This study concerns the 2D inverse problem of the retrieval, using external field data, of either one of the two physical parameters, constituted by the real and imaginary parts of the permittivity, of a z-independent cylindrical dielectric specimen subjected to an external, z-independent, quasistatic electric field. Six other parameters enter into the inverse problem. They are termed nuisance parameters because: 1) they are not retrieved during the inversion and 2) uncertainty as to their actual values can adversely affect the accuracy of the retrieval of the permittivity. This inverse problem is shown to have an exact, mathematically-explicit, solution, both for continuous and discrete input data, whose properties, with respect to the various nuisance parameter uncertainties, are analyzed, first in a mathematical, and subsequently in a numerical manner for noiseless data. It is found that: a) optimal inversion requires data registered at only a small number of sensors, b) the inverse solution, satisfying pre-existing physical constraints, exists and is unique. Moreover, the inverse solution is shown to be unstable with respect to three nuisance parameter uncertainties, the consequence of which is large retrieval inaccuracy for small nuisance parameter uncertainties, acting either individually or in combination.

A dual-polarized multiple-input-multiple-output (MIMO) antenna integrated with electromagnetic band-gap (EBG) is proposed. The MIMO antenna consists of two dual-polarized (0°and 90° polarizations) antenna elements. Each element includes four symmetrical arc-shaped slots. A mushroom-shaped EBG structure with four slots at its fringe is designed to enhance the gain of MIMO antenna. The bandwidth (return loss > 10 dB) of the proposed antenna is from 5.70 to 5.93 GHz, and the peak gain is 5.45 dBi. The isolation between the ports of adjacent antenna elements can be as small as less than -20 dB. The dual-polarized MIMO antenna with EBG has a compact volume of 44.5×77.5×1.6 mm³ and canbe suitable for 5.8 GHz WLAN application.

A novel dual-helix monopole antenna with circular polarization (CP) operation is proposed. By utilizing a pair of asymmetrical strip-sleeves shorted at the ground plane, the proposed CP design at 2.45 GHz ISM band can easily be achieved and provides the impedance bandwidth (RL≧10 dB) about 240 MHz and the 6 dB axial-ratio (AR) bandwidth about 126 MHz. The measured peak gain and radiation efficiency are about 9.1 dBic and 81% across the operating bands, respectively.

This paper presents a compact multilayer hybrid coupler based on a microstrip viatransition and short transmission line with a capacitor on each side to reduce circuit size. The microstrip via-transition is connected to two microstrip lines in different layers to configure a sandwich structure. To reduce the passive component circuit size, the design method uses a microstrip via-transition and a short transmission line with capacitors on each side. To validate the microstrip via- transition and short transmission line with capacitor, a multilayer hybrid coupler is implemented at a center frequency of 2 GHz. The measured characteristics agreed well with the simulation results, and above 90% circuit-size reduction compared with conventional couplers was realized.

A low-power on-off-keying impulse-radio (IR) ultra-wideband (UWB) pulse generator (PG) intended for wireless-powered IR-UWB radio applications is presented. The proposed PG has high flexibility, the center frequency, output power and pulse-width (PW) are controllable depending on channel conditions and data rates. Qualitative frequency-domain and transient analyses are presented. A new figure-of-merit (FoM) is proposed such that a more precise comparison between different PGs can be made. The PG is successfully implemented in a TSMC 90 nm CMOS process, measurements show the energy consumption and FoM to be 2.8-7.5 pJ/pulse and 1.6-2.6% respectively. The output swing and PW are 277-329 mV_p-p and 509-1088 ps respectively. The core area is 0.092 mm².

Magnetic lens based on metamaterials has helped to increase the inductive coupling of two-coil system in wireless power transfer. By coordinate transformation, the spatially mapped metamaterials are proposed in this paper for a new magnetic concentrator in two-coil system to improve the mutual coupling. To achieve such metamaterials, the virtual rectangular domain is spatially mapped into a deformed spherical shell. The effects of such mapped spherical shell, functioning as magnetic concentrator, are simulated and evaluated. The fabrication and simplification of this magnetic concentrator are also considered. Finally, this model of spherical shell is compared with that of a traditional magnetic concentrator to demonstrate its advantage.

A time-efficient method is proposed to calculate the near-field time-domain physical-optics (TD-PO) integral to analyze the transient electromagnetic fields scattered from three-dimensional perfectly conducting objects under the illumination of a pulsed plane wave. It is shown that the TDPO integral can be reduced to a close-form expression by introducing locally expanded Green-function approximations used in conjunction with the surface partitioning. As a result, the near-field TD-PO response to a general pulsed plane wave excitation is derived by a convolution of the excitation waveform with the TD-PO impulse response, which can be performed in a closed form. To satisfy the causality, i.e., the transient field cannot travel away from the sources faster than the speed of light, the high-order derivative of a modulated-Gaussian wave is specified as the excitation waveform. The efficiency and accuracy of the proposed near-field formulas are validated through numerical examples.

In this article, a novel compact triple-band monopole antenna for WLAN/WiMAX applications is proposed. The proposed antenna is designed on an FR-4 substrate with thickness of 0.8 mm, relative permittivity of 4.4, and loss tangent of 0.02. It consists of a square ring, an open ended stub, and an inverted T-shaped stub. Three bands covering 2.3-2.76, 3.387-3.73, and 4.97-6.28 GHz are achieved, which cover all the 2.5/3.5/5.5 GHz WiMAX and 2.4/5.2/5.8 GHz WLAN operation bands. Moreover, the presented antenna has a compact size of 24 × 36 mm². Experimental results show that the proposed antenna gives good gains and has nearly omnidirectional radiation patterns across all the operation bands.

A new method for designing compact Wilkinson power dividers with three order harmonics suppression is presented. The quarter-wavelength transmission line in the traditional Wilkinson power divider is replaced by two pairs of parallel coupled lines with one end connected in series with an open stub. With this structure, the quarter-wavelength line will be shorter and three attenuation poles can be added in the stopband. As a result, this newly proposed structure carries the functions of impedance matching at operating frequency and three orders harmonics suppression. In this study, an example of power divider operating at 1 GHz is designed and fabricated. The measured results show good performance at the operating frequency. In addition, the second, third and fourth harmonics suppressions are 43 dB, 49 dB and 37 dB, respectively, which validates the feasibility of the proposed design.

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.

A waveguide standard is introduced for validation purposes on the measurement accuracy of electric and magnetic properties of materials at microwave frequencies. The standard acts as a surrogate material with both electric and magnetic properties and is useful for verifying systems designed to characterize engineered materials using the Nicolson-Ross-Weir technique. A genetic algorithm is used to optimize the all-metallic structure to produce a surrogate with both relative permittivity and permeability within a target range across S-band. A mode-matching approach allows the user to predict the material properties with high accuracy, and thus compensate for differences in geometry due to loose fabrication tolerances or limited availability of component parts. The mode-matching method also allows the user to design standards that may be used within other measurement bands. An example standard is characterized experimentally, the errors due to uncertainties in measured dimensions and to experimental repeatability are explored, and the usefulness of the standard as a verification tool is validated.

Decomposition of the electromagnetic energy into its stored and radiated parts is instrumental in the evaluation of antenna Q and the corresponding fundamental limitations on antennas. This decomposition is not unique and there are several proposals in the literature. Here, it is shown that stored energy defined from the difference between the energy density and the far field energy equals the energy expressions proposed by Vandenbosch for many but not all cases. This also explains the observed cases with negative stored energy and suggests a possible remedy to them. The results are compared with the classical explicit expressions for spherical regions where the results only differ by the electrical size ka that is interpreted as the far-field energy in the interior of the sphere. Q

The Radio Frequency IDentification (RFID) Low Frequency (LF) serial loops structure is proposed to improve TAGs detection when a TAG coil-antenna rotates by any angle, due to the tagged pebble moving. The detection zones of two types of TAGs (the token and glass TAG) and two types of reader coils, in function of the TAG size, TAG orientation and shape of the reader coils are tested. The effect of the proposed multi-coil inductively coupled is confirmed by measurement using a commercial LF RFID system.

In this paper, a new approach using quasi-self-complementary antenna (QSCA) to reduce the wideband mutual coupling is proposed and discussed. QSCA element proposed in this paper is composed of a semi-circular radiation patch and a complementary-cut ground plane, which is easy to achieve ultra-wideband operation because its impedance is frequency independent. The proposed compact four-element ultra-wideband (UWB) multiple-input multiple-output (MIMO) array consists of four QSCA elements, and by arranging them anticlockwise, a good impedance matching and high port-to-port isolation (|S₁₁| covers 2.95-12.1 GHz with |S₂₁| = |S₃₁|≤-15 dB, |S₄₁|≤-17.8 dB) can be achieved. Notably, the isolation is obtained without using any other decoupling methods and totally benefits from the asymmetrical radiation property of QSCA. As an example, the proposed four-element UWB MIMO array is fabricated and tested. And the measured radiation pattern, gains and total efficiencies are displayed and show good performances which make it a nice candidate for future UWB diversity applications.

Previous ink characterization results published in the paper are corrected by new characterization measurements from Co ink consisting of the same Co nanoparticles bound together with poly(methyl methacrylate). New measurement result is reported as vol% whereas previous result was reported as wt.%. Correlation 50 vol% = ∼90 wt.%.

Previous ink characterization results published in the paper are corrected by new characterization measurements from Co inks based on same cobalt nanoparticles bound together with poly(methyl methacrylate). New measurements results are reported as vol% whereas previous results were reported as wt.%. Correlations are 30 vol% = ∼80 wt.%, 40 vol% = ∼86 wt.% and 50 vol% = ∼90 wt.%.

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.