[SI-LIST] Re: FEM/BEM/MOM
- From: Geoff Stokes <gstokes@xxxxxxxxx>
- To: "'si-list@xxxxxxxxxxxxx'" <si-list@xxxxxxxxxxxxx>
- Date: Thu, 28 Aug 2003 11:25:02 +0100
Sorry I haven't time right now. Just put some relevant words into Google
and you'll learn a lot!
www.google.co.uk
Also I'm sure some of your colleagues at Cadence have looked into this.
Best wishes
Geoff
> -----Original Message-----
> From: Nimish Aggarwal [mailto:nagarwal@xxxxxxxxxxx]
> Sent: 28 August 2003 11:23
> To: Geoff Stokes
> Subject: RE: [SI-LIST] Re: FEM/BEM/MOM
>
>
> Hi Geoff
>
> Can you give the pointers for
> Explanation of all these 3 methods?
>
> Thanks & Regards
> Nimish
>
> -----Original Message-----
> From: Geoff Stokes [mailto:gstokes@xxxxxxxxx]
> Sent: Thursday, August 28, 2003 3:14 PM
> To: 'si-list@xxxxxxxxxxxxx'
> Subject: [SI-LIST] Re: FEM/BEM/MOM
>
> Hi Ben
>
> FEM Finite Element Method - I think maybe as used in Ansoft HFSS
> www.ansoft.com
>
> BEM Boundary Element Method
> http://www.wessex.ac.uk/conferences/2003/bem25/
>
> MoM Method of Moments
> e.g. NEC, FEKO, AWR Microwave Office
>
> 3D solvers include Ansoft HFSS and CST Microwave Studio
> (Finite Integral
> method).
> www.cst.de
>
> I can see that the problem usually comes down to formulation of a
> lumped-element model of high frequency effects. The field
> solvers give
> linear network parameters, e.g S or Y to which the model must
> be fitted, or
> the parameters might be used directly in a simulator - that
> is possible for
> small systems in Cadence.
>
> Planar solvers are useful for dealing with PCB traces in the
> x-y plane,
> usually called 2 1/2 D because they give useful but not full
> description in
> the z-direction. Some 3D solvers are full-wave descriptions
> in terms of
> Maxwell's equations and that's clearly going to be the most accurate
> approach. It wasn't really practical until recently, when
> high speed desk
> top computing power became available at a reasonable price.
> The differences
> are mathematical - don't ask me too much about that! The
> main thing to
> understand is that a nodal circuit schematic analysis of any
> kind is a gross
> approximation, and the error increases with increasing
> frequency. This is
> because varying currents produce varying fields which cause
> couplings and
> radiation not represented in the schematic. A further
> complication is that
> the fields themselves inherently involve a time delay, and that makes
> extraction of lumped-element models extremely difficult.
>
> Just a little diversion to show the error in a schematic:
> An old example often quoted is the problem of connecting two one farad
> capacitors together by a switch; one is at 1V potential, the
> other zero.
> The initial energy is 1/2 CV**2 =3D 0.5 joule. After closing
> the switch th=
> ere
> is charge distribution, and energy =3D 1/8 +1/8 =3D 0.25
> joule. Where did =
> the
> missing 0.25 joule go? If you did an electrical degree, you'd see the
> paradox. If you studied high frequencies, you'd know the
> answer. (I did a
> Physics degree, then built RF circuits, so for me a capacitor is not a
> capacitor.)
>
> The answer is
> 1) it's not physically possible to put two capacitors
> together at one point
> 2) therefore they are separated by a distance
> 3) therefore on closing the switch, the discharge current
> travels a distance
> 4) the conductors have finite conductivity
> 5) therefore there is a varying electromagnetic field and energy is
> dissipated and radiated
> 6) please don't talk about too much about inductance because
> it's only an
> approximation.
>
> Best wishes
> ______________________________________________=20
>
> Geoff Stokes
> Systems Engineer, Signal Management Group
>
> Zetex plc=20
> Lansdowne Road, Chadderton, Oldham, OL9 9TY,=A0 UK=20
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>
>
> > -----Original Message-----
> > From: Ben Rothchild [mailto:benrothchild@xxxxxxxxx]
> > Sent: 28 August 2003 09:31
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] FEM/BEM/MOM
> >=20
> >=20
> > Hello Everybody,
> >=20
> > 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.=20
> >=20
> > Can somebody explain in extremely layman
> > terms what they mean ( for a=20
> > person with a background of undergraduate
> > degree in Electrical engineering).
> >=20
> > Thank you very much
> >=20
> > Ben
> >=20
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