• Journal of Electrical Engineering and Technology
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• v.3 no.1
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• pp.121-124
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• 2008

This paper presents the fabrication and field emission of carbon nanotube field emitters for a micro mass spectrometer. The carbon nanotube is an adequate material as a field emitter since it has good characteristics. We have successfully fabricated a diode field emitter and a triode field emitter. Each field emitter has been constructed using several micromachining processes and a thermal CVD process. In the case of the diode field emitter, to increase the electric field, the carbon nanotubes are selectively grown on the patterned nickel catalyst layer. The electron current of the diode field emitter is 73.2 ${\mu}A$ when the anode voltage is 1100V. That of the triode field emitter is 3.4 pA when the anode voltage is 1000V.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.384-384
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• 2011

Carbon nanotubes (CNTs) have been studied as an ideal material for field emitters due to the high aspect ratio, excellent electrical property and good mechanical strength. There were many reports on CNT emitters fabricated on rigid substrates, but rare reports about CNT flexible field emitters. Recently, we considered that CNTs can be a good candidate for a flexible field emitter material because of their excellent Young's modulus and elasticity, which could not be achieved with metal tips or semiconducting nanowire tips. In this work, we demonstrated the CNT flexible field emitters fabricated by a simple method and studied the field emission properties of the CNT flexible field emitters under various bending conditions. The flexible field emitters showed stable and uniform emission characteristics. Especially, there is no remarkable change of the field emission properties at the CNT flexible field emitters according to the bending conditions. The CNT flexible field emitters also exhibited a good field emission performance like the low turn-on field and high emission current. Therefore, we suggest that the CNT flexible emitters can be used in many practical applications under different bending conditions.

• Computers and Concrete
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• v.30 no.5
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• pp.323-337
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• 2022

This paper proposes a numerical model to simulate the rotational behavior of steel fiber in fresh cement-based materials in the presence of a magnetic field. The results indicate that as the aspect ratio of fiber increases, the required minimum magnetic field intensity to make fiber rotate in viscous fluid increases. The optimal magnetic field intensity is 0.03 T for aligning steel fiber in fresh cement-based materials to ensure that the applying time of the magnetic field can be conducted concurrently with the vibrating process to increase the aligning efficiency. The orientation factor of steel fiber in cement mortar can exceed 0.85 after aligning by 0.03 T of the uniform magnetic field. When the initial angle of the fiber to the magnetic field direction is less than 10°, the magnetic field less than 0.03 T cannot make the fiber overcome the yield stress of fluid to rotate. The coarse aggregate in steel fiber-reinforced concrete is detrimental to the rotation and alignment of the steel fiber. But the orientation factor of ASFRC under the 0.03T of the magnetic field can also exceed 0.8, while the orientation factor of SFRC without magnetic field application is around 0.6.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.341-342
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• 2007

3T MRI system에서 고해상도 영상을 얻기 위해서는 magnetic field를 균일하게 만들어야 한다. 특히 초고속 영상 기법인 Spiral scan 방식과 EPI scan 방식에서는 이미지 영역에서의 magnetic field의 inhomogeneity에 의해 영상의 왜곡이 심해진다. 본 논문에서는 magnetic field의 inhomogeneity를 단시간 내에 측정하기 위해 fast spin echo방식의 pulse sequence 제안하고, magnetic field를 분석하기 위한 field map의 구성과, field pattern의 효과적인 분석을 통하여, magnetic field를 균일하게 만드는 방법을 제안한다.

• Journal of Engineering Education Research
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• v.18 no.4
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• pp.3-12
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• 2015

The purpose of this study was to develop a pre-training program of engineering college students for maximizing the effectiveness of internship or field training. To pursue this goal, literature review was conducted for data collection about college and corporate pre-training program for internship or field training and pre-training program(draft) was proposed. A questionnaire survey was conducted with engineering professors, students and graduates to identify the needs for pre-training program(draft) for internship or field training. Based on the results, the contents of pre-training program for internship or field training were composed of basic liberal arts, basic competency, real information related with corporation or job, and information exchange network. And key consideration for operating the pre-training program for internship or field training were proposed with the management department, regulation for the obligatory participation, meaningful organizing content, feedback of needs.

• Structural Engineering and Mechanics
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• v.62 no.4
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• pp.497-506
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• 2017

A low damage self-centering braced frame equipped with post-tensioning strands is capable of directing damage to replaceable butterfly-shaped fuses. This paper investigates the seismic performance of rocking braced frame under near-field pulse-like ground motions compared to far-field records. A non-linear time history analysis is performed for twelve self-centering archetypes. A sensitivity analysis is carried out to examine the influences of ground motion types and modeling parameters. Findings represent the proper efficiency of the self-centering system under both far-field and near-field pulse-like ground motions.

• Journal of Biomedical Engineering Research
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• v.27 no.5
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• pp.229-236
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• 2006

The acoustic field analysis method is the superior calibration method for rectifying the ultrasonic probe sensitivity. This method also can be applied to evaluate the probe performance in clinical fields without numerical analysis and precise measurements. In this paper, we propose the method of acoustic field pattern analysis with probe channel division for the evaluation of diagnostic ultrasound probe characterization. In order to verify our purpose, we performed a set of experiments. We measured the acoustic-field pattern of the three inferiority probes by channel division to evaluate an acoustic field distribution and impulse response characteristics. By comparing the results of acoustic field measurement method with that of conventional method such as impulse response and live image test for linear array probes, it is demonstrated that the ultrasound field measurement method is more effective then conventional method in detection of defective elements.

• Journal of Electrical Engineering and Technology
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• v.9 no.6
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• pp.1995-2003
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• 2014

Power semiconductor devices have been the major backbone for high-power electronic devices. One of important parameters in view of power semiconductor devices often characterize with a high breakdown voltage. Therefore, many efforts have been made, since the development of the Insulated Gate Bipolar Transistor (IGBT), toward having higher level of breakdown voltage, whereby the typical design thereof is focused on the structure using the field ring. In this study, in an attempt to make up more optimized field-ring structure, the characteristics of the field ring were investigated with the use of theoretical arithmetic model and methodologically the design of experiments (DOE). In addition, the IGBT having the field-ring structure was designed via simulation based on the finding from the above, the result of which was also analyzed. Lastly, the current study described the trench field-ring structure taking advantages of trench-etching process having the improved field-ring structure, not as simple as the conventional one. As a result of the simulation, it was found that the improved trench field-ring structure leads to more desirable voltage divider than relying on the conventional field-ring structure.

• Journal of Engineering Education Research
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• v.17 no.6
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• pp.3-11
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• 2014

This study investigated the effects of WIE(Women into Engineering) programs on women engineers' employment and career duration. For this study, the 91 female graduates with a degree in the field of engineering of K university who graduated from 2010 to 2013 were collected. The female graduates with a degree in the field of engineering of K university were divided into 4 groups-an employment group of relevant field of major, an employment group of irrelevant field of major, a group of graduate school, and a group of unemployment. The results were: first, the female graduates' program participation scores showed meaningful diversity according to the types of employment of female graduates with a degree in the field of engineering. Among the 4 types of employment of female graduates with a degree in the field of engineering, the group of graduate schoolers got the highest program participation scores, and the employment group of relevant field of major got the second scores, the group of unemployment got the third scores, and the employment group of irrelevant field of major got the last scores. Second, The female graduates' program participation scores showed meaningful diversity according to the career duration of female graduates with a degree in the field of engineering. The career duration in accordance with the program participation scores showed meaningful difference between the employment group of relevant field of major and the employment group of irrelevant field of major.

• Earthquakes and Structures
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• v.18 no.3
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• pp.391-405
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• 2020

The use of passive energy dissipation devices has been widely used in the construction industry to minimize the probability of damage occurred under intense ground motion. In this study, collapse margin ratio (CMR) and fragility curves are the main parameters in the assessment to characterize the collapse safety of the structures. The assessment is done on three types of RC frame structures, incorporating three types of dampers, viscoelastic, friction, and BRB dampers. The Incremental dynamic analyses (IDA) were performed by simulating an array of 20 strong ground motion (SGM) records considering both far-field and near-field seismic scenarios that were followed by fragility curves. With respect to far-field ground motion records, the CMR values of the selected frames indicate to be higher and reachable to safety margin more than those under near-field ground motion records that introduce a high devastating impact on the structures compared to far-field excitations. This implies that the near field impact affects the ground movements at the site by attenuation the direction and causing high-frequency filtration. Besides that, the results show that the viscoelastic damper gives better performance for the structures in terms of reducing the damages compared to the other energy dissipation devices during earthquakes.