Battery-Free, Folding Robots Are Powered By Wireless Magnetic Field
A team of researchers from Harvard University's Wyss Institute has created battery-free folding robots that are capable of complex, repeatable movements - powered and controlled through a wireless magnetic field. "This system requires only basic, passive electronic components on the robot to deliver an electric current – the structure of the robot itself takes care of the rest," says Je-sung Koh, Ph.D. The robots are flat and thin plastic tetrahedrons, with the three outer triangles connected to the central triangle by hinges, and a small circuit on the central triangle. Attached to the hinges are coils made of metal shape-memory alloy (SMA) that can recover its original shape after deformation by being heated to a certain temperature. When the robot's hinges lie flat, the SMA coils are stretched out in their 'deformed' state; when an electric current is passed through the circuit and the coils heat up, they spring back to their original, relaxed state, contracting like tiny muscles and folding the robots' outer triangles in toward the center. When the current stops, the SMA coils are stretched back out due to the stiffness of the flexure hinge, thus lowering the outer triangles back down. The power that creates the electrical current needed for the robots' movement is delivered wirelessly using electromagnetic power transmission, the same technology inside wireless charging pads that recharge the batteries in cell phones and other small electronics. An external coil with its own power source generates a magnetic field, which induces a current in the circuits in the robot, thus heating the SMA coils and inducing folding.