A frequency bandgap is a range of wave frequencies that are prohibited from passing through a medium. The dispersion relation, which links the frequency to the wave number, enables us to illustrate the bandgaps. In [E. H. Lee, "A survey of variational methods for elastic wave propagation analysis in composites with periodic structures," in Dynamics of Composite Materials, E. H. Lee, ed., ASME, New York, 1972, pp. 122
Ani P. Velo, George A. Gazonas, Erwin Bruder, Nanc