In this paper, an absorber with multi-band, tunable, high Q, and high sensitivity, based on terahertz periodic two-dimensional patterned graphene surface plasmon resonance (SPR), is proposed. The absorber consists of a bottom metal film separated by a periodically patterned graphene metamaterial structure and a SiO₂ dielectric layer, where the patterned graphene layer is etched by “+” and “L” shapes and circles. It has simple structural features that can greatly simplify the fabrication process. We have analyzed the optical properties of a graphene surface plasmon perfect metamaterial absorber based on graphene in the terahertz region using the finite-difference method in time domain (FDTD). The results show that the absorber device exhibits three perfect absorption peaks in the terahertz bands of f1 = 1.55 THz, f2 = 4.19 THz, and f3 = 6.92 THz, with absorption rates as high as 98.70%, 99.63%, and 99.42%, respectively. By discussing the effects of parameters such as the geometrical dimensions of patterned graphene metamaterial structure “+” width W1, “L” width W2, circular width R, and the thickness of the dielectric layer on the absorption performance of absorber, as well as investigating the chemical potential and relaxation time of patterned-layer graphene material, it was found that the amplitude of the absorption peaks and the frequency of resonance of absorber devices can be dynamically adjusted. Finally, we simulated the spectra as the surrounding refractive index n varied to better evaluate the sensing performance of the structure, yielding structural sensitivities up to 382 GHz/RIU. Based on this study, we find that the results of our research will open new doors for the use of multi-band, tunable, polarization-independent metamaterial absorbers that are insensitive to large-angle oblique incidence.

In this paper, two parallel graphene strip structures are adopted to achieve tunable plasma-induced transparency (PIT) sensors in the terahertz band. Both graphene bands act as bright modes, and a PIT window appears due to the weak hybridization between them. A Lorentzian oscillation coupling model is fitted to the simulation results of the proposed structure by the finite-difference time-domain (FDTD) method and is in good agreement with the simulation results. The performance of the PIT system can be controlled by tuning the geometrical parameters of the structure. In addition, the resonant frequency of the PIT window can be dynamically adjusted by changing the chemical potential and carrier mobility of the graphene strips. When the chemical potential of graphene increases from 0.2 eV to 1 eV, the amplitude modulation depth of the PIT window (2.832 THz, 3.684 THz, and 4.386 THz) can reach 92.39%, 96.14%, and 90.4%, respectively. Furthermore, due to its dispersion characteristics, the realized PIT window has a sensitive response to the surrounding medium, and the sensitivity can be as high as 1.25 THz/RIU. This PIT effect-based graphene microstructure has important implications for the future design of terahertz modulators, optical switches, and ultrasensitive sensors.

Metasurfaces provide a powerful ability to control electromagnetic waves, but most metasurfaces only work in transmission or reflection mode. In this paper, a transmissive and reflective switchable metasurface is designed. The unit structure consists of two split-rings and vanadium dioxide (VO₂) film. Utilizing the phase change characteristics of VO₂, the designed metasurface works in transmission mode at 25 °C, while works in reflection mode at 68 °C. It can transform the incident circularly polarized wave at the frequency of 0.47 THz, achieving transmission cross-polarization conversion amplitude greater than 0.8 and reflection cross-polarization conversion amplitude greater than 0.9. By rotating the split-rings, full 2π gradient phase distribution is achieved. The switchable metasurface has the potential to design multifunctional devices. To prove the concept, anomalous refraction and reflection, single-foci and dual-foci focusing metalens are designed. The proposed metasurface provides an effective method to design temperature controlled meta-devices and other systems in terahertz communications.

A terahertz graphene metamaterial decoder, for the first time, is presented which can achieve 2 to 4 decoding function and can be used to detect the content of gaseous tetrahydrofuran in air. The characteristics of the decoder were simulated and optimized by using the finite integration time-domain (FITD) method. The performance of decoding and sensing of the device was investigated. When this device is used as a 2 to 4 decoder, the maximum modulation depth (MD) is 99.60%, the minimum extinction ratio (ER) is 12.63 dB, and the maximum insertion loss (IL) is 0.67 dB. When this device is used as a sensor for tetrahydrofuran detection, the sensitivity (S) can be up to 39.90 nm·L/mmol, along with a quality factor (Q) of 17.1 and a detection limit (DL) as low as 0.31 mmol/L. The results show that the performance of the device in both decoding and sensing functions is relatively well. Simultaneously, due to its insensitivity to the angle of incidence, this device has an anti-interference ability in complex environment. Therefore, this device possesses certain reference significance in decoding, detection, data communication, information anti-counterfeiting and other related fields.

A design is presented here that integrates a five-layer structure which can achieve multiple functions with tunable amplitudes with a dual-band band-pass filter and perfect absorber for sensing applications. When used as a band-pass filter, the design has two center frequencies at 0.708 and 1.733 THz with a 3dB bandwidth of 0.312 and 0.160 THz, respectively. Among them, the maximum transmission of the first frequency band can attain ≥90%, while that of the second frequency band exceeds 70%. Using the phase transition characteristics of VO ₂ as the amplitude modulation principle, the amplitude modulation depth can reach 89.36% and 94.24%, respectively. As a sensor, a perfect absorption peak generated by this structure at 1.478 THz was used, with an absorption rate of up to 99%. Simulation results showed its sensitivity, quality factor(Q), and figure of merit (FOM) could reach 0.247 THz/RIU, 21.497, and 3.592 RIU ^-1 , respectively. The combination of multiple functions gives our design important application values for band-pass filters, modulators, sensors, and other fields.

A terahertz metamaterial device based on plasma-induced transparency (PIT) and phase-change material (PCM), for the first time, to our knowledge, is proposed, which can achieve a 2–4 decoding function and a 2-bit encoding function. By changing the temperature of the VO₂ and adjusting the Fermi level of the graphene, a terahertz micro-nano device with polarization characteristics and the PIT effect is actively switched. When implementing the PIT effect, this device can achieve a 2-bit encoding function by separately controlling the Fermi level of the intermediate graphene layer, and the maximum modulation depth (MD) is 95%, the minimum extinction ratio (ER) is 10.42 dB, and the maximum insertion loss (IL) is 2.21 dB. When used as a metamaterial absorber (MMA), the device can achieve a 2–4 decoding function by changing the polarization angle of the incidence and the Fermi level of the top graphene layer, and the maximum modulation depth (MD) is 94.50%. The proposed switchable device has a simple structure and high integration degree, and is easy to tune. Therefore, this design will greatly promote the development of terahertz multifunctional devices.