About the Efficiency of Using Extended Fourier Transforms for Surface Characterization by the Deconvolution Technique

Deconvolution of echoes scattered by a surface tends to give the response function to a Dirac pulse incident on the surface. In some cases, this response function is easily related to the geometry of the scatterer and could be used to characterize it. In practical, the situation of the Dirac pulse with infinite bandwidth is not realized even by a broad band transducer which acts as a band-pass filter. We propose here some simple arguments to extend the Fourier spectrum in order to improve the results of deconvolution. Experiments are performed with targets consisting either of small plane surfaces of various shapes or of randomly rough surfaces. Results are in good agreement with those expected using the Kichhoff-Helmholtz integral

Polynomial Extrapolation Toward Low Frequencies of the Spectrum of Gated Ultrasonic Echoes for Deconvolution: Application to Defects in Solids

In order to get a correct evaluation of the response function of a scatterer in the time domain, a deconvolution operation is necessary. This operation is made difficult by the absence of information at low frequencies. We present a technique here whose purpose is the reconstruction of the low frequency part by extrapolation. Practically, the spectrum is sampled at given points and a polynomial passing by the same points is constructed. The samples in the unknown part are determined by trying different values and looking for a minimum distance between the actual spectrum and the approximating polynomial. Numerical results and an actual ultrasonic signal are presented

Ultrasonic Characterization of Rough Cracks

It has been reported before that frequency and angular information from ultrasonic scattering can be used to characterize smooth artificial defects in metals. In this study ultrasonic measurements from fractured and smooth penny-shaped cracks of the same size were carried out. Experimental procedures included the use of broad band and narrow band ultrasonic signals. From angular and frequency dependence of ultrasonic scattering measurements the size, shape, orientation and rms roughness of the fractured surface have been estimated. Ultrasonic measurements of these parameters have been compared to the actual parameters of the defect

Elastic Wave Scattering Methods: Assessments and Suggestions

I was asked by the meeting organizers to review and assess the developments over the past ten or so years in elastic wave scattering methods and to suggest areas of future research opportunities. I will highlight the developments, focusing on what I feel were distinct steps forward in our theoretical understanding of how elastic waves interact with flaws. For references and illustrative figures, I decided to use as my principal source the proceedings of the various annual Reviews of Progress in Quantitative Nondestructive Evaluation (NDE). These meetings have been the main forum not only for presenting results of theoretical research but also for demonstrating the relevance of the theoretical research for the design and interpretation of experiment. In my opinion a quantitative NDE is possible only if this relevance exists, and my major objective is to discuss and illustrate the degree to which relevance has developed. I apologize if any one feels slighted by my not mentioning a particular work To keep the size of “review” manageable, I had to be brief and to the point

About the Efficiency of Using "Extended" Fourier Transforms for Surface Characterization by the Deconvolution Technique

Deconvolution of echoes scattered by a surface tends to give the response function to a Dirac pulse incident on the surface. In some cases, this response function is easily related to the geometry of the scatterer and could be used to characterize it. In practical, the situation of the Dirac pulse with infinite bandwidth is not realized even by a broad band transducer which acts as a band-pass filter. We propose here some simple arguments to extend the Fourier spectrum in order to improve the results of deconvolution. Experiments are performed with targets consisting either of small plane surfaces of various shapes or of randomly rough surfaces. Results are in good agreement with those expected using the Kichhoff-Helmholtz integral.</p

About the Efficiency of Using "Extended" Fourier Transforms for Surface Characterization by the Deconvolution Technique

Deconvolution of echoes scattered by a surface tends to give the response function to a Dirac pulse incident on the surface. In some cases, this response function is easily related to the geometry of the scatterer and could be used to characterize it. In practical, the situation of the Dirac pulse with infinite bandwidth is not realized even by a broad band transducer which acts as a band-pass filter. We propose here some simple arguments to extend the Fourier spectrum in order to improve the results of deconvolution. Experiments are performed with targets consisting either of small plane surfaces of various shapes or of randomly rough surfaces. Results are in good agreement with those expected using the Kichhoff-Helmholtz integral.</p

Caracterisation des surfaces par deconvolution; methode d'extension de l'etendue spectrale utilisee

Par déconvolution de l'écho diffusé par une surface ou une cible on peut théoriquement accéder à la réponse impulsionnelle de ce diffuseur. Dans certains cas, cette réponse peut être reliée à la géométrie du diffuseur et utilisée pour le caractériser. En pratique, même dans le domaine de la spectroscopie ultrasonore, les transducteurs utilisés ont toujours une largeur de bande finie. Nous proposons ici une méthode d'élargissement du spectre de Fourier qui permet d'améliorer les résultats obtenus par déconvolution. Les expériences ont été réalisées avec des cibles formées, soit de petites surfaces planes de formes variées, soit de grandes surfaces aléatoirement rugueuses. Les résultats obtenus sont en bon accord avec ce que prévoit l'approximation de Kirchhoff-Helmoltz

Ultrasonic Characterization of Cement and Concrete

Ultrasonic velocity measurements are used to control the quality of fresh Concrete and to monitor the concrete mixtures during hardening or curing process. The goal of this research is to determine the time required for a given mixture of Concrete to be hard enough for form removal in a construction site. Currently the concrete form removal time is not accurately known. The early removals of the concrete forms results in weaker concrete and the late removal of the concrete forms prolong the construction time. The shear and rigidity moduli of freshly mixed concrete increases with time and this change can be monitored by measuring the ultrasonic velocity in the concrete as a function of time. In this paper we investigate the evolution of ultrasonic pulse wave velocity as a function of time in the concrete mixtures, with different water to cement ratio. The results obtained can be used to predict the setting time of concrete and also to control the quality of the concrete in the construction industry. The curing process is a series of chemical reactions by which the concrete mixture, when not stirred, gradually increases its viscosity and hardens industry, knowledge of the setting-time of the concrete for form removal or for the addition of a new edifice is crucial for speeding up the construction. Although there are published guidelines such as tables from the American Concrete Institute, currently this time interval cannot be accurately predicted. It depends on the uncontrollable parameters such as ambient temperature and humidity, among other factors.</p