A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

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High-impedance electromagnetic surfaces with a forbidden frequency band

We present experimental data, numerical simulations, and analytical transfer-matrix calculations for a two-dimensionally isotropic, left-handed metamaterial (LHM) at X-band microwave frequencies. A LHM is one that has a frequency band with simultaneously negative eeff(ω) and μeff(ω), thereby having real values of index of refraction and wave vectors, and exhibiting extended wave propagation over that band. Our physical demonstration of a two-dimensional isotropic LHM will now permit experiments to verify some of the explicit predictions of reversed electromagnetic-wave properties including negative index of refraction as analyzed by Veselago [Usp. Fiz. Nauk 92, 517 (1964), Sov. Phys. Usp. 10, 509 (1968)].

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Microwave transmission through a two-dimensional, isotropic, left-handed metamaterial

This paper develops a quasi-analytical and self-consistent model to compute the polarizabilities of split ring resonators (SRRs). An experimental setup is also proposed for measuring the magnetic polarizability of these structures. Experimental data are provided and compared with theoretical results computed following the proposed model. By using a local field approach, the model is applied to the obtaining of the dispersion characteristics of discrete negative magnetic permeability and left-handed metamaterials. Two types of SRRs, namely, the so-called edge coupled- and broadside coupled- SRRs, have been considered. A comparative analysis of these two structures has been carried out in connection with their suitability for the design of metamaterials. Advantages and disadvantages of both structures are discussed.

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Comparative analysis of edge- and broadside- coupled split ring resonators for metamaterial design - theory and experiments

Sound attenuation by sculpture

Over the past several years, metamaterials have been introduced and rapidly been adopted as a means of achieving unique electromagnetic material response. In metamaterials, artificially structured—often periodically positioned—inclusions replace the atoms and molecules of conventional materials. The scale of these inclusions is smaller than that of the electromagnetic wavelength of interest, so that a homogenized description applies. We present a homogenization technique in which macroscopic fields are determined via averaging the local fields obtained from a full-wave electromagnetic simulation or analytical calculation. The field-averaging method can be applied to homogenize any periodic structure with unit cells having inclusions of arbitrary geometry and material. By analyzing the dispersion diagrams and retrieved parameters found by field averaging, we review the properties of several basic metamaterial structures. © 2006 Optical Society of America OCIS codes: 160.0160, 160.1190, 260.2110, 350.5500.

Homogenization of metamaterials by field averaging (invited paper)

The authors describe the determination of the properties of accelerator cavities with particular emphasis on the damping of the higher order modes (HOMs). Because mode frequency spectra were determined for a large number of shorted waveguide lengths, a complete overall analysis of the mode spectrum was possible. Phase frequency plots have proved to be an invaluable aid in sorting out overlapping resonances and separating cavity resonances from waveguide resonances. Algorithms for the determination of the parameters of several resonances simultaneously have been developed. Determinations of Q from multiresonance analyses are compared to those from single resonance analyses, and the changes are typically found to be small. >

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Computer determination of HOM damping for a prototype JLC accelerator cavity and a prototype B factory cavity

In previous work we have proposed utilizing photonic band gap (PBG) structures as a new class of high-energy, high-intensity accelerator cavities. We have completed extensive MAFIA numerical calculations of multicell PBG structures, with each cell consisting of a square array of metal cylinders terminated by conducting sheets and surrounded by microwave absorber on the periphery. We find that our PBG structure has good higher order mode suppression, superior pumping properties, and potential fabricational advantages when compared to conventional cavity designs. These advantages scale favorably with increasing frequency, leading us to propose use of a PBG accelerator structure at the W-band (91.392 GHz).

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Photonic band gap accelerator cavity design at 90 GHz

A 1.8 m X-band damped-detuned structure (DDS-3) has been fabricated and characterized as part of the structure development program towards a TeV-scale e/sup +/e/sup -/ linear collider. In this joint venture, the Cu cells were precision-fabricated by LLNL, diffusion-bonded into a monolithic structure by KEK, and the structure completed and tested by SLAC. The overall process constitutes a baseline for future high-volume structure manufacture.

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Fabrication of DDS-3, an 11.4 GHz damped-detuned structure

By means of an analytic model and numerical simulations we demonstrate that the wake of a waveguide damped cavity contains a persistent component which decays as t/sup -3/2/ and thus is dominant at sufficiently large values of t. Because there are scenarios for which the effect gives rise to unacceptable beam instability, it cannot be ignored, but it seems likely that such an outcome can be avoided with proper design. >

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Persistent wakefields associated with waveguide damping of higher order modes

The power spectrum emerging from the damping manifolds of a DDS provides valuable quasi-local information on the displacement of a drive beam from the axis of individual cells, where the displacement may be due to beam offset, small cell misalignment, or a combination of the two. The degree of localization and the indexing of frequency to cell number is determined directly from the spectral function theory. Examples for specific DDS designs are presented. These relations can be used to determine geometrical misalignment patterns.

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N.M. Kroll

Papers

Computer determination of HOM damping for a prototype JLC accelerator cavity and a prototype B factory cavity

Photonic band gap accelerator cavity design at 90 GHz

Fabrication of DDS-3, an 11.4 GHz damped-detuned structure

Persistent wakefields associated with waveguide damping of higher order modes

Analysis and application of microwave radiation from the damping manifolds of the SLAC damped detuned structures (DDS)