Lately, I have been messing around with inductors and wireless power transfer. I have studied couple online tutorials on RLC circuits. I thought I have basic knowledge and good ground to actually build something, but sadly no... I am trying to couple two air core inductors, I tried lots of combinations so I will only show the latest one
Rx and Tx coils, Both have value of 1.6uH
Tx 1.6uH with 900pF cap in series. Rx 1.6uH with 900pF in a parallel combination, later I added 100ohm resistor in parallel to lower damping factor. Resonant frequency isenter image description here 4.19410MHz.
I drive mosfet with a square wave from a function generator at the resonant frequency. And I get nice sine wave between cap and inductor. I am using peak detector circuit to measure voltage drop when I get two coils close. But voltage drop never occurs, so I am pretty sure coupling doesn't happen. Anyone know what the problem is? I used different types of inductors for Rx as well, drum core, resistor shape ones with different inductance and cap values, but with no luck so far.
Maybe the problem is related to Q factor of Rx coil. I am not sure if I understand Q factor correctly but according to online calculator dumping factor of receiving coil is 0.21 so it is underdamped and its Q is rather high, but the bandwidth is pretty high too, almost 10MHz, not sure how that affects receiving coil.
EDIT: The reason I chose single layer coil is that I want to design flat double sided PCB coil later with a spiral shape. That's why I am experimenting with one layer spiral coil design. Sorry for not inclouding this information from the beginning
http://imgur.com/a/Efp0r coils picture.
http://imgur.com/a/KvyAt circuit schematic.