Radio-Controlled Microactuator Based on Shape-Memory-Alloy Spiral-Coil Inductor

• Published in: Journal of microelectromechanical systems 2013-04, Vol.22 (2), p.331-338
• Main Authors: Mohamed Ali, Mohamed Sultan, Bycraft, B., Bsoul, A., Takahata, K.
• Format: Article
• Language: English
• Subjects: Actuators; Applied sciences; Coils; Cross-disciplinary physics: materials science; rheology; Electronics; Exact sciences and technology; General equipment and techniques; Heating; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Materials science; Mechanical engineering. Machine design; Methods of nanofabrication; Micro- and nanoelectromechanical devices (mems/nems); Microactuators; micromachining; Physics; Precision engineering, watch making; radio control; Radio frequency; Self-assembly; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; shape memory alloys (SMAs); Temperature measurement; Transducers; Wireless communication; Wireless sensor networks
• ISSN: 1057-7157; 1941-0158
• DOI: 10.1109/JMEMS.2012.2221161

This paper reports a bulk-micromachined shape-memory-alloy (SMA) actuator in the form of a spiral coil that constitutes an inductor-capacitor resonant circuit. The out-of-plane actuation of the SMA spiral-coil inductor is wirelessly controlled using external radio frequency (RF) magnetic fields. The resonant circuit is used as a frequency-selective wireless heater in which the SMA inductor produces heat to activate its own actuation when resonated with the RF magnetic field. The direct integration of bulk-micromachined nitinol SMA with a threshold temperature of 65 ° C into a planar microfabrication process is enabled to build the 3-D spiral-coil SMA actuator in a self-assembled manner using a SiO 2 reset layer patterned on the SMA coil. The fabricated SMA structure yields an out-of-plane displacement of 466 μm in the cold state. The full actuation to the flat state is reached at 70°C upon tuning the field frequency to ~ 230 MHz with an RF output power of 0.7 W. The developed actuator is demonstrated to provide a maximum force of 30 mN. The temporal response of the actuator is revealed to be two to three times faster than that of previously reported wireless SMA actuators with separate heat sources.