Linear antenna array design is a multi-parameter, multi-objective, and nonlinear problem which requires optimal design parameters to get desired performance. To achieve desired performance through multi-objective optimization process, a compromise among desired objectives is essential. In such a situation to make a rational decision on global optimization to avoid arbitrary compromise to any objective, we introduced two fuzzy logic biased/fuzzy biased optimization techniques. We proposed fuzzy logic biased biogeography based optimization algorithm and fuzzy biased gravitational search optimization algorithm to solve M-element nonlinear linear antenna array design problem. In our design problem, we have considered a 16-element dipole-linear antenna array. The optimal design problem incudes thirty one design parameters (sixteen lengths, and fifteen spacings) and four performance parameters such as directivity, front to maximum side-lobe level, half power beamwidth, and front to back ratio. The result shows that applications of fuzzy biased optimizations are more efficient for solving multi objective problem. While analysing the linear antenna array, mutual coupling is taken into account for numerical analysis using method of moment.
We investigate the diffraction modeling of a plane wave by an infinitely thin and deformed perfectly conducting strip. We show that the diffraction pattern in the Fraunhofer domain can be obtained from efficiencies calculated for a periodic surface with an interpolation relationship; the elementary pattern of the periodic surface is identical to the strip. We consider the case where the deformation amplitude of the strip is small compared to its width. In this case, the propagation equation written in a curvilinear coordinate system is solved by a perturbation method inspired from quantum physics and extended to imaginary eigenvalues for evanescent waves. In the Fraunhofer approximation domain where the only waves are the propagative waves, the diffraction pattern obtained for a sinusoidal profile strip shows the phenomenon well known as apodization. Classically this phenomenon is obtained for physical optics with a slot in a screen with a variable transparency function similar to the profile function of the strip.
Two approximation methods are presented for fast calculations of the monostatic scattering from axially symmetric scatterers coated with electromagnetic absorbers. The methods are designed for plane wave illumination parallel to the axis of rotation of the scatterer. The first method is based on simulating the scattering of a perfect electric conductor (PEC) enclosing the absorber coated scatterer, and multiplying the result with the squared magnitude of the absorber reflection coecient in a planar scenario. The second method is based on simulating the scattering scenario in a physical optics (PO) solver, where the electromagnetic absorber is treated as reflection dyadic at the outer surface of the scatterer. Both methods result in a significant acceleration in computation speed in comparison to full wave methods, where the PO method carries out the computations in a number of seconds. The monostatic scattering from different geometries have been investigated, and parametric sweeps were carried out to test the limits where the methods yield accurate results. For specular reflections, the approximation methods yield very accurate results compared to full wave simulations when the radius of curvature is on the order of half a wavelength or larger of the incident signal. It is also concluded that the accuracy of the two methods varies depending on what type of absorber is applied to the scatterer, and that absorbers based on ``volume losses'' such as a carbon doped foam absorber and a thin magnetic absorber yield better results than absorbers based on resistive sheets, such as a Salisbury absorber.
The SHADE and L-SHADE variants of the Differential Evolution global search and optimization algorithm are used to compute optimized excitations for a Log Periodic Dipole Array antenna and to numerically solve the Pantoja-Bretones-Martin suite of antenna benchmark problems. Comparison to published data shows that SHADE and L-SHADE both are effective and efficient algorithms for solving the array excitation problem and the Pantoja-Bretones-Martin wire antenna benchmarks. L-SHADE clearly is more efficient on the array problem, but overall on the benchmarks the opposite is true, albeit to a lesser degree. The data support the view that neither algorithm is generally better than the other for the type of wire antenna problems considered here. Rather, which algorithm is more efficient is highly dependent on the specific antenna being optimized. In terms of the quality of their solutions, however, both algorithms accurately return the benchmarks' known global optima while both converge on different optimal array excitations that result in very similar objective function fitnesses.
This paper describes the design of an experimental radio frequency (RF) heating system for efficiently heating waste activated sludge (WAS), a byproduct of wastewater treatment plants. Thermal pretreatment is used to increase the bio-gas yield from subsequent anaerobic processes which use WAS. The RF heating system operates at a frequency of 13.56 MHz and the frequency was selected based on a study of the electrical properties of WAS. RF heating has advantages over microwave heating including access to very efficient RF generators, and RF applicators can be designed to provide uniform heating through large load volumes, overcoming limitations of microwave heating which has a shallow penetration depth in the load. Experimental results for the RF heating system show a dc to RF power conversion efficiency of 85% and a power transfer efficiency from the amplifier to load of more than 86% over a temperature range from 20˚C to 120˚C.
Analytical expressions that include arbitrarily directed fields on all laminate boundaries can be used for calculation of the fields inside the laminate when the boundary fields are known from, e.g., measurements. A linear laminate block could be used in non-destructive testing for comparisons between different laminates. This article contains derivation of Fourier series of harmonically time varying, traveling electromagnetic fields in homogeneous, anisotropic approximations of laminates. The component of the magnetic field strength in the stacking direction is used as a source term in twodimensional Poisson equations for the magnetic field strength in other directions. This approximation is here used in three dimensions under the precondition that the conductivity is much smaller in the laminate stacking direction than in the other directions. Sine interpolation and different choices of types of boundary conditions are discussed. Different alternative subdivisions of the Poisson boundary value problems are treated. Shorted derivations of simple analytical expressions are given for both traveling and standing waves in two dimensions. Results from Fourier series in the three-dimensional case are compared with results from finite element calculations.
The spatial resolution of an imaging system is a key factor, which steers its performance for complex target detection, characterization and recognition. Active electromagnetic imaging systems with limited frequency bandwidth and synthetic aperture may fail to discriminate important details during the imaging process, due to their insufficient resolution properties. Spectral estimation methods may be used to overcome such limitations through dedicated signal processing techniques. This study proposes a new signal processing chain, which is able to cope with near-field and wide-band configurations, to significantly improve 2-D resolution, using classical spectral estimation methods. This work is based on an efficient handling and compensation of critical signal properties, such as near-field and wide bandwidths, which make the proposed technique able to deal with very general imaging configurations, such as near/far-ranges, narrow/wide-beamwidths and -bandwidths, very short aperture... Experimental results obtained at millimeter-wave are shown to demonstrate the performance and versatility of the proposed approach.
In this article, a set of closed-form expressions is proposed to predict the resonant frequency, quality factor, input impedance, bandwidth efficiency, directivity and gain for a coax-fed electromagnetically coupled rectangular patch antenna. The computed results obtained with the present model are compared with the experimental and HFSS simulated results. The present model shows less error against the experimental and simulated results.
Quantitative microwave holography is a recent imaging methodology that shows promise in medical diagnostics. It is a real-time direct inversion algorithm that reconstructs the complex permittivity from S-parameter measurements on an acquisition surface outside of the imaged object. It is recognized that this imaging method su ers from limitations in tissue imaging due to a forward model which linearizes a highly nonlinear scattering problem. It is therefore important to study its limitations when reconstruction is aided by certain pre- and post-processing filters which are known to improve the image quality. The impact of ltering on the quantitative result is particularly important. In this work, the reconstruction equations of quantitative microwave holography are derived from rst principles. The implementation of two linearizations strategies, Born's approximation and Rytov's approximation, is explained in detail in the case of a scattering model formulated in terms of S-parameters. Furthermore, real-space and Fourier-space lters are developed to achieve the best performance for the given linearized model of scattering. Simulated and experimental results demonstrate the limitations of the method and the necessity of ltering. The two approximations are also compared in experimental tissue reconstructions.
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