Abstract
Second harmonic generation is one of the most sensitive and reliable nonlinear elastic signatures for micro-damage assessment. However, its detection requires powerful amplification systems generating fictitious harmonics that are difficult to discern from pure nonlinear elastic effects. Current state-of-the-art nonlinear ultrasonic methods still involve impractical solutions such as cumbersome signal calibration processes and substantial modifications of the test component in order to create material-based tunable harmonic filters. Here we propose and demonstrate a valid and sensible alternative strategy involving the development of an ultrasonic phononic crystal waveguide transducer that exhibits both single and multiple frequency stop-bands filtering out fictitious second harmonic frequencies. Remarkably, such a sensing device can be easily fabricated and integrated on the surface of the test structure without altering its mechanical and geometrical properties. The design of the phononic crystal structure is supported by a perturbative theoretical model predicting the frequency band-gaps of periodic plates with sinusoidal corrugation. We find our theoretical findings in excellent agreement with experimental testing revealing that the proposed phononic crystal waveguide transducer successfully attenuates second harmonics caused by the ultrasonic equipment, thus demonstrating its wide range of potential applications for acousto/ultrasonic material damage inspection.
Highlights
Unlike acoustic metamaterials in which the band gap mechanism is similar to that of vibration absorbers[17], band gaps in Phononic crystals (PCs) are physically induced by the Bragg scattering effect, i.e. through the coupling with counter-propagating waves excited resonantly when the GLW wave-vector matches kBG = 2π/Λ and leading to destructive interference in specific frequency bands
We here develop a perturbative coupled-mode theory based on GLW propagation in order to identify band gaps in PC waveguides as function of material properties and geometrical features such as the corrugation depth 2∈, the average plate thickness 2h, and the corrugation period Λ and distance D [see Fig. 1(c)]
We develop a theoretical framework for the design of PC waveguide transducers and we experimentally demonstrate that they are able to filter out undesired second order nonlinear elastic effects in NEWS experiments
Summary
Despite much progress in the design of PCs of types (a) and (b), substantial modifications of the host structure such as holes and inclusions are generally required for the tuning of band gaps This could significantly affect the fabrication complexity and, the structural integrity of components, preventing their use in real applications. We overcome this limitation by developing the first prototype of nonlinear ultrasonic sensing device using PC structures with periodic waveguides and providing theoretical and experimental evidence of its functionality Such a PC transducer consists of a piezoelectric sensor bonded on a circular plate with sinusoidal corrugations that is integrated on the surface of the test component without altering its mechanical and geometrical properties. The PC waveguide sensor is designed to exhibit stop bands at GspLeWcifipcrosepcaognatdiohnarinmsoinnuicsofrideqaul ceonrcriuesga2tfe0dwpitlahteths.e support of a perturbative theoretical framework describing
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
