While vanadium dioxide is already known for its ability to change size, shape, and physical identity, a team of researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory say that super strength can now be added to that list of attributes. They demonstrated a micro-sized robotic torsional muscle/motor made from vanadium dioxide, which for its size is a thousand times more powerful than a human muscle, was able to catapult objects 50 times heavier than itself over a distance five times its length within 60 milliseconds.

What makes vanadium dioxide highly coveted by the electronics industry is that it is one of the few known materials that’s an insulator at low temperatures but abruptly becomes a conductor at 67 degrees Celsius. This temperature-driven phase transition from insulator-to-metal is expected to one day yield faster, more energy efficient electronic and optical devices. However, vanadium dioxide crystals also undergo a temperature-driven structural phase transition whereby when warmed they rapidly contract along one dimension while expanding along the other two. This makes vanadium dioxide an ideal candidate material for creating miniaturized, multi-functional motors and artificial muscles.

The team fabricated a micro-muscle on a silicon substrate from a long “V-shaped” bimorph ribbon comprised of chromium and vanadium dioxide. When the V-shaped ribbon is released from the substrate it forms a helix consisting of a dual coil that is connected at either end to chromium electrode pads. Heating the dual coil actuates it, turning it into either a micro-catapult, in which an object held in the coil is hurled when the coil is actuated, or a proximity sensor, in which the remote sensing of an object (meaning without touching it) causes a “micro-explosion,” a rapid change in the micro-muscle’s resistance and shape that pushes the object away.

They say that multiple micro-muscles can be assembled into a micro-robotic system that simulates an active neuromuscular system, and the torsional motion allows the device to remotely detect a target and respond by reconfiguring itself to a different shape. This simulates living bodies where neurons sense and deliver stimuli to the muscles and the muscles provide motion.

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