Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Wireless Power Transfer by Means of Electromagnetic Radiation Within an
  Enclosed Space   In this paper, wireless power transfer by means of electromagnetic radiation
is investigated. Formulas are derived for the efficiency of the power transfer
in free space, in the presence of reflecting surfaces, and within enclosed
spaces. It is found that the presence of reflecting surfaces has the capacity
to substantially enhance the efficiency of power transfer at long range. An
upper limit is also found for the transferred power when constraints are
imposed on certain forms of undesired absorption. For the sake of simplicity,
only the efficiency of the radiative power transfer is considered. Losses due
to resistance in the antenna structures or inefficiencies in RF to DC
conversion are neglected.

8
The categories of this paper are: hep-ex
7
The categories of this paper are: hep-th
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
18
The categories of this paper are: econ
29
The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph