244 research outputs found
A COMPACT ULTRA-WIDE BAND PRINTED LOG-PERIODIC ANTENNA USING A BOW-TIE STRUCTURE
In this letter, an ultra-wideband compact printed log periodic dipole (LPD) array antenna is designed to operate between 500MHz and 6 GHz frequencies. The proposed LPD antenna structure consists of one bow-tie dipole and 15 regular dipole elements. The bow-tie element is introduced to improve the antenna's performance at the lowest frequencies below 1 GHz and at the same time to reduce the antenna size maintaining a good performance. An experimental antenna prototype has been designed, optimized, fabricated, numerically and experimentally assessed. The obtained results are very promising, and they demonstrated that the presented antenna prototype is able to operate in the range between 500MHz and 6 GHz with an average gain of 6 dBi and a very compact size
Sub-ppm NO2 Detection through Chipless RFID Sensor Functionalized with Reduced SnO2
NO2 is an important environmental pollutant and is harmful to human health even at very low concentrations. In this paper, we propose a novel chipless RFID sensor able to work at room temperature and to detect sub-ppm concentration of NO2 in the environment. The sensor is made of a metallic resonator covered with NO2-sensitive tin oxide and works by monitoring both the frequency and the intensity of the output signal. The experimental measurements show a fast response (a few minutes) but a very slow recovery. The sensor could therefore be used for non-continuous threshold monitoring. However, we also demonstrated that the recovery can be strongly accelerated upon exposure to a UV source. This opens the way to the reuse of the sensor, which can be easily regenerated after prolonged exposure and recycled several times
Reliability of RF MEMS capacitive and ohmic switches for space redundancy configurations
In this paper RF MEMS switches in coplanar waveguide (CPW) configuration designed for redundancy space applications have been analyzed, to demonstrate their reliability in terms of microwave performances when subjected to DC actuations up to one million cycles. As a result, both the investigated structures fulfill the current electrical requirements expected for redundancy logic purposes
MusA: Using Indoor Positioning and Navigation to Enhance Cultural Experiences in a museum
In recent years there has been a growing interest into the use of multimedia mobile guides in museum environments. Mobile devices have the capabilities to detect the user context and to provide pieces of information suitable to help visitors discovering and following the logical and emotional connections that develop during the visit. In this scenario, location based services (LBS) currently represent an asset, and the choice of the technology to determine users' position, combined with the definition of methods that can effectively convey information, become key issues in the design process. In this work, we present MusA (Museum Assistant), a general framework for the development of multimedia interactive guides for mobile devices. Its main feature is a vision-based indoor positioning system that allows the provision of several LBS, from way-finding to the contextualized communication of cultural contents, aimed at providing a meaningful exploration of exhibits according to visitors' personal interest and curiosity. Starting from the thorough description of the system architecture, the article presents the implementation of two mobile guides, developed to respectively address adults and children, and discusses the evaluation of the user experience and the visitors' appreciation of these application
Assessment of ORDYL SY 355 dry film for RF MEMS 0-level packaging
RF MEMS must be protected by a suitable package. A simple and cheap solution is to use quartz caps bonded by a polymer. This work reports on the use of ORDYL SY 355, a photosensitive dry film. The caps fabrication and bonding process were developed and tests were performed to define performance. Shear tests demonstrated good adhesion to the substrate and water immersion the sealing capability. Caps bonded on CPW and microstrip lines demonstrated negligible or very low impact on the RF performance in the 0-30GHz tested frequency band. Preliminary tests on capped RF MEMS switches indicated good performance of both capacitive and ohmic contact switches. Yield of ohmic switches resulted more sensitive to process conditions requiring a more accurate control
Selective Response of Mesoporous Silicon to Adsorbants with Nitro Groups
We demonstrate that the electronic structure of mesoporous silicon is
affected by adsorption of nitro-based explosive molecules in a
compound-selective manner. This selective response is demonstrated by probing
the adsorption of two nitro-based molecular explosives (trinitrotoluene and
cyclotrimethylenetrinitramine) and a nonexplosive nitro-based arematic molecule
(nitrotoluene) on mesoporous silicon using soft X-ray spec- troscopy. The Si
atoms strongly interact with adsorbed molecules to form Si-O and Si-N bonds, as
evident from the large shifts in emission energy present in the Si L2,3 X-ray
emission spectroscopy (XES) measurements. Furthermore, we find that the energy
gap of mesoporous silicon changes depending on the adsorbant, as estimated from
the Si L2,3 XES and 2p X-ray absorption spectroscopy (XAS) measurements. Our ab
initio molecular dynamics calculations of model compounds suggest that these
changes are due to spontaneous breaking of the nitro groups upon contacting
surface Si atoms. This compound-selective change in electronic structure may
provide a powerful tool for the detection and identification of trace
quantities of airborne explosive molecules.Comment: 27 pages, 9 figure
Infrared Sensor System for Mobile-Robot Positioning in Intelligent Spaces
The aim of this work was to position a Mobile Robot in an Intelligent Space, and this paper presents a sensorial system for measuring differential phase-shifts in a sinusoidally modulated infrared signal transmitted from the robot. Differential distances were obtained from these phase-shifts, and the position of the robot was estimated by hyperbolic trilateration. Due to the extremely severe trade-off between SNR, angle (coverage) and real-time response, a very accurate design and device selection was required to achieve good precision with wide coverage and acceptable robot speed. An I/Q demodulator was used to measure phases with one-stage synchronous demodulation to DC. A complete set of results from real measurements, both for distance and position estimations, is provided to demonstrate the validity of the system proposed, comparing it with other similar indoor positioning systems
Optical properties of structurally-relaxed Si/SiO superlattices: the role of bonding at interfaces
We have constructed microscopic, structurally-relaxed atomistic models of
Si/SiO superlattices. The structural distortion and oxidation-state
characteristics of the interface Si atoms are examined in detail. The role
played by the interface Si suboxides in raising the band gap and producing
dispersionless energy bands is established. The suboxide atoms are shown to
generate an abrupt interface layer about 1.60 \AA thick. Bandstructure and
optical-absorption calculations at the Fermi Golden rule level are used to
demonstrate that increasing confinement leads to (a) direct bandgaps (b) a blue
shift in the spectrum, and (c) an enhancement of the absorption intensity in
the threshold-energy region. Some aspects of this behaviour appear not only in
the symmetry direction associated with the superlattice axis, but also in the
orthogonal plane directions. We conclude that, in contrast to Si/Ge, Si/SiO
superlattices show clear optical enhancement and a shift of the optical
spectrum into the region useful for many opto-electronic applications.Comment: 11 pages, 10 figures (submitted to Phys. Rev. B
Role of the electro-thermo-mechanical multiple coupling on the operation of RF microswitch
A phenomenological approach is proposed to identify some effects occurring within the structure of the microswitch conceived for radio frequency application. This microsystem is operated via a nonlinear electromechanical action imposed by the applied voltage. Unfortunately, it can be affected by residual stress, due to the microfabrication process, therefore axial and flexural behaviors are strongly coupled. This coupling increases the actuation voltage required to achieve the so-called ‘‘pull-in'' condition. Moreover, temperature may strongly affect strain and stress distributions, respectively. Environmental temperature, internal dissipation of material, thermo-elastic and Joule effects play different roles on the microswitch flexural isplacement. Sometimes buckling phenomenon evenly occurs. Literature show that all those issues make difficult an effective computation of ‘‘pull-in'' and ‘‘pull-out'' voltages for evenly distinguishing the origin of some failures detected in operation. Analysis, numerical methods and experiments are applied to an industrial test case to investigate step by step the RF-microswitch operation. Multiple electro-hermomechanical coupling is first modeled to have a preliminary and comprehensive description of the microswitch behavior and of its reliability. ‘‘Pull-in'' and ‘‘pull-out'' tests are then performed to validate the proposed models and to find suitable criteria to design the RF-MEM
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