9 research outputs found
Ceramic Stress Sensor Based on Thick Film Piezo-Resistive Ink for Structural Applications
No full textThis paper presents a ceramic stress sensor with the dimension of a coin, able to measure the compressive force (stress) applied to its two round faces. The sensor is designed and engineered to be embedded inside concrete or masonry structures, like bridges or buildings. It provides good accuracy, robustness, and simplicity of use at potentially low cost for large-scale applications in civil structures. Moreover, it can be calibrated temperature compensated, and it is inherently hermetic, ensuring the protection of sensitive elements from the external environment. It is, therefore, suitable for operating in harsh and dirty environments like civil constructions. The sensor directly measures the internal stress of the structure, exploiting the piezo resistivity of thick film ink based on ruthenium oxide. It is insensitive with respect to the stiffness of the embedding material and the variation of the surrounding material properties like concrete hardening, shrinkage, and creep as it decouples the two components of stress
Stress sensor for monitoring the health state of fabricated structures such as constructions, buildings, infrastructures and the like.
No full textThe present invention relates to a stress sensor for monitoring the health state of fabricated structures such as constructions, buildings, infrastructures and the like. Here below, specific reference will be made to concrete building
structures, without thereby limiting the scope of the invention to this type of structure and/or this material. The invention applies in general to structures or parts of structures of any type that are fabricated from liquid or fluid materials at the time of fabrication or production and then hardened, for example plastics, for which it is desired to monitor the stress state over time
Structural health monitoring of concrete arcs using multi-axial stress sensors
No full textIn recent years the monitoring and damage evaluation/identification of concrete structures has become of major importance due to the ageing and the occurrence of some accidents [1]. For existing structures, the only possibility of doing structural health monitoring (SHM) is by applying (magnetic, piezoelectric and/or optical) sensors on the surface of the structure itself. However, if a new concrete structure is to be built, one could think of inserting these sensors directly into the structure. Using “external” sensors usually leads to more complicated algorithms for the identification of structural ageing/faults and, eventually, to the impossibility of identifying defects in certain critical positions [2]. Thus, “internal” sensors would be of great use for thorough SHM algorithms.
For large-scale applications in civil structures an innovative low-cost stress sensor has been developed that provides high accuracy, robustness and simplicity of operation. The sensor directly measures the internal stress of the structure both normal and tangential to the sensor surface [3], exploiting the piezo-resistivity of thick inks based on ruthenium oxide [4]. Moreover, the sensor can easily be calibrated, temperature compensated and is inherently hermetic, ensuring a protection of the sensitive elements from the external environment. Pads and cables are waterproof and suitable for a reliable operation in harsh environments.
An array of these sensors was installed in tunnel concrete arcs and used to assess the behaviour of these beams under static and cyclic loading under laboratory conditions. The obtained results confirm the targets of the design: the sensors were capable of identifying internal loads of the structure as well as of local imperfections
Multi-axial stress sensor for structural health monitoring
No full textAll civil structures experience aging and deteriorate with time. To ensure structural integrity, civil structures should thus be equipped with sensors for Structural Health Monitoring (SHM) with the aim of developing automated monitoring systems and facilitate inspections for damage detection. Nowadays, optical sensors and accelerometer are mostly used for SHM [1]. However, it has been shown that stress sensors could improve the reliability of monitoring systems as well as the accuracy of damage identification [2]. Of course, these stress sensors should be low cost to be spread within the structure. MEMS technology is therefore the most promising technology. Existing MEMS stress sensors have very limited full-scale and they are unable to separate the contributions of normal and shear stresses at material-package interface.
This paper presents a multi-axial stress sensor based on thick film piezo-resistive ink [3] that is capable of measuring both the out-of-plane and the in-plane internal stresses of the structures being monitored. By decoupling the two components of stress, the sensor is insensitive with respect to the variation of the surrounding material properties and boundary/installation conditions. The proposed stress sensor consists of three layers of ceramics, two thick protection layers and a thin middle layer bonded together by means of a bonding glass. The top surface of the middle layer contains the piezo-resistive gauges that are connected to form two Wheatstone bridges: one bridge senses in-plane strains and the other one senses both in-plane and out-of-plane strains [4]. The design of the sensor and the position of the sensing elements were optimized by means of a commercial Finite Element software.
A series of prototypes were produced and tested in laboratory by means of compression tests, imposing different boundary conditions and materials, up to a compression force of 5 kN that corresponds to a normal pressure of 10 MPa. Also, the influence of working temperature was assessed. By linearly combining the two bridge outputs, the influence of boundary conditions on the compression stress component can be minimized. Inserting the sensor in standardized concrete samples having size of 15x15x15 cm the influence of inclusions close to the sensor can be also assessed. Again, the influence of inclusions on the compression stress is shown to be negligible unless the inclusion is very close to the 3D resistors
MEMS piezoresistive multiaxial stress sensor
No full textLAUREA MAGISTRALEIn questo lavoro di tesi magistrale è riportato lo sviluppo di un sensore
MEMS multiassiale capace di distinguere quattro diversi componenti
di uno stato di sforzo. Il sensore è stato progettato ed ottimizzato
in modo da garantire le migliori prestazioni possibili. È
stata identificata la minima dimensione possibile ed è stata proposta
una configurazione elettronica. In fine, il comportamento del sensore
è stato validato attraverso simulazioni al fine di confermare le sue
caratteristiche ed ottenere una taratura numerica.
Due applicazioni sono state studiate attraverso simulazioni FEM
come implementazioni del sensore: l’inserimento in composto epossidico
per stimare gli sforzi indotti sul die dai processi di packaging,
e l’implementazione in una cella di carico per distinguere la forza
principale da altri disturbi esterni.
Questo lavoro si è basato su un’attenta analisi dei tipici problemi,
limitazioni e obiettivi dei sensori di sforzo basati su piezoresistività
proponendo una soluzione innovativa per il progetto e lo sviluppo di
sensori multiassiali.In this master thesis is reported the development of a MEMS multiaxial
stress sensor able to measure four different components of a stress
field. The sensor has been designed and optimized in order to ensure
best possible performances. Minimum possible size has been identified
and the electronic layout proposed. Finally, sensor’s behaviour
has been validated by simulations in order to assess its characteristics
and to provide numerical calibration.
Two applications have been studied with FEM for the sensor to
be implemented: to be inserted in Epoxy molding compound to estimate
packaging induced rnal stresses on silicon dies, and to be implemented
in a load cell package to distinguish the main force from
other external interferences.
This work has been based on a careful analysis of the typical problems,
limitations and objectives of piezoresistive stress sensors proposing
an innovative solution for multiaxial sensors design and development
MEMS load cell for high load applications
No full textLAUREA MAGISTRALEIn questo lavoro di tesi si riporta lo sviluppo di un sensore di forza
MEMS per alti carichi, fino ad un massimo di 5kN, basato sulle proprietà
piezoresistive del silicio.
Tale lavoro si compone della progettazione, seguita da simulazione
tramite modelli ad elementi finiti, di un prototipo di package, elemento
chiave che permette al sensore di sostenere così alti carichi, e
di un layout degli elementi piezoresistivi che permetta al sensore di
riconoscere il carico verticale applicatogli, a prescindere da eventuali
carichi planari.
Il tutto è stato basato su un’ attenta analisi dei materiali e delle
problematiche tipiche dello sviluppo di un MEMS package, insieme
all’analisi di un nuovo possibile modo di sfruttare la piezoresistività
del silicio.In this thesis work is reported the development of a MEMS force sensor
for measuring high loads up to a maximum of 5kN, based on silicon
piezoresistivity.
For the sensor has been designed and simulated, with finite element
models, a package prototype, key element that makes the sensor
able to bear such high loads, together with the layout of the piezoresistive
elements that allows the sensor to recognize the vertical load
applied to it, discarding eventual planar loads.
This work has been based on a careful analysis of the typical materials
and problematics related to MEMS packaging technology and
by the analysis of new possible way to exploit silicon piezoresistivity
Pre-shaping techniques for reducing residual vibrations
No full textLAUREA MAGISTRALEIn this work a pre-shaping technique is used in order to reduce the residual vibrations of a vibrating system in a point-to-point motion. In this method the acceleration profile is made-up of a summation of sinusoidal terms with given motion time.
By considering the residual mechanical energy of the system as a cause of its steady state residual vibrations, this method finds the relations among the harmonic amplitudes, in order to avoid the residual vibrations at a given natural frequency by minimizing the amount of system residual mechanical energy.
In order to have a system robust with respect to the uncertainties in the evaluation of the natural frequency, a method is presented that makes the residual vibrations null at two different reference frequencies around the estimated one. In this way, there is a large around of the estimated frequency, where the residual vibration is maintained low. Moreover, the thesis analyzes the influence of different choice of the reference frequencies and the motion time on the amount of residual vibrations.
This method is also used in order to design a filter that decreases the residual vibrations of the system with respect to a given motion profile for the support. So this filter is robust with respect to system parameter uncertainties and also it’s not sensitive to motion command profile
Mechatronic design and optimization of new MEMS load sensors
No full textIn questa tesi di dottorato viene proposta una panoramica generale sulla classificazione dei diversi tipi di sensori di carico con le relative tecnologie e soluzioni di packging esistenti. Inoltre, considerando come approccio tecnologico l'effetto piezoresistivo, vengono discusse diverse idee innovative che forniscono soluzioni efficaci per realizzare sensori di stress basati sulle applicazioni. Come soluzione miniaturizzata, viene presentato lo sviluppo di un sensore di forza multi-assiale MEMS generico, in grado di misurare quattro diversi componenti di un campo di stress. Il sensore è stato progettato e ottimizzato per garantire le migliori prestazioni possibili utilizzando le tecnologie e le soluzioni ingegneristiche attuali. È stata identificata la dimensione minima possibile e proposto il layout elettronico. Inoltre, il comportamento del sensore è stato validato dall'analisi FEM al fine di valutarne le caratteristiche e fornire una calibrazione numerica. Come approccio orientato all'applicazione viene proposto un package meccanico adeguato con funzionalità innovative per arrivare ad una cella di carico miniaturizzata ad alta precisione in grado di sopportare carichi elevati.
Come soluzione su macro-scala, viene descritta la progettazione e lo sviluppo di un sensore di forza bi-assiale a basso costo basato sulla tecnologia piezoresistiva a film spesso. Combinando le funzionalità innovative già discusse, questo sensore è in grado di misurare le componenti assiali e laterali dello stress. Inoltre, questo sensore è ermetico e robusto, adatto per misurazioni a lungo termine. Questo lo rende una soluzione integrabile all'interno di strutture in calcestruzzo con lo scopo di monitorarne la salute strutturale. Il design del sensore di sforzo bi-assiale e le sue prestazioni sono stati ottimizzati e validati dall'analisi FEM. Una serie di prototipi sono stati prodotti e testati in laboratorio mediante test di compressione, considerando condizioni al contorno e materiali diversi per valutare corretto funzionamento del sensore. Alcuni sensori sono stati immersi in campioni di calcestruzzo, allo scopo di verificarne le prestazioni in termini di misurazione del carico e la loro qualità di interazione a lungo termine all'interno calcestruzzo. Infine, una serie di questi sensori è stata installata nei conci di un tunnel, per valutare il comportamento dei conci stessi sotto carico statico e ciclico in laboratorio. I risultati riportati confermano gli obiettivi del progetto: i sensori sono stati in grado di identificare i carichi interni della struttura e le imperfezioni locali.Within this PhD thesis, as a general overview, a classification of different types of load sensors with their relative technologies as well as existing packaging solutions is reported. Moreover, considering piezoresistivity effect as the technological approach, several innovative design features which provide effective solutions to realize application-based stress sensors are discussed and their value-added contributions with respect to the state of the art outlined as well. As a micro-scale solution, the development of a general purpose MEMS multi-axial stress sensor, able to measure four different components of a stress field is presented. The sensor has been designed and optimized in order to ensure best possible performance by using today available surface engineering solutions and technologies. Minimum possible size has been identified and the electronic layout proposed. Besides, sensor’s behaviour has been validated by FEM analysis in order to assess its characteristics and to provide numerical calibration. Moreover, as an application oriented approach a proper mechanical package with an innovative functionality is proposed to bring out a miniaturized high precision load cell which can withstand up to high amount of loads. Instead, as a macro-scale solution, the design and development of a low-cost in-plane stress sensor based on thick-film piezoresistivity technology is described. By combining already discussed innovative features, this sensor is able to measure the axial and in-plane components of stress. Moreover, this sensor is hermetic and robust for long-term measurements which makes it a proper solution to be merged inside concrete structures with the purpose of doing structural health monitoring. The design of in-plane stress sensor as well as its performance have been optimized and validated by FEM analysis. On top of that, a series of prototypes were produced and tested in laboratory by means of compression tests, imposing different boundary conditions and materials to assess the working concept of the sensor. Furthermore, some sensors have been merged inside concrete samples to verify their performance in terms of load measurement and their long-term quality interaction within concrete materials. Finally, an array of these sensors has been installed in tunnel segments and used to assess the behaviour of these segments under static and cyclic loading within laboratory conditions. The reported results confirm the targets of the design: the sensors were capable of identifying internal loads of the structure as well as of local imperfections.DIPARTIMENTO DI MECCANICADynamics and vibration of mechanical systems and vehicles30CIGADA, ALFREDOROCCHI, DANIEL
