Tunable transmission and harmonic generation in nonlinear metamaterials
  We study the properties of a tunable nonlinear metamaterial operating at microwave frequencies. We fabricate the nonlinear metamaterial composed of double split-ring resonators and wires where a varactor diode is introduced into each resonator so that the magnetic resonance can be tuned dynamically by varying the input power. We show that at higher powers the transmission of the metamaterial becomes power dependent, and we demonstrate experimentally power-dependent transmission properties and selective generation of higher harmonics. 
Ilya V. Shadrivov, Alexander B. Kozyrev, Daniel W. van der Weide, and   Yuri S. Kivshar