1,721,014 research outputs found
Metodi e tecnologie per ispezioni con onde ultrasoniche guidate di piastre e gusci in composito
No full textTra le tecnologie proposte per il monitoraggio strutturale (in inglese Structural Health Monitoring o SHM), quelle che usano onde ultrasoniche guidate sono considerate tra le più promettenti e versatili per le applicazioni che riguardano i materiali compositi. Con onde guidate ci si riferisce ad onde meccaniche che si propagano in strutture o in elementi strutturali, le guide d’onda, con almeno una dimensione caratteristica paragonabile alla lunghezza d’onda delle onde stesse. L’interazione tra la lunghezza d’onda e la geometria della guida d’onda dà luogo all’esistenza di svariate onde meccaniche. Tali onde variano in numero e mutano le loro caratteristiche di propagazione quali lunghezza d’onda, velocità, attenuazione e forma d’onda, al variare della frequenza (comportamento dispersivo).
Le implementazioni tipiche di questi sistemi prevedono un sistema software/hardware che controlla una rete di trasduttori piezoelettrici posti sulla struttura da controllare, attraverso i quali si generano e ricevono onde guidate che sondano la struttura stessa. Mediante procedure di analisi dei segnali registrati ai trasduttori, le metodologie cercano di risalire allo stato di integrità del componente.
La concreta possibilità di integrare una simile tecnologia di monitoraggio ad onde guidate in strutture in composito è attualmente limitata da: (i) scarsità di strumenti per la modellazione della propagazione in materiale composito; (ii) ingombro della strumentazione e cablature non compatibili con il monitoraggio permanente; (iii) limitata validazione delle tecnologie in condizioni operative ambientali (iv) elevati costi di integrazione. Per superare queste limitazioni sono allo studio nuovi trasduttori piezoelettrici e tecniche avanzate di elaborazione di segnale
Direct Spread Spectrum Modulation and Dispersion Compensation for Guided Wave-based Communication Systems
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Spiral-shaped piezoelectric sensors for Lamb waves direction of arrival (DoA) estimation
No full textA novel strategy to design piezoelectric sensors suited for direction of arrival (DoA) estimation of incoming Lamb waves is presented in this work. The designed sensor is composed by two piezoelectric patches (P1, P2) to be bonded on the structure to be inspected. In particular, by exploiting the Radon Transform, the proposed procedure computes the shape of P2 given the shape of P1 so that the difference in time of arrival (DToA) of the Lamb waves at the two patches is linearly related to the DoA while being agnostic of the material dispersion curves. With a dedicated processing procedure, the waveforms acquired and digitized from the two electrodes can be used to retrieve DoA information. Numerical and experimental results show that DoA estimation performed by means of the proposed shaped transducers is extremely robust
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
Structural Health Monitoring Reliability Enhancement by an Automated Sensor Tuning Procedure
No full textNowadays, Structural Health Monitoring (SHM) is rising as the most promising collection of tools to enhance the safety of structures belonging to different contexts, including the civil, aerospace and industrial fields. SHM applications require a minimum level of reliability and accuracy, thus demanding for self-test analysis and calibration procedures. Typically, these procedures are carried out manually by means of expensive bench instruments, resulting to be time consuming and cumbersome. Moreover, in–situ sensor calibration is not always possible, especially in large scale scenarios or harsh environments. To overcome these limitations, the current work proposes an innovative tuning procedure purposely designed for stamp–size and low–power sensor node prototypes developed within the SHM research group of the Advanced Research Center of Electronic Systems (ARCES) of the University of Bologna. In particular, the capability to perform an automatic tuning procedure without any kind of external bench instrument is demonstrated, allowing for a simplification of the procedure and on–line self–test analysis, speeding up the process. The extraction of the main tuning parameters (such as time constants, voltage biases, time shifts) and their automatic estimation have been embedded within the sensor node firmware. Finally, an experimental campaign has been executed to validate the performance of the entire procedure
A Tilt Sensor Node Embedding a Data-Fusion Algorithm for Vibration-Based SHM
Full text linkThis work describes a miniaturized sensor network based on low-power, light-weight and small footprint microelectromechanical (MEMS) sensor nodes capable to simultaneously measure tri-axial accelerations and tri-axial angular velocities. A real-time data fusion algorithm based on complementary filters is applied to extract tilt angles. The resulting device is designed to show competitive performance over the whole frequency range of the inertial units. Besides the capability to provide accurate measurements both in static and dynamic conditions, an optimization process has been designed to efficiently make the fusion procedure running on-sensor. An experimental campaign conducted on a pinned-pinned steel beam equipped with a network comprising several sensor nodes was used to evaluate the reliability of the developed architecture. Performance metrics revealed a satisfactory agreement to the physical model, thus making the network suitable for real-time tilt monitoring scenarios
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