Artificial muscle

Artificial muscles, also known as muscle-like actuators, are materials or devices that mimic natural muscle and can change their stiffness, reversibly contract, expand, or rotate within one component due to an external stimulus (such as voltage, current, pressure or temperature). The three basic actuation responses—contraction, expansion, and rotation—can be combined within a single component to produce other types of motions (e.g. bending, by contracting one side of the material while expanding the other side). Conventional motors and pneumatic linear or rotary actuators do not qualify as artificial muscles, because there is more than one component involved in the actuation. Owing to their high flexibility, versatility and power-to-weight ratio compared with traditional rigid actuators, artificial muscles have the potential to be a highly disruptive emerging technology. Though currently in limited use, the technology may have wide future applications in industry, medicine, biorobotics, and many other fields. While there is no general theory that allows for actuators to be compared, there are "power criteria" for artificial muscle technologies that allow for specification of new actuator technologies in comparison with natural muscular properties. In summary, the criteria include stress, strain, strain rate, cycle life, and elastic modulus. Some authors have considered other criteria (Huber et al., 1997), such as actuator density and strain resolution. As of 2014, the most powerful artificial muscle fibers in existence can offer a hundredfold increase in power over equivalent lengths of natural muscle fibers. Researchers measure the speed, energy density, power, and efficiency of artificial muscles; no one type of artificial muscle is the best in all areas.