[SI-LIST] Re: FEM/BEM/MOM
- From: Chris Cheng <chris.cheng@xxxxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Thu, 28 Aug 2003 14:41:32 -0700
Ben,
While some people will disagree, I think Boundary Element Method BEM and
Method of Moment are essentially the same. Some researchers in UK like to
call it BEM while Professor Roger Harrington likes to call it MoM.
What are the underlying algrithms of BEM and FEM is not important but the
way they are optimized and intended target problems are worth noting.
FEM is based on discretizing the entire simulation space. The resulting
matrix to solve is therefore sparse. Based on the above characteristics, it
is best for a closed enivornment like an electrical motor or mechanical
enclosure. Since the matrix is sparse, typically it is solved by implicite
methods, as a result you can trade accuarcy with speed by allowing the
convergence to be less accurate and you will get your answer quick. The
problem with discretizing the entire space is if you have an open boundary
like transmission lines or planar structures like vias on pcb or package
planes, you will end up needing a lot of discretize space to solve.
On the other hand, BEM or MoM is based on discretizing just the boundary
surface with the Green's functional. The resulting matrix is much smaller
but dense. It is best for an open boundary enivornment since you only have
to discretize the surface instead of the empty space. As a result, it is
great for transmission line or PCB/package/connnector type problems since
they are by definition open boundaries. However, because the matrix is
dense, it is typically solved by explicit method and it takes time to pivot
the matrix and there is not much you can trade off to speed things up.
Put them into a smart programmers hand, both of them can get smiliar results
in similar speed. But I would check the performance of a FEM simulator in
open space problems and their accuracy compared with known closed form
solutions. It is relatively easy to cheat by relaxing the convergence
criteria to get a superfast simulation speed.
HTH
Chris
-----Original Message-----
From: Ben Rothchild [mailto:benrothchild@xxxxxxxxx]
Sent: Thursday, August 28, 2003 1:31 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] FEM/BEM/MOM
Hello Everybody,
When looking at Signal Integrity tools one
comes across terms like FEM, BEM, MOM
as well as some others like 2D, 2.5D,3D
field solvers.
Can somebody explain in extremely layman
terms what they mean ( for a
person with a background of undergraduate
degree in Electrical engineering).
Thank you very much
Ben
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