Our Lab
Graduate student Nick Wolff takes low frequency vibration data from a geophone (orange device), and digitizes and autocorrelates it.
Pin transducers are attached to samples of an open-celled aluminum foam. Ultrasound with wavelengths comparable to strut lengths is introduced to the samples. The resulting diffusion, absorption, and resonances are used to ascertain the structure of the foam.
An ultrasonic flux image of a single crystal of Silicon at a frequency of 15 MHz was used as the cover of an issue of Physics Today. The poattern is related to the anisotropy of the crystal and due to the interference of rays from different parts of a folded group velocity surface. R. Weaver, M. Hauser and J. P. Wolfe, "Acoustic Flux Imaging in Anisotropic Media," Zeitschrift fur Physik B 90, 27-46 (1993)
A random assembly of aluminum beads, sintered under moderate temperature and pressure. The structure has an ultrasonic band gap that diminsishes with the degree of sintering. "Ultrasonic band gaps in aggregates of sintered aluminum beads," Acustica 84, 628-631 (1998)
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Research Scientist Oleg Lobkis conducting an experiment on diffuse ultrasound in a disordered plate in a vacuum.
Dispersion relation for railroad rail – the frequency of vibration ω versus real and imaginary parts of wavenumber k. Only the low-frequency range is presented. The propagating branches become evanescent if frequency drops below the associated cutoffs. The additional evanescent branches emerge from local extrema of the imaginary branches. The larger the imaginary parts of their wavenumbers, the shorter is the distance over which the evanescent fields decay.
Former graduate student Vesna Damljanovic conducts a scanned laser vibrometer measurement of a railroad rail. The small electromagnetic shaker (seen at the end of rail) vibrates the rail with constant frequency, exciting infinitely many modes of vibration. The red dot on the rail indicates where the vibrations are measured by the laser interferometer.
Professor Weaver adjusts the shaker attached to the rail.