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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

A simulation method for design and development of magnetic shape memory actuators

Schiepp, Thomas January 2015 (has links)
The systems/products and their design processes have become more and more complicated due to the fact that their requirements in terms of function, durability, reliability and energy efficiency have been increased significantly and that their leading time has to be short and their materials cost has to be low. To meet these requirements, individual parts and subsystems have to offer increased functionality and efficiency themselves. It has been found that smart materials, such as piezo ceramics or various shape memory alloys as well as less known dielectric elastomers or magnetic shape memory alloys, offer ideal preconditions to fulfil such requirements. Among the various shape memory alloys, the Magnetic Shape Memory (MSM) alloy is a kind of smart material that can elongate and contract in a magnetic field. Based on the MSM alloy a new type of smart electromagnetic actuators have been designed and developed. This kind of actuator exhibits the features above. Typically, the MSM material is a monocrystalline Ni-Mn-Ga alloy, which has the ability to change its size or shape very fast and many million times repeatedly. State-of-the-art alloys are able to achieve a magnetic field induced strain of up to 12%. The magneto-mechanical characteristic of MSM alloys is being constantly improved. However, as far as the author is aware, there are no efficient and commercially available tools for engineers to design MSM-based actuators. To achieve this, simulation tools for design are indispensable. This thesis is dedicated to this task. In this PhD thesis, new design and simulation techniques for MSM-based actuators have been studied. In particular, three simulation methods have been proposed. These three methods extend standard magneto-static FEM simulation techniques by taking into account the magneto-mechanical coupling and the magnetic anisotropy of the MSM materials. They differ in terms of the necessary a priori alloy characterisation (i.e., measurement effort), computational complexity and consequent computing time. The magneto-mechanical characteristics of the MSM material are a necessary and fundamental ingredient for this type of simulation. However, the characterisation of the MSM materials is a very challenging task and requires specific modifications to standard measurement approaches. So, in this thesis, some specific measurement methods of the magneto-mechanical characteristics of the MSM materials have been proposed, designed and developed. It is described how existing measurement instruments can be modified to measure the unique magneto-mechanical characteristics of MSM, so they are applicable and with practical values. Various tests have been carried out to validate the new methods and the necessary characterisations of the properties of MSM materials have been performed, such as the measurement of the permeability of MSM under a defined stress during elongation. The new measurement results have been analysed and the findings have been used to design and develop the simulation methods. The three simulation methods can be used to predict and optimise the current-elongation behaviour of an MSM element under the load of a mechanical stress while excited by a magnetic field. Extensive experiments have been carried out to validate these three simulation methods. The results show that the three methods are relatively simple but, at the same time, very effective means to model, predict and optimise the properties of an MSM actuator using finite element tools. In addition, the experiment results have also shown that the simulation methods can be used to gain some deep insights into the magneto-mechanical interaction between the MSM element and the electromagnetic actuator. In this thesis an evolutionary algorithm which works together with the simulation methods has been developed to achieve individual optimised solutions in very short times. In summary, from the experiment results, it has been found that the measurements and simulation methods proposed and developed in this thesis; enable designers to perform simulations for a high-quality actuator design based on the magneto-mechanical properties of MSM alloys. This is the first time that a MSM can be characterised for simulation purposes in a fast and precise way to predict MSM and electromagnetic actuator interactions and identify and optimise the design parameters of such actuators. However, these simulation methods are strongly dependent on the measurement of the magneto-mechanical characteristics of magnetic shape memory alloys, whose precision can be further improved. To reach commercial success as well higher precision in the simulation prediction, further achievements in the field of material science (e.g. smoothness of mechanical curves) are also necessary.
42

Investigation of novel multi-layer spoke-type ferrite interior permanent magnet machines

Xia, Bing January 2017 (has links)
The permanent magnet synchronous machines have been attracting more and more attention due to the advantages of high torque density, outstanding efficiency and maturing technologies. Under the urges of mandatory energy efficiency requirements, they are considered as the most potential candidates to replace the comparatively low-efficient induction machines which dominate the industrial market. However, most of the high performance permanent magnet machines are based on high cost rare-earth materials. Thus, there will be huge demands for low-cost high-performance permanent magnet machines. Ferrite magnet is inexpensive and abundant in supply, and is considered as the most promising alternative to achieve the goal of low cost and high performance. In consideration of the low magnetic energy, this thesis explored the recent developments and possible ideas of ferrite machines, and proposed a novel multi-layer spoke-type interior permanent magnet configuration combining the advantages of flux focusing technique and multi-layer structure. With comparable material cost to induction machines, the proposed ferrite magnet design could deliver 27% higher power with 2-4% higher efficiency with exactly the same frame size. Based on the data base of International Energy Agency (IEA), electricity consumed by electric machines reached 7.1PWh in 2006 [1]. Considering that induction machines take up 90% of the overall industrial installation, the potential energy savings is enormous. This thesis contributes in five key aspects towards the investigation and design of low-cost high-performance ferrite permanent magnet machines. Firstly, accurate analytical models for the multi-layer configurations were developed with the consideration of spatial harmonics, and provided effective yet simple way for preliminary design. Secondly, the influence of key design parameters on performance of the multi-layer ferrite machines were comprehensively investigated, and optimal design could be carried out based on the insightful knowledge revealed. Thirdly, systematic investigation of the demagnetization mechanism was carried out, focusing on the three key factors: armature MMF, intrinsic coercivity and working temperature. Anti-demagnetization designs were presented accordingly to reduce the risk of performance degradation and guarantee the safe operation under various loading conditions. Then, comparative study was carried out with a commercial induction machine for verification of the superior performance of the proposed ferrite machine. Without loss of generality, the two machines had identical stator cores, same rotor diameter and stacking length. Under the operating condition of same stator copper loss, the results confirmed the superior performance of the ferrite machine in terms of torque density, power factor and efficiency. Lastly, mechanical design was discussed to reduce the cost of mass production, and the experimental effort on the prototype machine validates the advantageous performance as well as the analytical and FEA predictions.
43

The processing and characterisation of recycled NdFeB based magnets

Adrwish, Salahadin Muhammed Ali January 2013 (has links)
The scrap magnets were turned into a powder using the HD process. The powder was milled for specific times and sintered for 1-3hrs at 1090 °C. The magnet samples were measured using a permeameter to determine their magnetic properties. Cross sections of these samples were then mounted in bakelite and subject to metallographic studies using SEM analysis by means of Joel6060 and 7000. Some of the recycled magnets did achieve magnetic properties close to the starting magnets. It was shown that the nature of the starting magnets determines the appropriate sintering conditions during recycling. Sintering for 3hrs was good for magnets with high oxygen content but too long for fresh material and magnets with lower oxygen content, as indicated by the dilatometer measurements. Some magnets were studied further due to a lean rare content. These were treated with various heat treatments and other techniques (e.g. grain boundary diffusion) and the addition of various additives such as Dy, Co, Nd, Nband Tb. A study of how reactive recycled magnets in 3% salt-bath (Sodium Chloride NaCI) compared with starting magnets. The corrosion study was conducted over 30 weeks where results had indicated that recycled magnets have better corrosion resistance than the original material. This was due mainly to the shape of the magnets and the magnets being anisotropic, where there is a concentration of corrosion sites on the poles. The corrosion initiated at the Nd rich phase where it propagates further as time goes on. Furthermore, the magnetic properties decrease over the period, as expected. An investigation was made into the use of scrap magnetic powder in bonded magnets using tin as binder was also undertaken.
44

Έλεγχος στροφών ασύγχρονου κινητήρα με ηλεκτρονικό μετατροπέα ισχύος : ανάλυση και εφαρμογή

Παπαλουκάς, Βασίλειος, Λύμουρας, Γεώργιος 28 May 2009 (has links)
Η παρούσα διπλωματική εργασία αποτελεί μια μελέτη επί του ελέγχου των κινητήρων επαγωγής που στόχο έχει τη διερεύνηση της επίδασης των διαφορετικών σημάτων ανάδρασης (ανάλογο στροφών και ανάλογο του τετραγώνου στοφών) στην απόκριση του συστήματος κίνησης. Για το σκοπό αυτό αναπτύχθηκε ενδελεχώς η σχετική θεωρία, μελετήθηκε η παθητικότητα ηλεκτρομηχανικών συστημάτων, χρησιμοποιήθηκε συγκεκριμένος ηλεκτρονικός μετατροπέας και κατασκευάστηκε μετατροπέας σήματος συνεχούς ρεύματος ανάλογος του αριθμού των στροφών και του τετραγώνου του. Στα πλαίσια της εργασίας εξετάστηκε PI έλεγχος βασισμένος στον βαθμωτό (Scalar V/f) έλεγχο, με σήμα αρνητικής ανάδρασης ρεύμα ανάλογο του αριθμού και του τετραγώνου του αριθμού των στροφών. Μελετήθηκε η απόκριση του κινητήρα και για τους δύο ελέγχους για διαφορετικές τιμές των παραμέτρων KP και KI, και διερευνήθηκε ποιες είναι αυτές ώστε να έχουμε βέλτιστη απόκριση. Συγκεκριμένα ποιες παρουσιάζουν την μικρότερη υπερύψωση, τον μικρότερο χρόνο αποκατάστασης, το μικρότερο σφάλμα μόνιμης κατάστασης. Επίσης εξετάστηκε η επίδραση της κάθε παραμέτρου στην διαμόρφωση της εσωτερικής ενέργειας του κινητήρα. / This diploma thesis forms a study on control techniques of induction motors which comes with the intention to explore the effets of different signals of feedback (proportional to the number of revolutions and to the square of the number of revolutions) on the output of the motor. For this purpose sedulous analysis of relevant theory was carried out, passivity of electromechanical systems was studied, a specific electronic commutator was used and a converter of constant current signal proportional to the number of revolutionsand to the square of the number of revolutions was developed. In this thesis a PI controller based on the Scalar V/f control with a signal of current of negative feedback was examined. The output of the motor for both the controls aid for different values of the parameters KP and KI was examined, and it was investigated which of them lead to an optimal output of the motor. It was studied more specifically which of them result in the optimal overshoot, settling time and the error of the permanent mode. Furthermore, it was inquired the impact of its parameter on the modulation of the intrinsic power of the motor.
45

Arrays of magnetic nanostructures : a dynamical and structural study by means of X-ray experiments

Heldt, Georg January 2014 (has links)
The work in this PhD thesis covers two strands of x-ray experiments: firstly, the characterisation of large arrays of dense structures by means of x-ray scattering, and, secondly, the investigation of hybrid anisotropy square structures with x-ray microscopy. The ability to accurately characterise large arrays of nanoscale magnetic structures is a key requirement for both scientific understanding and technological advance such as bit patterned recording media (BPM). In this work small angle x-ray scattering (SAXS) was investigated as a characterisation technique for large arrays of patterned structures. Dense arrays of magnetic nanostructures were prepared on x-ray transparent membranes and measured. The SAXS data was then modelled to obtain structure parameters such as the mean structure diameter, the diameter distribution and the mean position variance with statistical significance. Arrays (500 x 500 μm2) of nominally uniform nanostructures with centre-to-centre distances between 250 nm-50 nm were structurally characterised and compared to structure diameters obtained by optical scanning electron microscopy measurements. The mean structure diameter was found to be between 39 nm-15nm and agree within the errors with the diameter obtained from SEM measurements. This work provides accurate data on the distribution (variance) of nanostructure sizes which is key for modelling these arrays for applicationin BPM. In the second part of the work, the static and dynamic properties of patterned hybrid anisotropy square structures ([Co/Pd]-Py) were investigated by using time-resolved scanning transmission X-ray microscopy (STXM). In these patterned structures the magnetisation in the layers change both in magnitude and direction and gives rise to interesting new domain configurations. The reciprocal interaction between magnetic vortices in the Py layer and locally circular stripe domains in the Co/Pd was investigated and a mutual domain imprint between the layer was observed. In dynamic excitation experiments the precession of the vortex core is studied and showed good agreement with micromagnetic simulations made by Hrkac and Bryan. As demonstrated patterned hybrid anisotropy square structures have promising magnetic properties with potential applications in data storage (vortex switching) or spintronics (vortex oscillators).
46

Étude à coeur des propriétés de matériaux innovants par la compréhension de la propagation d'une onde électromagnétique à travers une onde de choc / Interaction between shock waves and electromagnetic waves to measure in situ properties of new materials

Rougier, Benoit 09 January 2019 (has links)
La détermination des propriétés des matériaux soumis à des chocs est un enjeu essentiel dans de nombreux domaines industriels. L’objectif de cette thèse est de proposer une nouvelle méthode fondée sur l’interrogation en bande millimétrique d’un solide soumis à un choc. Deux paramètres doivent être mesurés simultanément, la vitesse du choc et la vitesse matérielle associée afin de pouvoir construire la polaire de choc du matériau d’étude. Dans un premier temps, un état de l’art des techniques de mesure existantes est réalisé pour cibler les performances et limites de l’existant. Dans un second temps, on s’intéresse à la modélisation de la propagation des ondes électromagnétiques dans des milieux à plusieurs interfaces en mouvement et avec un gradient d’indice pour représenter des cas de choc soutenu et non soutenu. Enfin, des campagnes expérimentales d’impact plan sont présentées sur différents matériaux, inertes et explosifs, pour confronter la théorie développée aux résultats de mesure. Pour le cas des chocs soutenus, les résultats sont en très bon accord et permettent de valider le modèle. Le cas des chocs non soutenus est plus complexe. Une approche par réseau de neurones est envisagée pour permettre de remonter aux vitesses et aux indices de réfraction. Enfin, des mesures de la permittivité complexe de nombreux explosifs sont présentées. / The mechanical properties of solids under shock wave loading are a key factor in many industrial applications. This work aims at defining a new approach for the simultaneous measurement of shock wave and particle velocity during a shock event, using millimeter wave interrogation. With the two determined parameters, the shock polar of any material can be derived. First, a review of the classical methods to determine these quantities is presented, to identify the advantages and limits of such techniques. A modelization work is then performed to understand the propagation of electromagnetic waves in a stratified mediumwith moving interfaces and different refractive index in each of the layers. Such a configuration can be used to describe both steady and unsteady shocks on solids. Last, experimental results of plane impact tests on both inert and reactive materials are presented and analyzed to comfort the modelization. For steady shocks, the results are in very good agreement and prove the developed model to be adequate. The case of unsteady shocks is more complex, and a neural network approach is described to solve the problem. Finally, new data on the permittivity of high explosives and a new setup are described.
47

Διερεύνηση χαρακτηριστικών ασύγχρονης μηχανής διπλού κλωβού με τη μέθοδο πεπερασμένων στοιχείων

Αθανασόπουλος, Δημήτριος 01 February 2013 (has links)
Η παρούσα διπλωματική εργασία εκπονήθηκε στο τμήμα Ηλεκτρολόγων Μηχανικών και Τεχνολογίας Υπολογιστών του Πανεπιστημίου Πατρών. Το θέμα που πραγματεύεται είναι η μελέτη των τριφασικών ασύγχρονων μηχανών διπλού κλωβού με διαφορετικά υλικά στις αυλακώσεις του δρομέα. Τα κύρια αντικείμενα που ερευνώνται είναι δύο. Το πρώτο είναι η ανάλυση και η κατανόηση της ηλεκτρομαγνητικής συμπεριφοράς κινητήρων διπλού κλωβού με διαφορετικά υλικά στις αυλακώσεις του δρομέα. Το δεύτερο είναι η μελέτη σφαλμάτων δρομέα σε μηχανές διπλού κλωβού και οι μέθοδοι διάγνωσης αυτών. / This thesis was carried out at the Department of Electrical and Computer Engineering, University of Patras. The subject matter is the study of three-phase Asynchronous Double Cage Induction Motors with Different Rotor Bar Materials (motor double cage with different materials in the slots of the rotor). The main objects that are being investigated are two. The first is the analysis and understanding of the electromagnetic behaviour of double cage motors with different materials in the slots of the rotor. The second is the study of faults in the rotor in machines dual cage and the diagnostic methods.
48

Magnetic DNA detection sensor for point-of-care diagnostics

Chaychian, Sara January 2014 (has links)
This thesis focuses on inductive base sensor design at MHz range frequency. The background theory, design, experiments and results for a new magnetic particles sensor is presented. A new magnetic sensor based on a planar coil was investigated for DNA pathogen detection. Change in inductance of the planar coil due to the presence of magnetic particles with varying mass was measured. The experimental set-up consisted of different sized planar coil with associated electronics for inductance measurements. The best sensor performance was accomplished using two different inductors while oscillating at frequencies 2.4MHz using 9.5μH inductor and 7.2MHz with 85μH inductor. The sensor has very large signal to noise ratio (580×103), while the average amount of frequency drift was 0.58. This sensor was tested with various types of magnetic particles. In addition, iron-oxide nanoparticles were synthesized through water in oil microemulsion method and with an average size of 25nm. The best sensitivity achieved for detection of 50μg iron-oxide particles was with the bead size of 10nm. 81Hz frequency shift was attained in regard to that amount of particles. This research shows that increasing the resonance frequency to 7.2MHz can cause the larger output signal difference (frequency shift) in the presence of magnetic particles; however, the sensor stability is the most important factor for determining the detection resolution and sensitivity. The sensitivity is better if the sensor can detect smaller amount of magnetic sample. The results of this research demonstrate that while the sample consists of smaller size particles, the sensor can detect the lower amount of sample. This is due to the heating effect of nanoparticles. On the other hand the sample distance from the sensor has a major impact on the sensitivity too; the shorter the distance, the higher the sensitivity. This technique can potentially be extended to detect several different types of bacterial pathogens and can be modified for multiplex quantitative detection. This sensing technique will be incorporated into a handheld, disposable microfluidic chip for point-of-care diagnostics for sexually transmitted diseases.
49

Développement de circulateurs à ferrite originaux par l’élaboration d’une démarche de conception fiable / Development of original designs of ferrite circulators based on a reliable methodology

Turki, Hamza 11 December 2018 (has links)
Les circulateurs à ferrite sont des dispositifs essentiels et indispensables dans les chaînes de communication radiofréquences. Ils assurent l’aiguillage des signaux selon leur provenance, en favorisant la propagation de l’onde EM dans une direction plutôt que dans une autre. De ce fait, ils permettent de dissocier les signaux d’émission et de réception. Ils utilisent les propriétés d’anisotropie et de non-réciprocité des matériaux ferrites lorsque ces derniers sont aimantés par un champ magnétique statique. Leur mise au point s’avère assez délicate. D’un point de vue industriel, pour répondre à un cahier des charges, sont souvent obligés aujourd’hui de partir de designs existants qu’ils font évoluer « au coup par coup » grâce au savoir-faire de quelques spécialistes. Des réglages longs, fastidieux, et coûteux sont donc nécessaires et ils ne garantissent pas toujours une solution optimum. Il est en outre souvent difficile d’imaginer de nouveaux designs. Le principal but de ces travaux de thèse est de mettre au point une méthode de conception fiable permettant de prendre en compte les phénomènes physiques mis en jeu (perméabilité tensorielle, effets magnétostatiques, modélisation numérique robuste) afin d’obtenir des dispositifs opérationnels, sans réglage et aux performances optimisées. / Biased ferrite circulators have known a great technological progress, searching for fulfill the exponential growth of many new applications. Their operation is directly linked to the anisotropic characteristic of ferrite material to create non-reciprocity phenomenon. Their design remains quite complicated in view of several limitations of their high-frequency modelization. The main goal of this thesis is to establish a complete methodology which aims to take into account all the physical features related to such a device, to offer a reliable results with optimized performances and to minimize the post-tuning step which remains problematic for the industry of circulators.
50

Διερεύνηση της επίδρασης σφηνών στα ηλεκτρομαγνητικά χαρακτηριστικά τριφασικής ασύγχρονης μηχανής

Παναγιώτου, Παναγιώτης 05 February 2015 (has links)
Στην παρούσα διπλωματική εργασία σχεδιάστηκε με χρήση του προγράμματος OPERA Electromagnetic Design ένας Ασύγχρονος Τριφασικός Κινητήρας κλωβού σε δύο διαστάσεις και μελετήθηκε η συμπεριφορά αυτού και των χαρακτηριστικών ηλεκτρομαγνητικών μεγεθών του κατά την τοποθέτηση ημιμαγνητικών σφηνών στις αυλακώσεις του στάτη. Έγινε χρήση σφηνών διαφορετικού μεγέθους και κατασκευασμένων από ημιμαγνητικά υλικά. Έτσι, προέκυψαν τρεις (3) νέοι κινητήρες που στην έκταση της παρούσας εργασίας καλούνται ΄΄μοντέλα΄΄. Στη συνέχεια, με τη χρήση αυτών των μοντέλων έγινε Ηλεκτρομαγνητική Ανάλυση με τη Μέθοδο των Πεπερασμένων Στοιχείων (FEM-Finite Element Method or FEA-Finite Element Analysis) που χρησιμοποιεί το λογισμικό OPERA. Επίσης, μελετήθηκε η επίδραση που έχει το σχήμα και το υλικό κατασκευής των σφηνών στα ηλεκτρομαγνητικά μεγέθη και τη λειτουργική συμπεριφορά του κινητήρα. Τέλος, εξετάστηκαν οι επιδράσεις που επιφέρει το κλείσιμο του ανοίγματος των αυλακώσεων –συναρτήσει, πάντα, του μεγέθους/σχήματος των σφηνών- στο ηλεκτρομαγνητικό πεδίο και στις χαρακτηριστικές του Ασύγχρονου Τριφασικού Κινητήρα. Εξετάστηκαν τόσο τα χωρικά και χρονικά μεγέθη, όσο και η συμπεριφορά αυτών στο πεδίο της συχνότητας (αρμονική ανάλυση – αρμονικό περιεχόμενο). Έγινε αξιοποίηση των γεωμετρικών και ηλεκτρικών χαρακτηριστικών ενός συγκεκριμένου τετραπολικού κινητήρα κλωβού, ισχύος 4kW, με 28 αυλακώσεις στο δρομέα και 36 αυλακώσεις στο στάτη. Ο σχεδιασμός των κινητήρων έγινε με τη συμβατική μέθοδο, ήτοι με χρήση των σχεδιαστικών εργαλείων που προσφέρονται μέσω της επιφάνειας εργασίας του προγράμματος και όχι με χρήση κώδικα. Πλεονέκτημα της μεθόδου αποτελεί το γεγονός ότι για τους τρεις κινητήρες που προέκυψαν με την τοποθέτηση των διαφόρων σφηνών δεν απαιτήθηκε εκ νέου σχεδιασμός, αλλά προσαρμογή της εκάστοτε χρησιμοποιηθείσας σφήνας στο αρχικό μοντέλο κινητήρα. Κατά τη μελέτη όλων των μοντέλων λάβαμε υπόψιν τόσο τη γραμμική όσο και τη μη γραμμική Β-Η χαρακτηριστική του σιδηρομαγνητικού υλικού. Η ανάλυση οδήγησε στο συμπέρασμα ότι με τη χρήση των κατάλληλων σφηνών μπορούμε να επιτύχουμε εξομάλυνση των κυματομορφών του ρεύματος και της ηλεκτρομαγνητικής ροπής και μείωση των ανώτερων αρμονικών. Όλα αυτά οδηγούν σε βελτίωση του βαθμού απόδοσης του κινητήρα. / The influence of semi-magnetic wedges on the electromagnetic variables and the harmonic content in 3-phase squirrel cage induction motors.

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