Dielectric nonlinearity: Nonlinear-optics effects in a micromechanical resonator:

Coupling of nonlinear polarization in a dielectric medium in a piezoelectric film to mechanical motion leads to a resonator with nonlinear behavior in the acoustic frequency range. Nonlinear dielectric effects are well known to occur at the high optical frequencies typical of lasers, with second harmonic generation (the summation of identical photons to achieve a single photon of twice their energy) being an archetypal signature. Nonlinear dielectric behavior in a low frequency resonator is yet to be achieved however. We transduce nonlinear behavior in a dielectric medium into a range of mechanical effects—including second harmonic generation—via a piezoelectric material. This demonstration provides a platform for studying nonlinear acoustics, and may offer interesting new device functionality.

Read it here: www.nature.com/articles/s41378-018-0013-6