration of the mixer presented in this paper is two balanced cascode FET mixers with common-source self-bias circuits for single power supply operation. The dimension of the fabricated circuit including two active baluns intermodulation characteristic with two-tone excitation are also measured, showing -28.17 dBc at IF power of -30 dBm.

• Journal of electromagnetic engineering and science
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• v.15 no.4
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• pp.206-212
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• 2015

This paper introduces new wideband antenna-filter-antenna (AFA) uniform arrays that can be utilized as frequency selective surfaces (FSS) with low loss and sharp roll-off response, which are highly desirable characteristics for millimeter wave applications. The design adopts a simple 3-layer single polarization structure consisting of two patch antennas and a resonator. Both simulations and measurements are used to characterize the performances of the proposed design. Overall results show 18.5% 10-dB bandwidth. For the targeted band the insertion loss is less than 0.2 dB. Possible applications include quasi-optical amps, grid mixers and radomes for aircraft radar antennas.

• Journal of Advanced Marine Engineering and Technology
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• v.27 no.2
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• pp.299-304
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• 2003

Static mixer consists of a straight pipe of circular cross section into which individual elements are inserted to cut, fold, twist and re-combine the mixing fluid. The number of elements and their shape required in any application depend on the complexity of the mixing process. The objectives of this study are to develop a new static mixer and to perform the experimental investigation of pressure drop in order to evaluate the performance of the new one. The mixing fluid used is Glycerin. The pressure drop is measured using a hydraulic manometer and the correlation of Z-factor is suggested as a function of Re. The Z-factors of SSC and YNU mixer are about 40% lower than and 4% higher than that of the Sulzer one.