Self-Focusing of Rayleigh Waves: Simulation and Experiment

In earlier work [1,2] a simple idea for self-focusing of a linear array has been used for Rayleigh and Lamb waves. The self-focusing procedure automatically moves the focal region of the array towards the defect that produces the largest backscattered signal by adjusting the excitation times of the elements of the array. Experimental results demonstrate the ability to self-focus Rayleigh waves and Lamb waves on defects in thick slabs and thin sheets. The aim of this paper is to supplement the experimental results with a measurement model of the self-focusing of surface waves. A model for the surface wave generated by a single element of the linear array has been developed. The field generated by the entire array has been simulated by using superposition

A 160-Gb/s OTDM demultiplexer based on parametric wavelength exchange

Parametric wavelength exchange (PWE) has been demonstrated as a versatile device in providing different functionalities. In this paper, we will concentrate, numerically and experimentally, on one of these functionalities, namely, all-optical time demultiplexing of 160-Gb/s return-to-zero (RZ) signals based on a pulsed-pump PWE in a 400 m highly nonlinear dispersion-shifted fiber. Experimental results show power penalties < 2.7 dB at bit-error rate of 10-9 for all demultiplexed 10-Gb/s RZ signals. We also derive theoretical expressions for the conversion/residual efficiencies and investigate the impact of pump pulse width and phase mismatch on these efficiencies. Furthermore, the impacts of pulsed-pump wavelength and power level on the characteristics of the switching window are investigated numerically. As a result, the demultiplexer can be easily upgraded to an add-drop multiplexer because of the complete exchange nature of PWE, which is justified by the surviving channels' waveform performance. © 2009 IEEE.published_or_final_versio

Ultrasonic characterization of GRC with high percentage of fly ash substitution

New applications of non-destructive techniques (NDT) with ultrasonic tests (attenuation and velocity by means of ultrasonic frequency sweeps) have been developed for the characterization of fibre-reinforced cementitious composites. According to new lines of research on glass-fibre reinforced cement (GRC) matrix modification, two similar GRC composites with high percentages of fly ash and different water/binder ratios will be studied. Conventional techniques have been used to confirm their low Ca(OH)(2) content (thermogravimetry), fibre integrity (Scanning Electron Microscopy), low porosity (Mercury Intrusion Porosimetry) and good mechanical properties (compression and four points bending test). Ultrasound frequency sweeps allowed the estimation of the attenuation and pulse velocity as functions of frequency. This ultrasonic characterization was correlated successfully with conventional techniques. (C) 2015 Elsevier B.V. All rights reserved.This work has been supported by the Government of Spain under Grant TEC2011-23403 01/01/2012Genovés Gómez, V.; Gosálbez Castillo, J.; Miralles Ricós, R.; Bonilla Salvador, MM.; Paya Bernabeu, JJ. (2015). Ultrasonic characterization of GRC with high percentage of fly ash substitution. Ultrasonics. 60:88-95. https://doi.org/10.1016/j.ultras.2015.02.016S88956

Prospective of the Application of Ultrasounds in Archaeology

[EN] This paper presents a prospective analysis of non destructive testing (NDT) based on ultrasounds in the field of archaeology applications. Classical applications of ultrasounds techniques are reviewed, including ocean exploration to detect wrecks, imaging of archaeological sites, and cleaning archaeological objects. The potential of prospective applications is discussed from the perspective of signal processing, with emphasis on the area of linear time variant models. Thus, the use of ultrasound NDT is proposed for new ceramic cataloguing and restoration methods.This work has been supported by the Generalitat Valenciana under grant PROMETEO/2010/040, and the Spanish Administration and the FEDER Programme of the European Union under grant TEC2011-23403 01/01/2012.Salazar Afanador, A.; Rodriguez Martinez, A.; Safont Armero, G.; Vergara Domínguez, L. (2012). Prospective of the Application of Ultrasounds in Archaeology. IOP Conference Series: Materials Science and Engineering. 42:1-5. https://doi.org/10.1088/1757-899X/42/1/012010S154

Ultrasonic signal modality: A novel approach for concrete damage evaluation

[EN] In this paper, a new approach for characterizing material damage, using ultrasonic waves, is proposed. Two concrete series with two types of cement with different C3A content and similar mechanical properties were subjected to external sulphate attack (ESA) and evaluated using a novel Recurrence Plot Quantification Analysis (RQA) method. This brand new technique was compared with several methods, such as mechanical tests (compressive and flexural strength determination), dynamic test (dynamic modulus) measurements, and traditional ultrasonic measurements (propagation velocity and ultrasonic wave attenuation). In these experiments, RQA showed a high sensitivity to damage in spoiled series, improving the reliability of damage detection with ultrasonics in non-homogeneous materials compared to other non-destructive techniques. Interesting advantages of this new non-destructive technique are: a) the RQA parameter is normalized (range of 0 to 1); b) a calibration process is not required; c) the values of its standard deviation show the dispersion of the damage. It can contribute greatly to the diagnosis of the degree of damage to a material, when combined with other traditional measures such as the attenuation of the material.This work was supported by the Spanish Government under grants TEC2011-23403, BIA2014-55311-C2-1-P and BIA2014-55311-C2-2-P. This work is protected by the Spanish Patent and Trademark Office (SPTO) under reference P201630212.Carrión García, A.; Genovés, V.; Gosálbez Castillo, J.; Miralles Ricós, R.; Paya Bernabeu, JJ. (2017). Ultrasonic signal modality: A novel approach for concrete damage evaluation. Cement and Concrete Research. 101:25-32. https://doi.org/10.1016/j.cemconres.2017.08.011S253210