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Making Resistive Magnets (2009) (nationalmaglab.org)
22 points by mindcrime 9 days ago | hide | past | web | favorite | 4 comments

So, a "resistive magnet" is basically the same thing as your school science fair "bell wire wound on a nail" electromagnet, except it is made from very precisely manufactured copper plates stacked with insulators and drilled to accommodate flowing water. That's very interesting technology, plus the nesting of the "coils" for multiple "layers" on the magnets.

It's kinda analogous to winding an electromagnet very carefully, but the stacked design (along with the holes) allows for easy and effective liquid cooling. It's a somewhat outside of the box thinking of magnet design.

I find it curious that I'm just learning about this now - I've never, ever have seen this kind of magnet construction discussed anywhere (and it is apparently a long-used technique)? I would expect such a design to be discussed in numerous areas (or even just mentioned), but I've never seen anything about it in popular press magazines or books, or anywhere else except now?

I wonder why that is? Is it only because such magnets are for very specialized use-cases, and fabricating one is outside the capability of most organizations, let alone individuals? Or are the use-cases such that almost no one else needs them (ultra-high current and high Tesla output) - and those that do would be in the circles that know about this construction?

Again, I just find it strange; I mean, in my life, I've found books and other sources that detail how to build STMs, CAT Scanners, and Radio Telescopes - but nothing of the nature of a magnet like this (and overall, it's fairly simple in concept and construction).

It would be nice to know sort of the "back of the napkin" scale for types of electromagnets.

The magnets they talk about are 35 Tesla. I wonder what kinds of numbers you get from a fridge magnet, a bell wire+nail, or a crt or.. how many teslas (T) in a tesla (car)?

Most transformers and solenoids/electromagnets are less than 2 T (two Tesla) because the saturation density isn't much higher than that for typical core material. Much the same applies to electric motors.

See, for instance:

and for some easily readable background on transformers showing simple calculations for flux density:

The magnets described in the article don't have ferromagnetic cores so they do not suffer from the same problem. On the other hand the technique is not really applicable to power transmission or motive power.

The bitter plate design process is one of the most beautiful things about material engineering that exists!

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