Localized modes and classical wave spectral gaps

Summary form only given. The author presents a class of spectral gap materials based on the idea of localized modes. The advantages of spectral gaps formed by local resonances are summarized. The gaps are neither related to nor pinned by the periodicity of the structure. Thus, spectral gaps are possible for any periodic structure, provided the filling fraction exceeds a certain threshold. The gaps are tunable by adjusting the local resonant unit. Spectral gaps can be formed with lattice constant, or the basic length scale of the structure, orders of magnitude smaller than the relevant wavelength in the bandgap region. Examples of both photonic crystals and elastic bandgap crystals (sonic crystals) fabricated from locally resonant structures are discussed.