A Sensing System for Defects Detection in Reinforced Aluminium Panels by Ultrasonic Guided Waves Sensors

Detection of a Submillimeter Notch-Type Defect at Multiple Orientations by a Lamb Wave A0 Mode at 550 kHz for Long-Range Structural Health Monitoring Applications

“…Transmission and reception of the UGW is realized with two transducers coupled to the laminated with plexiglass wedges. The authors of the present paper have also applied and expanded this criterion by using UGW IDTs at a lower frequency equal to 650 kHz to detect defects in a reinforced aluminum laminate [ 19 ].…”

“…Finally, for the efficient selection of the A 0 mode at 550 kHz, we decided to use an IDT designed with the ratio; a pitch between fingers of IDT equal to λ = 5 mm was selected as shown by the straight line illustrated in Figure 2 (top). The choice of this operating mode was the subject of a preliminary experimental study published in [ 19 ] and later was proved to be effective for covering distances of approximately 70 cm in [ 23 ] the 4.1 mm thick aluminum laminate.…”

“…This greater pitch is sufficient to model in 3D the UGW propagation in bulk and keep the storage and computation time affordable for the simulation of a long-range investigation. Once the UGW mode and wavelength have been established, to obtain an efficient selection of the desired mode in transmission, we adopted the IDT type [19,23] with a fingers pitch of p = λ = 5 mm and a finger length of L = 110 mm and a six fingers element. The latter dimension has been decided to approximate a plane wave of the selected mode incident on the defect at long ranges.…”

“…Finally, for the efficient selection of the A 0 mode at 550 kHz, we decided to use an IDT designed with the λ d ratio; a pitch between fingers of IDT equal to λ = 5 mm was selected as shown by the straight line λ d illustrated in Figure 2 (top). The choice of this operating mode was the subject of a preliminary experimental study published in [19] and later was proved to be effective for covering distances of approximately 70 cm in [23] According to this choice, the tool [22] allows the investigation of the through thickness In-plane and Out of Plane displacements at the selected frequency. By performing this analysis, we found that antisymmetric modes A0 and A1 have both quite large values up to the notch defect depth b = 3 mm.…”