Acoustic metamaterials have attractive potential in elastic wave attenuation and wave guiding over specific frequency ranges. In this research, we apply acoustic metamaterial into the manipulation of stationary wave in a finite beam, i.e., tailoring vibration modes of the structure. Rather than geometrical modification, we demonstrate that vibration modes can be adjusted by combing the resonance and bandgap characteristics of piezoelectric metamaterial. For instance, it’s shown that new vibration modes can be created while the region with excitation applied has minimum displacement. Furthermore, it’s illustrated that resonance region of the metamaterial beam can be arbitrarily assigned due to the adaptiveness of the piezoelectric metamaterial beam. The analytical investigations are confirmed with finite element simulations.
In this research, by combining the concept of elastic metasurfaces with piezoelectric transducer with shunted circuitry, we investigate the designs of elastic metasurfaces, consisting of an array of piezoelectric transducers shunted with negative capacitance, which is capable of modulating wave fronts adaptively. In order to construct different adaptive elastic metasurfaces, different phase profiles along the interface can be framed through properly adjusting the negative capacitance values. Flat planar lenses for focusing transmitted A0 Lamb waves are achieved, and possess the flexibility of changing focal locations through electromechanical tunings. Additionally, nonparaxial self-bending beams with arbitrary trajectories and source illusion devices can also be accomplished owing to the free manipulation of phase shifts. With their versatility and tunability, the adaptive elastic metasurfaces could pave new avenues to a wide variety of potential applications, such as nondestructive testing, ultrasound imaging, and caustic engineering.
Due to the attractive potential in elastic wave attenuation and wave guiding, acoustic metamaterials have received
much attention. Different from the more conventional metamaterials that possess only mechanical
displacement/deformation, the electro-mechanical metamaterials analyzed in this paper utilize the two-way electromechanical
coupling of piezoelectric transducers and local resonance induced by LC (inductor-capacitor) shunt circuits,
which features enlarged design space as well as adaptivity. We report an adaptive piezoelectric gradient index (GRIN)
lens featuring focusing acoustic wave. The proposed GRIN lens is comprised of arrayed piezoelectric unit-cells with
individually connected inductive shunt circuits. Taking advantage of wave velocity shifting in the vicinity of local
resonant frequency of unit-cell and specifically arranged LC shunt circuits, we can focus the transverse wave adaptively
by adjusting the inductive loads, i.e., tuning the inductances. Analytical investigations and finite element simulations
are performed. This tunable GRIN lens can be used as acoustic metamaterial for various acoustic devices operating
with broadband frequencies.
Metamaterial possesses a number of attractive features such as frequency filtering, wave guiding, wave focusing,
etc. Conventionally, the realization of metamaterial is through the careful design of unit-cell of a mechanical structure
which typically exhibits spatial periodicity. In this research, we propose the development of adaptive metamaterial
beams with coupled circuits between adjacent piezoelectric transducers to realize multi-targeted bandgaps. To
characterize the wave propagation attenuation, a numerical model based on the transfer matrix method and Bloch theory
is formulated to predict the complex band structure of the infinite periodic structure. It is shown theoretically that
three separate bandgaps can be generated compared to only one in the conventional LC-shunt since three resonating
loops can be formed in the circuit due to the coupling effect. Consequently, wave propagation or vibration can be
suppressed effectively inside those bandgap frequencies when the structure is subjected to vibration sources with
multiple frequency components.
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