Which Coil Shape is Better for Eddy Current Measurements?

[JJ91]

Hi,

I'm currently in a dead spot of my mini-project where I've to decide upon the coil shape. I can't find adequate definition of both coils by the means of:
- size
- losses
- frequency range
- inductance
- skin depth

which makes it impossible to argue which one would be better.

I'm wondering whatever there is good reading or this aspect should be defined by finite element analysis (using trial version of MagNet)?

In more detail a coil will be used in instrument which uses eddy currents to measure coating thickness.

 

[marcusl]

You don't specify, so I'll assume that you are measuring material in the shape of a slab, and that the coil will be held over the material like holding a metal detector over the ground. A pancake coil generates a field that is far more spread out and nonuniform, assuming that the spiral starts at the center and is wound uniformly outwards. The solenoid's coil is more concentrated directly underneath the coil. on the other hand, a flat coil can be made to have a more uniform field if you customize the windings , leaving a current-free central disk. Go ahead and model them, then decide which is more desirable for your application.