Mu-Metal for shielding RF - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: November 22, 2020, 08:52:56 am
content: Hi,I found contradicting information about Mu-Metal shielding RF. Does anybody have any correct/proven infos about how effective it is to shield RF?Most likely it is dependent on the RF frequency...?If so then what frequency ranges does it shield?Thank you

author: tggzzz
author_rank: Super Contributor
timestamp: November 22, 2020, 10:21:28 am
content: Quote from: ricko_uk on November 22, 2020, 08:52:56 amIf you summarise the conflict, we may be able to give you a quick precise answer.Without that we either have to spend a lot of our time (not) answering your question, or simply point you to info you could find with google.You may findthishelpful in future.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 22, 2020, 10:30:54 am
content: In the RF range, especially higher frequencies (like > 10 kHz) any metal is good for shielding. The effect is mainly from conductivity.Not so high conductivity can be a slight advantage inside closed cavities to dampen resonance, but there are extra dampers (e.g. ferrite) that are more effective.At lower frequencies one has more like separate magnetic and electric fields. Here Mu-Metal is good in shielding weak low frequency fields (like < 100 Hz, down to DC). With stronger fields Mu Metal may saturate and normal steel / electrical steel can be better.

author: Mechatrommer
author_rank: Super Contributor
timestamp: November 22, 2020, 10:58:25 am
content: Quote from: ricko_uk on November 22, 2020, 08:52:56 amits contradicting maybe due to its a function of some formula or physical properties. different geometries, number of holes and how big, thickness will affect shielding effectiveness. good EMR shielding manufacturer will provide you with (average?) attenuation plot... such as what you can found herehttps://core.ac.uk/download/pdf/228156102.pdf..i'm not sure if there is any simpler than the facts...https://www.sciencedirect.com/topics/engineering/electromagnetic-shieldinghttps://en.wikipedia.org/wiki/Electromagnetic_shieldingif you want more proven fact, is you make a prototype and measure NF with SA, just like shariar did.. ymmv.

author: pwlps
author_rank: Frequent Contributor
timestamp: November 22, 2020, 11:08:45 am
content: To add to what Kleinstein said you might have a look here:https://en.wikipedia.org/wiki/Skin_effectThe formula for the skin depth gives you an idea about the required thickness for a metallic non-magnetic shielding in function of frequency.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 22, 2020, 05:18:06 pm
content: Note that bulk metals' mu drops off as frequency rises. Although I don't know offhand how much this is due to the effect of measurement (skin effect itself gets involved!). Usually somewhere in the low MHz. If it's still primarily due to skin effect, then the shielding effectiveness will be excellent. If it's due to mu reduction, then by some frequency, it will trend towards the bulk resistance of the metal, which will be significantly worse than copper or aluminum for example.I want to say I've seen plots comparing different shielding materials, and copper wins out at high frequencies (comparing same thicknesses), which shouldn't be surprising. Given the much lower cost of aluminum, or mild steel for that matter, if you aren't strapped for space or weight -- you can easily afford to just use more thickness.Tim

author: coppercone2
author_rank: Super Contributor
timestamp: November 22, 2020, 07:07:26 pm
content: I wanted a hydrogen annealing oven for this but the project got way out of hand. When you consider everything for doing it yourself, a stick welder and mild steel plate is your only cheap option (~1000$ to get it all set up with decent equipment if you can stomach a crappy welding table).

author: ricko_uk
author_rank: Super Contributor
timestamp: November 25, 2020, 06:11:52 pm
content: Thank you all, now things start making more sense also related to some of the other posts I initially came across.

author: jonpaul
author_rank: Super Contributor
timestamp: November 25, 2020, 06:16:43 pm
content: Hello:Mu metal specs and app notes are available from the original manufacturer:https://magnetic-shield.com/http://www.co-netic.com/There are two types netic and co-netic for high or low H fields.I believe the EMI shielding is exactly like any metal shield, and that the special properties of u and perm are specifi to shielding H fileds only, NOT E fileds, for example power transformers and CRTs.Open to your thoughts,Jon