New robotic 'muscle' thousand times stronger

Scientists have developed a new robotic 'muscle', thousand times more powerful than a human muscle, which can catapult objects 50 times heavier than itself - faster than the blink of an eye.
Researchers with the Lawrence Berkeley National Laboratory in US demonstrated a micro-sized robotic torsional muscle/motor made from vanadium dioxide that is able to catapult very heavy objects over a distance five times its length within 60 milliseconds.
"We've created a micro-bimorph dual coil that functions as a powerful torsional muscle, driven thermally or electro-thermally by the phase transition of vanadium dioxide," said study leader, Junqiao Wu.
"Using a simple design and inorganic materials, we achieve superior performance in power density and speed over the motors and actuators now used in integrated micro-systems," Wu said.

What makes vanadium dioxide highly coveted by the electronics industry is that it is one of the few known materials that is 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 miniaturised, multi-functional motors and artificial muscles.
Wu and his colleagues fabricated their 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 causes a "micro-explosion," a rapid change in the micro-muscle's resistance and shape that pushes the object away.