Showing papers in "Progress in Electromagnetics Research M in 2016"

The Performance Improvement of THz Antenna via Modeling and Characterization of Doped Graphene

Abstract: The improvement of Terahertz (THz) antenna requires efficient (nano)materials to operate within the millimeter wave and THz spectrum. In this paper, doped graphene is used to improve the performance of two types of patch antennas, a rectangular and an elliptical antenna. The surface conductivity of conventional (non-doped) graphene is first modeled prior to the design and simulation of the two graphene based antennas in an electromagnetic solver. Next, different graphene models and their corresponding surface conductivities are computed based on different bias voltages or chemical doping. These configurations are then benchmarked against a similar antenna based on conventional metallic (copper) conductor to quantify their levels of performance improvement. The graphene based antennas showed significant improvements for most parameters of antenna than that of the conventional antenna. Besides that, the higher chemical potentials resulting from higher biasing voltages also resulted in this trend. Finally, the elliptical patch graphene antenna indicated better reflection performance, radiation efficiency and gain than a rectangular patch operating at the same resonant frequency.

Performance Evaluation of Micro Rain Radar Over Sumatra through Comparison with Disdrometer and Wind Profiler

Abstract: 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 (< 1mm), 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.

Surface-Plasmon-Polaritons at the Interface of Nanostructured Metamaterials

Abstract: The rigorous modeling and analysis of surface waves at the boundary of two metamaterials are presented. The nature of the phenomenon of the surface-plasmon-polaritons and the influence of various parameters on it are investigated. We have analyzed the properties of structures incorporating nanostructured metamaterials. Surface-plasmon-polaritons at the interface of such metamaterials are studied. We demonstrate the ways to control the properties of the surface waves. Each metamaterial comprises alternating metal and dielectric layers. We analyze the dependence of the dispersion characteristics on the materials employed in metal-dielectric compound. The consistency of the dispersion diagrams and effective permittivity is studied. The Drude model is introduced in the metal dispersion in order to take into account the effects of the structure on dielectric properties.

On the Feasibility of Assessing Burn Wound Healing Without Removal of Dressings Using Radiometric Millimetre-Wave Sensing

Abstract: The authors present transmission data, taken at Ka (36GHz) and W (95 GHz) bands in the millimetre-wave region of the electromagnetic spectrum, for various dressing materials used in the treatment and management of burn wounds. The results show that such materials are highly transparent (typically > 90% transmission) and, in their dry state, will permit the sensing of the surface of the skin through the thick layers (> 2 cm) of different dressings typically applied in medical treatment of burn wounds. Furthermore, the authors present emissivity data, taken at the same frequency bands, for different regions of human skin on the arm and for samples of chicken flesh with and without skin and before and after localised heat treatment. In vivo human skin has a lower emissivity than chicken flesh samples, 0.3–0.5 compared to 0.6–0.7. However, changes in surface emissivity of chicken samples caused by the short-term application of heat are observable through dressing materials, indicating the feasibility of a millimetre-wave imaging to map changes in tissue emissivity for monitoring the state of burn wounds (and possibly other wounds) non-invasively and without necessitating the removal of the wound dressings.

Design of Polarization-Insensitive Dual Band Metamaterial Absorber

Abstract: 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.

Cumulative Distributions of Rainfall Rate over Sumatra

Abstract: The microwave radio links above 5 GHz suffer from attenuation due to precipitation. The need for employing higher frequencies has therefore encouraged research into rain attenuation due to precipitation. The natural variations of tropical precipitation occur in a wide range of time-scales, so does probably the behavior of radio communication links. This paper examines the variations of cumulative distribution of rainfall in Sumatra from an optical rain gauge measurement with a near continuous record of operation over eleven consecutive years (2002-2012). The worst month statistics were also examined and all results were compared with the ITU-R model. Of some natural variations of rainfall rate investigated, the diurnal variation had the most significant effect on the cumulative distribution of rainfall rate. The ITU-R model overestimated the rainfall rate for the first half of the day (00:00-11:59 LT) whereas it underestimated the rainfall rate until 0.01% of time for the second half of the day (12:00-23:59 LT) before the model starts to overestimate. The ITU model overestimated 52.85% of rainfall rate at 0.01% of time for the first half of the day and underestimates 7.59% for the second half. Considerable differences between the recorded data and the ITU-R model for the annual, seasonal, and intreaseasonal variations are only significant at small time percentage (≤ 0.01%). The relationship of worst month statistics was also slightly different from the ITU-R model. This result reinforces the previous studies on the limitation of the ITU-R model for the tropical region.

Highly Coherent Supercontinuum Generation in the Normal Dispersion Liquid-Core Photonic Crystal Fiber

Abstract: In this paper, a liquid-core photonic crystal fiber (LCPCF) with small hollow-core filled by chalcogenide material CS2 is designed. The supercontinuum (SC) generation in such a LCPCF with nonlinear coefficient of 3327 W−1·km−1 at 1550 nm and wide normal dispersion regime spanning from 1200 to 2500 nm is numerically studied by solving the generalized nonlinear Schrödinger equation. The influences of the pump pulse parameters on the SC spectral width and coherence are demonstrated, and the optimum pump condition for the SC generation is determined. Our study work can provide an alternative way for obtaining highly coherent SC, which is important for the applications in optical coherence tomography, frequency combs, and ultrashort pulse generation.

Superresolution Imaging for Forward-Looking Scanning Radar with Generalized Gaussian Constraint

Abstract: A maximum a posteriori (MAP) approach, based on the Bayesian criterion, is proposed to overcome the low cross-range resolution problem in forward-looking imaging. We adapt scanning radar system to record received data and exploit deconvolution method to enhance the real-aperture resolution because the received echo is the convolution of target scattering coefficient and antenna pattern. The Generalized Gaussian distribution is considered as the prior information of target scattering coefficient in MAP approach for the reason that it could express different target scattering coefficient properties with the control of statistic parameter. This constraint term makes the proposed algorithm useful in different applications. On the other hand, the reconstruction problem can also be viewed as the lp-norm (0

Novel Finite Airy Array Beams Generated from Gaussian Array Beams Illuminating an Optical Airy Transform System

Abstract: In this work, a novel family of Finite Airy array beams have been produced by an optical Airy transform system illuminated by Gaussian Array beams. Based on the generalized HuygensFresnel integral, an analytical expression is developed to describe the pattern properties of the beam generated at the output plan of the optical system. The well-known Finite Airy beam generated from the fundamental Gaussian beam using an optical Airy transform system is deduced, here, as a particular case of the main result of the actual study. Numerical calculations are performed to show the possibility to create a multitude of Finite Airy array beams with controllable parameters depending on the number of beamlets, the distance between the adjacent modules and the positions and orientations of the beamlets.

Polarizability Tensor Calculation Using Induced Charge and Current Distributions

Abstract: We develop a semi-analytical approach to calculate the polarizability tensors of an arbitrary scatterer. The approach is based on numerical integration from induced charges and currents on the scatterer. By taking the advantages of the present approach, we calculate the polarizability tensors of any arbitrary scatterer in a homogeneous isotropic medium. This approach, in comparison to other reported approaches, is simple, easily implemented, and does not require spherical harmonic expansion or complicated far-field calculations. We examine the validity of the approach using several examples and compare the results with other approaches.

EMI Shielding Effectiveness of Composites Based on Barium Ferrite, PANI, and MWCNT

Abstract: An electromagnetic interference (EMI) shielding material based on the composite of BaFe12O19, polyaniline (PANI) and multi-walled carbon nanotube (MWCNT) was proposed. The constituents of the composite were brought together through mechanical mixing and the in-situ polymerization of aniline on the BaFe12O19 and MWCNT surfaces. A series of composite with different MWCNT wt% loadings (0, 5, 10, 15, 20 and 25wt%) was prepared, and its effect on the EMI shielding performance was investigated. X-ray diffraction analysis was performed on all synthesized composites to confirm the phase formations. FESEM micrographs reveal the PANI particle formation on both BaFe12O19 and MWCNT surfaces. Electromagnetic measurements were done by using a rectangular waveguide connected to a network analyser to obtain the permeability, μr, permittivity, εr, and shielding effectiveness (SEA and SER). The increase in the MWCNT loading results in the enhancement of the composite’s shielding performance to a certain limit. Optimum EMI shielding performance is shown by sample PBM4 (20wt% MWCNT) with SER and SEA values of 5.14 dB at 8.2 GHz and 36.41 dB at 12.4 GHz, respectively. The influence of different MWCNT loadings (0, 5, 10, 15, 20 and 25wt%) on the EMI shielding performance of a composite consisting of BaFe12O19, polyaniline (PANI) and multi-walled carbon nanotube (MWCNT) were investigated.

Design of a Dual-Band MIMO Dielectric Resonator Antenna with Pattern Diversity for WiMAX and WLAN Applications

Abstract: 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 TEx 121/TEy 211 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 frequency 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 5.2GHz, respectively. Simulated and measured reflection coefficients, envelope correlation, diversity gain and mean effective gain, are in good agreement.

Comparison Guidelines and Benchmark Procedure for Sparse Array Synthesis

Abstract: A benchmarking procedure for sparse linear array synthesis methods is proposed. Our approach is based on the comparison of the performance of the array synthesis algorithm under test with the performance of a reference solution based on a optimally equispaced array. The benchmark procedure is demonstrated considering some examples regarding sparse synthesis method proposed in literature. Guidelines for the correct comparison of synthesis methods and some “tough problems” for the test of new sparse synthesis algorithms are also provided.

Spectral Domain Analysis of Gyrotropic Anisotropy Chiral Effect on the Input Impedance of a Printed Dipole Antenna

Abstract: A theoretical analysis of a printed dipole antenna on a gyrotropic-anisotropy chiral dielectric substrate is presented. The study is based on numerical techniques for the characterization of electromagnetic propagation in chiral media. The general complex wave equation and the dispersion relation for such a medium are derived in the spectral domain. The spectral Green's function of a grounded dielectric chiral slab is developed, and the spectral domain moment method impedance matrix elements are calculated. The effect of the chiral gyrotropy element on the input impedance of a dipole antenna printed on a grounded chiral substrate is analyzed using the Galerkin-based Method of Moments.

Analytical Synchronization Analysis of Line-Start Permanent Magnet Synchronous Motors

Abstract: A main challenge in designing line-start permanent magnet synchronous motors is synchronization analysis and determination. The transient time-step finite element simulations are often required in the design process, which is computationally expensive. An attractive alternative is to use an analytical synchronization model, which is time efficient and thus viable to be included in an optimization procedure. In this paper, two variants of the energy-based analytical synchronization model are proposed. Their viability and performance are compared with those of the existing analytical method and validated by transient finite element simulations. It is shown that the proposed methods have a better resolution and accuracy in determining the synchronization status of line-start permanent magnet motors.

Extension of thin wire techniques in the fdtd method for debye media

Abstract: There are applications of the finite difference time domain (FDTD) method, which need to model thin wires in dispersive media. However, existing thin wire techniques in the FDTD method are developed only for the conductive and dielectric media. The article presents a modification of oblique thin wire formalism proposed by Guiffaut et al. and a minor modification for the technique proposed by Railton et al. for applications with Debye media. The modifications are based on auxiliary differential equation (ADE) method. The modifications are validated by calculations of grounding potential rise (GPR) of a horizontal electrode buried in soil with dispersive properties.

''Double-Humped Effect'' in the Turbulent Collision Magnetized Plasma

Abstract: Statistical moments of the spatial power spectrum of multiple scattered ordinary and extraordinary waves in the turbulent collision magnetized plasma with aligned anisotropic electron density irregularities are investigated using modify smooth perturbation method taking into account diffraction effects. Correlation function and variances of the phase fluctuations are obtained for arbitrary correlation function of the electron density fluctuations. "Double-humped Effect" is investigated analytically and numerically using the anisotropic Gaussian spectral function of electron density irregularities for the polar ionospheric F-region applying the experimental data. Investigation of the anisotropy of the F layer irregularities is of great interest in ionospheric physics. It is well known that the irregularities are elongated in the direction of the geomagnetic field of lines, but especially at high latitudes they are also found to be anisotropic in the plane perpendicular to the external magnetic field vector. The anisotropy is usually investigated by correlation analysis of radio signals from satellites, observed by space receiver on the ground. The fluctuations in amplitude and phase (scintillations) of radio waves passing through the ionosphere are caused by spatial irregularities in the electron density. The spatial fluctuations in phase cause fluctuations of the angle of arrival at the observation points. Broadening of the spatial power spectrum (SPS) of scattered electromagnetic (EM) waves in the turbulent collision magnetized plasma for both power-law and anisotropic Gaussian correlation functions of electron density fluctuations was analyzed in (1) using the complex ray (-optics) approximation. "Double-humped Effect", the features of the SPS, spectral width and shift of its maximum of multiple scattered EM waves in the turbulent collisionless magnetized plasma were considered in (2, 3). The influence of the collision frequency between plasma particles on the statistical characteristics of scattered EM waves in the turbulent magnetized plasma with both electron density and external magnetic field fluctuations was investigated in (4). The present paper reports the results of an analysis of the SPS, which is related to fluctuations of the radio refractive index in the F region. Analytical expressions of the correlation function of phase fluctuations of scattered both ordinary and extraordinary waves are obtained for the arbitrary correlation functions of electron density fluctuation using modify smooth perturbation method taking into account the diffraction effects. The "Double-humped Effect" in the collision magnetized plasma with elongated electron density irregularities is considered for the first time. Formation of a gap in the SPS of scattered radiation is analyzed numerically for the polar ionospheric F -region using the anisotropic Gaussian spectral function of electron density fluctuations. This spectrum contains angle of aligned plasma irregularities to the direction of an external magnetic field and anisotropy factor. The numerical calculation is computed based on experimental data. Finally, paper concludes the obtained results and their significance.

Diagnosis of the AC Current Densities Effect on the Cathodic Protection Performance of the Steel X70 for a Buried Pipeline Due to Electromagnetic Interference Caused by HVPTL

Abstract: This paper diagnoses the effect of the AC current densities induced by the electromagnetic interferences between high voltage power line and buried power line on the cathodic protection performances of the X70 steel in the simulated soil. First, the induced voltage onto the pipeline was calculated for various power line configurations, separation distances between transmission line and pipeline and parallelism lengths. The induced AC current density was computed function to the induced voltage, soil resistivity, and holiday diameter. Then, the electrochemical characters of the X70 steel, at various AC current densities, are measured using the potentiodynamic method. The electrochemical parameters obtained by the electrochemical tests are used as boundary conditions in the cathodic protection simulation model. The results indicate that, under influence of AC current densities, the X70 steel is more susceptible to corrosion, and the cathodic protection is unable to maintain the protection potential.

Direction-Controllable Electromagnetic Acoustic Transducer for SH Waves in Steel Plate Based on Magnetostriction

Abstract: 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.

EMI Consideration of High Reliability DC-DC Converter: in Aerospace Based Electric Transport System Charger Application

Abstract: High reliability and low electromagnetic interference (EMI) are two important factors for many industrial applications such as air based electric transport system charger (AETSC). Therefore, it is essential to introduce high reliability and low EMI power converters. This paper presents a new high reliability and low current ripple DC-DC converter. For the proposed converter, a spectrum analysis approach for suppressing the EMI using chaotic sinusoidal pulse width modulation is provided. In addition, the proposed converter has radio frequency (RF) EMI lower than 100 kHz. However, for higher than 100 kHz, EMI issue of the proposed converter has unsuitable situation. 1. NOMENCLATURE A: amplitude of signal, fc: carrier signal, υm(τ ): unitary amplitude of modulated signal, kω: a controlled factor, TC : the main frequency of switch which is a constant, xn :t henth output of chaotic mapping, β: a modulation factor.

Millimeter-Wave Holographic Imaging Algorithm with Amplitude Corrections

Abstract: Security detection is becoming extremely important with the growing threat of terrorism in recent years. An effective millimeter-wave (mmw) holographic imaging system is presented in this paper, which can be applied in nondestructive detection such as security detection in airport or other public locations. The imaging algorithm is an extension of the work before as it takes the decay of the amplitude with range into account. The experiment result of an imaging system working at 28-33 GHz frequencies indicates good quality of the algorithm.

Visualization of eddy current distributions for arbitrarily shaped coils parallel to a moving conductor slab

Abstract: To visualize eddy current distribution (ECD) of an arbitrarily shaped coil arranged parallel to a moving conductor slab, an exact theoretical solution is derived using an analytical method based on the double Fourier transform method. The arbitrarily shaped coil is regarded as a plane coil of a single turn, and both DC and AC excitation currents can be applied. Furthermore, ECD charts are obtained when the conductor slab is moving. We calculate some examples with respect to a circular coil, rectangular coil, and triangular coil and show the effect of coil excitation frequency and speed of the conductor on ECDs. Results show that the eddy current generated in the moving conductor slab is composed of current induced by the excitation frequency and conductor speed.

Large Linear Random Symmetric Arrays

Abstract: In this work linear random arrays are studied. It is shown that random symmetric linear arrays can be more easily characterised (with respect to the asymmetric ones) in terms of the first and second order statistics of the array factor magnitude. In particular, the non-stationarity of the array factor can be taken into account while studying the array response. Accordingly, this leads to more accurate predictions as far as the side-lobe level is concerned.

A Novel Resistance Network Node Potential Measurement Method and Application in Grounding Grids Corrosion Diagnosis

Abstract: In this paper, a novel resistance network node potential measurement technique based on 16-channel cycle method is presented, and a grounding grids corrosion diagnosis measurement system with 16 channels is built from this method. Through this measurement system, 1680 valid potential data and 1560 effective branch voltage data can be collected in one measurement by only 16 risers on the grounding grid. The stability error of the excitation current source is less than 0.15%, and the error of the applicable acquisition data is about 1% according to system data tests. Built on the measurements, an underdetermined sensitivity equation for solving the increasing multiple of branch resistance is put in place to determine the corrosion status of grounding grids. The experimental results show that the plenty of data is necessary when solving the underdetermined equation and also show that the system is under a high stability, high accuracy, and can comply with the requirements of corrosion diagnosis for grounding grids.

Hybrid Excited Vernier Machines with All Excitation Sources on the Stator for Electric Vehicles

Abstract: In this paper, two new hybrid excited vernier machines with surface and interior V-shaped PM arrays are proposed. By integrating the vernier structure and field excitation windings together, the proposed machines not only retain the merit of high torque of permanent magnet vernier, but also offer flexible flux adjustment to enable a wide speed range with the introduction of field windings. Different from existing hybrid excited vernier machines having magnets on the rotor, the proposed machines is designed with all excitation sources on the stator. Therefore, temperature rise of magnets of the proposed machines is much easier to control, which in turn reduce the risk of irreversible demagnetization of magnets and enhance the reliability. The electromagnetic performances of the two proposed machines are comprehensively analyzed and quantitatively compared by using the time-stepping finite-element method, verifying the theoretical analysis.

Analysis of Microwave Scattering from a Realistic Human Head Model for Brain Stroke Detection Using Electromagnetic Impedance Tomography

Abstract: Brain stroke incidences have arisen at an alarming rate over the past few decades. These strokes are not only life threatening, but also bring with them a very poor prognosis. There is a need to investigate the onset of stroke symptoms in a matter of few hours by the doctor. To address this, Electromagnetic Impedance Tomography (EMIT) employing microwave imaging technique is an emerging, cost-effective and portable brain stroke diagnostic modality. It has the potential for rapid stroke detection, classification and continuous brain monitoring. EMIT can supplement current brain imaging and diagnostic tools (CT, MRI or PET) due to its safe, non-ionizing and non-invasive features. It relies on the significant contrast between dielectric properties of the normal and abnormal brain tissues. In this paper, a comparison of microwave signals scattering from an anatomically realistic human head model in the presence and absence of brain stroke is presented. The head model also incorporates the heterogenic and frequency-dispersive behavior of brain tissues for the simulation setup. To study the interaction between microwave signals and the multilayer structure of head, a forward model has been formulated and evaluated using Finite Element Method (FEM). Specific Absorption Rate (SAR) analysis is also performed to comply with safety limits of the transmitted signals for minimum ionizing effects to brain tissues, while ensuring maximum signal penetration into the head.

Electromagnetic Waves Attenuation in the Sandstones with Grains of Different Size at Imbibition and Drying

Abstract: The results of experimental measurements of the complex dielectric permittivity (CDP) of powders of quartz granules with different sizes saturated with water and salt solution of weak concentration are given in the frequency band from 20 kHz to 1GHz. It is shown that at values of saturation level from 0.6 to 0.9 the relaxation phenomena caused by interfacial polarization on the water-air bound can be observed. The result shows considerable reduction of attenuation in gradually saturated rocks, which allows for deeper sensing during georadar mapping. It is determined that in the dielectric relaxation band and at frequencies below it the hysteresis of the real part of the CDP and equivalent specific conductivity can be observed. Its character significantly depends on the sizes of granules. It is shown that the behavior of CDP and attenuation of an electromagnetic wave at frequencies from 0.1 to 10 MHz complicatedly depends on the sizes of granules, saturation level, salinity of the saturating solution and saturation history.

Electromagnetic Waves Radiation by a Vibrators System with Variable Surface Impedance

Abstract: The problem of electromagnetic waves radiation by a vibrators system with variable distributed surface impedance along their axes located in free space is solved by the generalized method of induced electromotive forces (EMF). The distinctive peculiarity of this method is the use of the functional distributions, obtained as a result of the analytical solution of the integral equation for the current by the asymptotic averaging method before, as the basic approximations for the currents along the impedance vibrators. The multi-parameter characteristics of three-element and multi-element antennas with variable impedance vibrators are calculated.

Backscattering Analysis for Snow Remote Sensing Model with Higher Order of Surface-Volume Scattering

Abstract: The study of earth terrain in Antarctica is important as this region has a direct impact on global environment and weather condition. There have been many research works in developing remote sensing technologies, as it can be used as an earth observation technique to monitor the polar region [11, 15]. In previous studies, remote sensing forward model has been developed to study and understand scattering mechanisms and sensitivity of physical parameters of snow and sea ice. This paper is an extended work from previous studies [16–19], where an improved theoretical model to study polar region was developed. Multiple-surface scattering, based on an existing integral equation model (IEM) that calculates surface scattering and additional second-order surface-volume scattering, were added in the model from prior research works [7] for improvement in the backscattering calculation. We present herein the application of this model on a snow layer above ground which is modeled as a volume of ice particles that are closely packed and bounded by irregular boundaries above a homogenous half space. The effect of including multiple surface scattering and additional surface-volume scattering up to second order in the backscattering coefficient calculation of snow layer is studied for co-polarized and cross-polarized returns. Comparisons with satellite data are also done for validation. Results show improvement in the total backscattering coefficient for cross-polarized return in the studied range, suggesting that multiple-surface scattering and surface-volume scattering up to second order are important scattering mechanisms in the snow layer and should not be ignored in polar research.

Diagnosis of Coupled Resonator Bandpass Filters Using VF and Optimization Method

Abstract: This paper presents a hybrid method combining a vector fitting (VF) and a global optimization for diagnosing coupled resonator bandpass filters. The method can extract coupling matrix from the measured or electromagnetically simulated admittance parameters (Y -parameters) of a narrow band coupled resonator bandpass filter with losses. The optimization method is used to remove the phase shift effects of the measured or the EM simulated Y -parameters caused by the loaded transmission lines at the input/output ports of a filter. VF is applied to determine the complex poles and residues of the Y -parameters without phase shift. The coupling matrix can be extracted (also called the filter diagnosis) by these complex poles and residues. The method can be used to computer-aided tuning (CAT) of a filter in the stage of this filter design and/or product process to accelerate its physical design. Three application examples illustrate the validity of the proposed method.