Conference Abstract:

136th Meeting of the Acoustical Society of America, 
Norfolk, Virginia, USA  (12-16 Oct 1998)

Dependence of surface wave nonlinearity on propagation direction in crystalline silicon 
R. E.
Kumon, M. F. Hamilton (Department of Mechanical Engineering, The University of Texas at Austin, Austin, TX 78712-1063), Yu. A. Il'inskii,  E. A. Zabolotskaya (MacroSonix Corporation, 1570 East Parham Road, Richmond, VA 23228).

The nonlinearity matrix elements Rlm (corresponding to generation of harmonic l+m) for a surface wave in a crystal depend on both the plane of propagation and the direction of propagation in that plane [Hamilton et al., Nonlinear Acoustics in Perspective, R. J. Wei, ed. (Nanjing University Press, Nanjing, 1996), pp. 64-69]. We considered propagation at angle q with respect to the 100 direction in the (001) plane of crystalline silicon. Because of symmetry it is sufficient to investigate Rlm(q) for 0 q 45. Consider first R11, which corresponds to second-harmonic generation. The sign of R11 indicates whether finite-amplitude effects cause a waveform to steepen forward or backward. We obtain R11 < 0 for 0 q < 21 and 32 < q 45, with R11 > 0 for 21 < q < 32. Moreover, it appears that all elements Rlm(q) have the same sign dependence and zero crossings (q @ 21 and q @ 32). Numerical simulations reveal that for 0 q < 21 and 32 < q 45 positive segments of the longitudinal particle velocity waveform steepen backward in space (i.e., opposite what a sound wave does in air), they propagate almost linearly at q @ 21 and q @ 32, and between these angles they steepen forward. Nonlinearity thus varies far more strongly than small-signal sound speed as a function of propagation direction. [Work supported by ONR.]

Technical Area: Physical Acoustics (Nonlinear Acoustics)
(PACS) Subject Classification number(s): 43.25.Fe

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Ronald Kumon / Acoustics Group / UT Austin / Created 13 May 1998 / Updated 13 May 1998