Some people have trouble visualizing magnetic fields and this clip might help:

https://www.youtube.com/watch?v=4c6fRmyh4q8

Look at how he slices a solenoid coil and analyzes a series of current-carrying conductors all in a line.  Look at the magnetic field subtended by each wire and see where the cancellation and addition is between the wires.  Just forget about both sets of wires in the slice of the solenoid coil and just focus on the magnetic field produced by one set of wires.

This is very similar to a pancake coil where you take that concept and rotate the slice of wires around an axis to get a pancake coil but in this case with current-carrying wires that are in concentric circles.  Obviously when you go from concentric circles to a spiral the magnetic field stays essentially the same.

Thanks Milehigh,

So when looking at the magnetic field of the pancake coil i should turn my hall sensor 90°, then skim the surface.

I did that and now the magnetic field follows a more realistic path, as we have a gradual increase and decrease from
the outside inwards, then flipping polarity in the middle and again increasing / decreasing.

See drawing on how i imagin that field now.

Itsu

Itsu:

I changed and annotated your drawing.  Note that I define north and south areas above and below the hole in the pancake coil.  If you just look at that 3D volume area, it somewhat resembles what would be taking place in a bar magnet.

I am not comfortable with your concept of defining the upper and lower halves of the left and right lobes,  as "North" or "South."  It's all somewhat of a grey area that is hard to define.   It becomes a question of an "observer" and "perceived magnetic field direction."

I will annotate another image to show you what I mean.

A related question is, "Where is the 'North' and 'South' for a long straight current-carrying wire?"   This is an example of where the concept of "North" and "South" breaks down.

MileHigh

Quote from: itsu on April 17, 2017, 03:13:40 PM
Thanks Milehigh,

So when looking at the magnetic field of the pancake coil i should turn my hall sensor 90°, then skim the surface.

I did that and now the magnetic field follows a more realistic path, as we have a gradual increase and decrease from
the outside inwards, then flipping polarity in the middle and again increasing / decreasing.

See drawing on how i imagin that field now.

Itsu

Hey Itsu

Im sure you are using analog hall sensors. Where the outer perimeter of the blue and read bubbles of field, is that perimeter where the hall does not register any longer? Just wondering. Also, does the hall register higher around the outer edge of the coil than on the flat sides? In Teslas transmitter and receiver diagram he shows another 2 turn winding at the outer perimeter of the pancakes for the transmitter and receiver, where the outer winding is the primary on the transmitter and the outer winding is the sec on the receiver. So it would be interesting if there is a concentration of flux at the outer edge of the pancake as that may be the reason for placement of that 2 turn coil in relation to the pancake as he shows, of which is one of my tests on the list.

Thanks for showing

Mags

Quote from: MileHigh on April 17, 2017, 03:48:14 PM
Itsu:



I am not comfortable with your concept of defining the upper and lower halves of the left and right lobes,  as "North" or "South."  It's all somewhat of a grey area that is hard to define.   It becomes a question of an "observer" and "perceived magnetic field direction."


MileHigh

I was seeing that also. But if he just went across from the far left of the coil to the far right, without flipping the hall 180 in the middle, then that is what he recorded. Make sense?  So just one half can be mirrored and all is correct

Mags