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Mechanical tuning of metamaterial lattices was demonstrated [Appl. Phys. Lett. 90, 201919-3 (2007)]. Measurements in an anechoic chamber were used to find the transmission and reflection from a metamaterial slab consisting of printed boards. By changing the spacing between the boards, the mutual inductance between the split ring resonators was changed, thus changing the resonant frequency of the structure. In addition, superlattice structures were created, where the lattice spacing alternates between two different values. The result is resonance splitting, where two different modes can be seen in the reflection and transmission responses. A two dimensional metamaterial was also created by placing a second set of boards perpendicular to the first (see picture).

We have created nonlinear spling ring resonators [Opt. Express 14, 09344 (2006)], the basic building block required to create a nonlinear metamaterial. By including varactor diodes in additional slits in the outer ring, the variable capacitance allows the resonator frequency to be tuned by up to 26%. This can be performed using either a DC voltage applied through a biasing network, or by self tuning due to the application of an RF signal. The positioning of the varactor in an extra slit in the outer coil allows for nonlinear behaviour to occur at much lower power levels than in previously reported work.

Recent theoretical and experimental results have shown the possibility of creating novel types of micro-structured materials that demonstrate the property of negative refraction. In particular, the composite materials created by arrays of wires and split-ring resonators can possess a negative real part of magnetic permeability and negative dielectric permittivity for microwaves. These materials are referred to as left-handed metamaterials. They were mentioned first as a theoretical curiosity about 35 years ago, but recent experimental demonstrations of such newly-engineered materials have involved the development of new fundamental physical concepts and ideas, also initiating hot debates. A brief overview of this field and a summary of our activities can be found in the recent article (Pdf format, 7 Mb) we published in "The Physicist".

Our group aims both to the study of microscopic properties of left-handed composite metamaterials with nonlinear inclusions [Phys. Rev. Lett. 91, 037401 (2003)] and macroscopic electrodynamic properties of structures containing left-handed materials.

The study of nonlinear properties [Phys. Rev. Lett. 91, 037401 (2003)] of metallic composite structures revealed the novel type of material nonlinearity, when the effective magnetic permeability of the material becomes the function of external magnetic field. Changing the intensity of the electromagnetic wave one can not only change the material parameters, but also realize switching between transparent left-handed state and opaque dielectric state.

Our study of macroscopic electrodynamic systems focuses on guiding properties of planar structures with LHMs as well as transmission properties of photonic band-gap structures with left-handed materials.

We have studied both linear and nonlinear surface waves localized at the interface separating a left-handed medium and a conventional [or right-handed (RH)] dielectric medium [Phys. Rev. E. 69, 016617 (2004)]. We have demonstrated that the interface can support both TE- and TM-polarized surface waves - surface polaritons. We have described the intensity-dependent properties of nonlinear surface waves in three different cases, i.e., when both the LH and RH media are nonlinear and when either of the media is nonlinear. In the case when both media are nonlinear, we have found two types of nonlinear surface waves, one with the maximum amplitude at the interface, and the other one with two humps. In the case when one medium is nonlinear, only one type of surface wave exists, which has the maximum electric field at the interface, unlike waves in right-handed materials where the surface-wave maximum is usually shifted into a self-focusing nonlinear medium. We have discussed the possibility of tuning the wave group velocity in both the linear and nonlinear cases, and show that group-velocity dispersion, which leads to pulse broadening, can be balanced by the nonlinearity of the media, so resulting in soliton propagation. The results of the numerical simulations of a pulse propagation along the interface, which show the structure of the energy flow in the pulse can be found at the ANU Vizlab page.

The study of guided waves in planar LH waveguides [Phys. Rev. E 67, 057602 (2003)] was a natural expansion of our activity. We have studied the LH slab waveguide and presented a comparison of the properties of conventional dielectric waveguides and LH waveguides.

Periodic structures with left-handed materials exhibit an unusual band-gap, when the average on the period refractive index vanishes. We have analyzed transmission of a layered photonic structure (a one-dimensional photonic crystal) consisting of alternating slabs of two materials with positive and negative refractive index. For the periodic structure with zero averaged refractive index, we demonstrate a number of unique properties of the beam transmission observed in strong beam modification and reshaping [Appl. Phys. Lett. 82, 3820 (2003)]