• Proceedings of the KIEE Conference
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• 2007.10a
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• pp.483-484
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• 2007

In this paper, we describe a chip design technique for instrumentation amplifier using a nested-chopping technique. Conventional chopping technique uses a pair of chopper, but nested chopping technique uses two pairs of chopper to reduce residual offset and 1/f noise. The inner chopper pair removes the 1/f noise, while the outer chopper pair reduces the residual offset. Our instrumentation amplifier using a nested chopping technique has residual offset under 100 nV. We also implement very low frequency filter. Since this filter needs very large RC time constant, we use a technique named 'diode connected PMOS' to increase R with small die area. The total power consumption is 3.1 mW at the supply voltage of 3.3V with the 0.35um general CMOS technology. The die area of implemented chip was $530um{\times}300um$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.6
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• pp.531-537
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• 2006

A micromachined piezoelectric microspeaker was fabricated with a highly c-axis oriented ZnO thin film on a silicon-nitride film having compressive residual stress. When it was measured 3 mm away from the microspeaker in open field, the largest sound pressure level produced by the fabricated microspeaker was about 91 dB at around 2.9 kHz for the applied voltage of $6\;V_{peak-to-peak}$. The key technologies to these successful results were as follows: (1) the usage of a wrinkled diaphragm caused by the high compressive residual stress of silicon-nitride thin film, (2) the usage of the highly c-axis oriented ZnO thin film.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.617-618
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• 2012

Recently as the inactive response characteristics of the existing RCD(Residual Current protective Device) used on low voltage power distribution system, so control of overload and electric short circuit faults, major causes of electrical fires, are not enough. Therefore, this paper is proposed a prevention apparatus using neutral line voltage and semiconductor switching devices for the prevention of electrical disasters in low voltage power distribution system caused by overload or electric short circuit faults. The proposed prevention apparatus confirms the excellent characteristics in response velocity and accuracy in comparison with the conventional circuit breaker(RCD) through various operation performance analysis.

• Structural Engineering and Mechanics
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• v.76 no.5
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• pp.619-629
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• 2020

In current study, surface/interface effects for pull-in voltage and viscous fluid velocity effects on dimensionless natural frequency (DNF) of fluid-conveying piezoelectric nanosensor (FCPENS) subjected to direct electrostatic voltage DC with nonlinear excitation, harmonic force and also viscoelastic foundation (visco-pasternak medium and structural damping) are investigated using Gurtin-Murdoch surface/interface (GMSIT) theory. For this analysis, Hamilton's principles, the assumed mode method combined with Lagrange-Euler's are used for the governing equations and boundary conditions. The effects of surface/interface parameters of FCPENS such as Lame's constants (λI,S, μI,S), residual stress (τ0I,S), piezoelectric constants (e31psk,e32psk) and mass density (ρI,S) are considered for analysis of dimensionless natural frequency respect to viscous fluid velocity u̅f and pull-in voltage V̅DC.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.6
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• pp.876-880
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• 2013

The major causes of electrical fire are classified to short circuit fault, overload fault, electric leakage and electric contact failure. The principal factor of the fire is electric arc or spark accompanied with such electric faults. Earth Leakage Circuit Breaker (ELB) and Molded_case Circuit Breaker (MCCB), that is, Residual Current Protective Devices (RCDs) used on low voltage distribution lines cut off earth leakage and overload, but the RCD can not cut off electric arc or spark to be a major factor of electrical fire. As the RCDs which are applied in low voltage distribution panel are prescribed to rated breaking time about 30[ms] (KS C 4613), the RCDs can't perceive to the periodic electric arc or spark of more short wavelength level. To improve such problems, this paper studies on an arc fault circuit interrupter (AFCI) using the distorted voltage wave in electric arc faults. The proposed voltage sensing type AFCI is an electrical fire prevention apparatus of new conception that operates a circuit breaker with sensing the instantaneous voltage drop of line voltage at electrical faults occurrence. The proposed AFCI is composed of control circuit topology using some semiconductor switching devices. Some experimental tests of the proposed AFCI confirm practicality and the validity of the analytical results.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.8
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• pp.22-29
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• 2006

According to the recent revision of KS on the basis of the IEC, equipotential grounding systems has been come into focus and the use of surge protective devices(SPD) has been increased radically in order to operate the power system stably. $Z_nO$ varistor with non-linear resistance, which has an outstanding voltage-current(V-I) characteristic, is mainly used in power system to limit surge voltage and divert surge current. $Z_nO$ varistors are packaged several types based on the circuit assembly to be connected to a.c. power line. When the user assemble the $Z_nO$ varistors into parallel or series circuit package, there are my things to be taken into consideration including functions and thermal stability because they are directly related to the safety. We compare stabilities of each assembly type by measuring residual voltage, discharge current, leakage current and surface temperature concerned to the protection performances between a single device with a 40[kA] of current capacity and parallel or series circuits type of varistor package.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.489-494
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• 2001

In this thesis, the microstructure and electrical properties of ZnO varistors were investigated according to ZnO varistors with various formulation. A∼E's ZnO varistor ceramics were exhibited good density, 95% of theory density and low porosity, 5%, wholly. The average grain size of A-E's ZnO varistor ceramics exhibited 11.89$\mu\textrm{m}$, 13.57$\mu\textrm{m}$, 15.44$\mu\textrm{m}$, 11.92$\mu\textrm{m}$, 12.47$\mu\textrm{m}$, respectively. Grain size of C's ZnO varistor is larger and grain size of A and D's are smaller than other varistors. In the microstructure, A∼E's ZnO varistor ceramics sintered at l130$^{\circ}C$ was consisted of ZnO grain(ZnO), spinel phase(Zn$\sub$2.33/Sb$\sub$0.67/O$_4$), Bi-rich Phase(Bi$_2$O$_3$) and inergranular phase, wholly. Reference voltage of A∼E's ZnO varistor sintered at 1130$^{\circ}C$ decreased in order D, E > A > B > C's ZnO varistors. Nonlinear exponent of varistors exhibited high characteristics, above 30, wholly. Consequently, C's ZnO varistor exhibited good nonlinear exponent, 68. Lightning impulse residual voltage of A, B, C and E's ZnO varistors suited standard characteristics, below 12kV at current of 5kA.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.157-163
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• 2004

Dependence of residual compressive stress of diamond-like carbon (DLC) films on relative humidity was investigated. Polymeric, graphitic and diamond-like carbon films were prepared by r.f.-PACVD using methane or benzene with the negative self bias voltage of the substrate ranging from -100 to -800 V. In-situ measurements of the residual stress were carried out in an environment chamber where the relative humidity was varied from 10％ to 90％. In dense DLC film of high residual compressive stress and hardness, we could not observe any change in the residual compressive stress with relative humidity. However, in the cases of graphitic and polymeric DLC films, abrupt change in the residual stress occurred by changing the relative humidity. The quantity of the stress change was inversely proportional to the film thickness, which means that the stress change with humidity is not due to the penetration of the water molecule into the film structure, but due to surface interaction between water molecules and film surface.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.1
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• pp.72-77
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• 2015

When connecting 6 lead wires from stator windings to the terminals of 3 phase induction motors for Y or ${\triangle}$ connection, it is feared that the polarities of windings could be reversed each other if the wire tags are lost or erased, resulting in inadmissibly high current to motors in case of starting. To protect motors against such situations, some test procedures are necessary during wire connection which need to be easy ways to electricians without particular tools except a general multi-tester and with less time-consuming in the field. This study focuses on a test measure to satisfy these requirements which is able to provide them a convenient procedure for winding polarity discrimination considering the field condition. Here, the proposed measure utilizes the residual magnetism of the rotor and checks the indication of voltage or current at windings which are induced by the residual flux of rotor when rotating it by hands with 3 stator windings connected in the form of I connection. Principle characteristics and experiment results for this method are analyzed in the view of the effectiveness and applicability for the winding polarity discrimination.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.612-614
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• 1997

Silicon based micro mirror array is a highly efficient component for use in optical applications such as adaptive optical systems and optical correlators. A micro mirror array designed, fabricated and tested here is consisted of $5{\times}5$ single layer polysilicon, electrostatically driven actuators. In this paper, deflection characteristics and pull-in behavior of the actuators for analog control was studied and particularly, the influence of the residual stress in flexure beams for the restorative force of actuators was considered. The springs are modeled as a residual stress-free spring and a spring with residual stress. In calculation, a mirror with the residual stress-free springs has 30.3N/m spring constant and 31.1V pull-in voltage. On the other hand, a mirror with the stressed springs has 23.6N/m and 27.4V respectively. The experimental result, which is 20.5N/m and 25.5V, shows that the stressed springs ore well modeled.