One step forward passive baseline-free imaging using nonlinear secondary noise sources

Lynda Chehami (1, 2) , Marina Terzi (3) , Emmanuel Moulin (1, 2) , E. Chatelet (4, 5) , Francesco Massi (6) , Julien de Rosny (7)

1 TPIA - IEMN - Transduction, Propagation et Imagerie Acoustique - IEMN
2 IEMN - Institut d’Électronique, de Microélectronique et de Nanotechnologie - UMR 8520
3 LAUM - Laboratoire d'Acoustique de l'Université du Mans
4 LaMCoS - Laboratoire de Mécanique des Contacts et des Structures [Villeurbanne]
5 DCS - Dynamique et Contrôle des Structures
6 University of Rome "Tor Vergeta"
7 IL - Institut Langevin - Ondes et Images (UMR7587)

This paper introduces the concept of secondary noise sources for passive defect localization in structures. The proposed solution allows for the exploitation of the principle of Green's function retrieval from noise correlation, even in the absence of an adequate ambient noise. The main principle is to convert a part of low-frequency modal vibrations into highfrequency noise by exploiting the frictional contact nonlinearities. The device consists of a mass-spring resonator coupled to a flexible beam by a rough frictional interface. The extremity of the beam, attached to the surface of a plate, excites efficiently flexural waves in the plate up to 30 kHz when the primary resonator vibrates around its natural frequency, i.e. a few dozens Hz. A set of such devices is placed at random positions on the plate surface, and lowfrequency excitation is provided by a shaker. The generated high-frequency noise is recorded by an array of eight piezoelectric transducers attached to the plate. A differential correlation matrix is constructed by subtracting correlation functions computed from noise signals at each sensor pairs, before and after the introduction of a local heterogeneity mimicking a defect. Then dispersive beamforming is applied on the differential correlation matrix to locate the defect. This technique shows good results for linear defects, but refers to a measurement on a baseline healthy sample, which can be strongly affected by environmental conditions. In this context, we propose, in second part, an acoustic reference-free method for localizing defects in thin plates. The new approach is based on the combination of pump-probe measurements and beamforming imaging. The pump-probe scheme here means the simultaneous excitation of lowfrequency vibrations and high-frequency acoustic pulses generated by a piezoelectric transducer and recorded by an array of sensors. The role of pumping vibrations is in imposing changes to loading conditions for a defect (here a model Hertzian contact i.e. a small ball pressed against the tested plate) while the ultrasonic Lamb wave pulses probe the defect in various loading states. Then beamforming algorithm is used to detect and locate the origin of modulation.

Domaines: Physique [physics]; Sciences de l'ingénieur [physics]

Lynda Chehami, Marina Terzi, Emmanuel Moulin, E. Chatelet, Francesco Massi, et al.. One step forward passive baseline-free imaging using nonlinear secondary noise sources. International congress on Ultrasonics, ICU 2023, Sep 2023, Pekin, China. ⟨hal-04447843⟩