The paper presents a study of dynamic thermal processes in ultra-high-speed microgenerators power of 55 W with the rotational speed of 800,000 rpm for UAV. A large-scale study of current works devoted to this topic were done where the main shortcomings were identified. A mathematical description of heat exchange processes in microelectromechanical energy converters with a flight time of no more than 10 minutes was developed in a non-stationary formulation. A study of the thermal state of the microgenerator operating in a short-term mode without a special cooling system is conducted. An experimental study of the heating dynamics of its active parts is carried out using the method of physical analogies. On the basis of experimental studies, the FEMM model is verified. Afterwards, combined electromagnetic and thermal calculations of microgenerator are conducted.

The radiation properties of a copper-patch antenna designed for resonating at the frequency of 0.7 THz, which is used in aerospace applications, is presented. These properties are then compared to those of a graphene-patch antenna presenting the same dimensions. We show how the use of graphene, as a tunable material, allows to dynamically modify the frequency of operation of the antenna as well as its radiation pattern. Our results show that the return loss peak reaches -29 dB, at the operating frequency, which is almost twice the value obtained with the copper patch. This increase in the return loss peak is also accompanied by an improvement in the gain of the antenna from 5.73 dB in the case of the copper patch to 7.16 dB in the case of graphene. We focus our interest on how the reconfigurable radiation properties of the graphene-patch antenna are directly related to the graphene surface conductivity.

In this work, we study a multichannel filter by using one-dimensional photonic crystal (1DPC) based on Thue-Morse sequence (TMS). We use a dielectric defect layer between binary sequence cells with a TMS structure. First, we show transmission in terms of wavelength for the structure without defect layers. Then, we plot transmission in terms of wavelength for a different number of defect layer periods (N) in normal incidence. The analysis shows that there are two photonic bang gaps (PBG) in visible and infrared regions and two defect modes in each one for N = 1. Moreover, the number of defect modes is increased by increasing N. So, by tuning them, this structure can be used as a multi-channel filter within an optical wavelength range.

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.

We propose a novel approach for the broadband generation of orbital angular momentum (OAM) carrying beams based on the Archimedean spiral. The mechanism behind the antenna is theoretically analyzed and further validated by numerical simulation and physical measurement. The results show that the spiral-based antenna is able to reliably generate the OAM carrying beams in an ultra-wide frequency band. Of particular interest is the fact that the mode number of radiated beams is reconfigurable with a change in operating frequency. Prototypes of a single-arm spiral antenna (SASA), a multi-arm spiral antenna (MASA), and a compact multi-arm spiral antenna (CMASA) are investigated and demonstrated to support our arguments. The proposed approach provides an effective and competitive way to generate OAM carrying beams in radio and microwave bands, which may have potential in wireless communication applications due to its characteristics of simplicity, broadband capacity and reconfiguration opportunities.

In this work, reflectarray antennas are proposed for their use as probes in compact antenna test ranges. For that purpose, the quiet zone generated by a single oset reflectarray is enhanced, overcoming the limitation imposed by the amplitude taper of the feed antenna. First, the near field is characterized by a radiation model which computes the near eld of the reflectarray as far field contributions of each element, which are modeled as small rectangular apertures and thus taking into account the active element pattern. Then, a phase only synthesis is performed with the Levenberg-Marquardt algorithm in order to improve the size of the generated quiet zone. Due to the nature of the application, this near eld synthesis takes into account both the amplitude and phase, making it a more challenging task than an amplitude-only synthesis. The optimization is focused on flattening the amplitude while trying to preserve the phase front generated by the reflectarray.

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.

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 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.

Linear-to-circular polarizers operating from roughly 17 to 65 GHz, and angles of incidence up to 60° are reported. These polarizers convert incident, linearly polarized radiation into circular polarization upon transmission. First, previous designs inspired by the optics community using cascaded waveplates are scaled down to mm-wave frequencies. The naturally occurring anisotropic crystals that the optics community employed are replaced here with metamaterials. The range of incidence angles is improved by utilizing biaxial, artificial dielectrics whose permittivity in the $x$, $y$ and $z$ directions are all engineered. Next, an ultra-wideband linear-to-circular polarizer consisting of cascaded sheet impedances is reported. The cascaded sheet impedance polarizer utilizes a combination of meanderline and metallic patch geometries. The principal axes of each patterned metallic sheet are oriented at an optimized angle, which increases the design degrees of freedom and performance. This polarizer has the advantages of being thinner and easier to fabricate than the polarizer utilizing cascaded waveplates, but is more difficult to design. Both polarizers rely heavily on genetic algorithm optimization in the design process to realize multiple octaves of bandwidths and robust performance at wide angles of incidence. The polarizers are fabricated with commercial printed-circuit-boards, and then experimentally characterized.

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 describes a highly robust and efficient parallel computing method for the transient simulation of low-frequency electromagnetics with nonlinear materials and/or permanent magnets. In this method, time subdivisions are introduced to control the memory usage and nonlinear convergence. A direct block triangular matrix solver is applied to solve the formulated block matrix for each subdivision. This method has been implemented using the Message Passing Interface (MPI) for distributed memory parallel processing. Depending on the number of available MPI processes and physical memory, the entire nonlinear transient simulation can be divided into several subdivisions along the time-axis such that each MPI process handles only the computation for one time-step. Application examples are presented to demonstrate that this method can achieve excellent scalability of speedup.

There is no doubt that electrified vehicles are superseding internal combustion engine vehicles for road transportation. Among them, electric vehicles (EVs) have been identified as the greenest road transportation while hybrid EVs have been tagged as the super ultra-low emission vehicles. In this paper, the definition, classification, merits and demerits of electric and hybrid vehicles are first introduced. Then, after revealing their multidisciplinary technologies and development trends, the state-of-the-art electromagnetics research in electric and hybrid vehicles are discussed, with emphasis on electric motors for electric propulsion, electric machine systems for hybrid propulsion, wireless power transfer technologies for park-and-charge a well as move-and-charge, electromagnetic interference and compatibility issues in EVs, electromechanical flywheels for energy storage and magnetic sensors for EV operation. Meanwhile, the development trend of these research areas is revealed.

In this paper, the AC interference produced by an overhead power transmission line on a buried metallic pipeline is estimated using a circuital method based on the well-known Carson's formulae and a two-dimensional finite element numerical code. The finite element formulation used in this paper implicitly takes into account the mutual inductive coupling between all the considered conductors, and it allows a more detailed analysis in cases where a nonhomogeneous soil is present. The FEM approach includes a procedure which has been developed to enforce that the sum of the currents flowing through the soil, pipeline and eventual overhead ground wire is equal to zero. A case study has been identified, and the results obtained by the two approaches have been compared and discussed

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 suers 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.

This study describes the techniques and signal properties of a large, powerful, and linear-scanning 1.5 MHz induction field scanner. The mechanical system is capable of quickly reading the volume of relative large objects, e.g., a test person. The general approach mirrors Magnetic Induction Tomography (MIT), but the details differ considerably from currently-described MIT systems: the setup is asymmetrical, and it operates in gradiometric modalities, either with coaxial excitation with destructive interference or with a single excitation loop and tilted receivers. Following this approach, the primary signals were almost completely nulled, and test objects' real or imaginary imprint was obtained directly. The coaxial gradiometer appeared advantageous: exposure to strong fields was reduced due to destructive interference. Meanwhile, the signals included enhanced components at higher spatial frequencies, thereby obtaining a gradually improved capability for localization. For robust signals, the excitation field can be powered towards the rated limits of human exposure to time-varying magnetic fields. Repeated measurements assessed the important signal integrity, which is affected by the scanner´s imperfections, particularly any motions or respiratory changes in living beings during or between repeated scans. The currently achieved and overall figure of merit for artifacts was 58 dB for inanimate test objects and 44 dB for a test person. Both numbers should be understood as worst case levels: a repeated scan with intermediate breathing and drift/dislocations requires 50 seconds, whereas a single measurement (with respiratory arrest) takes only about 5 seconds.

This letter presents the synthesis of a broadband rat-race consisting of a miniaturized broadband rat-race hybrid and transmission line cascades. This broadband technique involves connecting a cascade of transmission lines with lengths equal to a quarter of the wavelength at the design frequency to each port of a previously proposed rat-race hybrid. Butterworth and Chebyshev performances of the broadband rat-race hybrid are also reported. The broadband rat-race hybrid was implemented on an FR4 substrate using spiral inductors and chip capacitors. For the frequency range of 420-800 MHz, which corresponds to a relative bandwidth of more than 62%, the broadband rat-race hybrid exhibited power splits of -3.8 ± 1.0 dB, return losses of greater than 19 dB, and isolation between output ports of greater than 20 dB. The phase difference between S₂₁ and S₄₁ was 180° ± 3°.

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.