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

yes,  i know what you mean, its more the direction of the magnetic field lines that are detected, not the north or south poles.
My hall sensor detects the arrow direction in your above drawing.

Itsu 

Quote from: Magluvin on April 17, 2017, 03:52:13 PM
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

Hi Mags,

no it is like my (and MH's) drawing above, when skimming from top to bottom (TBP coil vertical like my earlier picture) from the upper edge to the middle hole we see a increase/decrease of strength, same with the next part after the hole (no changing of the Hall sensor) increase / decrease until the lower edge (opposite direction detected)

Hope that is clear   


Itsu

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

Very nice result on the frequency scan. Your coil's parameters are very similar to mine, and that's great as our results can be more easily compared.

See MH's drawings for how the field "circulates" around the windings and thus around the whole disk, like a big torus or donut in space. With a big enough disk the lines would actually be parallel to the disk surface over much of the disk, only becoming orthogonal at the edge and at the hole.


But what about the results I posted earlier where I show that there is still plenty of induction, hence plenty of alternating magnetic field,  going on even when the current sensing resistor voltage indicates no voltage across the resistor?

In this annotated drawing, the "eye" symbol is the observer, and "North" is "a magnetic field direction coming towards you" and "South" is "a magnetic field direction moving away from you."

It may look strange, but it actually all makes perfect sense.  What is "North" and "South" is a function of the observer's position.

QuoteA 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.

Right you are, and out the window with it is the concept of the "Bloch Wall". Generations of children have been fooled by looking at bar magnets painted red on one half and blue on the other half, and iron filings on paper to "map" the lines external to the magnet. Once Oersted figured out how the field actually surrounds a current-carrying wire, and people started cutting up bar magnets into smaller and smaller pieces, the true picture started to emerge. But they still paint bar magnets with colors by halfs,  rather than arrows and circulating lines parallel to the bar internally.