Bianisotropic response of asymmetrical acoustic scatterers, including the quadrupole couplings
Phys. Rev. Applied 24, 034059 – Published 22 September, 2025
DOI: https://doi.org/10.1103/f795-m3ss
Abstract
Acoustic materials with Willis coupling have coupled constitutive equations, which lead to the cross-coupling between the monopole and dipole, analogous to the bianisotropic phenomena in electromagnetism. Though significant progress has been made in recent years in understanding Willis coupling, the extension of which to higher-order responses is still lacking. Here, an effective acoustic polarizability tensor is derived to understand the bianisotropic response of asymmetrical acoustic scatterers including the quadrupole couplings, in which the constraint of Helmholtz equation on the local field (pressure, velocity and the spatial derivatives of velocity) is utilized. Then, an experiment for the directivity enhancement of a point source near the asymmetrical acoustic scatterer is carried out, and a spatial Fano resonance phenomenon is observed.
