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When paraffin wax melts it exhibits a large, relatively incompressible volume expansion. This can be used in microactuators for strong and large displacements, a rare combination among actuators. Furthermore, paraffin is inexpensive, inert and environmentally friendly, as well as easily processed and actuated. Together, these properties give paraffin actuators great potential for use in both low-cost and high-performance applications. In microfluidics, the miniaturization of various analysis systems decreases the volumes of samples and reagents needed, as well as the analysis throughput time. Using on-chip micropumps increases the efficiency of the microfluidic system, but a challenge for such pumps is the high back-pressure associated with separation, filtration or narrower channels. The objective of this thesis is to increase the understanding of paraffin in microactuators, as well as to further explore its possibilities and limitations. The main application area has been on-chip micropumps. For low-cost applications, actuators, pumps and dispensers have been fabricated in plastics and then evaluated. The dispenser is intended for on-chip storage and dispensing of liquids in a lab-on-a-chip that could be used in, e.g., point-of-care testing (POCT). For high-performance applications, metallic actuators, pumps and dispensers have been accomplished. The micropump is the world’s strongest mechanical micropump in sub-cubic centimetre size, capable of pressures of above 5 MPa. Possible applications are strong microhydraulics, on-chip chromatography, or medical microdosage systems. A limitation of paraffin is the relatively slow thermal actuation. In this thesis the thermal properties have also been turned into an advantage: Directional solidification is used to accomplish multiple stable states of the actuator displacement, withheld without any power consumption. For the future, the high-pressure capability may be improved by new designs. Optimization of speed and power consumption can be made by further work on modelling as well as on drive and control of the heating.

Microactuators are needed to convert energy into mechanical work at the microscale. Thermal microactuators can be used to produce this needed mechanical work. The purpose of this research was to design, fabricate, and test thermal microactuators for use at the microscale in microelectromechanical systems (MEMS). The microactuators developed were tested to determine the magnitude of their deflection and estimate their force. Five groups of thermal microactuators were designed and tested. All of the groups used the geometrically constrained expansion of various segments to produce their deflection. The first group, Thermal Expansion Devices (TEDs), produced a rotational displacement and had deflections up to 20 µm. The second group, Bi-directional Thermal Expansion Devices (Bi-TEDs) were similar to the TEDs. The difference, as the name implies, was that the Bi-TEDs deflected up to 6 µm in two directions. Thermomechanical In-plane Micromechanisms (TIMs) were the third group tested. They produced a linear motion up to 20 µm. The fourth group was the Rapid Expansion Bi-directional Actuators (REBAs). These microactuators were bi-directional and produced up to 12 µm deflection in each direction. The final group of thermal microactuators was the Joint Actuating Micro-mechanical Expansion Systems (JAMESs). These thermal microactuators rotated pin joints up to 8 degrees. The thermal microactuators studied can be used in a wide variety of applications. They can move ratchets, position valves, move switches, change devices, or make connections. The thermal microactuator groups have their own unique advantages. The TIMS can be tailored for the amount of deflection and output force they produce. This will allow them to replace some microactuator arrays and decrease the space used for actuation. The Bi-TEDs and REBAs are bi-directional and can possibly replace two single direction micro-actuators. The JAMESs can be attached directly to a pin joint of an existing mechanism. These advantages allow these thermal microactuator groups to be used for a wide variety of applications.

This thesis introduces two ortho-planar MEMS devices that can be used to position microcomponents: the XZ Micropositioning Mechanism and the XYZ Micromanipulator. The displacement and force relationships are presented. The devices were fabricated using surface micromachining processes and the resulting mechanisms were tested. A compliant XYZ Micromanipulator was also designed to reduce backlash and binding. In addition, several other MEMS positioners were fabricated and tested: the Micropositioning Platform Mechanism (MPM), the Ortho-planar Twisting Micromechanism (OTM), and the Ortho-planar Spring Micromechanism (OSM).

This thesis presents methods for the wafer-level integration of shape memory alloy (SMA) and electrostatic actuators to functionalize MEMS devices. The integration methods are based on heterogeneous integration, which is the integration of different materials and technologies. Background information about the actuators and the integration method is provided. SMA microactuators offer the highest work density of all MEMS actuators, however, they are not yet a standard MEMS material, partially due to the lack of proper wafer-level integration methods. This thesis presents methods for the wafer-level heterogeneous integration of bulk SMA sheets and wires with silicon microstructures. First concepts and experiments are presented for integrating SMA actuators with knife gate microvalves, which are introduced in this thesis. These microvalves feature a gate moving out-of-plane to regulate a gas flow and first measurements indicate outstanding pneumatic performance in relation to the consumed silicon footprint area. This part of the work also includes a novel technique for the footprint and thickness independent selective release of Au-Si eutectically bonded microstructures based on localized electrochemical etching. Electrostatic actuators are presented to functionalize MEMS crossbar switches, which are intended for the automated reconfiguration of copper-wire telecommunication networks and must allow to interconnect a number of input lines to a number of output lines in any combination desired. Following the concepts of heterogeneous integration, the device is divided into two parts which are fabricated separately and then assembled. One part contains an array of double-pole single-throw S-shaped actuator MEMS switches. The other part contains a signal line routing network which is interconnected by the switches after assembly of the two parts. The assembly is based on patterned adhesive wafer bonding and results in wafer-level encapsulation of the switch array. During operation, the switches in these arrays must be individually addressable. Instead of controlling each element with individual control lines, this thesis investigates a row/column addressing scheme to individually pull in or pull out single electrostatic actuators in the array with maximum operational reliability, determined by the statistical parameters of the pull-in and pull-out characteristics of the actuators. / QC20100729

This thesis presents the development of a fault detection and diagnosis (FDD) procedure capable of capturing, isolating and identifying multiple abrupt parametric faults. The proposed method relies on parameter estimation deployed in a set membership framework. This approach presupposes the utilization of a linearly parametrizable model and the a priori knowledge of bounded noise errors and parameter perturbations. Under these assumptions, a data-hyperspace is generated at every time instant. The goal of set membership identification (SMI) is the determination of the parametric set, formed as an orthotope or ellipsoid, within which the nominal parameter vector resides and intersects with the data-hyperspace. The fault detection mechanism is activated when the normal operation of the SMI procedure is interrupted due to an empty intersection of the data-hyperspace and the estimated parametric set. At the detection instant, a resetting procedure is performed in order to compute the parameter set and the data-hyperspace that contain the varied nominal parameter vector, allowing the SMI algorithm to continue its operation. During the fault isolation, consistency tests are executed, relying on the projections of the worst case parametric sets and the ones arisen from the normal operation of SMI. A faulty component is indicated when these projections do not intersect, while the distance of their centers is used for fault identification. In case of the ellipsoidal SMI-based FDD and under the assumption of a time invariant parameter vector, a new fault detection criterion is defined based on the intersection of support orthotopes of ellipsoids. A more accurate estimation of the time instant of fault occurrence is proposed based on the application of a backward-in-time procedure starting from the fault detection instant, while the conditions under which a fault will never be detected by the orthotopic and ellipsoidal SMI based FDD are provided. This dissertation explores the efficiency of the proposed FDD methodology for capturing failure modes of two microelectromechanical systems; an electrostatic parallel-plate microactuator and a torsionally resonant atomic force microscope. From an engineering point of view, failure modes appeared in the microcomponents of the microactuator and the TR-AFM are encountered as parameter variations and are captured, isolated and identified by the proposed FDD methodology. / Σε αυτή την διατριβή, παρουσιάζεται η ανάπτυξη μιας διαδικασίας Ανίχνευσης και Διάγνωσης Σφαλμάτων, η οποία είναι ικανή να εντοπίζει, απομονώνει και αναγνωρίζει πολλαπλά, απότομα παραμετρικά σφάλματα. H προτεινόμενη μέθοδος βασίζεται στην αναγνώριση του συνόλου συμμετοχής των παραμέτρων. Ο στόχος της Αναγνώρισης Συνόλου Συμμετοχής είναι ο καθορισμός του παραμετρικού συνόλου εντός του οποίου κείται το ονομαστικό διάνυσμα παραμέτρων, δεδομένου ότι το ονομαστικό διάνυσμα παραμέτρων ανήκει επίσης σε έναν υπερχώρο δεδομένων. Το παραμετρικό σύνολο απεικονίζεται ως ένα ορθότοπο ή ένα ελλειψοειδές, λόγω της εύκολης μαθηματικής τους περιγραφής. Έτσι, η διαδικασία Αναγνώρισης Συνόλου Συμμετοχής αντιστοιχεί σε ένα πρόβλημα βελτιστοποίησης, το οποίο αποσκοπεί στον υπολογισμό του ορθοτόπου ή ελλειψοειδούς το οποίο περιέχει το ονομαστικό διάνυσμα παραμέτρων και τέμνεται με τον υπερχώρο δεδομένων. Ο μηχανισμός Ανίχνευσης Σφαλμάτων ενεργοποιείται όταν διακόπτεται η φυσιολογική λειτουργία της Αναγνώρισης Συνόλου Συμμετοχής, λόγω της κενής τομής μεταξύ των εκτιμώμενου παραμετρικού συνόλου και του υπερχώρου δεδομένων. Τη χρονική στιγμή ανίχνευσης ενός σφάλματος, εφαρμόζεται μια διαδικασία επαναρύθμισης που σκοπεύει στον υπολογισμό του νέου παραμετρικού συνόλου, το οποίο περιέχει το μεταβεβλημένο ονομαστικό διάνυσμα παραμέτρων και τέμνεται με το υπερχώρο δεδομένων. Κατά τη διάρκεια της διαδικασίας απομόνωσης του σφάλματος, εκτελούνται τεστ συμβατότητας, τα οποία βασίζονται στις προβολές των νέων παραμετρικών συνόλων και στις προβολές των παραμετρικών συνόλων χείριστης περίπτωσης, ενώ η απόσταση των κέντρων των προβολών χρησιμοποιείται για αναγνώριση σφάλματος. Στην περίπτωση που η Ανίχνευση και Διάγνωση Σφαλμάτων πραγματοποιείται βασιζόμενη στην Αναγνώριση Συνόλου Συμμετοχής με ελλειψοειδή και θεωρώντας το ονομαστικό διάνυσμα παραμέτρων χρονικά αμετάβλητο, ορίζεται ένα νέο κριτήριο ανίχνευσης σφαλμάτων, χρησιμοποιώντας την τομή των περιβαλλόντων ορθοτόπων των ελλειψοειδών. Σε αυτή την περίπτωση, ένα σφάλμα ανιχνεύεται όταν η τομή αυτή είναι κενή. Ακόμη, προτείνεται μια πιο ακριβής εκτίμηση της χρονικής στιγμής εμφάνισης του σφάλματος, ενώ παρατίθενται οι συνθήκες υπό τις οποίες ένα σφάλμα μπορεί να μην ανιχνευθεί ποτέ με την εφαρμογή των προτεινόμενων μεθόδων. Η συγκεκριμένη διατριβή επίσης ερευνά την αποτελεσματικότητα της προτεινόμενης μεθοδολογίας Ανίχνευσης και Διάγνωσης Σφαλμάτων για τον εντοπισμό των τρόπων εκδήλωσης σφαλμάτων σε δύο μικροηλεκτρομηχανικά συστήματα (ΜΗΜΣ), έναν ηλεκτροστατικό μικροεπενεργητή παράλληλων πλακών και ένα ατομικό μικροσκόπιο συντονισμού στρέψης. Από πλευράς μηχανικής, οι τρόποι εκδήλωσης σφαλμάτων στα δομικά στοιχεία του μικροεπενεργητή ή του ατομικού μικροσκοποίου αντιμετωπίζονται ως απότομες παραμετρικές, οι οποίες εντοπίζονται και διαγιγνώσκονται από τις προτεινόμενες μεθόδους.