Wireless Tagging and Actuation with Shaped Magnetoelastic Transducers.

Abstract

The promise and the challenges of patterned, micro-scale magnetoelastic transducers and their integration with silicon is the focus of this thesis. As demonstrations, wireless magnetoelastic chip-scale resonant rotary motors and miniaturized magnetoelastic tags are investigated. The motors consist of a magnetoelastically-actuated stator, a silicon rotor, a “hub” structure, and DC and AC coils. Two generations are described. The first-generation motor uses a stator with a bilayer of silicon (ø8 mm x 65 µm thick) and magnetoelastic foil (Metglas™ 2826MB bulk foil, ø8 mm x 25 µm thick). The motor provides bi-directional rotation capability, and typical resonant frequencies of the clockwise and counterclockwise modes are 6.1 kHz and 7.9 kHz, respectively. The counterclockwise mode provides a rotation rate of ≈100 rpm, start torque of 30 nN∙m, a step size of 74 milli-degree and a capability for driving a 100 mg payload while a 8 Oe DC and a 6 Oe-amplitude AC magnetic field are applied. The second-generation of motors includes bilayer standing wave and traveling wave designs (ø5 mm stators) with integrated capacitive sensors for real-time position measurement and speed estimation. Clockwise and counterclockwise mode shapes with resonant frequencies of 12 kHz and 22.4 kHz, respectively, are measured for the standing wave motor. Two mode shapes (with π/2 spatial phase difference) at resonant frequencies of 30.2 kHz and 31.7 kHz are measured for the traveling wave motor. The wireless actuation capability and the hybrid integration of the bulk magnetoelastic material with silicon show promise for use in many microsystems. A lithographically patterned, frame-suspended hexagonal magnetoelastic tag design (ø1.3 mm x 27 µm thick) is also investigated. These tags provide ≈75x signal amplitude improvement compared to a non-suspended disc tag, while occupying ≈100x smaller area than typical commercial ribbon tags. Signal strength can also be boosted by taking advantage of tag signal superposition. Linear signal superposition of the response has been experimentally measured for clustered sets of frame-suspended tags that include as many as 500 units. Miniaturized tags with sufficient signal strength may enable new applications, such as distributing the tags into a network of cracks and subsequently mapping the distribution.