Browsing by Author "Chang, Y. H."

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A widely tunable dual-wavelength CWTi : sapphire laser with collinear output
(2008-03-03)
Luo, C. W.
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Yang, Y. Q.
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Mak, I. T.
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Chang, Y. H.
;
Wu, K. H.
We report a collinear output and tunable dual-wavelength CW Ti:sapphire laser with a simple cavity configuration. The wavelength splitting range is easily tuned from 10 nm to 110 nm, which provides 56 THz bandwidth for terahertz generation. The total output power of two colors with the spatial mode of TEM00 is between 700 mW and 300 mW, for small and large wavelength splittings, respectively, under 5 W argon-ion laser pumping. (C) 2008 Optical Society of America.
Crossover from negative to positive magnetoresistance in a Si delta-doped GaAs single quantum well
(2010-07-01)
Lo, Shun-Tsung
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Chen, Kuang Yao
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Su, Yi-Chun
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Liang, C. -T.
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Chang, Y. H.
We have performed magnetoresistance measurements on a Si delta-doped GaAs single quantum well With increasing temperature T, a crossover from negative magnetoresistance (NMR) to positive magnetoresistance (PMR) can be observed Our experimental results suggest that such a crossover corresponds to a transition from variable range hopping regime to activated electron transport. This is also consistent with the measured non-monotonic carrier density dependence on T. (C) 2010 Elsevier Ltd All rights reserved.
Low threshold current, low resistance 1.3 mu m InAs-InGaAs quantum-dot VCSELs with fully doped DBRs grown by MBE
(2007-01-01)
Yu, Hsin-Chieh
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Wang, Jyh-Shyang
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Su, Yan-Kuin
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Chang, Shoou-Jinn
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Kuo, Hao-Chung
The processing technology of 1.3 mu m InAs-InGaAs quantum-dot VCSELs with fully doped DBRs grown by MBE will be demonstrated. The threshold currents of the fabricated devices with 10 mu m oxide-confined aperture are 0.7mA, which correspond to 890A/cm(2) threshold current density. And the threshold voltage of the device is 1.03V and maximum output power is 33 M. The series resistance is 85 Omega which is 10 times lower then our preliminary work and 3 times lower then intracavity contacted InAs-InGaAs quantum-dot VCSEL. This relatively lower resistance can even comparable with the best result reported in InGaAs oxide-confined VCSELs with intracavity contact.
Optimal design of rectangular composite flat-panel sound radiators considering excitation location
(2014-02-01)
Jiang, C. H.
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Chang, Y. H.
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Kam, T. Y.
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機械工程學系
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Department of Mechanical Engineering
The optimal excitation locations of rectangular composite sound radiation plates to produce relatively smooth sound level pressure (SPL) curves are determined using an optimal design method. In the optimal design process, the vibration of the plate is analyzed using the Rayleigh-Ritz method, the sound pressure produced by the plate is calculated using the first Rayleigh integral, and the optimal excitation location is determined using a global optimization technique. The experimental SPL curves of several sound radiators were measured to verify the accuracy of the theoretical predictions. In the determination of the optimal excitation location, the trial radius of the circular excitation force is used in the vibro-acoustic analysis to predict the theoretical SPL curve of the plate, a SPL discrepancy function is established to measure the sum of the squared differences between the SPLs at the chosen excitation frequencies and the average value of such SPLs, and a global minimization technique is used to search for the best estimate of the radius of the circular excitation force by making the SPL discrepancy function a global minimum. The optimal excitation locations of several composite sound radiators with different aspect ratios and layups are determined using the proposed method. (C) 2013 Elsevier Ltd. All rights reserved.
Probing Landau quantization with the presence of insulator-quantum Hall transition in a GaAs two-dimensional electron system
(2008-07-23)
Chen, Kuang Yao
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Chang, Y. H.
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Liang, C-T
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Aoki, N.
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Ochiai, Y.
Magneto-transport measurements are performed on the two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure. By increasing the magnetic field perpendicular to the 2DES, magneto-resistivity oscillations due to Landau quantization can be identified just near the direct insulator-quantum Hall (I-QH) transition. However, different mobilities are obtained from the oscillations and transition point. Our study shows that the direct I-QH transition does not always correspond to the onset of strong localization.
Sound radiation of panel-form loudspeaker using flat voice coil for excitation
(2017-01-15)
Jiang, C. H.
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Kam, T. Y.
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Chang, Y. H.
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機械工程學系
;
Department of Mechanical Engineering
A novel panel-form loudspeaker in which the panel of the speaker is excited by the forces generated through the flat voice coil of a rectangular electro-magnetic type exciter for sound radiation is presented. The exciter when properly designed has the advantage of exerting appropriate loads to the panel so that the major sound pressure level (SPL) dips of the speaker can be suppressed or even eliminated. For designing such panel-form speaker, a method formulated on the basis of the classical plate theory (CPT), Ritz method, and first Rayleigh integral is proposed for predicting the SPL curve of the speaker. An experimental investigation was performed to verify the feasibility of the proposed method. The effects of some system parameters on the major SPL dips of the proposed panel-form speakers are investigated by means of several numerical examples. The optimal locations of flat voice coils for exciting several panel-form speakers are determined to illustrate the important role of excitation location for enhancing sound quality of such speakers via the removal or suppression of the major SPL dips. (C) 2016 Elsevier Ltd. All rights reserved.