Showing papers in "IEEE journal on multiscale and multiphysics computational techniques in 2022"

Semi-Analytical Model Using the Uniform Theory of Diffraction for Single Feed High Gain Antenna Structure

Abstract: The recent advancement in commercial electromagnetic computational solvers, along with the computational processing resources gives a huge advantage for antenna designers to study complex structures and optimize their performance. In addition, the huge leap in processors speeds, and the advent of parallel processing techniques made it possible to reduce the computation time dramatically. Consequently, this made it less attractive for designers to explore fast analytical models for their structures. The main drawback of the full and blind dependence on commercial solvers in the design process is the lack of the physical insight for the operating mechanism of the structure. On the other hand, despite that numerical and analytical series solutions can give an accurate solution to the electromagnetic problem being studied, they hardly can give an insight on the internal interactions and the operating mechanism of the structure. In this work we provide a semi-analytical model along with a thorough physical insight for a single feed high gain antenna structure. The provided model not only gives a powerful insight into understanding the radiation mechanism, but also is very computationally effective, and allows the use of antenna theory intuition, where the structure can be perceived as an antenna array, and the principles of array factor, power tapering, etc. can be intuitively used to understand and manipulate the structure radiation behavior.

Incident Plane-Wave Source Formulations for Leapfrog Complying-Divergence Implicit FDTD Method

Abstract: The commonly used unconditionally stable finite-difference time-domain (FDTD) methods such as alternating direction implicit (ADI)-FDTD, and its one-step formulation, leapfrog ADI-FDTD, have been found to violate the divergence condition of Gauss's law. The recently proposed leapfrog complying-divergence implicit (CDI)-FDTD not only addresses this problem, but also features many advantages, including unconditional stability, minimal floating-point operations and one-step leapfrog update. To further expand its application, this paper presents the incident plane-wave source formulations for leapfrog CDI-FDTD. Two stable and efficient formulations with different advantages are presented for introducing the far-zone plane-wave source into the FDTD problem space, namely, the scattered-field (SF) formulation and total-field / scattered field (TF/SF) formulation. To deal with the discontinuity and inconsistency across TF/SF boundaries, the fields on the boundaries need special treatments with careful modifications to ensure stability and proper plane-wave injection. Numerical results show that the incident fields can be effectively injected into the problem space with the stability of leapfrog CDI-FDTD maintained in both formulations. In addition, comparisons of radar cross sections computed using leapfrog CDI-FDTD, leapfrog ADI-FDTD and explicit FDTD with both SF and TF/SF formulations are presented. These demonstrate the advantages of leapfrog CDI-FDTD method in solving far-zone plane-wave source problems, including high efficiency, unconditional stability and complying divergence.

Full-Wave Methodology to Compute the Spontaneous Emission Rate of a Transmon Qubit

Abstract: The spontaneous emission rate (SER) is an important figure of merit for any quantum bit (qubit), as it can play a significant role in the control and decoherence of the qubit. As a result, accurately characterizing the SER for practical devices is an important step in the design of quantum information processing devices. Here, we specifically focus on the experimentally popular platform of a transmon qubit, which is a kind of superconducting circuit qubit. Despite the importance of understanding the SER of these qubits, it is often determined using approximate circuit models or is inferred from measurements on a fabricated device. To improve the accuracy of predictions in the design process, it is better to use full-wave numerical methods that can make a minimal number of approximations in the description of practical systems. In this work, we show how this can be done with a recently developed field-based description of transmon qubits coupled to an electromagnetic environment. We validate our model by computing the SER for devices similar to those found in the literature that have been well-characterized experimentally. We further cross-validate our results by comparing them to simplified lumped element circuit and transmission line models as appropriate.

Simulation of Surface Enhanced Raman Scattering From Nanoparticles With Wideband Nested Equivalence Source Approximation

Abstract: Surface Enhanced Raman Scattering (SERS) has been widely used in the fields of surface science, spectral analysis, biosensors, and biomedical detection. A wideband nested equivalent source approximation (WNESA) accelerated method of moments (MoM) of multiple material regions is proposed, for the analysis of SERS by nanostructure. The SERS affected by the diameter and distance between gold nanospheres for dimer structure is studied through numerical simulations with WNESA. It is found that nanoparticles-based SERS substrates with different dimensions and distances will produce different excitation wavelengths and SERS enhancement factors, by evaluating the variation of hot spot positions with wavelengths. The computational complexity of WNESA for SERS substrate simulation is O(N log N), where N is the number of unknowns. Significant improvement of the design efficiency of nanostructures for increasing the magnitude of SERS can be achieved.

Fourier Transform, Dirac Commutator, Energy Conservation, and Correspondence Principle for Electrical Engineers

Abstract: The canonical commutation relation is a fundamental postulate of the quantum theory regarding the operators needed in quantum description of physical observables. It is shown that the Fourier transform is derivable from this seemingly simple postulate along with the basic properties of the position and momentum operators. Further discussions on the canonical commutation relation reveal its connection to a more fundamental notion that energy must be conserved. This discussion also unveils the mathematical homomorphism between the classical and quantum theories for systems represented by sum separable Hamiltonians. Another link between the classical and quantum theories is established by the correspondence principle which states that the classical theory emerges from quantum theory in the limit of vanishingly small Planck constant. Finally, the quantum Maxwell’s equations, which have been derived in our previous works, are presented and briefly discussed, and the 3-D mode transform is derived that can be interpreted as a generalization of the Fourier transform. We present both the details and meanings of the 3-D mode transform which will serve as a foundation for a full 3-D quantum finite-difference time-domain method.

FDTD Computation of Space/Time Integrated Electromagnetic Lagrangian: New Insights Into Design of Mutually Coupled Antennas

Abstract: In this paper, we develop a formalism based on electromagnetic Lagrangian which provides new insights about the near-field reactive energy density around generic antennas for arbitrary spatio-temporal excitation signals. Using electric and magnetic fields calculated via FDTD technique and interpolation routines,we compute the EM Lagrangian density around antennas (thin-wire dipoles, Yagi-Uda Arrays and planar UWB Monopoles). Spatial maps of time-integrated EM Lagrangian density sheds light onto the capacitive/inductive nature of reactive energy density distribution around antennas and highlight its inherent connection with inter-element mutual coupling. Furthermore, we demonstrate that by minimizing the temporal fluctuations of spatially integrated EM Lagrangian density, it is possible to design MIMO antennas with wide impedance bandwidth and low mutual coupling.

Iterated Crank-Nicolson Procedure With Enhanced Absorption for Nonuniform Domains

Abstract: In multi-dimension problems, huge sparse matrices must be calculated according to Crank-Nicolson (CN) procedure which results in degeneration of efficiency and accuracy. Based on the iterated CN procedure, domain decomposition method, an alternative scheme is proposed for the termination of unbounded uniform finite-difference time-domain domains. Meanwhile, absorbing boundary condition is proposed in the iterated CN procedure which is incorporated with the higher order concept. The proposed scheme employs the explicit scheme during the calculation rather than the implicit one. Thus, the calculation of matrices can be avoided. It shows the advantages especially in efficiency and accuracy compared with implicit schemes. Such conclusion can be further demonstrated through the numerical example. From results, it can be concluded that the proposed scheme shows efficiency improvement and accurate maintenance. Compared with other procedures, it also holds its considerable effectiveness in nonuniform domains. For comparison, it can maintain considerable performance compared with the others.

The Associated Hermite FDTD Method With the Thin-Wire Modeling in Low-Frequency Cases

Abstract: To analyze the thin-wire model in low-frequency cases, the unconditionally stable Associated Hermite finite-difference time-domain (AH FDTD) method is proposed in this paper. The thin wire model combined with the AH domain operators is applied to update the coefficient matrix equation of the 3-D AH FDTD method to get the final solution. Two examples related with a dipole antenna and a Yagi antenna are set up to verify the proposed algorithm. Compared with the conventional FDTD method, the efficiency for the proposed method is enhanced by as high as a factor of 15 while keeping a sound accuracy in low-frequency cases.

A Machine Learning Generative Method for Automating Antenna Design and Optimization

Abstract: To facilitate the antenna design with the aid of computer, one of the practices in consumer electronic industry is to model and optimize antenna performances with a simplified antenna geometric scheme. The ease of handling multi-dimensional optimization problems and the less dependence on the engineers' knowledge and experience are the key to achieve the popularity of simulation-driven antenna design and optimization for the industry. In this paper, we introduce a flexible geometric scheme with the concept of mesh network that can form any arbitrary shape by connecting different nodes. For such problems with high dimensional parameters, we propose a machine learning based generative method to assist the searching of optimal solutions. It consists of discriminators and generators. The discriminators are used to predict the performance of geometric models, and the generators to create new candidates that will pass the discriminators. Moreover, an evolutionary criterion approach is proposed for further improving the efficiency of our method. Finally, not only optimal solutions can be found, but also the well trained generators can be used to automate future antenna design and optimization. For a dual resonance antenna design, our proposed method is better than the other mature algorithms.

A Machine Learning Generative Method for Automating Antenna Design and Optimization

Abstract: To facilitate the antenna design with the aid of computer, one of the practices in consumer electronic industry is to model and optimize antenna performances with a simplified antenna geometric scheme. The ease of handling multi-dimensional optimization problems and the less dependence on the engineers' knowledge and experience are the key to achieve the popularity of simulation-driven antenna design and optimization for the industry. In this paper, we introduce a flexible geometric scheme with the concept of mesh network that can form any arbitrary shape by connecting different nodes. For such problems with high dimensional parameters, we propose a machine learning based generative method to assist the searching of optimal solutions. It consists of discriminators and generators. The discriminators are used to predict the performance of geometric models, and the generators to create new candidates that will pass the discriminators. Moreover, an evolutionary criterion approach is proposed for further improving the efficiency of our method. Finally, not only optimal solutions can be found, but also the well trained generators can be used to automate future antenna design and optimization. For a dual resonance antenna design, our proposed method is better than the other mature algorithms.

Error-Controllable Scheme for the LOD-FDTD Method

Abstract: The implicit locally one-dimensional finite-difference time-domain (LOD-FDTD) method is useful for designing plasmonic devices and waveguide structures. By using a large timestep size, the implicit LOD-FDTD method can reduce the computational time; however, this involves a trade-off with accuracy. To overcome this trade-off, we propose an error-controllable scheme for the LOD-FDTD method, wherein the fast inverse Laplace transform is employed to generate the electromagnetic field in arbitrary time domain from that in complex frequency domain. Compared to the conventional LOD-FDTD method, our scheme provides higher accuracy with more efficient calculations.

Characterization of Transmission Lines in Microelectronic Circuits Using the ARTEMIS Solver

Abstract: Modeling and characterization of electromagnetic wave interactions with microelectronic devices to derive network parameters has been a widely used practice in the electronic industry. However, as these devices become increasingly miniaturized with finer-scale geometric features, computational tools must make use of manycore/GPU architectures to efficiently resolve length and time scales of interest. This has been the focus of our open-source solver, ARTEMIS (Adaptive mesh Refinement Time-domain ElectrodynaMIcs Solver), which is performant on modern GPU-based supercomputing architectures while being amenable to additional physics coupling. This work demonstrates its use for characterizing network parameters of transmission lines using established techniques. A rigorous verification and validation of the workflow is carried out, followed by its application for analyzing a transmission line on a CMOS chip designed for a photon-detector application. Simulations are performed for millions of timesteps on state-of-the-art GPU resources to resolve nanoscale features at gigahertz frequencies. The network parameters are used to obtain phase delay and characteristic impedance that serve as inputs to SPICE models. The code is demonstrated to exhibit ideal weak scaling efficiency up to 1024 GPUs and 84% efficiency for 2048 GPUs, which underscores its use for network analysis of larger, more complex circuit devices in the future.

Modeling of Resonant Tunneling Diode Oscillators Based on the Time-Domain Boundary Element Method

Abstract: We demonstrate how the coupling of a full-wave time-domain boundary element method (BEM) solver with a circuit solver can be used to model 1) the generation of high frequency oscillations in resonant tunneling diode (RTD) oscillators, and 2) the mutual coupling and synchronization of non-identical RTDs with significant differences in frequencies to achieve coherent power combination. Numerical simulations show a combined output power of up to 3.7 times a single oscillator in synchronized devices. The non-differential conductance of the RTD is modeled as a lumped component with a non-linear current-voltage relationship. The lumped element is coupled to the radiating structure using a finite-gap model in a consistent and discretisation independent manner. The resulting circuit equations are solved simultaneously and consistently with time-domain electric field integral equations that model the transient scattering of electromagnetic (EM) fields from conducting surfaces that make up the device. This paper introduces three novel elements: (i) the application of a mesh independent feed line to the modelling of feed lines of RTD devices, (ii) the coupling of the radiating system to a strongly non-linear component with negative differential resistance, and (iii) the verification of this model with circuit models where applicable and against the experimental observation of synchronisation when two RTDs are placed in close proximity. These three elements provide a methodology that create the capacity to model RTD sources and related technology.

Physics-Based Automatic Recognition of Small Features Located in Highly Similar Structures With Electromagnetic Scattering Data

Abstract: A physics-based automatic target recognition (ATR) technique is developed to accurately identify small features located in highly similar structures with electromagnetic (EM) scattering data. Automatic target recognition is important due to its widely practical applications. The traditional ATR is usually based on images produced from EM scattering data and sophisticated algorithms. Wideband angular and frequency sweeps are necessary to generate sufficient EM scattering data to produce images with high resolution for the imagery-based ATR to obtain correct recognition results, especially for multiscale structures with small local features. These seriously limit the efficiency of the imagery-based ATR and its practicability. To implement ATR more efficiently, we turn to the physics-based ATR and employ principal component analysis (PCA). The physics-based ATR with PCA can exactly classify objects of different types with one-frequency scattering data and avoid expensive frequency sweeps. However, the pre-existing average feature center (AFC) criterion model for PCA in the literature can only distinguish objects with significant differences and fails to recognize small features located in highly similar structures. Hence, an improved classification criterion for PCA is proposed to precisely identify highly similar structures with different small features. Some numerical examples illustrate the satisfactory performance of the proposed technique.

Physics-Based Automatic Recognition of Small Features Located in Highly Similar Structures With Electromagnetic Scattering Data

Abstract: A physics-based automatic target recognition (ATR) technique is developed to accurately identify small features located in highly similar structures with electromagnetic (EM) scattering data. Automatic target recognition is important due to its widely practical applications. The traditional ATR is usually based on images produced from EM scattering data and sophisticated algorithms. Wideband angular and frequency sweeps are necessary to generate sufficient EM scattering data to produce images with high resolution for the imagery-based ATR to obtain correct recognition results, especially for multiscale structures with small local features. These seriously limit the efficiency of the imagery-based ATR and its practicability. To implement ATR more efficiently, we turn to the physics-based ATR and employ principal component analysis (PCA). The physics-based ATR with PCA can exactly classify objects of different types with one-frequency scattering data and avoid expensive frequency sweeps. However, the pre-existing average feature center (AFC) criterion model for PCA in the literature can only distinguish objects with significant differences and fails to recognize small features located in highly similar structures. Hence, an improved classification criterion for PCA is proposed to precisely identify highly similar structures with different small features. Some numerical examples illustrate the satisfactory performance of the proposed technique.

Computational Techniques for Design and Analysis of Time-Varying Capacitor Loaded Transmission Lines Using FDTD and Simulink

Abstract: In this paper, MATLAB based computational approaches for the design and analysis of time-varying capacitor- loaded transmission lines using the finite-difference time-domain (FDTD) technique and the Simulink design environment are presented. The FDTD formulation for multiple lumped capacitors loaded in series on a transmission line is discussed and extended to include time variation of capacitance. The design methodology for the same is also discussed using MATLAB's Simulink using the RF Blockset Library. The developed FDTD formulation and the Simulink method are then used to design a mixer with time-varying capacitors loaded transmission line.

Direct Computation of the PEC Body of Revolution Modal Green Function for the Electric Field Integral Equation

Abstract: We propose a five-term recurrence relation for the direct computation of the modal Green function (MGF) arising in the electric field integral equations (EFIE), when solving the scattering of PEC bodies of revolution. It is shown that, by considering it as an infinite penta-diagonal matrix, the proposed five-term recurrence relation can be solved in a stable manner in $O(M)$ steps for $M$ modes with high and controllable accuracy. By evaluating the performance of the proposed five-term recurrence relation for several scatterers of different geometries, we show that the proposed approach enables an accurate computation with a simple algorithm.

FDTD Method With Explicit Non-Iterative and Second Order Treatment for Kerr Nonlinearities

Abstract: The finite-difference time-domain (FDTD) method is a very popular numerical method used to solve Maxwell's equations in various types of materials, including those with nonlinear properties. When solving the nonlinear constitutive equation that models Kerr media, Newton's iterative method is accurate but computationally expensive, while the conventional explicit non-iterative method is less expensive but not very accurate. In this work, we propose a new explicit non-iterative algorithm to solve the Kerr nonlinear constitutive equation that achieves a quadratic convergence rate. This method attains a similar accuracy to Newton's method but does with a significant reduction in computational cost. To demonstrate the accuracy and efficiency of our method, we provide several numerical examples, including the simulations of four-wave mixing and soliton propagation in one and two dimensions.

Analysis of Sound Propagation Across Acoustic Ducts With Discontinuities Using a High Precision Finite Element Method

Abstract: A high-precision numerical method is presented to model acoustic wave propagation along a duct with discontinuities. The discontinuous duct can be divided into homogeneous and inhomogeneous substructures. The inhomogeneous substructures are purely discretized by the conventional finite element method, while only cross-sectional areas need to be discretized for homogeneous substructures. The Legendre transformation is then used to transform the semi-discretized problem from the Lagrangian system into the Hamiltonian system. A Riccati equation-based high precision integration method is taken to perform the integral along the longitudinal direction, i.e., the homogeneous direction, to generate stiffness matrices of substructures. The final system stiffness matrix is obtained by assembling stiffness matrices of homogeneous substructures with stiffness matrices of inhomogeneous substructures. Numerical examples are provided to validate the proposed method, and these examples have shown high efficiency and accuracy compared with the conventional finite element method.

Exact Solution of New Magnetic Current Based Surface-Volume-Surface EFIE and Analysis of Its Spectral Properties

Abstract: A novel magnetic current based Surface-Volume-Surface Electric Field Integral Equation (SVS-EFIE-M) is presented for the problem of scattering on homogeneous non-magnetic dielectric objects. The exact Galerkin Method of Moments (MoM) utilizing both the rotational and irrotational vector spherical harmonics as orthogonal basis and test functions according to the Helmholtz decomposition is implemented to solve SVS-EFIE-M analytically for the case of dielectric sphere excited by an electric dipole. The field throughout the sphere is evaluated and compared against the exact classical Mie series solution. The two are shown to agree to 12 digits of accuracy upon a sufficient number of basis/test functions taken in the MoM solution and the Mie series expansion. This exact solution validates the rigorous nature of the new SVS-EFIE-M formulation. It also reveals the spectral properties of its individual operators, their products and their linear combination. The spectrum of the MoM impedance matrix is also obtained. It is shown that upon choosing basis and test functions in $L^{2}(S)$ space and evaluating testing inner products in the same space, the MoM impedance matrix features bounded condition number with increasing order of discretization and/or at low frequencies. This makes the proposed SVS-EFIE-M formulation free of oversampling and low-frequency breakdowns giving it advantage both over its SVS-EFIE-J predecessor and classical double-source integral equations such as PMCHWT, Muller, and others suffering from this type of numerical instabilities inherent to their inferior spectral properties.

Manifold Harmonics and Their Application to Computational Electromagnetics

Abstract: The eigenfunctions of the Laplace-Beltrami operator (LBO), or manifold harmonic basis (MHB), have many applications in mathematical physics, differential geometry, machine learning, and topological data analysis. MHB allows us to associate a frequency spectrum to a function on a manifold, analogous to the Fourier decomposition. This insight can be used to build a framework for analysis. The purpose of this paper is to review and illustrate such possibilities for computational electromagnetics as well as chart a potential path forward. To this end, we introduce three features of MHB: (a) enrichment for analysis of multiply connected domains, (b) local enrichment (L-MHB) and (c) hierarchical MHB (H-MHB) for reuse of data from coarser to fine geometry discretizations. Several results highlighting the efficacy of these methods are presented.

A Stable Weighted Residual Finite Element Formulation for the Simulation of Linear Moving Conductor Problems

Abstract: The finite element method is one of the widely employed numerical techniques in electrical engineering for the study of electric and magnetic fields. When applied to the moving conductor problems, the finite element method is known to have numerical oscillations in the solution. To resolve this, the upwinding techniques, which are developed for the transport equation are borrowed and directly employed for the magnetic induction equation. In this work, an alternative weighted residual formulation is explored for the simulation of the linear moving conductor problems. The formulation is parameter-free and the stability of the formulation is analytically studied for the 1D version of the moving conductor problem. Then the rate of convergence and the accuracy are illustrated with the help of several test cases in 1D as well as 2D. Subsequently, the stability of the formulation is demonstrated with a 3D moving conductor simulation.

Variability in Specific Absorption Rate From Variation in Tissue Properties

Abstract: This study evaluates the variance of specific absorption rate (SAR) due to expected variance in the dielectric properties of tissues in a 3D anatomical human head model exposed to a half-wave dipole antenna at 835 and 1900 MHz. Stochastic finite difference time domain (S-FDTD) is applied to calculate variations in the local SAR, and the 1- and 10-gram averaged SAR values. These are also compared at 835 MHz to variations found from Monte Carlo FDTD. It is found that for both frequencies dielectric property variance results in a variance of peak 1- or 10-gram SAR of approximately 30% to 55% of the mean SAR, depending on the frequency. These results show that to reach 95% confidence with the calculated SAR values for evaluating exposure guidelines, statistical variations in tissue electrical properties must be taken into account.

Efficient Numerical Evaluation of Singular Integrals in Volume Integral Equations

Abstract: We present a method for the numerical evaluation of 6D and 5D singular integrals appearing in Volume Integral Equations. It is an extension of the Sauter-Schwab/Taylor-Duffy strategy for singular triangle-triangle interaction integrals to singular tetrahedron-tetrahedron and triangle-tetrahedron interaction integrals. The general advantages of these kind of quadrature strategy is that they allow the use of different kinds of kernel and basis functions. They also work on curvilinear domains. They are all based on relative coordinates tranformation and splitting the integration domain into subdomains for which quadrature rules can be constructed. We show how to build these tensor-product quadrature rules in 6D and 5D and further show how to improve their efficiency by using quadrature rules defined over 2D, 3D and 4D simplices. Compared to the existing approach, which computes the integral over the subdomains as a sequence of 1D integrations, significant speedup can be achieved. The accuracy and convergence properties of the method are demonstrated by numerical experiments for 5D and 6D singular integrals. Additionally, we applied the new quadrature approach to the triangle-triangle interaction integrals appearing in Surface Integral Equations.

A Hybrid EM/QM Framework Based on the ADHIE-FDTD Method for the Modeling of Nanowires

Abstract: A new modeling formalism to compute the time-dependent behavior of combined electromagnetic (EM) and quantum mechanical (QM) systems is proposed. The method is geared towards highly multiscale geometries, which is vital for the future design of nanoelectronic devices. The advocated multiphysics modeling formalism leverages the alternating-direction hybrid implicit-explicit (ADHIE) finite-difference time-domain (FDTD) method for the EM fields and is combined with a novel ADHIE method for the EM potentials. Additionally, we tackle the QM problem using a new split real and imaginary part formulation that includes higher-order spatial differences and arbitrary time-dependent EM potentials. The validity of the proposed formalism is theoretically discussed by deriving its stability condition and calculating the numerical dispersion relation. Furthermore, the applicability of our modeling approach is proven through several numerical experiments, including a single-particle Maxwell-Schrödinger (MS) system as well as a many-particle Maxwell-Kohn-Sham (MKS) system within the time-dependent density-functional theory (TDDFT) framework. These experiments confirm that the novel ADHIE method drastically decreases the computation time while retaining the accuracy, leading to efficient and accurate simulations of light-matter interactions in multiscale nanoelectronic devices.

Numerical Simulation and Experiment for the Bottom Boundary of Riprap of Seawall by GPR

Abstract: Seawall engineering is essential in preventing typhoon storm surge disasters in coastal areas. Usually, the engineering measure of throwing the stone to form a riprap layer is adopted to enhance seawall stability and anti-erosion property. Determining the thickness of the riprap layer is an essential step in the evaluation of engineering measurement, and the key is to determine the burial depth of the bottom boundary of the riprap. A seawall is taken as the research object. The propagation process of the electromagnetic wave in the seawall is simulated by the finite difference time domain (FDTD) method, the propagation law and profile response characteristics of the electromagnetic wave are obtained, and the method's feasibility is confirmed theoretically. Further field test and drilling detection results are used to calibrate the electromagnetic wave velocity, and the top and bottom interface of the riprap layer is divided, which provides a basis for the measurement of the riprap body.

Estimating Fields in Spacecraft Cavities: Experimental Validation and Optimization of Finite-Difference Time-Domain and Power Balance Computational Tools

Abstract: Electromagnetic fields in representative spacecraft cavities were successfully predicted using finite-difference time-domain and power balance computational tools. Results were validated with measurements of two test articles, showing excellent correlation in shielding effectiveness from 300 MHz to 18 GHz. The validated tools were then extended to predict fields inside representative, to-scale payload fairings including common systems and components like satellite payloads, antennas, acoustic blankets, and a cable harness. Various computational techniques were used to compare their speed and accuracy. Ultimately, we conclude that a multi-fidelity approach – combining full-wave, statistical, and hybrid solutions – is beneficial and necessary for complex and large cavity problems. The tools and techniques presented here can serve as part of a toolkit to rapidly estimate shielding effectiveness, the impact of payloads, and overall fields in spacecraft cavities.

Dome-Shaped mmWave Lens Antenna Optimization for Wide-Angle Scanning and Scan Loss Mitigation Using Geometric Optics and Multiple Scattering

Abstract: This paper presents a new accurate and efficient design methodology for complex integrated lens antenna (ILA), to achieve wide-angle beam coverage with scan loss mitigation at the millimeter-wave (mmWave) spectrum. The proposed ILA comprises inhomogeneous curvatures with internal and external center off-sets, in which multiple parameters instigate high order and non-linear behaviors. A two-dimensional (2-D) ray-tracing model is used to estimate the refractions on the elliptically curved boundaries based on geometrical optics. This approach is integrated into the particle swarm optimization of the 2-D ray-tracing model to determine the near-optimum geometric configuration of the ILA. Denoted as Geometric Optics-based Multiple Scattering (GOMS), the computational memory usage is reduced by a factor of 10,000 using this approach. The devised ILA achieves a wide-angle beam coverage of 156° with a scan loss of 2.10 dB alongside a broad impedance bandwidth of 35.0 GHz to 42.0 GHz. The measurement results for the performance of the fabricated prototype of the ILA validate the wide-angle scanning with scan loss mitigation inferred from the simulation results. This confirms the effectiveness of this method for complex design challenges involving multi-variants and restricted computational resources.

Space-Mapping Based Automatic Design of SIW-Based Directional Coupler With Arbitrary Power Ratio

Abstract: In this paper, an automatic design method allowing efficient design of substrate integrated waveguide (SIW) directional coupler with any given power ratio between 3 dB and 20 dB has been proposed. Due to excessive electromagnetic (EM) simulation time of SIW structure, the space mapping technique is exploited to accelerate the design process. An EM-simulation based dielectric rectangular waveguide (RWG) model acts as the surrogate to reduce the simulation time. A two-stage optimization scheme including a differential evolution (DE) algorithm and a Nelder-Mead (NM) simplex algorithm is used to obtain initial surrogate design. Suitable objective functions are proposed for surrogate optimization and for parameter extraction procedure of space mapping technique. Our proposed method is verified with an X band SIW directional coupler with four different power ratio designs, which are 3dB, 10dB, 15dB and 20dB. The experimental results confirm the effectiveness and efficiency of the method.