Smart foam for applications in passive-active radiation control

The development of a smart foam for passive-active noise control is discussed. The smart foam consists of cylindrically curved sections of PVDF film embedded in partially reticulated polyurethane acoustic foam forming a very thin, compact arrangement. The device is designed to reduce sound by the simultaneous action of the passive absorption of the foam (effective at high frequencies) and the active input of the PVDF element driven by an oscillating electrical input (effective at low frequencies). The PVDF actuator is configured to behave in a linear sense and to couple in-plane strain associated with piezoelectric effect with out-of-plane motion needed to radiate sound from the foam surface. The performance of the passive-active device is studied for controlling sound radiation from a vibrating piston. A feedforward LMS controller is used to minimize the signal from a far-field error microphone, Results of harmonic and broadband control are presented. The potential of the smart foam for globally reducing sound radiation in the low- and high-frequency range is demonstrated. (C) 1997 Acoustical Society of America.