Numerical calculations based on finite-difference timedomain (FDTD) simulations for metallic nanostructures in a broad optical spectrum require an accurate modeling of the permittivity of dispersive materials. In this paper, we present the algorithms behind BCALM (Belgium-CAlifornia Light Machine), an open-source 3D-FDTD solver simultaneously operating on multiple Graphical Processing Units (GPUs) and efficiently utilizing multi-pole dispersion models while hiding latency in inter-GPU memory transfers. Our architecture shows a reduction in computing times for multi-pole dispersion models and an almost linear speed-up with respect to the amount of used GPUs. We benchmark B-CALM by computing the absorption efficiency of a metallic nanosphere in a broad spectral range with a six-pole Lorentz model and compare it with Mie theory and with a widely used Central Processing Unit (CPU)-based FDTD simulator.

A research of a quasi-optical Bessel-Gauss resonator (QOBGR) at millimeter (MM) and submillimeter (SubMM) wavebands is presented in this paper. The design is based on the quasi-optical theory and technique. The iterative Stratton-Chu formula (ISCF) algorithm is employed to analyze the output characteristics of the cavity, including the resonant modes, phases, power losses and phase shifts. Analysis of the results demonstrates that the present design of the QOBGR can support zero order or any high order mode of the pseudo Bessel-Gauss beam. At the output plane the intensity distributions of these modes are modulated by a Gauss-shaped envelope, and their phase patterns have an approximate block-like profile. Tolerance analysis for the designed QOBGR is also done. Lastly, a comparison of resonating modes is made between QOBR (quasi-optical Bessel resonator) and QOBGR when both are configured with the same geometric parameters.

Statistical characteristics of multiply scattered electromagnetic waves in turbulent magnetized plasma with both electron density and external magnetic field fluctuations are considered. Analytical expression for phase fluctuations of scattered radiation is derived using the smooth perturbation method. Correlation and wave structure functions of the phase fluctuations, angle-of-arrivals are obtained for arbitrary correlation functions of fluctuating plasma parameters and external magnetic field taking into account the diffraction effects. The evolution of a double-peaked shape in the spatial power spectrum of scattered radiation is analyzed numerically for both anisotropic Gaussian and power-law spectra of electron density fluctuations using experimental data. Phase portraits of external magnetic field fluctuations have been constructed for different non-dimensional spatial parameters characterizing a given problem.

This paper presents a compact conical beam antenna based on quarter-mode substrate integrated waveguide (QMSIW). The antenna array is consisted of six isosceles right-angled triangle metallic patch printed on the upper side of the substrate in a windmill-shape and diagonal periodic metallic via holes drilled along the hypotenuse of the triangle patch. The planer structure exhibits conical beam radiation. The typical radiation is obtained at 5.2 GHz with conical beam radiation pattern. The measured gain is about 5.36 dBi and the radiation efficiency is around 50%.

A modified Schwarz-Christoffel transformation (SCT) is used to obtain guided- and radiated-wave characteristics of a singly-curved rectangular patch antenna. The method is to map a straight channel into an arbitrarily-curved channel. This simplifies the problem to that of a planar rectangular patch antenna. Applying conventional SCT to the problem confronts two difficulties: The region under investigation is elongated, and it has curved boundaries. Therefore, SCT is modified to handle the problem. Input impedance, VSWR and radiation patterns of a conformal patch antenna on a parabolic surface are obtained utilizing the proposed SCT and either numerical or analytical treatment of a planar patch antenna, and the results are verified. Effect of parabolic curvature on the above-mentioned characteristics is investigated.

The round-corner design of an all symmetric edge-coupled bandpass filter (BPF) is presented. The manufacturing tolerances and its effects of frequency shift on the design of the edge-coupled are investigated. Consequently, the round-ended design method is proposed in order to compensate the open-end effect in the half-wavelength resonator section with the round-ended corners rather than decrementing the lengths in a conventional way, and an experience formula and a corresponding procedure are devised for the design of such filters. The widths of all the half-wavelength resonators are set equal to avoid discontinuities in the interior of the filter. The filter is realized on a ceramic filled soft substrate with dielectric constant of 6.2. For obtaining the de-embedded measured results at the device plane an in-house customized through-reflect-line (TRL) calibration kit is produced. Three kinds of filters at different center frequencies are manufactured, and their measured results are in good agreement with the simulated ones after calibration.

This paper presents a novel compressed sensing based track before detect (CS-TBD) algorithm. The proposed algorithm reconstructs the whole radar scenario (direction of arrival (DOA)-Doppler plane) for each range gate at consecutive scans using an improved stagewise orthogonal matching pursuit (StOMP) algorithm, resulting in a three-dimensional range-DOA-Doppler space. It then performs temporal tracking in the newly built three-dimensional range-DOA-Doppler space, based on the information from multiple illuminations during each scan, as well as among consecutive scans. In the proposed CS-TBD algorithm, the improved StOMP algorithm together with the temporal tracking, can effectively distinguish true targets from false targets and clutter based on information from multiple illuminations.

A new method to design a miniaturized ring coupler consisting of multiple open stubs on the inside of the ring is proposed. It is shown that this coupler topology may be seen as fully-distributed composite right/left handed (CRLH) small-size phase shifters, cascaded in a ring configuration. The CRLH phase shifter is analyzed in detail and a design method is proposed, pointing out the condition to obtain a reduction of its length. Using the fully-distributed CRLH based phase shifter, a ring coupler is configured and analyzed in comparison with the traditional ring coupler, showing that both couplers have similar characteristics. To validate the proposed design method, a 3-dB CRLH based ring coupler is designed and fabricated. The experimental results show a very good agreement with the predicted results obtained by electromagnetic simulation. The printed area of the fabricated coupler is 49% smaller compared to the traditional ring coupler.

This paper deals with the finite element analysis and experimental study concerning the influence of the one broken bar and rotor dynamic eccentricity faults on the magnetic field outside a squirrel-cage induction motor. The spatial distribution of the magnetic field, the time variation of the magnetic flux density in a point outside the machine and the time variation of the output electromotive force delivered by a coil sensor are evaluated based on the finite element models of the healthy and faulty states of the motor. The increase of amplitude from the healthy to the faulty states of some low frequency harmonics measured in the nearmagnetic field is emphasized. For the one broken bar fault, the increase of the amplitudes of specific harmonics of the coil sensor electromotive force, with frequency lower than 25 Hz, is experimentally confirmed.

This paper describes a novel FSS which functions as band stop filter to shield the GSM 1800 MHz downlink band. The FSS is designed to operate with the resonant frequency of 1820 MHz which is the centre frequency for the GSM 1800 MHz downlink band. The novelty is attributed to its unique geometry and the circular apertures endowed with it. The proposed geometry provides shielding effectiveness of 20 dB alongside with 133 MHz bandwidth. The structure holds identical response for both TE and TM Modes of polarization. In addition, the geometry with its circular apertures, a hitherto unexplored feasibility serves the purpose of ventilation and heat dissipation. The simulated results are validated using experimental measurements.

This paper presents an approach to the design of novel diplexers with pairs of transmission zeros for each output port. A rotationally symmetric structure with shorted circuited stubs is proposed to achieve diplexer operation, and the diplexer exhibits a good filtering performance with a pair of transmission zeros allocated at two sides of the passbands as well. The analysis of the rotationally symmetric structure bandpass filter is also presented in this paper in detail. Moreover, the interdigital coupled-lines are introduced to improve the out-of-band performance of the proposed rotationally symmetric diplexer. In order to verify the proposed structure, first a diplexer with rotationally structure operating at 2.4/2.73 GHz with simulated insertion loss of 1.217/0.930 dB is designed and simulated, then a diplexer with interdigital coupled-lines operating at 5/5.8 GHz with measured insertion loss of 1.524/1.524 dB is designed, simulated and measured to improve the passband selectivity, and the measured results are in good agreement with simulated ones.

This paper presents an effective weighted-L₁-sparse representation of array covariance vectors (W-L₁-SRACV) algorithm which exploits compressed sensing theory for direction-of-arrival (DOA) estimation of multiple narrow-band sources impinging on the far field of a uniform linear array (ULA). Based on the sparse representation of array covariance vectors, a weighted L₁-norm minimization is applied to the data model, in which the weighted vector can be obtained by taking advantage of the orthogonality between the noise subspace and the signal subspace. By searching the sparsest coe±cients of the array covariance vectors simultaneously, DOAs can be effectively estimated. Compared with the previous works, the proposed method not only has a super-resolution but also improves the robustness in low SNR cases. Furthermore, it can effectively suppresses spurious peaks which will disturb the correct judgment of real signal peak in the signal recovery processing. Simulation results are shown to demonstrate the efficacy of the presented algorithm.

In this paper, a double-layer split-ring resonator structure chiral metamaterial was proposed which could exhibit pronounced circular dichroism (CD) effect and negative refractive index at microwave frequencies. Experiment and simulation calculations are in good agreement. The retrieved effective electromagnetic parameters indicate that the lower frequency CD effect is associated with the negative refractive index property of the left circularly polarized (LCP) wave, and the upper one is to the right circularly polarized (RCP) wave. The mechanism of the giant CD effect could be further illustrated by simulated surface current and power loss density distributions.

In this study, we report the simulation, fabrication and characterization of a dual-band fractal metamaterial used for terahertz sensing application. By applying the fractal structures of square Sierpinski (SS) curve to the split-ring resonators (SRRs), more compact size and higher sensitivity can be achieved as privileges over conventional SRRs. The influence of different geometrical parameters and the order of the fractal curve on the performances are investigated. Then overlayers are added to the fractal SRRs in order to explore the performance of the entire system in terms of sensing phenomenon. The changes in the transmission resonances are monitored upon variation of the overlayer thickness and permittivity. Measured results show good agreement with simulated data. At the second resonance of the second-order SS-SRRs, maximum frequency shifts of 19.8 GHz, 26.3 GHz and 37.8 GHz were observed for a 2 μm, 4 μm and 10 μm thickness of photoresist. The results show good sensitivity of the sensors suggesting they can be used for a myriad of terahertz sensing applications in biology and chemistry.

An accurate characterization of the wave propagation inside tunnels is of practical importance for the design of advanced communication systems. This paper presents a five-zone propagation model for large-size vehicles inside tunnels. Compared with existing models, the proposed model considers the influence of the large size of the vehicle, and covers all propagation mechanism zones and their dividing points. When a large-size vehicle is passing the transmitter, the received power suffers a deep fading as the direct wave is blocked by the vehicle itself. This zone is called the near shadowing zone. Then, when the vehicle has moved past the transmitter, the line of sight is recovered. If the vehicle is still close to the transmitter, the free space propagation zone starts. Then, as the distance increases, the vehicle enters the multi-mode propagation zone, where higher order modes are significant. Further away, when high order modes are greatly attenuated, guided propagation is stabilized. Finally, when the vehicle is extremely far from the transmitter, the waveguide effect vanishes because of the attenuation of reflected rays. Two sets of measurements are employed to validate the model. Results show good agreement, and therefore, the model presents an effective way to predict the propagation inside tunnels for large-size vehicles.

This paper analyzes and discusses the effect of the electromagnetic absorption by human head against variation of head dielectric properties at 900, 1800 and 1900 MHz. The characteristics of helical antenna and its substrates with variation in human head dielectric properties are simulated by implementing finite-difference time-domain (FDTD) method using CST Microwave studio. The variations in human head dielectric properties were manipulated by increasing and decreasing 10% and 20% of each of the human head dielectric properties. In this paper, SAR values increase with increment of head conductivity, and increment of head permittivity and head density lead to decrement of SAR values. Helical antenna with substrate of FR4 results in higher SAR values in all frequency exposures. The head SAR values are higher with higher frequency exposures. The helical antenna with substrate of Rogers RO3006 (loss free) is found to be better over FR4 and Rogers RO4003 (loss free), which contributes towards much lower SAR values in all GSM frequency bands exposure.

In order to analyze the Doppler spectrum of three-dimensional (3-D) moving targets above a time-evolving sea surface, a hybrid method with acceleration techniques is proposed to simulate the electromagnetic (EM) scattering from the composite moving model. This hybrid iterative method combines Kirchhoff approximation (KA) and the multilevel fast multipole algorithm (MLFMA) to solve the EM backscattering from the rough sea surface and the targets, respectively, then mutual EM coupling effects between them are taken into account through an iterative process. To overcome the vast computational cost in the iterative process, acceleration approaches which can greatly reduce the calculation time are applied. Coupling area on the sea surface is truncated according to geometrical optic principle. Then a fast far-field approximation (FAFFA) is applied to speed up the mutual interactions between the targets and the sea surface. A successive iteration method is proposed to reduce the convergence steps for the MLFMA process. The accuracy and efficiency of this hybrid method with accelerations are demonstrated. Doppler spectra of backscattering signals obtained from such numerical EM simulations are compared for different incident angles, target velocities and surface models. The broadening effects of the Doppler spectra due to the mutual EM coupling interactions are studied.

A technique is described for the electromagnetic reconstruction of the location, shape, dielectric constant, and conductivity of buried homogeneous cylinders of elliptic cross-section. The inversion procedure is based on the Differential Evolution algorithm and the forward problem is solved using the single boundary integral method. Simulation results are presented which demonstrate that this hybrid approach can offer a conceptually simple yet efficient and reasonably robust method for the imaging of buried objects and voids.

Conventional reflector based Impulse Radiating Antennas (IRA's) are designed with conical taper transmission line feed. A novel feed design approach is used to enhance gain of the IRA without increasing diameter of the reflector. This paper discuses conventional and new IRA designs of different input impedances. IRA with conventional feed and with new dipole feed is designed for both 200 Ω and 100 Ω input impedance category. The IRA with new feed design offers better gain compared to conventional IRA for both 200 Ω and 100 Ω input impedance category. These antenna designs are analyzed using the Finite Difference Time Domain (FDTD) method and the result obtained shows that IRAs with new dipole feed offers better gain than IRAs with conventional feed for respective input impedance category without any compromise in time domain characteristics. A half IRA with new feed with input impedance of nearly 50 Ω was realized and measured to establish the advantage of new dipole feed IRA.

The lumped network alternating direction implicit finite difference time domain (LN-ADI-FDTD) technique is proposed as an extension of the conventional ADI-FDTD method in this paper, which allows the lumped networks to be inserted into some ADI-FDTD cells. Based on the piecewise linear recursive convolution (PLRC) technique, the current expression of the loaded place can be obtained. Then, substituting the expression into the ADI-FDTD formulas, the difference equations including an arbitrary linear network are derived. For the sake of showing the validity of the proposed scheme, lumped networks are placed on the microstrip and the voltage across the road is computed by the lumped network finite difference time domain (LN-FDTD) method and LN-ADI-FDTD method, respectively. Moreover, the results are compared with those of obtained by using the circuital simulator ADS. The agreement among all the simulated results is achieved, and the extended ADI-FDTD method has been shown to overcome the Courant-Friedrichs-Lewy (CFL) condition.