• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.279-282
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• 2004

In this paper, A new type of piezoelectric step motor using piezoelectric torsional actuator and a pair of one-way clutch bearing is designed, manufactured and tested. The torsional actuator consists of 16-polygonal tube that can produce angular displacement using shear mode of piezoceramic. One-way clutch bearing convert oscillation of torsional actuator into continuous rotation. After performance testing of torsional actuator, the optimum condition for driving motor is investigated in terms of wave shape, excitation frequency and electrical field. The performance of the motor is experimentally evaluated. As a result, square wave has larger rotation speed than sin wave, and the maximum rotation speed of 57 rpm is measured at 3850 Hz and 100V/mm.

• Journal of Korean Society on Water Environment
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• v.32 no.6
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• pp.649-669
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• 2016

This study explored the analytical conditions for 21 veterinary antibiotics which have been popularly sold in South Korea in 2014 but have not yet been targeted in EPA method 1694. Most of the selected antibiotics were separated by a reverse-phase C18 column with a combination of (buffered) water and organic polar solvent, which was commonly methanol and acetonitrile in the gradient elution mode. Volatile additives such as formic acid, ammonium acetate and ammonium formate were usually added to the mobile phases to minimize asymmetrical and tailing of antibiotics' peaks and to increase their ionization in mass spectrometry. The analytical methods of aminoglycoside antibiotics were distinct from those of the other antibiotics in terms of adoption of ion-pair chromatography (IPC) and hydrophilic interaction liquid chromatography (HILIC) capable of retaining and separating extremely polar compounds due to their hydrophilicity. Trifluoroacetic acid or heptafluorobutyric acid was frequently added to the mobile phase as an ion-pair reagent for the IPC. Tandem mass spectrometry was numerously applied to the detection of antibiotics using positive electrospray ionization (ESI) and the selected reaction monitoring (SRM) mode. All reviewed analytical methods had been/were validated by evaluating recovery, limits of detection and quantification, decision limit or detection capability of the methods.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.1
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• pp.1-10
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• 1999

In this paper, a method of canceling and suppressing differential-mode crosstalk-noise signals caused by non-uniform coupling between two transmission lines in UTP(Unshielded Twisted Paris) modular jacks is discussed. Differential-mode crosstalk-noise signals in balanced transmission lines in UTP modular jacks were suppressed by inserting auxiliary capacitance between balanced transmission line pairs which are located closely enough to be effectively coupled each other. To verify the effectiveness of the inserted capacitances, precisely calculated auxiliary capacitances were applied to 10 pin modular jacks which are used in local area networks at 100 Mb/s with unshielded twisted pair-cables. The NEXT(Near-End Crosstalk) losses were measured to prove its applicability.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.45-46
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• 2006

In this paper, a dual stage servo mechanism has been developed for image tracking system to improve transient control performances such as small rise time, small overshoot, small settling time, etc. A secondary stage, a platform, actuated by a pair of electro-magnets is mounted on a conventional elevation gimbal. In this mechanism, the gimbal provides large range but slow motion and the platform provides small range but fast positioning. A sliding mode control is applied to the platform positioning to attain robust performances and stability in the presence of the disturbance related to dynamic coupling of the gimbal and the platform. Results from experiments illustrate that the suggested dual stage mechanism controlled by the sliding mode control is effective in improving transient responses and attenuating the disturbance related with dynamic coupling.

• Journal of Biomedical Engineering Research
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• v.26 no.4
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• pp.215-221
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• 2005

We describe the development of a prototype multi-channel electrical impedance tomography (EIT) system. The EIT system can be equipped with either a single-ended current source or a balanced current source. Each current source can inject current between any chosen pair of electrodes. In order to reduce the data acquisition time, we implemented multiple digital voltmeters simultaneously acquiring and demodulating voltage signals. Each voltmeter measures a differential voltage between a fixed pair of adjacent electrodes. All voltmeters are configured in a radially symmetric architecture to optimize the routing of wires and minimize cross-talks. To maximize the signal-to-noise ratio, we implemented techniques such as digital waveform generation, Howland current pump circuit with a generalized impedance converter, digital phase-sensitive demodulation, tri-axial cables with both grounded and driven shields, and others. The performance of the EIT system was evaluated in terms of common-mode rejection ratio, signal-to-noise ratio, and reciprocity error. Future design of a more innovative EIT system including battery operation, miniaturization, and wireless techniques is suggested.

• Journal of the Korean Solar Energy Society
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• v.34 no.1
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• pp.48-57
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• 2014

The transient and synchronization behaviors of a TA (thermo acoustic) laser pair were investigated experimentally for various crossing angles and different separation distances between the laser openings. Sound waves generated by the lasers were measured and analyzed at or near the focusing point by means of microphones, SPL meters, and a commercial software called Signal-Express. The two TA lasers were acoustically coupled through the air mass between their openings, and the only mode-locking operation that could be achieved was the one that was nearly $180^{\circ}C$ out of phase. The time to achieve synchronization was found to be dependent upon the initial mistuning of the frequencies and the crossing angle between the laser axes. The synchronization process could also be accelerated by turning on the laser with the lower power input first.

• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.63-67
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• 2013

We perform an optical vestigial sideband (VSB) filtering using a pair of Fabry-Perot (FP) filters. The transmittance curve of each FP filter is made to have sharp skirts using an offset between input and output coupling fibers. Moreover, the accurate periodicity of FP filters in the optical frequency domain enables the simultaneous VSB filtering of a large number of optical channels. With this VSB filtering technique, we transmit 12.5-GHz spaced $64{\times}12.4-Gb/s$ wavelength-division-multiplexing channels over a single-mode fiber up to 150 km without any dispersion compensations. When the channel spacing is reduced to 10 GHz, we achieve the spectral efficiency of 1 bit/s/Hz in conventional optical intensity modulation systems up to 125 km.

• Journal of the Korean Solar Energy Society
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• v.31 no.6
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• pp.1-7
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• 2011

Sound waves and acoustic energy generated by two identical TA (ThermoAcoustic) lasers were analyzed and studied. One end of the ceramic stack was heated by a thin NiCr wire wound around that end. The other end of the stack was cooled by natural convection of atmospheric air. The wavelength of the sound waves generated by a single TA laser was four times the tube length and the amplitude of the waves increased with the heating rate. SPL (SoundPressure Level) meters and microphones were employed to measure and study the sound waves at different distances from the glass tube opening and at the focusing point of the TA laser pair for different laser position arrangements. The sound waves of the two TA lasers at the focusing point were found to be almost 180 degrees out of phase when the openings of the two lasers were very close to each other and the angle between the laser axes was small. When the two TA lasers were placed far apart, the sound wave amplitudes and the phase difference between the two laser outputs varied periodically with time. The frequencies of the sound waves changed when the openings of the two TA lasers were in close vicinity and the angle between the laser axes exceeded a certain value. In this case, the glass tube opening was no longer a pressure anti-node and the wavelength of the fundamental mode was not equal to four times the tube length.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.3 s.106
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• pp.272-279
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• 2006

In this paper, we evaluate the performance of frame synchronization words of pilot bit patterns which are used for the channel estimation and frame synchronization confirmation in W-CDMA(Wide band Code Division Multiple Access) system. W-CDMA system also uses compressed mode to make measurements from another frequency without a full dual receiver terminal. It is confirmed by using computer simulation that the proposed frame synchronization words also maintain the frame synchronization property in the compressed mode by using the complementary mapping relationship of preferred pair ROC(Receiver Operating Characteristic) curves with probability of detection and false alarm are used to analized the performance of the proposed frame synchronization words by using the various detection metrics such as LLRT(Log Likelyhood Ratio Test), GLRT(Generalied Likelyhood Ratio Test), soft and hard correlation tests in AWGN and Rayleigh fading channels. It is expected that the research results fer the performance of pilot bit patterns of this paper can be useful reference for the design and implementation of frame synchronization in 3rd generation W-CDMA system.

• Korean Journal of Optics and Photonics
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• v.10 no.3
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• pp.195-200
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• 1999

We made sharp optical fiber tips with less than 100 nm diameter by using the heating and pulling method with a good repetition and fabricated the photon scanning tunneling microscope (PSTM) using constant intensity mode. The 3-dimensional PZT (Piezoelctric transducer) scanner made of a long PZT tube is consisted of three divided parts, that is, a pair of $\pm$ x and a pair of $\pm$y scanning parts and a z scanning part for the fine approach and scanning. The scanning dimension is 1.43 $\mu\textrm{m}$$\times$1.76 $\mu\textrm{m}$. The height of a optical tip to maintain a constant height within $1/{\lambda}_0$ (${\lambda}_0$ is the incident wavelength) from surface of a specimen to a optical tip is controlled automatically by using the electric feedback circuit. The 3-dimensional shape of standing evanescent waves generated on the surface of a dove prism was measured successfully by using the constant intensity mode PSTM.