Well, thanks for your precious oppinion.
i really appreaciate it ! ^_^
Actually, the frequency i am using is more than 100 kHz. Is there any winding techinique i should apply ? Currently, i am using multi layer solenoid winding. The efficiency is up to 20% only.
And then for some reason, i have to use wireless power transfer. That's why i chose air core transformer.
There is still a big problem. Because of i am using 12 V dc step input ( not AC power ), the back emf of primary inductor is causing great heat problem to the device. Is there any solusion i can refer to ?
Best regards for all !