Vibro-acoustic responses of poroelastic plates made from recycled materials

Poroelastic plates with a range of properties have been made from recycled automotive materials. The flexibility of these plates provides an additional attenuation mechanism through acoustically-induced vibration of the elastic frame. Predicted deflection spectra at the centre of clamped poroelastic plates in response to direct mechanical point excitation and have been found to be in fairly good agreement with data. The governing equations of flexural vibration of a fluid-loaded clamped porous plate have been derived and solved numerically. Air loading is predicted to have to have a relatively small effect on plate deflection but is predicted to reduce the mean square velocity compared with the in-vacuo condition. The insertion loss due to an air-backed rectangular porous plate mounted on one wall of a flow duct has been measured. Without air flow the porous plate 'lining' provides a small transmission loss that peaks near 800 Hz. Air flow is found to increase the overall transmission loss and shifts the maximum in the transmission loss spectrum to a lower frequency. Data obtained with a one cm thick flexible foam plate clamped six cm from the end of a large impedance tube show resonances resulting from the frame elasticity.