• The Journal of the Acoustical Society of Korea
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• v.38 no.6
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• pp.710-715
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• 2019

A transmission line based bowed string model is built by analogizing a vibrating string to an electrical transmission line and implementing the calculation for the frictional bow-string force given by a digital bow into a circuit. The performance of the proposed model is demonstrated by showing that the velocity of the string at the bowing point from the proposed model is consistent with that from the finite difference form of the wave equation for a bowed string by the digital bow.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.152-157
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• 2005

Recently, higher speeds have been promoted in old overhead-lines. For high-speed operation in electric railways, increasing contact loss of the pantograph is one of the most important subjects. The contact loss causes power interruption and increases wear of contact strips and contact wires. In order to investigate the causes of contact loss and to work out effective improvement methods, theoretical analyses, experiments have been carried out. First of all, the wave propagating velocity (phase velocity) and characteristics of contact wire are one of the important indices for the current collecting performance. In this paper, mathematical formula arc derived for the prediction of the traveling wave velocity. The measured values in the experiment agree well with the theoretical predictions.

• Journal of the Korean Institute of Telematics and Electronics
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• v.7 no.2
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• pp.13-20
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• 1970

The dispersion characteristics of tape meander line were analyzed by electromagnetic field theory. The several different tape meander lines were photoetched on copper printed-bakelit substrate, and these tape meander line structures were inserted into the X-band waveguide. Phase bridge method was used for the dispersion characteristics measurement of meanderline. The measured. results were plotted on diagram(Brillouin diagram) and compared with theoretical values. Measured results were consistent with theoretical Values. But, on the measured diagram, passband midfrequency was lower than theoretical value. It was believed that the discrepancy was due to the backelite loading. The group velocity of stagger tuned meander line was higher than that of uniform meander live, and the freqnency band of constant group velocity of stagger tuned meanderline was sider than that of uniform meander line.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1994.05a
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• pp.21-24
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• 1994

A piezoelectric actuator. which is composed of a piezoelectrically driven stator and a rotor, Is made and the characteristics are investigated experimentally is a new ultrasonic actuator which transforms rotary motion to linear one is proposed and proved to work successfully. If an ultrasonic wave is excited to propagate in the stator, particles on the internal surface move elliptically. Since the internal surface is machined as an internal thread and an external thread(rotor) is put into the stator. the external thread is rotated through the friction force and moved in the axial direction. The traveling wave is excited by a piezoelectric element bonded to the stator. This idea is firstly proposed by S. Ueha, et al. in 1987. However, efficiency of their actuator is less than 3%. In this study, in order to improve characteristics of this type actuator, we used various pitches and number of the screw thread, and materials of rotor, and we obtained good charcteristics.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.696-701
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• 2005

조화가진력이 작용하는 고정경계를 가진 완전원판의 비선형 진동에 대한 응답특성을 연구하였다. 원판의 비대칭모드의 고유진동수 근처에 가진주파수가 작용하는 주공진에서의 응답은 정상파(standing wave)뿐만 아니라 진행파(traveling wave)가 존재 한다고 알려져 있다. 주공진 근처의 정상상태 응답곡선에서 최대한 5개의 안정한 응답이 존재하는 것으로 밝혀졌으며, 이들은 1개의 정상파와 4개의 진행파로 나타난다. 이 진행파 중 2개는 가진진동수가 변화함에 따라 Hope분기에 의해 안정성을 잃은 후 주기배가운동을 거쳐 흔돈운동에 이르게 된다. 초기조건에 의해 각각의 끌개(attractor)에 흡인되는 흡인영역의 경계를 주평면의 개념을 통하여 구하였으며, 가진진동수가 변화함에 따라 안정한 해가 혼돈운동에 이르는 과정에 대해 흡인영역의 경계가 변화되는 특성을 관찰하였으며, 흡인영역 경계에 대한 프랙털 차원(fractal dimension)을 계산하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.6
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• pp.1231-1243
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• 1997

Digital satellite communication channels have nonlinearities with memory due to saturation characteristics of traveling wave tube amplifier in the satellite and transmitter/receiver linear filters. In this paper, we propose a network structure and a learning algorithm for complex pi-sigma network (CPSK) and exploit CPSN in the problem of equalization of nonlinear satellite channels. The proposed CPSN is a complex-valued extension of real-valued pi-sigma network that is a higher-order feedforward network with fast learning while greatly reducing network complexity by utilizing efficient form of polynomials for many input variables. The performance of the proposed CPSN is demonstrated by computer simulations on the equalization of complex-valued QPSK input symbols distorted by a nonlinear channel modeled as a Volterra series and additive noise. The results indicate that the CPSN shows good equalization performance, fast convergence, and less computations as compared to conventional higher-order models such as Volterra filters.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.11
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• pp.50-58
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• 2000

A Mach-Zehnder type $Ti:LiNbO_3$ optical modulator with a grooved $SiO_2$ buffer layer, was evaluated in terms of an electrode structure. The finite element method was performed to find out the optinum design parameters of electrodes. characteristic impedance ($Z_o$), MW effective index ($N_{eff}$) and attenuation constant ($a_o$)of fabricated traveling-wave electrodes were measured and compared with those obtained by the simulation expectation. For an optical modulator with 11${\mu}m$thick electrodes and a grooved $SiO_2$ buffer layer, the 3dB bandwidth based on the RF measurement results turned out to be 18GHz.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.37 no.1
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• pp.1-11
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• 2000

We propose a predistorter to compensate for nolinear distortion induced by a high power amplifier employed in multi carrier-code division multiple access (MC-CDMA) systems. The proposed scheme rests upon the fixed point iteration (FPI) associated with the contraction mapping theorem. Unlike the predistorter based on the FPI already presented by the authors in other literatures which operates on complex-valued modulation signals, the proposed predistorter in this paper deals with real-valued FPI on modulation signal amplitudes, resulting in less complexity. Simulation results on a BPSK-modulated, 64-subcarrier synchronous MC-CDMA baseband system with a traveling wave tube amplifier in the transmitter, indicate that the proposed predistorter achieves significant improvement in terms of bit error rate and total degradation over those without the predistorter. Moreover, the proposed predistorter outperforms the complex-valued counterpart, in particular, for small output back-off levels.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.47 no.10
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• pp.8-16
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• 2010

An orthogonal frequency division multiplexing (OFDM) system is a special case of multicarrier transmission, where a single data stream is transmitted over a number of lower-rate subcarriers. One of the main reasons to use OFDM is to increase robustness against frequency-selective fading or narrowband interference. However, in the radio systems the distortion introduced by high power amplifiers (HPA's) such as traveling wave tube amplifier (TWTA) considered in this paper, is also critical. Since the signal amplitude of the OFDM system is Rayleigh-distributed, the performance of the OFDM system is significantly degraded by the nonlinearity of the HPA in the OFDM transmitter. In this paper, we propose a simplicial canonical piecewise-linear (SCPWL) model based digital predistorter to compensate for nonlinear distortion introduced by an HPA in an OFDM system. Computer simulation is carried on an OFDM system under additive white Gaussian noise (AWGN) channels with 16-QAM and 64-QAM modulation schemes and modulator/demodulator implemented with 1024-point FFT/IFFT. The simulation results demonstrate that the proposed predistorter achieves significant performance improvement by effectively compensating for the nonlinearity introduced by the HPA.

• Journal of the Korean Institute of Telematics and Electronics
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• v.12 no.3
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• pp.13-19
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• 1975

A detailed analysis has been carried out of a zigzag traveling wave electro-optic laser modulator usin3 CuCl, KDP Crystal. The inclusion of such practical factors as M/W and optical loss results in an optimum design in which modulator dimensions and bandwidth limitation are uniquely determined by optical and M/W dielectic properties of modulating crystal. The main conclusion of the analysis are: (1) CuCl, KDP may be used to produce 50% modulation over bandwidth of 10(GHz) with less than (watt) of modulating power. (2) The upper modulation frequency limit is set by a cutoff frequency which arises from finite width of optical beam.