Smart structures and actuators: Past, present, and future

The Defense Advanced Research Projects Agency (DARPA) currently supports several programs with a focus on smart materials and structures. Two of these programs, the Smart Materials and Structures Demonstration Program and the Compact Hybrid Actuators Program (CHAP), will be described and reviewed. The Smart Materials and Structures Demonstration projects aim to show the value of smart materials-based actuation systems in realistic applications. The CHAP efforts focus on the development of new types of useful electro-mechanical and chemo-mechanical actuators that exceed the specific power and power density of traditional electromagnetic and hydraulic-based actuation systems by a factor of ten for a range of applications. Outlined are the expected capabilities, significant technical challenges, and performance advantages foreseen in successful development and transition of the technologies targeted for exploration. The primary focus of the DARPA Smart Materials and Structures Demonstrations projects has been to apply existing smart materials in an appropriate device form to reduce noise and vibration and to achieve aerodynamic and hydrodynamic flow control in a variety of structures. Achievement of the program objectives will potentially create paradigm shifts for the design of undersea vehicles, helicopter rotor blades, aircraft wings, and engine inlets. Examples of these devices include small, high bandwidth devices for acoustic signature reduction; small, powerful actuators capable of fitting into the confined interior space of a rotating helicopter rotor blade for noise reduction; and flexible smart material driven control surfaces that will permit seamless and discrete span-wise shape changes for improved aerodynamic performance. Expected performance benefits are quantified and technical issues, especially those related to the smart materials and devices, will be identified and highlighted. In addition to the Smart Demos program, DARPA is sponsoring a new research effort entitled Compact Hybrid Actuator Program and several related SBIR topics. These projects focus on the development of electro-mechanical and chemo-mechanical actuators. In order to achieve efficiencies over those of electromagnetic actuators, these devices will take advantage of the high energy density of smart material transduction elements as well as innovative and efficient energy conversion of hydrocarbon fuels. These technologies include smart material-driven hydraulic systems, duty-cycle combustion systems, mechanically amplified systems, the control and drive electronics associated with these systems, as well as development efforts for magnetic shape memory alloys. The advantages of reduced volume, reduced power consumption and the high system reliability afforded by distributed actuation may allow compact hybrid actuation to supplant traditional actuation systems in many military and commercial platforms. It is for this reason that applications such as adaptive airframes, robotic locomotion, Unmanned Air Vehicles, and small-scale guided munitions have been targeted for transition.