• Journal of Electrical Engineering and Technology
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• v.12 no.4
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• pp.1556-1565
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• 2017

This paper depicts the design, implementation and analysis of efficient resonant based wireless power transfer (WPT) technique using three magnetic coupled coils. This work is suitable for mid ranged device due to small form factor while minimizing the loading effect. A multi turned loop size resonator is exploited for both the transmitter and receiver for longer distance. In this paper, class-E power amplifier (class-E PA) is introduced with an optimum power tracking mechanism of WPT system to enhance the power capability at mid-range with a flat gain. A robust method of finding optimum distance is derived with an experimental analysis of the designed system. In this method, the load sensitive issue of WPT is resolved by tuning coupling coefficient at considerable distances. Our designed PA with a drain efficiency of 77.8% for a maximum output of 5W is used with adopted tuning technique that improves the overall WPT system performance by 3 dB at various operating points.

• Smart Structures and Systems
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• v.25 no.4
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• pp.423-432
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• 2020

In this paper, a novel but practical approach named series/parallel multi-sensing technique was proposed to evaluate the bolt looseness in a bolt group. The smart washers (SWs), which were fabricated by embedding a Lead Zirconate Titanate (PZT) transducer into two flat metal rings, were installed to the bolts group. By series connection of SWs, the impedance signals of different bolts can be obtained through only one sweep. Therefore, once the loosening occurred, the shift of different peak frequencies can be used to locate which bolt has loosened. The proposed multi input single output (MISO) damage detection scheme is very suitable for the structural health monitoring (SHM) of joint with a large number of bolts connection. Another notable contribution of this paper is the proposal of 3-dB bandwidth root mean square deviation (3 dB-RMSD) which can quantitatively evaluate the severity of bolt looseness. Compared with the traditional naked-eye observation method, the equivalent circuit based 3-dB bandwidth can accurately define the calculation range of RMSD. An experiment with three bolted connection specimens that installed the SWs was carried out to validate our proposed approach. Experimental result shows that the proposed 3 dB-RMSD based multi-sensing technique can not only identify the loosened bolt but also monitor the severity of bolt looseness.

• Journal of Integrative Natural Science
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• v.10 no.4
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• pp.216-224
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• 2017

In the terrain of the Korean peninsula, mountainous and flat lands are complexly distributed in small areas. Therefore, local severe weather develops and disappears in a short time due to the influence of the terrain. Particularly in the case of local severe weather with heavy wind that has the greatest influence on aviation meteorology, the scale is very small, and it occurs and disappears in a short time, so it is impossible to predict with fragmentary data alone. So, we use weather radar to detect and predict local severe weather. However, due to the development of wireless communication services and the rapid increase of wireless devices, radio wave jamming and interference problems occur. In this research, we confirmed through the cases that when the radio interference echo which is one of the non-precipitation echoes that occur during the operation of the weather radar is displayed in the image, its form and shape are shown in a long bar shape, and have a strong dBZ. We also found the cause of the interference through the radio tracking process, and solved through the frequency channel negotiation and AP output minimizing. The more wireless devices increase as information communication technology develops in the future, the more emphasized the problem of radio wave interference will be, and we must make the radio interference eliminated through the development of the radio interference cancellation algorithm.

• Journal of the Korean Society of Tobacco Science
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• v.21 no.1
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• pp.5-9
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• 1999

In recent years, the line of increase in policy on tobacco production triggered a rise in the loading volume per bulk curing barn, and manufacturers boosted the output of their blowers in order to prevent dirty leaves in the process of curing. for this reason, we studied the effect of the reducing air flow in bulk curing chamber from the color fixing stage to the stem drying stage of flue curing process on physical properties of cured leaves. The control of air flow was composed of the reducing air velocity of blower by means of a voltage regulator (slidac), and condition before color fixing stage was all the same with the conventional curing method. As a result, an effectiveness of improvement in the physical properties of cured leaves were observed. The leaves cured by this method were somewhat orange in color of upper stalk position, better bodied, and less brittle compared with the leaves produced by conventional curing. However, the leaves cured by this method had a little sharpness and harshness. As to the physical properties, there was decreased in occurrence of flat leaves than that of conventional ones. On the other hand, in case of reducing air flow during the curing process, increase of price per kg reached to about 5 % compared with those of conventional curing method.

• The KIPS Transactions:PartC
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• v.12C no.7 s.103
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• pp.1025-1030
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• 2005

Cooperative communications among users in multiple access wireless environments is an efficient way to obtain the powerful benefits of multi-antenna systems without the demand for physical arrays. This paper proposes a solution to optimize the weights of partnering users' signals for the minimum error probability at the output of maximum likelihood (ML) detector under the transmit power constraints by taking advantage of channel state information (CSI) feedback from the receiver to the transmitter. Simulation programs are also established to evaluate the performance of the system under flat Rayleigh fading channel plus AWGN (Additive White Gaussian Noise).

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2000.11a
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• pp.150-153
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• 2000

In this paper, we have designed a 2 stage MMIC power amplifier which has flat gains of in-band and reasonable out-band cutoff characteristics using 0.5$\mu\textrm{m}$ MESFET libra교 of ETRI. For the 1st stave, we obtaind P$_{1dB}$ of 9.2 dBm and gain 10.8 dB using 6 finger D-MESFET and P$_{1dB}$ of 18.4 dBm and gain of 10.8 dB using 14 finger D-MESFET for the 2nd stage, which is power matched using LIBRA's embedded TUNER. Also in-band gain flatness and out-band cutoff characteristics are obtained by attaching LC tank in the output matching circuit. The designed 2 stage MMIC power amplifier has bandwidth of 0.95～2.8 GHz, gain of 20 dB and P$_{1dB}$of 17.2 dBm. Especially gain flatness of $\pm$0.8dB was obtained in 1.8～2.5 GHz frequency ranges. And chip size is 1.4$\times$1.4 mm..4 mm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.10a
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• pp.353-356
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• 1997

Hydraulically driven manipulators are superior to electrically driven ones in the power density and electrical insulation. But an electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and this parameter fluctuations are greater than those of electrically driven manipulator. So this is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous field task such as the maintenance task of high voltage active electric line or the automatic excavation task by hydraulic excavator. In this report, we propose robust force control algorithm, which can be applied to there real field task such as the construction field, nuclear plant and so on. Proposed force controller has the same structure as that of disturbance observe for position control. The difference between force and position disturbance observer is that the input and output of disturbance observer are forces in the case force disturbance observer and the plant varies much compared to the case of position control. In the design of force disturbance observer, generalized plant is derived and the stabilized filter is designed by H infinity control theory to ensure the robuts t stability even though the stiffness of environment changes from sponge to steel, and the contact surface also changes from flat to round shape. Experimental results show that highly robust force tracking by a 6-link electro-hydraulic manipulator could be achieved under various environment conditions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.2
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• pp.111-118
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• 2020

Recently, bioenergy research using microalgae, one of the most promising biofuel sources, has attracted much attention. Cell disruption, which can be classified as physical or chemical, is essential to extract functional ingredients from microalgae. In this study, we investigated the cell disruption efficiency of Chlorella sp. using low-frequency non-focused ultrasound (LFNFU). This is a continuously physical method that is superior to chemical methods with respect to environmental friendliness and low processing cost. A flat panel photobioreactor was employed to cultivate Chlorella sp. and its growth curve was fitted both with Logistic and Gompertz models. The temporal change in cell reduction by cell disruption using LFNFU was fitted with a Logistic model. The experimental conditions that were investigated were the initial concentration of microalgal cells, relative amplitude of output ultrasound waves, processing volume of microalgal cells, and initial pH value. The optimal conditions for the most efficient cell disruption were determined through the various tests.

• Membrane and Water Treatment
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• v.8 no.6
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• pp.529-541
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• 2017

A multi-effect air gap membrane distillation (ME-AGMD) module for pesticide wastewater treatment is studied with internal heat recovery, sensible heat of brine recovery, number of stages and the use of fresh feed as cooling water in a single module is implemented in this study. A flat sheet polytetrafluroethylene (PTFE) membrane was used in the 4-stage ME-AGMD module. The maximum value of permeate flux could reach $38.62L/m^2h$ at feed -coolant water temperature difference about $52^{\circ}C$. The performance parameter of the module like, specific energy consumption and gain output ratio (GOR) was investigated for the module with and without heat recovery. Also, the module performance was characterized with respect to the separation efficiency of several important water quality parameters. The removal efficiency of the module was found to be >98.8% irrespective water quality parameters. During the experiment the membrane fouling was caused due to the deposition of the salt/crystal on the membrane surface. The membrane fouling was controlled by membrane module washing cycle 9 h and also by acidification of the feed water (pH=4) using 0.1M HCl solution.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1678-1688
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• 2016

This paper presents a capacitive power transfer (CPT) system using a Class-E resonant inverter. A Class-E resonant inverter is chosen because of its ability to perform DC-to-AC inversion efficiently while significantly reducing switching losses. The proposed CPT system consists of an efficient Class-E resonant inverter and capacitive coupling formed by two flat rectangular transmitter and receiver plates. To understand CPT behavior, we study the effects of various coupling distances on output power performance. The proposed design is verified through lab experiments with a nominal operating frequency of 1 MHz and 0.25 mm coupling gap. An efficiency of 96.3% is achieved. A simple frequency tracking unit is also proposed to tune the operating frequency in response to changes in the coupling gap. With this resonant frequency tracking unit, the efficiency of the proposed CPT system can be maintained within 96.3%-91% for the coupling gap range of 0.25-2 mm.