THESIS
2022
1 online resource (xix, 104 pages) : illustrations (chiefly color)
Abstract
Low-frequency wave absorption in domains of acoustics and mechanics is an old yet not fully
closed topic in terms of both theoretical research and practical applications. This thesis intends to
present a comprehensive study on this subject by reviewing recent breakthroughs and proposing
new metamaterial-based designs aiming for simpler construction, better compactness, and higher
flexibility.
I start with revisiting the development of metamaterial research, elucidating its
fundamental physical pictures and highlighting new wave control possibilities offered by it,
followed by a detailed review of sound absorption structures, for both conventional types and
metamaterial-based types, with an emphasis on the recent breakthrough of causality-law-aspired
optimal absorber design. Finally, to...[
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Low-frequency wave absorption in domains of acoustics and mechanics is an old yet not fully
closed topic in terms of both theoretical research and practical applications. This thesis intends to
present a comprehensive study on this subject by reviewing recent breakthroughs and proposing
new metamaterial-based designs aiming for simpler construction, better compactness, and higher
flexibility.
I start with revisiting the development of metamaterial research, elucidating its
fundamental physical pictures and highlighting new wave control possibilities offered by it,
followed by a detailed review of sound absorption structures, for both conventional types and
metamaterial-based types, with an emphasis on the recent breakthrough of causality-law-aspired
optimal absorber design. Finally, to further explore physical opportunities beyond the causality
constraint, two new types of absorbers are presented for acoustic and vibrational absorption, respectively.
A conceptual design of using a tunable active wall to achieve arbitrarily low frequency
airborne sound absorption and continuously adjustable acoustic functionalities is proposed based
on the impedance match condition and impedance adjustment through amplitude tuning of the
phase-matched motion. Both FEA simulation results and demonstration experiments yield
convincible results supporting this theoretical conception.
A new type of compact and low-frequency responsive mechanical resonator is conceived
to remove primary vibrational energies from the noise source in order to tackle noise reduction
problems requiring high attenuation. The idea exploits coupling between translational and
rotational motions, leading to a significantly enhanced oscillator mass which we model as an
inertia amplification effect. Experimental characterization on fabricated prototypes verifies the
analytical description, showcasing gigantic amplification factors and ultralow resonance
frequencies within a compact and ultra-lightweight device. By further adopting a structural
modification and utilizing mode hybridization between the normal spring-mass resonance and the
inertia-amplified resonance, an inertia-amplification-based absorber with total absorption
capability and broadened bandwidth is presented analytically and numerically.
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