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The free oscillations of a micromagnetic system around a saturated equilibrium are considered. Magnetization dynamics is described by the Landau--Lifshitz--Gilbert (LLG) equation. The LLG equation is linearized around the equilibrium and put in the form of a generalized eigenvalue problem for suitable self-adjoint operators connected to the micromagnetic effective field. The spectral properties of this problem are studied. The spatial discretization of the problem is analyzed and numerical computation of the resonant oscillations for a magnetic thin-film are performed. Index Terms--Ferromagnetic resonance, generalized eigenvalue problem, normal modes, resonant frequencies.

The paper deals with the numerical study of the electromagnetic response of a metallic nanoparticle to an external electromagnetic field, within the framework of the classical electrodynamics. The conduction electrons of the nanoparticle are modeled as a compressible electron fluid, whose dynamics are described by means of the linearized hydrodynamic equations. The electromagnetic field scattered by the nanoparticle is evaluated by a full-wave 3-D model based on an integral equation where the unknown is the current density. The fluid quantum pressure arising from the kinetic energy of the degenerate conduction electron gas gives rise to non-local effects that strongly influence the plasmon oscillations. Index Terms--Edge elements, integral formulation, nanoparticles, non-local effects, plasmon oscillations.

This paper deals with the identification of low-order accurate macromodels describing electrically long lossy multiconductor transmission lines. The formulation is based on the generalized method of characteristics, whose key feature is the extraction of delays from the propagation operators. We describe and compare different delay extraction approaches, in view of the identification of the macromodels. In particular, we propose a new identification procedure enhancing the results coming from a vector fitting algorithm by a further nonlinear identification step. This gives more general properties to the model implementation (e.g., a state space realization with no repeated pole), possibly improving the accuracy at the same time. Some reference case studies are analyzed to highlight the key features of the proposed approach. Index Terms--Distributed parameter circuits, frequency-domain synthesis, rational approximation, transient analysis, transmission lines (TLs).

An integral formulation to model, in the frequency domain, the electromagnetic response of three-dimensional (3-D) structures formed by metallic carbon nanotubes and conductors, within the framework of the classical electrodynamics, is described. The conduction electrons of the metallic nanotube are modeled as an infinitesimally thin cylindrical layer of compressible fluid, whose dynamics are described by means of the linearized hydrodynamic equations. The resulting integral equations are solved numerically by the finite element method using the facet elements and the null-piny decomposition. The proposed formulation is applied to study carbon nanotube interconnects and dipole antennas and some related results are outlined. The solutions highlight the high-frequency effects due to the electron inertia and the fluid pressure. In particular, since the kinetic inductance matrix dominates over the magnetic one, proximity effects are negligible. Index Terms--Electrodynamics, finite elements, fluid model, integral formulation, metallic carbon nanotubes.

A general and effective method is presented to numerically solve the electric field integral equation (EFIE) for topologically complex conducting domains by the finite element method. A new technique is proposed to decompose the surface current density into a solenoidal part and a nonsolenoidal remainder to avoid the low frequency breakdown. The surface current density field is approximated through div-conforming (facet) elements. The solenoidal part is represented through the null space of the discrete approximation D of the surface divergence operator in the subspace spanned by the facet elements, whereas the nonsolenoidal remainder is represented through its complement. The basis functions of the null space and its complement are evaluated, respectively, by the null and pseudo-inverse of the matrix D. The completeness of the null-pinv basis functions is studied. Unlike the loop-star and loop-tree basis functions, the null-pinv basis functions allow to deal with topologically complex conducting domains in a general and readily applicable way. A topological interpretation of the 'null-pinv' decomposition is given and a general and simple method to evaluate the null and pseudo-inverse of D is proposed. The computational complexity of the proposed method is discussed. Index Terms--Div-conforming (facet) elements, low frequency breakdown, multiply connected domains, null space, null-pinv decomposition, surface integral equations.

The 'standard' transmission line model describes accurately the propagation of electric signals along conducting wires, if the distance between them is much smaller than both their length and the smallest characteristic wavelength of the signals. This paper presents an 'enhanced' transmission line model that is able to describe the propagation along perfectly conducting wires in a homogeneous dielectric, and also when the distance between the wires is comparable with the smallest characteristic wave-length of the signals. The enhanced model is obtained, with suitable approximations, starting from a full-wave analysis of the problem and using an integral formulation based on the electromagnetic potentials satisfying the Lorentz gauge. It differs from the standard transmission line model, only in its constitutive relations, that is, in the relation between the per unit length (p.u.l.) magnetic flux and the current intensity, and in the relation between the electric voltage and the p.u.l. electric charge. In the standard model, these relations are of the algebraic type, and in the enhanced one they are of the convolution type, expressing nothing more than a very simple physical fact: the values of the p.u.l. flux and voltage at the generic abscissa along the wires depend on the entire distribution of the current and the p.u.l. charge, respectively. The kernels of the convolution integrals have the logarithmic singularity typical of the surface distributions and takes into account proximity effects. The solution of the enhanced model highlights the high-frequency effects due to dispersion and radiation that the standard model is unable to provide. Good agreement with the solutions obtained by a full-wave electromagnetic numerical code is achieved. Index Terms--Full-wave analysis, integral formulations, radiation losses, transmission line models, wire structures.

This brief proposes a new procedure to extend to nonuniform transmission lines, a time-domain model commonly used to describe uniform transmission lines. The line is represented at its terminations as a dynamic two-port, where each port is composed by a dynamic one-port connected in series with a controlled voltage source. The procedure is applied to nonuniform lines with exponential, linear and Gaussian profile of the parameters. The numerical analysis of some case-studies is carried out. Index Terms--Distributed circuits, nonuniform transmission lines, transient analysis.

This paper deals with mathematical models of magnetic hysteresis implemented by assembling hysterons of play and stop type. A procedure for the identification of these models is described, and their behaviors are compared to experimental results. A comparison to the Preisach and Prandtl-Ishlinskii models is performed. It is shown that the Play-Type Model is a possible alternative to Preisach's algorithm, whereas the Stop-Type Model is apt to represent the inverse of Preisach's operator. Simulations adopting both models are reported and compared to experimental data. Moreover, an application to the analysis of a ferroresonant circuit is studied, both numerically and experimentally. Index Terms - Magnetic hysteresis hysterons, Preisach model.

Linear transmission lines with nonlinear terminal resistors are considered. Each resistor is assumed to be voltage controlled or current controlled and weakly active. These distributed circuits are shown to have a unique solution, which passes at a given instant through a given value, if the characteristics of the terminal resistors satisfy certain inequalities. In particular, if the resistors are locally passive, then the solution is unique. Transmission lines with terminal resistors that are locally active may admit several solutions that have the same initial value. In these cases, the uniqueness of solution is obtained adding 'small' capacitances in parallel to the voltage controlled resistors and 'small' inductances in series to the current controlled resistors. Index Terms - Normal forms, transmission lines, uniqueness.

Optical properties of plasma lenses strongly depend on the magnetic field distribution. Its measurement with conventional magnetic probes is quite critical for such application. In this paper the measurement of the magnetic field in z-pinch discharge, based on Faraday effect in optical fibers, is described. It is shown that it is possible, using a quite simple and relatively low cost experimental setup, to detect the field dynamics inside the discharge tube assuring low disturbance, a large bandwidth, and a high signal to noise ratio. Applications to several kinds of plasma lenses and further development are discussed.

The problem of magnetic forces in magnetizable fluids is discussed and classical formulas for volume force density (Kelvin, Helmholtz) are reviewed. The general problem of hydrostatic equilibrium of a magnetic liquid subject to magnetic field is formulated. On the basis of this formulation, the displacement of a linear magnetic fluid subject to the field produced by sheet-shaped coils is numerically computed by using the finite-elements method and an appropriate fixed-point iterative technique. Index Terms--Helmholtz, Kelvin formulas, magnetic fluids (MFs), magnetic forces.

Linear multiconductor transmission lines can be effectively represented in the time domain as a dynamic multiport through the describing input and transfer impulse responses. Unfortunately, these responses cannot be analytically evaluated for the most general case of lossy lines. In addition, they cannot even be evaluated numerically due to the presence of irregular terms such as Dirac pulses, functions that actually approximates Dirac pulses, and functions of the type 1/[square root of t]. Nevertheless, all these irregular terms can be isolated from the regular ones. This paper proposes an analytical method to evaluate exactly the irregular terms. This method is based on the perturbation theory of the spectrum of symmetric matrices and can be easily and effectively applied to the most general case of frequency-dependent lossy multiconductor lines. Once the irregular parts of the impulse responses are known, it is possible to evaluate accurately the regular ones through simple numerical methods, as shown through some examples. Index Terms - Frequency-dependent parameters, impulse responses, multiconductor transmission lines.