EM Simulation Research Articles

Compact Multilayer Reconfigurable Dual-Band Filters using Mixed Resonators

In this paper, we realize a compact reconfigurable dual-band bandpass filter using memristive switches. The filter consists of two fourth-order single-band bandpass filters with mixed resonators. For the filter implementation, we use microstrip technology. In order to miniaturize the footprint area, around two times, we adopt the multilayer technology. The proposed filter has two operating modes: (1) dual-band bandpass (2BP) with both switches in the OFF state, and (2) single-band bandpass (1BP) for the switches in the ON state. A commercial RF memristor is not available yet, so we emulate its ON/OFF state with short- or open-circuit for the filter prototype fabrication. Measurements of the microstrip prototype validate the proposed design and are in good agreement with the 3D EM and circuit simulations. For 2BP mode, the central frequencies are 2.42[Formula: see text]GHz and 5.19[Formula: see text]GHz, while the 3[Formula: see text]dB fractional bandwidths (3dB FBW) are 7.7% and 5.35%, respectively. On the other hand, 1BP mode has a lower central frequency equal to 2.42[Formula: see text]GHz and the 3dB FBW is 7.6%, while the higher passband is suppressed more than 25[Formula: see text]dB. The footprint area is 0.37 [Formula: see text].18 [Formula: see text], when [Formula: see text] is given for the lower central frequency at 2.42[Formula: see text]GHz.

Radiofrequency Coil Tuning Using Matching Circuit Co-Simulation with Magnetic Resonance Integral Equations

Abstract The proposed extension to the conventional circuit co-simulation (CCS) method reliably and efficiently introduces arbitrary matching networks into CCS routines and is here dubbed as matching circuit co-simulation (MCCS). It further achieves coil tuning for resonance and an optimum scattering parameters condition that resembles a fully matched coil. Combined with magnetic resonance integral equations (MARIE), the proposed MCCS further accurately produces a full EM simulation of the coils. We first validated MARIE with the MCCS routine to use it to model simple single-channel coils and parallel transmit (pTx) head arrays coupled with Duke, a digital human body model. Having successfully validated the MCCS routine, we swept through both tuning and matching network parameters to optimize the coil. While optimizing for all parameters simultaneously is a viably efficient option for coil models of low complexity, these models are not realistic, and we found that it becomes a highly computationally expensive problem to solve for more complex coil geometries, such as birdcage coils and pTx coils with higher number of channels, especially when shielding is included. Consequently, we separated tuning and matching into two steps, by first tuning the coil to the right frequency, and then introducing matching networks to enhance the power transmission into the body. We observed lower on-diagonal S-parameters after matching in all pTx coils, but 1 coil still had strong cross-coupling. Finally, electromagnetic fields obtained via MARIE for separate port excitation were successfully combined using MCCS.

A 128-channel receive array with enhanced SNR performance for 10.5 tesla brain imaging.

To develop and characterize the performance of a 128-channel head array for brain imaging at 10.5 tesla and evaluate the potential of brain imaging at this unique, >10 tesla magnetic field. The coil is composed of a 16-channel self-decoupled loop transmit/receive array with a 112-loop receive-only (Rx) insert. Interactions between the outer transmitter and the inner 112Rx insert were mitigated using coaxial cable traps placed every 1/16 of a wavelength on each feed cable, locating most preamplifier boards outside the transmitter field and miniaturizing those placed directly on individual coils. The 128-channel array described herein achieved 77% of ultimate intrinsic SNR in the center of the brain. Transmit field maps obtained experimentally on a phantom with and without the receive array were similar and matched EM simulations, leading to FDA approval for human imaging. Anatomical and functional data, including with power demanding sequences, were acquired successfully on human volunteers. Counterintuitive to expectations based on magnetic fields ≤7T, the higher channel counts provided SNR gains centrally, capturing ∼80% uiSNR. Fraction of uiSNR achieved centrally in 64Rx, 80Rx, and 128Rx arrays suggested that a plateau was being reached at 80%. At this plateau, linear to approximately quadratic B 0 dependent SNR gains for the periphery and the center, respectively, were observed for 10.5T relative 7T.

A Multi-Layer Techno-Economic-Environmental Energy Management Optimization in Cooperative Multi-Microgrids with Demand Response Program and Uncertainties Consideration.

This paper presents a multi-layer, multi-objective (MLMO) optimization model for techno-economic-environmental energy management in cooperative multi-Microgrids (MMGs) that incorporates a Demand Response Program (DRP). The proposed MLMO approach simultaneously optimizes operating costs, MMG operator benefits, environmental emissions, and MMG dependency. This paper proposed a new hybrid ε-lexicography-weighted-sum that eliminates the need to normalize or scalarize objectives. The first layer of the model schedules MMG resources with DRP to minimize operating costs (local generation and power transactions with the utility grid) and maximize MMG profit. The second layer achieves the environmental operation of the MMG, while the third layer maximizes MMG reliability. This paper also proposed a new application of a recently developed enhanced equilibrium optimizer (EEO) for solving the three-layer EM problem. In addition, the uncertainties of solar power generation, wind power generation, load demand, and energy prices are considered based on the probabilistic 2m + 1 Point estimation method (PEM) approach. Three case studies are presented to verify the proposed MLMO approach on an MMG test system. In Case I, a deterministic EM is solved to simulate the MMG as a single layer to minimize costs and maximize benefits through DRP, while Case II solves the MLMO optimization problem. Simulation results show that the proposed MLMO technique reduces environmental emissions by 2.45% and 3.5% in its optimization layer and at the final layer, respectively. The independence index is also enhanced by 2.49% and 4.8% in its layer only and as a total increase, respectively. Case III is for the probabilistic EM simulation; due to the uncertain variables effect, the mean value in this case is increased by about 2.6% over Case I.

Optimum design of a novel Ku-band rasorber for RADAR warfare systems using ML neural network

The design, fabrication, and testing of a conformal Frequency Selective Rasorber (FSR) operating at A-T-A mode is designed for RADAR warfare systems. In the design of a miniaturized single-layer FSR element, multiple parameters influencing the absorption and transmission characteristics need to be optimized. This simulation using conventional methods consumes more simulation time. Thus, the geometrical parameters are optimized and predicted using supervised machine learning (ML) techniques to expedite the process. The multiple output regression neural network (MORNN) is used to generate multiple input and output features from the dataset. The ML algorithm is trained using the datasets generated from the electromagnetic solver using which a scalable FSR is synthesized. The reflection coefficient, (|S11|), and transmission coefficient (|S21|) are used as input data, and the dimension of the FSR unit cell for the user input frequency requirements are derived as output data. The extracted dimensions of the FSR offered a small mean square error (MSE) of 0.02 between the desired and observed results. The designed FSR offers absorption at 11.5 GHz and 18.9 GHz while the transmission window extends from 15.02 GHz to 16.09 GHz. The neural network results are endorsed using the EM simulation tool and validated by experimental measurements.

A fast and effective approach for microstrip filter design using GA and TL-model

Microwaves and RF technology and their components like filters, antennas, etc. are commonly used in wireless networking and communication systems, wireless security systems, radar systems, and environmental remote sensing. In this paper, a fast and effective procedure has been proposed for microstrip filter design using a genetic algorithm (GA) with a transmission line model (TL). GA is modified to be highly efficient and accurate by encoding the topology. For the fixed filter topology, the electrical parameters of the filter are encoded in a single chromosome. To make the proposed procedure fast and effective, a transmission line model has been employed to compute the fitness value in GA. To demonstrate the effectiveness of the proposed procedure, a wideband second-order bandpass filter with a center frequency of 2.3 GHz is examined with a pair of short-circuited stubs and a pair of open-circuited stubs. The optimized design is validated using full-wave methods (MoM and EM simulator CST). The results show a low insertion loss of 0.1 dB and return loss better than 30 dB and a wide bandwidth of 46.95% with − 3 dB cutoff frequencies at 1.76 GHz and 2.84 GHz.

Frequency tunable dual band graphene-silicon ceramic-based two-port THz radiator with circular polarization and high isolation features

In this work, a two-port graphene-ceramic-based antenna is designed and discussed. Some important features for the proposed two-port radiator are (a) the feed layout produces dual radiating modes, i.e., HEM11δ and HEM12δ inside the ceramic at 2.6 and 5.2 THz, respectively; (b) the asymmetrical swastik-shaped aperture creates the circularly polarized waves within dual operating bands, i.e., 2.71–2.84 and 5.15–5.42 THz; (c) a coating of graphene over ceramic makes the radiator frequency tunable by varying its chemical potential; and (d) deep neural network (DNN) and XGBoost-based machine learning (ML) algorithms are used to predict the |S11| parameter of the designed antenna in order to reduce the computational complexity. By comparing the optimized outcome obtained from HFSS with the CST EM simulator and predicted values from ML algorithms, it is verified that the designed two-port radiator works in dual frequency bands, i.e., 2.4–3.2 and 5.0–5.43 THz. Stable values of MIMO, as well as the far-field parameter, confirm the applicability of the designed antenna for THz wireless applications.

Microwave characterization of nanomaterials using planar slot resonator

Nanomaterial characterization using microwaves is needed in nanoscale semiconductor devices, microwave imaging, EM shielding, and wireless communication. Many nanomaterials are used as metallic or dielectric layers in these applications. In this paper, we report the characterization of nanomaterials using planar Microwave Slot Resonator (MSR) which was designed and studied using 3D EM simulation tool. The response of MSR is parameterized which offers a platform to calculate relative permittivity (ε r) and conductivity (σ) from measured high frequency response of nanomaterial loaded MSR. With simplified method, this microwave characterization offers accurate and faster results which be used in design, calculation and numerical analysis of nanomaterial based electronic/optoelectronic devices and sensor/shielding applications.

Compact Ultra-Wideband Wilkinson Power Divider in Parallel Stripline with Modified Isolation Branches.

An efficient design method for a compact and ultra-wideband multi-stage Wilkinson power divider in a parallel stripline (PSL) is proposed. To enhance the frequency bandwidth of the proposed power divider while reducing its size, the isolation branch is modified; that is, two capacitors are connected to both sides of a resistor at each isolation branch. For an efficient design process, the PSL power divider is equivalently represented by two microstrip power dividers, and the design equations are derived. Based on the design equations, an in-house algorithm is utilized to optimally determine the design parameters, including the line impedance, resistance, and capacitance of each stage. For example, a three-stage PSL power divider is designed with three λ/4 transmission lines at a base frequency of 5 GHz. To verify the accuracy of the design procedure, 3D EM simulations and measurements are performed, and the results show good agreement. Compared with the conventional three-stage Wilkinson power divider, the proposed PSL power divider achieves a wider frequency bandwidth of 1.16 to 6.51 GHz (139.5%) and a 23% shorter transmission line length of 207°, while exhibiting an insertion loss of 0.7 to 1.4 dB.

Ultra-Wideband Vertical Transition in Coplanar Stripline for Ultra-High-Speed Digital Interfaces.

A design method for an ultra-wideband coplanar-stripline-based vertical transition that can be used for ultra-high-speed digital interfaces is proposed. A conventional via structure, based on a differential line (DL), inherently possesses performance limitations (<10 GHz) due to difficulties in maintaining constant line impedance and smooth electric field transformation, in addition to the effects of signal skews, FR4 fiber weave, and unbalanced EM interferences. DL-based digital interfaces may not meet the demands of ultra-high-speed digital data transmission required for the upcoming 6G communications. The use of a coplanar stripline (CPS), a type of planar balanced line (BL), for the vertical transition, along with the ultra-wideband DL-to-CPS transition, mostly removes the inherent and unfavorable issues of the DL and enables ultra-high-speed digital data transmission. The design process of the transition is simplified using the analytical design formulas, derived using the conformal mapping method, of the transition. The characteristic line impedances of the transition are calculated and found to be in close agreement with the results obtained from EM simulations. Utilizing these results, the CPS-based vertical transition, maintaining the characteristic line impedance of 100 Ω, is designed and fabricated. The measured results confirm its ultra-wideband characteristics, with a maximum of 1.6 dB insertion loss and more than 10 dB return loss in the frequency range of DC to 30 GHz. Therefore, the proposed CPS-based vertical transition offers a significantly wider frequency bandwidth, i.e., more than three times that of conventional DL-based via structures.

Design of Miniaturized 90-Degree Hybrid Coupler with Wide Rejection Band Using Neural Network.

In this paper, a 3 dB 90-degree hybrid coupler with size reduction and harmonics rejection was designed. In the proposed coupler structure, four simple low-pass filters (LPFs) were applied. An artificial neural network (ANN) was used to determine the dimensions of the applied LPFs based on EM simulation data. The applied ANN model could also provide the desired LPF parameters, including the cut-off frequency (fc), bandwidth (BW), and insertion loss (IL). Designing an applied LPF involves complex mathematical calculations and simulations to optimize parameters. However, by utilizing neural networks, the design process can be significantly streamlined and automated. Neural networks have the ability to learn complex patterns and relationships within data, making them well suited for optimizing the performance of applied components. The proposed 90-degree hybrid coupler works correctly at 1800 MHz and has a small size of 16.6 mm × 15.15 mm, which provides a 73% size reduction compared to a normal 1800 MHz coupler. The designed coupler not only decreases the circuit size but also provides a wide rejection band from 4.8 GHz to 11.2 GHz, which suppresses the second to sixth harmonics. The insertion loss parameter of this 90-degree hybrid coupler is less than 0.1 dB at the working frequency, which shows the superior performance of the proposed coupler.

Investigation of Planar Antenna Performances on Commercially Available Dielectric Materials

Planar RF antennas with their conformal geometry, good RF performances and ease of construction find a wide range of applications ranging from mobile phones to RADAR and wearable electronic gadgets to medical implant devices. The selection of a suitable dielectric material is by far the most crucial step in the antenna design process to achieve the desired RF characteristics. The directivity, efficiency and bandwidth of an antenna depend on the substrate dielectric constant, loss tangent and material thickness. This paper investigates the RF performances of two planar antennas designed using two commercially available dielectric materials namely RT Duroid and FR4 with a full wave 3D EM simulation tool. The results show the superior RF characteristics of the antenna designed using RT Duroid over FR4. The antenna designed with RT Duroid substrate is fabricated and the measurement results obtained are found to be in good agreement with the simulation results.

A Low-Cost Patch-Antenna for Non-Invasive Brain Cell Detection

Cancer is one of the most and frequent causes of death around the world. Brain tumor is a critical and dangerous type and has a few difficulties of the techniques used for its detection; it is hard to determine its location when it is small at an early stage. The purpose of this work is to design a patch antenna sensor that is a low-cost microstrip which is suitable to detect a brain cancer tumor. The computer simulation technology CST Studio Suite 3D EM simulation and analysis was used to design a patch antenna with different frequencies of 2.8 GHz, 3.9 GHz, 5GHz and 5.6GHz to diagnose brain tumors. A comparison study between these resonance frequencies (lower-band (L-B) 2 GHz, middle-band (M-B) 3.9-5 GHz and upper-band (U-B) &gt; 5 GHz) has been performed with six layers of brain phantom of fat, dura, brain, skin, CSF (Cerebrospinal Fluid) and skull. The designed patch sensor was assessed on both scenarios without and with a tumor cell on a brain phantom. Three parameters have been observed, the frequency phase shift, the deep amount of reflection return loss and power absorption were used to indicate the presence of the tumor cell. This study concludes that the middle-band (M-B) results in good penetration and better return loss depth around - 20dB. Meanwhile, the higher band provides high resolution of 21 MHz phase-shift but with only depth value of difference return loss of -0.1dB. The proposed work could provide a pathway on the design of patch sensors for biomedical applications.

A High-Gain Directional 1 × 8 Planar Antenna Array for 2.4GHz RFID Reader Applications

This research paper deals with a directional high gain PCB [Formula: see text] antenna array for 2.4[Formula: see text]ISM band utilizations. To achieve this antenna array, a well-matched equal-split 9[Formula: see text]dB-power splitter is designed and integrated with the suggested antenna array. It exhibits a wide operating range of 506[Formula: see text]MHz (2.022–2.528[Formula: see text]GHz) and splits the feed power to 8 equal-in-phase output quantities. Then eight identical patch elements with good reflection coefficient, high gain and excellent radiation efficiency are connected at the eight-output ports of the 1 × 8-power divider in order to obtain an array antenna consisting of eight radiating elements. A quarter-wave impedance adapter is utilized to obtain a perfect matching of impedance between patches and the power divider. The suggested directional antenna resonates at 2.4[Formula: see text]GHz with good impedance matching via offering reflection coefficient [Formula: see text][Formula: see text]dB and voltage standing wave ratio (VSWR) of 1.16. Moreover, it offers good radiation traits like the enhanced gain of 14.76[Formula: see text]dB, an excellent radiating efficiency equals about 98.86% and a directional radiation pattern. Initially, the proposed planar directional antenna array has been designed and simulated utilizing high-frequency structure simulator (HFSS) EM simulation tool, the results are validated with another simulation tool via computer simulation technology (CST) software. This printed antenna array is a potential candidate to operate at around 2.4[Formula: see text]GHz for RFID reader utilizations due to its outstanding impedance and radiation characteristics.

Effective modeling of metasurface‐loaded circularly polarized dielectric resonator‐based MIMO antenna for sub‐6.0‐GHz band using machine learning algorithms

SummaryIn this article, a dual‐port dielectric resonator antenna (DRA) is modeled using machine learning (ML) algorithms, that is, deep neural network (DNN), random forest, and XGBoost. The unique properties of the proposed article are as follows: (i) Two different diversity techniques, that is, pattern (with the help of metallic wall) and polarization (mirror image of the aperture), improve the isolation value between the ports; (ii) ML algorithms are used to optimize and predict the reflection coefficient as well as mutual coupling of the proposed antenna. The accuracy of ML algorithms is verified by using the HFSS EM simulator and experimental validation. Error is less than 1%–2% between the value predicted from ML algorithms and HFSS/experimental results. The proposed design is working well in between 2.4 and 4.02 GHz with a 3‐dB axial ratio from 2.84 to 2.95 GHz. All these features make the radiator employable to the sub‐6.0‐GHz frequency band.

Model of slot antenna for MPECVD of carbon nanostructure

A model of a slotted waveguide antenna for microwave plasma enhanced chemical vapor deposition (MPECVD) of carbon nanostructures at low pressure is developed. The performance of two slot applicator for the production of dense plasma in the working gas (argon) at a frequency of 2.45 GHz is investigated by EM field simulator. Results show that dimensions of the symmetrical slots (length l ≤ λg/2, width of d = 6-10 mm) and optimized angle (φ=32° with respect to the waveguide central line) have a strong influence on the impedance matching of the waveguide to the dielectric window and plasma column (1.5 < SWR < 2.5), and on the radiation efficiency. The dielectric plate and plasma column density were taken into account in the model in the optimisation of the dimensions of the slots. The mode structure of standing surface waves in the plasma column is investigated at three values of plasma density and results for the radial (n=1) and azimuthal wave numbers (m=3, 4, 5) are in agreement with experimental results.

Flexible Double‐Layer Adjustable Frequency Selective Surfaces Based on 3D Cross‐Shaped Kirigami Structure

AbstractFrequency‐selective surfaces (FSS) with flexible treatment can be employed in various applications. This paper develops a mechanically constructed flexible double‐layer adjustable FSS based on a 3D cross‐shaped kirigami structure design. Through mechanical stretching, the kirigami structure partly adhered to the ecoflex substrate enables this FSS to modulate the resonant frequencies of two filter bands synchronously. Meanwhile, the structural deformation triggered by mechanical stretching may function as a switch to adjust the filter band with a higher resonant frequency. According to the results of EM experiments and simulations, in the absence of stretching, the undeformed FSS with a double‐layer structure has two filter bands. Compared to the undeformed configuration, the stretching induces structural deformation, which results in apparent resonant frequency shifts of both the two filter bands and the contraction of the filter band with higher resonant frequency. A buckling model that has been theoretically, cumulatively, and experimentally proven is utilized to investigate the structural deformation of this FSS caused by stretching. It is convenient to switch flexible double‐layer adjustable FSS' deformation by mechanical method. This flexible double‐layer adjustable FSS offers a new design strategy for the application of FSS, paving the route for new developments in electromagnetic compatibility.

A miniaturized left‐handed circularly‐polarized printed radiator for direct broadcast satellite application

SummaryThis article presents a highly compact printed radiator for direct broadcast satellite (DBS) systems that exhibits good gain and left‐handed circular polarization. The inferred pattern is accomplished by etching two isosceles triangles, one from each of the four corners of a square. From the center of the newly acquired structure, a circular geometric design is made up of 16 isosceles‐scaled triangles has been etched. This arrangement induces resonance in the antenna, aligning it with the desired frequency. The proposed antenna is designed using PCB laminated Rogger 5880 material and simulated in a CST EM simulator. The antenna under consideration exhibits a significant size reduction, achieving a miniaturization ratio of 21.03%. The LHCP antenna resonated at 12.61 GHz and offered a decent LHCP gain of 7.95 dBic. It gives 0.56 GHz CP bandwidth, which covers the DBS service band entirely. It also provides 96.43% radiation efficiency and 44.27 dB/m correction factor, respectively. All the measured findings of the prototype agree with its simulated one.

A Modified Quadrature Birdcage Coil Incorporated With a Curved Feature for In Ovo MR Imaging.

Goal: This study presents a novel MRI coil design approach explicitly tailored for chick embryo measurements, with the primary objective of improving sensitivity and coverage. Methods: The limitations posed by conventional birdcage coils were addressed by introducing a curvature feature into a standard coil. The performance of the modified coil was assessed using EM simulations and experimental evaluations, which were subsequently validated using a 7 T MRI scanner. A comparative analysis was conducted against a standard quadrature low-pass birdcage coil to evaluate key factors. Results: The proposed coil demonstrated improved SNR and uniformity, particularly in the proximity of the end-rings. These results were consistent with the findings obtained from the simulations. Conclusions: The use of our innovative birdcage coil design holds promise and offers practical potential for in ovo studies.

Fast Subsurface EM Simulation Based on the Mixed Finite-Element Method and Second-Order Arnoldi Algorithm

Fast Subsurface EM Simulation Based on the Mixed Finite-Element Method and Second-Order Arnoldi Algorithm