Inductive Heating
In this experimental setup a screwdriver can be heated till 600 degrees with this small coil, without heating the coil itself.
Optimum frequency at which the RF-field is converted to heat is chosen at which the skin-depth of the metal object is half the size.
This frequency rices with the inverse square root of its size.
The size of the (Litz-)wire should be tuned at this frequency.