Enhanced millimeter-wave transmission through subwavelength hole arrays

We explore, both experimentally and theoretically, the existence in the millimeter-wave range of the phenomenon of extraordinary light transmission through arrays of subwavelength holes. We have measured the transmission spectra of several samples made on aluminum wafers by use of an AB Millimetre quasi-optical vector network analyzer in the wavelength range 4.2-6.5 mm. Clear signals of the existence of resonant light transmission at wavelengths close to the period of the array appear in the spectra.     

Babinet principle applied to the design of metasurfaces and metamaterials

The electromagnetic theory of diffraction and the Babinet principle are applied to the design of artificial metasurfaces and metamaterials. A new particle, the complementary split rings resonator, is proposed for the design of metasurfaces with high frequency selectivity and planar metamaterials with a negative dielectric permittivity. Applications in the fields of frequency selective surfaces and polarizers, as well as in microwave antennas and filter design, can be envisaged. The tunability of all these devices by an applied dc voltage is also achievable if these particles are etched on the appropriate substrate.     

Dual-band double-negative-index fishnet metamaterial at millimeter-waves

An effective negative refractive index (NRI) is demonstrated and experimentally verified for the first two propagation bands of a fishnet-like metamaterial at millimeter-wave frequencies. The dual-band NRI behavior is achieved by engineering the diffraction order (±1, ±1) associated with the internal mode supported between holey layers to correspond with the second propagation band. In addition to the experimental interferometric technique that accounts for the handedness of the propagation, numerical results are given to predict the dual-band effective NRI and to confirm dual-band negative refraction for a prism composed of the proposed metamaterial.     

Non-nested configuration of algebraic limit cycles in quadratic systems

This work deals with algebraic limit cycles of planar polynomial differential systems of degree two. More concretely, we show among other facts that a quadratic vector field cannot possess two non-nested algebraic limit cycles contained in different irreducible invariant algebraic curves.     

Optimization of Tapered Bragg Reflectors in Microstrip Technology

The frequency responses of tapered Bragg reflectors made by etching one row of holes on the ground plane of a microstrip line are analyzed, comparing different windows and their effects on the rejection level, the bandwidth, the side lobe level and the abruptness of the main stop band.     

Modeling and Testing of Uniform Fiber Bragg Gratings Using 1-D Photonic Bandgap Structures in Microstrip Technology

A way to model and test fiber gratings and fiber grating-based systems in the microwave range is proposed. The method rests on the equivalence relationship found between a fiber grating and a one-dimensional microstrip photonic bandgap structure that consists of a periodic pattern of circles etched in its ground plane. The equivalence assures that the frequency-response of the fiber grating is an upshifted replica of the corresponding frequency to its equivalent microstrip device. Both apodized and nonapodized uniform fiber gratings have been considered and the feasibility of the proposed method has been shown in simulation and measurement.     

Quasioptical Transmission Lines for ECRH at TJ-II Stellarator

Two mirror lines have been used to transmit the microwave power from the powerful microwave generators to the TJ-II plasmas. Both lines have been tested at nominal power level and they are in operation now. This paper deals with the final design of the transmission lines and their testing. Before starting operation at high power level, measurements of the wave beam parameters at low power level were performed. Two horn antennas were designed to simulate the gyrotron output. The results are presented in this paper. A computer code based on Huygens diffraction theory was developed to simulate the propagation of the beam along the mirror lines. A comparison of the theoretical and the experimental results is also shown here.     

Synthesis,crystal structures and in vitro anticancer activities of two copper(II) coordination compounds

Transition Metal Chemistry - Two new Cu(II) coordination compounds, [Cu2(cca)(phen)4](ClO4)2(H2O)5.5, 1, and [Cu2(OH)(oda)(phen)2)](ClO4), 2, where cca?=?4-carboxycinnamate;...     

Analysis and design of electromagnetic crystals in microstrip technology using a fibre grating model

Electromagnetic crystals (EC) in microstrip technology have been recently proposed as efficient Bragg reflectors. They are implemented by etching the ground plane or by drilling the substrate following a periodic pattern. In this paper we propose a simple and fast fibre Bragg grating (FBG)-based model for the synthesis and analysis of these microstrip ECs with sinusoidal patterns. The method rests on the analogy found between the frequency responses of a microstrip EC and a FBG. Based on this analogy, an equivalence relationship between the physical parameters of a microstrip EC and those of an equivalent FBG has been established. The equivalence assures that the frequency response of the microstrip EC is a down-shifted replica of the one corresponding to its equivalent FBG. This model avoids the use of the time-consuming electromagnetic calculations involved in the analysis of the microstrip ECs as well as the trial method employed until now in the synthesis, since a FBG response arises immediately from coupled-mode theory. At the same time the theoretical difficulties encountered in the formal derivation of coupled-mode theory for microstrip ECs are also avoided by the equivalence relationship found.     

Corrugated Horn Antenna for Low-Power Testing of the Quasioptical Transmission Lines at TJ-II Stellerator

This paper presents the design and characterisation of a millimetre-wave corrugated horn antenna to perform low power measurements of the main parameters of the quasioptical transmission lines of the Electron Cyclotron Resonance Heating (ECRH) at TJ-II stellerator experiment working in Madrid (E). The antenna generates a practically pure Gaussian Beam at 53.2 GHz that simulates the stellerator gyrotron output beam. Simulations of the designed corrugated horn, by using a specially developed computer code, are presented. The far field radiation pattern of the constructed prototype was measured at the ESTEC Compact Antenna Test Range (CATR). The measurement results are in excellent agreement with those obtained from simulations.