1. A system comprising:a radio frequency (RF) signal source configured to produce an RF signal;
an impedance matching network that includes:
a first planar inductor with a first terminal and a second terminal, wherein the first terminal of the first planar inductor is coupled to the RF signal source,
a second planar inductor with a first terminal and a second terminal, wherein the first terminal of the second planar inductor is coupled to the second terminal of the first planar inductor, and the second terminal of the second planar inductor is coupled to a ground reference terminal, and
a first variable inductor network coupled in series with the second planar inductor;
a first electrode that is electrically coupled to the second terminal of the first planar inductor of the impedance matching network; and
a second electrode.