1,721,025 research outputs found
Abeunt studia in mores. Saggi in onore di Mario Melchionda
No full textI saggi raccolti in questo volume ruotano attorno ad alcuni degli interessi principali di Mario Melchionda. Si concentrano su tre principali aree di interesse: il rinascimento inglese, e i suoi rapporti con l’età classica e l’Italia, spaziando dal teatro alla lirica alla poesia epica; le letterature in lingua inglese degli ultimi due secoli; e la traduzione letteraria, esplorata nei rapporti e negli intrecci tra più lingue. Inevitabilmente, tra le tre parti del volume gli echi e i rimandi si inseguono
Innovative optoelectronic and photonic devices and systems for Space applications
Full text linkLe missioni spaziali per osservazione della Terra o per scopi scientifici richiedono giroscopi per la misurazione della velocità angolare con performance elevate (risoluzione nell’intervallo 0.1 – 1 °/h e stabilità della polarizzazione nell’intervallo 0.001 – 0.1 °/h) per un accurato controllo dell’ assetto e dell’orbita del satellite.
Affidabilità, resistenza alle radiazioni, robustezza, tolleranza agli urti, volume ridotto e basso consumo energetico sono i requisiti tipici dei sensori di velocità angolare di nuova generazione per applicazioni spaziali.
In tale contesto, i risonatori ad anello fotonici stanno emergendo come elementi chiave di sistemi con elevate performance e dimensioni compatte. In particolare, per testarne l’affidabilità in ambiente spaziale, è stata dimostrata sperimentalmente un’ elevata resistenza alle radiazioni di un risonatore ad anello in InP investito da radiazioni γ.
Nella tesi sono state discusse le potenzialità di un risonatore ad anello con elevato fattore di qualità Q, che funge da elemento sensibile di un giroscopio ottico risonante (RMOG) miniaturizzato con performance elevate. L'elemento chiave del giroscopio proposto è un semplice risonatore ad anello basato su Si3N4 con un cristallo fotonico monodimensionale presente lungo l’intera circonferenza del risonatore ad anello, denominato 1D-PhCRR. Il funzionamento si basa sullo sfruttamento dell'effetto di luce lenta, tipico dei cristalli fotonici, che garantisce un miglioramento del fattore di qualità di oltre 3 ordini di grandezza rispetto ad un semplice risonatore ad anello con medesimo raggio. Un PhCRR con fattore di qualità > 109, è stato teoricamente dimostrato mediante l’utilizzo di un modello matematico basato sulla teoria dei modi accoppiati (CMT). Tali performance garantiscono una risoluzione teorica del giroscopio < 0.05 °/h con un volume ridotto (< 1 cm3), conforme ai requisiti degli operatori spaziali. Lo sviluppo del 1D-PhCRR è stato condotto nell'ambito del contratto NPI dell'Agenzia Spaziale Europea (ESA), che sponsorizza le attività di dottorato.
Oltre a risultare idoneo come elemento sensibile nei sottosistemi di controllo di assetto e orbita, il PhCRR potrebbe essere utilizzato per implementare diverse funzionalità nei payload di futura generazione per telecomunicazioni o per l’ osservazione della Terra.
Negli ultimi anni, un notevole interesse è stato rivolto verso payload per telecomunicazioni in grado di essere adattati ed ottimizzati dopo il lancio, secondo le diverse esigenze degli utenti in termini di larghezza di banda, area di interesse ed allocazione delle frequenze. La fotonica nel regime delle microonde risulta essere l’approccio più adatto per soddisfare i requisiti dei payload di futura generazione per telecomunicazioni. In tale contesto, è stato proposto un filtro notch basato su PhCRR in silicio con larghezza di banda B = 10.43 GHz ed extinction ratio ER > 40 dB, con risposta in frequenza con profilo gaussiano, ottenuta mediante inserimento ed ingegnerizzazione di difetti all’interno del cristallo fotonico. Implementando giunzioni p-i-n in corrispondenza dei difetti, è stato dimostrato un ampio intervallo di variazione della frequenza centrale di filtraggio (15 GHz), in un rapido tempo di commutazione (≈ 1 ns) ed un consumo di energia pari a 47 mW.
Inoltre, è stata proposta l’architettura innovativa di un’ oscillatore optoelettronico miniaturizzato in banda Ka, basata sul PhCRR progettato. È stato calcolato teoricamente un rumore di fase a 10 kHz di offset dalla portante (40 GHz) pari a circa -155 dBc/Hz con potenza elettrica in uscita> 10 dBm. Tali performance rappresentano un notevole miglioramento rispetto agli oscillatori optoelettronici riportati allo stato dell'arte.
L'elevata purezza del segnale oscillante è stata sfruttata per la progettazione di un generatore di segnale chirpato, utile per i sistemi SAR (radar ad apertura sintetica) ad alta risoluzione per l'osservazione della Terra, con un prodotto tempo-larghezza di banda di 3200 e un rumore di fase di circa -116 dBc/Hz. Per sistemi SAR, è stata progettata una linea di ritardo fotonica tunabile in banda X, basata su un cristallo fotonico realizzato mediante pattern di uno strato di grafene, in grado di garantire un elevato angolo di puntamento in fase di trasmissione del segnale e la più alta figura di merito riportata allo stato dell’ arte.Science and Earth observation missions require high-class gyroscopes, having a resolution in the range 0.1 – 1 °/hr and a bias stability in the range 0.001 – 0.1 °/hr, for an accurate control of the satellite attitude and orbit.
High reliability, high radiation resistance, high robustness, high shock tolerance, small volume, low power consumption and reduced mass are typical requirements of new generation angular rate sensors for Space applications.
In this context, the photonic ring resonators are emerging as key building blocks. The radiation hardness of a ring resonator useful for Space applications has been investigated, demonstrating a negligible worsening of the performance under γ radiations.
In this thesis, the potentiality of an ultra-high-Q ring resonator, acting as sensitive element of a resonant micro-optic gyroscope architecture (RMOG), has been discussed, aiming to design a chip-scale, high performing gyroscope.
The key element of the proposed RMOG configuration is a Si3N4-based simple ring resonator with a one-dimensional photonic crystal included along the whole optical path, called as 1D-PhCRR. Its operation is based on the exploitment of the slow light effect, typical of the PhC, providing an improvement of the Q-factor respect a simple ring resonator more than 3 order of magnitude. The Si3N4 PhCRR with Q > 109, has been theoretically demonstrated by using a self-made mathematical model, based on the Coupled Mode Theory (CMT). This performance ensures a gyro resolution < 0.05 °/hr with a small volume (< 1 cm3), compliant to the Space operators’ requirements. The development of the 1D-PhCRR has been carried out in the framework of the European Space Agency NPI contract, that sponsor the PhD activities.
Besides its suitability for attitude and orbit control sub-systems, the PhCRR could be used to implement several functionalities in the next photonic-based generation telecom payloads and for Earth observation purpose.
Telecom satellites are the most mature Space applications. In the last decades, Space operators require flexible telecom payload that can be adapted and optimized after the launch, according to the varying user demands in terms of bandwidth, coverage, and frequency allocation. The microwave photonic represents the most suitable approach to fulfil the next-generations telecom payloads requirements.
In this context, photonic-based microwave filters have been investigated, and the design of a silicon – based PhCRR with a bandwidth B = 10.43 GHz and ER > 40 dB, acts as notch filter, has been reported. By inserting and engineering defects into the PhC section, superimposed the PhC on a ring resonator section, a Gaussian-shaped frequency response, with very steep sidewalls, has been simulated. A continuous tuning of the filtering central frequency (15 GHz), with a fast switching time (≈ 1 ns) and power consumption of 47 mW is ensured, by exploiting the free carrier plasma dispersion effect in correspondence of PhC defects.
Furthermore, the theoretical feasibility of a miniaturized Ka-band optoelectronic oscillator, based on the designed PhCRR, with a phase noise at 10 kHz offset from the carrier of about -155 dBc/Hz and an output electric power > 10 dBm has been demonstrated, that represent a remarkable improvement respect to the state-of-the-art.
The high purity of the oscillating signal has been exploited for the design of a linearly chirped microwave generator, useful for high-resolution Synthetic Aperture Radar (SAR) systems for Earth Observation, with a time-bandwidth product of 3200 and a phase noise of about -116 dBc/Hz.
The design of an ultra-compact graphene-based optical delay line useful for the beamsteering/beamforming in X-band, is reported to ensure a wide swath size of SAR systems, with high range resolution, simulating the highest figure of merit reported at the state-of-the-art
Effect of Doping Concentration and Band Offset on the Efficiency of Homojunction Perovskite Solar Cells
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Analysis of the Divider Control Policy for a Fractional Low-Power Time Synchronization Algorithm
No full textHighly Sensitive Mach-Zehnder Interferometer Glucose Biosensor with Subwavelength Grating in Flexible Substrate
No full textGoing Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
COTS Devices for Space Missions in LEO
Full text linkIn the framework of the NewSpace revolution, time-to-market and budget constraints drive the development of small and medium-sized satellites in Low Earth Orbit (LEO) orbit. The adoption of Commercial Off-the-Shelf (COTS) components represents the current trend to fulfill the NewSpace goals, given their low cost, wide product availability, small time-to-market, and the ability to integrate the most recent advancements in space applications. However, migrating from radiation-hardened (rad-hard) devices to COTS ones requires ensuring comparable reliability levels. To this end, an 'up-screening' of the COTS devices and systems should be performed in compliance with widely adopted standard regulations, such as those used by ESA or NASA. In this paper, we review COTS components and systems, such as diodes, Bipolar Junction Transistors (BJTs), Field Effect Transistors (FETs), Operational Amplifiers (OPAMPs), memories, and Field Programmable Gate Arrays (FPGAs), proven-flight or ad-hoc tested for compliance with standard regulations. In conclusion, the most promising devices in terms of cost and radiation tolerances are identified, providing useful benchmarks for space engineers developing COTS-based innovative systems
Preliminary Characterization of a Non-contact Breath Monitoring System for Infants
No full textRespiratory disorders are the highest cause of mortality among infants. Technologies for health monitoring can help to avoid those underhanded events. In this paper, we propose a system for respiratory health monitoring. The system is non-invasive and the monitoring is performed in a contactless manner since it is based on Time-of-Flight sensors and post-processing. To validate the proposed system we proposed an experimental setup aiming to precisely emulate the breathing activity. The emulator is built around a step motor and a microcontroller, and it allows to seamlessly emulate breathing patterns. Preliminary results from the experimental campaign in a real-world scenario prove the effectiveness of the approach
Tunable narrow band add-drop filter design based on apodized long period waveguide grating assisted co-directional coupler
Full text linkTunable add/drop filter based optical interconnects are an integral part of data centers as well as optical communications. Although add/drop filters based on ring resonators and waveguide Bragg gratings are well developed, long period waveguide grating (LPWG) based add/drop filters have little been investigated so far. In this article, we propose an apodized LPWG assisted co-directional coupler for narrow band add/drop filtering by combining silicon (Si) waveguide with titanium dioxide (TiO2) waveguide geometry. The proposed structure has been analyzed by combining the finite element method (FEM) and transfer matrix method (TMM), showing a good side lobe suppression ratio (SLSR) equal to 25.7 dB and an insertion loss of 0.6 dB. Owing to the high group index difference of Si and TiO2 waveguides, a narrow band response of 1.4 nm has been achieved with 800μm long LPWG. The opposite thermo-optic coefficients of Si and TiO2 ensures a good thermal tunability of the central wavelength. Considering a thin metallic heater of titanium nitride (TiN) the thermal tuning efficiency is found to be 0.07 nm/mW. Further, two LPWGs have been cascaded to realize a tunable dual channel filter with a minimum channel spacing of 185 GHz and a channel crosstalk better than 20 dB, showing its potential application towards dense wavelength division multiplexing
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