• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.3
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• pp.1-9
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• 2003

In this paper, we designed a highly suppressed sidelobe ladder type RF SAW bandpass filter based on 1-port resonator, for 800 MHz mobile communication system. In order to get the highest device characteristics, we optimized some important parameters such as the electrode thickness, electrode lambda weghting of the reflectors, and static capacitance ratio. Furthermore, we fabricated the Tx and Rx. filter using optimized parameters. Implemented filters can be used in 800 MHz mobile communication system and external impedance matching circuits are not needed. RF filter was fabricated on 36$^{\circ}$LiTaO$_3$ substrates with Al-Cu (W 3 %)and mounted 3.8mm$\times$3.8mm$\times$1.5mm SMD package. Developed filters has 2.3 dB insertion loss in the 25 MHz pass-band, 33MHz with 3-dB insertion loss, stop-band rejection of 30 dB, passband ripple is less than 0.5 The power durability of the filters measured about 3.5W and the maximum temperature variation within -2$0^{\circ}C$~8$0^{\circ}C$ was 0.09 dB/$^{\circ}C$ of 3-dB insertion loss.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.43 no.3
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• pp.59-65
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• 2011

The saw dust of tropical hardwood, Nyatoh(Palaquium Spp.), was used as a raw material for the preparation of the high valued microcrystalline cellulose(MCC). Three pulping methods, soda pulping, Kraft pulping, and acid-sulfite pulping were applied to obtain cellulose from the saw dust. The residual impurities were removed with the additional bleaching processes: (A) $ClO_2{\rightarrow}H_2O_2$; (B) $ClO_2{\rightarrow}O_3$; (C) $O_3$. For the acid treatment for MCC preparation, the $H_2SO_4$, with three concentration, 20%, 40%, 60% were applied and the effects of $H_2SO_4$ concentration on the properties of MCC were evaluated. The results indicated that the MCC obtained by acid-sulfite pulping followed with $O_3$ treatment and 40% $H_2SO_4$ treatment showed less residual lignin, higher brightness and crystallinity than that of Avicel MCC.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.5
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• pp.130-136
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• 2001

Generally, a metal slitting saw is plain milling cutter with thickness less than 3/16 inch. This is used for cutting a workpiece that high dimensional accuracy and surface finish is necessary. A small thin milling cutter like a metal slitting saw is useful for machining a narrow groove. In this case, built up edge(BUE) is severe at each tooth and affects the surface integrity of the machined surface and tool wear. It is well known that tool geometry and cutting conditions are decisive factors to remove BUE. In this paper, we optimized the geometry of the milling cutter and selected cutting conditions to remove BUE by the experimental investigation. The experiment was planned with Taguchi method based on the orthogonal array of design factors such as coating, rake angle, number of tooth, cutting speed, feed rate. Response table was obtained from the number of built-up edge generated at tooth. The optimized tool geometry and cutting conditions could be determined through response table. In addition, the relative effect of factors was identified bh the analysis of variance (ANOVA). Finally, coating and cutting speed turned out important factors for BUE.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.884-887
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• 2012

무선 센서 네트워크 기술은 상시적으로 물리정보를 획득할 수 있기 때문에 광범위한 응용분야에서 수요가 증가하고 있다. 또한 무선 센서 네트워크에 적용되는 무선 센서 시스템은 일반적으로 배터리를 장착하여 회로에 전력을 공급해주는 방식을 사용한다. 그러나 센서가 적의 기지근처, 인체 조직내 삽입, 건물의 내벽 등과 같이 배터리를 교체할 수 없는 곳에 위치해 있는 경우, 반영구적인 사용에 제한이 있기 때문에 무전원 무선 센서의 개발이 절실히 필요하다. 특히, 이러한 센서를 새롭게 개발하고 검증하려며 센서의 주파수 특성을 분석해야 하는데 기존에는 단순한 파형만을 분석할 수 있는 일반적인 계측기를 사용할 수밖에 없었다. 따라서 본 논문에서는 기존의 계측기보다 유연성 있고 효율적으로 무전원 무선 센서의 개발과 검증이 가능하도록 신호의 모니터링과 신호발생기를 에뮬레이션하는 NI LabVIEW기반의 SAW System Analyzer와 SAW Reader Emulator 시스템을 설계하고 개발하였다.

• The Journal of the Acoustical Society of Korea
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• v.19 no.2
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• pp.33-39
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• 2000

We have studied to obtain the frequency characteristics of the Surface Acoustic Wave(SAW) bandpass filter, having low shape factor, it's interdigital transducer(IDT) was formed on the 35° Y-cut X-propagation Quartz substrate and was evaporated by Aluminium. And then, we performed computer-simulation by a simulator. And, we can design that the apodization weighted type IDT as an input transducer of the filter and the withdrawal weighted type IDT as an output transducer of the filter from the results of our computer-simulation. Also, we have employed that the number of pairs of the input and output IDT are 2200 pairs and 1000pairs, respectively and used the Kaiser-Bessel window function in order to minimize the effect of ripple. And, while the width and the space of IDT's finger are 6㎛ m and 5.75㎛, respectively and we could obtain the resonable results when the IDT thickness was 6000Å in consideration of the ratio of SAW's wavelength, and IDT aperture is 2mm. Frequency response of the fabricated SAW bandpass filter has the property that the center frequency is about 70MHz, shape factor is less than 1.3, bandwidth at the 1.5dB is probably 1.3MHz, out-band attenuation is almost -45dB, insertion loss is 19dB and ripple in the width of bandpass is 1dB approximately. Therefore, these frequency characteristics of the fabricated SAW bandpass filter are agreed well with the designed values.

• Journal of Technologic Dentistry
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• v.32 no.4
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• pp.403-415
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• 2010

Purpose: The purpose of this study was to examine the eyesight and life habits of college students in an attempt to provide some information on the protection of their eyesight. Methods: The subjects in this study were 311 students in the department of dental technology at a college of health, on whom a survey was conducted. A crosstabulation analysis was carried out to show the joint distribution of general characteristics and several variables involving the use of glasses or contact lenses and life habits. Results: 77.5% of the students currently wore glasses due to weak sight. 9.3% took an eye test on a regular basis, and 31.2% did that every six months. As for the length of the length of daily mean reading time, 55.3% spent one hour or less reading books. The most common distance between eyes and books during their reading(44.7%) was 21 to 25. Concerning a reading posture, the biggest group(54.3%) lay down or lay on their face while they read books. 45.0 % spent less than an hour watching TV per day on average, and 27.0% were on the computer for 30 minutes to less than an hour per day on average. The greatest group(63.0%) made use of basic indoor lighting when they were on the computer at night, and 62.1% saw eye doctors to take an eye test. In relation to how to protect eyesight, the biggest group(50.5%) spent less time being on the computer. Conclusion: As the eyesight of college students fails due to reading, TV, computer, and improper ways and posture of doing or using those things, every college definitely should provide education on eye health as one of general education courses.

• 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.

• Journal of the Korean Society of Visualization
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• v.14 no.1
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• pp.57-61
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• 2016

We report a finding of fast(exceeding 2,000 K/s) heating of polydimethylsiloxane(PDMS), one of the most commonly-used microchannel materials, under cyclic loadings at high(~MHz) frequencies. A microheater was created based on the finding. The heating mechanism utilized vibration damping of sound waves, which were generated and precisely manipulated using a conventional surface acoustic wave(SAW) microfluidic system, in PDMS. The penetration depths were measured to range from $210{\mu}m$ to $1290{\mu}m$, enough to cover most microchannel heights in microfluidic systems. The energy conversion efficiency was SAW frequency-dependent and measured to be the highest at around 30 MHz. Independent actuation of each interdigital transducer(IDT) enabled independent manipulation of SAWs, permitting spatiotemporal control of temperature on the microchip. All the advantages of this microheater facilitated a two-step continuous flow polymerase chain reaction(CFPCR) to achieve the billion-fold amplification of a 134 bp DNA amplicon in less than 3 min. In addition, a technique was developed for establishing dynamic free-form temperature gradients(TGs) in PDMS as well as in gases in contact with the PDMS.

• Wind and Structures
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• v.23 no.2
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• pp.91-107
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• 2016

Flow-excited acoustic resonance in ducted cavities can produce high levels of acoustic pressure that may lead to severe damage. This occurs when the flow instability over the cavity mouth, which is created by the free shear layer separation at the upstream edge, is coupled with one of the acoustic modes in the accommodating enclosure. Acoustic resonance can cause high amplitude fluctuating acoustic loads in and near the cavity. Such acoustic loads could cause damage in sensitive applications such as aircraft weapon bays. Therefore, the suppression and mitigation of these resonances are very important. Much of the work done in the past focused on the fluid-dynamic oscillation mechanism or suppressing the resonance by altering the edge condition at the shear layer separation. However, the effect of the downstream edge has received much less attention. This paper considers the effect of the impingement edge geometry on the acoustic resonance excitation and Strouhal number values of the flow instabilities in a ducted shallow cavity with an aspect ratio of 1.0. Several edges, including chamfered edges with different angles and round edges with different radii, were investigated. In addition, some downstream edges that have never been studied before, such as saw-tooth edges, spanwise cylinders, higher and lower steps, and straight and delta spoilers, are investigated. The experiments are conducted in an open-loop wind tunnel that can generate flows with a Mach number up to 0.45. The study shows that when some edge geometries, such as lower steps, chamfered, round, and saw-tooth edges, are installed downstream, they demonstrate a promising reduction in the acoustic resonance. On the other hand, higher steps and straight spoilers resulted in intensifying the acoustic resonance. In addition, the effect of edge geometry on the Strouhal number is presented.

• Journal of the Korean Society of Costume
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• v.54 no.5
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• pp.109-123
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• 2004

The purpose of this study is to examine features of parts of Jikryung and relations among the features. Results of the study can be described as follows. 1. The short front and long rear of Jikryung was changed into the long front and long rear of the dress in the late 16th century. Kalgit of quasi-square style as double collar was changed into that of common collar in the late 16th century and then into common semi-circle collar in the early 17th century, when double Sup was also changed Into single Sup. Narrow sleeves of Jikryung were replaced by bean chaff-shaped in the late 16th century and then by wide ones in the early period of the next century. The shape of the side hem of Jikryung was changed from rectangle into trapezoid in the early 17th century Triangle-shaped Moo was changed into trapezoid-shaped one in the late 16th century and then again into triangle in the late 17th century 2. Changes in shapes of the parts of Jikryung were made with them correlated. The collar of Jikryung saw change in its form from double to common as its width was reduced. Double Sup was changed into single one and the narrow, short coat string into the long one as Jikryung became a dress needing less adjustment. The sleeves widened as the length of whajang increased. The side hem of Jikryung saw change in its shape from rectangular to trapezoidal one as its position was changed. Trapezoidal Moo was replaced by triangular one as the sleeve of Jikryung was changed in shape. 3. Changes in shapes of the parts of Jikryung influenced the aesthetic beauty of the dress itself In its first period, Jikryung was simple with long, slim silhouettes. In its second period, the dress was rich with increased volume. Finally in its third period, the dress was characterized by the harmony of simpleness and richness.