Dissertations / Theses on the topic 'DRR and near-field control'

2010/2011
The material presented in this thesis is the result of the Ph.D. activity carried on between January 2009 and December 2012 at the Ph.D. school in Information Engineering of the University of Trieste. After a brief introduction on the involved topics, the final objective of this thesis is that of presenting the original results, consisting in the development of power pattern synthesis algorithms for arbitrary antenna arrays including, in particular, arrays for satellite applications. Since the earlier satellite missions of last century, satellite communication systems have received growing attention due to the opportunities they offer and their greater flexibility with respect to alternative solutions adopting other media, such as, for example, fiber optic cables. The enormous spread of satellites, for both military and civilian applications, has been achieved thanks to the experienced technological progress, which has allowed an increase of satellite capacities. The need of constantly increasing the capacity of commercial communications satellites resulted in the continuing evolution of the antenna systems onboard the satellites. The business environment has driven the architecture of satellites' systems towards more efficiency and cost consciousness while at the same time, providing flexible access to a growing diversity of services and customers. Antennas that provide a multiplicity of frequency reuse coverage beams through either spatial or polarization isolation have been developed, resulting in the evolution of satellite antennas from a simple omnidirectional dipole to multiple-beam, dual-polarized configurations with frequency reuse between the beams for increased capacity. These requirements translate into high-gain, high-efficiency antennas with low side-lobe levels and excellent polarization purity. Moreover, since new requirements are often determined after the satellite is operational, antennas adjustable to produce a wide variety of radiation patterns have become popular. These are the so-called multiple-beam antennas, which can adjust their radiation coverage areas according to new demands. Multiple-beam antennas are currently being used for direct-broadcast satellites, personal communication satellites, military communication satellites, and high-speed Internet applications. High-gain multiple-beam antenna systems usually take one of three generic forms: lens, reflector or direct radiating array. Thus, arrays of antennas can be used in multiple-beam systems either to feed other types of antennas, or directly as radiating structures. The material of this thesis is mainly related to the synthesis algorithms for antenna arrays. In particular, many analytical and numerical techniques for the power pattern synthesis of antenna arrays have been carefully studied and analyzed. Some of them are suitable only for linear or rectangular arrays, the others for arrays of more complicated geometries. Furthermore, it is extremely important, for power synthesis techniques in satellite applications, to be able to consider additional constraints. These typically are the phase-only reconfigurability of the radiated beams, the control of the cross-polar patterns, which allows the polarization re-use and/or the control of the cross-polar interference, the dynamic range ratio reduction which comports simpler feeding networks and lower mutual coupling between array elements, and the near-field reduction, which allows to take into account the antennas operating environment. A numerical iterative algorithm has been developed during the Ph.D. school in Information Engineering, suitable for arrays of arbitrary geometry, thus including sparse and conformal arrays, which are often used in satellite applications. The algorithm allows to solve the power pattern synthesis problem, which is an inherently non linear problem. The solution is achieved using the alternating projections algorithm, which is a numerical iterative technique for finding a point of the intersection between two sets. It will be seen that the projections method has previously already been applied to problems of image processing and also in the antenna pattern synthesis. However, the results and the computational burden are strongly related to the projection operators, which in turn, strictly depend on the definition of the adopted distance, thus on the definition of the sets adopted in the formulation of the problem. Thus, the main originality of the developed algorithms consists in an extremely advantageous definition of the sets involved in the solving scheme, which, along with the adopted distance, allow an easy evaluation of the projection operators and thus a simple solving procedure. The thesis is organized as follows. Chapter 1 introduces the satellite antennas, analyzing some solutions adopted in the past. Particular attention is devoted to multiple-beam antennas (MBAs) and in particular to arrays of antennas, which can constitute the feeding system of reflector MBAs, or which can be used as direct radiating antennas themselves. Chapter 2 presents analytical and numerical methods of power pattern synthesis for antenna arrays proposed in the literature. First, the classical analytical methods, suitable for linear arrays of equally spaced elements are presented. Then, numerical iterative methods are analyzed. Attention is devoted to both deterministic and stochastic algorithms. A section is dedicated to the near-field constraint, due to its importance in practical real applications. In fact, taking into account the effect of the antenna operating environment is of fundamental importance: obstacles or mounting platforms, as well as other electronic devices located in proximity of the antenna, may strongly degrade the radiated far-field pattern. Then, Chapter 3 presents the developed algorithm. Precisely, the evolution is described from a synthesis algorithm suitable for arbitrary phase-only reconfigurable arrays to a powerful algorithm for phase-only antenna arrays, including several additional constraints, such as the dynamic range ratio reduction, the cross-polar pattern synthesis and the near-field reduction. Moreover, in its final form, the algorithm also allows to minimize the power radiated in the side-lobe regions of both the co- and cross-polar patterns and the electric energy stored in the near-field region of interest. Numerical results validating the effectiveness of the proposed algorithm are presented in Chapter 4 and the conclusions are summarized in Chapter 5. Finally, the appendix mathematically describes the classical alternating projections method and the genetic algorithms, which have been used as global optimization algorithms for comparison purposes.
Il materiale presentato in questa tesi è il risultato dell'attività svolta durante il dottorato tra gennaio 2009 e dicembre 2012 presso la scuola di dottorato in ingegneria dell'informazione dell'università di Trieste. Dopo una breve introduzione sugli argomenti trattati, l'obiettivo ultimo della tesi è quello di presentare i risultati originali che consistono nello sviluppo di algoritmi di sintesi di potenza per antenne a schiera di geometria arbitraria tra le quali, in particolare, schiere per applicazioni satellitari. Fin dalle prime missioni spaziali del secolo scorso, le comunicazioni satellitari hanno ricevuto attenzione crescente grazie alle opportunità che offrono e alla loro maggior flessibilità rispetto a soluzioni alternative che utilizzano altri sistemi, come ad esempio i cavi in fibra ottica. Grazie agli sviluppi tecnologici avvenuti, che hanno reso possibile un aumento delle capacità dei satelliti, si è sperimentata una vasta diffusione di satelliti per applicazioni militari e civili. La necessità di aumentare costantemente la capacità dei satelliti per comunicazioni commerciali ha comportato una continua evoluzione delle antenne da satellite. L'ambiente commerciale ha spinto l'architettura dei sistemi satellitari verso una miglior consapevolezza di efficienza e costi consentendo, allo stesso tempo, un accesso flessibile a un sempre maggior numero di servizi e di utenti. Sono state sviluppate antenne che consentono una molteplicità di fasci con riutilizzo della frequenza grazie ad isolamento spaziale o di polarizzazione. Questo ha generato un'evoluzione delle antenne da satellite dal semplice dipolo omnidirezionale ad antenne a fascio multiplo, con alto guadagno, alta efficienza, bassi lobi laterali ed elevata purezza di polarizzazione. Inoltre, poichè nuove necessità spesso emergono una volta che il satellite è già operativo, si sono diffuse antenne da satellite configurabili in modo da poter produrre diversi diagrammi di radiazione. Queste sono le così dette antenne riconfigurabili, che possono modificare le regioni coperte in base a nuove necessità. Antenne a fascio multiplo vengono usate correntemente in trasmissioni dirette via satellite, satelliti per comunicazioni personali, satelliti per comunicazioni militari e applicazioni Internet ad alta velocità. I sistemi di antenne a fascio multiplo ad elevato guadagno generalmente sono di uno dei seguenti tre tipi: lenti, riflettori o antenne a schiera. Dunque le antenne a schiera si possono trovare nelle applicazioni satellitari sia come strutture per alimentare altri tipi di antenne, sia come strutture radianti direttamente. Il materiale presentato in questa tesi è principalmente legato agli algoritmi di sintesi per antenne a schiera. In particolare, sono stati attentamente studiati e analizzati diversi metodi, analitici e numerici, per la sintesi di potenza di antenne a schiera. Alcuni di questi sono applicabili solo a schiere lineari o rettangolari, altri a schiere di geometria più complicata. Inoltre, è estremamente importante per gli algoritmi di sintesi di potenza di schiere per applicazioni satellitari essere in grado di considerare vincoli addizionali. Questi tipicamente sono la riconfigurabilità del fascio tramite controllo di sola fase, il controllo del diagramma cross-polare, che permette di ottenere il riutilizzo di polarizzazione e/o di controllare l'interferenza cross-polare, la riduzione della dinamica, che permette l'utilizzo di reti di alimentazione più semplici e un abbassamento del mutuo accoppiamento tra gli elementi della schiera, e la riduzione del campo vicino, che permette di tener conto dell'ambiente in cui opera l'antenna. Durante il dottorato è stato sviluppato un algoritmo numerico iterativo per schiere di geometria arbitraria, perciò comprese le schiere sparse e conformi, spesso impiegate in applicazioni satellitari. L'algoritmo permette di risolvere il problema (intrinsicamente non lineare) di sintesi di potenza. La soluzione è ottenuta mediante l'impiego del metodo delle proiezioni succesive, un metodo numerico iterativo per trovare un punto nell'intersezione tra due insiemi. Tale metodo è stato usato in passato in problemi di elaborazione delle immagini e anche in problemi di sintesi di antenne a schiera. Ciononostante, i risultati e il carico computazionale sono direttamente legati ai proiettori, che a loro volta sono strettamente dipendenti dalla definizione della distanza adottata, dunque degli insiemi coinvolti nel problema. Perciò, la principale originalità degli algoritmi sviluppati consiste in una definizione degli insiemi estremamente vantaggiosa in quanto, assieme alla scelta della distanza, permette di valutare facilmente i proiettori e perciò permette di ottenere una procedura di soluzione semplice. La tesi è organizzata come segue. Il primo capitolo introduce le antenne da satellite analizzando alcune soluzioni utilizzate in passato. Particolare attenzione è rivolta alle antenne a fascio multiplo e in particolare alle antenne a schiera, che possono costituire il sitema di alimentazione di antenne a riflettore multifascio o che possono esse stesse essere usate come elementi radianti. Il secondo capitolo presenta metodi analitici e numerici per la sintesi di potenza per antenne a schiera proposti in letteratura. Dapprima vengono presentati i metodi analitici classici, validi per schiere lineari di elementi equispaziati. Successivamente vengono analizzati i metodi numerici iterativi, sia stocastici, sia deterministici. Una sezione a parte è dedicata al vincolo sul campo vicino, vista la grande importanza che riveste nelle applicazioni pratiche. Infatti è di fondamentale importanza tener conto degli effetti dell'ambiente in cui l'antenna opera in quanto ostacoli o strutture di montaggio, così come altri apparati elettronici in prossimità dell'antenna, possono causare forti interferenze e degradare notevolmente il diagramma di campo lontano. Il capitolo 3 presenta gli algoritmi sviluppati. Precisamente, viene delineata l'evoluzione da un algoritmo di sintesi di potenza per schiere riconfigurabili di geometria arbitraria con controllo si sola fase, a un potente algoritmo di sintesi di sola fase con diversi vincoli addizionali, quali la riduzione della dinamica, la sintesi del fascio cross-polare e la riduzione del campo vicino. Inoltre, nella sua forma finale, l'algoritmo permette di minimizzare la potenza irradiata nelle regioni di lobi laterali di entrambi i diagrammi, co- e cross- polare, e l'energia immagazzinata nella regione di campo vicino presa in considerazione. I risultati numerici che provano l'efficacia del metodo sono presentati nel capitolo 4 e le conclusioni sono riassunte nel capitolo 5. Infine, l'appendice descrive matematicamente il classico metodo delle proiezioni successive e gli algoritmi genetici, che sono stati scelti come termine di paragone tra gli algoritmi di ottimizzazione globale.
XXIV Ciclo
1983

The Near field properties of a 6" radius model propeller, and the Active Noise Control(ANC) of the Blade Passing Tone (BPT) have been studied. The study has been careful toidentify and separate the effects of the hydrodynamic near field and the geometric near field. The near and far field radiation regions of a model propeller were consideredseparately. Firstly to determine if far field control affects the near field noise levels and secondly to determine how the far field noise levels are affected by near field control. It has been found that active noise control (ANC) of the propeller blade passing tone (BPT)can be achieved within the geometric near field, however the extent of the effective control is small. The near field optimized ANC can result in as much as 10.5 dB ofreduction of the BPT, however this noise reduction can only be achieved over a small spatial region. For this experimental arrangement there is no effective ANC directlybehind the propeller. Whenever ANC is optimized for near field noise it results in far field noise levels of up to 15.2 dB above the uncontrolled far field propeller levels. The far field optimized control shows no detrimental effects in the near field noise environment.

Photonic antennas are metallic (or dielectric) nanoscale structures that convert propagating light into highly confined fields, and vice versa, in analogy to common radio antennas but on nanometric scales that lead to interaction with light. As such, they can enhance and confine electric fields at the nanoscale. These properties can be exploited in applications that require high signal-to-background ratios and sub-diffraction illumination volumes, such as for super-resolution microscopy or in bio-sensing at high physiological concentrations. Furthermore, when in close proximity to single emitters, photonic antennas can affect their emission properties. This latter property allows for improving fluorophore characteristics, such as reduced photobleaching or increased quantum yield. Although there are already numerous studies on these effects and their possible applications, some of the properties of photonic antennas are still not fully understood or exploited. Moreover, the degree by which optical antennas influence fluorescence properties depends crucially on the near-field interaction between the emitter and the antenna. This requires ultimate control of their relative position and orientation which has been challenging to achieve in most experimental configurations. This Thesis aims to study interactions between antennas and emitters in contexts that have not been deeply studied yet, and to use them for applications where they allow us to observe molecular mechanisms that are not accessible with conventional diffraction-limited optical methods. The research has revolved around fabrication and the application of photonic antennas engineered at the apex of tapered optical fibres and manipulated using a near-field scanning optical microscope. Such an approach guarantees full control of the antenna position with respect to the sample with nanometric precision. We developed and characterized new antenna designs with different optical properties tuned for the specific application of interest. For example, most antenna designs are aimed to enhance the electric field, ignoring the magnetic contribution of the total field. In this Thesis, we use dielectric antennas to enhance the emission from magnetic dipoles. This opens new fields of application of nanoantennas, such as increased sensitivity in chiral spectroscopy. Furthermore, extending the study of photonic antennas and their interaction with multiple emitters commands for new antenna designs that are broadband and thus have the ability of influencing fluorophores with different spectral properties. Most commonly used antennas are resonant in a narrow region of the visible spectrum, so that their applications are restricted to single-colour imaging and/or biosensing. Here, we design antennas to be broadband in the visible spectrum. This is interesting from both fundamental and applied points of view. On the one hand, we used broadband antennas in the context of Förster Resonance Energy Transfer (FRET) to manipulate the interaction between a single donor and a single acceptor emitter on the nanoscale. On the other hand, the fluorescent enhancement for multiple wavelengths opens up the possibility of performing multicolour super-resolution imaging or detecting the interactions between differently labelled species on a living cell. In this Thesis, we combine these broadband antennas with high temporal resolution methods such as Fluorescence Correlation Spectroscopy (FCS) or Fluorescence Cross-Correlation Spectroscopy (FCCS) to investigate the diffusion and interaction of multiple species on the membrane of living cells with both sub millisecond temporal and nanometric spatial resolution. The dissertation finishes with a brief discussion of the main results achieved in this research and proposes new avenues for future research in the field.
Las antenas fotónicas son estructuras nanométricas metálicas (o dieléctricas) que convierten luz que se propaga en campos muy confinados, y vice versa,en analogía con las antenas de radio comunes pero en escalas nanométricas que permiten su interacción con la luz. Como tales, pueden aumentar y confinar campos eléctricos en la nanoescala. Estas propiedades se pueden explotar en aplicaciones que requieren altos niveles de señal sobre el fondo o volúmenes de iluminación por debajo del límite de difracción, como en el caso de la microscopía de superresolution o de la detección de compuestos biológicos a altas concentraciones. Cuando están cerca de emisores individuales, las antenas fotónicas pueden también afectar sus propiedades de emisión. Esto permite mejorar las características de los fluoróforos, reduciendo su 'photobleaching' o incrementando su eficiencia cuántica. Aunque hay numerosos estudios sobre estos efectos y sus posibles aplicaciones, algunas propiedades de las nanoantenas todavía no se comprenden totalmente o no han sido explotadas. Además, el grado en el que las nanoantenas afectan las propiedades de los fluoróforos depende fuertemente de la interacción de campo cercano entre el emisor y la antena. Esto requiere un control muy preciso de su posición y orientación relativas, algo complejo de lograr en la mayoría de las configuraciones experimentales. Esta Tesis estudia las interacciones entre antenas y emisores en contextos que no han sido estudiados en detalle hasta ahora, y las utiliza para aplicaciones donde nos permitirán observar mecanismos moleculares que no son accesibles con métodos ópticos convencionales limitados por difracción. Este estudio se centra en la fabricación y aplicación de nanoantenas construidas en la cara final de fibras ópticas que serán manipuladas usando un microscopio de campo cercano. Esta metodología garantiza un control total de la posición de la antena con respecto a la muestra con precisión nanométrica. Hemos desarrollado y caracterizado nuevos diseños de antena que presentan diferentes propiedades ópticas adaptadas a la aplicación de interés. Por ejemplo, la mayoría de las antenas están diseñadas para incrementar el campo eléctrico, ignorando la contribucón magnética al campo total. En esta Tesis, utilizamos antenas dieléctricas para aumentar la emisión de dipolos magnéticos. Esto abre nuevos campos de aplicación de las nanoantenas, tales como mayor sensibilidad en espectroscopía de quiralidad. Además, para ampliar el estudio de las antenas fotónicas a su interacción con varios emisores se necesitan nuevos diseños de antenas que sean de banda ancha y permitan por tanto afectar fluróforos con distintas propiedades espectrales. La mayoría de las antenas que se utilizan tienen una resonancia bastante estrecha, por lo que sus aplicaiones se limitan a detección o escaneo en un solo color. En esta Tesis, diseñamos antenas con resonancias que abarcan buena parte del espectro visible. Esto es interasante tanto desde el punto de vista fundamental como aplicado. Por un lado, utilizamos estas antenas de banda ancha en el contexto Förster Resonance Energy Transfer (FRET) para manipular la interacción entre un único donante y un único receptor en la nanoescala. Por otro lado, el aumento de fluorescencia en múltiples longitudes de onda abre la posibilidad de realizar imágenes multicolor o de detectar interacciones entre especies con distintos marcajes en células vivas. Aquí combinamos estas antenas de banda ancha con métodos de alta resolución temporal, tales como Fluorescence Correlation Spectroscopy (FCS) o Fluorescence Cross-Correlation Spectroscopy (FCCS), para investigar la difusión e interacción de múltiples especies en la membrana de células vivas, con una resolución espacial de nanómetros y temporal por debajo de los milisegundos. La Tesis finaliza con una breve discusión de los principales resultados alcanzados en esta investigación y propone nuevas vías para futuras investigaciones en el campo.

Multiple fans are sometimes used in an array configuration to cool various types of electronic equipment. In addition to adding another noise source, using two fans with closely spaced blade passage frequencies (BPF) can create an annoying beat frequency. A two fan array with each fan having a different BPF was considered. The fans were theoretically modeled at the BPF and first harmonics. Each fan has two acoustic paths to the far field. Thus, each fan was modeled as a two source array. The first control configuration consisted of one control filter using six control sources and six error sensors in a fully coupled control system designed to control both fans simultaneously. The second configuration used two independent controllers with three control sources and three error sensors, one controller per fan. Experimentally, the averaged narrow band reduction of the BPFs and the second harmonic of the two independent controllers were 15.6 and 7.4 dB respectively, compared to a reduction of 14.4 and 5.7 dB at the two frequencies using a single control loop. The results suggest that independent controllers perform better than the single control loop for the fan array studied. Optimization of active noise control systems has increased performance but sometimes with decreased robustness. Two control source configurations for the sound power reduction of a simple source were analyzed by modeling the control systems. The two control source configurations were four symmetric control sources surrounding the noise source and an optimized linear array of four control sources. Simulation results show the linear array control source configuration is more sensitive to microphone placement errors, with a 20-33 dB reduction in attenuation for a microphone placement error of 2 mm compared to a 0.8 dB drop in attenuation for the symmetric case. The linear array configuration was found to be more sensitive to the microphone placement errors compared to the symmetric configuration. A 2.5 mm change in one microphone position causes an average of 6 dB loss in attenuation for the linear array configuration compared to a 0.6 dB loss for the symmetric configuration.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.
This thesis was scanned as part of an electronic thesis pilot project.
Cataloged from PDF version of thesis
Includes bibliographical references (p. 117-119).
Electromagnetic formation flight is the process of using electromagnetic actuators (coils) on multiple spacecraft to produce relative (internal) forces in order to control the relative position and orientation of the spacecraft. This thesis demonstrates the ability to experimentally generate the relative internal electromagnetic forces in a short duration full 6DOF environment. Next the thesis limits itself to a two-satellite system and thus is able to perform a state reduction that constrains the motion to an arbitrary two-dimensional plane in 3-dimensional space showing that this is not actually a constraint on the real system for a two satellite formation. A feedback control law is proposed and simulated in this constrained space demonstrating position control of the underactuated system. Some theoretical guarantees are derived from contraction analysis. Finally time and energy optimal paths for a series of maneuvers are conceived by application of the GPOPS - II numerical optimization software. The results show further that the underactuated system is capable of arbitrary position control with the limitation being that it is unable to simultaneously control attitude and position to desired states because the attitude is used to "steer" the magnetic dipole therefore the desired angle is set by the position controller rather than an external reference. Overall this thesis shows the viability from the controllability perspective of underactuated electromagnetic formation flight for future space missions.
by Alexander James Buck.
S.M.

Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in the acoustic far field of the ANC system. The experimental results are compared to the theoretical pressure null locations in order to determine the efficacy of the point source model. The results closely matched the point source model with a loudspeaker as the primary source, and the sound power reduction was greatly reduced when error sensors were placed in non-ideal locations. A weakness of the current near-field modeling process is that a point monopole source is used to characterize the acoustic noise from an axial cooling fan, which may have multipole characteristics. A more complete characterization of fan noise may be obtained using a procedure based on the work of Martin and Roure [J. Sound Vib. 201 (5), 577--593 (1997)]. Pressure values are obtained over a hemisphere in the far field of a primary source and the contributions from point source distributions up to the second order, centered at the primary source, may be calculated using a multipole expansion. The source information is then used in the aforementioned theoretical near-field calculation of pressure. The error sensors are positioned using the complete fan characterization. The global far-field attenuation for the multipole expansion model of fan noise is compared to that of previous experiments. Results show that the multipole expansion model yields a more accurate representation the near field, but is not successful in achieving greater sound power reductions in the far field.

Research presented herein involved the use of a smart skin treatment used for the attenuation of turbulent boundary layer induced interior noise. The treatment consisted of several Smart Foam actuators each having a reference and error sensor along with a feed forward, filtered-x controller. Studies were performed to determine if the use of multiple instances of single input, single output (SISO) control systems could be implemented with success given the difficulty of actively suppressing turbulent boundary layer induced interior noise. Further, this research will lead to the development of an integrated Smart Foam element consisting of a Smart Foam actuator, reference sensor, error sensor and SISO controller in one complete, stand--alone unit. Several topics were studied during this effort: reference sensing, error sensing, actuator design, controller causality, correlation of turbulent flow and resulting plate vibration, and coherence between plate vibration and the interior noise field. Each study was performed with the goal of improving the performance of active attenuation of turbulent boundary layer induced interior noise. Depending on the configuration of the control system, control was performed using either experiments or simulations based on experimental data. Within the desired control band of 400--800~Hz, attenuation of up to -3.1~dB$_A$ was achieved at the error sensors and up to -1.4~dB$_A$ within the observer plane relative to the uncontrolled case. However, over a band of greater coherence from 480--750~Hz, attenuation of up to -4.8~dB$_A$ was achieved at the error sensors and up to -2.6~dB$_A$ within the observer plane. Further, peak attenuation of up to -12~dB$_A$ was achieved within the observer plane. Studies were also conducted to increase the low frequency performance of the Smart Foam treatment. These experiments used tuning masses placed on the tops of the integrated Smart Foam elements to tune them to the fundamental mode of the vibrating plate. This treatment was used to reactively attenuate plate vibration such that the radiated acoustic field would be minimized. These experiments resulted in -6~dB$_A$ global attenuation at the plate fundamental resonance. Further, it was shown that the reactive treatment did not inhibit active control.
Ph. D.

Acoustic noise pollution is an environmental aggressor in everyday life. Aero- dynamically generated noise annoys and was linked with health issues. It may be caused by high-speed turbulent free flows (e.g. aircraft jet exhausts), by airflow interacting with solid surfaces (e.g. fan noise, wind turbine noise), or it may arise within a confined flow environment (e.g. air ventilation systems, refrigeration systems). Hence, reducing the acoustic noise levels would result in a better life quality, where a systematic approach to decrease the acoustic noise radiation is required to guarantee optimal results. Computational predic- tion methods able to provide all the required flow quantities with the desired temporal and spatial resolutions are perfectly suited in such application areas, when supplementing restricted experimental investigations. This thesis focuses on the use of numerical methodologies in compressible flow applications to understand aerodynamically noise generation mechanisms and to assess technologies used to suppress it. Robust and fast steady-state Reynolds Averaged Navier-Stokes (RANS) based formulations are employed for the optimal design process, while the high fidelity Large Eddy Simulation (LES) approach is utilized to reveal the detailed flow physics and to investigate the acoustic noise production mechanisms. The employment of fast methods on a wide range of cases represents a brute-force strategy used to scrutinize the optimization parameter space and to provide general behavioral trends. This in combination with accurate simulations performed for particular condi- tions of interest becomes a very powerful approach. Advance post-processing techniques (i.e. Proper Orthogonal Decomposition and Dynamic Mode Decomposition) have been employed to analyze the intricate, highly turbulent flows. The impact of using fluidic injection inside a convergent-divergent nozzle for acoustic noise suppression is analyzed, first using steady-state RANS simulations. More than 250 cases are investigated for the optimal injection location and angle, amount of injected flow and operating conditions. Based on a-priori established criteria, a few optimal candidate solutions are detected from which one geometrical configuration is selected for being thoroughly investigated by using detailed LES calculations. This allows analyzing the unsteady shock pattern movement and the flow structures resulting with fluidic injec- tion. When investigating external fluidic injection configurations, some lead to a high amplitude shock associated noise, so-called screech tones. Such unsteady phenomena can be captured and explained only by using unsteady simulations. Another complex flow scenario demonstrated using LES is that of a high ve- locity jet ejected into a confined convergent-divergent ejector (i.e. a jet pump). The standing wave pattern developed in the confined channel and captured by LES, significantly alters the acoustic noise production. Steady-state methods failed to predict such events. The unsteady highly resolved simulations proved to be essential for analyzing flow and acoustics phenomena in complex problems. This becomes a very powerful approach when is used together with steady-state, low time-consuming formulations and when complemented with experimental measurements.

QC 20141202

Computer and Information Science
Ph.D.
This dissertation evaluates the design of several defense schemes for wireless medical devices to address security issues. These schemes are designed to enable efficient and effective access control of wireless medical devices in both non-emergency and emergency situations. In recent years, the range of available wireless medical devices has increased and includes cardiac pacemakers, insulin pump, defibrillators, cochlear implants, neurostimulators, and various drug delivery systems. Unfortunately, most existing wireless medical devices lack sufficient security mechanisms to protect patients from malicious attacks. Thus, with the rise in use of medical implants, security becomes a critical issue as attacks on wireless medical devices may harm patients. Security on wireless medical devices is a relatively new field, which has not been thoroughly researched yet. The authors of a lot of articles have proposed token based, certification based and proximity based schemes to address the issue. However, most of the current solutions have many limitations and cannot be widely applied. Therefore, better solutions are needed. In order to address this issue, we design a novel and multiple-layer access control framework for wireless medical devices. In a low layer level, we utilize bi-channel technology and multi-factor authentication to defend against various attacks at wireless medical devices. Our system utilizes near field communication (NFC) to do device pairing and uses the medical device's wireless radio to perform remote programming. This approach defends against most attacks because our NFC pairing scheme guarantees that the successful communication range between the programmer and wireless medical devices is less than 6cm. When the patient is in a crowded area such as on public transportation, a different person's mobile devices and the patient's medical devices may be located less than 6cm apart; we use the patient's cell phone to detect such an environment. To avoid attacks in crowded areas, we design a scheme to detect such a situation using the patient's cell phone. User involvement is used on non-implantable medical devices (IMDs) and a patient access pattern based access control (PAPAC) scheme is used on IMDs. We also design a response time based scheme to defend against fake patient attacks. Our analyses and experiments show that the protection schemes are efficient and effective. In a high layer level, we design patient infusion pattern based access control (PIPAC) scheme for wireless medical devices. Specifically, insulin pumps are most widely applied wireless medical devices. The pump parameters and doses can be adjusted by anyone with an easily obtained USB device. The hacker can deliver a lethal dose without knowing the device's serial number in advance. To address this issue, we propose a PIPAC for wireless insulin pumps. This scheme employs a supervised learning approach to learn normal patient infusion patterns in terms of the dosage amount, rate, and time of infusion, which are automatically recorded in insulin pump logs. The generated regression models are used to dynamically configure a safe infusion range for abnormal infusion identification. Our proposed algorithms are evaluated with real insulin pump logs used by several patients for up to 6 months. The experimental results demonstrate that our scheme can reliably detect a single overdose attack with a success rate up to 98\% and defend against a chronic overdose attack with a very high success rate. For IMDs in non-emergency case, the PAPAC scheme we design utilizes the patient's IMD access pattern to address resource depletion (RD) attacks. It is a novel support vector machine (SVM) based scheme. This SVM based scheme is very effective at defending against RD attacks. Our experimental results show that the average detection rate is above 90\%. For IMDs in emergency cases, we design a novel biometrics based two-level secure access control scheme that utilizes a patient's biometrics to prevent unauthorized access to the IMD. The scheme consists of two levels: level-one employs a patient's some basic biometrics and is lightweight; level-two uses a patient's customized iris data to achieve effective authentication. The experimental results show that our IMD access control scheme is very effective and has small overhead in terms of battery, CPU and memory. Thus, it is suitable for IMDs. Both the false acceptance rate (FAR) and false rejection rate (FRR) are close to zero with a suitable threshold. Protecting wireless medical devices is a very challenging task due to their extremely limited resource constraints. It is necessary to balance the overhead of security schemes and security requirements. In this dissertation, we will first discuss security vulnerabilities in wireless medical device systems. Then we will present our framework using smart phones and other technologies, such as near field communication based access control. Further, we will describe the detailed design of this framework. Finally, extensive experiments show that our schemes can achieve good performance with small overhead.
Temple University--Theses

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Today there exist a myriad of different types of physical access control systems (PACS) that use a smart card or mobile device as a key. The mobile device enabled smart locks, as they are often referred to, operate using either Wi-Fi or Bluetooth. This thesis has explored the use of a third emerging wireless technology called Near Field Communication (NFC) available in mobile devices such as smartphones. Near Field Communication (NFC) technology is a relatively new technology that is on the rise and is included in almost every new mobile device. By leveraging Near Field Communication (NFC) enabled mobile devices, a highly secure access control system can be achieved and developed taking advantage of the computational power of smartphones in comparison to traditional methods the business implications are huge, Several different authentication and encryption protocols, mobile operating systems and Near Field Communication (NFC) modes of operation where analyzed and evaluated. After considerations technical considerations the Secure Remote Password authentication protocol on top of Near Field Communication (NFC) card emulation (CE) scheme with the client application running on smartphones operating system (OS) was selected. This thesis shows that Near Field Communication (NFC) enables a mobile device to act as a key in a secure access control system (PACS) and as the user base for NFC grows larger so will the likelihood that we will come to see more of these types of systems in business and organizations.

In diesem Beitrag wird ein analytischer Ausdruck für die Bestimmung des Sollwerts der Läuferflussverkettung einer Asynchronmaschine (ASM) bei der feldorientierten Regelung vorgestellt. Dieser Wert wird durch das Lösen des Wirkungsgradoptimierungsproblems für jeden Betriebspunkt hergeleitet. Bei der Berechnung werden die Begrenzung der Spannungen sowie der Ströme als Nebenbedingungen in Betracht gezogen. Dieser Algorithmus eignet sich für industrielle Anwendungen, aber auch für Tranktionsantriebe, die mit ASM betrieben werden.
In this contribution, an analytic expression for the reference value of the flux linkage of an induction machine during field oriented control is proposed. This value results from solving the efficiency optimization problem of the ASM at each operational point. The restrictions on the motor voltages and currents are also considered in the optimization problem as constraints.The proposed method is suitable for industrial applications such as electric cars equipped with induction motors.

La fatigue mécanique et thermique des structures métalliques est l’une des altérations majeures dans les centrales de production d’énergie. Une détection précoce des défauts de surface par des procédés de contrôle non destructif (CND) permet une maintenance préventive pertinente des installations en évitant d’avoir à démonter ou remplacer des composants sains. Actuellement, la majorité des solutions automatisées de CND est basée sur des techniques utilisant les ultrasons ou les courants de Foucault. Cependant, malgré leurs sensibilité et résolution spatiale élevées, ces méthodes ne sont pas nécessairement adaptées à la détection de tous les défauts de surface rencontrés en pratique. Les limites des méthodes de contrôle conventionnelles par courants de Foucault et ultrasons pour détecter des micro-fissures de surface dans les métaux justifient l’intérêt d’évaluer le potentiel de nouvelles techniques. Les travaux de thèse présentés dans ce mémoire se focalisent sur l’apport des méthodes microondes, Dans ce document, nous démontrons la faisabilité de la détection de micro-fissures de surface dans les métaux à l’aide de sondes micro-ondes résonantes en champ proche. En particulier, à partir de simulations et de mesures réalisées sur des maquettes de test contenant des entailles électroérodées rectangulaires, nous mettons en évidence la sensibilité et la résolution spatiale élevées des sondes originales de type filtre Dual-Behavior Resonator (DBR)
The fatigue and ageing of metal materials under operation conditions are major concerns in energy production plants. An early and non-destructive diagnostic of surface defects would allow one to carry out relevant preventive maintenance operations without dismantling or prematurely changing healthy components. Nowadays, most of the automated non-destructive testing (NDT) solutions available to detect the surface-breaking defects are based on ultrasound or eddy current techniques. Despite their high sensitivity and spatial resolution, they are unable to meet all the requirements of every real situation. Consequently, in order to supplement the available acoustic and electromagnetic NDT toolkits, it sounds relevant to evaluate the potential of new techniques to detect micro-cracks on metal surfaces. The aim of this work is the development of microwave methods allowing the detection of surface-breaking defects on metals. In this report, we demonstrate how micro-cracks at the surface of metals can be detected and imaged by using near-field microwave resonators. In particular, we present simulation data and measurement results carried out on mock-ups with EDM rectangular surface notches highlighting the high sensitivity and spatial resolution of the original dual-behavior resonator (DBR) filter probes

碩士
國立交通大學
機械工程系
89
In this era of information explosion, a near-field optical disk drive is an important innovation of higher capacity and higher density. Due to the demand of 500nm track pitch density and 50nm only flying height of the R/W head, previous actuators are not able to conduct track seeking and following well. In this study, dual-stage control is proposed. Coarse control is carried out by a voice coil motor, whereas a piezoelectric material of PZT undertakes fine tuning. A PID controller is used for VCM. Since it is complicated to generate a plant model including an air bearing and structural elasticity, a neural network controller is developed to deal with both fine tuning and flying height control. This work compares both results of backpropagation and backpropagation through time in the neural network control. The latter outperforms the former whether runout disturbance exists or not. The latter proves better due to its capability dealing with time varying system. A laser Doppler vibrometer is used to measure PZT vibration in experiments, and an early design of R/W head is built for the sake of fine tuning and flying height control.

碩士
國立交通大學
機械工程系
91
Near-field optical disk drives represent a novel technique for optical data recording and its research is undergoing in both academics and industry. To achieve high precision in focusing for near-field data recording, it is essential to develop servo systems that can maintain a constant flying height, for which a piezoelectric bender can compensate the vibration of rotating optical disk. Due to the hysteresis phenomenon in piezoelectric material, advanced controllers other than linear ones must be constructed to accomplish a competent servo system. In this thesis, adaptive inverse control is developed to overcome nonlinear effects. The structure of adaptive inverse control can be separated into two main parts, one is system identification, and the other is controller adaptation. The control scheme is implemented with LMS-sensed adaptive filter or neural networks. Research results demonstrate that the developed method can compensate piezoelectric material hysteresis.

碩士
國立中正大學
物理研究所
86
A tapping-mode tuning fork force sensing method for near-field scanning opticalmicroscope has been successfully developed. Using tuning fork and normalstraight near-field fiber probe, a simple working mechanismof tapping-mode was achieved. Asymmetric construction of mechanical excited tapping-modetuning fork generates better stability and sensitivity than that in shearforce mode or other non-optical method. Resultsshowed the vibration of twotines is out of phase 180 degrees. The attaching of fiber probe only changesthe Q and resonance frequencyof the sensing tine slightly. Force curves ofshear force mode and tapping-mode fiber tip in air or in water demonstratedthat force interaction of tapping-mode is more sensitive and simplified. Stable and clear images of 500 nm standard polystyrene spheres wereobtainedin air or water by this novel method.

博士
國立臺灣科技大學
電子工程系
105
In this thesis, it is proposed to use the control field to make the design of the antenna can easily meet the requirements of SAR, the other antenna design also introduced the use of loop structure to produce reverse current to make the energy is more dispersed, less likely to form a centralized hot spots, It is also helpful to reduce the SAR value, and the application of Adjacent Frequency design, multi-path to produce multi-resonant, to achieve the effect of broadband. The first propose antenna, it is shown that the one fifth wavelength radiator combines with a printed ground-line which protrudes from ground-plane jointly with parasitic metal-loading, which can be used to control the near-fields of a mobile phone antenna. The human’s hand and head effect on impedance bandwidth and radiation characteristics of the proposed antenna is studied. The input power of 24dBm in CDMA, GSM and WCDMA bands, and the input power of 21dBm in DCS and PCS bands all meet the specific absorption rate (SAR) limit of 1.6 mW/g and hearing aid compatibility (HAC) of M3 and M4 level. The second propose antenna, it is a novel multi-band broadband antenna for mobile handsets application. It is proposed and analyzed in this paper. An asymmetric T-type monopole antenna with a shorting-line is designed to be operated in long term evolution (LTE, 698MHz-960MHz, 1710MHz-2170MHz, 2500MHz-2690MHz) and wireless local area network (WLAN, IEEE 802.11ac, 5150MHz-5850MHz) bands. The experimental results indicate that the bandwidths for VSWR of 3:1 achieved were 37.75%, 24.63%, 11.46% and 21.76% at 800MHz, 1900MHz, 2600MHz and 5500MHz, respectively. The specific absorption rate (SAR) for an input power of 24dBm in LTE band, and an input power of 13dBm in IEEE 802.11ac band meet the SAR limit of 1.6 mW/g. Experimental results verify the prediction of the theoretical analysis.

The electromagnetic properties of various plasmonic nanostructures are investigated. These nanostructures, which include random clusters, controlled clusters and particle-film hybrids are applied to surface-enhanced Raman scattering (SERS). A variety of techniques are utilized to fabricate, characterize, and model these SERS-active structures, including nanoparticle functionalization, thin film deposition, extinction spectroscopy, elastic scattering spectroscopy, Raman scattering spectroscopy, single-assembly scattering spectroscopy, transmission electron microscopy, generalized Mie theory, and finite element method.

Initially, the generalized Mie theory is applied to calculate the near-field of the small random clusters to explain their SERS signal distribution. The nonlinear trend of SERS intensity versus size of clusters is demonstrated in experiments and near-field simulations.

Subsequently, controlled nanoparticle clusters are fabricated for quantitative SERS. A 50 nm gold nanoparticle and 20nm gold nanoparticles are tethered to form several hot spots between them. The SERS signal from this assembly is compared with SERS signals from single particles and the relative intensities are found to be consistent with intensity ratios predicted by near-field calculation.

Finally, the nanoparticle/film hybrid structure is studied. The scattering properties and SERS activity are observed from gold nanoparticles on different substrates. The gold nanoparticle on gold film demonstrates high field enhancement. Raman blinking is observed and implies a single molecule signal. Furthermore, the doughnut shape of Raman images indicates that this hybrid structure serves as nano-antenna and modifies the direction of molecular emission.

In additional to the primary gap dipole utilized for SERS, high order modes supported by the nanoparticle/film hybrid also are investigated. In experiments, the HO mode show less symmetry compared to the gap dipole mode. The simulation indicates that the HO modes observed may be comprised of two gap modes. One is quadrupole-like and the other is dipole-like in terms of near-field profile. The analytical treatment of the coupled dipole is performed to mimic the imaging of the quadrupole radiation.

Dissertation

碩士
國立交通大學
機械工程系
88
The flying head design in near-field optical disk drives applies the near-field optics theory to overcome the limit of conventional optical disk techniques, thereby substantially increasing data storage capacity. To that end, enhancing control performance to improve the tracking speed and accuracy is required. This study aims to develop a sliding mode based repetitive learning controller, which incorporates characteristics of sliding mode control into repetitive learning control. The reason for using sliding mode control is attributed to robust properties dealing with model uncertainty and disturbances. The learning algorithm utilizes shape functions to approximate influence functions in integral transforms and estimate the control input to perform seeking movement. It learns at each sampling instant the desired control input without prior knowledge of system dynamics. To validate the proposed method, this work conducts track-seeking experiments, in which a resistance device and an optical grating respectively read position feedback signals of the pickup head.

In this work, femtosecond laser pulses are used to launch optical excitations on different nanostructures. The excitations are confined below the diffraction limit and propagate along the nanostructures. Fundamental properties of these ultrashort optical near fields are determined by characterizing the far-field emission after propagation with a setup developed for this task. Furthermore, control of the nanooptical excitations' spatial and temporal evolution is demonstrated for a designed nanostructure
In dieser Arbeit werden Femtosekunden-Laserpulse verwendet, um optische Moden auf verschiedenen Nanostrukturen anzuregen. Die optische Energie ist dabei unterhalb des Beugungslimits lokalisiert und die Anregungen propagieren entlang der Nanostrukturen. Grundlegende Eigenschaften dieser ultrakurzen optischen Nahfelder werden durch die Charakterisierung der Fernfeld-Emission nach der Propagation bestimmt. Dabei wird eine Messmethode verwendet die eigens für diese Aufgabe entwickelt wurde. Darüber hinaus wird die Steuerung der räumlichen und zeitlichen Entwicklung der nanooptischen Anregungen auf einer für diesen Zweck entworfenen Nanostruktur demonstriert

碩士
國立交通大學
機械工程系
90
Based on near-field optics, a flying pickup head is employed in optical disk drives, so as to increase data storage capacity and density. However, it remains to enhance flying height control performance of the pickup head. This study attaches a piezoelectric bender to the pickup head. System identification is carried out to obtain a transfer function as the plant model. For real-time control, this study uses a DSP motion control card to execute control algorithm and uses a double-beam laser doppler interferometer for sensing head-disk spacing. A PID control method deals with the PZT bender motion to maintain a stable flying height, in spite of optical disk deformation and flying head vibration during near-field disk rotation at 5400rpm.

碩士
國立清華大學
動力機械工程學系
94
A near-field readout system using a traditional optical head has been proposed as a technology to increase the storage capacity. However, designing the far-field and the near-field controls so that they both can coordinate in an optimal manner presents challenges to control engineers. In this thesis, we develop a systematic procedure which uses the information on the plant dynamics, hardware limitations and performance specifications to design a far-near field control for optical disc drives. The experiments indicate that the controller designed can move the optical head rapidly from far field to near field without colliding with the optical disc. To further enhance the control performance, a quantization effect reduction (QER) method to reduce output error due to DAC quantization noises is also proposed. The QER technique offers a simple method of reshaping the spectrum of the quantization noise to minimize the output error. The proposed QER method decouples the quantization effect from control system that it does not affect the original control response. The limitation and optimality of the QER method are examined carefully. Experimental results reveal that output error caused from quantization error is reduced by more than a factor of five.

碩士
國立交通大學
機械工程系
89
The flying head design in near-field optical disk drives applies the near-field optics theory to overcome the limit of conventional optical disk drive techniques, thereby substantially increasing data storage capacity. To that end, enhancing control performance to improve tracking speed and accuracy is required. This study aims to develop fuzzy control based reinforcement learning, which incorporates characteristics of reinforcement learning control into fuzzy control. Fuzzy control has excellent characteristics of dealing with model uncertainty, nonlinearity and easy implementation. Reinforcement learning is specially suitable for rough feedback signals; however, the measured feedback signals for an optical head is also rough in focusing, seeking and following. To carry out the present controller, it is not necessary to obtain beforehand the mathematical model of the pickup head. This work constructs fuzzy rules based model based on input-output data of the pickup head and tune fuzzy membership functions by reinforcement learning. During voltage excitation, a bimorph PZT simultaneously undergoes two axes deformation, which can be used for both tracking control and flying height control. To validate the proposed bimorph PZT method, this work conducts measurements.

碩士
國立交通大學
機械工程系
88
The flying optical pickup head in near-field optical disk drives applies the near-field optics theory to overcome the limit of conventional optical disk techniques, thereby substantially increasing data storage capacity. The flying pickup head and disk constitute an air bearing similar to that in hard disk drives. Wavelet transform has been an emerging analysis tool since 1980’s. As a time-frequency transform, the wavelet transform is an alternative to the short-time Fourier transform. Based on both wavelet transform and neural network, this study aims to develop wavelet network controllers to achieve track-seeking for near-field optical disk drives. To validate the proposed method, this work conducts experiments, in which a resistance device and an optical grating respectively read the position feedback signal of the pickup head.

碩士
國立交通大學
機械工程系
90
In order to overcome the diffraction limit of conventional optical disk drives, the flying pickup head in near-field optical disk drives enables the slider to fly at a stable spacing above the disk surface, thereby substantially increasing storage capacity and density. Hence, enhancing control performance to improve focusing speed and accuracy is required. To sense flying height in control experiments, a gap capacitance servo measures capacitance variation between the pickup head and disk surface and process voltage signals out of the capacitor by demodulation. Sliding mode control inherited with robust properties can deal with model uncertainty and disturbances. Therefore, a DSP control card executes a sliding mode control algorithm to compensate the vibration of the optical disk surface and achieve a stable flying height for the pickup head.

碩士
國立交通大學
機械工程系所
93
To realize near-field optics and hence increase storage capacity and density in near-field optical disk drives, the flying pickup head has to enable the slider to fly at a stable height above the disk surface. Since both the precision of track pitch and the flying height reach nanoscale, it remains to increase the motion accuracy of a pickup head. In this study, a PZT bender is used as an actuator of the pickup head while quadrant photodetectors are used as sensors. Based on an optical lever method and addition-and-subtraction operations in op-amp circuits, the relative position variation between a disk and a pickup head is measured. This study designs a sliding mode controller inherited with robust properties to deal with model uncertainty and external disturbances, so as to maintain stable flying height.

碩士
國立交通大學
機械工程系
91
Near-field optical disk drives can overcome the diffraction limit of conventional techniques, thereby substantially increasing storage capacity and density. Since the precision of track pitches and the flying height lie within range of nanometers, it is required to enhance control performance to improve focusing speed and accuracy. In this study, a PZT bender is used as a fine actuator of the pickup head. Due to hysteresis of the PZT material, a discrete sliding mode controller inherited with robust properties is developed to deal with model uncertainty and external disturbances, so as to maintain a stable flying height. In the experiment, a gap capacitance sensor utilizes an FM system to extract capacitance change corresponding to flying height variation. Furthermore, to investigate the transient response at the head/disk interface, wavelet transform with flexible time-frequency resolution is applied to analyze transient behavior, and identify the dynamic characteristics as the system subject to impulsive shock loading.

博士
國立交通大學
機械工程系所
95
This study aims to realize near-field optics and solves the requirement of data increasing recording capacity. For near-field recording, the distance between the slider and optical disk surface, i.e. the flying height must maintain stable. As a flying height actuator, a piezoelectric bender is used to implement the flying height control in near-field optical disk drives. Firstly, this study designs a flying pickup head including a piezoelectric bender to complement VCM to control both focusing and track-seeking/track-following motions simultaneously. The pickup head structure differs from traditional CD-ROM and DVD-ROM pickup heads. Secondly, the pickup head is very close to an optical disk whose surface contains numerous grooves. Thus the dynamics between the optical disk and the pickup head must be investigated. Different from laser Doppler interferometers, an optical lever method using two quadrant photodetectors is developed to measure the flying height variation of a pickup head above a rotating disk. Finally, adaptive inverse control and PID control are used to implement focusing and track-following, respectively. Coupling between focusing and track-following is incorporated in derivation and computer simulation. This study analyzes the effect of grooved surface on flying, carries out experiments for flying height measurement and control with the pickup head, and investigates effects of horizontal deflection of the bender on track-following. For air bearing disturbance canceling, the proposed method is validated. Regarding simulation, dealing with air flow disturbance the previous method only cancels 43 %. By contrast, the proposed method can cancel disturbance up to 80 %. In experiments, the proposed method yields tracking error of 13 %, in contrast to 27 % by using the previous method.

博士
國立交通大學
機械工程系所
93
This study aims to control the flying height of pickup heads in near-field optical disk drives. Near-field optical disk drives apply the near-field optics theory to replace conventional optical disk drives, thereby substantially increasing data storage capacity. In order to achieve near-field optical recoding, the distance between the objective lens and disk surface, i.e. the flying height must keep within the range of sub-wavelength. As a flying height actuator, a piezoelectric bender is used in this study to complement an air bearing at the head/disk interface to perform the feedback control in order to decrease flying height variation due to disk vibration and tilt. Firstly, this study aims to develop a sliding-mode based learning controller for eliminating repetitive error in flying height control. It incorporates characteristics of sliding mode control into learning control. The reason for using sliding mode control is attributed to its robust properties dealing with model uncertainty and disturbances. The learning algorithm utilizes shape functions to approximate influence functions in integral transforms and estimate the control input to reduce repetitive error. Thus, the repetitive component in the flying error can be compensated and a stable flying height can be maintained under a periodic disk vibration. In addition, this study presents a discrete frequency-shaped sliding mode control law for flying height control of near-field optical disk drives. Frequency shaping is conducted such that filtered state variables are penalized at the disk vibration frequency using inverse notch filters in LQR weighting functions. Hence, the controller can achieve stable flying height in the presence of certain frequency vibration of optical disks. Using the proposed methods, this study carries out experiments for flying height control with the pickup head. According to experimental results, the proposed methods are validated in comparison with conventional controllers.

博士
國立交通大學
機械工程系所
93
Conventional optical disk drives are faced with diffraction limit. To substantially increase data storage capacity and density, near-field optical disk drives remain to be realized. The slider of a flying pickup head in a near-field optical disk drive has to fly at a very low and stable height above the disk surface. To sense the slider flying height, a gap capacitance method is developed in this study to measure capacitance variation between the pickup head and disk surface. The capacitance varying with the flying height is modulated by a Colpitts oscillator. Subsequent demodulation accounts for height variation of the flying pickup head. Measurement results of this method are verified by using a laser Doppler interferometer. The interface between the slider and optical disk constitutes an air bearing. The air bearing force is affected by disk rotation speed and deformation, which represent low-frequency periodic disturbance to the slider. A repetitive control method is adopted to eliminate the periodic disturbance. H∞ control inherited with robust properties and sliding control can deal with model uncertainty and disturbances. Therefore, this study designs two controllers. One is a repetitive controller cascaded by an H∞ controller, while the other error-feedback sliding mode control. The proposed controllers are validated by simulation and experimental results.

碩士
國立交通大學
工學院精密與自動化工程學程
101
This thesis uses a PID controller to control the pickup head flying height in a near-field optical disk drive. Near-field optical theory applied to an optical pickup head can improve optical disk drive storage capacity. In order to achieve near-field optical recoding, the distance between the objective lens and disk surface, i.e. the flying height must keep within the range of sub-wavelength. In such small flying clearance, head disk crash risk will become higher and higher. This study uses National Instrument sbRIO-9602 embedded device using closed-loop control voice coil motor by the PID method to reduce the flying height variation induced by media waviness under critical clearance. The result successfully avoids the pickup head to crash media surface and reduces the flying height to 750nm.

碩士
國立成功大學
電信管理研究所
104
Safety and convenience are two key factors of the access control systems. In semi-open environments, it’s difficult to manage access control due to the variety of users. In this case, multilayered delegation provides flexibility in access control systems. But in past access control systems, keys revocation is the major issue. So an ideal access control system require four characteristics: safe, convenient unlocking, convenient revocation and delegation ability. However, there are disadvantages in all of related works, such as the demand of Internet, no multilayered delegation, the lack of key life cycle and incomplete revocation. To improve the weaknesses of related works, provide administrators facilitation to manage keys and opearte the model in all scenarios. This study proposes Multilayered Delegable Access Control Model (MDAC), which combines the features of semi-offline architecture and multi-level authorization mechanism. It’s designed by RSA encryption, a chain of binding hardware serial numbers, and the system architecture can be applied to multi-level delegation. This work can not only effectively avoid key copying, tampering and other security risks, but execute delegation ability without going through the server. Furthermore, it’s possible to unlock the doors and revoke the key when smartphones are offline, and has the feature of key life cycle management including key valid period and access times control. User’s key is always limited by the life cycle whenever he/she is unlocking the door or delegating the key to someone. Our proposal provides administrators facilitation to manage keys and is able to apply to all access control scenarios.

碩士
輔仁大學
電機工程學系碩士班
104
This design integrates the near field communication (NFC) reader of a smartphone device with the door lock control system to provide a convenient single button operation. This design also offers three operation modes to the user in order to allow a one-time password (OTP) with a time stamp permission to match the user's password to thus enhance the door’s security. The door lock control system is fixed on the door, and also provides both the sleep state and the standby state to save power consumption for a long time operation.

The damaging effects of strong ground motions on highway bridges have revealed the limitations of conventional design methods and emphasized the need for innovative design concepts. Although seismic isolation systems have been proven to be an effective method of improving the response of bridges during earthquakes, the performance of base-isolated structures during near-field earthquakes has been questioned in recent years. Near-field earthquakes are characterized by long period and large- velocity pulses. They amplify seismic response of the isolation system since the period of these pulses usually coincides with the period of the isolated structures. This study explores the feasibility and effectiveness of shape memory alloy (SMA)-based isolation systems in order to mitigate the response of bridge structures against near-field ground motions. SMAs have several unique properties that can be exploited in seismic control applications. In this work, uniaxial tensile tests are conducted first to evaluate the degree to which the behavior of SMAs is affected by variations in loading rate and temperature. Then, a neuro-fuzzy model is developed to simulate the superelastic behavior of SMAs. The model is capable of capturing rate- and temperature-dependent material response while it remains simple enough to carry out numerical simulations. Next, parametric studies are conducted to investigate the effectiveness of two SMA-based isolation systems, namely superelastic-friction base isolator (S-FBI) system and SMA/rubber-based (SRB) isolation system. The S-FBI system combines superelastic SMAs with a flat steel-Teflon bearing, whereas the SRB isolation system combines SMAs with a laminated rubber bearing rather than a sliding bearing. Upon evaluating the optimum design parameters for both SMA-based isolation systems, nonlinear time history analyzes with energy balance assessment are conducted to compare their performances. The results show that the S-FBI system has more favorable properties than the SRB isolation system. Next, the performance of the S-FBI systems is compared with that of traditional isolation systems used in practice. In addition, the effect of outside temperature on the seismic response of the S-FBI system is assessed. It is revealed that the S-FBI system can successfully reduce the response of bridges against near-field earthquakes and has excellent re-centering ability.

Near-field Acoustical Holography is a tool that is conventionally used to visualize sound fields through an inverse process in a three-dimensional space so that either sound field projections or sound source localization can be performed. The visualization is conducted by using sound pressure measurements taken in the near-field region close to the surface of the unknown sound source. Traditional Fourier-based Near-field Acoustical Holography requires a large number of measurement inputs to avoid spatial truncation effects. However, the use of a large number of measurements is usually not feasible since having a large number of microphones is costly, and usually the array is limited in size by the physical environment, thus limiting the practicality of this method. In the present work, because of the desire to reduce the number of microphones required to conduct acoustical holography, a method known as Statistically Optimized Near-field Acoustical Holography initially proposed by Steiner and Hald was analyzed. The main difference between the present work and the concept mentioned by Steiner and Hald is the cylindrical coordinate system employed here for the purpose of experimenting on a bladeless fan, which resembles a cylindrical structure and which could be assumed to be a cylindrical source. The algorithm was first verified via simulations and measurements, and was then applied to experimental data obtained via pressure measurements made with a cylindrical microphone array. Finally, suggestions for noise control strategies for the bladeless fan are described, based on the measurement results.

This thesis examines the effects of spatial location, Reynolds number and near exit flow modification on the development region of a round, free, turbulent jet. It is based on the publications generated by the author. The experiments were carried out over the range of Reynolds numbers between 10000 < ReD < 50000, where ReD is calculated based on the jet exit mean velocity and the nozzle exit diameter. The measurements were performed in the near- to intermediate-field region of a free jet defined between 0 ≤ x/D ≤ 30. In order to control the flow near the exit, two wire rings, with square cross-sections, of sides h = 1.5 mm, and outer diameter Dwire = 71.6 mm (positioned in the shear layer and called Rsl) and Dwire = 60 mm (positioned in the potential core and called Rpc) were placed at a stand-off distance downstream of the jet nozzle exit plane x/D = 0.03. Both stationary and flying hot wires were used to investigate the jet flow field. The results showed a considerable reduction in the jet spread rate and turbulence intensity using the passive rings. The reduction in the velocity decay rate was more obvious in the case of Rsl in lower Re; however, it was observed that as Re increases, the velocity decay rate became nearly the same for both cases of Rsl and Rpc. The axial velocity spectra showed the initial shear layer instability (shear layer mode) was suppressed while the jet preferred instability (preferred mode) remained active as the shear layer and potential core were modified. This shows the separation of these modes and is at variance with ideas that appeared in the literature that claimed the dependency of these two modes.
Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-04-27 16:06:31.03