Yi-Li Xu

A Novel Tunable Absorber Based on Vertical Graphene Strips

A novel type of graphene strips based three-dimensional absorber is proposed, which shows a dynamic tunability of absorbing band. The proposed structure is based on a two-dimensional array of vertical graphene strips with dielectric substrates beneath them. An absorption peak is obtained at the plasmon resonant frequency of the graphene strips. The relationship between the plasmon resonant frequency and the dimensions of absorber obeys the scaling law. Furthermore, by using the trapezoid graphene strips together with the hybrid electrostatic biases, the absorbing bandwidth can be improved significantly. In addition, the absorber shows a good stability with various incident angles and polarizations.

Three-dimensional tunable frequency selective surface based on vertical graphene micro-ribbons

A novel type of vertical graphene micro-ribbons-based three-dimensional frequency selective surface (FSS) is demonstrated to realize dynamic tunability of the frequency selectivity in both center frequency and bandwidth. Different from most available graphene-based FSSs, whose substrates are vertical to the incident direction, in the proposed FSS the substrate is parallel to the incident direction, which results in a small insertion loss for the passband. A stopband is obtained at the plasmon resonant frequency of the graphene micro-ribbons. An equivalent circuit model of the proposed FSS is derived. Additionally, according to the scaling law, the transmission zero frequency can be predicted rapidly and accurately. Based on the combination of the equivalent circuit model and scaling law, the transmission property of the FSS structure is analyzed. Finally, it is shown that the bandwidth of the proposed FSS can be easily extended by a hybrid electrostatic bias.

Tunable Microwave Absorber Based on Patterned Graphene

Two approaches to realize a tunable absorber based on patterned graphene metasurface are proposed in this paper. In the first approach, different from available absorption amplitude tunable absorbers, the center frequency of the absorber can be tuned by the surface resistance of the graphene in a wide range while maintaining a large absorption coefficient. The second approach, by implying the stack of graphene as the absorbing layer, can introduce a remarkable shift of the center frequency. These two approaches are theoretically illustrated using equivalent circuits and 3-D full wave simulation. Samples that are optically transparent are also fabricated and measured in a rectangular waveguide. A good correlation between simulation and measurement results is obtained.

A Shielding Structure for Crosstalk Reduction in Silicon Interposer

High-density interconnects including redistribution layers (RDLs) and through-silicon-vias (TSVs) in silicon interposer require effective crosstalk-reduction signaling schemes. In this letter, a novel ground RDL lines structure utilizing ohmic contact is proposed for coupling mitigation, where the conventional insulator layer between the silicon substrate and the ground RDL lines is removed. An equivalent circuit model is developed to capture the coupling reduction mechanism. The proposed structure is then verified by the full-wave simulations. Finally, a test sample is fabricated and measured. The measurement results show a good correlation with those of the developed equivalent circuit model.

Experimental demonstration of transparent microwave absorber based on graphene

A novel transparent microwave absorber is proposed in this paper. Fluorine-doped tin oxide glass, glass and monolayer graphene are applied as the reflector layer, substrate and absorbing layer respectively to form a Salisbury absorber. The performance of the absorber is measured by the rectangular waveguide. An improved equivalent circuit model is proposed to analyze the transparent absorber. There is a good correlation between absorption coefficients obtained from the equivalent circuit model, 3-D full wave simulation and measurement. As high as 95% incident power can be absorbed by using the proposed absorber.

Modeling and design of multifunctional nanomaterial based flexible antenna

This paper presents the design of a novel flexible transparent butterfly antenna based on 2D nanomaterial graphene-metal grid, and its performance is simulated. In order to characterize the conductivity of graphene, the CVD-grown graphene is transferred to the ring-shape Teflon substrate. The graphene is then sandwiched between two APC-7 coaxial connectors and the S-parameters under TEM normal incident waves are measured to extract the surface conductivity through transmission matrix, in which the de-embedding process can be avoided. The graphene-metal grid based antenna is fed by a coplanar waveguide (CPW) and the polyethylene terephthalate (PET) is selected as the substrate which needs to be both transparent and flexible. A CPW-fed slot-coupled patch antenna is designed and the performance is simulated. Consequently, the features of the antenna are explored when the antenna is bended at different degree along different axes.

Transparent Microwave Absorber Based on Patterned Graphene: Design, Measurement, and Enhancement

A patterned graphene-based transparent microwave absorber is proposed in this paper. Graphene is transferred onto polyethylene terephthalate (PET) film, and patterned as μm-level periodic patches, so that a capacitive and resistive graphene surface is obtained at microwave band. By placing this graphene/PET film on the top of a glass substrate and applying fluorine-doped tin oxide film as the reflective layer, transparent absorber working at Ku band is realized. The optical transmittance of the fabricated graphene/PET film reaches around 80% in the whole optical light range, while the absorption coefficient reaches 90% at 12.6 GHz. By analyzing the parasitic effects in the rectangular waveguide measurement, a good agreement is obtained among the measurement, three-dimensional full-wave simulation, and the equivalent circuit. Two configurations are further analyzed to enhance the absorption level and the working bandwidth of the absorber. 100% absorption and 3 GHz bandwidth broadening are realized.

Graphene-silicon diode loaded patch antenna

In this paper, we proposed a graphene-silicon diode loaded patch antenna, which is fabricated on silicon wafer. The structure of patch antenna is perfectly compatible with the diode process. Its equivalent circuit and frequency-tunable characteristics are analyzed with an equivalent circuit model. The result is verified by 3-D full-wave simulation. This patch antenna, which is directly printed on silicon wafer, finds a potential application of graphene in GHz frequency band and can be easily integrated with other integrated circuits.

Signal transmission along Cu-graphene heterogeneous interconnects

This paper analyzes and compares the frequency responses of both Cu based interconnect and heterogeneous interconnect which consists of graphene sheets and Cu. By using partial element equivalent circuit (PEEC) method, the equivalent electric parameters of these two kinds of interconnects are obtained. A driver-interconnect-load (DIL) model and an equivalent single conductor (ESC) circuit are utilized to study the performances of the heterogeneous interconnect in different conditions. The heterogeneous interconnect shows advantages over the traditional Cu based interconnect.

Exploring graphene loaded antenna for GHz potential applications by experiment

Graphene has become a hot topic since it was discovered. However, articles about using graphene in passive devices, especially the GHz band antennas for modern communication application, have been less reported so far. In this work, a dipole antenna printed on a substrate is proposed and experimentally investigated, where the graphene sheet is connected to the ends of the dipole. This dipole is designed to explore the benefits of using graphene in GHz antennas by experiment. Experimental results indicate that the bandwidth for S11 <; -10 dB obtains an approximately 14.9% increase, covering 9.96-11.5 GHz after the graphene sheet is applied. Moreover, a series of simulation results come to the same conclusion that the bandwidth of dipole antennas can be enhanced after using graphene sheet. Since graphene is transparent and flexible, these results are also useful for potential applications of graphene in GHz antennas and devices, especially those in transparent and soft structure.