This paper proposes an optimization method to improve the efficiency of air core inductors, which are frequently employed in near field communication, wireless power transfer, and power conversion systems. We propose a modification to the PEEC based method, which aims at further reducing the computational complexity associated with complex 3D topologies. The main idea is to optimize 3D structures based on a 2D analysis. The device low frequency behavior is estimated based on the full 3D topology, while corrections resulting from high frequency effects are estimated based on a 2D approximation. As a result, since 2D formulations are used to estimate the high frequency effects, it is possible to obtain small mesh sizes, and hence to decrease the computational load, enabling a fast iterative design process. In addition, the proposed method requires no special commercial software, and can be easily implemented in Matlab. Results are compared to a standard commercial FEM tool, CST EM studio, and the results match well.
A novel artificial magnetic conductor (AMC) structure for realizing gain enhancement of a double-T monopole antenna for 2.4/5.6 GHz dual-band WLAN operation is presented. First, an initial AMC unit cell is proposed, and a 2x5 array of this unit cell is placed behind a double-T monopole antenna as a ground plane, then the AMC structure is modified and improved to achieve better performance. Briefly, more than 4 dB gain improvement and other desirable characteristics including suitable radiation patterns and adequate bandwidths are reported from the simulation results of the final designed structure, and the simulation is performed by CST MWS 2014 in any of the mentioned frequencies. Finally, the validity and applicability of this design are demonstrated through experimental results of the fabricated antenna.
Wideband collocated antennas for multiple input multiple output (MIMO) systems are proposed. The structure is disposed on two substrate layers. On the first top substrate, a disc monopole is etched. The top of the second substrate contains a tapered slot antenna in a form of a Vivaldi antenna and two reflector elements in the form of half disc. The designed antenna can switch among five radiation patterns which radiate in different directions of space with only two excitation ports. All antennas have a relative bandwidth at least 23%. The antenna elements exhibit a low mutual coupling since they are around -17 dB over the considered bandwidths. This performance is believed because the disc monopole mainly has a broadside radiation while the Vivaldi antenna radiates in end-fire directions. With an overall length of about a half guided wavelength, the proposed structure is believed suitable for applications needing radiation pattern diversity.
An intentional focusing of High-Power Microwave (HPM) energy on microelectronic systems can produce effects that will potentially upset or damage the target. However, the physical mechanisms at work within the device are not often well understood. We provide a detailed understanding of the physical mechanisms involved in a common-source Metal Oxide Semiconductor (MOS) transistor inverter when Pulsed Microwave Excitation (PME) in a frequency range from 10 MHz to 1 GHz is applied on the gate terminal. Our study is based on the measurements of the current waveforms on all transistor access and explains the MOS response with and without the Radio-Frequency (RF) interference.
A compact triple-band monopole antenna covering WLAN/WiMAX bands is investigated in this Paper. The proposed antenna has a compact size of 36 x 25 mm2 and consists of a circular ring, a split ring radiator and a trapezoid coplanar waveguide-fed structure. The antenna covers three distinct bands of 2.27-2.55 GHz, 3.23-4.14 GHz, and 5.08-6.03 GHz for WLAN and WiMAX applications. To validate the proposed design, prototype is fabricated, and measurement is carried out. Good performances of gain, radiation pattern and efficiency have also been obtained.
Traditional passive millimeter wave imaging (PMMW) mechanism measures intensity-only radiometric energy of the scene, and the limited information restricts the subsequent process of target detection and recognition. Polarimetric phenomena provide an extra dimension of information and are utilized to improve the PMMW imaging performance. Based on linear polarization characteristics for terrain identification in our previous work, the horizontal, vertical and 45 degree linearly polarimetric images are obtained by manually changing the polarization orientation of the radiometer with a selfdesigned rotating installation. Then the related Stokes parameters and the linearly polarized angle are calculated for principal component analysis (PCA). Pixels with similar polarimetric characteristic are clustered in the score-plot feature space. Then the clusters are extracted to realize object segmentation of the raw image. Three types of objects including metallic stuff, lawn and concrete park are finally segmented, demonstrating that the proposed segmentation is feasible and effective.
In this work, a quad-band omnidirectional slot antenna array is proposed. The structure consists of two closely-spaced radiating elements fed using coplanar waveguide (CPW) line. This combined structure is then integrated in a tapered slot etched on the antenna to enable operation in four frequency bands (0.8, 1.8, 2.6 and 3.45 GHz) for LTE and WiMAX applications with at least -10 dB of reflection coefficient. The antenna dimensional parameters are also studied to understand its behaviour and eects on its performance in facilitating the optimization process. Measurements of the fabricated antenna on a low-cost FR4 substrate validate its operation centred at 0.845 (from 0.77 to 0.92 GHz), 1.74 (from 1.59 to 1.9 GHz), 2.655 (2.59 to 2.72 GHz) and 3.49 GHz (from 3.28 to 3.7 GHz). Meanwhile, simulated and measured radiation patterns of the proposed antenna in all bands agree well and are omnidirectional, making is suitable for application in mobile terminals.
A compact dual-band bandpass filter implemented with an embedded coplanar waveguide (ECPW) resonator and a capacitively loaded resonator (CLR) in substrate integrated waveguide (SIW) cavity is presented and analyzed in this paper. Three transmission zeroes (TZs), of which two are located in the middle of the two passbands and one located in the upper stopband, are obtained to improve the inner-band isolation and the selectivity of the filter. The center frequencies and bandwidths of the two passbands can be easily tuned by changing the geometrical parameters of the two resonators. The proposed dual-band SIW filter is demonstrated with center frequencies located at 8.41/14.29 GHz. The measured insertion loss is -1.28/-1.91 dB with the corresponding fractional bandwidth (FBW) of 21.2%/7.3%. The measured results are in good agreement with the simulated ones.
Propagation path loss models are useful for the prediction of received signal strength at a given distance from the transmitter; estimation of radio coverage areas of Base Transceiver Stations (BTS); frequency assignments; interference analysis; handover optimisation; and power level adjustments. Due to the differences in: environmental structures; local terrain profiles; and weather conditions, path loss prediction model for a given environment using any of the existing basic empirical models such as the Okumura-Hata's model has been shown to differ from the optimal empirical model appropriate for such an environment. In this paper, propagation parameters, such as distance between transmitting and receiving antennas, transmitting power and terrain elevation, using sea level as reference point, were used as inputs to Artificial Neural Network (ANN) for the development of an ANN based path loss model. Data were acquired in a drive test through selected rural and suburban routes in Minna and environs as dataset required for training ANN model. Multilayer perceptron (MLP) network parameters were varied during the performance evaluation process, and the weight and bias values of the best performed MLP network were extracted for the development of the ANN based path loss models for two different routes, namely rural and suburban routes. The performance of the developed ANN based path loss model was compared with some of the existing techniques and modified techniques. Using Root Mean Square Error (RMSE) obtained between the measured and the model outputs as a measure of performance, the newly developed ANN based path loss model performed better than the basic empirical path loss models considered such as: Hata; Egli; COST-231; Ericsson models and modified path loss approach.
A new compact and simple design of UWB antenna with triple band-notched characteristic is proposed in this paper. The first band notch for 3.3-3.8 GHz (WiMAX) is created by cutting a line slot in the radiating patch. The second band rejection for 5.1-5.8 GHz (WLAN) is achieved by etching out an elliptical split ring resonator (ESRR) from the patch placed just above the feed line and patch junction. And the third notch for 7.25 GHz-7.75 GHz (X-band satellite downlink frequency) is created using rectangular split ring resonator (RSRR) in the feed line. Each notch can be adjusted without disturbing the others. A 10 dB return loss wide bandwidth (3.1-10.6 GHz) and VSWR>2 for the stopbands has been measured.
This paper presents a microwave imaging for brain tumour detection utilizing Forward-Backward Time-Stepping (FBTS) inverse scattering technique. This technique is applied to solve electromagnetic scattered signals. It is proven that this technique is able to detect the presence of tumour in the breast. The application is now extended to brain imaging. Two types of results are presented in this paper; FBTS and FBTS integrated with image segmentation as a pre-processing step to form a focusing reconstruction. The results show that the latter technique has improved the reconstructions compared to the primary technique. Integration of the image segmentation step helps to reduce the variation of the estimated dielectric properties of the head tissues. It is also found that the optimal frequency used for microwave brain imaging is at 2 GHz and able to detect a tumour as small as 5 mm in diameter. The numerical simulations show that the integration of image segmentation with FBTS has the potential to provide useful quantitative information on the head internal composition.
In this paper, an efficient broadcasting technique for digital-video and audio broadcasting (DVB/DAB) is proposed using High-Altitude Platforms (HAP) and a new adaptive beamforming technique. The proposed beamforming technique uses two cascaded weighting functions to generate uniform flat footprint with improved link performance compared to terrestrial systems. These two weighting functions include flattening and smoothing coefficients to generate flat power distribution with lower sidelobe levels. Simulation results show that the generated coverage beam pattern has low sidelobe levels that is more than 40 dB below the main coverage level with less than 1 dB variation over the main coverage lobe level. Also, an almost uniform bit-energy to noise power spectral density can be achieved over the coverage area with minor variations due to the changing slant distance over the coverage area of broadcasting HAP.
An analytical model based on the Bethe's theory of diffraction by small holes is presented to predict the shielding effectiveness (SE) of metallic rectangular enclosure with electrically large aperture under plane wave illumination over a wide frequency range (0~3 GHz). In this model, the aperture is represented as electric and magnetic dipoles located at the center of the aperture, and the coupling relation between external plane wave and electromagnetic field inside the enclosure is established. The approximate solution of electromagnetic field distribution inside the enclosure is obtained in terms of the integrals of the electric and magnetic dynamic Green function. Finally, the influence of enclosure thickness on SE is calculated by introducing thickness attenuation coefficient. The model considers the effect of the thickness on the calculation results and is simple with low computation complex and high estimation accuracy. Besides, the effects of parameters like enclosure and aperture dimensions, aperture and observation point positions, incident and polarization direction of the plane wave on SE can be analyzed comprehensively based on the model. Simulation results of the proposed model are in accord with that of the TLM method, which verifies the accuracy and reliability of the model.
This paper presents a new approach for linear antenna array failure correction using geometry optimization of the failed antenna elements. It is done by changing the length and spacing of failed elements while the spacing and length of remaining elements are fixed. The flower pollination algorithm based on the characteristic of flowering plants has been used to correct the radiation pattern of linear antenna array with desired side lobe level and minimum return loss. Simulations are performed using Matlab. Two examples are given to show the effectiveness of the proposed method. In addition, the obtained results from simulation on Matlab are also validated by the results obtained from FEKO analysis.
This work tries to design an Eddy current braking system that can brake at a very high speed within a short time or a short distance. In order to maximize the braking force and reduce lateral forces that can cause track deformation or damage, a double-sided linear permanent magnet Halbach array is proposed in this paper. Two possible designs (Type I and Type II) have been investigated. By using mathematic models, Finite Element Method (FEM) and experimental results, Type I design of a double-sided linear permanent magnet Halbach array is selected. Compared with the other design, Type I design can provide a much larger braking force. Moreover, the analysis also shows that the mathematic models can well capture the characteristic of Type I design. Thus these models are used to design a set of optimal design parameters such as the length and thickness of permanent magnet block to maximize flux density and braking force per unit mass of permanent magnets. The optimal performance is validated by using FEM.
Remote sensing has been used widely in studying the earth terrain such as snow or sea ice due to its fast, convenient and long-term monitoring capabilities. SAR images acquired could be used to analyze the condition of snow, snow water equivalent (SWE), surface roughness and others. Theoretical models have also been developed to understand how microwave interacts with the snow medium and the scatterers embedded inside the medium. Conventionally, spherical shape of scatterers is commonly used to represent the ice particles embedded inside snow where the actual shape of scatterers can vary. This paper is to present a theoretical model based on radiative transfer formulation that utilizes computational electromagnetics in the modelling of scattering from arbitrary shape of scatterers. The paper also studies the effect of scatterer shape on scattering mechanisms and total backscattering coefficient. Numerical solution of Relaxed Hierarchical Equivalent Source Algorithm (RHESA) was integrated with existing radiative transfer theoretical model to simulate a layer of random discrete snow medium. Several shapes of scatterers were simulated, and theoretical simulation were compared with ground truth measurement data with promising results.
A 2D metal photonic crystal structure with a rectangular lattice is designed for directed wave propagation in the microwave frequency band. The dispersion curve of EPC is computed for designing the directed period array.In order to favor the computing ,the rectangular period array is studied,which is differenr from the refrerence that is designed in optical range and uses the dielectric rods and hexagonal structure to compose the period array. The computed dispersion curves are combined with the theory of finite thick period array for obtainning the directed wave propagation structure. The influence of the number of metal rods on the antenna directionality is investigated, and the simulation results are compared and analyzed. It is found that when the number of transverse metal rods increases, the directionality of the antenna is enhanced, and the radiant power of the sidelobe radiation can be reduced. Based on the simulation results, the actual 2D metal photonic crystal array is constructed for the measurement validation.According to measurement results, the antenna located in the center of the array can get good directionality at 3.1 GHz.
Knowledge of peat depth distribution is vitally important for accurately estimating carbon stock within tropical peatlands. These estimates aid in understanding the role of tropical peatlands in global environmental change processes. This study evaluates the potential of C-band dual-polarization synthetic aperture radar (SAR) data for peat depth classification on oil palm plantations in Siak Regency, Riau Province, Indonesia. Specifically, features derived after the ground-range radar cross section (sigma-naught or sigma0) and slant-range perpendicular radar cross section (gamma-naught or γ0) for both polarization channels of C-band Sentinel-1 data were compared and evaluated on monthly basis, during 2015, for discriminating peat depth classes using the decision tree classifier. Overall, γ0 features yielded a higher value of distance factors (DF) for peat depth classes, for both polarization channels, than those produced by the sigma0, indicating a better performance in discriminating peat depth classes. Moreover, the seasonal variation of rainfall intensity was discovered to be influencing feature selection for peat depth classification. Thus, the combination of γ0 features derived in the much rain months was selected for separating the shallow- and medium-peat classes, whereas those derived in the less rain months was selected for discriminating the deep- and very deep-peat classes. In addition, the developed methodology gave the best accuracy for the very deep-peat class, with 76% and 67.86%, producer's accuracy (PA) and user's accuracy (UA), respectively, followed by the shallow-peat class that yielded a PA of 64% and UA of 80%. Subsequently, the deep-peat class produced a PA of 58% and UA of 59.18%, whereas the medium-peat class yielded the lowest PA and UA, of 54% and 49.09%, respectively. This study showed that the C-band dual-polarization SAR data have potential for classifying peat depth classes, particularly on oil palm plantations, and might serve as an efficient tool in peat depth classification used for sustainable management of tropical peatlands.
This paper presents the principle and design of an experimental bench of an oversaturated superconducting machine with radial flux density. A designed experimental bench is under construction to validate the computation principle of the inductor. Also, this work describes the encountered problems and lays out the tools that permit to study a high power oversaturated superconducting machine.
In this work, a new analytical matrix formulation approach for the characterization of a microwave planar structure printed on a complex medium is detailed. The approach is based on the Generalized Exponential Matrix Technique (GEMT) combined with the Method of Moments (MoM)and Galerkin's procedure. The mathematical calculation development is a robust approach that exclusively uses matrix formulations starting from Maxwell's equations until the derivation of a compact form of the Green's tensor of the studied structure. Reduced complexity and calculation simplicity foundation of the applied approach have actually incited the authors to consider the case study of a complex bianisotropic lossy chiral substrate medium. The complexity of the medium is expressed by full tensors form of all four constitutive parameters: permittivity, permeability and magnetoelectric parameters, each is represented by a nine-element tensor. To investigate the electromagnetic behavior of complex media, results of particular bianisotropy cases are presented and discussed. Original results of the biaxial chiral anisotropy case are carried out, discussed and compared with data available in literature.