Parameters Of Metamaterials Research Articles

Active infrared tuning of metal–insulator-metal resonances by VO2 thin film

VO2 is a promising phase change material offering a large contrast of electric, thermal, and optical properties when transitioning from semiconductor to metallic phase. Here we show that a hybrid metamaterial obtained by proper combination of a VO2 layer and a nanodisk gold array provides a tunable plasmonic gap resonance in the infrared range. Specifically, we have designed and fabricated a metal–insulator-metal gap resonance by inserting sub-wavelength VO2 film between a flat gold layer and a gold nanodisk resonator array. The resonance of the hybrid metamaterial is centered in the useful 3–5 μm range when VO2 is in its semiconductor state. The experimental study highlights a monotonical spectral tuning of the resonance when increasing temperature up to 50 °C above the room temperature, providing a continuous resonance shift of almost 1 μm in the mid-infrared range. Wavelength range and intensity tunability can be further optimized by modifying the thicknesses of the layers and metamaterial parameters.

Analysis of Low-Frequency Sound Absorption Performance and Optimization of Structural Parameters for Acoustic Metamaterials for Spatial Double Helix Resonators

Low-frequency noise absorbers often require large structural dimensions, constraining their development in practical applications. In order to improve space utilization, an acoustic metamaterial with a spatial double helix, called a spatial double helix resonator (SDHR), is proposed in this paper. An analytical model of the spatial double-helix resonator is established and verified by numerical simulations and impedance tube experiments. By comparing the acoustic absorption coefficients of the spatial double-helix resonator, it is shown that the results of the analytical model, the numerical model, and the experiments are in good agreement, proving the accuracy of the theoretical model. The effects of different structural parameters on the peak sound absorption coefficient and resonance frequency are quantitatively revealed. The impedance variation law of the model is obtained, and the resistance and reactance distributions at the resonance frequency are analyzed. In the optimization model, the Back Propagation (BP) network is used to construct the mapping between the structural parameters and the resonance frequency and sound absorption coefficient, and this is used as the constraints of the equation, which is combined with Wild Horse Optimization (WHO) to establish the BP-WHO optimization model to minimize the volume of the spatial double helix resonator. The results show that, for a given noise frequency, the optimized structural parameters enhance the space utilization without affecting the performance of the space double helix resonator.

Acoustic metamaterials of double-layer structure for sound insulation

Insulation against air-borne sound is one of the earliest research fields of acoustic metamaterials. The sound insulation of the conventional sound insulation structure is generally limited by the law of mass. When the density of the structural surface is doubled, the low-frequency sound insulation is only increased by 6dB.In our report, we introduce a double-layer resonator-type acoustic metamaterial, which consists of two honeycomb sandwich panels, two perforated panels, and a thin air layer. Firstly, for two singer -layer resonator-type acoustic metamaterial, different sound absorption frequency points were designed. Secondly, a calculation model of sound insulation metamaterial with double-layer resonator type is established. The results show that the sound insulation performance of the structure greatly breaks through the law of mass in the frequency range of 165Hz-3150Hz. Finally, for the application requirements of the manufacturer, the compartment wall components and composite sound insulation door core components are designed. The reasonable design of Double-layer resonator-based honeycomb metamaterial structural parameters can solve the problem of low-frequency noise of thin-layer lightweight structure.

Inherent Temporal Metamaterials with Unique Time-Varying Stiffness and Damping.

Time-varying metamaterials offer new degrees of freedom for wave manipulation and enable applications unattainable with conventional materials. In these metamaterials, the pattern of temporal inhomogeneity is crucial for effective wave control. However, existing studies have only demonstrated abrupt changes in properties within a limited range or time modulation following simple patterns. This study presents the design, construction, and characterization of a novel temporal elastic metamaterial with complex time-varying constitutive parameters induced by self-reconfigurable virtual resonators (VRs). These VRs, achieved by simulating the resonating behavior of mechanical resonators in digital space, function as virtualized meta-atoms. The autonomously time-varying VRs cause significant temporal variations in both the stiffness and loss factor of the metamaterial. By programming the time-domain behavior of the VRs, the metamaterial's constitutive parameters can be modulated according to desired periodic or aperiodic patterns. The proposed time-varying metamaterial has demonstrated capabilities in shaping the amplitudes and frequency spectra of waves in the time domain. This work not only facilitates the development of materials with sophisticated time-varying properties but also opens new avenues for low-frequency signal processing in future communication systems.

Enhancement of broadband terahertz trace absorption spectrum based on angular multiplexing of trapezoidal dielectric grating

Terahertz spectroscopy provide a fast, label-free, and non-destructive method for detecting bio-medical molecules, with wide applications in national security, pharmacy, and healthcare. However, detecting terahertz absorption spectra of trace analytes still faces significant challenges. In recent years, metamaterial parameter multiplexing technology has been used to detect the terahertz fingerprint spectra of trace substances. This paper proposes a new structure based on the angle-multiplexing enhancement principle of a trapezoidal dielectric grating to enhance the terahertz absorption spectra of thin-film analytes. By scanning the incident wave angle, a series of resonance absorption peaks can be obtained. The enhanced absorption spectrum formed by the envelope of absorption spectrum peaks increases by 141 times compared to directly measuring the absorption spectrum of the same film. This structure provides a new and effective means for terahertz trace detection using metamaterial parameter multiplexing technology.

Enlargement of the localized resonant band gap by using multi-layer structures

Multi-layer structures possess highly geometrically tunable optical resonances to change the surface plasmon frequencies in the wide range. A simple analytic model is presented to describe the plasmon hybridization of multi-layer metamaterial structures with multipole resonances. We theoretically demonstrate that the number of plasmon modes increases with the number of layers, which results in the enlargement of the localized resonant optical band gap. To explore the interaction between incident fields and multi-layer structures, we derive the closed-form perturbed field in terms of a generalized polarization matrix, whose dimension matches the number of layers. This enables us to obtain the eigenmode frequencies and their corresponding eigenfunctions for three-dimensional multi-layer concentric spheres and two-dimensional multi-layer concentric cylinders in a vacuum setting. These findings offer nanoscientists a general design principle that can be applied to facilitate the proper selection of the metamaterial parameters, thereby inducing the desired resonance and enabling customized applications to be realized.

Ultra-narrow dual-band perfect absorber based on double-slotted silicon nanodisk arrays

Due to its unique advantage of optical properties, nanophotonic metamaterials have gained extensive applications in perfect absorbers. However, achieving both dual-band and ultra-narrow linewidth in absorbers simultaneously remains a challenge for typical metal-dielectric based metamaterials. In this work, a dual-band ultra-narrow perfect absorber consisting of a double slotted silicon nanodisk array that located on a silver film with a silica spacer layer is proposed theoretically. By combining the hybrid mode excited by the coupling of diffraction wave mode and magnetic dipole mode with the anapole–anapole interaction, two absorption peaks can be induced in the near-infrared regime, achieving nearly perfect absorbance of 99.31% and 99.61%, with ultra-narrow linewidths of 1.92 nm and 1.25 nm respectively. In addition, the dual-band absorption characteristics can be regulated by changing the structural parameters of the as-proposed metamaterials. The as-designed metamaterials can be employed as efficient two-channel refractive index sensors, with sensitivity and figure of merit (FOM) of 288 nm RIU−1 and 150 RIU−1 for the first band, and sensitivity and FOM of up to 204 nm RIU−1 and 163.2 RIU−1 for the second band. This work not only opens up a new design idea for the realization of dual-band perfect absorber synchronously with ultra-narrow linewidth, but also provides potential attractive candidates for developing dual-frequency channel sensors.

Application of multi-objective optimization genetic algorithm to design terahertz metamaterials with fano resonances

In the prosperous development of terahertz (THz) metamaterials, Fano resonances have gained attention due to their potential applications in ultrasensitive systems. The performance of Fano resonance is directly influenced by the geometrical parameters of the element structure. However, the traditional design rules for Fano resonances in metamaterials rely on an empirical trial-and-error strategy, necessitating significant effort to achieve optimal results. To address this issue, we propose a design method in this study that utilizes the finite integration technique in time domain (FITD) along with a multi-objective optimization genetic algorithm for the intelligent design of metamaterial structures exhibiting the Fano resonance phenomenon. The FITD method is primarily used to calculate the Fano resonance with different metamaterial geometric structure parameters, while the genetic algorithm efficiently selects the optimal solution. Our method, characterized by high efficiency and complete independence from prior knowledge, could offer a new design technique for metamaterials with specific functions, thereby contributing to the development of THz applications.

Deep learning-based inverse design of lattice metamaterials for tuning bandgap

In this paper, deep learning neural networks is used to predict the band structure of metamaterial lattices, and proactive inverse design is employed in bandgap modulation. A parametric design of the metamaterial lattice is proposed to achieve a rich design space. The corresponding band structure data is calculated by finite element method (FEM) to construct the data set. We successfully bypass complex theoretical or numerical methods to establish the mapping relationship between the lattice geometry parameters of metamaterials and the band structure data by constructing and training fully connected neural networks and convolutional neural networks (CNN). By combining the trained neural network model into an inverse design method of bandgap tuning, the geometric parameters of the metamaterial lattice can be obtained directly by inputting the target band structure. Finally, three object band structures are designed and verified by finite element simulation and experiment, which verifies the effectiveness of the inverse design method. This design approach can be extended to design other metamaterial properties.

Loss Analysis of the Electromagnetic Metamaterial Applied to Antenna Size Reductions

The research of transformation electromagnetics uses spatial coordinate transformation method to transform Maxwell’s equations for the propagations of electromagnetic waves in space, thereby achieving the goal of designing the path of electromagnetic waves, which eventually leads to a more complex tensor design of its constitutive parameters of metamaterials. This demand for artificial design of material parameters has been combined with the rapid development of micro-scale, molecular-scale, and atomic-scale experimental engineering techniques in recent years, enabling metamaterials to be developed, fabricated, and applied in various frontier fields. In this paper, the metamaterial electromagnetic wave concentrator used to reduce the antenna size is mainly discussed and detailed simulations and researches on the electromagnetic lossy conditions of the metamaterial parameters are given, which can better verify the electromagnetic scattering performance under actual engineering conditions. Solutions and quantitative simulations for the attenuation characteristics are also provided, which can deepen the research on the engineering performance of the metamaterial electromagnetic transformation devices.

Fractal acoustic metamaterials with near-zero index and negative properties

A subwavelength two-dimensional fractal acoustic metamaterial was designed based on the Hilbert fractal curve and spatial curl concept. The equivalent acoustic parameters of the fractal acoustic metamaterial were extracted by the equivalent parameter method, and the acoustic metamaterial exhibited near-zero density and negative density properties at specific frequency points. The analysis based on the finite element method shows that the acoustic prism constructed by using the near-zero density property of this acoustic metamaterial can realize the single-channel acoustic unidirectional transmission and multichannel acoustic unidirectional transmission effect, the bidirectional acoustic conduction and multidirectional acoustic conduction effect, and the bidirectional sound insulation effect. We also investigated the effect of embedding rigid scatterers inside the prism on the acoustic one-way transmission performance. Based on the acoustic direction selection mechanism of the near-zero refractive index acoustic metamaterial, arbitrary modulation of the plane acoustic wave emission direction can be achieved by changing the angle of the acoustic prism emission interface. In addition, the negative density property of the acoustic metamaterial is used to design an acoustic triangular prism to realize the acoustic negative refraction phenomenon. next, we discuss the trend of the influence of the geometrical parameters of the metamaterial on its effective properties, where the modulating wave frequency gradually moves to lower frequencies as the geometrical parameters of the metamaterial structural units increase. Finally, we fabricated the corresponding experimental samples of acoustic prisms using 3d printing technology and conducted experimental tests. The results show that the measured acoustic pressure field distribution matches well with the analytical results of the finite element method, which proves the accuracy of the results and the reasonableness of the structure, indicating that acoustic prisms composed of this acoustic super-material are expected to be used in ultrasonic imaging, acoustic energy rectification and other fields.

Investigation of a new magnetorheological elastomer metamaterial plate with continuous programmable properties for vibration manipulation

Metamaterial plates have attracted considerable attention due to their unprecedented elastic wave manipulation abilities. Currently, the band gap and other properties of traditional metamaterial plates are fixed, and the material parameters of most metamaterials cannot be dynamically and continuously adjusted. To address this issue, a two-dimensional (2D) magnetorheological elastomer (MRE) programmable metamaterial plate (MREPMP) with local resonance was proposed. The proposed MREPMP was composed of a thin steel plate and a periodic array of resonators, consisting of MREs and electromagnetic mass blocks. It not only has a compact structural design, but also enables real-time vibration control and programming wave manipulation by altering the amplitude of the current. The dispersion relation of the proposed MREPMP was theoretically calculated based on the plane wave expansion (PWE) method and the simulated transmissibility was numerically calculated using the finite element method in COMSOL. Subsequently, a prototype of the MREPMP was fabricated, and vibration tests were conducted to assess its programmable vibration manipulation functionalities. Two different types of defect paths were used as excitations and the corresponding real-time vibration manipulation performance was analyzed. The simulation results agree with the experimental results, showing that the MREPMP can dynamically tune the band gap and activate different waveguides through continuous online programming. This paper opens up a new idea for tunable manipulation of wave propagation.

Omnidirectional broadband phase modulation by total internal reflection.

Phase modulation plays a crucial role in shaping optical fields and physical optics. However, traditional phase modulation techniques are highly dependent on angles and wavelengths, limiting their applicability in smart optical systems. Here, we propose a first-principle theory for achieving constant phase modulation independent of incident angle and wavelength. By utilizing a hyperbolic metamaterial and engineering-specific optical parameters, different reflective phase jumps are achieved and tailored for both transverse electric (TE) and transverse magnetic (TM) waves. The aimed reflection phase difference between TE and TM waves can be thus achieved omnidirectionally and achromatically. As an example, we propose a perfect omnidirectional broadband reflection quarter wave plate. This work provides fundamental insights into manipulating optical phases through optical parameter engineering.

Design and reinforcement-learning optimization of re-entrant cellular metamaterials

The demand for cellular metamaterials exhibiting multiple desired properties has become increasingly prominent due to the complexity of engineering applications. In this study, a novel dual-functional re-entrant cellular metamaterial is proposed for excellent bandgap characteristics and enhanced energy absorption capacities. A structural evolutionary route of the metamaterial unit cell is developed through the introduction of flexural ligaments and geometric circles, which leads to the achievements in both superior bandgap and enhanced energy absorption. Firstly, the wave propagation characteristics of cellular metamaterials in three evolved configurations are analyzed systematically. Bandgap properties and the generation mechanism are revealed by mode shape analysis. Then, the Q-learning algorithm in reinforcement learning is employed to optimize significant structural parameters of cellular metamaterials to acquire the maximum bandgaps. The certain stability and efficiency of the algorithm are discussed by the evolutionary optimization of metamaterial unit cells with different configurations. Additionally, the energy absorption capacities of metamaterials with optimal microstructure configurations are investigated numerically. Plateau stress and specific absorption energy are compared under various impact velocities, with improved performance observed in the novel cellular metamaterials. The findings of this study offer a promising avenue for advancing the development of dual-functional metamaterials with tailored properties for diverse applications.

Wave-speed management of dipole, bright and W-shaped solitons in optical metamaterials

Wave-speed management of soliton pulses in a nonlinear metamaterial exhibiting a rich variety of physical effects that are important in a wide range of practical applications, is studied both theoretically and numerically. Ultrashort electromagnetic pulse transmission in such inhomogeneous system is described by a generalized nonlinear Schrödinger equation with space-modulated higher-order dispersive and nonlinear effects of different nature. We present the discovery of three types of periodic wave solutions that are composed by the product of Jacobi elliptic functions in the presence of all physical processes. Envelope solitons of the dipole, bright and W-shaped types are also identified, thus illustrating the potentially rich set of localized pulses in the system. We develop an effective similarity transformation method to investigate the soliton dynamics in the presence of the inhomogeneities of media. The application of developed method to control the wave speed of the presented solitons is discussed. The results show that the wave speed of dipole, bright and W-shaped solitons can be effectively controlled through spatial modulation of the metamaterial parameters. In particular, the soliton pulses can be decelerated and accelerated by suitable variations of the distributed dispersion parameters.

Optimized Design of Plasma Metamaterial Absorber Based on Machine Learning

Metamaterial absorbers have become a popular research direction due to their broad application prospects, such as in radar, infrared imaging, and solar cell fields. Usually, nanostructured metamaterials are associated with a large number of geometric parameters, and traditional simulation designs are time consuming. In this paper, we propose a framework for designing plasma metamaterial absorbers in both a forward prediction and inverse design composed of a primary prediction network (PPN) and an auxiliary prediction network (APN). The framework can build the relationship between the geometric parameters of metamaterials and their optical response (reflection spectra, absorption spectra) from a large number of training samples, thus solving the problem of time-consuming and case-by-case numerical simulations in traditional metamaterial design. This framework can not only improve forward prediction more accurately and efficiently but also inverse design metamaterial absorbers from a given required optical response. It was verified that it is also applicable to absorbers of different structures and materials. Our results show that it can be used in metamaterial absorbers, chiral metamaterials, metamaterial filters, and other fields.

Phononic Band Structure by Calculating Effective Parameters of One-Dimensional Metamaterials

Using a theory of homogenization that consists in the discretization of the inclusion of a binary phononic crystal in small volumes, in which the material parameters can be expanded in Fourier series, we have determined the dependence of the effective elastic parameters as a function of the frequency. In particular, the frequency dependence of all the elements that constitute the effective tensors of stiffness (moduli of elasticity) and density was analyzed for a 1D phononic crystal conformed of materials whose main characteristic is the high contrast between their elastic properties. In this dynamic case of homogenization, it was found that the effective parameters can reproduce the exact dispersion relations for the acoustic modes that propagate along the periodicity direction of the crystal. Particularly, in the second pass band (high-frequency branch) corresponding to the transverse vibrational modes, the homogenized elastic phononic crystal exhibits a metamaterial behavior because the effective C44-component (shear modulus) and dynamic mass density were found to be both negative. It is noteworthy that the study derived from this homogenization technique can lead to design of double negative metamaterial systems for potential applications.

Analysis of a Strip Antenna Located at a Plane Interface of Uniaxial Metamaterials

A rigorous solution is found to the problem of determining the current distribution and input impedance of a straight strip antenna located at a plane interface of two uniaxial metamaterials. The anisotropy axes of the metamaterials are parallel to each other and to the medium interface. The antenna is oriented perpendicular to these axes and excited by a given time-harmonic voltage. Using the Fourier transform technique, singular integral equations for the antenna current are derived and solved for all possible combinations of the metamaterial parameters. Closed-form representations for the current distribution and input impedance of an infinitely long strip are obtained and their generalization to the case of a finite-length antenna is discussed.

Effect of symmetry breaking on multi-plasmon-induced transparency based on single-layer graphene metamaterials with strips and rings.

A single-layer graphene metamaterial consisting of a horizontal graphene strip, four vertical graphene strips, and two graphene rings is proposed to realize tunable multi-plasma-induced transparency (MPIT) by the coupled mode theory and the finite-difference time-domain method. A switch with three modulation modes is realized by dynamically adjusting the Fermi level of graphene. Moreover, the effect of symmetry breaking on MPIT is investigated by controlling the geometric parameters of graphene metamaterials. Triple-PIT, dual-PIT, single-PIT can be transformed into each other. The proposed structure and results provide guidance for applications such as designing photoelectric switches and modulators.

Inverse design of slow light devices at telecommunication band based on metamaterials using a deep learning attempt

Slow light devices have important applications in many fields such as optical communication, optical storage, optical signal shaping and synchronization. Although a variety of high-performance slow light devices can be purchased in the market, it is still a worthwhile research topic to design slow light devices according to specific wavelengths and requirements. Here we employ machine learning method to inverse design electromagnetically induced transparency (EIT) based slow light devices in communication band using metal–dielectric hybrid metamaterials. Three characteristic points of transmittance as well as the group refractive index and bandwidth are chosen as input parameters. By replacing the complex fully connected layer with a one-dimensional convolutional neural network (1DCNN) layer to optimize the fully connected network, the proposed model can break the limitation of passive modulation and find the best slow light structure parameters. The slow light parameters could reach a bandwidth of 38.71 nm and average group refractive index of 10.51. In addition, the model can predict hybrid metamaterial structure parameters of slow light devices in the communication band from 1400 nm to 1600 nm. By combining active and passive modulation technologies, our proposed method improves the adjustment range of design parameters of slow light devices. The procedure can be potentially applied in the design of other nano optical devices.