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numerous programs are starting up, little progress has been made in imitating even the most primitive aspects of smart biomaterials. Substantial opportunities exist to model not only the nonlinear response of these complex systems but also the self-assembly processes by which they form.
Currently, adaptive control is achieved through integration of structures, sensors, and actuators. All the armed services, including the Navy, have extensive programs devoted to extending these concepts to smart structures capable of responding to their environment. Sensors remain the limiting element. Nonlinear science is essential to the design of adaptive control systems.
Passive-control systems based on smart materials are a logical extension of current active-control systems. Self-healing materials, for example, could extend the life of critical components. Materials that simply provide a prefailure signature would improve reliability and safety. A material that acts as its own corrosion sensors is an example. Materials with tailored sound absorption characteristics would be of obvious interest to the Navy.
The ultimate passive material system would act as its own sensor. It would convert an incoming disturbance to a control signal and then respond appropriately, for example, with a shape change. Speculative systems based on magnetostrictive alloys, shape memory alloys, and piezoelectric ceramics are under study at several laboratories. Primitive examples (e.g., foam packing) of these concepts already exist.