[SI-LIST] Re: How good are tools to predict Radiated Emissions ?

The tools and models are as good as the info that we feed; if there is
'garbage in'; there will only be garbage out!

Board level EMC simulations:
        > Most of the tools provide means to 'check' against set of
rules and identify      violations; yes using 3D field solver type of
tools give prediction, still those also         can do the job if you
have the models created with accuracy
        > On the near-filed probing: there is a misconception that we
can take the near-      filed probes/sniffing devices and pin-point the
device or area of trouble; this for     sure is an 'imaginary' wish!
Overall system level testing:=20
        > In the EMC testing one of the main area of subjectivity is
'typical        configuration'; since this is application and usage
dependant, some individuals     push for so called 'worst case' and give
nightmare to teams and poor engineers;  as many of you know there is
nothing like perfect 100% in real world...
        > Once test configuration is identified and all concerned agree,
then the        process is not that bad; certain notorious frequencies
do pop-up depending on  technology/interface used like SAS, Ethernet...
as long as the circuit deign was        done right (avoid big current
loops, proper decoupling, enough copper for power       as well as GND)
and proper grounding & shielding techniques used, you can be    sure of
a solid design.
Why the tweaking is costly?
        > The reason why 'tweaking cost is pretty big' as the original
poster wrote is         because people try to 'band-aid' solutions and
try to get an 'eye catching' result     quickly! Consider EMI as a
water-balloon. If you press in one place it WILL pop-   up in another
area! So there is no magic; the only way is to attack at the source.
> So doing a good review at the design stage is the cost effective and
proper  way to avoid EMI problems later; if you want to quickly build
the board and take      care of EMI later, then its perfect path for
disaster!

The reason EMC is such a complicated filed and lot of 'brainy' folks
work tirelessly is because of the combinational effects; let's say clock
"A" radiates certain energy; if there is another clock "B" that radiates
some energy as well; now the combinational effect could only be
predicted by using complicated field-solver tools (creating correct
models is another big headache). Since it's not too simple to create
such models and simulate, invariably companies prefer to test in the
real board; this way there is no need to do second guessing.

Thanks,
Kannan

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Silqun Leung
Sent: Monday, May 29, 2006 9:31 AM
To: kalevi@xxxxxxxxxx; weirsi@xxxxxxxxxx; Shiraz.Bashir@xxxxxx; SI-List
Subject: [SI-LIST] Re: How good are tools to predict Radiated Emissions
?

Actually, there is something.  For the complex board one can use Ansoft
SIwave to compute the radiated far and near fields.  If you want to
place this board into a housing/enclosure, this near or far field
solution can be passed via co-simulation to HFSS for the 3D analysis.

Regards,
Silqun

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Kai Keskinen
Sent: Saturday, May 27, 2006 7:31 PM
To: weirsi@xxxxxxxxxx; Shiraz.Bashir@xxxxxx; SI-List
Subject: [SI-LIST] Re: How good are tools to predict Radiated Emissions
?

FloEMC passes the IEEE test cases for radiated emissions. It is intended
to model the effects of packaging and takes into account things such as
slots, cavities, EMI gaskets with lower conductivity than metal etc. It
is helpful in creating packaging with high shielding effectiveness. None
of the tools let you take a complex board, stick it into a package or
housing, and then push a button to predict far field emissions.



-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of steve weir
Sent: Friday, May 26, 2006 12:57 PM
To: Shiraz.Bashir@xxxxxx; SI-List
Subject: [SI-LIST] Re: How good are tools to predict Radiated Emissions
?


There has been much disappointment in this area.  Tools can show
relative noise sources.  Absolute accuracy seems poor.
Steve.
At 09:48 AM 5/26/2006, Bashir, Shiraz \(GE Healthcare\) wrote:
>How good are tools to predict Radiated Emissions ?
>
>I mean..we can layout a board using some flow. Then use a tool to
see=3D20
>how this design will do from Radiated Emissions perspective..
>Did anyone of you have experience in this area ?
>
>Are there any tools which can pull in products' packaging
(mechanical=3D20
>housing/ plastics, connectors location, length of slots etc..) and take

>into account for analysis for Radiated Emissions..
>
>Reason I am asking is that most of the company I know including =
mine=3D20
>heavily rely on actual testing in-house (3 meter chambers) and
outside=3D20
>(10 Meters) which is risky..
>Because project is near completion and any tweaks cost big $s.
>
>Please let me know.
>Shiraz Bashir
>GE Healthcare
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