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 φ8 -mm magnetoelastic stator lithographically micromachined from Metglas 2826MB-bulk-foil with 25 μm 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 nN ·m, ≈23 mdeg, and 9 mg, respectively. Design S uses a stator that is a sandwich of Si (φ8 mm diameter and 65 μm thickness) and magnetoelastic foil (φ8 mm diameter and 25 μm 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 nN ·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.