• 한국소음진동공학회논문집
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• 제12권5호
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• pp.374-379
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• 2002

A new active muffler system has been developed and its superior performance on both noise reduction and engine torque increase is demonstrated with experiment. Main characteristic of the proposed muffler system is the use of destructive interference by transmission path difference of divided exhaust pipes to reduce major exhaust noise components thereby overcoming problems of other active exhaust noise control methods. The exhaust pipe is divided into two sections and joined again downstream. One divided pipe has a sliding mechanism to vary its length, which is controlled to make half wavelength transmission path difference for the major engine rpm frequency. In this system one divided pipe is used to control major rpm frequency and its Harmonics and another pipe is used to control noise component double the frequency of rpm. An after-market tuning muffler, which has very simple internal structure and minimal back pressure, is also installed to remove remaining wideband noise. To make the system to be small enough to be practical, conventional muffler is also installed and used in low rpm range and active muffler is only employed in high rpm range. Noise reduction of the proposed system is comparable to conventional passive muffler. The engine dynamo test has proved the proposed system can recover almost all the torque lost by conventional muffler.

• 한국전자파학회논문지
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• 제10권2호
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• pp.237-246
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• 1999

본 논문에서는 corrugated 구조 도파관의 저역통과 특성과 이중 계단형 불연속 구조 도파관의 고역통과 특성 을 결합하여 기존의 반파장 공진기를 이용한 여파기보다 크기가 상당히 작고 SpUriOUS 특성이 우수한 소형 도파관 대역통과 여파기를 설계하였다. 불연속면에서 발생하는 고차 모드에 의한 영향을 고려하기 위하여 최저차 모드만으로 설계한 여파기의 특성을 길이 보상을 통해 수정하였고, 모드 정합법을 이용한 특성 해석 프로그램과 상용 소프트웨어 $OSA90^{TM}$을 통해 최적화 하였다. 중심주파수 10 GHz, 대역폭 800 MHz의 7단 대역통과 여파기 를 대칭 구조로 설계, 제작하였다. 측정 결과에서 중심주파수 9.97 GHz, 대역폭 840 MHz, 삽입손실 0.97 dB의 특성을 얻었고, 그 길이는 64.38 mm이다. 첫 번째 spunous 응답은 26.1 GHz에서 나타났다.

• Journal of Magnetics
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• 제14권2호
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• pp.66-70
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• 2009

The dynamic magneto-mechanical behaviors in a type of iron-nickel-based ferromagnetic alloy with constant elasticity were investigated as a function of both the DC bias magnetic field ($H_{dc}$) and the frequency. The rectangular plate-like samples were excited to vibrate at a half-wavelength, longitudinal resonance by an AC magnetic field superimposed with various $H_{dc}$. The experimental results found that the strain coefficient at resonance reached 819.34 nm/A and the effective mechanical quality factor ($Q_m$) was greater than 2000. The ratio of the maximum variation of the Young's modulus over $H_{dc}$ to the value of the Young's modulus at a zero bias field was only ${\sim}0.83%o$ because of the so-called constant elasticity. The resonant strain coefficients and $Q_m$ are strongly dependent on $H_{dc}$, which indicates a promising potential for use in DC and quasistatic magnetic field sensing.

• ETRI Journal
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• 제23권3호
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• pp.97-105
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• 2001

$1.6\;{\mu}m$ emission originated from $Pr^{3+}:\;(^3F_3,\;^3F_4)\;{\longrightarrow}\;^3H_4$ transition in $Pr^{3+}-\;and\;Pr^{3+}/Er^{3+}$-doped selenide glasses was investigated under an optical pump of a conventional 1480 nm laser diode. The measured peak wavelength and fullwidth at half-maximum of the fluorescent emission are ~1650nm and 120nm, respectively. A moderate lifetime of the thermally coupled upper manifolds of ${\sim}212{\pm}10{\mu}s$ together with a high stimulated emission cross-section of ${\sim}(3{\pm}1){\times}10^{-20}\;cm^2$ promises to be useful for $1.6{\mu}m$ band fiber-optic amplifiers that can be pumped with an existing high-power 1480 nm laser diode. Codoping $Er^{3+}$ enhances the emission intensity by way of a nonradiative $Er^{3+}:\;^4I_{13/2}\;{\longrightarrow}\;Pr^{3+}:\;(^3F_3,\;^3F_4)$ energy transfer. The Dexter model based on the spectral overlap between donor emission and acceptor absorption describes well the energy transfer from $Er^{3+}$ to $Pr^{3+}$ in these glasses. Also discussed in this paper are major transmission loss mechanisms of a selenide glass optical fiber.

• Journal of electromagnetic engineering and science
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• 제11권3호
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• pp.143-151
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• 2011

This paper presents a survey of recent wireless power transfer systems. The issue of wireless power transfer is to achieve a highly efficient system with small positioning errors of the facilities setting. Several theories have been presented to obtain precise system design. This paper presents a summary of design theory for short range power transfer systems and detailed formulations based on a circuit model and an array of infinitesimal dipoles. In addition to these theories, this paper introduces a coil array scheme for improving the efficiency for off axis coils. In the microwave range, tightly coupled resonators provide a highly efficient power transfer system. This paper present san-overlay resonator array consisting of half wavelength microstrip line resonators on the substrate with electromagnetically coupled parasitic elements placed above the bottom resonators. The tight couplings between the waveguide and the load resonator give strong power transmission and achieve a highly efficient system, and enables a contact-less power transfer railroad. Its basic theory and a demonstration of a toy vehicle operating with this system are presented. In the last topic of this paper, harmonic suppression from the rectenna is discussed with respect to acircular microstrip antenna with slits and stubs.

• Transactions on Electrical and Electronic Materials
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• 제10권6호
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• pp.185-188
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• 2009

The effects of the growth temperature on the properties of ZnO thin films were investigated by using X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectrophotometry, and Hall measurements. The ZnO films were deposited by rf magnetron sputtering at various growth temperatures in the range of 100-$400{^{\circ}C}$. A strong c-axis preferred orientation is observed for all of the samples. As the growth temperature increases, the crystalline orientation of the ZnO (002) plane is not changed, but the full width at half maximum gets smaller. The dependence of the electron concentration, mobility, and resistivity on the growth temperature exhibits that the ZnO films have a higher electron concentration at higher temperatures, thus giving them a low resistivity. The optical transmittance and band gap energy, calculated from the spectra of optical absorbance, show a significant dependence on the growth temperature. As for the sample grown at $100{^{\circ}C}$, the average transmittance is about 90% in the visible wavelength range and the band gap is estimated to be 3.13 eV.

• 대한전자공학회논문지TE
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• 제37권1호
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• pp.18-26
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• 2000

본 논문에서는 광대역 특성을 가진 고주파 압전 변환기를 이론적으로 고찰하였고, 압전변환기를 제작하여 이론값과 실험값을 비교, 분석하여 그 응용가능성을 확인하였다. ZnO(3.825${\mu}m$/Pt/Sapphire(0001)구조의 압전변환기의 공진주파수는 827.47MHz로서 압전체의 반파장주파수에서 공진이 일어남을 알 수 있었다. 또한, 삽입손실은 약 -50dB이었고, 최소의 삽입손실은 이론적인 분석과 잘 일치하였다.

• Applied Science and Convergence Technology
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• 제23권5호
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• pp.279-283
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• 2014

Al doped ZnO thin films have been deposited by a RF magnetron sputtering technique from a ZnO (2 wt.% $Al_2O_3$) target onto glass substrates heated at temperature ranging from RT to $400^{\circ}C$. X-ray diffraction analysis shows that the deposits have a preferential growth along the c-axis of a hexagonal structure. The full with at half maximum decreases from 0.45 to $0.43^{\circ}$ in the studied temperature range. The root main square surface roughness increases with substrate temperature from 1.89 to 2.67 nm. All films are transparent up to 80% in the visible wavelength range and the adsorption edge is red-shifted with substrate temperature from RT to $400^{\circ}C$. The sheet resistance increases from 92 ohm/sq to 419 ohm/sq when the deposition temperature increases from RT to $400^{\circ}C$. The increment of sheet resistance is caused by lowered carrier concentration resulting from an increase in surface roughness.

• 한국전자파학회논문지
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• 제21권3호
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• pp.253-261
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• 2010

본 논문에서는 서로 다른 공진점을 갖는 공진기들을 이용하여 이중 대역 통과 필터를 구현하였다. 서로 다른 공진점을 갖는 $\lambda_g$/2 공진기들을 이용하여 각 공진기들의 동작 주파수가 서로의 동작 주파수에 영향을 미치지 않는 것을 이용하여 이중 대역 통과 필터를 설계하였다. 하측 통과 대역은 $\lambda_g$/2 공진기와 $\lambda_g$/4 공진기를 이용하였고, 상측 통과 대역은 이중 모드 공진기를 이용하여 설계하였으며, 하측 통과 대역의 공진기는 상측 통과 대역의 급전부로 동작한다. 제안된 구조는 WLAN 대역인 2.45/5.2 GHz와 2.45/5.8 GHz에서 동작하도록 설계 제작되었다.

• 한국항공우주학회지
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• 제33권3호
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• pp.65-70
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• 2005

잘못된 미지정수는 잘못된 위치값을 사용자에게 제공하여 자세결정에 큰 오차를 발생시킨다. 본 논문에서는 이동하는 항체에 4개 이상의 GPS 안테나를 고정시켜 정확한 자세결정을 수행할 때 다중경로를 추정하는 방법을 제안하였다. 4개 이상의 GPS 안테나에서 얻은 측정값이 같은 수신기 시계오차를 갖게 되면, 안테나 사이의 기하학적 관계를 이용하여 자세결정을 보다 효과적으로 수행할 수 있다. 안테나 사이의 거리를 반파장으로 만들어 미지정수 검색의 과정 없이 미지정수를 결정하고, GPS 반송파 측정값에 존재하는 다중경로 오차를 추정할 수 있다. 본 논문은 GPS 반송파 측정값의 다중경로 오차를 추정하는 알고리즘을 제시하고 수학적인 증명을 하였으며, 이 결과를 시뮬레이션을 통해 검증하였다.