[SI-LIST] Re: FEM/BEM/MOM

thanks for the nice explanation. Can you perhaps add in a description of 
FDTD? I would like to have a similarly straightforward understanding of 
that along with how it compares with the other methods, where it best 
applies, etc.

thanks!
kim

At 02:41 PM 8/28/2003, Chris Cheng wrote:
>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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