Enhanced sound absorption in two-dimensional continuously graded phononic crystals

A two-dimensional continuously graded phononic crystal (CGPC) is proposed, which consists of continuously graded structures. A model considering viscous and thermal effects is established, and the predicted sound absorption coefficient and specific acoustic impedance of CGPC are qualitatively verified by experimentally measured results. The effective refractive indexes of CGPC monotonically increase along the incident acoustic wave at a specific frequency. The increased effective refractive indexes of CGPC result in enhanced acoustic scattering. Enhanced acoustic scattering lengthens the propagation path, subsequently more dissipated energy, which improves the sound absorption performance of CGPC, compared with uniform phononic crystal.