Metamaterial Array Research Articles

Experimental observation of multi-functional plasma-metamaterial composite for manipulation of electromagnetic-wave propagation

Although microwaves are widely used in our daily life, their propagations are left free with disordered absorption and scattering in most scenes, without any sophisticated controls of their paths. Microwave metamaterials have increased our regulation options in which cloaking is extensively studied, but their exploratory aspects so far are insufficient for multiple requests for wireless-communication availability in our daily life space. Here, we show our plasma-metamaterial composite device that becomes an absorber, a scatterer, or a flattener (including cloaking effects) by changing a narrow-range microwave frequency (2.6–3.1 GHz, in the middle of the S band). A radio frequency high-power input ranging to 400 W is used to generate plasma in vacant space in a metamaterial array, and this metamaterial creates a space with an abnormal permeability (μ) in which 0<μ<1, while the plasma works as a dynamic negative- or positive-permittivity (ε) medium with a spatial gradient. In this ε–μ parameter region, a state with negative ε is a significant source for absorbance, and scattering is dominant with a small positive value of ε. Among them, propagation flattening of microwaves mainly due to the cloaking condition takes place with the adequate set of μ and ε and suitable spatial gradient of refractive index. This microwave manipulation is experimentally verified by monitoring scattering energy of propagating microwaves.

Metamaterial array based meander line planar antenna for cube satellite communication

This research article presents a design and performance analysis of a metamaterial inspired ultra-high frequency (UHF) compact planar patch antenna for the CubeSat communication system that could be smoothly integrated with commercially available 2U Cube Satellite structure and onboard subsystem. The proposed antenna consists of two layers, one is two different width meander line antenna patch with partial ground plane and another layer is 3 × 2 near-zero-indexed metamaterial (NZIM) metamaterial array structure with ground plane. The NZIM array layer has been utilized to minimize the coupling effect with Cube Satellite structure and improve the frequency stability with enhanced antenna gain and efficiency. The fabricated antenna can operate within the lower UHF frequency band of 443.5–455 MHz. with an average peak gain of 2.5 dB. The designed antenna impedance stability characteristic has been explored after integration with the 2U Cube Satellite body layout. Besides, the antenna communication performance has been verified using 2U Cube Satellite free space path loss investigation. Small antenna volume with trade-off between the antenna size and performance are the key advantages of the proposed design, as the antenna occupies only 80 × 40 × 3.35 mm3 space of the 2U Cube Satellite body structure and the geometrical parameters can be designed to provide the best performance between 449 and 468.5 MHz.

Bi-functional metamaterial quadrilateral array with non-interfering anisotropy

We propose an anisotropic metamaterial quadrilateral array with metallic wires inserted in the perforated dielectrics over a ground plane, possessing the gradient index property and the epsilon-near-zero characteristic respectively in different polarization directions. As a result, such a metamaterial array possessing the non-interfering anisotropy features would be able to collimate electromagnetic fields as a zone plate reflector when we feed it at the focus in the broadside direction, while being capable of generating four directive beams as an ENZ lens when excited in the center. The proposed design of metallic-wire embedded perforated dielectrics can be effectively applied to building up versatile devices with more advanced functionalities that are fundamentally dependent on the anisotropic properties of hybrid metamaterials.

Double negative bend headed I-shaped metamaterial based Terahertz optical power splitter

Terahertz (THz) technology has piqued the interest of many researchers due to the fascinating characteristics of THz waves. Two new metamaterial array architectures are proposed in this paper to investigate power splitting via backward wave propagation. The first array pattern is a rectangular array arrangement, which is defined analytically and suggested as a power splitter in the TE (transverse electric) mode. From the proposed rectangular metamaterial array pattern, another cavity array structure was proposed which successfully increased DNG (double negative) response inside the metamaterial device and produced better splitting performance in the DNG condition. The unit cell and array patterns had almost identical effective parameter results, but some of them changed because the air-dielectric-metal combination was increased. The power splitter is demonstrated at the 0.91 THz frequency range where it shows the effective permittivity is −6, permeability is −6, and the refractive index is −6. At 0.94 THz, the DNG backward wave divider has negative effective parameters with an effective permittivity of −5.8, permeability of −5.8, and refractive index of −5.8.Both of the analytical structure patterns are proposed for optical power splitter and divider applications, which are used in various microwave circuits, such as mixers, balanced amplifiers, and antenna arrays.

Metamaterials subwavelength terahertz resonant cavities

One of the unique properties of metamaterials is the ability to manipulate electromagnetic waves at subwavelength scales, made possible by their structure on these scales. Here, rather than consider effective bulk properties, we consider the properties of microscopic features based on considering resonant unit cells. We used wire array metamaterials to form localized resonant cavities by changing the resonance frequency of one or more unit cells, surrounded by unchanged unit cells that do not support resonance for the propagating mode (i.e. forming a band gap). We validate our approach experimentally with electromagnetic waves in the terahertz range, demonstrating and characterizing subwavelength resonant cavities in this range. These resonant cavities can pave the way for ultra-compact subwavelength waveguides and other optical components.

Active Control of Nanodielectric-Induced THz Quasi-BIC in Flexible Metasurfaces: A Platform for Modulation and Sensing.

A bound state in the continuum (BIC) is a nonradiating state of light embedded in the continuum of propagating modes providing drastic enhancement of the electromagnetic field and its localization at micro-nanoscale. However, access to such modes in the far-field requires symmetry breaking. Here, it is demonstrated that a nanometric dielectric or semiconductor layer, 1000times thinner than the resonant wavelength (λ/1000), induces a dynamically controllable quasi-bound state in the continuum (QBIC) with ultrahigh quality factor in a symmetric metallic metasurface at terahertz frequencies. Photoexcitation of nanostrips of germanium activates ultrafast switching of a QBIC resonance with 200% transmission intensity modulation and complete recovery within 7 ps on a low-loss flexible substrate. The nanostrips also form microchannels that provide an opportunity for BIC-based refractive index sensing. An optimization model is presented for (switchable) QBIC resonances of metamaterial arrays of planar symmetric resonators modified with any (active) dielectric for inverse metamaterial design that can serve as an enabling platform for active micro-nanophotonic devices.

A broadband acoustic panel based on double-layer membrane-type metamaterials

Low-frequency noise is a growing problem in large structures of modern transportation technologies. In this study, we report a large-scale acoustic panel made of double-layer membrane-type metamaterials (DMAMs) for broadband noise reduction. A complete theoretical model based on the unit cell is fully developed and extended for finite multi-celled membrane-type acoustic metamaterial (MAMs) array. A large-scale acoustic panel constructed from 8 × 8 DMAM unit cells is proposed. To deal with the global compliance of the large-scale support structure, the double-layer panel frame structure with large bending stiffness is designed to shift the global resonances to higher frequencies and provide an efficient way to well maintain the MAM's performance. Moreover, the double-layer configuration further guarantees ultra high transmission loss within the frequency range of interest. Experiments are carried out to validate the analytical and numerical predictions. Excellent transmission loss ranging from 20 to 59 dB within ten third octave bands (0.32–2.5 kHz) is observed, deeply breaking the mass density law. We believe the proposed design and the associated theoretical model could serve as an efficient tool for designing acoustic metamaterial-based panels and soundproof walls with high noise reduction in low/middle frequency regions.

3D Printed Metamaterial Capacitive Sensing Array for Universal Jamming Gripper and Human Joint Wearables

The metamaterial sensor array has the ability to conform to a spherical surface as shown. The slight separation between the array and the sphere implies that the array is not only limited to a spherical surface but can conform to other curved surfaces. A blown-up view shows capacitive sensor electrodes being embedded within the metamaterial sensor array. Further details can be found in the article, number 2001082, by Jian Zhu, Wen Feng Lu, and co-workers.

Advanced Electromagnetic Metamaterials for Temperature Sensing Applications

Metamaterials with novel properties have excited much research attention in the past several decades. Many applications have been proposed and developed for the reported metamaterials in various engineering areas. Specifically, for the resonant-type metamaterials with narrow resonance line width and strong resonance strength, the resonant frequency and strength are highly depended on the changings of meta-atom structure and/or substrate media properties induced by the environment physical or chemistry parameters varying. Therefore, physical or chemistry sensing applications for the resonant-type metamaterial units or arrays are developed in recent years. In this mini review, to help the researchers in those fields to catch up with the newly research advances, we would like to summarize the recently reported high-performance metamaterial-inspired sensing applications, especially the temperature sensing applications, based on different kinds of metamaterials. Importantly, by analyzing the advantages and disadvantages of several conventional metamaterial units, the newly proposed high quality-factor metamaterial units are discussed for high-precision sensing applications, in terms of the sensitivity and resolution. This mini review can guide researchers in the area of metamaterial-inspired sensors to find some new design routes for high-precision sensing.

Electrically Tunable Left-Handed Textile Metamaterial for Microwave Applications.

An electrically tunable, textile-based metamaterial (MTM) is presented in this work. The proposed MTM unit cell consists of a decagonal-shaped split-ring resonator and a slotted ground plane integrated with RF varactor diodes. The characteristics of the proposed MTM were first studied independently using a single unit cell, prior to different array combinations consisting of 1 × 2, 2 × 1, and 2 × 2 unit cells. Experimental validation was conducted for the fabricated 2 × 2 unit cell array format. The proposed tunable MTM array exhibits tunable left-handed characteristics for both simulation and measurement from 2.71 to 5.51 GHz and provides a tunable transmission coefficient of the MTM. Besides the left-handed properties within the frequency of interest (from 1 to 15 GHz), the proposed MTM also exhibits negative permittivity and permeability from 8.54 to 10.82 GHz and from 10.6 to 13.78 GHz, respectively. The proposed tunable MTM could operate in a dynamic mode using a feedback system for different microwave wearable applications.

3D Printed Metamaterial Capacitive Sensing Array for Universal Jamming Gripper and Human Joint Wearables

Existing stretchable capacitive sensor arrays face challenges in decoupling normal forces and stretch stimuli which restrict its applications into soft robotics. Herein, a metamaterial capacitive sensor array with 6 × 6 sensors is developed for the detection of normal forces on curved deforming surfaces common to both the soft universal jamming gripper and human elbow. The fabrication process involves the 3D printing of carbon black thermoplastic polyurethane (PI–ETPU) electrodes and thermoplastic polyurethane (TPU) insulation based on commercially available multimaterial fused deposition modeling (FDM). This metamaterial capacitive sensor array is unaffected by a uniaxial stretch of up to 21.6% and remains capable of detecting normal forces. The sensor array structure possesses a negative Poisson's ratio which is desirable for improving compliance and conformability to adhered expanding surfaces. Consequently, normal force‐distribution and proximity detection capabilities on curved deforming surfaces are demonstrated on a soft universal jamming gripper for measuring gripping forces and identifying object shapes. Conformal force‐sensing joint wearable on a human elbow with an individualized Poisson's ratio is explored as another application. The possibility of programming Poisson's ratio of a metamaterial capacitive sensing array opens new avenues for potential sensing applications into soft robotics and personalized wearables.

A Portable Electromagnetic Head Imaging System Using Metamaterial Loaded Compact Directional 3D Antenna

A non-invasive, low-powered, and portable electromagnetic (EM) head imaging system is presented using metamaterial (MTM) loaded compact directional 3D antenna. The antenna consists of two slotted dipole elements with $2\times 3$ and $3\times 3$ finite MTM array elements in top and ground, respectively, and folded parasitic elements that operate within the frequency range of 1.12 GHz to 2.5 GHz. The MTM array elements are optimized to enhance the overall performance regarding antenna bandwidth, realized gain, efficiency, and directionality in both free space and proximity to the head model. The mathematical modelling is also analyzed to justify the integration of MTM unit cells to the top and ground side of the antenna. The impact of MTM on SAR analysis is also performed. A tissue-mimicking 3D head phantom is fabricated and measured to validate the antenna performance. A nine-antenna portable setup is used with the fabricated phantom to measure and collect the scattering parameters that are later analyzed to detect and reconstruct the haemorrhage images by applying the updated IC-CF-DMAS algorithm. The overall performance demonstrates the feasibility of the proposed system as a portable platform to successfully detect, locate and monitor the haemorrhages inside the head in EM imaging system.

Molecular Chirality Detection with Periodic Arrays of Three-Dimensional Twisted Metamaterials.

Rapid detection of the handiness of chiral molecules is an important topic for pharmaceutical industries because chiral drugs with opposing handiness sometimes exhibit unwanted side effects. In this research, a rapid optical method is proposed to determine the handiness of the chiral drug "Thalidomide". The platform is a large array of three-dimensional (3D) twisted metamaterials fabricated with a novel method by combining nanospherical-lens lithography (NLL) and hole-mask lithography (HML). The fabrication is high-throughput and the twisted metamaterials cover a large area. Strong circular dichroism (CD) response is observed in the near-infrared (NIR) region, which enables the chiral detection to be performed by a low-cost and portable spectroscope system. The proposed nanofabrication method significantly improves the capabilities of NLL and HML, which can be quickly adapted to fabricate various periodic 3D metamaterials. In addition, the results of this research pave the road for the rapid penetration of nanophotonics into the pharmaceutical industries.

Active tunable THz metamaterial array implemented in CMOS technology

Terahertz (THz) modulators offer multifaceted capabilities for various practical applications such as THz imaging, wireless communications, sensing, etc. However, compared to the modulation devices used for other electromagnetic bands, the ubiquitous proliferation of THz applications is severely impeded by the tremendous lack of complementary metal-oxide-semiconductor (CMOS)-compatible technology. Here we demonstrated a CMOS-based active tunable THz metamaterial array (C-ATTMA) with split-ring resonators (SRRs). The THz metamaterial can be externally controlled with an electrically controlled dynamic. The C-ATTMA fabricated by the 180 nm CMOS technology featuring a resonant frequency of 0.30 THz was connected to the source and drain of a bottom metal-oxide-semiconductor field-effect transistor (MOSFET) through the vias. By delicately controlling the MOSFET gate voltage, the equivalent circuit response of the C-ATTMA was actively engineered, enabling tailoring THz resonance frequencies. Under a gate voltage of 1.8 V, we successfully realized a resonant frequency shift of ∼35 GHz and 3° phase shift. The equivalent circuit successfully explained the principle of the change. Inductor–capacitor (LC) resonance and electric dipole resonance of single-layer and double-layer SRRs have also been studied. The exhibited CMOS-compatible electrically regulated THz metamaterials provided a potential method for voltage regulation of THz, which may contribute to THz wireless communications, information encryption, THz compressed sensing and imaging, etc.

Sound energy enhancement via impedance-matched anisotropic metamaterial

Sound energy enhancement realized by electronic circuit designs plays a vital part in many fields, including acoustic communication, medical imaging, acoustic positioning and sound energy harvesting. The same effect, actually, can be achieved based on anisotropic acoustic meta-structures without electronic components, which has rarely been studied before. Fabricated by 3D printing technology, a two-way spiral-shaped metamaterial and its two-dimensional array are designed in the study, which is capable to realize sound energy enhancement. Due to the impedance matching design, the meta-structure shows almost opposite transmission behaviors in orthogonal directions. The sound wave compression and resonance effects come from the high-refractive-index medium, leading to enlarged acoustic signals inside the waveguide. For the array with an inside point sound source, an energy enhancement phenomenon occurs in the wave emission area outside the structure. Through experimental results and numerical simulations, it is revealed that the sound intensity of the emission wave can be increased more than fifteen-fold compared with the insulation condition in the range of 4.8–5.8 kHz, when the anisotropic metamaterial array is applied. The flexibility of the anisotropic meta-structure and corresponding array designs enables versatile applications demanding excellent sound signal and broadband performance.

WS2 Monolayers Coupled to Hyperbolic Metamaterial Nanoantennas: Broad Implications for Light–Matter-Interaction Applications

Due to their atomic layer thickness, direct bandgap, mechanical robustness and other superior properties, transition metal dichalcogenides (TMDCs) monolayers are considered as an attractive alternative to graphene for diverse optoelectronic applications. Yet, due to the very nature of atomic layer thickness, the interaction of light with TMDCs is limited, hindering overall efficiency for optical applications. Therefore, in order for TMDCs to become a true candidate as the material of choice for optoelectronics, there is a need for a mechanism which significantly enhances the interaction of light with TMDCs. In this paper, we demonstrate about 30-fold enhancement of the overall photoluminescence emission intensity from a WS2 monolayer, by its coupling to a hyperbolic metamaterial nanoantenna array. This enhancement corresponds to nearly 300-fold enhancement per individual nanoantenna. This overall enhancement is achieved by the combination of enhancing the excitation (absorption) efficiency, alongside with enhancing the radiative decay rate. Our result paves the way for the use of TMDCs in diverse optoelectronic applications, ranging from light sources and photodetectors to saturated absorbers and nonlinear media.

Effect of Metamaterial Cells Array on a Microstrip Patch Antenna Design

Abstract In this paper, a microstrip patch antenna (MPA) design was developed to verify the performance of a metamaterial cell array (MTM) Capacitive Loaded Loop (CLL) immersed in the substrate. The metamaterial was obtained from metal laminates designed inside a dielectric material, with dimensions carefully calculated to have the effective negative permittivity and permeability, consequently the negative refractive index, in a certain frequency range. In this case, the geometric control of the unit cell parameters allowed its organization in a periodic arrangement to be immersed in the MPA substrate. Simulated and experimental results were obtained and compared for some parameters of the antenna, which showed a good relationship between MTM and MPA performance.

Homogenization of 3D metamaterial particle arrays for oblique propagation via a point-dipole analysis

A rigorous technique for the consistent calculation of the effective parameters of infinite three-dimensional metamaterial particle arrays in the realistic case of oblique wave propagation, is presented in this paper. The extracted polarizabilities of the consisting scatterer and the numerically retrieved wavenumber for the obliquely propagating electromagnetic waves are systematically inserted into a properly modified first-principles homogenization technique, thus leading to the characterization of the effective medium. Finally, the proposed methodology is applied to two popular, anisotropic metamaterial resonators.

Active Metamaterial Antenna With Beam Scanning Manipulation Based on a Digitally Modulated Array Factor Method

In this communication, we report the scanning manipulation on radiation beams with an active metamaterial (MTM) antenna using p-i-n diode switches. Thanks to the MTM antenna possessing periodical configuration with isolated units, p-i-n diodes in each unit are capable of being actuated individually with OFF/ON-states (coding sequences 0/1), equivalently tuning the phase constant β of each cell either in state β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> or state β <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> . Therefore, for MTM array with a certain number of units, we can obtain plenty of tunable states presented via digitally coding sequence combinations, thereby manipulating beam scanning in a fixed frequency band. Especially, for the first time, we propose the digitally modulated array factor (DMAF) method for the MTM array: introducing unit-cell dispersion curves of both 0/1 states to the array factor, thus, map the digitally coding sequences linearly to the scanning beams at a fixed frequency, resulting in scanning functionalities. Experiments are implemented with applying micro-control-unit (MCU) to the active MTM antenna for driving p-i-n diodes, and measurements demonstrate beam scanning continuously from -30° to +30° at fixed frequencies around 5 GHz, validating the proposed method.

Active metamaterial polarization modulators for the Terahertz frequency range

Active control of chirality in the terahertz frequency range is of great importance in many scientific areas, which include research into fundamental optical phenomena, investigation of novel materials, spectroscopy, imaging, wireless communications and chemistry. The lack of efficient, integrated and fast-reconfigurable polarization modulators has hindered, so far, the full exploitation of applications in all the aforementioned fields. Metamaterials are artificial resonant elements possessing unique remarkable properties such as high efficiency and miniaturization capability. The interplay of metallic metamaterial arrays with electrostatically tunable monolayer graphene has been demonstrated to be a valid approach for the realization of a novel class of THz devices. In this work, the realization of active chiral graphene/metamaterial modulator is presented. The versatility of this experimental approach allowed the device integration with broadband sources such as terahertz time domain spectrometers as well as with quantum cascade lasers. A continuous rotation of the polarization plane > 30° has been reported with a reconfiguration speed > 5 MHz. These results pave the way to the integration of fast terahertz polarization modulators in all the applications where these devices are in great demand.