• Tribology and Lubricants
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• v.37 no.2
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• pp.41-47
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• 2021

An experimental device was developed for analysis of hydraulic oil characteristics with dielectric constant sensors. Online analysis is the most effective method of the three methods used for analyzing lubricant oils. This is because it can monitor the machine condition effectively using oil sensors in real time without requiring excellent analysis skill and eliminates human errors. Determining the oil quality usually requires complex laboratory equipment for measuring factors such as density, viscosity, base number, acid number, water content, additive, and wear debris. However, the electric constant is another indicator of oil quality that can be measured on-site. The electric constant is the ratio of the capacitance of a capacitor using that material as a dielectric, compared with a similar capacitor that has a vacuum as its dielectric. The electric constant affects the factors such as the base oil, additive, temperature, electric field frequency, water content, and contaminants. In this study, the tendency of the electric constant is investigated with a variation of temperature, water content, and dust weight. The experimental device can control working temperature and mix the contaminants with oil. A machine condition monitoring program developed to analyze hydraulic oil is described. This program provides graph and digital values with variation of time. Moreover, it includes an alarm system for when the oil condition is bad.

• Smart Structures and Systems
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• v.16 no.6
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• pp.1091-1105
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• 2015

Piezoelectric coefficient and dielectric constant of PZT-5H vary with electric field. In this work, variations of these coefficients with electric field are included in finite element modelling of a cantilevered plate instrumented with piezoelectric patches. Finite element model is reduced using modal truncation and then converted into state-space. First three modal displacements and velocities are estimated using Kalman observer. Negative first modal velocity feedback is used to control the vibrations of the smart plate. Three cases are considered v.i.z case 1: in which variation of piezoelectric coefficient and dielectric constant with electric field is not considered in finite element model and not considered in Kalman observer, case 2: in which variation of piezoelectric coefficient and dielectric constant with electric field is considered in finite element model and not considered in Kalman observer and case 3: in which variation of piezoelectric coefficient and dielectric constant with electric field is considered in finite element model as well as in Kalman observer. Simulation results show that appreciable amount of change would appear if variation of piezoelectric coefficient and dielectric constant with r.m.s. value of electric field is considered.

• Journal of Environmental Science International
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• v.13 no.2
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• pp.149-159
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• 2004

In the removal of heavy metals from the mine deposit using electrokinetic processes, the effects of operation under both constant current and constant potential conditions were estimated. The results of soil pH distributions for DDW-20 V and DDW-100 mA cases after the electrokinetic remediation tests were observed. In the former case, soil pH was not much changed and kept to almost constant value just little higher than initial soil pH of 3.52, except near the cathode, which was about pH 5. While in the latter case, soil pHs of anode and the cathode regions were less than pH 3 and about 6, respectively. The electroosmotic flow to the cathode increased rapidly till 10 hrs and decreased steadily and then maintained to constant rate until the end of operation at constant current condition. Electric potential gradient was continuously increased to as much as 34.375 V/cm. At the steady state, values of the apparent electric conductivity for DDW-20 V and DDW-100 mA were around 40 ${\mu}\textrm{s}$/cm and 30 ${\mu}\textrm{s}$/cm, respectively. In the DDW-100mA test, Cu, Cd, and Zn except Pb showed the tendency of moving toward the cathode. While in the DDW-20 V case, it was observed that Cu, Zn, and Pb except Cd were not moved to any directions. The results of the tests demonstrated that the electrokinetic soil remediation process could be operated better under constant current condition than constant electric potential condition.

• Proceedings of the KIEE Conference
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• 1999.07c
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• pp.1331-1333
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• 1999

In Haenam-Cheju HVDC link several modes of operations and controls are provided, which are constant frequency control, constant power control and constant current control. This paper describes basic control action of converters under three control modes and shows EMTDC simulation results at ground fault and steady state respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.05e
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• pp.57-60
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• 2003

This paper explained electric field distribution's characteristics of dielectric pellets with a shape of ball to voltage. When discharge gap of electrode and input voltage are each 20[mm], 10000[V], the electric field simulation results of dielectric pellets with a shape of ball with relative dielectric constant of several kind measured stronger electric field near electric pellets with a shape of ball of ${\phi}5$[mm] than $1{\phi}$[mm] and $3.33{\phi}$[mm] at atmosphere. And the maximum electric field of dielectric pellets with a shape of ball over ${\phi}5$[mm] increased about 5[%] to maximum electric field of electric pellets with a shape of ball ${\phi}5$[mm]. And the result of simulation, when relative dielectric constant of dielectric pellets with a shape of ball is 100, it measured about 90[%] of maximum electric field of dielectric pellets with a shape of ball with relative dielectric constant over 1000.

• Proceedings of the KIEE Conference
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• 2003.11c
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• pp.720-723
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• 2003

Electric stimulation of teeth is used for assessing pulp vitality. Because of very high and wide range of impedance of the enamel, electric pulp testers use high voltage, high output impedance and alternative current source. Most pulp testers use voltage stimulation method and their stimulating threshold levels significantly depend on each individual. Therefore, a constant current stimulator is necessary to minimize the effect of wide variation in enamel thickness. In this study, we constructed a constant current source type of pulp tester with the maximum current of 150 uA.

• Korean Chemical Engineering Research
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• v.59 no.2
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• pp.247-253
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• 2021

Electrocoalescence is an active technique in petroleum industry, formation of raindrop in cloud, and digital microfluidics. In the present work, electrocoalescence of two droplets under the constant electric potential in air was studied. Through this experiment, we found that the electrocoalescence process could be divided three phases; deformation, formation of liquid bridge, and merging. And the condition for formation of liquid bridge between two droplets was obtained. For the connection of experimental result in constant potential condition with general case in constant charge condition, relationship of charge and potential difference was deduced by numerical computation. In high electric potential case, flat interfaces after recoiling were observed. It was interpreted through a numerical simulation of electric field.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.10
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• pp.799-804
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• 2018

In this paper, a method for measuring the dielectric constant of a planar dielectric substrate using the free space material constant measurement method in a general measurement environment is proposed. Two horn antennas and a network analyzer were used for S-parameter measurement and the transmission and reflection coefficients of a planar dielectric substrate were calculated from the measurement results. To obtain a reliable dielectric constant in a low-precision-measurement environment, only the magnitude of the transmission coefficient, which has a small error due to the measurement environment, is used for dielectric constant estimation. Finally, the dielectric constant is determined by comparing the measured results at different frequencies.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.203-206
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• 2004

To analysis the electrokinetic phenomena in the ground dependent on the way of applied electric power, such as constant current and constant voltage, the governing equations are derived considering advection, diffusion, ionmigration, and then they were formulated using by finite difference method. The developed program is verified by comparing the tested and predicted results reported in present papers. The results indicate that the slightly small electrical potential is predicted for constant current and for constant voltage pH near to the cathode was small than the test results. But the other predictions including the final suction, pH of electrolyte and cumulative flow are similar to the test results and predictions.

• Journal of the Korean Ceramic Society
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• v.26 no.6
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• pp.802-810
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• 1989

The temperature dependence of piezoelectric strain constant and the electric field induced strain are investigated as a function of PT in 0.5[xPT-(1-x)PZ]-0.5PNN ceramics. The piezoelectric strain constant d31 has the highest value(360$\times$10-12m/V) at PT=0.68. The temperature dependence of d31 is improved as Curie temperature of sample is increased, and the electric field dependence of induced strain is decreased with the coercive field increased. This ceramic system shows both piezoelectric effect and electrostrictive effect under the applied electric field. The piezoelectric of tetragonal phase is higher than that of rhombohedral phase, and the magnitude of electrostrictive constant is appeared in the order of morphotropic, rhombohedral and tetragonal phase. The piezoelectric strain constant with applied field must be considered theelectrostrictive effect due to 90$^{\circ}$domain wall displacements, and the displacement of bimorph type actuator agrees with the calulated value well.