Metamaterial Blocks Research Articles

Laminated miniaturized low-frequency metamaterial block for near-field wireless power transmission applications

Laminated miniaturized low-frequency metamaterial block for near-field wireless power transmission applications

Selective superinvisibility effect via compound anapole

We introduce a general concept and consider a characteristic approach to obtain the narrow-band suppression of total electromagnetic scattering independent of the irradiation conditions for the compound dielectric structures supporting unique anapole states. To emphasize this independence from the irradiation conditions, we call the selective superinvisibility effect. We show that the realization of this concept allows us to reach simultaneously several goals significantly suppress the scattering (at a certain wavelength); provide the scattering suppression for any polarization and direction of incidence waves; accumulate electromagnetic energy in the near-field zone and inside of the scatterer. The combination of these physical properties in a compound structure makes it possible to consider them as building blocks for two-dimensional or three-dimensional metamaterials with the selective transparent property practically independent of the irradiation conditions. Our study includes theoretical modeling based on a multipole approach and a corresponding experimental verification.

Bio-Inspired Nanomembranes as Building Blocks for Nanophotonics, Plasmonics and Metamaterials.

Nanomembranes are the most widespread building block of life, as they encompass cell and organelle walls. Their synthetic counterparts can be described as freestanding or free-floating structures thinner than 100 nm, down to monatomic/monomolecular thickness and with giant lateral aspect ratios. The structural confinement to quasi-2D sheets causes a multitude of unexpected and often counterintuitive properties. This has resulted in synthetic nanomembranes transiting from a mere scientific curiosity to a position where novel applications are emerging at an ever-accelerating pace. Among wide fields where their use has proven itself most fruitful are nano-optics and nanophotonics. However, the authors are unaware of a review covering the nanomembrane use in these important fields. Here, we present an attempt to survey the state of the art of nanomembranes in nanophotonics, including photonic crystals, plasmonics, metasurfaces, and nanoantennas, with an accent on some advancements that appeared within the last few years. Unlimited by the Nature toolbox, we can utilize a practically infinite number of available materials and methods and reach numerous properties not met in biological membranes. Thus, nanomembranes in nano-optics can be described as real metastructures, exceeding the known materials and opening pathways to a wide variety of novel functionalities.

Metamaterial-enabled arbitrary on-chip spatial mode manipulation

On-chip spatial mode operation, represented as mode-division multiplexing (MDM), can support high-capacity data communications and promise superior performance in various systems and numerous applications from optical sensing to nonlinear and quantum optics. However, the scalability of state-of-the-art mode manipulation techniques is significantly hindered not only by the particular mode-order-oriented design strategy but also by the inherent limitations of possibly achievable mode orders. Recently, metamaterials capable of providing subwavelength-scale control of optical wavefronts have emerged as an attractive alternative to manipulate guided modes with compact footprints and broadband functionalities. Herein, we propose a universal yet efficient design framework based on the topological metamaterial building block (BB), enabling the excitation of arbitrary high-order spatial modes in silicon waveguides. By simply programming the layout of multiple fully etched dielectric metamaterial perturbations with predefined mathematical formulas, arbitrary high-order mode conversion and mode exchange can be simultaneously realized with uniform and competitive performance. The extraordinary scalability of the metamaterial BB frame is experimentally benchmarked by a record high-order mode operator up to the twentieth. As a proof of conceptual application, an 8-mode MDM data transmission of 28-GBaud 16-QAM optical signals is also verified with an aggregate data rate of 813 Gb/s (7% FEC). This user-friendly metamaterial BB concept marks a quintessential breakthrough for comprehensive manipulation of spatial light on-chip by breaking the long-standing shackles on the scalability, which may open up fascinating opportunities for complex photonic functionalities previously inaccessible.

High-FOM Temperature Sensing Based on Hg-EIT-Like Liquid Metamaterial Unit.

High-performance temperature sensing is a key technique in modern Internet of Things. However, it is hard to attain a high precision while achieving a compact size for wireless sensing. Recently, metamaterials have been proposed to design a microwave, wireless temperature sensor, but precision is still an unsolved problem. By combining the high-quality factor (Q-factor) feature of a EIT-like metamaterial unit and the large temperature-sensing sensitivity performance of liquid metals, this paper designs and experimentally investigates an Hg-EIT-like metamaterial unit block for high figure-of-merit (FOM) temperature-sensing applications. A measured FOM of about 0.68 is realized, which is larger than most of the reported metamaterial-inspired temperature sensors.

Acoustic computational metamaterials

<p indent="0mm">Although digital signal processors have been widely used to perform complex computing tasks, they still suffer from some limitations, including the complexity, low speed, and high-power consumption caused by expensive analog-to-digital converters. For this reason, there has recently been a strong interest in wave-based analog computing, which avoids analog-to-digital conversion and can perform massively parallel operations, especially based on artificially designed metamaterials. A new analog computing scheme based on sound waves has been proposed. This computing system, called computational metamaterials, can be as fast as the wave speed and as small as the wavelength. It can perform complex mathematical operations on incoming wave packets, and can even perform calculations on integral and differential equations. These functions are expected to realize a new generation of ultra-fast, compact and efficient computing hardware based on sound wave propagation. The development of acoustic computing metamaterials has gone from the computation of a single mathematical operation, the tunable design and computing circuit and computational network that integrate multiple computing blocks, to the topological insulator computational metamaterial proposed for the robustness of computation. The computation of a single mathematical operation can be divided into space and time domain. The difference of main design principles is dimension of time and space. The spatial acoustic computational metamaterials mainly require the realization of spatial distribution of Green’s function of required calculation in materials. And the time-domain acoustic computational metamaterial needs to design the frequency spectrum to realize the transfer function. Both the space domain and the time domain acoustic computing metamaterials realize operations, such as integration, derivative, and differential equations. The proposed tunable acoustic computational metamaterials are aimed at the problem that the function of the metamaterials cannot be changed while the structure is fixed. By introducing tunable parameters into the metamaterial, it realizes the integration of integral, derivative and other functions on the same metamaterial. The proposal of acoustic metamaterial calculation circuit and calculation network has raised the complexity of metamaterial calculation by another dimension. By introducing the design of acoustic circuit components, such as acoustic switches, the sound waves are controlled to propagate in different circuits, and complex operations, such as series and parallel connection of multiple different metamaterial blocks are realized. Acoustic metamaterial computing network combines the design ideas of acoustic holography and convolutional neural network (CNN). Each pixel unit of the metamaterial is equivalent to a neuron in the CNN, and the propagation of sound waves between different metamaterial layers in the medium is equivalent to the signal propagation between neurons in different layers. Through training and learning, machine learning tasks, such as handwritten number recognition, have been completed. In view of the computational robustness, the proposed topological insulator computational metamaterials, by introducing the boundary mode of topological protection, ensure that the acoustic computational metamaterials can still guarantee the accuracy of the calculation even when the structure parameter is disturbed. In the future, the research of nonlinear computational metamaterials will receive more and more attention, and it will be possible to apply to the fields of nonlinear equation solving, nonlinear filtering, image processing methods and so on. In this review, we discussed the latest developments in the field of acoustic computational metamaterials and studied the latest superstructures used to perform analog computing. We further introduced the applications of acoustic computational metamaterials, including image processing, edge detection, equation solving, and machine learning. Finally, we look forward to key research issues and possible future directions.

Broadband microwave coding metamaterial absorbers

In this paper, a broadband metamaterial microwave absorber is designed, simulated and measured. Differently from the traditional method which is only based on unit cell boundary conditions, we carried out full-wave finite integration simulations using full-sized configurations. Starting from an elementary unit cell structure, four kinds of coding metamaterial blocks, 2 × 2, 3 × 3, 4 × 4 and 6 × 6 blocks were optimized and then used as building blocks (meta-block) for the construction of numerous 12 × 12 topologies with a realistic size scale. We found the broadband absorption response in the frequency range 16 GHz to 33 GHz, in good agreement with the equivalent medium theory prediction and experimental observation. Considering various applications of metamaterials or metamaterial absorbers in the electromagnetic wave processing, including the radars or satellite communications, requires the frequency in the range up to 40 GHz. Our study could be useful to guide experimental work. Furthermore, compared to the straightforward approach that represents the metamaterials configurations as 12 × 12 matrices of random binary bits (0 and 1), our new approach achieves significant gains in the broadband absorption. Our method also may be applied to the full-sized structures with arbitrary dimensions, and thus provide a useful tool in the design of metamaterials with specific desired frequency ranges.

Practical realisation of an active acoustic metamaterial building block

Acoustic metamaterials (AMMs) have been demonstrated as an alternative approach to achieving high levels of noise control using an array of subwavelength unit cells, exhibiting behaviour not seen in conventional materials. Specifically, active AMMs offer the potential for greater levels of broadband wave manipulation, tunability and adaptability. However, determining the optimal control source strengths that achieve broadband negative effective material properties is not straightforward. This study presents a practical method of designing an active system that directly minimises the effective material properties. The optimal control source strengths required for both single monopole and single dipole control sources to minimise the effective bulk modulus and the effective density respectively have been calculated via an optimisation procedure. The ability of the proposed active AMM building blocks to achieve broadband negative effective material properties is tested experientially through offline simulations using measured frequency responses. Interestingly, the optimised single monopole and optimised single dipole control sources achieve broadband negative effective bulk modulus and density respectively. However, when combining the two optimised control sources, the active control system only achieves bands of double negativity and, thus, only exhibits bands of negative refractive index.

Acoustic metamaterial blocks nearly all sound

Acoustic metamaterial blocks nearly all sound

Multifunction acoustic modulation by a multi-mode acoustic metamaterial architecture

Exotic acoustical features, like acoustic transparency, ultrasonic beam focusing, acoustic band gap and super lensing capability using a single metamaterial architecture is unconventional and unprecedented in the literature, demonstrated herein. Conventional metamaterials can focus an ultrasonic beam at specific frequency which results into unwanted distortion of the output wave fields at neighboring sonic frequencies in the host medium. However, ultrasonic wave focusing by virtue of negative refraction and simultaneous transparency of the metamaterial at sonic frequencies are uncommon due to their frequency disparity. To circumvent this problem and to avoid the unwanted distortion of wave at sonic frequencies, metamaterial with an array of butterfly-shaped thin ring resonators are proposed to achieve the beam focusing at ultrasonic frequency (37.3 kHz) and keep the structure transparent to the sonic frequencies (<20 kHz). The butterfly metamaterial with local ring resonators or butterfly crystals (BC) were previously proposed to create wide band gaps (∼7 kHz) at ultrasonic frequencies above 20 kHz. However, in this study a unique sub-wavelength scale wave focusing capability of the butterfly metamaterial utilizing the negative refraction phenomenon is demonstrated, while keeping the metamaterial block transparent to the propagating wave at lower sonic frequencies below the previously reported bandgaps.

Carbon aerogels towards new candidates for double negative metamaterials of low density

While metal is commonly used to construct electromagnetic metamaterials, herein carbon aerogel constitutes the first example of application as building blocks for metamaterials of low density. The carbon aerogel is synthesized by the sol-gel polymerization of resorcinol with formaldehyde followed by supercritical fulid drying and carbonization. The resulting nanostructure of carbon aerogel is adjusted by the concentrations of the reactants and catalysts in precursor solutions. Negative permittivity and negative permeability are simultaneously achieved in the low density carbon aerogel. The plasma-like negative permittivity is explained well by the low frequency plasmonic state in carbon networks. Equivalent circuit models and conductivity property indicate that permittivity values have heavy dependence on the framework and micropores of carbon aerogel. Negative permeability is attributed to the high-frequency magnetic response of induced circulating currents. The calculation analysis indicates that permeability values have a linear relation with (ω)0.5, showing a relaxation-type spectra unlike “magnetic plasma” of typical metamaterials. This work offers a novel and potentially powerful route for constructing metamaterials with ultralow density at the nanoscale, and can expand the potential applications of metamaterials especially under extreme conditions.

RCS reduction for grazing incidence based on coding metasurface

A coding metasurface is proposed for reducing radar cross section (RCS) under grazing incidence. Two elements with different reflection phases are selected for the metasurface, and 7 × 7 artificial magnetic conductor unit cells are utilised to construct a metamaterial block. Then the arrangement of blocks is optimised by particle swarm algorithm (PSA). The phase difference between two elements contributes to RCS reduction under grazing incidence. The obtained results demonstrate that a wideband RCS reduction is achieved by the coding metasurface ranging from 6 to 13 GHz. In addition, the monostatic RCS reduction is also achieved under a grazing incidence. For x-polarised incidence, the monostatic RCS reduction is >6 dB from 77° to 90°. For y-polarised incidence, the monostatic RCS reduction is >6 dB from 69° to 80°, and the maximum reduction is 17.5 dB under the 75° incident angle.

Integration in analog optical computing using metasurfaces revisited: toward ideal optical integration

In this paper, we introduce a modified optical integrator based on suitably designed metamaterial blocks. The integration is performed on an impinging wave pattern as it propagates through these blocks. So far, various metamaterial-based optical integrators have been implemented with appropriate performance in the case of zero-DC input signals. However, these integrators suffer from low accuracy when fed by signals rich in low-frequency contents. The latter property arises from truncation of low-frequency contents of the input wave in the Fourier domain. To solve this shortcoming, we propose a new metasurface-based structure which reflects low-frequency parts of the input signal in the Fourier domain. This subtracted part is then measured in the input and compensated in the detected output signal. The numerically simulated output responses verify superior performance of the proposed structure compared to conventional metamaterial-based optical integrator in the case of input signals with considerable low-frequency contents. These findings may lead to remarkable achievements in light-based plasmonic signal processors at nanoscale, which can replace their bulky conventional dielectric lens-based counterparts.

Design and Realization of Virtual Line Source Using Metamaterials

A metamaterial-embedded 2-D electric line source radiating inside a ground recess is presented. The media embedding a recessed antenna is designed based on transformation electromagnetics (TE) such that the embedded antenna yields the same far-field radiation characteristics as an antenna over a flat conducting ground plane, i.e., forming a virtual antenna. The transformation media comprise a negative-index superlens of finite dimensions and anisotropic impedance-matching blocks. Resonant inclusion-based metamaterials are designed at 5 GHz for their realization using standard printed-circuit technologies. Required metamaterial blocks are assembled for an effective 2-D TE-polarized configuration in a parallel-plate waveguide simulator. Field-mapping measurement confirms formation of a virtual radiator above the ground.

Three-Dimensional Simultaneous Arbitrary-Way Orbital Angular Momentum Generator Based on Transformation Optics.

In wireless communications, people utilize the technology of diversity against multipath fading, so as to improve the reliability of communication equipment. One of the long-standing problems in diversity antennas is the limited number of diversity in a certain space. In this paper, we provide a solution to this issue by a three-dimensional (3D) simultaneous arbitrary-way orbital angular momentum (OAM) generator (3D SAWOG) based on transformation optics. The proposed 3D SAWOG consists of a metamaterial block and a group of transformation cylinders, by which arbitrary-way planar wavefronts can be converted to helical wavefronts with various topological charges simultaneously. The 2D four-way OAM generator and the 3D SAWOG are analyzed, designed, and simulated. The simulation results validate the performance of a 3D SAWOG successfully, indicating that the proposed model possess a high mode purity and expansibility. The SAWOG can be used as a novel diversity antenna array due to the orthogonal property among different modes, which could provide more degrees of freedom than traditional dual-polarization antennas, further improving the reliability of the communication systems.

Asymmetric backscattering from the hybrid magneto-electric meta particle

The optical theorem relates the total scattering cross-section of a given structure with its forward scattering, but does not impose any restrictions on other directions. Strong backward-forward asymmetry in scattering could be achieved by exploring retarded coupling between particles, exhibiting both electric and magnetic resonances. Here, a hybrid magneto-electric particle (HMEP), consisting of a split ring resonator acting as a magnetic dipole and a wire antenna acting as an electric dipole, is shown to possess asymmetric scattering properties. When illuminated from opposite directions with the same polarization of the electric field, the structure has exactly the same forward scattering, whereas the backward scattering is drastically different. The scattering cross section is shown to be as low as zero at a narrow frequency range when illuminated from one side, while being maximal at the same frequency range when illuminated from the other side. Theoretical predictions of the phenomena are supported with both numerical and experimental conformations, obtained at the GHz frequency range, and all are in a good agreement with each other. HMEP meta-particles could be used as building blocks for various metamaterials assembling solar cells, invisibility cloaks, holographic masks, etc.

Solving constant-coefficient differential equations with dielectric metamaterials

Recently, the concept of metamaterial analog computing has been proposed (Silva et al 2014 Science 343 160–3). Some mathematical operations such as spatial differentiation, integration, and convolution, have been performed by using designed metamaterial blocks. Motivated by this work, we propose a practical approach based on dielectric metamaterial to solve differential equations. The ordinary differential equation can be solved accurately by the correctly designed metamaterial system. The numerical simulations using well-established numerical routines have been performed to successfully verify all theoretical analyses.

Tunable beam steering enabled by graphene metamaterials.

We demonstrate tunable mid-infrared (MIR) beam steering devices based on multilayer graphene-dielectric metamaterials. The effective refractive index of such metamaterials can be manipulated by changing the chemical potential of each graphene layer. This can arbitrarily tailor the spatial distribution of the phase of the transmitted beam, providing mechanisms for active beam steering. Three different beam steerer (BS) designs are discussed: a graded-index (GRIN) graphene-based metamaterial block, an array of metallic waveguides filled with graphene-dielectric metamaterial and an array of planar waveguides created in a graphene-dielectric metamaterial block with a specific spatial profile of graphene sheets doping. The performances of the BSs are numerically analyzed, showing the tunability of the proposed designs for a wide range of output angles (up to approximately 70°). The proposed graphene-based tunable beam steering can be used in tunable transmitter/receiver modules for infrared imaging and sensing.

Quasi-conformal transformation optics with elasto-electromagnetic metamaterials: Design algorithm

We report here a design method that is used to determine the initial shapes of elasto-electromagnetic metamaterial blocks with respect to the given shape of a hiding object when these blocks are applied to the problem of carpet cloaking. Starting from the inhomogeneous permittivity distribution of a cloak, derived using transformation optics, we use an inverse process to design the initial shape of a uniform permittivity material for an arbitrary value of Poisson's ratio in the range from −1 to 0.5. Then, by elastic compression of the initially uniform metamaterial, we obtain the inhomogeneous permittivity distribution that is required for cloaking. Our design method is then experimentally verified by measurements of the electric field profiles in smart metamaterial cloaks.

Magnetic Purcell factor in wire metamaterials

We present an experimental study of the magnetic Purcell effect in finite arrays of the wire metamaterial. By directly measuring the spatial-frequency map of the Purcell factor, we explicitly demonstrate how the Purcell factor is enhanced at the Fabry-Pérot resonances of the wire metamaterial block in microwave frequency range. The experimental results are in a good agreement with theoretical and numerical estimations.