Local Resonance Mechanism Research Articles

Tunable topological valley transport in acoustic topological metamaterials

Valley Hall topological insulators (VHTIs) in condensed matter physics have been recently extended to acoustic systems and have attracted great attention. However, the current acoustic topological insulators (ATIs) are mainly based on the mechanism of Bragg scattering in phononic crystals. Their demonstration and application are limited by factors, such as non-tunable structure and lattice-scale size. Here, we propose and engineer a tunable ATI by using a metamaterial structure to realize topologically valley-projected edge states. The topological metamaterial consists of a honeycomb lattice array of 2D triple split ring (TSR) based on local resonance mechanism. We numerically demonstrate the robustness of edge sound transport and flexible manipulation of sound propagation paths in the proposed topological metamaterial. Theoretical analysis, numerical simulation and experimental measurement all confirm the existence of edge states. This study may enrich the design of ATIs with tunability and have potential applications in flexible manipulation of sound propagation.

Liquid crystal integrated metamaterial for multi-band terahertz linear polarization conversion

We experimentally investigate the linear polarization conversion for terahertz (THz) waves in liquid crystal (LC) integrated metamaterials, which consist of an LC layer sandwiched by two orthogonally arranged sub-wavelength metal gratings. A Fabry–Perot-like cavity is well constructed by the front and rear gratings, and it shows a strong local resonance mechanism, which greatly enhances the polarization conversion efficiency. Most importantly, the Fabry–Perot-like resonance can be actively tuned by modulating the refractive index of the middle LC layer under the external field. As a result, the integrated metamaterial achieves multi-band tunable linear polarization conversion.

Transmission control of acoustic metasurface with dumbbell-shaped double-split hollow sphere

Complex structures, large size and limited manipulation of acoustic waves are the problems that restrict the development of acoustic metasurfaces. Here, we report a transmission-type acoustic metasurface based on local resonance mechanism, which is composed of meta-atomic units called dumbbell-shaped double-split hollow spheres (DSDSHS). This metasurface with subwavelength scale has the advantage of simple structure and easy preparation, and can realize the full manipulation of sound waves. Negative refraction with different transmission angles and high intensity plate focusing lens are realized in the air environment of audible frequency. The proposed metasurface has potential applications in the miniaturization and integration of sound transmission and sound energy collection, opening a new opportunity for manipulation of acoustic wavefront.

Light-weight large-scale tunable metamaterial panel for low-frequency sound insulation

To overcome the traditional problem of blocking low-frequency noise, this letter proposes a design of large-scale metamaterial panel with periodic tunable resonant cell arrays. Numerical calculations show that the tunable metamaterial panels exhibit multiple local resonance mechanisms, which result in sound transmission loss (STL) improvements over traditional mass law in low-frequency regions. The effective dynamic mass density and the tunability of sound insulation performance are further examined. Moreover, large-scale tunable metamaterial panel samples with 36 (6 × 6) unit cells are fabricated. And experimental measurements of sound insulation performance are conducted to validate the theoretical predictions.

Silver loaded anodic aluminum oxide defective photonic crystals and their application for surface enhanced Raman scattering

Here, the fabrication of the Ag nanoparticles loaded one-dimensional anodic aluminum oxide defective photonic crystals (Ag@AAO DPCs) with controllable structure parameters is reported using specially designed periodic pulse anodization and vacuum thermal evaporation techniques. The constructed Ag@AAO DPCs films have ordered distributed nanopore surface, high-quality defect state and tunable photonic band gap, which are ideally suited for the surface-enhanced Raman scatting (SERS) substrates that use local electric field and defect state resonance mechanisms. These sbustrates exhibit excellent SERS performance for rhodamine B (rhB) testing with high sensitivity and reproducibility. In which the logarithmic intensity of Raman signal peak at 1646 cm−1 versus the concentration of rhB presents a linear relationship, and the detection limitation can reach to the order of 10−10 mol/L, the enhancement factor can increase to the order of 105, especially when the defect state energy level position is matched with the incident light. This means that the Ag@AAO DPCs can be used as SERS substrates for the trace detection of organic dye molecules. Compared to the common Ag@AAO substrate, the main reasons for the SERS signal enhancement of the Ag@AAO DPCs are attributed to the synergistic effect of the enhanced local electric field strengthened by the Bragg reflection of PC structure and electron transformation induced by the defect state resonance with the incident light. This would be a promising way for applications for surface enhanced Raman scattering.

Review of Phononic crystals and acoustic metamaterials

As a new type of acoustic functional material, phononic crystal has great research value and application environment. It is a periodic structure of two or more elastic materials, which are derived from photonic crystals. The main research work on phononic crystals focuses on the two band gap formation mechanisms of Bragg scattering and local resonance, and some new methods of vibration reduction and noise reduction can be obtained by studying its banding mechanism. Similarly, a “metamaterial” has been proposed for the ability to achieve new vibration reduction and noise reduction, which is a composite structure or material with physical properties not available in natural materials. By analysing the acoustic metamaterials of various structures, in this work we can understand how to achieve vibration reduction and noise reduction under the local resonance mechanism.

3D acoustic metamaterial-based mechanical metalattice structures for low-frequency and broadband vibration attenuation

In this paper, a new type of three-dimensional (3D) truss-lattice structures for low-frequency and broadband elastic wave absorption is proposed. The local resonance mechanism used in acoustic/elastic metamaterials (AMs) for generating low-frequency bandgaps, in which elastic waves cannot pass through, is introduced into the continuous body-centered cubic lattice structures by only making the cross-struts in each unit-cell have a radius jump discontinuity. This method is easy to realize for practical engineering compared with the conventional acoustic metamaterials usually made of different materials. The band structures of the 3D AM-based lattice structures are calculated and the edge modes of each bandgap are analyzed to understand the effects of each component of the unit-cell on the bandgap formation. The effects of the structural and material parameters on the bandgaps are investigated and two kinds of composite AM-based lattice structures are suggested for broadening the bandgap width based on the parametric study. As the design is based on increasing the radii of some parts of the cross-struts inside the unit-cell, the mechanical properties are enhanced. The limiting conditions of the static properties of the 3D AM-based lattice structures for broadening the bandgaps are illustrated. Finally, experiments were carried out to validate the results. This design strategy provides new possibilities for the development of lattice truss structures with both bearing and vibration reduction requirements.

Abundant hot-spot construction between Ni/C nanotubes with enhanced localized surface plasmon resonance for Radar wave absorption

In this work, a simple bottom-up chemical method has been used for the construction of Ni/C core/shell nanoparticles, which are composed of 10–15 nm metal Ni cores and 2–4 nm thick carbon nanotube or shells. Interestingly, all the mini Ni/C nanoparticles aggregate into bulky nanorods with ~200 nm diameter and several micrometer long. The uniform carbon nanoshells guarantee the formation of a large number of hot-spots between metal Ni nanoparticles, which results in the greatly strengthened and broadened Radar wave absorption based on a localized surface plasmon resonance (LSPR) mechanism. For Ni/C nanotubes, the absorption bandwidth is up to 7.7 GHz when the reflection loss is over −10 dB, which means that about 1/2 EM wave can be effectively absorbed in the general Radar wave range of 2–18 GHz. Compared with dispersed Ni nanoparticles or Ni/C nanoparticles, every electromagnetic (EM) wave absorption character index of this product is greatly improved. So this work provides a new bottom-up construction method for EM absorption hot-spots.

Metamaterial improved nonlinear ultrasonics for fatigue damage detection

This article presents an improved nonlinear ultrasonic technique for fatigue damage detection utilizing a kind of carefully designed aluminum-lead composite metamaterial. It focuses on developing a bandgap metamaterial to improve the accuracy and identifiability of the superharmonic features from fatigue cracks by eliminating the inherent nonlinear components in the nonlinear ultrasonic technique. The study starts with the unit cell design through modal analysis by applying the Bloch–Floquet boundary condition to obtain the band structure. Based on the local resonance mechanism, by adjusting the height ratio between the aluminum and lead cylinders, the bandgaps covering the required frequency ranges can be opened up. Then, a chain of regularly arranged unit cells is modeled to analyze the spectral response and verify the bandgap effect through harmonic analysis. The targeted ultrasonic frequency component of guided waves within the bandgap can be mechanically filtered out. Subsequently, a finite element model of the pitch-catch active sensing procedure for fatigue crack detection is constructed via the coupled-field transient dynamic analysis. Nonlinear ultrasonic experiments with the designed metamaterial are carried out to verify the theoretical and numerical investigations. This paper demonstrates that the metamaterial, with its outstanding wave manipulation capability, shows great potential on structural health monitoring and nondestructive evaluation applications. The paper finishes with summary, concluding remarks, and suggestions for future work.

2D underwater acoustic metamaterials incorporating a combination of particle-filled polyurethane and spiral-based local resonance mechanisms

This paper develops an underwater acoustic metamaterial plate with potential advantages of low-frequency broadband sound absorption and high hydrostatic pressure resistance. In this research, a new acoustic metamaterial embedding particle-filled polyurethane (PU) and spiral-based local resonance mechanism for underwater sound absorption is investigated numerically and experimentally. Specifically, the proposed metamaterial is composed of particle-filled PU damping materials and a square lattice of spiral resonators. The thickness of the proposed plate structure occupying most of the area is thin and equals to 4 mm. Wave propagation properties of the proposed metamaterial are obtained by using the finite element (FE) method. Compared to the underwater sound absorption coefficient, the formation mechanisms of the locally resonant band gaps are investigated based on the modal analysis of plate modes and local resonances. Results show that the location and bandwidth of newly generated locally low-frequency resonant band gaps are greatly affected by the interaction between particle-filled PU and the spiral resonator within every periodic cell. In addition, the theoretical results of the underwater sound absorption coefficient of the proposed metamaterial are compared with the experimental results. In the frequency domain [0.8 kHz, 6 kHz], the average sound absorption coefficient of the proposed metamaterial plate under normal atmospheric pressure is 0.54. Furthermore, the sound absorption coefficient of the proposed structure is experimentally studied under different hydrostatic pressure conditions. Specifically, the proposed metamaterial structure achieves average sound absorption coefficient of 0.51 in the frequency range [1.5 kHz,6kHz] under 0.5 MPa.

Wave propagation control in periodic track structure through local resonance mechanism

Excessive vibration and noise radiation of the track structure can be caused by the operation of high speed trains. Though the track structure is characterized by obvious periodic properties and band gaps, the bandwidth is narrow and the elastic wave attenuation capability within the band gap is weak. In order to effectively control the vibration and noise of track structure, the local resonance mechanism is introduced to broaden the band gap and realize wave propagation control. The locally resonant units are attached periodically on the rail, forming a new locally resonant phononic crystal structure. Then the tuning of the elastic wave band gaps of track structure is discussed, and the formation mechanism of the band gap is explicated. The research results show that a new wide and adjustable locally resonant band gap is formed after the resonant units are introduced. The phenomenon of coupling and transition can be observed between the new locally resonant band gap and the original band gap of the periodic track structure with the band gap width reaching the maximum at the coupling position. The broader band gap can be applied for vibration and noise reduction in high speed railway track structure.

A local resonance mechanism for thermal rectification in pristine/branched graphene nanoribbon junctions

Using non-equilibrium molecular dynamics simulations, we investigate thermal rectification (TR) in pristine/branched graphene nanoribbon (GNR) junctions. The results indicate that the TR ratio of such junctions can reach 470% under small temperature bias, which has distinct superiority over asymmetric GNR and many other junctions. Moreover, the TR ratio decreases rapidly as the applied temperature bias increases. It seems to be against common sense that the TR ratio generally increases with temperature bias. Phonon spectra analyses reveal that the observed phenomena stem from the local resonance of longitudinal phonons in branched GNR region under negative temperature bias. Furthermore, the influence of ambient temperature, system length, branch number, and defect density is studied to obtain the optimum conditions for TR. This work extends local resonance mechanism to GNR for thermal signal manipulation.

Wave propagation in viscoelastic phononic crystal rods with internal resonators

In the present work, the wave propagation in a viscoelastic phononic crystal rod with internal periodic dissipative resonators is investigated. The Kelvin-Voigt model is utilized to describe the viscoelastic behavior of host materials. The Bloch theorem is adopted to analyze the band structure of the rod. The effect of the free oscillation frequency of the resonators on the band structure is firstly studied. It is found that by tailoring the dynamic characteristics of the resonators, the coupling of the Bragg scattering (BS) and local resonance (LR) mechanisms can be harnessed to effectively widen the band gaps and enhance the wave attenuation. Then, the effects of the viscosity of the host materials and the damping of the resonators on the band structure, especially the two nearly coalescent band gaps (the first Bragg and LR ones), are investigated respectively. Furthermore, the combined effect of the two dissipative sources is also discussed. The present work is expected to be helpful to the design and applications of phononic crystals and metamaterials.

Accordion-like metamaterials with tunable ultra-wide low-frequency band gaps

Composite materials with engineered band gaps are promising solutions for wave control and vibration mitigation at various frequency scales. Despite recent advances in the design of phononic crystals and acoustic metamaterials, the generation of wide low-frequency band gaps in practically feasible configurations remains a challenge. Here, we present a class of lightweight metamaterials capable of strongly attenuating low-frequency elastic waves, and investigate this behavior by numerical simulations. For their realization, tensegrity prisms are alternated with solid discs in periodic arrangements that we call ‘accordion-like’ meta-structures. They are characterized by extremely wide band gaps and uniform wave attenuation at low frequencies that distinguish them from existing designs with limited performance at low-frequencies or excessively large sizes. To achieve these properties, the meta-structures exploit Bragg and local resonance mechanisms together with decoupling of translational and bending modes. This combination allows one to implement selective control of the pass and gap frequencies and to reduce the number of structural modes. We demonstrate that the meta-structural attenuation performance is insensitive to variations of geometric and material properties and can be tuned by varying the level of prestress in the tensegrity units. The developed design concept is an elegant solution that could be of use in impact protection, vibration mitigation, or noise control under strict weight limitations.

Dynamic optical properties of gold nanoparticles/cholesteric liquid crystal arrays

Abstract

Terahertz polarization mode conversion in compound metasurface

A compound metasurface for terahertz (THz) wave polarization mode conversion has been experimentally investigated, which is integrated with an H-shaped metallic metamaterial and 45° arranged subwavelength dielectric grating on the two surfaces of a Si substrate. The polarization mode conversion from a TM to a TE resonance mode is achieved at 1.3 THz for forward transmission and 0.63 THz for backward transmission. Based on this property, a unidirectional transmission is obtained with the highest extinction of 23 dB at 0.63 THz. Moreover, due to the multiple reflections and subwavelength integration, a localized resonance mechanism in this metasurface greatly enhances the polarization conversion rate, reduces the insertion loss, and expands the operating bandwidth from 0.3 to 1.6 THz, not merely at the π phase matching point, which are quite different with the properties of the discrete metallic metamaterial and dielectric grating. This work provides an efficient way towards practical applications in THz broadband polarization conversion, polarization resonance mode manipulation, and unidirectional transmission.

Flexural wave suppression by an elastic metamaterial beam with zero bending stiffness

In this paper, different from Bragg scattering or local resonance mechanisms, a novel mechanism of an ultra-low-frequency broadband for flexural waves propagating in a one-dimensional elastic metamaterial beam with zero bending stiffness is proposed, which consists of periodic hinge-linked blocks. The dispersion relationship of this kind of metamaterial beam is derived and analyzed, from which we find that these hinge-linked blocks can produce the zero bending stiffness. Thus, the flexural waves within the metamaterial beam can be suppressed, and an ultra-low-frequency wide band-gap is formed in which the first branch is generated by the zero bending spring and the second branch by the negative velocity of the metamaterial beam. Numerical results show that the elastic metamaterial beams with zero bending stiffness can indeed generate an ultra-low-frequency wide band gap even starting from almost zero frequency, such as from 0 Hz to 525 Hz in our structure. Therefore, the puzzle of realizing an ultra-low-frequency broadband of flexural waves may have been better solved, which could be applied in controlling ultra-low-frequency elastic waves in engineering. At the request of the Editor and the Publisher this article is being retracted. It was inadvertently published in Journal of Applied Physics due to the significant overlap of data, experimental approach, and results with another publication with no acknowledgment.

A design of active elastic metamaterials for control of flexural waves using the transformation method

The ability to control flexural wave propagation is of fundamental interest in many areas of structural engineering and physics. Metamaterials have shown a great potential in subwavelength wave propagation control due to their inherent local resonance mechanism. In this study, we propose a transformation method to derive the material properties of a flexural waveguide and implement the functionality based on a design of active elastic metamaterials. The numerically demonstrated flexural waveguide can not only steer an elastic wave beam as predicted from the transformation method but also exhibit various unique properties including extraordinary wave beam deflection and tunabilities over a broad frequency range and various steering directions. The waveguide is equipped with an array of active elastic metamaterials composed of the electrorheological elastomer subjected to adjustable electric fields. Such metamaterial-based waveguides provide a new design methodology for guided wave signal modulation devices and could be useful for applications such as tunable beam steering, high signal-to-noise sensors, and structural health monitoring.

Radiative transition, local field enhancement and energy transfer microcosmic mechanism of tellurite glasses containing Er3+, Yb3+ ions and Ag nanoparticles

Er3+-doped, Er3+/Yb3+ co-doped tellurite glass with and without Ag NPs were synthesized by melt-quenching method. The high resolution transmission electron microscopy (HR-TEM) and selected area electron diffractions (SAED) manifest growth of Ag NPs. The UV–vis–NIR absorption spectroscopy and fluorescence spectroscopy were measured. The optical band gap and multiphonon relaxation rate constants were calculated. The electronic band structure and local density of state (DOS) of Ag NPs are calculated. The fluorescence emission and enhancement mechanism including localized surface plasmon resonance (LSPR) and energy transfer (ET) microcosmic mechanism were discussed. The electric field distributions of Ag NPs are emulated by FDTD solutions software. Local field enhancement (LFE) induced by LSPR and lightning rod effect was found to be responsible for the fluorescence enhancement while energy transfer from Ag NPs to rare-earth was considered ignorable in the samples without photoluminescent emission.

Twisted vector field from an inhomogeneous and anisotropic metamaterial

We propose a metamaterial design for realizing inhomogeneous and anisotropic effective media based on the localized waveguide resonance mechanism. Such a design can be easily achieved in experiment and enables us to simultaneously manipulate the wavefront and the state of polarization of the transmitted electromagnetic field by the polarization-sensitive extraordinary optical transmission. Numerical simulations, including the generation of the hybridized vector fields (especially twisted vector fields that are azimuthally polarized carrying a helical phase), prove the feasibility of our proposal. It could be expected as a good candidate of the specially designed subwavelength element for creating the exotic vector fields beyond the functionality of the existing vector fields in a wide spectral regime, especially the terahertz and radio regimes.