• Journal of Sensor Science and Technology
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• v.13 no.6
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• pp.417-423
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• 2004

In order to obtain wide-beam characteristics and variable resonant frequency of a ultrasonic transducer for the array source, an electrode of transverse mode piezoelectric vibrator is divided, and an electronic inductance is connected to the divided electrodes. The electronic inductance is made by GIC (General Impedance Converter) circuit. Because the GIC circuit is made of OP-Amps and other passive elements, the value of the inductance can be selected easily. As the results, the electronic inductance is variable in the range from 0.2 mH to 1.2 mH. Using the inductance, the resonance frequency of the transducer can be changed in the range from 73 kHz to 86 kHz. In the directivity of the transducer, it is confirmed that the beam width of the transducer is wider than $80^{\circ}$ at -3 dB in water.

• Corrosion Science and Technology
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• v.3 no.6
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• pp.227-232
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• 2004

The carboxylates as a corrosion inhibitor has been studied by many researchers because of its environmental safety and low depletion rate. However, conventional test methods of inhibitor such as weight loss measurements, linear polarization resistance and corrosion potential monitoring etc., evaluate uniform corrosion of metals. These methods are unable to evaluate crevice-related corrosions, which are encountered in most of heat exchanging facilities. In order to choose the optimum corrosion inhibitor, the appropriate test methods are required to evaluate their performances in service environment. From this point of view, polarization technique was used to evaluate the characteristics of sodium heptanoate on corrosion behavior for carbon steel. Especially a thin film crevice sensor technique were applied to simulate the crevice corrosion in this study. From these experiments, we found that oxygen as an oxidizing agent was required to obtain stable passive film on the metal. Presence of oxygen, however, accelerated crevice corrosion. Potential shift by oxygen depletion and weakened inhibitive film inside the crevice were responsible for such accelerated feature. It is shown that film for corrosion inhibition is a mixture of sodium heptanoate and iron (II) heptanoate as reaction product of iron surface and sodium heptanoate. The iron (II) heptanoate which has been synthesized by reaction of heptanoic acid and ferrous chloride in methanol solution forms bidentate complex.

• The Journal of the Acoustical Society of Korea
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• v.19 no.5
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• pp.84-90
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• 2000

The bearing detection of radiated target noise is very important at underwater acoustic measurement and passive detection. It differs the arrival tines of received signal at each sensor. Therefore, the bearing can be obtained from the time delay. This paper proposes a new algorithm using the RLSL adaptive filter for TDE. The proposed method is particularly attractive when there is a limitation of priori information about the received signal spectra and when the delay is subject to variation. As the simulation results, it is shown that the proposed algorithm has better convergence characteristics and TDE speed, and so that the usefulness of proposed algorithm is confirmed.

• Journal of Institute of Control, Robotics and Systems
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• v.12 no.8
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• pp.746-751
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• 2006

In this paper, we present tracking algorithm for the indoor moving object. We research passive method using a camera and image processing. It had been researched to use dynamic based estimators, such as Kalman Filter, Extended Kalman Filter and Particle Filter for tracking moving object. These algorithm have a good performance on real-time tracking, but they have a limit. If the shape of object is changed or object is located on complex background, they will fail to track them. This problem will need the complicated image processing algorithm. Finally, a large algorithm is made from integration of dynamic based estimator and image processing algorithm. For eliminating this inefficiency problem, image based estimator, Mean-shift Algorithm is suggested. This algorithm is implemented by color histogram. In other words, it decide coordinate of object's center from using probability density of histogram in image. Although shape is changed, this is not disturbed by complex background and can track object. This paper shows the results in real camera system, and decides 3D coordinate using the data from mean-shift algorithm and relationship of real frame and camera frame.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.43 no.7
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• pp.1206-1213
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• 1994

This paper presents the operation principle and design rule of the Rogowski coil which can measure the transient current and describes the calibration and application experimental results for performance evaluation. It is obtained that the response curves of the Robowski coil with the turns of 300 and the passive integrator to sinusoidal input give a good linearity up to the frequency of 500 [kHz] and the current measurement system gaving the Rogowski coil is the frequency bandwidth of 40 [Hz]~700 [kHz]. As an application experiment for the fabricated modeling power transmission line, the impulse current, which limitates the direct lightning return stroke to overhead ground wire, is measured by the Rogowski coil and its fast Fourier transformation is carried out. The equivalent circuit of the Rogowski coil considering the stray capacitances is proposed, and the theoretical analysis is in good agreement with the measurement results. Also, it is found that for high frequency domain the stray capacitance such as a distributed capacitance to the shield and the capacitance between windings of coil should be considered in designing the Rogowski coils since the resonance originates from the stray capacitance and the self-inductance of the Rogowski coil.

• Journal of the Korea Society of Computer and Information
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• v.16 no.3
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• pp.1-7
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• 2011

An attack aircraft such as a fighter needs an accurate location information of a target for the exact air-to-air or air-to-ground attack. In this paper a method is proposed that generates a location information of an air-to-ground target just in use of HMD without the target tracking sensors such as the radar and the FLIR. HMD is an embedded device to induce the seeker header to indicate the direction of a pilot's head. As a simulation result, it is founded that the target location information is able to be generated with a high degree of precision by using of HMD as a passive sensor.

• Journal of Power Electronics
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• v.11 no.5
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• pp.743-750
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• 2011

This article deals with the sensor-less control of a DC Motor via a SEPIC Converter-Full Bridge combination powered through solar panels. We simultaneously regulate, both, the output voltage of the SEPIC-converter to a value larger than the solar panel output voltage, and the shaft angular velocity, in any of the turning senses, so that it tracks a pre-specified constant reference. The main result of our proposed control scheme is an efficient linear controller obtained via Lyapunov. This controller is based on measurements of the converter currents and voltages, and the DC motor armature current. The control law is derived using an exact stabilization error dynamics model, from which a static linear passive feedback control law is derived. All values of the constant references are parameterized in terms of the equilibrium point of the multivariable system: the SEPIC converter desired output voltage, the solar panel output voltage at its Maximun Power Point (MPP), and the DC motor desired constant angular velocity. The switched control realization of the designed average continuous feedback control law is accomplished by means of a, discrete-valued, Pulse Width Modulation (PWM). Experimental results are presented demonstrating the viability of our proposal.

• The Journal of Korea Robotics Society
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• v.1 no.1
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• pp.81-88
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• 2006

Control of a robot manipulator in contact with the environment is usually conducted by the direct feedback control using a force-torque sensor or the indirect impedance control. In these methods, however, the control algorithms become complicated and the performance of position and force control cannot be improved because of the mechanical properties of the passive components. To cope with such problems, redundant actuation has been used to enhance the performance of position control and force control. In this research, a Double Actuator Unit (DAU) is proposed, with which the force control algorithm can be simplified and can make the robot ensure the safety during the external collision. The DAU is composed of two actuators; one controls the position and the other modulates the joint stiffness. Using this unit, it is possible to independently control the position and stiffness. The DAU based on the planetary gears is investigated in this paper. Performance using the DAU is also verified by various experiments. It is shown that the manipulator using this mechanism provides better safety during the impact with the environment by reducing the joint stiffness appropriately on detecting the collision of a manipulator.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.141-141
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• 2019

토양수분은 수문 분석에 있어 매우 중요한 인자 중 하나이며 최근 기후변화로 인한 가뭄, 홍수 및 산불발생과 같은 물 관련 재해 발생에 직 간접적으로 영향을 미치기 때문에 지표 토양수분산정은 매우 중요하다. Sentinel-1 SAR(Synthetic Aperture Radar)는 능동형 위성으로 10m의 공간해상도로 제공되기 때문에 기존의 토양수분 전용위성인 SMOS(Soil Moisure and Ocean Salinity), SMAP(Soil Moisture Active Passive) 및 GCOM-W1(Global Change Observation Mission Water) 등 다르게 고해상도 토양수분 산정이 가능하다. 그러나 Sentinel-1 SAR 센서에서는 고해상도 지표 관측 이미지 자료만 제공하며, 토양수분 자료를 직접적으로 제공하지 않는다. 따라서 본 연구에서는 2018년도 Sentinel-1 A/B IW(Interferometric Wide swath) 모드의 VH(Vertical Transmit - Horizontal Receive) 편파 영상과 Sentinel-1 SAR 위성자료 전처리 도구인 SNAP(Sentinel Application Platform)을 이용하여 후방산란계수를 산정하였으며, 산정된 후 방산란계수와 농촌진흥청에서 제공하는 65개 지점의 실측 TDR(Time Domain Reflectrometry) 토양수분의 관계를 이용하여 회귀모형을 도출 및 토양수분 공간분포를 산정하였다. 비록 불확실성은 어느정도 발생 하였으나, 전체적으로 TDR 관측값과 $10m{\times}10m$ 해상도의 Sentinel-1 SAR 기반 토양수분이 일치하는 경향을 보였다. 본 연구 결과는 수문, 농업, 산림, 재해 등 다양한 분야에 활용될 수 있을 것으로 판단된다.

• Safety and Health at Work
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• v.9 no.4
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• pp.479-485
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• 2018

The aim of this study is to validate an integrated air monitoring approach for assessing airborne formaldehyde (FA) in the workplace. An active sampling by silica gel impregnated with 2,4-dinitrophenylhydrazine, a passive solid phase microextraction technique using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine as on-fiber derivatization reagent, an electrochemical direct-reading monitor, and an enzyme-based badge were evaluated and tested over a range of 0.020-5.12 ppm, using dynamically generated FA air concentrations. Simple linear regression analysis showed the four methods were suitable for evaluating airborne FA. Personal and area samplings in 12 anatomy pathology departments showed that the international occupational exposure limits in the GESTIS database were frequently exceeded. This monitoring approach would allow a fast, easy-to-use, and economical evaluation of both current work practices and eventual changes made to reduce FA vapor concentrations.