Albert J. Tucker
Office of Naval Res., Arlington, VA 22217
Acoustic holography has allowed the theoretical concept of identifying and separating radiating supersonic surface waves (identified by low wave numbers) from nonradiating subsonic surface waves (high wave numbers) to be verified experimentally. Frequency-wave-number filtering, which embodies the idea of spatial and temporal filtering, may hold the key for assessing advances in active noise control as well as for developing innovative concepts for damping treatments for passively controlling radiation. For implementation of active control, spatial anti-aliasing filters for sensors and shaped structural actuators (which prevent actuation of high wave numbers) may provide a path to stable active control technology for complex structures. The physical understanding that supersonic radiating waves are membrane waves of structures and fast compressional or shear waves of elastic bodies can lead to new ideas for incorporating damping mechanisms within structures. To extend the concept of spatial-temporal filtering to arbitrary bodies, further analytical, experimental, and signal processing efforts will be required.