Index of content:
Volume 119, Issue 3, March 2006
- ACOUSTIC SIGNAL PROCESSING 
119(2006); http://dx.doi.org/10.1121/1.2168413View Description Hide Description
Nonlinear elastic wave spectroscopy (NEWS) has been shown to exhibit a high degree of sensitivity to both distributed and isolated nonlinear scatterers in solids. In the case of an isolated nonlinear scatterer such as a crack, by combining the elastic energy localization of the time reversal mirror with NEWS, it is shown here that one can isolate surfacial nonlinear scatterers in solids. The experiments presented here are conducted in a doped glass block applying two different fixed frequency time-reversed signals at each focal point and scanning over a localized nonlinear scatterer (a complex crack). The results show a distinct increase in nonlinear response, via intermodulation distortion, over the damaged area. The techniques described herein provide the means to discriminate between linear and nonlinear scatterers, and thus to ultimately image and characterize damaged regions.
119(2006); http://dx.doi.org/10.1121/1.2168415View Description Hide Description
A stochastic volatility model incorporating the exponential power distributions is adopted in the present study to analyze exponentially decaying pulses in the presence of background noises of various magnitudes. The discussions are focused on its effectiveness in the determination of the instant of the pulse initiation and the decay constant. The results are compared with those obtained by the conventional short-time Fourier transform. It is found that the present stochastic volatility model can retrieve the instant of the pulse initiation and the decay constant within engineering tolerance even when the noise is slightly stronger that the pulse amplitude. Its performance is substantially better than that of the Fourier transform when the frequency of the decay pulse fluctuates.