Localized Resonance Research Articles

Breakdown of thermalization in spin chains with single-ion anisotropy

The principles of ergodicity and thermalization constitute the foundation of statistical mechanics, positing that a many-body system progressively loses its local information as it evolves. Nevertheless, these principles can be disrupted when thermalization dynamics lead to the conservation of local information, as observed in the phenomenon known as many-body localization. Quantum spin chains provide a fundamental platform for exploring the dynamics of closed interacting quantum many-body systems. This study explores the dynamics of a spin chain with S≥1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$S\\ge 1/2$$\\end{document} within the \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$J_1-J_2,$$\\end{document} incorporating a non-uniform magnetic field and single-ion anisotropy. Through the use of exact numerical diagonalization, we unveil that a nearly constant-gradient magnetic field suppresses thermalization, a phenomenon termed Stark many-body localization (SMBL), previously observed in S=1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$S=1/2$$\\end{document} chains. Furthermore, our findings reveal that the sole presence of single-ion anisotropy is sufficient to prevent thermalization in the system. Interestingly, when the magnitudes of the magnetic field and anisotropy are comparable, they compete, favoring delocalization. Despite the potential hindrance of SMBL by single-ion anisotropy in this scenario, it introduces an alternative mechanism for localization. Our interpretation, considering local energetic constraints and resonances between degenerate eigenstates, not only provides insights into SMBL but also opens avenues for future experimental investigations into the enriched phenomenology of disordered free localized S≥1/2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$S\\ge 1/2$$\\end{document} systems.

Optical spectra of silver clusters and nanoparticles from 4 to 923 atoms from the TDDFT+U method

The localized surface-plasmon resonances of coinage-metal clusters and nanoparticles enable many applications, the conception and necessary optimization of which require precise theoretical description and understanding. However, for the size range from few-atom clusters through nanoparticles of a few nanometers, where quantum effects and atomistic structure play a significant role, none of the methods employed previously has been able to provide high-quality spectra for all sizes. The main problem is the description of the filled shells of d electrons which influence the optical response decisively. We show that the DFT+U method, employed with real-time time-dependent density-functional theory calculations (RT-TDDFT), provides spectra in good agreement with experiment for silver clusters ranging from 4 to 923 atoms, the latter representing a nanoparticle of 3 nm. Both the electron-hole-type discrete spectra of the smallest clusters and the broad plasmon resonances of the larger sizes are obtained. All calculations use the value of the effective U parameter that provides good results in bulk silver. The agreement with experiment for all sizes shows that the U parameter is surprisingly transferable. Our results open the pathway for calculations of many practically relevant systems including clusters coupled to bio-molecules or to other nano-objects.

Phonon transmission and localization in disordered side branching graphene aperiodic lattice

Blocking phonon transport via localized resonance is a crucial method for controlling heat transfer and enhancing thermoelectric performance in nanostructures. However, the effects of disorder and asymmetrically distributed side branches on thermal transport and local resonant hybridization in two-dimensional materials remain insufficiently understood. In this work, we investigate the influence of symmetric and asymmetric disordered side branches on phonon transport in branching graphene superlattices. Our results demonstrate that aperiodic superlattices (ap-SL) can reduce thermal conductivity by up to 21% compared to periodic superlattices. The reduction in thermal conductivity in ap-SL is primarily due to phonon Anderson localization caused by disordered side branches. Interestingly, the localization lengths of symmetric and asymmetric ap-SLs are comparable, resulting in similar thermal conductivity in both cases. This finding suggests that the randomness in the upper and lower branches of asymmetric graphene superlattices does not significantly affect phonon transmission. Consequently, our work indicates that differences in symmetry between the upper and lower edge branches of graphene nanoribbons can be disregarded during experimental preparation without influencing their thermal conductivity.

Plasmon-enhanced two photon excited emission from edges of one-dimensional plasmonic hotspots with continuous-wave laser excitation.

One-dimensional junctions between parallelly and closely arranged multiple silver nanowires (NWs) exhibit a large electromagnetic (EM) enhancement factor (FR) owing to both localized and surface plasmon resonances. Such junctions are referred to as one-dimensional (1D) hotspots (HSs). This study found that two-photon excited emissions, such as hyper-Rayleigh, hyper-Raman, and two-photon fluorescence of dye molecules, are generated at the edge of 1D HSs of NW dimers with continuous-wave near-infrared (NIR) laser excitation and propagated through 1D HSs; however, they were not generated from the centers of 1D HSs. Numerical EM calculations showed that FR of the NIR region for the edges of 1D HSs was larger than that for the centers by ∼102 times, resulting in the observation of two-photon excited emissions only from the edge of 1D HSs. The analysis of the NW dimer gap distance dependence of FR revealed that the lowest surface plasmon (SP) mode, compressed and localized at the edges of 1D HSs, was the origin of the large FR in the NIR region. The propagation of two-photon-excited emissions was supported by the higher-order coupled SP mode.

A new local resonance metamaterial for flat and cylindrical structures depended on elastic chiral spiral beams

A new local resonance metamaterial for flat and cylindrical structures depended on elastic chiral spiral beams

Additively Manufactured Stainless Steel Wind Tunnel Model Support Featuring Honeycomb Structures for Vibration Attenuation

Wind tunnel model support (WTMS) is an indispensable component of wind tunnel testing. However, the presence of vibrations within the model‐support system can compromise the accuracy of data and give rise to significant safety hazards. In this study, an approach for vibration attenuation by incorporating honeycomb structures into the design of the WTMS is proposed. To this end, stainless steel WTMSs with integrated honeycomb structures are fabricated by selective laser melting (SLM). Results showed that stainless steels prepared under optimized SLM processing parameters exhibit high crystallinity and consist of single‐phase Fe–Cr–Ni alloy. The stainless steels exhibited robust mechanical properties, including a tensile strength of ≈1 GPa, an elongation of ≈8%, and a compressive strength of ≈1.4 GPa. These exceptional mechanical properties can be attributed to the formation of a cellular structure and tangled dislocations. The first‐order and the third‐order resonant response of WTMS honeycomb structures can be effectively reduced. The vibration reduction mechanism can be attributed to the occurrence of local resonance when the natural frequency of the internal periodic unit of the WTMS closely matched the vibration frequency of the model. The utilization of honeycomb structures holds significant potential for achieving vibration attenuation in WTMS.

Bandgap formation mechanism in tacticity inspired elastic mechanical metastructures

Tacticity is long known as a significant contributor in changing the chemical and mechanical properties of the polymers drastically. This study explores mechanism of bandgap formation in elastic mechanical metastructures designed with a focus on tacticity. We introduce metabeams, comprising a primary slender beam embedded with short secondary beams featuring end masses at their tips. The investigation delves into the numerically simulated vibration characteristics of metabeams using finite element analysis, with a subsequent comparison to experimental results for fabricated metabeams. Employing a unit-cell design approach that manipulates spatial and physical parameters, we explore a wide range of uniform and non-uniform metabeam configurations based on the distance between secondary beams and distribution of local resonators as per tacticity. Hence, drawing inspiration from tacticity, we extend our investigation to isotactic and syndiotactic metabeams, altering physical parameters (mass) within the unit cell for both configurations. The strategic distribution of end masses on attached secondary beams introduces unique characteristics to isotactic and syndiotactic metabeams, allowing for the modulation of bandgaps without altering the natural frequencies of the resonators in symmetric and anti-symmetric metabeam designs. Our research demonstrates, incorporating tacticity in metabeam design offers a novel and unconventional approach to modulate the bandgap formation mechanism.

Understanding of topological mode and skin mode morphing in 1D and 2D non-Hermitian resonance-based meta-lattices

Recent advances have demonstrated that the non-Hermitian skin effect (NHSE), induced by system non-Hermiticity, can manipulate the localization of in-gap topological edge modes (TEMs) within mechanical topological insulators. This study introduces a straightforward analytical framework to elucidate the competition between NHSE and TEM localization in a classical mechanical meta-lattice, highlighting its impact on the dynamic behavior of TEMs within separate Bragg scattering band gaps (BSBGs). We propose a 1D non-Hermitian meta-lattice featuring a locally resonant system with active feedback control, characterized by a real-valued transfer function. This local resonance creates two separate BSBGs, each hosting a TEM defined by non-Hermitian bulk-edge correspondence. Our theoretical and numerical analyses reveal that the NHSE, with its asymmetric localization within the two BSBGs, can shift the localization of TEMs in distinct ways. This leads to an asymmetric phase transition, wherein one TEM can be delocalized and relocalized by tuning the transfer function, while the other maintains its initial localization. Moreover, we extend the mechanism of 1D asymmetric TEM delocalization to the non-Hermitian morphing of TEMs, showcasing notable examples such as temporal and spatial topological wave pumping with space- and time-dependent transfer functions in 1D time-varying and 2D stacked meta-lattices. This research bridges a gap between non-Hermitian mechanical constructs and their potential applications in classical mechanics, reinterpreting known topological wave control in 1D and uncovering new mechanisms in 2D.

Simplified site response analysis for regional seismic risk assessments

Seismic risk assessment on a regional scale requires an estimation of ground motion intensity and its spatial variation over large geographical areas. This task is particularly challenging in the presence of very soft soil deposits where significant amplification occurs at specific frequencies that are often referred to as local resonances. It is often not feasible to conduct a nonlinear site response analysis at thousands of sites of interest across a region such as an urban area due to the computational effort involved and the required detailed information on soil profiles at each site. Thus, in regional seismic risk analyses the hazard is typically represented by a field of response spectral ordinates estimated by ground motion models. This study proposes a simplified site response analysis procedure to improve the characterization of spectral ordinates to be used in regional seismic risk assessments. In the proposed procedure, reduced-order models are used to conduct site response analysis using very few parameters to transform response spectra at rock outcrop into response spectra at the surface of each of the sites. A particular emphasis is given to soft-soil sites characterized by low shear-wave velocities overlaid on rock or firm soils. A non-uniform continuous shear beam model with a parabolic variation of shear modulus along the depth and modal damping is used in combination with Random Vibration Theory. It is shown that the proposed approach provides better estimates than those of ground motion models or physics-based ground motion simulation models which often cannot capture the local resonances. Site-specific validation of the shear beam model and overall simplified site response analysis is performed at four soft-soil sites in San Francisco, California. Despite its simplicity, it is shown that the proposed procedure adequately captures the amplitudes and spectral shapes of the motions. It is also shown that in conjunction with ground motion models or physics-based models, the proposed simplified site response analysis procedure can be used to efficiently simulate the seismic hazard on a regional scale through an example of a regional seismic hazard analysis of 160 softer soil sites in Downtown San Francisco during the Loma Prieta earthquake.

The acoustic Galton board

Phononic crystals are a class of materials with periodic structures that influence the propagation characteristics of acoustic waves through periodically arranged structural units. Here, we have developed the acoustic Galton board (AGB), a groundbreaking apparatus that serves as a cost-effective and user-friendly tool for demonstrating phononic crystal properties such as band gaps, Bragg scattering, and local resonance. The device comprises an elastic wave signal generator, an enhanced Galton board featuring a sophisticated pillar-nail array, and a signal receiver. The experimental results we have obtained demonstrate the significant impact of the AGB on elastic wave dispersion, effectively creating bandgaps that impede wave transmission within specific frequency ranges while allowing unhindered propagation in others. Furthermore, the AGB can simulate phononic crystals using both the Bragg scattering mechanism, achieved through the design of periodic rigid pillar-nail arrays, and the locally resonant mechanism, facilitated by the design of pillar-nail arrays with composite material structures. Additionally, the AGB can extend its applications to serve as a simulation tool for elastic metamaterials.

Ultra-broadband underwater meta-absorber with gradient impedance-matched composite material

Abstract We have developed an underwater acoustic meta-absorber that exhibits ultra-broadband absorption, with most of absorption coefficients exceeding 0.9 across the frequency range of 1 kHz−20 kHz. This performance is achieved through the localized trapping of acoustic waves and efficient energy dissipation, facilitated by local resonances within meticulously designed, impedance-matched composite materials. The designed gradient structure of the absorber allows for a reduced width of 84 mm (0.05λ at 1 kHz) and a customizable length, determined by the number of unit cells, each with a length of 15 mm (0.01λ at 1 kHz). This different design approach yields an ultra-broadband meta-absorber of compact dimensions, offering a promising alternative for the development of underwater absorption metamaterials and their practical applications.

Observation of high frequency Alfvén eigenmodes excited by RF-accelerated minority hydrogen ions in the EAST tokamak

Abstract The paper presents the original observation of high frequency Alfvén eigenmode excited by fast minority hydrogen ions accelerated by ion cyclotron range of frequency waves in EAST. The frequency of high frequency Alfvén eigenmodes is around 0.75~8*Ω H, where Ω H is the cyclotron frequency of hydrogen ions evaluated at the low-field side plasma edge. It tracks the on-axis magnetic field B t and the edge plasma electron density n e via the Alfvenic relation ω~ B t *n e -1/2. The high frequency Alfvén eigenmodes are always accompanied by sub-cyclotron modes in several experiments at EAST, consistent with the high frequency Alfvén eigenmode detected on other conventional tokamaks, namely ASDEX Upgrade and DIII-D. Based on the previous study, these sub-cyclotron modes are consistent with the spectrum splitting produced by toroidal mode numbers[Nuclear Fusion 43, 228 (2003)]. We also found that the location of eigenmode excitation of high frequency Alfvén eigenmode driven by RF-accelerated minority hydrogen ions remains unchanged even though the cyclotron resonance location of hydrogen ions varies with B t.

Resonance Enhancement of the Faraday Effect in a agnetoplasmonic Composite

The paper presents the results of a theoretical and experimental study of the enhancement of the magneto-optical Faraday effect in a magnetoplasmonic nanocomposite, caused by localized plasmon resonance (LPR) in metal nanoparticles. The nanocomposite comprises a three-layer structure of self-assembled gold nanoparticles in a bismuth-substituted iron-garnet matrix. It is shown theoretically and experimentally that the enhancement of the magneto-optical Faraday effect is determined by the action of a magnetic field on the magnetoplasmonic composite as an effective medium as a whole. In this case, in the magnetoplasmonic nanocomposite, the Faraday effect is enhanced at the LPR wavelengths and is slightly weakened in the region of short wavelengths relative to the LPR. It is theoretically shown that the complex gyration index in the off-diagonal terms of the effective permittivity tensor for the magnetoplasmonic composite, in addition to rotation of the polarization plane, leads to the appearance of alternating ellipticity in the vicinity of the plasmon resonance, which is observed in the form of asymmetry of magneto-optical rotation.

Au@Pt nanoparticles-based signal-enhanced lateral flow immunoassay for ultrasensitive naked-eye detection of SARS-CoV-2.

With SARS-CoV-2 N protein as a model target, a signal-enhanced LFIA based on Au@Pt nanoparticles (NPs) as labelsis proposed. This Au@Pt NPs combined the distinguished localized surface plasma resonance (LSPR) effect of Au NPs and the ultrahigh peroxidase-like catalytic activity of Pt NPs. Au@Pt NPs could trigger substrate chromogenic reaction, generating acolor signal orders of magnitude darker than their intrinsic color. In the detection, after the coloration of the strips, 3,3',5,5'-tetramethylbenzidine (TMB) and H2O2 were added, and adark blue chelate (OxTMB) was produced soon, enhancing the band color significantly. After the signal amplification, the naked-eye detection limit for N protein reached 40pg/mL. The detection sensitivity enhanced more than 1000 times than that without signal amplification. Compared with mainstream LFIA requiring complex readout instruments, theAu@Pt-based LFIA achieved a comparable sensitivity usingnaked eyesdetection. This point is crucial, especially for unprofessional users or low-resource areas. Hence, this signal-enhanced LFIA may serve as a sensitive, cost-effective, and user-friendly detection method. It can shorten the testing window period and help identify early infections.

Temperature dependence of gold nanostar particles morphology and its SERS application

ABSTRACT Gold nano-star particles (GNS) have broad application prospects in Raman enhancement, photovoltaic, and catalysis fields because of the hot spot effect of their tip structure. However, metal nanoparticles will accumulate heat during applications of high-power laser-focused irradiation, which may lead to the morphological degradation of the nanoparticles. In this paper, we have studied the effect of annealing temperature on the surface tip structure of GNS. Firstly, GNS with the multi-tip structure were synthesised by the two-step method, and GNS thin films were prepared by self-assembly technique without auxiliaries. By means of SEM characterisation, the film is found to be compact and uniform. Secondly, we systematically studied the morphology degradation of GNS at 100°C, 150°C, 200°C and 250°C. The results show that the tip of GNS does not change obviously until the temperature reaches 200°C. Then the four kinds of GNS films were used as surface-enhanced Raman scattering (SERS) substrates, and their Raman enhancement properties have been studied with adenine as the analyte, and stronger Raman enhancement effect can be found for the tip of nanoparticles. For a SERS substrate corresponding to an annealing temperature of 100°C, we have obtained the limit sensitivity of adenine molecule of 10−9 M. Finally, the surface electric field distribution and local resonance spectrum curves of four kinds of gold nanoparticles with different tip sizes were simulated theoretically by using the finite element method, and the results are consistent with the experimental data.

Shear horizontal wave propagation on a piezoelectric substrate with periodic gradient local resonant metasurfaces

In this paper, analytical solutions for shear horizontal (SH) waves propagating in a piezoelectric (PE) substrate with periodic gradient mass oscillators are obtained. Both wave-mode method and spectral method are used to obtain the dispersion equation of SH waves. The influences of mass-spring oscillators on dispersion curves and the wave mode shapes are discussed via numerical examples. It reveals that the numerical results obtained by wave-mode method and spectral method are well matched. In addition, the mass-spring oscillators have evident effects on the propagation characteristic of SH waves, and the effects are closely related with the frequency. Moreover, the widths of the local resonant and Bragg resonant bandgaps become evident wider when oscillator's natural resonance frequency is close to the Bragg scattering frequency. In particular, based on our proposed structure, we can design a sensor with advantages such as filtering and only sensitive to specific frequencies, amplify lossless signals and multi frequency sensitivity.

Experimental analysis of Local Defect Resonance in an aluminum plate

In the context of non-destructive evaluation and testing of structures, the use of Local Defect Resonance is promising for the detection of delamination-type defects in composites. In this context, an experimental analysis Local Defect Resonance is proposed. It is here carried out on a model system: a thin aluminum plate with a Flat Bottom Hole (FBH) defect consisting in a self-adhesive aluminum sheet (a shim) adhesively bonded over a circular through hole. First, the local defect resonance frequencies and mode shapes are analyzed assuming linear vibrations of the structure. Then, a nonlinear approach is used to compare two types of FBH defects, a first flawless one and a second one including a damaged area. For this purpose a high amplitude vibration around the resonance frequencies are used in order to generate high order harmonics. This enhancement is identified as associated with mainly quadratic nonlinearity.

Experimental and numerical investigation of soundproof panels using acoustic metamaterials with porous material

Acoustic panels are often used in buildings and automobiles. For sound absorption in panels, high sound absorption performance in a wide frequency band can be achieved by combining porous sound absorption, resonant sound absorption, vibration sound absorption, and acoustic metamaterials. This study proposes a highly sound-absorbing panel structure by using an acoustic metamaterial that generates local resonance to a double-walled structure filled with porous material. In the soundproof panel of this study, local resonance is generated by a structure in which slits are made in a porous material. By the through-holes of the slits, local resonance occurs, but sound leakage and thermal viscosity in the slits may affect the sound absorption effect. Therefore, in this study, sound transmission loss for various cases with differing factors such as the use of porous materials, the presence of spiral slits, and layer configurations are compared through the acoustic analysis and experiments. The results substantiate that the proposed panel structure has high soundproofing performance in wide frequency ranges, each driven by distinct physical principles.

Diatom frustule-inspired elastic metamaterials

Although a universally accepted definition of elastic metamaterials does not exist yet, the latter are often associated to man-made or artificially engineered media possessing properties typically not available in Nature. Pioneering studies have recently demonstrated that complex structural organizations, often arranged in a periodic and/or gradient manner and spanning multiple length scales, typically found in many biological systems, exhibit extraordinary absorption/reflection functionalities enhanced by local resonances or Bragg scattering mechanisms. This has opened the road to new designs of bio-inspired metamaterial. In this context, here we investigate the elastic dynamic response of diatom frustules, i.e., the exoskeleton structures of photosynthetic algae ubiquitously present throughout the planet in water environments. Firstly, we analyse and record their structural arrangement in nano- and micro- scales by using the Scanning Electro Microscopy (SEM) and the optical profilometer. The results of the analysis are transferred to the metamaterial design. Secondly, through numerical models, we show the possibility of certain frustule-inspired geometries to behave as frequency selective elastic filters thanks to the presence of elastic bandgaps. The work herein contributes to the perspective of elastic metamaterials inspired by Nature.

Magnetorheological metamaterials for active broadband tuning of vibration attenuation

We propose a class of magnetorheological metamaterial plates with tunable band gaps achieved by means of a frequency-feedback control law. This approach allows for the intelligent tracking of excitation frequencies that enables an active control of band gap bounds. The active control mechanism is implemented through intelligent local resonators integrated into a main structure which comprise a mass and a magnetorheological elastomer (MRE) sensitive to an external magnetic field. The influence of the external magnetic field on vibration attenuation is examined using the Galerkin method. Next, a closed-loop frequency feedback control strategy is employed to dynamically adjust the band gap in response to excitation frequencies. This strategy significantly broadens the effective band gap range of the metamaterial plate. Besides, we studied the effect of MRE damping on broadband vibration reduction, underscoring its pivotal role in the band gap control for our magnetorheological metamaterials.