This article deals with the generalized procedure of designing and optimizing multi-ring radial and thrust permanent magnet bearings (PMBs) with an axial air gap for maximum force and stiffness per volume of the magnet. Initially, the procedure of determining optimized design variables in both the configurations is presented using the MATLAB codes written for solving the three dimensional (3D) equations of force and stiffness in PMB having `n' number of rings on the stator and rotor. The maximized results of the forces in both radial and thrust multi-ring PMBs are validated with the values obtained using finite element analysis (FEA). Then, the correlation between the optimized parameters and the air gap is obtained, and curve fit equations for the same are proposed in terms of stator outer diameter. Further, curve fit equations establishing the relationship between the maximized bearing features, and the aspect ratio (L/D4) of the bearing are expressed for different values of air gap in both the radial and thrust bearings. Finally, the generalized method of designing and optimizing the multi-ring PMB is demonstrated with a specific application. A designer can use the presented curve fit equations for optimizing design variables and calculating maximized bearing features in multi-ring radial and thrust PMBs easily just by knowing the bearing features for a single ring pair.
In this article quad-band circular antenna is designed for multiband devices operated close to human body, and the investigation on parametric study for length of feed, width of feed, and length of ground is carried out. Specific absorption rate (SAR) is also evaluated and found to exceed standard limits for lower band. Further investigation to reduce the value of SAR leads to the design of an annular ring antenna with partial ground. Parametric study on the ratio of outer to inner ring radii is carried out to excite higher resonant modes and optimize the performance of annular ring antenna. SAR is evaluated for different bands, and 9{\%} reduction is observed for same dimensions of circular antenna with partial ground, but SAR still exceeds the limit for lower band. A novel approach of using dual feeds with half operating input power in magnitude and 180° out phase at each port for SAR reduction and performance optimization is presented in this work. Annular ring antenna with parametric study on variation in the ratio of ring radii and circular defect in ground structure is performed, and it leads to wideband operation, gain enhancement, and reduction in SAR. SAR reduction achieved is in the range of 66.93% to 82.15% in 1-gram of tissue and 64.43% to 82.20% in 10-gram of tissue at different bands and well within the limits for all the operating bands.
Analytical solution and numerical results are provided for the problem of plane wave scattering by an electrically large Perfect Electric Conductor plate located vertically over a simple lossy dielectric half-space. The incoming monochromatic homogeneous plane wave is assumed to be incident from an arbitrary direction and decomposed into TE and TM components. Physical Optics approximation is used for estimating the currents induced on the plate. The scattered fields are obtained explicitly by evaluating the Electric Field Integral Equation analytically incorporating the set of Green functions by R.W.P. King which apply under High Contrast Approximation. Amplitude and phase variations of the numerical distance and attenuation function are illustrated in HF-MW band ranges. Azimuth and elevation patterns for total scattered electric fields are illustrated with emphasis on the relative contributions of surface wave fields depending on operating frequency and refractivity. An analytical procedure to extract free space RCS information from measured/calculated data is introduced based on the asymptotic behaviours of surface waves and its stability is tested numerically.
This work aims at completing the Wiener-Hopf analysis of a canonical problem referring to an extra-ordinary transverse electromagnetic wave propagating within a parallel plane waveguide loaded with magnetized plasma when incident normally at the truncated edge of its upper conductor. The complicated mathematical issues faced herein comes from the non-symmetric Kernel functions involved in the related integral equation. This property puts two challenging issues, first the rarely occurring factorization of non-symmetric Kernels and secondly the handling of unidirectional surface and leaky waves. Although the formulation of the Wiener-Hopf equations was carried out in our previous work, these two challenges were not confronted, since that work has been completed only in regard to the closed-shielded geometry which involves a symmetric Kernel. Thus, the novel contribution of this work refers to completing the analysis of the open geometry by handling the factorization of the related non-symmetric Kernel, to evaluate the radiated field as well as to study the unidirectional waves for their near and far fields.
This work presents a novel semi-analytical model for magnetic field calculation in a high-speed surface-mounted permanent-magnet machine with conducting and permeable retaining sleeve. The retaining sleeve with conducting material and non-homogeneous permeability affects the machine electromagnetic performance by altering main flux inductance and developed torque profile. This performance deviation can be attributed to eddy-current reaction field and saturation, the latter occurring due to pole-to-pole leakage flux. Saturation is modeled with a space-varying relative permeability, expressed as a Fourier series. Eddy currents are evaluated with an auxiliary winding, defined as a surface current density in the conducting region. The proposed method is based on well-established Maxwell-Fourier method. This permits other analysis, such as slotting effect through subdomain technique. The assumptions considered for the developed semi-analytical solution in two-dimensional problem are presented in depth and confronted with finite-element method results, confirming validity of proposed methodology.
An approach towards beamforming for a uniform linear array (ULA) based on a novel optimization algorithm, designated as Fibonacci branch search (FBS) is presented in this paper. The proposed FBS search strategy was inspired from Fibonacci sequence principle and uses a fundamental branch structure and interactive searching rules to obtain the global optimal solution in the search space. The structure of FBS is established by two types of multidimensional points on the basis of shortening fraction formed by the Fibonacci sequence, and in this mode, interactive global searching and local optimization rules are implemented alternately to reach global optima, avoiding stagnating in local optimum. At the same time, the rigorous mathematical proof for the accessibility and convergence of FBS towards the global optimum is presented to further verify the validity of our theory and support our claim.Taking advantage of the global search ability and high convergence rate of this technique, a robust adaptive beamformer technique is also constructed here by FBS as a real time implementation to improve the beamforming performance by preventing the loss of optimal trajectory. The performance of the FBS is compared with five typical heuristic optimization algorithms, and the reported simulation results demonstrate the superiority of the proposed FBS algorithm in locating the optimal solution with higher precision and reveal the further improvement in adaptive beamforming performance.
In this paper, a new super-resolution and highly stable DOA estimation technique of coherent sources is introduced. Furthermore, the proposed technique is applied to the data collected from the AWR1243 mm-wave 76-81 GHz frequency modulated continuous wave (FMCW) radar to estimate the DOAs of real targets. A virtual antenna array is proposed to increase the array aperture size and the dimension of the data covariance matrix which effectively helps in de-correlating the received signals and in increasing the number of detectable sources and hence improving the detection resolution. Moreover, a significant improvement in the DOA estimation capability is achieved by handling the frequency domain of the received signals instead of their time-domain representations. That is because the signal to noise ratio (SNR) is increased by a multiplication factor when it is transformed using FFT which acts as a filter for the noise. The simulation results proved the superiority of the proposed technique compared to the state of the arts in this field, especially at low SNR that approaches -35 dB.
Double Elliptical Micro-strip Patch Antenna (DEMPA) is a newer family of patch antennas which possesses higher design flexibility and has greater potential for getting miniaturized than Elliptical Micro-strip Patch Antenna (EMPA). The DEMPA is made out of a Double Elliptical Patch (DEP) which is designed as a combination of two half-elliptical patches either with a common minor axis and two different semi-major axes or with a common major axis and two different semi-minor axes. There are only two design parameters for an EMPA, its semi-major axis and semi-minor axis, whereas a DEMPA has three because of either two different semi-major axes or two different semi-minor axes. A parametric study is required to understand the relationship among these three design parameters and antenna characteristics such as return loss, impedance, resonant frequency and gain. The present work is a statistical study, using the concept of Design of Experiments (DOE), of the impact of these design parameters on the return loss at resonant frequency within the frequency band of 8.50 GHz-10.55 GHz which has been earmarked for radiolocation applications by regulating agency. The Central Composite Design (CCD) technique in the Response Surface Methodology (RSM) of DOE has been employed here to develop empirical relationship between the design parameters and response variable. Numerical models were developed using Ansoft's HFSS as per the design matrix provided by Minitab. The concept of DOE helped to establish statistically significant parametric relationship between the design parameters and antenna return loss with the minimum amount of design effort. The predictive ability of regression model was confirmed by using numerical models of two DEMPAs that were not utilized to build the empirical relationship, one among which had been fabricated, tested and reported in literature.
There has been a presented modal approach for analyzing the scattering of plane waves that are incident on penetrable gratings with metallic fins lined over both exterior surfaces of each conducting bar to create flanged apertures, which altogether is covered on both sides by multiple dielectric layers. The new degrees of freedom afforded by the special complex geometry offer ways to improve the capabilities of various applications such as beam deflectors, resolution of spectroscopic gratings, grating couplers, and grating pulse compression/decompression, as shall be demonstrated herein for the latter two. All of these entail higher-order diffraction modes, which are advantageously studied by the aforementioned analytical tool. Outcomes of measurements on a fabricated prototype that agree well with expectations from theory are also presented.
There has been a presented modal approach for analyzing the scattering of plane waves that are incident on penetrable gratings with metallic fins lined over both exterior surfaces of each conducting bar to create flanged apertures, which altogether is covered on both sides by multiple dielectric layers. The new degrees of freedom afforded by the special complex geometry offer ways to improve the capabilities of various applications such as beam deflectors, resolution of spectroscopic gratings, grating couplers, and grating pulse compression/decompression, as shall be demonstrated herein for the latter two. All of these entail higher-order diffraction modes, which are advantageously studied by the aforementioned analytical tool. Outcomes of measurements on a fabricated prototype that agree well with expectations from theory are also presented.
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