1. Universidade de São Paulo, LSI‐EPUSP, C.P. 8174, São Paulo, SP, 01051, Brazil
2. Center for Sensors Technologies, Department of Electrical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104‐6390
3. Universidade de Campinas, DSIF‐FEE, C.P. 6101, Campinas, SP, 13081, Brazil