Browsing by Author "Chang, WR"

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Acoustic pulse propagation in a fluctuating ocean with range-dependent sound-speed profile
(1996-04-01)
Chang, WR
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Tarng, JH
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交大名義發表
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電信工程研究所
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National Chiao Tung University
When an acoustic pulse propagates in a randomly fluctuating ocean with a deterministic sound-speed profile, it is distorted since every frequency component experiences different extents of scattering from the random inhomogeneity and echo numbers. Here, the split-step method is used to simulate an acoustic pulse with a 3-kHz carrier propagating through a turbulent ocean with range-independent/-dependent sound-speed profiles. It is found that (1) the ocean is a frequency-selective fading channel; (2) the received pulse profile is dependent on the received depth, sound-speed distribution, fluctuation strength, and scale length of turbulence in oceans; (3) the rms pulsewidth is broadened by several times its initial value as a consequence of pulse echoes and pulse wandering of every pulse realization of the ensemble; (4) the rms pulsewidth is increased when the fluctuation strength increases or the scale length decreases; and (5) the statistical properties of the propagating pulse are similar for both the range-independent and -dependent cases in the mean square sense. (C) 1996 Acoustical Society of America.
Acoustic pulse propagation in a range-dependent turbulent ocean
(1995)
Tarng, JH
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Chang, WR
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電信工程研究所
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Institute of Communications Engineering
Fabrication and microstructure of the dc-magnetron-sputtered YBa2Cu3O7-x superconducting thin films
(1996-04-01)
Koo, HS
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Tseng, TY
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Chang, WR
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Tu, GC
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材料科學與工程學系
Systematic investigations were conducted to determine the effect of deposition conditions on the microstructure and superconducting properties of YBa2Cu3O7-x thin films produced by d.c. magnetron sputtering on (001) MgO substrate. The films were c-axis preferentially oriented with respect to the (001) MgO surface at substrate temperatures of 680-700 degrees C. X-ray diffraction patterns clearly indicated the existence of the c-axis alignment normal to the substrate surface and some second phases. The second phases, including a Cu-rich phase and Y2O3, were identified by energy dispersive X-ray spectrometer and the microstructures were analysed by electron and;atomic force microscopes.
Three-dimensional modeling of 900-MHz and 2.44-GHz radio propagation in corridors
(1997-05-01)
Tarng, JH
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Chang, WR
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Hsu, BJ
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交大名義發表
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電信工程研究所
A three-dimensional (3-D) propagation model, combined with a patched-wall model, has been developed to predict radio loss in a corridor environment, The ray-tracing technique is used and combined with the ray-fixed coordinate system to simplify the computations of transmission, reflection, and diffraction coefficients in 3-D space, The computed path loss is compared with the measured value of 900-MHz and 2.44-GHz radio propagation along a hallway and gives a reasonable agreement, It is also found that the fields transmitted through the interior walls give the major contribution to the received field when the radio path lies around a corner.