Low frequency coupling and mode interference in an inhomogeneous lattice of finite length

Jean Kergomard (1) , Marc Pachebat (2)

1 LMA - Laboratoire de Mécanique et d'Acoustique [Marseille]
2 Sons

The propagation through a lattice made with two waveguides periodically coupled by perforations is studied at low-frequencies. A degree of inhomogeneity is introduced with parametrically opened diaphragms inserted into one waveguide of the lattice. Analytical results obtained thanks to the fourth-order transfer matrix formalism illustrate three physical phenomena. The first phenomena is the effect of the perforations, the second is the effect of the inhomogeneity of the lattice, and the third is the effect of the interference between propagating modes when the system have finite length. These results give analytical expressions for the insertion loss, the characteristic impedance or propagation constants, that can be of practical interest for understanding and designing non local acoustic treatments for automotive and turbofan engines. The cases of a strongly inhomogeneous lattice and almost homogeneous lattice and their transition to homogeneous and branched resonator cases are discussed.

Mots clés: Waveguide; Inhomogeneous Lattice; Low Frequency

Domaines: Acoustique [physics.class-ph]; Acoustique [physics.class-ph]

Jean Kergomard, Marc Pachebat. Low frequency coupling and mode interference in an inhomogeneous lattice of finite length. Forum Acusticum, Sep 2014, Krakow, France. 6 p. ⟨hal-01058175⟩