An interesting application of left-handed metamaterials is proposed and numerically verified. Specifically, a structure consisting of a conventional dielectric slab adjacent to a metamaterial slab of the same width but of opposite material characteristics, is used as a radome. The behaviour of the structure for normal as well as for oblique incidence is considered. The results are satisfactory in both cases. It is shown that cylindrical structures similar to the aforementioned straight structures could also be used as radomes. However, the behaviour of the structure is non-reciprocal for incoming and outgoing waves. The dispersive finite-difference time-domain method is applied to study all the structures and the numerical results verify that the straight conjugate slabs are transparent in normal incidence and reduce the reflections for oblique incidence, which are the desirable characteristics for a radome.

A metamaterial‐scanning near‐field optical microscope is proposed to study a subwavelength object consisting of a pair of long slits. The device comprises a metamaterial slab adjacent to the object and a subwavelength probe consisting of a single long slit which slides along the other side of the slab. A finite‐difference time‐domain (FDTD) simulation is performed, which provides the field‐intensity contours outside the device. It is found that by using two slabs of different widths (with and without probe), in the cases considered, the resolution is better when the probe is present. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 587–590, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21415

The dispersion relations for metamaterial cylindrical guides ore, found and their Brillouin diagrams are drawn for different guide parameters. It is found that the transverse propagation coefficient of the first TMz mode and the first TEz mode can be either real or imaginary. The longitudinal propagation coefficient of the first TMz mode starts at Zero frequency and ends at a frequency where it is equal to the wave-number of the surrounding dielectric medium, while the longitudinal propagation coefficient of the first TEz mode starts at this same firequency and ciftenvards grows indefinitely. The first hYbrid mode of order one as well as subsequent modes are also studied. It is found for the first TMz and TEz modes, the group velocity is almost constant, whether the transverse propagation coefficient is real or imaginary. Moreover, interesting coupling effects can be obtained by using adjacent metamaterial and dielectric cylindrical guides. (C) 2004 Wiley Periodicals, Inc.

Near-field optical signals are imaged in the vicinity of nano-holes using two different near-field optical microscopes. The experimental results are compared with electromagnetic field calculations based on a modal approximation. It turns out that an optical fibre detects the Poynting vector whereas the apertureless tip is sensitive to the field amplitude.

Expressions are given for the overall reflection and transmission coefficients of a multilayered structure consisting of metamaterial and dielectric slabs. Small‐reflection approximations are discussed. Two applications are proposed: anti‐reflection coatings and high‐reflection coatings. For the first application, a structure consisting of two slabs of the same width and opposite permittivities is studied. If the structure is placed between two semi‐infinite media of the same kind, the reflection vanish, while if these two media are different, the reflection depends only on their characteristics and on the angle of incidence. This device could be advantageously used as an antenna radome. For the second application, a structure consisting of a large number of identical pairs of slabs of high and low opposite permittivities and of the same widths, embedded in the same medium, is studied. This structure's transmittance variation with frequency shows no ripples, and has a large passband and a monotonous quasi‐symmetric rise to the right and to the left of the central frequency. The distinctive feature of these devices is the weakening of the influence of the frequency, the angle of incidence or the polarization on the propagation processes. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 460–465, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20005

Wave propagation along a rectangular metallic waveguide, loaded with a longitudinal metamaterial slab adjacent to air, is studied in this paper. The dispersion relations have been obtained and the β − ω diagrams have been drawn for various width ratios of the metamaterial to air regions. For real propagation coefficients, in the 0 < β < k0 range, the group velocity could be negative, very low or constant, depending on the frequency range and on the width ratios of the two regions. In some cases, it has been found that the propagation coefficient is complex although the media are lossless: there is no net energy flow through any cross section of the guide so that the energy present is only stored reactive energy, and this seems to be due to strong coupling processes occurring in the device. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 123–127, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20067

Metamaterial slab coupling to another metamaterial slab or to a dielectric slab is studied, taking into consideration regular trigonometric modes as well as hyperbolic modes. The first TM even mode has been given special attention, since it exhibits interesting filtering properties. The coupling coefficient frequency variation of the structures has been investigated. It is found that, for a given frequency, the thinner the width of the slabs or the lower their permittivity, the higher the coupling between them. (C) 2004 Wiley Periodicals, Inc.

The coupling between two identically excited, dissimilar rectangular dielectric waveguides, whose axes are parallel, is studied as a function of frequency and of the geometrical and the electrical properties of the structure. It is found that, for a given permittivity ratio, the power transfer between the guides is maximal, but not complete, at some particular frequency. It is also found that, for a given frequency, the power transfer between the guides is complete for the appropriate combination of permittivity and size of the guides, thus the same propagation coefficient is achieved for both. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 136–139, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10996

Surface‐wave propagation along a metamaterial slab with negative permittivity and permeability is analyzed. The dispersion relations are determined for the TM and TE (odd and even) modes. The Brillouin diagrams are drawn and show that, for odd modes after cutoff, there is an initial frequency range for which there are two possible propagation coefficients. All the even modes exhibit the same behaviour except the first one. In this case a band‐pass region appears, suggesting that the device could be used as a filter. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 38: 392–395, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11070

The coupling between two identical square dielectric waveguides with parallel axes has been studied for various configurations, in which one of the guides was arbitrarily rotated with respect to the other. In one case, the first guide was kept fixed while the second guide was rotated from 0degrees to 180degrees. It was found that the coupling coefficient was maximal when the inclination angle was 0degrees or 180degrees and vanished when it was 90degrees. In another case, one corner of the first guide faced one corner of the second guide. It was found that the coupling coefficient was less than half the maximal value obtained for the previous configuration. This study has a practical aspect; it proposes a possible way to select an appropriate coupling in order to satisfy a given engineering design.

Thr response of multilayered chiral filters is investigated at oblique incidence. It is found that there is a slight degradation with respect to the same filter operating at normal incidence. A possible application is proposed fbr this device: a reflector or a subreflector fed at two different frequencies by two feeds situated on each side of a multilayered chiral filter functioning as a frequency-selective surface. The response of this device is well behaved, and is similar for TE and TM modes. (C) 2001 John Wiley & Sons, Inc.

The reflection and transmission coefficients of electromagnetic waves, whose transverse electric and magnetic field components possess a given symmetric distribution hare been determined by the rigorous analysis of tehse components at the aperture plane of a semi-infinite chiral slab, either embedded between two semi-infinite dielectric media and placed in front of an air half space, or totally immersed in a uniform dielectric medium. The discrete spectrum of incident and reflected surface modes as well as the continuous spectrum of reflected and transmitted modes have been taken into consideration in this analysis. The ensuing integral equations have been transformed by using an appropriate complete set of basis functions, into a system of algebraic equations which have been solved numerically. The tangential components of the electromagnetic field at the aperture plane, the radiation field in the far region, as well as the transmission and reflection coefficients variation as a function of chirality have been obtained, and different excitation schemes have been analyzed. (C) 2000 John Wiley & Sons, Inc.

Strong electric-field enhancements at the apex of a tungsten tip illuminated by an external light source were recently predicted theoretically. We present an experimental study of the dependence of this effect on the polarization angle of the incident light. It is shown that the intensity of the light scattered by the tungsten tip of an apertureless scanning near-field optical microscope is 2 orders of magnitude higher when the incident light is p polarized than when it is s polarized. This experimental result is in good agreement with theoretical predictions and provides an easy way to test the quality of the tips.

A perfectly conducting halfplane of finite thickness much smaller than the wavelength of the incident electromagnetic wave is investigated The geometry of the structure is defined according to a transformation which is a particular case of the Schwarz-Christoffel transformation, representing a step with a slightly concave edge instead of the usual straight one. The solutions of the partial differential equations describing the structure are given for specific ranges of the variables, and the results obtained with this method are compared to those obtained with an independent numerical method for a step with a straight edge. Good agreement is obtained between the two sets of results, except right around the edges of the steps in the two structures, due to the different shapes involved. It is shown that the width of the structure has but a slight influence on the value of the electric field, while the angle of incidence of the incoming wave has a strong influence on this value. (C) 1999 John Wiley & Sons, Inc.

A new near-field optical microscope working in transmission is presented. Lateral optical resolution less than 10 nm is obtained with a pure metallic probe. Polarization images of a metallic step confirmed the good resolution by comparison with an analytical model. We also demonstrate the capability of the microscope to obtain images with polarization effects. The good resolution is used for the observation of small gold aggregates which confirm that this microscope is able to make spectroscopic measurements of the optical effect induced by a nanometric scale particle. The polarization sensibility allows us to measure near-field magneto-optical contrast on a multi-layer sample with magnetic domains. These results are promising for magneto-optical characterization with nanometre resolution.

A vibrating metallic conical probe has been used in near-field microscopic measurements to obtain optical resolutions much smaller than th wavelength. Numerical simulations of these complex problems have drawn most of the attention in the past. We propose here an analytical expression for the electric field intensity in the near region of a probe situated above the surface of a semi-infinite dielectric medium. It is given as a function of the observation point location, with the cone aperture, the dielectric medium permittivity, and the characteristics of the incident plane wave as parameters. (C) 1998 John Wiley & Sons, Inc.

The use of multi-layered chiral structures as filters in the microwave frequency range is studied in this paper. These chiral devices can replace their dielectric counterparts when the synthesis of the latter has furnished values of refractive indices which are unavailable, and, in addition, they are able to rotate the plane of polarization of the transmitted wave by a given angle. These features are achieved due to the extra degree of freedom provided by the chirality admittance. The sensitivities of the two kinds of filters are calculated, analyzed and compared. The dependence of the permittivity of the medium on the chirality admittance is taken into account in order to evaluate its influence on the characteristics of the chiral filter and to compensate for it. Finally an accurate model which considers lossy frequency dependent parameters, is used to design a wide stop-band filter. The chiral filter is compared to a dielectric one: a large attenuation at the stop-band, a steep response at the cutoff frequency and a wide stop-band, are the three main advantages of the chiral filter over its dielectric counterpart.

A variational method involving the transverse components of the electric field and their transverse derivatives has been used to calculate the dispersion curves of the higher-order modes of an electromagnetic wave propagating along a lossless rectangular chirowaveguide with perfectly conducting walls. The agreement between the variational results and those obtained by a finite-difference method is excellent for the dominant mode, but deteriorates for higher-order modes. The chirowaveguide modes have been labeled, and their cut-off frequencies have been given as functions of the ratio of the guide dimensions. © 1996 John Wiley & Sons, Inc.

A variational expression involving the transverse components of the electric field and their transverse derivatives is established for the propagation coefficient of an electromagnetic wave propagating along a lossless rectangular chirowaveguide with perfectly conducting walls. The solution providing the propagation coefficient of the dominant mode is given in terms of a very simple analytical expression enabling a tractable analysis of the device. The propagation coefficient of a second propagating mode is obtained simultaneously. The agreement between these variational results and those obtained by other methods is found to be very good

In this paper, the coupling between circular parallel dielectric waveguides of unequal radii and of different permittivities is analyzed with various coupling criteria such as the coupling coefficient, the transmitted power and the supermodes propagation coefficients. A method due to Arnaud is used to evaluate the coupling coefficient because it is simple and tractable. The results we have obtained have been found to be in good agreement with those obtained by other authors. Graphs of the coupling have been given as a function of the normalized frequency and as a function of the permittivity for equal and for unequal radii. Physical interpretations have been proposed for same results.