In this paper we demonstrate how so-called polynomial chaos expansions can be used to create efficient algorithms for uncertainty quantification in some classes of problems related to wave propagation in stochastic environment. We provide an example from telecommunication.
High-altitude electromagnetic pulse (HEMP) radiated from both primary and secondary currents, which are induced by a nuclear explosion, is computed by using the Jefimenko's equation. The effects of geomagnetic field is considered in computing the primary current, and the rough sea surface is considered in computing the reflected electric field in the frequency domain. The waveforms of HEMP near sea surface and a few km above it are simulated. The impulse and pulse characteristics are discussed, as well as the variation of peak field magnitude when the observation point is moved away from beneath the burst point.
In this paper the analysis of the static and dynamic behavior of a non-hysteretic superconductive passive linear bearing is described. The high translational symmetry of the magnetic field seen by the superconductor assures a usable long stroke in the order of several tens of millimeters. The linear bearing in combination with an actuating system for only one degree of freedom can be used for accurate long-stroke precision positioning systems for cryogenic environments with zero hysteresis in the movement. The dynamics of the system is investigated using an integral formulation which transforms the solution of the field equations in the solution of an equivalent electric network. The knowledge of the currents in the equivalent network allows to evaluate all the electromagnetic quantities (fields, forces, eddy currents, ...) in the system. Finally, the coupling with the equation of the rigid body permits to simulate the electro/mechanical behavior of the system with six degree of freedom (6 DOF).
This paper describes the original results obtained in the field of multi-beam annular ring antenna array pattern synthesis for the modes TM11 and TM12, by applying an iterative algorithm for phased arrays, which is able to produce low side-lobe levels patterns with multiple prescribed main lobes. The ring antenna analysis builds on the modified cavity model; this letter permits to take account of the fringing field effects by virtue of the dynamic permittivity. The proposed method is based on the adaptive particle swarm optimization algorithm. This solution is characterized by its simple implementation and a reduced computational time to achieve the desired radiation patterns. These advantages make the presented algorithm suitable for a wide range of communication systems. The original results obtained in the field of antenna array pattern synthesis are presented to illustrate the performance of the proposed method.
Inductive power transfer is recently a common method for transferring power. This technology is developing as the modern technologies need to get more efficient and updated. The power transfer efficiency has potential to get better. There are different ways to achieve a desirable efficiency. In this paper, a suitable geometry of a coil for transferring power as a transmitting coil is examined. In this work, three types of geometries are designed. Frequency analysis at frequency range (10 kHz-50 kHz) is done to investigate behaviour of various geometries. Magnetic field, electric field, magnetic flux density, and current density for various geometries are presented and compared. Magnetic flux density is measured via an experimental setup and is compared to simulated one to verify the validity of simulation results.
Shear-horizontal (SH) wave is commonly used in monitoring and detecting steel plate structures. Electromagnetic acoustic transducer (EMAT) based on magnetostriction owns higher transducing efficiency and can be applied in non-contact situations. In some practical applications, it is necessary to inspect the structure on a specific direction and the inspecting direction is required to be variable and accurately controllable. This work proposes a novel direction-controllable EMAT for SH0 mode waves based on magnetostriction. Theoretical foundation and analysis on the magnetostriction model of the new EMAT and working parameters determination are conducted. The detailed structure and design of the new EMAT are presented, with the pre-magnetized open annular nickel strap bonded to the steel plate providing the circumferential static bias magnetic field, and the cooperation of embedded conductors in the rotating slider and open metal rings providing the dynamic magnetic field. Besides, the experimental system for the performance verification of the new EMAT is setup. Three indexes, the dead zone angle, focus angle and consistency error are defined to evaluate the performance quantitatively. The dead zone angle of the new EMAT is 28.74°; the focus angle is 10.7°; the consistency error is only 1.4%. Experimental results show that the proposed direction-controllable EMAT is highly directional. The stimulating direction can be accurately controlled, and the circumferential consistency is fairly high. The direction-controllable EMAT can hopefully provide a practical solution for directional monitoring and inspecting for steel plate structures.
With increasing interest in the usage of wearable wireless communication technologies at 1.8 & 2.4 GHz and 5 & 9 GHz band of frequencies, investigations on the human body interaction with these devices are becoming important. This paper provides a microstrip-based multi-band monopole antenna for body Wearable Wireless Devices (WWD), covering licensed and license-free wireless technologies at UHF/UWB when placed on human body. Five parts of the body were considered to evaluate the electromagnetic (EM) effects on the body. Specific Absorption Rate (SAR) values were found to range from 0.09-0.25 W/kg by using numerical modelling. The thermal effects were investigated experimentally using infrared thermography, and temperature changes not exceeding 1˚C were noticed. Analyses of numerical, simulated and experimental results show that infrared thermography, a temperature-based technique, can be used to evaluate the compliance of WWDs with safety exposure limits for various wireless applications.
Antenna characteristics including mutual coupling and polarization/depolarization have great effects on the performance of Multiple-input multiple-output (MIMO) system. In this paper, new close-form expressions of signal vector, signal power and signal correlation incorporating mutual coupling and polarization/depolarization are derived firstly. On this basis, we presents a new MIMO channel model, which takes into account antenna effects such as mutual coupling and antenna polarization, as well as propagation effects like scattering, clustering and channel depolarization. In particular, the detailed expressions of a 2×2 MIMO channel considering mutual coupling and polarization configurations of slanted ±45° and V/H are derived. Finally, these expressions are applied on the propagation scene of suburban macro cellular to analyze the channel correlation and capacity, which is very helpful in designing and optimizing a MIMO system.
Theoretical, software-computed and experimental evaluations of the exposure levels to electromagnetic fields generated by GSM 900, GSM 1800 and 3G base stations in urban areas, including determination of the minimum safe distances for population and occupational exposure, are presented. Using the software package SPECTRAemc with the P.1546 propagation wave model and a topographic digital map, the electromagnetic field levels were assessed considering the height of the receiving antenna to be at the height of human. At a few locations in the direction of maximum radiation intensity, in situ measurements of the electric field strength were performed. The base station power densities measured at a few exposure sites were in the range of 0.11 (μW/cm2) to 6.73 (μW/cm2). The results of Kosovo experimental survey are compared with surveys done in 21 countries in five continents. The power density values obtained in Kosovo are higher, but many times below the safety standard limits.
In this paper, a novel scheme for inverse synthetic aperture radar (ISAR) imaging under low signal-to-noise ratio (SNR) condition is proposed. The method is a preprocess of the high-resolution range profiles and relies on the oversampling in the azimuth direction. It divides the entire coherent processing interval into segments according to the down sampling factor. In each segment, original low SNR echoes are noncoherently integrated to obtain a new high SNR echo. With the new high SNR echoes, conventional methods for ISAR imaging can perform much better and obtain a better focused ISAR image. The presented algorithm has the advantage of effectiveness under low SNR condition and computational efficiency. Experimental results based on both the simulated and real radar data of an airplane verify the superiority of the proposed strategy.
In this paper the authors perform a comparison among three different stator structures for a Tubular Permanent Magnet Linear Machine. Each structure is characterized by its own lamination which is expected to contribute to the overall performance of the machine. A detailed analysis of the main figures of merit of the three configurations has been carried out in order to identify the configuration with the best characteristics. Significant data such as flux distribution, rated voltage and current, force on the moved and power losses have been compared. The results show that the choice of a mixed stator lamination allows to improve the performance of these machines.
In this paper a recent new quasi-TEM surface impedance approach has been applied to fast characterization of multiconductor microstrip lines in terms of inductance and resistance matrices and conductor losses. Application examples for frequency-dependent parameters of interconnect circuits with up to five conductors (three-, four-, and five-strips) have been reported. The propagation characteristics and attenuation of multimode symmetrical multiconductor system are obtained. The effectiveness of the applied approach is confirmed by comparison of the computed numerical results with those obtained by full-wave simulators. They are found to be in good agreement.
This paper presents a mathematical analysis of the magnetic field homogeneity for an Equilateral Triangular Helmholtz (ETH) coil. The magnetic field analysis is based on the Biot-Savart law in which a Taylor series approximation is performed to obtain the analytical distance that complies with the Helmholtz condition between the pair of coils. This is done to compare the magnetic field distributions of the ETH and the Circular Helmholtz (CH) coils for the parameters side length (2a, 3a) and radius (a) respectively. Furthermore, an approximate expression of the magnetic field homogeneity with regard to the side length parameter is obtained and finally a computational model of the ETH coil using COMSOL® is performed in order to validate the calculated and experimental results. The results show that the ETH coils have a lower magnetic field homogeneity than the CH coils for the described parameters, and the implementation of either one basically depends on the application specifications.
In this paper, a dual-band multiple-input multiple-output dielectric resonator antenna (DRA) with pattern diversity is presented. L-shape of the DRA produces patterns diversity at the lower band whereas, at the upper band, it is caused by exciting TEx121/TEy211 mode in the DRA. Two copper strips are pasted at the corner of the dielectric radiator to improve matching at both the bands. A cylindrical air-gap introduced in the radiator improves isolation up to 25 dB and 20 dB at lower and upper bands, respectively. The MIMO system possesses pattern diversity and isolation without applying any special decoupling technique. The design covers the WiMAX and WLAN bands at 3.6 and 5.2 GHz, respectively. Simulated and measured reflection coefficients and envelope correlation are in good agreement.
Based on the theory of ionospheric heating, with the self-consistent model in the low ionosphere, the Extremely-Low-Frequency (ELF) and Very-Low-Frequency (VLF) waves generated by modulated beat-wave ionospheric heating are analyzed theoretically. In the consideration of the stratified ionosphere, the magnetic fields generated by the equivalent ELF/VLF dipole source above thesea surfaceare studied by using the quasi-longitudinal approximation method.Taking the high latitude regions as an example, the variations of the electron temperature, the increments of Pedersen and Hall conductivities and the changing of the oscillating current densitywith the modulation frequency in beat-wave heating are numerically discussed. The distribution of the magnetic fields ispresented. It turns out that in high latitude regions, the efficiency of rectangular wave modulated heating ingenerating ELF/VLF wave is higher than that of modulated beat-wave heating, and the order of magnitude of the magnetic fields received above the sea surface is 10-7 in beat-wave modulation.
This paper proposes a hybrid method to accelerate the calculation of the monostatic radar cross section (RCS) of perfect electric conducting (PEC) targets. In a sense, the proposed method can be considered as a fast adaptive cross approximation (FACA)-based method. The FACA is firstly used to compress the excitation matrix which come from the beforehand defined incident plane waves. It decreases the time and memory on the generation of decomposition form matrices throughout the comparison with the conventional adaptive cross approximation (ACA). Furthermore, the computational complexity of solution is further reduced by using the sparsified ACA (SPACA) algorithm after dividing the target into blocks. Consequently, the proposed method turns out to be efficient and accurate for calculating two-dimensional (2D) monostatic RCS.
Micro Rain Radar (MRR) is a vertical pointing microwave profiler to measure hydrometeors and related parameters in high resolution. However, it is known that the MRR suffers from certain limitations due to several factors. This paper evaluates the performance of the MRR installed at Kototabang, west Sumatra, Indonesia (0.20˚S, 100.32˚E, 864 m above sea level). The DSD and rainfall rate from the MRR standard processing method had been evaluated by using collocated measurements of MRR, Parsivel disdrometer and Optical Rain Gauge (ORG) during 2014. Furthermore, 1.3 GHz wind profiler (BLR) observation was used to examine the vertical profiles of radar reflectivity and Doppler velocity. It was found that there were noticeable differences between the MRR and Parsivel in the small and large size ends of the DSD. At small sized drop (< 1 mm), the DSD spectra of MRR was higher than that obtained by the Parsivel otherwise it was smaller for large sized drop (> 2 mm). Underestimation of large sized drops in the MRR could be responsible for the underestimation of surface rainfall rate and daily rainfall. The source of differences in the DSD seems the measurement shortcomings such as attenuation correction and vertical wind effects, particularly during heavy rain. The shortcomings were observed from the comparison of mean Doppler velocity profiles between the MRR and the BLR. While the melting layer height of the two instruments was the same, the mean Doppler velocities of MRR shown downward increasing (DI) pattern through all rainfall intensities. On the other hand, for the BLR, the DI was only observed for heavy rain (> 10 mm/h), while downward decreasing was observed for light rain (< 5 mm/h). Similar pattern was also observed for the vertical profile of radar reflectivity. Thus, some corrections are needed for heavy rain, nevertheless, the MRR installed at Kototabang can be utilized for light rain. Comparisons indicated that the mean Doppler velocity and the DSD for the light rain as well as Z-R relation were in reasonable agreement with the reference of BLR, Parsivel and previous studies using the MRR.
A new design has been proposed for a single layer polarization-insensitive dual-band metamaterial absorber at C and X bands. The proposed structure consists of a periodic arrangement of a circular resonator embedded in a square resonator. A commercially available FR4 dielectric has been used as a substrate with metallic grounded bottom and imprints on the other side. This structure resonates at 5.5 GHz and 8.9 GHz with absorptivity of 99.8% and 99.97%, respectively. It exhibits polarization-insensitive behaviour for Transverse Electric and Transverse Magnetic polarization under oblique and normal angles of incidence. The field distributions have been studied for better understanding of the absorption mechanism. The fabricated structure has been tested, and the experimental results are similar to the simulated ones. This polarization-insensitive metamaterial absorber with its ease of design and nearly unity absorption can be used for radar applications.
Permanent-magnet synchronous motors (PMSM) used for HEV/EV drivetrain have many non-linear characteristics including saturation, slotting effects and non-sinusoidal back-emf. However, accurate torque control and rigorous on-board-diagnose require precise modelling that goes far beyond capacity of conventional Space Vector based PMSM model considering only fundamental frequency. By considering the higher harmonics of PMSM, this paper introduces a novel PMSM model named Generalized Space Vector Model (GSVM) based on Fourier series reconstruction of magnetic coenergy. Firstly, two-dimensional Fourier series supplemented by polynomial fitting is introduced to reconstruct the numerical solution of coenergy from Finite Element Analysis (FEA). Secondly, analytical models of flux linkage, electric torque and voltage equation in stator current oriented synchronous frame are derived based on the reconstructed coenergy model. Finally, the steady and dynamic characteristics of GSVM are validated against experimental results.
The use of conformal antennas in a MIMO link scenario is investigated. Conformal slot antennas are considered both in the transmitter and the receiver. First, a new modified correlation coefficient is derived that goes beyond the Clarke coefficient and takes into account the element radiation pattern. Secondly, a hybrid formulation that accounts for the impact of the mutual coupling and the pattern dependent correlation on the capacity is presented. The mutual coupling for slots placed circumferentially on a paraboloid substrate is derived using a rigorous approach based on Uniform Theory of Diffraction (UTD). The capacity is evaluated for the case of Rayleigh fading channel considering the new pattern dependent correlation coefficient and the conformal antenna mutual coupling. The planar case is included as a limiting case. It is shown that for conformal antennas on a paraboloid the capacity degradation compared to the planar case is up to 0.5 bps/Hz due to coupling and correlation.