Switchable broadband/narrowband absorber based on a hybrid metasurface of graphene and metal structures.

This paper proposes a switchable broadband/narrowband absorber based on a hybrid metasurface comprising graphene and metal in the millimeter-wave regime. The designed absorber achieves broadband absorption when the surface resistivity of graphene Rs = 450 Ω/◻ and narrowband absorption when Rs = 1300 Ω/◻ and 2000 Ω/◻. The physical mechanism behind the graphene absorber is explored by analyzing the distributions of power loss, electric field, and surface current densities. An equivalent circuit model (ECM) based on transmission-line theory is derived to theoretically investigate the performance of the absorber, with ECM results in good agreement with simulation results. Furthermore, we fabricate a prototype and evaluate its reflectivity by applying various biasing voltages. The results obtained from the experiment are also consistent with those obtained from the simulation. When the external bias voltage is changed from +1.4 V to -3.2 V, the proposed absorber has an average reflectivity ranging from -5 dB to -33 dB. The proposed absorber has potential applications in radar cross-section (RCS) reduction, antenna design, electromagnetic interference (EMI) shielding, and EM camouflage techniques.

Broadband electrically tunable linear polarization converter based on a graphene metasurface.

In this study, a broadband tunable reflective graphene-based linear polarization converter (GLPC) is proposed based on the graphene-ionic liquid-ITO structure (GIIS) integrated with a periodic double split ring resonator (DSRR) in the millimeter-wave regime. The tuning characteristic of the designed GLPC is analyzed using full-wave simulations and the equivalent circuit model method (ECM), which is based on multi-section transmission lines. There is a good agreement between ECM and simulation results. A comprehensive physical mechanism for the proposed broadband GLPC is then achieved by analyzing the surface current distributions. After manufacturing, the GLPC prototype's co- and cross-polarized reflection coefficients were measured using various bias voltages. The reflectivity can be controlled from -4.5 to -20 dB by changing the bias voltage in the range of +1.1 to -3.3 V. The designed GLPC can provide a tunable polarization conversion within the frequency range of 15.5∼35 GHz and shows a more than 75% conversion efficiency. The results of the simulation and the measurement are also in good agreement. The designed GLPC has potential applications in radar cross-section reduction, antenna design, and stealth technology by reconfiguring its polarized reflection characteristic dynamically.

[Studies on the oxidation of tyrosine induced by hydroxyl radical with fluorescence spectroscopic method].

Dityrosine is a marker of tyrosine oxidation. To study effecting factors of hydroxyl radical on tyrosine oxidation, synchronous fluorescence spectra with two dimensional correlation was used. The results showed that the peak position and intensity of dityrosine changed while pH value varied. In the system of tyrosine oxidation, with the increment of tyrosine concentration, the concentration of dityrosine decreased. With the increment of hydrogen peroxide concentration, the concentration of dityrosine increased. The oxidation reaction was prone to taking place in acid conditions while difficult to develop in basic conditions. With the development of oxidation reaction, the fluorescence intensity of dityrosine increased and then decreased. Two dimentional correlation synchronous fluorescence spectra showed that the variation in the intensity at 292 nm preceded that of 281, 300 and 374 nm. Thus, fluorescence spectroscopy was simple and easy for studying tyrosine oxidation induced by hydroxyl radical.