1. School of Electrical and Electronics EngineeringNanyang Technological University Singapore 639798 Singapore
2. School of Precision Instrument and Opto‐ElectronicsTianjin University 92 Weijin Road, Nankai District Tianjin 300072 P. R. China
3. Department of Biomedical EngineeringUniversity of Michigan Ann Arbor MI 48109 USA
4. School of Chemical and Biomedical EngineeringNanyang Technological University Singapore 639798 Singapore