Title:
Acoustic Metamaterials for Enhanced Wave Control
Acoustic Metamaterials for Enhanced Wave Control
Author(s)
Craig, Steven R.
Advisor(s)
Shi, Chengzhi
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Abstract
Acoustic metamaterials have redefined the limits of acoustic wave control with composite
structures that realize effective material properties that go beyond those of natural
materials. These extraordinary material properties enable imaging beyond the diffraction
limit, negative effective sound speeds, and acoustic cloaking. Metamaterials continue to be
a hot topic in the scientific community, as these resonant structures push the boundaries of
acoustic wave control with unprecedented functionality. The primary goal of this work is
to advance the prevalence, practicality, and scope of acoustic metamaterial research with
novel materials that uniquely tailor wave fields for a variety of acoustic-based applications.
Each chapter uses foundational metamaterial physics to advance our understanding of
acoustic wave control with composite structures. The first section develops the theory and
performs simulations for a non-Hermitian complementary metamaterial (NHCMM) with
tunable active feedback loop circuits that improve the acoustic transmission through an
intact human skull. This lays the foundation for ultrasonic brain imaging and neural
therapies that require high frequency acoustic waves to penetrate deep within the brain.
With a similarly designed metamaterial, we compare the accessible range of the effective
density and bulk modulus for unit cells with symmetric and asymmetric feedback loop
circuits. The asymmetric circuits result in a Willis coupled response that dramatically
broadens the metamaterial’s attainable parameter range. We also demonstrate asymmetric
wave transmission at high efficiency with passive Willis coupled metagratings for acoustic
beam steering at extreme angles. Lastly, we use transformation acoustics to correct focused
and self-bending acoustic beams that become distorted in anisotropic media. These developments advance acoustic-based technologies for biomedical imaging, noise control,
underwater communication, and structural acoustic applications.
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Date Issued
2022-12-13
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Resource Type
Text
Resource Subtype
Dissertation