Metamaterial Unit Cell Research Articles

One-Dimensional Photonic Crystals Comprising Two Different Types of Metamaterials for the Simple Detection of Fat Concentrations in Milk Samples

In this study, we demonstrate the reflectance spectrum of one-dimensional photonic crystals comprising two different types of metamaterials. In this regard, the designed structure can act as a simple and efficient detector for fat concentrations in milk samples. Here, the hyperbolic and gyroidal metamaterials represent the two types of metamaterials that are stacked together to construct the candidate structure; meanwhile, the designed 1D PCs can be simply configured as [G(ED)m]S. Here, G refers to the gyroidal metamaterial layers in which Ag is designed in a gyroidal configuration form inside a hosting medium of TiO2. In contrast, (ED) defines a single unit cell of the hyperbolic metamaterials in which two layers of porous SiC (E) and Ag (D) are combined together. It is worth noting that our theoretical and simulation methodology is essentially based on the effective medium theory, characteristic matrix method, Drude model, Bruggeman’s approximation, and Sellmeier formula. Accordingly, the numerical findings demonstrate the emergence of three resonant peaks at a specified wavelength between 0.8 μm and 3.5 μm. In this context, the first peak located at 1.025 μm represents the optimal one regarding the detection of fat concentrations in milk samples due to its low reflectivity and narrow full bandwidth. Accordingly, the candidate detector could provide a relatively high sensitivity of 3864 nm/RIU based on the optimal values of the different parameters. Finally, we believe that the proposed sensor may be more efficient compared to other counterparts in monitoring different concentrations of liquid, similar to fats in milk.

Mechano-adaptive meta-gels through synergistic chemical and physical information-processing

Global functional adaptation after local mechanical stimulation, as in mechanobiology and the mimosa plant, is fascinating and ubiquitous in nature. This is achieved by locally sensing mechanical deformation with precise thresholds, processing this information via biochemical circuits, followed by downstream actuation. The integration of such embodied intelligence allowing for mechano-to-chemo-to-function information-processing remains elusive in man-made systems. By merging the fields of chemical circuits and metamaterials, we introduce adaptive metamaterial hydrogels (meta-gels) that can accurately sense mechanical stimuli (local touch and global strain), transmit this information over long distances via reaction-diffusion signaling, and induce downstream mechanical strengthening by growing nanofibril networks, or soft robotic actuation through competitive swelling. All elements of the sensor-processor-actuator system are embedded in the device, functioning autonomously without external feeding reservoirs. Our concept enables designing advanced life-like materials systems that synergistically combine two worlds – chemical circuits for chemical information-processing and metamaterial unit cells for physical information-processing.

Simultaneous low-frequency vibration isolation and energy harvesting via attachable metamaterials

In this study, we achieved energy localization and amplification of flexural vibrations by utilizing the defect mode of plate-attachable locally resonant metamaterials, thereby realizing compact and low-frequency vibration energy suppression and energy harvesting with enhanced output performance. We designed a cantilever-based metamaterial unit cell to induce local resonance inside a periodic supercell structure and form a bandgap within the targeted low-frequency range of 300–450 Hz. Subsequently, a defect area was created by removing some unit cells to break the periodicity inside the metamaterial, which led to the isolation and localization of the vibration energy. This localized vibration energy was simultaneously converted into electrical energy by a piezoelectric energy harvester coupled with a metamaterial inside the defect area. Consequently, a substantially enhanced energy harvesting output power was achieved at 360 Hz, which was 43-times higher than that of a bare plate without metamaterials. The proposed local resonant metamaterial offers a useful and multifunctional platform with the capability of vibration energy isolation and harvesting, while exhibiting easy handling via attachable designs that can be tailored in the low-frequency regime.

Metamaterial enhanced sensor for powder material classification

In this paper, a simple and efficient approach is presented to classify different power materials based on a one port microwave sensor in X-band. This classification focuses on powder materials, unlike prior studies that focused on liquids (castor oil, neem oil, sunflower oil, sesame oil, and mahua oil), this classification represents a shift towards powdered materials. The response of the proposed sensor is enhanced by adding a metamaterial (MTM) unit cell of F-shape to focus electromagnetic waves on the sample under test. This metamaterial-based sensor is designed to differentiate between different types of materials based on the corresponding reflection coefficient. The sample under test is included inside a dielectric box inserted inside a rectangular waveguide. The MTM unit cell is added on the front face of this box towards the direction of the incident wave. The resonance frequency depends on the characteristics of the powder material inside the box. The MTM unit cell enhances this resonance to simplify the process of classification of different materials. The measured results show that the proposed sensor can detect a wide range of powder materials, including clay, cement, sand, and mixtures: cement & sand, and clay & sand. The designed sensor can be used in various applications, including detection and classification of different powder materials in industrial applications.

Gain enhancement of mm-wave antenna using graded index lens integrated frequency selective surface for 5G NR FR2 applications

In this study, the gain of a printed antenna is boosted for utilization in 5G systems by employing a phase-oriented graded index-type lens system. In the prescribed design, various metamaterial unit cells are arranged as arrays with radial phases for the graded meta lens to optimize transmission characteristics. The suggested arrangement creates a meta lens with spatially varying surface impedance and locally varying refractive index, allowing the conversion of spherical wavefronts into planar wavefronts for beam collimation in the 5G band. The focal length-to-diameter ratio (f/d) is fixed at 0.38 in this prescribed design. The integration of the FSS structure with the patch antenna enhances the efficiency above 98% and increases gain by 2.635dBi owing to the focusing effect of the properly placed lens. The prescribed planar lens is easy to realize during manufacturing compared to 3D lenses. The meta lens integrated patch yields a gain of around 8.936dBi at 29 GHz. The performance of the lens antenna is evaluated through simulation studies and then validation of results is performed with experimental arrangement to ensure accuracy and reliability of the suggested methodology for gain enhancement of the functioning antenna at FR2 5G spectrum.

Design of broad quasi-zero stiffness platform metamaterials for vibration isolation

Adaptability and reliability are challenges in designing vibration isolation structures, and mechanical metamaterials featuring broad quasi-zero stiffness (QZS) platforms are among the most promising candidates for addressing this issue. This paper proposes a novel design of vibration isolation metamaterials featuring a broad QZS platform to achieve vibration control in complex environments. The metamaterial unit cells are designed by integrating horizontal and diagonal beams based on the mechanism combining Euler buckling and flexural deformation. Herein, the component made of diagonal beams is configured to exhibit negative stiffness behavior, while the designed support components aim to relax the boundary constraints of the diagonal beam component, thereby mitigating the negative stiffness effect. By tuning the synergistic effects between horizontal and diagonal beams, QZS features can be achieved over a broad range of displacements. A combination of theoretical analysis, finite element method and experiment is employed to investigate the payload and QZS features of metamaterials comprehensively. Notably, the designed unit cell maintained a considerably broad QZS platform, with static experiments revealing that this platform accounts for approximately 55 % of the total loading range. Furthermore, the designed metamaterials exhibit excellent vibration isolation performance in the low-frequency range, with vibration experiments demonstrating that the unit cell can effectively shield vibrations across almost the entire range when the support mass corresponds to the QZS payload. The geometric parameters of the metamaterial configuration that influence the range of the QZS platform are also explored. In conclusion, the proposed mechanical metamaterials have a tunable and broad QZS platform with considerable potential for use in customized low-frequency vibration isolation applications.

Novel metamaterial array-based dual port MIMO antenna using low profile substrate with feature multiband, and high isolation for sub-6G, IoT, and WiMAX applications

This article represents a single-layered two-port MIMO antenna loaded into a compact plane-patterned metamaterial (MTM) structure for a 5G communication system. The antenna operates at three bands to investigate metamaterial properties in addition to diversity parameters, an arrangement of a series of arrays suggested a 2-port design antenna and a circular-shaped split ring resonator unit cell was developed. The design of a single port antenna utilizes 1 × 3 MTM unit cells for each component. This antenna operates within a frequency range ranging from 1 GHz to 15 GHz. Additionally, the suggested MIMO antenna offers a dominant isolation of –55dB. The measurement’s results show that, with an entire antenna size of 112 mm × 26.5 mm and a 3.33 GHz bandwidth, the MIMO antenna is achieved with good efficiency and CCL < 0.35, considerable DG > 9.97dB, ECC < 0.18, and TARC <–9.97. The presented design is suitable for medical imaging, RFID, Bluetooth, Wi-Fi, WiMAX, IOT, satellite communication systems, and the 5G and sub-6 GHz spectrum.

Synthesis and characterization of flexible CaCoAlFe2O4 based microwave substrate for triband polarization-insensitive metamaterial absorber

This study investigated CaxCo(0.90-x)Al.01Fe2O4 nanoparticle synthesized using the sol–gel synthesis method to achieve a flexible substrate with a high dielectric constant value. The XRD, FESEM, and dielectric characteristic is analyzed to explore the performance of the suggested Ox Wheels-shaped (OWS) metamaterial absorber unit cell. The X-ray diffraction (XRD) analysis found significant peaks at 30° (318), 33° (176), 35° (794), 43° (232), 53° (116), 57° (256), 62° (304), and 74° (126) planes. The dielectric constant values of the prepared nanomaterial materials are 4.52 (X = 90 %), 4.73 (X = 60 %), and 5.07 (X = 30 %) due to the deviations in raw material compositions. The prepared, flexible substrate is used in the anticipated OWS metamaterial absorber unit cell, and analysis has been widely considered and continuously concerned due to their excellent ultra-thin thickness, lightweight, and high absorbance resonance features. The predicted structure reached S21 response at 3.47 GHz, 7.05 GHz, and 10.76 GHz with the magnitude of −24.11 dB, −17.07 dB, and −19.19 dB, respectively, using CST simulation software. The absorber prototype is measured for further investigation within the frequency range of 2.25–2.76, 5.84–6.15 GHz, and 9.63–9.76 GHz, where maximum magnitude is achieved at 2.50 GHz, 6.02 GHz, and 9.70 GHz, respectively. This specific resonance frequency reached the highest 99.61 %, 98.03 %, and 98.79 % absorption, which covers the S, C, and X band frequency spectrum. Various electrical, magnetic, mechanical, and multi-parameter responses are examined to achieve almost perfect absorption (PA). The enormous range of possible uses of metamaterial, such as absorber wave modification, infrared imaging, radiative cooling, energy harvesting, and chemical detection, makes it appreciated. The CaCoAlFe2O4 ferrite-based flexible metamaterial absorber structure has ultra-thin, flexible, and non-corrosive advantages.

A novel Star-4 honeycomb with the inclined ligaments for enhanced tunability of wave propagation behaviors

The dynamic mechanical properties of mechanical metamaterials based on the honeycomb structures are widely concerned, especially the wave propagation behaviors. In this study, a novel type of honeycomb is designed by combing the Star-4 structure with the inclined ligaments. A dynamic analysis model of the Star-4 honeycomb with the inclined ligaments (S4HILs) is established based on the periodic description by the Bloch’s theorem and the discretization by the finite element theory of Timoshenko beam. The band gap characteristics calculated by the proposed model are compared with the frequency responses obtained by the commercial software to provide the modeling validation. The boundary vibration modes of S4HILs are compared to reveal the formation and closure mechanism of band gap. Moreover, the effects of different types of geometrical features on the band gap distribution and the macro-Poisson’s ratio are systematically investigated. The group velocity is finally discussed according to the global dispersion relation to explore the directivity of wave propagation. The results indicate that the inclined ligament can significantly enhance the tunability of wave propagation behaviors, which is mainly reflected in the broadened regulation range of band structure, Poisson’s ratio, and group velocity. This work provides an innovative idea for the regulation of wave propagation behaviors though the connection design between mechanical metamaterial unit cells.

Unilateral contact for a free mass in mass impact based metamaterial unit cell for vibration control

This paper presents a novel free mass in mass impact-based metamaterial for vibration control. An LCP-based algorithm is thoroughly discussed and presented to model a unilateral contact between the inner free mass impacting against the outer mass upon excitation. Firstly, the proposed solver is validated with the known concepts of physics. Further, a comprehensive investigation has been performed on the transmission spectrum and effective mass of the proposed unit cell, for varying radius of inner mass, coefficient of restitution and mass ratio. A non-linearity is developed in the system due to the impact between the two masses, which further causes an energy transfer from the outer mass to the inner mass. Therefore, upon excitation, the displacement in the outer mass reduces and hence the transmittance. The proposed unit cell also shows a prospective negative effective mass which can prove helpful for efficient vibration control.

Compact metamaterial-based single/double-negative/near-zero index resonator for 5G sub-6 GHz wireless applications

The concept, performance, and analyses of distinctive, miniaturized metamaterial (MTM) unit cell addressing the forthcoming Sub 6 GHz 5G applications are presented in this paper. Two circular split-ring resonators (CSRR) with two parallel rectangular copper elements in front of the design and a slotted square element in the background make up the suggested metamaterial. It has a line segment with tunable features that is positioned in the center of the little ring copper structure. The suggested design offers a significant operating frequency band of 220 MHz together with a resonance of transmission coefficient S21 at 3.5 GHz. Furthermore, in two (z & x) principal axes of wave propagation, wide-range achievement, single/double-negative (S/DNG) refractive index, negative permittivity, and near-zero permeability properties were demonstrated. Through varying central slotted-strip line length, resonance frequencies can be selectively altered. Moreover, the metamaterial has overall dimensions of 9 × 9 mm2 and is composed on a Rogers 5880 RT substrate. In order to create the suggested MTM's equivalent circuit, which shows similar coefficient of transmission (S21), a proposed design’s numerical simulation is carried out in the CST micro-wave studio. This simulation is after that put to comparison with manufacturing of the design.

Design of a novel compact low specific absorption rate multiple input multiple output antenna for 5G sub-6 GHz terminals

This investigation presents a new design and analysis of a fourteen elements massive multiple input multiple output (MIMO) compact low specific absorption rate (SAR) antenna system for 5G and beyond terminals. The MIMO antennas are realized for sub-6 GHz LTE-band 46 (5.1-5.8 GHz) long-term evolution 5G wireless communication services. The proposed antenna system is designed on an FR-4 dielectric constant 4.3 substrate consisting of the main board and four sideboards. The radiating elements are developed on the sideboards consisting of a monopole antenna and two metamaterial unit cells, as well as the feed line is designed on the principal board. The overall volume of the proposed structure is 150×80×7.5 mm. Through the use of the metamaterial unit cells, the proposed antennas have been arranged in close proximity without developing a strong mutual coupling. The results obtained were very important in terms of impedance matching, isolation among the antennas, and good gain. Even, the SAR analysis at the operating frequency band of 5.5 GHz proves that the proposed MIMO antenna system satisfies safety standards set for human exposure at the international level. Therefore, the proposed massive MIMO antenna structure is a potential solution for future communication applications.

An automated design framework for composite mechanical metamaterials and its application to 2D pentamode materials

Until relatively recently most mechanical metamaterial classes being studied have been composed of a single solid constituent phase and design has focused almost exclusively on structural geometry. Additional design dimensions can be introduced by accepting heterogeneity and varying materiality, i.e., allowing mechanical properties to vary across the metamaterial's unit cells or even from cell to cell in the metamaterial domain, creating composite metamaterials. This higher dimensionality significantly expands the effective property envelope, but the additional complexity also presents a significant hurdle. To overcome the design challenge, an automated design framework is proposed that leverages modern evolutionary computation techniques, combined with finite element analysis for fitness evaluation, to a discretized or voxelated design domain. However, this approach introduces stochastic and statistical aspects to the design process, which requires additional processing to successfully extract useful solutions. A case study is presented in which the proposed automated design framework is used to generate 2D structures that exhibit pentamode-like behavior. Pentamode metamaterials, which are best known for extreme bulk-to-shear modulus ratios (B/G), offer unique control over effective elastic properties and make for a particularly interesting test case. The evolutionary objective was defined as maximizing B/G over a voxelated square 2D domain. It was found that the evolutionary process converges to a solution relatively rapidly, generally in less that a hundred generations. B/G ratio values of 10,000 and more were obtained, largely exceeding those commonly found in the literature for experimental pentamode metamaterials. These generated designs feature reduced stress concentrations due to the elimination of point-like connections between lattice struts, which addresses a key practical limitation of diamond lattice pentamodes. It was observed that whatever the initial variety of elastic moduli values across the voxels of the design domain, as evolution progressed this variety collapsed to a much smaller number, most often a binary composite of very stiff voxels with a limited number of much softer voxels at key locations that acted as hinges.

Cross‐talk reduction in metamaterial and non‐uniform transmission lines

AbstractThe electromagnetic compatibility analysis of RF circuitry is essential due to the adverse effects on sensitive components. Two metamaterial unit cells with slow‐wave properties are presented for cross‐talk reduction in transmission lines. The analytical expressions for computing equivalent lumped elements of the lines are then provided. The dispersion diagram is obtained from the parameters extracted from the measurement. A microstrip as the generator line and five identical CRLH unit cells as the receptor line are then used and a significant reduction in cross‐talk is observed in comparison to conventional lines. A non‐uniform transmission line with two different CRLH unit cells as the receptor line is then employed and found effective in further cross‐talk reduction between the lines. The lengths of the lines and numbers of cells are kept the same in all lines for comparison. The simulated results are validated by measurements.

Evaluating the Impact of Geometric Dimensions of a Multi-Split Ring Resonator

In this paper, a metamaterial unit cell is designed and simulated based on the concept of multiple split-ring resonators (SRRs) in a compact size. The presented nested modified SRR resonator construct has the advantage of achieving more usable split gaps by increasing capacitance, resulting in a lower operational resonance frequency and improved sensitivity over typical SRR metamaterials. The impact of several split ring resonator geometric characteristics, such as the gap space, the width of the copper lines, the inner rings length, and the outer ring length on magnetic permeability and permittivity was analyzed. The modified metamaterial can be utilized for 5G mobile applications.

Tuneable double negative (DNG) Tri-Hexagonal split ring resonator metamaterial for 5G application

This paper introduces a compact tuneable metamaterial (MTM) unit cell featuring a tri-hexagon and tri-square split ring resonator (THTSSSR) structure designed for 5G communication applications. Metamaterials are employed to achieve unique electromagnetic properties not found in natural materials. The design process involves the arrangement of three square rings and three hexagon rings as metallic patches on a Rogers substrate (RT 5880), measuring 7 x 7 mm2 with a thickness of 1.575 mm. The proposed design exhibits double negative (DNG) properties, with resonances in the transmission coefficient (S21) at 3.493 GHz and a bandwidth of −10 dB covering frequencies between 3.057 and 3.711 GHz. Numerical simulations conducted using finite-integration techniques (FIT) in CST Microwave Studio validate the design's effectiveness, with confirmation through the Advanced Design System (ADS). The MTM unit cell demonstrates tuneable attributes, including negative permittivity ranging from 3.39 to 5 GHz and negative permeability from 3.39 to 3.86 GHz. These findings highlight the compactness and tunability of the proposed design, making it promising for 5G communication applications.

Simulation-based approach to estimate influencing factors on acoustic resonance spectra of additively manufactured mechanical metamaterials

Acoustic Resonance Testing is a nondestructive testing method based on the analysis of eigenfrequencies of structures. While it is a well-established technique for conventionally manufactured parts, more research is needed to use the technique to quantify the properties of complex, filigree structures like additively manufactured parts. Therefore, this work examines simulation-based generation of synthetic data to estimate influencing factors caused by additive manufacturing. Using numerical eigenfrequency analysis, a systematic study of the vibration modes of a Ti6Al4V metamaterial unit cell with multistable mechanical behaviour reveals the interplay between the material properties, geometrical parameters and manufacturing-induced defects. The simulations enable the identification of specific eigenfrequencies for which the highest influence of manufacturing variations on the vibration modes are to be expected in experiments, for example, with regards to the Young’s modulus, spring width, or deflection-induced change in geometry. Frequency shift plots visualize the predicted effects of different parameters and form the basis for future guided experimental design and analysis for complex structures. The simulation-based approach allows a screening of multiple influencing factors, which is not possible experimentally. The simulation-based generation of synthetic data will contribute to the improvement of the interpretation of acoustic spectra and will extend the acoustic resonance testing for more complex structures.

Study on the Equivalent Stiffness of a Local Resonance Metamaterial Concrete Unit Cell

This paper addresses the pressing scientific problem of accurately predicting the equivalent stiffness of local resonance metamaterial concrete unit cells. Existing theoretical models often fail to capture the nuanced dynamics of these complex systems, resulting in suboptimal predictions and hindering advancements in engineering applications. To address this deficit, this paper proposes a novel two-dimensional theoretical vibration model that incorporates shear stiffness, a crucial yet often overlooked parameter in previous formulations. Motivated by the need for improved predictive accuracy, this paper rigorously validates a new theoretical model through numerical simulations, considering variations in material parameters and geometric dimensions. The analysis reveals several key findings: firstly, the equivalent stiffness increases with elastic modulus while the error rate decreases, holding geometric parameters and Poisson’s ratio constant. Secondly, under fixed geometric parameters and coating elastic modulus, the equivalent stiffness rises with an increasing Poisson’s ratio, accompanied by a decrease in error rate. Importantly, this paper demonstrates that the proposed model exhibits the lowest error rate across all parameter conditions, facilitating superior prediction of equivalent stiffness. This advancement holds significant implications for the design and optimization of metamaterial structures in various engineering applications for vibration isolation, with promising enhancements of performance and efficiency.

Design of flexural wave bessel metasurface with resonant pillar-type metamaterials

In this paper, we design a flexural wave Bessel metasurface with resonant pillars, which converts the flexural wave produced by a point into a Bessel beam. The refractive index is determined through the application of the generalized Snell’s law, subsequently discretized into pixel blocks. These blocks facilitate implementation via the use of metamaterial unit cells. The metasurface is realized by resonant pillar-type metamaterials, and composed of 41 different independent unit cells obtained by retrieving the energy bands. Simulation results demonstrate that the designed metasurface exhibits effective focusing for flexural wave. Additionally, the self-reconstruction effect of the Bessel metasurface is verified through the introduction of obstacles. This research provides a new perspective for the application of Bessel beam in the domain of flexural wave.

Controlled circular dichroism with graphene-based metamaterial for terahertz wave

This article explores the design and analysis of a metal-graphene hybrid metamaterial structure tailored for tunable circular dichroism (CD) effects in the terahertz (THz) frequency regime. Chiral metamaterials have garnered considerable interest in photonics due to their versatile applications, including sensing, polarization manipulation, and chiral imaging. The proposed metamaterial unit cell features four meta-atoms with C4 rotational symmetry, composed of gold on a polyimide substrate. By strategically integrating the graphene sheets above the gold patterns, selective control over the absorption efficiency for the incident wave of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light is achieved. The study demonstrates that adjusting graphene chemical potential enables precise modulation of CD from 0.80 to 0.10 across a wide THz frequency spectrum. Furthermore, the article investigates the structure optical response for incident angles ranging up to 75°, revealing stable CD behavior up to 30° and intriguing dual-band effects beyond 50°. These findings underscore the potential of the proposed metamaterial for practical applications in photonics, sensing, and chiral imaging, offering tunable control over the CD effects in the THz regime.