Three-Dimensional Single-Port Labyrinthine Acoustic Metamaterial: Perfect Absorption with Large Bandwidth and Tunability

materials. Here, we report on the design, fabrication, and experimental characterization of a three-dimensional single-port labyrinthine acoustic metamaterial. By using curled perforations with one end closed and with appropriate loss inside, the metamaterial can perfectly absorb airborne sounds in a low-frequency band. Both the position and the relative width of the band can be tuned flexibly. A trade-off is uncovered between the relative absorption bandwidth and thickness of the metamaterial. When the relative absorption bandwidth is as high as 51%, the requirement of deep-subwavelength thickness (0.07 lambda) can still be satisfied. We emphasize that the perfect absorption with large tunability in relative bandwidth (from 9% to > 180%) was not attainable previously and may find applications ranging from noise reduction to sound imaging.