From modal mixing to tunable functional switches in nonlinear phononic crystals.

We introduce a paradigm for spatial and modal wave manipulation based on nonlinear phononic crystals and explore its potential for engineering wave control systems with tunable, adaptive, and multifunctional characteristics. Our approach exploits nonlinear mechanisms to stretch the frequency signature of the wave response and distribute it over multiple modes, thereby activating a mixture of modal characteristics and enabling functionalities associated with high-frequency optical modes, even while operating in the low-frequency regime. To elucidate the versatility of this approach, we consider different granular crystal configurations that span the available landscape of crystal topologies and wave control functionalities. The ability to switch between complementary functionalities allows rethinking nonlinear phononic crystals as programmable acoustic ports that form the building blocks of a new structural logic framework enabled by nonlinearity.