1. School of Electrical Engineering, University of Jinan, Jinan 250022, China, and also with the Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong (e-mail: zhangmenghua@mail.sdu.edu.cn).
2. Department of Mechanical Engineering, The Hong Kong Polytechnic University, Hong Kong (e-mail: mmjxj@polyu.edu.hk).