Experimental adaptive control of sound radiation from a panel into an acoustic cavity using active constrained layer damping

Sound radiation from a panel into an enclosure is attenuated using active constrained layer damping (ACLD) that is controlled by an adaptive least mean square (LMS) algorithm. Five of the enclosure walls are rigid and the other wall, which is flexible, is made of a 0.4064 mm thick aluminum plate. The plate is partially treated with ACLD, which consists of a visco-elastic sheet sandwiched between two piezo-electric films. One of the piezo-films is bonded to the surface of the plate and used directly to control the plate vibration whereas the second piezo-film is utilized to control the shear deformation of the visco-elastic layer to enhance its energy dissipation characteristics. In this manner, the sound radiation can be controlled by active and/or passive control strategies with each operating separately, when the first film is activated, or in unison when the second film is energized in response to the sound pressure inside the enclosure. Comparisons are made between the effectiveness of the two control strategies in attenuating the sound radiation into the enclosure. The results indicate that combining active and passive controls, as in the case of the ACLD treatment, is more effective in controlling the sound radiation. Moreover, such a control strategy is found to require lower control inputs than when the active and passive control actions are used separately.