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NASA research into rotor blades. Rotor blades made with piezoelectric materials can flex when subjected to electrical fields, not unlike the way human muscles work when stimulated by a current of electricity sent from the brain. NASA and the Defense Advanced Research Projects Agency, also known as DARPA, the U.S. Army, and the Boeing Company have experimented with smart material actuated rotor, or SMART, technology, which includes the piezoelectric materials. Tests in a NASA wind tunnel of this SMART rotor hub confirmed the ability of advanced helicopter-blade active control strategies to reduce vibrations and noise. NASA research into rotor blades. Creator: NASA. (KEYSTONE/HERITAGE IMAGES/HERITAGE SPACE)