Acoustics in solid foams

We study how morphology of foam, such as pore size distribution, open membrane fraction and distribution of membrane aperture sizes, affects its acoustical properties and its performances for building applications (sound isolation, acoustic reverberation control). Our goal is to provide a comprehensive view of relationships between the foam microstructure and its acoustical behavior. Experimental and numerical methods are used to achieve this task. For experiments, solid foams are fabricated by using milli-fluidic techniques in order to control the pore size distribution and the gas fraction. The open membrane fraction and the distribution of membrane aperture sizes are characterized by optical microscopy and/or X-ray microtomography. Acoustical measurements are performed by the three-microphone impedance tube method. Our numerical methods use an indirect approach to study the acoustical behavior of foam. This approach is based on semi-phenomenological models which decouples the problems (viscous loss, thermal conduction, solid frame oscillation) involved in the sound propagation trough porous media. Such a model is the Johnson-Champoux-Allard-Lafarge (JCAL) model considering a rigid solid frame. This model links the acoustical behavior to visco-thermal parameters such as viscous permeability , tortuosity , viscous characteristic length , thermal permeability  and thermal characteristic length . Our work consists (i) to calculate all these parameters by using numerical methods (Finite Element method, or pore-network method for viscous permeability and tortuosity) applied to various numerical microstructures, (ii) to produce physical models allowing us to describe these visco-thermal parameters.

Related Papers:

– Acoustics of monodisperse open-cell foam: An experimental and numerical parametric study, V. Langlois, A. Kaddami, O. Pitois, C. Perrot, JASA (2020).

– Tuning membrane content of sound absorbing cellular foams: Fabrication, experimental evidence and multiscale numerical simulations, V.H. Trinh, V. Langlois, J. Guilleminot, C. Perrot, Y. Khidas, and O. Pitois, Mater. Des. 162, 345 (2019).

– Electrical conductivity and tortuosity of solid foam: Effect of pore connections, V. Langlois, V.H. Trinh, and C. Perrot, Phys. Rev. E 100, 013115 (2019).