1 Institute of Electromagnetics and Acoustics and Key Laboratory of Electromagnetic Wave Science and Detection Technology, Xiamen University, Xiamen 361005, China
2 Shenzhen Research Institute of Xiamen University, Shenzhen 518057, China
3 Department of Electrical Engineering, City University of Hong Kong, Hong Kong 999077, China
4 Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore
5 Department of Materials Science and Engineering, National University of Singapore, Singapore 117575, Singapore