Induction heater 3kW

Hello,
I have some question about induction heater. So I bought made PCB 3kW power induction heater , and now I just have to make induction coil of 100 uH inductance for that PCB board. I made one but it has too small inductance and took too much current and stop working. Could anyone told me how to do that the coil will be small as possible, and which ferrite rod can I use that I will reach 100 uH inductance because the PCB need that inductance to work properly. I can set the frequency on PCB from 15 to 45 kHz.
Thank you.

http://radyne.com/what-is-induction/about-inductors/ much the same as http://www.dw-inductionheating.com/induction heating coil design.pdf
in formulas http://www.diva-portal.org/smash/get/diva2:630122/FULLTEXT01.pdf
+
http://www.dicks-website.eu/coilcalculator/index.html
http://ludens.cl/Electron/lmeter/lmeter.html
**broken link removed** ~ http://info.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html