Research team: Andy Elliott, Rodolfo Venegas, Olga Umnova
An omnidirectional sound absorber based on the acoustic analogy of the electromagnetic metamaterial "black hole" has been developed and tested. The resulting prototype (1.5 m in diameter) was composed of a hollow cylindrical absorbing core and a graded index matching layer which employs multiple rods of varying size and spacing to adjust the impedance of the layer to that of the absorbing core. The structure was tested in an anechoic chamber and the semi-analytical model used in the design process was validated. Finally, the theory is extended to allow for losses in the metamaterial matching layer and it is shown that improved performance may be achieved with a dual purpose layer which acts as an absorber whilst also providing the required impedance matching condition.
The work on this project was supported by DSTL, UK Contract No. DSTLX1000063985.