Micromachined rectangular-spiral-coil actuator for radio-controlled cantilever-like actuation

• Wireless RF MEMS actuator based on shape memory alloy (SMA) is reported.
• SMA-coil-based resonant circuit functions as RF-to-thermomechanical transducer.
• SMA heater/actuator is radio-controlled to produce cantilever-like motions.
• Device offers >2× force, 2× more power-efficient response, and high frequency selectivity.
• Widely adopted cantilever-mode design potentially broadens application opportunity.

This paper reports of a micromachined shape-memory-alloy (SMA) actuator in the shape of a rectangular spiral coil that is designed to perform cantilever-like actuation. The SMA-coil actuator itself forms a passive resonant circuit that functions as a wireless heat source activated using external radio-frequency (RF) electromagnetic fields for frequency-selective control of the actuation. The SiO2 stress layers are selectively patterned on the actuator structure of nickel–titanium SMA, or Nitinol, to manipulate the cantilever profile at the nominal cold state. RF radiation with varying field frequencies shows strong frequency dependence of wireless heating, actuation displacement, and force generation by microfabricated actuators with resonant frequencies of 170–245 MHz. The actuators excited at resonance exhibit maximum out-of-plane displacement and force of 215 μm and 71 mN, respectively. The developed wireless SMA actuator not only provides >2× the force and 2× more power-efficient response compared to the preceding design with similar self-heating mechanism but also offers broader potential applications brought by its commonly adopted cantilever-based actuation.