Spectral Green’s function for wave excitation and propagation in a piezoelectric, continuously twisted, structurally chiral medium

Abstract

A continuously twisted, structurally chiral medium ͑CTSCM͒ is a reciprocal medium whose constitutive properties vary helicoidally along its axis of spirality ͑say, the z axis͒, and the corresponding piezoelectric medium is abbreviatedly called the PCTSCM. Very recent progress in thin-film research is presented here to show that technologically significant CTSCM's and PCTSCM's are waiting in the wings and calling for theoretical advances in the understanding of wave excitation and propagation in these novel materials. A spectral Green's function is obtained as a bilinear composition of two matrices, after implementing a spatial Fourier transform in the xy plane as well as the Oseen transformation. As a result, multilayered media problems as well as grating problems utilizing CTSCM's and PCTSCM's become accessible to theoretical exploration leading to novel transducers, sensors, and other devices.

Thin-Film Metamaterials Called Sculptured Thin Films

“…4. Such films can be used as acoustic filters, both for polarization and bandwidth [77,78,79,80,81]. These films could also be used as MEMS elements, particularly for sensing.…”

Microscopic Model for Elastostatic and Elastodynamic Excitation of Chiral Sculptured Thin Films

“…Provided its half-pitch is large enough, a chiral STF will appear as a periodically nonhomogeneous continuum to an elastodynamic wave, and will then function as a so-called continuously twisted structurally chiral medium (CTSCM) introduced several years ago [26]. As discussed elsewhere [27], chiral STFs with $ 10 mm (and larger) will have elastodynamically significant helicoidal structures. At the time of this writing, chiral STFs of $ 1 mm have been fabricated [27,28]; so that the future is very likely to yield CTSCMs fabricated by physical vapor deposition.…”

The Combined Effects of Chiral Operation in Multilayered Bianisotropic Substrates

“…the stepwise variation will appear to be continuous, and under such circumstances the above structure can then be thought of as a smoothly non-homogeneous medium with helicoidally varying properties [6][7][8][9][10][11][12]. Physically, all constitutive parameters of the bianisotropic substrate above should be a function of the operating frequency and must be within the confines of a realizable range, and [15] …”

“…In this contribution, our attention is concentrated on the effects of chiral operation on the radiation characteristics of a dipole antenna placed on some grounded multilayered bianisotropic substrates, and this chiral operation is realized by stacking up a certain number of bianisotropic biaxial chiral plates in a way of the consecutive principal axes of four constitutive tensors c (i) (c = ε, µ, ξ e , ξ m ) describing either right-or left-handed spirality, or ranging the orientation of biasing magnetic field in the right-or left-handed spirality in Faraday chiral plates. The bianisotropic chiral substrates possessing such structural features can be regarded as the typical cases of helicoidal bianisotropic media [7][8][9][10][11][12]. In the following sections the mathematical treatment is based on the exponential matrix technique in spectral domain, and the motivation for this study is not only of academic importance, but also essential for the potential applications of bianisotropic media.…”

“…Bianisotropic linear materials are characterized by four independent constitutive tensors, and till now significant theoretical research progress has been achieved concerning the electromagnetic characteristics and potential applications of some bianisotropic materials. For instance, the dyadic Green's function theory for source radiation and wave propagation in uniaxial and helicoidal bianisotropic media [2][3][4][5][6][7][8], wave reflection and transmission properties of multilayered bianisotropic slabs and their potential applications for making novel non-reflection coatings and filters [9][10][11][12][13][14][15], the guided hybrid mode features in some bianisotropic waveguides [16][17][18][19][20][21][22][23][24], the dispersion characteristics of bianisotropic microstrip transmission lines and the effects of bianisotropic substrate and su-perstrate on the radiation of sources [25][26][27][28], the scattering from some particular bianisotropic objects [29][30][31], the edge effect in bianisotropic region [32,33], and the macroscopic properties of bianisotropic mixtures as well as experimental investigations on the effective constitutive parameters of uniaxial bianisotropic composites [34][35][36][37][38][39], et al In these studies the authors usually pay attention to the diverse chiral effects in bianisotropic med...…”