Re: squeezing a field

On Wed, 23 Oct 2024 18:14:57 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

john larkin <jl@glen--canyon.com> wrote:

I'm designing a small PCB with essentially 5 sync buck switching
regulators. Board space is tight so I want to put the inductors on the
bottom of the multilayer board. There's a 0.2" gap between the bottom
of the board and a big aluminum flange.
 
Unshielded drum cores have the most energy storage per volume or
dollars. They store energy in the universe instead of in ferrite. Good
cooling too.
 
Something like this just fits
 
https://www.digikey.com/en/products/detail/bourns-inc/SRN8040TA-470M/6155133
 
Its mag field lines will bounce off the PCB planes and the flange,
change from the classic bar magnet pattern into a pancake . I wonder
what that will do to its electrical behavior.
 
 
 

>
Not a whole lot.  In the near-field region, B obeys Laplace’s equation,
which means among other things that the field falls off on the length scale
of the gap, not of the whole inductor.
>
Cheers
>
Phil Hobbs

You are right. A similar part is 47 uH in free air, 44.6 mounted on a
multilayer board, and 42.1 squeezed between the board and a big chunk
of aluminum.

So it will work.