Browsing by Author "Chen, P. Y."

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Experimental and numerical studies of local current mapping on a PEM fuel cell
(2008-10-01)
Hwnag, J. J.
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Chang, W. R.
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Peng, R. G.
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Chen, P. Y.
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Su, A.
Local current distribution on a PEM fuel cell has been mapped experimentally by using a special-designed single cell fixture. it is composed of a composite cathodic flow-field plate, a membrane electrode assembly (MEA) and a stainless-steel anodic flow-field plate. An array of 16 individual conductive segments was distributed on the composite plate. A self-made MEA is in direct contact with the segmented current collectors. Regional-averaged current through each segment is determined by using the Hall-effect sensor. To ensure the data reliability, a comparison of polarization curves was made between the composite flow-field plate and the conventional flow-field plate. Then, the effects of flow-field patterns, dew points of the cathodic feedings and cathodic stoichiometrics on the local current distribution were examined. The transient variation of the local current distribution on the cathode under supersaturated conditions was further visualized to illustrate the flooding phenomena in different flow patterns. This technique developed by the present work has contributed to knowledge and understanding the local current distributions in a PEM fuel cell that is helpful in designing the fuel-cell components. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.
Improved field emission properties of thiolated multi-wall carbon nanotubes on a flexible carbon cloth substrate
(2007-10-03)
Chuang, F. T.
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Chen, P. Y.
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Cheng, T. C.
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Chien, C. H.
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Li, B. J.
In this paper we report the observation of enhanced field emission properties from thiolated multi-wall carbon nanotubes ( MWCNTs) produced by a simple and effective two- step chemical surface modification technique. This technique implements carboxylation and thiolation on the MWCNTs synthesized by microwave plasma chemical vapor deposition ( MPCVD) on the flexible carbon cloth substrate. The resulting thiolated MWCNTs were found to have a very low threshold field value of 1.25 V mu m(-1) and a rather high field enhancement factor of 1.93 x 10(4), which are crucial for applications in versatile vacuum microelectronics.
Microstructures and electrical properties of lead-based PBZNZT and lead-free BNKT piezoelectric ceramics using microwave sintering
(2011-05-01)
Chen, P. Y.
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Chen, C. S.
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Chou, C. C.
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Tseng, T. Y.
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Chen, H. D.
This paper is a comparative study involving sintering conditions (different sintering temperatures and time), process (conventional and microwave sintering), microstructures, and electrical measurements to investigate the mechanism of microwave absorption, and the difference in the microstructural characteristics and electrical properties of lead-based and lead-free ceramics. The lead-based piezoelectric ceramics are x(0.94PbZn(1/3)Nb(2/3)O(3) + 0.06BaTiO(3)) + (1 - x) PbZr(y)Ti(1) (y)O(3) where x = 0.5, y = 0.52 (abbreviated as PBZNZT) and the lead-free ceramics are (Bi(0.5)(Na(1-x)K(x))(0.5))TiO(3) where x = 0.18 (abbreviated as BNKT), all sintered by microwave heating. Experimental results indicate that PBZNZT and BNKT specimens have different microwave absorption efficiencies. Compared with BNKT samples, PBZNZT samples absorb microwave radiation more efficiently in MWS process. This might be attributed to the contribution of the dielectric constant and dipole loss which might dominate the absorption of microwave energy for ferroelectric and piezoelectric materials. HRTEM and energy dispersive spectroscopic investigations show that the grain boundaries of MWS samples exhibit less PbO and ZnO segregation than those of CS samples form PBZNZT specimens. On the other hand, BNKT specimens exhibit no compositional segregation at the grain boundaries after the CS and MWS processes. In addition, the MWS process can achieve a more uniform composition and crystallization in PBZNZT and BNKT ceramics, thus improving the electrical properties. (C) 2011 Elsevier B.V. All rights reserved.
Nanomanipulation measurement and PIC simulation of field-emission properties from a single crystallized silicon nano-emitter
(2007-06-06)
Cheng, T. C.
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Hsu, K. H.
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Chen, P. Y.
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Huang, W. J.
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Wu, J. S.
The field-emission characteristics of a single silicon nano-emitter were investigated by means of experiments and simulation models. The emitter array was fabricated by dry etching using an inductively coupled plasma (ICP) through a three-step process. A novel experimental technique was developed to precisely measure the field-emission current from a single silicon emitter. Accompanying these measurements, a parallelized three-dimensional particle-in-cell (PIC) code, in which the Fowler - Nordheim emission law was implemented at the emitter surface, was employed to simulate the emission current both with and without taking into account the space charge effect. Results show that the simulated I - V relationship when considering the space - charge effect was in excellent agreement with the actual measurements. Noticeably, the predicted turn-on voltage was found to be within only 9.3% of the experimental data. In addition, both the predicted and experimental data demonstrated a consistent single linear slope in the FN plot, which indicates that the field emission from a single silicon tip is a barrier-tunnelling, quantum mechanical process.
Optimal design of integrally gated CNT field-emission devices using a genetic algorithm
(2007-10-03)
Chen, P. Y.
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Chen, C. H.
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Wu, J. S.
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Wen, H. C.
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Wang, W. P.
A method to optimize the focusing quality of integrally gated CNT field- emission ( FE) devices by combining field- emission modeling and a computational intelligence technique, genetic algorithm ( GA), is proposed and demonstrated. In this work, the e- beam shape, as a characteristic parameter of electron- optical properties, is calculated by field- emission simulation modeling. Using a design tool that combines GA and physical modeling, a set of structural and electrical parameters for four FE device groups, including double- gate, triple- gate, quadruple- gate and quintuple- gate type, were optimized. The resultant FE devices exhibit satisfactory e- beam focusabilities and the extracted parameters with the best performance for each type of FE device were represented to be fabricated by a VLSI technique. The GA- based automatic design parameter extraction will significantly benefit the design of integrated electron- optical systems for versatile vacuum micro- and nano-electronic applications.
Synthesis design of artificial magnetic metamaterials using a genetic algorithm
(2008-08-18)
Chen, P. Y.
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Chen, C. H.
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Wang, H.
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Tsai, J. H.
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Ni, W. X.
In this article, we present a genetic algorithm (GA) as one branch of artificial intelligence (AI) for the optimization-design of the artificial magnetic metamaterial whose structure is automatically generated by computer through the filling element methodology. A representative design example, metamaterials with permeability of negative unity, is investigated and the optimized structures found by the GA are presented. It is also demonstrated that our approach is effective for the synthesis of functional magnetic and electric metamaterials with optimal structures. This GA-based optimization-design technique shows great versatility and applicability in the design of functional metamaterials. (C) 2008 Optical Society of America.