Abstract:

A new type of noise suppression device known as ``smart foam'' that integrates a distributed piezoelectric polymer actuator (the active component) between individual layers of sound-absorbing foam (the passive component) is discussed. Smart foam acts as a hybrid active/passive surface coating as it adaptively modifies the acoustic impedance of a vibrating surface. The potential of such a device to reduce low- and high-frequency sound radiation from a simple acoustic source (piston) has been demonstrated. In this experimental study, an array of smart foam modules are implemented to yield a net decrease in the sound power radiated by a vibrating, baffled plate in an anechoic environment. A MIMO feedforward filtered-x LMS algorithm is used to minimize the error signals provided by microphones located in close proximity of the smart foam array for harmonic and broadband plate excitations. Two different reference signals, i.e., the voltage sent to the plate disturbance actuator and the signal from an accelerometer directly mounted on the plate, are investigated and compared in terms the sound attenuation achieved. The capability of smart foam for reducing plate sound radiation is demonstrated. Smart foam is relatively lightweight, which makes it a good candidate for interior aircraft noise control applications. [Work supported by NASA LaRC.]