Surface Acoustic Wave (SAW) devices are key components in RF and IF stages of many electronic systems. A Surface Acoustic wave is a mechanical wave, which is excited on the surface of a piezoelectric substrate, when an alternating electric voltage is applied through a comb-like interdigital transducer (electrodes) patterned on it. Most SAW applications to date have been in the sub-2GHz region, but emerging applications require SAW devices at higher frequencies. The traditional models are inadequate to account for pronounced second order effects at the GHz range and also new microfabrication techniques are required to obtain quality devices as the critical dimensions shrink into the nano-scale range at these frequencies. The finite element method (a numerical method of solving differential equations) has the potential to account for these effects and ever increasing sub-micron processing capabilities of LIGA (X-ray lithography) present a promising outlook for high frequency SAW device modeling and fabrication respectively. <p>A finite element model has been developed using commercial software ANSYS for one port SAW resonators and is presented in this thesis. The one port SAW resonators are generally connected in form of ladder networks to form low-loss SAW filters. The spacing between the electrodes and the velocity of the SAW determine the frequency of operation of these devices. A finite element model has been developed for three different types of SAWdevices namely Rayleigh, leaky and longitudinal leaky SAW (LLSAW). The LLSAW has higher velocity as compared to other two types and hence considered in this work as a good prospect for high frequency SAW devices. <p>A full finite element model could not be solved due to high computing requirements and hence some assumptions were made and the results were validated against published results in the literature. The results indicate that even with simplifying assumptions and approximations FE model provides reasonably accurate results, that can be used in device design. Some of the simulations (in LLSAW based devices) in this work were also done with a view towards using LIGA (X-ray lithography) for fabrication of high frequency devices as they have the capability for high aspect ratios.

Surface Acoustic Wave (SAW) devices are key components in RF and IF stages of many electronic systems. A Surface Acoustic wave is a mechanical wave, which is excited on the surface of a piezoelectric substrate, when an alternating electric voltage is applied through a comb-like interdigital transducer (electrodes) patterned on it. Most SAW applications to date have been in the sub-2GHz region, but emerging applications require SAW devices at higher frequencies. The traditional models are inadequate to account for pronounced second order effects at the GHz range and also new microfabrication techniques are required to obtain quality devices as the critical dimensions shrink into the nano-scale range at these frequencies. The finite element method (a numerical method of solving differential equations) has the potential to account for these effects and ever increasing sub-micron processing capabilities of LIGA (X-ray lithography) present a promising outlook for high frequency SAW device modeling and fabrication respectively. <p>A finite element model has been developed using commercial software ANSYS for one port SAW resonators and is presented in this thesis. The one port SAW resonators are generally connected in form of ladder networks to form low-loss SAW filters. The spacing between the electrodes and the velocity of the SAW determine the frequency of operation of these devices. A finite element model has been developed for three different types of SAWdevices namely Rayleigh, leaky and longitudinal leaky SAW (LLSAW). The LLSAW has higher velocity as compared to other two types and hence considered in this work as a good prospect for high frequency SAW devices. <p>A full finite element model could not be solved due to high computing requirements and hence some assumptions were made and the results were validated against published results in the literature. The results indicate that even with simplifying assumptions and approximations FE model provides reasonably accurate results, that can be used in device design. Some of the simulations (in LLSAW based devices) in this work were also done with a view towards using LIGA (X-ray lithography) for fabrication of high frequency devices as they have the capability for high aspect ratios.

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-03-02T13:45:50Z No. of bitstreams: 1 filipemagnomayrinkniquini.pdf: 2365421 bytes, checksum: 954638a44d09253760fe05bbb286600f (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-03-06T19:40:13Z (GMT) No. of bitstreams: 1 filipemagnomayrinkniquini.pdf: 2365421 bytes, checksum: 954638a44d09253760fe05bbb286600f (MD5) / Made available in DSpace on 2017-03-06T19:40:13Z (GMT). No. of bitstreams: 1 filipemagnomayrinkniquini.pdf: 2365421 bytes, checksum: 954638a44d09253760fe05bbb286600f (MD5) Previous issue date: 2009-05-11 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Esta Dissertação apresenta o desenvolvimento de uma nova ferramenta matemática para a análise de sistemas de corrente contínua integrados a sistemas de potência CA. A metodologia é fundamentada no domínio da frequência e é baseada nas equações de injeção de correntes e no fluxo de potência harmônico, estruturados numa programação esparsa e num sistema totalmente unificado, possuindo grande agilidade e robustez na simulação dos sistemas. São construídos modelos completos e detalhados dos principais componentes do sistema, com representação completa e explícita dos sistemas CA e CC, bem como das características não-lineares dos conversores de potência, permitindo uma completa análise dos efeitos harmônicos no sistema, inclusive no que diz respeito aos acoplamentos harmônicos. A modelagem proposta visa suprir as limitações geralmente encontradas nas metodologias que se baseiam no domínio da frequência para a simulação de sistemas CC, desenvolvendo uma ferramenta eficiente para análise desses sistemas no domínio da frequência. O sistema permite a análise de elos CC de alta complexidade, como conversores de 12 pulsos e acoplamentos assíncronos. A validação do modelo desenvolvido é realizada através de simulações comparativas no domínio do tempo pelo ATP (Alternative Transients Program). / This dissertation presents the development of a new mathematic methodology to simulate and to analyze DC networks integrated to AC power systems. The proposed methodology is developed in frequency domain and it is based on three-phase harmonic current injection equations structured in a Newton-Raphson unified matrix system. This scheme allows the complete and explicit representation of integrated DC and AC systems, as well as the modeling of power converters non-linear characteristics. The agility and robustness in computational simulation using the proposed model are guaranteed by sparse and memory management techniques. The developed methodology presents an efficient harmonic simulation tool that overcomes the limitations of existing methods for integrated AC/DC systems simulation. The proposed model can simulate HVDC system of high complexity such as the ones based on 12-pulses converters and used to interconnect unbalanced and asynchronous AC networks. The validation is accomplished by comparative simulations between the developed methodology in frequency domain against the ATP (Alternative Transients Program) in time domain.

Diploma thesis deals with static and dynamic analyses of a slender bridge structure behavior. The footbridge structure model was created in ANSYS 14.5 programing system. Static and a modal analyses were made afterwards and according to these analyses dynamic wind load and dynamic pedestrian load were applied. Wind load was applied as option of deck without a handrail and as option of deck with fully airtight handrail. Pedestrians were perceived as group of pedestrians and as a sparse crowd. Both applied loads were solved by harmonic analyses. Results of these analyses are resonance curves and tables of accleration.