Perfect acoustic absorption by subwavelength metaporous composite

We present a design of a low-frequency perfect acoustic absorption metaporous composite with frequency tunability and the insensitivity to the incident angle based on a critical coupling mechanism. The metaporous composite is constructed by embedding an Archimedean spiral structure in traditional porous materials. We verified the tunable balance of the dissipation and leakage of the metaporous composite by adjusting the slit orientation of the embedded spiral and the width and depth of the porous materials. Our simulations show that the composite's thickness is 1/20th of the corresponding wavelength at the perfect absorption (PA). Experiment and complex frequency plane analysis confirm the perfect acoustic absorption. The simulations show that the acoustic absorption of the system is highly efficient (0.95), up to a large oblique incidence, e.g., 60°. We also achieve the dual-band PA by embedding two spirals or using the higher order mode of a single spiral. The proposed composite absorber provides promising potential for low-frequency noise reduction applications.