Numerical simulation of electromagnetic acoustic transducers using distributed point source method

In spite of many advances in analytical and numerical modeling techniques for solving different engineering problems, an efficient solution technique for wave propagation modeling of an electromagnetic acoustic transducer (EMAT) system is still missing. Distributed point source method (DPSM) is a newly developed semi-analytical technique developed since 2000 by Placko and Kundu (2007) [12] that is very powerful and straightforward for solving various engineering problems, including acoustic and electromagnetic modeling problems. In this study DPSM has been employed to model the Lorentz type EMAT with a meander line and flat spiral type coil. The problem of wave propagation has been solved and eddy currents and Lorentz forces have been calculated. The displacement field has been obtained as well. While modeling the Lorentz force the effect of dynamic magnetic field has been considered that most current analyses ignore. Results from this analysis have been compared with the finite element method (FEM) based predictions. It should be noted that with the current state of knowledge this problem can be solved only by FEM.     

Phase dynamics of a Josephson junction ladder driven by modulated currents

Phase dynamics of disordered Josephson junction ladders (JJLs) driven by external currents which are spatially and temporally modulated is studied using a numerical simulation based on a random field XY model. This model is considered theoretically as an effective model of JJLs with structural disorder in a magnetic field. The spatiotemporal modulation of external currents causes peculiar dynamical effects of phases in the system under certain conditions, such as the directed motion of phases and the mode-locking in the absence of dc currents. We clarify the details of effects of the spatiotemporal modulation on the phase dynamics.     

Persistent currents and magnetization in two-dimensional magnetic quantum systems

Persistent currents and magnetization are considered for a two-dimensional electron (or gas of electrons) coupled to various magnetic fields. Thermodynamic formulae for the magnetization and the persistent current are established and the “classical” relationship between current and magnetization is shown to hold for systems invariant both by translation and rotation. Applications are given, including the point vortex superposed onto an homogeneous magnetic field, the quantum Hall geometry (an electric field and an homogeneous magnetic field) and the random magnetic impurity problem (a random distribution of point vortices).     

Application of the method of equivalent edge currents to composite scattering from the cone-cylinder above a dielectric rough sea surface

Compared with scattering from a rough surface only, composite scattering from a target above a rough surface has become so practical that it is a subject of great interest. At present, this problem has been solved by some numerical methods which will produce an enormous calculation amount. In order to overcome this shortcoming, the reciprocity theorem (RT) and the method of equivalent edge currents (MEC) are used in this paper. Due to the advantage of RT, the difficulty in computing the secondary scattered fields is reduced. Simultaneously, MEC, a high-frequency method with edge diffraction considered, is used to calculate the scattered field from the cone-cylinder target with a high accuracy and efficiency. The backscattered field and the polarization currents of the rough sea surface are evaluated by the Kirchhoff approximation (KA) method and physical optics (PO) method, respectively. The effects of the backscattering radar cross section (RCS) and the Doppler spectrum on the size of the target and the windspeed of the sea surface for different incident angles are analysed in detail.     

Edge plasmon polaritons on a half-plane

The effect of electromagnetic retardation on the spectrum of edge plasmons in a semi-infinite two-dimensional electron system is considered. The problem is reduced to complicated integral equations for the potentials, which are solved upon a major simplification of the kernel. The spatial distribution of the potentials, charges, and currents is analyzed. It is shown that edge plasmon polaritons in the high-conductivity two-dimensional system are characterized by a high Q factor at all frequencies, including those lower than the reciprocal electron relaxation time τ^-1.     

Sound scattering by a body in a planar layered waveguide

In the framework of the theory of integral equations, the problem of sound diffraction by pressure-release and acoustically stiff inhomogeneities of an oceanic waveguide is considered. The iteration method is used to obtain recurrent relations for the surface currents. The relations describe the diffraction process as a sequence of interactions between the body and the waveguide boundaries (multiple reflections). The validity condition for the zero-order approximation, which ignores multiple reflections, is formulated and physically justified.     

New full-wave theory for scattering from rough metal surfaces—the correction current method: the TE-polarization case

A new full-wave theory of scattering from metal surfaces with one-dimensional roughness profiles is presented. A primary field and a complete system of modal functions (radiation modes) are defined to be relatively simple in structure (plane-wave-type fields) and to satisfy the boundary conditions at the rough surface, individually and rigorously. These fields will not necessarily satisfy Maxwell's equations. But compliance with these equations is enforced by the introduction of fictitious current distributions, associated with each of these fields, and chosen such that these 'passive' currents compensate for any field errors. In addition, each radiation mode is assumed to include an 'active' current distribution in the form of a current sheet which generates this mode. The composite field, formulated as a superposition of the primary field and the radiation modes, must be source free. It cannot involve any active or passive currents; and this zero-current requirement is then used to solve the scatter problem by an iterative procedure which, in a step-by-step fashion, eliminates the passive currents of the primary field and radiation modes by the active currents of the radiation modes. The result is a composite field that satisfies all requirements (Maxwell's equations, boundary conditions and radiation condition) while all fictitious current distributions are eliminated by mutual compensation. This composite field is therefore the solution of the scatter problem. This new theory—involving fictitious current distributions—is unconventional. But after definition of the primary field and the radiation modes, it is straightforward and conceptually transparent. The first-order scatter pattern is reciprocal and bridges the gap between the small-perturbation method and the physical optics method. Since the passive currents quantify the field errors, the theory allows the establishment of an error criterion which indicates when field errors can be expected to be small. The results are compared with those of existing theories. The present paper presents the TE case; the TM case, which is more complex, will be described in a follow-on paper.

(Some figures in this article are in colour only in the electronic version)     

Algorithms for computing the components of the generalized transport tensor taking into account surface currents

Application of the first collision probability (FCP) method to the system with boundary conditions of given currents or white reflection is considered. The equations of the method are generalized for the anisotropic case by introducing several angular modes in each zone.     

The statistical distribution of magnetic critical currents determined by HTSC film morphology

An analysis is made of the geometric and morphological properties of YBCO superconducting films and of their effect on the magnetic and transport phenomena. A study is presented of the statistical characteristics of critical currents derived from the variation of trapped magnetic flux induced by passing a pulsed transport current. It is shown that the critical currents in the materials under study have a specific statistical distribution, whose main properties are due to the morphology of their structure and can be determined by geometric-probability analysis. The superconducting film is considered as a percolation system. An empirical normal-phase cluster-area distribution function was used to derive the distribution function of magnetic critical currents, which describes adequately the experimental data on how transport current affects trapped magnetic flux. The critical current for transition of a film to the resistive state has been calculated. Fiz. Tverd. Tela (St. Petersburg) 41, 1739–1742 (October 1999)     

环形等离子体平衡时维持场电流的计算

本文介绍一个计算轴对称任意截面环形等离子体平衡问题的方法。先选定等离子体边界和环电流分布,用有限元方法解平衡方程的边值问题。借助于虚壳原理,得到用平衡方程解表示的能够产生平衡时所需要的维持场的虚壳电流。计算虚壳电流在等离子体区的维持场,以它为根据,采用积分方程开拓,求等离子体区外某位形上的维持场电流分布。解决这个问题的主要困难是当磁场向外开拓时遇到了不适定问题。我们用奇异值分解方法解不适定的Fredholm第一类积分方程。这个方法能容易地找到稳定解,对解决这个平衡问题是简单有效的。我们以七种等离子体截面形状,三种电流分布为具体模型,在三种维持场电流分布位形上给出了维持场电流分布。还给出了维持场形态,维持场总电流与等离子体总电流的比较,并简单讨论了维持场对等离子体整体稳定性的影响。 关键词：     

Finite Larmor radius and Hall effects on thermal instability of a compressible plasma

The effects of compressibility, finite Larmor radius (FLR) and Hall currents are considered on the thermal instability of a plasma in the presence of a uniform horizontal magnetic field. For stationary convection, the compressibility has a stabilizing effect whereas FLR and Hall currents have stabilizing as well as destabilizing effects. For (C _pβ/g)<1, the system is stable. The magnetic field, FLR and Hall currents introduce oscillatory modes in the system for (C _pβ/g)>1.     

Electrical relaxation and the strong-field effect when injection currents are present in metal-oxide-semiconductor systems

The transient currents and stationary current-voltage characteristics of Ta-Ta₂Q₅-MnO₂ systems with negative tantalum polarity are considered. It is shown that in this case space-charge limited currents flow through the system with an exponential distribution of the trap energy when there are deep donor centers. In the intensefield region the Poole-Frenkel effect begins to have an important effect on the injection currents. An appropriate theory is developed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 94–97, May, 1981.     

Electric field and field-aligned currents produced by asymmetric ring current

The formation of the problem concerning calculation of the electric field and field-aligned currents in the magnetosphere and ionosphere produced by asymmetric ring current is considered with the approach and equations developed by [1–3]. These equations were used previously for estimation of the electric field in the ionosphere and magnetosphere appearing in the process of spreading of energetic particles injected into the trapping zone of the magnetosphere as a result of nuclear explosion. According to this theory, energetic particles injected into a ring current produce an asymmetric divergent ring current, field-aligned currents, a global electric field and currents in the ionosphere. Space Research Center, Polish Academy of Sciences, Warsaw, Poland. Published from Izvestiya Vysshikh. Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 4, pp. 423–431, April, 1998.     

Oscillation regularity in noise-driven excitable systems with multi-time-scale adaptation

We investigate oscillation regularity of a noise-driven system modeled with a slow after-hyperpolarizing adaptation current (AHP) composed of multiple-exponential relaxation time scales. Sufficiently separated slow and fast AHP time scales (biphasic decay) cause a peak in oscillation irregularity for intermediate input currents I, with relatively regular oscillations for small and large currents. An analytic formulation of the system as a stochastic escape problem establishes that the phenomena is distinct from standard forms of coherence resonance. Our results explain data on the oscillation regularity of the pre-B?tzinger complex, a neural oscillator responsible for inspiratory breathing rhythm generation in mammals.     

Electromagnetic Radiation of Accelerated Charged Particle in the Framework of a Semiclassical Approach

The problem of the electromagnetic radiation produced by charge distributions in the framework of a semiclassical approach proposed in the work by Bagrov, Gitman, Shishmarev, and Farias Jr. [J. Synchrotron Rad. 27 , 902–911 (2020)] is addressed here. In this approach, currents, generating the radiation are considered classically, while the quantum nature of the radiation is kept exactly. Quantum states of the electromagnetic field are solutions of Schrödinger's equation, and relevant quantities to the problem are evaluated with the aid of transition probabilities. This construction allows us to introduce the quantum transition time in physical quantities and assess its role in radiation problems by classical currents. Radiated electromagnetic energies are studied in detail and a definition for the rate at which radiation is emitted from sources is presented. In calculating the total energy and rate radiated by a pointlike charged particle accelerated by a constant and uniform electric field, it is discovered that these results are compatible with results obtained by other authors in the framework of the classical radiation theory under an appropriate limit. Numerical and asymptotic analyses of the results are also performed.     

Synthesis of current on a strip from a given realizable radiation pattern

A theory of synthesis of current on a strip from a given realizable radiation pattern is developed. The theory chooses the space of currents from the condition that the near-zone field is limited. The space of patterns is defined as the image of the space of currents due to current-to-pattern mapping. For these spaces, the Hilbert structure is introduced and the basis is constructed. As a result, the problem of synthesizing current from a given pattern is reduced to expansion over the basis. A numerical example is considered.     

Electrogradient EMF and volt-ampere characteristics of inhomogeneous systems

This paper studies the manifestation of electrogradient effects in the shape of the voltampere characteristics (VAC) of inhomogeneous conducting sandwich structures of the SSS and MSM types (S stands for n-type semiconductor, and M for metal) during the passage of a current perpendicular to the interfaces between the materials. It is shown that on the ohmic portion of the VAC the Peltier effect in the general case causes the conductivity of the sandwich system to drop. In the region of heating currents the VAC displays segments that are quadratic with respect to the current. The case when the VAC remains linear in the region of heating currents is considered.     

The electromagnetic radiation from sources above an ideally conducting expanding sphere

Electromagnetic fields are considered which are created by external currents of the traveling-wave type above an ideally conducting expanding sphere. A specific calculation is carried out, and the shape of the pulse is discussed as a function of the parameters of the problem.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 211–220, February, 1972.The author thanks V. N. Krasil'nikov for the stated problem, and A. A. Andronov and V. I. Semenova for discussing the results of the work.     

The conservation laws for deformed classical models

The problem of deriving the conservation laws for deformed linear equations of motion is investigated. The conserved currents are obtained in the explicit form and used in the construction of constants of motion. The equations for the set of non-interacting oscillators with arbitrary scale-time as well as theκ-Klein-Gordon equation are considered as an example of application of the method.