Coupled Oscillator Model Research Articles

Sound production biomechanics in three-spined toadfish and potential functional consequences of swim bladder morphology in the Batrachoididaea).

The relationship between sound complexity and the underlying morphology and physiology of the vocal organ anatomy is a fundamental component in the evolution of acoustic communication, particularly for fishes. Among vertebrates, the mammalian larynx and avian syrinx are the best-studied vocal organs, and their ability to produce complex vocalizations has been modeled. The range and complexity of the sounds in mammalian lineages have been attributed, in part, to the bilateral nature of the vocal anatomy. Similarly, we hypothesize that the bipartite swim bladder of some species of toadfish (family Batrachoididae) is responsible for complex nonlinear characters of the multiple call types that they can produce, supported by nerve transection experiments. Here, we develop a low-dimensional coupled-oscillator model of the mechanics underlying sound production by the two halves of the swim bladder of the three-spined toadfish, Batrachomoeus trispinosus. Our model was able to replicate the nonlinear structure of both courtship and agonistic sounds. The results provide essential support for the hypothesis that fishes and tetrapods have converged in an evolutionary innovation for complex acoustic signaling, namely, a relatively simple bipartite mechanism dependent on sonic muscles contracting around a gas filled structure.

Electromagnetically Induced Absorption Overcomes the Upper Limit of Light Absorption: Dipole-Dipole Coupling with Phase Retardation in Plasmonic-Dielectric Dimers.

Electromagnetically induced absorption (EIA) by a phase-retarded coupling is theoretically investigated using a dimer composed of a plasmonic and dielectric particle. This phase-retarded coupling originates from the particles interacting with each other through their scattered intermediate fields (in between near and far fields). Our analysis based on the coupled-dipole method and an extended coupled-oscillator model indicates that EIA by the phase-retarded coupling occurs due to constructive interference in the scattered fields of the particles. By employing the finite element method, we demonstrate that the absorption of the plasmonic particle is dramatically enhanced by tuning the interparticle distance and achieving constructive interference. In contrast to EIA by near-field coupling, which has been intensively researched using coupled plasmonic systems, EIA by a phase-retarded coupling enables us to strengthen the absorption of plasmonic systems more significantly. This significant absorption enhancement is expected to be beneficial to advancing various applications, such as energy harvesting and radiative cooling.

Plexcitonic optical chirality in the chiral plasmonic structure-microcavity-exciton strong coupling system.

Chiral plexcitonic systems exhibit a novel chiroptical phenomenon, which can provide a new route to design chiroptical devices. Reported works focused on the two-mode strong coupling between chiral molecules and nanoparticles, while multiple-mode coupling can provide richer modulation. In this paper, we proposed a three-mode coupling system consisting of a chiral Au helices array, a Fabry-Pérot cavity, and monolayer WSe2, which can provide an extra chiral channel, a more widely tunable region, and more tunable methods compared to two-mode coupled systems. The optical response of this hybrid system was investigated based on the finite element method. Mode splitting observed in the circular dichroism (CD) spectrum demonstrated that the chiroptical response successfully shifted from the resonant position of the chiral structure to three plexcitons through strong coupling, which provided a new route for chiral transfer. Furthermore, we used the coupled oscillator model to obtain the energy and Hopfield coefficients of the plexciton branches to explain the chiroptical phenomenon of the hybrid system. Moreover, the tunability of the hybrid system can be achieved by tuning the temperature and period of the helices array. Our work provides a feasible strategy for chiral sensing and modulation devices.

Coupled harmonic oscillators model with two connected point masses for application in photo-induced force microscopy

Abstract To comprehensively describe the operation of photo-induced force microscopy (PiFM), we have developed a model based on coupled harmonic oscillators. This model features two point masses connected by massless elastic wires, offering greater intuitiveness compared to existing PiFM models. It simplifies these models into a unified theoretical framework. By solving the equations of motion using adjusted oscillator parameters, we have successfully replicated all dynamic features from previous theories. These features include resonance frequencies and shapes of eigenmodes, as well as the responses to various external forces in the two PiFM modes: direct coupling and sideband coupling. Furthermore, by integrating our model with a recently developed photo-induced thermal expansion force model, which covers both tip-enhanced and global expansions, we have managed to uncover the underlying physical mechanism responsible for the unique signal behaviors observed in sideband coupling mode, where the signal plot, as a function of sample thickness, unexpectedly exhibits a peak followed by a valley, rather than a proportionally increasing signal. Our study has the potential to enhance the comprehension of various other physical phenomena associated with PiFM in the future.

Boosting multi-mode strong coupling in a hybrid vertical split-ring resonator metamaterial for magnetoplasmonic sensing

Achieving multi-mode strong coupling between different modes in nanoscale is challenging due to the large damping rate of the system. Here, we report an effective way to achieve multi-mode plasmonic and magnetic resonances strong coupling via introducing the localized surface plasmon resonance into the designed dimer vertical split-ring resonator (DVSRR) magnetoplasmonic metamaterial. Due to strong near-field enhancement and far-field scattering suppression, the Rabi splitting energy could be enhanced from 144 meV to 286 meV. Benefiting from the multi-mode strong coupling, three distinct Kerr reversals are obtained in the Kerr spectrum, which provides a feasible route for achieving multi-mode magnetoplasmon-sensor, with high FoM of 4265/RIU, 135/RIU and 3995/RIU, respectively. The hybrid branches are analyzed with weighting coefficients that are calculated by the three coupled oscillator model.

Turning whispering-gallery-mode responses through Fano interferences in coupled all-dielectric block-disk cavities.

Here, we theoretically demonstrate a strategy for efficiently turning whispering-gallery-mode (WGM) responses of a subwavelength dielectric disk through their near-field couplings with common low-order electromagnetic resonances of a dielectric block. Both simulations and an analytical coupled oscillator model show that the couplings are Fano interferences between dark high-quality WGMs and bright modes of the block. The responses of a WGM in the coupled system are highly dependent on the strengths and the relative phases of the block modes, the coupling strength, and the decay rate of the WGM. The WGM responses of coupled systems can exceed that of the individual disk. In addition, such a configuration will also facilitate the excitation of WGMs by a normal incident plane wave in experiments. These results could enable new applications for enhancing light-matter interactions.

Incomplete Resyllabification and Ambisyllabic Gestural Coupling in Spanish

In the generative literature, the pattern of coronal fricative lenition found in the traditional Chinato Spanish dialect is commonly cited as a phonological argument that the resyllabification of word-final prevocalic consonants is complete, in the sense that onsets derived by resyllabification are structurally identical to canonical (word-level) onsets. However, recent acoustic studies of Northern-Central Peninsular Spanish have problematized the completeness of resyllabification with experimental evidence that /s̺/ is shorter and more voiced as a derived onset than as a canonical onset. Using a split-gesture, competitive, coupled oscillator model of the syllable in Articulatory Phonology, which divides consonants into a separate constriction and release gesture, we propose a novel representation of ambisyllabicity that predicts the phonetic behavior of derived onset /s̺/ in Northern-Central Peninsular Spanish. We then show that ambisyllabic coupling permits a simpler phonological analysis of coronal fricative lenition in Chinato Spanish as compared to alternative accounts. Our analysis makes typological predictions that are confirmed by patterns from other contemporary Spanish varieties. Lastly, we examine the consequences of ambisyllabicity for the analysis of Spanish rhotic consonants, which have also been argued to support complete resyllabification. We offer an analysis of rhotics that is entirely compatible with an ambisyllabic representation of incomplete resyllabification.

Co-evolving dynamics and topology in a coupled oscillator model of resting brain function

Dynamic models of ongoing BOLD fMRI brain dynamics and models of communication strategies have been two important approaches to understanding how brain network structure constrains function. However, dynamic models have yet to widely incorporate one of the most important insights from communication models: the brain may not use all of its connections in the same way or at the same time. Here we present a variation of a phase delayed Kuramoto coupled oscillator model that dynamically limits communication between nodes on each time step. An active subgraph of the empirically derived anatomical brain network is chosen in accordance with the local dynamic state on every time step, thus coupling dynamics and network structure in a novel way. We analyze this model with respect to its fit to empirical time-averaged functional connectivity, finding that, with the addition of only one parameter, it significantly outperforms standard Kuramoto models with phase delays. We also perform analyses on the novel time series of active edges it produces, demonstrating a slowly evolving topology moving through intermittent episodes of integration and segregation. We hope to demonstrate that the exploration of novel modeling mechanisms and the investigation of dynamics of networks in addition to dynamics on networks may advance our understanding of the relationship between brain structure and function.

Dissipative phase transition in an open Tavis–Cummings model with a two-photon drive

We investigate the steady-state quantum phases and associated collective phenomena of an open Tavis–Cummings (TC) model driven by a two-photon source. The standard (non-dissipative) TC model describes the quantum phases of an ensemble of N q two-level quantum emitters interacting with a single-mode electromagnetic field. The interplay among coherent driving, dissipation, and dipole interactions of the open TC model results in emergent collective phenomena, leading to a dissipative or non-equilibrium phase transition from the normal to the superradiant phase. We solve the Liouvillian equation analytically using the semi-classical mean-field approximation. We carry out stability analysis of the steady-state phases and determine the phase boundary. The use of Holstein–Primakoff transformation in the thermodynamic limit reduces the system to an effective coupled-oscillator model, the solution of which yields collective modes.

Surface-acoustic-wave-driven graphene plasmonic sensor for fingerprinting ultrathin biolayers down to the monolayer limit

Surface plasmon polaritons in graphene can enhance the performance of mid-infrared spectroscopy, which is key for the study of both the composition and the conformation of organic molecules via their vibrational resonances. In this paper, a plasmonic biosensor using a graphene-based van der Waals heterostructure on a piezoelectric substrate is theoretically demonstrated, where far-field light is coupled to surface plasmon-phonon polaritons (SPPPs) through a surface acoustic wave (SAW). The SAW creates an electrically-controlled virtual diffraction grating, suppressing the need for patterning the 2D materials, that limits the polariton lifetime, and enabling differential measurement schemes, which increase the signal-to-noise ratio and allow a quick commutation between reference and sample signals. A transfer matrix method has been used for simulating the SPPPs propagating in the system, which are electrically tuned to interact with the vibrational resonances of the analytes. Furthermore, the analysis of the sensor response with a coupled oscillators model has proven its capability of fingerprinting ultrathin biolayers, even when the interaction is too weak to induce a Fano interference pattern, with a sensitivity down to the monolayer limit, as tested with a protein bilayer or a peptide monolayer. The proposed device paves the way for the development of advanced SAW-assisted lab-on-chip systems combining the existing SAW-mediated physical sensing and microfluidic functionalities with the chemical fingerprinting capability of this novel SAW-driven plasmonic approach.

Synchronisation transitions in supply chain networks

In this paper, we examine the transition process between synchronous and desynchronous states in supply chain networks, which is strongly correlated to network topology. While most research has focused on the merits of steady-state synchronisation behaviour, very little has been published on the interdependencies between structural and dynamic synchronisation properties in supply chain networks. Synchronisation processes are described by a variety of coherent state dynamics that exhibit very different transition paths. In this research, we developed a new coupled oscillator model to analyse and evaluate these transient dynamics in more detail. Canonical network models are first described, including hub-and-spoke, tree-mesh, and tree topologies, which are then applied to real-world problems in the automotive industry. We found specific synchronisation transitions in automotive supply networks such as explosive and delayed synchronisation. In particular, we show that (i) in a hub-and-spoke supply network, the number of suppliers per hub affects synchronisation transitions only at larger frequency spreads, (ii) scale-free networks with short path lengths generated by the power law connectivity are unable to synchronise as long as a critical cluster coefficient is exceeded, and (iii) interruptions in tree networks cause nonlinear synchronisation losses for upstream suppliers as a function of the interruption time.

Strong plasmon − phonon coupling for graphene/ hBN thermal emitter atomic system

The surface plasmon polaritons of graphene coupled with hyperbolic phonon polaritons of hexagonal boron nitride (hBN) have been considered as the ideal platform to enhance thermal emitter, which provides a powerful tool to implement energy conversion and thermal management. The conventional approaches for the strong plasmon − phonon coupling rely on the bulk hBN materials, which usually have a large footprint and display little tunability. Recently, hBN atomic emitter has been demonstrated that its peak emissivity is hopefully as high as the bulk hBN emitters. Here, we propose a graphene/hBN thermal emitter atomic system to flexibly modify the spectral emissivity by the strong plasmon − phonon coupling effect, which can be separately manipulated by the graphene width, chemical potential of graphene, number of hBN atomic layers and hBN width. Our scheme is hopefully realizing a comparable function with the bulk graphene/hBN system. Furthermore, we employ coupled oscillator model involving three oscillators to investigate the energy exchange and mode evolution between three plasmon − phonon hybridized modes, providing an excellent agreement with simulated and theoretical results. Consequently, optically manipulating plasmon − phonon interaction opens a broad design space for the spectral emissivity control, which explores the mid-infrared applications of advanced graphene thermo-optoelectronics and electrically driven thermal emitters.

Programmable self-organization of heterogeneous microrobot collectives

At the microscale, coupled physical interactions between collectives of agents can be exploited to enable self-organization. Past systems typically consist of identical agents; however, heterogeneous agents can exhibit asymmetric pairwise interactions which can be used to generate more diverse patterns of self-organization. Here, we study the effect of size heterogeneity in microrobot collectives composed of circular, magnetic microdisks on a fluid-air interface. Each microrobot spins or oscillates about its center axis in response to an external oscillating magnetic field, in turn producing local magnetic, hydrodynamic, and capillary forces that enable diverse collective behaviors. We demonstrate through physical experiments and simulations that the heterogeneous collective can exploit the differences in microrobot size to enable programmable self-organization, density, morphology, and interaction with external passive objects. Specifically, we can control the level of self-organization by microrobot size, enable organized aggregation, dispersion, and locomotion, change the overall shape of the collective from circular to ellipse, and cage or expel objects. We characterize the fundamental self-organization behavior across a parameter space of magnetic field frequency, relative disk size, and relative populations; we replicate the behavior through a physical model and a swarming coupled oscillator model to show that the dominant effect stems from asymmetric interactions between the different-sized disks. Our work furthers insights into self-organization in heterogeneous microrobot collectives and moves us closer to the goal of applying such collectives to programmable self-assembly and active matter.

Coupled-oscillator model to analyze the interaction between a quartz resonator and trapped ions

The novel application of a piezoelectric quartz resonator for the detection of trapped ions has developed in the observation of the quartz-ions interaction under non-equilibrium conditions, opening new perspectives for high-sensitive motional frequency measurements of radioactive particles. Energized quartz crystals have (long) constant-decay times in the order of milliseconds, permitting the coherent detection of charged particles within short times. In this publication we develop in detail a model governing the interaction between trapped $^{40}$Ca$^+$ ions and a quartz resonator connected to a low-noise amplifier. We apply this model to experimental data and extract relevant information like the coupling constant $g=2\pi \times 1.449(2)$~Hz and the ions' modified-cyclotron frequency in our 7-tesla Penning trap. The study on the latter is specially important for the use of this resonator in precision Penning-trap mass spectrometry. The improvement in sensitivity can be accomplished by increasing the coupling constant through the quality factor of the resonator. This can develop in the use of the hybrid quartz-ion system for other applications.

Parameter estimation of two coupled oscillator model for pure intrinsic thermo-acoustic instability

A nonlinear phenomenological model of two coupled oscillators is proposed, which is able to describe the rich nonlinear behaviour stemming from an unstable pure intrinsic thermo-acoustic (ITA) mode of a simple combustion system. In an experimental bifurcation analysis of a pure ITA mode, it was observed that for increasing mean upstream velocity the flames loose stability through a supercritical Hopf bifurcation and subsequently exhibit limit cycle, quasi-periodic and period-2 limit cycle oscillations. The quasi-periodic oscillations were characterised by low frequent amplitude and frequency modulation. It is shown that a phenomenological model consisting of two coupled oscillators is able to reproduce qualitatively all the different experimentally observed regimes. This model consists of a nonlinear Van der Pol oscillator and a linear damped oscillator, which are nonlinearly coupled to each other. Furthermore, a parameter estimation of the model parameters is conducted, which reveals a good quantitative match between the model response and the experimental data. Hence, the presented phenomenological dynamical model accurately describes the nonlinear self-excited acoustic behaviour of premixed flames and provides a promising model structure for nonlinear time-domain flame models.

Manipulating the Chirality of Moiré Metasurface by Symmetry Breaking

AbstractThe chirality of materials is of great significance in many fields. Metasurfaces with chirality have attracted great attention in the past decades because of their ability to miniaturize the device into the nanoscale. An important class of chiral metasurfaces is the Moiré pattern assembled by two layers of metasurfaces. However, Moiré metasurfaces usually have limited circular dichroism. Here, the origin and the limiting factor of the chirality of Moiré metasurfaces using the chiral coupled oscillator model is analyzed. It is demonstrated that, with the help of a non‐Hermitian Hamiltonian, the chirality can be improved by breaking the symmetry in the positive and negative k directions. The best result is achieved when both the two components have lowest transmission. In addition, the chiral anisotropy of a Moiré metasurface in full momentum space is studied, and it is shown that the chirality can be further improved in certain directions. The chiral anisotropy of Moiré metasurfaces may be used in applications such as optical information storage, structured color, unidirectional light coupling, sensitive chiral sensors, chiral nonlinear optics, chiral lasers, and Bose–Einstein condensation.

Rabi splitting and unidirectional reflectionless propagation in one-dimensional topological plasmonic crystal

In this paper, we study the strong coupling between the topological edge state and Fabry–Perot cavity state in a one-dimensional plasmonic crystal heterostructure. Finite element method simulations show that a significant plasmonic Rabi splitting is achieved in the near-infrared region and Rabi energy can reach up to 45.5 meV. A dual-band near-perfect absorption phenomenon can be observed, and a coupled oscillator model is proposed to explain the origin of Rabi splitting. In addition, the dual-band unidirectional reflectionless plasmonic propagation in the Rabi splitting region is investigated, and the non-Hermitian scattering matrix is used to verify the existence of double exceptional points. The study may find applications in plasmonic switchers, on-chip sensors, diode-like devices, and filters.

Fano Resonance in Near-Field Thermal Radiation of Two-Dimensional Van der Waals Heterostructures.

Two-dimensional (2D) materials and their vertically stacked heterostructures have attracted much attention due to their novel optical properties and strong light-matter interactions in the infrared. Here, we present a theoretical study of the near-field thermal radiation of 2D vdW heterostructures vertically stacked of graphene and monolayer polar material (2D hBN as an example). An asymmetric Fano line shape is observed in its near-field thermal radiation spectrum, which is attributed to the interference between the narrowband discrete state (the phonon polaritons in 2D hBN) and a broadband continuum state (the plasmons in graphene), as verified by the coupled oscillator model. In addition, we show that 2D van der Waals heterostructures can achieve nearly the same high radiative heat flux as graphene but with markedly different spectral distributions, especially at high chemical potentials. By tuning the chemical potential of graphene, we can actively control the radiative heat flux of 2D van der Waals heterostructures and manipulate the radiative spectrum, such as the transition from Fano resonance to electromagnetic-induced transparency (EIT). Our results reveal the rich physics and demonstrate the potential of 2D vdW heterostructures for applications in nanoscale thermal management and energy conversion.

Moiré Metasurface with Triple-Band Near-Perfect Chirality

Chiral metasurfaces have been proven to possess great potential in chiroptical applications. However, the multiband chiral metasurface with near-perfect circular dichroism has not been well studied. Also, the widely used bilayer metasurface usually suffers from the interlayer alignment and weak resonance. Here, we propose a twisted Moiré metasurface which can support three chiral bands with near-unity circular dichroism. The Moiré metasurface can remove the restriction of interlayer alignment, while maintaining a strong monolayer resonance. The two chiral bands in the forward direction can be described by two coupled-oscillator models. The third chiral band is achieved by tuning the interlayer chiral mode on resonance with the intralayer mode, to eliminate the parallel and converted components simultaneously. Finally, we study the robustness and tunability of the triple-layer Moiré metasurface in momentum space. This work provides a universal method to achieve three near-unity circular dichroism bands in one metasurface, which can promote applications of chiral metasurfaces in multiband optical communication, chiral drug separation, sensing, optical encryption, chiral laser, nonlinear and quantum optics, etc.

Human-exoskeleton oscillation model and qualitative analysis of interaction and functional practicality of exoskeletons

In the previous exoskeleton research, the development method of the exoskeleton-function-expectation prediction in the initial design stage is lacking, which is not conducive to reviewing the system-parameter influences on exoskeleton performances, nor to exploring the exoskeleton optimization direction. In this paper, a human-exoskeleton oscillation model is designed by integrating the main functions of one load-supporting exoskeleton in the gravity direction into the double-mass coupled oscillator model. The model simplifies the human-exoskeleton coupling motion into the human-exoskeleton oscillation motion in the gravity direction, and in the oscillation process qualitatively calculates the multiple functional expectations of the exoskeleton, such as the load-supporting capability, the human-exoskeleton interaction force, the oscillation response of the backpack and the power-assistance ability. By comparing the test results of the model with previous research, the model performance was analyzed. And further, the reasons for the unsatisfying load-supporting efficiency of previous exoskeletons were explained and the influences of system parameters for the system expectations were evaluated, which helps to provide a theoretical basis for improving the exoskeleton load-supporting efficiency and human-body comfort. In addition, the combination of the exoskeleton supporting static load and the suspension system buffering dynamic load is a new direction, and the model of the paper is also beneficial to evaluate the interference degree of the exoskeleton to the suspension system.