The resonant elements that grant metamaterials their unique properties have the fundamental limitation of restricting their useable frequency bandwidth. The development of frequency-agile metamaterials has helped to alleviate these bandwidth restrictions by allowing real-time tuning of the metamaterial frequency response. We demonstrate electrically-controlled persistent frequency tuning of a metamaterial, allowing lasting modification of its response using a transient stimulus. This work demonstrates a form of memory capacitance which interfaces metamaterials with a class of devices known collectively as memory devices.
The use of a temperature bias in our experiment is required only to put a particular VO2 film into a regime where the IMT is highly hysteretic, although our VO2 does exhibit some hysteretic qualities even at room temperature. More promisingly, several VO2 fabrication techniques are known to reduce the phase-transition temperature down to room temperature and thus will enable VO2-hybrid memory metamaterials to operate at ambient conditions. Additionally, any material which posses a hysteretic response in either its permittivity or permeability at a suitable frequency range could be used in a hybrid-metamaterial design to obtain memory effects analogous to those we demonstrated here. The correlated electron state which gives VO2 the divergent permittivity used in this demonstration is only effective up to mid-infrared. Combination of other hysteretic materials with metamaterials operational in near-infrared and visible could easily push this effect to higher frequencies which are beneficial for a variety of practical applications