1. Department of Electrical Engineering, Tamkang University, New Taipei City 251, Taiwan
2. Graduate Institute of Optoelectronic Engineering, National Chung Hsing University, Taichung 402, Taiwan
3. Department of Electrical Engineering, National Chung Hsing University, Taichung 402, Taiwan
4. Department of Chemical and Materials Engineering, National University of Kaohsiung, Kaohsiung 811, Taiwan
5. Department of Aeronautical Engineering, Chaoyang University of Technology, Taichung 413, Taiwan