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We introduce a novel approach to evaluate how the design properties of morphing metamaterial influence shape-changing experiences. We leverage parametric design to create cutting patterns that change the Density and Geometry material properties. Using laser-cutting, we apply the patterns to a non-stretchable woven textile, resulting in a stretchable metamaterial that we actuate using an electromagnetic coil. This systematic design approach leads to programmatic control over the material movement, making it suitable for controlled evaluation of perceived experience. In a 2×2 mixed-method study, we assess how the metamaterial’s Density and Geometry properties impact the observed experience. Our findings indicate that such changes significantly and independently affect participants’ perceived emotions, mood, associations, and preferences. Our research contributes to the body of work of systematic studies in the shape-changing community. By using our morphing metamaterial design and implementation technique, coupled with our controlled evaluation of specific design properties, we have revealed new insights about the influencing factors of shape-changing experiences. We have incorporated these insights into our morphing metamaterial design guidelines, which outline the impact of Density and Geometry properties on an observer’s perceived emotions. We hope our work will open up new possibilities for expressive, evocative metamaterial-focused shape-changing experiences. [ABSTRACT FROM AUTHOR]

In recent years, particular physical phenomena enabled by non-Hermitian metamaterial systems have attracted significant research interests. In this paper, a non-Hermitian three-dimensional metamaterial near the exceptional point (EP) is proposed to demonstrate extremely asymmetric absorption and reflection. Unlike its conventional counterparts, this proposed metamaterial is constructed with a loss-assisted design. Localized losses are introduced into the structure by combining our technique of graphene-based resistive inks with conventional printed circuit board process. Extremely asymmetric absorption and reflection near the EP are experimentally observed by tuning the loss between split ring resonators in the meta-atoms. Simultaneously, by linking the equivalent circuit model (ECM) with the quantum model, an equivalent non-Hermitian transmission matrix is constructed. We show that tuning the structure parameters of the ECM produces a metamaterial system with EP response. Our system can be used in the design of unidirectional metamaterial absorbers. Our work contributes to future works on the manipulation of EP to develop precision sensing and other applications in the 3D metamaterial platform. [ABSTRACT FROM AUTHOR]

Dynamic and responsive structural color devices present promising opportunities for sensing and display technologies, with applications including point‐of‐care diagnostics, portable/wearable sensors, and low‐power full‐color displays. However, it is often difficult to generate a large and quantitatively meaningful colorimetric response especially toward weak stimuli. Here, dual‐band hyperchromatic structural color (HSC) is presented as an approach to overcome these challenges. Within this framework, a dual‐band mesoporous silicon rugate filter metamaterial co‐designed is experimentally realized for use with a dichromatic (red/green) illuminant. This is shown to enable an amplified red‐to‐green color transition with a substantially smaller wavelength shift than conventional structural color devices, Δλ ≪ |λG – λR|, as well as a direct quantitative mapping between the observed chromaticity and the input stimulus. This approach is experimentally demonstrated for the spatiotemporally resolved sensing of refractometric stimuli including small‐molecules and volatile organic compounds (VOCs) with a ≈0.08 nm equivalent spectral resolution. This approach is entirely scanning‐free, enabled by simple color imaging, and does not require advanced spectroscopic (hyperspectral) imaging or interferometric imaging to obtain meaningful quantitative and spatiotemporally resolved information pertaining to the sensor's attributes. These results demonstrate dual‐band HSC as a promising approach for realizing low‐cost and high performance dynamic structural color devices and sensors. [ABSTRACT FROM AUTHOR]

We present a new selective Metamaterial Perfect Absorber (MPA) consisting of zinc oxide embedded silver (Ag@ZnO), designed for applications in infrared stealth technology. The numerical simulation included a wide frequency range from 1 to 1000 THz and shows that the design MPA structure presented two absorption peaks at the desired wavelengths of 1.7 µm and 6.5 µm. The absorptivity of both peaks reached approximately 93.1% and 93.5%. The first peak at 1.7 µm decreases the scattering of IR laser beams from the surface of the MPA structure and also lowers the infrared tracks that could direct laser-guided devices to its specific target. On the other hand, the second peak reduces the surface heat wave. The suggested MPA (Ag@ZnO) structure is activated by a plane wave using a full wave vector and a broad frequency domain solution. In the framework of computer simulation technology (CST) Microwave Studio, uses both Finite-Difference-Time-Domain (FDTD) and Finite-Element-Method (FEM) techniques to predict the optical behavior of the proposed MPA structure. Both peaks achieved a high value of absorptivity due to the simultaneous excitation of the electric and magnetic dipole at resonance wavelength. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Microelastic topological metamaterials (METMs) are of great use in the robust conveying and harvesting of high‐frequency ultrasonic energies. However, current METMs only hold topological edge states of a single flexural mode, restricting their capacity to convey ultrasonic energies of other polarized elastic waves. Moreover, the potential of METMs for ultrasonic energy harvesting remains unexplored. To address these challenges, an all‐polarized elastic topological metamaterial (AETM) is developed, capable of simultaneous conveying and harvesting of ultrasonic energies from elastic waves of all polarizations. This AETM supports broadband topological edge states for both out‐of‐plane and in‐plane modes, enabling the robust conveying of ultrasonic energies from all‐polarized elastic waves. Subsequently, by integrating the AETM with a piezoelectric energy harvester, efficient harvesting of ultrasonic energies conveyed by the AETM is achieved. Notably, the developed AETM with structural simplicity can be easily integrated into micro‐electromechanical systems (MEMSs) for on‐chip ultrasonic wave communication and energy harvesting. This work advances the development of topological metamaterials that can concurrently convey and harvest ultrasonic energies from all‐polarized elastic waves, offering significant potential for various MEMS applications. [ABSTRACT FROM AUTHOR]

In practical engineering, noise and impact hazards are pervasive, indicating the pressing demand for materials that can absorb both sound and stress wave energy simultaneously. However, the rational design of such multifunctional materials remains a challenge. Herein, inspired by cuttlebone, we present bioinspired architected metamaterials with unprecedented sound-absorbing and mechanical properties engineered via a weakly-coupled design. The acoustic elements feature heterogeneous multilayered resonators, whereas the mechanical responses are based on asymmetric cambered cell walls. These metamaterials experimentally demonstrated an average absorption coefficient of 0.80 from 1.0 to 6.0 kHz, with 77% of the data points exceeding the desired 0.75 threshold, all with a compact 21 mm thickness. An absorptance-thickness map is devised for assessing the sound-absorption efficiency. The high-fidelity microstructure-based model reveals the air friction damping mechanism, with broadband behavior attributed to multimodal hybrid resonance. Empowered by the cambered design of cell walls, metamaterials shift catastrophic failure toward a progressive deformation mode characterized by stable stress plateaus and ultrahigh specific energy absorption of 50.7 J/g—a 558.4% increase over the straight-wall design. After the deformation mechanisms are elucidated, a comprehensive research framework for burgeoning acousto-mechanical metamaterials is proposed. Overall, our study broadens the horizon for multifunctional material design. Noise and impact hazards are pervasive in engineering, necessitating materials capable of absorbing both sound and stress wave energy. Here, we present bioinspired metamaterials with exceptional sound-absorbing and mechanical properties using a weakly-coupled design strategy. These materials incorporate multi-layered resonators for superior acoustic performance and cambered cell walls for enhanced structural strength. They achieve an average absorption coefficient of 0.80 across the 1.0 to 6.0 kHz range, all within a sleek 21 mm thickness. Furthermore, the design transitions failure modes from catastrophic to progressive, resulting in a remarkable 558.4% increase in energy absorption compared to conventional designs. [ABSTRACT FROM AUTHOR]

Magnetic resonance imaging (MRI) is a crucial medical imaging modality, with parallel MRI accelerating scans but often reducing the signal-to-noise ratio (SNR). Recent advances in metamaterials have shown considerable potential in enhancing the SNR of MRI and consequently improving the quality of parallel MRI. In this study, we present a nonlinear metamaterial comprising nonlinear meta-atoms designed to selectively enhance the radio-frequency reception field in MRI, while minimizing interference with the radio-frequency transmission field. We develop an electromagnetic field-circuit joint simulation process for analyzing and optimizing the nonlinear response. Experimental validation confirms that nonlinear metamaterial integration in a surface coil array delivers a 3-fold SNR increase for parallel MRI compared to using the surface coil array alone. This research advances our understanding of such metamaterials and demonstrates their potential for practical utilization in MRI and clinical settings, thereby promising substantial enhancements in imaging capabilities. The study demonstrates nonlinear metamaterials can effectively enhance the signal-to-noise ratio of parallel magnetic resonance imaging in the phantom and in-vivo imaging. The findings underscore metamaterials' potential to advance medical imaging. [ABSTRACT FROM AUTHOR]

In this work, we propose elastic metamaterials with phase discontinuities to steer the propagation of near-source bulk waves in a semi-infinite elastic medium. Our design exploits an array of embedded subwavelength resonators with tailored masses to attain a complete phase shift spanning 0−2π. This phase control allows for diverse wave functionalities, such as directional refraction and energy focusing. Through the use of dispersion diagrams and the generalized Snell's law, along with a multiple scattering formulation, we analytically demonstrate the effectiveness of our design in achieving the desired wavefront manipulation. The proposed design has the potential to advance the field of guiding elastic waves using metamaterials and find practical applications in areas such as isolating ground-borne vibrations in densely urbanized regions and energy harvesting. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

In this article, we present the design and experimental validation of a labyrinthine metamaterial for vibro-acoustic applications. Based on a two-dimensional unit cell, different designs of finite-size metamaterial specimens in a sandwich configuration including two plates are proposed. The design phase includes an optimization based on Bloch-Floquet analysis with the aims of maximizing the band gap and extruding the specimens in the third dimension while keeping the absorption properties almost unaffected. By manufacturing and experimentally testing finite-sized specimens, we assess their capacity to mitigate vibrations in vibro-impact tests. The experiments confirm a band gap in the low- to mid-frequency range. Numerical models are employed to validate the experiments and to examine additional vibro-acoustic load cases. The metamaterial's performances are compared with benchmark solutions, usually employed for noise and vibration mitigation, showing a comparable efficacy in the band gap region. To eventually improve the metamaterial's performance, we optimize its interaction with the air and test different types of connections between the metamaterial and the homogeneous plates. This finally leads to metamaterial samples largely exceeding the benchmark performances in the band gap region and reveals the potential of interfaces for performance optimization of composed structures. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

The unique properties of metamaterials are determined by the configuration and spatial arrangement of artificially designed unit structures. However, the configuration and mechanical properties of conventional metamaterials are challenging to reverse and adjust. Based on curved beams, two types of novel three-dimensional (3D) multi-stable metamaterials with reconfigurable deformation and tunable mechanical properties are designed and fabricated using a four-dimensional (4D) printing method. The effects of temperature and curved-beam thickness on the force-displacement curves and multi-stable snapping sequence of the 3D multi-stable metamaterials are investigated by finite-element analysis (FEA) and experiments. In addition, based on the designed four-branch multi-stable metamaterials, three- and six-branched multi-stable structures are designed by changing the number of curved-beam branches. It is shown that, owing to shape memory effects, the 3D multi-stable metamaterials can realize mechanical programmability, and the multi-stable deformation sequence can be precisely regulated by varying the temperature and curved-beam thickness. These 4D-printed multi-stable metamaterials provide valuable contributions to the design of programmable multi-stable metamaterials and their applications in soft robots and intelligent structures. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

In this work, we investigate the dynamics of Scholte–Stoneley waves (SSWs) travelling along elastic metasurfaces, e.g. thin resonant structures embedding mechanical oscillators, placed at the interface between solid and fluid. To this purpose, an analytical dispersion law, valid in the long-wavelength regime, is derived and used to reveal the hybridization of SSWs with the collective resonance of the mechanical oscillators and the conversion of SSWs into leaky modes within the fluid. The analytical predictions are validated through numerical simulations that include both dispersive and harmonic analysis. Our findings disclose the capabilities of elastic metasurfaces in filtering, trapping and converting SSWs along fluid–solid interfaces, thus supporting the design of novel devices for solid–fluid interaction across various engineering applications, including microfluidics. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1)'. [ABSTRACT FROM AUTHOR]

This article focuses on characterizing a class of quasi-periodic metamaterials created through the repeated arrangement of an elementary cell in a fixed direction. The elementary cell consists of two building blocks made of elastic materials and arranged according to the generalized Fibonacci sequence, giving rise to a quasi-periodic finite microstructure, also called Fibonacci generation. By exploiting the transfer matrix method, the frequency band structure of selected periodic approximants associated with the Fibonacci superlattice, i.e. the layered quasi-periodic metamaterial, is determined. The self-similarity of the frequency band structure is analysed by means of the invariants of the symplectic transfer matrix as well as the transmission coefficients of the finite clusters of Fibonacci generations. A high-frequency continualization scheme is then proposed to identify integral-type or gradient-type non-local continua. The frequency band structures obtained from the continualization scheme are compared with those derived from the Floquet–Bloch theory to validate the proposed scheme. This article is part of the theme issue 'Current developments in elastic and acoustic metamaterials science (Part 1).' [ABSTRACT FROM AUTHOR]

A customized metamaterial tailored for a specific functionality holds significant appeal in practical applications, yet its alteration after the structure is established can be challenging. A novel design for Fibonacci‐array inspired acoustic metamaterials is introduced, which are constructed using metamaterial bricks with unique physical mechanisms. This design aims to achieve multifunctional low‐frequency sound absorption. The Fibonacci sequence arrangement flexibly modulates the coupling between metamaterial bricks, thereby improving energy‐dissipating efficiency. Additionally, the strategic alignment enhances the wave‐absorbing properties of the metamaterial, allowing it to demonstrate remarkable absorption effects across targeted frequency bands. By controlling the resonance effect of metamaterial bricks in intensive and sparse modes, the proposed design exhibited frequency‐selective performance, resulting in three absorption peaks at 323, 687, and 1113 Hz, respectively, across low‐ to high‐frequency ranges. Furthermore, the broadband absorption performance, characterized by strong coupling strength, enables continuous sound absorption over a low‐frequency band from 290 to 440 Hz. This is supported by theoretical analysis, numerical simulations, and experimental results, showcasing the flexible modulation of the propagation characteristics of sound waves. Overall, this functionally actuated design dramatically enhances the tunability of the metamaterials and offers a promising avenue for multifunctional application in noise‐control engineering. [ABSTRACT FROM AUTHOR]

Photonic metamaterials interact with light at the micro–nano scale, enabling unprecedented optical manipulation capabilities, which play a key role in nonlinear optics, spin optics, negative index, and zero index materials. Recently, thin‐film lithium niobate on insulator (LNOI) has emerged as a promising platform for integrated photonics due to its unique material properties, including an excellent electro–optic effect, wide transparency window, and low waveguide losses. Metamaterial structures are promising for constructing novel integrated photonic circuit building blocks on LNOI as they can provide advantageous circuit functionality. In this work, as a proof of concept, high‐performance polarization manipulating devices including polarization splitter rotator (PSR), polarization rotator (PR), and polarizer are demonstrated using photonic metamaterials on the etchless LNOI platform by introducing a silicon nitride layer on the top of LNOI wafer as the loading material. In this way, full advantage of lithium niobate (LN) can be taken to achieve various high‐performance integrated photonic devices, while avoiding the etching of LN and simplifying the fabrication process greatly, which can bring bright prospects for achieving large‐scale lithium niobate integrated photonic circuits. [ABSTRACT FROM AUTHOR]

Since adopting 5G technology, a notable rise in the prevalence of electromagnetic (EM) waves in the environment has become a significant concern. To reduce EM interference, broadband metamaterial absorbers offer an alternative solution for protecting devices in defense, communication, and healthcare applications, unlike their narrowband counterparts. This article presents a numerical investigation of an ultra‐thin, polarization‐insensitive metamaterial absorber (MMA) that uses metasurfaces and provides electromagnetic interference (EMI) reduction, covering the FR2/mmWave licensed N258 and N261 bands with an oblique incidence angle of up to 15 degrees. Comprehensive simulations are performed within the CST Studio Suite S2 2023 to examine the absorber's performance. Under normal incidence, the proposed MMA exhibits a wideband absorbency response exceeding 90% within the frequency range of 24.30–28.12 GHz. Moreover, the physical absorption mechanism is explained with electric and magnetic field distributions, including surface current distributions. Confirmation of the lack of mutual interaction among neighboring unit cells is established through testing with 1 × 2 and 2 × 2 arrays. An equivalent circuit model is also developed to confirm the EM simulation findings. The notable features of the proposed MMA make it an exceptional candidate for EM shielding applications, providing EMI reduction and covering the N258 and N261 bands. [ABSTRACT FROM AUTHOR]

The confinement of waves within a waveguide can enable directional transmission of signals, which has found wide applications in communication, imaging, and signal isolation. Extending this concept to static systems, where material deformation is piled up along a spatial trajectory, remains elusive due to the sensitivity of localized deformation to structural defects and impurities. Here, we propose a general framework to characterize localized static deformation responses in two-dimensional generic static mechanical metamaterials, by exploiting the duality between space in static systems and time in one-dimensional non-reciprocal wave systems. An internal time-reverse symmetry is developed by the space-time duality. Upon breaking this symmetry, quasi-static load-induced deformation can be guided to travel along a designated path, thereby realizing a stress guide. A combination of time-reverse and inversion symmetries discloses the parity-time symmetry inherent in static systems, which can be leveraged to achieve directional deformation shielding. The tailorable stress guides can find applications in various scenarios, ranging from stress shielding and energy harvesting in structural tasks to information processing in mechanical computing devices. [ABSTRACT FROM AUTHOR]

Architected materials exhibit unique properties and functionalities based on the geometric arrangement of their constituent materials. In most cases, these parameters are fixed, requiring that the system be redesigned and reconstructed if different properties are desired. Both stimuli‐responsive materials and modular designs have been used to enable re‐programmable properties in the past, but often have limitations, such as the need for a continuous application of external stimuli or power, or unwanted global morphing. In this study, a locally stable anti‐tetra chiral (LSAT) metamaterial is introduced consisting of independently multistable units that can deform and change state without inducing changes in the global morphology. Adjacent cells are only weakly coupled, allowing the collective metamaterial to be switched between many different possible states. Local bistability enables re‐programmable heterogeneity, such as the snapping of cells along an edge or diagonally within the architected material. Utilizing finite element analysis (FEA), the influence of key geometric parameters on the re‐programmability of the metamaterials is systematically investigated. The effect of these parameters on properties such as shear stiffness, Poisson's ratio, and vibration are also investigated using experimental prototypes. This re‐programmable metamaterial promises to expand the design space for mechanical systems, with potential applications in non‐traditional computation, robotic actuation, and adaptive structures. [ABSTRACT FROM AUTHOR]

Inspired by the differences in the barbed structures of some plant stems and cat tongues in different directions, a reusable and easy-to-recover barbed metamaterial was designed, with its mechanical properties analyzed theoretically and numerically. The results show that, in the reciprocating motion of the barbs, when the barb rectangular section sizes are 1 mm × 1 mm, the length is 20 mm, and the angle with the vertical direction is 60°, the maximum reaction force in the forward contact process with the blocking rib will be about 20 times of the maximum reaction force in the reverse contact process, and the former energy consumption is about 200 times of the latter. With the decrease of the angle between the barb and the vertical direction, the barb structure will exhibit a higher energy absorption capacity and a reduced energy requirement for recovery. Similarly, with the increase of the barb length, the structure energy absorption will be lower and the energy required for recovery will reduce. These characteristics indicate that, the structure possesses excellent impact resistance and energy absorption capacity. Structures with significant energy disparities between forward and backward motions are more easily recoverable, and the energy absorption efficiency can be enhanced by carefully designing the angles and lengths of the barbs. [ABSTRACT FROM AUTHOR]

We propose a structure utilizing a double-layer aluminum ring resonator embedded in a dielectric layer of metamaterial to demonstrate the appearances of unidirectional reflectionlessness, asymmetric reflection, and asymmetric transmission for the incident linear and circular polarizations. A significant feature of this structure is that it allows multiple functions to be implemented in the same structure without changing any structure parameters. For the vertical incident x- and y-polarizations, not only significant unidirectional reflectionlessness and asymmetric reflection effects are verified but also the strong linear to circular polarization conversions are illustrated in both transmission and reflection modes. For the vertical incidences of right-handed and left-handed circular polarizations, unidirectional reflectionlessness and asymmetric reflection are also demonstrated in detail. In addition, when linearly or circularly polarized waves are incident obliquely, the structure exhibits a stable asymmetric transmission phenomenon within a wide incident angle range. Furthermore, it also supports the occurrences of unidirectional reflectionlessness and asymmetric reflection stably within wide ranges of incident angle, resonator spacing, and rotation angle of the upper aluminum ring. [ABSTRACT FROM AUTHOR]

Deep learning techniques provide a new approach to the design and optimization of electromagnetic metamaterials. This study used a convolutional neural network and long short-term memory (CNN–LSTM) hybrid network to design and optimize a broadband metamaterial reflective linear polarization converter. The data augmentation method was also employed in few-shot learning to reduce optimization costs and improve model prediction performance. With the inverse prediction, a linear polarization converter that perfectly covers the Ku-band was obtained and fabricated with flexible printed circuit technology. Both simulation and experimental results indicate that this network can accurately predict the structural parameters. The polarization converter not only achieves remarkable broadband polarization conversion efficiency spanning the 2.2–18 GHz range but also maintains precise cross-polarization control across the entire Ku-band. The mean polarization conversion ratio in the Ku-band was calculated to be an impressive 99.69%. Finally, the mechanism of polarization conversion and the influence of each structural parameter on its performance further verify the optimality of the inverse design model. The use of CNN–LSTM deep learning methods significantly simplified the design process of electromagnetic metamaterials, reducing design costs while ensuring high design precision and excellent performance. [ABSTRACT FROM AUTHOR]

Near-field radiative heat transfer (NFRHT) between electronic components has become an important factor in the development of high-performance optoelectronic devices. Here, a metamaterial containing graded particles is proposed and measured. Two NFRHT peaks are excited by the local surface plasmon mode and surface plasmon mode. The results show that the filling factor and gradient factor have important effects on the NFRHT properties of the metamaterial. These measurement results provide the experimental basis for the application of gradient metamaterials in optoelectronic devices. [ABSTRACT FROM AUTHOR]

This paper investigates the potential of a transition metal nitride, Vanadium Nitride (VN), in designing a nanostructured absorber for infrared wavelengths. A simple and plain nano circular ring composed of VN is printed over a metal-backed lossy substrate to implement broadband absorber. The proposed VN-based absorber offers an exceptional absorption characteristic across the large operating wavelength from 1000 to 2400 nm with an absorption threshold of 90%. The absorption properties of this VN absorber have also been analyzed by varying the oblique angles of the optical light and it exhibits a good absorption value of more than 70% even at θ = 60°. Due to the symmetry in the nano-ring of VN, it also achieves the polarization-insensitive response by varying the rotation angles (polarization angles). Moreover, the multi-reflection interference theory has been introduced to verify the simulation results of the proposed VN-absorber. Because of its thermal robustness, mechanical stability, and wide absorption bandwidth, it holds promise for applications in solar cells and thermophotovoltaics. [ABSTRACT FROM AUTHOR]

The demand for faster and more reliable wireless communication has led to the emergence of 6G technology. One of the key features of 6G is the utilization of terahertz (THz) frequencies for data transmission, which can provide significantly higher data rates compared to previous generations. By extending the near-field sensing range, the communication distance can be increased, leading to improved coverage and performance in 6G systems. The proposed solution is achieved through the integration of metamaterials, which are artificially designed structures with unique electromagnetic properties. By incorporating metamaterials into the design of THz antennas, we can manipulate the near-field region and enhance its sensing capabilities. Near field enhancement can also be achieved through the use of reflectors, non-uniform spacing, and dielectric lenses. Plasmonic structures and chiral metamaterials are also effective. It is achieved by tailoring the electric and magnetic response of the metamaterials, which can effectively concentrate the THz radiation within the near-field region of the antenna. The proposed model reached 98.23% resolution, 92.51% sensitivity, 93.78% range, 88.58% frequency response, 94.02% directivity, 94.62% cross talk reduction. The enhanced near-field sensing range for THz antennas will have a significant impact on the performance of 6G communication systems. It will not only extend the communication distance but also improve signal quality and reduce power consumption. It will pave the way for the realization of ultra-high-speed and reliable 6G wireless communication, making it a potential game-changer in the future of telecommunications. [ABSTRACT FROM AUTHOR]

A continuum theory of pantographic lattices, based on second-grade elasticity, is presented. The proposed model is able to describe the mechanical behavior of a type of material structure made up of multiple layers of pantographic sheets connected with a third family of fibers. Thus, these materials are characterized by an orthogonal pattern of fibers that can bend, stretch and twist. Numerical experiments illustrate the predictive potential of the model when the material is subjected to different types of mechanical loads, including compression, torsion and two kinds of bending. Analyzing the material responses for these various tests makes it possible to reveal unusual deformation patterns characteristic of such "pantographic blocks." Numerical simulations using the finite element method are intended to assist in designing an experimental program using 3D-printed specimens made of different materials. [ABSTRACT FROM AUTHOR]

This study proposes a new, doubly re-entrant auxetic unit-cell design that is based on the widely used auxetic honeycomb structure. Our objective was to develop a structure that preserves and enhances the advantages of the auxetic honeycomb while eliminating all negative aspects. The doubly re-entrant geometry design aims to enhance the mechanical properties, while eliminating the buckling deformation characteristic of the re-entrant deformation mechanism. The effects of the geometric modification are described and evaluated using two parameters, offset and deg. A series of experiments were conducted on a wide range of parameters based on these two parameters. Specimens were printed via the vat photopolymerization process and were subjected to a compression test. Our aim was to investigate the mechanical properties (energy absorption and compressive force) and the deformation behaviour of these specimens in relation to the relevant parameters. The novel geometry achieved the intended properties, outperforming the original auxetic honeycomb structure. Increasing the offset and deg parameters results in increasing the energy absorption capability (up to 767%) and the maximum compressive force (up to 17 times). The right parameter choice eliminates buckling and results in continuous auxetic behaviour. Finally, the parameter dependency of the deformation behaviour was predicted by analytical approximation as well. [ABSTRACT FROM AUTHOR]

The manipulation of acoustic waves is becoming increasingly crucial in research and practical applications. The coordinate transformation methods and acoustic metamaterials represent two significant areas of study that offer innovative strategies for precise acoustic wave control. This review highlights the applications of these methods in acoustic wave manipulation and examines their synergistic effects. We present the fundamental concepts of the coordinate transformation methods and their primary techniques for modulating electromagnetic and acoustic waves. Following this, we deeply study the principle of acoustic metamaterials, with particular emphasis on the superior acoustic properties of polymers. Moreover, the polymers have the characteristics of design flexibility and a light weight, which shows significant advantages in the preparation of acoustic metamaterials. The current research on the manipulation of various acoustic characteristics is reviewed. Furthermore, the paper discusses the combined use of the coordinate transformation methods and polymer acoustic metamaterials, emphasizing their complementary nature. Finally, this article envisions future research directions and challenges in acoustic wave manipulation, considering further technological progress and polymers' application potential. These efforts aim to unlock new possibilities and foster innovative ideas in the field. [ABSTRACT FROM AUTHOR]

Abstract3D additive manufacturing of metamaterials, especially honeycomb structures, has gained prominence in industrial manufacturing for their exceptional mechanical properties and energy absorption (EA) capabilities. This study introduces a novel circular tubular honeycomb structure to enhance EA characteristics. Through quasi-static compression experiments and finite element simulations, specific energy absorption (SEA) of various circular structures is analyzed. Results show that the circular tubular honeycomb structure excels in SEA performance, lightweight construction, and reduced Poisson’s ratio. An equation for structural neutral layer offset is derived and validated, showcasing potential in thin-walled pipe-in-pipe (PIP) interlayers. [ABSTRACT FROM AUTHOR]

Compared to homogeneous beams, metamaterial-based sandwich beams are known to be lighter and provide better mechanical characteristics. However, their application has mainly been limited to large-scale structures, and their potential for granting small-scale structures enhanced characteristics has not been fully explored yet. The present manuscript aims to investigate nonlinear vibration in size-dependent metamaterial-based sandwich microbeams with hexagonal and triangular lattice cores. To do so, well-known homogenization techniques based on modeling the representative volume element (RVE) of the lattice have been utilized to find the equivalent properties of the nonlinear cores. Moreover, the modified strain gradient theory is used to obtain the governing equation of motion for a small-scale microbeam and the multiple scales method is adopted to investigate the free vibration and primary resonance of the discretized system. Further, size effects and the effect of geometry on the free and forced nonlinear vibration of lattice sandwich beams are examined. In addition to highlighting the size effects, the results indicate that properly implementing nonlinear metamaterials in microbeams can enhance and tune vibrational performance across various length scales. The results of the present paper can provide a more detailed perception of the concept of nonlinear metamaterial-based microbeams and their application in MEMS/NEMS devices. [ABSTRACT FROM AUTHOR]

The behavior of a coned disk spring can be significantly affected by friction or restraint, yet the existing theoretical solutions cannot fully capture these influences. The limitation is particularly problematic for analyzing the behavior of coned disk springs with bi-stability. This paper proposes an explicit solution that can predict the behavior of the coned disk spring under these boundary conditions. The solution considers detailed influences of friction and restraint at the edges of the coned disk spring on its moment equilibrium and location of the neutral fiber. The theoretical results are validated using existing literature, FE analysis, and a series of tests. The theoretical solution confirms that the friction force at the edge of the coned spring significantly affects the axial response of the spring but not its bending moment or distribution of tangential stress. The bending moment and overall behavior of the coned disk spring are, on the other hand, very sensitive to restraints in radial directions. The proposed explicit solution shows good accuracy for coned disk springs with restrained radial stretching and rotation. The solution is particularly useful for coned disk springs in multistable structures and metamaterials. [ABSTRACT FROM AUTHOR]

In this paper, we numerically investigate a tunable and switchable metamaterial absorber operating in the mid-infrared region. The metamaterial structure comprises an array of metal–dielectric concentric nanodisks and a metal square patch on a substrate coated with thin dielectric and metal layers. The two dielectric regions induce two absorption bands, which can be independently tuned by changing the refractive index and geometrical parameters of the dielectric layers. In an optimised geometry, a dual-band to a single-band switchable frequency response is achieved by interchanging the refractive index of the dielectric layers. The origin of the resonant absorptions is traced to the simultaneous excitation of electric and magnetic fields in the dielectric regions. Due to architectural symmetry, the investigated structure is polarisation-insensitive and exhibits high absorption over a wide range of angles. [ABSTRACT FROM AUTHOR]

In this paper, a toroidal metamaterial for achieving highly sensitive sensors in the terahertz (THz) frequency range is proposed. Such a subwavelength structure consists of a pair of mirror-symmetric metal split-ring resonators and a single metal wire. By exciting the structure with vertically incident electromagnetic waves, high-Q transmission peaks are generated at 2.40 and 2.44 THz. Near-field analysis reveals that the reverse-flowing currents in the metal split-ring resonators and the metal wire create a pair of magnetic dipoles connected end to end, resulting in a vortex-like magnetic field known as a toroidal dipole. Calculations of multipole scattering energy further confirm that the rapidly enhanced toroidal dipole is the primary factor responsible for the high-Q transmission peaks. This toroidal metamaterial can be used to design refractive index sensors with a sensitivity of up to 20 GHz/RIU, enabling the detection of subtle changes in the surrounding environment's parameters. Our strategy paves an alternative route to the development of highly sensitive sensors for biological and chemical molecules in the THz frequency range. [ABSTRACT FROM AUTHOR]

The combination of 3D printing, polymer derived ceramics, and electromagnetic wave (EMW) absorption metamaterials is particularly useful for spacecraft stealth in extreme environments and is gradually gaining significant interest. While the 3D printing of SiOC has been extensively researched, the high temperature stability and mechanical performance of SiOC are not as favorable as SiCN. However, it remains challenging to prepare SiCN metamaterials with both high mechanical and microwave absorption properties by 3D printing. Herein, we demonstrate a SiCN EMW absorption metamaterial with high mechanical properties using digital light processing 3D printing, which achieves a minimum reflection loss of −31.01 dB (99.9 % absorption), and the widest effective absorption bandwidth covers the entire X-band from 8.2 to 12.4 GHz. And the EMW absorption performance can be adjusted based on the size of the unit structure. [ABSTRACT FROM AUTHOR]

This paper presents a multifunctional tuneable wideband metasurface absorber based on phase-changing Vanadium dioxide (VO2). The 'quad isotropic VO2 circular sectors' are constructed on amorphous silicon dioxide (SiO2), backed with 0.2 µm-thick gold layer to design the proposed absorber. This novel wideband tunable structure can independently be used as a reflector and absorber as an EMI shield; hence, this multi-functionality in a single structure proves novel and unique in the terahertz frequency range. This unit cell offers a bandwidth of 3.5 THz with more than 90% of absorptivity under normal wave incidence. The equivalent circuit model, surface currents, and field distributions are further investigated to provide a better understanding of structural evolution. Moreover, a wideband absorption has been observed up to the 60° incident angle for both the transverse modes, showing a polarization-insensitive behavior due to the symmetricity in the structure. The parametric study explores, optimizes, and demonstrates various other main characteristics and parameters of the proposed absorber. The novel structure offers shielding effectiveness (SE) higher than 40 dB throughout the frequency band under both normal and oblique incidence. This outstanding performance makes it a strong contender for EMI-EMC applications. Furthermore, it shows great potential in the field of terahertz technology, such as terahertz imagers, detectors, sensors, and other wideband applications. [ABSTRACT FROM AUTHOR]

Lattice metamaterials, a class of structures utilized for geometric lightweighting and enhancing structural integrity, feature interconnected elements arranged in specific patterns. These patterns confer unique properties beneficial for improving stiffness, damping, energy absorption, and strength across various applications. However, computational simulation of lattice structures for design and optimization presents significant challenges due to nonlinear and elastic/inelastic effects like instabilities, contacts, rate-dependence, and plasticity. Current methods heavily rely on finite element analysis (FEA), yet they entail high computational complexity and do not fully align with experimental observations. Moreover, additive manufacturing (AM) technologies introduce additional computational complexity due to process-induced anisotropic behaviors. This paper proposes a computational model to construct an effective descriptor by integrating metamaterial topological information with AM conditions. This descriptor serves as a surrogate for FEA models. Additionally, a database is established to correlate the descriptor with experimentally acquired mechanical responses of additively manufactured metamaterials. The bidirectional operation of the envisaged descriptor fulfills two objectives: informing the mechanical response of novel metamaterial models and guiding design and AM processes based on desired outcomes. Model validation demonstrates significant concurrence between predicted and experimental results, evidencing the model's capability to capture inherent nonlinearity in both design and process. [ABSTRACT FROM AUTHOR]

Over the past decade, optical sensors have made significant advances. An optical sensor examines the environmental impact through the change of an optical signal and offers advantages such as low cost and label-free detection. In this study, a sensor consisting of a single graphene layer and a slit positioned on the substrate is proposed. The strip gap made to improve the excitation of graphene plasmons allowed to achieve 96.2% high transmission resonance mode. This demonstrates the ability of the sensor surface to detect changing environmental conditions. The results show that the sensitivity of the sensor is 6282 nm/RIU when the sensor surface is exposed to analytes with different refractive indices. The use of a single graphene sheet eliminates the need for a metal resonator and achieves a higher sensitivity compared to some experiments recently published in the literature. Thus, the disadvantage of significant ohmic losses in metal resonators is avoided. Furthermore, a thorough discussion of various factors, including the modification of the strip gap width on the graphene layer and electrical tunability, led to the achievement of optimal sensitivity. [ABSTRACT FROM AUTHOR]

With advances in terahertz technology, achieving high and nearly constant birefringence over a wide frequency range plays an extreme role in many advanced applications. In the past decade, significant research efforts have been devoted to creating new systems or elements with high birefringence. To our knowledge, the maximum birefringence attainable using artificial crystals, intrinsic liquid crystals or fiber-based systems has been less than unity. More importantly, the birefringence created in previous studies has exhibited a strong frequency dependence, limiting their practical applications. In this work, we propose a novel approach to achieve extraordinarily high birefringence over a broad terahertz frequency band (>100 GHz). To address the limitation of frequency dependence, we combined the principle of metamaterials with the form birefringence concept. First, we designed a metamaterial with an exceptionally high refractive index, thoroughly characterizing it using simulations and analytical analysis. Next, we systematically investigated the form birefringence concept, exploring its frequency response, geometric limitations, and complex refractive index differences between constituent elements. Finally, we designed a hybrid material system, combining the strengths of both metamaterials and form birefringence. Our results demonstrate the feasibility of achieving a birefringent medium exceeding three orders of magnitude higher than previous reports while maintaining a time-invariant frequency response in the sub-terahertz regime. [ABSTRACT FROM AUTHOR]

The aim of the article is to study the forces arising in a conductive DNA-like double helix in the field of a microwave electromagnetic wave. These forces must be considered for both actual DNA molecules and double DNA-like helices that serve as components of metamaterials and metasurfaces. The helix comprises twenty-and-a-half turns and has geometric parameters proportional to the size of an actual DNA molecule. The forces acting on the strands of a double helix, both in the central region and at the edges of the helix, are investigated. It has been demonstrated that the aforementioned forces induce a change in the shape of the helix, specifically the mutual repulsion of the strands, as well as their stretching and twisting in the field of electromagnetic waves. Consequently, exposure to an electromagnetic wave under half-wave resonance can damage the double helix. Conversely, the impact of electromagnetic waves has the potential to introduce novel avenues for controlling the shape of the double helix. [ABSTRACT FROM AUTHOR]

Rapid deployment of automation in today's world has opened up exciting possibilities in the realm of design and fabrication of soft robotic grippers endowed with sensing capabilities. Herein, a novel design and rapid fabrication by 3D printing of a mechano‐optic force sensor with a large dynamic range, sensitivity, and linear response, enabled by metamaterials‐based structures, is presented. A simple approach for programming the metamaterial's behavior based on mathematical modeling of the sensor under dynamic loading is proposed. Machine learning models are utilized to predict the complete force–deformation profile, encompassing the linear range, the onset of nonlinear behavior, and the slope of profiles in both bending and compression‐dominated regions. The design supports seamless integration of the sensor into soft grippers, enabling 3D printing of the soft gripper with an embedded sensor in a single step, thus overcoming the tedious and complex and multiple fabrication steps commonly applied in conventional processes. The sensor boasts a fine resolution of 0.015 N, a measurement range up to 16 N, linearity (adj. R2–0.991), and delivers consistent performance beyond 100 000 cycles. The sensitivity and range of the embedded mechano‐optic force sensor can be easily programmed by both the metamaterial structure and the material's properties. [ABSTRACT FROM AUTHOR]

In this research, we designed a disc structure metamaterial emitter using silver and titanium dioxide for radiative cooling applications. We used COMSOL Multiphysics software for numerical simulations, considering temperature changes induced by atmospheric and surface radiation. The results of the numerical simulations demonstrated that the designed emitter had an average emissivity of 89.5% within the atmospheric transparency window, which spans from 8 to 13 µm. Furthermore, the designed emitter has the potential to achieve a radiative cooling power of 200.4 W/m2 at an ambient temperature of 300 K and can reach an equilibrium temperature of 268.25 K. Impressively, the designed emitter can cool down to 31.75 °C below the ambient temperature. Based on the results of our research, metamaterial emitter has the potential to be crucial components in the development of energy-efficient radiative cooling devices. Therefore, this work further contributes to the advancement of passive radiative coolers based on metal–dielectric–metal. [ABSTRACT FROM AUTHOR]

A perfect metamaterial absorber (MMA) using a SiO2 substrate has been designed. The suggested absorber model was created by implementing graphene as a metallic layer for the structured patch and copper in the ground plane of the design. The geometry of the prescribed absorber was finalized by cutting the rectangular and circular slots and loading the open-ended dual rings on the structure. Furthermore, the approach based on equivalent circuit modeling (ECM) with mathematical analysis for the proposed MMA is thoroughly discussed. The simulation outcome (S11) obtained with the help of CST software has been compared with the ECM analysis result. The proposed absorber shows a perfect absorbance of 99.97% at the operating frequency of 6.15 THz. The absorption characteristics of the suggested structure have been parametrically investigated as a function of oblique incidence and polarization angles. Furthermore, the designed structure has been analyzed by using various substrates and conducting materials to achieve the optimal value of the absorption peak as a percentage. Overall, the compact, ultra-thin, simple geometry of the prescribed MMA with a high absorption peak and polarization-insensitive nature makes it a suitable choice for utilization in sensing, imaging, and detection in the terahertz regime. [ABSTRACT FROM AUTHOR]

Multimode silicon photonics, leveraging mode-division multiplexing technologies, offers significant potential to increase capacity of large-scale multiprocessing systems for on-chip optical interconnects. These technologies have implications not only for telecom and datacom applications, but also for cutting-edge fields such as quantum and nonlinear photonics. Thus, the development of compact, low-loss and low-crosstalk multimode devices, in particular mode exchangers, is crucial for effective on-chip mode manipulation. This work introduces a novel mode exchanger that exploits the properties of subwavelength grating metamaterials and symmetric Y-junctions, achieving low losses and crosstalk over a broad bandwidth and a compact size of only 6.5 µm × 2.6 µm. The integration of SWG nanostructures in our design enables precise control of mode exchange through different propagation constants in the arms and metamaterial, and takes advantage of dispersion engineering to broaden the operating bandwidth. Experimental characterization demonstrates, to the best of our knowledge, the broadest operational bandwidth covering from 1,420 nm to 1,620 nm, with measured losses as low as 0.5 dB and extinction ratios higher than 10 dB. Enhanced performance is achieved within a 149 nm bandwidth (1,471–1,620 nm), showing measured losses below 0.4 dB and extinction ratios greater than 18 dB. [ABSTRACT FROM AUTHOR]

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In this study, we propose a high-temperature radar-absorbing structure that combines the ceramic material (YSZ, yttria-stabilized zirconia) with a metamaterial (SRR, split-ring resonator) structure without including additional lossy materials. Although metals typically reflect electromagnetic waves, we found that adjusting the shape of the 3D metal structure and placing dielectric materials in between can impart wave-absorption functionality. The shape of the metamaterial pattern structure was designed using the commercial program CST Studio Suite. The SRR structure was fabricated using metal 3D printing, and YSZ was coated onto the fabricated metal structure using thermal spraying techniques. The proposed radar-absorbing structure was verified using free space measurement equipment, demonstrating a reflection loss characteristic of less than −10 dB over a bandwidth of approximately 0.8 GHz within the X-band. [ABSTRACT FROM AUTHOR]

The suppression of vibration and noise has always been an important issue in engineering，and metamaterials have shown significant application value in vibration and noise reduction. In this paper，a novel hollow starshaped chiral metamaterial is designed by incorporating chiral structural characteristics into traditional hollow starshaped metamaterials and further evolves it into a solid star-shaped chiral metamaterial. The bandgap formation mechanism is analyzed through vibration mode analysis，and the effects of different structural parameters on the bandgap are studied. The propagation characteristics of elastic waves in the structure are investigated through dispersion surfaces，wave propagation direction，group velocity，and phase velocity. Finally，the transmission characteristics of finite periodic structures are studied. The results show that the solid star-shaped chiral metamaterial can generate an ultra-wide bandgap with a width of 5 116 Hz. The bandgap formation is mainly due to the rotational vibrations of the concave stars and ligaments dissipating the energy of elastic waves. Additionally，a decrease in the inner concave angle α and an increase in the angle θ between the ligaments and the horizontal direction result in a wider largest bandgap. The finite periodic structure can generate significant displacement amplitude attenuation within the bandgap range. This novel metamaterial has excellent vibration isolation performance.

Abstract VO2 is a promising phase change material offering a large contrast of electric, thermal, and optical properties when transitioning from semiconductor to metallic phase. Here we show that a hybrid metamaterial obtained by proper combination of a VO2 layer and a nanodisk gold array provides a tunable plasmonic gap resonance in the infrared range. Specifically, we have designed and fabricated a metal–insulator-metal gap resonance by inserting sub-wavelength VO2 film between a flat gold layer and a gold nanodisk resonator array. The resonance of the hybrid metamaterial is centered in the useful 3–5 μm range when VO2 is in its semiconductor state. The experimental study highlights a monotonical spectral tuning of the resonance when increasing temperature up to 50 °C above the room temperature, providing a continuous resonance shift of almost 1 μm in the mid-infrared range. Wavelength range and intensity tunability can be further optimized by modifying the thicknesses of the layers and metamaterial parameters.

Abstract Silicon photonic index sensors have received significant attention for label-free bio and gas-sensing applications, offering cost-effective and scalable solutions. Here, we introduce an ultra-compact silicon photonic refractive index sensor that leverages zero-crosstalk singularity responses enabled by subwavelength gratings. The subwavelength gratings are precisely engineered to achieve an anisotropic perturbation-led zero-crosstalk, resulting in a single transmission dip singularity in the spectrum that is independent of device length. The sensor is optimized for the transverse magnetic mode operation, where the subwavelength gratings are arranged perpendicular to the propagation direction to support a leaky-like mode and maximize the evanescent field interaction with the analyte space. Experimental results demonstrate a high wavelength sensitivity of − 410 nm/RIU and an intensity sensitivity of 395 dB/RIU, with a compact device footprint of approximately 82.8 μm2. Distinct from other resonant and interferometric sensors, our approach provides an FSR-free single-dip spectral response on a small device footprint, overcoming common challenges faced by traditional sensors, such as signal/phase ambiguity, sensitivity fading, limited detection range, and the necessity for large device footprints. This makes our sensor ideal for simplified intensity interrogation. The proposed sensor holds promise for a range of on-chip refractive index sensing applications, from gas to biochemical detection, representing a significant step towards efficient and miniaturized photonic sensing solutions. Graphical Abstract

Acoustic asymmetric focusing (AAF) has attracted widespread attention owing to its great potential in medical ultrasound. The recent development of acoustic metamaterials and metasurfaces has provided various concepts to achieve AAF systems. Generally, the previously demonstrated AAF lenses were limited to one-dimensional structures, leading to difficulties in practical applications. The realization of AAF in three-dimensional (3D) space based on a two-dimensional (2D) device still remains a challenge. Here, we experimentally and numerically study a 2D AAF lens based on mode converters composed of two pairs of phased unit cells I and II and a step waveguide. Based on the phase profile of sound focusing and the step waveguide of mode converters, we experimentally design and demonstrate a type of 2D AAF lens and observe acoustic focusing and asymmetric transmission simultaneously in 3D space under the excitation of the zero-order wave. Both the phenomena arise from the phase modulation of the lens and the cutoff frequency of the first-order wave for the step waveguide, respectively. The fractional bandwidth (the ratio of the bandwidth to the center frequency) of the lens can reach about 0.14. The proposed 2D AAF lens, as well as its associated mode converter, paves the way for the asymmetric manipulation of sound in 3D space that has potential applications in practical sound devices. [ABSTRACT FROM AUTHOR]

Application of metamaterial in realistic devices requires reliable approaches for effective material parameters. We demonstrate that a general homogenization procedure is non-versatile relative to the approach associated with the device functionality either inside or outside the structure. We exemplify it with internal and external treatments for the effective permittivity of a metamaterial in a lens consisting of dielectric rods. The dependence of the focal length on the permittivity and frequency of the incident field is determined, and the composite metalens with an ordinary lens are compared. The focal length is the same for both lens types. The approaches are compared to obtain effective permittivity values. The results show that different methods of homogenization are to be considered for a property description depending on the needs. [ABSTRACT FROM AUTHOR]