The versatility of surface acoustic wave (SAW) devices stems from the accessibility of the propagation path to modification and detection. This has led to the integration of SAWs in a variety of novel fields, including quantum information processing. The development of technologically competitive devices requires the use of gigahertz frequency SAWs. This thesis develops fabrication processes for high frequency interdigital transducers on gallium arsenide. Optically lithography was used to create linear and stepped transducers, with a minimum feature size of 2 um, that were driven at their fifth harmonic. The highest frequency achieved was 1435 MHz, but the power absorbed was less than 3% and insertion losses were greater than -80 dB. Further improvements in the design and fabrication are required if optically fabricated transducers are to be an alternative to transducers with narrower finger widths. Electron-beam lithography techniques were developed and used to create transducers with finger widths of 500 and 400 nm, with fundamental resonance frequencies of 1387 and 1744 MHz, respectively. The power absorbed was 3 to 6% with insertion losses greater than -45 dB. The performance characteristics can be improved by the removal of residual resist on the surface of the transducer. An indispensable tool for the characterization of one-port transducers is an all optical probe to measure the displacement field of a SAW. This work details the design and construction of a scanning Sagnac interferometer, that is capable of measuring the outward displacement of a surface. The spatial resolution of the interferometer was 2.4 +/- 0.2 um and the displacement sensitivity was determined to be 4 +/- 1 pm. The instrument was used to map the SAW displacement field from a 358 MHz transducer, with results showing the resonant cavity behaviour of the fingers due to Bragg reflections. It also allowed for the direct detection of the SAW amplitude as a function of the driving frequency of the transducer. The results showed good agreement with the related S21 scattering parameter. Lastly, the interferometer was used to image the attenuated propagation of SAWs through a phononic crystal. Results showed good agreement with theoretical simulations. / Thesis (Master, Physics, Engineering Physics and Astronomy) -- Queen's University, 2009-12-08 12:28:35.962

Aluminum nitride (AlN) thin films were deposited on SiO2/Si substrates using the reactive RF magnetron sputtering in this thesis. By means of the analysis of XRD, SEM, TEM and AFM, the optimal deposition conditions of highly C-axis oriented AlN films were obtained with RF power of 190W, sputtering pressure of 3mTorr, nitrogen concentration (N2/N2+Ar) of 30%, and substrate temperature of 400¢J. The characteristics of films annealed at temperature range from 600¢J to 1150¢J with N2 flow for 2 hours has been studied. Experimental results reveal that the films retain the high quality up to 800¢J. But when the temperature above 1000¢J, AlN films will be oxided to AlO:N. In addition, the interdigital transducers (IDTs) were fabricated on the films annealed at 800¢J for 2 hours to study the characteristics of SAW devices. The results show that the central frequency, insertion loss and phase velocity of SAW were 182.25 MHz, -12.95 dB and 5824 m/sec, respectively. At the same time, we try to match the impedence of devices and improve the frequency response by using a simulation program. After the impedence was matched, the insertion are not strongly improved but the frequency response and closed-in sidelobe rejection exhibit better. The effects of temperature on the SAW devices show that the central frequency almost does not shift when the temperature increases. But the insertion loss slightly increases with the temperature increased, the variation is about -0.02 dB/¢J.

M.Ing. / The aim of Spoornet is to provide a minimise predictable service. In order to provide a predictable service, it is necessary to move trains safely and effectively from the place of departure to their destination. The keywords here are safely and effectively. Although support functions such as infrastructure and train control procedures are vital in moving the train, the train or rolling stock as it is generally known, warrants some attention. Defects on the rolling stock are very costly to Spoornet. This is mainly due to the fact that a defect on the rolling stock that goes undetected can cause damage to the rolling stock and the infrastructure. This damage can eventually lead to derailments. Considering that a derailment can cost Spoornet millions of rand and cause delays to the services, it is only logical to spend time preventing derailments. It is for this reason that a workgroup was formed to investigate and solve the problem of defects causing derailments and delays by developing an early warning system. The need for an integrated train condition monitoring system became apparent when considering an early warning system. The objectives of the integrated train condition monitoring system are to provide train condition information to different users, and alarms on detection of emergency or dangerous conditions. Various train defects that may cause damage or derailments were identified. One of them being a flat wheel on a rail vehicle. A flat wheel is characterised by the flattening of the wheel on one or more positions on its circumference, so that the wheel does not have an even and completely round profile. Flat wheels are mostly caused by the wheels of a vehicle becoming locked during braking, and sliding along the rail track. The friction created by this action grinds a flat spot on the wheel. The flat wheel leads to a decline in the riding quality of the rolling stock and a rise in the levels of vibration and noise is evident. But more importantly, the flat spot causes the wheel to roll unevenly, creating impacts on the rail on some points. It is these impacts that can cause damage to the rail and the rolling stock. Depending on the length of the flat spot, the vehicle type and speed, the stresses may be sufficient to cause final failure of the rail or initiate fatigue cracks in the rail. Severe flat wheels are a safety hazard and can in some cases, cause derailments and consequent delays to trains. Smaller flat spots contribute to track deterioration and so increase maintenance costs by damaging the rails, sleepers and ballast. Flat wheels can thus be very costly to Spoornet and its public image. In addition to safety and economic considerations, wheel flats reduce the comfort levels in the passenger coaches and the noises they make is annoying. In an attempt to restrict the damage caused by flat wheels, most railway administrations place a limit on the length of the flats that may stay in service. But to effectively find a flat wheel on rolling stock is currently a very expensive exercise. Flat wheels can be detected by an audible knocking sound when standing next to the rail. This sound is impossible for the driver to hear and therefore goes undetected. Normally flat wheels are detected by random inspection of the rolling stock or when they are brought in for a routine service. The service cycle on rolling stock can be up to 24 months in Spoornet. Considering that a flat wheel has an impact roughly every 3m, a serious flat generates roughly 160 000 impacts on a single trip on the coal heavy haul export line. It is therefore clear that a flat wheel can cause a considerable amount of damage between service cycles. The severity of the problem is however not accurately defined in Spoornet, because up to a few months ago there was no detection system in use to determine the distribution of flat wheels. The research department of the Deutsche Bundesbahn however considers rail fractures due to the flat wheels to be a serious problem with a significant annual replacement cost. There are thus sound safety and economic reasons for wishing to understand the mechanisms of flat wheels and to develop an early warning system using an automatic detector.

[pt] O presente trabalho apresenta uma modelagem da geração de ondas guiadas em estruturas laminadas compósitas através de atuadores piezoelétricos interdigitais.O estudo foi desenvolvido a partir de uma técnica que se baseia na teoria discreta de Reddy e modela os campos de deslocamento e esforços e velocidades generalizadas nas interfaces de uma estrutura laminada. O modelo desenvolvido representa trechos da estrutura em questão através de suas matrizes de impedância, relacionando os esforços e velocidades generalizadas nas interfaces de cada trecho. Após a validação do modelo através da comparação com o método dos elementos finitos, via um pacote comercial, onde foi mostrado que os campos calculados pelos dois métodos obtiveram resultados bastante aproximados nas diferentes faixas de freqüência, foi demonstrada a capacidade do modelo proposto de representar atuadores piezoelétricos interdigitais gerando modos guiados desacoplados em vigas laminadas compósitas. Foram modeladas vigas de alumínio e de ARALL e, após o cálculo das suas curvas de dispersão e dos pontos em que os seis primeiros modos são aproximadamentenão dispersivos, projetaram-se atuadores capazes de gerar de forma desacoplada alguns dos modos guiados nas vigas. A técnica proposta, que pode ser facilmente adaptada pa4ra a simulação da excitação de ondas de Lamb em placas, é capaz de modelar com precisão a rseposta em altas freqüências e pode servir como uma ferramenta valiosa para o desenvolvimento de atuadores interdigitais na monitoração em tempo real da integridade estrutural de compósitos laminados. / [en] The present work is concerned with modeling interdigital piezoeletric actuators for the excitation of guide waves in composite laminated beams. The proposed model is based on Reddys layerwise laminate theory, which relies on piece- wise constant interpolations of the displacement and eletric potential distributions along thethickness of a laminated structure. The laminated beam is also divided in pieces along its span direction, and each piece is represented by an impedance matrix that associates generalized forces with particle velocities on the interfaces of each piece, and also with the applied voltage along the electrodes of the piezoeletric element. Validation of the model was performed with the aid of a commercial Finite Element code. The model was explored to simulate the excitation of uncoupled guided wave modes incomposite laminated beams fabricated from aluminum or ARALL, which is a laminate made ofalternating layers of aluminum and arami-epoxy fiber reinforced composite. From the frequency spectrum of guided waves in the laminated beam, frequencies amd wavelengths at which the first six modes are approximately non-dispersive where determined. With this information, interdigital actuators, capable of generating uncoupled, or weakly coupled, guided modes in the beam were simulated. The proposed model, which is able to accurately reproduce responses in the high frequency/short wavelength range, could be easily adapted to simulate the extation of Lamb waves in laminated plates, and may be a valuable tool in the development of interdigital actuators for health monitoring of laminated composites.

Ce travail porte sur l’étude de matériaux micro/nano structurés permettant l’ingénierie des structures de bande dans le domaine des ondes élastiques. Nous nous sommes intéressés en particulier à l’intégration de ces matériaux dans les dispositifs électro-acoustiques et l’étude de l’interaction avec les ondes acoustiques de surface.La démarche consiste à mener des simulations par la méthode des éléments finis, pour calculer les structures de bande et les spectres de transmission. Nous avons étudié l’effet des paramètres géométriques et élastiques des micro-plots sur les branches acoustiques représentant les modes de surface. Nous avons ensuite discuté l’effet de la symétrie de l’arrangement sur la polarisation des modes de surface. Nous avons également étudié l’effet de la symétrie sur la sensibilité des modes de surface à une variation de température.Sur le plan expérimental, Nous avons élaboré des transducteurs inter-digités sur un substrat piézoélectrique de LiNbO3. Nous avons intégré divers cristaux phononiques composés de micro-plots de Ni, obtenues par électrodéposition. Les spectres de transmission ont été mesurés à l’aide d’un analyseur de réseau et comparés aux résultats theoriques.En dehors des cristaux phononiques basés sur des plots du nickel, d’autres structures ont également été présentées dans ce travail, incluant des matériaux bidimensionnels à base de nanoparticules magnétiques auto-assemblées et des nanofils du nickel électrodéposés à travers des membranes nano-poreuses d’alumine. / This work concerns the study of micro/nano structured materials for the engineering of band structures in the field of elastic waves. We were interested in particular to the integration of these materials in electro-acoustic devices and the study of the interaction with the surface acoustic waves.The approach is to carry out the simulation using the finite element method to calculate the band structures and the transmission spectra. We studied the effect of geometrical and elastic parameters of micro-pillars on acoustic branches representing surface modes. Then we discussed the effect of the symmetry of the arrangement on the polarization of the surface modes. We also investigated the effect of the symmetry on the sensitivity of surface modes with the variation of temperature.Experimentally, we have developed interdigital transducers on a piezoelectric substrate of LiNbO3. We have fabricated various phononic crystals composed of nickel micro-pillars, obtained by electrodeposition. The transmission spectra were measured by a network analyzer and compared with the theoretical results.Besides the phononic crystals based on nickel pillars, some other periodic micro/nano structures were also involved in this work, such as two dimensional materials based on self-assembled magnetic nanoparticles and nickel nanowires electroplated through nano-porous alumina membranes.