• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.1
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• pp.8-18
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• 2000

We presented a BGA(Ball Grid Array) package for RF circuit modules and extracted its electrical parameters. As the frequency of RF system devices increases, the effect of its electrical parasitics in the wireless communication system requires new structure of RF circuit modules because of its needs to be considered of electrical performance for minimization and module mobility. RF circuit modules with BGA packages can provide some advantages such as minimization, shorter circuit routing, and noise improvement by reducing electrical noise affected to analog and digital mixed circuits, etc. We constructed a BGA package of ITS(Intelligent Transportation System) RF module and measured electrical parameters with a TDR(Time Domain Reflectometry) equipment and compared its electrical parasitic parameters with PCB RF circuits. With a BGA substrate of 3${\times}$3 input and output terminals, we have found that self capacitance of BGA solder ball is 68.6fF, and self inductance 146pH, whose values were reduced to 34% and 47% of the value of QFP package structure. S11 parameter measurement with a HP4396B Network Analyzer showed the resonance frequency of 1.55GHz and the loss of 0.26dB. Routing length of the substrate was reduced to 39.8mm. Thus, we may improve electrical performance when we use BGA package structures in the design of RF circuit modules.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.1
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• pp.137-147
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• 2013

In this paper, an 1.2V 8b 1GS/s A/D Converter(ADC) based on a folding architecture with a resistive interpolation technique is described. In order to overcome the asymmetrical boundary-condition error of conventional folding ADCs, a novel scheme with an odd number of folding blocks and a fractional folding rate are proposed. Further, a new digital encoding technique with an arithmetic adder is described to implement the proposed fractional folding technique. The proposed ADC employs an iterating offset self-calibration technique and a digital error correction circuit to minimize device mismatch and external noise The chip has been fabricated with a 1.2V 0.13um 1-poly 6-metal CMOS technology. The effective chip area is $2.1mm^2$ (ADC core : $1.4mm^2$, calibration engine : $0.7mm^2$) and the power dissipation is about 350mW including calibration engine at 1.2V power supply. The measured result of SNDR is 46.22dB, when Fin = 10MHz at Fs = 1GHz. Both the INL and DNL are within 1LSB with the self-calibration circuit.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.44 no.3
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• pp.61-69
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• 2007

This paper proposes new preprocessing algorithm to extract minutiae in the process of fingerprint recognition. Fingerprint images quality enhancement is a topic phase to ensure good performance in a topic phase to ensure good performance in a Automatic Fingerprint Identification System(AFIS) based on minutiae matching. This paper proposes an algorithm to improve fingerprint image preprocessing to extract minutiae accurately based on directional filter. We improved the suitability of low quality fingerprint images to better suit fingerprint recognition by using valid ridge vector and ridge probability of fingerprint images. With the proposed fingerprint improvement algorithm, noise is removed and presumed ridges are more clearly ascertained. The algorithm is based on five step: computation of effective ridge vector, computation of ridge probability, noise reduction, ridge emphasis, and orientation compensation and frequency estimation. The performance of the proposed approach has been evaluated on two set of images: the first one is self collected using a capacitive semiconductor sensor and second one is DB3 database from Fingerprint Verification Competition (FVC).

• Journal of The Korean Astronomical Society
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• v.53 no.4
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• pp.87-98
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• 2020

The Korea Astronomy and Space Science Institute (KASI) has been developing a next-generation coronagraph (NGC) in cooperation with NASA to measure the coronal electron density, temperature, and speed simultaneously, using four different optical filters around 400 nm. KASI organized an expedition to demonstrate the coronagraph measurement scheme and the instrumental technology during the 2017 total solar eclipse (TSE) across the USA. The observation site was in Jackson Hole, Wyoming, USA. We built an eclipse observation system, the Diagnostic Coronal Experiment (DICE), composed of two identical telescopes to improve the signal-to-noise ratio. The observation was conducted at four wavelengths and three linear polarization directions in the limited total eclipse time of about 140 seconds. We successfully obtained polarization data for the corona but we were not able to obtain information on the coronal electron temperature and speed due to the low signal-to-noise ratio of the optical system and strong emission from prominences located at the western limb. In this study, we report the development of DICE and the observation results from the eclipse expedition. TSE observation and analysis with our self-developed instrument showed that a coronagraph needs to be designed carefully to achieve its scientific purpose. We gained valuable experience for future follow-up NASA-KASI joint missions: the Balloon-borne Investigation of the Temperature and Speed of Electrons in the Corona (BITSE) and the COronal Diagnostic EXperiment (CODEX).

• Journal of Korean society of Dental Hygiene
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• v.14 no.3
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• pp.381-390
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• 2014

Objectives : The purpose of the study is to investigate the relationship between job-stress and temporomandibular joint(TMJ) disorder in dental hygienists. This study will provide the basic data to improve the working condition and the quality of life. Methods : The subjects were 229 dental hygienists at general hospitals in Seoul, Korea. A self-reported questionnaire was filled out from May 20 to June 20, 2013. The questionnaire consisted of 4 questions of demographic features, 11 questions for TMJ symptoms and 5 questions for job stress. The data were analyzed by frequency analysis, chi-square test, Mann-Whitney U test and multiple job-stress logistic regression analysis using SPSS version 21.0. Results : During the last six months, 53.3%(122 persons) of the dental hygienists had TMJ disorder symptoms including joint noise(40.6%, 93 persons), TMJ pain(31.4%, 71 persons) and limitation of TMJ(21.8%, 50 persons). Job-stress is divided into two ranges including high stress group(4.3-5.0 points) and low stress group(0.0-3.6 points) in TMJ pain and joint noise(p<0.05). TMJ pain was closely related to low back pain, pelvis pain and tension headache arising from the uncomfortable working posture. Conclusions : It is necessary to prevent the job stress in the dental hygienists by the improvement of working condition, emotional stability, and frequent postural change.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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• pp.748-755
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• 2012

Friction causes self-excited vibration, stick-slip vibration and any other friction-induced phenomena. That kinds of vibrations cause chatter and squeal. In order to predict such vibrations accurately, employing an accurate friction model is very important because a dynamic behavior of a system with friction is dominantly governed by a friction model. A Coulomb friction model is the most widely known model. Coulomb friction model is useful model to obtain analytical solutions of the system with friction and the model gives relatively good simulation result. However, defining a friction force at a stick state in simulation is hard because of the characteristic itself and a Coulomb friction model is discontinuous function between a static and a dynamic friction coefficient. Therefore, applying the Coulomb friction model to a simulation is not appropriate. In order to resolve these problems, an approximated Coulomb friction model was developed using simple and continuous function. However, an approximated Coulomb friction model cannot realize stick. Therefore, an approximated Coulomb friction model cannot describe friction phenomena accurately. In order to analyze a friction phenomenon accurately, a friction model for a simulation was proposed in this paper. A proposed friction model realizes stick and gives reasonably good results compared to results obtained by the simulation employing an approximated Coulomb friction model. Accuracy of a proposed friction model was verified by comparing experimental results.

• Journal of the Korean Society of Safety
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• v.32 no.3
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• pp.151-159
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• 2017

This study deals with characteristics and risk of a PM based on user survey result, road driving test and data analysis of PM accident. Text mining method is applied to extract PM accident data from Big Data, which are claim data of private insurance company. Road driving test and survey on safety, convenience, noise, overtake ability, steering ability, and climbing ability of PM are performed to evaluate user's safety and convenience considering domestic road condition. As the result of claim data analysis, annual average increase rate of PM accident is 47.4% and average compensation of personal mobility is higher than that of bicycle by maximum 1.5 times. 79.8% of PM accident is self-caused accident due to unskilled driving and age-specific diagnosis rate of driver over 60 is higher than that of under 60. Diagnosis rate of over 60 at lower limb, foot, rib and spine is especially higher than that of under 60. As the result of road driving test and user survey, satisfaction level on safety and convenience of PM is evaluated as close to that of bicycle and satisfaction level of PM is increased after boarding. Overtake ability, steering ability, and climbing ability of PM are evaluated as same or better than that of bicycle but warning equipment to pedestrian or bike such as horn is required because noise level of PM during driving is too low. Finally, user survey result shows that bicycle road is suitable for PM and safety standard, advance-education and insurance are required for PM. It is suggested that drivers' license for PM can be replaced by advance-education. Results of this study can be used to prepare safety measures and legal basis for PM operation.

• Journal of Radiation Protection and Research
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• v.41 no.2
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• pp.81-86
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• 2016

Background: For positron emission tomography (PET) application, cadmium zinc telluride (CZT) has been investigated by several institutes to replace detectors from a conventional system using photomultipliers or Silicon-photomultipliers (SiPMs). The spatial and energy resolution in using CZT can be superior to current scintillator-based state-of-the-art PET detectors. CZT has been under development for several years at the Korea Atomic Energy Research Institute (KAERI) to provide a high performance gamma ray detection, which needs a single crystallinity, a good uniformity, a high stopping power, and a wide band gap. Materials and Methods: Before applying our own grown CZT detectors in the prototype PET system, we investigated preliminary research with a developed discrete type data acquisition (DAQ) system for coincident events at 128 anode pixels and two common cathodes of two CZT detectors from Redlen. Each detector has a $19.4{\times}19.4{\times}6mm^3$ volume size with a 2.2 mm anode pixel pitch. Discrete amplifiers consist of a preamplifier with a gain of $8mV{\cdot}fC^{-1}$ and noise of 55 equivalent noise charge (ENC), a $CR-RC^4$ shaping amplifier with a $5{\mu}s$ peak time, and an analog-to-digital converter (ADC) driver. The DAQ system has 65 mega-sample per second flash ADC, a self and external trigger, and a USB 3.0 interface. Results and Discussion: Characteristics such as the current-to-voltage curve, energy resolution, and electron mobility life-time products for CZT detectors are investigated. In addition, preliminary results of gamma ray imaging using 511 keV of a $^{22}Na$ gamma ray source were obtained. Conclusion: In this study, the DAQ system with a CZT radiation sensor was successfully developed and a PET image was acquired by two sets of the developed DAQ system.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.8
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• pp.104-109
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• 2020

Recently, vibration and noise have become an important issue in the auto industry. Asphalt vibration damping pads are used to reduce the noise and vibration of automobile bodies, and asphalt is used for many mass-produced parts due to its simple attachment process and low processing costs. In this study, the self-adhesion of asphalt pads using Joule heating was evaluated. To create the asphalt pad for the experiment, the asphalt pad was molded into a specific thickness by using SGACC material and rubber used in the vehicle body as a main component and a modified resin and filler. The SGACC material was 200 mm in length, 200 mm in width, and 0.7 mm in thickness. The asphalt pad was 200 mm in length, 100 mm in width, and 3 mm in thickness. The equipment was composed of a TR (Transformer) DC254kVA and a TC (Time controller) for a current of up to 20,000 A. The current for the Joule heating was set to 7.0 kA and a 3/1 cycle, for which the adhesion of the asphalt pad over the current flow time was evaluated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.5
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• pp.480-488
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• 2012

The aircrafts with high aspect ratio wings made by a composite material have been developed, which enable high energy efficiency and long-term flight by reducing air resistance and structural weight. However, they have difficulties in securing the aeroelastic stability such as the flutter because of their long and flexible wings. The flutter is unstable self-excited-vibration caused by interaction between the structural dynamics and the aerodynamics. It should be verified analytically prior to first flight test that the flutter does not happen in the range of flight mission. Normally, the finite element model is used for the flutter analysis. So it is important to construct the finite element model representing dynamic characteristics similar to those of a real aircraft. Accordingly, in this research, to acquire dynamic characteristics experimentally the modal test of the aircraft with high aspect ratio composite wings was conducted. And then the modal parameters from the finite element analysis(FEA) were compared with those from the modal test. To make analysis results closer to test results, the finite element model was updated by means of the sensitivity analysis on variables and the optimization. Finally, it was proved that the updated finite element model is reliable as compared with the results of the modal test.