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We propose a tunable directional coupler based on a two-dimensional photonic crystal made of dielectric elastomer rods embedded in air background. In the interaction region, the inclusions are a dielectric elastomer cylindrical actuator made of a hollow cylinder sandwiched between two compliant electrodes. By applying a voltage between the compliant electrodes, the radial strain of the silicon-made actuator and the coupling characteristics of the photonic crystal coupler are investigated. The coupling length of the photonic crystal coupler depends on the voltage applied between the electrodes, which is analyzed by the plane wave expansion method. Due to the radial strain of the dielectric elastomer under external voltage, the tunable photonic crystal coupler is realized. Numerical simulations obtained by the finite-difference time-domain method confirmed the feasibility of the tunable photonic crystal coupler. OCIS codes: 130.3120, 230.5298.

The axisymmetric dynamic stability of rotating sandwich circular plates with a constrained damping layer subjected to a periodic uniform radial loading along the outer edge of the host plate is studied in the present paper. The viscoelastic material in middle layer is assumed to be frequency dependent and incompressible, and complex representations of moduli are used. Equations of motion of the system are derived by the finite element method where the geometry stiffness matrices induced by rotation and external load are evaluated from solutions of static problems. Bolotin's method is employed to determine the regions of dynamic instability while the eigenvalue problems with frequency dependent parameters are solved by the modified complex eigensolution method. Numerical results show that the effects of constrained damping layer tend to stabilize the circular plate system and the widths of unstable regions decrease with increasing of rotational speeds. [DOI: 10.1115/1.1688765]

The stability of a cantilever column, carrying a concentrated mass at the free end and resting on an elastic foundation of the Winkler-type, subjected to uniformly distributed in-plane follower forces is studied by 'Timoshenko beam theory' finite elements. In order to more quickly and efficiently obtain the critical load for such a nonconservative system, a simple and cost-effective numerical technique which utilizes the eigenvalue sensitivity with respect to the follower force is introduced instead of the conventional trial-and-error technique. The high accuracy and rapid rate of convergence through the combination of the present finite element model and the solution technique are demonstrated with the numerical example given. The influence of some system parameters on the critical load is also discussed.

The acoustic bending waveguide can be designed by engineering the index distribution in a bending structure. We employ a two-dimensional graded sonic crystal (GSC) to realize a graded index medium. The refractive indices of a graded index medium can be discretized and the discrete refractive indices are approximated by using GSCs. The effective refractive indices of the sonic crystals are obtained by using the plane wave expansion method. Simulations and transmission spectra of the bending waveguides with the continuous index variation and the GSC approximation are calculated by using the finite-element-method. The results show that the acoustic bending waveguide based on the GSC can be achieved in the low frequency limit and its operating frequency is broadband. [ABSTRACT FROM AUTHOR]

The electromagnetic wave propagation of a two-dimensional optical black hole with graded index photonic crystals for transverse magnetic modes is studied. The implementation of the proposed system is validated in the metamaterial regime. The finite element method is employed in order to confirm the optical properties of the designed device. Numerical simulations show that the light incident on the device is bent toward the central area and absorbed by the inner core. As a result, the artificial optical black hole can effectively absorb the incident waves from all directions. The structure is composed of two kinds of real isotropic materials, which eases the experimental fabrication. [ABSTRACT FROM AUTHOR]