engleski

Investigation of Negative Permeability, Negative Permittivity and Backward Meta-materials in Waveguide Environment

Recent introduction of artificial materials with simultaneously negative effective permittivity and negative effective permeability (Smith et. al., Phys. Rev. Lett. (18), 2000) have gained considerable attention. In such a &#8216 ; ; backward&#8217 ; ; (or &#8216 ; ; left-handed&#8217 ; ; ) material, direction of phase velocity (wave vector k) is opposite to the direction of energy flow (Poynting vector P). This unique property causes reversion of some basic electromagnetic phenomena such as Snell law and Doppler effect. Several ideas for application of new material, such as high resolution electromagnetic lens (Pendry, Phys. Rev. Lett., (18), 2000) and sub-wavelength resonator (Engheta, ICEA 2001 proc., 2001) have already been suggested. So far, the backward materials have been studied experimentally in free-space environment (or in scattering chamber which simulates free-space propagation). Experimental investigations of waveguide filled with backward material has not been reported yet. On the other hand, a waveguide offers possibility of testing meta-material within a small, closed space, loosing requirements on size of a sample. Some of the results of on-going research on rectangular waveguide filled with backward material will be presented in this talk. Since the electromagnetic field in dominant (TE01) mode of the rectangular waveguide can be thought of two planar waves, the previously reported artificial two-dimensional materials can be used for filling. In on-going experiments, negative permittivity is achieved using an array of parallel thin wires (Pendry, J. Phys. Cond. Matter., (12), 1998). Both the FDTD simulation and experiments show shift of the cut-off to the higher frequency (comparing with an empty waveguide), due to plasma-like behaviour of negative permittivity achieved by thin wires. Negative permeability is achieved by two-dimensional array of loaded loops (Hrabar et al, ICECOM 2001 proc., 2001) or split ring resonators (Pendry et al, IEEE Trans. MTT, (11), 1999). A waveguide with this structure exhibits very pronounced (>80 dB) stop-band associated with resonance behaviour of negative permeability. The waveguide which contains both thin wires and loaded loops exhibits a pass-band. The pass-band central frequency may be different of central frequency of the negative permeability stop-band. This shift of frequency is caused by interaction between wires and loops. The phase of S21 parameter has positive gradient within the pass-band, indicating negative differential group velocity associated with backward propagation. The waveguide T junction filled with prism shaped wire-loop material is simulated using FDTD method. Results verify anomalous reflection at the air-material boundary indicating reversion of Snell law. Future research efforts will be directed toward experimental investigation of different waveguide components filled with wire-loop structures. The optimisation of the waveguide backward structure, in order to minimise interaction between elements and improve matching, will be attempted. We also envisage to experimentally confirm reversion of Doppler effect in waveguide filled with backward material.

waveguide; left-handed material; backward material

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