Shear axial modes in a PCTSCM, Part VIII: Spectral holes with dissimilar materials but without phase defects

Sufficiently thick layers of piezoelectric, continuously twisted, structurally chiral materials (PCTSCMs) exhibit the circular Bragg phenomenon in a narrow frequency regime, when irradiated by a normally incident shear wave; and the introduction of a phase defect between two identical PCTSCMs gives rise to spectral reflection and transmission holes. We show, here, that an alternative structure made of two different PCTSCMs can be used to produce spectral holes, provided that the constitutive properties and the dimensions of the two PCTSCMs are in a certain relationship. No phase defect is present in the alternative structure, but its effect is effectively simulated by the contrast in the material properties of the two PCTSCMs. (C) 2005 Elsevier B.V All rights reserved.