Help with results of a Wirelles Power Transfer Circuit.

Hi, I am testing a WPT circuit.
The input sinusoidal signal of the primary coil is from the function generator with Vrms=7,9V and frequency 130KHz.

I am using inductive coupling method with a cap in parallel with the Tx and Rx coils.

When I have the distance between two coils lower than 2cm and without any load on the receiver coil, the voltage in Rx is higher than the Tx coil.

The results are;

Distance VrmsRx
1cm 15,27V
2cm 8,81V

For distances higher than 2cm the Rx voltage is less than Vpp in Tx and make sence to me.

I don't understand why the voltage on Rx can be higher than Tx voltage if I built the inductors with the same diameter and number of turns.

Thank you!

The Rx voltage can be even much higher than generator output voltage, only limited by the coil quality factor and receiver coil load.

Assume that you apply a current source Iin to a parallel RLC, at the resonant frequency, the voltage across the RLC will be Iin * R. The value of R affects the quality factor and the gain of the resonator.

In your experiment, the signal generator may have loading effects, and, lower the quality factor of the primary coil. However, since you don't have any load on the receiver coil, the quality factor of the secondary coil is higher than the primary one (even though you are using the same L and C in Rx and Tx).

The signal generator may also increase C at the primary. I think this can affect the experiment too.