اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدGenerating an electromagnetic multipole by oscillating currents
110
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Based on the relation between a plane phased array and plane waves we show that a spherical current layer or a current sphere proportional to a multipole electric field and situated in a uniform medium generates the same multipole field in all space. We calculate TE and TM multipoles inside and outside the spherical layer. The $l=1$ TM multipoles are localized at the origin with a focal spot with full width at half maximum of $0.4lambda$ in the lateral axes and $0.58lambda$ in the vertical axis. The multipole fields near the origin are prescriptions for the current distributions required to generate those multipole fields. A spherical layer can couple to a multipole source since the oscillation of the electrons in the layer due to the multipole field generates the multipole field in all space, which in turn can drive the multipole currents. Exciting a multipole in a polarizable sphere or spherical layer can couple it to another polarizable sphere or spherical layer.
قيم البحث
اقرأ أيضاً
The multipole expansion is a key tool in the study of light-matter interactions. All the information about the radiation of and coupling to electromagnetic fields of a given charge-density distribution is condensed into few numbers: The multipole mom
ents of the source. These numbers are frequently computed with expressions obtained after the long-wavelength approximation. Here, we derive exact expressions for the multipole moments of dynamic sources that resemble in their simplicity their approximate counterparts. We validate our new expressions against analytical results for a spherical source, and then use them to calculate the induced moments for some selected sources with a non-trivial shape. The comparison of the results to those obtained with approximate expressions shows a considerable disagreement even for sources of subwavelength size. Our expressions are relevant for any scientific area dealing with the interaction between the electromagnetic field and material systems.
The transformation media concept based on the form-invariant Maxwells equations under coordinate transformations has opened up new possibilities to manipulate the electromagnetic fields. In this paper we report on applying the finite-embedded coordin
ate transformation method to design electromagnetic beam modulating devices both in the Cartesian coordinates and in the cylindrical coordinates. By designing the material constitutive tensors of the transformation optical structures through different kinds of coordinate transformations, either the beam width of an incident Gaussian plane wave could be modulated by a slab, or the wave propagating direction of an omni-directional source could be modulated through a cylindrical shell. We present the design procedures and the full wave electromagnetic simulations that clearly confirm the performance of the proposed beam modulating devices.
The quark production in classical color fields is investigated with a focus on the induction of an electromagnetic current by produced quarks. We show that the color SU(2) and the SU(3) theories lead significantly different results for the electromag
netic current. In uniform SU(2) color fields, the net electromagnetic current is not generated, while in SU(3) color fields the net current is induced depending on the color direction of background fields. Also the numerical study of the quark production in inhomogeneous color fields is done. Motivated by gauge field configurations provided by the color glass condensate framework, we introduce an ensemble of randomly distributed color electric fluxtubes. The spectrum of photons emitted from the quarks by a classical process is shown.
We describe the experimental implementation of a superluminal ({it i.e.} faster than light {it in vacuo}) polarization current distribution that both oscillates and undergoes centripetal acceleration. Theoretical treatments lead one to expect that th
e radiation emitted from each volume element of such a polarization current will comprise a v{C}erenkov-like envelope with two sheets that meet along a cusp. The emission from the experimental machine is in good agreement with these expectations, the combined effect of the volume elements leading to tightly-defined beams of a well-defined geometry, determined by the source speed and trajectory. In addition, over a restricted range of angles, we detect the presence of cusps in the emitted radiation. These are due to the detection over a short time period (in the laboratory frame) of radiation emitted over a considerably longer period of source time. Consequently, the intensity of the radiation at these angles was observed to decline more slowly with increasing distance from the source than would the emission from a conventional antenna. The angular distribution of the emitted radiation and the properties associated with the cusps are in good {it quantitative} agreement with theoretical models of superluminal sources once the effect of reflections from the earths surface are taken into account.
In this paper, we study the interactions of electromagnetic waves with a non-dispersive dynamic medium that is temporally dependent. Electromagnetic fields under material time-modulation conserve their momentum but not their energy. We assume a time-
variation of the permittivity, permeability and conductivity and derive the appropriate time-domain solutions based on the causality state at a past observation time. We formulate a time-transitioning state matrix and connect the unusual energy transitions of electromagnetic fields in time-varying media with the exceptional point theory. This state-matrix approach allows us to analyze further the electromagnetic waves in terms of parity and time-reversal symmetries and signify parity-time symmetric wave-states without the presence of a spatially symmetric distribution of gain and loss, or any inhomogeneities and material periodicity. This paper provides a useful arsenal to study electromagnetic wave phenomena under time-varying media and points out novel physical insights connecting the resulting energy transitions and electromagnetic modes with exceptional point physics and operator symmetries.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
