It is worth to mention, that (95) tends to be self resonant frequency, in the case that Cext is null. Due to the quite complex form of (90) and (95) it is hard to get an analytical expression for the optimal resonant frequency (or the optimal external capacitance for the particular coil). But it is possible to plot Q versus f and from this curve the value of frequency that maximize the quality factor can be identified. After evaluating the optimal frequency of operation and substituting it to (95) optimal value for the external capacitance can be obtained.