Musings on wireless power transfer

Here, without much comment, we offer up some initial thoughts and experimental results…

Experimentation was done using a pair of hand-turned copper coils formed on PVC drainpipe, of nominal diameter 10cm. Both coils had 50 turns. The first coil was driven directly from a signal generator* which was capable of a range of frequencies up to about 20 kHz. The second coil was attached to an AC voltmeter and had the possibility of adding a range of capacitors (from 0 μF up to 5 μF) across it in parallel.


(* The signal generator we used was actually just a laptop with a modified speaker. The speaker cone had been removed and replaced with a pair of 4mm sockets.)


The software we used to drive the speaker was called ‘Scope’ by Christian Zeitnitz. It is free for personal use and is a great piece of software – it can turn your PC into an oscilloscope or a signal generator – or both at the same time!


Although in theory we could use two speakers at the same time, since all sound cards have a stereo output, we decided not to in case the power amplifier inside our $15 modified speakers suffered from any kind of crosstalk between channels.

Angular separation of coils

Angle v output p.d

Investigating angular separation

Transverse (lateral) displacement of coils

Investigating overlap

Longitudinal displacement of coils


Effects of placing capacitors across the second coil


1 microfarad coil resonance curve

So, what happens if we vary the capacitance across the secondary coil?


5 coils compared

Relating this back to theory…

Relationship between resonance f and C_edited-1