This work studies the influence of material coatings, especially combined natural and metamaterials, on the radiation properties of a practical dipole like antenna, represented by a slotted conducting sphere. The selected geometry allows an exact solution to the problem, and thus the development of exact expressions for the antenna parameters, like the radiated power and directivity. It is shown that for materials with combined positive and negative parameters, mode resonances can occur at thinner coatings, the thickness of which can be made diminishingly small by proper selection of coating parameters. In particular, at these resonances the antenna directivity, while being finite, becomes independent of the antenna size and coating parameters.
2. Mushiake, Y. and R. E. Webster, "Radiation characteristics with power gain for slots on a sphere," IRE Trans. Antennas Propag., Vol. 5, No. 1, 47-55, Jan. 1957.
doi:10.1109/TAP.1957.1144465
3. Kerker, M., The Scattering of Light and Other Electromagnetic Radiation, Academic Press, New York, 1969.
4. Towaij, S. J. and M. A. K. Hamid, "Diffraction by a multilayered dielectric-coated sphere with an azimuthal slot," Proc. IEEE, Vol. 119, 1209-1214, Sep. 1971.
5. Shafai, L. and R. K. Chugh, "Resonance effects in slotted spherical antennas coated with homogeneous materials," Can. J. Phys., Vol. 51, 2341-2346, 1973.
doi:10.1139/p73-306
6. Huang, M. D. and S. Y. Tan, "Efficient electrically small prolate spheroidal antennas coated with a shell of double-negative metamaterials," Progress In Electromagnetics Research, Vol. 82, 241-255, 2008.
doi:10.2528/PIER08031604
7. Wu, B.-I., W.Wang, J. Pacheco, X. Chen, T. M. Grzegorczyk, and J. A. Kong, "A study of using metamaterials as antenna substrate to enhance gain," Progress In Electromagnetics Research, Vol. 51, 295-328, 2005.
doi:10.2528/PIER04070701
8. Hamid, A. K., "Axially slotted antenna on a circular or elliptic cylinder coated with metamaterials," Progress In Electromagnetics Research, Vol. 51, 329-341, 2005.
doi:10.2528/PIER04082301
9. Li, C. and Z. Shen, "Electromagnetic scattering by a conducting cylinder coated with metamaterials," Progress In Electromagnet ics Research, Vol. 42, 91-105, 2003.
doi:10.2528/PIER03012901
10. Brovenko, A., P. N. Melezhik, A. Y. Poyedinchuk, N. P. Yashina, and G. Granet, "Resonant scattering of electromagnetic wave by stripe grating backed with a layer of metamaterial," Progress In Electromagnetics Research B, Vol. 15, 423-441, 2009.
doi:10.2528/PIERB09052302
11. Choi, J. and C. Seo, "High-e±ciency wireless energy transmission using magnetic resonance based on negative refractive index metamaterial," Progress In Electromagnetics Research, Vol. 106, 33-47, 2010.
doi:10.2528/PIER10050609
12. Han, L., S. Chen, A. Schulzgen, Y. Zeng, F. Song, J.-G. Tian, and N. Peyghambarian, "Calculation and optimization of electromagnetic resonances and local intensity enhancements for plasmon metamaterials with sub-wavelength double-slots," Progress In Electromagnetics Research, Vol. 113, 161-177, 2011.
13. Siakavara, K. and C. Damianidis, "Microwave filtering in waveguides loaded with artificial single or double negative materials realized with dielectric spherical particles in resonance," Progress In Electromagnetics Research, Vol. 95, 103-120, 2009.
doi:10.2528/PIER09061506
14. Engheta, N. and R. W. Ziolkowski, Metamaterials Physics and Engineering Explorations, IEEE Press, Wiley Interscience, New Jersey, 2006.
15. Eletheriades, G. V. and K. G. Balmain, Negative-reflection Metamaterials, Fundamental Principles and Applications, John Wiley and Sons Inc., New Jersey, 2005.
doi:10.1002/0471744751
16. Caloz, C. and T. Ito, "Electromagnetic Metamaterials, Transmission Line, Theory and Microwave Applications," John Wiley and Sons Inc., New Jersey, 2006.
17. Harrington, R. F., Time-harmonic Electromagnetic Fields,, McGraw-Hill, New York, 1961.
18. Balanis, C. A., Advanced Engineering Electromagnetics, John Wiley and Sons, Inc., 1989.
19. Balanis, C. A., Antenna Theory, Analysis and Design, 3rd Ed., John Wiley and Sons Inc., New Jersey & Canada , 2005.
20. Budden, K. G. and H. G. Martin, "The ionosphere as a whispering gallery," Proceedings of the Royal Soc. of London. Series A Mathematical and Physical Sciences, Vol. 265, No. 1323, 554-569, Feb. 1962.
doi:10.1098/rspa.1962.0042
21. Stockman, M. I., "Nanofocusing of optical energy in tapered plasmonic waveguides," Physical Review Letters, Vol. 93, No. 13, 2004, DOI: 10.1103/PhysRevLett.93.137404.
doi:10.1103/PhysRevLett.93.137404
22. Seo, M. A., H. R. Park, S. M. Koo, D. J. Park, J. H. Kang, O. K. Suwal, S. S. Choi, P. C. M. Planken, G. S. Park, N. K. Park, Q. H. Park, and D. S. Kim, "Terahertz field enhancement by a metallic nano slit operating beyond the skin-depth limit," Nature Photonics, 152-156, 2009, DOI: 10.1038/NPHOTON.2009.22.
doi:10.1038/nphoton.2009.22
23. Sadiq, D., J. Shirdel, J. S. Lee, E. Selishcheva, N. Park, and C. Lienau, "Adiabatic nanofocusing scattering-type optical nanoscopy of individual gold nanoparticles," Nano Letter, Vol. 11, 1609-1613, 2011.
doi:10.1021/nl1045457
24. Kang, J. H., D. S. Kim, and Q. H. Park, "Local capacitor model for plasmonic electric field enhancement," Physical Review Letter, 1-2, 2010, DOI: 10.1103/PhyRevLett.102.093906.