Reducing extrinsic damping of surface acoustic waves at gigahertz frequencies

Gelda, Dhruv

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https://hdl.handle.net/2142/100417 Copy

Description

Title

Reducing extrinsic damping of surface acoustic waves at gigahertz frequencies

Author(s)

Gelda, Dhruv

Issue Date

2017-01-31

Director of Research (if dissertation) or Advisor (if thesis)

Sinha, Sanjiv

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

Surface Acoustic Waves, Damping , Bragg Reflectors

Abstract

High-frequency surface acoustic waves (SAWs) in the GHz range can be generated using absorption from an ultrafast laser in a patterned metallic grating on a substrate. Reducing the attenuation at these frequencies can yield better sensors as well as enable them to better probe phonon and electron-phonon interactions near surfaces. It is not clear from existing experiments which mechanisms dominate damping at high frequencies. We calculate damping times of SAWs due to various mechanism in the 1-100 GHz range to find that mechanical loading of the grating on the substrate dominates dissipation by radiating energy from the surface into the bulk. To overcome this and enable future measurements to probe intrinsic damping, we propose incorporating distributed acoustic Bragg reflectors (DABRs) in the experimental structure. Layers of alternating materials with contrasting acoustic impedances embedded a wavelength away from the surface serve to reflect energy back to the surface. Using numerical simulations, we show that a single Bragg reflector is sufficient to increase the energy density at the surface by more than five times. We quantify the resulting damping time to find that it is longer than the intrinsic damping time. The proposed structure can enable future measurements of intrinsic damping in SAWs at 100 GHz.

Graduation Semester

2017-05

Type of Resource

text

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http://hdl.handle.net/2142/100417

Copyright and License Information

Copyright 2015 Dhruv Gelda

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