<p align="justify">Many different active control techniques can be used to control the vibrations of a mechanical structure: they however require at least a sensitive signal amplifier (for the sensor), a power amplifier (for the actuator) and an analog or digital filter (for the controller). The use of all these electronic devices may be impractical in many applications and has motivated the use of the so-called shunt circuits, in which an electrical circuit is directly connected to a transducer embedded in the structure. The transducer acts as an energy converter: it transforms mechanical (vibrational) energy into electrical energy, which is in turn dissipated in the shunt circuit. No separate sensor is required, and only one, generally simple electronic circuit is used. The stability of the shunted structure is guaranteed if the electric circuit is passive, i.e., if it is made of passive components such as resistors and inductors.</p> <p align="justify">This thesis compares the performances of the electric shunt circuits with those of classical active control systems. It successively considers the use of piezoelectric transducers and that of electromagnetic (moving-coil) transducers.</p> <p align="justify">In a first part, the different damping techniques are applied on a benchmark truss structure equipped with a piezoelectric stack transducer. A unified formulation is found and experimentally verified for an active control law, the Integral Force Feedback (IFF), and for various passive shunt circuits (resistive and resistive-inductive). The use of an active shunt, namely the negative capacitance, is also investigated in detail. Two different implementations are discussed: they are shown to have very different stability limits and performances.</p> <p align="justify">In a second part, vibration isolation with electromagnetic (moving-coil) transducers is introduced. The effects of an inductive-resistive shunt circuit are studied in detail; an equivalent mechanical representation is found. The performances are compared with that of resonant shunts and with that of active isolation with IFF. Next, the construction of a six-axis isolator based on a Stewart Platform is presented: the key parameters and the main limitations of the system are highlighted.</p>

Este trabalho apresenta uma metodologia de projeto de atuadores eletromagnéticos lineares inovadora para aplicação em sistemas de suspensão semiativa e ativa. A metodologia, apresentada na forma de fluxograma, define critérios para determinar os requisitos de força e curso que um atuador deve desenvolver considerando um sistema mecânico vibratório com um grau de liberdade com excitação harmônica de base quando o método de controle skyhook é aplicado. Um atuador eletromagnético linear de bobina móvel com duplo arranjo de quase-Halbach que apresenta elevada densidade de força, reduzida massa móvel, ausência de força de relutância e baixa ondulação de força é definido como estudo de caso. Um modelo numérico parametrizado em elementos finitos do comportamento eletromagnético de um passo polar do dispositivo é criado e analisado, considerando restrições dimensionais, com os objetivos de projeto definidos como: elevada densidade de força e reduzida ondulação de força com acionamento brushless CA. Com base no modelo de um passo polar do dispositivo, define-se o volume ativo que o mesmo deve apresentar e, a partir deste, todas as dimensões são definidas de forma a atender os requisitos de projeto. Uma vez definidas as dimensões do atuador com base no modelo eletromagnético, realiza-se a modelagem térmica numérica que permite avaliar qual a máxima densidade de corrente elétrica aplicável de forma que a temperatura, estipulada como máxima, nos enrolamentos não seja excedida. Ainda, a distribuição térmica permite determinar a temperatura de operação dos ímãs permanentes que têm curva de operação dependente da temperatura. A partir dos resultados da simulação térmica e do modelo eletromagnético para um passo polar, realizou-se o acoplamento eletromagnético-térmico por meio da correção das propriedades dos ímãs permanentes e aplicando uma densidade de corrente eficaz dependente das dimensões do modelo parametrizado. O modelo acoplado é simulado e analisado, de modo que as dimensões finais do atuador podem ser obtidas atendendo aos mesmos objetivos de projeto previamente mencionados, respeitando os limites de operação térmica. Adicionalmente, são apresentados modelos analíticos do comportamento eletromagnético e térmico do atuador que podem servir de base para implementação da metodologia proposta, se esta for baseada em modelos analíticos, e podem futuramente ser empregados para a aplicação de otimização matemática do dispositivo. Por fim, um protótipo do dispositivo é construído de forma a validar a metodologia proposta. Com este protótipo são realizados ensaios de densidade de fluxo magnético no entreferro, tensão induzida a vazio, força estática e ensaio dinâmicos com o dispositivo instalado em uma bancada de testes de vibrações controladas desenvolvida durante o projeto. Os resultados mostram a eficácia da metodologia proposta, uma vez que os resultados experimentais mostraram boa concordância com os resultados esperados. / This work presents an innovative linear electromagnetic actuator design methodology for application in semi-active and active suspension systems. The methodology, synthesized in a flowchart, sets criteria to determine requirements such as axial force and stroke that an actuator should develop considering a vibration system with one degree of freedom with harmonic base excitation when the skyhook control method is applied. A linear moving-coil electromagnetic actuator with dual quasi-Halbach arrays of permanent magnets that presents high force density, low moving-mass, no reluctance force and low force ripple is defined as a case study. A finite element numerical parameterized model that describes the electromagnetic behavior of one pole pitch of the device is created and analyzed, considering dimensional constraints, with the design objectives defined as: high force density and low ripple of force with brushless AC drive. Based on the model of one pole pitch of the device the active volume and all dimensions are defined in order to meet the design requirements. Once the actuator dimensions are defined, based on the electromagnetic model, a numerical thermal model was constructed, which allows to evaluate the maximum applicable electric current density so that the maximum temperature at the windings is not exceeded. Furthermore, the thermal distribution gives the operating temperature of the permanent magnets, which present performance highly dependent on temperature. With the results of the thermal simulation, the electromagnetic-thermal coupling is performed by correcting permanent magnet properties and by applying a parametric-dependent effective current density. The coupled model is simulated and analyzed so that the final dimensions of the actuator can be obtained with the same design objectives previously mentioned, while respecting thermal operating limits. In addition, the work presents analytical models of the electromagnetic and thermal behavior of the actuator that can be the basis for implementation of the proposed methodology, if it is based on analytical models, and can further be used for the application of mathematical optimization of the device. Finally, a prototype was built to validate the proposed method. Measurements were carried out to assess magnetic flux density in the air gap, open-circuit induced voltage, static force and dynamic tests with the device installed in a test bench that was developed during this work. The results show the effectiveness of the proposed method since experimental results have shown good agreement with the expected results.

Este trabalho apresenta uma metodologia de projeto de atuadores eletromagnéticos lineares inovadora para aplicação em sistemas de suspensão semiativa e ativa. A metodologia, apresentada na forma de fluxograma, define critérios para determinar os requisitos de força e curso que um atuador deve desenvolver considerando um sistema mecânico vibratório com um grau de liberdade com excitação harmônica de base quando o método de controle skyhook é aplicado. Um atuador eletromagnético linear de bobina móvel com duplo arranjo de quase-Halbach que apresenta elevada densidade de força, reduzida massa móvel, ausência de força de relutância e baixa ondulação de força é definido como estudo de caso. Um modelo numérico parametrizado em elementos finitos do comportamento eletromagnético de um passo polar do dispositivo é criado e analisado, considerando restrições dimensionais, com os objetivos de projeto definidos como: elevada densidade de força e reduzida ondulação de força com acionamento brushless CA. Com base no modelo de um passo polar do dispositivo, define-se o volume ativo que o mesmo deve apresentar e, a partir deste, todas as dimensões são definidas de forma a atender os requisitos de projeto. Uma vez definidas as dimensões do atuador com base no modelo eletromagnético, realiza-se a modelagem térmica numérica que permite avaliar qual a máxima densidade de corrente elétrica aplicável de forma que a temperatura, estipulada como máxima, nos enrolamentos não seja excedida. Ainda, a distribuição térmica permite determinar a temperatura de operação dos ímãs permanentes que têm curva de operação dependente da temperatura. A partir dos resultados da simulação térmica e do modelo eletromagnético para um passo polar, realizou-se o acoplamento eletromagnético-térmico por meio da correção das propriedades dos ímãs permanentes e aplicando uma densidade de corrente eficaz dependente das dimensões do modelo parametrizado. O modelo acoplado é simulado e analisado, de modo que as dimensões finais do atuador podem ser obtidas atendendo aos mesmos objetivos de projeto previamente mencionados, respeitando os limites de operação térmica. Adicionalmente, são apresentados modelos analíticos do comportamento eletromagnético e térmico do atuador que podem servir de base para implementação da metodologia proposta, se esta for baseada em modelos analíticos, e podem futuramente ser empregados para a aplicação de otimização matemática do dispositivo. Por fim, um protótipo do dispositivo é construído de forma a validar a metodologia proposta. Com este protótipo são realizados ensaios de densidade de fluxo magnético no entreferro, tensão induzida a vazio, força estática e ensaio dinâmicos com o dispositivo instalado em uma bancada de testes de vibrações controladas desenvolvida durante o projeto. Os resultados mostram a eficácia da metodologia proposta, uma vez que os resultados experimentais mostraram boa concordância com os resultados esperados. / This work presents an innovative linear electromagnetic actuator design methodology for application in semi-active and active suspension systems. The methodology, synthesized in a flowchart, sets criteria to determine requirements such as axial force and stroke that an actuator should develop considering a vibration system with one degree of freedom with harmonic base excitation when the skyhook control method is applied. A linear moving-coil electromagnetic actuator with dual quasi-Halbach arrays of permanent magnets that presents high force density, low moving-mass, no reluctance force and low force ripple is defined as a case study. A finite element numerical parameterized model that describes the electromagnetic behavior of one pole pitch of the device is created and analyzed, considering dimensional constraints, with the design objectives defined as: high force density and low ripple of force with brushless AC drive. Based on the model of one pole pitch of the device the active volume and all dimensions are defined in order to meet the design requirements. Once the actuator dimensions are defined, based on the electromagnetic model, a numerical thermal model was constructed, which allows to evaluate the maximum applicable electric current density so that the maximum temperature at the windings is not exceeded. Furthermore, the thermal distribution gives the operating temperature of the permanent magnets, which present performance highly dependent on temperature. With the results of the thermal simulation, the electromagnetic-thermal coupling is performed by correcting permanent magnet properties and by applying a parametric-dependent effective current density. The coupled model is simulated and analyzed so that the final dimensions of the actuator can be obtained with the same design objectives previously mentioned, while respecting thermal operating limits. In addition, the work presents analytical models of the electromagnetic and thermal behavior of the actuator that can be the basis for implementation of the proposed methodology, if it is based on analytical models, and can further be used for the application of mathematical optimization of the device. Finally, a prototype was built to validate the proposed method. Measurements were carried out to assess magnetic flux density in the air gap, open-circuit induced voltage, static force and dynamic tests with the device installed in a test bench that was developed during this work. The results show the effectiveness of the proposed method since experimental results have shown good agreement with the expected results.

Este trabalho apresenta uma metodologia de projeto de atuadores eletromagnéticos lineares inovadora para aplicação em sistemas de suspensão semiativa e ativa. A metodologia, apresentada na forma de fluxograma, define critérios para determinar os requisitos de força e curso que um atuador deve desenvolver considerando um sistema mecânico vibratório com um grau de liberdade com excitação harmônica de base quando o método de controle skyhook é aplicado. Um atuador eletromagnético linear de bobina móvel com duplo arranjo de quase-Halbach que apresenta elevada densidade de força, reduzida massa móvel, ausência de força de relutância e baixa ondulação de força é definido como estudo de caso. Um modelo numérico parametrizado em elementos finitos do comportamento eletromagnético de um passo polar do dispositivo é criado e analisado, considerando restrições dimensionais, com os objetivos de projeto definidos como: elevada densidade de força e reduzida ondulação de força com acionamento brushless CA. Com base no modelo de um passo polar do dispositivo, define-se o volume ativo que o mesmo deve apresentar e, a partir deste, todas as dimensões são definidas de forma a atender os requisitos de projeto. Uma vez definidas as dimensões do atuador com base no modelo eletromagnético, realiza-se a modelagem térmica numérica que permite avaliar qual a máxima densidade de corrente elétrica aplicável de forma que a temperatura, estipulada como máxima, nos enrolamentos não seja excedida. Ainda, a distribuição térmica permite determinar a temperatura de operação dos ímãs permanentes que têm curva de operação dependente da temperatura. A partir dos resultados da simulação térmica e do modelo eletromagnético para um passo polar, realizou-se o acoplamento eletromagnético-térmico por meio da correção das propriedades dos ímãs permanentes e aplicando uma densidade de corrente eficaz dependente das dimensões do modelo parametrizado. O modelo acoplado é simulado e analisado, de modo que as dimensões finais do atuador podem ser obtidas atendendo aos mesmos objetivos de projeto previamente mencionados, respeitando os limites de operação térmica. Adicionalmente, são apresentados modelos analíticos do comportamento eletromagnético e térmico do atuador que podem servir de base para implementação da metodologia proposta, se esta for baseada em modelos analíticos, e podem futuramente ser empregados para a aplicação de otimização matemática do dispositivo. Por fim, um protótipo do dispositivo é construído de forma a validar a metodologia proposta. Com este protótipo são realizados ensaios de densidade de fluxo magnético no entreferro, tensão induzida a vazio, força estática e ensaio dinâmicos com o dispositivo instalado em uma bancada de testes de vibrações controladas desenvolvida durante o projeto. Os resultados mostram a eficácia da metodologia proposta, uma vez que os resultados experimentais mostraram boa concordância com os resultados esperados. / This work presents an innovative linear electromagnetic actuator design methodology for application in semi-active and active suspension systems. The methodology, synthesized in a flowchart, sets criteria to determine requirements such as axial force and stroke that an actuator should develop considering a vibration system with one degree of freedom with harmonic base excitation when the skyhook control method is applied. A linear moving-coil electromagnetic actuator with dual quasi-Halbach arrays of permanent magnets that presents high force density, low moving-mass, no reluctance force and low force ripple is defined as a case study. A finite element numerical parameterized model that describes the electromagnetic behavior of one pole pitch of the device is created and analyzed, considering dimensional constraints, with the design objectives defined as: high force density and low ripple of force with brushless AC drive. Based on the model of one pole pitch of the device the active volume and all dimensions are defined in order to meet the design requirements. Once the actuator dimensions are defined, based on the electromagnetic model, a numerical thermal model was constructed, which allows to evaluate the maximum applicable electric current density so that the maximum temperature at the windings is not exceeded. Furthermore, the thermal distribution gives the operating temperature of the permanent magnets, which present performance highly dependent on temperature. With the results of the thermal simulation, the electromagnetic-thermal coupling is performed by correcting permanent magnet properties and by applying a parametric-dependent effective current density. The coupled model is simulated and analyzed so that the final dimensions of the actuator can be obtained with the same design objectives previously mentioned, while respecting thermal operating limits. In addition, the work presents analytical models of the electromagnetic and thermal behavior of the actuator that can be the basis for implementation of the proposed methodology, if it is based on analytical models, and can further be used for the application of mathematical optimization of the device. Finally, a prototype was built to validate the proposed method. Measurements were carried out to assess magnetic flux density in the air gap, open-circuit induced voltage, static force and dynamic tests with the device installed in a test bench that was developed during this work. The results show the effectiveness of the proposed method since experimental results have shown good agreement with the expected results.

<p align="justify">Many different active control techniques can be used to control the vibrations of a mechanical structure: they however require at least a sensitive signal amplifier (for the sensor), a power amplifier (for the actuator) and an analog or digital filter (for the controller). The use of all these electronic devices may be impractical in many applications and has motivated the use of the so-called shunt circuits, in which an electrical circuit is directly connected to a transducer embedded in the structure. The transducer acts as an energy converter: it transforms mechanical (vibrational) energy into electrical energy, which is in turn dissipated in the shunt circuit. No separate sensor is required, and only one, generally simple electronic circuit is used. The stability of the shunted structure is guaranteed if the electric circuit is passive, i.e. if it is made of passive components such as resistors and inductors.</p><p><p><p align="justify">This thesis compares the performances of the electric shunt circuits with those of classical active control systems. It successively considers the use of piezoelectric transducers and that of electromagnetic (moving-coil) transducers.</p><p><p><p align="justify">In a first part, the different damping techniques are applied on a benchmark truss structure equipped with a piezoelectric stack transducer. A unified formulation is found and experimentally verified for an active control law, the Integral Force Feedback (IFF), and for various passive shunt circuits (resistive and resistive-inductive). The use of an active shunt, namely the negative capacitance, is also investigated in detail. Two different implementations are discussed: they are shown to have very different stability limits and performances.</p><p><p><p align="justify">In a second part, vibration isolation with electromagnetic (moving-coil) transducers is introduced. The effects of an inductive-resistive shunt circuit are studied in detail; an equivalent mechanical representation is found. The performances are compared with that of resonant shunts and with that of active isolation with IFF. Next, the construction of a six-axis isolator based on a Stewart Platform is presented: the key parameters and the main limitations of the system are highlighted.</p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Η παρούσα διδακτορική διατριβή εστιάστηκε στη μελέτη συστημάτων ακουστικής εκπομπής για απευθείας αναπαραγωγή ψηφιακού ήχου. Η ερευνητική διαδικασία βασίστηκε στον προσδιορισμό και βελτίωση των δυνατοτήτων δύο διαφορετικών υλοποιήσεων ακουστικής μετατροπής: i. Ένα υβριδικό πρωτότυπο θερμοακουστικό στοιχείο και ii. Μια συστοιχία 32 ηλεκτροδυναμικών μεγαφώνων σχεδιασμένη, ώστε να αναπαράγει ψηφιακά ηχητικά σήματα. Η θερμοακουστική μετατροπή προσφέρει μια εναλλακτική τεχνική για υλοποιήσεις ακουστικών στοιχείων. Είναι βασισμένη στο μετασχηματισμό των διακυμάνσεων της θερμικής ενέργειας σε ακουστικό κύμα που προκαλούνται από τη ροή του ηλεκτρικού σήματος ήχου σε μια συσκευή στερεάς κατάστασης που λειτουργεί χωρίς τη χρήση οποιουδήποτε κινούμενου τμήματος ή μηχανισμού. Η υλοποίηση αυτής της τεχνικής ηχητικής αναπαραγωγής, μελετάται με τη χρήση ενός πρωτότυπου μετατροπέα ο οποίος αναπτύχθηκε πάνω σε πλακέτα κρυσταλλικού πυριτίου (silicon wafer). H απόδοση της συσκευής αυτής βελτιώνεται ιδίως όσον αφορά στις μη γραμμικές παραμορφώσεις που προσθέτει ο φυσικός μηχανισμός κατά την αναπαραγωγή των ακουστών συχνοτήτων. Για τις ανάγκες της ερευνητικής μελέτης κατασκευάσθηκε εξειδικευμένο στάδιο οδήγησης, ενώ επίσης αναπτύχθηκαν εργαλεία που προσομοιώνουν την απόδοση αυτών των συσκευών. Οι ψηφιακές συστοιχίες μεγαφώνων (DLAs) σήμερα βασίζονται σε μικρούς μετατροπείς κινούμενου πηνίου για την ανακατασκευή ακουστικών σημάτων από ροές ψηφιακού ήχου. Τα σημαντικά ζητήματα απόδοσης για τα συστήματα αυτά αναλύονται από την παρούσα διατριβή, με στόχο να ερμηνευθεί η απόκριση συχνότητας και οι ρυθμοί των διακριτών (on/off) μεταβάσεων των μεγαφώνων, εξαιτίας των ψηφιακών σημάτων. Λεπτομερείς προσομοιώσεις που επιτρέπουν την πραγματοποίηση συγκρίσεων για μια πανομοιότυπη συστοιχία 32 μετατροπέων η οποία τροφοδοτείται από αναλογικά σήματα, σε παρόμοια τοποθέτηση και ενεργοποίηση των στοιχείων. Οι μελέτες αυτές παράγουν πρωτότυπα αποτελέσματα για τις απαιτήσεις σε ηλεκτρική ενέργεια και την ευαισθησία της συστοιχίας, καταλήγοντας στο συμπέρασμα ότι αυτά τα δύο συστήματα επιτυγχάνουν συγκρίσιμες επιδόσεις. / The present Phd Thesis is focused on the study of acoustic transduction systems for direct digital audio signal emission. The research process was based on the evaluation and optimization of the behavior of two different implementations: i. A novel hybrid thermoacoustic device and ii. A loudspeaker array consisting of 32 moving coil speakers designed for digital audio reproduction. Thermoacoustic transduction offers an alternative technique for transducer implementations, based on the transformation of thermal energy fluctuations into sound after the direct application of the electrical audio signal on a solid state device which operates without the use of any moving/mechanical components. Here, an implementation of this sound generation technique is studied based on a prototype developed on silicon wafer and its performance is optimised, especially with respect to non-linear distortions within the audio band. For the purposes of the research study a specialised driving circuit was constructed and also the appropriate tools were developed to simulate the performance of these devices. Digital loudspeaker arrays currently are based on small moving-coil speakers to reconstruct acoustic signals out of binary audio streams. An overview of significant performance issues for such systems is given here to explain frequency response and speaker discrete transition rates due to the digital data. Detailed simulations provided comparisons for a 32-speaker DLA with similar arrangements of speakers driven by analogue signals. These tests produce novel results for electrical power requirements and array sensitivity, concluding that these two systems achieve comparable performance.