I want to pick up some kind of ferrous sheet material for general purpose shielding. Mu metal or permalloy sheets are crazy expensive, small and few suppliers. Carbon steel is cheap but not the best shield (too much carbon). Wrought iron is an excellent shield highly permeable, 100% iron, no carbon, but its not available in sheets. Then I came across this stuff, iron foil. Cheap, has anyone used it? I understand the idea is to redirect magnetic fields with a shield, as no material actually stops the field. But controlled redirection of a field getting near a sensitive input for example.
https://www.ebay.com/itm/372501495398
https://www.engineeringtoolbox.com/...eability Medium , 0.999834 21 more rows
https://www.ebay.com/itm/372501495398
https://www.engineeringtoolbox.com/...eability Medium , 0.999834 21 more rows
Last edited:
The permeability of iron depends on grain size and work-hardening. Annealed material will have the best performance,
and the purer the metal the more effect you can have through annealing. If this foil is cold-rolled it may be in a work-hardened
state.
and the purer the metal the more effect you can have through annealing. If this foil is cold-rolled it may be in a work-hardened
state.
Mmmm annealed sheet steel is also cheap. I guess it depends on what you're shielding too, mu metal can saturate quickly around a power transformer where steel would not, maybe being better depending on the field. But mu metal around an input transformer would be better than steel, it has no chance of saturating. I already have plenty of annealed steel sheets, softer for sure. The steel retailers all carry 4130 or 4340 alloys 4130 is much softer but has no nickel, 4340 is much stronger harder but has a percent or two nickel going for it. My gut feeling is the 4130 might be better for shielding solely on softness, maybe.
Last edited:
The foil may be a good contender from a magnetic shape anisotropy standpoint, just make sure the plane of the sheet never intersects the object you're shielding otherwise you will direct the field into it.
For low radiated frequencies, pure steel is far better than mumetal. And of course it is also about the depth of the screen. 5mm of steel is imo needed for a traffo for the lowest frequencies. Maket it complicate. Perhaps L shapped steel thick foil is your better if you have a chassis around your polluting traffo.
The higher the frequecies the thinner the material and also its composition...copper and mumetal for instance are good for RF...no thickness needed but proofness of the case : thin slots and so on. For a traffo you need more thick wall that vaccum (direct) the field along its sides...
The higher the frequecies the thinner the material and also its composition...copper and mumetal for instance are good for RF...no thickness needed but proofness of the case : thin slots and so on. For a traffo you need more thick wall that vaccum (direct) the field along its sides...
I experimented a bit with magnetic shielding when I built a phono preamplifier. The main issue was stray magnetic field from the mains toroidal transformer.
Putting a steel shield cap on the first tubes had no effect at all. Not to mention aluminium caps.
Placing a steel plate between the transformer and the tubes had no effect at all.
Placing a permalloy sheet between the transformer and the tubes helped a bit. The permalloy sheet was about 0.3 mm thick, 12 cm wide, and it came in a 0.5 meter roll, found on eBay.
Putting a steel shield cap on the first tubes had no effect at all. Not to mention aluminium caps.
Placing a steel plate between the transformer and the tubes had no effect at all.
Placing a permalloy sheet between the transformer and the tubes helped a bit. The permalloy sheet was about 0.3 mm thick, 12 cm wide, and it came in a 0.5 meter roll, found on eBay.
It all depends on what you want to shield. You can use a old/broken toroidal transformer. Remove the copper and wind down the core.
The thicker the laminates the better. Only for very sensitive projects you need mumetall.
The thicker the laminates the better. Only for very sensitive projects you need mumetall.
Mu saturates quite easily. That is one reason why any serious Mu shield, as TVRgeek says, is done in layers. The outside layer saturates but that's less field on an inner layer. 3 layers is very common.
You can also go fat. Common 'iron' (all steel now) Sch40 steam/drain pipe is good for the cost (BAD for weight, and worse if layered 1-1/4" inside a 3" etc).
The multiple layer is probably to keep the shape anisotropy, sheets need to remain thin to maintain the field specifically in the plane of the sheet. Its similar to transformer core composite graphite-steel, which guides the magnetic field better than a pure steel core.