Phononic crystal with adaptive connectivity: A new approach to 'smart' materials

In recent times, mechanical metamaterials and a phononic crystals have attracted the attention of some groups, as they allow to exploit on a larger scale phenomena known from solid state physics, such as the creation of band gaps at certain frequencies. The peculiarity of metamaterials is that their effective properties emerge from the periodic geometric organization of their unit cells rather than from the constituting bulk materials. Furthermore, metamaterials can be built in any size, ranging from the nanometer to the meter scale, and out of any material to suit different needs.

In a contribution recently published online, we demonstrate how the inclusion of small amounts of piezoelectric material into the unit cell of a phononic crystal allows to  implement new functionalities into this interesting kind of structures. The most immediate demonstration of the application of such a system will be, for example, a tunable logic port based on elastic waves, where channels composed of tunable phononic crystals in a two-dimensional structure will be used to separate different frequency components from a mixed frequency signal. Yet, the long term goal of this research will be a new class of truly smart materials that derive their properties equally from their geometry, material properties and logic (in the sense of the electronic elements that will be integrated into them).