The paper proposes an ultra-narrow band graphene refractive index sensor, consisting of a patterned graphene layer on the top, a dielectric layer of SiO₂ in the middle, and a bottom Au layer. The absorption sensor achieves the absorption efficiency of 99.41% and 99.22% at 5.664 THz and 8.062 THz, with the absorption bandwidths 0.0171 THz and 0.0152 THz, respectively. Compared with noble metal absorbers, our graphene absorber can achieve tunability by adjusting the Fermi level and relaxation time of the graphene layer with the geometry of the absorber unchanged, which greatly saves the manufacturing cost. The results show that the sensor has the properties of polarization-independence and large-angle insensitivity due to the symmetric structure. In addition, the practical application of testing the content of hemoglobin biomolecules was conducted, the frequency of first resonance mode shows a shift of 0.017 THz, and the second resonance mode has a shift of 0.016 THz, demonstrating the good frequency sensitivity of our sensor. The S (sensitivities) of the sensor were calculated at 875 GHz/RIU and 775 GHz/RIU, and quality factors FOM (Figure of Merit) are 26.51 and 18.90, respectively; and the minimum limit of detection is 0.04. By comparing with previous similar sensors, our sensor has better sensing performance, which can be applied to photon detection in the terahertz band, biochemical sensing, and other fields.

This study introduces an innovative dual-tunable absorption film with the capability to switch between ultra-wideband and narrowband absorption. By manipulating the temperature, the film can achieve multi-band absorption within the 30–45 THz range or ultra-wideband absorption spanning 30–130 THz, with an absorption rate exceeding 0.9. Furthermore, the structural parameters of the absorption film are optimized using the particle swarm optimization (PSO) algorithm to ensure the optimal absorption response. The absorption response of the film is primarily attributed to the coupling of guided-mode resonance and local surface plasmon resonance effects. The film’s symmetric structure enables polarization incoherence and allows for tuning through various means such as doping/voltage, temperature and structural parameters. In the case of a multi-band absorption response, the film exhibits good sensitivity to refractive index changes in multiple absorption modes. Additionally, the absorption spectrum of the film remains effective even at large incidence angles, making it highly promising for applications in fields such as biosensing and infrared stealth.

Perfect metamaterial absorbers have attracted researchers’ attention in solar energy harvesting and utilization. An ideal solar absorber should provide high absorption, be ultra-wideband, and be insensitive to polarization and incident angles, which brings challenges to research. In this paper, we proposed and optimized an ultra-wideband solar absorber based on Ti-Al₂O₃ cross elliptical disk arrays to obtain the ultra-wideband absorption of solar energy. The addition of a cavity greatly improves the energy-absorbing effect in the operating band, which has research value. The absorption spectrum and field distribution were analyzed by the finite difference time domain method. For the physical mechanism, the electric and magnetic field distribution indicates that ultra-wideband absorption is caused by propagation surface plasmon resonance (SPR), localized SPR and Fabry–Perot (F-P) resonance excited between Ti and Al₂O₃ disks. The results demonstrate that the absorption bandwidth with the absorption rate beyond 90% reaches 1380 nm (385–1765 nm), and the average absorption reaches an astonishing 98.78%. The absorption bandwidth matches the main radiation bandwidth of the solar energy, which is approximately 295–2500 nm according to the data from the literature, and the total thickness of the structure is only 445 nm. Moreover, the ultra-wideband solar absorber is insensitive to the polarization angle and oblique incidence angle. The proposed ultra-wideband solar absorber has research and application value in solar energy harvesting, photothermal conversion and utilization.

By integrating the design principles of broadband metamaterial absorbers with woven structures, this study introduces a woven composite metamaterial (WCM) made of resin and AlCuFe quasicrystals, enabling optical materials to operate efficiently across a wide spectral range while withstanding mechanical deformation. This lightweight metamaterial features a unique 3D four-way braided structure combined with Dirac semimetals. Static analysis reveals that AlCuFe quasicrystals significantly enhance mechanical properties, with a Young's modulus reaching 38 GPa in the z direction and 18 GPa in the x and y directions at 40% fiber content and a 30° weaving angle. Frequency domain simulations show a high average absorption rate of 83.4% in the 3–12 μm range, primarily due to internal electromagnetic coupling. The study further reveals that the electromagnetic properties of the WCM are closely related to fiber content and weaving angle. As a lightweight optical material, the WCM shows strong application potential in fields such as aerospace and electromagnetic countermeasures.

Here, the broadband absorber can achieve electromagnetic wave absorption at 18–28 THz and realize multi-layer Fermi energy tunable. In addition, it shows high irrelevance between incident angle and polarization direction.

In this study, a dynamically tunable terahertz device based on a VO₂–graphene hybrid metasurface is proposed, which realizes the dual functions of ultra-wideband absorption and efficient transmission through VO₂ phase transformation. At 345 K (metallic state), the device attains an absorption efficiency exceeding 90% (average 97.06%) in the range of 2.25–6.07 THz (bandwidth 3.82 THz), showing excellent absorption performance. At 318 K (insulated state), the device achieves 67.66–69.51% transmittance in the 0.1–2.14 THz and 7.51–10 THz bands while maintaining a broadband absorption of 3.6–5.08 THz (an average of 81.99%). Compared with traditional devices, the design breaks through the performance limitations by integrating phase change material control with 2D materials. The patterned graphene design simplifies the fabrication process. System analysis reveals that the device is polarization-insensitive and tunable via graphene Fermi energy and relaxation time. The device’s excellent temperature response and wide angular stability provide a novel solution for terahertz switching, stealth technology, and sensing applications.