DOW-UAP-D141, AAWSAP DIRD, Metamaterials for Aerospace Applications, April 2010

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Metamaterials for Aerospace Applications Prepared by: Acquisition Support Division (DW0-3) Defense Warning Office Directorate for Analysis Defense Intelligence Agency AAP Person 78 Administrative Note COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized. This product is one in a series of advanced technology reports produced in FY 2009 under the Defense Intelligence Agency, Defense Warning Office's Advanced Aerospace weapon System Applications (AAWSA) Program. Comments or questions pertaining to this document should be addressed to JAAP Person 1 AAWSA Program Manager, Defense Intelligence Agency, ATTN: CLAR/DWO-3, Bldg 6000, Washington,

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Definition of Metamaterials .................................................................................... 1 Applications to Sub-Diffraction Imaging: Super-Lens and Hyper-Lens .................. 6 Applications to Circuits and Waveguide Miniaturization: Slowing Down and Manipulating Electromagnetic Pulses (EMP) Using Advanced Metamaterials ....... 16 Metamaterials for Energy Harvesting ................................................................... 20 Nonlinear Non-Reciprocal Chiral Metamaterials: For Developing Novel Optical Isolators and "One-Way" Microwave Mirrors ....................................................... 27 Tunable Switchable Metamaterials....................................................................... 30 Summary and Conclusions ................................................................................... 31 Figure 1. Example of a Metamaterial Component: The Magnetic Split Ring Figure 2. Example of Another Metamaterial Component: Electric Ring Resonator Figure 3. Geometry of Original Planar Metamaterial Unit Cells (OE1-OE6) and Their Figure 4. Recent Optical Metamaterials for Telecommunication Wavelength and Mid-Infrared Indefinite Permittivity Material .......................................... 5 Figures. Schematic of The Super-lens With n=-1 Refractive Index Corresponding Figure 6. Schematic of the SiC-based Super-lens Which is Imaging Sub-wavelength Holes Buried Under the SiO2 Layer.......................................................... 8 Figure 7. Theoretical Concepts (left panel) and Experimental Implementation (right panel) of an Optical Hyperlens Capable of Magnifying Sub- Diffraction Objects to Observable (larger than Size................................. 9 Figure 8. Hyperlens Based on a Converging Array of Metal Wires ........................ 10 Figure 9. Far-Field Super-lens (FSL) Based on an Indefinite Permittivity Metamaterial Placed Between the Object and the Image-Releasing Figure 10. Tomographic Multi-Beam Multi-Detector Holography of Sub-Wavelength Objects Using Indefinite Permittivity Medium (IPM) ........................... 12 Figure 11. First Experimental Demonstration of Propagating Sub-Diffraction Waves in the Indefinite Permittivity Medium (IPM) ....................................... 13 Figure 12. Schematic for 2-Beams/2-Detectors Interferometric Measurement and Numerical Simulation................................................................... 14 Figure 13. Experimental Setup for 2-Beams/2-Detectors Interferometric Measurement in the Lab and Preliminary Experimental Results .......... 15

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Figure 14. Schematic of Pulse Compression in Magnetized Plasma ...................... 16 Figure 15. Trapped Rainbow: A Waveguide With Negative Index Core Can Stop Figure 16. "Plasmonic Molecule" Exhibiting EIT ................................................... 18 Figure 17. True Multi-Layer Metamaterial With a Unit Cell Shown in Figure16: Radiative Antenna (Single Metal Strip) Coupled to a Dark Antenna (Two Perpendicular Metal Bars) .......................................................... 19 Figure 18. "Perfect" Narrow-Band Microwave Absorber....................................... 20 Figure 19. Wide-Angle Plasmonic Absorber Based on Negative Index Figure 20. Specific Design of a Wide-Angle Plasmonic Absorber Based on Negative Figure 21. Experimental Reflectivity vs. Wavelength and Theoretical Plot of Figure 22. Preliminary Attempts to Design a Better Absorber Using Complementary Figure 23. Engineering the Complex Reflectivity Coefficient Using the Concept of a Figure 24. Example of a Generic Chiral Metamaterial ........................................... 28 Figure 25. Example of Time-Irreversibility of Light Propagation Inside the Twisted Fiber Core............................................................................................ 29 Figure 26. THz Properties of an Electric Split Ring Resonator .............................. 31

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Definition of Metamaterials A metamaterial is defined as an artificial medium whose properties (mechanical, optical, magnetic, or other) cannot be found in naturally-occurring materials. The emphasis of this study will be on electromagnetic and optical metamaterials. Such metamaterials can exhibit rather extreme properties, such as negative refractive index, which implies that both electric permittivity and magnetic permeability must be negative because of the unusual phase relationship between the electric and magnetic fields. Specifically, in most (positive index, including vacuum) media one uses the right-hand rule to define the relationsh[p between electric field ( magnetic field ( and the propagation wavenumber ( f ). The physical basis of the right-hand rule is that the direction of energy propagation defined by the Poynting vector =cEx HI 47Z' and the direction of the phase velocity (defined by the wavenumber k) must coincide. That does not hold true for negative index metamaterials where the two directions are opposite, therefore, the left-handed relationship must hold for the three vectors. Nevertheless, the "left-handed" designation did not withstand the test of time because it was causing confusion and creating irrelevant allusions to helical (a.k.a. chiral) structures. Although chiral structures can indeed exhibit negative index behavior (Reference 2), chirality is not necessary. A typical metamaterial consists of resonant elements such as Split Ring Resonators (SRR). An example of an SRR is shown in Figure 1. The main function of the SRR is to enable strong magnetic response of the structure. A simple empirical formula exists for the magnetic permeability of a metamaterial comprised of the SRRs: where is the resonant frequency of the SRR, and F is proportional to the volume filling factor of SRRs. It is noteworthy that SRRs are designed in such a way that it has a large capacitance. As the result, the resonant frequency of an SRR is small, (that is, the SRR-containing cell is very sub-wavelength). In the example shown in Figure 1 (taken from Reference 6), the unit cell operated at = 10 GHz is A/10. I n fact, the sub-wavelength size of the meta material is what distinguishes them from their close cousins: photonic crystals. By properly designing magnetic SRRs, it is possible to achieve any value of µ for any given frequency. Special challenges exist for optical structures, though, as will be explained below.

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in-plane lattice parameters are av= a,= 10/3 mm, The ring is square, with edge length I =3 mm and tracewidth w tangent). The Cu film, from which the SRRs are patterned, is 17 µm thick. The parameters rand s are given in the table together with the associated value of µ,. (Reference 6) Electric properties of metamaterials can be similarly controlled. An example of a planar electrically-active metamaterial is shown in Figure 2. Figure 2. Example of Another Metamaterial Component: Electric Ring Resonator (ERR). This component provides tunable resonant electric response to the incident electromagnetic field, and can be utilized for engineering the frequency-dependent dielectric