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This paper focuses on the characterization of radio propagation, and data communication in a marine environment. More specifically, we consider signal propagation when three different sub-gigahertz industrial, scientific, and medical (ISM) bands, i.e., 169 MHz, 434 MHz, and 868 MHz, are used. The main focus of the paper is to evaluate the path loss (PL), i.e., the power loss that a propagation radio wave would experience when communication occurs between a sail boat and a buoy. We describe the measurement results obtained performing three different radio power measurement campaigns, at the three different aforementioned ISM sub-gigahertz bands. We also want to correlate the radio propagation quality with the weather conditions present in the measurement areas. The obtained results show that higher distances are achieved by transmitting at lower frequencies, i.e., 169 MHz, and, on average, the propagation is directly dependent from the dew point index. [ABSTRACT FROM AUTHOR]

This article presents a theoretical study of an absolute, ratiometric inductive position sensor (IPS) based on eddy currents. The aim is to describe the working principle of the sensor, having as key components a transmitting coil, the receiving coils, and the conductive target, by introducing area-of-overlap functions. We show that each target–receiver pair needs the adoption of a different reconstruction formula for the identification of the target position, whereas in the literature the usual inverse tangent function is applied for every possible pair. Then, we seek the target–receiver pair that maximizes the amplitude of the induced voltages on the receivers. The results show that to achieve the maximum value of the induced voltages, the best choice is to have a rectangular target and rectangular receivers. To verify the theory, a simulation and optimization method has been applied to the rectangular receiver coils on two rotary IPS realized with printed circuit board (PCB) technology. Measurements performed on the prototypes have shown an increment of the induced voltage of more than 57% with respect to the commonly used sinusoidal receivers. However, a linearity error of 1.5%FS is obtained by using the inverse tangent reconstruction formula. When using the formula provided by the theory, the linearity error becomes 0.6%FS for the nonoptimized prototype and below 0.15%FS for the optimized one. [ABSTRACT FROM AUTHOR]

In this work, the solution to the eddy current problem for slowly moving conductors is investigated with the volume integral formulation of the electric field integral equation (EFIE). On the one hand, the formulation gives the possibility to mesh only the conductors; on the other hand, the inductance matrix is fully populated, thus limiting the size of the problem. Furthermore, the standard solution implies the reassembling of the stiffness matrix for each position assumed by the moving conductors. This results in a limit in the size of the problem to treat and a relevant cost in the computation time. To overcome this limit, in this work, the mutual coupling part of the system with two conductors is computed on the fly, thus giving the possibility to solve problems with a higher number of unknowns. Finally, to speed up the solution of the system, the Gauss–Seidel (GS) iterative techniques and the fast multipole method (FMM) are applied to take into account the mutual effects between the conductors. A comparison of the proposed method with a reference one shows the effectiveness of this technique. [ABSTRACT FROM AUTHOR]

This paper introduces a novel methodology to optimize the design of a ratiometric rotary inductive position sensor (IPS) fabricated in printed circuit board (PCB) technology. The optimization aims at reducing the linearity error of the sensor and amplitude mismatch between the voltages on the two receiving (RX) coils. Distinct from other optimization techniques proposed in the literature, the sensor footprint and the target geometry are considered as a non-modifiable input. This is motivated by the fact that, for sensor replacement purposes, the target has to fit a predefined space. For this reason, the original optimization technique proposed in this paper modifies the shape of the RX coils to reproduce theoretical coil voltages as much as possible. The optimized RX shape was obtained by means of a non-linear least-square solver, whereas the electromagnetic simulation of the sensor is performed with an original surface integral method, which are orders of magnitude faster than commercial software based on finite elements. Comparisons between simulations and measurements performed on different prototypes of an absolute rotary sensor show the effectiveness of the optimization tool. The optimized sensors exhibit a linearity error below 0.1% of the full scale (FS) without any signal calibration or post-processing manipulation. [ABSTRACT FROM AUTHOR]

We examine the construction of reluctivity and Ohm's constitutive matrices for discrete geometric approaches using nonregular hexahedra 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. Index Terms--Constitutive matrices, discrete geometric approaches, eddy-currents.

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. Index Terms--Discrete formulations, eddy-currents, nondestructive evaluations.

We propose a geometric reinterpretation of the Nodal Force Method in the framework of a pair of discrete formulations for magnetostatics on complementary meshes. Index Terms--Discrete approaches, forces, magnetostatics.

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. Index Terms--Cell method, constitutive matrices, discrete approaches, eddy currents.

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. Index Terms--Cell complexes, cell method, constitutive matrices, eddy currents.

The aim of this article is to describe and model a sawtooth crash in RFX-mod2 and compute the eddy currents induced in the stabilizing shell surrounding the plasma for two alternative gap concepts and the subsequent error field. The sawtooth crash displacement of the plasma column is represented by a vacuum model coupled with a suitable magneto-quasi-static (MQS) volume integral (VI) formulation. [ABSTRACT FROM AUTHOR]

Magic formulas are the geometric identities at the root of modern compatible schemes for polyhedral grids. We present rigorous yet elementary proofs of the magic formulas originating from Stokes theorem. The proofs enlighten new fundamental aspects of the mass matrices produced with the magic formulas. First, the construction of the mass matrices works for an unexpectedly broad type of mesh cells. Second, they show that dual nodes can be arbitrarily positioned thus extending the construction of the dual barycentric grid. [ABSTRACT FROM AUTHOR]

This contribution addresses the exploitation of mirror symmetry (formally, the abelian D1 and D2 dihedral symmetry groups) in various integral formulations for eddy current problems. The novelty of the contribution is in particular how to rigorously treat non-simply-connected conductors when computing the first cohomology group generators on the symmetry cell of the problem only. [ABSTRACT FROM AUTHOR]

In this work, a surface current plasma model is coupled to a volume integral formulation for studying the interaction between tokamak tearing modes (TMs) and the machine metallic structures surrounding the plasma. By evaluating the passive response on a set of pickup probes, TMs’ amplitude is estimated. [ABSTRACT FROM AUTHOR]

This contribution addresses the solution of eddy-current problems by means of a volume integral formulation based on the electric vector potential on a computational domain that exhibits a cyclic symmetry. Even if grids discretizing the domain are typically composed of tetrahedral or hexahedral elements, the proposed approach also works for general polyhedral meshes, such as those ones obtained by subgridding. In this article, an algorithm to compute a set of suitable cohomology generators needed when the conductors are not simply connected is introduced first. Besides being purely combinatorial, with linear-time worst case complexity and suitable with polyhedral meshes, it reuses a code that computes generators for triangular surface meshes, with obvious advantages concerning the implementation effort. Second, the formulation and the algorithm for cohomology computation are tweaked to be able to solve eddy-current problems with cyclic symmetry reserving specific attention to the construction of suitable tree–cotree decomposition for the problem gauging. [ABSTRACT FROM AUTHOR]

The cell method (CM) or discrete geometric approach (DGA) in the time domain, already introduced by Codecasa et al. in 2008 for the coupled Ampere–Maxwell and Faraday equations, is here recast as a Galerkin Method similar to the finite-element method (FEM). In particular, it is shown to be a mixed method comprising an explicit scheme and two discontinuous Galerkin (DG) FEM spaces formulated on dual meshes, in which each of the two function spaces provides a continuous numerical flux choice for its dual mesh counterpart. The implemented version is shown to compare favorably in terms of accuracy and efficiency with respect to the classic conforming FEM scheme using Whitney elements. When tested on the same tetrahedral mesh, the Courant–Friedrichs–Lewy (CFL) condition for the proposed approach is a factor of 2 less restrictive on the time step with respect to the curl-conforming FEM scheme. [ABSTRACT FROM AUTHOR]

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]

There are two ways of solving eddy current problems with an edge element $h$ -conforming formulation in the case of non-simply-connected conductors: first employs a “fake” artificial conductivity in part of the insulator. Second uses the cohomology theory to define a scalar magnetic potential in the whole insulator. This contribution provides, for the first time, a thorough comparison between these methods. We concentrate on the accuracy and computational effort required to solve a problem using both of the two methods. [ABSTRACT FROM AUTHOR]

This contribution addresses the exploitation of cyclic symmetry in boundary integral formulations for eddy current problems formulated with a magnetic scalar potential. The novelty of the contribution is how to rigorously treat non-simply connected conductors. In particular, a general algorithm to compute a set of suitable cohomology generators is introduced. The algorithm is purely combinatorial and exhibits a linear-time worst-case complexity. [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]

We present an effective technique to solve eddy current problems on the conductors of arbitrary topology by an iterative geometric formulation suitable for an arbitrary polyhedral mesh. The formulation is based on the reformulation of the volume integral formulation in a form suitable to be solved by fixed point iterations. Given that nowadays, the computation of Biot–Savart fields can be performed efficiently on graphics processing units, the right-hand side of the systems is constructed at each fixed point iteration without computing the inductance matrix, which is fully populated. The proposed technique is useful in eddy current problems at industrial frequency where meshing the complement of conductors is hard, thus representing a sound alternative to integral formulations. [ABSTRACT FROM AUTHOR]

An innovative approach has been recently proposed for the voltage breakdown prediction in high-voltage systems, insulated by large vacuum gaps. This approach is based on complementary geometric formulations for electrostatics coupled to the analytical solution of the equations of motion for charged particles. In this paper, a goal-oriented local mesh refinement technique is introduced, which allows to increase the rate of convergence of the solution, enabling an effective voltage breakdown prediction also in large-scale systems with complex geometries. [ABSTRACT FROM AUTHOR]

Solving eddy current problems formulated by using a magnetic scalar potential in the insulator requires a topological pre-processing to find the so-called first cohomology basis of the insulating region, which may be very time-consuming for challenging industrially driven problems. The physics-inspired Dłotko–Specogna (DS) algorithm was shown to be superior to alternatives in performing such a topological pre-processing. Yet, the DS algorithm is particularly fast when it produces as output not a regular cohomology basis but a so-called lazy one, which contains the regular one but it keeps also some additional redundant elements. Having a regular basis may be advantageous over the lazy basis if a technique to produce it would take about the same time as the computation of a lazy basis. In the literature, such a technique is missing. This paper covers this gap by introducing modifications to the DS algorithm to compute a regular basis of the first cohomology group in practically the same time as the generation of a lazy cohomology basis. The speedup of this modified DS algorithm with respect to the best alternative reaches more than two orders of magnitudes on challenging benchmark problems. This demonstrates the potential impact of the proposed contribution in the low-frequency computational electromagnetics community and beyond. [ABSTRACT FROM AUTHOR]

Integral formulations are attractive for solving eddy-current problems in complex electromagnetic systems, since they do not require the discretization of the complement of the conducting structures. This paper addresses the coupling of volume-integral and surface-integral formulations for eddy-current problems on general star-shaped polyhedral and polygonal meshes. [ABSTRACT FROM AUTHOR]

This paper presents in detail the extension of the T-Ω formulation for eddy currents based on higher-order hierarchical basis functions so that it can automatically deal with conductors of arbitrary topology. To this aim, we supplement the classical hierarchical basis functions with nonlocal basis functions spanning the first de Rham cohomology group of the insulating region. Such nonlocal basis functions may be efficiently and automatically found in negligible time with the recently introduced Dłotko–Specogna (DS) algorithm. The approach presented in this paper merges techniques together which to some extent already existed in literature but they were never grouped together and tested as a single unit. [ABSTRACT FROM AUTHOR]

A new biosensor for the real-time analysis of thrombus formation is reported. The fast and accurate monitoring of the individual thrombotic risk represents a challenge in cardiovascular diagnostics and in treatment of hemostatic diseases. Thrombus volume, as representative index of the related thrombotic status, is usually estimated with confocal microscope at the end of each in vitro experiment, without providing a useful behavioral information of the biological sample such as platelets adhesion and aggregation in flowing blood. Our device has been developed to work either independently or integrated with the microscopy system; thus, images of the fluorescently labeled platelets are acquired in real-time during the whole blood perfusion, while the global electrical impedance of the blood sample is simultaneously monitored between a pair of specifically designed gold microelectrodes. Fusing optical and electrical data with a novel technique, the dynamic of thrombus formation events in flowing blood can be reconstructed in real-time, allowing an accurate extrapolation of the three-dimensional shape and the spatial distribution of platelet thrombi forming and growing within artificial capillaries. This biosensor is accurate and it has been used to discriminate different hemostatic conditions and to identify weakening and detaching platelet aggregates. The results obtained appear compatible with those quantified with the traditional optical method. With advantages in terms of small size, user-friendliness and promptness of response, it is a promising device for the fast and automatic individual health monitoring at the Point of Care (POC). [ABSTRACT FROM AUTHOR]

Let Ω be a bounded domain of R3 whose closure Ω¯ is polyhedral, and let T be a triangulation of Ω¯. We devise a fast algorithm for the computation of homological Seifert surfaces of any 1-boundary of T , namely, 2-chains of T whose boundary is γ. Assuming that the boundary of Ω is sufficiently regular, we provide an explicit formula for a homological Seifert surface of any 1-boundary γ of T . It is based on the existence of special spanning trees of the complete dual graph and on the computation of certain linking numbers associated with those spanning trees. If the triangulation T is fine, the explicit formula is too expensive to be used directly. To overcome this difficulty, we adopt an easy and very fast elimination procedure, which sometimes fails. In such a case a new unknown can be computed using the explicit formula and the elimination algorithm restarts. The numerical experiments we performed illustrate the efficiency of the resulting algorithm even when the homology of Ω is not trivial and the triangulation T of Ω¯ consists of millions of tetrahedra. [ABSTRACT FROM AUTHOR]