Hi,
I'm designing a miniature 100mH inductor, the external diameter of the inductor is limited to 3.6mm, the length could be 20-30mm, resistance should be less than 240 Ohm. The operating frequency is between 10..30 KHz. The coil should have closed magnetic field lines to avoid interaction with external objects / fields.
At the moment I can't find the right ferrite core shape - currently I'm using ferrite rods but the coil becomes very sensitive to external objects/fields. Ideally the inductor should consists from two parts - a central core (see attached image) and the external pipe (where the core is inserted) which is closing the field lines. I'll appreciate any information how to get such ferrite cores. Also any other ideas how to close the magnetic field lines will be appreciated (like some thin soft ferrite tape, ferrite powder & epoxy, etc.).
Best regards,
Luben