1. Laboratory for Soft Machines & Electronics School of Packaging Department of Mechanical Engineering Department of Electrical and Computer Engineering Michigan State University East Lansing MI 48824 USA
2. Department of Mechanical Engineering & Materials Science Duke University Durham NC 27708 USA
3. U.S. Naval Research Laboratory Washington DC 20375 USA
4. School of Optical and Electronic Information and Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology Wuhan Hubei 430074 China
5. Department of Civil and Environmental Engineering Massachusetts Institute of Technology Cambridge MA 02139 USA
6. Department of Electrical & Computer Engineering Duke University Durham NC 27708 USA