1,720,965 research outputs found
Design of an Integrated Rectenna on Multi-layer High-Resistivity Silicon Substrate
No full textThis paper presents the design of a rectenna integrated on silicon, using a multilayer substrate composed of silicon and air. The rectenna is designed to harvest microwave energy at 2.45 GHz. The substrate structure is composed of three layers of high-resistivity silicon (HRSi, εr = 11.7)
where the central layer presents an air cavity obtained through etching process. The chosen feeding structure for the antenna is based on a planar microstrip feeding line while for the rectifier a planar matching network is adopted to allow the maximum power transfer. The adopted rectifier topology is a voltage doubler, consisting of a pair of Skyworks SMS7630-079LF Schottky diodes. The synthetized low-permittivity substrate is compatible with on-chip systems silicon and assure a 84 % radiation efficiency with a maximum gain of 7.76 dBi, for the patch
antenna. The overall efficiency of the rectenna is 45% for a received power level of 7 dBm
A Predictive-Model-Assisted Moisture Content Sensor by Monitoring the DC-Unstable States of a Microwave Self-Oscillating Antenna
No full textThis work presents a portable moisture content (MC) sensor, for tree hydration control, adopting a microwave self-oscillating antenna. The operating principle exploits the dependence of the oscillator nonlinear steady-state regimes on the dispersive load, represented by a patch antenna loaded by wood in different MC conditions. A novel read-out approach that eliminates radio frequency (RF) measurements and relies solely on the oscillator's steady-state dc bias conditions is proposed. First, a free-running oscillator, adopting a pseudomorphic highly electron mobility transistor (pHEMT) is designed in the 2.4-GHz band, with a 50-Ω load. The tuning capabilities are analyzed by nonlinear/electromagnetic (NL/EM) co-simulation, with the oscillator loaded by the dispersive patch-antenna impedances corresponding to different hydration conditions. A comprehensive experimental campaign of the fabricated prototype characterizes the wood sample. By tuning the HEMT bias voltages, distinguishable dc drain currents are retrieved and correlated with the wood's hydration state. These results are fully validated by an independent method based on the standard weighting procedure. Consequently, moisture monitoring can be conducted automatically by a low-cost microcontroller (μController) and the system can be adopted as a portable device for the proposed purposes. To enable the adaptivity to new unseen data and different MC scenarios, a low-computation machine learning (ML) algorithm is developed, enabling the system to operate in real time and as a stand-alone system
Boosting Microwave Hydration Sensors Performance with Machine Learning Techniques
Full text linkThis study introduces innovative non-invasive hydration microwave sensors combined with machine learning (ML) algorithms for monitoring purposes. Specifically, a miniaturized complementary-split ring resonator (CSRR) operating in the 2÷ 3 GHz band for assessing human skin hydration through near-field interaction, and a separate patch antenna operating at 2.45 GHz for tracking the drying process of greenwood. The design process involves full-wave simulations to evaluate the resonators and patch antenna capability to effectively penetrate skin layers and wood structures. After fabrication on cost-effective substrates, extensive testing measurements were conducted on different mediums. Human volunteers' proximal wrist areas are monitored over six days with multiple daily measurements under various dietary conditions. Concurrently, the greenwood sample is assessed over twenty days in a controlled climate chamber. The spectral data obtained from the resonator and the patch antenna are analyzed using advanced multivariate data analysis (MVDA). The results confirm the method's effectiveness in accurately categorizing hydration levels and emphasize its potential for practical hydration monitoring applications due to its cost-effectiveness and operational efficiency
Controllo della temperatura di esercizio di dispositivi elettronici mediante celle di Peltier
No full textIn questa tesi si è studiato come affrontare il problema dello smaltimento di calore attraverso dispositivi termoelettrici come le celle di Peltier. I punti focali di cui si è discusso sono il funzionamento fisico dei moduli, le loro figure di merito ed i fattori che le determinano, le applicazioni in cui le celle vengono utilizzate e due esempi di dimensionamento. In particolare all'ultimo punto si sono distinti due ipotesi di utilizzo: la prima ha riguardato il dimensionamento di una modulo di Peltier accoppiato da un dissipatore passivo, mentre nella seconda si è visto come utilizzare questi dispositivi in presenza di un controllore TEC ed un dissipatore attivo. Successivamente alle due ipotesi di funzionamento è stato fatto un confronto delle soluzioni proposte analizzandone vantaggi e svantaggi, tra cui costi e consumi in potenza
Analisi Numerica di Metasuperfici Planari Riconfigurabili che sfruttano Nanomateriali Tunabili
No full textQuesta tesi si occupa di descrivere lo studio di una metasuperficie planare riconfigurabile, operante nella banda frequenziale a 5.8 GHz ,che sfrutta materiali innovativi, a basso costo e a basso consumo di potenza per generare riflessioni anomale del fascio
d’onda incidente in maniera dinamica.
I metamateriali sono compositi artificiali aventi una struttura tridimensionale periodica, progettata per produrre un materiale non disponibile in natura che possiede delle proprietà elettromagnetiche anomale promettenti.
Alcune caratteristiche che rendono i metamateriali interessanti sono le piccole dimensioni delle strutture elementari comparate alla lunghezza d’onda della radiazione elettromagnetica con cui esse interagiscono e la periodicità con cui queste strutture elementari vengono replicate.
Nel primo capitolo di questo elaborato vengono introdotte le tematiche che riguardano i metamateriali, le limitazioni di queste strutture e quindi l’utilizzo di strutture semplificate come le metasuperfici. E’ posta particolare attenzione alla tematica della riconfigurabilità che in questo studio viene trattata in diversi modi: tramite capacità variabili e tramite materiali ferroelettrici.
Il secondo capitolo descrive la progettazione delle celle elementari definendo il caso di studio sul quale ci siamo concentrati ed è fornita un'analisi dei risultati di fase dell’onda piana riflessa dalla metasuperficie al variare della capacità inserita nella struttura elementare. Vengono inoltre presentati alcuni risultati sperimentali del comportamento capacitivo di materiali ferroelettrici che verranno usati, come l’ossido di afnio zirconio.
Il terzo capitolo è dedicato alla trattazione dei risultati ottenuti a riguardo dei diagrammi di radiazione per le differenti configurazioni di celle unitarie di cui è composta
la MS 20x20 progettata, sottolineando le capacità da beam steerer. Vengono inoltre discussi i risultati della simulazione EM relativi all’antenna utilizzata come feeder
Going 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Selezione automatica di rettificatori a RF SIMO mediante autopolarizzazione di HEMT
Full text linkNella tesi viene proposto un sistema innovativo di Energy Harvesting per radiofrequenze a 2.45 GHz. Si tratta di un sistema single-input multiple-output ad ampissimo range dinamico di potenza in ingresso che sfrutta il fenomeno di autopolarizzazione di dispositivi non lineari come gli HEMT per selezionare autonomamente, e senza alcun controllo esterno, il ramo di rettificazione più adeguato al fine di ottenere la massima RF-to-DC conversion efficiency possibile. Inoltre il sistema garantisce il massimo isolamento fra i rami che compongono il circuito sfruttando l'ottimizzazione dei Large Signal S-Parameters dei singoli stadi del sistema
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