This paper highlights emerging medical applications for magnetoelastic sensing and actuation, each taking advantage of the wireless capabilities and small form factor enabled by the magnetoelastic transduction technique. Magnetoelastic transduction leverages the strong coupling between stress, strain, and magnetization intrinsic to some materials – notably amorphous metals and rare earth crystalline alloys. This coupling provides inherently wireless transduction that does not require any onboard power; these traits are especially advantageous in diagnostic and therapeutic medical implant applications. This paper first describes the basic transduction technique, and considerations for design and fabrication of medical systems which utilize the technique. These considerations include material selection, magnetic biasing, packaging, and interrogation approaches. The first application highlighted is stent monitoring, in which the masssensitive magnetoelastic resonator is integrated along the inner sidewall of the stent to provide early detection of stent occlusion. Prototype tests indicate clinical feasibility and a full scale range from zero stent occlusion to full stent occlusion. Wireless ranges of up to 15 cm in situ have been achieved using 25 mm long resonators. The second application is wireless strain sensing, which can be useful for orthopedic implants and orthodontia. A differential strain sensor is described, with a dynamic range of 0-1.85 mstrain – accommodating typical palatal expander strain – and a sensitivity of 12.5x103 ppm/mstrain. Finally, a wireless actuator intended to agitate fluid for mitigation of encapsulation of glaucoma drainage devices is shown. Peak actuator vibration amplitudes of 1.5 μm – sufficient to affect cell adhesion in other studies – are recorded at a wireless range of 25-30 mm.
S. R. Green and Y. B. Gianchandani, "Wireless magnetoelastic transducers for biomedical applications," Proc. SPIE 10194, Micro- and Nanotechnology Sensors, Systems, and Applications IX, 1019412 (Presented at SPIE Defense + Security: April 10, 2017; Published: 18 May 2017); https://doi.org/10.1117/12.2263677.
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