I hope you enjoyed this blog and that you will take the required steps to secure your WiFi network. And as a reminder, none of the passwords we cracked were used for unauthorized access to these WiFi networks or any other information accessible via these networks.
The traditional methods used for detecting cracks are mainly based on the measurement of global deformations. Unfortunately, the sensitivity and precision of this type of measurement are quite weak, the density of cracking must reach comparatively high values before its impacts start to be detectable in terms of deformations [19,20,21]. Acoustic emission (AE) can be a promising technique [8,10]. Listening to AE events gives information earlier than the visible opening of cracks, but the interpretation of results is always a difficult matter. This is because most AE events occur just before the propagation of microcracks [4]. The lack of significant AE activity at the initial stages of loading causes difficulty in distinguishing between background noise and acoustic events related to the crack. The techniques using ultrasonic waves velocity are particularly interesting because of the direct relationship between characteristics of wave propagation and the stage of damage to the material [22].
CRACK Step 7 - Micro WIN SMART V2.2 (SETUP CRACK)l
Addressing these challenges and extracting damage/change information from complex diffuse waves have been the subjects of the vast number of studies. For example, in [26], investigated small cracks under environmental changes. In [27], presented the efficacy of the ultrasonic technique in discerning healing from its failure. In [28], studied real crack and influence on the diffusion parameters (degradation of the signal scattered from structural deformation). The diagnosis of large cracks/notches and the monitoring of crack propagation using diffuse ultrasonic wave can be found in [28,29]. In [30], Michaels and Michaels have presented the structural change in a simple aluminum specimen using short-time cross-correlation of two diffuse ultrasonic signals recorded from the same transmitter and receiver, before and after damage. Anugonda et al. [31] investigate the propagation and scattering of ultrasound in concrete structure and determined the diffusion parameters. In [32], Won presented the measurement of the artificial cracks varying depth in the concrete specimens with diffuse ultrasound. Eunjong et al. [33] examined the water permeability and chloride ion penetrability of cracked concrete sample using diffuse ultrasonic signal and shown that the relations between crack width, water flow, and diffuse ultrasound parameters. Considering this, the diagnosis of propagation of microcracks in reinforcement concrete remains a significant challenge for NDT techniques, despite the special interest in making such degradation since these cracks may lead to undesirable premature failure. Advanced signal processing techniques, such as time-frequency domain analysis, statistical, matching pursuit, and other, could be useful for determination of damage-sensitive features. In most of the cases, different NDT techniques produce multiple decisions, often conflicting about the integrity of the monitored structure. In [34], the distributed fiber optic and coda wave techniques for damage investigation in concrete structure are presented, and they showed that both techniques achieved earlier damage detection than standard sensors. However, no statistical methods have been used to compare all the techniques. The above challenge led researchers to use fusion techniques at different levels of data processing. Information-level fusion has been used after data transferred into abstractions. In NDT techniques, distracted decisions at a high level of abstractions may be produced by several techniques about the integrity of the structure/material [35]. Typically, decision fusion is applied at the final stage of the process of evaluation. Ideally, decision fusion reduces the level of uncertainty in the decision made by different techniques and produce more trusted decisions with high level of confidence.
As it can be concluded from above literature review, the information fusion on various levels is a very helpful technique, which can provide earlier crack detection in undamaged structures due to the appropriately constructed decision-making algorithm. Moreover, for successful detection of damage one need to apply the processing algorithms with enough sensitivity to detect early cracks in a structure. Finally, the appropriate threshold should be established to distinguish between healthy and damaged structure and minimize the possibility of false damage indications. In this paper, the authors combined all these approaches in order to develop a damage detection system based on embedded sensors, which is sensitive to microcracks and robust to false damage indications, simultaneously. The originality of this paper covers the application of newly developed features based on advanced signal processing measures and functions, selection of the most sensitive ones to cracks, and their implementation into the fusion algorithm, which resulted in increasing of overall sensitivity to damage in considered benchmark structure. 2ff7e9595c
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