1. Research and Development Center, Fortune Electric Company, Taoyuan 320, Taiwan
2. Department of Mechanical Engineering, National Central University, Taoyuan 320, Taiwan
3. Department of Systems and Naval Mechatronic Engineering, National Cheng Kung University, Tainan 701, Taiwan
4. Department of Physics, National Taiwan University, Taipei 10617, Taiwan
5. Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118, USA