Workers using an implantable cardioverter defibrillator (ICD) are classified by European Directive 2013/35/EU as being at particular risk because of the potential interference between implanted medical devices and electromagnetic fields. The aim of the study was to investigate ICD function using a human-shaped phantom in high magnetic fields of a shunt reactor at a 400 kV substation. We used the phantom in the following experiment periods: isolated from the ground, grounded by a foot, or grounded by a hand. We performed five ICD tests using five different ICD devices. In experiment place A, the magnetic field was over 1000 μT, and in experiment place B, the exposure was over 600 μT. We did not find any disturbances in the ICDs. However, we conducted only 5 ICD experiments in real exposure situations at 400 kV substations. Although it is not possible to draw a strong conclusion regarding risk level, the risk of such ICD disturbances from magnetic field exposure at 400 kV substations does not appear to be high.
Many government-led wind farms are being constructed in Korea as sources of clean and renewable energy. However, construction of these wind farms is continuously opposed by nearby military bases that operate X-band tracking radar because the amplitude and phase of the electromagnetic waves reflected from the wind turbines may interfere with tracking radars installed along the coastline of the Korean peninsula. This paper proposes a method to analyze the effect of a wind farm on tracking radar, and presents the results of using the radar cross section of the blade of a real turbine predicted by the method of physical optics. Simulation results using various flight scenarios demonstrate that the tracking accuracy may be considerably degraded; thus appropriate action is required to eliminate this effect.
Fundamental properties of carbon nanotube antenna are firstly investigated to predict the antenna bundle response. The carbon nanotube effects are mathematically introduced via a quantum mechanical conductivity. This paper presents a new formulation based on integral equations system to study the coupled carbon nanotube antennas. The proposed integral equations system is numerically solved by the moments method. Each dipole antenna is excited at its center by a gap voltage source. The aim of the developed method is to investigate the antennas interaction effects for any coupling distance. The obtained input impedances, the current distributions and the antenna radiation patterns are in agreement with those obtained by the effective conductivity method or by the array factor method, according to the coupling distances.
In performing the experiments, the interference source has the form of a hollow PVC tube wrapped with a current-carrying coil, while the detector has the form of a PIN (Positive-Intrinsic-Negative) photodiode. The experimental results show that the electromagnetic disturbance (EMD) signal effect is dependent on the number of turns, the direction of the electromagnetic field, and the frequency and amplitude of the interference voltage. Specifically, it is shown that when the electromagnetic field acts in the opposite direction to that of the laser beam, the intensity and optical power of the detected signal decrease with an increasing interference frequency or amplitude. By contrast, when the electromagnetic field acts in the same direction as that of the laser beam, the intensity and optical power increase with an increasing interference frequency or amplitude. In addition, it is shown that the effect of EMD on the intensity of the laser beam increases with an increasing laser beam dispersion (i.e., an increasing distance from the laser source).
This paper proposes an imaging method of multi-direction swath and digital beamforming (DBF) in elevation for spaceborne Hybrid Phased-MIMO SAR that combines traditional phased-array radar with a new technique for multiple-input multiple-output (MIMO) radar to achieve multifunctional synthetic aperture radar (SAR). At first, we build a signal model and derive a virtual control matrix of the Hybrid Phased-MIMO SAR. Furthermore, considering the image overlap and range ambiguity caused by multiple direction imaging, we present adaptive Digital Beamforming based on Linearly Constrained Minimum Variance (LCMV). In this approach, the first constraint is dedicated to make the overall beamformer response equal the quiescent response in the desired signal region so that the signal is not cancelled when it is present, and additional constraints are included to assure proper reception of the desired signal and form nulls in the direction of interference at the same time. The diagonal loading method is combined with this method to reduce small eigenvalue interference for its eigenvector, which improves the convergence speed in sidelobe. The substantial improvements offered by the proposed adaptive Digital Beamforming technique as compared to previous techniques are demonstrated analytically and by simulations through analysis of the corresponding range compression results and achievable output performance of interference suppression. Simulation results validate the effectiveness of the adaptive DBF.
An analytical expression of an Airy-Gauss beam passing through a fractional Fourier transform (FRFT) system is derived. The normalized intensity distribution, phase distribution, centre of gravity, effective beam size, linear momentum, and kurtosis parameter of the Airy-Gauss beam are demonstrated in FRFT plane, respectively. The influence of the fractional order p on the normalized intensity distribution, phase distribution, centre of gravity, effective beam size, linear momentum, and kurtosis parameter of the Airy-Gauss beam are examined in FRFT plane. The fractional order p controls the normalized intensity distribution, phase distribution, centre of gravity, effective beam size, linear momentum, and kurtosis parameter. The period of the normalized intensity, phase, and centre of gravity versus the fractional order p is 4. The period of effective beam size, linear momentum, and kurtosis parameter versus the fractional order p is 2. The periodic behaviors of the normalized intensity distribution, phase distribution, centre of gravity, effective beam size, linear momentum, and kurtosis parameter can bring novel applications such as optical switch, optical micromanipulation, and optical image processing.
In high power operations, the ageing of power semiconductor modules has been often observed by several failures due to high temperature cycling. The main failures may be metallization reconstruction, solder delaminations, bond wire lift-offs or bond wire heel crackings, conchoidal breaking of ceramics. The paper focuses on the non-contact monitoring of the ageing of the aluminum metallization top layer and of the solder bottom layer of a power die, using the eddy current method. The ageing is assumed to induce a decrease of these layers conductivity. The evaluation of both layers conductivity changes are estimated using artificial neural networks starting from eddy current data provided by finite element computations carried out in the case of several aged die configurations. The error of estimation is less than a few percent in the considered cases and it demonstrates the relevance of the eddy current method to monitor the ageing state of power modules. The proposed approach provides relevant results which will be validated on experimental data in future works.
This article describes an improved design procedure for shaped-beam reflectarrays, which is advanced mainly in accuracy and concision. Specifically, the excitation has been computed by a new approach named local simulation instead of mathematical modeling, which demonstrates more advantage in precision. The intersection approach has been applied to optimization, and it is improved by introducing a new multi-stage strategy into the synthesis process to avoid local minima. Moreover, the phase-only optimization, calculation of the reflection phase data table and the simulation verification processes are combined as a co-simulation procedure by VBScript (Visual Basic Script). This procedure is very beneficial to design reflectarrays with efficiency. As an example, a reflectarray consists of 621 dual-loop elements is optimized, and a good sectored-cosecant squared beam result is obtained.
In order to decouple traditional levitation windings and armature windings, a new self-decoupling magnetic levitation generator (SDMLG) is proposed for wind turbines. This new generator adopts double-stator structure. The armature windings are in the outer stator, and the levitation windings are in the inner stator. The rotor is made of a distributed hollow structure, so that it can effectively decouple the levitation subsystem and armature subsystem. The new structure and operating principle of the generator are presented in this paper. Then the expressions of levitation forces are deduced by analyzing magnetic flux distributions and winding flux linkages. Finite-element analysis method (FEA) is used as the tool for analyzing the performance of the new generator. And the results verify that the levitation windings and armature windings are effectively decoupled.
Suspended particles in the atmosphere during sand and dust storms have numerous consequences on electromagnetic wave propagation in arid regions. The electromagnetic wave signal may suffer attenuation and cross polarization upon encounter with the suspended particles. However, meager information has hitherto been reported about effect of storms on the telecommunication systems operating in such regions. This paper presents a survey of current understanding of the electromagnetic wave propagation in sand and dust storms. A review of the literature covering electromagnetic scattering theory and applications is given. The review describes the principle of approach and technology adopted for the investigation highlighting both strengths and drawbacks. Detailed parametric assessment of the effects of storms on wave propagation as it concerns signal attenuation and cross polarization is also carried out. The results demonstrate that most authors have calculated the attenuation effect, revealing that it is not very significant unless very high suspended dust densities are assumed (i.e. during severe sand and dust storms). A few papers indicate the possibility of more significant cross polarisation. The obvious gap in knowledge of this field is finally also clearly established.
Electromagnetic wave propagation in arid and semi-arid regions is influenced by sand and dust storms. Meagre information has hitherto been reported as to the effect of storms on telecommunication systems operating in such regions. This paper presents a survey of current understanding of the electromagnetic wave propagation during sand and dust storms. In the first part of the review, detailed parametric assessment of some electrical and mechanical properties affecting wave propagation in sand and dust storms is given. The second part of the review (Part-II) describes the principle of approach and technology adopted for the investigation highlighting both strengths and drawbacks. The results demonstrate that most authors have calculated signal attenuation effect, revealing that it is not very significant unless very high suspended dust densities are assumed (i.e. during severe sand and dust storms). A few papers indicate the possibility of more significant cross polarisation. Part-I explicitly gives an account of the sand and dust storms' phenomenon, reviews the storms' parameters affecting electromagnetic wave propagations and discusses the microwave and millimeter wave bands.
We obtain a Sturm-Lioville matrix equation of motion (SLME) for the study of electromagnetic wave propagation in layered anisotropic structures. Conducting media were taken into account so that ohmic loss is considered. This equation can be treated using a 4×4 associated transfer matrix (T) in layered anisotropic structures, where the tensors: permittivity, permeability and the electric conductivity have a piecewise dependence on the coordinate perpendicular to the layered structure. We use the SLME eigenfunctions and eigenvalues to analyze qualitatively the numerical instability (Ωd problem) which potentially affects practical applications of the transfer matrix method. By means of the SLME coefficients we show analytically that T determinant value can be used to keep a check on the numerical accuracy of calculations. We derive equations to analyze wave propagation in linear layered isotropic structures. The SLME approach is applied on two typical layered structures to verify theoretical predictions and experimental results.
Given that building occupants and more importantly public safety personnel regularly use stairwell to move about different floors in a multi-floor building, wireless network coverage for the setting may come as necessary in order to ensure seamless telecommunication connectivity. Nevertheless, wireless network planning pertaining to multi-floor stairwell scenario requires unique radio characterization since the scenario is different from other indoor environments. This paper presents a frequency dependent path loss and shadowing model for the multi-floor stairwell environment that was developed and tested at six dog-leg style stairwells. The empirical model covers frequency spectrum from 0.7 GHz up to 2.5 GHz which envelop numerous public safety and long term evolution operating bands. The model demonstrates good precision and is shown to outperform standard path loss model when comparison was made since it includes site-specific parameters describing radio characteristics natural to stairwell setting. The straightforward mathematical expression of the model can easily be applied when setting up or studying wireless network for the stipulated frequency range with respect to the multi-floor stairwell.
Knowledge of propagation media, typically gathered through physical experiments and simulations, is absolutely critical in successful transceiver design. In the case of medical implants, physical experiments are extremely difficult. Therefore, we rely on simulations in most studies. In this paper, Path Loss (PL) between implanted antennas, as a measure of propagation channel characteristics, is investigated using High Frequency Structure Simulator (HFSS) and Remcom's XFDTD 7 (XF7). An Electrically Coupled Loop Antenna (ECLA) is designed to study PL inside human body models at different frequency bands: Medical Implanted Communication Services (MICS) band (402-405 MHz), Industrial Scientific and Medical (ISM) band (2.4 2.5 GHz) and 3.5 GHz band (3.55-3.65 GHz). The ECLA has dimensions (5×5×3 mm3), (3×3×3 mm3) and (2×2×2 mm3) at MICS, ISM and 3.5 GHz respectively. ECLA performance inside human body models is studied at the allowed frequency bands. The effects of frequency bands, human model electrical properties, and distance between implants on PL are considered. Simulation results are validated with experimental work. Our results show that the ECLA at MICS band has the lowest Specific Absorption Rate (SAR) and the highest allowed input power. Also, the MICS band has the lowest PL inside the human body model, shown to be less than 90 dB in the worst case scenario.
The Floquet-Bloch theorem allows waves in infinite, lossless periodic media to be expressed as a sum of discrete Floquet-Bloch modes, but its validity is challenged under the realistic constraints of loss and finite extent. In this work, we mathematically reveal the existence of Floquet-Bloch modes in the electromagnetic fields sustained by lossy, finite periodic layered media using Maxwell's equations alone without invoking the Floquet-Bloch theorem. Starting with a transfer-matrix representation of the electromagnetic field in a generic layered medium, we apply Fourier transformation and a series of mathematical manipulations to isolate a term explicitly dependent on Floquet-Bloch modes. Fourierdomain representation of the electromagnetic field can be reduced into a product of the Floquet-Bloch term and two other matrix factors: one governed by reflections from the medium boundaries and another dependent on layer composition. Electromagnetic fields in any finite, lossy, layered structure can now be interpreted in the Fourier-domain by separable factors dependent on distinct physical features of the structure. The developed theory enables new methods for analyzing and communicating the electromagnetic properties of layered metamaterials.
This paper presents a computationally efficient technique for designing electrically thick differentially-driven rectangular microstrip antennas with coaxial probe feed. It concerns the use of a transmission line model for probe positioning, along with a full-wave field simulator that yields accurate results with reduced number of required full-wave simulations. An electrically thick antenna was designed with the proposed technique to operate at 2442 MHz, having its radiation patterns and input impedance measured and compared against a single-feed rectangular microstrip antenna to demonstrate the advantages of using differential feed to reduce cross-polarization in H-plane.
An iterative solution scheme based on the magnetic field integral equation (MFIE) to compute electromagnetic scattering for arbitrary, perfect electrically conducting (PEC) objects is topic of this contribution. The method uses simple and efficient approaches for the computation of surface current interactions which are typically found in the well-known iterative physical optics (IPO) technique. However, the proposed method is not asymptotic, since no physical optics (PO) concepts are utilized. Furthermore, a least squares correction method is introduced, which is applied not on the complete current vector, but on individual groups of currents. This helps to quickly reduce the residual error and to improve convergence. The result is a simple method which is capable to improve the simulation results obtained by pure asymptotic methods such as PO or shooting and bouncing rays (SBR). The method can be regarded as a simplified iterative method of moments (MoM) technique. Numerical examples show that the proposed approach is advantageous e.g. in problem cases where the neglect of diffraction effects or currents in shadow regions would cause large errors. It also provides an improved prediction of the peak scattering contributions.
The boundary layer temperature profile is very essential for modeling atmospheric processes, whose information can be obtained using radiosonde data generally. Beside this, ground-based multi-channel microwave radiometer (GMR) offers a new opportunity to automate atmospheric observations by providing temperature, humidity and liquid water content with high time resolution, such as MP-3000A ground-based multi-channel radiometer. An experiment in east coast of China for profiling boundary layer temperature was performed at Qingdao Meteorological Station from 1 March to 23 April in 2014 using an MP-3000A radiometer. Three techniques have been applied to retrieve the boundary layer temperature profile by using the experimental data, namely the linear regression method, the back propagation (BP) neural network method and the 1-D Variational (1D-VAR) method. Elevation scanning is introduced to help improve the accuracy and resolution of the retrievals for each technique. These results are compared with the radiosonde data at the same time. The preliminary results achieved by each method show that the average day root-mean-square (rms) error for temperature is within 1.0 K up to 2 km in height. The 1D-VAR technique seems to be the most effective one to improve the precision of the boundary layer temperature profile.
In this paper, we propose to realize ultra-wide-band absorber (UWBA) based on anomalous refraction/reflection of phase gradient metasurfaces(PGM). To achieve high absorption and meanwhile keep small thickness at low frequencies, PGM is incorporated into conventional magnetic materials (MM). The absorptivity is increased due to prolonged propagation length in the MM, which is produced via anomalous refraction/reflection mediated by the PGM. Three typical composite configurations of PGM-based absorbers are investigated and an UWBA design method is finally formulated. Due to small thickness and ultra-wide bandwidth, such absorbers possess great application potentials in EM protection, RCS reduction, etc.
In this paper, an efficient mode reduction technique for eigenmode expansion method is developed to analyze 2-D waveguide grating structures which are a special class of piecewise uniform waveguides. To take advantage of the periodicity property of the structure, the eigenmode expansion method (EEM) is used with the scattering matrix method and a recursive-doubling procedure. In this situation, our proposed mode reduction technique achieves a significant speedup for gratings with large number of periods. Comprehensive numerical examples on the waveguide gratings are studied to validate the efficiency of our proposed mode reduction technique.