This material is based upon work supported by the National Science Foundation under Grant No. 0708469, No. 0737297, No. 0837677, Air Force Office of Scientific Research (AFOSR), and Wright Center for Sensor System Engineering (WCSSE). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation, the United States Air Force, Department of Defense or the U.S. Government.