Now-a-days sensors are not limited only to industry or research laboratories but have come to common man’s usage. From kids toys to house hold equipment like washing machine, microwave oven as well as in automobiles, a wide variety of sensors and actuators can be easily seen. The aim of the present thesis work is to discuss the design, development, fabrication and testing of miniaturized piezoresistive, absolute type, low pressure sensor and flow sensor. Detailed performance study of these sensors in different ambient conditions (including harsh environment such as radiation, temperature etc.) has been reported. Extensive study on designing of thin silicon diaphragms and optimization of piezoresistor parameters is presented. Various experiments have been performed to optimize the fabrication and packaging processes. In the present work, two low range absolute type pressure sensors (0-0.5 bar and 0-1 bar) and a novel flow sensor (0-0.1 L min-1) for gas flow rate measurement are developed. The thesis is divided into following six chapters. Chapter 1: It gives a general introduction about miniaturization, MEMS technology and its applications in sensors area. A brief overview of different micromachining techniques is presented, giving their relative advantages and limitations. Literature survey of various types of MEMS based pressure sensors along with recent developments is presented. At the end, the motivation for the present work and organization of the thesis is discussed. Chapter 2: In this chapter, various design aspects of low, absolute type pressure sensors (0-0.5 bar and 0-1 bar) are discussed in detail. Static analysis of the silicon diaphragms has been carried out both analytically as well as through finite element simulations. Piezoresistive analysis is carried out to optimize the piezoresistor dimensions and locations for maximum sensitivity and minimum nonlinearity. All the Finite Element Analyses (FEA) were carried out using Coventorware software. A novel approach for the selection of resistor parameters (sheet resistance, length to width ratio) is reported . Finally, the expected performance of the designed sensors is summarized. Chapter 3: This chapter is divided into two parts. The first part presents the fabrication process flow adopted to develop these low range absolute pressure sensors. Two fabrication process approaches (wet etching and dry etching) which are used to fabricate the thin diaphragms are discussed in detail. Following an overall description, various aspects of the fabrication are elaborated on, like mask design, photolithography process, ion-implantation, bulk micromachining and wafer bonding. The required parameters for implantation doses, annealing cycles, low stress nitride deposition and anodic bonding are optimized through extensive experimental trials. The second part of this chapter discusses about the different levels of packaging involved in the realization of pressure sensors. Finite Element Analyses (FEA) of Level -0 and Level-1 packages has been carried out using ANSYS software to optimize the packaging materials. Exhaustive experimental studies on the selection of die attach materials and their characterization is carried out. Based upon these studies, the glass thickness and die-attach materials are selected. Chapter 4: The chapter discusses the measurement of the fabricated devices. The wafer level characterization which includes I-V characterization, measurement of offset and full scale output is discussed first. And then the temperature coefficient of resistance and offset is measured at wafer level itself. The performance characteristics like sensitivity, nonlinearity, hysteresis and offset of packaged pressure sensors is presented for all the variants (0.5 bar and 1 bar sensors fabricated by KOH and DRIE process) and their comparison with simulated values shows a close match. The measurement of dynamic characteristics using in-house developed test set-up are presented. The next section discussed detailed study about the stability of the developed sensors. The last part of this chapter reports the harsh environment characterization of the sensors viz. high temperature, humidity exposure, radiation testing etc. Chapter 5: The development of a novel micro-orifice based flow sensor for the flow rate measurement in the range of L min-1 is presented in this chapter. The sensing element is a thin silicon diaphragm having four piezoresistors at the edges. A detailed theoretical analysis showing the relationship between output voltage generated and flow rate has been discussed. The flow sensor is calibrated using an in-house developed testing set-up. Novelty of the design is that the differential pressure is measured at the orifice plate itself without the need of two pressure sensors or u-tube which is required otherwise. Chapter 6: This chapter summarizes the salient features of the work presented in this thesis with the conclusion. And then the scope for carrying out the further work is discussed.

Evaluation of the performance of a product and its components under impact loading is one of the key considerations in design. In order to assess resistance to damage or ability to absorb energy through plastic deformation of a structural component, impact testing is often carried out to obtain the 'Force - Displacement' response of the deformed component. In this context, it may be noted that load cells and accelerometers are commonly used as sensors for capturing impact responses. A drop-weight impact testing set-up consisting of a moving impactor head with a lightweight piezoresistive accelerometer and a strain gage based compression load cell mounted on it is used to carry out the impact tests. The basic objective of the present study is to assess the accuracy of responses recorded by the said transducers, when these are mounted on a moving impactor head. In the present work, a novel approach of theoretically evaluating the responses obtained from this drop-weight impact testing set-up for different axially loaded specimen has been executed with the formulation of an equivalent lumped parameter model (LPM) of the test set-up. For the most common configuration of a moving impactor head mounted load cell system in which dynamic load is transferred from the impactor head to the load cell, a quantitative assessment is made of the possible discrepancy that can result in load cell response. Initially, a 3-DOF (degrees-of-freedom) LPM is considered to represent a given impact testing set-up with the test specimen represented with a nonlinear spring. Both the load cell and the accelerometer are represented with linear springs, while the impacting unit comprising an impactor head (hammer) and a main body with the load cell in between are modelled as rigid masses. An experimentally obtained force-displacement response is assumed to be a nearly true behaviour of a specimen. By specifying an impact velocity to the rigid masses as an initial condition, numerical solution of the governing differential equations is obtained using Implicit (Newmark-beta) and Explicit (Central difference) time integration techniques. It can be seen that the model accurately reproduces the input load-displacement behaviour of the nonlinear spring corresponding to the tested component, ensuring the accuracy of these numerical methods. The nonlinear spring representing the test specimen is approximated in a piecewise linear manner and the solution strategy adopted and implemented in the form of a MATLAB script is shown to yield excellent reproduction of the assumed load-displacement behaviour of the test specimen. This prediction also establishes the accuracy of the numerical approach employed in solving the LPM system. However, the spring representing the load cell yields a response that qualitatively matches the assumed input load-displacement response of the test specimen with a lower magnitude of peak load. The accelerometer, it appears, may be capable of predicting more closely the load experienced by a specimen provided an appropriate mass of the impactor system i.e. impacting unit, is chosen as the multiplier for the acceleration response. Error between input and computed (simulated) responses is quantified in terms of root mean square error (RMSE). The present study additionally throws light on the dependence of time step of integration on numerical results. For obtaining consistent results, estimation of critical time step (increment) is crucial in conditionally stable central difference method. The effect of the parameters of the impact testing set-up on the accuracy of the predicted responses has been studied for different combinations of main impactor mass and load cell stiffness. It has been found that the load cell response is oscillatory in nature which points out to the need for suitable filtering for obtaining the necessary smooth variation of axial impact load with respect to time as well as deformation. Accelerometer response also shows undulations which can similarly be observed in the experimental results as well. An appropriate standard SAE-J211 filter which is a low-pass Butterworth filter has been used to remove oscillations from the computed responses. A load cell is quite capable of predicting the nature of transient response of an impacted specimen when it is part of the impacting unit, but it may substantially under-predict the magnitudes of peak loads. All the above mentioned analysis for a 3 DOF model have been performed for thin-walled tubular specimens made of mild steel (hat-section), an aluminium alloy (square cross-section) and a glass fibre-reinforced composite (circular cross-section), thus confirming the generality of the inferences drawn on the computed responses. Further, results obtained using explicit and implicit methodologies are compared for three specimens, to find the effect, if any, on numerical solution procedure on the conclusions drawn. The present study has been further used for investigating the effects of input parameters (i.e. stiffness and mass of the system components, and impact velocity) on the computed results of transducers. Such an investigation can be beneficial in designing an impact testing set-up as well as transducers for recording impact responses. Next, the previous 3 DOF model representing the impact testing set-up has been extended to a 5 DOF model to show that additional refinement of the original 3 DOF model does not substantially alter the inferences drawn based on it. In the end, oscillations observed in computed load cell responses are analysed by computing natural frequencies for the 3 DOF lumped parameter model. To conclude the present study, a 2 DOF LPM of the given impact testing set-up with no load cell has been investigated and the frequency of oscillations in the accelerometer response is seen to increase corresponding to the mounting resonance frequency of the accelerometer. In order to explore the merits of alternative impact testing set-ups, LPMs have been formulated to idealize test configurations in which the load cell is arranged to come into direct contact with the specimen under impact, although the accelerometer is still mounted on the moving impactor head. One such arrangement is to have the load cell mounted stationary on the base under the specimen and another is to mount the load cell on the moving impactor head such that the load cell directly impacts the specimen. It is once again observed that both these models accurately reproduce the input load-displacement behaviour of the nonlinear spring corresponding to the tested component confirming the validity of the model. In contrast to the previous set-up which included a moving load cell not coming into contact with the specimen, the spring representing the load cell in these present cases yields a response that more closely matches the assumed input load-displacement response of a test specimen suggesting that the load cell coming into direct contact with the specimen can result in a more reliable measurement of the actual dynamic response. However, in practice, direct contact of the load cell with the specimen under impact loading is likely to damage the transducer, and hence needs to be mounted on the moving head, resulting in a loss of accuracy, which can be theoretically estimated and corrected by the methodology investigated in this work.

Elektro-ultrazvuková spektroskopie je založena na interakci dvou signálů, elektrického střídavého signálu s frekvencí fE a ultrazvukového signálu s frekvencí fU. Ultrazvukový signál mění vzdálenost mezi vodivými zrny ve vzorku a tím mění jeho celkový elektrický odpor R. Změna odporu R je proměnná s frekvencí ultrazvukového signálu fU. Vzorek, který obsahuje mnoho defektů ve své struktuře, vykazuje vysokou změnu odporu R v porovnání se vzorkem bez defektů při stejné hodnotě ultrazvukového a elektrického signálu. V disertační práci je popsána elektro-ultrazvuková metoda na tlustovrstvých rezistorech, hořčíkových slitinách, monokrystalech Si a CdTe, varistorech a také jeden z prvních pokusů aplikace elektro-ultrazvukové spektroskopie na horninové vzorky a tak diagnostikovat jejich stav poškození. V našem případě byl proměřen vzorek žuly. Jelikož se jedná o nedestruktivní metodu testování, tak má tato metoda velmi perspektivní budoucnost. Tato metoda je citlivá na všechny defekty ve vzorku. Její výhodou je, že se měří velikost signálu ne frekvenci danou rozdílem nebo součtem budících frekvencí fE a fU a tím se dá dosáhnout vysoké citlivosti. V mém případě byl vždy měřen signál na rozdílové frekvenci fi = fE-fU.

Im Mittelpunkt dieser Arbeit stand die Darstellung sensitiver Blockcopolymere und deren Gele, die als Ausgangsmaterialien in Sensor- und Aktorsystemen einsetzbar sind. Die Vereinigung verschiedener Ansprechparameter stellt erhöhte Anforderung an die Synthese. Geringe Ansprechzeiten lassen sich mit einer Gelgröße im µm-Bereich erreichen. Hydrogele dieser Größenordnungen können durch nachträgliche Vernetzung funktioneller linearer Polymere ermöglicht werden. Die Makroinitiatormethode ermöglichte den Aufbau verschiedener linearer photovernetzbarer Blockcopolymere. Zum Einen wurde das temperatursensitive P(n-BuAc)-block-P(PNIPAAm-co-DMIAAm) erhalten, des Weiteren gelang die Darstellung der multi-sensitiven Blockcopolymere P2VP-block-P(NIPAAm-co-DMIAAm) und P4VP-block-P(NIPAAm-co-DMIAAm). Die Blockcopolymere wurden mit variierenden Blocklängen und Verhältnissen sowie mit unterschiedlichem Vernetzergehalt dargestellt. Die Charakterisierung der Blockcopolymere erfolgte mittels 1H-NMR-Spektroskopie, GPC-Messungen (Zusammensetzung) und DSC-Messungen (thermische Eigenschaften). Das Löslichkeitsverhalten in wässrigen Medien wurde durch Dynamische Lichtstreuung bestimmt. Die Beschreibung des Quellverhaltens der vernetzten Schichten erfolgte durch vornehmlich durch optische Methoden (SPR/OWS, WAMS, Ellipsometrie). Die Veränderung des E-Moduls in Abhängigkeit äußerer Parameter konnte mittels AFM untersucht werden. Die Reaktion der Schichten wurde gegenüber Temperatur, pH-Wert und Salzkonzentrationen getestet. Die charakterisierten Filme konnten im Anschluss als sensitive Schichten in piezoresistiven Sensorsystemen verwendetet werden.

Orientador: Carlos Lenz Cesar / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-20T14:50:59Z (GMT). No. of bitstreams: 1 Marques_GustavoPires_M.pdf: 1771357 bytes, checksum: 8ee6919633e2615608f25b33bec98e96 (MD5) Previous issue date: 2005 / Resumo: O microscópio de força atômica é uma ferramenta que possibilita a medida de forças precisamente localizadas com resoluções no tempo, espaço e força jamais vistas. No coração deste instrumento está um sensor a base de uma viga (cantilever) que é responsável pelas características fundamentais do AFM. O objetivo desta pesquisa foi usar a deflexão deste cantilever para obter uma calibração rápida e precisa da força da armadilha da pinça óptica, assim como testar e comparar com os método tradicionalmente utilizados para este propósito. Para isso, foi necessário analisar e entender o condicionamento de sinais utilizados no AFM. Foram estudados cantilever tradicionais, cujo sistema de detecção é baseado na deflexão de um feixe laser em conjunto com fotodetectores, bem como cantilevers piezoresistivos. Cantilevers piezoresistivos fornecem uma alternativa simples e conveniente aos cantilevers ópticos. A integração de um elemento sensorial dentro do cantilever elimina a necessidade de um laser externo e de um detector utilizados na maioria dos AFMs. Isto elimina a etapa delicada de alinhamento da laser ao cantilever e fotodetector que normalmente precede uma medida com AFM, uma simplificação que expande o potencial do AFM para o uso em meios adversos, como câmaras de ultra alto vácuo ou, como no caso específico das Pinças Ópticas, onde existem esferas em solução líquida e também restrições de dimensão / Abstract: The atomic force microscope (AFM) is a tool that enables the measurement of precisely localized forces with unprecedented resolution in time, space and force. At the heart of this instrument is a cantilever probe that sets the fundamental features of the AFM. The objective of this research has been using the deflection of this cantilever to get a fast and accurate calibration of optical tweezers trap force, as well as testing and comparing to the traditionally used methods of calibration for this purpose. For that it was necessary to resolve and understand the sensors signals conditioning used in the AFM. Traditional cantilevers, whose detection system is based on the deflection of a laser beam in addition with a photodetector, as well as piezoresistive cantilevers has been studied. Piezoresistive cantilevers provide a simple and convenient alternative to optically detected cantilevers. Integration of a sensing element into the cantilever eliminates the need for the external laser and detector used in most AFMs. This removes the delicate step of aligning the laser to the cantilever and photodetector which usually precedes an AFM measurement, a simplification which expands the potential of the AFM for use in difficult environments such as ultrahigh vacuum chambers or, as in Optical Tweezers specific case, where there are spheres into a liquid solution as well as dimensional constraints / Mestrado / Física / Mestre em Física

L’objectif de cette thèse est le développement d’un nouveau capteur de forcemulti-axes destiné à mesurer les composantes de friction impliquées dans lecontact doigt/objet lors la micromanipulation dextre. Des études théoriques etdes simulations par éléments finis ont conduit à la conception de ce capteurMEMS piézorésistif composé d’une plate-forme centrale munie d’une microbille,entourée d’une table compliante. D’après les résultats de simulations, ce capteur estcapable de mesurer indépendamment les forces normales et de frottement (couplageréciproque inférieure à 1%) avec une bonne sensibilité. Différents runs de fabricationnous ont permis d’obtenir des dispositifs exploitables. La structure mécanique de cescapteurs a été validée par la mesure des fréquences de résonance qui sont en accordavec les résultats de simulation. Des premiers résultats expérimentaux en termesde mesure de force ont ensuite été obtenus grâce au développement d’un banc detest (structure robotique, actionneurs, caméras, etc.). Nous nous sommes égalementintéressés à la problématique de l’étalonnage des capteurs de micro et nanoforceà l’aide de ressorts magnétiques reliés à des masses mesurables. Nous avons, danscette optique, mis au point une stratégie d’estimation et de compensation passivedes perturbations mécaniques en utilisant un principe différentiel. Cette approchea été appliquée à un capteur de nanoforce basé sur la lévitation diamagnétique et aabouti à des résultats prometteurs : une résolution inférieure au nanonewton a puêtre obtenue. / Sensor enabling to characterize the finger/object contact involved in dexterousmicromanipulation. Theoretical studies and finite elements simulations have lead tothe conception of this piezoresistive MEMS sensor composed of a central platformwith a micro-ball and surrounded by a compliant table. According to the simulationresults, this sensor is able to independently measure the normal and friction forces(crosstalk less than 1 %) with a good sensitivity. Several runs of fabrication allowedus to obtain usable devices. The mechanical structure of such sensors has beenvalidated by the measurement of resonance frequencies that are consistent with thesimulation results. The first experimental results in terms of force measurement werethen obtained through the development of a test bench (robotic structure, actuators,cameras, etc.). We were also interested in the problem of calibration of micro andnanoforce sensors using magnetic springs connected to measurable masses. In thiscontext, we developed an estimation strategy and a passive rejection of mechanicaldisturbances using a differential principle. This approach was applied to a nanoforcesensor based on the diamagnetic levitation and yielded promising results: a resolutionlower the nanonewton level could be obtained.