• Title/Summary/Keyword: Resonant Frequency Ratio

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Performance analysis of atomic magnetometer and bandwidth-extended loop antenna in resonant phase-modulated magnetic field communication system

  • Hyun Joon Lee;Jung Hoon Oh;Jang-Yeol Kim;In-Kui Cho
    • ETRI Journal
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    • v.46 no.4
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    • pp.727-736
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    • 2024
  • Telecommunications through an electrically conductive medium require the use of carrier bands with very-low and ultralow frequencies to establish radiofrequency links in harsh environments. Recent advances in atomic magnetometers operating at very-low frequencies have facilitated the reception of digitally modulated signals. We demonstrate the transmission and reception of quadrature phase-shift keying (QPSK) signals using a multi-resonant loop antenna and atomic magnetometer, respectively. We report the measured error vector magnitude according to the symbol rate for QPSK modulation and analyze the bandwidth of a receiver based on the atomic magnetometer. The multi-resonant loop antenna noticeably enhances the bandwidth by over 70% compared with a single-loop antenna. QPSK modulation for a carrier frequency of 20 kHz and symbol rate of 150 symbols per second verifies the feasibility of demodulation, and the measured error vector magnitude and signal-to-noise ratio are 7.29% and 30.9 dB, respectively.

Wind-induced vibration characteristics and parametric analysis of large hyperbolic cooling towers with different feature sizes

  • Ke, Shitang;Ge, Yaojun;Zhao, Lin;Tamura, Yukio
    • Structural Engineering and Mechanics
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    • v.54 no.5
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    • pp.891-908
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    • 2015
  • For a systematic study on wind-induced vibration characteristics of large hyperbolic cooling towers with different feature sizes, the pressure measurement tests are finished on the rigid body models of three representative cooling towers with the height of 155 m, 177 m and 215 m respectively. Combining the refined frequency-domain algorithm of wind-induced responses, the wind-induced average response, resonant response, background response, coupling response and wind vibration coefficients of large cooling towers with different feature sizes are obtained. Based on the calculating results, the parametric analysis on wind-induced vibration of cooling towers is carried out, e.g. the feature sizes, damping ratio and the interference effect of surrounding buildings. The discussion shows that the increase of feature sizes makes wind-induced average response and fluctuating response larger correspondingly, and the proportion of resonant response also gradually increased, but it has little effect on the wind vibration coefficient. The increase of damping ratio makes resonant response and the wind vibration coefficient decreases obviously, which brings about no effect on average response and background response. The interference effect of surrounding buildings makes the fluctuating response and wind vibration coefficient increased significantly, furthermore, the increase ranges of resonant response is greater than background response.

Resonant Properties of Modified $PvTiO_3$System Ceramics for High frequency Resonator (고주파 레조네이터용 변성 $PvTiO_3$계 세라믹스의 공진특성)

  • 민석규;류주현;박창엽;김종선;윤현상;정회승
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.07a
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    • pp.976-980
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    • 2001
  • In this study, P $b_{0.88}$(L $a_{a}$N $d_{l-a}$)$_{0.08}$(M $n_{1}$3/S $b_{2}$3/)$_{0.02}$ $Ti_{0.98}$ $O_3$system ceramics were manufactured for 20 MHz class resonator application. Electromechanical coupling factor, mechanical quality factor and dynamic range of 3rd overtone thickness vibration mode were measured as the variations of La and Nd molar ratio. Mechanical quality factor and dynamic range at $\alpha$=0.6 composition ceramics showed the highest value of 2, 691 and 52.37 dB, respectively. The tempearture coefficient of resonant frequency measured from -2$0^{\circ}C$ to 8$0^{\circ}C$ showed an excellent value of 5ppm/$^{\circ}C$ at $\alpha$ = 1 composition ceramics. ceramics.s.

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Resonant Frequency in Rectangular Microstrip Patch Antenna on Anisotropic Substrates with Airgap and Permittivity Superstrate (공기갭과 유전체 덮개층을 갖는 이방성 기판 위의 마이크로스트립 패치 안테나의 공진 주파수 해석)

  • 윤중한;이상목;곽경섭
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.26 no.11B
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    • pp.1600-1606
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    • 2001
  • Resonant frequency in rectangular microstrip patch antenna on anisotropic substrates with airgap and superstrate are analyzed. Dyadic Green function is derived for selected anisotropic material by constitutive relation. From these results, integral equations of electric fields are formulated using Fourier transform in space region. The electric field integral equations are discretized into the matrix form by applying Galerkin\`s moment method. Sinusoidal functions are selected as basis functions because they resemble in the actual standing wave on the patch. To verify the validity of numerical result, we compare our result with existing one and get a good agreement between them. From the numerical results, the resonant frequency in the variation of air gap, patch length and anisotropy ratio are presented and analysed.

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Design of Compact Circularly Polarized Microstrip Patch Antenna with T-slits Loading (T-슬릿 부설에 의한 소형 원편파 마이크로스트립 패치 안테나 설계)

  • 김영두;신경섭;원충호;이홍민
    • Journal of the Institute of Electronics Engineers of Korea TC
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    • v.41 no.10
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    • pp.103-108
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    • 2004
  • In this paper, a compact patch antenna with four T-slits fed by crossed aperture coupling is proposed for miniaturized Portable GPS handsets. The mechanism for compact size antenna is investigated with the behavior of the currents on the radiating patch. The equivalent surface current path due to the slits is lengthened, reducing the resonant frequency at a fixed patch size. The results of embedded T-slits for compact antenna size show that the resonant frequency is significantly lowered from 2.545GHz to 1.575GHz, corresponding to a 44.65% antenna size reduction compared to reference design. Experimental results show that good CP radiation patterns are obtained and impedance bandwidth (VSWR $\leq$ 2), 3dB axial ratio are about 21MHz, 19MHz at the center resonant frequency, respectively.

Acoustic Tests on Atmospheric Condition in a Liquid Rocket Engine Chamber (액체로켓엔진 연소실에서의 상온 음향 시험)

  • Ko, Young-Sung;Lee, Kwang-jin;Kim, Hong-Jip
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.1
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    • pp.16-23
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    • 2004
  • Acoustic characteristics of unbaffled and baffled combustion chamber are experimentally investigated under atmospheric condition to preliminarily determine baffle for mitigation of combustion instability. To investigate the effect of the baffle which has several configurations such as radial baffles and hub/blade baffle, resonant-frequency shift and damping factors of the chamber were analyzed and compared quantitatively with those of the unbaffled combustion chamber. From a view of acoustic characteristics, radial baffles with several configurations have not much difference in resonant-frequency shift and damping factor ratio with each other. On the other hand, hub and blade baffle is very effective to suppress the first tangential mode which was found to be the most harmful acoustic mode in KSR(Korean Sounding Rocket)-III engine. But more study on design parameters such as hub size and axial length should be done for complete optimization of hub and blade baffle. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

Microwave Dielectric Properties of the MgTiO$_3$-SrTiO$_3$Ceramics (MgTiO$_3$-SrTiO$_3$세라믹스의 마이크로파 유전특성)

  • 최의선;이문기;정장호;김강;이영희
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.07a
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    • pp.843-846
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    • 2000
  • The (1-x)MgTiO$_3$-xSrTiO$_3$(x=0.02∼0.08) ceramics were fabricated by conventional mixed oxide method. The sintering temperature and time were 1250$^{\circ}C$∼1400$^{\circ}C$, 2hr., respectively. The structural and microwave dielectric properties were investigated by varying sintering temperature and composition ratio. In the (1-x)MgTiO$_3$-xSrTiO$_3$(x=0.02) ceramics, the cubic SrTiO$_3$and hexagonal MgTiO$_3$phases were coexisted. The dielectric constant was increased and the temperature coefficient of resonant frequency( $\tau_f$) was decreased with addition of SrTiO$_3$. The temperature coefficient of resonant frequency($\tau_f$) was gradually varied from negative value to positive value with increasing the SrTiO$_3$.

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Ferrite-based wideband circularly polarized microstrip antenna design

  • Mashhadi, Mostafa;Komjani, Nader;Rejaei, Behzad;Ghalibafan, Javad
    • ETRI Journal
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    • v.41 no.3
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    • pp.289-297
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    • 2019
  • In this paper, a wideband, circularly polarized patch antenna is proposed that leverages the unidirectional resonant modes of a circular patch mounted on top of a grounded dielectric-ferrite substrate. The proposed antenna is fed via the proximity coupling method and several parasitically coupled patches are placed on a dielectric superstrate to enhance the impedance bandwidth of the antenna. The resonant modes of the structure rotate only in the clockwise or counter clockwise directions. In the frequency range where the effective permeability of the ferrite layer is negative, the resonance frequencies of these modes differ significantly, which produces a large axial ratio (AR) bandwidth. For the proposed antenna, the numerical results show the 10 dB impedance bandwidth to be around 44% and the 3 dB axial ratio bandwidth to be higher than 64%.

Optimal Design of Air-spring and Active Control of Vibration Isolation Table (공기스프링의 최적설계 및 방진 테이블의 능동 제어)

  • An, Chae-Hun;Kim, Ho-Sung;Yim, Kwang-Hyeok;Jin, Kyong-Bok;Rim, Kyung-Hwa
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2006.11a
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    • pp.909-914
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    • 2006
  • Vibration isolation tables are mostly required in precise measurement and manufacturing system. Among the vibration isolation tables, an air spring is the most favorable equipment because of low resonant frequency and high damping ratio. However, it is difficult to design the air spring with the required stiffness and damping ratio. Futhermore, whenever conventional active control methods are applied to the air spring, it may be difficult to obtain effective control performance due to high nonlinearity of air spring. In this paper, the optimal design of the air spring is performed using genetic algorithm to bring out low resonant frequency and high damping ratio. Also, active control of the vibration isolation table with 3-DOF model is proposed using the adaptive control method. Through experiments, optimal design is shown to be effective. And performance of the proposed control method is verified to be better than those of the passive control method and the conventional active control methods.

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Analysis and Control of A Fixed Frequency LCL-type Isolated Bidirectional Converter (고정주파수 LCL타입 절연형 양방향 컨버터 해석 및 제어)

  • Park, Sangeun;Cha, Hanju
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.30 no.3
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    • pp.65-72
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    • 2016
  • This paper discussed the LCL-type & Isolated bidirectional dc-dc converter(BDC) with dual full bridge inverter. In order to verify the analysis of the BDC, Experimental prototype has been designed and implemented to supply constant voltage regardless of loads and proposed a method to select switching frequency that depended on two inductors' inductance ratio and transformer parameters. The proposed converter has been composed of LCL resonant network with unit inductance ratio ($L_r/L_f$=1) and then operated with fixed duty, 50% duty ratio and fixed frequency. There are some characteristics that input voltage and output voltage of the BDC is nearly identical and zero voltage turn-on switching is possible in forward and reverse mode. Finally, it has been showed that BDC is possible to commutate operating mode normally and provide constant output voltage in selected switching frequency.