ON FREE WAVE PROPAGATION IN ANISOTROPIC LAYERED MEDIA

The method of reverberation-ray matrix （MRRM） is extended and modified for the analysis of free wave propagation in anisotropic layered elastic media. A general, numerically stable formulation is established within the state space framework. The compatibility of physical variables in local dual coordinates gives the phase relation, from which exponentially growing functions are excluded. The interface and boundary conditions lead to the scattering relation, which avoids matrix inversion operation. Numerical examples are given to show the high accuracy of the present MRRM.

The propagation of Lamb waves in an anisotropic plate bordered with liquid layers

Based on elastic wave propagation theory, the dispersion equation for a thin anisotropic plate (such as commonly used Zinc okide in micro-transducers) bordered with liquid layers is derived. Higher symmetry crystals, such as orthorhombic, tetragonal, cubic, isotropic, are included in this analysis as well. For the case of one liquid layer loading, numerical calcu- lations show that the phase velocity changes periodically with the thickness of the liquld layer. When the thickness 2d of the anisotropic plate is very small, mass sensing application of Ao mode Lamb wave is also discussed.

Understanding angle-resolved polarized Raman scattering from black phosphorus at normal and oblique laser incidences

The selection rule for angle-resolved polarized Raman(ARPR)intensity of phonons from standard grouptheoretical method in isotropic materials would break down in anisotropic layered materials(ALMs)due to birefringence and linear dichroism effects.The two effects result in depth-dependent polarization and intensity of incident laser and scattered signal inside ALMs and thus make a challenge to predict ARPR intensity at any laser incidence direction.Herein,taking in-plane anisotropic black phosphorus as a prototype,we developed a so-called birefringence-linear-dichroism(BLD)model to quantitatively understand its ARPR intensity at both normal and oblique laser incidences by the same set of real Raman tensors for certain laser excitation.No fitting parameter is needed,once the birefringence and linear dichroism effects are considered with the complex refractive indexes.An approach was proposed to experimentally determine real Raman tensor and complex refractive indexes,respectively,from the relative Raman intensity along its principle axes and incident-angle resolved reflectivity by Fresnel’s law.The results suggest that the previously reported ARPR intensity of ultrathin ALM flakes deposited on a multilayered substrate at normal laser incidence can be also understood based on the BLD model by considering the depth-dependent polarization and intensity of incident laser and scattered Raman signal induced by both birefringence and linear dichroism effects within ALM flakes and the interference effects in the multilayered structures,which are dependent on the excitation wavelength,thickness of ALM flakes and dielectric layers of the substrate.This work can be generally applicable to any opaque anisotropic crystals,offering a promising route to predict and manipulate the polarized behaviors of related phonons.

Absorption of electromagnetic wave by inhomogeneous,unmagnetized plasma

In this article,a novel and normalized Ztransform finite-difference time-domain(ZTFDTD)method is presented.This method uses a more general form of Maxwell’s equations using the E,H,D fields.The iterative model of D-E-H-D can be obtained by using the Z-transform resulted frequency-dependent formula between D and E.The advantages of the ZTFDTD consist in that the discrete equations are simple,the results are precise,easy to program and capable of dealing with the key technologies of finite-difference time-domain(FDTD),such as absorbing boundary conditions(uniaxial anisotropic perfectly matched layer,UPML)and near-to-farfield transformation.The ZTFDTD method is then used to simulate the interaction of electromagnetic wave with plasma.Using a simplified two-dimensional model,the stealth effect of inhomogeneous,unmagnetized plasma is studied both in different electron densities of plasma,different electromagnetic wave frequencies and different plasma collision frequencies.The numerical results indicate that plasma stealth is effective in theory and a reasonable selection with the plasma parameters that can greatly enhance the effectiveness of plasma stealth.