Search

This contribution introduces a novel method for constructing mass matrices for general tetrahedral elements. By considering the construction of the reluctivity mass matrix as an example, a new derivation of a recipe to geometrically construct a symmetric positive semi-definite and consistent mass matrix is provided. It is shown why such a matrix can be used inside formulations where the mass matrix is right multiplied by the appropriate incidence matrix. Then, a second recipe is introduced to produce a consistent and symmetric positive definite matrix. The proposed method is based on an original algebraic technique that differs fundamentally from what is available in the literature. The proposed recipe opens also the possibility to improve the conditioning of the resulting elementary mass matrices. [ABSTRACT FROM AUTHOR]

In this paper, we apply for the first time the nonlinear-embedding technique to the design of power amplifiers (PAs) based on laterally-diffused metal-oxide-semiconductor (LDMOS) field-effect transistors. Such a design technique is based on setting the transistor load line at the intrinsic current-generator plane, according to well-known theoretical guidelines. Then, the selected operating condition can be transposed at any design frequency at the extrinsic transistor terminals, by means of a model of the device nonidealities, such as the nonlinear intrinsic capacitances and the linear parasitic effects. A harmonically-tuned high-efficiency class-F and a wideband class-AB PAs operating within the FM broadcasting band 88 ÷ 108 MHz based on a 10-W LDMOS are then designed and realized. To definitely assess the validity of the proposed approach for the LDMOS technology, we compare the measured performance on the fabricated PAs with the expected predictions. [ABSTRACT FROM AUTHOR]

A fundamental extension for a recently introduced numerical scheme for the time-domain solution of Maxwell’s equations on tetrahedral meshes is introduced: the algorithm is here shown to be able to handle materials with finite electric resistivity, without losing any of its amenable properties. A theoretic stability analysis, valid for the extended algorithm, is presented for the first time, and a Courant–Friedrich–Lewy sufficient condition on the maximum time step allowed for the scheme to be stable is derived analytically. This result is completely novel for finite-difference time-domain (FDTD)-like approaches on tetrahedral grids. Finally, the accuracy of the extended algorithm is tested with respect to the well-known implicit finite-element method scheme on tetrahedral grids, to the canonical FDTD scheme on Cartesian orthogonal grids, and to a commercial code implementing FDTD with staircasing mitigation techniques. [ABSTRACT FROM AUTHOR]

A recently introduced time-domain method for the numerical solution of Maxwell’s equations on unstructured grids is reformulated in a novel way, with the aim of implementation on graphical processing units (GPUs). Numerical tests show that the GPU implementation of the resulting scheme yields correct results, while also offering an order of magnitude in speedup and still preserving all of the main properties of the original finite-difference time-domain algorithm. [ABSTRACT FROM AUTHOR]

The frequency-domain wave propagation problem is notoriously difficult to solve through iterative methods because it leads to a symmetric but indefinite linear system. For this reason, direct methods are usually employed at the expense of great memory usage. Convergence of iterative methods, however, could be obtained by regularizing the wave equation. We introduce such regularization in discrete geometric approach framework on polyhedral grids. Moreover, we extend the regularization to the impedance boundary condition. [ABSTRACT FROM AUTHOR]

We present a numerical method named mixed high order (MHO) to obtain high order of convergence for electrostatic problems solved on general polyhedral meshes. The method, based on high-order local reconstructions of differential operators from face and cell degrees of freedom, exhibits a moderate computational cost thanks to hybridization and static condensation that eliminate cell unknowns. After surveying the method, we assess its effectiveness for 3-D problems by comparing, for the first time in literature, its performances with classical conforming finite elements. Moreover, we emphasize the algebraic equivalence of MHO in the lowest order with the analog formulation obtained with the discrete geometric approach or the finite-integration technique. [ABSTRACT FROM AUTHOR]

This paper first introduces a simplified construction of the constitutive matrices for general polyhedral meshes. These constitutive matrices are geometrically defined by means of simple closed-form expressions involving the geometric elements of the primal and dual meshes. Then, we solve for the first time the Maxwell’s eigenvalue problem on general polyhedral meshes. In particular, we analyze the convergence of the eigenvalues when the mesh is adaptively refined by using the subgridding technique together with the constitutive inconsistency as error indicator. [ABSTRACT FROM AUTHOR]

Numerical simulation of anechoic chambers is an important topic nowadays, since it can provide useful data about the performance of an electromagnetic compatibility site. However, the mathematical nature of the problem, the physical dimensions of the simulated sites, and the frequency ranges pose nontrivial challenges to the numerical simulation. Computational requirements, in particular, will quickly become unmanageable if adequate techniques are not employed. In this paper, we describe a novel approach, based on equivalent elements, that enables the simulation of large chambers with modest computational resources. The method is then validated against 558 real measurement results. [ABSTRACT FROM AUTHOR]

This paper presents a general technique to apply excitations in the framework of discrete geometric numerical methods using dual grids, such as discrete geometric approach and finite integration technique. The technique overcomes some limitations of the impedance boundary condition we proposed in a previous work, especially when dealing with waveguides, where specific excitation modes must be applied. The proposed approach is based on a scattering/total field decomposition, which, if needed, allows to study scatterings due to objects. [ABSTRACT FROM AUTHOR]

An electromagnetic wave propagation problem can be formulated according to a pair of complementary formulations, called the e -formulation and the h -formulation. The two formulations are linked to each other by Maxwell’s curl equations, and, in the continuous setting, they are perfectly equivalent in describing the wave propagation phenomenon. However, this is not true in the discrete setting, where the two formulations, in general, give different solutions. In the past decades, complementary formulations were widely studied for static problems and eddy-current problems, where they were exploited as error estimators for adaptive refinement schemes. Moreover, the so-called bilateral energy bounds arise for some problems whether theoretically or at least numerically. However, to the best of our knowledge, little attention has been given to complementarity in the wave propagation problems. In this paper, we propose an adaptive refinement scheme using the constitutive error as an estimator, and then, we investigate the behavior in terms of bilateral energy bounds. [ABSTRACT FROM AUTHOR]

This paper presents how a plane wave excitation could be modeled in the context of the discrete geometric approach (DGA) by means of an impedance boundary condition, a capability that DGA was lacking. A methodology for the construction of an equivalent model of an anechoic wall is then presented as an application of the developed theory. The advantages of the resulting model are twofold: considering all the geometric details of the anechoic material requires more computational resources; in addition when an entire anechoic chamber is to be modeled, it is easier to deal with a flat wall rather than one covered with cones and ferrite tiles. The proposed equivalent model allows for a great simplification, while maintaining a good degree of accuracy. [ABSTRACT FROM PUBLISHER]

The numerical modeling of nanoscale electron devices needs the development of accurate and efficient numerical methods, in particular, for the numerical solution of the Schrödinger problem. If FEMs allow an accurate geometric representation of the device, they lead to a discrete counterpart of Schrödinger problem in terms of a computationally heavy generalized eigenvalue problem. Exploiting the geometric structure behind the Schrödinger problem, we will construct a numerically efficient discrete counterpart of it, yielding to a standard eigenvalue problem. We will also show how the two approaches are only partially akin to each other even when lumping is applied. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a novel inversion technique to measure the volume of thrombus induced under blood flow conditions in a lab-on-a-chip device. The device is composed by a microscope slide where gold electrodes are sputtered and by a polydimethylsiloxane microchannel placed on the top of the slide. A thrombogenic substance is placed on the slide in such a way that hemostasis is induced when whole blood flows in the microchannel. The novel idea behind the inversion technique is to fuse optical and electrical impedance data to obtain a quasi-real-time reconstruction of thrombus volume. This is not possible with present state-of-the-art optical imaging based on confocal microscopy, which provides the thrombus volume estimation only at the end of the thrombus formation. [ABSTRACT FROM AUTHOR]

This paper presents a novel discrete model for cell membranes and electrodes contact impedances alternative to the widely used finite elements. The finite element approach can be considered as a tool for constructing finite dimensional systems of equations that approximate the specific electroquasistatic biological problem on the discrete level. Although the finite element technique is explained typically in terms of variational or weighted-residual approaches, another, less familiar way is available to reformulate geometrically the same physical problem. This approach, referred to as discrete geometric approach, allows a direct link between geometry and the degrees of freedom describing the specific biological problem. It is straightforward to implement in any finite element open software and it assures a correct modeling of voltages and currents playing a fundamental role in a biological problem. The validation has been performed, as a first step, against analytical solutions; then, we considered impedance measurements regarding erythrocytes in whole blood flowing in microchannels at high shear rates. [ABSTRACT FROM PUBLISHER]

This paper aims at comparing the pseudospectral method and discrete geometric approach for modeling quantization effects in nanoscale devices. To this purpose, we implemented a simulation tool, based on both methods, to solve a self-consistent Schrödinger–Poisson coupled problem for a 2-D electron carrier confinement according to the effective mass approximation model (suitable for FinFETs and nanowire FETs). [ABSTRACT FROM PUBLISHER]

A numerical model of the cathode of a proton-exchange membrane fuel cell (PEMFC) based on the discrete geometric approach is presented. The current density distribution inside a PEMFC cathode is simulated. The discrete formulation of a steady-state conduction problem in nonisotropic media is coupled to nonlinear boundary conditions representing the charge transfer at catalyst layers. The cathode performance is assessed under different load conditions by assuming a constant voltage operation mode. Results are in good agreement with those presented in the literature. [ABSTRACT FROM PUBLISHER]

The aim of the paper is to present an automatic and general technique, suitable with the A-X geometric eddy-current formulation, to impose sources over massive conductors of any shape. For this purpose, the localized source approach is used, which does not require the solutions of steady-state conduction problems in the preprocessing stage. Nevertheless, this approach needs a thick cut in each active conductor, which is usually found "by hand." In this paper, an automatic and general algorithm to compute such thick cuts is introduced. Some benchmark problems are presented to demonstrate the generality and the robustness of the algorithm. [ABSTRACT FROM AUTHOR]

A perturbation method for the T - Ω geometric formulation to solve eddy-current problems is introduced. The proposed formulation is applied to the feasibility design of a nondestructive evaluation device suitable to detect "long" longitudinal flaws in hot steel bars. [ABSTRACT FROM AUTHOR]

As a first step, we will investigate the extent of the consistency error for a hexahedral primal grid due to the use mass matrices of finite elements within the discrete geometric approach (DGA) as discrete counterparts of the constitutive relations. Such matrices are constructed by resorting to mixed elements edge and face vector functions. Then, we will propose a novel set of geometric vector basis functions for hexahedra that guarantee consistency and stability of the constitutive matrices for the DGA constructed according to the so-called energetic approach. [ABSTRACT FROM AUTHOR]

The aim of this paper is to present a 3-D time-domain eddy-current A formulation based on the discrete geometric approach (DGA) over unstructured and nonorthogonal hexahedral dual grids. The resulting differential algebraic system of equation, solved by means of a singly-diagonally implicit Runge-Kutta (SDIRK) variable step-size solver, leads to very accurate results at reduced computational costs, as shown by numerical analysis. [ABSTRACT FROM AUTHOR]

The aim of this paper is to introduce a Discrete Geometric Approach to solving 2-D non-linear magnetostatic problems. In particular, an efficient algorithm will be presented to solve magnetostatics in isotropic non-linear media by means of a Newton-Raphson scheme, in which the Jacobian is calculated analytically. Results on a reference configuration (TEAM Workshop Problem 25) are reported and discussed. [ABSTRACT FROM AUTHOR]

We propose a discrete geometric formulation based on a magnetic scalar potential and on the circulation of an electric vector potential to solve eddy-current problems for nondestructive evaluation of steel bars with longitudinal defects. [ABSTRACT FROM AUTHOR]

We examine the construction of reluctivity and Ohm's constitutive matrices for discrete geometric approaches using nonregular hexa-hedra as primal volumes. The effect of element deformation on the representation of uniform fields have been investigated for static fields. Then convergence and accuracy of the proposed matrices has been carried out using an eddy-current problem as working example. [ABSTRACT FROM AUTHOR]

We propose a geometric reinterpretation of the Nodal Force Method in the framework of a pair of discrete formulations for magneto- statics on complementary meshes. [ABSTRACT FROM AUTHOR]

We examine the construction of a symmetric positive definite conductance matrix for eddy-current problems, using a discrete approach. We construct a new set of piecewise uniform basis vector functions on both the primal and the dual complex. We define these vector functions for both tetrahedra and prisms. [ABSTRACT FROM AUTHOR]

Using a geometric formulation for eddy currents, we present a geometric approach to constructing approximations of the discrete magnetic and Ohm's constitutive matrices. In the case of Ohm's matrix, we also show how to make it symmetric. We compared the impact on the solution of the proposed Ohm's matrices, and an iterative technique to obtain a consistent right-hand-side term in the final system is described. [ABSTRACT FROM AUTHOR]

The paper deals with the electromagnetic analysis of the superconducting multistrand cables used to manufacture magnets for fusion research. An analysis method is described, in which the cable is represented as an equivalent lumped network, whose parameters are automatically computed starting from the cable geometrical data. The network is then solved in transient regime. [ABSTRACT FROM AUTHOR]

Deals with a study which presented the solution of a three-dimensional magnetostatic problem using the finite formulation of an electromagnetic field. Background on finite formulation and space discretization; Constitutive equation; Magnetostatic formulations; Numerical experiments and discussion; Conclusion.

Deals with a study which applied the finite formulation method to the solution of plane electrostatic problems on triangular and quadrilateral primal mesh elements. Information on global variables in finite formulation; Electric constitutive equation; Numerical results and discussion; Conclusion.

Focuses on a study which described an approach to plasma magnetic boundary identification in tokamak reactors. Discussion on the reconstruction of the plasma magnetic contour as a discrete identification problem; Description of magnetic measurements; Integration of the linear algebraic and differential equations; Analysis of results.

Deals with the application of the Genetic Algorithms (GA) to solve the inverse problem of the synthesis of the magnetic configuration for Magnetic Resonance Imaging. Description of the Genetic Algorithms; Details on the synthesis problem; Results of the application of the GA; Sensitivity analysis; Conclusions.

Provides information on a study which examined a method for the identification of plasma magnetic contour in machines for fusion research using magnetic measurements. Description of the identification problem; Application and results; Conclusions.