Sound Absorbing Resonator Based on the Framed Nanofibrous Membrane

The sound absorbing means are based on a resonance membrane formed by a layer of polymeric nanofibers, which is restricted by a frame. The resonance membrane is then, upon impact of sound waves, brought into forced vibrations, whereby the kinetic energy of the membrane is converted into thermal energy by friction of individual nanofibers, by the friction of the membrane with ambient air and possibly with other layers of material arranged in its proximity. Moreover, part of the kinetic energy of the membrane is transmitted to the frame, to which the membrane is securely attached, and other part is converted into thermal energy due to increased friction in its inner structure, which is caused by the fact that the neighboring parts of the membrane, separated at least partially by the frame or its elements, may vibrate with mutually different periods and/or deviations. The frame is formed by a mesh of grid that can be regular in order to obtain uniform properties over the whole area of the sound absorbing material. The size and shape of the mesh affect the sound absorption or more precisely resonance behavior of the means. To obtain desired sound absorbing characteristics, the resonance membrane is connected to the frame with positive, zero, or negative tension

Resonance Effect of Nanofibrous Membrane for Sound Absorption Applications

Nanofibrous layers have unique acoustic properties due to the large specific surface area of the nanofibers, where viscous losses may occur and also the ability of the nanofiber layer to resonate at its own frequency. The resonance membrane is then, upon impact of sound waves of low frequency, brought into forced vibrations, whereby the kinetic energy of the membrane is converted into thermal energy by friction of individual nanofibers, by the friction of the membrane with ambient air, and possibly with other layers of material arranged in its proximity, and part of the energy is also transmitted to the frame, by which means the vibrations of the resonance membrane are damped. When sound waves hit the nanofiber membrane, they introduce forced vibrations in the case of resonance which have maximal amplitude. The principle of the technology is achieved by the synergy of perforated plate in the form of a cavity resonator with nanofibrous layer in the form of resonant membrane. The parameters of the resonant nanofibrous membrane together with the shape and volume of the perforations then determine which sound frequencies will be damped and to what extent

Theoretical assessment of sound absorption coefficient for anisotropic nonwovens

The anisotropy factor as a function of fiber arrangement, fiber fineness and sample thickness has been derived from the theories of soundwave transformation due to phase changing. The sound absorption coefficient of the anisotropic fibrous material is then theoretically calculated. The fibrous materials were prepared so that the fibers are arranged parallel (perpendicularly laid fiber web called STRUTO technology) in the direction of soundwave propagation or perpendicularly (longitudinally laid fiber web) to the direction of sound propagation. The sound absorption coefficient was measured due to the Impedance tube. The theoretical results are in good agreement with experimental findings

Different Structures of PVA Nanofibrous Membrane for Sound Absorption Application

The thin nanofibrous layer has different properties in the field of sound absorption in comparison with porous fibrous material which works on a principle of friction of air particles in contact with walls of pores. In case of the thin nanofibrous layer, which represents a sound absorber here, the energy of sonic waves is absorbed by the principle of membrane resonance. The structure of the membrane can play an important role in the process of converting the sonic energy to a different energy type. The vibration system acts differently depending on the presence of smooth fibers in the structure, amount of partly merged fibers, or structure of polymer foil as extreme. Polyvinyl alcohol (PVA) was used as a polymer because of its good water solubility. It is possible to influence the structure of nanofibrous layer during the production process thanks to this property of polyvinyl alcohol