Optimized structures for vibration attenuation and sound control in nature: A review

Nature has engineered complex designs to achieve advanced prop-erties and functionalities through millions of years of evolution. Many organisms have adapted to their living environments by pro-ducing extremely efficient materials and structures exhibiting opti-mized mechanical, thermal, and optical properties, which current technology is often unable to reproduce. These properties are often achieved using hierarchical structures spanning macro-, meso-, mi-cro-, and nanoscales, widely observed in many natural materials like wood, bone, spider silk, and sponges. Thus far, bioinspired ap-proaches have been successful in identifying optimized structures in terms of quasistatic mechanical properties, such as strength, tough-ness, and adhesion, but comparatively little work has been done as far as dynamic ones are concerned (e.g., vibration damping, noise in-sulation, sound amplification). In particular, relatively limited knowl-edge currently exists on how hierarchical structure can play a role in the optimization of natural structures, although concurrent length scales no doubt allow multiple frequency ranges to be addressed. Here, we review the main work that has been done to analyze struc-tural optimization for dynamic mechanical properties, highlighting some common traits and strategies in different biological systems. We also discuss the relevance to bioinspired materials, in particular in the field of phononic crystals and metamaterials, and the poten-tial of exploiting natural designs for technological applications.