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Liu Y.,Northwestern Polytechnical University | Zhou X.,National Research Institute of Radio Spectrum Management | Song K.,Northwestern Polytechnical University | Wang M.,Northwestern Polytechnical University | Zhao X.,Northwestern Polytechnical University
Journal of Physics D: Applied Physics | Year: 2015

We develop a gradient phase discontinuities ultrathin planar metasurface based on chiral branched gammadion structure (CBGS) that provides extreme control of electromagnetic wavefronts across single-sheet design. The introduction of the branch can provide antiparallel magnetic moment, which tunes the chirality of the CBGS. In the CBGS metasurface, the transmission phase of a circularly polarized wave can be varied from -180° to +180°. We experimentally demonstrate a beam-refracting CBGS metasurface with refracting a normally incident plane wave to an angle of 17°. The performances of the proposed metasurface at oblique incidence are also presented. The CBGS metasurface can find a wide range of applications over the entire electromagnetic spectrum including single-surface lenses, fully controlling light in direction, and polarization controlling devices. © 2015 IOP Publishing Ltd. Source


Li B.,Xian Jiaotong University | Wang W.J.,Xian Jiaotong University | Yin Q.Y.,Xian Jiaotong University | Li H.X.,University of Louisville | Yang R.,National Research Institute of Radio Spectrum Management
Science China Information Sciences | Year: 2013

In this paper, we propose an energy-efficient cooperative geographic routing (ECGR) to reach energy-efficient routing in wireless sensor networks (WSN). ECGR takes full advantage of cooperative diversity and geographic routing. At physical layer, cooperative nodes transmit the same packet in a cooperative way to achieve farther transmission distance of each hop without more energy consumption. While at the network layer, ECGR adaptively selects the appropriate cooperative nodes to form forwarding clusters to forward the packet to the destination when we consider energy consumption and geographic information of the sensor nodes. Meanwhile, in order to fully assess the energy consumption, we take circuit energy consumption of the sensor nodes into consideration. According to the description above, we increase the transmit distance of each hop; and thereby reducing and balancing the overall network energy consumption among nodes to extend the lifetime of the network. © 2013 Science China Press and Springer-Verlag Berlin Heidelberg. Source


Liu Y.,Northwestern Polytechnical University | Zhou X.,National Research Institute of Radio Spectrum Management | Zhu Z.,Northwestern Polytechnical University | Zhao X.,Northwestern Polytechnical University
Journal of Physics D: Applied Physics | Year: 2016

We present broadband near-zero-index metamaterials composed of dielectric resonators and metallic rods, whose permittivity ε and permeability μ are near-zero simultaneously. It is notable that the values of permittivity ε are equal to those of permeability μ over a broadband frequency range of 8.45 GHz to 10.5 GHz, indicating the impedances of the proposed near-zero-index metamaterials match vacuum in this broadband. The broadband near-zero-index metamaterials for manipulating radiation sources are analyzed. We also demonstrate numerically that such near-zero-index metamaterials can offer a unique grating condition in a phased array antenna, with the beam scanning angle range beyond the critical angle limit of the grating lobe. © 2016 IOP Publishing Ltd. Source


Liu Y.,Northwestern Polytechnical University | Zhou X.,National Research Institute of Radio Spectrum Management | Song K.,Northwestern Polytechnical University | Gu S.,Northwestern Polytechnical University | And 3 more authors.
Applied Physics Letters | Year: 2014

We demonstrate a type of nonlinear meta-atom creating a dual-band nonlinear left-handed metamaterial (DNLHM). The DNLHM operates at two distinct left-handed frequency bands where there is an interval of one octave between the two center frequencies. Under the illumination of a high-power signal at the first left-handed frequency band corresponding to fundamental frequency (FF), second-harmonic generation (SHG) is observed at the second left-handed band. This means that our DNLHM supports backward-propagating waves both at FF and second-harmonic (SH) frequency. We also experimentally demonstrate quasi-phase-matching configurations for the backward SHG. This fancy parametric process can significantly transmits the SH generated by an incident FF wave. © 2014 AIP Publishing LLC. Source


Li J.,National Research Institute of Radio Spectrum Management | Feng J.,Communication University of China | Kang S.,China Mobile | Guo Y.,National Research Institute of Radio Spectrum Management
2013 8th International ICST Conference on Communications and Networking in China, CHINACOM 2013 - Proceedings | Year: 2013

Cooperative spectrum sensing has been recognized as a promising way to improve the sensing performance in distributed cognitive radio networks (DCRNs). Unfortunately, the human-like nature of DCRNs offers an ideal environment for individual selfishness. The presence of selfish SUs who are unwilling to contribute could cause catastrophic damage to any well designed cooperative spectrum sensing schemes. In this paper, we propose an incentive mechanism based on social selfishness (SSIM) to address the selfishness problem for cooperative spectrum sensing. Following the social perspective, this mechanism changes user individual selfishness into social selfishness. That is, SUs are inspired to share sensing information for the SUs with whom they have strong social tie. The evaluation of such social tie is given in SSIM. Finally, simulation results validate the effectiveness of SSIM. © 2013 IEEE. Source

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