Full-wave Electromagnetic Simulation Research Articles

A systematic approach for the development of wide band band pass filters using resonators

In this paper, for the first time a novel and systematic approach is presented to construct a wideband Band Pass Filters (BPFs) with high selectivity and stopband response. Two BPFs (Filter I and Filter II) were built on a Taconic (TLX-9) substrate using semi-circular tapered coupled lines, Defected Microstrip Structures (DMSs), Defected Ground Structures (DGS), and Stepped Impedance Resonators (SIRs). The precision of the design procedure is confirmed through 3-D full wave Electro-Magnetic (EM) simulation software where two wideband filters were designed for L, S, and C-bands. Additionally, parametric analysis has been done to evaluate the performance of both wideband filters with key features such as return loss, insertion loss, Band Width (BW), selectivity, and stopband response. Even-odd mode analysis has been implemented using the ABCD matrix that acts as a source for mathematical analysis of Filter I. Eventually, two wideband filters have been fabricated and tested for their effectiveness, and the measured results of two wideband filters are in line with the simulated ones with slight deviations due to fabrication tolerances and connector losses. The prototyped Filter I functions as a bandpass in the frequency range of 2.4 GHz to 4.8 GHz with a maximum insertion loss of 0.85 dB and return loss of 19.5 dB thereby providing 64% Fractional Band Width (FBW). Near 19 dB rejection is observed in the lower and upper stopband regions with BW (stopbands) greater than 2 GHz. Moreover, Filter II is also fabricated and tested. The experimental return loss of 20 dB and insertion loss (maximum) of 0.73 dB over the passband (1.9 GHz to 3.4 GHz) were found with 0.7 Selectivity Factor (SF). More than 20 dB attenuation of stopbands (lower and upper) was achieved. Thus, the fabricated wideband BPFs operate in L, S, and C-bands for radars, satellite and long-distance radio communications, and military telemetry applications.

WLAN monopole antenna design by Siamese convolutional neural network and KNN exploiting Gaussian process

In the process of antenna design, surrogate models can generally be used, but modeling requires a large number of samples. Although full wave electromagnetic simulation software can handle this task, obtaining a large number of samples is time-consuming, however too small number of sample may lead to lower accuracy of the trained surrogate model. Inspired by semi-supervised learning methods, this paper uses Siamese convolutional neural networks (SCNN) and K-nearest neighbor (KNN) algorithms to generate highly reliable virtual samples and expand the training sample set, further improving the accuracy and robustness of the surrogate model by exploiting Gaussian process (GP) models. The proposed method is named SCNN-KNN-GP, which is used for the design of WLAN dual band monopole antennas. Moreover, the relationships between the performance of the proposed model and the increased number of virtual samples and the coefficient of the KNN are studied, resulting in a more excellent surrogate model structure.

Optimization Assisted by Neural Network-Based Machine Learning in Electromagnetic Applications

We introduce an optimization assisted by a neural network (ONN) predictor to the electromagnetic community. ONN belongs to the class of the surrogate model-based optimization approaches, and approximates the objective function using a non-linear approximator – neural network. We provide a comprehensive description of the ONN algorithm and the details of its mathematical formulations. We apply ONN to optimize three popular benchmark functions and compare its performance with some commonly used optimization algorithms, namely particle swarm optimization, genetic algorithm, and Bayesian optimization. For the first time, we demonstrate ONN’s applicability and effectiveness in antenna design problems by optimizing a six-element Yagi-Uda antenna and by solving a challenging ten-dimensional dual-band slotted patch antenna constrained optimization problem. To achieve this, ONN is linked with a full-wave electromagnetic simulation solver through an application user interface. The optimized slotted patch is fabricated and measured to demonstrate how ONN can be part of the full antenna design process. Our empirical results indicate that ONN requires less objective function evaluations to reach the same qualitative point and reaches better optimal points for the same number of iterations for the studied benchmark functions and antenna optimization problems compared to the aforementioned baseline optimization algorithms.

The effect of frequency (64-498MHz) on specific absorption rate adjacent to metallic orthopedic screws in MRI: A numerical simulation study.

The imaging of patients with implanted electrically-conductive devices via magnetic resonance imaging at ultra-high fields is hampered by uncertainties relating to the potential for inducing tissue heating adjacent to the implant due to coupling of energy from the incident electromagnetic field into the implant. Existing data in the peer-reviewed literature of comparisons across field strengths of tissue heating and its surrogate, the specific absorption rate (SAR), is scarce and contradictory, leading to further doubts pertaining to the safety of imaging patients with such devices. The radiofrequency-induced SAR adjacent to orthopedic screws of varying length and at frequencies of 64 to 498MHz was investigated via full-wave electromagnetic simulations, to provide an accurate comparison of SAR across MRI field strengths. Dipole antennas were used for RF transmission to achieve a uniform electric field tangential to the screws located 120mm above the antenna midpoints, embedded in a bone-mimicking material. The input power to the antennas was constrained to achieve the following targets without the screw present: (i) E=100V/m, (ii) B1 + =2 μT, and (iii) global-average-SAR=3.2W/kg. Simulations were performed with a spatial resolution of 0.2mm in the volume surrounding the screws, resulting in 76-137 MCells, noting the maximum 1g-averaged SAR value in each case. Simulations were repeated at 128 and 297MHz for screws embedded in muscle tissue. The peak SAR, occurring at the resonant screw length, substantially increased as the frequency decreased when the input power to the dipole antenna was constrained to achieve constant electric field in background tissue at the screws' locations. A similar pattern was observed when constraining input power to achieve constant B1 + and global-average-SAR. The dielectric properties of the tissue in which the screws were embedded dominated the SAR comparisons between 297 and 128MHz. The study design allowed for a direct comparison to be performed of SAR across frequencies and implant lengths without the confounding effect of variable incident electric field. Lower frequencies produced substantially larger SAR values for implants approaching the resonant length for the worst-case uniform incident electric field along the screws' length. The data may inform risk-benefit assessments for imaging patients with orthopedic implants at the new clinical field strength of 7Tesla.

Polarization-insensitive graphene-based THz rasorber with ATA characteristics

This paper presents a polarization-insensitive rasorber implemented with absorption-transmission-absorption (ATA) characteristics over three consecutive frequency ranges in the terahertz (THz) band. The proposed rasorber is made of a two-layer periodic structure. These two layers are separated by a spacer made of glass substrate. The unit cells of the top layer have a modified swastika geometry metallization, which is loaded with graphene strips to make it lossy and provide dual-band absorption. In the bottom plane frequency selective surface (FSS), a square ring is engraved on the metal layer to obtain bandpass characteristics between two stopbands provided by the top layer. The designed rasorber works in the THz frequency range. It provides wideband absorption with a from to THz with a fractional bandwidth (BW) of around An in-band transmission window is designed with a in the frequency of to THz provides a large BW of GHz () for THz communication. Within this transmission band, the lowest insertion loss of is obtained at 0.686 THz. It provides the absorption of more than in both the lower band ( THz, BW) and the higher band ( THz, BW). The simulated response of the designed rasorber using a full-wave electromagnetic simulator and calculated through ECM are found to be in good agreement.

Systematic methods for the synthesis of equidistant MIMO arrays

Abstract. Finding a feasible antenna arrangement for multiple input multiple output (MIMO) arrays to serve a specific purpose is a first crucial step towards a successful MIMO radar system design. Design methods to synthesize uniformly weighted and equidistant MIMO arrays are proposed and investigated. The methods can be used to gain a design foundation for 1D or 2D arrays without software tools or programming effort. Since the presented approach does not consider electromagnetic fields, electromagnetic full-wave simulations might be required additionally. The method is based on sequentially copying and displacing antenna groups with the help of a number scheme. A nomenclature is proposed to classify the degrees of freedom in the design procedure. If the antennas are aligned to a uniform grid, a polynomial representation of the array can be chosen alternatively. This method is beneficial when redundancies of a produced array and where they appear must be analyzed. A new design problem arises when an array is to consist of only transceiving antennas, which can be analyzed with polynomial multiplication. One strategy to find a suitable MIMO array consisting of transceiver elements is given and evaluated.

Analytical equivalent circuit modeling and analysis of complex BGA for 3D silicon-interposer packaging

Through analyzing different cross-sections of the complex ball grid array (CBGA) sandwiched by silicon interposers, various distributed capacitances of the CBGA and the significance of the CBGA's coplanar capacitances are revealed. From the analyses, the composition of the CBGA's capacitance is found to have similarity with that of the coplanar waveguide's capacitance. Based on the electric-field coupling mechanism of the coplanar waveguide, geometrical analysis of the CBGA, and analysis of multiconductor transmission lines, analytical equations are derived to allow accurate modeling the equivalent circuit of the CBGA for 3D silicon-interposer packaging. The modeled equivalent circuit of the CBGA is validated with the full wave electromagnetic simulation, and it is demonstrated to have a good accuracy up to 40 GHz. Moreover, the CBGA structure can be further optimized for impedance matching with the guidance of the derived analytical equations.

Refractive index measurement of IP-S and IP-Dip photoresists at THz frequencies and validation via 3D photonic metamaterials made by direct laser writing

Direct laser writing (DLW) is widely used to fabricate complex metamaterials (MMs) and photonic devices for nanoscale applications across the electromagnetic frequency spectrum. While the optical properties of conventional photoresists used in DLW are well studied in the visible and infrared range, it is still unclear how they behave at lower frequencies. Here, we measure the refractive index and absorption of IP-S and IP-Dip photoresists within the THz range of the electromagnetic spectrum. Further, we utilize THz time-domain spectroscopy (THz-TDS) to experimentally measure the laser-processed three-dimensional (3D) MM structures. We conduct full-wave electromagnetic simulations using the measured refractive index values to validate our experiments. The THz-TDS measurements are in excellent agreement with the theoretical predictions verifying the validity of our refractive index measurements. This study aims to support and lead future investigations utilizing standard DLW photoresists for photonic applications in the THz range.

Reduced-cost microwave modeling using constrained domains and dimensionality reduction

Development of modern microwave devices largely exploits full-wave electromagnetic (EM) simulations. Yet, simulation-driven design may be problematic due to the incurred CPU expenses. Addressing the high-cost issues stimulated the development of surrogate modeling methods. Among them, data-driven techniques seem to be the most widespread owing to their flexibility and accessibility. Nonetheless, applicability of approximation-based modeling for real-world microwave components is hindered by a high nonlinearity of the system characteristics, dimensionality issues, and broad ranges of operating parameters the model should cover to make it practically useful. Performance-driven modeling frameworks deliver a partial mitigation of these problems through appropriate spatial orientation of the metamodel domain, which only encapsulates high-quality designs and not the entire space. Unfortunately, the initial model setup cost is high, as defining the domain requires database designs that need to be a priori acquired. This paper introduces a novel approach, where the database designs are replaced by random observables, and dimensionality of the domain is reduced using spectral analysis thereof. The major contributions of the work include implementation of the explicit dimensionality reduction of the confined surrogate model domain and introducing this concept into a complete cost-efficient framework for modeling of microwave components. Comprehensive benchmarking demonstrates excellent performance of the introduced framework, both in terms of predictive power of the rendered surrogates, their scalability properties, as well as low computational overhead associated with the model setup.

Multi-Functional Reconfigurable Intelligent Surfaces for Enhanced Sensing and Communication.

In this paper, we propose a reconfigurable intelligent surface (RIS) that can dynamically switch the transmission and reflection phase of incident electromagnetic waves in real time to realize the dual-beam or quad-beam and convert the polarization of the transmitted beam. Such surfaces can redirect a wireless signal at will to establish robust connectivity when the designated line-of-sight channel is disturbed, thereby enhancing the performance of wireless communication systems by creating an intelligent radio environment. When integrated with a sensing element, they are integral to performing joint detection and communication functions in future wireless sensor networks. In this work, we first analyze the scattering performance of a reconfigurable unit element and then design a RIS. The dynamic field scattering manipulation capability of the RIS is validated by full-wave electromagnetic simulations to realize six different functions. The scattering characteristics of the proposed unit element, which incorporates two p-i-n diodes have been substantiated through practical implementation. This involved the construction of a simple prototype and the subsequent examination of its scattering properties via the free-space measurement method. The obtained transmission and reflection coefficients from the measurements are in agreement with the anticipated outcomes from simulations.

Theoretical method for the analysis and design of tunable terahertz graphene-based Faraday polarization rotators.

A theoretical method is presented that facilitates the analysis and design of graphene-based tunable terahertz polarization rotators. Most previous designs are based on a three-dimensional (3-D) full-wave electromagnetic simulation; thus, it is time-consuming to get well-tuned structural parameters. Using the proposed method, the transmission response of the polarization rotator is directly calculated for a given set of structural parameters. Hence, the need of the electromagnetic simulation is lifted. The accuracy of the proposed method is rigorously validated, as excellent agreement between the theoretical and simulation results is observed. Using the method, a rotator of 12THz central frequency with a small magnetic bias field of 0.5T and a small unit cell of 0.5 by 0.5(µm)2 is designed. It is shown that the center frequency can be increased to any desired frequency, without the need of a large magnetic bias, by reducing the unit cell size. The method presented in this work can be extended for the analysis and design of other tunable terahertz nonreciprocal devices, such as isolators, circulators, phase shifters, and switches.

Accessing new avenues of photonic bandgaps using two-dimensional non-Moiré geometries

Photonic crystals (PhC) formed by 2-D non-Moiré geometries are realized in this work. Non-Moiré (NM) tiles are the contours of trigonometric functions that generate exciting shapes and geometries. Photonic bandstructure calculations reveal that 2-D NM geometries exhibit new avenues of photonic bandgaps compared to the regular circular rod-based PhCs. The band structures are anisotropic and show, intriguing orientation-dependent partial bandgaps. A few of the orientation-dependent frequency selective properties of the realized NM geometry-based PhCs are demonstrated using full-wave electromagnetic simulations. The proposed geometries are practically realizable, and in this work, we experimentally demonstrate the fabrication process using the 3-D printing technique for microwave frequencies.

High-efficacy global optimization of antenna structures by means of simplex-based predictors

Design of modern antenna systems has become highly dependent on computational tools, especially full-wave electromagnetic (EM) simulation models. EM analysis is capable of yielding accurate representation of antenna characteristics at the expense of considerable evaluation time. Consequently, execution of simulation-driven design procedures (optimization, statistical analysis, multi-criterial design) is severely hindered by the accumulated cost of multiple antenna evaluations. This problem is especially pronounced in the case of global search, frequently performed using nature-inspired algorithms, known for poor computational efficiency. At the same time, global optimization is often required, either due to multimodality of the design task or the lack of sufficiently good starting point. A workaround is to combine metaheuristics with surrogate modeling methods, yet a construction of reliable metamodels over broad ranges of antenna parameters is challenging. This work introduces a novel procedure for global optimization of antenna structures. Our methodology involves a simplex-based automated search performed at the level of approximated operating and performance figures of the structure at hand. The presented approach capitalizes on weakly-nonlinear dependence between the operating figures and antenna geometry parameters, as well as computationally cheap design updates, only requiring a single EM analysis per iteration. Formal convergence of the algorithm is guaranteed by implementing the automated decision-making procedure for reducing the simplex size upon detecting the lack of objective function improvement. The global optimization stage is succeeded by gradient-based parameter refinement. The proposed procedure has been validated using four microstrip antenna structures. Multiple independent runs and statistical analysis of the results have been carried out in order to corroborate global search capability. Satisfactory outcome obtained for all instances, and low average computational cost of only 120 EM antenna simulations, demonstrate superior efficacy of our algorithm, also in comparison with both local optimizers and nature-inspired procedures.

Complementary analysis of specific absorption rate safety for an 8Tx/16Rx array with central symmetry of elements for magnetic resonance imaging of the human heart and abdominopelvic organs at 7 T.

A complementary safety assessment of the specific absorption rate (SAR) of the electromagnetic energy was performed in a prototype 8Tx/16Rx RF array for cardiac magnetic resonance imaging (MRI) at 7 T. The study aimed to address two critical aspects of 7-T SAR safety not always explicitly examined by coil vendors: (i) the influence of an RF-array position on a peak SAR value, and (ii) the risk of exceeding the permitted maximal SAR in the tissue surrounding conductive passive implants. The full-wave 3D electromagnetic simulations for the thorax with shifted array position and the whole-body volume in the presence of a dental retainer, an intrauterine contraceptive device (IUD), and a hip joint implant, were performed for two human voxel models. The effect of the array displacement on the SAR was simulated for seven array locations on the thorax shifted from the central position in different directions on 50 mm. The peak SAR values for both models were analyzed for the three phase-only transmit vectors optimized for B1 + homogeneity and transmit efficiency. Peak SAR values due to the shifts of the array position increase up to ≈50%. The worst-case peak SAR value for a dental retainer was found to be in the range of 10% of the maximal SAR in the tissue within the array's borders. For the IUD and artificial hip joint implants the effect was found to be negligible (peak SAR < 1% of the SAR within array borders). In addition to simulations for cardiac MRI, we performed a preliminary B1 + shimming and SAR-safety analysis for the same RF-array at various positions lower on the body trunk to assess a potential application in imaging abdominopelvic organs (prostate, kidney, and liver). The most promising target for an ad hoc alternative application of the array was found to be the prostate.

Large area optimization of meta-lens via data-free machine learning

Sub-wavelength diffractive optics, commonly known as meta-optics, present a complex numerical simulation challenge, due to their multi-scale nature. The behavior of constituent sub-wavelength scatterers, or meta-atoms, needs to be modeled by full-wave electromagnetic simulations, whereas the whole meta-optical system can be modeled using ray/ Fourier optics. Most simulation techniques for large-scale meta-optics rely on the local phase approximation (LPA), where the coupling between dissimilar meta-atoms is neglected. Here we introduce a physics-informed neural network, coupled with the overlapping boundary method, which can efficiently model the meta-optics while still incorporating all of the coupling between meta-atoms. We demonstrate the efficacy of our technique by designing 1mm aperture cylindrical meta-lenses exhibiting higher efficiency than the ones designed under LPA. We experimentally validated the maximum intensity improvement (up to 53%) of the inverse-designed meta-lens. Our reported method can design large aperture ( ~ 104 − 105λ) meta-optics in a reasonable time (approximately 15 minutes on a graphics processing unit) without relying on the LPA.

Dispersion and Polarization Control in Below-Cutoff Circular Waveguides Using Anisotropic Metasurface Liners

This article explores the application of metasurface (MTS) liners in perfect-electric-conducting (PEC) circular waveguides for cutoff manipulation and the introduction of controllable chiral properties. A dispersion equation is derived to predict the propagation characteristics of a circular waveguide lined with an MTS exhibiting a general full tensor surface admittance response. A design procedure for the MTS liner is presented and validated with three design examples. Two of the examples use a capacitively loaded grid topology akin to a Jerusalem cross structure aligned with the principal coordinate system of the waveguide, resulting in a diagonal susceptance tensor. These two examples are used to demonstrate how the dispersion properties of the waveguide can be significantly modified based on the geometry of the MTS-lined waveguide system and the surface admittance exhibited by the MTS. The third design consists of a rotated fully printed Jerusalem cross structure with a general tensor susceptance, which is found to produce a separation in the dispersion curves of the left-and right-hand circularly polarized modes in the waveguide while also producing below-cutoff propagation. Theoretically predicted dispersions are validated with full-wave electromagnetic simulations.

Reduction of electromagnetic coupling between parallel high speed interconnects using defected Microstrip structure

In the context of designing printed circuit boards (PCBs) for the upcoming fifth generation double data rate (DDR5) technology, the issue of electromagnetic coupling emerges as a significant challenge. To address this concern, a comprehensive approach to mitigating both forward and backward coupling is proposed in this paper. The presented research introduces an innovative solution by incorporating a Defect Microstrip Structure (DMS) with a meticulously designed mitered meander shape. This unique structure is strategically imposed within the victim microstrip lines, aiming to effectively curtail coupling effects between interconnected microstrip lines. By embedding the mitered meander DMS onto the microstrip line, the electromagnetic (EM) coupling strength is substantially reduced. The reduction in coupling is primarily attributed to the achievement of an optimized ratio between capacitive and inductive coupling among the interconnected microstrip lines. The effectiveness of the proposed method is rigorously evaluated through a series of full-wave electromagnetic simulations. These simulations encompass microstrip lines etched both with and without the integration of the mitered meander-shaped DMS. The analytical framework leverages the ANSYS Structure Simulator (HFSS), a powerful tool for evaluating electromagnetic behaviour.

Engineerable wavevector diagrams of non-Moiré geometry-based photonic crystals for beam steering applications

The wavevector diagrams or eigenfrequency contours (EFCs) (also called dispersion surfaces) are the best tools to explore the optical properties of photonic crystals (PhCs). Many optical phenomena, such as self-collimation, super-prism, negative refraction, and lensing, have been extensively explored in PhCs based on EFCs. Also, several approaches have been continuingly pursued to modulate the EFCs of PhCs for molding the flow of light. This work presents the modulated wavevector diagrams of PhCs formed by asymmetric non-Moiré (NM) patterns. The NM patterns are contours of trigonometric functions that generate attractive tiles and shapes. Employing such shapes to design a PhC tailors the dispersion of PhCs with stretching, squeezing, and shape-modulated EFCs. Based on the modulated EFCs of the proposed structures, we demonstrate the direction-dependent beam steering phenomenon. The ray tracing, full-wave electromagnetic simulations, far-field patterns, and electric field profiles corroborate the beam steering application of the modulated EFCs. We anticipate that the modulated EFCs of non-Moiré pattern-based PhCs are useful for reconfigurable wave optics and beam steering applications.

A novel radial network for feeding concentric ring antenna arrays

This paper presents a novel radial network for feeding concentric ring antenna arrays. The proposed feeding network consists of a radial network of 1 input to 20 outputs. Two stages are required for this planar radial network: a radial power divider of 1 to 5 and a cascade Wilkinson power divider of 1 to 4 to generate 20 outputs that feed to a concentric rings antenna array. The proposed radial network provides a feeding network having balance in magnitude and phase to be applied in antenna systems based on a concentric rings array geometry. The paper provides as an interesting contribution the full antenna system considering the proposed radial feeding network (1 to 20) and the concentric rings antenna array. Full wave electromagnetic simulations and experimental measurements are implemented to verify the performance of matching, bandwidth and radiation pattern of the full system taking the mutual coupling into account.

Physics-Driven Machine-Learning Approach Incorporating Temporal Coupled Mode Theory for Intelligent Design of Metasurfaces

Metasurfaces find a wide variety of applications in the last decades due to their powerful ability to manipulate electromagnetic (EM) waves. Traditional approaches for metasurface design require massive full-wave EM simulations to achieve optimal geometrical parameter values, resulting in an inefficient design process of metasurfaces. In this article, we propose a physics-driven machine-learning (ML) approach incorporating temporal coupled mode theory (CMT) to improve the design efficiency and implement an intelligent design of metasurfaces. In the proposed approach, a surrogate model (i.e., neuro-CMT model) is developed to speed up the prediction of EM responses of metasurfaces. A three-stage method is used to develop the neuro-CMT model. First, we perform full-wave EM simulations of unit cells only containing single-and double-resonators for different geometrical design parameter values. Second, we extract the single-and double-resonator CMT parameters for each geometrical parameter value by fitting the corresponding EM responses based on CMT equations. Third, we train neural networks to learn the relationships between the CMT parameters and geometrical parameters for single-and double-resonator systems, respectively. These trained neural networks, in conjunction with the multiresonator CMT equation, become an efficient tool to accurately predict the EM responses of any arbitrary coupled multiresonator systems. The proposed neuro-CMT model can be further utilized for metasurface design optimizations. Two metasurface absorbers are given as examples to demonstrate the efficient and intelligent advantages of our proposed approach.