Jorge Carbonell

Experimental evidence of left handed transmission through arrays of ferromagnetic microwires

Experimental evidence of left-handed transmission is demonstrated through an array of ferromagnetic microwires. We used amorphous magnetic microwires to take advantage of both electric and magnetic responses locally generating a double negative medium at microwave frequencies, where the ferromagnetic resonance effects take place. The dilution of the responses of the ferromagnetic material provided by the organization of the microstructure in the form of an array provides a means of synthesizing a tailored response to electromagnetic radiation. Finally, transmission characteristics of the analyzed array can be tuned as a function of the applied external magnetic field.

Design and experimental verification of backward-wave propagation in periodic waveguide structures

Experimental results for the demonstration of backward-wave or double-negative (DNG) propagation in waveguide technology combining inductive windows and split-ring resonators are presented and discussed in depth. A novel segmented prototype has been designed, fabricated, and measured, thus allowing the analysis and discussion of different length structures. The experimental characterization proves the DNG nature of the devices by comparing the phase of the transmission coefficient S/sub 21/ for different length structures. Dielectric and metallic losses linked to the resonators also limit the transmission levels of these very compact structures in the longitudinal dimension, and the sources of such losses are interpreted through the comparison of measured results with full-wave electromagnetic simulations.

Negative-Zero-Positive Refractive Index in a Prism-Like Omega-Type Metamaterial

Negative-zero-positive index refraction was demonstrated numerically on the basis of full-wave analysis of a microstructured omega-type array and experimentally via angle resolved transmission measurement of a prism-type prototype. The experimental results are interpreted in terms of characteristic impedance and refractive index retrieved by a Fresnel inversion technique. The possibility to balance the dispersion characteristics with a negative-zero-positive index is demonstrated over X - and Ku -bands.

Symmetrical frequency response in a split ring resonator based transmission line

A coplanar waveguide line based on a split ring resonator technology and loaded with metallic strips and capacitances is proposed. The addition of series capacitances to previous unit cell implementations dramatically improves the upper band rejection levels and provides a transmission response almost symmetric. The configuration also exhibits a band pass response with a right-handed character as a result of the balance between advance and delay phase offsets contrary to the conventional left-handed lines. The interpretation is based on an equivalent circuit model, full-wave electromagnetic analysis, and measured responses of a prototype designed for microwave operation.

A 2% Bandwidth C-Band Filter Using Cascaded Split Ring Resonators

A 2% bandpass filter with an out-of-band rejection in excess of 30 dB was demonstrated experimentally for operation in the C-band (central frequency at 4.5 GHz). Narrow bandwidth and high rejection were achieved by cascading three double split-ring resonators (SRRs) magnetically coupled to a coplanar waveguide (CPW) and three pairs of shunt wires between the central strip and the ground metal layers. This configuration, directly inspired from the so-called metamaterial technology, takes advantage of the high dispersion of the loaded transmission line, induced by a negative magnetic response via the resonators, and of a negative permittivity effect via the shunt wires. The optimization of: 1) the symmetry; 2) the out-of-band rejection; and 3) the fractional bandwidth was carried out in two stages, i.e., by engineering the plasma frequencies of the electrical and magnetic systems and by tapering the tightly coupled cascaded unit cells in order to achieve an overlap of their individual responses.

FROM REJECTION TO TRANSMISSION WITH STACKED ARRAYS OF SPLIT RING RESONATORS

We report on free space transmission experiments carried out on stacked split ring resonator (SRRs) arrays operating at microwave frequencies. We start from the case of a single frequency selective surface which exhibits a rejection at the SRR resonance frequency. By stacking SRR arrays in the propagation direction, we then show experimentally the possibility to induce a transmission band just below this resonance frequency. Full wave analysis shows the role played by the longitudinal and transverse coupling efiects in the electromagnetic properties of such bulk metamaterials, with the appearance of a transmission band resulting from an artiflcial magnetic activity.

Lumped elements circuit of terahertz fishnet-like arrays with composite dispersion

We have analyzed and characterized a terahertz stacked holes array over a broad transmission bandwidth. In this context, we identify the key contributions of the surface plasmon modes related to the periodicity of array, and of the subcut off transmission through the holes responsible of a ground left-handed dispersion branch. The experimental verification of a multimode electromagnetic behavior is performed by time domain spectroscopy, with a complementary assessment by full-wave analysis. A circuitlike approach appears suitable for the understanding of a zero-gap transition between the left- and right-handed characteristics, opening the way of nonvanishing group velocity in a near-zero index propagation medium. Such a balanced composite operation, pointed out over the past in the dual element transmission line approaches, is thus generalized for a stacked subwavelength holes array, whose operation can be compared to the one of the so-called fishnet structures.

Highly selective left-handed transmission line loaded with split ring resonators and wires

The frequency selectivity of coplanar transmission lines loaded with split ring resonators and shunt strips was dramatically improved owing to a blueshift of the electrical plasma frequency by oversizing the strip width. Beyond a higher rejection level, which was expected as a consequence of the deepening of the forbidden gap between the left- and right-handed dispersion branches, a huge enhancement in the loaded Q quality factors, while maintaining low insertion losses were also pointed out. This Q factor improvement was a consequence of a decrease in the coupling between the resonators and the transmission line.

Duality and Superposition in Split-Ring-Resonator-Loaded Planar Transmission Lines

Three types of coplanar transmission lines loaded with split-ring resonators (SRRs) and including series gaps and/or shunt wires are analyzed in this letter. The phase advance originally predicted for these microstructures can be modified and their frequency selectivity can be enhanced while maintaining the advantage of miniaturization. Full-wave electromagnetic simulations and measurement of different prototypes operating in S- and C-frequency bands are performed for retrieving the effective permittivity and permeability. It is shown that right-handed transmission bands can be obtained slightly below the resonance frequency of the SRRs, giving an effective control of the propagation characteristics in magnitude and phase of these planar transmission lines.

A Controllable Bandwidth Filter Using Varactor-Loaded Metamaterial-Inspired Transmission Lines

This letter presents a tunable bandwidth bandpass filter based on varactor-loaded metamaterial coplanar waveguide (CPW) lines. The CPW lines are based on series gaps and split-ring resonators. The varactors are reverse-biased semiconductor diodes connected between both sides of each series gap. This configuration, directly inspired from the so-called metamaterial technology, takes advantage of the high dispersion of the loaded transmission line. Therefore, strong permittivity and permeability responses induced by means of the resonators are obtained. A single varactor-loaded transmission line is first analyzed. Then, a third-order tunable filter with fractional bandwidth tuning range from 5.8% to 21.5% is experimentally assessed. The proposed filters can be used in several practical applications such as multichannel wireless and satellite communication systems, where reconfigurable devices are often required.