25,772 research outputs found
Electromagnetic field energy density in artificial microwave materials with negative parameters
General relations for the stored reactive field energy density in passive
linear artificial microwave materials are established. These relations account
for dispersion and absorption effects in these materials, and they are valid
also in the regions where the real parts of the material parameters are
negative. These relations always give physically sound positive values for the
energy density in passive metamaterials. The energy density and field solutions
in active metamaterials with non-dispersive negative parameters are also
considered. Basic physical limitations on the frequency dispersion of material
parameters of artificial passive materials with negative real parts of the
effective parameters are discussed. It is shown that field solutions in
hypothetical materials with negative and non-dispersive parameters are
unstable
Reconfigurable Reflectarrays and Array Lenses for Dynamic Antenna Beam Control: A Review
Advances in reflectarrays and array lenses with electronic beam-forming
capabilities are enabling a host of new possibilities for these
high-performance, low-cost antenna architectures. This paper reviews enabling
technologies and topologies of reconfigurable reflectarray and array lens
designs, and surveys a range of experimental implementations and achievements
that have been made in this area in recent years. The paper describes the
fundamental design approaches employed in realizing reconfigurable designs, and
explores advanced capabilities of these nascent architectures, such as
multi-band operation, polarization manipulation, frequency agility, and
amplification. Finally, the paper concludes by discussing future challenges and
possibilities for these antennas.Comment: 16 pages, 12 figure
A Survey of Physical Layer Security Techniques for 5G Wireless Networks and Challenges Ahead
Physical layer security which safeguards data confidentiality based on the
information-theoretic approaches has received significant research interest
recently. The key idea behind physical layer security is to utilize the
intrinsic randomness of the transmission channel to guarantee the security in
physical layer. The evolution towards 5G wireless communications poses new
challenges for physical layer security research. This paper provides a latest
survey of the physical layer security research on various promising 5G
technologies, including physical layer security coding, massive multiple-input
multiple-output, millimeter wave communications, heterogeneous networks,
non-orthogonal multiple access, full duplex technology, etc. Technical
challenges which remain unresolved at the time of writing are summarized and
the future trends of physical layer security in 5G and beyond are discussed.Comment: To appear in IEEE Journal on Selected Areas in Communication
3-D printed UWB microwave bodyscope for biomedical measurements
© 2019 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.In this letter, a three-dimensional (3-D) printed compact ultrawideband (UWB) extended gap ridge horn (EGRH) antenna designed to be used for biological measurements of the human body is described. The operational frequency covers the microwave band of interest from 0.5 to 3.0 GHz (for an S 11 under -7 dB). The 3-D printed EGRH antenna is dielectrically matched to the permittivity of the human body, and because of its compactness, it can be visualized as a general-purpose microwave probe among the RF biomedical community. The probe has proven its capability as a pass-through propagation sensor for different parts of the human body and as a sensor detecting a 1 cm diameter object placed inside an artificial head phantom.Peer ReviewedPostprint (author's final draft
Tomorrow's Metamaterials: Manipulation of Electromagnetic Waves in Space, Time and Spacetime
Metamaterials represent one of the most vibrant fields of modern science and
technology. They are generally dispersive structures in the direct and
reciprocal space and time domains. Upon this consideration, I overview here a
number of metamaterial innovations developed by colleagues and myself in the
holistic framework of space and time dispersion engineering. Moreover, I
provide some thoughts regarding the future perspectives of the area
Feasibility study on application of microwave radiometry to monitor contamination level on insulator materials
This paper introduces a novel method for monitoring contamination levels on high voltage insulators based on microwave radiometry. Present contamination monitoring solutions for high voltage insulators are only effective in predicting flashover risk when the contamination layer has been wetted by rain, fog or condensation. The challenge comes where the pollution occurs during a dry period prior to a weather change. Under these conditions, flashover can often occur within a short time period after wetting and is not predicted by measurements taken in the dry period. The microwave radiometer system described in this paper measures energy emitted from the contamination layer and could provide a safe, reliable, contactless monitoring method that is effective under dry conditions. The relationship between equivalent salt deposit density and radiometer output is described using a theoretical model and experimentally verified using a specially designed X-band radiometer. Results demonstrate that the output from the radiometer is able to clearly distinguish between different levels of contamination on insulator materials under dry conditions. This novel contamination monitoring method could potentially provide advance warning of the future failure of wet insulators in climates where insulators can experience dry conditions for extended periods
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