Elastic Wave Energy Research Articles

Gravity-guided snapping sequence in 3D modular multistable metamaterials

The snapping sequence of multistable metamaterials is critical for their applications in elastic wave control and energy release. Despite being a fundamental property, the effect of gravity on the snapping sequence has never been studied. This paper investigates the mechanical mechanism how structural gravity affects the snapping sequence of multistable metamaterials to construct deterministic static and dynamic snapping sequences. A biaxial snap-through availability three-dimensional (3D) modular multistable metamaterial (MMM) is developed. The 3D MMM is assembled from unit cells consisting of a dismountable middle bar (M-bar) and a fixed frame containing two bistable curved beams. Except experimental tests and numerical simulations, analytical analyses are also conducted to verify the snapping sequence induced by gravity in the 3D MMM. In addition, given that the M-bar is dismountable, the effects of its length on the mechanical properties and the impact resistance of the 3D MMM are discussed in detail. It is found that gravity can guide both static and dynamic deterministic snapping sequences of the 3D MMM to optimize the process of elastic wave propagation and energy release, and the proposed 3D MMM can enhance structural impact resistance through elastic deformations.

Localization of elastic surface waves based on defect modes in non-Bragg structures

Abstract The non-Bragg defect mode (NBDM) of elastic surface waves is experimentally investigated by inserting a defect in the middle of an antisymmetric periodic corrugated aluminum plate, which has been known as the non-Bragg structures since the observed band gaps are different from the traditional Bragg ones. Generally, the non-Bragg band gaps, existing away from the Bragg ones in a perfectly periodic waveguide, are created by the resonances of different transverse guided modes. The transmission spectra of elastic surface waves in antisymmetric structures with defects reveal the presence of defect modes within the non-Bragg gaps. Notably, the NBDM exhibits significant distribution characteristics in comparison to the traditional Bragg defect mode, including more complex elastic wave higher-order modes and localized wave energy near the defect. Consequently, the NBDM observed in the antisymmetric periodic waveguide with defects holds potential for utilization in other elastic wave functional devices, including filters and wave intensifiers.

Low-frequency air-coupled transducer based damage detection in composite materials

In this paper results of simulations of non-contact elastic wave generation in the composite panel based on acoustic to elastic wave transformation are presented. For this purpose simulations of acoustic wave generation and processing are based on the FEM method in COMSOL. Elastic wave generation and propagation are based on the spectral element method (SEM) in the time domain. The SEM model utilises time-varying acoustic pressure distributions calculated in the FEM. The SEM allows to simulate the interactions of elastic waves with the delamination. Damage localization is based on RMS elastic wave energy maps. In this research a panel made of carbon fibre-reinforced polymer composite is investigated. Research related to low-frequency air-coupled transducer (ACT) is presented. The utilisation of low-frequency waves allows for the reduction of the effects of the wave attenuation in composite material. The proposed combination of FEM and SEM gives an efficient tool for the simulation of non-contact wave generation for non-destructive testing analysis.

Dual-functional perforated metamaterial plate for amplified energy harvesting of both acoustic and flexural waves

Metamaterials with defect states are commonly utilized in energy harvesting from acoustic and elastic waves due to their remarkable ability to localize waves. In this study, a novel piezoelectric energy harvester based on a perforated double-pillars metamaterial plate with a point defect, which offers the advantage of efficiently harvesting both ambient acoustic and flexural wave energy, is proposed. The proposed structure incorporates a locally resonant mechanism that enhances the concentration of vibration energy at the defect band frequency. Then, the amplified wave energy is efficiently converted into electrical energy by attaching a piezoelectric patch at the defect position. To initiate this investigation, the differential quadrature method is employed to theoretically estimate the boundary frequencies of the first band gap. Subsequently, this study investigates how holes size, electrical boundary conditions, and electrical circuit connections affect the energy harvesting of both acoustic and flexural waves. Correspondingly, the mechanisms behind their effects are thoroughly explained. Numerical results demonstrate that the wave energy localization performance can be remarkably amplified with an increasing holes radius, and the harvesters with the 1mm holes radius generate voltages that are approximately 2.12 and 1.44 times higher than those with the 0mm holes radius from acoustic and flexural waves, respectively. Furthermore, variations in the defect band frequency and corresponding wave localization behavior depend on the specific electrical boundary conditions and circuit connection approaches, ultimately leading to distinct results in the output electrical energy. These findings present valuable insights and guidelines for the development of high-performance electronic applications in the context of acoustic and elastic wave energy harvesting.

An Investigation of the Energy Harvesting Capabilities of a Novel Three-Dimensional Super-Cell Phononic Crystal with a Local Resonance Structure.

Using the piezoelectric (PZT) effect, energy-harvesting has become possible for phononic crystal (PnC). Low-frequency vibration energy harvesting is more of a challenge, which can be solved by local resonance phononic crystals (LRPnCs). A novel three-dimensional (3D) energy harvesting LRPnC is proposed and further analyzed using the finite element method (FEM) software COMSOL. The 3D LRPnC with spiral unit-cell structures is constructed with a low initial frequency and wide band gaps (BGs). According to the large vibration deformation of the elastic beam near the scatterer, a PZT sheet is mounted in the surface of that beam, to harvest the energy of elastic waves using the PZT effect. To further improve the energy-harvesting performance, a 5 × 5 super-cell is numerically constructed. Numerical simulations show that the present 3D super-cell PnC structure can make full use of the advantages of the large vibration deformation and the PZT effect, i.e., the BGs with a frequency range from 28.47 Hz to 194.21 Hz with a bandwidth of 142.7 Hz, and the maximum voltage output is about 29.3 V under effective sound pressure with a peak power of 11.5 µW. The present super-cell phononic crystal structure provides better support for low-frequency vibration energy harvesting, when designing PnCs, than that of the traditional Prague type.

Realization of elastic wave energy flow density based on MATLAB

Realization of elastic wave energy flow density based on MATLAB

Achromatic ribbed elastic meta-structure for ultra-broadband flexural wave manipulation

Elastic metasurfaces have shown remarkable ability in exotic wavefront manipulations based on the generalized Snell’s law (GSL), stimulating great promise for many potential applications, such as elastic wave signal processing, vibration control, and energy harvesting. However, elastic metasurfaces suffer from strong narrow-band confinement and dispersion modulation due to the inherent velocity-dispersive properties and the dispersion of the accumulated phase during propagation. To address this issue, we propose a novel conceptual design paradigm of achromatic ribbed elastic meta-structures (AREMs) beyond the narrow-band limit for the ultra-broadband manipulation of flexural waves in thin plates. We establish an analytical model for ribbed subunits to accurately solve the phase shift and amplitude of the transmitted waves. In addition, we reveal the relationship between broadband achromatic functionality and subunit phase shift dispersion. We theoretically design and numerically demonstrate three flexural wave manipulation functionalities in an ultra-broadband frequency range of 1–10 kHz, including flexural wave deflection, focusing, and splitting, with a relative bandwidth of 163.6 %. Finally, we experimentally verify the ultra-broadband flexural wave manipulation capabilities of AREMs. Our study may open new horizons for ultra-broadband high-efficiency achromatic and structurally simplified flexural wave-based devices, with promising extensions to other elastic wave modes.

Roton-like dispersion via polarisation change for elastic wave energy control in graded delay-lines

While roton dispersion relations had been restricted to correlated quantum systems at low temperature, recent works show the possibility of obtaining this unusual dispersion in acoustic and elastic metamaterials. Such phenomenon has been demonstrated in periodic structures by means of beyond-nearest-neighbour interactions, following the formulation firstly developed by Brillouin in the ′50s. In this paper, we demonstrate both numerically and experimentally that beyond-nearest-neighbour connections are not a necessary condition to obtain this unusual dispersion relation in elasticity. Leveraging the intrinsic complexity of elastic systems supporting different types of waves, we demonstrate that mode locking can be applied to obtain roton dispersion, without the need of elastic or magnetic interactions between non nearest neighbours. Moreover, the combination of roton dispersion and rainbow physics enables spatial separation of the energy fluxes with positive and negative group velocity.

Defect-Band Splitting of a One-Dimensional Phononic Crystal with Double Defects for Bending-Wave Excitation

Extensive prior research has delved into the localization of elastic wave energy through defect modes within phononic crystals (PnCs). The amalgamation of defective PnCs with piezoelectric materials has opened new avenues for conceptual innovations catering to energy harvesters, wave filters, and ultrasonic receivers. A recent departure from this conventional paradigm involves designing an ultrasonic actuator that excites elastic waves. However, previous efforts have mostly focused on single-defect scenarios for bending-wave excitation. To push the boundaries, this research takes a step forward by extending PnC design to include double piezoelectric defects. This advancement allows ultrasonic actuators to effectively operate across multiple frequencies. An analytical model originally developed for a single-defect situation via Euler–Bernoulli beam theory is adapted to fit within the framework of a double-defect set-up, predicting wave-excitation performance. Furthermore, a comprehensive study is executed to analyze how changes in input voltage configurations impact the output responses. The ultimate goal is to create ultrasonic transducers that could have practical applications in nondestructive testing for monitoring structural health and in ultrasonic imaging for medical purposes.

Achromatic elastic metalens for high-performance confocal piezoelectric energy harvesting

In this study, we analytically, numerically, and experimentally investigated a high-performance confocal piezoelectric energy harvesting system. We achieved a significantly enhanced electrical performance through a Mikaelian lens, which achromatically focuses ambient elastic waves, resulting in the formation of a highly amplified strain energy field in the piezoelectric energy harvester. Previous studies on piezoelectric energy harvesting platforms have limitations, such as the focal position changing with operating frequencies and impedance mismatching owing to inclusions or holes. To address these problems, we utilized the self-focusing ability based on the conformal mapping theory and achromatic ability based on the Kirchhoff–Love thin plate theory to design our Mikaelian lens-based piezoelectric energy harvesting platform. The proposed platform demonstrates a remarkable elastic wave focusing ability at an identical focal position for a broad frequency range. The experimentally visualized wave fields matched well with the numerically calculated full-wave harmonic simulation results. We achieved highly amplified output power up to 1.44 mW within a broad range from 40 to 60 kHz out of the same focal point owing to confined elastic wave energy; the output power extracted at this confocal position was up to 3.76 times higher than that extracted at the lens start position. Our highly performance and broadband achromatic piezoelectric energy harvesting platform lays an attractive foundation for designing potential applications, such as wireless sensing, structural health monitoring, and biomedical devices.

Multiband elastic wave energy localization for highly amplified piezoelectric energy harvesting using trampoline metamaterials

In this study, we investigate high-performance piezoelectric energy harvesting at multiband frequencies. Previous harvesting platforms were limited to a high-frequency range and exhibited poor electrical performance. Our proposed piezoelectric energy-harvesting platform, which is based on a periodically arranged trampoline metamaterial, exhibits a remarkable electrical output at both low and high frequencies. The proposed harvesting platform broadens the bandgap induced by Bragg scattering in the high-frequency range, and the local resonance is critical in opening a wide bandgap in the low-frequency range. By breaking the periodicity, we generate multiband defect states for flexural wave trapping under fundamental physical phenomena. We experimentally demonstrate flexural wave localization in the defect cavity, while a confined wave is converted into high-performing electrical energy using a piezoelectric element. We measure 1.37 V and 4.05 V as output voltage, and 24.4 μW and 1.28 mW as output power at the 1st and 2nd defect modes, respectively, which are 188% and 400% compared with the bare plate. Our high-power energy-harvesting platform has potential applications as a renewable and sustainable energy source in various fields, such as structural health monitoring, signal processing, and sensors.

Mechanism of vorticity amplification by elastic waves in a viscoelastic channel flow

Inertia-less viscoelastic channel flow displays a supercritical nonnormal mode elastic instability due to finite-size perturbations despite its linear stability. The nonnormal mode instability is determined mainly by a direct transition from laminar to chaotic flow, in contrast to normal mode bifurcation leading to a single fastest-growing mode. At higher velocities, transitions to elastic turbulence and further drag reduction flow regimes occur accompanied by elastic waves in three flow regimes. Here, we demonstrate experimentally that the elastic waves play a key role in amplifying wall-normal vorticity fluctuations by pumping energy, withdrawn from the mean flow, into wall-normal fluctuating vortices. Indeed, the flow resistance and rotational part of the wall-normal vorticity fluctuations depend linearly on the elastic wave energy in three chaotic flow regimes. The higher (lower) the elastic wave intensity, the larger (smaller) the flow resistance and rotational vorticity fluctuations. This mechanism was suggested earlier to explain elastically driven Kelvin-Helmholtz-like instability in viscoelastic channel flow. The suggested physical mechanism of vorticity amplification by the elastic waves above the elastic instability onset recalls the Landau damping in magnetized relativistic plasma. The latter occurs due to the resonant interaction of electromagnetic waves with fast electrons in the relativistic plasma when the electron velocity approaches light speed. Moreover, the suggested mechanism could be generally relevant to flows exhibiting both transverse waves and vortices, such as Alfven waves interacting with vortices in turbulent magnetized plasma, and Tollmien-Schlichting waves amplifying vorticity in both Newtonian and elasto-inertial fluids in shear flows.

Porous-Solid Metaconverters for Broadband Underwater Sound Absorption and Insulation

Existing solid composite structures composed of several viscoelastic materials and metals mainly exploit diverse resonances, damping, and scattering to realize underwater acoustic wave functionalities. However, low-frequency broadband underwater sound absorption and insulation are still hard to capture with an acoustic coating possessing subwavelength thickness and lightweight nature simultaneously. This paper reports the systematic simulated and experimental validations of a porous-solid underwater metaconverter, consisting of a rubber layer and a topology-optimized elastic metasurface to exhibit broadband functionalities of sound absorption and insulation caused by the strong reflective and transmitted longitudinal-to-transverse wave conversion, while sustaining broadband impedance matching. Various results confirm the predicted capabilities of underwater broadband high-efficiency sound absorption (>80%) or insulation (20 dB) within the range of 2–10 kHz for a large- and limited-size sample, providing an estimate of the energy-converting effect and phenomenon. The present study provides possibilities for elastic wave energy dissipation, harvesting, and underwater acoustic stealth via metasurfaces.4 MoreReceived 9 December 2022Revised 3 February 2023Accepted 28 February 2023DOI:https://doi.org/10.1103/PhysRevApplied.19.044074© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAcoustic metamaterialsAcoustic wave phenomenaArchitectural acousticsCloakingMechanical & acoustical propertiesUnderwater acousticsPhysical SystemsPorous mediaTechniquesSound wave techniquesCondensed Matter, Materials & Applied Physics

Local-Resonance-Induced Dual-Band Topological Corner States of Flexural Waves in a Perforated Metaplate

Despite their proven effectiveness in localizing and steering subwavelength elastic waves, locally resonant elastic topological insulators (TIs) with surface-mounted or embedded resonators are often challenged because of their structural complexity and the difficulty in realizing multiple topological band gaps. Here we present a second-order elastic TI (SETI), made of a perforated metaplate with a series of etched C-shaped slots, to achieve dual-band topological corner states. The etched slots in the metaplate form a type of cantileverlike oscillator, the multimodal bending resonances of which couple with the flexural vibration modes of the metaplate, resulting in multiple locally resonant band gaps. Judiciously configuring these slots in a ${C}_{4v}$-symmetric lattice enables topologically distinct metastructures and creates a SETI. We numerically and experimentally observe the dual-band corner states in two broad topological band gaps. Our platform for observing the topological effects in a perforated metaplate greatly simplifies the fabrication of metastructures for implementing locally resonant elastic TIs, benefiting applications of TIs at the subwavelength scale such as elastic wave trapping and energy amplification.

Enhanced piezoelectric energy harvesting based on sandwiched phononic crystal with embedded spheres

In recent years, metamaterial/ phononic crystal (PnC) based energy harvesters are gaining interest due to their excellent elastic wave manipulation and energy trapping capabilities. Here, we propose a novel PnC comprising of Tungsten Carbide (WC) spheres embedded in epoxy resin matrix. The sphere-epoxy composite is encapsulated by Aluminum (Al) holey structure and the device is sandwiched between two Al plates. Numerical analysis of band structure reveals a wide phononic band gap (BG) from 50.65 kHz to 71.12 kHz. These BGs can be engineered by varying geometric parameters of the unit cell viz., the radius of the sphere and thickness of Al plates. A point defect is introduced by removing the central sphere of the 5 × 5 PnC to facilitate the robust localization of evanescent wave defect modes within the bandgap. Moreover, it is observed that, by altering the radius of the defect sphere, the number of defect modes and their shift can be reconfigured. A PnC based energy harvester is implemented by attaching a piezoelectric disk (PZT-5H) onto the defect PnC just above the defect site. This arrangement of PZT disk converts the highly resonant mechanical defect mode into electrical energy, thereby allowing vibration energy harvesting. Finally, we show that the power enhancement can be achieved by ∼12 times with the proposed PnC compared to the bare Al block.

Detection of Sleeve Grouting Compactness Based on Acoustic Emission Technology

Sleeve grouting compactness has a significant effect on the mechanical properties of rebar connections. However, a detection method for the grouting compactness inside the sleeve is still lacking. Therefore, the aim of this paper is to propose a new acoustic emission (AE) detection technology for horizontal defects and vertical defects in sleeves with different grout compactness. The basic waveform characteristic of the AE signal is analyzed. The results show that the count of acoustic emission signals decreases with the increase of grouting compactness, and the reduction rate of vertical defects is larger than that of horizontal defects. The acoustic emission waveform is further processed through wavelet packet decomposition. It is found that with the increase of grouting compactness, the composition of approximately 125-187.5 kHz in the signal is accelerated to approximately 62.5-125 kHz. The grouting compactness index is constructed by wavelet packet energy ratio. With the increase of grouting compactness, the compactness index decreases exponentially, indicating that the presence of defects can greatly reduce the attenuation of elastic wave energy. The compactness index is highly consistent with the size of defects and has little relationship with the distribution of grout materials. Experiments show that the proposed method is effective when grout defects reach a certain degree and provides a new method for sleeve grouting compactness detection.

Correlating multimode strain and electrode configurations for high-performance gradient-index phononic crystal-based piezoelectric energy harvesting.

A gradient-index phononic crystal (GRIN PnC) capable of manipulating wave propagation can serve as an excellent input wave energy focusing platform for amplifying energy harvesting power generation. However, despite its remarkable focusing capability, the finite wavelength of the propagating elastic waves in the focal area causes voltage cancellation inside a piezoelectric element under multimode strains having opposite directions; this limits the capacity of the GRIN PnC-based energy harvesting system. This study demonstrates a rational electrode configuration for a piezoelectric energy harvesting (PEH) device that can maximize the performance of a given GRIN PnC platform. The multimode strain analysis experimentally performed on the PEHs distributed over the focusing area confirms that the patterned electrode PEH configuration is the most effective in alleviating strain and voltage cancellation while efficiently transferring the focused elastic wave energy. Furthermore, a proper combination of electrical connections between the patterned electrodes substantially increases the piezoelectric potential across the ceramic by maximizing the strain difference. The simultaneous tailoring of the piezoelectric ceramic composition and the electrode configuration leads to a maximum power generation of 7.06 mW even under off-resonance conditions, the largest ever reported in elastic wave energy harvesting.

Implications of slow fault slip for hydraulic-fracturing-induced seismicity

Since the discovery of slow-slip phenomena, scientific understanding of the behavior of active fault systems has been transformed significantly. It is now recognized that tectonic fault systems are characterized by a spectrum of slip behavior, from “regular” (stick-slip) earthquakes that radiate elastic wave energy and occur on a timescale of seconds, to slow-slip events with durations ranging from minutes to years. More recently, slow-slip phenomena have been observed and modeled in association with injection-induced seismicity. This includes evidence for predominantly slow fault slip during injection that triggered dynamic rupture elsewhere on a fault. In the case of hydraulic fracturing, slow-slip behavior is consistent with the frictional characteristics of faults in clay-rich rocks. A change in pore pressure or slip rate can cause a fault to transition from slow to unstable slip. Through real-time monitoring of slip-slip processes and, potentially, the development of operational adjustments to reduce the hazard of damaging ground motions, a better understanding of slow-slip processes could contribute to improved risk mitigation for induced earthquakes. Effective tools for direct observation of slow-slip processes include tiltmeters, strainmeters, global navigation satellite systems, interferometric synthetic aperture radar, and distributed fiber-optic sensing.

Technology for the creation of ferroelectric regular domain structures using interfering elastic waves

Objectives. In many laboratories around the world, work is underway in the field of domain engineering of ferroelectrics. For a number of years, RTU MIREA has been conducting research on the creation of a high-performance technology for the formation of ferroelectric photonic and phononic crystals. The technology is characterized by a short duration of the technological cycle and provides the necessary depth of spatially periodic domain inversion. The key element of the technology is the combined effect of a uniform electric field and interfering high-frequency elastic waves that create a temperature grating. The technology is universal in relation to ferroelectrics of varying degrees of acoustic transparency, which is achieved by using highly dissipative liquid electrodes of a certain thickness. In this case, the energy of elastic waves practically does not penetrate into the ferroelectric, so the manifestation of undesirable effects is excluded. The purpose of this review article is to analyze the results of work carried out at RTU MIREA in the field of technology for the formation of ferroelectric regular domain structures (RDSs) during the period from 2008 to the present.Methods. Provisions of the theory of propagation, refraction and interference of elastic waves in condensed media are used, in particular, the Newtonian model of a liquid as applied to shear waves, as well as computer simulation. When considering the main stages of the Double Pulse heterothermal technology for the formation of RDSs, methods of analysis and synthesis were applied.Results. The possibility of forming not only micro-, but also submicron RDSs is shown. Recommendations are given on the choice of the type and specific properties of liquid electrodes, the angles between the direction of propagation of interfering waves, and their frequency. It is shown, in particular, that the use of highly dissipative ionic liquids as liquid electrodes creates favorable conditions for the formation of an RDS with a short period at room temperature. Thus, on shear waves with electrodes based on LiPF6-PC at a frequency of 300 MHz, RDS with a period of about 2 цт can be created. The main technological parameters are determined both for the case of the action of longitudinal elastic waves and for the case of shear waves with horizontal polarization. The results are applicable to ferroelectrics such as lithium niobate, potassium titanyl phosphate, and lead zirconate titanate.Conclusions. The proposed and studied methods are focused on the mass production of devices based on RDSs, in particular, on the manufacturing of optical parametric oscillators, acoustoelectronic devices, as well as terahertz wave generators and second harmonic oscillators. The technology has a short duration of the technological cycle, comparable to the polarization switching time in the used ferroelectric.

Theoretical and experimental study on interface stiffness measurement of rough surface using improved acoustic model

Structural health monitoring (SHM) of interface stiffness is of great significance in many fields, such as accurate rotor dynamics modeling and interface friction performance analysis. Acoustic wave is an important interface detection method. However, the interface mechanics and elastic wave theory are relatively independent, and the interaction mechanism between the contact asperity parameters and the energy transfer of elastic waves has not been thoroughly explored. The existing interface stiffness detection indexes do not consider the uncertainty of boundary parameters, which easily leads to the degradation of detection performance and limits the promotion of interface stiffness detection. In this paper, we proposed an acoustic model considering contact interface and boundary effects integrating microwave transmission line theory. A new interface stiffness detection index is constructed to ensure the robustness of the detection results. The relationship between contact parameters and elastic wave energy transfer is analyzed, and the robustness of different detection indexes and the uncertainty of different detection methods are compared. The experimental results of the pressure-bearing connection structure are obtained to verify the correctness of the acoustic model and the feasibility of the detection method. The proposed method is further applied to multi-bolted structures, and the robustness of the proposed method is discussed. The results show that the proposed method has the ability of in-situ interface stiffness detection and potential engineering utility.