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This article presents a method to monitor corrosion remotely, based on highly nonlinear solitary waves, which are compact and nondispersive. In the study presented in this article, two types of solitary wave transducers were used to monitor accelerated localized corrosion on a steel plate. The first type consists of a chain of spherical particles surmounted by a commercial solenoid wired to, and controlled by, a data acquisition system used to lift and release the first particle of the chain and induce the mechanical impacts and stress waves in the chain. The chain included a piezoelectric wafer disk, also wired to the same data acquisition system, to sense, digitize, and store the propagating waves for post-processing. The second type of transducer was identical to the first one but the data acquisition system was replaced by a wireless node that communicated with a mobile device using a Bluetooth connection. Eight transducers were used to monitor the plate for over a week to detect the onset and progression of localized corrosion. Corrosion detection was performed by extracting a few features from the time waveforms and feeding these features to an outlier analysis algorithm based on the Mahalanobis distance. The results of the experiment showed the effectiveness of the proposed monitoring approach at detecting defects close to the transducers and confirm previous numerical predictions by the authors. The experiments also provided evidence that the performance of the wireless transducers is nearly identical to the performance of their wired counterparts, paving the way to a new paradigm for the structural health monitoring of remote structural components in harsh environments. [ABSTRACT FROM AUTHOR]

This paper investigates the asymmetric propagation of acoustic waves in a one-dimensional chain of spherical particles coupled with asymmetric intruders. The chain passes acoustic waves along one direction (forward configuration) whereas partially blocks the acoustic energy propagating along the opposite direction (reverse configuration). A numerical analysis is conducted to investigate this asymmetric propagation by simulating a statically compressed chain of particles interacting via Hertzian contact and subjected to small amplitude periodic displacements at one end. The amount of acoustic energy transmitted through the chain in both configurations is studied and quantified in terms of the acoustic energy transfer ratio, defined as the ratio of the acoustic power at the last particle to the acoustic power at the first particle. The effect of the applied frequency and number of particles in the chain on the transfer ratio is investigated. In addition, a parametric study is performed to evaluate the effects of geometric and material properties on the efficiency of asymmetric acoustic wave propagation in the proposed system. The results show that the proposed design supports asymmetric propagation of low frequency acoustic waves. [ABSTRACT FROM AUTHOR]