A plasma actuator is a form of advanced servomechanism being developed primarily for aircraft control surfaces as of 2011. The actuator system uses the flow of plasma, which is a highly-ionized gas, to create an easily-moldable surface that can function as typical ailerons or flaps do on aircraft, creating drag and lift at key points in flight maneuvers such as takeoffs and landings. The effect is created by high-voltage alternating electrical current and uses normal atmospheric air to create the plasma gas itself.
The specifications for a plasma actuator follow a rectangular, multi-layered pancake-like design in the general shape of an aircraft wing. Two sheets of electrode conductors are separated by a dielectric insulating material. One electrode sheet is exposed atop the dielectric medium, and one is embedded within it and off-center from the other electrode. Air flows over the exposed electrode first, and, as high-voltage current is passed through the system, a plasma region of gas forms in the air directly behind the top electrode and above the embedded one, which can then be controlled and shaped to affect air flow over the entire actuator region while in flight. This mimics the effect of a mechanical aileron without requiring moving parts or hydraulic systems, while also creating a more versatile shape with potentially greater control over the aerodynamics of the aircraft.
The Air Force Research Laboratory (AFRL) in the US has been researching the plasma actuator since at least 2006 for use in supersonic aircraft designs. Such devices are believed to offer greater reliability than traditional mechanical flaps with the likelihood of reduced weight for the body of the vehicle, which would offer it greater maneuverability and long-range capabilities. In research at AFRL, the plasma actuator has been tested in a wind tunnel at speeds up to five times that of the speed of sound.
The technology for a plasma actuator system is seen as relatively practical as of 2011. This is, in part, because plasma technology is commonly employed in consumer devices such as fluorescent lighting and television plasma screens, and does not require the high temperatures to generate it where it is produced naturally by stars. The ability to switch a plasma field on and off at extremely high rates also gives the technology a unique advantage in aircraft maneuvers that cannot be accomplished by conventional hydraulic means.
Some of the limitations of the technology still exist as of 2011. Controlling the flow rate for the actuator has required the addition of fluidic oscillators, where two plasma actuator systems work in tandem to create pulsed or modulated flow schemes. The function of the actuator parts are also inherently based on the density of the surrounding gas that is converted to a plasma, so the altitude for aircraft, as well as their velocity, can have direct effects on performance that have to be fine-tuned before it can be counted on to perform in a reliable manner when needed.
