1. Key Laboratory of Road and Traffic Engineering of Ministry of Education, Tongji University, Shanghai 200092, P. R. China
2. Department of Electrical and Computer Engineering, National University of Singapore, 4 Engineering Drive 3, Singapore 117576, Singapore
3. Center for Intelligent Sensors and MEMS, National University of Singapore, Block E6 #05-11, 5 Engineering Drive 1, Singapore 117608, Singapore