Parasitic capacitance versus the associated magnetic axis

[antigua]

I was discussing something interesting I had read about coil capacitance in this thread guitarnuts2.proboards.com/post/80474/thread involving some interesting information presented on  this web page coil32.net/theory/self-capacitance.html . I starting a new thread because it's tangential to the other thread, and issues of parasitic capacitance are a big deal in their own right. 

Here are two excerpts of interest:

the RF coil is the distributed structure around which there is an electromagnetic field - the single entity in which the vectors of the electric and magnetic fields are always perpendicular and the electrical and magnetic components of the field can not exist independently of each other.



...

Since the magnetic field lines are mainly located along the axis of the coil, the electric vector of the wave is located perpendicular to the axis, and the components of the electric field parallel to the axis (between turns) is almost negligible.

One reason I hadn't read this sooner is that it deals with single layer air coils,  but I'm hungry for information, so I read it anyway. There is application of the physics presented to multilayer coils, and that is the fact that electric fields move perpendicular to the magnetic field associated with the electric field. Here's a picture (or do the "right hand rule" with your hand):




The implication is that coil windings only capacitively couple with neighboring layers, but not neighboring winds within the same layer. 

Another question that arises... when it comes to pickup shielding, how much capacitive coupling happens with metals above and below the coil (tops of covers, Tele bridge base plates), versus metals that are beside the coil (the sides of covers, the Tele bridge mounting plate)? 

If this is all true, it could have an impact on design decisions, and how pickups makers go about reducing unwanted capacitance. 

[andyholmes]

I was reading a document called Self-Capacitance of Inductors that somewhat covers multi-layer coils and conductive core coils. Most of the math is over my head, but he seems to disagree about, or at least not preclude, capacitance between turn-to-turn windings in the same layer.

It can be seen that the basic cell is the same for two adjacent turns of the same layer and two adjacent turns of different layers. Therefore, the inner part of the winding can
be divided into identical basic cells. Only the cells adjacent to the core and shield differ from the turn-to-turn cells.

[ms]

Feb 23, 2017 16:24:26 GMT -5 andyholmes said:

I was reading a document called Self-Capacitance of Inductors that somewhat covers multi-layer coils and conductive core coils. Most of the math is over my head, but he seems to disagree about, or at least not preclude, capacitance between turn-to-turn windings in the same layer.

It can be seen that the basic cell is the same for two adjacent turns of the same layer and two adjacent turns of different layers. Therefore, the inner part of the winding can
be divided into identical basic cells. Only the cells adjacent to the core and shield differ from the turn-to-turn cells.

i think turn to turn no the same layer is out.  A reference in the document that Antigua quotes from is convincing.  If the field pointing between two turns is very small, there is no reason for charge to collect and thus not much capacitance.