Localized Resonance Research Articles

Dispersion Engineering by Hybridizing the Back-Folded Soft Mode of Monomode Elastic Metamaterials with Stiff Acoustic Modes.

In many cases, the hybridization of two or more excitation modes in solids has led to new and useful dispersion relations of waves. Well-studied examples are phonon polaritons, plasmon polaritons, particle-plasmon polaritons, cavity polaritons, and magnetic resonances at optical frequencies. In all of these cases, the lowest propagating mode couples to a finite-frequency localized resonance. Herein, the unusual metamaterial phonon dispersion relations arising from the hybridization of an ordinary acoustical phonon mode with a back-folded soft or easy phonon mode of a monomode elastic metamaterial are discussed. Conceptually, the single easy mode can have strictly zero wave velocity. In reality, its wave velocity is very much smaller than that of all other modes. Considering polymeric three-dimensional printed elastic monomode metamaterials at ultrasound frequencies, it is shown theoretically and experimentally that the resulting pronounced avoided crossing, with a frequency splitting comparable to the mid-frequency, leads to backward-wave behavior for the lowest band over a broad frequency range, conceptually at zero loss.

Local Government Resonance on Disaster Potential Issues

Ring of fire that surround Indonesia from east to the west made this country become potential vulnerable to various types of natural disasters, Morowali is a district located in central sulawesi province that one of a disaster-prone area. It is traversed by the Matano fault which connected to Palu Koro fault which is a fault with approximately 8 mm active movement per year. This study aims to see how far the local government of Morowali responds to the issue of potential disasters, consider that Morowali district is one of the areas designated by the state government as a special economic zone. This study using an exploratory case study that does not see phenomena only from problems but also in the form of social activities, groups, and organization. Niklas Luhmann's concept of resonance is the main reference in describes the interconnection between systems and the environment. Research data obtained using in-depth interviews, focus group discussions, and field observations. The informants in this study were executive and legislative board. The results show that the executive and legislative response to the issue of potential natural disasters shows the resonant capacity of two functional systems politics and economics are weak, which shows that the government's system should encourage the concept of proactive adaptation to strengthen its response to the existing potential disasters and create security for the Morowali community.

Free-layer damping influence on the evanescent wave in a strip containing periodic acoustic black holes

This work demonstrates the transformation of wave motions in a periodic two-dimensional (2D) ABH structure with one-dimensional (1D) lattice subject to the damping dissipation. The free-layer damping (FLD) treatment is employed to achieve the damping dissipation. Numerical results, alongside analyses based on the local dispersion relation model, expose the effect of dissipation on bandgap (BG), which is always accompanied by the ABH-featured local resonance. Analyses show that the dissipative periodic ABH strip enables comparable attenuation intensity as that in its corresponding non-dissipation periodic ABH strip due to fact that the periodic ABH strip has two types of BG: (i) one shows infinite group velocity and constant lattice phase; (ii) another is accompanied by the discontinuous dispersion curves for the same flexural wave. The minimal attenuation inside these two BGs is less affected by the dissipation level. The discontinuity phenomenon inside the BG is attributed to the coupling between different flexural wave evanescent modes. As a result, the reduction of minimal attenuation inside the BG is less sensitive to the dissipation level. This attenuation variation subject to the damping dissipation inside the BG is distinguished from the weakened attenuation in traditional local resonance BG, in which there always exists a phase jump by π/a. Along with the ABH-enhanced dissipation, the dissipative periodic ABH strip enables broadband attenuation by inducing wide complex waves, while obtaining considerable attenuation intensity.

Inertial amplification plates for low-frequency sound and vibration reduction

Reduction of vibration and sound radiation in the low-frequency range is a challenging task. In this work, a lever-type inertial amplification (LIA) mechanism is proposed to enhance the vibration reduction capability of thin plates. The mechanism consists of a rigid lever hinged on the host plate at two separate locations and a small mass mounted at the end of the lever. Band-structures of the unit cell and vibration transmissibility of the finite LIA plate are computed using the finite element method. Numerical results show that compared with the local resonant (LR) plates with the same added mass, the proposed LIA plates generate wider and deeper complete bandgaps at the same target frequency. The Bragg bandgaps occurring at higher frequencies are also broader compared with those of the LR plates due to a stronger impedance mismatch between the host plate and the attachments. Moreover, the vibration reduction performance of the LIA plate presents unique direction-dependent characteristics: maximum vibration attenuation is achieved when the LIA mechanisms are installed parallel to the wave propagation direction.

Development of Acoustic Metamaterial Sheets with Two-Dimensional Array of Hollow Local Resonators

Novel practical acoustic metamaterial sheets with hollow local resonators that can be processed with simple integral molding have been developed. This acoustic metamaterial is a variant of the acoustic metamaterial sheet reported by our group in 2021, which consists of two-dimensionally connected non-hollow-shaped stubs embedded with metal weights. Each hollow-shaped stub can work as a local resonator using the vibration mode of a circular membrane. This acoustic metamaterial can handle lower frequencies even with smaller and lighter stubs compared to those with the non-hollow-shaped stubs we previously reported. It has a particular advantage when used for objects with limited space and weight. It is also possible to control the resonant frequency by altering the material properties or adjusting the shape and size of the stub. It has been experimentally shown that significant sound insulation performance exceeding the mass law can be obtained around the resonant frequencies of the hollow stubs. We show the results of finite element method simulations, modal vibration testing, and transmission loss measurements.

Vibration attenuation band tuning by active stiffness control of local resonators of metamaterials

This paper presents a design of metamaterials with a broader bandgap by active stiffness control of local resonators. A series of cantilever beams are connected to the host structure, serving as local resonators to open the bandgap for vibration attenuation. The piezoelectric transducers bonded on the cantilever beams are shunted to a negative capacitance-negative inductance series circuit (NCNL). The variation of the effective modulus of the piezoelectric sample when connected to NCNL is discussed. In addition, the effect of the NC circuit and negative capacitance in series with positive inductance (NC-L) circuit on the effective modulus of shunted piezoelectric transducers is also analyzed for comparison. By tuning the NCNL circuit, the elastic modulus of the beam-type resonator exhibits frequency-dependent, which will achieve active stiffness tuning. Subsequently, the transmittance analysis of a metamaterial beam with active stiffness resonators is conducted using finite element method. The finite element results show that a broader attenuation band can be achieved by properly selecting the parameters of NC-NL circuits. This work provides a promising method for effective vibration attenuation using metamaterials.

Tunable low-frequency broadband metamaterial beams composed of hierarchical annular cantilevers

Tuning the resonance frequency of the local resonators in an active way and obtaining a broad bandgap at low frequency is a long-lasting challenge for traditional elastic metamaterials. This work proposes a kind of tunable metamaterial beam to isolate flexural waves, which are composed of hierarchical annular cantilevers with a steel mass block embedded in the center of each unit cell. To obtain a broad low-frequency bandgap, a genetic algorithm-based size optimization is utilized to determine the optimal geometry parameters of the unit cell. The tunability of the metamaterial beam is realized by attaching different numbers of permanent magnets to the embedded mass block. Such a tuning approach makes the change of the resonator’s mass available. Moreover, based on the rainbow effect, ultra-broadband flexural wave attenuation is realized by forming a gradient metamaterial beam. Both numerical and experimental results verify the good flexural wave attenuation ability of our proposed tunable metamaterial beam.

A micro random laser of dye solution-filled tube system based on electrospun fibers

Random lasers (RLs) have good application prospects in speckle-free imaging, micro sensing and micro-nano photonic devices due to their properties such as cavityless, miniaturization and low-spatial coherence. The minimization, emission mechanism and lasing property control of RLs still need to be explored. In this paper, we present a novel micro RL system in a dye solution-filled tube, where the coherent random lasing action is facilitated by the integration of electrospun fibers and gold nanoparticles (Au NPs). The electrospun fibers serve as the scattering medium, while the Au NPs produce the local plasmon resonance effect. The interaction effect improves the photon scattering rate, makes the photons form a ring resonator in the system, and realizes the coherent RL in the tube system. The microtube RL has a very small size, a convenient preparation method and stable emission properties. It can withstand more than 2000 times pumping while maintaining a stable emission intensity. The electrospun fibers are stable and uniform in morphology, which makes it easy to achieve mass production of microtube RL. The speckle-free imaging experiment shows the RL has low spatial coherence, which indicates that it’s a good choice for micro speckle-free imaging. This work provides a convenient way to realize micro coherent RLs by electrospun fibers and could pave a way for applications in photonic devices.

Topological electromagnetic waves in dispersive and lossy plasma crystals

Topological photonic crystals, which offer topologically protected and back-scattering-immune transport channels, have recently gained significant attention for both scientific and practical reasons. Although most current studies focus on dielectric materials with weak dispersions, this study focuses on topological phases in dispersive materials and presents a numerical study of Chern insulators in gaseous-phase plasma cylinder cells. We develop a numerical framework to address the complex material dispersion arising from the plasma medium and external magnetic fields and identify Chern insulator phases that are experimentally achievable. Using this numerical tool, we also explain the flat bands commonly observed in periodic plasmonic structures, via local resonances, and how edge states change as the edge termination is periodically modified. This work opens up opportunities for exploring band topology in new materials with non-trivial dispersions and has potential radio frequency (RF) applications, ranging from plasma-based lighting to plasma propulsion engines.

Band Gap Formation In A Beam With Attached Local Resonators And Periodically Arranged Intermediate External Supports

In the paper a comparative study of a band gap formation mechanism is presented in finite and infinite homogeneous beams rested on periodically arranged intermediate external supports and periodically attached local mass-spring resonators. The transfer matrix method in conjunction with Bloch-Floquet’s approach is extended to study the flexural wave vibration and phonon band gaps generated by both of external intermediate supports and local resonators. The eigenvalue vibration problems are formulated for pinned and clamped multi-span finite length beams and the equation defining eigen frequencies are obtained. The novelty of the paper is the analytical and numerical results concerning formation of band gaps caused by local resonators and intermediate external supports. Աշխատանքում ներկայացված է պարբերաբար տեղակայված միջանկյալ արտաքին հենարաններին հենված և տեղային ռեզոնատորներով միացված հեծանում հաճախությունների արգելված գոտիների կազմավորման համեմատական վերլուծությունը: Տրանսֆեր մատրիցների մեթոդի հետ զուգակցված, Բլոխ-Ֆլոկեի տեսության շրջանակում հետազոտված է արգելված գոտիների գոյացման մեխանիզմները՝ պայմանավորված ինչպես հենարաններով, այնպես էլ ռեզոնատորներով: Ձևակերպվել են եզրային խնդիրները և ստացվել են ամրակցված և հոդակապորեն հենված վերջավոր երկարության բազմաթռիչք հեծանների սեփական արժեքները որոշող հավասարումները: В работе представлен сравнительный анализ механизма образования запретных зон частот в балке с присоединенными локальными резонаторами и опертой на периодически расположенные промежуточные внешние опоры. В рамках теории Блоха-Флоке в сочетании метода трансфер матриц исследован механизм образования запретных зон, генерируемых как опорами так и резонаторами. Сформулированы краевые задачи и получены уравнения определяющие собственные частоты защемленных и шарнирно опертых многопролетных балок конечной длины.

Increasing planet-stirring efficiency of debris discs by ‘projectile stirring’ and ‘resonant stirring’

ABSTRACT Extrasolar debris discs are detected by observing dust, which is thought to be released during planetesimal collisions. This implies that planetesimals are dynamically excited (‘stirred’), such that collisions are sufficiently common and violent. The most frequently considered stirring mechanisms are self-stirring by disc self-gravity, and planet-stirring via secular interactions. However, these models face problems when considering disc mass, self-gravity, and planet eccentricity, leading to the possibility that other, unexplored mechanisms instead stir debris. We hypothesize that planet-stirring could be more efficient than the traditional secular model implies, due to two additional mechanisms. First, a planet at the inner edge of a debris disc can scatter massive bodies on to eccentric, disc-crossing orbits, which then excite debris (‘projectile stirring’). Second, a planet can stir debris over a wide region via broad mean-motion resonances, both at and between nominal resonance locations (‘resonant stirring’). Both mechanisms can be effective even for low-eccentricity planets, unlike secular-planet-stirring. We run N-body simulations across a broad parameter space, to determine the viability of these new stirring mechanisms. We quantify stirring levels using a bespoke program for assessing rebound debris simulations, which we make publicly available. We find that even low-mass projectiles can stir discs, and verify this with a simple analytic criterion. We also show that resonant stirring is effective for planets above ${\sim 0.5\, {\rm M_{Jup}}}$. By proving that these mechanisms can increase planet-stirring efficiency, we demonstrate that planets could still be stirring debris discs even in cases where conventional (secular) planet-stirring is insufficient.

Lightweight sound insulation optimization of simply supported locally resonant plate

A theoretical model of the normal sound insulation of a rectangular locally resonant (LR) plate with simply supported boundary conditions is established. The accuracy of the model is verified through comparison with finite element simulation results. Considering a 1-m2 aluminum plate as the research object, a non-dominated genetic algorithm is introduced. The algorithm optimizes the lightweight sound insulation of an LR finite plate with a center frequency band of 20–800 Hz as the optimization objective of maximum average sound insulation and minimum mass. The optimization parameters are substrate thickness and local resonance parameters (including resonator target frequency (fobj), number of resonators, additional mass ratio, and resonator damping). Optimization results indicate that the average sound insulation fluctuates at approximately 2 dB due to changes in fobj. The results also provide an optimal solution to the algorithm. The optimal sound insulation value curve of LR plates corresponding to different surface densities of intermediate improved cases is fitted and compared with the sound insulation value of an equal-mass bare plate. Under lightweight optimization, the resonators are deemed capable of improving the local frequency band sound insulation. In contrast, the wideband average sound insulation can approximate but not surpass the insulation provided by the equal-mass bare plate. In practical applications, an LR plate that can improve the local frequency band sound insulation and ensure the overall lightweight sound insulation performance of the wide frequency band can be obtained. This can be achieved by analyzing the frequency spectrum of optimal points in the lightweight sound insulation optimization process. Relevant research can provide a basis for the evaluation and design of the low-frequency sound insulation of plates for transportation equipment, such as airplanes, high-speed trains, and cars.

Impact damage detection in woven CFRP laminates based on a local defect resonance technique with laser ultrasonics

This paper presents a local defect resonance (LDR)-based approach to detect barely visible impact damages (BVIDs) in woven CFRP laminates using laser-ultrasonic guided waves. In the experiments, broadband guided waves were excited by an Nd:YAG pulsed laser to induce resonant vibrations of BVIDs. The laser was scanned on the designed area of the woven CFRP laminates by using a galvano mirror system. A fixed broadband PZT sensor received the waves propagated from all the laser irradiation points and the datasets of the recorded waveforms were further processed to visualize the wavefield in the scanned area. A robust post-processing method was proposed to extract automatically the LDR frequencies and to obtain the image of the BVID. The feasibility of the proposed method was well validated on a woven CFRP laminate with a single BVID. In order to evaluate the detection performance, we compared our proposed method with other traditional methods, i.e., root mean square (RMS) and weighted RMS. As a result, it was found that our proposed post-processing procedure could visualize the BVID with higher contrast. Furthermore, the detection of multiple BVIDs using the developed method was demonstrated successfully.

Double defects in trampoline effect and Helmholtz coupled acoustic metamaterial for broadband piezoelectric energy harvesting

An acoustic metamaterial with double defects is proposed to widen bandwidth and improve energy collection. Defects can limit elastic waves to achieve energy localization. The introduction of defects in acoustical supermaterials can improve energy localization and amplify the effect, but single defects are easily limited by narrow bandwidth. Therefore, the bandwidth is broadened by adding double defects to the acoustic supermaterial. At the same time, the existence of double defect can influence the coupling effect of each other to a certain extent, which is helpful to the improvement of energy recovery. In order to further enhance the local resonance at the defect location, the trampoline effect and Helmholtz resonator are used to further enhance the energy recovery. Using finite element method (FEM) simulations, the comparison results show the double defect enhances energy recovery and broadens bandwidth of energy collection compared with single defect, and the maximum voltage output is about 0.86V under the effective sound pressure of 100dB.

Local resonance mechanism for enhancing the thermoelectric performance of PBCF-graphene nanoribbons

Phonon local resonance mechanism can effectively block phonon transport and thus reduce phonon thermal conductance. Inspired by this, we investigated the thermoelectric performance of Armchair-PBCF-graphene nanoribbons (A-PBCF-GNRs) and its branched structures by using non-equilibrium Green's function method. The results show that the thermoelectric performance of branched A-PBCF-GNRs can be significantly improved. Especially, the room-temperature ZT value of single branch A-PBCF-GNRs (SB-A-PBCF-GNRs) and double branch A-PBCF-GNRs (DB-A-PBCF-GNRs) can reach to 0.56 and 0.80, which is 1.5 and 2 times greater than that of A-PBCF-GNRs. Analysis shows that this is mainly attributed to the significant decrease in thermal conductance of branched A-PBCF-GNRs caused by the localized electronic and phonon states. Moreover, the mode resolved phonon transmission probabilities demonstrated that the local resonance mechanism of branched structure blocks the low-frequency acoustic phonon transmission. This work indicates the broad application prospects of the local resonance mechanism of branched structure in the thermoelectric field.

Superhydrophobic silicone microcup array on periodic microswelling structure of silicone rubber formed by 193 nm ArF excimer laser-induced photodissociation

Many reports have been made on the study of imparting high functionality to materials surface by micro/nanofabrication of three-dimensional structures. In various three-dimensional structural geometries, the nanocups enable high-sensitivity analysis by combining with localized plasmon resonance. On the other hand, the formation of microcups and their applications have not been found much. In this paper, we found a new formation method of the silicone microcups and suggested its application. Single layer of silica glass microspheres was formed on silicone rubber, then a 193 nm ArF excimer laser irradiated the surface. Main chains of SiOSi bonds of the silicone rubber underneath the microspheres could be photodissociated to lower the molecular weight, resulting in the photochemical formation of periodic microswelling structure of silicone rubber. Concurrently, a hemispherical microcup was also formed on each the microswelling structure. The optimal laser irradiation conditions for their formation as well as the chemical etching time of microspheres were examined. It was also confirmed that the microcups are consisted of silicone. Moreover, the microcups exhibit superhydrophobicity. The results make it possible to confine the microcups in an air gap underwater, and it is expected to be applied as a micropower storage device that functions in seawater.

Bandgap regulations of longitudinal wave for a nonlinear metastructure isolator with high-static-low-dynamic stiffness

Linear structures are inherently difficult to exhibit mechanical properties with high-static-low-dynamic stiffness (HSLDS), which means that linear isolators with these structures struggle to have both high-quality load-bearing capacity and low-frequency isolation ability at the same time. To address this issue, we have designed a high-load-capacity local resonance (LR) nonlinear metastructure isolator for low-frequency vibration isolation of target objects. We reveal the regulation mechanism of longitudinal wave attenuation in such metastructures and conduct comparative study by finite element method (FEM) and experiments for a 3D printed prototype metastructure. The results show that in specific excitation frequencies, the LR nonlinear metastructure with a cantilever beam oscillator having a natural frequency of 11.7 Hz triggers a LR mechanism. Under the action of the nonlinear isolator, the vibration transmissibility is as low as 10 % at the center frequency of the bandgap under the base excitation. Furthermore, the dispersion equation of such nonlinear metastructures is derived, and through the analysis of the regulation of bandgaps, the variation trend of the transmissibility of nonlinear metastructure isolators is effectively predicted. The calculation method and design idea of this metastructure isolators provide a new approach for vibration isolation.

Modal analysis of waveguide for the study of frequency bandgaps of a bounded periodic medium

A novel method based on waveguide modal analysis is presented to evaluate the effectiveness in terms of frequency bandgaps of bounded periodic metamaterials. The effect of the size of the bounded medium, i.e., the number of periodic unit cells, on the frequency bandgaps predicted by Floquet–Bloch theory in the infinite case is investigated and quantified. The waveguides considered in this work have a bounded cross-section and an infinite longitudinal axis simulated by Perfectly Matched Layers. Its useful area is made of a bounded 1D or 2D-periodic matrix-inclusion metamaterial. In the 2D-periodic case, an approach combining the waveguide modal analysis with the Floquet–Bloch transform is further proposed. Applying the proposed method, the SH-waves propagating in a waveguide are studied by using the finite element method. The discrete spectrum of the waveguide and the associated attenuated or trapped wave modes are calculated and analyzed, which provides, within a semi-analytic framework, an exact characterization regarding the attenuation coefficient and the frequency bandgaps of the studied bounded periodic medium. More particularly, effectiveness indicators are defined to compare the width and the position of frequency bandgaps between the bounded and infinite cases as a function of the cell number. Last but not least, the proposed method is also successfully applied to bounded periodic media with local resonators to characterize their filtering and attenuation effectiveness, which shows its interest in such a case of great practical interest.

Local resonance bandgap control in a particle-aligned magnetorheological metamaterial

Stimuli-responsive elastic metamaterials augment unique subwavelength features and wave manipulation capabilities with a degree of tunability, which enables them to cut across different time scales and frequency regimes. Here, we present an experimental framework for robust local resonance bandgap control enabled by enhanced magneto-mechanical coupling properties of a magnetorheological elastomer, serving as the resonating stiffness of a metamaterial cell. During the curing process, ferromagnetic particles in the elastomeric matrix are aligned under the effect of an external magnetic field. As a result, particle chains with preferred orientation form along the field direction. The resulting anisotropic behavior significantly boosts the sensitivity of the metamaterial’s elastic modulus to the imposed field during operation, which is then exploited to control the dispersive dynamics and experimentally shift the location and width of the resonance-based bandgap along the frequency axis. Finally, numerical simulations are used to project the performance of the magnetically-tunable metamaterial at stronger magnetic fields and increased levels of material anisotropy, as a blueprint for broader implementations of in situ tunable active metamaterials.

Vibration mitigation using finite graded metamaterials: a rod with attached local resonators

The paper concerns the analysis of vibration transmission and mitigation in a finite rod performing axial vibrations with attached multiple damped resonators. The resonators are not assumed to be periodically spaced or to have similar dynamic properties. The behaviour is analysed in terms of waves travelling between the discontinuities. Reflection and transmission coefficients of the rod with one local resonator attached are utilised in the analysis. Values of these coefficients for each of the attached resonators, along with the boundary conditions and field transfer function, are used to derive analytical expressions for the displacement of the finite rod at any point. Once the displacement is determined, the transmission loss is calculated. Moreover, the eigenfrequencies of the graded metamaterial finite rod are identified using the phase closure principle. The influence of the mass, the damping and the location of the resonators on the vibration attenuation are investigated. Numerical examples are presented. Good agreement is noted between the results of the analytical studies and finite element simulations in COMSOL. It is shown that the graded metamaterial rod can provide better vibration attenuation as compared to the conventional periodic metamaterial.