570 research outputs found
Engineered Electromagnetic Metasurfaces in Wireless Communications: Applications, Research Frontiers and Future Directions Mohsen Khalily, Senior Member, IEEE, Okan Yurduseven, Senior Member, IEEE, Tie Jun Cui
Full text linkSurface electromagnetics (SEM), as a sub-discipline of electromagnetic (EM) science, is strongly linked with the ability to manipulate an arbitrary EM wavefront. This exceptional capability of manipulating the surface-bound and free-space EM waves for the guidance and control of anomalous reflection, refraction and transmission has catapulted an abundance of new research frontiers. This has resulted in the realization of many novel applications for modern real-life platforms and the introduction of several new modelling techniques and engineering approaches to give rise to some unconventional devices. Consequently, EM engineered metasurfaces, due to numerous emerging applications, are beginning to revolutionize the EM industry. Recently, the practical usage of metasurfaces has gained a substantial amount of interest and traction for a wide range of applications in microwave, millimetre-wave (mmWave), Terahertz (THz) and even optical wavelengths. This tutorial is aimed at presenting a plethora of EM metasurface applications and research frontiers to illustrate a broader impact of SEM in real-world platforms, advanced communication systems and new devices
Parametric Design of Parabolic Reflector Antenna with Switchable Cosecant-Squared Pattern
No full textThis paper deals with the parametric analysis of multi-beam parabolic reflector antennas employed for air and coastal surveillance radars. Novel designs are introduced to obtain electronically switchable cosecant-squared and pencil beam radiation patterns, without making any changes on the reflector geometry. The analytical regularization method (ARM) is used as a fast and accurate way to solve the problem of E-polarized wave diffraction by parabolic shaped perfectly electrical conductive (PEC) cylindrical reflector with finite thickness. The numerical procedure is initially verified by the analytical and numerical methods, and the calculated radiation characteristics are presented for the proposed antenna configurations
Indirect microwave holographic imaging of concealed ordnance for airport security imaging systems
Full text linkIn this paper, indirect microwave holographic imaging of concealed ordnance is demonstrated. The proposed imaging technique differs from conventional microwave imaging methods in that it does not require the direct measurement of the complex field scattered from the imaged object but mathematically recovers it from intensity-only scalar microwave measurements. This brings the advantages of simplifying the hardware implementation and significantly reducing the cost of the imaging system. In order to demonstrate the ability of the proposed technique to reconstruct good quality images of concealed ordnance, indirect microwave holographic imaging of a metallic gun concealed in a pouch is carried out for airport security imaging applications. It is demonstrated that good resolution amplitude and phase images of concealed objects can be recovered when back-propagation is applied
Strength classification of Okan from Gabon by the combination of visual and machining grading
No full textTimber as a renewable source has been extensively applied among European countries in the construction field. Among more than 1000 available wood species which could be potentially applied as engineered wood, tropical hardwood takes up a significant portion and has advantages of high mechanical resistance and remarkable biological durability against micro-organisms compared to coniferous species and European grown hardwood. Okan has been part of this development, as a hardwood species mostly from the West African regions.The objective of this thesis is to investigate the strength influencing features, calculate corresponding characteristic values and establish the correlation between the influencing factors and the bending strength with the least deviation and create a representative Okan strength predicting model. Abstracted from literature and dataset, geographically speaking, climate, precipitation, soil quality, water sources are expected to have varying degrees of impacts on mechanical properties. From the material perspective, knot ratio, fiber orientation (slope of grain & ring angle), moisture content, density, Modulus of elasticity (dynamic, static) are important factors. Several experiments about hardwood bending strength have been conducted. However, none of those focus on the growth ring angle and the 3D effect of the fiber orientation. To dive deep into Okan, a series of laboratory tests are conducted, including non-destructive inspection, a four-point bending test on 20 beams (10 stored in the dry condition, 10 stored in the wet condition) with the assistance of digital image correlation technology [DIC]). Except for the regulated experimental procedure, two innovative visual inspection methods based on image processing via Matlab were conducted and verified, which turns out the automation method has preferable efficiency and precision. However, this method could hardly identify compression failure. To avoid the compression failure, beams with the dynamic modulus of elasticity less than 18500 N/mm^2 are supposed to be checked again by the inspector. All possible influencing factors are well determined by the above-mentioned testing.Influencing factors of the fracture section form could be concluded from the observation of damaged samples. The slope of grain and growth ring work together to determine the form of the governing crack section. From the experimental outcome, it is clear to observe the linear correlation between mechanical properties and moisture content grouped by the slope of grain. Constant k= 0.13 for bending strength is found, k = 0.05 is found for dynamic modulus of elasticity. The experimental results yield the following adjusted characteristic values: bending strength 63.56 N/mm^2, dynamic modulus of elasticity 21134.55 N/mm^2, density 866.58 kg/mm^3. Based on 20 beams, this batch of Okan could be graded to D55 which is higher than D30-D35 yielded from the dataset. Besides, Okan beams from Gabon could also be graded into D55. Current European standards advise that the reasonable slope of grain range for tropical hardwood is 0 to 0.1. Through the calculation of the theoretical slope of grain of the dataset and experimental samples, increasing the threshold of the slope of grain to 0.3 should be considered in the testing program. Further promotion to 0.2 doesn’t improve the grading outcome and even worsen it.The linear regression result of modulus of elasticity and bending strength is more preferable than density and bending strength in literature and experimental results, which proves the modulus of elasticity is a good indicator of bending strength. Large scatter happens in the regression of the Hankinson formula. In the combination of two basic models, the new proposed model has an optimized coefficient of determination (R^2 = 0.685). The distribution function of the bending strength of the dataset has preferrable overlapping with the theoretical bending strength calculated from the new strength model. To keep the model on the safe side, a safety factor y = 0.9 is applied.It is still unclear if the growth ring angle has a clear numerical relationship with mechanical properties. However, the growth ring angle does bring apparent influences on the form of the fracture section. The 3D effect of fiber orientation needs further investigation
Compact parabolic reflector antenna design with cosecant-squared radiation pattern
No full textThis paper deals with the parametric analysis and proper design of parabolic reflector antennas to obtain pencil-beam, cosecant-squared and inverse cosecant-squared radiation patterns for air and coastal surveillance radars. A novel design is introduced to obtain both pencil-beam and cosecant-squared radiation patterns by using the same modified parabolic reflector antenna structure fed by an H-plane horn feeder which can be adjusted as symmetric or asymmetric feeder by changing the bottom flare angle. The analytical regularization method (ARM) is used as a fast and accurate way to solve the problem of E-polarized wave diffraction by parabolic shaped perfectly electrical conductive (PEC) cylindrical reflector with finite thickness. The numerical procedure is initially verified by the analytical and numerical methods, and the calculated radiation characteristics are presented for the proposed antenna configurations
Analysis of back wall smoothing and multisource feeding effects for H-plane horn radiator
No full textDirect-fed reduced size patch antenna using array of cSRR in the ground plane
No full textIn this article, a novel design for a reduced size microstrip patch antenna is presented and discussed. It is demonstrated that by embedding an array of complimentary split ring resonators in the ground plane, size reduction of 11.2%, together with an increased bandwidth of 202.6% can be achieved
Indirect Microwave Holography and Through Wall Imaging
Full text linkIn this paper, a review of indirect microwave holography for through-wall imaging is presented. Indirect microwave holography is an imaging technique, enabling the complex object scattered fields (amplitude and phase) to be mathematically recovered from intensity-only, scalar microwave measurements. By removing the requirement to use vector measurement equipment to directly measure the complex fields, indirect microwave holography significantly reduces the cost of the imaging system and simplifies the hardware implementation. The application of a back-propagation algorithm enables the reconstructed amplitude and phase images to be obtained at the plane of the concealed object. In order to demonstrate the validity of the reviewed approach, experimental work is carried out on a metallic gun concealed under a 5 cm thick plywood wall and it is demonstrated that the indirect microwave holographic through wall imaging can produce good resolution amplitude and phase images when back-propagation is applied. Through wall imaging of a concealed dielectric box representing non-metallic ordnance is also performed to demonstrate the ability of the technique to reconstruct through-wall images of concealed dielectric objects. An investigation of the resolution characteristics of the system suggests diffraction limited resolution can be achieved
Integration of Microwave Antennas with Solar PV for Multiband and Wideband Mobile, WLAN and WiMAX Applications
No full textThe primary goal of this research is to investigate the existing photovoltaic antenna integration techniques and develop a new solar antenna integration topology in order to address the drawbacks of these techniques.
With the increasing demands for low-profile antennas and a growing move towards the microgeneration of electricity, primarily by photovoltaics, photovoltaic antennas are of
increasing importance with a growing amount of research in this area being developed. At present there are a number of designs for photovoltaic antennas which could be divided
into two distinct categories. The first type is the use of solar cells as an RF ground plane, whilst the second type involves the use of solar cells as an RF radiating element. Both techniques bring significant challenges if they are to be widely adopted. Considering the first technique, using a solar cell as an RF ground plane introduces an optical shading problem, which significantly reduces the solar efficiency of the solar antennas using this integration topology. To this end, meshing the RF radiating element is investigated in this thesis to achieve optical transparency at the expense of increasing the cost and complexity
of the fabrication process of photovoltaic antennas. Conversely, using a solar cell as an RF radiating element limits the ability to modify the resonance response using traditional RF bandwidth enhancement techniques due to the fact that solar cells need to have a homogeneous structure to achieve optimum solar performance.
In order to address these challenges, a third solar antenna integration topology is proposed in this thesis. This method is based upon the use of solar cells as an RF stacked parasitic patch element suspended above the conventional RF radiating element of the integrated antennas. This integration topology enables the integrated solar cells to achieve an optimum solar efficiency due to their suspended position eliminating the shading problem. It also enables the RF radiating element to be modified to excite multiple TMmn propagation modes to achieve enhanced resonance response for multiband and wideband applications. This new topology has been further developed and applied to design a dual-polarised photovoltaic antenna for polarisation diverse communication systems, which has been extended to produce a photovoltaic array antenna for beam steering applications.
This thesis addresses a major knowledge gap in the field of photovoltaic antennas. As a result of this, greater understanding of the design procedures of photovoltaic antennas and associated trade-offs from such designs is developed. Using this knowledge, novel designs that overcome the associated problems of current photovoltaic antennas are presented
Wideband metamaterial solar cell antenna for 5 GHZ Wi-Fi communication
No full textIn this paper, a novel design for a wideband integrated photovoltaic (PV) solar cell patch antenna for 5 GHz Wi-Fi communication is presented and discussed. The design consists of a slot loaded patch antenna with an array of complimentary split ring resonators (cSRR) etched in the ground plane. This is then integrated with a solar cell element placed above the patch, where the ground plane of the solar cell acts as a stacked antenna element from an RF perspective. The design is simulated on CST Microwave Studio and fabricated. The results indicate that an impedance bandwidth of 1 GHz is achieved to cover the 5 GHz Wi-Fi band with a gain of between 7.73 dBi and 8.18 dBi across this band. It is also demonstrated that size reduction of up to 25% can be achieved. Moreover, it is noted that using a metamaterial loaded ground plane acts as an impedance transformer, therefore the antenna can be fed directly with a 50 Ω microstrip feed line, hence further reducing the overall size
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