Lluis Jofre

RF MEMS Integrated Frequency Reconfigurable Annular Slot Antenna

A new kind of double- and single-arm cantilever type DC-contact RF MEMS actuators has been monolithically integrated with an antenna architecture to develop a frequency reconfigurable antenna. The design, microfabrication, and characterization of this ¿reconfigurable antenna (RA) annular slot¿ which was built on a microwave laminate TMM10i ( ¿r = 9.8, tan ¿ = 0.002), are presented in this paper. By activating/deactivating the RF MEMS actuators, which are strategically located within the antenna geometry and microstrip feed line, the operating frequency band is changed. The RA annular slot has two reconfigurable frequencies of operation with center frequencies f low = 2.4 GHz and f high = 5.2 GHz, compatible with IEEE 802.11 WLAN standards. The radiation and impedance characteristics of the antenna along with the RF performance of individual actuators are presented and discussed.

Circular Beam-Steering Reconfigurable Antenna With Liquid Metal Parasitics

A novel antenna reconfiguration mechanism based on the displacement of liquid metal sections is presented. The liquid nature of the moving parts of the antenna helps avoid the main disadvantage of mechanically-actuated reconfigurable antennas which is the mechanical failure of their solid parts due to material fatigue, creep or wear. Furthermore, the displacement of liquid elements can be more effectively performed than in the case of solid materials by applying precise microfluidic techniques such as continuous-flow pumping or electrowetting. The reconfiguration mechanism is demonstrated through the design, fabrication and measurement of a radiation pattern reconfigurable antenna. This antenna operates at 1800 MHz with 4.0% bandwidth and is capable of performing beam-steering over a 360° range with fine tuning. The antenna is a novel circular Yagi-Uda array, where the movable parasitic director and reflector elements are implemented by liquid metal mercury (Hg). The parasitics are placed and rotated in a circular microfluidic channel around the driven element by means of a flow generated and controlled by a piezoelectric micropump. The measured results demonstrate good performance and the applicability of the microfluidic system.

Electromagnetic Modeling of RFID-Modulated Scattering Mechanism. Application to Tag Performance Evaluation

Radio-frequency identification (RFID) technology relies on the modulated scattering technique (MST) as a means to convey the information from the tag to the reader. The interaction mechanism between the reader and the tag is described in a physically meaningful way by the reciprocity theorem which is deeply rooted into Maxwell equations. This approach provides a simple and yet complete formulation that allows to fully describe the interaction between the reader and the tag, even in complex environments. From this formulation, a clear understanding is derived on how the different design tradeoffs affect system performance. Based on this approach, the paper is focused on several issues of practical relevance for antenna tag design such as maximum power transfer, maximum sensitivity, and nonlinearity effects.

Planar and cylindrical active microwave temperature imaging: numerical simulations

A comparative study at 2.45 GHz concerning both measurement and reconstruction parameters for planar and cylindrical configurations is presented. For the sake of comparison, a numerical model consisting of two nonconcentric cylinders is considered and reconstructed using both geometries from simulated experimental data. The scattered fields and reconstructed images permit extraction of very useful information about dynamic range, sensitivity, resolution, and quantitative image accuracy for the choice of the configuration in a particular application. Both geometries can measure forward and backward scattered fields. The backscattering measurement improves the image resolution and reconstruction in lossy mediums, but, on the other hand, has several dynamic range difficulties. This tradeoff between forward only and forward-backward field measurement is analyzed. As differential temperature imaging is a weakly scattering problem, Born approximation algorithms can be used. The simplicity of Born reconstruction algorithms and the use of FFT make them very attractive for real-time biomedical imaging systems.

A Parasitic Layer-Based Reconfigurable Antenna Design by Multi-Objective Optimization

A parasitic layer-based multifunctional reconfigurable antenna (MRA) design based on multi-objective genetic algorithm optimization used in conjunction with full-wave EM analysis is presented. The MRA is capable of steering its beam into three different directions (θi = -30°, 0°, 30°) simultaneously with polarization reconfigurability (Pj = Linear, Circular) having six different modes of operation. The MRA consists of a driven microstrip-fed patch element and a reconfigurable parasitic layer, and is designed to be compatible with IEEE-802.11 WLAN standards (5-6 GHz range). The parasitic layer is placed on top of the driven patch. The upper surface of the parasitic layer has a grid of 5 5 electrically small rectangular-shaped metallic pixels, i.e., reconfigurable parasitic pixel surface. The EM energy from the driven patch element couples to the reconfigurable parasitic pixel surface by mutual coupling. The adjacent pixels are connected/disconnected by means of switching, thereby changing the geometry of pixel surface, which in turn changes the current distribution over the parasitic layer, results in the desired mode of operation in beam direction and polarization. A prototype of the designed MRA has been fabricated on quartz substrate. The results from simulations and measurements agree well indicating ~8 dB gain in all modes of operation.

Terahertz graphene optics

AbstractThe magnitude of the optical sheet conductance of single-layer graphene is universal, and equal to e2/4ħ (where 2πħ = h (the Planck constant)). As the optical frequency decreases, the conductivity decreases. However, at some frequency in the THz range, the conductivity increases again, eventually reaching the DC value, where the magnitude of the DC sheet conductance generally displays a sample- and doping-dependent value between ∼e2/h and 100 e2/h. Thus, the THz range is predicted to be a non-trivial region of the spectrum for electron transport in graphene, and may have interesting technological applications. In this paper, we present the first frequency domain measurements of the absolute value of multilayer graphene (MLG) and single-layer graphene (SLG) sheet conductivity and transparency from DC to 1 THz, and establish a firm foundation for future THz applications of graphene.

Curriculum greening and environmental research co-ordination at the Technical University of Catalonia, Barcelona

Abstract The Technical University of Catalonia is currently working on a process of curriculum greening and co-ordination of environmental research as set out in its Environment Plan. This paper gathers the various projects that have been and are being implemented by the University in this area and assesses the results obtained so far.

Frequency and Radiation Pattern Reconfigurability of a Multi-Size Pixel Antenna

Pixel reconfigurable apertures constitute one of the most adaptable structures regarding antenna reconfiguration, being capable to achieve frequency and pattern compound reconfiguration. However, pixel antennas require a large amount of switches (typically above 100) that severely impact the antenna efficiency, complexity, cost and reconfiguration time. This paper presents a novel technique to mitigate the inherent complexity of pixel antennas by including multiple sized pixels divided over driven and parasitic regions. The technique has been applied to a planar monopole architecture leading to a low-complexity prototype of small dimensions and requiring only 12 switches. Its reconfiguration properties have been fully characterized through exhaustive measurements. Frequency reconfiguration is achieved from 1 GHz to 6 GHz with simultaneous beam-steering capabilities, being capable of synthesizing at each frequency an omnidirectional pattern and up to 5 directive patterns steered towards directions covering an angular range of almost 180°.

RFID Multiprobe Impedance-Based Sensors

In this paper, a passive multiprobe sensor using conventional UHF radio frequency identification (RFID) tags is presented. The RFID link between the reader and the tag is analyzed from a general point of view by means of reciprocity principle, to obtain a compact and explicit expression of the response of RFID tags that can be exploited in sensing measurements. A calibration scheme to remove nonlinearities in the response of RFID tags, which are due to the scavenging powering mechanism of passive tags, is also presented along with measurements. Finally, experimental results and discussion of a complete multiprobe sensing scenario are used to show the different challenges involved and how to overcome them.

Conservation Properties of Unstructured Finite-Volume Mesh Schemes for the Navier-Stokes Equations

The Navier-Stokes equations describe fluid flow by conserving mass and momentum. There are two main mesh discretizations for the computation of these equations, the collocated and staggered schemes. Collocated schemes locate the velocity field at the same grid points as the pressure one, while staggered discretizations locate variables at different points within the mesh. One of the most important characteristic of the discretization schemes, aside from accuracy, is their capacity to discretely conserve kinetic energy, specially when solving turbulent flow. Hence, this work analyzes the accuracy and conservation properties of two particular collocated and staggered schemes by solving various problems.