Miniature Wireless Magnetoelastic Resonant Motor With Frequency Selectable Bidirectional Rotation

This paper presents the analysis, fabrication, and experimental results of wirelessly actuated chip-scale rotary motors. Two designs are described. Design M is actuated by a $\phi 8$ -mm magnetoelastic stator lithographically micromachined from Metglas 2826MB-bulk-foil with 25 $\mu\hbox {m}$ thickness. It operates at a resonant frequency of 11.35 kHz while 3-Oe dc and 2-Oe amplitude ac magnetic fields are applied. The measured rotation speed, start torque, calculated driving step size, and payload are 44 r/min, 2 $\hbox {nN} \cdot \hbox {m}$ , $\approx$ 23 mdeg, and 9 mg, respectively. Design S uses a stator that is a sandwich of Si ( $\phi 8$ mm diameter and 65 $\mu\hbox {m}$ thickness) and magnetoelastic foil ( $\phi 8$ mm diameter and 25 $\mu\hbox {m}$ thickness) to tailor the stiffness. The typical resonant frequencies of clockwise (CW) mode and counterclockwise (CCW) mode are 6.1 and 7.9 kHz, respectively. The CCW mode provides a rotation rate of about 100 r/min, start torque of 30 $\hbox {nN} \cdot \hbox {m}$ , and driving step size of 74 mdeg while 8-Oe dc and 6-Oe amplitude ac magnetic fields are applied. Bidirectional rotation is realized by switching the applied frequency, thereby exciting the stator in a slightly different mode shape. Design S shows at least 43-mg payload capability. $\hfill$ [2012-0207]