Metamaterial Research Research Articles

Optical and Plasmonic Properties of Epitaxial and Oxidative Controlled Titanium Nitride Thin Films

The present study is an effort to develop negative-permittivity, high melting point, mechanically hard, and chemically stable materials beyond commonly employed plasmonic metals such as gold and silver, which are often device incompatible in terms of real operating environments. The material studied here is titanium nitride (TiN), which possess free electron gas density similar to of gold and silver, and embodies refractory metals’ characteristics. The aforementioned advantages of TiN are taken to the next level by transforming them to oxynitrides (TiON) with a precise control in oxygen composition that can, in turn, be used to tune the electronic band structure of transition metal nitrides, opening another new dimension to transition metals nitride based plasmonics and metamaterials research. This presentation will report a pulsed laser-assisted synthesis, detailed structural characterization using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), soft x-ray absorption spectroscopy (XAS), non-Rutherford Backscattering spectrometry (RBS), and plasmonic properties of three sets of TiN/TiON thin films. The first two sets of TiN films were grown 600 and 700 °C under a high vacuum condition. The third set of TiN film was grown in the presence of 5 mTorr of molecular oxygen at 700 °C. The purpose of making these three sets of TiN/TiON films was to understand the role of film crystallinity and role of oxygen content of TiN films on their optical and plasmonic properties. The results have shown that TiN films deposited in a high vacuum are metallic, have large reflectance, and high optical conductivity. The TiN films, grown in 5 mTorr, were found to be partially oxidized with room temperature resistivity nearly three times larger than those of the TiN films grown under high vacuum conditions. The optical conductivity these films were analyzed using a Kramers-Kronig transformation of reflectance and a Lorentz-Drude model; the optical conductivity determined by two different methods agrees very well, indicative of reliable estimate of the absolute value of reflectance in the first place. Then, it allows us to determine and analyze the complex dielectric function over a broad spectral range. We notice the existence of significant spectral weight below the interband absorptions, described by two Lorentzians, one around 250 cm-1 and one around 2,500 cm-1. We discuss here the dependence of the two bands on the deposition conditions and their effect on the plasmonic performances of TiN/TiON thin films, in particular on the surface plasmon polariton (SPP) and localized surface plasmon resonance (LSPR) quality factors.

Study on Bandgap of Two‐Dimensional Square Lattice Acoustic Metamaterial with Multiembedded Cores

Acoustic metamaterials have been widely studied for their excellent ability of vibration isolation. In this article, a 2D square lattice acoustic metamaterial structure with multiembedded cores is proposed. Based on Bloch's theorem and finite element method, the band structures and bandgap properties of the structure are calculated and analyzed, and the vibration isolation ability of the structure is investigated. The effects of structural parameters on the bandgap property are analyzed. Thus, the anisotropy of the structure is also analyzed by the contours of phased velocity and group velocity. The results show that the structure has significant bandgap properties and vibration isolation. The second‐order similarity ratio has significant effects on the bandgap property. Via increasing the second‐order similarity ratio, the total bandgap width and low‐frequency bandgap width are widened. In addition, the structure has significant anisotropy, and the energy of elastic wave propagates at the direction of 45° and 135°. The research in this article supplements the design and research of 2D lattice acoustic metamaterials and makes a beneficial exploration for future engineering applications.

Widening the frequency bandgap and reducing thermal conductivity in phononic crystals by tuning structural parameters using a novel computational simulation method

This paper introduces and models a phononic structure based on single-crystal silicon, aiming to investigate the width of its frequency bandgap and the impact of key parameters on thermal conductivity. The modeled phononic crystal structure features a periodic arrangement of cylindrical holes in a silicon matrix. This research holds the potential to enhance thermal management performance of thermal metamaterials. Utilizing a 3D finite element method (FEM) model in COMSOL, we have computed phonon dispersion to estimate thermal conductivity. The study systematically has explored the influence of phononic crystal parameters—specifically, porosity, lattice constant, and thickness—along with their interactions on both thermal conductivity and frequency bandgap width.A comprehensive investigation of these parameters has been conducted for their optimization to achieve the maximum frequency bandgap width and minimum thermal conductivity using the response surface method model. Eigenfrequencies and wave vector parameters are extracted from the finite element model using a MATLAB script. Subsequently, thermal conductivity is calculated through the Callaway–Holland model, a simplification of the Boltzmann transport equation (BTE).Our results indicate that the frequency bandgap begins to form at approximately 43% porosity for a lattice constant and thickness of 100 nm each. Furthermore, adjusting the parameters led to a significant reduction in thermal conductivity, decreasing from 43.89 W m−1 K−1 to 0.39 W m−1 K−1. The novelty of our research lies in thermal conductivity control of phononic crystal metamaterials through their parameter variations, or a predictive method of thermal conductivity and its parameter sensitivity. This study advances the state of the art in phononic crystal metamaterial research, contributing to improved thermal management performance by enlarging frequency bandgaps.Overall, our findings deepen the understanding of how porosity, lattice constant, and thickness influence thermal conductivity and frequency bandgap width. They offer valuable insights into optimizing phononic crystal parameters, enhancing thermal management performance, and designing more efficient and effective phononic crystal structures.

Design and performance of a dual-band plasmonic perfect absorber for infrared refractive index sensing

In this study, we introduce what we believe is an innovative design for a plasmonic perfect absorber (PPA) that is based on half-cut disk resonator metamaterials. This design exhibits remarkable stability and versatility, demonstrating effective functionality across a wide range of incident angles for both transverse electric (TE) and transverse magnetic (TM) polarization. The distinct operational characteristics of the PPA are highlighted by the presence of two corresponding absorption peaks at wavelengths of 870 and 1599 nm, where it achieves outstanding maximum absorption rates of 98.99% and 97.5%, respectively. The design’s ultra-narrow resonance peaks are indicative of its high-quality factors, which are vital for enhancing sensitivity in plasmonic sensory applications. This characteristic renders our PPA an exceptional candidate for refractive index (RI) sensing, where precision is critical. The dual-band perfect absorber (PA)-based sensor demonstrates significant RI sensitivity, with values approximately equal to 365 nm/RIU at the first absorption peak and 733 nm/RIU at the second. Our findings elucidate the exceptional potential inherent in this novel dual-band perfect absorber design. The versatility and efficiency across varied applications not only contribute to the existing body of knowledge but also pave the way for future advancements in plasmonic sensor technologies and metamaterial research.

Multi-band and polarization-insensitive electromagnetically-induced transparency based on coupled-resonators in a metamaterial operating at GHz frequencies

The analogy of electromagnetically-induced transparency (EIT) has emerged as an intriguing phenomenon in metamaterials research, enabling precise control over electromagnetic wave propagation. In this work, a metamaterial is investigated to achieve polarization-insensitive and multi-band transparency in microwave region. The metamaterial unit-cell consists of three coupled resonators, engineered to exhibit distinct resonance frequencies within the GHz spectrum and their coupling results in transparency windows. The functionality of the metamaterial is validated experimentally, demonstrating dual-band transparency windows at 4.6 and 6.4 GHz. Additionally, under oblique incidence, a third transparency peak arises, and the achieved triple-band EIT peaks can be maintained above 67% up to an incident angle of 60°. Our work contributes a metamaterial platform offering multi-band EIT behavior and polarization insensitivity at GHz frequencies. The proposed structural design leverages coupled-resonator configurations to achieve enhanced control over electromagnetic wave propagation, promising significant advancements in both fundamental research and practical applications. These include advanced signal processing, high-efficiency filters, and sensors operating in GHz communication and radar systems.

Towards an optimal design of acoustic Luneburg lenses.

Although the concept of acoustic Luneburg lenses was first proposed more than 50 years ago, its physical realization became feasible only in the last decade, owing to advancements in metamaterials research. Since then, numerous studies have explored the potential of these devices from the acoustic perspective. However, a comprehensive understanding of the mechanisms associated with the optimal performance of these lenses remains underexplored in the literature. This study conducts numerical investigations to identify parameters enhancing acoustic gain in Luneburg lenses. The analyses are conducted with the results obtained from a flattened Luneburg lens model based on the lattice Boltzmann method. Results, scaled with the Helmholtz number, He, indicate that the maximum acoustic gain occurs at He = 1.3, with performance sustained over a wide range of Helmholtz values. Analysis of surface impedance reveals underperformance for Helmholtz values below 0.5 due to viscous dissipation and above 2.0 due to Bragg reflections. These results provide a basis for evaluating the Helmholtz parameters that optimize the acoustic gain of Luneburg lenses.

A nonlinear career path for acoustic metamaterial research

Acoustic metamaterials are designed materials which have specific functionality to control acoustic or elastic waves. Over the last 20 or so years, metamaterials have proven to be a promising approach for noise control such as acoustic absorption control of acoustic fields such as holography. My technical research has focused on acoustic metamaterials for over 15 years and that work has taken me on a very nonlinear path through 4 institutions over the course of my career. When I was leaving school, like many students or those early in their career in research or industry, I expected that my professional path would be fairly linear but the reality has taken unexpected twists and turns. In this talk, I will describe my own career path researching acoustic metamaterials. This path has included multiple cross-country moves with noise control using acoustic metamaterials as a common theme.

A brief report on nanophotonics and metamaterials landscape in India

AbstractHere, we describe a set of research results in the domain of Nanophotonics and Metamaterials that represent the broad N &M landscape in India. These results were presented in an online BRICS meeting, and were collated based on the criteria deemed appropriate for the said forum. Results presented at the meeting encompass various areas, including nano-optics, nano-opto-mechanics, integrated photonic devices, plasmonics, metal-enhanced fluorescence, bio relevant photonics and metamaterials. Research topics such as Anderson localization of light, exceptional points in non-Hermitian systems, manipulation of nanoscale mechanical motion, efficient mode coupling in integrated photonics etc are discussed. Furthermore, miniaturized SPR sensors, coupling between metal nanostructures and semiconductor quantum dots, biosensing applications, metamaterials and random lasing, and customizable optical functionalities for sensing, and energy conversion are also elaborated upon. In the end, a brief listing of more recent selected publications is presented. This review article highlights the diverse and promising avenues in nanophotonics and metamaterials research in India.

Acoustic metamaterials characterization via laser plasma sound sources

Phononic crystals and acoustic metamaterials are expected to become an important enabling technology for science and industry. Currently, various experimental methods are used for evaluation of acoustic meta-structures, such as impedance tubes and anechoic chambers. Here we present a method for the precise characterization of acoustic meta-structures that utilizes rapid broadband acoustic pulses generated by point-like and effectively massless laser plasma sound sources. The method allows for broadband frequency response and directivity evaluations of meta-structures with arbitrary geometries in multiple sound propagation axes while also enabling acoustic excitation inside the structure. Experimental results are presented from acoustic evaluations of various phononic crystals with band gaps in the audible range, notably also in the very low frequencies, validating the predictions of numerical models with high accuracy. The proposed method is expected to boost research and commercial adoption of acoustic metamaterials in the near future.

Electromagnetic characteristics analysis of dual-frequency magnetic single negative metamaterials

Abstract With the development of multi-frequency wireless transmission technology, it is necessary to expand the research of single-frequency metamaterials in the multi-frequency field. The dual-frequency metamaterial studied adopts a nested square spiral structure, which can resonate at two frequencies, and the real part of the equivalent permeability of metamaterial changes dramatically at the resonance frequency, and the equivalent electromagnetic parameter exhibits anomalous characteristics in the two frequency bands. Firstly, the effects of the number of turns, the width of the copper wire, the spacing of the copper wire, and the length of the outermost edge of inner and outer helical coils are investigated, respectively, using the HFSS software on the resonance frequency of dual-frequency metamaterials, which improves the study of dual-frequency metamaterials with nested square spiral structure. Then, based on the results of the change rule of resonance frequency with the four types of influencing factors, the dual-frequency metamaterials with the real part of the equivalent permeability close to -1 at 6.78 MHz and 13.56 MHz are designed, which is of certain reference significance for the subsequent practical design of dual-frequency metamaterials to satisfy the needs of the project.

Solitons of the Twin-Core Couplers with Fractional Beta Derivative Evolution in Optical Metamaterials via Two Distinct Methods

The rapid advancements in metamaterial research have brought forth a new era of possibilities for controlling and manipulating light at the nanoscale. In particular, the design and engineering of optical metamaterials have created advances in the field of photonics, enabling the development of advanced devices with unprecedented functionalities. Among the myriad of intriguing metamaterial structures, the nonlinear directional couplers with beta derivative evolution have emerged as a significant avenue of exploration, offering remarkable potential for light propagation and manipulation. This study obtains the solitary wave solutions for twin-core couplers having spatial-temporal fractional beta derivative evolution by using two different methods, the Bernoulli method and the complete polynomial discriminant system method. By graphing some of the obtained solutions, the effect of the beta derivative has been shown. The findings would be beneficial to understand physical behaviours in nonlinear optics, particularly twin-core couplers with optical metamaterials.

Demonstration and Control of "Spoof-Plasmon" Scattering from 3D Spherical Metaparticles.

Geometries that replicate the behavior of metal nanostructures at much lower frequencies via texturing surfaces so they will support a surface wave have been a central pillar of metamaterials research. However, previous work has focused largely on geometries that can be reduced to symmetries in one or two dimensions, such as strips, flat planes, and cylinders. Shapes with isotropic responses in three dimensions are important for applications, such as radar scattering and the replication of certain nanoscale behaviors. This work presents a detailed exploration of the scattering behavior of 3D spherical "spoof plasmonic" metaparticles, based on the platonic solids. Their behavior is compared to an effective medium model through simulation and experiment, and the vast range of behaviors that can be produced from a metal sphere of a given radius via tuning its internal structure is explored in detail.

Acoustic metamaterial samples preparation for impedance tube measurements—The influence of different 3D printing techniques and mechanical post-processing on the simulation compliance

Prototyping of acoustic metamaterials frequently involves the use of additive manufacturing techniques. It offers the best price and the option for complex structure production, which is beneficial in the R&D process. Previously, some differences in acoustic metamaterial sound absorption measurement dispersions regarding using 3D printing techniques for sample preparation were noted. The sound absorption sensitivity on different printing settings or materials is usually omitted. The paper will present the research on the impedance tube measurements of absorbing metamaterial manufactured with different 3D printing methods and post-processed with mechanical and chemical treatment. Two approaches to metamaterial construction were analyzed in the current study—the single-solid metamaterial and the structure divided into parts, where the influence of assembly methods was investigated. To achieve the best compatibility with FEM or TMM modeling results, different post-processing techniques were involved, such as drilling, grinding, and sealant use. The presentation will describe the valuable paths used in sample preparation to achieve better compatibility between the measurements and simulations. The need for a comprehensive part preparation description in metamaterials research and papers will be discussed. [Work funded and supported by the Polish Government, National Centre of Research and Development, agreement no. LIDER/11/0065/L-12/20/NCBR/2021.]

Rapid validation of water wave metamaterials in a desktop-scale wave measurement system

Metamaterials have a unique ability to manipulate wave phenomena beyond their natural capabilities, and they have shown great promise in electromagnetic and acoustic wave control. However, their exploration in hydrodynamics remains limited. This article introduces a novel desktop-scale wave measurement system, specifically designed for the rapid prototyping and validation of water wave metamaterials. By utilizing 3D printing, the system accelerates the transition from theoretical designs to practical testing, offering a versatile and user-friendly platform. This is further enhanced by a synchronized stereo-camera setup and advanced data processing algorithms, enabling precise measurement and reconstruction of water wave behavior. Our experimental results demonstrate the system’s effectiveness in capturing intricate interactions between engineered structures and water waves. This significantly advances rapid prototyping for water wave metamaterial research, underscoring the system’s potential to catalyze further innovation in this emerging field.

Linear-frequency conversion with time-varying metasurfaces

Frequency conversion is a hallmark of nonlinearity. The spectral manifestations, emergent within a system, can typically be attributed to a marked nonlinearity within the material properties, complex geometric configurations, and/or the unique functional form of interactions taking place in the constitutive subsystems. These phenomena, irrespective of their origins, have been harnessed and exploited in applications ranging from the generation of entangled photons, a cornerstone in quantum technologies, to nanomechanical frequency mixing, advancing subsurface scanning probe microscopy. Here, we propose a frequency conversion mechanism based on time-varying metasurfaces, an emerging frontier in metamaterial research. We show how temporal properties of metasurfaces can effectively emulate a nonlinear medium, thereby facilitating frequency conversion. The proposed material configuration has the potential not only to advance integrated photonics and quantum optics, but also to create opportunities in quantum sensing, quantum materials, and crucially quantum communications. Published by the American Physical Society 2024

A review of acoustic metamaterials applied to noise control in civil engineering

Over the past 10 years, the research of acoustic metamaterials has branched out in many directions, presenting numerous potentially applicable geometries for the composition of noise control structures, such as structural resonators, acoustic resonators, and membranes. Therefore, keeping track of these multiple applications can be considered a rather difficult task. Moreover, the application of this novel concept in civil engineering has a high potential. In this context, an article review is proposed, identifying the most important acoustic metamaterial concepts that were applied or could be applied in civil engineering. The study performs a qualitative survey of articles in this segment, classifying the leading literature proposals, according to physical principles of cells working and to the facility of application in civil engineering, considering the production factors and construction implementation. It was found that the number of works with this focus is incipient when compared to the strictly theoretical works. A great number of articles contain dimensions and geometric propositions that feature difficulties of precise and large-scale manufacturing in the current civil construction scenario, which is traditionally less industrialized and technological. Finally, the advantages and disadvantages of the physical principles and acoustic structures were compared to point out ways that allow the development and popularization of acoustic metamaterials in civil engineering.

Tunable Epsilon‐and‐Mu‐Near‐Zero Metacomposites

AbstractEpsilon‐and‐mu‐near‐zero (EMNZ) metamaterials have garnered significant attention in near‐zero‐parameter metamaterial research for their exceptional ability to attain concurrent near‐zero permittivity and permeability. Nowadays achieving EMNZ properties through the use of metacomposites remains a novel endeavor. Presented here is an innovative approach of near‐zero‐parameter metacomposites, illustrating excellent and tunable EMNZ properties in the radio frequency regime. The self‐organization approach is applied to construct the conductive 3D network and the circuits, serving as the underlying framework for achieving EMNZ properties. Near‐zero permeability is effectively maintained while permittivity reaches epsilon‐near‐zero frequency regime. Efficient manipulation of electromagnetic parameters is initially realized via adjusting component content in metacomposites. Significantly, an excellent EMNZ property is observed as carbon content reaches 15 wt.% at 915 MHz. Through both numerical simulations and experimental testing, the PGC metacomposites have exhibited tunneling effects and directional emission characteristics, confirming their EMNZ properties. Besides, the Lego‐like adjustment facilitates the achievement of EMNZ property and advances the EMNZ frequency point to 700 MHz, expanding the EMNZ range. Furthermore, thanks to the remarkable excitation effect of photo‐induced adjustment, the metacomposite with low‐carbon content also achieves extraordinary EMNZ properties. This research offers promising self‐organized EMNZ metacomposites and lays the foundation for future endeavors in precisely adjusting near‐zero parameters.

Non‐Hermitian Topological Phononic Metamaterials

AbstractNon‐Hermitian (NH) physics describes novel phenomena in open systems that allow generally complex spectra. Introducing NH physics into topological metamaterials, which permits explorations of topological wave phenomena in artificially designed structures, not only enables the experimental verification of exotic NH phenomena in these flexible platforms, but also enriches the manipulation of wave propagation beyond the Hermitian cases. Here, a perspective on the advances in the research of NH topological phononic metamaterials is presented, which covers the exceptional points and their topological geometries, the skin effect related to the topology of complex spectra, the interplay of NH effects and topological states in phononic metamaterials, etc.

Acoustic and mechanical metamaterials for energy harvesting and self-powered sensing applications

Metamaterials are artificially engineered structures that exhibit extraordinary properties beyond the constituent materials, making them attractive for various applications in optics, acoustics, and mechanics. Energy harvesting is an eco-friendly technology that recycles ambient wave and mechanical energy by converting it into valuable electricity. The unique properties of metamaterials offer exciting opportunities to enhance energy harvesting performance by manipulating input wave direction and amplitude or increasing strain levels on energy conversion materials and devices. Recently, there has been a surge in research on incorporating energy manipulation capabilities of phononic crystals, locally-resonant acoustic metamaterials, and mechanical metamaterials into energy harvesting systems, including acoustic and elastic wave focusing and localization and mechanical energy trapping phenomena. In this review, we provide a classification of acoustic and mechanical metamaterials utilized for energy harvesting and self-powered sensing, followed by a comprehensive comparison of how each metamaterial has been integrated and the extent to which it contributes to quantitative improvements in energy and sensing performance. We also discuss the potential of unexplored metamaterials whose concepts are intriguing but have not yet been applied to energy harvesting or self-powered sensing, and discuss the vision and future direction of metamaterial research in this exciting field.

Metamaterial‐Augmented Head‐Mounted Audio Module

AbstractRecent developments in metamaterial research have shown promising progress in overcoming the fundamental physical limitations of acoustics. While the majority of this research is curiosity‐driven and focused on fundamental physics, there has been a scarcity of acoustic metamaterials research that can have a direct and immediate impact on real‐world applications. In this study, an acoustic metamaterial inside a head‐mounted audio module is incorporate to achieve a 3–7 dB broadband sound pressure level (SPL) improvement in the bass range (50–700 Hz), which is the most challenging frequency range for radiation enhancement. The adoption of the acoustic metamaterial not only enhances voltage sensitivity near the intrinsic metamaterial resonance frequency, but also extends the broadband enhancement to a lower transducer resonance frequency by carefully engineering the metamaterial‐transducer resonant coupling. The improvement of the audio module is demonstrated through fully coupled electrical‐mechanical‐acoustical numerical simulations using finite element analysis, which are validated against comprehensive measurements including electrical impedance analysis, speaker diaphragm displacement analysis, voltage sensitivity and power sensitivity analysis, and spectrogram. This study not only offers a promising path to improve the audio module quality without increasing the size, but also represents an important milestone toward using acoustic metamaterial research to solve audio industry challenges.