Metamaterial Surface Research Articles

Minimizing Indoor Sound Energy with Tunable Metamaterial Surfaces

The advent of broadband and tunable acoustic metamaterials, amenable to be fabricated into flat panel geometry, offers broad, emerging possibilities for room acoustics. In particular, the fine tuning of surface acoustic impedance becomes possible to optimize specific room acoustic goals. In this initial simulation study we examine the possibility of minimizing the averaged level of energy density (${L}_{e}$), both globally and locally in an enclosed room. The relationship curve between surface impedance and global ${L}_{e}$ shows an optimal value that can reduce ${L}_{e}$ by about $15$--$20\phantom{\rule{0.2em}{0ex}}\mathrm{dB}$ over a wide audible frequency regime. Moreover, partial coverage of the room surface by the optimally tuned acoustic metamaterial already demonstrates considerable effectiveness. We compare and verify our numerical model with the statistical-diffusive acoustics model and find good agreement in the high-frequency regime. In the low-frequency regime, the energy inhomogeneity caused by wave interference can be utilized to create a quiet zone for specific targeted frequency by optimally tuning the surface impedance values at discretized locations on the four walls.

High-performance infrared thermal radiation suppression metamaterials enabling inhibited infrared emittance and decreased temperature simultaneously

Infrared thermal radiation suppression techniques are vital to the survival of various vehicles/targets, and low-emissivity materials are conventionally employed to reduce infrared radiant power of targets. However, infrared radiant power depends not only on infrared emittance but also heavily on the temperature according to Steven-Boltzmann law (P=εσT4). In this work, it is for the first time, a novel type of infrared stealth material based on tailoring radiative properties in an ultra-broadband ranging from 0.4 µm to 14 µm is proposed. A low emittance in atmosphere window (3–5 µm, 8–14 µm) is achieved to suppress infrared radiation, and a high emittance from 5 to 8 µm is obtained to reduce temperature via radiative cooling from metamaterial surface to the atmosphere. Meanwhile, low absorptance in the solar spectra (0.4–2.5 µm) can help to resist the solar heat. As a result, the infrared radiant power in the atmospheric window is prominently reduced benefiting from low emittance and decreased temperature. This work helps guide the design of more effective infrared stealth materials and paves the way for the applications of metamaterials in infrared stealth applications.

Design and analysis of nanopatterned graphene-based structures for trapping applications

Trapping, levitating, and manipulating nanoscale objects with light forces shaped by patterned metamaterials continues to hold great interest for optical and condensed matter physics and engineering. Successful developments to date have concentrated on constraining movement only in one dimension, along the vertical axis to a material plane. Here we propose a realistic structure, consisting of alternating layers of graphene and dielectric, and periodically nanopatterned on the surface, that is capable of levitating and trapping nanoscale particles in two dimensions: one perpendicular and one parallel to the material plane. Repulsive forces arising from high- $k$ modes of the metamaterial provide particle levitation along the vertical axis. At the point where this repulsive force balances the downward gravitational force, the particle is trapped at stable equilibrium. Periodic nanopatterning in the metamaterial surface furnishes the second, horizontal axis constraining particle motion. We show that the equilibrium position above the surface can be controlled by adjusting both the Fermi level and the number of graphene layers. Furthermore, to explicate the role of the high-$k$ modes in generating the repulsive forces, we also propose a semianalytical method to calculate both the potential well and the forces generated by dipole radiation above the nanopatterned surface.

Active terahertz time differentiator using piezoelectric micromachined ultrasonic transducer array.

The rapid growth of information technology is closely linked to our ability to modulate and demodulate a signal, whether in the frequency or in the time domain. Recent demonstrations of terahertz (THz) modulation involve active semiconductor metamaterial surfaces or use of a grating-based micromirror for frequency offset tuning. However, a wideband and active differentiator in the THz frequency band is yet to be demonstrated. Here, we propose a simple method to differentiate a THz pulse by inducing tiny phase changes on the THz beam path using a piezoelectric micromachined ultrasonic transducer array. We precisely demonstrate that the modulated THz signal detected after the piezoelectric device is proportional to the first-order derivative of the THz pulse. The proposed technique will be able to support a wide range of THz applications, such as peak detection schemes for telecommunication systems.

Dynamically tunable angular optical transparency induced by photonic topological transition in graphene-based hyperbolic metamaterials

Based on photonic topological transition (PTT), the dynamically tunable angular optical transparency of graphene-based hyperbolic metamaterials is theoretically and numerically investigated in mid-infrared region. The results indicate that an ultra-narrow angular optical transparency window with angular full width at half maximum of 0.8° appears near the transition point of PTT for TM waves, which is achieved by tailoring the metamaterial's equi-frequency surface from closed ellipsoid to open hyperboloid. In addition, we further propose the application of TM-pass/TE-reflect polarization beam splitter in the case of normal incidence. Besides, the broadband of angular optical transparency can be realized by changing the Fermi level of graphene.

Polarization-Insensitive Fractal Metamaterial Surface for Energy Harvesting in IoT Applications

A novel fractal-based metamaterial unit cell, useful for ambient power harvesting, is proposed to operate within the 2.45 GHz Wi-Fi band. The simulated fractal cell offers very high absorption coefficients, a wide-angle and polarization-insensitive behavior, and very small size. A 9 × 9 fractal-based metamaterial harvester is designed and simulated, by demonstrating a very high harvesting efficiency equal to 96.5% at 2.45 GHz. The proposed metamaterial configuration could be very appealing for the implementation of high efficiencies and compact harvesting systems for wireless sensor network applications.

3D Printed Meta‐Helmet for Wide‐Angle Thermal Camouflages

AbstractThermal camouflage utilizes the manipulation of heat fluxes to conceal an arbitrary object in various environments from being detected via thermography. In the past decade, the field of thermal metamaterials and the technique of 3D printing have been rapidly developed, which makes nonintuitive heat flux manipulation feasible. However, when thermal metamaterials are applied to the thermal camouflaging, their conductivities are dependent on the properties of background, leading to the damage of background integrality. Moreover, previous thermal camouflaging schemes have mostly worked in the 2D regime, largely restricting their functional angles and application scenarios, especially in complex environments. Here, wide‐angle radiative thermal camouflaging is realized by using a 3D‐printed meta‐helmet of extremely anisotropic thermal conductivities. Based on 3D coordinate transformation, this meta‐helmet directly maps temperature distributions from the background to the metamaterial surface without damaging background integrity. The non‐invasive device is efficient in wide‐angle thermal camouflage by rendering the same emissivity to the background medium and can self‐adjust to various even unknown background thermal fields, which is demonstrated in numerical simulations and experiments. This work opens a door to the 3D transformation‐thermotics‐based devices for versatile practical applications in thermal infrared stealth of macro‐sized objects and others.

Dynamically tunable excellent absorber based on plasmon-induced absorption in black phosphorus nanoribbon

The realization of plasmon-induced absorption (PIA) via local plasmon resonance coupling on the surface of two-dimensional metamaterials based on nanostructures heavily depends on the well-designed patterned antenna. However, due to the limitation of nanostructures’ size and the difficulty of material formation, it is challenging to achieve the expected performance of such a device. We propose and numerically simulate PIA in response to mid-infrared using two black phosphorus (BP) layers that are composed of upper double BP ribbons and lower single BP ribbons to avoid BP chips patterning. The theoretical transmission spectrum of the structure calculated by the coupled mode theory is in good agreement with the simulated curve. The resonant intensity of the reflection window is affected by interlayer spacing, and the resonant wavelength of the reflection window can be realized by dynamically varying carrier density. The absorption performance of the system can be enhanced not only by the gold mirror that is totally reflected at the bottom of the structure but also by the polarization angle of the incident wave. The designed system could be expected on various optical devices, including plasmonic sensors, dual-frequency absorbers, and switch controllers.

Dyakonov Plasmon–Polaritons Propagating along the Surface of a Hyperbolic Metamaterial

Plasmon–polaritons of the type of Dyakonov surface waves propagating along the plane boundary of a hyperbolic metamaterial with an arbitrary orientation of its crystallographic axis are considered. Conditions of the existence of fast, slow, leaking-in, leaking-out, forward, and backward plasmon–polaritons are found. A waveguide in the shape of an asymmetric layer of a hyperbolic metamaterial is examined. An expression for the electromagnetic energy density in this metamaterial is given.

Optical switching and beam steering with a graphene-based hyperprism

It is well established that the topological transition of the iso-frequency surface (IFS) of hyperbolic metamaterials from the ellipsoid to hyperboloid provides unique capabilities for controlling the propagation of the wave. Here, we present a graphene-based hyperprism (GHP) structure that uses an electronically controlled modulation strategy to achieve optical switching and wide-angle beam steering functions. Numerical simulation results show that, by regulating the chemical potential of GHP, the optical switching system can achieve high transmission (97%) and zero transmission, as well as the beam steering system can reach a maximum adjustable angle of 52.94°. Furthermore, the effects of Fermi energy and relaxation time on transmittance are also investigated. These works may provide new opportunities for applications such as optical data storage, modulators, and integrated photonic circuits.

Second-order correlation function of fluorescence from a few atoms near plasmonic surface

We have used a full quantum mechanical approach to study the second-order correlation function of a system of a few two-level atoms coupled via plasmons. By the usage of quantum regression theory we have developed a new model that allows us to fully investigate the dependence of photon bunching and anti-bunching effects to the interaction between atoms, fields and surrounding medium. Using Dicke basis for several atomic systems, we show that Dicke states can be coupled via various relaxation processes near plasmonic and metamaterial surfaces, and as a result, the second-order correlation function has various characteristic time scales related to the supperadiant and subradiant transitions and these prediction can be observed experimentally.

Metamaterial based sucrose detection sensor using transmission spectroscopy

In the present study, metamaterial based optical sensor is proposed and optimization of the proposed optical sensor for sucrose detection is done. In this paper single negative metamaterial surface is fabricated using E-beam lithography technique to be used as an optical sensor for broad wavelength range using UV–Vis–NIR spectrometer. The resultant sensitivity and detection accuracy of the proposed metamaterial based sensor is higher than simple thin film sensor, i.e. 1740.8 (nm/RIU) and 0.893 respectively. The center wavelength of the proposed optical sensor is 967 and 933 nm for gold and metamaterial based-sensor respectively, which ensures the larger bandwidth available in the case of metamaterial based-sensor. It is observed that high surface to volume ratio of metamaterial surface ensures the better sensitivity of the proposed sensor. Simple structure of presented metamaterial surface also makes sure reliable and precise fabrication of metamaterial surface.

Dielectric control of localized plasmons in terahertz metamaterials

We present an experimental time-domain-spectroscopy study of the plasmonic resonance behavior of metamaterial surfaces in the terahertz regime. We determine the effective refractive index of the dielectric environment and its influence on meta-atoms built of connected dipoles. Our findings show that an analytical calculation of their resonance frequencies including higher order modes is possible and yield a method of frequency response prediction for complex meta-atom geometries. By modifying the dielectric environment, we introduce a way to control independently frequency and linewidth of the localized plasmons. Unlike the resonance frequency, which is strongly affected by a modification, the losses are robust against changes of the surrounding media. It is shown that the interaction channel between the single elements is dominantly mediated by the substrate. Our experimental findings can therefore contribute to the future conception of actively controllable complex photonic device structures.

Experiments With a Compact Wireless Power Transfer System Using Strongly Coupled Magnetic Resonance and Metamaterials

The technology for inductive wireless power transfer (IWPT) by using strongly coupled magnetic resonance has been applied successfully to supply energy to several applications such as biomedical implants, radio frequency identification systems, Internet-of-Things sensors, and battery chargers for personal devices. In order to attain high values of efficiency and reach, the technology requires the employment of coils with high values of quality factor. However, this feature can only be found by using large wire coils. A compact IWPT system composed of printed coils, which typically have low values of quality factor, is proposed in this paper. An evolutionary algorithm is used to optimize the printed coil geometry so that it presents the greatest value of quality factor possible, according to the imposed restrictions. With the aim to improve the system efficiency and reach, the effect of metamaterial surfaces inclusion is investigated. In addition, in order to increase the amount of power processed by the system, a low-cost self-oscillating electronic converter is proposed to power it.

Surface acoustic wave modes in two-dimensional shallow void inclusion phononic crystals on GaAs

The possibility to control supersonic acoustic wave propagation is intriguing, but when modeling phononic crystal devices, supersonic surface acoustic waves are mired by radiative attenuation and, hence, eschewed in many device designs. In this paper, we study supersonic surface acoustic wave modes in shallow hole phononic crystals computationally with respect to the three bulk wave sound barriers of cubic (001) GaAs. From a first principles modeling approach of linear elasticity, the finite element method, and with the aid of characterization parameters for systematic modal categorization, detailed nuances are observed for supersonic surface waves propagating along the [110]-direction of GaAs with a periodically patterned surface. Modes of interest are distinguished by possessing both strain energy and squared polarization ratios above defined thresholds. The square array of shallow inclusions imparts a metamaterial surface layer effect that results in marked changes in the dispersion, the bulk wave hybridization, and the modal interactions of the surface modes in the Γ-X direction of the phononic crystal, which are characterized by their modal profiles and attenuation via bulk wave radiation. From these findings, we propose an extended sound cone concept to accommodate supersonic surface acoustic waves with low attenuation. Furthermore, at frequencies above the shear vertical bulk dispersion line, well-bounded surface acoustic wave modes are revealed, and the phenomenon of these supersonic modes with limited bulk wave coupling is explored. From these detailed band structures, the systematic method of mode characterization reveals deeper insights into modes that exist in shallow phononic crystals on cubic GaAs.

Surface Lattice Resonances in THz Metamaterials

Diffraction of light in periodic structures is observed in a variety of systems including atoms, solid state crystals, plasmonic structures, metamaterials, and photonic crystals. In metamaterials, lattice diffraction appears across microwave to optical frequencies due to collective Rayleigh scattering of periodically arranged structures. Light waves diffracted by these periodic structures can be trapped along the metamaterial surface resulting in the excitation of surface lattice resonances, which are mediated by the structural eigenmodes of the metamaterial cavity. This has brought about fascinating opportunities such as lattice-induced transparency, strong nearfield confinement, and resonant field enhancement and line-narrowing of metamaterial structural resonances through lowering of radiative losses. In this review, we describe the mechanisms and implications of metamaterial-engineered surface lattice resonances and lattice-enhanced field confinement in terahertz metamaterials. These universal properties of surface lattice resonances in metamaterials have significant implications for the design of resonant metamaterials, including ultrasensitive sensors, lasers, and slow-light devices across the electromagnetic spectrum.

Tunable optical angular selectivity in hyperbolic metamaterial via photonic topological transitions.

An ultra-narrow angular optical transparency window based on photonic topological transition (PTT) is theoretically and numerically investigated in a low-loss hyperbolic metamaterial (HMM) platform, which consists of aligned metallic nanowires embedded indielectric host matrices. Our results indicate that, near the transition point of PTT, the designed system exhibits high-efficiency optical angular selectivity close to normal incidence by tailoring the topology of metamaterial's equi-frequency surface (EFS). Moreover, the operating wavelength (λ0) is flexibly tunable by selecting appropriate material and geometrical parameters, which provides significant guidance for the later experimental design. Our method is further applied to super-resolution imaging, with a resolution of at least λ0/4 and over a significant distances (>12λ0). The HMM-supported angularly selective system could find promising applications for high-efficiency light manipulation and lensless on-chip imaging.

Novel non-fiber optical metamaterial waveguide for monitoring canal and pipeline structures

The electromagnetic metamaterials are the recent entrants, into the classification of smart materials for structural health monitoring (SHM). Their applications in SHM have raised the curiosity due to their rapid executable speeds in wide-frequency domains. The speed of obtaining health output signals for engineering structures is about 1/100th of the time taken by existing smart material-based frequency domain techniques such as piezoelectric material-based techniques. Recently, we developed an ultra-sensitive near-field sensing technique using metamaterial localized surface plasmon (LSP) ‘sensor’ which produced diagnosable ‘confined surface electromagnetic waves’ for SHM. This paper presents the same near-field sensing technique in the frequency domain but using metamaterial ‘waveguides’ based on propagating surface plasmon polaritons (SPPs)/surface waves. For the experiments, a novel robust metamaterial waveguide coupling zone was designed and applied for monitoring longitudinal and lateral displacements in civil engineering prototype structures such as channels and pipelines. In the context of SHM, coupling zone and metamaterial waveguide resemble fiber Bragg grating (FBG) sensor and optical fiber waveguide, respectively. Thus, if properly realized, these metamaterials can co-exist with the existing FBG/optical fiber techniques for applications in civil engineering.

Polarization Conversion Metamaterial Surface With Staggered-Arrangement Structure for Broadband Radar Cross Section Reduction

A polarization conversion metamaterial surface (PCMS) with low radar cross section (RCS) is presented in this letter. The PCMS is composed by a periodic array of lantern-shaped metal units. The optimized effective phase difference is about 40.6%, and the 10 dB RCS reduction bandwidth is from 11.0 to 17.0 GHz. To further broaden the operational bandwidth, a staggered-arrangement PCMS (SPCMS-2) is adopted. The overall phase difference is shifted to lower frequency, and a 10 dB RCS reduction bandwidth is obtained over a wide band from 9.0 to 16.0 GHz. To verify the correctness of these designs, both the PCMS and SPCMS-2 arrangements are fabricated and tested. The measured results are consistent with the simulation results very well.

A Waveguide Slot Filtering Antenna With an Embedded Metamaterial Structure

A novel waveguide slot filtering antenna with an embedded metamaterial is presented. This filtering antenna consists of a common waveguide slot antenna with longitudinal slots cut on the top broad wall of its rectangular waveguide and a metamaterial surface embedded in the bottom broad wall. The metasurface replaces the conventional metal plane in the form of a bed of nails. In the operating frequency band, the metasurface works as a perfect electric conductor, so the antenna radiates as the traditional waveguide slot antennas. While in the stopband, the metasurface performs as a perfect magnetic conductor to suppress the propagation of electromagnetic wave in the waveguide cavity, so the interference signal is rejected and a filter function is achieved. To show the design process and verify its feasibility, a filtering antenna prototype working in the $C$ -band and having a stopband in the $X$ -band is designed, fabricated, and tested. A good agreement between simulation and measurement is obtained, demonstrating efficient radiations in the working band and a strong suppression of more than 35 dB in the stopband.