Full-wave Analysis Research Articles

Spectral-Domain Method of Moments for the Modal Analysis of Line Waveguides

A rigorous full-wave modal analysis based on the method of moments in the spectral domain is presented for line waveguides constituted by two-part impedance planes with arbitrary anisotropic surface impedances. An integral equation is formulated by introducing an auxiliary current sheet on one of the two half planes and extending the impedance boundary condition of the complementary half plane to hold on the entire plane. The equation is then discretized with the method of moments in the spectral domain, by employing exponentially weighted Laguerre polynomials as entire-domain basis functions and performing a Galerkin testing. Numerical results for both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">bound</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">leaky</i> line waves are presented and validated against independent results, obtained for isotropic surface impedances with the analytical Sommerfeld–Maliuzhinets method and for the general anisotropic case with a commercial electromagnetic simulator. The proposed approach is computationally efficient, can accommodate the presence of spatial dispersion, and offers physical insight into the modal propagation regimes.

Design of Miniaturized FSS with High Angular Stability Utilizing a Novel Closed Loop

In this paper, we propose a miniaturized 2.5-dimensional (2.5D) frequency selective surface (FSS) structure with high angular stability. A novel closed-loop FSS is formed by combining the Jerusalem cross (JC) structure with the conventional rectangular closed loop using vias. This approach further enhances the coupling performance of the FSS and thus achieves miniaturized design. The unit cell size of the proposed FSS is 0.019λ0 × 0.019λ0 at the resonant frequency, and the metal is printed on a dielectric substrate with a thickness of 0.003λ0. The proposed FSS has a resonant frequency of 850 MHz and exhibits band-stop characteristics. It is insensitive to the incident angle with a good operating performance in both the TE and TM wave modes. Therefore, it can be well used as an electromagnetic shield for the GSM 850 band. In order to facilitate the rapid analysis and design of the FSS, the equivalent circuit model is further analyzed and established, and values of the corresponding lumped components are derived. In addition, a prototype FSS is fabricated using printed circuit board technology and is tested in a microwave anechoic chamber. The full-wave analysis simulation, equivalent circuit model simulation, and practical measurement results reflect a high level of consistency.

Full-wave electromagnetic analysis of lightning strikes to wind farm connected to medium-voltage distribution lines

This paper studies the voltages developed on a wind turbine (WT) and a medium-voltage distribution line (MVDL) connected to a wind farm subjected to lightning strikes and located on frequency-dependent (FD) soils. The ground potential rise (GPR), voltages at the blade tip and on phase conductors of the MVDL are calculated using the full-wave electromagnetic software XGSLab® employing the rigorous Partial Element Equivalent Circuit (PEEC) method. The wind farm comprises four wind turbines with interconnected grounding systems using cables buried in resistivity soils of 1,000 and 5,000 Ω m. The voltages are computed for the first positive impulse (FPI) of 100-kA 10/350μs and for the subsequent negative impulse (SNI) of 50-kA, 1/200μs. Results have shown that voltage peaks increase notably as the soil resistivity increases. When the WTs are assumed, oscillations in the GPR waveforms for the SNI occur due to the multiple reflections between the blade and the turbine’s base. However, the voltages for the FPI present smooth time-domain responses. Furthermore, the overvoltages developed at the MVDL are significantly dependent on the soil resistivity and lightning current waveform.

Reflection and refraction of higher-order Hermite-Gaussian beams: a vector wave analysis.

Hermite-Gaussian beams, as a typical kind of higher-order mode laser beams, have attracted intensive attention because of their interesting properties and potential applications. In this paper, a full vector wave analysis of the higher-order Hermite-Gaussian beams upon reflection and refraction is reported. The explicit analytical expressions for the electric and magnetic field components of the reflected and refracted Hermite-Gaussian beams are derived with the aid of angular spectrum representation and vector potential in the Lorenz gauge. Based on the derived analytical expressions, local field distributions of higher-order Hermite-Gaussian beams reflection and refraction at a plane interface between air and BK7 glass are displayed and analyzed.

Design and analysis of a water-soluble BSA protein biosensor based on a plasmonic nanodisk resonator

This paper presents the design and full-wave analysis of a label-free biosensor based on a plasmonic nanodisk resonator with a radius of 350 nm to sense the concentration of water-soluble Bovine Serum Albumin (BSA) protein. The finite element method (FEM) has been used to analyze its optical characteristics and sensing performance. The designed biosensor has a compact structure with a higher quality factor, narrower FWHM, higher sensitivity, and larger FOM compared to similar plasmonic refractive-index sensors.

Birefringent Glass-Engraved Tilted Pillar Metasurfaces for High Power Laser Applications.

Birefringent materials-which are highly needed in high power laser systems-may be limited in usage due to the laser-induced damage threshold of traditional birefringent materials. This work reports here on all-glass metasurfaces, fabricated by angled etching through sacrificial metal nanoparticle (NP) etching masks, for generation of effective birefringence in the formed layer. As a result, a fused silica metasurface, monolithic to the underlying substrate, is demonstrated to exhibit a birefringence of 6.57° under 375nm illumination. Full-wave analysis shows a good agreement with the measurement and presents potential paths forward to increasing the effective metasurface birefringence. This is the first demonstration, to the best of knowledge, of an etching technique to obtain the resulting tilted pillar-like nanofeatures. The anisotropy of the metasurface nanoelements along the two window in-plane major axes presents different effective paths for the two polarizations and thus generates birefringence in a nonbirefringent material. Additionally, the imparted anisotropy lends itself to manipulation of physical properties of the surface as well, with metasurface feature orientation suppressing water flow along one principal axis and giving rise to water flow steering capabilities.

Full-Wave Numerical Analysis of Dual-Band EPatch Antenna and Reactive Loading Technique to Ascertain the Impedance Driving Point Function

Full-Wave Numerical Analysis of Dual-Band EPatch Antenna and Reactive Loading Technique to Ascertain the Impedance Driving Point Function

Can Perfectly Electric Conducting Obstacles Modify the Permeability of Metamaterial? An Investigation Using Lorentz, Floquet, and Full-Wave Models

The Lorentz model shows that inclusion of perfectly electric conducting (PEC) obstacles in a host medium introduces both electric and magnetic polarizabilities that modify the permittivity and permeability tensors of the composite medium. On the other hand, the Floquet eigenmodal analysis shows that the PEC obstacles, while modify the permittivity tensor, have no effect on the permeability tensor. Interestingly, numerical results obtained from full wave analyses of metamaterial-slabs support the Floquet model. The source for the inaccuracy in Lorentz model is critically examined. Characteristic features of metamaterials made with non-resonant and resonant types of obstacles are investigated and the numerical results obtained from four independent models are compared and discussed.

Shaped Omnidirectional Reflector Fed by a Dielectric Lens Associated with a Coaxial Feed Horn

The paper explores an omnidirectional antenna configuration composed of a reflector fed by a shaped dielectric lens associated with a coaxial TEM horn. A simple formula describes the lens shape obtained by applying Fermat’s principle to control the rays’ caustic emerging from the dielectric interface. Based on geometrical optics (GO) principles, a synthesis technique defines the reflector shape to control the antenna radiation pattern in the vertical plane. Concatenated conic describes the reflector generatrix. The study employs a full-wave analysis to validate the designs and explores the proposed configuration to attend two distinct far-field specifications.

Comparison of Terahertz Transceiver Array Topologies in Multiobject Imaging

We investigate the effect of side lobe level (SLL) and multipath propagation in millimeter-wave(mmWave) and terahertz (THz) imaging systems for various transceiver array topologies. This work considers practical limitations in high-resolution active imaging systems and focuses on electrically large, planar antenna array topologies. As such, we investigate the imaging performance of sparse transmitting/receiving (Tx/Rx) array topologies that enable high angular/spatial resolution imaging with minimum hardware complexity. We show that 1) properly tapering the sparse array excitation can mitigate image clutter caused by high side lobes and 2) sparse arrays are more vulnerable to multipath reflections and clutter in dense scenes with highly reflective surfaces. We present both full-wave numerical analysis and laboratory experiments (250-300 GHz) to verify and compare the imaging array performance for several exemplary scenes.

Design and full-wave analysis of a dual-purpose compact all-optical integrated circuit for ultra-fast signal processing

Design and full-wave analysis of a dual-purpose compact all-optical integrated circuit for ultra-fast signal processing

Integro-Differential Analysis of Resonant Magnetic Metasurfaces With Equivalent Medium Approximation

This paper proposes a strategy to consider the dielectric effects in the thin-wire integro-differential formulation and applies it to analyzing microstrip metasurfaces that support magnetic resonances. These structures comprise a periodic arrangement of subwavelength unit cells; therefore, the thin-wire approximation can be applied to analyze them. However, the substrate is usually disregarded. This work achieves more accurate results with a homogeneous equivalent medium approximation considering the dielectric properties. Moreover, an experimental methodology is presented to validate this implementation for each device as well as for the complete system. The proposed formulation is numerically solved with the Method of Moments, and the results show close agreement with experimental data. Besides, it leads to a significant reduction in the computation time compared to a full-wave analysis, which makes this approach also compelling for designing inductive wireless power transfer systems and magnetic resonators.

Exotic light transition between superluminal and subluminal group velocity in a [formula omitted] coupled slab waveguide

We propose a rigorous full-wave modal analysis based on the eigenmodes approach (“supermodes”), that allows the calculation of the transverse electric (TE) and transverse magnetic (TM) stationary propagation eigenmodes in a coupled PT-symmetric slab waveguide. Our findings show that the group velocity, for the fundamental TE0 supermode, passes from superluminal to subluminal speed over both sides of a critical point (CP), located near to the exceptional point (EP). We also demonstrate that the first higher-order supermode, TE1, exhibits a slow light phenomenon around the EP.

Generalized total internal reflection at dynamic interfaces

Recent research developments in the area of spacetime metamaterial structures and systems have raised new questions as to how the physics of fundamental phenomena is altered in the presence of spacetime modulation. In this context, we present a generalized and comparative description of the phenomenon of total internal reflection (TIR) at different dynamic interfaces. Such interfaces include, beyond the classical interfaces corresponding to the boundaries of moving bodies (moving interface--moving matter systems), interfaces formed by a traveling-wave step modulation of an electromagnetic parameter (e.g., refractive index) (moving interface--stationary matter systems) and fixed interfaces between moving-matter media (stationary interface--moving matter systems). We first resolve the problem using the evanescence of the transmitted wave as the criterion for TIR and applying the conventional technique of relative frame hopping (between the laboratory and rest frames), which results in closed-form formulas for the relevant critical (incidence, reflection, phase refraction, and power refraction) angles. We then introduce the concept of catch-up limit between the dynamic interface and the transmitted wave as an alternative criterion for the critical angle. We use this approach both to analytically verify the critical angle formulas, further validated by full-wave (FDTD) analysis, and to explain the related physics, using Fresnel-Fizeau drag and spacetime frequency transition considerations. These results might find various applications in ultrafast optics, gravity analogs, and quantum processing.

Reconfigurable Holographic Surface: A New Paradigm to Implement Holographic Radio

Ultramassive multiple-input, multiple-output (MIMO) is one of the key enablers in the forthcoming 6G networks to provide high-speed data services by exploiting spatial diversity. In this article, we consider a new paradigm, termed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">holographic radio</i> for ultramassive MIMO, where numerous tiny and inexpensive antenna elements are integrated to realize high directive gain with low hardware cost. We propose a practical way to enable holographic radio by a novel metasurface-based antenna, i.e., reconfigurable holographic surface (RHS). Specifically, RHSs incorporating densely packed tunable metamaterial elements are capable of holographic beamforming. Based on the working principle and hardware design of RHSs, we conducted full-wave analyses of RHSs and built an RHS-aided point-to-point communication platform supporting real-time data transmission. Both simulated and experimental results show that the RHS has great potential to achieve high directive gain with a limited size, thereby substantiating the feasibility of RHS-enabled holographic radio. Moreover, future research directions for RHS-enabled holographic radio are also discussed.

H-plane SIW horn antenna with enhanced front-to-back ratio for 5G applications

Millimeter-wave (mmWave) antennas are indispensable components in the fifth-generation (5G) wireless communication systems. With the inherent advantages of integration capability, substrate integrated waveguide (SIW) antenna is an excellent choice for applications in the mmWave frequency bands. However, reflection losses occur at dielectric-filled thin apertures of SIW antennas. These reflections can be overcome by impedance matching between the aperture and the free space. In this study, we introduce an mmWave SIW horn antenna having impedance matching transitions (IMTs) across the horn's aperture width. The designed antenna, operating in the 24-28 GHz band, is simulated with a full-wave analysis tool. The simulation results of the modified SIW horn have been confirmed by the experimental results and shown to be satisfactory. The IMTs result in an enhancement of the front-to-back ratio (FTBR). The modified SIW horn antenna with a novel printed transition achieves sidelobe levels (SLLs) of better than ?9 dB at 27 GHz, with an enhanced FTBR above 15 dB. In the 24?28 GHz band, the antenna has a reflection coefficient variation of better than ?10 dB.

Design and Full-Wave Analysis of Ultra-Broadband Metamaterial Absorbers Based on Ring Resonators for Solar Energy Harvesting

Design and Full-Wave Analysis of Ultra-Broadband Metamaterial Absorbers Based on Ring Resonators for Solar Energy Harvesting

Multi-task cascaded assessment of signal quality for long-term single-lead ECG monitoring

Background and objectivesIn long-term electrocardiogram (ECG) monitoring, the use of wearable devices for signal acquisition inevitably introduces noise, which could reduce the diagnostic capability. In order to improve the efficiency of signal analysis and the accuracy of clinical diagnosis, it is necessary to automatically evaluate the signal quality of ambulatory ECG. In this study, a novel multi-task cascaded method is proposed for signal quality assessment. MethodsBased on single-lead ECG, various signal quality indices were derived to assess three classes of signal qualities (clear ECG ideal for full wave analysis, mildly contaminated ECG available for ventricular activity-based analysis, severely contaminated ECG difficult to be analyzed) through a two-step classification corresponding to different tasks. The optimized subsets of quality indices were selected with a criterion of maximal-mean-minimal-variance. Different machine learning models were then trained and tested on public datasets. ResultsThe results show that random forest using the optimal feature subsets had the best performance, with the overall classification accuracy of 93.76%, 95.13% and 99.61% on the three unknown test sets, respectively. Meanwhile, for the identification of acceptable and unacceptable signals in the first task, the AUC on the test sets reached 0.9967, 0.9959 and 1.0000, respectively. ConclusionsThis paper presents a novel signal quality assessment framework, which could provide helpful feedback for ECG processing in specific application scenarios. It is expected to greatly promote accurate and efficient ECG-based diagnosis in long-term monitoring.

Parallel full-wave electromagnetic field analysis based on hierarchical domain decomposition method

Parallel full-wave electromagnetic field analysis based on hierarchical domain decomposition method

Millimeter-wave coding radial-periodic metasurface for manipulating beam-pointing angle of conical-beam radiation

In this article, a millimeter wave coding radial-periodic metasurface conical-beam (CB) antenna for manipulating beam-pointing angle (BPA) is presented. The proposed structure is excited by a high-gain CB planar antenna. The novelty of the proposed design lies in its BPA manipulating mechanism, obtained by radial-periodic metasurfaces (MS) located on the top of the source CB antenna. Full-wave analysis and experimental validation verified the proposed design performance, achieving simulated 10.2% 10-dB impedance bandwidth (BW) covering 27.19–30.12 GHz, whereas the measured BW is 11.7%, covering 26.86–30.2 GHz; as well as 6–18° BPA coverage in the elevation plane with a measured peak gain of 7.7–9.86 dBi in the 27–28 GHz range. The proposed structure exhibits good CB radiation performance with wide BW, flexible BPA control capability, and stable gain variation. Consequently, the proposed structure can be a potential candidate for applications that need wide beam coverage.