Efficient FDTD Implementation of the ADE-Based CN-PML for the Two-
Dimensional TMz Waves
Jianxiong Li
1
, Haolin Jiang
1
, and Naixing Feng
2
1
School of Electronics and Information Engineering
Tianjin Polytechnic University, Tianjin, 300387, China
lijianxiong@tjpu.edu.cn, houlinjohn@gmail.com
2
Institute of Electromagnetics and Acoustics
Xiamen University, Xiamen, 361005, China
fengnaixing@gmail.com
Abstract ─ An efficient, unsplit-field and unconditional
stable implementation of the stretched coordinate
perfectly matched layer (SC-PML) is proposed for
terminating the finite-difference time-domain (FDTD)
method. Via incorporating the Crank-Nicolson
Douglas-Gunn (CNDG) and the auxiliary differential
equation (ADE) methods, respectively, the proposed
PML formulations can take advantage of the
unconditional stability of the CNDG method which has
smaller numerical anisotropy than the existing
alternately direction implicit (ADI) method. A
numerical test carried out in a 2D free space FDTD
domain is provided to validate the proposed CNDG-
based PML. It has been shown that the proposed PML
can not only overcome the Courant-Friedrich-Levy
(CFL) stability constraint, but attenuate the propagating
waves efficiently.
Index Terms ─ Auxiliary differential equation (ADE),
Crank-Nicolson Douglas-Gunn (CNDG), finite-
difference time-domain (FDTD), perfectly matched
layer (PML).
I. INTRODUCTION
The finite-difference time-domain (FDTD) method
plays an important role in the design and simulation of
electromagnetic behaviors [1]. As an explicit numerical
method, the Yee’s FDTD is conditionally stable, which
means that the FDTD time-step is constrained by the
Courant-Friedrich-Levy (CFL) limit to maintain
stability and makes the FDTD method not very efficient
in analyzing electrically small structures [1]. In order to
remove the CFL stability constraint on time step and
improve computational efficiency, unconditionally
stable methods such as the alternating-direction implicit
FDTD (ADI-FDTD) scheme and the Crank-Nicolson
FDTD (CN-FDTD) scheme have been introduced in [2-
6]. As pointed in [5], the ADI’s accuracy is inferior to
that of CN scheme. The CN-FDTD with Douglas-Gunn
(DG) algorithm (denoted as CNDG FDTD method) is
developed in [6] to overcome the drawbacks that the
CN-FDTD with a huge irreducible matrix is hardly to
be solved without approximate algorithms.
In addition, one of the greatest challenges of
applying the FDTD method is the development of
absorbing boundary conditions (ABCs) which truncate
open region problems to simulate the extension of the
computational domain to infinity [1]. It has been shown
that the perfectly matched layer (PML), introduced by
Berenger, is one of the most effective ABCs [7]. The
stretched coordinate PML (SC-PML) has the advantage
of simple implementation in the corners and edges of
the PML regions [8].
To our knowledge, there is only one literature
about the formulation of the 2D unconditionally stable
PML based on an approximate CN scheme [9]. The
method in [9] is a split-field PML for 2D TEz waves.
In this paper, an alternative efficient,
unconditionally stable and unsplit-field PML, denoted
as ADE CNDG-PML, is constructed for 2D TMz
waves. The formulation is based upon incorporating the
CNDG algorithm and auxiliary differential equation
(ADE) method into the PML implementation.
II. FORMULATION
For simplicity, the PML is constructed for 2D TMz
waves only for truncating the free space. The
frequency-domain modified Maxwell’s equations in the
SC-PML can be written as:
1
z
xy
E
jH cS
y
Z
w
w
, (1)
1
z
yx
E
jH cS
x
Z
w
w
, (2)
1054-4887 © 2015 ACES
Submitted On: November 6, 2014
Accepted On: April 2, 2015
688ACES JOURNAL, Vol. 30, No. 6, June 2015