Implementation of Design-Optimized Metasurfaces as Frequency Filters for Symmetric Plate Waves
Restricted (Penn State Only)
Author:
Sridhar, Sashank
Graduate Program:
Engineering Science and Mechanics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 11, 2024
Committee Members:
Parisa Shokouhi, Thesis Advisor/Co-Advisor Clifford Jesse Lissenden, III, Committee Member Albert Segall, Program Head/Chair Jacques Riviere, Committee Member
A promising candidate in the pursuit of wave control is a "metamaterial" whose ability to act on waves is contingent upon its physical composition rather than its chemical properties. In the context of plates, researchers have explored the potential of a locally-resonant (LR) metasurface to steer, trap and inhibit Lamb wave propagation within specific frequency ranges referred to as bandgaps. While numerous LR metasurfaces have been devised for flexural (A0) waves with simple beams and rods, there is a dearth of designs for extensional (S0) Lamb waves, whose wave motion is primarily in-plane. A metasurface built with local "four-arm” resonators demonstrated effectiveness in filtering out the S0 mode at 50 kHz due to a structural antiresonance. This study centers on a local resonator design strategically developed with topology optimization method (TOM) and antiresonance matching as the objective. The performance of an optimal "elephant" resonator was compared against the four-arm resonator in a series of numerical investigations ranging from analysis of the individual resonator to verification of S0 transmission bandgaps for a full-scale metasurface. In the experimental phase, ultrasonic measurements were conducted with both metasurface types, showing remarkable correspondence to the predicted numerical bandgap. Validating the antiresonance TOM approach, this work lays the groundwork for future development of LR metasurfaces.
