Experimental study of a smart foam sound absorber

Abstract

This article presents the experimental implementation and results of a hybrid passive/active absorber (smart foam) made up from the combination of a passive absorbent (foam) and a curved polyvinylidene fluoride (PVDF) film actuator bonded to the rear surface of the foam. Various smart foam prototypes were built and tested in active absorption experiments conducted in an impedance tube under plane wave propagation condition at frequencies between 100 and 1500 Hz. Three control cases were tested. The first case used a fixed controller derived in the frequency domain from estimations of the primary disturbance at a directive microphone position in the tube and the transfer function between the control PVDF and the directive microphone. The two other cases used an adaptive time-domain feedforward controller to absorb either a single-frequency incident wave or a broadband incident wave. The non-linearity of the smart foams and the causality constraint were identified to be important factors influencing active control performance. The effectiveness of the various smart foam prototypes is discussed in terms of the active and passive absorption coefficients as well as the control voltage of the PVDF actuator normalized by the incident sound pressure.

Active sound control with smart foams using piezoelectric sensoriactuator

“…For the actuator design of the smart foam prototype considered in this study, the in-plane displacement components of the PVDF membrane results in its predominant out-of-plane displacement. The electric displacement vector [D] reduces to its third component only, along the z-direction (thickness direction) (Leroy et al, 2009(Leroy et al, , 2011. Similar line of argument reduces the permittivity matrix [C p ] into the coefficient c 33 with the electric field E z applied across the thickness of the PVDF membrane.…”

“…The finite element model for the poroelastic medium is based on an exact (u, p) formulation of the poroelastic domain (Debergue et al, 1999;Atalla et al, 2001). The modeling utilizes quadratic poroelastic, elastic, fluid, and piezoelectric elements to implement the weak integral formulation of these different media involved in the problem along with the associated coupling and boundary conditions (Leroy, 2008;Leroy et al, 2009Leroy et al, , 2011. The primary loudspeaker has been modeled with a fixed harmonic displacement imposed on all the nodes of the left waveguide termination on Figure 1, while the electrical excitation imposed on the PVDF membrane has been modeled with a fixed harmonic electric potential imposed on the piezoelectric domain.…”

“…For the present application, an approximate calculation shows that the absorption coefficient (a) varies as a ¼ 1.14r, from where the high-and low-frequency and low-frequency limits can be determined based on a chosen satisfactory value of 'a'. Previous studies with smart foam have shown good noise control effectiveness (over specific frequency bandwidths) in acoustic radiation control problems (Fuller et al, 1994(Fuller et al, , 1996 and also in enhancing the broadband absorption coefficient for normally incident plane waves (Leroy, 2008;Leroy et al, 2009Leroy et al, , 2011. Recent study on the transmission control problem with smart foam reveals its capability in creating an acoustic isolation on the transmission side (downstream of the smart foam) under optimum control input (Kundu et al, 2009;Kundu and Berry, 2011).…”

Active Control in an Anechoic Room: Theory and First Simulations

“…So-called "hybrid" absorbers have thus been studied, combining absorbing materials and transducers driven so that the resulting device exhibits the performances of a conventional passive lining at higher frequencies and suitable performances at lower frequencies. Such systems have also been thoroughly investigated, with varying combinations of passive material, actuator, and control strategies [14,15,16,17,18,19,20].…”

Modeling of a distributed device for simultaneous reactive vibration suppression and energy harvesting

“…A passive vibration control device is considered, termed smart foam by Gentry et al (1997), which utilizes a distributed poroelastic spring layer in which a curvature of piezoelectric film is embedded. Smart foam was intended to serve as a combined passive and active acoustic-structural device and was successfully employed in active noise control experiments (Guigou and Fuller, 1999;Leroy et al, 2011). Marcotte et al (1999) studied this device with the addition of a distributed top mass layer, the resulting embodiment then combining passive vibration absorber dynamics alongside the potential of active control.…”