scholarly journals Application of metamaterials for the microwave antenna realizations

2012 ◽  
Vol 9 (1) ◽  
pp. 1-7
Author(s):  
Tatjana Asenov ◽  
Nebojsa Doncov ◽  
Bratislav Milovanovic
Keyword(s):  
Microwave Antenna ◽  
Gradient Index ◽  
Microwave Antennas ◽  
Lens Antennas ◽  
Left Handed

In this paper, the application of left-handed metamaterials for the realization of microwave antennas has been considered. Special emphasis is placed on lens antennas based on gradient-index metamaterials, and their advantages and enhanced features in comparison with conventional microwave antennas are highlighted.

scholarly journals Peter John Bell Clarricoats. 6 April 1932—17 January 2020

2021 ◽  
Author(s):  
Christopher Snowden ◽  
Yang Hao
Keyword(s):  
Optical Waveguides ◽  
Academic Career ◽  
Vice President ◽  
Gold Medal ◽  
Advisory Council ◽  
Microwave Antenna ◽  
Electromagnetic Propagation ◽  
Microwave Antennas ◽  
Radio Science ◽  
Applied Electromagnetics

Peter Clarricoats made fundamental contributions as a microwave engineer in the fields of applied electromagnetics for microwave and optical waveguides, and microwave antenna feeds. Peter was also a pioneer of optical fibres, and established the theory of electromagnetic propagation on dielectric and ferrite structures. In the course of this, he discovered that such structures can, under some conditions, support ‘backward waves’ and that guides can propagate complex modes. Over 40 years of his academic career, Peter Clarricoats had numerous notable achievements, including pioneering designs for shaped reflectors, reconfigurable reflectors and especially corrugated horns for microwave antennas. The latter are now universally used in satellite ground stations and in spacecraft. He published what became standard reference texts on corrugated horns for microwave antennas, microwave horns and feeds. He served as vice-president of both the Institution of Engineering and Technology and the International Union of Radio Science, and from 1998 to 2000 was chairman of the Defence Scientific Advisory Council. He was appointed a CBE in 1996. He is the recipient of the 2001 Distinguished Achievement Award of the Institute of Electrical and Electronics Engineers Antennas and Propagation Society, and in 2015 he received the Sir Frank Whittle Gold Medal from the Royal Academy of Engineering.

Three-Dimensional Gradient-Index Materials and Their Applications in Microwave Lens Antennas

2013 ◽  
Vol 61 (5) ◽  
pp. 2561-2569 ◽  
Author(s):  
Hui Feng Ma ◽  
Ben Geng Cai ◽  
Teng Xiang Zhang ◽  
Yan Yang ◽  
Jiang ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Gradient Index ◽  
Lens Antennas

Cerebral blood flow and the thermal properties of the brain: a preliminary analysis

1989 ◽  
Vol 70 (4) ◽  
pp. 592-598 ◽  
Author(s):  
Michael Salcman ◽  
Eiji Moriyama ◽  
Henry J. Elsner ◽  
Herman Rossman ◽  
Robert A. Gettleman ◽  
...  
Keyword(s):  
Blood Flow ◽  
Cerebral Blood Flow ◽  
Thermal Properties ◽  
Specific Heat ◽  
Correlation Coefficient ◽  
Microwave Antenna ◽  
Microwave Antennas ◽  
Hydrogen Clearance Method ◽  
The Brain ◽  
Hydrogen Clearance

✓ Safe and effective use of hyperthermia for the treatment of brain tumors requires precise control of the distribution of temperatures (that is, the thermal field) within the tumor and within the adjacent brain. Major influences upon the distribution of temperatures include the passive thermal properties of the brain, such as its specific heat (Cb), and the contribution of cerebral blood flow (CBF). Recently, an electrical-mechanical analog model of heat flow within the brain has been developed from which an expression for CBF has been derived: CBF = Cb/(τρc) where τ is the thermal decay constant, ρ is the density of blood, and c is its specific heat. To test this model a series of experiments was carried out in adult dogs in which stereotaxically implanted microwave antennas operating at 2450 MHz, fluoro-optical thermometry probes, and platinum electrodes were used to simultaneously measure CBF by thermal washout and hydrogen clearance techniques. The correlation coefficient for estimates of CBF derived by the two methods in 52 paired observations was 0.89. Measurements of CBF were more reliable at increased distances from the microwave antenna, since CBF is sensitive to the degree of temperature elevation (ΔT). The ratio of post-heating CBF to pre-heating CBF varies linearly with ΔT and has a correlation coefficient of 0.86. When values of CBF determined by the hydrogen clearance method were employed in the above equation, it was possible to derive Cb as 0.70 ± 0.08 cal/gm-°C. Use of this value for Cb in this equation produces estimates of CBF by thermal clearance that are within 10% of the values for CBF as measured by the hydrogen clearance method. It is concluded that this model of thermal flow within the brain may have heuristic value for treatment planning and that microwave antennas and fluoro-optical probes may represent a new methodology for the clinical estimation of CBF. These methods have recently been employed in patients undergoing combined hyperthermia and chemotherapy.

scholarly journals Design and characterization of a foam-based Mikaelian lens antennas in millimeter waves

2014 ◽  
Vol 7 (6) ◽  
pp. 769-773 ◽  
Author(s):  
Jonathan Bor ◽  
Benjamin Fuchs ◽  
Olivier Lafond ◽  
Mohamed Himdi
Keyword(s):  
Millimeter Waves ◽  
Low Cost ◽  
Primary Source ◽  
Gradient Index ◽  
60 Ghz ◽  
Lens Antennas ◽  
Flat Shape ◽  
Interesting Alternative ◽  
Focusing Properties

The design principles and radiation performances of Mikaelian lens antennas are presented. The ways to manufacture gradient index lenses are briefly reviewed. An innovative technique based on the variation of the foam density is described and applied to the Mikaelian lenses. This yields low cost and lightweight gradient index lenses. The focusing properties of Mikaelian lenses are compared numerically to Luneburg lenses. A foam-based planar Mikaelian lens antenna is manufactured and its radiation performances are characterized at 60 GHz. With its flat shape in contact to the primary source, the cylindrical Mikaelian lens turns out to be, for focusing purposes, an interesting alternative to the well-known Luneburg lens.

scholarly journals Specific Resonant Properties of Non-Symmetrical Microwave Antennas

Sensors ◽  
2021 ◽  
Vol 21 (3) ◽  
pp. 939
Author(s):  
Ján Labun ◽  
Pavol Kurdel ◽  
Alexey Nekrasov ◽  
Mária Gamcová ◽  
Marek Češkovič ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Measurement Process ◽  
Microwave Antenna ◽  
Experimental Measurements ◽  
Constant Parameter ◽  
Microwave Antennas ◽  
Resonance Parameters ◽  
Series Resonant ◽  
Scale Models ◽  
Modernization Process

The aircraft avionics modernization process often requires optimization of the aircraft itself. Scale models of aircraft and their antennas are frequently used to solve this problem. Here we present interesting properties of the resonant antennas, which were discovered serendipitously during the measurement process of some microwave antennas’ models as part of an aircraft modernization project. Aircraft microwave antennas are often designed as non-symmetric flat microwave antennas. Due to their thin, low and longitudinally elongated outer profile, they are also called tail antennas. An analysis of the resonant properties of non-symmetric antennas was performed in the band from 1 GHz to 4 GHz. The length of the antenna models ranged from 2 cm to 7 cm. The width of the antennas, together with the thickness of the strip, was always a constant parameter for one measured set of six antennas. In the measurement and subsequent analysis, attention was focused on the first-series resonant frequency (λ/4) of each antenna. During the evaluation of the resonance parameters, the flat microwave antenna models showed specific resonant properties different from those of conventional cylindrical microwave antennas. This article aims to inform professionals about these unknown specific properties of non-symmetrical antennas. The results of experimental measurements are analyzed theoretically and then visually compared using graphs so that the reader can more easily understand the properties observed. These surprising observations open up some new possibilities for the design, implementation, and use of flat microwave antennas, as found in modern aircraft, automobiles, etc.

Single molecule optical diffraction: A tool for understanding the structure of triple stranded left-hand helical cellulose

1989 ◽  
Vol 47 ◽  
pp. 1024-1025
Author(s):  
George C. Ruben ◽  
William Krakow
Keyword(s):  
Single Molecule ◽  
Helical Structure ◽  
Optical Diffraction ◽  
Maximum Diameter ◽  
Primary Cell Wall ◽  
Cellulose Synthesis ◽  
Left Hand ◽  
Left Handed ◽  
Freeze Dried ◽  
Diffraction Patterns

Tobacco primary cell wall and normal bacterial Acetobacter xylinum cellulose formation produced a 36.8±3Å triple-stranded left-hand helical microfibril in freeze-dried Pt-C replicas and in negatively stained preparations for TEM. As three submicrofibril strands exit the wall of Axylinum , they twist together to form a left-hand helical microfibril. This process is driven by the left-hand helical structure of the submicrofibril and by cellulose synthesis. That is, as the submicrofibril is elongating at the wall, it is also being left-hand twisted and twisted together with two other submicrofibrils. The submicrofibril appears to have the dimensions of a nine (l-4)-ß-D-glucan parallel chain crystalline unit whose long, 23Å, and short, 19Å, diagonals form major and minor left-handed axial surface ridges every 36Å.The computer generated optical diffraction of this model and its corresponding image have been compared. The submicrofibril model was used to construct a microfibril model. This model and corresponding microfibril images have also been optically diffracted and comparedIn this paper we compare two less complex microfibril models. The first model (Fig. 1a) is constructed with cylindrical submicrofibrils. The second model (Fig. 2a) is also constructed with three submicrofibrils but with a single 23 Å diagonal, projecting from a rounded cross section and left-hand helically twisted, with a 36Å repeat, similar to the original model (45°±10° crossover angle). The submicrofibrils cross the microfibril axis at roughly a 45°±10° angle, the same crossover angle observed in microflbril TEM images. These models were constructed so that the maximum diameter of the submicrofibrils was 23Å and the overall microfibril diameters were similar to Pt-C coated image diameters of ∼50Å and not the actual diameter of 36.5Å. The methods for computing optical diffraction patterns have been published before.

Left handed GDPs and students

BDJ ◽  
1995 ◽  
Vol 178 (12) ◽  
pp. 448-448 ◽  
Author(s):  
J M Brown
Keyword(s):  
Left Handed
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