Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generating an electromagnetic multipole by oscillating currents   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 $0.4\lambda$ in the lateral axes
and $0.58\lambda$ 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.

23
The categories of this paper are: solv-int
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
35
The categories of this paper are: mtrl-th
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
6
The categories of this paper are: astro-ph
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph
9
The categories of this paper are: nlin
30
The categories of this paper are: q-alg