Determining the Bounds of Frequency Stop-Bandgap in Elastodynamic Metasurfaces for S0 Lamb Wave Excitation
Open Access
Author:
Keirn, Jeremy
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
Keywords:
S0 Lamb Waves Bandgap Metasurface Local Resonance Topology Optimization
Abstract:
It has been shown that elastodynamic metasurfaces can be used to create a stop-bandgap for guided waves such as the fundamental symmetric Lamb wave mode (S_0 mode). These metasurfaces rely on the local resonances of surface-mounted resonators to hybridize with incident S_0 Lamb waves in a waveguide (i.e. a thin plate). This type of control of Lamb waves is achieved by tuning the resonator topology to apply an appropriate Auld boundary condition at its base when attached to a plate that is made from the same material. Recent studies for surface waves in bulk media have shown that there is a possible connection between the width of the bandgap and the resonances and antiresonances in the frequency response function (FRF) of the resonators under an appropriate base excitation. This study attempts to show that a similar connection exists for a locally resonant metasurface and the associated Lamb waves. Using a combination of simulations from COMSOL Multiphysics 6.2 and experiments on a 1 mm aluminum plate, it is shown that the width of the bandgap is determined by both the resonances and antiresonances of the resonators. With this understanding of the limits of the bandgap, a topology optimization process can be used to generate resonator geometries with increased distance between the resonances, which results in an increase in the width of the bandgap.
