We review and critique the recent developments on multifunctional oxide materials, which are gaining a good deal of interest. Recongnizing that this is a vast area, the focus of this treatment is mainly on high-κ dielectric, ferroelectric, magnetic, and multiferroic materials. Also, we consider ferrimagnetic oxides in the context of the new, rapidly developing field of negative-index metamaterials. This review is motivated by the recent resurgence of interest in complex oxides owing to their coupling of electrical, magnetic, thermal, mechanical, and optical properties, which make them suitable for a wide variety of applications, including heat, motion, electric, and magnetic sensors; tunable and compact microwave passive components; surface acoustic wave devices; nonlinear optics; and nonvolatile memory, and pave the way for designing multifunctional devices and unique applications in spintronics and negative refraction-index media. For most of the materials treated here, structural and physical propertie...

Oxides, Oxides, and More Oxides: High-κ Oxides, Ferroelectrics, Ferromagnetics, and Multiferroics

In this paper, a horn antenna filled with a metamaterial structure as lens inner the aperture is presented. Unlike conventional curve lenses, the lens is designed in the present work using a fully flat structure, which results in a great improvement for the directivity of the horn antenna based on the zero refraction characteristics of the metamaterial. In this structure, a periodic-structure metamaterial with three-layer metal grids is designed using the CST Microwave Studio for optimization and its zero refraction property is validated. For the characterization of the antenna, the electric-field distribution in radiation area, reflection parameter (S11), gain and radiation pattern are calculated. The results show that the gain of a wide flare angle horn antenna is enhanced with over 2 dB between 16.10–17.30 GHz after the metamaterial is utilized. Therefore, the metamaterial lens horn structure results in a miniaturized antenna design approach compared to the optimum conventional horn of the same aperture size and gain in the interested frequency band.

A novel flat lens horn antenna designed based on zero refraction principle of metamaterials

We studied the far field radiation properties of a new resonator antenna composed of split ring resonators (SRRs) and a monopole. It is shown that the antenna size at the operation frequency (3.52 GHz) is approximately one tenth of the free space wavelength (λ/10). Moreover, increasing the number of SRRs yields steerability properties. These achievements provide a way to create rather small steerable resonant antennas.

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Radiation properties of a split ring resonator and monopole composite

We use coordinate transformation theory to realize substrates that can modify the emission of an embedded source. Simulation results show that with proper transformation functions the energy radiated by a source embedded in these space variant media will be concentrated in a narrow beam. The thickness of the slab achieved with our transformations will no longer be restricted by the evanescent modes and the source can be placed at any position along the boundary of the substrate without affecting the radiation pattern. We also discuss the case where reduced parameters are used, which still performs well and is physically realizable.

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Directive Emission Obtained by Coordinate Transformation

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Directive emission obtained by coordinate transformation

Simulations have been carried out on metamaterials in the microwave regime. S-parameters obtained from waveguide simulations of a unit cell are used to retrieve the effective permittivity and permeability with which we compute the far-field radiation of a monopole embedded in a metamaterial substrate using an analytic method. We find that the analytic method is able to predict features of the experimental results, implying that within a certain frequency range, we can treat the metamaterial as being anisotropically homogeneous. Based on the methodology, a structure is optimized for the application of metamaterials as antenna substrate to enhance directivity by minimizing its refractive index. The experimental results are presented and compared with the analytic calculations. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 680–683, 2006; Pubished online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.21441

Peter Kao

Papers

Anisotropic metamaterials as antenna substrate to enhance directivity