Inverse design of metamaterials for wave control

Metamaterials are engineered materials, whose spatially periodic arrangement of their constituent materials endows the composite assembly with rather unconventional properties, when macroscopically observed. In the context of the three wave-supporting physics regimes -elastodynamics, acoustics, and electromagnetics- metamaterials present unique opportunities for previously unimaginable user control over the resulting wave behavior.

To date, the design of metamaterials is mostly done on an ad hoc basis, relying mostly on one-of-a-kind or incremental physical experiments and forward computational modeling.

This dissertation introduces a systematic methodology, rooted in inverse problem theory, for engineering the dispersive properties of periodic media to meet a priori, user-defined, wave control objectives. Both scalar and vector waves are considered.

In the developed methodology, the material properties and geometry parameters of the unit cell of the periodic medium become the inversion variables. The inversion is driven by the user-defined wave control objective, constrained by the dispersive characteristics of the unit cell.

Though the methodology is flexible enough and can accommodate fairly broad dispersion engineering objectives, here the focus is on band-gaping propagating waves at user-defined frequency ranges. Numerical results in the frequency domain demonstrate that the inversion process yields unit cells that indeed attain the user-defined dispersive behavior. The inverted-for unit cells are then used to build metamaterial assemblies of not only finite periodicity, as opposed to infinite, but of fairly narrow periodicity, and are tested in the time domain against broadband excitations: it is shown that it is possible to attain the desired wave control with sub-wavelength size metamaterial assemblies.