Linear actuators from Artificial Muscle Inc., Menlo Park, Calif. (, rely on an electroactive polymer that expands or contracts in response to a voltage input. Two conic sections made of the polymer are mounted opposite each other. When one is activated, it pushes the output shaft in one direction. Activating the other moves the shaft back in the opposite direction. The actuators are silent, efficient, and have high power densities, according to the company. They are also smaller, lighter, and less costly than conventional electromagnetic motor-based actuators. Potential applications include valve actuators, diaphragm pumps, generators, motors, sensors, and even speakers.