Theory of Supercoupling, Squeezing Wave Energy, and Field Confinement in Narrow Channels and Tight Bends Using Epsilon-Near-Zero Metamaterials

In this work, we investigate the detailed theory of the supercoupling, anomalous tunneling effect, and field confinement originally identified in [M. Silveirinha, N. Engheta, Phys. Rev. Lett. 97, 157403, (2006)], where we demonstrated the possibility of using materials with permittivity near zero to drastically improve the transmission of electromagnetic energy through a narrow irregular channel with very subwavelength transverse cross-section. Here, we present additional physical insights, describe new applications of the tunneling effect in relevant waveguide scenarios (e.g., the "perfect" or "super" waveguide coupling), study the effect of metal losses in the metallic walls, and the possibility of using epsilon-near zero materials to confine energy in a subwavelength cavity with gigantic field enhancement. In addition, we systematically study the propagation of electromagnetic waves through narrow channels filled with anisotropic epsilon-near zero materials. It is demonstrated that these materials may have interesting potentials, and that for some particular geometries the reflectivity of the channel is independent of the specific dimensions or parameters of epsilon-near zero transition. We also describe several realistic metamaterial implementations of the studied problems, based on standard metallic waveguides, microstrip line configurations, and wire media.Comment: under revie

[Study of Factors Influencing the Cadmium Adsorption in a Series of Belgian Soils]

The aim of this study is to compare the respective cadmium adsorption capacities in a series of 47 selected soil samples, representative of a large scale of belgian soils. For this purpose, adsorption isotherms have been carried out by equilibrating soils with solutions of CaCl2 0.0033 M, at different concentrations of Cd (ranging from 0.01 to 20 mg/l each one being spiked with the radio isotope Cd-109. Data closely obey the Freundlich equation and indicate two distinct adsorption mechanisms as to whether the inputs of Cd are in trace amounts or at high rates. It must be noted that the adsorption capacity of cadmium may vary considerably depending on the origin and the physico-chemical characteristics of the soils samples. Statistical analysis points out that the adsorbed amounts of Cd measured at equilibrium concentrations of 0.01 mg/l (Q10ppb) and 1 mg/l (KF) of the metal in the soil solution, are mainly determined from the soil pH. This parameter explains by itself 80 % (KF) to 85 % (Q10ppb) of the variation in adsorption, when the latter is expressed in a logarithmic form. Part of the residual variation is explained by the organic matter content and, to a lesser extent, by the content in clay or free iron oxides. A simple empirical relationship taking into account pH and cation exchange capacity (CEC) is proposed for estimating the relative Cd retention capacities of soils. Analysis of this relationship obviously gives evidence that acid soils, at pH less than 5.5 retain relatively not much metal. Above this level, the adsorption capacity increases exponentially with pH. This increase is taking place all the more rapidly as the soil contains more clay, iron oxide and especially organic matter which precisely are parameters reflecting as a whole in the exchange capacity of soils