Sound propagation in and low frequency noise absorption by helium-filled porous material

Sound propagation in and low frequency noise absorption by helium-filled porous material.

Low-frequency noise is difficult to deal with by traditional porous material due to its inherent high acoustic impedance. This study seeks to extend the effective range of sound absorption to lower frequencies by filling a low density gas, such as helium, in the porous material. Compared with conventional air-filled absorption material, the helium-filled porous material has a much reduced chara...

Title Sound propagation in and low frequency noise absorption byhelium - filled porous material

1 Theory of sound propagation in superfluid - filled porous media

The theory of sound propagation in macroscopically isotropic and homogeneous porous media saturated with superfluid 4 He(so-called HeII) has been developed neglecting all damping processes. The case when the normal fluid component is locked inside a porous medium by viscous forces is investigated in detail. It is shown that in this case one shear wave and two longitudinal, fast and slow wave pr...

Sound Absorption of Porous Material in Combination with Perforated Facings

The absorption characteristics of porous absorbers in combination with perforated facings was investigated. The effect of the hole size, hole pattern and open area ratio were examined. The absorption coefficients for an absorber of uniform cross-section were compared to those for an absorber with a tapered cross-section for various volumes of absorbent and different perforated facings.

Low-Frequency Sound Propagation in Lipid Membranes

In the recent years, we have shown that cylindrical biological membranes such as nerve axons under physiological conditions are able to support stable electromechanical pulses called solitons. These pulses sharemany similarities with the nervous impulse, for example, thepropagationvelocityaswell as themeasured reversibleheatproductionandchanges in thickness and length that cannot be explained w...