shielding signal inductors?

[coppercone2]

You can buy shielded inductors (through hole), in some values. often its not available.

I read the datasheet for some, and it says iron shield.

I ordered an assortment of shielded inductors, but I might want different values.

You can buy amorphous cobalt, mu metal or pure iron sheet in workable form to cover a inductor to make its shielded version.

What is a good choice if you just want to put a turn and a 1/4 on a axial inductor, and then wrap it in some tape? This would be for signal inductors (no more then like 1 Amps)

Any other tips would be welcome. Alot of these inductors are obsolete , or 5000 minimum order.

this would be for wound inductors (hand made)

Does thickness of the shield scale with inductance value? (they are all the same size part) I see shielded ones have reduced frequency response. How would different materials effect it? Are they gonna start crawling when you switch them from iron to mu metal?

I was planning on trying all three materials, but I also thought it might be a waste of money (and that I should stick to iron like one of the manufacturers said).


The SRF between a shielded and unshielded 100nH (dielectric core) one is from ~700MHz and ~250MHz. Presumably with a iron shield, so the penalty is more then 60% frequency response loss. How would it compare if you used amorphous or mu-metal of the same size compared with the iron shield it has?


However, a shielded and unshielded ferrite inductor (1uH axial, 1Amp) that look very similar, they have the 157 (unshielded) to 140 (shielded). Does this mean that for a ferrite part, having the shield makes little difference, but with a dielectric core part it makes a big difference? The parts are not super identical but similar. I thought something along the lines if you have a ferrite core (good magnetic) surrounded by a skin of magnetic material, it won't really change it too much. What if its thick?


I am thinking with the air coil one, the SRF is being reduced by the capacitance of the shield. In the cored version, you already have a core that is somewhat conductive acting like a capacitor, so adding another layer on top does less, but I thought it might do more then my analysis of manufactured parts leads me to believe. But then it also makes me think, it does not matter much what metal is used?

I got supposedly pure iron and some kind of amorphous cobalt to experiment with. I thought about mu metal but it seems sketchy, I thought it might mis behave. I also got a book on electroplating, and found some possible ways to iron or magnetic 'alloy' plate objects, theoretically you can plate a inductor after giving it a strike of copper. There is some baths that use ferric and nickel or cobalt to make some kind of plate that sounds like a pretty magnetic material, supposedly with low stress!

[Kleinstein]

There should be relatively little need for mu metal or amorthous material for shielding an inductor. There are different reasons for shielding:
1) reduce the effect of added magnetic matrial or metal on the inductance
2) reduce the pick up of an external field, especially hum
3) reduce the effect of an external DC field in effecting a magnetic core, like unintentional flux gate effect

Depending on the frequency band, just a conductive metal gives enough shielding.
For the last effect it is more about strong flields and enough iron thickness is needed to really devert a stron field.

[coppercone2]

well the amorphous stuff I think is corrosion resistant, and it comes with adhesive on it, so it might be easier to implement, and look better. Iron will need protection. I think stainless-like stuff is more of a modern design choice, because its OK to leave it unpainted.

 I am hoping the amorphous cobalt sheet works. With iron, I think I would roll it up, tape it up, spot weld stitch it, and then use varnish on it. With the amorphous film, I think you can directly wrap the inductor and its done.


The iron shield inductors may end up looking like communism.I trust that red varnish but damn it really stands out.



Unless I just heat shrink it. But shiny looks cool 

[richnormand]

When I was working with photomultiplier tubes for single photon work you could get sheets of mu-metal. It was used as an electrostatic (grounded) and magnetic shield for the tube.
But it was mostly good at low frequencies. I would guess that it would work well with hand made inductors to stop the mag field going out but at the same time it might change the inductance.
If too close it would look like a shorted turn. OK if you use the inductor as a filter less so as an LC situation.
If you can afford some distance  it might be easier to shield the sensitive circuit than shield the inductor?

[coppercone2]

I don't know, I wanted to stock it, they sell it but its missing values.

if its picking up noise some where I don't think shielding the circuit will help  though

Like what are you gonna do put filters everywhere to deal with noise coming in from the outside of the circuit? I am not in antarctica. and I bet the generator there is noisy too. I found prototyping with boxes is wonderful in theory but in practice its extremely inconvenient. Even putting  final project in a box is shit load of work. Anything with enclosure shielding... it seems to only be theoretically practical. I wonder how many people actually do it. You would think its common but what I see people want to do is have a bare PCB with wires soldered to it, let alone design in interconnects or a enclosure. if anyone is doing enclosures their 3d printer lol

if people are arguing about the subtraction of a few ceramic caps, they will most likely suffer from a heart attack after buying copper, or lol price materials like nickel silver sheet

and then you get clowned trying to weld DIY enclosures up. 200+ hours of tig and a $2000 box pan break, maybe your getting somewhere, if you have the time on top of that.

and then, you have a dogma to keep the inductor away from the altoids tin or whatever cheap mechanical constraint you found

I think its very much worth investigating, I am not sure if treating the inductor like a smelly boar is actually a smart engineering decision that leads education

 I saw someone working a hole saw into a enclosure crammed into some machine tool at work and I thought he was gonna put someones head in there, its not popular at all

I knew something was up when I started looking at getting a english wheel 

[coppercone2]

I am also thinking how to test this stuff. I thought to take a transformer (i.e. MOT) and cut it into a axial inductor. I know you can focus the field better if you form a C but I wanted a more broad field

[coppercone2]

I took apart a large transformer for the begining of the large laminated inductor I wanted to make. A 2:1 transformer 16 Awg 15A, without its primary (10A rated) shows 10mH at 1KHz with the I parts removed. I want to cut the E apart so I can just have a axial inductor.

I don't know if it will beat out a medium (1/2 coke can) sized ferrite inductor that I have, which is also 10mH. I think with its full windings it might.

I wonder if it will be useful for testing the shielded inductors with external field.

I always wanted a large axial laminated inductor anyway.

The laminations are difficult to debur and alot of them are bent. The sheet metal deburring tool (drag handle) works OK but its tedious. For flattening I suppose I need to strike them on an anvil.

You can make a big inductor from the middle of the E, a large inductor from the I's, and then if you cut the remaining L's apart (made from the E) you can make a few medium inductors, and you have a bunch of small squares left over to make odd cube shaped inductors. 

[coppercone2]

the amorphous cobalt is a interesting material. It  feels very springy, and it does get attracted to a magnet somewhat strongly. Seems like its very easy to use. A transformer lamination is much more strongly attracted to a large magnet then the roll of amorphous foil I have, maybe this is because of the low saturation.

The hymu 80 is also somewhat magnetic, but when paired with a giant magnet, you would not feel it. The iron transformer lamination sticks way stronger.

I guess these materials can only be evaluated by tests, you would think they are weak shielding material if you try to test it by hand


The hymu 80 is springy and looks like it will be annoying to form around a inductor, the amorphous tape looks like the best material from a convenience standpoint


The iron foil was poorly packaged and creative materials were used (i.e. a stretched bag was used to tie the roll together). At least it did not come in soviet cardboard but it did give me a kind of bad vibe. It is more formable then the hymu 80 but its still real tough


I got done making my e6 per decade or better series of shielded inductors from 100nH to 100mH. Now I need to buy air coils and torroids that look interesting.

These parts look sick
https://www.ebay.com/itm/201954630377

shame its iron core


And I gave up on the modified transformer, it was starting to feel pretty bleak to work on those old rusty laminations, and the aspect ratio is pretty incorrect. I decided its a foolish pursuit, so I bought a nice big 20mH inductor instead 

Got lots of class 1 ceramic caps TH too, for easy experiments. ~90 different values (skipping anything under 30pF). That was weighing on me heavily but it looks like the correct approach for doing experiments with noise and stability etc. Having all the advanced equipment and then ending up with y5u seems kinda like messing up the front end of the project.