[1] Xi An Jiao Tong Univ, Sch Mech Engn, Xian, Shaanxi, Peoples R China
[2] State Key Lab Strength & Vibrat Mech Struct, Xian 710049, Shaanxi, Peoples R China
[3] Nanyang Technol Univ, Sch Elect & Elect Engn, Singapore 639798, Singapore
[4] ASTAR, Inst Microelect, 2 Fusionopolis Way,08-02 Innovis Tower, Singapore 138634, Singapore
[5] Univ Minnesota, Dept Elect & Comp Engn, Minneapolis, MN 55455 USA