Full-wave Finite Element Research Articles

Miniature Microstrip Antenna with and without a Superstrate at THz Frequency

This paper presents comparative study of a rectangular Microstrip patch antenna at Terahertz (THz) frequency ranging from 0.6 to 1 THz with and without superstrate. The results report ed here were obtained using Ansoft HFSS 11.0 which uses full wave finite element method for simulation. In this study the miniature antenna was simulated first and then we load it with a superstrate and varied the height of the superstrate to optimize the antenna performance. Here in this paper we have selected 4 antenna configurations to compare. First antenna is a simple rectangular patch, second antenna is having a superstrate of height 50 microns, Third antenna is with a superstrate of 75 micron height and the fourth antenna is with a superstrate of 100 micron. Best performance of antenna i.e., -10dB bandwidth of around 19% was achieved at central frequency of 0.5 THz and 75 micron superstrate height.

Electro-Thermal Scaling Constraints in Chip-Scale Power Inductors

Two-dimensional (2-D) full-wave finite-element (FE) solution of Maxwell's equations including thermal heating and diffusion in micro-fabricated power inductors suggests significant heating caused by increased AC resistance and eddy current losses, especially at increased power switching frequencies when conducting large currents. The simulation results indicate that severe thermal constraints arise when sourcing currents in excess of 5 amps in DC-DC power converters switching at frequencies in excess of 5 MHz. A simple circuit model is presented to evaluate the effect of frequency-dependence in power inductors on the efficiency and load regulation of point-of-load (POL) DC-DC power converters that utilize advanced silicon power MOSFETs and Gallium Nitride (GaN) power transistors.

A Detector of an Invisible Carpet Cloaking Structure

Based on transformation optics, we propose a device to detect the presence of a carpet cloaking structure at near field. By using complementary media, the detective device can optically cancel a certain volume of reflective metal and reveal the hidden medium inside the metal. The detective performance of this device is confirmed by full-wave finite-element simulations. It is shown that the detective device is invisible when there is no carpet cloak in the system, yet it becomes visible with the presence of the carpet cloak. The device works at near field, but the response can be found even at the far field. Furthermore, it is shown that the device can detect both anisotropic and isotropic carpet cloaking structures. The investigation may provide a unique method to detect a carpet cloak and contribute to the design of novel optical devices, such as far field detectors for a nanoscale medium.

Cylindrical optimized nonmagnetic concentrator with minimized scattering

By using optimized transformation function, we research on a minimized scattering nonmagnetic concentrator, which can realize impedance matching at the inner and the outer boundaries. It has been demonstrated that the optimized transformation function method can improve the concentrating performance remarkably. The cylindrical anisotropic shell can be mimicked by radial symmetrical sectors which alternate in composition between two profiles of isotropic dielectrics, and the permittivity in each sector can be properly determined by the effective medium theory. The nonmagnetic concentrator has been validated by full-wave finite element simulations. We can believe that this work will improve the flexibilities for the EM concentrator design.

A NOVEL TWO-LAYER STACKED MICROSTRIP ANTENNA ARRAY USING CROSS SNOWFLAKE FRACTAL PATCHES

In this paper, a novel approach was used to design two-layer stacked high-gain microstrip antenna array with improved bandwidth and high aperture e-ciency. Cross Snow∞ake fractal microstrip patches were employed as radiation elements. Varieties of antenna arrays with difierent fractal iterations were optimized by using the Genetic Algorithm (GA) associated with 3D full-wave Finite Element Method (FEM) in order to investigate the in∞uence of the Cross Snow∞ake fractal radiators. As compared with the conventional square patches, the Cross Snow∞ake fractal conflguration provides extremely high ∞exibility to achieve a wideband performance and maintains higher aperture e-ciency at operating frequency band. A prototype antenna with 2£2 Cross Snow∞ake radiators was fabricated and measured. Both simulated and measured results show that the proposed antenna has some promising performances to be more specially, the measured impedance bandwidth is 22.9% (from 5.18GHz to 6.52GHz) when S11 < i10dB; the simulated gain is 12.0dBi and its corresponding aperture e-ciency is up to 87.4% at the working frequency 5.8GHz.

基于MEMS工艺的高增益低副瓣太赫兹波纹喇叭天线设计

本文提出了一种基于微电子机械系统(MEMS)工艺的高增益低副瓣太赫兹波纹喇叭天线设计方法。利用三维全波有限元电磁仿真软件Ansys HFSS，对角锥喇叭的波纹开槽尺寸和条数进行参数分析和优化设计，获得了在275 GHz至580 GHz的有效带宽内(回波损耗小于10 dB)增益超过8 dB和副瓣电平小于-13 dB的太赫兹波纹喇叭天线。结果表明波纹开槽可有效提高太赫兹喇叭天线增益并压低副瓣，同时也说明MEMS工艺可有效用于太赫兹功能器件设计。 A novel high gain and low side-lobe terahertz (THz) corrugated horn antenna based on Micro-electro-me- chanical-systems (MEMS) technology is proposed. Properties of the antenna for different corrugated groove sizes and numbers are investigated and optimized by using three-dimensional (3D) electromagnetic full-wave finite element method (FEM) simulation software package Ansys High Frequency Structure Simulator (HFSS). The gain and side-lobe of the THz antenna can be designed greater than 8 dB and less than -13 dB, respectively in the band wide for 10 dB return loss from 275 GHz to 580 GHz. The results show that the corrugated groove can effectively improve the gain and depress the side-lobe of the horn antenna at the THz frequency range. Meantime, the THz functional devices could be effectively fabricated using MEMS technology.

Use of the full-wave Finite Element Method for the numerical electromagnetic analysis of LEMP and its coupling to overhead lines

The computation of lightning-originated surges on overhead power lines due to nearby lightning return strokes requires accurate models for the calculation of both the incident lightning electromagnetic pulse (LEMP) and the coupling of this field to the line conductors. The availability of numerical algorithms for the resolution of full-wave Maxwell's equations (also called numerical electromagnetic analysis – NEA) could provide benchmark results useful to assess the uncertainties introduced by approximate models and solution methods. This paper presents and discusses the results of LEMP and lightning-induced voltages calculations obtained using a time-domain full-wave Finite Element Method (FEM) model. The results obtained by the FEM model are compared with those provided by traditional approaches based, for the LEMP calculation, on the combined use of the dipole technique and the Cooray–Rubinstein formula and, for the LEMP-to-line coupling, on the Agrawal et al. model.

A Versatile Design Strategy for Thin Composite Planar Double-Sided High-Impedance Surfaces

A novel methodology is introduced for the design synthesis of thin planar realizations of volumetric high-impedance or artificial magnetic conducting surfaces (AMC). The design synthesis involves optimization of two different metallic frequency selective surface (FSS) type structures printed on each side of a thin dielectric substrate material. This technique eliminates the need for a complete metallic backplane common in conventional AMC designs, making use of the same dielectric substrate for two high-impedance surfaces; one on each side. Optimization of the FSS unit cell geometries is carried out with a robust genetic algorithm (GA) technique that is combined with a full-wave periodic finite element boundary integral (PFEBI) electromagnetic simulation code for fast and accurate optimization of desired AMC performance at a single frequency or over multiple frequency bands. Several examples of thin AMC ground planes are optimized for use in the X-band. Additional design examples that provide AMC behavior on one side and absorber behavior on the other are also provided. Lastly, an example illustrating the utility of the double-sided AMC separator structure is shown for a design targeting the standard Wi-Fi frequencies of 2.4 GHz and 5.2 GHz.

Radiation Model for Terahertz Transmission-Line Metamaterial Quantum-Cascade Lasers

We present the use of the cavity antenna model in predicting the radiative loss, far-field polarization and far-field beam patterns of terahertz quantum-cascade (QC) lasers. Metal–metal waveguide QC-lasers, transmission-line metamaterial QC-lasers, and leaky-wave metamaterial antennas are considered. Comparison of the fundamental and first higher order lateral mode in a metal-metal waveguide QC-laser shows distinct differences in the radiation characteristics. Full-wave finite-element simulations, cavity model predictions and measurements of far-field beam patterns are compared for a one-dimensional leaky-wave antenna. Lastly, an active leaky-wave metamaterial antenna with full backward to forward wave beam steering is proposed and analyzed using the cavity antenna model.

Terahertz composite right-left handed transmission-line metamaterial waveguides

We report terahertz metamaterial waveguides based on the concept of composite right/left-handed transmission-lines. The waveguides are implemented in a metal-insulator-metal geometry fabricated with spin-coated Benzocyclobutene and contact photolithography. Angle-resolved reflection spectroscopy shows strong resonant absorption features corresponding to both right-handed and left-handed (backward wave) propagating modes within the leaky-wave bandwidth. Tuning of the waveguide dispersion is achieved by varying the effective lumped element series capacitance. The experimental results are in good agreement with full-wave finite element method simulations as well as an intuitive transmission-line circuit model.

Influence of the Non-Linear UHF-RFID IC Impedance on the Backscatter Abilities of a T-Match Tag Antenna Design

In ultra-high-frequency radio-frequency-identification (UHF-RFID) the conjugate complex matching of the packaged UHF-RFID transponder IC and the tag antenna structure is important to increase the reading range of the transponder tag. Quite often half-wavelength dipole-like antenna structures are used. Due to the fact that the impedances of the packaged IC and the dipole antenna structure are in different domains, a matching structure is needed to accomplish the conjugate complex matching. A common technique to carry out the matching is the so called T-match. Since the nominal input impedance of the IC depends on the applied antenna voltage (and in a strongly non-linear way), the backscatter abilities of the tag are also functions of the applied voltage. In the present work those dependencies are investigated in terms of full-wave finite element simulations and measurements.

A Rigorous Solution to the Low-Frequency Breakdown in Full-Wave Finite-Element-Based Analysis of General Problems Involving Inhomogeneous Lossless/Lossy Dielectrics and Nonideal Conductors

Existing methods for solving the low-frequency breakdown problem associated with full-wave solvers rely on low-frequency approximations, which has left a number of research questions to be answered. The conductors are also generally treated as perfect conductors and the dielectric loss is not considered. In this work, a rigorous method that does not utilize low-frequency approximations is developed to eliminate the low frequency breakdown problem for the full-wave finite-element based analysis of general 3-D problems involving inhomogeneous lossless and/or lossy dielectrics and nonideal conductors. This method has been validated by the analysis of realistic on-chip circuits at frequencies as low as dc. Furthermore, it is applicable to both low and high frequencies. In this method, the frequency dependence of the solution to Maxwell's equations is explicitly and rigorously derived from dc to high frequencies. In addition to eliminating the low-frequency breakdown, such a theoretical model of the frequency dependence can be used to understand how the field solution, in a complicated 3-D problem with both lossless/lossy inhomogeneous dielectrics and nonideal conductors, should scale with frequency and at which frequency full-wave effects become important.

A Time-Varying Approach to Circuit Modeling of Plasmonic Nanospheres Using Radial Vector Wave Functions

Recent research has demonstrated the use of plasmonic nanoparticles (e.g., a silver or a gold nanosphere) as circuit elements. In these metallic nanoparticles, an electromagnetic wave at optical frequencies excites conduction electrons resulting in a plasmon resonance. The derived values of circuit components are based on the observation that the small size of the particle compared to the wavelength leads to lumped-impedance representations under the quasi-static approximation. In this paper, we show that circuit representations based on quasi-static approximations can often result in large errors for typical nanosphere sizes. To remedy this issue, we present a new approach based on time-varying fields, which uses vector wave functions to explicitly derive accurate resonance frequency and impedance expressions for these metallic nanospheres at and around the plasmon resonance. In particular, the proposed approach accurately predicts the dependence of the resonance frequency on the size of the nanoparticle and yields more accurate expressions for the equivalent <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$C$</tex></formula> lumped elements compared to the quasi-static model. The new impedance approach is still compatible with the process of cascading nanoparticles in series and parallel combinations to synthesize more complex nanocircuits. A comparison with Mie and full-wave finite-element simulation results demonstrates that our model provides accurate closed-form expressions, thereby extending the range of the impedance representation to larger radii nanoparticles.

Radio-wave imaging in a coal seam waveguide using a pre-selected enforced resonant mode

Abstract The efficacy of radio-wave imaging (RIM) in extended geological strata which are planar and regular, such as coal seams, continues to be questioned, because the electromagnetic wave excitation and propagation mechanisms remain unclear. To eradicate the doubts, a full-wave finite element simulation of a ‘realistic’ coal seam boundary value problem has been constructed and is described and analysed in this paper. The model is used to examine electromagnetic waves (near-fields) in the vicinity of the magnetic source and resonant modal patterns distant from it, for a range of electrical parameters for the coal medium and for a variety of possible boundary conditions. These studies suggest that only for very low loss seams can RIM be effective, and consequently a new guided electromagnetic wave (GEM) system has been proposed to circumvent the acknowledged deficiencies inherent in RIM.

Impedance and complex power of radiating elements under electromagnetic source transformation

AbstractTransformation optics is a methodology that has proven useful in the design of complex media used to alter and control electromagnetic waves in either passive space or regions that contain source distributions. Recently it has been shown that the application of source transformations can reshape field radiation patterns corresponding to arbitrarily shaped sources. In the accompanying numerical confirmations, the effect of source transformations on fundamental quantities that are critical to the design and evaluation of antenna based systems‐‐such as complex power and impedance, remain unexplored. In this paper, we present results of theoretical analysis as well as full wave finite element simulations, proving that the complex power and impedance associated with an electromagnetic source are not changed by source transformation methods. These results open the door to the application of source transformations for the design of practical antenna based systems, such as conformal and phased array antenna design. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26077

A rotatable and amplifying optical transformation device

We report a multifunctional device&#x2014;making an object enlarge and rotate simultaneously via composite optical transformation. The potential application, i.e., a rotatable and high-directivity two-beam lens antenna, is investigated in detail. Full-wave finite element simulations for the two-dimensional cases are performed to demonstrate the properties of this device.

Full-wave analysis of H-plane waveguide junction loaded with metallic posts

A hybrid method that combines moment method and mode matching technique is presented to study H-Plane waveguide discontinuity loaded with metallic posts at the junction of two waveguides. By expanding Eigen modes in waveguides, applying continuity of tangential fields at the discontinuity and finally nulling the tangential electric field on the post surface, a system of algebraic equations is solved to obtain current distribution on the posts and consequently scattering parameters of the structure. Then, as an application, an in-line dual-mode rectangular waveguide bandpass filter is analyzed using the proposed method along with generalized scattering matrix method. The numerical results are in good agreement with existing full wave finite element method in high frequency structure simulator (HFSS) results and measurements. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2011.

Theoretical investigation of terahertz amplifier by carbon nanotubes within transmission line metamaterials

AbstractTerahertz (THz) power amplification in coplanar waveguide composite right left‐handed transmission line (CPW CRLH TL) metamaterials with carbon nanotubes (CNTs) has been investigated. The negative differential resistance (NDR) behavior of the CNTs with appropriate DC voltage bias, which can be characterized as the feature of the Gunn‐type oscillator, Esaki‐like diode, or field effect transistor (FET), is used to provide the THz loss compensation/gain. From introducing gaps in the central signal line and short‐circuited stubs connected between the CPW central signal line and the ground are used to realize the left‐handed (LH) series capacitance CL and LH shunt inductance LL, respectively. The equivalent circuits model approach and effective medium method are employed to study the propagation constant γ = α + jβ of the CNT‐based active THz metamaterials, which are validated by three‐dimensional (3D) full‐wave finite element (FEM) and circuit model co‐design. Results indicate not only the negative attenuation constant α (gain) provided by CNTs but also the negative phase constant β (backward wave propagation with anti‐parallel phase and group velocities) by artificial TL configuration at THz frequency region. This planar structure could be used to design tunable THz devices with different DC bias voltage and also easily extended to two‐dimensional (2D) and 3D active microwave, IR, or optical metamaterials at room temperature. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:815–818, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25870

Composite medium with silver nanoparticles as an anti-reflection optical coating

It is theoretically shown that a thin composite slab comprised of a transparent host and uniformly oriented disc-like silver nanoparticles deposited onto a glass surface can act as an anti-reflection coating. The applicability of the effective-medium model for describing the optical properties of thin heterogeneous layers with moderate volume fraction of inclusions is verified using full-wave finite-element simulations.

Design of invisibility cloaks with an open tunnel

In this paper we apply the methodology of transformation optics for design of a novel invisibility cloak which can possess an open tunnel. Such a cloak facilitates the insertion (retrieval) of matter into (from) the cloak's interior without significantly affecting the cloak's performance, overcoming the matter exchange bottleneck inherent to most previously proposed cloak designs.We achieve this by applying a transformation which expands a point at the origin in electromagnetic space to a finite area in physical space in a highly anisotropic manner. The invisibility performance of the proposed cloak is verified by using full-wave finite-element simulations.