In this research work, in order to solve the unadjustability of traditional noble metal absorbers to meet the complex application requirements in the actual electromagnetic environment, we designed a simple tunable absorber based on graphene with tunable Fermi level. The performance of the proposed absorber is theoretically simulated by the finite difference time domain (FDTD) method. The proposed absorber has two perfect absorption peaks with high efficiency of 99.51% and 99.548% in its working band (90–155 μm). We have performed an in-depth analysis of the causes of perfect absorption and focused on the tunability of the absorber. The absorption frequency can be adjusted by controlling the relaxation time and Fermi level of graphene, and the same purpose can be achieved by changing the refractive index (relative dielectric constant) of the medium. In addition, we also explored the influence of the change of the top structure parameters on the absorption performance. The proposed absorber has the ability to adapt to different electromagnetic environments. In general, it can be flexibly regulated in practical applications, which will provide new possibilities for the development of many fields such as detection and communication. 

Multimode tunable terahertz absorber based on a quarter graphene disk structure

Intelligent microwave absorption (MA) materials possess the ability to dynamically change their microwave absorption performance, according to real‐time requirements, and it is of great significance in future civil and military fields. For the first time, the reduced graphene oxide/VO2 composite aerogels are developed with off/on switchable MA performance, and the switchable mechanism is originated from the unique phase change behavior of VO2. As temperature increases (>68 °C), the VO2 displays the phase change from monoclinic to rutile phase, which accompanies with significant changes in aerogel's electrical conductivity as well as its permittivity, and consequently leads to off/on switchable MA performance. Particularly, two different off/on switch modes, “on to off” and “off to on”, can be separately realized by different composite aerogels as temperature increases, and this off/on switchable MA performance is also confirmed with good cycling stability. More importantly, during the off/on switch process, the maximum changes for the effective absorption bands (ΔEAB) and RL values (ΔRL) can be as high as 7.27 GHz and 49 dB, which exceeds most current reports. Besides, the RCS simulations on aircrafts have been performed and verified this intelligent MA performance, thus providing useful guidance for next‐generation smart electromagnetic devices in various fields.

Intelligent Off/On Switchable Microwave Absorption Performance of Reduced Graphene Oxide/VO2 Composite Aerogel

• Ultralight magnetic composite foam with hierarchical structure is fabricated. • Loading of MXene/FeS on rGO promotes the formation of hierarchical impedance in foam. • Hierarchical impedance structure facilitates the entrance and dissipation of EMW. • Optimization of impedance structure improves absorption capacity and bandwidth. Developing high-performance broadband microwave absorption material becomes an urgent concern in the field of electromagnetic protection. In this work, an ultralight magnetic composite foam was constructed by electrostatic self-assembly of MXene on the surface of graphene skeletons, and subsequent hydrothermal anchoring of flower-shaped FeS clusters. Under the synergistic effect of MXene coating increasing conductive loss and FeS clusters improving magnetic loss, the rational construction of hierarchical impedance structure in foam can effectively promote the entrance and consumption of more incident electromagnetic waves. The minimum reflection loss (RL min ) reaches –47.17 dB at a thickness of 4.78 mm, and the corresponding effective absorption bandwidth (EAB) is up to 6.15 GHz. More importantly, the microwave absorption performance of composite foam can be further optimized by controlling the loading of MXene and thermal treatment at a low temperature. The maximum of EAB for GMF-300 can be extended to an unprecedented value of 11.20 GHz (covering 6.10–17.30 GHz). 

Hierarchical graphene@MXene composite foam modified with flower-shaped FeS for efficient and broadband electromagnetic absorption

Green EMI shielding: Dielectric/magnetic “genes” and design philosophy

Optofluidic sensors integrate photonics with micro/nanofluidics to realize compact devices for the label‐free detection of molecules and the real‐time monitoring of dynamic surface binding events with high specificity, ultrahigh sensitivity, low detection limit, and multiplexing capability. Nanophotonic structures composed of metallic and/or dielectric building blocks excel at focusing light into ultrasmall volumes, creating enhanced electromagnetic near‐fields ideal for amplifying the molecular signal readout. Furthermore, fluidic control on small length scales enables precise tailoring of the spatial overlap between the electromagnetic hotspots and the analytes, boosting light‐matter interaction, and can be utilized to integrate advanced functionalities for the pre‐treatment of samples in real‐world‐use cases, such as purification, separation, or dilution. In this review, the authors highlight current trends in nanophotonics‐enabled optofluidic biosensors for applications in the life sciences while providing a detailed perspective on how these approaches can synergistically amplify the optical signal readout and achieve real‐time dynamic monitoring, which is crucial in biomedical assays and clinical diagnostics.

Trends in Nanophotonics‐Enabled Optofluidic Biosensors

Multifunctional graphene/carbon fiber aerogels toward compatible electromagnetic wave absorption and shielding in gigahertz and terahertz bands with optimized radar cross section

To enhance and actively control terahertz (THz) anisotropy and chirality, we have designed and fabricated a THz composite device with a liquid crystal (LC) layer and Si anisotropic metasurface. By initial anchoring and electrically rotating the spatial orientation of the LC optical axis, the different symmetry relationships are obtained in this hybrid device. When the optical axis of LC is parallel or perpendicular to the optical axis of the Si metasurface, the anisotropy of the device will be enhanced or offset, which leads to a tunable phase-shift range of more than 180 ° . When there is an angle between the two optical axes, due to the destruction of the mirror symmetry in the LC-Si anisotropic medium, the highest circular dichroism of the device reaches 30 dB in the middle orientation state of the LC optical axis, and the active modulation can be realized by changing the bias electric field on the LC layer. This composite device demonstrates rich characteristics for the feasible manipulation of THz polarization conversion and chiral transmission, which can be applied in THz polarization imaging and chiral spectroscopy.

Dynamic terahertz anisotropy and chirality enhancement in liquid crystal-anisotropic dielectric metasurface

High-performance electromagnetic wave-absorbing (EMA) materials used in high-temperature environments are of great importance in both civil and military fields. Herein, we have developed the ultralight graphene/polyaramid composite foam for wideband electromagnetic wave absorption in both gigahertz and terahertz bands, with a higher service temperature of 300 °C. It is found that strong interfacial π-π interactions are spontaneously constructed between graphene and polyaramids (PA), during the foam preparation process. This endows the foam with two advantages for its EMA performance. First, the π-π interactions trigger the interfacial polarization for enhanced microwave dissipation, as confirmed by the experimental and simulation results. The composite foam with an ultralow density (0.0038 g/cm3) shows a minimum reflection loss (RL) of -36.5 dB and an effective absorption bandwidth (EAB) of 8.4 GHz between 2 and 18 GHz band. Meanwhile, excellent terahertz (THz) absorption is also achieved, with EAB covering the entire 0.2-1.6 THz range. Second, the interfacial π-π interactions promote PA to present a unique in-plane orientation configuration along the graphene surface, thus making PA the effective antioxidation barrier layer for graphene at high temperatures. The EMA performance of the foam could be completely preserved after 300 °C treatment in air atmosphere. Furthermore, the composite foam exhibits multifunctions, including good compressive, thermal insulating, and flame-retardant properties. We believe that this study could provide useful guidance for the design of next-generation EMA materials used in harsh environments.

Interfacial π-π Interactions Induced Ultralight, 300 °C-Stable, Wideband Graphene/Polyaramid Foam for Electromagnetic Wave Absorption in Both Gigahertz and Terahertz Bands.

Proteolysis is a key research field of biochemistry and plays an important role in biomedicine, the food industry, etc. Moreover, because many molecular collective vibration and rotation energy levels containing structural information of proteins, peptides, amino acids, and other molecules are located in the terahertz (THz) band, the THz spectroscopy can perform molecular-level characterization. Here, based on the traditional time-domain spectroscopy system, we propose a reflective polarization characterization method and use the resonance enhancement effect of the flexible chiral metasurface sensor to realize the sensing of bovine serum albumin (BSA) under the proteolysis of papain. Experimental results show that under different amounts of papain proteolysis, the THz polarization characteristic spectra of the BSA solution have significant differences. Its sensitivities of frequency shift, intensity, and polarization angle changes can reach the order of 106 GHz∙mL/mol, 106 dB∙mL/mol, and 106 °∙mL/mol, respectively, and the concentration detection accuracy of papain reaches in the order of nmol/mL. This work demonstrates a new THz label-free, on-chip, wearable, and microfluidic sensing method and device for protein detection. 

Terahertz polarization sensing of bovine serum albumin proteolysis on curved flexible metasurface

A terahertz (THz) all-dielectric metasurface with crescent cylinder arrays for chiral drug sensing has been demonstrated. Through the multipole expansion method, we theoretically found that breaking the symmetry of the metasurface can excite higher-order resonance modes and provide stronger anisotropy as well as enhanced sensitivity for the surroundings, which gives a better sensing performance than lower-order resonance. Based on the frequency shift and transmittance at higher-order resonance, we carried out the sensing experiments on (R)-(−)-ibuprofen and (S)-(+)-ibuprofen solution on the surface of this metasurface sensor. We were able to monitor the concentrations of ibuprofen solutions, and the maximum sensitivity reached 60.42 GHz/mg. Furthermore, we successfully distinguished different chiral molecules such as (R)-(−)-ibuprofen and (S)-(+)-ibuprofen in the 5 μL trace amount of samples. The maximum differentiation was 18.75 GHz/mg. Our analysis confirms the applicability of this crescent all-dielectric metasurface to enhanced sensing and detection of chiral molecules, which provides new paths for the identification of biomolecules in a trace amount.

Tianrui Zhang

Papers

Multifunctional graphene/carbon fiber aerogels toward compatible electromagnetic wave absorption and shielding in gigahertz and terahertz bands with optimized radar cross section

Dynamic terahertz anisotropy and chirality enhancement in liquid crystal-anisotropic dielectric metasurface

Interfacial π-π Interactions Induced Ultralight, 300 °C-Stable, Wideband Graphene/Polyaramid Foam for Electromagnetic Wave Absorption in Both Gigahertz and Terahertz Bands.

Terahertz polarization sensing of bovine serum albumin proteolysis on curved flexible metasurface

Terahertz Sensing for R/S Chiral Ibuprofen via All-Dielectric Metasurface with Higher-Order Resonance