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We numerically demonstrate a switchable metamaterial absorber with two states (i.e., ultra-broadband and narrowband) in the terahertz region. Such switchable functionalities are accomplished by using a simple absorption system consisting of a hybrid metamaterial with vanadium dioxide ( V O 2 ) and graphene. Theoretical calculations show that when V O 2 is in the metal state, the absorption system without a graphene ring can act as a broadband absorber. For the broadband absorber, the absorption bandwidth of 5.05 THz (i.e., 93%) can be obtained under the condition of over 90% absorption rate, covering a frequency range of 2.91–7.96 THz. Meanwhile, the absorber exhibits tunable characteristics, whose absorption rate can be continuously adjusted from 1% to 99% by controlling the conductivity of V O 2 from 2 × 1 0 2 to 2 × 1 0 5 S / m . It is polarization-insensitive with a large angle tolerance in both transverse electric and transverse magnetic waves. Multiple interference theory is used to analyze the mechanism of the broadband absorber, and the theoretical results are in good agreement with simulations. When the V O 2 is changed to the insulator state, the absorber system with a graphene ring can be switched to a narrowband absorber. This work will have great potential applications in the terahertz regime, such as tunable broadband absorbers, dynamic sensing, cloaking, and photodetectors.

In this paper, we demonstrate a tunable periodic hourglass-shaped graphene arrays absorber in the infrared (IR) and terahertz (THz) frequency bands. The effects of graphene geometric parameters, chemical potentials, periods, and incident angles on the pure absorption characteristics are studied by using the Finite Difference Time Domain (FDTD) method. In addition, this paper also analyzes the pure absorption characteristics of bilayer graphene arrays. The simulation results show that the maximum absorption reaches 38.2% for the monolayer graphene structure. Furthermore, comparing the bilayer graphene structure with the monolayer structure under the same conditions shows that the bilayer structure has a tunable dual-band selective absorption effect and has a higher maximum absorption of 41.7%. Moreover, it was found that there are dual-band tunable absorption peaks at 21.6   μ m and 36.3   μ m with the maximum absorption of 41.7% and 11%. The proposed structure is a convenient method which could be used in the design of graphene-based optoelectronic devices, biosensors, and environmental monitors.

The recent rise of active materials offers new opportunities for dynamically tunable metamaterial devices. However, metamaterial devices with a dynamically switchable function are in high demand. Inspired by previous studies, a dynamically switchable and tunable bifunctional THz (THz) metamaterial absorber based on vanadium dioxide ( V O 2 ) and graphene is proposed and investigated in this paper. Using the phase transition properties of V O 2 , the switchable performance between broadband near-perfect absorption and multiband near-perfect absorption can be achieved. When V O 2 is in the metallic state, the designed metamaterial absorber acts as a broadband near-perfect absorber with more than 90% absorption in the frequency range from 2.6 THz to 7.5 THz. Alternatively, the designed metamaterial absorber with the same geometry can be transformed into a tunable multiband absorber when V O 2 is converted to the insulated state. The performance of the absorber is analyzed by the multiple interference theory (MIT), which is in good agreement with the numerical simulation results. Due to the high symmetry of the structure, the presented absorber exhibits excellent polarization insensitivity and wide incident-angle stability, which opens a direction to design a new type of multifunctional metamaterial devices in the THz regime.

Abstract. A case of polycythemia vera (PV) associated with immunoglobulin A nephropathy (IgAN) in a 57-year-old man is described. The patient had a mild enlargement of the kidneys and elevated serum creatinine level, whereas the glomerular filtration rate was normal. Pathological observation under a light microscope showed mild mesangial hyperplasia. The urinary protein level was found to be positively correlated with changes in blood cell counts. After controlling blood pressure, anti-platelet, hydroxyurea treatment, the patient's proteinuria decreased and renal function remained in the normal range. PV associated with renal disease is rare and generally considered to be associated with hypervolemia or high-viscosity-induced renal hyperperfusion and hyperfiltration. This is a rare case of PV associated with IgAN without a high filtration rate. A review of the clinical features of PV associated with renal disease from previous literature was also conducted. The histological results of the cases varied and included IgAN, focal segmental glomerulosclerosis and membranoproliferative glomerulonephritis.