An Optimization Approach for the Design and Implementation of Metasurfaces to Control Symmetric Plate Waves

Open Access
- Author:
- Sridhar, Sashank
- Area of Honors:
- Engineering Science
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Parisa Shokouhi, Thesis Supervisor
Parisa Shokouhi, Thesis Honors Advisor - Keywords:
- Metasurface
Lamb waves
Metamaterial
Topology Optimization - Abstract:
- There are two abstracts attached - a technical and non-technical type: Technical: Researchers in optics, acoustics, and elastodynamics are at the forefront of tools to better control wave propagation and transport. One candidate is a “metamaterial” whose wave control properties are contingent upon its physical, not chemical, makeup. In the elastodynamic context, a “metasurface” has been shown to achieve many degrees of control for plate waves, including by inhibiting their propagation within certain frequency bands, called bandgaps. While many metasurfaces have been conceived for flexural-type waves, few designs have been tested for extensional-type waves, which rely on a different interaction mechanism. Recently, a unit cell called the “four-arm resonator” was shown to be effective for extensional modes at 50 kHz, but its design was not optimized [1]. The current study is based on resonator designs that were strategically developed by an inverse design problem. The efficacy of the various resonators at mitigating low-frequency extensional waves was evaluated in a two-fold investigation. First, they were modeled and tested in numerical simulations to compare their performance indicators with that of the four-arm resonator. In the experimental phase, ultrasonic measurements were taken with the four-arm resonator array mounted to a plate to gauge its exceptional “in-field” performance, which closely matched the results of a recent publication [1]. The results of this study are the first steps towards an optimized meta-plate for controlling extensional waves. Non-technical: Wave control is a centuries-old pursuit across disciplines in physics from optics to acoustics. Metasurfaces, or repeating surface elements, are a hotbed for research into controlling elastic wave propagation in solids. Recently, a metasurface consisting of a block and four arms (the four-arm resonator) was shown to curtail the propagation of waves in thin plates, but its design was not optimized [1]. The first part of the current study evaluates the performance of more systematically conceived designs in numerical models with respect to a baseline four-arm resonator. In the second part of the study, the exceptional performance of four-arm resonators was verified in lab experiments where it was found that an array effectively blocked the incident plate wave. The broad-scale implications of research in this domain include the development of more capable structural health monitoring (SHM) tools and “shields” to prevent seismic wave damage to infrastructure.