[1] Univ Maryland, Dept Mech Engn, College Pk, MD 20742 USA
[2] Univ Maryland, Fischell Dept Bioengn, College Pk, MD 20742 USA
[3] Univ Calif Berkeley, Dept Mech Engn, Berkeley, CA 94720 USA
[4] Berkeley Sensor & Actuator Ctr, Berkeley, CA USA
[5] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[6] Univ Calif Berkeley, 5135 Etcheverry Hall, Berkeley, CA 94720 USA