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.
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.
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.
This paper investigates an acoustic prism for continuous acoustic beam steering by a simple frequency sweep. This idea takes advantages of acoustic wave velocity shifting in metamaterials in the vicinity of local resonance. We apply this concept into the piezoelectric metamaterial consisting of host medium and piezoelectric LC shunt. Theoretical modeling and FEM simulations are carried out. It is shown that the phase velocity of acoustic wave changes dramatically in the vicinity of local resonance. The directions of acoustic wave can be adjusted continuously between 2 to 16 degrees by a simple sweep of the excitation frequency. Such an electro-mechanical coupling system has a feature of adjusting local resonance without altering the mechanical part of the system.
Piezoelectric transducers are widely employed in vibration-based energy harvesting schemes. Simple piezoelectric cantilever for energy harvesting is uni-directional and has bandwidth limitation. In this research we explore utilizing internal resonances to harvest vibratory energy due to excitations from an arbitrary direction with the usage of a single piezoelectric cantilever. Specifically, it is identified that by attaching a pendulum to the piezoelectric cantilever, 1:2 internal resonances can be induced based on the nonlinear coupling. The nonlinear effect induces modal energy exchange between beam bending motion and pendulum motions in 3-dimensional space, which ultimately yield multidirectional energy harvesting by a single cantilever. Systematic analysis and experimental investigation are carried out to demonstrate this new concept.
In this research, piezoelectric transducers are incorporated in an impedance-based damage detection approach
for railway track health monitoring. The impedance-based damage detection approach utilizes the direct
relationship between the mechanical impedance of the track and electrical impedance of the piezoelectric transducer
bonded. The effect of damage is shown in the change of a healthy impedance curve to an altered, damaged curve.
Using a normalized relative difference outlier analysis, the occurrences of various damages on the track are
determined. Furthermore, the integration of inductive circuitry with the piezoelectric transducer is found to be able
to considerably increase overall damage detection sensitivity.
Owing to the two-way electro-mechanical coupling characteristics, piezoelectric transducers have been widely used as sensors and actuators in sensing and control applications. In this research, we explore the integration of piezoelectric transducer with the structure, in which the transducer is connected with a Wheatstone bridge based circuitry subjected to chaotic excitation. It is shown that a type of Wheatstone bridge circuit with proper parameters configuration can increase sensitivity in detecting structural anomaly. Such integration has the potential to significantly amplify the response change when the underlying structure is subject to property change. Comprehensive analytical and experimental studies are carried out to demonstrate the concept and validate the performance improvement.
Piezoelectric transducers are widely employed in vibration-based energy harvesting schemes. The efficiency of
piezoelectric transducers fundamentally hinges upon the electro-mechanical coupling effect. While at the material
level such coupling is decided by material property, at the device level it is possible to vary and improve the energy
conversion capability between the electrical and mechanical regimes by a variety of means. In this research, a new
approach of compensating the effective flexibility of piezoelectric transducers by using non-contact magnetic effect is
explored. It is shown that properly configured and positioned magnet arrays can induce approximately linear
attraction force that can improve the electro-mechanical coupling of the piezoelectric energy harvester. Analytical and
experimental studies are carried out to demonstrate the enhancement.