• Journal of Sensor Science and Technology
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• v.27 no.4
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• pp.269-274
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• 2018

High-sensitivity signal-to-noise ratio (SNR) microphones are essentially required for a broad range of automatic speech recognition applications. Piezoelectric microphones have several advantages compared to conventional capacitor microphones including high stiffness and high SNR. In this study, we designed a new piezoelectric membrane structure by using the finite elements method (FEM) and an optimization technique to improve the sensitivity of the transducer, which has a high-quality AlN piezoelectric thin film. The simulation demonstrated that the sensitivity critically depends on the inner radius of the top electrode, the outer radius of the membrane, and the thickness of the piezoelectric film in the microphone. The optimized piezoelectric transducer structure showed a much higher sensitivity than that of the conventional piezoelectric transducer structure. This study provides a visible path to realize micro-scale high-sensitivity piezoelectric microphones that have a simple manufacturing process, wide range of frequency and low DC bias voltage.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.52 no.2
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• pp.74-80
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• 2003

In this paper, a robust two-degree-of-freedom(TDF) the speed control system using $H_{\infty}$ optimization method and real genetic algorithm is proposed for the robust stability and the robust performance in dc servo motor system. This control system composed of feedback and feedforward controller. The feedback(FB) controller with $H_{\infty}$ optimization method is designed for real genetic algorithm that is model matching problem using mixed sensitivity function. The feedforward(FF) controller with $H_{\infty}$optimization method is minimized the error between transfer function of the optimal model and the overall transfer function. The proposed robust two-degree-of-freedom speed control system is simulated to the dc servo motor. By the simulation, feedback controller can obtain the robust stability property and feedforward controller can obtain the robust performance property under modelling error. The performance of the dc servo motor is analyzed by the experiment setting. The validity of the proposed method is verified through being compared with pid(proportional integrated differential)control system design method for the dc servo motor.

• Journal of Electrical Engineering and Technology
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• v.4 no.3
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• pp.370-376
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• 2009

The influence of magnetic saturation on electromagnetic field distribution in both a permanent-magnet direct-current (PMDC) motor and a field-winding (wound-field) direct-current (FWDC) motor, with the same output mechanical power, has been studied. In this paper, an approximate analytical method and time-stepping Finite Element Method (FEM) are used for prediction of Back-EMF and electromagnetic torque. No-load and rotor-lucked conditions, according to experimental measurements, and the FEM and analytical method studies of the motors have been considered. A sensitivity analysis has also been successfully accomplished on the major design parameters that affect motor performance. At last, these two DC motors are compared, in spite of their differences, on the basis of measured output characteristics.

• Proceedings of the KIEE Conference
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• 1988.11a
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• pp.414-417
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• 1988

This paper presents a study on the operation of a digitally controlled DC servo motor drive at low speed region. Two schemes aiming to improve the transient behavior of the speed control system are considered. The first scheme is the current positive feedback scheme to reduce the sensitivity of the system with respect to the load torque variations. The second one is the speed observer based on a motor model. Finally, the two schemes are studied by simulation and then verified experimetally using a prototype DC motor drive.

• Proceedings of the KIEE Conference
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• 2000.07a
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• pp.373-375
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• 2000

By DC load flow approximation, we analyzed marginal cost that is the important factor of price signal for network congestion management and expressed as a function of load. In network congestion, a large scale electric network is partitioned into subnetwork to provide a effetive price signal through zonal pricing. We propose a new network partition technique using marginal cost sensitivity with a variety of load consumption.

• Interaction and multiscale mechanics
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• v.3 no.3
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• pp.257-266
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• 2010

A novel resonance based proximity DC current sensor is proposed. The sensor consists of a piezo sensed and actuated cantilever beam with a permanent magnet mounted at its free end. When the sensor is placed in proximity to a wire carrying DC current, resonant frequency of the beam changes with change in current. This change in resonant frequency is used to determine the current through the wire. The structure is simulated in micro and meso scale using COMSOL Multi physics software and the sensor is found to be linear with good sensitivity.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.12
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• pp.1045-1053
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• 2002

This paper describes characteristics of the developed current sensor by means of two identically wound magnetic cores forming a clamp like for measurement of a low DC, or AC current. This sensor consists of peak value detectors, a sensor of an electrically compensated current transformer type, a reference alternating voltage, Precision measuring circuits to measure the output signals of sensor with harmonics, and can be measured up to 2 A at DC, or AC current. The current sensor shows a measurement accuracy of less than 0.3% in the frequency range 40 Hz - 10 HBz. The resolution and sensitivity of the sensor were evaluated 0.1 mA and 10 mV/mA, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.04a
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• pp.11-13
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• 2002

The performance of DC current sensor based on giant magnetoimpedance (GMI) effect in amorphous ribbon has been tested. The ribbon after field annealing shows the maximum GMI ratio of 30 % at 100 kHz measuring frequency. In the sensor element of sample wound the circular form, GMI ratio and sensitivity are decreased due to internal stress. The sensor voltage output increases with applied DC current up to 1 A with a good linearity, of which direction can be known due to asymmetric characteristics.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.4
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• pp.735-741
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• 2009

This paper presents an algorithm for the permanent magnet shape optimization of a large scale BLDC(Brushless DC) motor to minimize the cogging torque. A response surface method (RSM) using multiquadric radial basis function is employed to interpolate the objective function in design parameter space. In order to get a reasonable response surface with relatively small number of sampling data points, additional sampling points are added on the basis of design sensitivity analysis computed by using FEM. The algorithm has 2 stages: the first stage is to determine the PM arc angle, and the 2nd stage is to optimize the magnet pole shape. The developed algorithm is applied to a 5MW BLDC motor to get a minimum cogging torque. After 3 iterations with 4 design parameters, the cogging torque is reduced to 13.2% of the initial one.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.2
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• pp.315-320
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• 2001

This paper describes a rotation-type field mill to measure the electric field intensity caused by thunderclouds on the ground level. The field mill developed is consisted of two isolated electrode vanes, a grounded stator and a rotor. To develop a high sensitive field mill, the principles and design rules of a rotation-type field mill are studied. Also, two types of calibration system, such as a cylindrical guard electrodes and a parallel-plate electrodes, are proposed to determine the sensitivity and frequency bandwidth of the field mill. From the calibration experiment, the frequency bandwidth and the sensitivity of the field mill are DC ~ 200 [Hz] and 0.267 [mV/V/m], respectively. Therefore, it can measure the electric field intensity from 73 [V/m] to 18.7 [㎸/m].