The control of vibrational energy within solids is a fundamental engineering challenge with numerous technological applications. While the control of electrons and photons has revolutionized computation and communication, the control of phonons, the quantized particle of vibrational energy, has been far less successful. Acoustic energy is a form of vibrational energy that involves coherent excitations of phonons to form larger elastic waves. It is this coherence that allows it to be a valuable engineering tool for applications in imaging, frequency/time control, and structural monitoring. Traditional methods of reflecting acoustic energy involve interfacing different phases of matter to reflect via an impedance mismatch, like air gaps and foams. The problem that this thesis addresses is that these methods are not scalable to extreme or nanoscale environments. The objective of this thesis is to demonstrate methods of reflecting acoustic energy by constructing solids with different types of chemical interactions, not by interfacing solids with different phases of matter. We investigate the transport of acoustic energy at the interface of two-dimensional materials. Two-dimensional materials are crystalline layers of atoms that interface with other materials via a weak van der Waals interaction. Our investigation applies both computational and experimental methods. The computational methods blend super-wavelength continuum models with sub-wavelength molecular dynamics simulations. Treating the interface as a thin plate coupled to a bulk elastic material by springs, we predict that the weak van der Waals interaction should produce a pressure-release boundary condition that reflects broad acoustic energy from infrasound to hypersound. These predictions are verified using pitch-catch experiments at 1 MHz in a water tank. The results of these experiments demonstrate a nearly three-decibel attenuation from one 2D layer. When normalized to the atomic thickness of the layer, this system provides orders of magnitude better isolation than foams, rubbers, or metasurfaces.
Electrical and Computer Engineering
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Bolivar, Jesus, "The Transport of Acoustic Energy at Two-Dimensional Material Interfaces" (2022). Electrical Engineering Theses and Dissertations. 46.