Shun-Hsyung Chang

Investigation of Low-Cost Surface Processing Techniques for Large-Size Multicrystalline Silicon Solar Cells

The subject of the present work is to develop a simple and effective method of enhancing conversion efficiency in large-size solar cells using multicrystalline silicon (mc-Si) wafer. In this work, industrial-type mc-Si solar cells with area of 125×125 mm2 were acid etched to produce simultaneously POCl3 emitters and silicon nitride deposition by plasma-enhanced chemical vapor deposited (PECVD). The study of surface morphology and reflectivity of different mc-Si etched surfaces has also been discussed in this research. Using our optimal acid etching solution ratio, we are able to fabricate mc-Si solar cells of 16.34% conversion efficiency with double layers silicon nitride (Si3N4) coating. From our experiment, we find that depositing double layers silicon nitride coating on mc-Si solar cells can get the optimal performance parameters. Open circuit (Voc) is 616 mV, short circuit current (Jsc) is 34.1 mA/cm2, and minority carrier diffusion length is 474.16 μm. The isotropic texturing and silicon nitride layers coating approach contribute to lowering cost and achieving high efficiency in mass production.

Underwater Acoustic Multimedia Communication Based on MIMO---OFDM

A transmission scheme is proposed based on multi-input multi-output orthogonal frequency-division multiplexing (OFDM) for underwater acoustic multimedia (UWAM) communication. The proposed scheme integrates direct mapping and space-time block code strategies, a power assignment mechanism, OFDM, adaptive modulation, and unequal error protection in a UWAM system. The proposed UWAM system employs high power, low speed modulation, with schemes providing significant error protection for transmission of sensor data messages requiring a stringent bit-error rate (BER). In contrast, low power, high speed modulation schemes with reduced error protection are provided for messages that can tolerate a high BER, such as image and audio signals. Simulation results show that the proposed scheme not only fulfils the quality of services requirements of a UWAM system, but also maximizes transmission bit rates or minimizes transmission power requirements.

A power assignment mechanism for underwater wireless multimedia

In this paper, we propose an orthogonal variable spreading factor (OVSF) based underwater wireless multimedia (UWM) system. An essential feature of this system is power assignment mechanism, direct mapping (DM) strategy, OVSF technology, unequal error protection schemes, and adaptive modulation are granted to messages that can tolerate high bit error rate (BER). Simulation results show that the proposed scheme can not only fulfill the quality of services (QoS) required by a UWM system, but also achieve the mission of maximum transmission bit rates or minimum transmission power. For the purpose of verifying the proposed argument, a simulation has been done and the results match the derivation very well.

Efficiency Improved by Forming Gas Treatment for Si-Based Solar Cell Applications

The photovoltaic (PV) effects have been investigated and improved using efficient treatments both on single-crystalline (sc) and on multicrystalline (mc) silicon (Si) solar cells. The major effect of forming gas (FG) treatment on solar cell performance is the fill-factor values, which increase 3.75% and 8.28%, respectively, on sc-Si and mc-Si solar cells. As for the optimal 15%- ratio and 40-minute FG treatment, the conversion efficiency () values drastically increase to 14.89% and 14.31%, respectively, for sc- and mc-Si solar cells. Moreover, we can measure the internal quantum efficiency (IQE) values increase with -FG treatment under visible wavelength (400~900 nm) radiation. Thus based on the work in this research, we confirm that passivation has become crucial both in PV as well as in microelectronics fields. Moreover, the developed mc-Si solar cell by proper FG treatment is quite suitable for commercial applications.

Modeling of Non-uniform Polarization for Multi-layered Piezoelectric Transducer for Energy Harvesting Devices

Mathematical and finite element models of non-uniform polarized piezotransducer are discussed, including implementation in finite-element (FE) package ACELAN. The results of numerical studies of single-layer and multilayered transducers are present. The developed modeling workflow was designed relative to manufacturing process of multi-layered transducers. The results were compared with theoretical model of piezoplate and with numerical experiments performed in ANSYS. Effective scheme of polarization and electrodes placement for three-layered transducer is described with possible preliminary polarization techniques.

Circuit Synthesis Using Pathological Elements

The concept of pathological nullor and mirror elements has proven to be a very valuable tool for circuit analysis, synthesis, circuit transformation and interrelation in the realizations using different active elements. The pathological elements provide a common framework for linear and nonlinear circuits. In this paper, the nullor and nullor-mirror equivalents are reviewed, and several new nullor-mirror equivalents are proposed. The nullor-mirror equivalents are conductive to reducing circuit complexity and synthesizing new functional circuits. Combining the nullor-mirror equivalents with circuit transformation techniques, more useful functional circuits with simpler circuit structures can be generated. The circuit synthesis using the proposed nullor-mirror equivalents is illustrated to demonstrate the usefulness and feasibility.

A new principle for circular APSK constellation optimization

In this paper, the symbol error rate for circular Amplitude-and-Phase Shift Keying (APSK) modulation in linear additive white Gaussian noise (AWGN) channel was theoretical evaluated and a new principle for optimal constellation design was proposed. The new principle can maximize the normalized Euclidean distance and reduce the variation between inter-ring and intra-ring distances for high level M-ary APSK modulation. The simulation results showed that the proposed optimal constellation can achieve lower symbol error rate (SER) than the Quadrature Amplitude Modulation (QAM) constellation.

Modeling and optimization of two-stage composite cure with the use open-mold tooling

The paper presents an optimal control synthesis for curing shell-like composite structures using open dies in an autoclave. The control synthesis is a multi-objective optimization problem where minimization objectives are deviations of temperature and degree of cure within a cured part, considering constraints imposed by thermo-kinetic properties of prepreg and manufacturing requirements. The control should eliminate the formation of early hard skin, resin-rich or resin-dry areas, insufficient consolidation, and uneven cure. Such a purpose can be achieved through uniform distribution of temperature and degree of cure within the cured structure. The optimization procedure, including the formulation of the cure problem and the finite element implementation where correct timing of heating-up and maintaining isothermal, is illustrated by an example of the shell-like composite structure manufactured by means of two-stage curing in an autoclave. The technique developed allows estimating the best achievable quality indicators of composite parts, finding key parameters of the control law, and considering all imposed constraints for decision-making.

Singular Nullor and Mirror Elements for Circuit Design

The singular nullor-mirror pathological elements as universal active elements have been found useful in solving circuit analysis and design problems. They find numerous applications in the synthesis, analysis and design of active networks such as modeling different active elements, nodal analysis, circuit transformations, synthesis of active filters, oscillators and other general networks. A summarization of several applications of singular nullor and mirror pathological elements is given in this chapter.

Optimal Design of Underwater Acoustic Projector with Active Elements Made from Porous Piezoceramics

Porous piezoceramic materials have received considerable attention due to their successful application in ultrasonic transducers, hydrophones and other piezoelectric devices. In order to formulate and solve the optimization problem for multilayered piezoelectric transducer with active porous piezoelectric layer, the calculation of the effective moduli for porous piezoelectric material has been previously performed. The obtained dependences of material properties on porosity allowed us to decrease the number of design variables. The multi-objective optimization problem based on the Pareto-frontier calculation has been solved using the live-link of finite-element (FE) package Comsol Multiphysics with MATLAB.