Albert J. Tucker
Office of Naval Res., 800 N. Quincy St., Arlington, VA 22311-5660
Originally the concept of active control conveyed the simple notion of creating ``antinoise'' or ``antivibration;'' these ideas implied that simple antiphase motions could be propagated to cancel unwanted noise. However, recent advances in signal processing, coupled with gigaflop digital signal processors, augur new ways to understand and control complex dynamic systems. Among these are shifting wave numbers from radiating to nonradiating components and modifying structural impedances to create large dynamic masses, stiffnesses, and/or damping. Hence one electronically modifies the dynamics of complex systems to achieve acoustic radiation reduction, or to have a physically lightweight structure emulate the dynamics of a heavier, stiffer structure. This fundamental scientific understanding offers new opportunities for development of new technology for control algorithms, sensors, and actuators. As a result, active control is emerging as viable addition to the engineering toolkit for noise and vibration reduction.