Reconfigurable Terahertz Research Articles

A pattern reconfigurable hybrid graphene-metal terahertz MIMO antenna with improved isolation by metasurface absorber for 6G communication

This paper introduces an innovative 2 × 2 MIMO, Multi-Input Multi-Output, antenna working in the sub-Terahertz (THz) band for 6G, 6-Generation, communications (0.1–1.2 THz). This antenna was designed with main metal octagonal patches and parasitic graphene elements, providing pattern reconfigurable antenna for Single-Input Single-Output (SISO) and MIMO applications. In the YZ-plane, aforementioned antenna illustrates a tunable pattern (0°, +70°, −70°) for SISO in three distinct states. In the XZ-plane, it obtains a versatile MIMO function with a controllable pattern (0°, ±20°, ±45°, ±75°) across four states, simultaneously. The adaptability of the radiation pattern is originated from changing graphene conductivity through biasing. In addition, a graphene metasurface was applied as an absorber, moderately improving isolation between 2 antenna elements, minimizing interference, and enhancing the overall system capability. The proposed schematization achieves a significant isolation up to −35 dB within the MIMO antenna’s operational frequency band. Moreover, the MIMO antenna touches a maximum gain of 9.5 dBi, maximum impedance bandwidth of approximately 91% during different states, 10 dBi Diversity Gain, and 2.62×10−7 ECC in the resonance frequency, which demonstrates novelty designing, remarkable pros, and broad applications in the landscape evolution of 6G communication networks.

A reconfigurable ultra-wideband high-purity multimode terahertz OAM antenna array based on graphene and vanadium dioxide

A reconfigurable ultra-wideband multimode terahertz OAM antenna array based on graphene and vanadium dioxide (VO2) is presented in this paper. The uniform circular array (UCA) composed of circularly polarized (CP) antennas, which include a ring radiation patch, a parasitic patch, a perovskite substrate and an irregular VO2 ground plane. The radiation patch is covered with a layer of graphene, by changing the chemical potential of graphene, the working bandwidth and axial ratio bandwidth of the antenna can be changed. By changing the phase state of VO2 (metal state / insulation state) to control the working state of the antenna. The impedance bandwidth (IBW) of the CP antenna proposed is 115.09% (1.73–6.42 THz), the axial ratio bandwidth (ARBW) is 43.97% (2.36–3.69 THz). Using the CP antenna unit can simplify the complex feed network, and only feeding the equal amplitude and equal phase excitation can realize the vortex wave. Changing the number and rotation angle of the antenna unit can realize multimode vortex waves with the l= 0, ±1, ±2, ±3, the purity is approximately 1, respectively. The proposed UCA has excellent application prospect in the 6G communication.

Reconfigurable terahertz multifunctional wave plates with VO2/Ge hybrid metasurfaces.

Active control of polarization using metasurfaces is crucial in terahertz optics, offering promising advancements in sensing, imaging, and telecommunications. Here, we developed reconfigurable terahertz multifunctional wave plates by leveraging vanadium dioxide/germanium hybrid metasurfaces. This approach allows for mutual role changing of metasurface among quarter-wave plate, half-wave plate, and full-wave plate, facilitated by the introduction of continuous-wave and pulse lasers. The photoinduced phase change of vanadium dioxide, along with the bridging control of germanium, plays a key role in the transition of multifunctional wave plates. Also, the analysis of polarization conversion ratio, ellipticity, and underlying physics demonstrates the ability of multifunctional wave plates. These discoveries deliver valuable insight into advanced polarization control and demonstrate the potential for innovative active-control devices.

Microelectromechanical System-Based Reconfigurable Terahertz Metamaterial for Polarization Filter, Switch, and Logic Modulator Applications.

The terahertz (THz) metamaterials integrated with microelectromechanical systems (MEMS) have led to the realization of dynamic control in amplitude, phase, polarization, and spin angular momentum of the THz wave. In this study, we demonstrate an MEMS-based reconfigurable THz metamaterial (RTM) composed of a split ring resonator (SRR) for real-time modulation of THz wave. By gradually increasing the polarization angle of the incident THz wave, the resonant frequency of SRR switches from 0.74 to 1.16 THz, and the maximum modulation depth is more than 70%. When the MEMS-based RTM is actuated by different DC bias voltages, the polarization-dependent transmission intensity and resonant frequency of the device can be actively tuned. MEMS-based RTM shows logical function characteristics that can be used for logic modulators by performing the driving voltages and polarization states as 2-bit input signals and quantizing the transmission response as "on" and "off" states. The logic gates of "NAND" are at 0.439 THz and "AND" is at 0.732 THz. These results offer potential applications for the proposed MEMS-based RTM in tunable and reconfigurable polarization filters, optical switches, programmable logic modulators, and so on.

Reconfigurable terahertz stretchable spoof surface plasmon polariton waveguide for filter applications

In this paper, a reconfigurable terahertz spoof surface plasmon polariton (SPP) waveguide is proposed on a stretchable polydimethylsiloxane (PDMS) substrate. The SPP unit incorporates a folded stub and a conventional V-shaped SPP groove, enhancing the equivalent capacitance and consequently reducing the cutoff frequency. The cutoff frequency of the proposed SPP unit can be tuned from 285 to 390 GHz with stretchable factors of 1 ∼ 1.2, thereby achieving a reconfigurable operating frequency. The horizontal dimension of the proposed SPP waveguide can be tuned from 6.36 mm to 7.12 mm. Moreover, the SPP waveguide can generate transmission continuous phase shifts of −30°, −60°, −90°, and −120° with stretchable factors of 1.05, 1.1, 1.15, and 1.2, respectively, in the 150–190 GHz band. Applying the characteristic mode theory, a split ring resonator (SRR) functions as the equivalent magnetic dipole, which remains unaffected by stretchable deformation. When loaded with four SRR cells, the proposed SPP waveguide generates a tunable passband with a fixed notched frequency at 193 GHz. Another stretchable SPP resonator serves as the equivalent electric dipole, operating from 284 GHz to 256 GHz in 1∼1.2 stretchable states. By loading three SPP resonators, the SPP waveguide can achieve a passband for the initial state, and a tunable stopband is introduced under 1.1 and 1.2 stretchable states. The proposed stretchable method provides a promising solution for planar terahertz components and systems with reconfigurable functions.

MEMS reconfigurable terahertz meta-absorber with polarization-dependent and sensing characteristics

This study presents and demonstrates a design of a micro-electro-mechanical system (MEMS) reconfigurable terahertz (THz) metamaterial absorber (TMA) that shows tunable free spectra range with a maximum value as 166 GHz in transverse magnetic mode and switchable resonance from 1.24 THz to 1.53 THz. The unit structure of TMA consists of two movable rectangular resonators aside and an x-shaped resonator at the center comprising two c-shaped resonators connected upside down. The material configuration of TMA is typical of the metal–insulator-metal sandwich configuration. That is a bottom Au layer preventing the penetration of the THz wave, a dielectric SiO2 layer to accommodate and absorb the incident wave, and a patterned Au structure array to select the resonant frequency. The electromagnetic response of TMA could be flexibly modulated when the structure is reconfigured by changing the gaps between x-shaped resonators and rectangular resonators based on the MEMS platform. Meanwhile, owing to the asymmetry of resonant structure, the electromagnetic response of TMA could be tuned from single-, dual-, triple- quad-resonances by varying the polarization state of incidence. Furthermore, the sensitivity of TMA is explored and demonstrated with remarkable linearity under a variation of the surrounding environment refractive index from 1.0 to 2.0. The feasibility of TMA is validated as the experimental absorption spectra are well meet the simulation results. The above results indicate the proposed TMA possesses great potential applications in multiple resonance switches, polarization switches, and highly efficient environmental sensors.

Synergy of 6G technology and IoT networks for transformative applications

SummaryThe rapid growth of Wi‐Fi networking and intelligent systems, fueled by the emergence of the Internet of Things (IoT), has enabled significant transformative advancements. The imminent arrival of sixth‐generation (6G) wireless networks offers more opportunities as fifth‐generation (5G) wireless networks improve IoT connections. This study explores the potential advantages of 6G technology and IoT networks, focusing on edge intelligence, reconfigurable smart surfaces, Terahertz communications, and blockchain integration. The study examines potential implementation challenges and highlights the potential impact of 6G on IoT device usage. This research outlines potential applications of 6G in many sectors like the internet of vehicles, healthcare, autonomous driving, unmanned aerial vehicles, satellite television, and industrial IoT. This research elaborates on specific research topics related to 6G‐IoT technologies to enhance understanding and practical applicability.

Graphene–metal hybrid based reconfigurable wideband terahertz antenna with improved far-field characteristics

Graphene–metal hybrid based reconfigurable wideband terahertz antenna with improved far-field characteristics

Reconfigurable Chiral Spintronic THz Emitters

AbstractCollective spin arrangements manifest diverse spin textures, encompassing ferromagnetism, antiferromagnetism, and chiral vortices. However, mapping these spin textures in ultrathin magnetic multilayers has remained elusive. A reconfigurable chiral spintronic terahertz emission method is introduced through investigations on a model system of synthetic antiferromagnet and the spin information of individual ferromagnet (FM) layers is extracted. Upon femtosecond photoexcitation of the synthetic antiferromagnet (FM1/Ru/FM2), the ferromagnets generate a pair of linearly polarized ultrafast spin currents, which, after relaxation at the FM/Ru interface, emit corresponding THz pulses. The Ruderman–Kittel–Kasuya–Yosida interactions between the two FMs give rise to magnetic‐field‐controlled spin textures causing a spin relaxation imbalance at the interfaces and induce a phase shift between the orthogonal components of the emitted terahertz fields, consequently reconfiguring the polarization of the emitted terahertz field from linear to circular. This approach offers a novel means of investigating electronic and magnetic states in ultrathin spintronic heterostructures, low‐dimensional quantum materials, topological insulators, and Weyl semimetals. Furthermore, it enables the exploration of spin textures, including skyrmions, merons, and solitons.

Huygens’ metasurface: From anomalous refraction to reflection

Huygens' metasurfaces (HMS) without any reflection or transmission are widely studied due to the high-efficiency manipulation of electromagnetic waves. In this work, three-layered metallic Huygens' metasurfaces are proposed and the geometry-dependences of anomalous refraction and reflection are investigated. The surface impedance and admittance are independently tailored by changing the length of metallic resonators, which is dictated by the introduction of the intermediate layer. Huygens’ metasurfaces can be geometrically engineered to realize anomalous refraction with an efficiency of 62% and anomalous reflection with an efficiency of 60%, respectively. It is anticipated that the proposed metasurface with tunable materials could achieve reconfigurable terahertz devices.

Reconfigurable screen-printed terahertz frequency selective surface based on metallic checkerboard pattern

We employed the screen-printing method to fabricate terahertz (THz) frequency selective surfaces (FSSs) featuring an inductive metallic checkerboard (i-MCB) pattern based on conductive silver ink onto a flexible polyethylene terephthalate substrate, chosen for its excellent THz transmission properties below 1 THz [Jin et al 2006 J. Korean Phys. Soc. 49 513–17]. Analytical studies, along with simulations and experiments, were conducted to investigate the filtering characteristics of the printed FSSs, confirming their functionality as a band-pass filter. Subsequently, we demonstrated the reconfigurability of a two-layer system by vertically stacking two layers. This was achieved by systematically shifting the position of the second layer in the x or y-direction relative to the first layer. Experimental verification revealed a significant variation in normalized transmission, ranging from 94% to 6% at 0.15 THz for type-I:i-MCBs and 90% to 5% at 0.20 THz for type-II:i-MCBs, respectively. This study presents a simple scheme for a reconfigurable screen-printed i-MCB-FSS operating in the THz range. Consequently, our findings demonstrate that screen printing method can effectively be employed for the large-scale production of THz FSSs.

Tri-channel independent switching terahertz filter based on metal-graphene hybrid coding metasurface

Terahertz (THz) filters are the core devices for practical application in THz communication technology. Recently, design of multi-channel filters with high modulation rates remains to be a challenge. In this paper, a three channels switchable THz filter based on metal-graphene hybrid metasurface is proposed. The unit cell is consisted of "n"-shaped and "u"-shaped split-ring resonators (SRRs) with different sizes, and the graphene bar is embedded at the gap of two SRRs. The four bandpass modes with single transparency windows, double two transparency windows, and three transparency windows can be freely switched by applying voltage to the left/right electrodes of the filters. Its central frequencies of transparency windows are located at 0.80 THz with modulation depth up to 49%, 1.14 THz (constant transparency windows), and 1.58 THz with modulation depth up to 68%, respectively. In addition, an equivalent circuit model is proposed to demonstrate the control mechanism. This research result not only provides a new method for the design of reconfigurable multifunctional THz modulation devices, but also give theoretical model to promote the development of multi-channel filter technology in THz communication technology.

Large and active circular dichroism in a photosensitive silicon based metasurface

Active circular dichroism (CD) is highly required for flexible polarization control in modern terahertz (THz) systems. In this work, we numerically achieve large and active CD in THz region by optically controlling photosensitive silicon in a gold/silicon hybrid cross-shape metasurface. At the incident angle of 75°, the proposed metasurface exhibits large CD. By tuning the conductivity of photosensitive silicon with an optical pump, the large CD (0.89) can be dynamically switched to 0.06 and the peak frequency is blue shifted around 0.09 THz. The simultaneous switching of CD strength and peak frequency is attributed to the variation of resonance modes between electric and magnetic dipole resonances. Our proposed active metasurface with dynamic CD has profound potential in the fields of reconfigurable THz devices.

Tunable dynamic metamaterial for negative refraction

The effective ability to manipulate the negative refraction behaviors of electromagnetic waves in the terahertz (THz) frequency range is of great interest for various practical applications in communication, imaging, and sensing. In this study, we propose a robust graphene-integrated metamaterial design for the dynamic manipulation of negative refraction at terahertz frequencies. Using the distinctive characteristics of graphene combined with the specially designed metamaterial structure, we demonstrated the active control of negative refraction by modulating the graphene's chemical potential from 0.0 to 1.0 eV. By dynamically tuning the carrier density of graphene, we create the switchable states of the negative index for the transmission or the reflection modes, tailoring the terahertz wave behavior in real time. In particular, in the case of different applied temperatures (through the bias applied voltages) of the proposed metamaterial, these two modes are maintained over 60% for both reflection and transmission while preserving the negative refractive index. Our results reveal the tunability of negative refraction, paving the way for developing reconfigurable THz meta-devices with enhanced functionalities in the near future.

Reconfigurable three multi-mode terahertz metasurface.

We designed a three reconfigurable multi-mode terahertz metasurface based on a concentric elliptical ring structure. The proposed unit cell is a concentric elliptical ring composed of copper, vanadium oxide and photosensitive silicon from the inside ring to the outside ring. The conductivity of photosensitive silicon and vanadium oxide can be adjusted by changing the external operating temperature and pump light intensity. The same unit cell can reconstruct three kinds of states with different properties, and they have completely different transmission characteristics in various terahertz bands. By encoding the arrangement, through changing external stimulus and operating frequencies, the reconfigurable terahertz metasurface can achieve multiple functions including terahertz focusing with adjustable focal length, vortex beam with different topological charge, and near-field imaging with different patterns. It provides what we believe to be a new idea for the field of information security and the design of multifunctional and multifrequency terahertz devices.

3-bit reconfigurable THz metasurface based on structured light illumination for vortex beams and holographic imaging

Metasurfaces have attracted widespread attention due to their excellent control ability of terahertz wavefronts. Terahertz metasurfaces have made rapid progress in areas such as biological detection, high-speed communication, and imaging. However, terahertz metasurfaces currently have a single function, and the primary goal of this research is to create a reconfigurable and multifunctional terahertz metasurface. In this work, we designed a novel eight-gaps-splits-ring resonator (EGSRR). The EGSRR is filled with photosensitive semiconductor material, and the metasurface unit's amplitude-phase characteristics are controlled by different encodings of structured light. Finally, under the incidence of right-handed circularly polarized (RCP) waves, 3-bit phase encoding of its reflected wave with cross-polarization is achieved. To verify the ability of metasurface to control terahertz wavefronts, the 3-bit metasurface units are assembled into an array to achieve different-order vortex beams and reconfigurable holographic images. The novel optically controlled reconfigurable metasurface not only has promising applications in generating vortex beams and holographic imaging, but it also represents a novel approach to designing multifunctional and programmable terahertz metamaterials.

Design of a Compound Reconfigurable Terahertz Antenna Based on Graphene

Design of a Compound Reconfigurable Terahertz Antenna Based on Graphene

Enhancing device efficiency using a reconfigurable terahertz wavefront modulator based on fermi level of graphene

This study investigates a Fermi-level-reconfigurable terahertz wavefront modulator composed of a hybrid material comprising graphene, silver metal, and silicon dioxide. Through theoretical simulation, analysis, and experimental investigations, it is found that graphene plays a crucial role in enhancing the performance of the modulator. Specifically, the presence of graphene increases the limiting factor of the modulator by 0.281, reduces the normalized modal field area by 0.15, decreases the transmission loss, and lowers the gain threshold by 30097 cm−1, thereby improving the efficiency, reliability, and stability of the device. The silicon dioxide and silver metal in the structure act as the primary reflective materials, achieving the effect of a metallic lens and validating the modulator's capability for efficient defocusing. Further investigations reveal that the carrier concentration of graphene can be easily controlled, allowing for manipulation of its physical properties through Fermi-level modulation. When incident light passes through the graphene array, it induces phase variations, altering the transmission path of light and thereby affecting the position of the defocused focal point, enabling dynamic adjustability. Under low Fermi-level control, the modulator achieves a 2πphase adjustment range with an average reflectivity of 75%. Thus, this provides potential for practical applications of more dynamic and tunable microdevices, particularly in the field of laser cutting technology and etching processes.

Room-temperature-grown tungsten oxide hybridized dipole cavities to realize thermally tunable terahertz surface plasmons

Recent developments in the field of terahertz (THz) subwavelength structures have inspired novel discoveries and innovations involving the use of multidimensional materials in fields such as spectroscopy, photonics, biomedical imaging, nonlinearity, and communication technology. In this context, metal oxide materials with adaptable electronic and optical properties have emerged as promising candidates to realize dynamically reconfigurable THz subwavelength devices. Therefore, we experimentally demonstrated temperature-tunable surface plasmon resonances (SPRs) in an array of tungsten oxide (WO3) hybridized subwavelength cavities. By using THz time-domain spectroscopy, we examined the thermally tunable dielectric properties of a WO3 thin film over a temperature range of 25 °C–110 °C. On the basis of the tunable optoelectronic properties of WO3, we implement a THz subwavelength dipole cavity that can exhibit a temperature-dependent dynamic modification in SPR characteristics. Such tunability could be used to fabricate novel active SPR-based plasmonic devices like temperature sensors, spatial modulators, filters, and integrated THz optoelectronic elements.

On‐Chip Non‐Volatile Reconfigurable THz Varifocal Metalens

AbstractImplementation of integrated, nonvolatile, and reconfigurable solutions for on‐chip terahertz (THz) metadevices holds great potential for applications in sensing, integrated circuits, and high‐speed communications. This study demonstrates the non‐volatile reconfigurable dynamic manipulation of THz on‐chip metadevices through optical modulation of Ge2Sb2Te5 (GST) and 2π phase shift of metasurfaces. The approach allows for the simultaneous realization of surface plasmons (SPs) excitation, wavefront shaping, and amplitude modulation in a single device. Using the principles of 2D holography, a reconfigurable multilevel THz SP metalens switch with a maximum extinction ratio of 29.9 dB is presented. The focusing intensity of the metalens can be continuously modulated by varying the pump laser energy. The implementation of the approach is further demonstrated by realizing a switchable THz SP varifocal metalens. Reconfigurable, reversible, and repeated switching is achieved through optical and thermal stimuli, resulting in switching contrast ratios of 7.4 dB and −44.4 dB in the amorphous and crystalline states of GST, respectively. The results demonstrate a promising route toward developing non‐volatile, reconfigurable, and energy‐efficient on‐chip THz integrated metadevices. By enabling the dynamic manipulation of THz waves on a single chip, the approach holds significant potential for advancing the field of terahertz‐integrated photonics.