Browsing by Subject "Leaky surface acoustic waves"

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    Anisotropy sensitivity of an acoustic lens with slit aperture
    (IEEE, 1993) Atalar, Abdullah; Ishikawa, I.; Ogura, Y.; Tomita, K.
    A conventional spherical acoustic lens is modified by restricting its aperture in the form of a slit to provide directional sensitivity. The spacing between the two parallel absorbing sheets forming the slit is adjustable to obtain varying slit widths. The resulting lens can be used in conjunction with V(Z) method to obtain leaky wave velocities of the sample under investigation as a function of direction. The theoretical V(Z) analysis of the lens involves a two-dimensional integral rather than one-dimensional integral of the conventional lens. Single crystal anisotropic materials are chosen as test samples. Reflection coefficients for anisotropic single crystals of given surface cut and orientation are calculated. Numerically evaluated V(Z) curves are used to deduce the surface wave velocity of the object for the given orientation. This is compared with the surface wave velocity directly calculated from the elastic parameters of the object. Results show the compromise between signal-to-noise ratio and angular resolution as the slit width is varied. V(Z) measurement results of a slitted lens are presented to be compared with calculated curves. The new lens is used to measure the acoustic velocity on the (001) surface of GaAs along varying directions with differing slit widths.
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    Response of acoustic imaging systems using convergent leaky waves to cylindrical flaws
    (IEEE, 1989) Gonalp, N.; Atalar, Abdullah
    Characterization of near-surface properties of materials by acoustic means is most convenienth done by surface-acoustic-waves (SAW) that are spatially confined to the surface. There are several techniques available to excite focused SAW's on the surfaces of non-piezoelectric materials for imaging purposes. A conventional acoustic microscope lens excites focused SANI's on the object surface, but with a low efficiency. SAW can be excited with a high efficiency using conical wavefronts as obtained from a conical axicon. Such methods can be used in a scanning arrangement to generate images of surface inho-mogeneities. In this paper, an analysis of imaging systems making use of convergent SAW's is given using angular spectrum approach and T-matrix formulation. Inhomogeneities on the object surface are assumed to be circular cylinders whose axes are perpendicular to the surface. The response of imaging systems to such defects is found as a function of defect position with respect to the focus point. Theoretical and experimental results are compared and are found to be in good agreement. © 1989 IEEE