Multiple scattering attenuation and anisotropy of ultrasonic surface waves

Multiple scattering of waves induces bulk effects such as attenuation and a nisotropy that are important in seismology, optics, medical imaging, and ot her fields involving propagation in disordered media. We report here measur ements of ultrasonic surface wave propagation in a strong-scattering, quasi periodic medium consisting of a grooved surface of aluminum. Using nonconta cting optical methods we have tracked the evolution of surface wave pulses within the scattering medium. Waves propagating parallel to the grooves pro pagate nearly attenuation and dispersion free, whereas waves propagating no rmal to the grooves are dispersed and exponentially attenuated with distanc e as energy is transferred from the direct pulse into the multiple-scatteri ng coda. We measure this attenuation length and show that there is, in addi tion, a scattering induced anisotropy in the phase velocity. (C) 1999 Ameri can Institute of Physics. [S0003-6951(99)04425-3].