I found many different DIY videos and posts demonstrating the concept of wireless power transfer using inductive coupling, however, they have limited explanation on theoretical calculations and design aspects. Thus, I hope to find some guidance on this forum. I focused my attention on the pancake and bifilar coil geometries since they seem to be compatible with the design constraints of the receiving coil. Since the receiving coil has design limitations, all bets are on the transmitter coil, so it must be more powerful to compensate for the low receiving efficiency. The goal is to be able to receive at least 100mW of power.
The Receiving Coil
The receiving coil will be a simple pancake coil PCB printed with the thickness of traces being 300um. The width and the spacing of the "flat wires" would be equal and can be >4mm, and the outer coil radius 100mm. These parameters would dictate the number of turns in the coil. At this point I am not concerned about the N1/N2 winding ratios of the transmitting and receiving coils since I am planning on using a voltage regulator at the receiver to maintain the required voltage.
The Transmitting Coil
The transmitting coil would be the Tesla's bifilar pancake coil - I would just pick a random speaker wire and make as many turns as needed to approximate the outer diameter of the receiving coil. It is not clear, though, how to wind the double-stranded wire: two strands side-by-side on the same plane (left), or one strand on top of the other forming a stack of two parallel coils (right)?
I have also seen some speculations on how to connect the two coils of the bifilar coil, and it is not clear which one is suitable for my application: the one that connects internal end of one coil to the external end of another coil (left), or the one that connects two internal ends (right)?
- What are the design recommendations for the Receiving coil (given above constraints)?
- What are the effects of the two winding approaches, and which one is more suitable for my application?
- How the coil interconnection approaches affect the overall power transmission efficiency and which one is more suitable for my application?
- Should I have thicker wire with less turns or a thinner wire with more turns for the transmitter coil?
- In both connection scenarios I end up with three points (x,y,z) to which I could connect the driver circuit. What are the connection approaches and driving options that are valid? I found several examples that use a single transistor and a battery to drive the transmitter coil, but I was hoping for a slightly more complex and effective suggestion.
- Is the spiral receiving coil (shown above) compatible with a bifilar type transmitting coil?