Ferrite powder

[Datubie]

Hi all,

In my free time I like to dabble with my DIY audio gear and lately I've been toying around with the concept of using ferrite powder to shield power a/c cables and audio interconnect cables. I'm a totan novice when it comes to this, but I imagine that the powder used would be the same composition to that of the stuff used in ferrite beads. I'd appreciate any advise & comments.

Also, it seems impossible to get small quantities (say 5 to 10 lbs)of ferrie powder. Can anyone reveal a source.

Thanks,

Ken

 

[MagMike]

Hello Ken,

Unfortunately, there are some pretty significant hurdles that'll have to be overcome for turning ferrite powder into something that'll provide shielding. It's not something I would recommend for a hobbyist, unless they have the equipment available.

The ferrite beads you mentioned are pressed & sintered to acheive a density sufficient for shielding purposes. Before pressing, the powder has to be mixed with a binder to hold the particles together during subsequent operations. Usually very high pressures & temperatures are required to obtain a high enough density so the material can filter out particular frequencies. Without going through these steps, the ferrite powder will not provide much filtering ability.

Most ferrite bead manufacturers have different materials & shapes for filtering different frequencies and cables. They even sell kits with a wide variety of parts, specifically for experimenting. You might have better luck obtaining a kit and tinkering with that.

Good luck!

 

[UKpete]

Datubie, I agree with Mike. I once experimented with impregnating a motor airgap winding with ferrite powder, its properties were poor. Also the ferrite powder was difficult to get hold of in small quantities, even for the large company I was working for.

Another factor is that ferrite is non-conducting so it will only give a degree of magnetic screening, not electromagnetic. So it will only be useful for screening where there are heavily conducting cables in the vicinity. Most noise is electromagnetic, hence coaxial cable etc has a copper screen, not a magnetic screen. I think the difference is that an electromagnetic screen works against nearby conductors carrying voltages, whilst a magnetic screen works against high current conductors. That may be an over-simplification.

 

[Datubie]

Thanks guys for you help. Something new learned.

 

[EdStainless]

The other issue with sceening/filtering is the fequency range. Because of the different conductivity/magnetic prop/and so on these different materials are used to block different selective noise. Al foil, Cu mesh and hard ferrites are all used for different effects.

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