Hi all,

I am attempting to replicate a paper:(https://arxiv.org/ftp/arxiv/papers/0901/0901.1350.pdf, "Second-Harmonic Generation and Spectrum Modulation by Active Nonlinear Metamaterial" ) using COMSOL and maybe LTSpice. I am trying to replicate both graphs (at end of paper) but firstly the graph showing the fundamental and second harmonics.

I have tried launching a wave (by specifying the H field at Scattering boundary as plane wave) in a transient run in COMSOL to measure the voltages across the gaps where the diode would be, followed by exporting resultant voltages into LTSpice and running them each through a circuit with the relevant diode. Following that I then reimport into COMSOL and excite the split gap with voltages output from LTSpice. This doesn't seem to produce second harmonics (I use a probe and look at the frequency spectrum of the Hx component of H field)

I have also tried doing all three steps in COMSOL by coupling circuit physics with an appropriate diode into my transient EM physics. i cannot get this to converge.

Any tips at all, even very general COMSOL or LTSpice tips would be appreciated.