1. Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa, AL 35487, USA
2. Department of Electrical Engineering, Columbia University, New York City, NY 10027, USA
3. Department of Electrical and Computer Engineering, Penn State Behrend, Erie, PA 16563, USA
4. Key Laboratory for Precision and Non-traditional Machining Technology of the Ministry of Education, Dalian University of Technology, Dalian, Liaoning 116024, China