Index of content:
Volume 116, Issue 6, December 2004
- NONLINEAR ACOUSTICS 
116(2004); http://dx.doi.org/10.1121/1.1823332View Description Hide Description
Nonlinear interaction of counterpropagating waves in solids is considered by using a general approach taking into account only the cumulative (resonant) nonlinear perturbations giving a nonzero contribution over the period and, consecutively, potentially able to significantly modify the linear solution. Different stress-strain relations are addressed, including those with hysteresis which serve as basic models for the recent acoustic experiments with rock and metals. An important case of the interaction of counterpropagating waves with close amplitudes in a high-Q resonator (bar) with hysteresis is specially addressed and compared with the case of a ring resonator.
116(2004); http://dx.doi.org/10.1121/1.1814119View Description Hide Description
Measurements of the top surface vibration of a buried (inert) VS 2.2 anti-tank plastic landmine reveal significant resonances in the frequency range between 80 and 650 Hz. Resonances from measurements of the normal component of the acoustically induced soil surface particle velocity (due to sufficient acoustic-to-seismic coupling) have been used in detection schemes. Since the interface between the top plate and the soil responds nonlinearly to pressure fluctuations, characteristics of landmines, the soil, and the interface are rich in nonlinear physics and allow for a method of buried landmine detection not previously exploited. Tuning curve experiments (revealing “softening” and a back-bone curve linear in particle velocity amplitude versus frequency) help characterize the nonlinear resonant behavior of the soil-landmine oscillator. The results appear to exhibit the characteristics of nonlinear mesoscopic elastic behavior, which is explored. When two primary waves and drive the soil over the mine near resonance, a rich spectrum of nonlinearly generated tones is measured with a geophone on the surface over the buried landmine in agreement with Donskoy [SPIE Proc. 3392, 221–217 (1998); 3710, 239–246 (1999)]. In profiling, particular nonlinear tonals can improve the contrast ratio compared to using either primary tone in the spectrum.