Ultrasonographie dentaire par techniques TR-NEWS

National audienceL'imagerie ultrasonore d'une molaire humaine est abordée expérimentalement par l'utilisation des méthodes TR-NEWS, symbioses des méthodes NEWS (Nonlinear Elastic Wave Spectroscopy) bien connues pour révéler les signatures non linéaires de la dégradation des matériaux solides endommagés d'une part, et des techniques de focalisation par symétries de retournement temporel (TR) et de réciprocité d'autre part. La complexité de la structure interne de la dent (email, structure tubulaire de la dentine, pulpe, distribution de cracks entre les tubules) est explorée via un système d'excitation ultrasonore optimisé par codage fréquentiel en balayage dans la bande 0.1-10 MHz (chirp-coded excitation). La réponse acoustique de la dent étalonnée en vitesse particulaire est mesurée à la surface de celle-ci par vibrométrie laser (sensibilité 125 mm/s/V). La mise en œuvre expérimentale de la technique TR-NEWS utilisant le système TRA de Artann Laboratories ( http://www.artannlabs.com/tra-electronic.html), associé à un traitement du signal symétrisé permet l'obtention d'un B-scan polaire (120°-350°) étalonné en vitesse particulaire et référencé spatialement par rapport à la surface de la dent. L'extraction de la signature non linéaire et de sa localisation seront alors conduites par l'utilisation des propriétés de symétries de la focalisation spatiale et temporelle des ultrasons produites par TR-NEWS

Ultrasonographie dentaire par techniques TR-NEWS

National audienceL'imagerie ultrasonore d'une molaire humaine est abordée expérimentalement par l'utilisation des méthodes TR-NEWS, symbioses des méthodes NEWS (Nonlinear Elastic Wave Spectroscopy) bien connues pour révéler les signatures non linéaires de la dégradation des matériaux solides endommagés d'une part, et des techniques de focalisation par symétries de retournement temporel (TR) et de réciprocité d'autre part. La complexité de la structure interne de la dent (email, structure tubulaire de la dentine, pulpe, distribution de cracks entre les tubules) est explorée via un système d'excitation ultrasonore optimisé par codage fréquentiel en balayage dans la bande 0.1-10 MHz (chirp-coded excitation). La réponse acoustique de la dent étalonnée en vitesse particulaire est mesurée à la surface de celle-ci par vibrométrie laser (sensibilité 125 mm/s/V). La mise en œuvre expérimentale de la technique TR-NEWS utilisant le système TRA de Artann Laboratories ( http://www.artannlabs.com/tra-electronic.html), associé à un traitement du signal symétrisé permet l'obtention d'un B-scan polaire (120°-350°) étalonné en vitesse particulaire et référencé spatialement par rapport à la surface de la dent. L'extraction de la signature non linéaire et de sa localisation seront alors conduites par l'utilisation des propriétés de symétries de la focalisation spatiale et temporelle des ultrasons produites par TR-NEWS

Nonlinear wave modulation and time reversal tomography of structural defects

National audienceClassical ultrasonic tomography generally uses source signals of constant amplitude. Mostly linear characteristics like ultrasonic amplitude, attenuation or time of flight in various directions are evaluated and used to structural defects imaging. On the other hand, more complex and nonlinear characteristics of elastic wave propagation, like 3rd harmonics etc. are starting to be also used for ultrasonic imaging e.g. in medicine, providing more sensitive indicators of small body changes and irregularities. Nonlinear parameters obtained by Nonlinear Elastic Wave Spectroscopy (NEWS) NDT techniques can give us better information about incipient damage zones than linear ones. The main advantage of NEWS consists not only in higher sensitivity but also in the ability to detect defects smaller than the ultrasonic wavelength. Some limitations of NEWS methodology are given by difficulties with more precise defects location when global excitation of larger or more complicated structures is applied. To overcome these constraints, further developments of NEWS techniques are desirable for nonlinear pseudo-tomography or tomography defects imaging. Two NEWS methods are considered: Nonlinear Wave Modulation Spectroscopy (NWMS) and Nonlinear Time Reversal Mirrors (NLTRM) with ESAM and DORT signal processing. Testing results, obtained on metallic and concrete parts illustrate performance of both procedures. Both NDT procedures are illustrated on the ASB (Actuator Steering Bracket) aircraft landing gear part subjected to fatigue loading. No arising defects were indicated by traditional NDT methods, although the slightly enhanced acoustic emission (AE) activity was observed to be concentrated in the area depicted by crosslets. The ASB sample was tested by the above NLTRM procedure after 25000 cycles. Sine-pulse train of frequency 389 kHz and 30&_mu;s duration has been used in primary excitation. Damaged zones detected by AE and NLTRM are overlapping, which confirms high sensitivity of proposed nonlinear methodology. Advantage of nonlinear tomography-like imaging methods is in their potentiality to acquire very complex information about the tested structure

Ultrasonic Imaging of Human Tooth using Chirp-Coded Nonlinear Time Reversal Acoustics

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Nonlinear ultrasonic spectroscopy using ESAM and DORT symbiosis

National audienceCombination of DORT (Décomposition de lOpérateur du Retournement Temporel) and ESAM (Excitation Symmetry Analysis Method) presented as a powerful tool for detection and localization of defects by analysis of their nonlinear signature[1,2]. The third order nonlinear responses are extracted from ESAM eigen-excitations and constitute the multistatic data matrix associated with the singular value decomposition. The symbiosis of ESAM-DORT provides a normalization process of singular values associated with scatterers, validated with simulations and experiments of acoustic propagation[3]. Piezoelectric transducers are used for both excitation and data acquisition. Transmitters consequently emit the excitation signals and corresponding responses are measured by the array of receivers. The amplitude of excitation signals is variable as to separate the nonlinear parts of the measured signal. ESAM signal pre-processing is used for nonlinear parts extraction. Separated signal records form linear and nonlinear multistatic data matrices. DORT method is applied on data matrices to separate echoes of defects in the tested medium. Data obtained from DORT method are used for evaluation of nonlinear parameters corresponding to separated defects and also for their localization. The procedure is completed by visualization of nonlinear signatures of detected defects which is referred to as pseudotomographic imaging. This ESAM-DORT approach improves the performance of the local TR-NEWS methods, which can be applied to the tomography of structural defects [1] C. Prada, S. Manneville, D. Spoliansky, and M. Fink, Decomposition of the time reversal operator: Detection and selective focusing on two scatterers , J. Acoust. Soc. Am., vol. 99, pp. 20672076, 1996. [2] S. Dos Santos and C. Plag, Excitation symmetry analysis method (ESAM) for calculation of higher order nonlinearities, International Journal of Non-Linear Mechanics, vol. 43, pp. 164169, 2008. [3] S. Dos Santos, S. Vejvodova, and Z. Prevorovsky, Local Nonlinear Scatterers Signature using Symbiosis of the Time-Reversal Operator and Symmetry Analysis Signal Processing, J. Acoust. Soc. Am. (2009) in pres

Ultrasonic wave propagation and mechanical properties of human skin stretched in vivo

December 9-13International audienc