• Journal of Sensor Science and Technology
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• v.28 no.5
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• pp.311-317
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• 2019

Rotating devices are commonly installed in power plants and factories. This study proposes a self-powered sensor node that is powered by converting the vibration energy of a rotating device into electrical energy. The self-powered sensor consists of a piezoelectric harvester for self-power generation, a rectifier circuit to rectify the AC signal, a sensor unit for measuring the vibration frequency, and a circuit to control the light emitting diode (LED) lighting. The frequency of the vibration source was measured using a piezoelectric-cantilever-type vibration frequency sensor. A green LED was illuminated when the measured frequency was within the normal range. The power generated by the piezoelectric harvester was determined, and the LED operation was assessed in terms of the vibration frequency. The piezoelectric harvester was found to generate a power of 3.061 mW or greater at a vibration acceleration of 1.2 g ($1g=9.8m/s^2$) and vibration frequencies between 117 and 123 Hz. Notably, the power generated was 4.099 mW at 122 Hz. As such, our self-powered sensor node can be used as a module for monitoring rotating devices, because it can convert vibration energy into electrical energy when installed on rotating devices such as air compressors.

• Journal of Soil and Groundwater Environment
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• v.25 no.3
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• pp.23-31
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• 2020

The performance of a downward-irradiation sonoreactor was investigated using calorimetry, KI dosimetry, luminol (Sonochemiluminescence, SCL) method, and aluminium foil erosion method as one of the basic steps for the optimal design of downward-irradiation sonoreactors. The applied frequency was 28 kHz and the input electrical power was 280 - 300 W. The liquid height, from the reactor bottom to the transducer module surface, ranged from 1λ (53.6 mm) to 2λ (107.1 mm). For various liquid heights, the magnitude of calorimetric power and the mass of cavitation-generated I₃^- ion varied significantly. It was found that the additional application of mechanical mixing resulted in higher sonochemical activity, especially in the cavitational active zone, which was induced by violent liquid flow in the reactor. In aluminium foil erosion tests, it was found that less ultrasound energy reached the bottom of the reactor due to the violent liquid flow and no significant sonophysical effect was observed for higher mixing rate conditions (100 and 200 rpm).

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.7
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• pp.760-770
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• 2013

Detecting grammatical errors from a text is a long-history application. In this paper, we compare the performance of two grammatical error detection techniques, which are implemented as a sub-module of an automated English scoring system. One is to use a full syntactic parser, which has not only grammatical rules but also extra-grammatical rules in order to detect syntactic errors while paring. The other one is to use a finite state machine which can identify an error covering a small range of an input. In order to compare the two approaches, grammatical errors are divided into three parts; the first one is grammatical error that can be handled by both approaches, and the second one is errors that can be handled by only a full parser, and the last one is errors that can be done only in a finite state machine. By doing this, we can figure out the strength and the weakness of each approach. The evaluation results show that a full parsing approach can detect more errors than a finite state machine can, while the accuracy of the former is lower than that of the latter. We can conclude that a full parser is suitable for detecting grammatical errors with a long distance dependency, whereas a finite state machine works well on sentences with multiple grammatical errors.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2167-2173
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• 2000

The HANARO (High-flux Advanced Neutron Application Reactor) has operated since 1995. The Cold Neutron(CN) hole was implanted in the reflector tank from the design stage. Before a vacuum chamber and a moderator cell for the cold neutron source are installed into the CN hole, it is necessary to measure the exact size of the inside diameter and thickness of the CN hole to prevent the interference problem. Due to inaccessibility and high radiation field in the CN hole, a mechanical measurement method is not permitted. The immersion ultrasonic technique is considered as the best method to measure the thickness and the diameter. The 4 axis manipulator of the 2 channel of a sensor module was fabricated. The transducer of 10 MHz results in 0.03 nun of resolution. The inside diameter and thickness for 550 points of the CN hole were measured using 2 channel ultrasonic sensors. The results showed that the thickness is in the range of 13-6.7 mm and inside diameter is in the range of o 156-165. These data will be a good reference in the design of a cold neutron source facility.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1658-1660
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• 2000

Simple signs were usually exchanged as the means of underwater communications. As people recently, need more informations for underwater activities, necessities of underwater communication systems exchanging hunman voice are increased. The purpose of this paper is understanding the ordinary characteristics of underwater communication and investigating the necessary conditions for a good underwater communication system by making a basic communication module. The experiment is achieved by applying AM (Amplitude Modulation) which is mainly used for the underwater communication systems and using common ultrasonic transducers. Ultrasonic transducers usually have narrow bandwidth for transducing electrical energy to mechanical energy. For improvement of sound reconstruction, transducers need more bandwidth which covers voice's frequency range, and goof linearity characteristics in this frequency range. As underwater transmissions have many factors to distort signals. Amplitude Modulation is not a proper way for underwater communications. Using digital signal by sampling human voice should be a good way for this systems, because digital communication simplify transmitting signals.

• Journal of Sensor Science and Technology
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• v.27 no.6
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• pp.380-385
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• 2018

Recently, interest in baseball has been increasing as the level of international baseball games, the popularity of domestic leagues, and the number of players entering the MLB has increased. In this paper, we propose a pitching system that can be applied to both professional and amateur baseball. The pitching system consists of a control module using MSB764T PLC, a pitching mechanism including AC motors and a ball feed rail, an HMI using the CHA-070WR model, inverter, etc. To pitch the breaking balls, the two AC motors each use an inverter to independently control the speed. The implemented pitching system was experimented on, investigating ball speed and ball movement according to RPM using the BUSHNELL Velocity Speed Gun. Experimental results on ball speed are similar to the theoretical data and the measured data. From the experimental data, it is confirmed that the damping coefficient value for the pitching ball is about 0.98. In the case of the breaking ball, the larger the difference between the speeds on the sides of the ball and the faster the ball speed, the larger the bending degree.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.1
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• pp.1-9
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• 2009

In this paper, a 2.4 GHz doppler radar system consisting of a doppler radar sensor and a baseband module were designed to detect heart beat and respiration signal without direct skin contact. The doppler radar system emits RF signal of 2.4 GHz toward human chest, and then detects phase modulation of the reflected signal so as to investigate cardiopulmonary activities. The heartbeat and respiration signals acquired from I/Q channels of the doppler radar system are applied to the pre-processing circuit, the amplification circuit, and the offset circuit of the baseband module. The designed system was tested on mouse, rabbit and mankind, which have different range of heart rates and respiration signals, to evaluate detection accuracy of the system. ECG acquisition system and respiration transducer were used to generate the reference signal. In our experiments, a performance of detection were found to be high in the case that the subject stays still. In this paper, we confirmed that non-contact heart beat and respiration detection using the doppler radar has the possibility and limitation according to distance, cardiopulmonary activities, range of heart rates and respiration.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.10
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• pp.992-997
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• 2010

The Propulsion Control Module(PCM) of Hall-thruster Propulsion System(HPS) for Science and Technology Satellite-3 (STSAT-3) has the flow control accuracy of less than ${\pm}$3% and the pressure control accuracy of less than ${\pm}$5%. The pressure controller adjusts pressure around the set point by using a Proportional Flow Control Valve (PFCV) and a high pressure transducer, while the flow controller regulates the flow rate using PFCV and the anode current telemetry of the Hall Thruster. The controllers are chosen as the Proportional and Integral(PI) type, and the PI gains are tuned based on the Matlab simulations. The result of the PCM test had the flow control accuracy of less than ${\pm}$1.87% and the pressure control accuracy of less than ${\pm}$5%. This paper describes the design, realization, and performance test results of the PCM.

• Journal of Korean Society of Environmental Engineers
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• v.37 no.2
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• pp.92-98
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• 2015

The physical effect induced by acoustic cavitation was investigated to accumulate basic data for the design of ultrasonic soil washing processes using aluminum foil erosion tests. A square aluminum foil was placed on the glass beads in the pyrex vessel submerged in the sonoreactor equipped with a 36 kHz ultrasound transducer module at the bottom. Cavitational erosion of foils was quantitatively analyzed for various glass bead diameter conditions (1, 2, and 4 mm), glass bead height conditions (5, 10, 15, and 20 mm), and water height conditions (5, 10, 15, and 20 mm). It was found that aluminum foil erosion significantly increased as the glass bead diameter increased and water height over the glass bead increased due to less attenuation of ultrasound and the optimization of sound field for cavitation. Moreover mechanical mixing was suggested to move constantly particles to the bottom area where the acoustic cavitation occurs most violently. It was because aluminium foil erosion by ultrasound transmitted through glass beads was relatively too weak.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.5 s.108
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• pp.461-475
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• 2006

In this paper, it is described about the tri-band mobile antenna system design to provide broadband multimedia and direct broadcasting services using goo-stationary Koreasat 3, simultaneously operated in Ka/K/Ku band. The radiating part of the antenna system with a fan beam characteristic in the elevation plane is composed of the quasi-offset dual shaped reflector and the tri-band feeder. The tri-band feeder is also composed of the Ka/K dual band feeder with the protruding dielectric rod, the circular polarizer, the ortho-mode transducer and the circular-polarized Ku band feed array. Especially, the Ka/K dual band circular polarizer was realized firstly using the comb-type structure. For fast satellite-tracking on the movement, the Ku band feed array has the structure of the $2{\times}2$ active phased array which can make electrical beams. And, the circular-polarized characteristic in the feed array was improved by $90^{\circ}$ rotating arrangement of four radiating elements polarized circularly by a $90^{\circ}$ hybrid coupler, respectively. Four beam forming channels to make electrical beams at Ku band are divided into the main beam channel and the tracking beam channel in the output, and noise temperature characteristics of each channel were analyzed on the basis of the contributions of internal sub_units. From the fabricated antenna system, the output power at $P_{1dBc}$ of Ka_Tx channel was measured more than 34.1 dBm and the measured noise figures of K/Ku_Rx channels were less than 2.4 dB and 1.5 dB, respectively, over the operating band. The radiation patterns with co- and cross-polarization in the tri-band were measured using a near-field measurement in the anechoic chamber. Especially, Ku radiation patterns were measured after correcting each initial phase of active channels with partial radiation patterns obtained from the independent excitation of each channel. The antenna gains measured in Ka/K/Ku band of the antenna system were more than 39.6 dBi, 37.5 dBi, 29.6 dBi, respectively. And, the antenna system showed good system performances such as Ka_Tx EIRP more than 43.7 dBW and K/Ku_Rx G/T more than 13.2 dB/K and 7.12 dB/K, respectively.