A portable box for 1/f and low noise measurements

[iMo]

As I wrote once - in late 80ties I worked in a lab which messed with 1/f noise measurements. Within my diploma work I created a measurement chamber for the LNA and the samples with all the necessary batteries. The result - see below. Inside that box we had an additional copper foil inner box. There is a single 5mm dia hole for the coax.
What is funny a friend of mine, who works there at university, showed to me my decades old box yesterday - they found it while they did a cleanup of the labs, with an intention to carry it to scrapyard.. ..
Thus I've shot a couple of pictures - for a record - the box weights some 25-30kg (an estimate), a little bit rusty here and there, but still in an excellent condition..
 

[Gyro]

Yep, that ought to keep most stuff out!

[Andreas]

So you really avoided 50 Hz line noise hum 
(which I have to test every time with a new set up).

with best regards
Andreas

[miro123]

My outer chamber is ~4..5kg AL case - from chamber 1 to battery chamber #2 - the link is electrical - optocoupler insulated. second picture shows the optical fiber connection for the outside world.

[Overspeed]

Hello

The old box looks to be a nice shit metal work made with professional skill .

To do it Quick and Dirty , that possible to built one '' double skin '' at good price with :

- Two ammo box as '' russian dolls ''  a 50 Cal / M2A1 Ammo Can to hold a 30 Cal / M19A1 Ammo Can
as ammo boxes are made in carbon steel box so that easy to TIG weld plate or even use rivets
- Two stainless steel box as used for surgical equipment sterilization

Regards
OS

[iMo]

It is not easy to shield 50Hz. Do the math - what kind of material and what thickness would you need in order to attenuate 50Hz x-times..

[DavidKo]

So you need to come and move it alone to scrapyard,  since it does not have handles only sharp edges . I must say nice mechanical work. I'm not sure if portable is the right word. It does include the trolley.

How it had performed in comparison with "standard" cookies box?

[coppercone2]

how much better would the steel box you made be if the sides were rounded off?

I thought there was a large problem with fringing

The impressive thing is that its from a single block. I believe if you weld it, there is a substantial loss.


Also for 1/f noise, is radiation significant? Does it make a difference to use lo-rad steel (i.e. pre July 16, 1945 or better purified)? Is there effect on something like high gain amplifiers? 1/f noise is rather slow, so if there is something happening because of nuclear radiation @ a low level, it might confound the problem

I often wanted to weld such a box, but I thought I might end up with a crock of shit because I don't have a big mill to make it out of a single block like that. Well, I mean the bottom is OK to weld on if you make the milled step, but the sides of your box are 1 part.

I wonder if you make that kind of box is it doable on a large band saw to make the walls, and fairly shallow milling on top and bottom plates. But I can see myself being assaulted if I asked them to spot weld the bandsaw blade after its inserted on the box some how !~


I think you should try to rescue this box... pure iron stock is kinda expensive, I only got smaller chunks before (to make bobbin)


These would be good for transport, if you size it correctly.
https://magswitch.com/collections/lifting

[iMo]

The walls are sheets, precisely machined, up to a mirror flatness, then at the edges welded with the same material. And yes, it was not optimal.
At that time we were discussing the ideal situation would be the get for example a piece of a 16inch naval gun from a sunk battleship in WWII, preferably far away from Bikini or Eniwetok atolls The chamber would be round and thick.. No idea what kind of material they used at that time..

[coppercone2]

I doubt it, the cannon is high pressure, I assume it would have carbon. You can't have a barrel wear. Though, they do use liners. The old story goes there would be a whole mob of guys with acetylene rosebud torches and someone feeding a bar of silver to get sucked through the entire thing when its red hot, to fix the liner in place... which might have high chromium content.

Well anyway, the corners look perfect. There is a nasty weld bead on the bottom


Making such a box has been on my mind for a decade or more lol

[coppercone2]

This brings me back to the unanswered question I posted several times.


If you have copper that is bonded to the iron (i.e. copper plating) is it the same performance as if you put a box in a box?

So if you copper plate the interior of the box, instead of making a smaller box to put inside. Does it matter??

I mean so long you had another lid (not to compromise the tight fitting magnetic seal with copper spacer).

So there would be a thick copper layer formed on the inside of the box, with a ledge, so a copper lid would fit in there to close it, and the steel would go on top (and the iron would have the labyrinth edge so it makes a tight fit directly to iron)


Because I did experiments with pure iron electroplating. It seems to work, enough to make a dime coin weakly magnetic. So I thought about putting a thin layer of iron on a copper box, though its much easier to put copper on iron. But I don't understand the performance difference between nested boxes and multilayer boxes. I know it needs two seals, one for magnetic material and one for electric material. But is there any other performance change?



And for magnetic gaskets, I wondered about a true gasket filled with ferrofluid.

[iMo]

"Skin depth" refers to the depth into a conductive material at which an electromagnetic (EM) signal's current density or amplitude decreases to about 37% (1/e) of its value at the surface. This phenomenon, known as the skin effect, depends on the frequency of the EM wave and the electrical properties of the material, such as its electrical conductivity. In essence, it describes how far into a substance a wave can penetrate before its power significantly diminishes

For highest freq RF copper plating will have similar effect as the foil, imho. The skin depths for RF in copper are sub-mm to umeters (like 100MHz is 6.5um, therefore we have copper clad aluminum patch cables ). So it depends always on the frequency. With 50Hz and copper is that different, the skin depth is 9mm.
For steel/iron/permalloy etc you need to know the resistivity, permeability etc and you will get skin depth. The shape is important as well, so basically a rocket science (you would need a simulator for that).

[coppercone2]

but does the insulation between the copper and steel have any effect? Because if you have plating, its direct connection. If its a box in a box its just capacitance and a ground strap (maybe).

If you draw the circuit, its like having or not having distributed "conductance" "G"


For stuff that is electroformed (substantially thick), not just a skin coat.


It does not appear to hamper a induction frypan, which is usually aluminum with some ferrocore

I wanted to know the effect of the conductance, if any.

[iMo]

I would say the materials and their purpose is so different, that it does not matter how they are wired or whether there is an isolation in between. The steel part is high resistance compared to copper, its role is to mess with magnetic part of the spectra, the copper shields mainly electric fields. The fields may produce some currents in both. To analyze that sandwich in such a detail you would need to take 4 Maxwell's equations and apply them on that 3 dimensional sandwich (steel/something/copper in the form of a box)..

[coppercone2]

That is what I was wondering about, you get a 'eddy current'. But then there is a copper shunt across it. I mean with the way eddy currents are drawn as a circle current in the material


Maybe the best way to study it... is to make a very thin copper layer on a non conductor and put a very thin metal layer on top of it. So both are thin and the interface is significant in size compared to each

[1audio]

You could use cast iron pipe and matching cast iron caps. In the US its available in larger diameters with 1/2" walls. The classic RF trick would be to silver plate it. (Silver plated sewer pipe? For only the best effluent.) It would weigh a ton. You would also want to degauss it.

[coppercone2]

cast  / grey iron is rather high in carbon, you need to get pure iron special

[1audio]

I would think 1/2"  thick iron would make up for less magnetic softness. Cast iron works pretty well on an induction cooktop. And no seams or gaps on a round pipe.

[CalibrationGuy]

I'm still stuck on the "portable box" part. On one of our ISO17025 audits, my auditor told me a story about an engineer who was so obsessed with noise that he had a shipping container buried underground to create a lab. No ac powered devices allowed. So yes, you can take this too far apparently...

TomG.

[coppercone2]

I think that is a good idea for studying a device? It's easy to find expenses that dwarf that by orders of magnitude to resolve engineering questions.

Kind of like its OK to buy some box for $200000 dollars but its not OK when you need physical space for some reason.

Its like a stupid meme. If you need a closet or structure for your work, its considered taboo. When you need something 10-100x more expenisve, its OK, especially if its software.

Maybe its because if its 'large' then facilities gets involved and they want a piece of the action or something. I always thought it had something to do with keeping secrets from facilities people. 

It seems to involve high society engineering fashion lol

The only thing I noticed that gets silly with EMC rooms is when people don't know what they are doing and there is like computers and monitors in them (regular, not some special NSA shielded ones), but none the less if you are interested in only a small part of the spectrum.. it may be logically correct even if its 'bad'.


Well, maybe in general.. it seems that low frequencies are not respected for some reason. It's not fashionable. I thought it might because lumped magnetic elements don't look fashionable/cool for non technical people, more like ugly, and there is no raw power involved that can be used to 'impress', as you would get with something like a ugly messy nuclear reactor or particle beam lol

Like I can imagine how much difficulty a project with some very expensive "ei core' transformer would get, because of its boxy appearance. It would need to be redesigned to have a low rectangular form factor (like a ferrari car) rather then a tall boxy factor. I mean like if the laminations were made from rusty looking neutronium.


@OP, if that box was 2x as tall, I have a feeling you would be physically assaulted by administrative non technical budget personnel at the university. You got lucky that its substantially wider then it is tall. Single "shoe box" form factor is kind of cool. If it was a double decker you would be in trouble. If it was 30% shorter, it might get a full page on the university department advert with super models.

I noticed that the larger 'ultrasonic cleaner' form factor devices (big tall rectangle) get banished/hidden. Especially if the interface is on the long side. If its on the short side it might be OK (similar to computer tower). Oscilloscopes are OK because they get rounded off like a boom box with clever slopes (the older ones, new ones are skinny)


Why is this cinder block here? its not a construction site

[iMo]

..
@OP, if that box was 2x as tall, I have a feeling you would be physically assaulted by administrative non technical budget personnel at the university. You got lucky that its substantially wider then it is tall. Single "shoe box" form factor is kind of cool. If it was a double decker you would be in trouble. If it was 30% shorter, it might get a full page on the university department advert with super models.
..

I trust readers generally understood that the word “portable” in this thread’s subject was intended humorously, not literally, and should be taken as a joke rather than serious.
 

[coppercone2]

Oh no, I did not consider the weight. I just mean how the shape looks

Engineering really needs to be 'all size friendly' or you end up with miniaturized atrocities

I think there is a strong rejection tendency for certain enclosure shapes, not to mention hatred of special structures (i.e. underground). I felt like I was getting '5th ave jewelry store' management decisions before, based on irrelevant cosmetic factors. Someone has to "like it". Like to say... get a more practical system authorized (upgrade).

They are worried about what non technical people will think, while I am worried about physical laws. In the eyes of laypeople, magnetic engineering is ugly. Thermodynamics can be ugly too, but it saved by copper or nickel plate (looks expensive/shiny). Aerospace gets 100% free pass (turbine blade, ogive shapes, sharp points, etc). PCB designs are governed by all sorts of strange visual dogma. And magnetic tends to make a disliked noise/hum (people think its wrong when they hear the noise, even if its just a perfectly sealed core vibrating).

this shape (or better yet, a planar) can run at 165C with a 50 amp inrush current and its OK but if there is a properly specced EI core instead its bad
https://talema.com/wp-content/uploads/products/pcb-mounting-transformer-70024K.jpg

I am just arguing that maybe he did not take it 'too far' to bury a shipping container for a experiment. Maybe it could be considered the worlds coolest experiment if its a 2/3 height shipping container

I like the non-magnetic structure university structure from the other thread. Stalins datcha was built like that too, apparently 

[Simmed]

..
@OP, if that box was 2x as tall, I have a feeling you would be physically assaulted by administrative non technical budget personnel at the university. You got lucky that its substantially wider then it is tall. Single "shoe box" form factor is kind of cool. If it was a double decker you would be in trouble. If it was 30% shorter, it might get a full page on the university department advert with super models.
..

I trust readers generally understood that the word “portable” in this thread’s subject was intended humorously, not literally, and should be taken as a joke rather than serious.
 

 

[coppercone2]

30kg is not that bad for portability IMO. Bag of cement is 90 lbs . Its common enough to move with 2 people

A benchtop RF shielded box weighs maybe 30-50lbs (the ones that has finger strips and feed throughs). They are widely used and stored on shelves. But they do come with handles.


Perhaps all that is missing from the design is handles.

I want to see this project revived with handles, rubber feet and bumpers, paint, decals, rounded edges, etc

The most 'dense' lab equipment I have is a 20A variac which is built into a very tight enclosure, I made a handle for that like a kettle bell on top.

[EC8010]

I trust readers generally understood that the word “portable” in this thread’s subject was intended humorously, not literally, and should be taken as a joke rather than serious.

It's portable. Many years ago, I worked for the BBC and eventually worked out the distinction between the BBC definitions of "portable" and "transportable". Both would be seriously heavy by modern standards, but "transportable" meant two handles (loudspeaker the size of a wardrobe), rather than one...