combining magnetic and electric shielding, shield behavior - Page 1
Forum section: electronics / rf-microwave

author: coppercone2
author_rank: Super Contributor
timestamp: May 27, 2025, 10:37:14 pm
content: I am doing experiments with iron and magnetic materials electroplating. I was wondering about if there is a complex interaction there between the materials.the cursory explanation is that:For instance Copper is one of the best shields for higher frequency energy (I guess true radiation). For lower frequencies you have a inbetween like nickel silver (nickel is slightly magnetic) and for the lowest frequencies you use a strong feromagnetic material like iron or better.The questions I have1) Does iron do anything different for frequency response when its near-field shielding (i.e. before the frenzel zone of antenna, the reactive region). In that region you still have distinct H and E fields. If something is right up close to an antenna, even if its high frequency (say a PCB antenna), does the shielding material of choice change from copper (which you would naturally use for high frequency). Because if its really close it looks like its still getting a distinct H field from the transmitter (coupling), seemingly making it desirable to say use a iron shield for a component near a microwave antenna? (though itseems to me even if its reactive it might have to do with the frequency properties of the magnetic material, so it can exhibit magnetic behavior.. I.E. iron might not be a good choice for some near fields even if they are 'magnetic' )2) same as one but in the frenzel region3) You can put a iron box in a copper box or a copper box in an iron box. In these cases there is a air gap between them, or a dielectric of some sort. What happens if the iron is ON the copper. I.e. you iron or mu metal plate a copper box. I think it would work the same because the copper is transparant to magnetic fields but I am not sure, maybe something with the eddy currents having a 'shunt' of copper connected on top of them?4) for true far field low frequency transmissions. Say 60Hz getting to a space probe very far away from earth (high earth orbit, seven wavelengths of 60hz) where the wave is 'radiation' and there is no induction. Do you still need an ferritic shield or is copper going to work correctly at this distance? I mean if you are trying to filter a earth source, not something that is generated by a nearby satellite. in this case does it have any purpose to put say iron there for a shield? if you can guarantee nothing gets close to it.So, do you actually look at just the frequency for shielding, or do you look at the distance to the transmitter and the frequency. ? (which would make iron essentially 'reactive' shielding ONLY). To me it makes sense because magnets react, meaning it has no utility at high distance. ?I mean for AC. I don't know about the DC magnetic field, that I guess is very slow AC because of pole reversal with a time constant of 5000 years... but it does seem to me that unless the distance is extreeeeeeemeeeeee you would need a magnetic shield for the earths magnetic field, always. Eventually would you be able to do with a copper shield for this when it becomes a wave? (say edge of universe)

author: Simmed
author_rank: Frequent Contributor
timestamp: May 27, 2025, 11:33:16 pm
content: so many variables to trybest is to play with FEMMshort answer : electroplating will need at least 0.2 0.3 mm thick i think ?and then there is the chart on the web

author: coppercone2
author_rank: Super Contributor
timestamp: May 27, 2025, 11:35:45 pm
content: That is not many variables IMO it should be easy to explainITs really two questions to answer that might solve the rest. I believe someone that actually understands the physics would know this as textbook:in reactive field (very near) region (at high frequency) do you still want copperin radiated fields (far) region (at low frequency) do you want steelI want to know if 'magnetic' shielding really means shielding for the reactive region of a transmitter. I bet user 'radiolistener' knows this onethe frenzel region might be the tricky thing to understand here, but that is less important then these fundamentals.Determining the thickness is something else entirely that is way more complicated and probably requires calculation. I just want to know the principle of the interaction of materials with near (reactive) and far (radiation)

author: radiolistener
author_rank: Super Contributor
timestamp: May 28, 2025, 07:17:32 am
content: There is no single definitive answer that works universally, as attenuation in the reactive (near-field) region depends not only on the material but also on frequency and geometry. While some generalizations can be made, near-field behavior is complex due to the strong coupling and interplay of electric and magnetic fields, which are highly geometry-dependent.To accurately assess the interaction of materials with near-field emissions, especially in complex geometries, full electromagnetic simulation (FEM or MoM-based modeling) is often necessary. This is especially true when entering the Fresnel region, where neither purely reactive nor far-field approximations apply cleanly.

author: coppercone2
author_rank: Super Contributor
timestamp: May 28, 2025, 07:28:32 am
content: would it ever be the case that in the reactive field region of a RF antenna, say 1 wavelength, a copper shield is not doing its job?Can you generalize if copper as a material is a cure all for being near a high frequency RF antenna.I guess I can try it. See what happens if I put a piece of copper tape on or near a near field probe and try to measure with it............... you would think magnet part would go through it (and heat it a little?), and compare it with scrap of iron or whatever magnetic thing I can find. I wonder if I have a nickel ferrite tile some whereLike if you have a PCB wifi antenna on some board and it has a shielded circuit nearby (portable device). I wonder if copper is always the best choice for that shield (if you don't consider cost). 2.4ghz is 12cm. Easy too be in the near field. Even if its some fancy circuit (i.e. uses separate batteries and opto coupler. 5v low power opamp with 2 coin cells)

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 28, 2025, 01:08:54 pm
content: Yes, in theory a shield made of multiple layers with gaps between them should be much more effective than without gaps. Similar to a double-paned window, which performs much better than a single pane of glass with the same overall thickness.Iron/steel is sometimes chosen over aluminum/copper when low-frequency coupling via magnetic fields is a concern. Using a high permeability material greatly reduces the skin depth, which can make a better shield despite having higher resistivity.But in practice, the major limitation on shields is their manner of construction, not the materials they're made out of. For example, a shield made by CNC from a solid block of material will outperform something made from bent sheet metal and rivets, probably regardless of material selection.

author: coppercone2
author_rank: Super Contributor
timestamp: May 28, 2025, 01:37:27 pm
content: Are you talking the seam from the rivet or the bends or the solder joints?I thought a soldered box would be high performance if made out of thicker sheet copper (gap antenna between rivet). I know the seams are a killer. But I always assumed a soldered seam would be very good if copper.The thing that brought this thread into life is the idea of "high frequencymagnetic coupling". Because within 12cm of a wifi antenna its supposedly the region where magnetic fields are still significant, even if the frequency is in the GHz. That's why I thought a near field probe could test it.

author: radiolistener
author_rank: Super Contributor
timestamp: May 28, 2025, 04:36:22 pm
content: What I mean is that in the near-field region, the electromagnetic fields have a very complex spatial structure and are highly sensitive to even small discontinuities or distortions - such as the shape or presence of a tiny piece of metal or dielectric.To some extent, it's possible to approximate the local impedance or coupling based on material properties and distance from the source, but this is a rough estimation at best. Due to the intricate and geometry-dependent nature of near-field interactions, there is no simple analytical solution. That’s precisely why full electromagnetic simulation tools like FEM or MoM solvers are used when accurate results are needed.The near-field region is far more complex than the far field, where electromagnetic behavior can often be approximated as simple plane-wave propagation. In the near field, electric and magnetic fields from different sources and modes overlap, creating complex and chaotic interference patterns. These patterns are highly sensitive to even minor changes in geometry, frequency, and material properties, making generalizations difficult and often requiring detailed electromagnetic simulation for accurate analysis.Copper shielding does not always yield better results than shielding made from materials like steel. The difference is most pronounced at low frequencies, where magnetic permeability plays a critical role. However, even high-frequency (microwave) circuits may require effective shielding against low-frequency interference. Therefore, shielding design must be approached holistically, taking into account the full frequency spectrum and the specific nature of the interference.There are no strict boundaries between what constitutes "high" or "low" frequencies, nor are there clear-cut thresholds for near vs far field distances. As a result, shielding is not a matter of choosing a single ideal approach, but rather finding an optimal balance based on the specific frequency range, field behavior, and system requirements.Even if the copper foil completely encloses the sensor without any gaps or seams, it is still unlikely to provide effective shielding in the reactive near-field region. At these distances, magnetic fields can penetrate deeply into thin conductive materials like copper, and the resulting attenuation may be insufficient just because at low frequencies the skin depth is greater.However, by carefully engineering the geometry of a shield, it is possible to achieve electromagnetic effects not typically found in natural materials. This approach forms the basis ofmeta-material technology, which enables tailored field manipulation through structured design rather than bulk material properties alone.

author: mtwieg
author_rank: Frequent Contributor
timestamp: May 28, 2025, 10:00:41 pm
content: Quote from: coppercone2 on May 28, 2025, 01:37:27 pmSure, if you make a box out of separate pieces of copper and solder them together along all the seams, that will perform nearly as well as a box formed from solid copper with no seams. Not very practical from a manufacturing standpoint though.QuoteIMO for choosing a material the most important figure of merit is skin depth at a given frequency. At low frequencies (like <1kHz), iron will have a much smaller skin depth than copper, and therefore provide better shielding (all else being equal, that is). As frequency increases, the effective permeability of iron decreases, and eventually its skin depth will be larger than copper.

author: coppercone2
author_rank: Super Contributor
timestamp: May 28, 2025, 10:48:58 pm
content: is there some document that might show shielding power vs multi materials. I feel like there should be a graph some where that shows when you put different thicknesses of nickel on a copper shield for some bandwidth. Like someone must have put that in a book because it seems like super common to want to know what that might do. Its practically a vendor option : 'not only can we stamp this shit out we can throw it in a tub of chemicals for you and make it silver colored. it might do something like this:'

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2025, 01:53:17 am
content: Does anyone have any theories what might happen with copper plated iron or iron plated copper for a shield (or some magnetic alloy more advanced then iron)? Speculation is fineMy theory is that it will workit might be already known, that is, can you put magnetic tape on aluminum or copperAnd more importantly:Is magnetic tape even a real product used by compliance lab for more strict compliance things that might go into magnetic (I see some mil standards got into this with helmholtz tests), or is it just a 'silly' product ?3M does sell something like ithttps://www.digikey.com/en/product-highlight/3/3m/high-permeability-magnetic-shielding-sheet-1380Did anyone ever see it put in some real engineering design to pass a test?https://incompliancemag.com/low-frequency-magnetic-field-shielding/I think more often then not people want to use the copper band shorting technique, because I have actually seen that on transformers, including one in a wall power supply I took apart IIRC (old). Not sure if I ever saw magnetic shielding outside of a CRT or steel chassis.

author: TimFox
author_rank: Super Contributor
timestamp: June 03, 2025, 01:59:57 am
content: Go to the website of “Magnetic Shield Corporation” for app notes.

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2025, 02:03:16 am
content: the documents on this page?https://www.magnetic-shield.com/quicklinks/Is there some big document in there or is it all little snipets?

author: TimFox
author_rank: Super Contributor
timestamp: June 03, 2025, 02:14:48 am
content: Tricky website.Go to Resources/All about shielding FAQs

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2025, 02:22:59 am
content: I see eeach of those links has a article I thought it brought you to the glossary for some reasonBecause I got my iron plating forming, with ferrous chloride, calcium chloride and a small amount of aluminum chloride. It turned orange brown milk and I thought it was either the aluminum causing a problem or that the ferrous chloride was bunk, but I added iron filings and a bit of hydrochloric acid and it turned into a clear green liquid over night, and there is shiny iron nodules that formed on the bottom that emit a tiny bit of hydrogen bubbles, now I need to do something with it. Same problem as with tin chloride, you get milk if its not treated properly.

author: radiolistener
author_rank: Super Contributor
timestamp: June 03, 2025, 09:19:06 pm
content: you can estimate attenuation from distance to the source, shielding material properties, thickness and frequency

author: TimFox
author_rank: Super Contributor
timestamp: June 03, 2025, 09:29:49 pm
content: Note that ferromagnetic shielding and conductive shielding act in different ways: (assuming shielding an interior volume from external fields in this discussion)Ferromagnetic shielding re-directs the external flux lines around the interior volume being shielded, with only a small fraction persisting inside the shield, so long as the flux density of the external field crammed into the narrower area of the shield is below saturation. In the linear approximation, the field inside the shield equals the geometrically-magnified flux density inside the shield wall divided by the permeability. Nickel alloys have higher permeability but lower saturation, so appropriate layers of iron and nickel alloys are often useful.Conductive shielding induces eddy currents in the conductor that counteract the field inside the volume.Of course, ferromagnetic materials may be conductive enough to perform both processes.

author: coppercone2
author_rank: Super Contributor
timestamp: June 03, 2025, 09:54:52 pm
content: But do they interact?? Because if you plate it, it becomes parallel electrically (conductive). The magnetic material is resistive in comparison to the copper, so the copper is like a distributed shunt from the perspective of the magnetic material. I thought it might lead to some other behavior. In basically every case I see, they are electrically insulated from each other to megaohm levels on DC and some capacitance. But if its one thing.... I don't know if there is another effect or what to search forI.e. the magnetic material I found has a conductivity something like 100 times lower then copper. I think 4uOhm vs 0.04 uOhm / square or whatever unit they use for thin stuff. And its thin, things seem to get weird with thin films.Frying pans seem to work fine with this (copper or aluminum that is welded to steel on the entire surface for a good pan (blast) ), but is anything else happening in there?I am asking if basically lets say you put a thin insulator between the magnetic and electric shield, that has negligible thickness but it insulates it (distributed) would it significantly change performance and if so why?i.e.1) copper with magnetic shield plated on it (its directly connected)2) copper with tiny air gap and then a magnetic shield on it (two very precise and steady nested boxes floating in zero g perfectly with a tiny gap between them)I think I am asking if it has some kind of new behavior because its a 'meta material' with different electrical properties despite very similar size and spacial location for both shields.From a transmission line it would be like decreasing G to short circuit levels, where there is normally only C. Leaky. But I don't know if its relevant, but the concept of what value is changing is the same

author: coppercone2
author_rank: Super Contributor
timestamp: June 04, 2025, 03:41:54 am
content: Lol I managed to make a magnetic penny with the iron plate and supposed iron sheet. Its super slow, it comes on shiny at the recommended current rate but its so god damn slow. I got it to go alot faster when I upped it but the surface finish became uglier. It very lightly sticks to a very powerful magnet.Chloride iron does appear to work if you use recommended current levels and take it real slowI need to build a stand for holding objects because I did it so bootlegI think its a good method, I would rather this then trying to make iron shield boxes for PCB.Made me wonder what kind of planet would use iron plating for a copper penny as protection. What kind of toxic ass atmosphere that would have. Like some kind of tin gas.