1. Department of Electrical & Computer Engineering; National University of Singapore; 4 Engineering Drive 3 Singapore 117576 Singapore
2. Center for Intelligent Sensors and MEMS; National University of Singapore; 4 Engineering Drive 3 Singapore 117576 Singapore
3. NUS Suzhou Research Institute (NUSRI); Suzhou Industrial Park Suzhou 215123 P. R. China
4. Graduate School for Integrative Science and Engineering; National University of Singapore; 119077 Singapore