Using shock waves to improve the sound absorbing efficiency of closed-cell foams

Abstract

Producing closed-cell foams is generally cheaper and simpler than open-cell foams.However, the acoustic and filtration efficiency of closed-cell foam materials is generally poor because it is very difficult for fluid or acoustic waves to penetrate into the material. A new method using shock waves to remove the membranes closing the cell pores (known as reticulation) and thus to improve the acoustic and filtration behavior of closed-cell foam material is presented. Various shock treatments have been carried out on polyurethane and polyimide foams and the following conclusions were drawn: (1) reticulation efficiency increased and thus the airflow resistivity and tortuosity decreased when increasing the amplitude of the shock treatment; (2) the rigidity of the foam is decreased; (3) the process is reliable and repeatable and (4) obtained acoustic performance is comparable to classical thermal reticulation.

Mechanical and acoustical properties of polylactic acid based multilayer-structured foam biocomposites

“…The latter is marked in Figure 9 with wavy lines. 36,37 This resonance effect consumes the acoustic energy in the form of vibrations and has further increased the multilayer-structured PLA foam ply’s transmission loss.…”

“…In addition, the reason for the higher increasing amplitude in the intermediate frequency range is that the sound-absorbing cotton has resonated with the sound at this frequency, which has improved the sound insulation. 36 Meanwhile, the sound-absorbing cotton enhances the absorption of the sound wave, which weakens the transmitted wave. 41 Similarly, it also caused better sound insulation in the biocomposites.…”

Sound Absorption Properties of Polyurethane Foams Derived From Waste Cooking Oil Incorporated With Waste Wood Fiber Filler

“…The methods involved in wave dissipation process are firstly, the sound absorption is increased by damping motions of the foams with the Red Meranti fillers, as explained with the effects of movements by Red Meranti fillers when polymer foam recovers from the deformation caused by the sound energy [20]. While, second method is the change in wave penetration pathways whereby the sound absorption was increased due to the pore structures in the foam matrix [7]. The increase of the airflow resistivity improves the absorption behavior in the whole frequency range until some point of pore size, but a too resistive porous material can demonstrates low sound absorption because it would be more difficult for the acoustic wave penetration.…”

“…Sound wave in the form of heat energy is produced due to the friction between air flowing in and or out of the cells [21,7]. The efficiency of sound wave absorbers can be evaluated by the sound absorption coefficient, α.…”

A method for fabricating a micro-structured surface of polyimide with open and closed pores

“…Because of these characteristics, PI was initially applied in the space and automotive industries, and is presently used as an alternative material in conventional areas such as sensors [2], sound absorption [3], electronics and so on. Recently, PI has been investigated for application in flexible displays [4].…”