A plane-wave-expansion method suited to the analysis of surface-acoustic-wave propagation in two-dimensional piezoelectric phononic crystals is described. The surface modes of a square-lattice Y-cut lithium niobate phononic crystal with circular void inclusions with a filling fraction of 63% are identified. It is found that a large full band gap with a fractional bandwidth of 34% exists for sur...

Brinkmann's plane-fronted gravitational waves with parallel rays — shortly pp-waves — are shown to provide, under suitable conditions, exact string vacua at all orders of the sigma-model perturbation expansion. 1. Introduction The condition for the vanishing of the conformal anomaly for a bosonic string in a curved space is expressed, in σ-model perturbation theory, as R µν +. .. = 0, where the...

We present a dynamically tunable mechanism of wave transmission in 1D helicoidal phononic crystals in a shape similar to DNA structures. These helicoidal architectures allow slanted nonlinear contact among cylindrical constituents, and the relative torsional movements can dynamically tune the contact stiffness between neighboring cylinders. This results in cross-talking between in-plane torsion...

This paper encapsulates the properties and implementation areas of Artificial Magnetic Conductor(AMC). It is characterized by having high surface impedance. The geometry of this structure is such that it does not support the propagation of surface waves and acts as a good ground plane in comparison to conventional metal conductors. Also, it reflects the waves in-phase rather than out of phase. ...

A detailed model of diffraction of plane and Gaussian beams on plane uniform phase Bragg gratings based on a Kogelnik's theory of coupled waves is presented. The model describes reflecting gratings (Bragg mirrors) with arbitrary orientation in a plane-parallel plate having no material losses. It takes into account spectral width and angular divergence of laser beams. The results of modeling are...

Diffraction of scalar plane waves by resistive surfaces are investigated by defining a new boundary condition in terms of the Dirichlet and Neumann conditions. The scattering problems of waves by a resistive half-plane and the interface between resistive and perfectly magnetic conducting half-planes are examined with the developed method. The resulting fields are plotted numerically. The numeri...

The existence of surface elastic waves at a mechanically free surface of granular phononic crystals is studied. The granular phononic crystals are made of spherical particles distributed periodically on a simple cubic lattice. It is assumed that the particles are interacting by means of normal, shear, and bending contact rigidities. First, Rayleigh-type surface acoustic waves, where the displac...

As a step towards understanding the properties of string theory in time-dependent and singular spacetimes, we study the divergence of density operators for string ensembles in singular scale-invariant plane waves, i.e. those plane waves that arise as the Penrose limits of generic spacetime singularities. We show that the scale invariance implies that the Hagedorn behaviour of bosonic and supers...

The existence of a Brewster wave number is demonstrated for the case of plane-wave reflection by a specularly smooth, planar interface joining two homogeneous, linearly elastic, isotropic solid half-spaces. Such a wave number is numerically shown to exist for two material combinations: steel-aluminum and steel-brass. The wave number can be such that plane waves are either propagating or evanesc...