Xunjun He

Terahertz (THz) metasurfaces have drawn considerable research interest, owing to their compelling potential in sensing, imaging, and wireless communication. However, most existing designs are constrained to a single predefined function, severely hindering their practical applicability in dynamic or multifunctional scenarios. Herein, we present a reconfigurable THz metasurface that enables on-demand functional transformation by harnessing the phase transition characteristics of vanadium dioxide (VO₂). The designed unit cell adopts a six-layer stacked configuration, sequentially comprising a VO₂ square ring, a first polyimide (PI) dielectric spacer, an elliptical gold patch, an intermediate VO₂ thin film, a second PI dielectric spacer, and a gold ground plane. When VO₂ is in its metallic phase, the metasurface operates as a metal–insulator–metal (MIM) absorber, achieving over 90% absorption in the frequency range of 1.01–1.91 THz. In the insulating state, it acts as a polarization converter, enabling efficient linear-to-circular polarization conversion (PC) with an axial ratio (AR) below 3 dB from 1.82 to 2.21 THz under linearly polarized (LP) incidence. Moreover, the metasurface exhibits robust performance under varying incident angles and different polarization conditions. Collectively, this design offers a flexible and reconfigurable platform for advanced THz devices, laying a solid foundation for THz communication, intelligent sensing, and imaging systems.

Epoxy resin (EP) has been extensively used in electrical insulation systems because of its favorable adhesion, chemical resistance, thermal stability, and dielectric reliability. Nevertheless, the dense three-dimensional network formed during curing generally gives EP a brittle nature, which restricts its use in insulating components that require both mechanical robustness and long-term reliability. In this work, a hydroxyl-terminated hyperbranched polymer (HBP-OH) was synthesized from itaconic acid (IA) and dipentaerythritol (DPE) through an Ax + By polycondensation route and then incorporated into an anhydride-cured epoxy system as a reactive toughening component. The influence of HBP-OH on the structure, mechanical behavior, dielectric response, and DC breakdown strength of the resulting HBP-OH/EP composites was systematically evaluated. The results demonstrate that HBP-OH effectively improves the mechanical performance of EP. At an HBP-OH loading of 9 wt%, the tensile strength increased from 15.00 MPa for pure EP to 33.27 MPa, while the elongation at break and flexural strength reached 6.5% and 88 MPa, respectively. Meanwhile, only a slight reduction in DC breakdown strength was observed at the optimal HBP-OH content. These results indicate that the proposed hyperbranched-polymer modification strategy can improve the toughness and strength of epoxy resin while retaining its dielectric and insulation performance, providing a feasible approach for developing epoxy insulating materials for high-voltage electrical equipment.

Vortex beams carrying orbital angular momentum have drawn considerable attention in terahertz (THz) wireless communications due to their unique properties. However, conventional metasurfaces typically support only a single vortex beam, substantially limiting both the capacity and functionality of THz communication systems. To overcome these constraints, we propose a polarization-frequency (P-F) multiplexed THz metasurface capable of generating multiple vortex beams with high mode purity. The meta-atom of this metasurface consists of an inner-cross structure (ICS), a ring-integrated outer-cross structure (RIOCS), and an outermost circular aperture metallic structure. By independently adjusting the dimensions of the ICS and the rotation angle of the RIOCS, full 2 π phase coverage can be achieved at two distinct frequencies under linear polarization and circular polarization (CP) incidences,, respectively, thereby enabling P-F multiplexing. As a proof of concept, two distinct metasurfaces were constructed using the proposed meta-atoms. By tuning the polarization state of the incident wave, these metasurfaces can generate four conventional vortex beams with topological charges of −2, +2, −1, and +1, as well as four specialized vortex beams featuring focused, diverging, and non-diffraction profiles. Consequently, the proposed design offers notable advantages in terms of increased channel number and capacity, demonstrating strong potential for applications in THz multifunctional integrated devices and high-capacity communications.

To meet the growing demand for materials combing high thermal conductivity and electrical insulation, we developed epoxy (EP) composites filled with zero-dimensional (0D) silver nanoparticles (AgNPs) and two-dimensional (2D) boron nitride nanosheets (BNNSs). This hybrid filler system synergistically enhances both thermal conductivity and dielectric properties, while retaining excellent electrical insulation. With only 1 wt% AgNPs and 15 wt% BNNSs, the composite achieved a dielectric constant of 4.17 at 100 Hz, outperforming pure EP. At 30 wt% BNNSs and the same AgNP loading, the in-plane and out-of-plane thermal conductivities reached 3.02 and 0.41 W·m⁻¹·K⁻¹, respectively, along with improved thermal stability. Moreover, the composite exhibited an electrical conductivity below 10⁻⁹ S/cm at 1000 Hz, confirming that the minimal metal filler content negligibly affects insulation. Thus, this work offers a feasible strategy for designing next-generation high-performance composites using 0D/2D hybrid fillers, highlighting their promising potential for advanced electronic packaging.

In recent years, Terahertz metasurfaces, as a class of two-dimensional artificial materials, have been extensively employed in areas such as wireless communications, holographic imaging, and modern optics, owing to their capability to precisely control the electromagnetic waves. However, once the geometric parameters of most metal metasurfaces are determined, their working frequency and functions will be restricted. To overcome these limitations, we propose a THz metasurface based on graphene-silicon dual optoelectronic materials. For the THz metasurface design, a full 2 π phase coverage is achieved by rotating the upper graphene open ring under circular polarization incidence, and the continuous 2 π phase is obtained by regulating the lower strip graphene with electrostatic doping under linear polarization incidence. By combining geometric phases with Fermi levels, dynamic reconfigurations of various wavefronts can be achieved, including deflected beams, deflected vortex beams, and focused beams. Furthermore, the dynamic control of the reflection amplitude is achieved by adjusting the conductivity of the photosensitive silicon with pump light. Such versatile and dynamic control underscores the broad application potential of this dual-photonic metasurface in modern optics and wireless communication systems.

Dynamic wavefront control plays a crucial role in advancing terahertz (THz) high-precision non-destructive testing, wireless communication and high-resolution imaging. However, existing approaches to THz dynamic wavefront control suffer from inherent limitations, such complex structures, narrow operational bandwidth, and the ability to tune only a single function, significantly restricting their practical applications. To overcome these challenges, we propose a dynamic reflective THz metasurface based on nested split-ring unit cells. The nested unit cell consists of an outer double-split VO₂ ring resonator and an inner single-split aluminum ring deposited on a central VO₂ circular patch. By, respectively, rotating the inner and outer rings in the insulator and metal states of VO₂, independent full 2π phase coverage at 1.07 THz can be achieved in both VO₂ states while maintaining high polarization-conversion efficiency with a PCR exceeding 0.98, thereby enabling efficient dynamic wavefront control. Using these unit cells, we constructed three distinct reflective metasurfaces that, respectively, generate broadband focusing beams with tunable focal lengths, broadband vortex beams with different topological charges, and a broadband beam that can be switched between focusing and vortex modes by changing the state of VO₂. The design offers considerable flexibility for developing compact, multifunctional THz devices, with promising potential for integrated THz systems, high-capacity communications, and high-resolution imaging.

In recent years, metal phthalocyanine (MPc)-based sensors have garnered significant interest for applications in environmental monitoring, biomedical diagnostics, and industrial process control, owing to their efficient and cost-effective sensing capabilities. In contrast to conventional inorganic materials, MPcs are a class of small-molecule materials characterized by a stable, π-conjugated macrocyclic framework with a tunable central metal ion. This structural architecture imparts unique physicochemical properties, including high chemical stability, excellent redox activity, structural versatility, considerable dielectric constant and electrical conductivity, along with pronounced optical absorption and excellent environmental stability. By incorporating different metal ions into the macrocyclic core, their functional characteristics can be precisely modulated to achieve high sensitivity and selectivity toward various gas, ion, or biomolecule targets. Leveraging these advantages, MPcs have been extensively utilized in diverse sensing platforms, such as photoelectric, gas, and biosensors. This review outlines recent advances in MPc-based sensor research and provides perspectives on their future development trends.

Organic-inorganic hybrid perovskites have emerged as promising candidates for terahertz modulators. However, existing devices suffer from low modulation depth and environmental instability, which severely hinder their practical applications. To overcome these limitations, we fabricated a ReS₂/FAPbI₃/p-Si dual type-II van der Waals heterojunction terahertz modulator using a solution-processed method. In this structure, the FAPbI₃ layer not only acts as a light-absorbing layer but also forms a type-II heterojunction with the underlying p-Si. Simultaneously, the ReS₂ capping layer protects the perovskite from moisture while forming the other type-II heterojunction at the ReS₂/FAPbI₃ interface, thus establishing a dual type-II heterojunction. The resulting THz modulator achieves a modulation depth of over 99% in a broadband range of 0.2-1.0 THz under continuous 800 nm laser illumination at 1500 mW/cm². Moreover, the device retains over 95% of its initial modulation depth even after six months of aging under constant 60% relative humidity or cyclic humidity conditions. Therefore, this work provides a cost-effective and versatile strategy for developing new THz devices with high performance, demonstrating promising potential for applications in THz imaging, communication, and signal processing.