With the development of metasurfaces and the improvement of manufacturing technology, it is important and imperative to design novel metasurfaces that can flexibly manipulate terahertz (THz) waves. In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in THz band. For absorption mode, the MFMS can absorb above 90% energy in the frequency band of 1.74-3.52 THz with the relative bandwidth of 67.6%. For both linear-linear and circular-circular polarization conversion modes, the relative bandwidth with over 90% polarization conversion rates (PCRs) reaches 49.3% in the frequency band of 1.54-2.55 THz. The working mechanism of the MFMS is analyzed by the surface current distributions, and its properties of the absorption and polarization conversion under oblique incident angles are investigated, respectively. The proposed metasurface has promising prospects in terahertz devices such as modulators, smart switches and other terahertz devices.

A reconfigurable multifunctional metasurface is proposed to realize the switching between broadband polarization conversion and perfect absorption by integrating the PIN diodes into the structure. An appropriate feed plate is designed to provide the bias voltage that controls the state of the diodes. When the diodes are in off-state, the metasurface will work in polarization conversion mode, which can convert the co-polarization wave into its cross-polarization state with polarization conversion ratio (PCR) of over 90% in the range from 2.97 to 6.03 GHz; While the diodes are in on-state, the metasurface exhibits perfect absorption with absorptivity of over 90% from 2.56 to 7.62 GHz, and the relative absorption bandwidth (RAB) reaches 99.4%. In addition, the metasurface is fabricated and measured to confirm the multifunctional performance. The proposed metasurface is expected to be applied in electromagnetic detection, stealth technology and communication system.

A dual-band and wide angle absorber with polarization insensitivity is built on basis of three proposed simple petal structure. It is found by simulations and experiments that the absorber exhibits good angular insensitivity for both TE and TM polarized waves. The absorber can achieve a dual-band absorptivity about 80% for TE polarization, and more than 95% for TM polarization when the incident angle is increased to 70 degrees. The absorption mechanism of the proposed absorbers is demonstrated by the surface current distributions at each absorption peak. The absorber is expected to be applied to electromagnetic pollution, radar technology, electromagnetic invisibility, etc.

A three-dimensional dual-band perfect absorber in the THz range (3-10 THz) is theoretically investigated. The absorber is composed of periodically placed cross-and disk-shaped graphene arrays on the top of a gold layer separated by a thick SiO ₂ dielectric spacer. The simulated results show two absorption peaks with near-unity absorbance (99.923% and 99.601%) at wavelengths 43.747 μm and 69.94 μm, respectively. Also, the absorber is insensitive to the polarization of the incident light and has a good tolerance to the incident angle whether it is TE or TM waves. Moreover, the peak wavelengths of the absorber can be flexibly modulated by varying the Fermi level μ _C of graphene while no need to refabricate the structure. This paper provides a new perspective for the design of graphene-based tunable multiband perfect THz absorbers, but not limited to THz absorbers, and may also be used in other THz graphene-based photonic devices.