EMI shielding question

[Michael]

How effective is mildly conductive material when it is used as a
shield? ?
The frequency range of interest is ~100kHz and up, probably way in the
GHz range (SMPS, and spark discharge)
The material is graphite-filled (40%) Ryton. Multimeter shows between
tens and hundreds of kOhms between probes placed few inches apart,
depending how hard I push the probes.
I have really nasty noise source (switcher and aprk discharge)
approximately 1/2" away from sensitive electronics which is inside of
the housing made of the material in question.
Silver coating would be a logistical nightmare.... Bilding copper
housing is am option, but still a PITA.

Can anybody refer me to an information source?

THANKS!!
Michael

 

[Michael]

I think you will be badly disappointed by the Ryton.
Look up the penetration depth formula for EM waves versus
volume conductivity. I think you will need an actual formed
metal container that has good seam conductivity and small holes.

The problem is that exact volume resistivity of the material (40%
carbon) is not known (proprietary issues?)

 

[John Popelish]

How effective is mildly conductive material when it is used as a
shield? ?
The frequency range of interest is ~100kHz and up, probably way in the
GHz range (SMPS, and spark discharge)
The material is graphite-filled (40%) Ryton. Multimeter shows between
tens and hundreds of kOhms between probes placed few inches apart,
depending how hard I push the probes.
I have really nasty noise source (switcher and aprk discharge)
approximately 1/2" away from sensitive electronics which is inside of
the housing made of the material in question.
Silver coating would be a logistical nightmare.... Bilding copper
housing is am option, but still a PITA.

Can anybody refer me to an information source?

I think you will be badly disappointed by the Ryton.
Look up the penetration depth formula for EM waves versus
volume conductivity. I think you will need an actual formed
metal container that has good seam conductivity and small holes.

 

[Wimpie]

How effective is mildly conductive material when it is used as a
shield? ?
The frequency range of interest is ~100kHz and up, probably way in the
GHz range (SMPS, and spark discharge)
The material is graphite-filled (40%) Ryton. Multimeter shows between
tens and hundreds of kOhms between probes placed few inches apart,
depending how hard I push the probes.
I have really nasty noise source (switcher and aprk discharge)
approximately 1/2" away from sensitive electronics which is inside of
the housing made of the material in question.
Silver coating would be a logistical nightmare.... Bilding copper
housing is am option, but still a PITA.

Can anybody refer me to an information source?

THANKS!!
Michael

Hello Michael,

I do not think that it is going to work. You will have some shielding
for low frequency E-field (when you ground it), but for your
application where you have strong varying electric and magnetic fields
you will need metal (reflective attenuation).

The thickness and mounting will depend on the required attenuation.

Best Regards,

Wim
PA3DJS

 

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The problem is that exact volume resistivity of the material (40%
carbon) is not known (proprietary issues?)- Hide quoted text -

Here is an article that covers many of the concepts of effective
shielding:
http://www.ce-mag.com/99ARG/Bjorklof137.html