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