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Optical security films have gained a lot of attention due to its potential application in authentication services. Electrode-free optical devices are in demand along with electrode devices due to its secure access to the decryption key and ability to hide information from public access. Our concern in this study is the examination of electrode-free optical security film. In such devices, hidden information can be viewed in black/white contrast or controlled birefringent colours, which are produced by patterned phase plate and polariser. In particular, we develop the model of stratified anisotropic media for theoretical description of reflective characteristics of optical security films. Our theoretical results are compared with experimental observations. Blue and yellow birefringent colours of supertwisted nematic liquid crystal cell are achieved by using theory of optical characteristics in anisotropic media and partial coherence. This theoretical analysis suggests new openings in the optimisation of liquid crystal security films. [ABSTRACT FROM AUTHOR]

The constructed closed form solutions for the long-wave limits for guided waves propagating in anisotropic crystals reveal a principal ability for existence of several long-wave limiting velocities exhibiting dependence on the wave normal. Numerical examples for guided waves propagating on the (1,0,0)-plane of several cubic crystals indicate existence of two distinct long-wave limiting velocities for all directions of the wave normal, except a possible discrete number of directions where two long-wave limiting velocities may coincide. [ABSTRACT FROM AUTHOR]

The closed form expressions for the low frequency velocity limits of Lamb waves propagating in anisotropic homogeneous, stratified and functionally graded (FG) plates with arbitrary elastic anisotropy and arbitrary (continuous) transverse variation of physical properties are constructed. The applied method is based on Cauchy sextic formalism coupled with the stratification convergence theorem for FG plates. The constructed solutions are obtained in the form of vanishing auxiliary determinants related to derivatives of the closed form solutions of dispersion equations. [ABSTRACT FROM AUTHOR]

Rayleigh – Lamb wave propagation in a heterogeneous medium containing an upper sandy layer in a perfect contact with isotropic elastic substrate is analyzed by applying the modified Cauchy sextic formalism. It is also proved that sandy material is essentially anisotropic and should be modeled as an anisotropic material with the cubic symmetry. The performed numerical analysis revealed essential peculiarities with respect to dispersion of Rayleigh – Lamb waves. The observed discrepancy in dispersion portraits of media with sandy layer and with isotropic layer, may be important for the nondestructive evaluation of presence sandy layers in the upper Earth crust. [ABSTRACT FROM AUTHOR]

In recent years, the study of thermoelastic waves generated by lasers has been undertaken by several researchers because the technique provides an efficient non-contact technique for generation and detection of ultrasonic waves. Laser-generated ultrasonic waves have diverse applications ranging from material characterization to defect characterization. Transient ultrasonic guided waves generated by a pulsed laser in anisotropic infinite plate are investigated in this article. An exact analytical method is adopted for this purpose. The governing equations and boundary conditions are first transformed from spatial-time domain into wavenumber-frequency domain using Fourier Transform. After solving these equations and satisfying the boundary conditions in the wavenumber-frequency domain, the Cauchy's residue theorem is used to get the response in the spatial domain and then the numerical integration is used to eventually obtain the response in time domain. Results for dispersion and transient guided waves in infinite silicon nitride (Si3N4) plates are presented. Numerical results show that pulsed laser excites mainly the lowest Lamb modes, namely, the lowest symmetric (S0) and antisymmetric (A0) modes. They also show that the transient response is dominated by the antisymmetric mode A0 which shows dispersion characteristic. This study provides a quantitative model for laser generated ultrasonic waves in an anisotropic plate and can be used for non-destructive evaluation. [ABSTRACT FROM AUTHOR]

The global reciprocity theorem for thermo-anisotropic elastodynamics, which relates body forces, surface tractions, displacements, temperatures and strains of two solutions of the field equations, states A and B, by integrals over a volume V and its bounding surface S, is derived and discussed in this article. The difference between various anisotropies enters via the stress-temperature tensor, which is different for different cases of anisotropy. The reciprocity theorem is used to analyze the dynamic response to high-intensity heating of a small surface region. The particular example of line-focused laser-beam irradiation of one side of a homogeneous elastic plate is worked out in some detail. For the time-harmonic case, the amplitude of the lowest anti-symmetric mode is obtained in a simple and elegant manner by application of the reciprocity theorem, where the desired mode is state A and state B is taken as a free anti-symmetric mode. The amplitude of any anti-symmetric or symmetric mode can be obtained in an analogous manner, and an appropriate selection of modes can be used with Fourier superposition to obtain the transient response. [ABSTRACT FROM AUTHOR]

In recent years, the study of thermoelastic waves generated by focused laser beams has been undertaken by several researchers because the technique provides a means for noncontact generation of ultrasonic waves. Laser-generated ultrasonic waves have diverse applications ranging from material characterization to nondestructive testing of defects. Transient ultrasonic guided waves generated in an anisotropic infinite plate by a pulsed laser beam are investigated in this study. A semi-analytical finite element method (SAFEM) is adopted for this purpose. In this method, the plate is divided into parallel layers through its thickness and the displacement and temperature in each layer are approximated by quadratic polynomials in the thickness direction (z). They are assumed to be continuous functions of time and in-plane cartesian coordinates (x, y). Transient response is calculated using Fourier transformations in time and space variables (x, y). The analysis technique is applicable to a generally anisotropic plate. Results for dispersion of guided waves and transient displacement in infinite silicon nitride (Si 3 N 4 ) plates are presented. Numerical results show that for the assumed form of heat deposition by the laser mainly the lowest Lamb modes, namely, the lowest symmetric ( S 0 ) and antisymmetric ( A 0 ) modes, are excited. They also show that the transient response is dominated by the antisymmetric mode A 0 , which shows characteristic dispersion. This study provides a quantitative model for laser-generated thermoelastic waves in an anisotropic plate and can be used for nondestructive evaluation. [ABSTRACT FROM AUTHOR]