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The objective of this thesis is to develop an analysis approach for formulation of transduction or input/output representations for magnetostrictive actuators. This transduction model is developed through application of an electro-magneto-mechanical impedance modeling approach which combines both the mechanical dynamics and coupled behavior of the actuator device. Lumped and continuous mechanical impedance elements model the actuator dynamics and the constitutive relationships for Terfenol-D characterize the electro-magneto-mechanical interaction. Experimental analysis of a Terfenol-D actuator serves to verify the developed models and provides an indication of actuator non-linearity. The developed transduction model allows for various device behavior analysis including dissipative power consumption, force and stroke output, and efficiency as a transducer. An actuator design strategy based upon the dynamics of the actuator and a driven external system is presented and allows for analysis of various actuator behaviors in terms of device parameters. The Terfenol-D actuator as a collocated actuator/sensor is also made possible with the transduction model. / Master of Science

The magnetoelectric (ME) effect, i.e., the induction of magnetization by an applied electric field (E) or a polarization by an applied magnetic field (H), is of great interest to researchers due to its potential applications in magnetic sensors. Moreover, the ME effect in laminate composites is known to be much higher than in single phase and particulate composites due to combination of the magnetostrictive and piezoelectric effects in the individual layers. Given that the highest ME coefficient have been found in Metglas/piezo-fiber laminate composites, this study was designed to investigate and enhance the magnetoelectric (ME) effect in Metglas/piezo-fiber laminate composites, as well as develop their potential for magnetic sensor applications. To initiate this investigation, a theoretical model was derived to analyze the thickness effect of the magnetostrictive, piezoelectric, epoxy and Kapton layers on the ME coefficient. As a result, the importance of the coupling effect by epoxy layers was revealed. I used spin-coating, vacuum bagging, hot pressing, and screen printing techniques to decrease the thickness of the epoxy layer in order to maintain homogeneity, and to obtain good repeatability of the 16 ME laminates fabricated at one time. This protocol resulted in a more efficient way to induce self-stress to Metglas/PZT laminates, which is essential for increasing the ME coefficient. With an enhanced ME effect in the Metglas/piezo-fiber laminates, magnetic field sensitivity could then be increased. An ME sensor unit, which consisted of a Metglas/PMN-PT laminate and a low noise charge amplifier, had a magnetic field sensitivity of 10 pT/Hz0.5 in a well-shielded environment. Stacking four of these ME laminates could further increase the signal-to-noise (SNR) ratio. I studied the optimized distance between a pair of Metglas/PZT ME laminates. A stack of up to four ME sensors was constructed to decrease the equivalent magnetic noise. The magnetic field sensitivity was effectively enhanced compared to a single laminate. Finally, a number of four Metglas/PZT sensor units array was constructed to further increase the sensitivity. ME laminate composites operated in passive mode have typically required an external magnetic bias field in order to maximize the value of the piezomagnetic coefficient, which has many drawbacks. I studied the ME effect in an Ni/Metglas/PZT laminate at zero bias field by utilizing the remnant magnetization between the Ni and Metglas layers. To further enhance this effect, annealed Metglas was bonded on the Metglas/PZT laminate since it is known that hard-soft ferromagnetic bilayers generate built-in magnetic field in these Metglas layers. As a result, giant αME values could be achieved at a zero bias field at low frequency range or at electromechanical resonance (EMR). The sensor unit consisting of self-biased ME laminate arrays is considerably smaller compared to a unit that uses magnet-biased ME laminates. Introducing the converse ME effect and nonlinear ME effect in Metglas/piezo-fiber laminates affords a variety of potential applications. Therefore, I theoretically and experimentally studied converse ME effects in laminates with longitudinally magnetized and longitudinally poled, or (L-L) mode. The optimum structure for producing the maximum effect was obtained for Metglas/PZT laminates. Additionally, the optimum structure and materials for enhancing the nonlinear ME effect in Metglas/PZT laminates are reviewed herein. In particular, this study revealed that modulating the EMR in laminates with high-Q piezo-fibers could enhance the SNR. The stress effect on nonlinear ME effect is also discussed—namely that magnetic field sensitivities can be enhanced by this modulation-demodulation technique. / Ph. D.

This thesis presents the design of various closed-loop real-time control of a novel linear magnetostrictive actuator. The novel linear magnetostrictive actuator which uses Terfenol-D as the magnetostrictive material was developed by Sadighi. It solves the problem of power consumption in a conventional magnetostrictive actuator. However, the control system of this magnetostrictive actuator cannot control the current in the coils, which limits the performances of the real-time position control. In the closed-loop real-time control system proposed in this thesis, the controller is designed depending on the change of current. The closed-loop real-time control design focused on the position control of the active element in the novel linear magnetostrictive actuator. The closed-loop position-control system of the linear magnetostrictive actuator was successfully designed by implementing a closed-loop current-control system as an inner loop of the entire control system. This design offers the flexibility to design various position controllers in the closed-loop position-control system. The closed-loop current-control design uses pulse-width modulation (PWM) signal to change the current in the coils of the novel linear magnetostrictive actuator. By changing the duty ratio of the PWM signal, the current in the coils can be changed from zero to its maximum value. With a current controller using an integrator with a gain of 10, the current can be controlled with high response time and an error of /- 0.01 A. The position-controller design was successfully conducted by using four different approaches. First, a proportional-integral-derivative (PID) controller which was designed by relay-auto tuning method with experiments exhibited a position error of ±1 μm with a 5 μm peak-to-peak position noise. Second, a PID controller which was designed by root-locus can control the position with a position error of /- 3-4 μm with a 5 μm peak-to-peak position noise. Third, a linear variable velocity controller exhibited a position error of /-5 μm with a 5 mu m peak-to-peak position noise. Then, the sliding mode control (SMC) exhibited a position error of /-5 μm with a 5 μm peak-to-peak position noise.

Στο παρών κείμενο μεταπτυχιακής εργασίας περιγράφεται η κλινική εφαρμογή μαγνητοσυστολικού αισθητήρα για τη μέτρηση του χρόνου πήξης ολικού αίματος. Περιγράφεται η αρχή λειτουργίας της συσκευής και η κατασκευή του πρωτότυπου μοντέλου. Τα επιμέρους κομμάτια της διάταξης σχεδιάστηκαν, μελετήθηκαν και υλοποιήθηκαν ειδικά για τη συγκεκριμένη εφαρμογή. Με τη χρήση της συσκευής, το βιολογικό φαινόμενο της πήξης του αίματος μετατρέπεται σε εύκολα μετρούμενο σήμα ηλεκτρικής τάσης. Η μετατροπή αυτή γίνεται με τη βοήθεια διάταξης επαγωγικών πηνίων (διέγερσης-λήψης), στο εσωτερικό των οποίων τοποθετείται μαγνητοελαστικό υλικό. Στην επιφάνεια του υλικού τοποθετείται σταγόνα (2 μl) τριχοειδικού αίματος. Η μεταβολή των ιξωδοελαστικών χαρακτηριστικών του δείγματος καθώς αυτό περνάει από την υγρή στη στέρεα φάση (θρόμβος), ανιχνεύονται μέσω της αντίστοιχης μεταβολής της διαπερατότητας του υλικού. Το αποτέλεσμα της μέτρησης είναι γράφημα τάσης-χρόνου. Από το γράφημα του κάθε δείγματος που μετρήθηκε με τη συσκευή κατά τη διάρκεια της κλινικής εφαρμογής του στο Ιπποκράτειο Νοσοκομείο Αθηνών, προέκυψε ένας πειραματικός χρόνος, ο χρόνος πήξης tπηξ. Ο χρόνος αυτός αποδείχθηκε ότι έχει στατιστικά σημαντική σχέση με τον εργαστηριακό χρόνο ροής ΒΤ (Bleeding Time) (p<0.01). Η πήξη του αίματος αποτελεί το σημαντικότερο κομμάτι του αιμοστατικού μηχανισμού του ανθρώπινου οργανισμού. Διαταραχές που σχετίζονται με δυσλειτουργίες του μηχανισμού αυτού θεωρούνται ιδιαίτερα κρίσιμες και απαιτούν άμεση διάγνωση και βέλτιστη θεραπευτική προσέγγιση. Υπό το πρίσμα αυτών των απαιτήσεων, η υλοποίηση της συγκεκριμένης αισθητήριας εφαρμογής προσβλέπει στη διερεύνηση μιας νέας απλής και οικονομικής μεθόδου για την εξέταση δειγμάτων αίματος, όσον αφορά την πήξη τους. / The present master thesis describes the principle of operation, the construction, and the clinical evaluation of a whole blood coagulation magnetostrictive sensor. The major parts of the setup where specially designed and constructed for the needs of the present implementation. The function of the sensor relates to the transformation of the biological process of blood, into an easy-to-measure voltage signal. This transformation is feasible with the placement of a magnetoelastic material inside a double coil setup (primary-secondary). A drop of capillary blood (2 μl) is placed on the surface of the material. Viscosity variations of the sample, while it passes from the liquid to the solid phase, are detected through the detection of the corresponding permeability variations of the material. The result of the measurements which took place at the Hippokratio Hospital of Athens, is a V(t) graph. For each sample which was measured, the corresponding graph was used to export the experimental value tcoag. This value was proved to have a statistically significant relationship with Bleeding Time (BT) (p<0.01). Blood coagulation is the most important part of the human hemostatic mechanism. The disorders relating to the dysfunction of this mechanism are considered critical and demand immediate diagnosis and optimum therapeutic approach. Under this view, the realization of the specific sensor apparatus targets to the investigation of a new simple and cost-effective method for blood coagulation testing.

Two new fiber optic magnetostrictive phase modulators and magnetometers using the highly magnetostrictive rare-earth iron compound Tb_xDy_l-xFe₂ are investigated. They demonstrated to have a high sensitivity, dynamic range, minimum field detectability, and a better structural suitability than metallic glasses. For the first sensor, the experimental linear phase shifting coefficient was 1.102 rad/Vp-m with the corresponding phase shift nonnalized to the magnetic field of 0.306 radiO-m. For the second sensor, the experimental linear phase shifting coefficient was 0.5 rad/Vp-m with the corresponding phase shift nonnalized to the magnetic field of 0.136 rad/G-m. A minimum detectable phase shift of better than 1 μrad was obtained, which corresponds to 2 μG/m for a 4 Hz bandwidth and 1 μG/â HZ per meter of fiber interaction length. The projected minimum detectable magnetic field for 30 meters, for the first sensor, is thus seen to be 3pT/â HZ. The experimental results presented have clearly demonstrated the utility of the Terfenol based magnetostrictive fiber optic phase modulator and magnetometer. / Master of Science

Magnetoelectric (ME) effect is defined as the change in dielectric polarization (P) of a material under an applied magnetic field (H) or an induced magnetization (M) under an external electric field (E). ME materials have attracted number of investigators due to their potential for improving applications such as magnetic field sensors, filters, transformers, memory devices and energy harvesters. It has been shown both experimentally and theoretically that the composite structures consisting of piezoelectric and magnetostrictive phases possess stronger ME coupling in comparison to that of single phase materials. Giant magnetoelectric effect has been reported in variety of composites consisting of bulk-sized ME composites and thin film ME nanostructures. In this dissertation, novel ME composite systems are proposed, synthesized and characterized in both bulk and thin films to address the existing challenges in meeting the needs of practical applications. Two applications were the focused upon in this study, tunable transformer and dual phase energy harvester, where requirements can be summarized as: high ME coefficient under both on-resonance and off-resonance conditions, broad bandwidth, and low applied DC bias. In the first chapter, three challenges related to the conventional ME behavior in bulk ME composites have been addressed (1) The optimized ME coefficient can be achieved without external DC magnetic field by using a self-biased ME composite with a homogenous magnetostrictive material. The mechanism of such effect and its tunability are studied; (2) A near-flat ME response regardless of external magnetic field is obtained in a self-biased ME composite with geometry gradient structure; (3) By optimizing interfacial coupling with co-firing techniques, the ME coefficient can be dramatically enhanced. Theses co-fired ME laminates not only exhibit high coupling coefficient due to direct bonding, but also illustrate a self-biased effect due to the built-in stress during co-sintering process. These results present significant advancement toward the development of multifunctional ME devices since it eliminates the need for DC bias, expands the working bandwidth and enhances the ME voltage coefficient. Next, magnetoelectric nanocomposites were developed for understanding the nature of the growth of anisotropic thin film structures. In this chapter following aspects were addressed: (1) Controlled growth of nanostructures with well-defined morphology was obtained. Microstructure and surface morphology evolution of the piezoelectric BaTiO3 films was systematically analyzed. A growth model was proposed by considering the anisotropy of surface energy and the formation of twin lamellae structure within the frame work of Structure Zone Model (SZM) and Dynamic Scaling Theory (DST). In parallel to BaTiO3 films, well-ordered nanocomposite arrays [Pb1.1(Zr0.6Ti0.4)O3/CoFe2O4] with controlled grain orientation were developed and investigated by a novel hybrid deposition method. The influence of the pre-deposited template film orientation on the growth of ME composite array was studied. (2) PZT/CFO/PZT thick composite film and BTO/CFO thin film were synthesized using sol-gel deposition (SGD) and pulsed laser deposition (PLD) techniques, respectively. The HRTEM analysis revealed local microstructure at the interface of consecutive constituents. The interfacial property variation of these films was found to affect the coupling coefficient of corresponding ME nanocomposites. Subsequently, a novel complex three-dimensional ME composite with highly anisotropic structure was developed using a hybrid synthesis method. The influence of growth condition on the microstructure and property of the grown complex composites was studied. The film with highly anisotropic structure was found to possess tailored ferroelectric response indicating the promise of this synthesis method and microstructure. Based on the laminated ME composites, three types of ME tunable transformer designs were designed and fabricated. The goal was to develop a novel ME transformer with tunable performance (voltage gain and/or working resonance frequency) under applied DC magnetic field. Conventional ME transformers need either winding coil or large external magnetic field to achieve the tunable feature. Considering the high ME coupling of ME laminate, two ME transformers were developed by epoxy bonding Metglas with transversely/longitudinally poled piezoelectric ceramic transformer. The influence of different operation modes toward magnetoelectric tunability was analyzed. In addressing the concern of the epoxy bonding interface, a co-fired ME transformer with unique piezoelectric transformer/magnetostrictive layer/piezoelectric transformer trilayer structure was designed. The design and development strategy of thin film ME transformer was discussed to illustrate the potential for ME transformer miniaturization and on-chip integration. Lastly, motivated by the increasing demand of energy harvesting (EH) systems to support self-powered sensor nodes in structural health monitoring system, a magnetoelectric composite based energy harvester was developed. The development and design concept of the magnetoelectric energy harvester was systematically discussed. In particular, the first dual-phase self-biased ME energy harvester was designed which can simultaneously harness both vibration and stray magnetic field (Hac) in the absence of DC magnetic field. Strain distribution of the EH was simulated using the finite element model (FEM) at the first three resonance frequencies. Additionally, the potential of transferring this simple EH structure into MEMS scalable components was mentioned. These results provide significant advancement toward high energy density multimode energy harvesting system. / Ph. D.

Une recherche bibliographique a permis de faire un état de l'art, d'une part des différents principespermettant de détecter le givre et d'autre part de l'application de matériaux magnétostrictifs à la mesure defaibles masses. La faisabilité et l’applicabilité de certains alliages amorphes et nanocristallins à la réalisationde capteurs de givre ont été démontrées.Suite à cet état de l'art, le principe de détection par résonateur magnétostrictif qui a été retenu, a faitl'objet d'une étude approfondie aboutissant à l'établissement d'un nouveau modèle analytique complet desrésonateurs magnétostrictifs sous forme de ruban. L'intérêt principal de ce modèle est la prise en compte depertes mécaniques et l'expression finale contenant la fonction de transfert complète entre les entrées et sortiesélectriques. Ainsi, la réponse en fréquence du modèle est vraiment similaire aux réponses expérimentales. Deplus, il apporte une explication aux retournements observés, pour certains harmoniques entre les fréquencesde résonance et d'antirésonance, pour lesquels l’origine n’avait pu être clairement identifiée.La mise en œuvre de ce nouveau modèle pour la caractérisation de rubans amorphes a montré qu'ilest possible de déterminer le coefficient de couplage à partir de la réponse en fréquence ainsi que le moduled'Young ou l'amortissement. On a donc pu tracer pour des rubans de 2605SC et 2826MB les évolutions avecle champ de polarisation des paramètres du résonateur. De l'évolution de ces paramètres, il est possible dereconstruire les courbes de magnétostriction d'un ruban, ce qui constitue actuellement une méthode decaractérisation.La mise en œuvre d'un prototype a permis de détecter du givre et ainsi de confirmer la faisabilité dela détection de givrage par ce moyen, mais les essais préliminaires qui sont très prometteurs n’ont puapporter une réponse quantitative du capteur soumis à un dépôt de givre. Des mesures utilisant des enceintesde givrage contrôlées en température et en hygrométrie constituent une première perspective. Par ailleurs, lesrésultats présentés dans ce manuscrit s’avèrent une bonne base pour la valorisation de ces travaux,notamment pour la réalisation d’un prototype de capteur, son conditionnement et sa mise en œuvre dans devraies conditions de givrage. / A review of literature allowed first to a state of the art of the different routes to detect the ice on theone hand and of the use of magnetostrictive materials to measure small masses. Both the feasibility andapplicability of metglasses and nanocrystalline alloys to frost resonating sensors have been clearlyestablished.The principle of magnetostrictive sensing resonator was developed and a new comprehensiveanalytical model of ribbonshaped magnetostrictive resonators was successfully achieved. The present modelincludes mechanical losses and the final expression contains the complete transfer function between the inputand output powers. Thus, the predicted frequency response of the model fairly fits to the experimental one.In addition, it clearly explains henceforth the reversals of some harmonic frequencies which occur from theresonance and antiresonance phenomena.The implementation of this new model for the characterization of amorphous ribbons showed thusthat it is now possible to well estimate the coupling coefficient from the frequency response and the Young'smodulus or damping. So we could draw developments with the bias field parameters of the resonator for2826MB and 2605SC amorphous ribbons. The evolution of these parameters allows the magnetostrictioncurves to be well established, that consists in a new characterization method.The implementation of a first prototype permits to detect frost, confirming thus the feasibility ofdetecting icing this way, but these promising preliminary tests could not bring quantitative data to model thefrost deposition on a resonating sensor. Measurements using pregnant icing controlled temperature andhumidity are a first perspective. Finally, it is important to emphasize that the present results appear as a goodsupport for the valorization of this study, especially to elaborate of a prototype sensor based onmagnetostrictive ribbons, its packaging and its implementation in in situ icing conditions.

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