Search Results (134)

Millimeter-wave (mmWave) antennas and antenna arrays have gained significant attention due to their pivotal role in emerging wireless communication, sensing, and imaging technologies. With the rapid deployment of 5G and the transition toward 6G networks, the demand for compact, high-gain, and reconfigurable mmWave antennas has intensified. This article highlights recent advancements in mmWave antenna technologies, including hybrid beamforming using phased arrays, dynamic beam-steering enabled by liquid crystal and MEMS-based structures, and high-capacity MIMO architectures. We also examine the integration of metamaterials and metasurfaces for miniaturization and gain enhancement. Applications covered include wearable antennas with low-SAR textile substrates, conformal antennas for UAV-based mmWave relays, and high-resolution radar arrays for autonomous vehicles. The study further analyzes innovative fabrication methods such as inkjet and aerosol jet printing, micromachining, and laser direct structuring, along with advanced materials like Kapton, PDMS, and graphene. Numerical modeling techniques such as full-wave EM simulation and machine learning-based optimization are discussed alongside experimental validation approaches. Beyond communications, we assess mmWave systems for biomedical imaging, security screening, and industrial sensing. Key challenges addressed include efficiency degradation at high frequencies, interference mitigation in dense environments, and system-level integration. Finally, future directions, including AI-driven design automation, intelligent reconfigurable surfaces, and integration with quantum and terahertz technologies, are outlined. This comprehensive synthesis aims to serve as a valuable reference for advancing next-generation mmWave antenna systems. Full article

This academic paper proposes a terahertz (THz) device featuring dynamic adjustability. This device relies on composite metamaterials made of graphene and vanadium dioxide (VO₂). By integrating the electrically adjustable traits of graphene with the phase transition attributes of VO₂, the suggested metamaterial device can achieve both broadband absorption and dual-band linear-to-circular polarization conversion (LCPC) in the terahertz frequency range. When VO₂ is in its metallic state and the Fermi level of graphene is set to zero electron volts (eV), the device shows remarkable broadband absorption. Specifically, it attains an absorption rate exceeding 90% within the frequency span of 2.28–3.73 terahertz (THz). Moreover, the device displays notable polarization insensitivity and high resistance to changes in the incident angle. Conversely, when VO₂ shifts to its insulating state and the Fermi level of graphene stays at 0 eV, the device operates as a highly effective polarization converter. It attains the best dual-band linear-to-circular polarization conversion within the frequency ranges of 4.31–5.82 THz and 6.77–7.93 THz. Following the alteration of the Fermi level of graphene, the device demonstrated outstanding adjustability. The designed multi-functional device features a simple structure and holds significant application potential in terahertz technologies, including cloaking technology, reflectors, and spatial modulators. Full article

In this paper, we propose a multi-mode switchable ultra-wideband terahertz absorber based on patterned graphene and VO₂ by designing a graphene pattern composed of a large rectangle rotated 45° in the center and four identical small rectangles in the periphery, as well as a VO₂ layer pattern composed of four identical rectangular boxes and small rectangles embedded in the dielectric layer. VO₂ can regulate conductivity via temperature, the Fermi level of graphene depends on the external voltage, and the graphene layer and VO₂ layer produce resonance responses at different frequencies, resulting in high absorption. The proposed absorption microdevices have three modes: Mode 1 (2.52–4.52 THz), Mode 2 (3.91–9.66 THz), and Mode 3 (2.14–10 THz), which are low-band absorption, high-band absorption, and ultra-wideband absorption. At 2.96 THz in Mode 1, the absorption rate reaches 99.98%; at 8.04 THz in Mode 2, the absorption rate reaches 99.76%; at 5.04 THz in Mode 3, the absorption rate reaches 99.85%; and at 8.4 THz, the absorption rate reaches 99.76%. We explain the absorption mechanism by analyzing the electric field distribution and local plasma resonance, and reveal the high-performance absorption mechanism by using the relative impedance theory. In addition, absorption microdevices have the advantages of polarization insensitivity, incident angle insensitivity, multi-mode switching, ultra-wideband absorption, large manufacturing tolerance, etc., and have potential research and application value in electromagnetic stealth devices, filters and optical switches. Full article

This article presents a comprehensive analysis of the technical characteristics of advanced versatile materials used in chipless radio-frequency identification (RFID) tags and antennas. The focus is on materials that are used as radiators and substrates. Crucial aspects include flexibility, weight, size, gain, environmental sustainability, efficiency, fabrication time and type, and cost. A comprehensive set of tables are presented that summarize and compare material properties. The materials include flexible high-tech ink substances, graphene, and liquid crystals, as well as metamaterials which possess properties that allow for an increased bandwidth. Printing techniques are discussed for high-performance high-resolution fabricated tags. This paper contributes by systematically comparing emerging materials for chipless RFID tags, highlighting their impact on performance and sustainability. It also provides practical guidance for material selection and fabrication techniques to enable next-generation wireless applications. It presents a broad understanding of various materials and their use. The paper provides direction for the deployment and utilization of inexpensive passive chipless RFID tags in future intelligent wireless networks. The advancement of chipless RFID is largely driven by the development of innovative materials, especially in the realm of advanced materials and smart materials, which enable the creation of more cost-effective, flexible, and scalable RFID systems. Full article

This paper presents a highly sensitive and tunable graphene-based metamaterial perfect absorber (MPA) operating in the near-terahertz band. The structure features a unique flower-like graphene pattern, consisting of a Au substrate, a SiO₂ dielectric layer, and the patterned graphene. Multiple reflections of incident light between the gold and graphene layers increase the duration and intensity of the interaction, resulting in efficient absorption at specific frequencies. The design utilizes surface plasmon resonance (SPR) to achieve near-perfect absorption of 99.9947% and 99.6079% at 11.7475 THz and 15.8196 THz, respectively. By tuning the Fermi level and relaxation time of graphene, it is possible to precisely control the frequency and absorptivity of the absorption peak, thereby demonstrating the dynamic tunability of the absorber. The high symmetry and periodic arrangement of the structure ensures insensitivity to the polarization angle of the incident light in the range of 0° to 90°, making it extremely valuable in practical applications. In addition, the absorber exhibits very high sensitivity to changes in ambient refractive index with a maximum sensitivity of 3.205 THz/RIU, a quality factor (FOM) of 11.3011 RIU⁻¹, and a Q-Factor of 48.61. It has broad application prospects in the fields of sensors, optoelectronic devices, and terahertz imaging. Full article

Due to the equipartition exciton property of graphene metamaterials, researchers have applied them to the design of absorbers and developed a series of absorbers covering different wavebands (including narrowband and broadband). In this paper, an absorber based on surface-isotropic excitations was designed with the help of graphene metamaterials and relevant simulations. The absorber exhibited six perfect absorption peaks in the mid-infrared band and had an extremely simple structure consisting of only three layers: a gold layer at the bottom, a dielectric layer made of silica in the middle, and patterned graphene at the top. This absorber possesses excellent tuning ability, and by applying an external bias to the graphene layer, the Fermi energy level of graphene can be adjusted, and thus the resonance frequency of the absorption peak can be tuned. Meanwhile, the effect of the graphene relaxation time on the absorber performance was investigated. In addition, the refractive index of the dielectric layer was found to be linearly related to the resonance frequency of the absorption peak. It is worth mentioning that the absorber structure possessed polarization insensitivity due to its central symmetry. Even when incident light with different polarizations was incident over a wide range of angles, the change in absorbance of the absorption peaks was negligible, demonstrating significant insensitivity to the angle of incidence. The sensor possesses excellent characteristics such as tunability, polarization insensitivity, incident angle insensitivity, and high sensitivity. This paper demonstrates the feasibility of a six-frequency sensor and opens up more ideas for the design of multi-frequency sensors. Full article

This paper proposes a switchable and tunable terahertz metamaterial absorber utilizing a graphene-VO₂ layered structure. The design employs reconfigurable seven-layer architecture from top to bottom as (topaz/VO₂/topaz/Si/graphene/topaz/Au). CST software 2018 was used to simulate the absorption properties of terahertz waves (0–14 THz). The proposed metamaterial exhibits dual functionalities depending on the VO₂ phase state. In the insulating state, the design achieves a tri-band response with distinct peaks at 3.12 THz, 5.65 THz, and 7.24 THz. Conversely, the VO₂’s conducting state enables ultra-broadband absorption from 2.52 THz to 11.62 THz. Extensive simulations were conducted to demonstrate the tunability of absorption: Simulated absorption spectra were obtained for broadband and multi-band states. Electric field distributions were analyzed at resonance frequencies for both conducting and insulating states. The impact was studied of VO₂ conductivity, loss tangent, and graphene’s chemical potential on absorption. The influence was investigated of topaz layer thickness on the absorption spectrum. Absorption behavior was examined of VO₂ under different states and layer configurations. Variations were analyzed of absorption spectra with frequency, polarization angle, and incident angle. The proposed design used for the detection of cervical and breast cancer detection and the sensitivity is about is 0.2489 THz/RIU. The proposed design holds significant promise for real-world applications due to its reconfigurability. This tunability allows for tailoring absorption properties across a broad terahertz range, making it suitable for advanced devices like filters, modulators, and perfect absorbers. Full article

We employed the CST Microwave Studio software 2020 and the FDID algorithm for simulation. We have designed a terahertz broadband absorber based on Dirac semimetals and graphene, achieving continuous broadband absorption with a rate exceeding 80% over the range from 7.6776 to 9.172 THz. This broadband absorber features two independent tuning modes, utilizing graphene and Dirac semimetals, and exhibits strong electromagnetic adaptability. Furthermore, we conducted an in-depth analysis of the physical mechanisms underlying the high absorption in these absorbers using impedance matching theory and localized surface plasmon resonance (LSPR) theory. Variations in the dielectric constants of different dielectric layers and the relaxation time of graphene can also modulate the absorption rate. In summary, our proposed terahertz broadband absorber, employing two distinct tunable materials, enhances the device’s flexibility and environmental adaptability, offering promising prospects for wideband absorption applications. Full article

Graphene oxide (GO) has emerged as a carbon-based nanomaterial providing a different pathway to graphene. One of its most notable features is the ability to partially reduce it, resulting in graphene-like sheets through the elimination of oxygen-including functional groups. In this paper, the effect of localized interactions in an Ag/GO/Au multilayer system was studied to explore its potential for photonic applications. GO was dip-coated onto magnetron-sputtered silver, followed by the deposition of a thin gold film to form an Ag/GO/Au structure. Micro-Raman Spectroscopy, SEM and Variable Angle Ellipsometry (VASE) measurements were performed on the Ag/GO/Au structure. An interesting behavior of the GO deposited on magnetron-sputtered silver with the formation of Ag nanostructures on top of the GO layer is reported. In addition to typical GO bands, Micro-Raman analysis reveals peaks such as the 1478 cm⁻¹ band, indicating a transition from sp³ to sp² hybridization, confirming the partial reduction of GO. Additionally, calculations based on effective medium theory (EMT) highlight the potential of Ag/GO structures in hyperbolic metamaterials for photonics. The medium exhibits dielectric behavior up to 323 nm, transitions to type I HMM between 323 and 400 nm and undergoes an Epsilon Near Zero and Pole (ENZP) transition at 400 nm, followed by type II HMM behavior. Full article

This paper explores the vibration behaviour of an elastically constrained graphene origami-enabled auxetic metamaterial beam subject to a harmonic external force. The effective mechanical properties of the metamaterial are approximated using a micromechanical model trained via a genetic algorithm provided in the literature. The three coupled equations of motion are solved numerically; a set of trigonometric functions is used to approximate the displacement components. The accuracy of the proposed model is confirmed by comparing it with the natural frequencies of a simplified non-metamaterial structure available in the literature. Following this validation, the investigation extends to investigate the forced vibration response of the metamaterial beam, examining the influence of the graphene origami distribution pattern and content, graphene folding degree, linear and shear layer stiffness, and geometrical parameters on the dynamic behaviour of the structure. The results generally highlight the considerable effect of the shear layer, modelled as a Pasternak foundation, on the vibration behaviour of the elastically constrained metamaterial beams. Full article

Graphene is considered to be one of the most promising reinforcement phases for nanocomposites due to its unique two-dimensional planar structure with excellent mechanical properties. After the design of origami, the 2D material will obtain a negative Poisson’s ratio in the in-plane direction and become a metamaterial with unusual mechanical properties. Inspired by this, an origami pattern is adopted for graphene at an atomic scale using a molecular dynamics (MD) approach, and then origami graphene is embedded into a single-crystal copper matrix to obtain origami graphene/copper nanocomposites with auxetic behaviors. In the modeling, the periodic boundary condition is chosen to exhibit the Poisson’s ratio of the whole system. Under the isothermal–isobaric ensemble, the interactions between C-C, Cu-Cu, and C-Cu atoms are, respectively, determined by three potential functions: AIREBO, EAM, and LJ. The effect of the origami graphene/copper interfacial gap on the critical strain of incremental Poisson’s ratio, critical strain of engineering Poisson’s ratio, and moduli of the origami graphene/copper nanocomposites is studied to determine the optimum distance between the two phases. The influences of the mass fraction of carbon atom and temperature on those properties are discussed in detail after the MD model is confirmed. Full article

The packing and assembly of Platonic solids have fascinated mathematicians for ages. Recently, this fundamental geometrical problem has also attracted the attention of physicists, chemists, and engineers. This growing interest is due to the rapid advancements in various related fields, ranging from the formation of colloidal crystals and the design of metal–organic frameworks to the development of ultra-lightweight metamaterials, which are closely tied to the fast-evolving 3D printing technology. Numerous reports have focused on the assembly of Platonic polyhedra, particularly tetrahedra, for which an optimal packing strategy remains unidentified to this day. However, less attention has been given to the dodecahedron and its networks. This work introduces a new type of framework, designed from regular dodecahedra combined with icosahedron-based binders. The relatively simple design protocol employed here results in a remarkable variety of intriguing networks, which could be potentially useful in fields such as architecture, regenerative medicine, or aeronautics. Additionally, the dodecahedral networks presented in this study led to the discovery of intriguing structures resembling distorted graphene sheets. These structures exhibit features characteristic of both graphene and diamond. Full article

In recent years, absorbers related to metamaterials have been heavily investigated. In particular, VO₂ materials have received focused attention, and a large number of researchers have aimed at multilayer structures. This paper presents a new concept of a three-layer simple structure with VO₂ as the base, silicon dioxide as the dielectric layer, and graphene as the top layer. When VO₂ is in the insulated state, the absorber is in the closed state, Δf = 1.18 THz (absorption greater than 0.9); when VO₂ is in the metallic state, the absorber is open, Δf = 4.4 THz (absorption greater than 0.9), with ultra-broadband absorption. As a result of the absorption mode conversion, a phenomenon occurs with this absorber, with total transmission and total reflection occurring at 2.4 THz (A = 99.45% or 0.29%) and 6.5 THz (A = 90% or 0.24%) for different modes. Due to this absorption property, the absorber is able to achieve full-transmission and full-absorption transitions at specific frequencies. The device has great potential for applications in terahertz absorption, terahertz switching, and terahertz modulation. Full article

Nowadays, metamaterial absorbers still suffer from limited bandwidth, poor bandwidth scalability, and insufficient modulation depth. In order to solve this series of problems, we propose a metamaterial absorber based on graphene, VO₂, gallium silver sulfide, and gold-silver alloy composites with dual-control modulation of temperature and electric field. Then we further investigate the optical switching performance of this absorber in this work. Our proposed metamaterial absorber has the advantages of broad absorption bandwidth, sufficient modulation depth, and good bandwidth scalability all together. Unlike the single inspired layer of previous designs, we innovatively adopted a multi-layer excitation structure, which can realize the purpose of absorption and bandwidth width regulation by a variety of means. Combined with the finite element analysis method, our proposed metamaterial absorber has excellent bandwidth scalability, which can be tuned from 2.7 THz bandwidth to 12.1 THz bandwidth by external electrothermal excitation. Meanwhile, the metamaterial absorber can also dynamically modulate the absorption from 3.8% to 99.8% at a wide incidence angle over the entire range of polarization angles, suggesting important potential applications in the field of optical switching in the terahertz range. Full article

A broadband absorber based on metamaterials of graphene and vanadium dioxide (VO₂) is proposed and investigated in the terahertz (THz) regime, which can be used for switch applications with a dynamically variable bandwidth by electrically and thermally controlling the Fermi energy level of graphene and the conductivity of VO₂, respectively. The proposed absorber turns ‘on’ from 1.5 to 5.4 THz, with the modulation depth reaching 97.1% and the absorptance exceeding 90% when the Fermi energy levels of graphene are set as 0.7 eV, and VO₂ is in the metallic phase. On the contrary, the absorptance is close to zero and the absorber turns ‘off’ with the Fermi energy level setting at 0 eV and VO₂ in the insulating phase. Furthermore, other four broadband absorption modes can be achieved utilizing the active materials graphene and VO₂. The proposed terahertz absorber may benefit the areas of broadband switch, cloaking objects, THz communications and other applications. Full article