Investigation of long acoustic waveguides for the very low frequency characterization of monolayer and stratified air-saturated poroelastic materials

When sound propagates in a porous medium, it is attenuated via several energy loss mechanisms which are switched on or off as the excitation frequency varies. The classical way of measuring acoustic materials uses Kundt impedance tube. However, due to its short length, measurements made steady state harmonic regimes. Its lower cutoff often limited few hundreds Hertz. Two long waveguides were assembled from water pipes and mounted create test-rigs for low-frequency characterization monolayer stratified air-saturated poroelastic materials. first waveguide was straight had length 120 m, while second coiled gain space 135 m long. appeal very low using impulsive waves (with rich spectral content) because incident can be separated time echoes extremities guides. transmission coefficient recovered two compared well with those transfer matrix method (TMM) used here combination Biot’s 1962 theory describe propagation dissipative media. This wave-material interaction model permitted recovery properties transmitted propagating air. parameters involved Young’s moduli, Poisson ratio microstructural such tortuosity permeability. Being able descend frequencies guarantees correct verification magnitude measured approaches unity towards static frequency. found equivalent provided data down order ?12 Hz.