FreeLists / si-list / [SI-LIST] Re: emi shielding

["Wani, Vijay (V)" <VWani@xxxxxxx>]

all:thanks for your time and response.

I understand the frequency range we worry about (30MHz - 2GHz), any metal
(or metallized plastic) would be overkill and effect of apertures will be
mostly determing factor for shielding effectiveness.
but, the shielding mechanism of conductive metals (or metallized plastics)
is mostly reflective rather than absorbtion. 

 if we have a meterial with absorbtion shielding mechanism (in 30 MHz-2GHz
frequency range), is there any advantage? i would guess, that will reduce
antenna effect in the system. would appreciate any thoughts.

vijay wani
Dow Chemical

-----Original Message-----
From: Pettit, Ghery [mailto:ghery.pettit@xxxxxxxxx]
Sent: Friday, November 09, 2001 12:14 PM
To: 'Wani, Vijay (V)'; 'emc-pstc@xxxxxxxxxxxxxxxxxx';
'si-list@xxxxxxxxxxxxx'
Subject: [SI-LIST] Re: emi shielding


Vijay,

The relative proportions are a function of frequency and the relative
conductivity and relative permittivity of the material.

The attached file is from a MathCAD 7.0 model that I put together a while
back.  The equations came from a Technit design guide published about 20
years ago.

You will note that in the frequency range that we usually worry about almost
any metal you might use is overkill.  It is the apertures that create the
problems.  The example in the document is copper.

I hope this helps.

Ghery Pettit, NCE



-----Original Message-----
From: Wani, Vijay (V) [mailto:VWani@xxxxxxx]
Sent: Friday, November 09, 2001 7:36 AM
To: 'emc-pstc@xxxxxxxxxxxxxxxxxx'; 'si-list@xxxxxxxxxxxxx'
Subject: emi shielding



hello:

as we know, threre are two main component of shielding effectiveness.
(Absorbtion and Reflection). is there any way to find out.. what percentage
of overall shielding is due to absorbtion / reflection for a given material?

thank you in advance.

Vijay Wani
Dow Chemical

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