Volume 126, Issue 1, July 2009
Index of content:
- ULTRASONICS, QUANTUM ACOUSTICS, AND PHYSICAL EFFECTS OF SOUND 
Determination of power-law attenuation coefficient and dispersion spectra in multi-wall carbon nanotube composites using Kramers–Kronig relations126(2009); http://dx.doi.org/10.1121/1.3125323View Description Hide Description
Using a broadband through-transmission technique, the attenuation coefficient and phase velocity spectra have been measured for a set of multi-wall carbon nanotube (MWCNT)-nylon composites (from pure nylon to 20% MWCNT by weight) in the ultrasonic frequency band from 4 to 14 MHz. The samples were found to be effectively homogeneous on spatial scales from the low end of ultrasonic wavelengths investigated and up . Using Kramers–Kronig relations, the attenuation and dispersion data were found to be consistent with a power-law attenuation model with a range of exponents from to over the measurement bandwidth. The attenuation coefficients of the respective samples are found to decrease with increasing MWCNT content and a similar trend holds also for the dispersion. In contrast, the mean phase velocities for the samples rise with increasing MWCNT content indicating an increase in the mechanical moduli.
Sensitivity of acoustic microscopy for detecting three-dimensional nanometer gaps embedded in a silicon structure126(2009); http://dx.doi.org/10.1121/1.3147493View Description Hide Description
The sensitivity of acoustic microscopy for detecting three-dimensional defects in a Si structure is reported. Circular, nanometer gaps with diameters ranging from 5 to were embedded in Si disks by a direct bonding technique, and these were visualized using acoustic microscopy. The limits of detection for the gap thickness and diameter were observed simultaneously in samples with gaps of 4 and 140 nm. The behavior of the sensitivity in detecting the gaps can be explained by a simple analytical model. It is shown experimentally and theoretically that the gap thickness and diameter are not independent variables as regards detection. The sensitivity of acoustic microscopy is governed by the three-dimensional features of the embedded defects.
Lamb wave characterization of corrosion-thinning in aircraft stringers: Experiment and three-dimensional simulation126(2009); http://dx.doi.org/10.1121/1.3132505View Description Hide Description
The development of automatic guided wave interpretation for detecting corrosion in aluminumaircraft structural stringers is described. The dynamic wavelet fingerprint technique (DWFT) is used to render the guided wave mode information in two-dimensional binary images. Automatic algorithms then extract DWFT features that correspond to the distorted arrival times of the guided wave modes of interest, which give insight into changes of the structure in the propagation path. To better understand how the guided wave modes propagate through real structures, parallel-processing elastic wave simulations using the finite integration technique (EFIT) has been performed. Three-dimensional (3D) simulations are used to examine models too complex for analytical solutions. They produce informative visualizations of the guided wave modes in the structures and mimic the output from sensors placed in the simulation space. Using the previously developed mode extraction algorithms, the 3D EFIT results are compared directly to their experimental counterparts.