The recently proposed artificial media with negative magnetic permeability and left-handed metamaterials are revisited at the light of the theory of artificial bi͑iso/aniso͒tropic media. In particular, the existence of bianisotropic effects in those materials is investigated, making use of an approximate model. Some unexplained properties of the electromagnetic-wave propagation through these media, revealed by closer inspection of previous numerical simulations and experimental work, are highlighted. It is shown that these peculiarities are properly explained if the bianisotropy is explicitly accounted for. The bianisotropy is related to the existence of magnetoelectric coupling in the artificial constituents ͑artificial atoms͒ of the medium. A simple modification of the artificial atom that precludes the bianisotropy is also proposed.

and F. Martin, Novel small resonant electromagnetic particles for metamaterial and filter design, Int Conf Electromagn Adv Applic (ICEAA), Torino, Italy, 2003. 13. M. Shamonin, E. Shamonina, V. Kalinin, and L. Solymar

A metallic planar particle, that will be called spiral resonator ͑SR͒, is introduced as a useful artificial atom for artificial magnetic media design and fabrication. A simple theoretical model which provides the most relevant properties and parameters of the SR is presented. The model is validated by both electromagnetic simulation and experiments. The applications of SR's include artificial negative magnetic permeability media ͑NMPM͒ and left-handed-media ͑LHM͒ design. The main advantages of SR's for such purpose are small electrical size at resonance, absence of magnetoelectric coupling ͑thus avoiding bianisotropic effects in the continuous medium made of these particles͒, and easy fabrication. Experimental confirmation of NMPM and LHM behavior using SR's is also reported.

Extraordinary optical transmission of light or electromagnetic waves through metal plates periodically perforated with subwavelength holes has been exhaustively analyzed in the last ten years. The study of this phenomenon has attracted the attention of many scientists working in the fields of optics and condensed matter physics. This confluence of scientists has given rise to different theories, some of them controversial. The first theoretical explanation was based on the excitation of surface plasmons along the metal-air interfaces. However, since periodically perforated dielectric (and perfect conductor) slabs also exhibit extraordinary transmission, diffraction by a periodic array of scatterers was later considered as the underlying physical phenomenon. From a microwave engineering point of view, periodic structures exhibiting extraordinary optical transmission are very closely related to frequency-selective surfaces. In this paper, we use simple concepts from the theory of frequency-selective surfaces, waveguides, and transmission lines to explain extraordinary transmission for both thin and thick periodically perforated perfect conductor screens. It will be shown that a simple transmission-line equivalent circuit satisfactorily accounts for extraordinary transmission, explaining all of the details of the observed transmission spectra, and easily gives predictions on many features of the phenomenon. Although the equivalent circuit is developed for perfect conductor screens, its extension to dielectric perforated slabs and/or penetrable conductors at optical frequencies is almost straightforward. Our circuit model also predicts extraordinary transmission in nonperiodic systems for which this phenomenon has not yet been reported.

At microwave frequencies, hollow metallic waveguides behave in certain aspects as a ''onedimensional plasma.'' This feature will be advantageously used for simulating the propagation of electromagnetic (EM) waves in left-handed metamaterials provided the hollow waveguide is periodically loaded with split ring resonators. It will be shown that EM transmission in this structure is feasible within a certain frequency band even if the transverse dimensions of the waveguide are much smaller than the associated free-space wavelength. This effect can be qualitatively and quantitatively explained by the left-handed metamaterial theory, thus providing a new experimental validation for such a theory. DOI: 10.1103/PhysRevLett.89.183901 PACS numbers: 41.20.Jb, 42.70.Qs, 78.20.Ek In 1968 Veselago [1] analyzed electromagnetic (EM) wave propagation through media having simultaneously negative electric permittivity and negative magnetic permeability. Since the E, H fields and the wave vector k of a propagating plane EM wave form a left-handed system in these materials, Veselago referred to them as ''lefthanded'' media. Other interesting properties of such media are, among others, negative refractive index and reversed Doppler effect [1]. The nonexistence of transparent left-handed media in Nature made Veselago's analysis and predictions remain for a long time as a mere theoretical curiosity. However, recently, microwave propagation through an artificial left-handed medium (or metamaterial) has been demonstrated by Smith et al. [2]. The left-handed metamaterial reported in this paper was, in fact, the superposition of two different artificial media: a two-dimensional plasma working below its plasma frequency and an artificial negative magnetic permeability medium (NMPM). Artificial plasmas are well-known materials that can be realized, for instance, by using a regular array of conducting wires [3]. Artificial NMPM have recently been proposed by Pendry et al. [4] and experimentally demonstrated by Smith et al. [2]. These latter media are composed of electrically small resonant particles, which show a very high diamagnetic susceptibility above and around its resonance frequency. When these particles are arranged in a regular lattice and illuminated in a proper way, their high diamagnetic susceptibility causes the resulting composite medium to have a negative effective magnetic permeability within a certain frequency range. In this range the resulting artificial medium is called an artificial NMPM. The split ring resonator (SRR) proposed by Pendry et al. [2,4] (see Fig. 1) fulfills all the requirements for the design of the aforementioned NMPM.The artificial plasma medium proposed in [2] was a simulated two-dimensional plasma, made by placing a regular array of metallic posts between two parallel metallic plates. Nevertheless, a significant simplification of the plasma simulation is possible by using a hollow metallic waveguide, as suggested by the dispersive behavior of these waveguides. It is well-known that hollow metallic w...