Reconfigurable ultra-sparse ventilated metamaterial absorber.

The impetus for examining ventilated acoustic metamaterials stems from the demand for increasingly efficient and adaptable noise reduction and sound wave manipulation techniques. However, for the present reconfigurable metamaterial absorbers, their absorption band and ventilation rate have not yet attained practical application at low frequencies (<1000 Hz). A theoretical and experimental demonstration of a reconfigurable ultra-sparse ventilated metamaterial absorber for low frequencies with highly sparse ventilation and tunability is presented. The acoustic absorber is based on triadic cylindrical Helmholtz resonators, and a coupled mode theory for three resonators is implemented to elucidate the underlying physics. The absorber achieves a sparsity level of more than 80%, with a measured wind velocity ratio higher than 95%. Furthermore, tunability is accomplished in the frequency range of 600 to 950 Hz through reconfiguration. Due to its simple structure, this metamaterial absorber can be easily fabricated in mass in the future, providing promising solutions for various acoustic engineering applications. [ABSTRACT FROM AUTHOR]