• 전자공학회논문지 IE
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• v.45 no.1
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• pp.31-37
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• 2008

A Wibro RF down converter of 2.3GHz band is designed and implemented in this paper. The problems that can occur in the receiver LNA(Low Noise Amplifier) to minimize additional purposes. In addition, 2.3GHz band from the 75 MHz downward to minimize the losses in the process, transform and improve efficiency, and achieve stable characteristics can be used to make high frequency characteristics of the device. Wibro repeater uses a TDMA(Time Division Multiplexing Access) method is needed because the RF switch. Production criterion specification, the input voltage from +8 V 1.2A of current consumption, 60dB gain and the noise figure of less than 2.5dB, VSWR(Voltage Standing Wave Ratio) less than 1.5, more than IMD(Inter Modulation Distortion) 60dB satisfied. Environmental conditions ($-20^{\circ}C$ to $70^{\circ}C$) to pass the test of reliability in a long time, that seemed crafted Wibro down converter be applied to the Wibro repeater.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.4
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• pp.344-350
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• 2009

This paper proposes a hybrid antenna with novel beam steering scheme. The antenna have a cassegrain structure composed of two reflectors. The main reflector is designed for high gain performance using parabola curvature, and the sub-reflector is plate and can be rotated by ${\pm}3^{\circ}$. Thus proposed antenna can steer a antenna beam using the inclination of sub-reflector. A feed array composed of 20 elements is adapted as a feeder for electrical beam steering, and the antenna can be possible to steer the beam by the feed array with sub-reflector. Proposed antenna was fabricated to be operated in Ka-band(30.085$\sim$30.885 GHz) for TX and K-band(20.355$\sim$21.155 GHz), which are the operation frequencies of the Korean satellite, Mugunhwa, to provide satellite multi-media service to vehicles. By the performance test, it can be known that the antenna has minimum gain of 47 dBi for TX and 44.4 dBi for TX and can steer the beam by ${\pm}2^{\circ}$ with sub-reflector.

• Polymer(Korea)
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• v.39 no.1
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• pp.114-121
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• 2015

Mutli-walled carbon nanotubes (MWCNTs) were surface-modified by a hydrofluoric acid solution to remove impurities and improve interfacial bonding and dispersion of nanotubes in an epoxy matrix. The crystallinity on the surface of treated MWCNTs was investigated by X-ray photoelectron spectroscopy and Raman spectroscopy. The mechanical properties were characterized by tensile test, and the enhancement of mechanical properties of the modified MWCNTs/epoxy composites was indicated by a 33% increase in tensile strength. The electromagnetic interference shielding effectiveness (EMI-SE) of modified MWCNTs/epoxy composites was improved with an increase in concentration of hydrofluoric solution, and EMI-SE showed the maximum increase with 25% HF. However, mechanical and EMI-SE properties didn't show further increase with over 50% HF concentration because the properties of MWCNTs were influenced by degradation of crystallinity and intrinsic properties of MWCNTs. The mechanical and electrical property enhancements of the polymer composites are attributed to the modification of MWCNTs which improve crystallinity of MWCNTs and dispersion in the epoxy resin.

• Journal of the Korean Society of Propulsion Engineers
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• v.2 no.2
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• pp.74-82
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• 1998

Combined cycle power plant is a system where a gas turbine or a steam turbine is used to produce shaft power to drive a generator for producing electrical power and the steam from the HRSG is expanded in a steam turbine for additional shaft power. The temperature of the exhaust gases from a gas turbine ranges from $400{\sim}650^{\circ}C$, and can be used effectively in a heat recovery steam generator to produce steam. Combined cycle can be classed as a topping and bottoming cycle. The first cycle, to which most of the heat is supplied, is a Brayton gas turbine cycle. The wasted heat it produces is then utilized in a second process which operates at a lower temperature level is a steam turbine cycle. The combined gas and steam turbine power plant have been widely accepted because, first, each separate system has already proven themselves in power plants as an independent cycle, therefore, the development costs are low. Secondly, using the air as a working medium, the operation is relatively non- problematic and inexpensive and can be used in gas turbines at an elevated temperature level over $1000^{\circ}C$. The steam process uses water, which is likewise inexpensive and widely available, but better suited for the medium and low temperature ranges. It therefore, is quite reasonable to use the steam process for the bottoming cycle. Recently gas turbine attained inlet temperature that make it possible to design a highly efficient combined cycle. In the present study, performance analysis of a 3 pressured combined cycle power plant is carried out to investigate the influence of topping cycle to combined cycle performance. Present calculation is compared with acceptance performance test data from SeoInchon combined cycle power plant. Present results is expected to shed some light to design and manufacture 150~200MW class heavy duty gas turbine whose conceptual design is already being undertaken.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.43 no.6 s.312
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• pp.65-84
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• 2006

In this paper, we present an improved image formation model and propose a color image enhancement based on the model. In the presented image formation model, an input image is represented as a product of global illumination, local illumination, and reflectance. In the proposed color image enhancement, an input RGB color image is converted into an HSV color image. Under the assumption of white-light illumination, the H and S component images are remained as they are and the V component image only is enhanced based on the image formation model. The global illumination is estimated by applying a linear LPF with wide support region to the input V component image and the local illumination by applying a JND (just noticeable difference)-based nonlinear LPF with narrow support region to the processed image, where the estimated global illumination is eliminated from the input V component image. The reflectance is estimated by dividing the input V component image by the estimated global and local illuminations. After performing the gamma correction on the three estimated components, the output V component image is obtained from their product. Histogram modeling is next executed such that the final output V component image is obtained. Finally an output RGB color image is obtained from the H and S component images of the input color image and the final output V component image. Experimental results for the test image DB built with color images downloaded from NASA homepage and MPEG-7 CCD color images show that the proposed method gives output color images of very well-increased global and local contrast without halo effect and color shift.

• Journal of IKEEE
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• v.15 no.1
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• pp.76-85
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• 2011

In this paper, we analysed RSS characteristics by external factors and presented an efficient algorithm for real-time location tracking and its hardware system. The proposed algorithm enhanced the ranging accuracy using Kalman Filter based on the RSS DB. The location tracking system that consists of the tag, AP(Access Point), a data collector(Data Receiver) with IEEE 802.15.4(ZigBee) network environment, and location tracking application that reveal locations of each tag is implemented for the test environment. The location tracking system presented in this paper is implemented with MSP430 microprocessor manufactured by TI(Texas Instrument), CC2420 RF chipset and the location tracking application. With the results of the experiment, the proposed algorithm and the system can achieve the efficiency and the accuracy of location tracking with the average error of 19.12cm, and its standard deviation of 5.31cm in outdoor circumstance. Also, the experimental result shows that exact tracking of position in indoor circumstance cannot achieve because of vulnerable RSS with external circumstance.

• Journal of Satellite, Information and Communications
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• v.12 no.3
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• pp.80-85
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• 2017

In this paper, a mircrowave breakdown of X-band circular waveguide cavity filter, which occurred during ground test, was introduced, and electro-magnetic field simulation results to identify a root cause, and the analysis of possibility of its occurrence on orbit operation were presented. Filter modeling for simulation was conducted with a commercial tool (FEST3D), and electric fields inside the filter were monitored at the input of 1 W continuous wave. In our observation, strong electric field intensities were monitored on the tuning screws especially at the input of band-edge frequencies. The threshold power levels for the breakdown were also estimated and compared with the input power levels actually injected to the filter. From this estimation, we could figure out that the power exceeding the breakdown threshold was injected to the filter so that strong electric fields were generated and temperature increased high, and this became a root cause of the electrical short. Our further analysis showed that this kind of microwave breakdown is not likely to occur on orbit operation, and multipactor is expected not to occur at the input of band-edge frequencies. As a measure to prevent the microwave breakdown, we suggested to avoid the injection of band-edge frequencies and inject lower power levels to the filter.

• Journal of the Korean Applied Science and Technology
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• v.33 no.2
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• pp.247-254
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• 2016

Since microzirconia has excellent thermal and mechanical properties with high chemical and electrical resistance, it can be used in various fields. When the surface of zirconia becomes hydrophilic, its dispersibility in water will be improved as well as the resistance to most hydrophobic contaminants will be increased. In this study, we investigated the introduction of a hydrophilic groups on the microzircornia surface through hydrolysis and condensation reactions with two different silanes containing hydrophilic functional groups, such as ${\gamma}$-aminopropyltrimethoxysilane (APS) and ${\gamma}$-ureidopropyltrimethoxysilane (UPS) at different pH and concentration conditions. A covalent bond formation between the surface hydroxyl groups of zirconia and that of hydrolyzed silanes was confirmed by ninhydrin test and FT-IR spectroscopy. However, the presence of Si on the surfaces of both silane modified microzirconias was unable to detect by SEM/EDS technique. In addition, particle size analysis results provide that the size of microzirconia was changed to smaller or bigger than that of original zirconia due to crushing and aggregation during the modification process. The water dispersibility was improved for only APS modifed zirconia (AS-2 and AS-3) under neutral pH condition, but the water dispersibility and stability for all cases of 0.5~2% UPS modifed zirconia (US series) were much improved.

• Journal of the Korean Geotechnical Society
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• v.31 no.11
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• pp.41-48
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• 2015

An investigation of a void and a loose layer of the ground is essential in order to prevent the losses of life and properties caused by subsidence and sinkage of the ground. Recently, studies on the ground penetrating radar survey have been actively conducted in order to estimate the void and the loose layer of the ground. However, an error can be committed by contrarily predicting a dense ground and a loose layer because the ground penetrating radar estimates an interface depth between geo-materials that have different electrical impedances. In this study, a loose ground depth is estimated using the characteristics of the reflected electromagnetic wave obtained from the ground penetrating radar survey. To gather the signals according to the loose ground depths, the ground penetrating radar survey is conducted on a field which underwent a huge ground settlement. In addition, the dynamic cone penetration test is performed to verify the result of the loose ground depth estimation from the ground penetrating radar survey. From the analysis of the reflection characteristics of the electromagnetic wave, a phase of an electromagnetic wave reflected from a denser soil layer is found to be identical with that of the first measured signal. On the other hand, a phase of an electromagnetic wave reflected from the loose soil layer is found to be opposed to that of the first detected signal. The comparison between the dynamic cone penetration index and electromagnetic signals by the ground penetrating radar shows that the estimated depth of the loose or dense layer is perfectly matched with a high reliability. The ground penetrating radar survey and the signal analysis performed in this study can be used not only for the survey of interface depth between the discontinuity layers but also for the estimation of the loose layer.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.17 no.1
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• pp.1-8
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• 2011

Background: The purpose of this study was to determine the effects of massage, stretching exercise, and scapular stabilization exercise in patients with upper trapezius myofascial pain syndrome (MPS). Methods: Twenty-three female patients with upper trapezius MPS were randomly allocated to three groups: massage, stretching exercise, and scapular stability exercise groups. Therapeutic intervention for all groups included general therapy such as hot pack, transcutaneous electrical nerve stimulation and ultrasound. Patients in the massage group (n=8), stretching group (n=7), and stabilization exercise group (n=8) received their respective therapy program after general therapy for 15 minutes. Therapeutic intervention for each group was performed three times per week for six weeks. All groups were tested four times: prior to the test, at three weeks, at six weeks, and at nine weeks. Results: Pain levels decreased significantly in the stretching and stabilization exercise groups over time (p<.05). The rate of change in pain level was significantly different among all groups (p<.01), and the stability exercise group experienced the lowest pain level. Pressure-pain level increased significantly in the stabilization exercise group over time (p<.05). The rate of change in pressure-pain level was significantly different among all groups (p<.01), and the stability exercise group had the highest pressure-pain level. The level of upper-extremity stability increased significantly in the stability exercise group over time (p<.05). The rate of change in the upper-extremity stabilization level was significantly different among all groups (p<.01), and the stability exercise group had the highest upper-extremity stability level. Conclusions: Scapular stabilization exercises proved to be the most effective therapy for MPS patients.