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This paper reports on the design and experimental characterization of evanescent waveguides loaded with split ring resonators SRRs supporting enhanced backward wave propagation. With respect to previous negative refractive index devices based on metallic waveguides, the use of a direct coaxial probe excitation inside an evanescent waveguide drastically improves transmission and reflection characteristics of the periodic structure. Moreover, the addition of metallic windows interleaved between consecutive resonators offers an extra degree of freedom in order to control interresonator couplings, and hence, device parameters like overall transmission, reflection, and bandwidth of the backward wave pass band. A numerical and experimental analysis of different structures overcoming the high loss issue of previously published results is detailed. An experimental validation of the proposed enhancements is done for periodic structures, where no individual tuning of the resonator sections is performed. The proposed technology mainly offers the advantage of miniaturization, and it could be combined in a further step with standard design techniques to provide frequency selective devices. Ministerio de Educación y Ciencia, Gobierno de España-TEC-2004-04313-C02-01 y TEC-2004-04249.C02-02 Generalitat Valenciana-ACOMP06/013 y GVA/2007/215

We present experimental results of electromagnetic wave modulation by the application of AC currents along a ferromagnetic microwire at the frequency range where left-handed transmission is observed. It is demonstrated that transmitted microwave signals through a waveguide mount are modulated by the current applied to the wire. From the measurements, we have extracted information about the magnetic susceptibility behavior of the microwires. © 2012 American Institute of Physics., Work partially supported by MICINN (Spain) under contracts with Refs. TEC 2010-19751 and CSD2008-00066 (CONSOLIDER Program).

We present the theoretical and experimental study of the effective permittivity of photonic crystal (PC) of parallel rods in the long-wavelength limit. Considering low-absorbing materials, we obtain analytical formulas for the imaginary part of the permittivity for the dielectric tensor. For the H-polarized mode propagating in a low-loss PC with rectangular symmetry we predict stronger azimuthal anisotropy for the imaginary part of permittivity than that for the real part. Measurements of microwave transmission through a PC of FR4 rods support the proposed theory. The obtained results may be used for optimization and tailoring of electromagnetic losses in artificial periodic structures.

Tuning of the transmission characteristics of amorphous ferromagnetic microwires through a dc current is demonstrated. These structures are studied in the frequency region where they present double negative behavior. It is found that their frequency response shifts with small dc currents circulating along the wires. It is observed that the dc current tends to compensate and even cancels the resonant peak associated to the static magnetic field applied along the wire axis. The phenomenon behind these findings is discussed in terms of the torque exerted by the field created by the current on the plane perpendicular to the wire axis.

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.

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.

International audience; 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