Hello.
I was thinking about building Faraday cage to shield the radiation EMI of ~1 to 100 MHz frequency from inside and asked several question here. One interesting answer is that The cage could be EMI amplifier with high Q as radiation is trapped inside with small loss for a reflection if shielding material is very good conductor. And this shield can not be 100% separated to other EMI sensitive devices.
That's why I have idea of utilizing radiation absorber for our EMI frequency range. I've found some product which are only good for GHz range as they're developed for high-frequency processing industry like smartphone and computer CPU.
Is there any product or company to provide the absorber exactly what I need?
Mr. Jang
Absorbers for lower freqs. usually have large dimensions and/or employ ferrite material loading in it. You may find some with TDK - http://tdkrfsolutions.com/products/absorbers
good luck!
Ferrite based absorbers work down to typically 30MHz. You need to consider the size of the enclosure compared to the wavelength. At very low frequencies where the enclosure is smaller than a wavelength then conventional wave based analysis is of limited value and a quasi-static approach is needed. The type and placement of energy dissipating materials can then be optimised. See
"New Screened Room Techniques for the Measurement of RFI." Journal of the Institution of Electronic and Radio Engineers. Vol 58, No 1. pp28-32, Jan/Feb 1988.
"The Operation of Antennas inside Non-anechoic Screened Enclosures." Proceedings of the IEE conference on Antennas & Propagation. York 1987. pp497-500.
Hm...I see that ratio of the size compared to signal wavelength is always important. Can I have quite different question in similar aspect? I have always wondered what happens on the voltage over ground plane when high amplitude AC return current flows over it. If there local voltage drop along straight line between current source and sink points on that plate or we can consider the plane as quasi-static such that whole plane is fluctuate similar manner in time? I guess it is also depending on the ratio mentioned above.
Ground currents obey Ohm's Law just like any other current so any two places between which a current flows will have a potential difference. Theoretical treatments of "ground" assume zero impedance. Remember also that as the frequency increases the ground conductor inductance gives rise to a reactive impedance.
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