Fraunhofer Building Innovation AllianceDesign and application of metamaterials for the reduction of noise and vibration for in- and outdoor environments
Transmission loss of a double-leaf wall over frequency (schematic). The two leaves are modeled as masses, the cavity in-between as a spring. Depending on the signs of the masses substantially different results are obtained: Two equal positive (real) masses yield the typical curve shape with a deep minimum (blue). If one mass is negative (a fictitious metamaterial), this minimum disappears (green). The optimum is achieved by two negative masses (red). The dotted lines mark the mass law and the rise at high frequencies with 18 dB per octave.
Metamaterials are artificial, heterogeneous, engineered structures with unusual properties like negative mass or negative stiffness. Realizations of such structures contain, e.g., internal resonators as substructures or consist of a periodic array of small-scale units. The peculiar apparent properties shall be exploited in three applications: sound transmission loss of lightweight double walls, low-frequency performance of noise barriers, and reduction of structure-borne sound. The project partners aim at a long-term market-driven cooperation on acoustic topics including transfer of results to the industry.
