Nanotube based engine

We discuss a mechanism for converting electrical energy into translational motion using a variable-shape bistable carbon nanotube. Clamping one tube end open and the other one closed, we use an applied voltage to switch the tube between mostly collapsed and mostly inflated shapes. Devices based on such a double-pinned tube geometry can operate as a voltage-controlled constant-force spring, a charge-controlled harmonic spring, or an electromechanical engine performing work by coupling to a propagating collapsed/inflated transition region. Making an analogy to ideal-gas thermodynamics, constant-voltage, constant-charge, and constant-geometry operational regimes correspond to isothermal, adiabatic and isochoric processes. Constant-voltage, constant-charge, and constant-geometry processes coupled can be combined into cycles analogous to those of a heat engine. Unlike a heat engine, the tube bistability enables it to collect useful work on both inflation and collapse motions, thus eliminating the need for external forces to restore the system to its initial state during the operational cycle.