• Journal of the Institute of Electronics Engineers of Korea SC
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• v.49 no.3
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• pp.75-81
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• 2012

In this paper, an efficient means to estimate the dispersion characteristics of active FSS (or ESS) is presented. We numerically investigate the effective permittivity and the transmission coefficient of 2D metal-fiber composites using linear-lumped impedance loading. We modify the GEC method which is applied to 2D fiber composite material with arbitrary fiber orientation. We show that by varying the impedance value it is possible to control the resonance frequency of the array as well as the bandwidth.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.517-521
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• 2001

Measurement techniques for the in-duct source characteristics of fluid machines can be classified into direct method and load method, according to whether the technique employs an external acoustic source or not. It has been known that the two methods yield different results and the load method used to come up with a negative source resistance, in spite of the fact that a very accurate prediction of radiated noise can be obtained by using any result. This paper is focused to the effect of time-varying nature of fluid machines on the output result. For this purpose, a simplified fluid machine consisting of a reservoir, a valve and a pipe is considered as representing a typical linear, periodic, time-varying system and the measurement techniques are simulated by utilizing the Hill equation and its steady-state forced response. In the load method, the source impedance turns out being dependent on the valve impedance at the calculation frequency and the valve and load impedances at other frequencies as well.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.05a
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• pp.480-485
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• 2004

If a wall separates the bounded and unbounded spaces, then the wall's role in transporting the acoustic characteristics of the two spaces is not well defined. In this paper, we attempted to see how the acoustic characteristical of two spaces are really affected by the spatial characteristics of the wall. In order to understand coupling mechanism, we choose a finite space and a semi-infinite space separated by the flexible or rigid wall and an opening. A volume interaction can be occurred in structure boundary and a pressure interaction can be happened in the opening boundary. For its simplicity, without loosing generality, we use rather simplified rectangle model instead of generally shaped model. The source impedance is presented to the various types of boundaries. The distributions of pressure and active intensity are also presented at the cavity and structure-dominated modes. The resulting modification, shifts of mode1 frequencies and changing of standing wave patterns to satisfy both coupled boundary conditions and governing equations, are presented.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.4 s.181
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• pp.60-66
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• 2006

For the purpose of finding out the sound field characteristics in a rectangular cavity, analytical and experimental studies are performed with white noise input. Two-microphone impedance tube method is used to measure the impedances of foamed aluminum. Foamed aluminum is well known metallic porous material which has excellent properties of light weight and high absorbing performance. And predicted impedances of foamed aluminum are compared with measured impedances. The predicted acoustical parameters are applied to the theoretical analysis to predict sound pressure field in the cavity. The measured sound absorption effects are compared with the predicted values for both cases with and without foamed aluminum lining in the cavity of the rectangular enclosure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.20 no.5
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• pp.436-442
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• 2007

Physical properties and impedance-humidity characteristics of carbon nitride films were investigated for micro-humidity-sensors. Carbon nitride films were deposited in low temperature and low power for application of semiconductor fabrication process, and empirical equation was proposed for thickness evaluation. Deposited films had an uniform and compact surface comparing with previously reported results, which was expected a good candidate for humidity sensing materials. Carbon nitride humidity sensors based on Si substrate revealed good humidity-impedance characteristics with a wide range of relative humidity and showed low hysteresis.

• Proceedings of the KIEE Conference
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• 1996.07c
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• pp.1876-1878
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• 1996

This paper describes the combination surge generator for applying performance tests of surge protective devices. The $8/20{\mu}s$ waveform applies to low impedance circuits and components and is commonly used to determine the characteristics of surge protective devices. And the $1.2/50{\mu}s$ waveform applies to high impedance circuits and components and is used for testing dielectric behavior. Therefore, the combination surge generator, which generates $1.2/50{\mu}s$ voltage waveform under open-circuit conditions and $8/20{\mu}s$ current waveform under short-circuit condition, was proposed. Also this generator can produce $10/1000{\mu}s$ as well as $0.5{\mu}s/100kHz$ ring waveform.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.629-630
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• 2008

Before applying the HTS power cable to the real utility, the system needs to be analyzed using certain simulation tools. The impedance of superconductor is changed due to the magnitude of current, temperature, and magnetic field. PSCAD/EMTDC does not provide the superconductor component which has the impedance characteristic. The authors have developed the HTS power cable component in EMTDC program which included the same electrical characteristics as real HTS power cable previously. Based on the research results, the authors analyzed fault current characteristics of HTS power cable using the developed EMTDC model component.

• Journal of Korea Multimedia Society
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• v.20 no.9
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• pp.1551-1558
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• 2017

Audio power amplifiers have been designed based on the premise that the impedance of loudspeakers is fixed at nominal 4 ohms or 8 ohms. However, it is known that the impedance varies with frequency and takes on the nominal value at some limited frequencies. The principle of the loudspeaker operation reveals that the sound pressure produced by the loudspeaker is proportional to the current flowing in the voice coil, not the voltage between the two terminals. We take the characteristics of the loudspeaker into account and compare the frequency responses of the loudspeaker in voltage-drive mode and current-drive mode via computer simulations, to conclude that the audio amplifier drive mode should be re-considered in an effort to improve the sound quality.

• Transactions of The Korea Fluid Power Systems Society
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• v.4 no.3
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• pp.22-27
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• 2007

The source flow ripple and the source impedance in hydraulic pump are characteristic values showing fluid-borne vibration characteristics decisively. We cannot measure these two characteristic values directly, but can measure them by some indirect methods. One representative indirect measuring method is ISO 10767-1. The authors constructed a hardware and a software for the measuring method based on ISO 10767-1. Through the error evaluation of the measured results, accuracy of the measuring method using ISO 10767-1 was examined in detail.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.957-959
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• 2014

The wave analysis of cylinders combined rigidly with a finite plate to identify the effect of the plate on the wave propagation. This paper uses the mobility and impedance coupling method to combine a infinite-length cylinder with the plate, and obtains the coupling forces induced by the vibration of the structure. The waveguide finite element method is used to calculate the wave characteristics of the cylinder excited by the forces. From the results, the dispersion diagram can be obtained. It contains the characteristics induced by the vibration and length of the internal plate. It also shows the wave propagation of elastic waves sustained in the cylinder.