Murata THT inductor polarity

[Zeyneb]

Hi there,

As I have bad faith in asking Murata tech support a question for my 1 piece a year application 
I hope someone here have experience with the 1300R, 1800R and 2200R series of general purpose THT inductors. In this case the 18R104C part for a dc-dc converter application.

Alright, so these parts have a polarity indicated by a short and a long lead length. I might vaguely remember getting informed about something like reducing EMI by connecting the noisy switching transistor on one lead and having the "quiet" node on the other lead.

Is there someone here who can provide clarity on this.

Many thanks,
Zeyneb

[thm_w]

https://www.mouser.ca/datasheet/2/281/1/kmp_1800r-2936251.pdf
https://article.murata.com/en-global/article/basic-facts-about-inductors-lesson-6

According to this guy the longer lead is the inner/bottom of the coil, but I don't see any references from murata to confirm: https://forum.allaboutcircuits.com/threads/different-length-legs-on-radial-through-hole-inductor.159165/

If it does actually matter you could also consider a shielded inductor as well.

[Zeyneb]

I have these inductors at home. Would it make sense to build the dc-dc converter on a breadboard and then
moving another inductor around the one on the breadboard to see in which orientation I have the least signal pick-up?

For this other inductor connecting 10 mOhm resistor between the leads and test leads to an oscilloscope? I've not much experience with this. I hope it makes sense.

I hope I communicated this clearly.

[trobbins]

If you have sufficient quantity, and can sacrifice one unit, then do a tear-down assessment to identify the lead going to the outermost layer.

[thm_w]

I have these inductors at home. Would it make sense to build the dc-dc converter on a breadboard and then
moving another inductor around the one on the breadboard to see in which orientation I have the least signal pick-up?

For this other inductor connecting 10 mOhm resistor between the leads and test leads to an oscilloscope? I've not much experience with this. I hope it makes sense.

I hope I communicated this clearly.

Its unlikely you'll measure a large difference, but yes, you could measure using an oscilloscope then flip the inductor around and measure again.
To do this you can connect the oscilloscope ground lead to the probe tip to form a loop. Or buy/make your own field probes:

[coppercone2]

that's fascinating, I thought it would be symetric enough to be basically really hard to measure. 5% really surprised me.

What does this, like a non isotropic core and coupling to nearby parts?

Maybe it has to do with the test fixture.. you would imagine if its on a bare PCB away from anything, 5 % seems crazy for machine made or film parts.

I heard about this phenomena before and I thought maybe 0.5% max error