Showing papers by "Osama M. Mukdadi published in 2003"

Transient ultrasonic guided waves in layered plates with rectangular cross section

Abstract: Transient ultrasonic guided waves in anisotropic layered plates with finite and infinite width are presented in this article. A semianalytical finite-element method is adopted to study the guided waves in both infinite- and finite-width elastic plates. Three-noded beam elements in the thickness direction are used in infinite plate model, whereas the cross section of the finite-width plate is represented by nine-noded quadrilateral elements. Propagation in the axial direction is modeled by analytical wave functions. Elastodynamic Green’s functions are derived using modal summation in the frequency–wave number and time–space domains. Results for dispersion and transient analysis of guided waves in infinite nickel plates are presented and compared with those of finite-width plates. Group velocities are calculated and wave arrival times are computed for different plate cross sections. Numerical results show a significant influence of the plate aspect ratio on the dispersion and transient wave response. The co...

An ultrasound based method for measuring multiple velocity components in opaque macro and micro flows

Abstract: We report here on the development of an ultrasound-based particle image velocimetry (PIV) system for measurement of multiple velocity components in opaque flows. The method takes advantage of the non-linear backscatter characteristics of small (1-5 /spl mu/) gas-filled microbubbles used as markers of flow trajectories. PIV algorithms, modified for use with ultrasound data, are applied to calculate the local velocity vector. Preliminary data from in vitro and in vivo studies are presented. The method should be useful for a variety of fluid diagnostics applications where optical access (as is required for conventional PIV techniques) is not available. This includes biomedical imaging and MEMS micro-fluidic applications.

Guided Acoustic Phonon Modes in Layered Anisotropic Nanowires

Abstract: Acoustic phonons play a critical role in energy transport in nanostructures. The dispersion of acoustic phonons strongly influences thermal conductivity. Recent observations show lower values of thermal conductivity in finite dimensional nanostructures than in the bulk material. In this work, we will present results for guided acoustic phonon modes in (a) a bilayered GaAs-Nb nanowire of rectangular cross section and (b) a trapezoidal Si nanowire. The former has been used for phonon counting in a nanocalorimeter for measuring thermal conductivity and the latter is commonly used in MEMS applications. A semi-analytical finite element (SAFE) analysis technique has been used to investigate the effects of layering, anisotropy, and boundaries on the dispersion of modes of propagation. Many interesting features of group velocities are found that show confinements around the corners, in the low velocity layer, and coupling of the longitudinal and flexural modes. These would strongly influence thermal conductivity and might provide means of nondestrutive evaluation of mechanical properties.Copyright © 2003 by ASME