• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.618-629
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• 2001

This paper presents a result of failure analysis and reliability evaluation for high voltage ceramic capacitors. The failure modes and failure mechanisms were studied in two ways in order to estimate component life and failure rate. The causes of failure mechanisms for zero resistance phenomena under withstanding voltage test in high voltage ceramic capacitors molded by epoxy resin were studied by establishing an effective root cause failure analysis. Particular emphasis was placed on breakdown phenomena at the ceramic-epoxy interface. The validity of the results in this study was confirmed by the results of accelerated testing. Thermal cycling test for high voltage ceramic capacitor mounted on a magnetron were implemented. Delamination between ceramic and epoxy, which might cause electrical short in underlying circuitry, can occur during curing or thermal cycle. The results can be conveniently used to quickly identify defective lots, determine $B_{10}$ life estimation each lot at the level of inspection, and detect major changes in the vendors processes. Also, the condition for dielectric breakdown was investigated for the estimation of failure rate with load-strength interference model.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.3
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• pp.253-260
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• 2016

This paper proposes a planar Log-Periodic Dipole Array(LPDA) antenna with light-weight supporting structure for installing on an aircraft. The proposed antenna is designed by applying a planar skeleton supporting structure that has light-weight for an aircraft and is capable of withstanding structural vibration. The material of the planar skeleton supporting structure is a Polyether ether ketone(Peek) which has excellent characteristics on strength and temperature. The proposed antenna is fabricated by attaching the radiating elements of the LPDA on both sides of the supporting structure. The changed input impedance due to the dielectric material of the supporting structure was compensated for by controlling the distance and length of several radiating elements. The 10-dB return loss bandwidths of the designed planar LPDA antenna with light-weight supporting structure are obtained as 0.4~3.1 GHz(7.3:1) in the simulation and 0.41~3.5 GHz(8.2:1) in the measurement. The average gains in 0.5~3 GHz band are 6.77 dBi in the simulation and 6.55 dBi in the measurement. Therefore, we confirm that the designed antenna is appropriate to be installed on an aircraft due to its light-weight structure and wideband directional radiation characteristics.

• The Korean Journal of Rheology
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• v.10 no.4
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• pp.195-201
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• 1998

We have studied the rheological and electrical properties of two types of electrorheological (ER) fluids based on semi-conductive polymers (poly(p-phenylene) and polyaniline). These semi-conductive polymer-based suspensions showed a dramatic increase in viscosity on the application of the static electric field due to the large value of conductivity ratio between particle and medium. The dynamic yield stresses of these ER suspensions exhibited a quadratic dependence on electric field strength at low electric fields and a linear one for high fields. They showed a maximum and then decreased with increasing bulk conductivity of particles. These yield stress behaviors under the static electric field were found to be closely related to the dielectric properties, which is in accord with Maxwell-Wagner interfacial polarization induced by the conductivity effects. In order to achieve better understanding of interfacial polarization effect on ER response and to improve the stability of ER suspension, different kinds of surfactants were employed for controlling the ER activity as well as for enhancing the colloidal stability of suspensions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.577-582
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• 2020

Electricity produced at power plants is distributed to consumers through several stages of substations. At this time, an ultra-high voltage transformer is needed in the initial transmission stage to transmit a voltage suitable for each consumer. A high voltage, non-uniform electric field is formed at the end of the winding of the ultra-high voltage transformer, which carries a risk of dielectric breakdown. The winding of the ultra-high voltage transformer is an electrode, which is the key to converting the magnitude of the voltage. A non-uniform electric field is formed along the shape of the winding end, resulting in high electrical stress. The static ring installed at the upper and lower ends of the winding is used to disperse the stress at the winding end. Several variables should be considered when designing a static ring. Among them, this study examined how the curvature of the static ring, the thickness of the insulating paper, the number of barriers, and barrier thickness affect the electrical stress of the static ring using the Finite Element Method. Suggestions to be considered when designing the static ring are proposed through the FEM results.

• Journal of the Korea Institute of Building Construction
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• v.13 no.6
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• pp.579-584
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• 2013

The stable fueling and water supply should be prerequisites to guarantee the operational sustainment of military command post. Meanwhile, in terms of the operational sustainment, it is verified that the current wave-guided below cutoff (WBC) system cannot satisfy the requirement of control associated with water supply and fueling within the command post. In this study, as the dielectric substance can block electromagnetic pulse (EMP), it was tried to identify the shielding effectiveness of the multi WBCs filled with water and diesel for attenuating the EMP effect using experiment based on the MIL STD 188-125-1. According to the experimental results, used water in the experiment show the shielding effectiveness from around 640 MHz frequency because of minerals contained in the water. Furthermore, it was noted that EMP attenuating strength of the WBC filled with diesel was enlarged from around 1,680 MHz frequency. Resultingly, it could be concluded that it is enough to supply stable water and diesel through the multi WBC to block EMP within the military command post for guaranteeing the military operations sustainment.

• Investigative Magnetic Resonance Imaging
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• v.16 no.2
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• pp.103-114
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• 2012

Purpose : In an attempt to further improve the radiofrequency (RF) magnetic ($B_1$) field strength in temporomandibular joint (TMJ) imaging, a 4-channel spiral-loop coil array with RF circuitry was designed and compared with a 4-channel single-loop coil array in terms of $B_1$ field, RF transmit (${B_1}^+$), signal-to-noise ratio (SNR), and applicability to TMJ imaging in 7T MRI. Materials and Methods: The single- and 4-channel spiral-loop coil arrays were constructed based on the electromagnetic (EM) simulation for the investigation of $B_1$ field. To evaluate the computer simulation results, the $B_1$ field and ${B_1}^+$ maps were measured in 7T. Results: In the EM simulation result and MRI study at 7T, the 4-channel spiral-loop coil array found a superior $B_1$ performance and a higher ${B_1}^+$ profile inside the human head as well as a slightly better SNR than the 4-channel single-loop coil array. Conclusion: Although $B_1$ fields are produced under the influence of the dielectric properties of the subject rather than the coil configuration alone at 7T, each RF coil exhibited not only special but also specific characteristics that could make it suited for specific application such as TMJ imaging.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.409-409
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• 2014

Recently hexagonal boron nitride (h-BN), III-V compound of boron and nitrogen with strong covalent $sp^2$ bond, is a 2 dimensional insulating material with a large direct band gap up to 6 eV. Its outstanding properties such as strong mechanical strength, high thermal conductivity, and chemical stability have been reported to be similar or superior to graphene. Because of these excellent properties, h-BN can potentially be used for variety of applications such as dielectric layer, deep UV optoelectronic device, and protective transparent substrate. Ultra flat and charge impurity-free surface of h-BN is also an ideal substrate to maintain electrical properties of 2 dimensional materials such as graphene. To synthesize a single or a few layered h-BN, chemical vapor deposition method (CVD) has been widely used by using an ammonia borane as a precursor. Ammonia borane decomposes into hydrogen (gas), monomeric aminoborane (solid), and borazine (gas) that is used for growing h-BN layer. However, very active monomeric aminoborane forms polymeric aminoborane nanoparticles that are white non-crystalline BN nanoparticles of 50~100 nm in diameter. The presence of these BN nanoparticles following the synthesis has been hampering the implementation of h-BN to various applications. Therefore, it is quite important to grow a clean and high quality h-BN layer free of BN particles without having to introduce complicated process steps. We have demonstrated a synthesis of a high quality h-BN monolayer free of BN nanoparticles in wafer-scale size of $7{\times}7cm^2$ by using CVD method incorporating a simple filter system. The measured results have shown that the filter can effectively remove BN nanoparticles by restricting them from reaching to Cu substrate. Layer thickness of about 0.48 nm measured by AFM, a Raman shift of $1,371{\sim}1,372cm^{-1}$ measured by micro Raman spectroscopy along with optical band gap of 6.06 eV estimated from UV-Vis Spectrophotometer confirm the formation of monolayer h-BN. Quantitative XPS analysis for the ratio of boron and nitrogen and CS-corrected HRTEM image of atomic resolution hexagonal lattices indicate a high quality stoichiometric h-BN. The method presented here provides a promising technique for the synthesis of high quality monolayer h-BN free of BN nanoparticles.

• Journal of the Korean Vacuum Society
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• v.17 no.3
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• pp.175-182
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• 2008

This study is concerned with the evaluation of the corrosion resistance of coated semiconductor equipment parts with various processes. To select the appropriate basis for evaluation, replacement parts were observed during the semiconductor manufacturing process. This study also ran a dry corrosion test using $Al_2O_3$, which is mostly used as a coating material. This test quantitatively measured the efficiency of coated parts. Surface morphology, leakage current and breakdown voltage were also evaluated. This study showed that a dry corrosion process led to the drop of electrical properties, for example, the leakage current increase and the dielectric strength decrease. The surface morphology test displayed that surface damage is largely dependent on the exposure time to corrosive environments. By using the values that changed during the corrosion process, it may be possible to contrive a method to evaluate the efficiency of coated parts with various processes.

• Journal of Sensor Science and Technology
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• v.4 no.3
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• pp.80-88
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• 1995

This paper presents the fabrication of a metal-insulator-metal(MIM) antifuse structure consisting of insulators sandwiched between top electrode, Al, and bottom electrode, TiW and additionally studies on antifuse properties depending on the condition of insulator. The intermetallic insulators, prepared by means of sputter, comprised of silicon oxide and tantalum oxide. In such an antifuse structure, silicon oxide layer is utilized to decrease the leakage current and tantalum oxide layer, of which the dielectric strength is lower than that of silicon oxide, is also utilized to lower the breakdown voltage near 10V. Finally sufficient low leakage current, below 1nA, and low programming voltage, about 9V, could be obtained in antifuse device comprising $Al/Ta_{2}O_{5}(10nm)/SiO_{2}(10nm)/TiW$ structure and OFF resistance of 3$3.65M{\Omega}$ and ON resistance of $7.26{\Omega}$ could be also obtained. This $Ta_{2}O_{5}/SiO_{2}$ based antifuse structures will be promising for highly reliable programmable device.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.480-480
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• 2008

Vacuum circuit breaker(VCB) is now emerging as an alternative of gas circuit breaker(GCB) which uses SF6 gas as insulating material whose dielectric strength is outstanding. But we have to reduce SF6 gas because SF6 gas is one of greenhouse gas and efforts to reduce greenhouse gas are now trend of the world. Therefore, we can say VCB is the optimal alternative of GCB because vacuum is environmentally friendly. The vacuum interrupter is the core part of VCB to interrupt arcing current. There are mainly two methods to extinguish arc. One is radial magnetic field (RMF) method and the other is axial magnetic field (AMF) method. We deals with RMF method in this paper. Compared with AMP, RMF arc quenching method has different principle to extinguish arc. In case of RMF method, pinch effect is much larger than AMF method. Because of pinch effect RMF type contact electrodes have the single large spot which is severly damaged and melted while AMF type contact electrodes have small and multiple spots which are slightly damaged and melted. To prevent contact electrode being damaged and melted from high temperature-arc, RMF method uses Lorentz force to move arc. In this paper we calculated and compared the arc driving force of two cases and we analyzed the force acting on each part of arc by means of commercial finite element method software Maxwell 3D. They have 3petals and we considered two cases. One is the case when fixed(upper) and movable(lower) contacts are in mirror arrangement (Case 1). The other is the case when one of two contacts (movable contact) is revolved at maximum angle as possible as it can be (Case 2). And at each case above, we analyzed arc driving force at two positions, position 1 is the closest to the center of contact and position 2 is near the edge of petal on fixed contact. As a result we could find that Case 2 generated stronger arc driving force than Case 1 at position 1. But at position 2 Case 1 generated stronger arc driving force than Case 2. This simulation method can contribute to optimizing spiral-type electrode designs in a view of arc driving force.