D. C. Vier

Impact of inherent periodic structure on effective medium description of left-handed and related metamaterials

We study the frequency dependence of the effective electromagnetic parameters of left-handed and related metamaterials of the split ring resonator and wire type. We show that the reduced translational symmetry speriodic structured inherent to these metamaterials influences their effective electromagnetic response. To anticipate this periodicity, we formulate a periodic effective medium model which enables us to distinguish the resonant behavior of electromagnetic parameters from effects of the periodicity of the structure. We use this model for the analysis of numerical data for the transmission and reflection of periodic arrays of split ring resonators, thin metallic wires, cut wires, as well as the left-handed structures. The present method enables us to identify the origin of the previously observed resonance-antiresonance coupling as well as the occurrence of negative imaginary parts in the effective permittivities and permeabilities of those materials. Our analysis shows that the periodicity of the structure can be neglected only for the wavelength of the electromagnetic wave larger than 30 space periods of the investigated structure.

Direct calculation of permeability and permittivity for a left-handed metamaterial

Recently, an electromagnetic metamaterial was fabricated and demonstrated to exhibit a “left-handed” (LH) propagation band at microwave frequencies. A LH metamaterial is one characterized by material constants—the permeability and permittivity—which are simultaneously negative, a situation never observed in naturally occurring materials or composites. While the presence of the propagation band was shown to be an inherent demonstration of left handedness, actual numerical values for the material constants were not obtained. In the present work, using appropriate averages to define the macroscopic fields, we extract quantitative values for the effective permeability and permittivity from finite-difference simulations using three different approaches.

Loop-wire medium for investigating plasmons at microwave frequencies

We present numerical simulations and microwave measurements on a loop-wire structure that acts as an effective medium exhibiting a well-defined bulk plasma frequency in the microwave regime, with an effective negative dielectric function below this plasma frequency. The dependence of this plasmonic response on the self-inductance of the constituent wire elements is made explicit. A finite structure, approximately spherical, composed of this inductive medium is studied, and reveals subwavelength surface plasmon resonances below the bulk plasma frequency.

Ab initio numerical simulation of left-handed metamaterials: Comparison of calculations and experiments

Using numerical simulation techniques, the transmission and reflection coefficients, or S parameters, for left-handed metamaterials are calculated. Metamaterials consist of a lattice of conducting, nonmagnetic elements that can be described by an effective magnetic permeability μeff and an effective electrical permittivity eeff, both of which can exhibit values not found in naturally occurring materials. Because the electromagnetic fields in conducting metamaterials can be localized to regions much smaller than the incident wavelength, it can be difficult to perform accurate numerical simulations. The metamaterials simulated here, for example, are based on arrays of split ring resonators (SRRs), which produce enhanced and highly localized electric fields within the gaps of the elements in response to applied time dependent fields. To obtain greater numerical accuracy we utilize the newly developed commercially available code MICROWAVE STUDIO, which is based on the finite integration technique with the per...

Performance of a negative index of refraction lens

A plano-concave lens with negative index of refraction has been designed and fabricated. Such lenses have been postulated for many years, but only recently has their realization been made possible through improved simulation and fabrication procedures. We report here the simulation, fabrication, and performance of such a lens. The lens images the source field and reproduces the results of standard Gaussian optics. The curved lens with negative index of refraction in the microwave frequency region of the electromagnetic spectrum has been compared to a plano-convex Macor positive index of refraction lens having the same radius of curvature.

Left-Handed Metamaterials

The response of a material to electromagnetic radiation can be entirely characterized by the material parameters: the electrical permittivity, or e, and the magnetic permeability, or μ. The range of possible values for the material parameters, as dictated by fundamental considerations such as causality or thermodynamics, extends beyond that found in naturally occurring materials. We thus seek to extend the material parameter space by creating electromagnetic metamaterials—ordered composite materials that display electromagnetic properties beyond those found in naturally occurring materials. Recently, we have demonstrated a metamaterial made of a repeated lattice of conducting, nonmagnetic elements that exhibits an effective μ and an effective e, both of which are simultaneously negative over a band of frequencies [1]. Such a medium has been termed Left-Handed [2], as the electric field (E), magnetic intensity (H) and propagation vector (k) are related by a left-hand rule. We introduce the reader to the expected properties predicted by Maxwell’s equations for Left-Handed media, and describe our recent numerical and experimental work in developing and analyzing this new metamaterial.

Steering Phased Array Antenna Beams to the Horizon Using a Buckyball NIM Lens

In this paper, we present the design, optimization, fabrication, and measurement of a negative index metamaterial (NIM) buckyball shell lens to steer phased array antenna (PAA) beams to the horizon. The conformal mapping technique of transformation optics is utilized in the design process to facilitate with lens fabrication. A new dual polarization unit cell is designed to avoid the issues associated with short cut wires, were a split ring resonator (SRR) and wire design to be used. The lens is measured using an actual PAA and it demonstrates to-the-horizon scanning as designed, although the material loss is high. An improved unit cell design is proposed to reduce several known loss mechanisms. A new lens design methodology using Bezier curves as seed surfaces is also described.

Thickness dependence of the superconducting transition temperature of YBCO

Abstract We have performed detailed structural and superconducting studies of YBCO single layers, YBCO/PrBCO/YBCO tri-layers, and YBCO/PrBCO superlattices. The results for single layers indicate that a nominally one unit cell thick YBCO film sandwiched between PrBCO layers is not superconducting. However, a superlattice with nominally one unit cell thick YBCO layers has a measurable superconducting temperature onset ( T c o ). These apparently contradictory results are reconciled by experiments on YBCO/PrBCO/YBCO tri-layers which, due to coupling across the PrBCO insulating layer, exhibit superconductivity for PrBCO thicknesses below 200 A. Structural studies show that the length scale of the superconductive coupling is much larger than the length scale of the step disorder and interdiffusion present in the film.

Observation of conduction electron spin resonance in both the normal and superconducting states of niobium

Abstract We report the first observation of Conduction Electron Spin Resonance (CESR) in both the normal and superconducting states of pure niobium. Surprisingly, the resonance displayed a g -value of 1.84 ± 0.01 in both states. The linewidth narrows considerably in the superconducting state, in qualitative agreement with calculations by Yafet.

Negative permeability from split ring resonator arrays

Summary form only. The range of values observed for the magnetic permeability, /spl mu/(/spl omega/), appears to be more restricted than the values observed for the electric permittivity, /spl epsi/(/spl omega/), where very large, and even negative values are observed. This is in part due to the simple fact that there are no magnetic monopoles to provide the analogous response to that of electrons. In particular, as one moves away from zero frequency, the magnitude of the magnetic response from most materials, or /spl mu/(/spl omega/), decreases rapidly, and has never been observed to take negative values. While the general lack of magnetic response is observed to be the case, Maxwells equations do not preclude a material having a large /spl mu/(/spl omega/), either positive or negative. The essential requirement on the material constants appears only to be d/d and d/d for frequency-dependent materials. Pendry et al. (1999) have introduced conducting nonmagnetic split ring resonators (SRRs), and predicted that periodic arrays of SRRs can have a resonantly enhanced effective permeability displaying frequency regions with large positive or negative values. Combining numerous SRRs into a lattice forms an effective medium, for which there exists a band of frequencies where the effective permeability is negative. The SRR medium offers the possibility of engineering materials to respond to time-varying magnetic fields as well as time-varying electric fields. Combining such composite media with standard materials offers the potential to yield novel and advantageous electromagnetic devices.