GUAN et al.: AN ACCURATE AND EFFICIENT FE-BI METHOD WITH GPU ACCE LERATION FOR 3-D ELECTROMAGNETIC AN
ALYSIS 6327
densities and fields can be globally solved from (3) and a com-
bination of (8) and (9). To couple FE and BI equations on con-
formal meshes, we can exp and the unknown current densities
and fields as
(10)
(11)
(12)
(13)
where
and are the RWG and the edge basis function
[1], respectively;
and d enote the nu mb er of degrees of
freedom (DOFs) on and inside
, respectively; , ,and
are the expansion coefficients yet to be determined. By substi-
tuting (10) – (13) to (3), (8) and (9), the coupled system equation
can be obtained as
(14)
where
(15)
in which X and Y can be either I or S , and
(16)
(17)
(18)
(19)
(20)
(21)
where
is the principal value of the operator ,and and
are the combination factors chosen as .For
brevity, we write ( 14 ) symbolically as
(22)
where
denotes the finite element sparse matrix assembled
from (15) and (16),
denotes the boundary integral full ma-
trix assembled from (17) and (18),
represents the unknown
solution vector, and
is the known ex citation vector given by
(19)–(21).
Compared with the traditi onal approach to constructing t he
FE-BI(CFIE) [1 ], [2], the proposed method first discretizes the
FE equation, the EFIE, and the MFIE individually, and then
combines them into a complete s ystem , which pro vid e s freedom
to choose proper t esting functions for different equations.
B. Choice of the Testing Functio ns
To obtain an accurate solution from the FE-BI(CFIE) algo-
rithm, the operators contained in the diag onal b lock
in (14)
has to be well tested by carefully cho osing the testing functions
and .
In general, there are two kind s of vector functions which
can be chosen as testing functions, the divergence- and the
curl-conforming functions. The typical divergence-conforming
functions a re the RWG [19], [20] and the BC function [13],
which are denoted as
and , r espectively. The typical
curl-conforming functions can be obtained by r otating the
RWG and the BC fun ctio n with respect to the normal direction,
which are denoted as
and , respectively. If we
choose
, the resulting FE-BI solution has a
poor numerical accuracy, and becomes even worse when it
deals with dielectric o bjects or objects with a thick co a ting
[1], [2], [5]. One reason for this inaccuracy is the troublesome
evaluation of the divergence of curl-conforming basis func-
tions, which results in a contour integral in the th ird t erm of
(17) [1], [15]. The other reason is that
is not a good testing
function for the operator
in (18) [1 4]–[18]. To remove
these problems, a simple approach is to set the coefficient
to zero, which reduces the FE-BI system to the FE-BI(EFIE )
with the EFIE tested by
. A ltho ugh the FE-BI(EFIE) m etho d
can provide an accurate solution, it suffers from the interior
resonance corruption [1 ], [2]. A better way to overcom e t his
problem is to choose p roper testing functions for b oth the EFIE
andtheMFIEbasedonthemathematical properties of the
integral operators.
Mathematically, the proper basis and testing functions for an
integral operator should be in the domain and the dual of the
range of the integral operator, respectively [25]. Because the
operators
and map a space of divergence-con-
forming functions onto itself, their dual of the range is the space
of the curl-conforming functions [13], [26]. In the finite-element
space, if
is ch osen as the basis function, a good candidate to
expand the dual of the range of
and is and
, respectively [13], [15], [17], [27]. Hence, to test the ,
,and operato rs in (18) well, the testing functions sh ould be