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Magneto‐optical activity is a significant way to achieve asymmetric transmission for spin photons. However, it is severely limited by the weak light‐matter interaction in the terahertz (THz) region. In this work, a magnetic Moiré grating (MMG) is constructed by sandwiching an Yttrium iron garnet (YIG) single crystal in a pair of twisted 2D subwavelength gratings. The twisted angle between two gratings introduces a strong geometric Moiré chirality related to the Moiré pattern. When an external magnetic field is applied to the YIG layer, three different symmetries of spacial mirror image, time reversal, and spin conjugation are broken simultaneously under the chiral coupling between magneto‐optical activity and Moiré chirality, leading to both the enhanced magneto‐optical chiral transmission and the nonreciprocal spin isolation. Under the magnetic field varying from −0.26 to +0.26 T in the experiment, the MMG achieves an active modulation of circular dichroism from 39 to −37.5 dB and optical activity from −35° to 30°. Moreover, the maximum spin isolation over 32.6 dB is also obtained near 0.5 THz. This mechanism provide a new way to realize independent manipulation and active modulation of THz spin photons more flexibly. [ABSTRACT FROM AUTHOR]

Terahertz (THz) technologies provide opportunities ranging from calibration targets for satellites and telescopes to communication devices and biomedical imaging systems. A main component will be broadband THz absorbers with switchability. However, optically switchable materials in THz are scarce and their modulation is mostly available at narrow bandwidths. Realizing materials with large and broadband modulation in absorption or transmission forms a critical challenge. This study demonstrates that conducting polymer‐cellulose aerogels can provide modulation of broadband THz light with large modulation range from ≈ 13% to 91% absolute transmission, while maintaining specular reflection loss < −30 dB. The exceptional THz modulation is associated with the anomalous optical conductivity peak of conducting polymers, which enhances the absorption in its oxidized state. The study also demonstrates the possibility to reduce the surface hydrophilicity by simple chemical modifications, and shows that broadband absorption of the aerogels at optical frequencies enables de‐frosting by solar‐induced heating. These low‐cost, aqueous solution‐processable, sustainable, and bio‐friendly aerogels may find use in next‐generation intelligent THz devices. [ABSTRACT FROM AUTHOR]

Chalcogenide phase‐change materials (PCMs) have offered an appealing material solution by acting as a switchable dielectric layer to tune the electromagnetic properties of terahertz metamaterials and metasurfaces. Here, this work demonstrates large‐scale and lithography‐free manufacturing of all‐PCM terahertz metasurfaces based on direct laser switching of crystalline micro‐domains in a thin film with high switching ratio of the emerging plasmonic PCM, In3SbTe2 (IST). The fabricated high‐quality IST metasurfaces achieve efficient plasmonic resonances and a large modulation depth with ultrafast response (full width at half maxima of the modulation time ≈1.6 ps) in a deep‐subwavelength switching volume. For the dynamic evolution of terahertz resonance modes, theoretical modeling reveals a delicate interplay between amorphous and crystalline IST due to the bonding‐structure‐induced different carrier lifetimes and spatially localized electric fields. These studies open new avenues for realizing all‐PCM terahertz ultrafast nanophotonics. [ABSTRACT FROM AUTHOR]

To meet the requirements of satellite communication (SATCOM), in this paper, a wideband high stability transmitarray antenna (TA) for SATCOM is proposed. The TA is composed of 225 metal-only unit cells that comprise three metallic layers with an air spacer in between. High stability is capable by adopting a simple metallic square loop and two pairs of orthogonal stubs with a 1 mm thickness of the layer, which ensures lower assembly complexity and higher integration. The proposed unit cell can also support linear polarization (LP) wave excitation and circular polarization (CP) wave excitation simultaneously. Meanwhile, the metal-only unit cell can operate without dielectric loss, which leads to higher working efficiency. By adjusting feature sizes, eight different kinds of the unit cell are designed to realize a 3-bit TA which enables obtaining a gain of 23.53 dBi. Finally, four TA prototypes have been fabricated and tested successfully. The measured result shows a 28.5% 3 dB gain bandwidth from 30 GHz to 40 GHz, which is in good consistency with the simulated design. This compact and mechanical robustness design provides an alternative proposal for SATCOM. [ABSTRACT FROM AUTHOR]

Because of the very low C solubility, Cu substrates possess a great advantage in growing the graphene film of monolayer or few layers with well‐developed uniformity. The self‐limited growth manner ensures the growth of nearly pure monolayer graphene, but it prevents the supply of C for the growth of adlayers after the complete growth of the top layer. Herein, a method to continuously supply C from one side of Cu substrate while maintaining sustained growth of multilayer graphene on the other side by separately controlling the atmosphere on two sides is studied. The growth rate and thickness of graphene can be controlled by tuning the oxygen flow and postgrowth time. Multilayer graphene with thickness (t) up to 100 nm is achieved. It demonstrates a potential application in terahertz shielding with a high shielding effectiveness (SE) of 25 dB and accordingly a high SE/t of 2.5 × 105 dB/mm. The study contributes to the controllable growth of graphene films in terms of layer numbers and can be scaled up to large‐area growth through the appropriate design of equipment. [ABSTRACT FROM AUTHOR]

Ultra‐thin rare earth iron garnet (RIG) films with a narrow ferromagnetic resonance (FMR) line width and a low damping factor have attracted a great deal of attention for microwave and spintronic applications. In this work, 200 nm Y3(GaAlFe)5O12 garnet (GaAl‐YIG) films were prepared on gadolinium gallium garnet (GGG) substrates by liquid‐phase epitaxy (LPE) with low saturation magnetization. The microstructural properties, chemical composition, and magnetostatic and dynamic magnetization characteristics of the films are discussed in detail. According to the structural analysis, these films exhibit a low surface roughness of less than 0.5 nm. The GaAl‐YIG films show an obvious temperature dependence of lattice parameter and strain state, and the film's parameter is perfectly matched with that of the GGG substrate at 810°C. There is a clear variation in the Pb level, which brings about a gradual enhancement of the coercivity and a diminution of the squareness ratio of magnetic hysteresis loops as the growth temperature is reduced. Slight changes in surface roughness, strain condition and content of Pb induce the FMR line width and damping factor to vary on a small scale. The line width is less than 10.17 Oe at 12 GHz and the damping factor is of the order of 10−4. All these properties demonstrate that these ultra‐thin GaAl‐YIG films are of benefit for the development of devices operated at lower frequencies and in lower fields. [ABSTRACT FROM AUTHOR]

The prospect of graphene‐based shielding materials in the form of fillers is limited by the cumbersome preparation of graphene. Herein, defect‐tunable porous graphene prepared by carbothermal shock using low‐value sucrose as a precursor is proposed as an effective shielding filler. The resultant porous graphene exhibits 32.5 dB shielding efficiency (SE) and 2.5–18 GHz effective bandwidth at a mass loading of 20 wt%, competing with the shielding performance of graphene fillers prepared by other methods. Particularly, defect‐rich graphene synthesized by increasing voltage and prolonging time shows increased electromagnetic (EM) wave absorption, echoing the current concept of green shielding. In addition, the strategy of controlling the discharge conditions to improve the absorption by the shield is developed in the terahertz band. The average SE and reflection loss of the samples in the THz band (0.2–1.2 THz) exhibit 40.7 and 15.9 dB at filler loading of 5 wt%, respectively, achieving effective shielding and absorption of THz waves. This work paves a new way for low‐cost preparation of graphene for EM interference shielding fillers. Meanwhile, it supplies a reference for the shielding research of the upcoming applications integrating multiple EM bands (such as sixth‐generation based integrated sensing and communication). [ABSTRACT FROM AUTHOR]

In this article, a millimeter‐wave frequency‐reconfigurable metasurface antenna by electrically controlling vanadium dioxide (VO2) is proposed and studied. As a phase change material, VO2 is an insulator at room temperature but can turn into high conductivity metallic state when activated by continuous direct current (DC) voltage. By integrating the VO2 film between two simple rectangle metasurface cells, a frequency‐reconfigurable paired metasurface structure (FRPMS) is achieved. The FRPMS can be considered as one unit when VO2 film is activated to metallic state while as two independent cells when VO2 film is in insulating state. In this way, the FRPMS can operate, respectively at 28 and 38 GHz with independent tunability. Moreover, a coplanar and staggered DC bias circuit with little effect on radiation is designed to switch the operating modes of VO2 easily. The antenna is fed by a stepped waveguide with ridges through a loop slot, which is suitable for dual‐band feeding with large frequency ratio. One prototype is fabricated and measured for demonstration. When the VO2 film is in metallic state, the measured working band covers from 28.5 to 29.6 GHz with the maximum gain of about 7.1 dBi. When cooled down to insulating state, the antenna can work in a higher band from 36.7 to 38.3 GHz with the maximum gain of about 7.9 dBi. Due to the advantages of simple structure, high gain and easy tuning, the antenna can be expected to use in mmW wireless communication. [ABSTRACT FROM AUTHOR]

Light interaction physical properties of MXenes are fundamentally important and promising for developing new broadband photodetection applications. In this work, the significant influence of intercalants on the photo‐electronic properties of MXenes is studied. It is found that the intercalated H2O‐induced inter‐flake resistance greatly restricts the photon excitation responsivity of Ti3C2Tx, resulting in a slow and irreversible resistance change under laser irradiation. After deintercalation of H2O by in situ laser writing, the resistance of Ti3C2Tx responds fast and reversibly to laser excitation and the variation range is proportional to laser power. By extending the findings to another MXene member, Mo2TiC2, the intercalant induced resistance is successfully developed for optoelectronic detection. By selectively deintercalating H2O in the as‐prepared Mo2TiC2 which is co‐intercalated by H2O and TMAOH, bare TMAOH intercalated Mo2TiC2 shows fast and reversible resistance changes with laser. Moreover, the resistance of bare TMAOH intercalated Mo2TiC2 shows a negative temperature coefficient behavior while the fully deintercalated Ti3C2Tx shows a positive temperature behavior. These findings elucidate the understanding of the optoelectronic properties of MXenes and provide insights into the engineering of interfacial chemistry of MXenes for performance enhancement toward various detectors/sensors beyond optoelectronic applications. [ABSTRACT FROM AUTHOR]

Metasurfaces can be used to manipulate the beam direction beyond the Snell's law by the constitutive gradient elements. Independent control of the phase response of each element is usually required for real‐time beam steering, which is very challenging at terahertz (THz) frequencies. Here a type of accordion‐shaped single‐element metagratings for THz beam scanning and angle‐adaptive retroreflection is proposed. The metagrating is carefully designed to enhance the +1st order diffraction while suppressing other orders for efficient beam steering. Benefiting from the periodic arrangement, dynamic beam steering is realized by imparting desired momentum via mechanical compression and rotation, instead of the complicated element‐by‐element modulation. Beam scanning in a plane and over the 3D space is experimentally validated with elevation angles from 45° to 75° and azimuthal angles over 360°. An angle‐adaptive retroreflector by adding a metallic plate to the metagrating is studied with near perfect theoretical diffraction efficiency for incident angles within 40°–85°. The physical mechanism of wide‐angle high efficiency is detailed by the mode analysis, and can be generalized into other frequencies. The study here may find applications in THz communications and radar detections, and open a new avenue to facilitate reconfigurable metadevices for wavefront modulation. [ABSTRACT FROM AUTHOR]

This work focuses on the evaluation of La0.5Sr0.5Co1‐xZnxO3 (LSCZ, x = 0.00–0.10) ceramics as an air‐fireable and economical functional material for thick film resistors. Solid‐state reaction experiments and first‐principles calculations were conducted to investigate the crystal structure, thermal behaviors, and electrical properties of LSCZ ceramics. The substitution of Zn2+ modified the bond properties, electron distribution, and band structure, resulting in more serious structural deformation, increasing the bond population of Co–O and weakening the charge transfer of LSCZ. Experimental results showed that the addition of Zn2+ lowered the densification temperature, activation energy, and crystallite size. As the ratio of Zn2+ increased, the conductivity and temperature coefficient of resistance showed a downward trend. Impedance variation with frequency and thermal aging tests were also performed. For the x = 0.05 specimen sintered at 1200°C, values of 95.5% for relative density, 2857 S/cm for conductivity, 1267 ppm/°C for temperature coefficient of resistance, –0.47% for conductivity change could be achieved. [ABSTRACT FROM AUTHOR]

Spatial light modulators (SLMs) exhibit a powerful capability of controlling electromagnetic waves. They are found to have numerous applications at terahertz (THz) frequencies, including wireless communication, digital holography, and compressive imaging. However, the development toward large‐scale, multi‐level, and multi‐functional THz SLM encounters technical challenges. Here, an electrically programmable THz metamaterial consisting of an array of 8×8 pixels is presented, in which the phase change material of vanadium dioxide (VO2) is embedded. After successfully suppressing the crosstalk from adjacent pixels, the THz wave can be modulated in a programmable manner. The switching speed of each pixel is in the order of 1 kHz. In particular, utilizing the hysteresis effect of VO2, the memory effect is demonstrated. The THz amplitude of each pixel can be written and erased by individual current pulses. Furthermore, multi‐state THz images can be generated and stored. This programmable metamaterial with memory function can be extended to other frequency bands and opens a route for electromagnetic information processing. [ABSTRACT FROM AUTHOR]

Terahertz (THz) absorption technology is promising in radar stealth, electromagnetic interference (EMI) shielding, and the upcoming 6G communication. However, the most popular metamaterial‐based THz absorbers suffer from complex fabrication process and/or narrowband characteristics. Here, a broadband, lightweight, and hydrophobic THz absorber is realized based on Ti3C2Tx MXene sponge foam (MSF) that is obtained by using a dip‐coating method. Due to the macroscopic impedance matching to free space and various microscopic morphologies of metallic Ti3C2Tx flakes inside porous architecture, the obtained MSF, with only 2 mm thickness, shows almost no THz reflection (minimum ≈ 0.00003%) and high THz absorption over 99.99% under the 100% qualified frequency bandwidth ranging from 0.3 to 1.65 THz. The new strategy of combining large‐pore‐size porous architecture with MXene‐like 2D metallic flakes paves a way to achieving high performance THz absorber with minimal thickness, which is of significance in electromagnetic stealth, shielding, and beyond. [ABSTRACT FROM AUTHOR]

Devices designed to dynamically control the transmission, reflection, and absorption of terahertz (THz) radiation are essential for the development of a broad range of THz technologies. A viable approach utilizes materials which undergo an insulator‐to‐metal transition (IMT), switching from transmissive to reflective upon becoming metallic. However, for many applications, it is undesirable to have spurious reflections that can scatter incident light and induce noise to the system. We present an electrically actuated, broadband THz switch which transitions from a transparent state with low reflectivity, to an absorptive state for which both the reflectivity and transmission are strongly suppressed. Our device consists of a patterned high‐resistivity silicon metamaterial layer that provides broadband reflection suppression by matching the impedance of free space. This is integrated with a VO2 ground plane, which undergoes an IMT by means of a DC bias applied to an interdigitated electrode. THz time domain spectroscopy measurements reveal an active bandwidth of 700 GHz with suppressed reflection and more than 90% transmission amplitude modulation with a low insertion loss. We utilize finite‐difference time domain (FDTD) simulations in order to examine the loss mechanisms of the device, as well as the sensitivity to polarization and incident angle. This device validates a general approach toward suppressing unwanted reflections in THz modulators and switches which can be easily adapted to a broad array of applications through straightforward modifications of the structural parameters. [ABSTRACT FROM AUTHOR]

The development of slag glass–ceramics has environmental and commercial value. However, new types of these materials are usually developed using the “trial and error” method because of little understanding of the relationship between the composition, processing, microstructure, and properties. In this paper, artificial neural network (ANN) technology was applied to investigate the relationship between the composition content and the properties of slag glass–ceramic. The investigation showed that the ANN model had an outstanding learning ability and was effective in complex data analysis. If the data set reflects the relationship of the composition and property, the trained network will learn the relationship and then give relatively accurate and stable prediction. A new “virtual sample” technology has also been created which improves the prediction performance of the network by providing greater accuracy and reliability. With this virtual sample technology, the ANN model can establish the exact relationship from a small-size-data set, and gives accurate predictions. This improved ANN model is a powerful and reliable tool for data analysis and property prediction, and will facilitate the material design and development of slag glass–ceramics. [ABSTRACT FROM AUTHOR]

Hydrogels, featuring high flexibility and stretchability, have intense wave‐matter interaction in the terahertz (THz) band and high transparency in the visible light band, making them promising materials for transparent THz absorbers in the optical windows of THz devices. However, conventional hydrogels suffer from poor environmental stability, as water evaporation or freezing at subzero temperatures weakens their THz absorption and visible transmittance. Here, An ion‐rich hydrogel film is presented to concurrently boost the THz wave‐ion and intermolecular interactions. The boosted interactions increase the ionic conduction loss and improve the antidrying and antifreezing performance. As a result, with polydimethylsiloxane (PDMS) as the encapsulation layer and antireflection layer, the flexible ionic‐hydrogel‐based THz absorber shows a high maximum reflection loss (RL) of 86.51 dB in the 0.5–4.5 THz range (100% qualified bandwidth) and a high average visible transmittance of 90.87% with a thickness of only 300 µm. Moreover, it still possesses a high average RL of 39.35 dB after 80 days at room temperature and a high average electromagnetic interference shielding efficiency (EMI SE) of 42.30 dB at −10 °C. This work demonstrates the feasibility of transparent ionic THz absorbers, offering inspiration for future ionic THz device designs. [ABSTRACT FROM AUTHOR]