ORCID Profile
0000-0002-8213-228X
Current Organisation
Beijing Institute of Technology
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Publisher: The Optical Society
Date: 25-06-2014
DOI: 10.1364/OE.22.016408
Publisher: AIP Publishing
Date: 03-2014
DOI: 10.1063/1.4868384
Abstract: We theoretically present a high gain planar antenna at terahertz (THz) frequencies by combing a conventional log-periodic antenna (LPA) with a low-index-metamaterial (LIM, |n| & 1). The LIM is realized by properly designing a fishnet metamaterial using full-wave finite-element simulation. Owing to the impedance matching, the LIM can be placed seamlessly on the substrate of the LPA without noticeable reflection. The effectiveness of using LIM for antenna gain enhancement is confirmed by comparing the antenna performance with and without LIM, where significantly improved half-power beam-width (3-dB beam-width) and more than 4 dB gain enhancement are seen within a certain frequency range. The presented LIM-enhanced planar THz antenna is compact, flat, low profile, and high gain, which has extensive applications in THz systems, including communications, radar, and spectroscopy.
Publisher: The Optical Society
Date: 24-10-2013
DOI: 10.1364/AO.52.007517
Publisher: IEEE
Date: 10-2012
Publisher: Wiley
Date: 07-05-2023
Abstract: The concept of geometric phase has attracted enormous interest in the metasurface community for achieving phase variation with simple geometrical rotation. Here, this work demonstrates for the first time a highly efficient dual‐band metasurface with independent phase responses for structures with different‐fold rotational symmetries. For proof of concept, a hybrid unit cell structure with nested resonators of different‐fold (single‐fold and threefold) is proposed, where geometric rotation independent phase shifts of two times and six times the rotation angle are achieved in lower and higher bands, respectively. By rotating the resonators within the unit cell, highly efficient independent full phase controls can be achieved with circularly polarized incident waves. The co‐polarized reflection efficiency exceeds 90% at the frequency domain from 10.95 to 11.75 GHz (corresponding to the inner resonator) and exceeds 80% between 14.10 and 14.43 GHz (corresponding to the outer resonator), with peak values of 94.7% at 11.55 GHz and 85.5% at 14.23 GHz, respectively. To validate the versatility of the design paradigm, a metasurface porotype is fabricated and experimentally tested by generating independent holographic images.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2023
Publisher: AIP Publishing
Date: 25-03-2013
DOI: 10.1063/1.4799281
Abstract: We present an effective method for actively controlling intrinsic resonances of optical metamaterials using graphene. Exploiting the Fermi level shift and associated variations in optical transitions of graphene due to voltage biasing, we attain the ability to significantly modulate the intrinsic resonance of the fishnet structure. Despite being atomically thin and having a weak optical response, graphene can be strongly coupled with the left-handed resonance of the fishnet metamaterial. We unambiguously demonstrate that the resonant transmission, absorption, and effective constitutive parameters of the graphene-coupled fishnet metamaterial can be precisely controlled by varying the bias voltage.
Publisher: Hindawi Limited
Date: 2014
DOI: 10.1155/2014/707491
Abstract: A slot-microstrip-covered and waveguide-cavity-backed monopulse antenna array is proposed for high-resolution tracking applications at Ka-band. The monopulse antenna array is designed with a microstrip with 2 × 32 slots, a waveguide cavity, and a waveguide monopulse comparator, to make the structure simple, reduce the feeding network loss, and increase the frequency bandwidth. The 2 × 32 slot-microstrip elements are formed by a metal clad dielectric substrate and slots etched in the metal using the standard printed circuit board (PCB) process with dimensions of 230 mm × 10 mm. The proposed monopulse antenna array not only maintains the advantages of the traditional waveguide slot antenna array, but also has the characteristics of wide bandwidth, high consistence, easy of fabrication, and low cost. From the measured results, it exhibits good monopulse characteristics, including the following: the maximum gains of sum pattern are greater than 24 dB, the 3 dB beamwidth of sum pattern is about 2.2 degrees, the sidelobe levels of the sum pattern are less than −18 dB, and the null depths of the difference pattern are less than −25 dB within the operating bandwidth between 33.65 GHz and 34.35 GHz for VSWR ≤ 2.
Publisher: IOP Publishing
Date: 07-2014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2013
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2013
No related grants have been discovered for Liming Si.