This paper investigates, using only Raman spectroscopy, the spectral differences among the synthetic ultramarine blue (J. B. Guimet) and three natural ultramarine blues (lazurites) corresponding to three lapis lazulis from different geographical sources (Chile, Afghanistan and Siberia). The synthetic ultramarine blue used as reference pigment is the identified in an artwork created around 1917 by the Catalonian modernist painter Ramon Casas i Carbó. This synthetic pigment is compared with the three natural ultramarine blues and, in his turn, the latter are also compared each other. In order to quantify the spectral differences, a rigorous methodology based on the Euclidean distance between homologue spectral segments (or intervals) has been developed and presented here. Copyright © 2014 John Wiley & Sons, Ltd.

This investigation is focused on the identification in ceramic artworks of certain nonstandard yellow/orange pigments whose composition is based, fundamentally, on lead, tin, and antimony oxides with or without silica. In this work, a comparative study (temporal and geographical) of the employment of these yellow pigments in different production centers, from Italy (Pesaro and Montelupo) and Spain (Talavera de la Reina), during the Renaissance and Baroque epochs has been proposed. For this purpose, special very ancient yellow pigments were acquired from the Stazione Sperimentale del Vetro, Murano‐Venezia (Italy). These reference pigments have been produced following strict and rigorous manufacturing recipes corresponding to Venezian fabrication processes for the 16th and 17th centuries. On the other hand, the portable characteristic of a new optical fiber Raman system has allowed us the access into the Museo de Cerámica de Barcelona in order to investigate the composition of the yellow and orange colors of an important ceramic collection belonging to this museum. The results are in good agreement with the ones obtained by other authors who have investigated the same topic. It is notable, first, the excellent performances that this portable Raman system offers in the direct and non‐invasive analysis of ceramic artworks and, second, the coincidences of the molecular results among these yellow pigments. This fact confirms that these pigments were commonly used either in Italian and Spanish ceramic objects during both Renaissance and Baroque epochs. Copyright © 2012 John Wiley & Sons, Ltd.

A metamaterial spacer composed of spiral resonators (SRs) and narrow metal strips has been tested to operate like a bidirectional artificial magnetic conductor (AMC) reflector at 2.45 GHz. The performance of the spacer has also been evaluated in a closely spaced multiple-antenna system applied to successfully increase the transmission capacity of a commercial wireless IEEE 802.11b router.

The use of a low-profile, lightweight, and easy-to-fabricate transpolarizing surface placed on one side of a trihedral corner reflector (TCR) as a polarimetric calibrator is presented in this letter. The transpolarizing TCR presents a high backscattered cross-polar response contrary to standard TCRs. The performance of this device has been tested at the X-band using the Universitat Politecnica de Catalunya ground-based synthetic aperture radar.

Patch antennas filled using different material loadings, both homogeneous and dispersive, are reviewed in order to assess its FBW value. A compact formulation proposed by Yaghjian and Best [1] to compute the FBW of antennas is successfully applied.

Artificial magnetic material (AMM) slabs composed of spiral resonators (SRs), operating in the mu-near-zero (MNZ) band, 0 < μr < 1, are investigated as slot antennas substrates for broadside radiation and directivity enhancement. Results for the slot antenna in free-space are compared with the slot antenna in presence of a single-layer and a four-layer SR AMM slabs.

A bidirectional metamaterial spacer composed by Spiral Resonators (SRs) and metal strips has been designed, simulated, fabricated, and tested to operate like an artificial magnetic conductor (AMC) reflector at 2.45 GHz. A prototype of the new metamaterial spacer has been used to decorrelate two closely spaced monopole antennas achieving a good isolation and matching over a wide frequency range. This design could be used to develop a more compact multi-antenna Wi-Fi (IEEE 802.llb/g) router.

The use of a transpolarizing surface placed on one side of a trihedral corner reflector (TCR) as polarimetric calibrator is presented in this paper. The transpolarizing-TCR presents a high back-scattered cross-polar response. This structure has been tested at 9.65 GHz (X-band) with the help of the UPC GB-SAR system.

The broadside power radiation enhancement has been tested for the case of a magnetic dipole in presence of an MNZ metamaterial substrate. In order to assess the theoretical estimations, a slot antenna on a ground plane has been fabricated and an AMC composed of 1 layer square spiral resonators has been used as an MNZ metamaterial slab. The radiation patterns have been measured in the anechoic chamber, achieving a gain in directivity of more than 1 dB. However, it should be taken into account that the thickness of the fabricated metamaterial slab (6 mm) is much smaller than the theoretical optimum thickness (hundreds of mm). The directivity of the antenna might be improved when increasing the number of layers of the metamaterial slab; in fact, in such a case, the leaky waves responsible of directive radiation are expected to be more significantly excited giving rise to the sought broadside power enhancement.

Transpolarizing surfaces are characterized for their property of rotating by 90deg the reflected electric field with respect to the incident one. Several transpolarizing surface designs are presented, and their potential applications and limitations, mostly for oblique incidence, are discussed.

A metamaterial spacer to decorrelate two closely spaced antennas has been designed and tested. The metamaterial spacer exhibits an artificial magnetic conductor (AMC) behavior around 2.6 GHz. Its performance has been checked against a simple inetal spacer (PEC), providing a quasi orthogonal radiation pattern and good results in terms of decoupling and decorrelating a two-antenna system. (c) 2008 Wiley Periodicals, Inc.

Metamaterial slabs made of magnetic resonators (artificial magnetic conductor, AMC surfaces) can provide unusual electromagnetic properties, such as the dual PMC/PEC behavior, when used as reflectors. This property has been assessed and tested with the design and fabrication of a one‐layer spiral AMC slab. Moreover, two bidirectional AMC surfaces have also been designed and measured. These structures, composed of spiral (SR) or capacitive loaded loop (CLL) resonators printed on dielectric strips, can provide 0° reflection coefficient phase when the incident electric field wave impinges on any side. A very low electrical thickness is achieved. Compact antenna systems with two (or more) close isolated antennas can be designed with such structures. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1949–1953, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22567

In this paper, a new solution to improve the correlation matrix of two closely spaced antennas is illustrated. Contrary to the use of a decoupling network, a physical separator between the antennas is considered. And hence, the use of a metallic plane (PEC) and a metamaterial surface (with bidirectional PMC response) are compared in terms of correlation matrix improvement and radiation patterns.

A novel transpolarizing or crosspolarizing surface has beeen proposed to be applied in polarimetric SAR calibrating systems, like trihedrals, since they can not provide initially a crosspolar response. So the traits-surface has been designed and measured in an anechoic chamber, providing good results for normal incidence.

Artificial Magnetic Conductors (AMCs) offer many reflecting applications. When non symmetrical elements (diagonal slots, offset vias) are used, a cross-polar reflected response is achieved given an incident copolar electric field. This electromagnetic property can be used for polarisation conversion or RCS reduction purposes. A cross-polarising surface composed of square patches and diagonal slots over a ground plane has been designed and measured, providing good results for normal incidence. (4 pages)

A transpolarizing reflector is proposed. It consists of periodic patches above a ground plane, with wide diagonal slots. For normal incidence, linear polarization along a principal direction is transformed into the orthogonal polarization with a 20-dB ratio over a 29.7% bandwidth. We prove that, in view of the diagonal symmetry of the structure, reflected fields in the principal directions must be in quadrature. The transpolarization bandwidth slowly decreases for incidence away from broadside. This surface very efficiently produces polarization conversion for circularly polarized incident fields. The quality of this conversion, described in terms of axial ratio, is obtained front the transpolarization level achieved in the linear polarization case. (c) 2006 Wiley Periodicals, Inc.

Simulations and measurements have been carried out of a 1-layer metamaterial slab made of spiral resonators that shows an AMC behavior, with an equivalent electrical width of lambda/12 for the thickness (z dimension) of the slab. This behavior has been experimentally verified through radiation pattern measurements. The results show that similar results are obtained by placing a PEC at a lambda/4 distance and by placing the antenna close to the AMC. This latter solution is lower profile

The AMC behavior of a reflecting surface is mainly related to the frequency where the 0deg crossing in the phase of its reflection coefficient takes place. This frequency gives the resonant frequency that characterizes the AMC surface. Two different designs of AMC surfaces showing quite different properties are presented in this communication. A first design proves the AMC behavior using metallic tubes with slotted square profile instead of the typical periodic arrangement of strips printed on a dielectric substrate; and the latter, shows the AMC performance of an artificial material when the electromagnetic waves impinge on its opposite faces.