Transcript Slide 1
METAMATERIALS and NEGATIVE REFRACTION Nandita Aggarwal Laboratory of Applied Optics Ecole Polytechnique de Federal Lausanne Presentation Overview Introduction to negative refraction Theoretical explanation Experimental verification Different structures as metamaterials • • • • SRR structure S-SRR structure EX-SRR structure Omega type structure Negative refraction in optical regime Applications • Super lenses • • High directive Antennas Cloak invisibility References Reversing light : Negative refraction Time reversal Time reversal and negative refraction Negative Refraction (Reversal of spatial evolution of phase) Disobeying Snell’s Law: Left handed materials Light makes negative angle with the normal Poynting vector has the opposite sign to the wave vector Negative Refraction Practical demonstration of negative Refraction Theoretical Explanation in brief Assumption: Wavelength used > spacing and size of the unit cell. Composite can be assumed homogeneous. µ(eff.) and ε(eff.) are structure dependent. Experimental Verification LHM material (Prism) Unit cell : 5mm Operating wavelength : 3cm (8-12 GHz) Al plates separation: 1.2 cm Radius of circular plates: 15 cm Detector was rotated around the circumference of circle in 1.5 degree steps Experimental Verification Refractive index of teflon : 1.4 +- 0.1 Refractive index of LHM : -2.7 +-0.1 Different Structures as Metamaterials • Split Ring Resonators + Metallic Wires • S shaped Split Ring Resonators • Extended S shape Split Ring Resonator • Fish scale • Omega type Split Ring Resonator + Metallic Wires Split Ring Resonator Dispersion curve for the parallel polariraztion. Dashed line shows the SRR with wires placed uniformly between them. S shaped Split Ring Resonators 3-D plot of S-shaped SRR Equivalent electrical circuit of SRR S shaped Split Ring Resonators Effective permeability for the S-SRR structure in the case of F1 = F2 = F = 0.3 S shaped Split Ring Resonators Two unit cells of a periodic arrayed structure (a) A broken rods array, (b) A capacitance-enlarged rods array, (c) A ‘S’- shaped rods array S shaped Split Ring Resonators The real part of the effective permittivity measured for configuration (b) and (c) with the change in value of h. Extended S-shaped Split Ring Resonators The ES-SRR structure with a period of 2 rings in the z direction and its analytical model Extended S-shaped Split Ring Resonators Effective Permeability Vs. Frequency Extended S-Shaped SRR Normal S-Shaped SRR Omega type structures Unit cell Picture of metamaterial actually realized and measured Omega type structures Snell refraction experimental results 3-D result with the three axes representing detected power in mW, Frequency in GHz and angle in degrees. 2-D curve extracted at 12.6 GHz from 3-D results. Negative refraction in optical regime Detailed history of development of magnetic resonance frequency as a function of time Applications • Superlens • Highly directive Antenna • Cloaking Superlens The electric component of the field will be given by some 2D fourier expansion: Propagating waves: Evanescent waves: Diffraction limit of the lens: Superlens Negative Refraction Makes a Perfect Lens • With this new lens, both propagating and evanescent waves contribute to the resoltuion of the image • Enhancement of evanescent waves i.e. amplification (though evanescent waves carry no energy still the results are surprising) of these waves was proven by Sir John Pendry in 2000. Superlens Perfect Lensing in Action A slab of negative material effectively removes an equal thickness of space for (A) The far field (B) The near field , translating the object into a perfect image Highly Directive Antennas Geometrical interpretation of the emission of a source inside slab of metamaterial having optical index close to zero Construction in reciprocal space Cloaking Invisible Man become a reality? "I still think it is a distant concept, but this latest structure does show clearly there is a potential for cloaking -- in the science fiction sense – to become science fact at some point," says Smith. Cloaking Cloaking Snapshots of time-dependent , steady-state electric field patterns. Cu cyllinder is cloaked A: Simulation of cloak with exact material properties B: Simulation with reduced material properties C: Experimental measurment of bare conducting cyllinder D: Experimental measurments of cloaked conducting cyllinder References 1. J.B Pendry Physics review Letters, Vol. 85, no. 18 (3966-3969) 2. John B. Pendry and David R. Smith DRS&JBP (final).doc, Physics Today 3. Costas M. Soukoulis, Stefan Linden, Science, Vol 315, (47-49) 4. H.S Chen et al. PIER 51, 231-247, 2005 5. D. Schurig, J.J. Mock, Science, Vol 314 (977-979); 2006 THANK YOU