1. Department of Electrical and Computer Engineering; National University of Singapore; 4 Engineering Drive 3 Singapore 117576 Singapore
2. NUS Suzhou Research Institute (NUSRI); Suzhou Industrial Park Suzhou 215123 P. R. China
3. Center for Intelligent Sensors and MEMS; National University of Singapore; E6#05-11F, 5 Engineering Drive 1 Singapore 117608 Singapore
4. Graduate School for Integrative Science and Engineering; National University of Singapore; Singapore 117576 Singapore