Wide low frequency bandgap in imperfect 3D modular structures based on modes separation

In this manuscript we experimentally study a modular metamaterial that is able to provide mechanical insulation for elastic wave propagation. Specifically, the structural design is based on the modes separa- tion principle, that entails the presence of ultra-wide bandgap at low frequencies, also in presence of few lattice elements. In this paper, we present a simple manufacturing process for the unit cell realization. This method, however, introduces imperfections given by folding and bonding operations: we demon- strate that upon a careful unit cell design and thanks to modes separation, the presence of defects is not relevant from the dynamical point of view and does not alter the filtering behavior. Moreover, we consider a simple assembly with repetition along a single direction, in order to investigate the metama- terial robustness with respect to the lack of 3D periodicity. Experimental data are compared to numerical simulations demonstrating the advantages of such design for real-life vibration isolation problems.