This paper presents the design of a compact and wideband surface wave antenna that exhibits very low profile and can be flush-mounted on a conformal platform. The proposed antenna comprises a tapered grounded ceramic slab, a unidirectional surface wave launcher, and a tapered impedance transition. The ceramic slab is smoothly tapered to transform the guided surface wave into radiated space wave over a wide frequency range. The surface wave launcher employs a probe-fed parallel plate waveguide with a modified parabolic reflecting wall and a metallic post, which are critical for effectively transforming the cylindrical waves to a unidirectional plane wave within a broad frequency range. Simulated results show that the proposed surface wave antenna achieves a wide operation bandwidth from 6.1 GHz to 18 GHz with a thickness of only 0.12 at the center frequency. Acceptable gain values with stable and quasi end-fire radiation beams are obtained over the entire frequency band. A prototype of the proposed antenna is fabricated and tested. Measured results are in good agreement with simulated ones.Index Terms-Flush-mounted, low-profile, surface wave antenna, surface wave launcher, wideband antenna. 0018-926X (c) He is currently serving as theSecretary of IEEE AP-S. His research interests include design of small and planar antennas for various wireless communication systems, analysis and design of frequency-selective structures and absorbers, hybrid numerical techniques for modeling RF/microwave components and antennas. He has authored or co-authored more than 130 journal papers and presented another 120 conference papers. Zhuozhu Chen (S'13) was born in Hunan province, China. He received the B.Eng. degree and the M.S. degree in electronic engineering from Beijing Institute of Technology, China, in 2010 and 2013, respectively. He is currently working toward the Ph.D. degree in electrical and electronic engineering at Nanyang Technological University, Singapore.His research interests include design of RF/microwave antennas and circuit.
A planar helical antenna is presented for achieving wideband end-fire radiation of circular polarization while maintaining a very low profile. The helix is formed using printed strips with straight-edge connections implemented by plated via-holes. The currents flowing on the strips and along via-holes of the helix contribute to the horizontal and vertical polarizations, respectively. Besides, the current on the ground plane is utilized to weaken the strong amplitude of the horizontal electric field generated by the one on the strips. Thus, a good circular polarization can be achieved. Furthermore, a tapered helix and conducting side-walls are employed to broaden the axial ratio bandwidth as well as to improve the end-fire radiation pattern. The designed antenna operates at the center frequency of 10 GHz. Simulated results show that the planar helical antenna achieves wide impedance bandwidth (|S11| < -10 dB) from 7.4 GHz to 12.8 GHz (54%) and 3 dB axial ratio bandwidth from 8.2 GHz to 11.6 GHz (34%), while retaining a thickness of only 0.11 at the center frequency. A prototype of the proposed antenna is fabricated and tested. Measured results are in good agreement with simulated ones. He is currently serving as the Secretary of IEEE AP-S. His research interests include design of small and planar antennas for various wireless communication systems, analysis and design of frequency-selective structures and absorbers, hybrid numerical techniques for modeling RF/microwave components and antennas. He has authored or co-authored more than 130 journal papers and presented another 120 conference papers.
Aims Lactic acid is a natural antimicrobial in food industry, and also exists in fermented food. It was reported that sublethally injured Escherichia coli could survive in acidic conditions. When conditions become advantageous, injured E. coli can restore physiological function, which is a potential threat in food industry. Recovery is a necessary step for discriminating injured bacteria, but the resuscitation mechanism of injured bacteria is still unknown. Methods and Results In our study, sublethal lactic acid treatment (pH 4·2, 60 min) posed oxidative stress on E. coli by decrease of superoxide dismutase (SOD) activity and overproduction of reactive oxygen species (ROS). Zinc with low concentration (1·0 mmol l−1) significantly increased the recovery ratio of injured E.coli induced by lactic acid. The recovery ratios of injured cell in minimal A medium (minA) with 1·0 mmol l−1 zinc reached to that with 3·0 mmol l−1 catalase (CAT). Conversely, the addition of zinc chelator N, N, N′, N′‐tetrakis (2‐pyridylmethyl) decreased the recovery ratio. Zinc accelerated resuscitation of injured E. coli by improving SOD activity, and decreasing ROS production. Deletion of sodC encoding Cu/ZnSOD, katE/katG encoding CAT or regulating gene rpoS significantly decreased the recovery ratio. Among all of the mutants in this study, ΔrpoS and ΔsodC showed the lowest recovery ratio, which means they played significant roles in the process of resuscitation. Conclusion We provided direct evidence that zinc mediated resuscitation of lactic acid‐injured E. coli by relieving oxidative stress. Zinc can be used as a low‐cost and effective agent to improve recovery ratio and detection efficiency of injured bacteria. Significance and Impact of the Study Antibacterial agents are a challenge for bacteria, but bacteria can survive as a sublethally injured state under stresses. Using injured E. coli induced by lactic acid as a model organism, we validated the significant role of zinc on resuscitation of injured cells.
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