Dissertations / Theses: 'Nearfield'

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Harris, Michael C. "Development of an Energy-Based Nearfield Acoustic Holography System." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd835.pdf.

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Abhayapala, P. Thushara D., and Thushara Abhayapala@anu edu au. "Modal Analysis and Synthesis of Broadband Nearfield Beamforming Arrays." The Australian National University. Telecommunications Engineering Group, 2000. http://thesis.anu.edu.au./public/adt-ANU20010905.121231.

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This thesis considers the design of a beamformer which can enhance desired signals in an environment consisting of broadband nearfield and/or farfield sources. The thesis contains: a formulation of a set of analysis tools which can provide insight into the intrinsic structure of array processing problems; a methodology for nearfield beamforming; theory and design of a general broadband beamformer; and a consideration of a coherent nearfield broadband adaptive beamforming problem. To a lesser extent, the source localization problem and background noise modeling are also treated. ¶: A set of analysis tools called modal analysis techniques which can be used to a solve wider class of array signal processing problems, is first formulated. The solution to the classical wave equation is studied in detail and exploited in order to develop these techniques. ¶: Three novel methods of designing a beamformer having a desired nearfield broadband beampattern are presented. The first method uses the modal analysis techniques to transform the desired nearfield beampattern to an equivalent farfield beampattern. A farfield beamformer is then designed for a transformed farfield beampattern which, if achieved, gives the desired nearfield pattern exactly. The second method establishes an asymptotic equivalence, up to complex conjugation, of two problems: (i) determining the nearfield performance of a farfield beampattern specification, and (ii) determining the equivalent farfield beampattern corresponding to a nearfield beampattern specification. Using this reciprocity relationship a computationally simple nearfield beamforming procedure is developed. The third method uses the modal analysis techniques to find a linear transformation between the array weights required to have the desired beampattern for farfield and nearfield, respectively. ¶: An efficient parameterization for the general broadband beamforming problem is introduced with a single parameter to focus the beamformer to a desired operating radius and another set of parameters to control the actual broadband beampattern shape. This parameterization is derived using the modal analysis techniques and the concept of the theoretical continuous aperture. ¶: A design of an adaptive beamformer to operate in a signal environment consisting of broadband nearfield sources, where some of interfering signals may be correlated with desired signal is also considered. Application of modal analysis techniques to noise modeling and broadband coherent source localization conclude the thesis.

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Terrell, Stephen John. "Design of a bistatic nearfield array for an expanded volume." Thesis, Available online, Georgia Institute of Technology, 2005, 2005. http://etd.gatech.edu/theses/available/etd-03172005-140730/unrestricted/terrell%5Fstephen%5Fj%5F200505%5Fmast.PDF.

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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2005.
Rogers, Peter, Committee Chair ; Ginsberg, Jerry, Committee Member ; Trivett, David, Committee Member. Includes bibliographical references.

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Möller, Elias [Verfasser]. "Handheld optoacoustic probe facilitating nearfield investigations through a transparent detector / Elias Möller." Hannover : Gottfried Wilhelm Leibniz Universität Hannover, 2020. http://d-nb.info/1222160412/34.

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Filyayev, Anton A. "Noise Source Evaluation of Misalignment and Elastomeric Couplings using Nearfield Acoustic Holography." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535373234815763.

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Sexton, Robert Christopher. "A nearfield investigation into the sound pressure levels of high speed jet plumes." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386665.

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Brandstetter, Matthias [Verfasser], and Markus [Akademischer Betreuer] Lippitz. "Apertureless Scanning Nearfield Optical Microscopy with Ultra-high Temporal Resolution / Matthias Brandstetter. Betreuer: Markus Lippitz." Bayreuth : Universität Bayreuth, 2016. http://d-nb.info/1082289116/34.

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Woolston, Scott R. "Development of methods to propagate energy density and predict farfield directivity using nearfield acoustic holography /." Diss., CLICK HERE for online access, 2009. http://contentdm.lib.byu.edu/ETD/image/etd3016.pdf.

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Woolston, Scott Richard. "Development of Methods to Propagate Energy Density and Predict Farfield Directivity Using Nearfield Acoustic Holography." BYU ScholarsArchive, 2009. https://scholarsarchive.byu.edu/etd/1726.

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Acoustical-based imaging systems have found merit in determining the behavior of vibrating structures. This thesis focuses on the continued development of the nearfield acoustic holography (NAH) approach. Conventional NAH consists of first measuring the pressure field on a two-dimensional conformal surface and then propagating this data back to the vibrating structure to obtain information about the source, such as the normal velocity distribution. Recent work has been done which incorporates particle velocity information into the traditional NAH measurements to reduce the number of measurements required. This advancement has made NAH a more affordable tool for acoustical imaging and sound field characterization. It is proposed that the inclusion of velocity information into traditional NAH can further increase its usefulness. By propagating the velocity and pressure values independently and recombining them on the reconstruction surface, the pressure field and energy density fields can be predicted at any point in the sound field. It is also proposed that the same NAH measurement can be used to predict farfield directivity. The inclusion of velocity values into the NAH technique also provides a means for predicting energy density (ED) anywhere within the acoustic field. These two developments would allow a single NAH measurement to provide much more information about an acoustic source and its radiated sound field. Experimental testing shows that NAH is successful at predicting the shape of the resulting ED field and directivity pattern with some error in amplitude. The best performance of the technique is with a planer source resulting in an average amplitude error of 18.5% over the entire field.

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Wright, Alan James. "Distortion in conformable masks for evanescent near field optical lithography." Thesis, University of Canterbury. Electrical and Computer Engineering, 2007. http://hdl.handle.net/10092/1161.

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In this thesis the in-plane pattern distortion resulting from the use of Evanescent Near Field Optical Lithography (ENFOL) masks was investigated. ENFOL is a high resolution low-cost technique of lithography that is able to pattern features beyond the diffraction limit of light. Due to its use of the evanescent near field, ENFOL requires the use of conformable masks for intimate contact. Such masks can stretch and skew as they come into contact with silicon substrates and therefore distort the high resolution features patterned on them. It was desired to measure this distortion to ascertain the patterning performance of ENFOL masks and possibly correct for any uniform distortion found. To this end a sophisticated measuring process was successfully demonstrated. This involved the use of a Raith 150 Electron Beam Lithography (EBL) system with precision laser interferometer stage and metrology software module for automated measurements. Custom software was written for the Raith to enable it to take additional measurements to compensate for electron beam drift. Processing algorithms were then employed to using the measurements to compensate for beam drift and correcting for shift and rotation systematic errors. The performance of the in-plane distortion measuring process was found to have a precision of 60nm. With the ability to measure distortion, ENFOL masks were used to pattern substrates and distortion was found to be large, on the order of 1µm. This is much larger than desired for sub 100nm patterning as is expected of ENFOL. The distortions were non-uniform patterns of localised displacements. This, the observation of Newton's rings beneath a test mask and the observation of a single particle distortion across measurements of the same mask across different loadings in the EBL pointed to particulate contamination causing the distortion. In order to prove beyond doubt that particulate contamination was the cause of the spurious distortions, mechanical modelling using the Finite Element Method (FEM) of analysis was employed. The results from this matched the distortions observed experimentally, particles 20-40µm modelling the observed distortion.

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Ward, Darren Brett, and db_ward@hotmail com. "Theory and application of broadband frequency invariant beamforming." The Australian National University. Faculty of Engineering and Information Technology, 1996. http://thesis.anu.edu.au./public/adt-ANU20050418.112459.

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In many engineering applications, including radar, sonar, communications and seismology, the direction of impinging signal wavefronts can be used to discriminate between competing sources. Often these source signals cover a wide bandwidth and conventional narrowband beamforming techniques are ineffective, since spatial resolution varies significantly across the band. In this thesis we consider the problem of beamforming for broadband signals, primarily when the spatial response remains constant as a function of frequency. This is called a frequency invariant beamformer (FIB).¶ Rather than applying the numerical technique of multi-parameter optimisation to solve for the beamformer parameters, we attempt to address the fundamental nature of the FIB problem. The general philosophy is to use a theoretical continuous sensor to derive relationships between a desired FI beampattern and the required signal processing structure. Beamforming using an array of discrete sensors can then be formulated as an approximation problem. This approach reveals a natural structure to the FIB which is otherwise buried in a numerical optimisation procedure.¶ Measured results from a microphone array are presented to verify that the simple FIB structure can be successfully implemented. We then consider imposing broadband pattern nulls in the FI beampattern, and show that (i) it is possible to impose an exact null which is present over all frequencies, and (ii) it is possible to calculate a priori how many constraints are required to achieve a null of a given depth in a FIB. We also show that the FIB can be applied to the problem of broadband direction of arrival (DOA) estimation and provides computational advantages over other broadband DOA estimators.¶ Through the theoretical continuous sensor approach, we show that the FIB theory can be generalised to the problem of designing a general broadband beamformer (GBB) which realizes a broadband angle-versus-frequency beampattern specification. Coupled with a technique for radial beampattern transformation, the GBB can be applied to a wide class of problems covering both nearfield beamforming (in which the shape of the impinging wavefront must be considered and farfield beamforming (which is simplified by the assumption of planar wavefronts) for a broadband beampattern specified over both angle and frequency.

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Colinas, Nilton Gilber. "Caracterização vibroacustica usando holografia acustica de campo proximo." [s.n.], 1999. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265385.

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Orientador: Jose Maria Campos dos Santos
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
Made available in DSpace on 2018-07-25T04:25:40Z (GMT). No. of bitstreams: 1 Colinas_NiltonGilber_M.pdf: 6668829 bytes, checksum: 0f5fe00364a351d5d5859c9c042c161c (MD5) Previous issue date: 1999
Resumo: Neste trabalho procurou-se explorar a técnica de Holografia Acústica de Campo Próximo (Nearfield Acoustic Holography - NAB), que tem se mostrado como uma forma de análise para problemas vibroacústicos. A holografia é um processo que permite determinar as características de um campo de ondas acústicas usando a Transformada de Fourier Discreta (Discrete Fourier Transform - DFT), a partir de uma grade de pontos de medições regularmente espaçados obtidos em um ambiente acústico onde a função de Green é conhecida. O presente trabalho apresenta uma breve revisão dos princípios desta técnica com uma aplicação na reconstrução de propriedades vibroacústicas de estruturas. O campo de pressão, campo de velocidade das partículas e intensidade acústica gerados por um elemento estrutural vibrante foram as grandezas reconstruídas através da técnica NAH em diferentes posições do espaço. A fim de minimizar os problemas de leakage oriundos do processamento dos sinais, a Série de Fourier Discreta Regressiva (Regressive Discrete Fourier Series - RDFS) foi utilizada como alternativa às técnicas de janelamento do sinal. Resultados obtidos para uma estrutura do tipo placa são analisados, validados e comparados com previsões teóricas
Abstract: In this work, the Nearfield Acoustic Holography technique - NAH was explored as an way to analyze vibroacoustic problems. Holography is a process that allows to determine acoustic fields characteristics using a Discrete Fourier Transform - DFT, from a regular grid of measurements obtained in an acoustic environment for which the Green' s function is known. This work presents a brief principle's review of this technique with an application on the reconstruction of the vibroacoustic properties of structures. The pressure field, particle velocity field and acoustical intensity generated by a vibrating structural element were reconstructed through the NAH technique in different spatial positions. ln order to minimize spatial leakage problems from signal processing a Regressive Discrete Fourier Series ¿ RDFS was utilized as an alternative to windowing techniques. Results obtained from a plate type structure were analyzed, validated and compared with theoretical predictions
Mestrado
Mecanica dos Solidos
Mestre em Engenharia Mecânica

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Moraes, Elson Cesar 1976. "Intensidade acustica supersonica : implementação e verificação." [s.n.], 2006. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265371.

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Orientador: Jose Maria Campos dos Santos
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho apresenta-se uma implementação e avaliação experimental da grandeza acustica denominada de Intensidade Acustica Supersonica (IAS), a qual permite determinar a parcela da intensidade acustica de uma fonte sonora que sera radiada para o campo distante. Tal grandeza permite quantificar de forma mais precisa a eficiencia de radiação ou não de radiadores acusticos na solução dos problemas de vibroacustica. A IAS origina-se da Holografia Acustica de Campo Proximo (Nearfield Acoustic Holography - NAH) e tem por objetivo identificar as regiões de uma fonte de ru?do que contribuem para a potencia sonora radiada para o campo distante (supersonica) filtrando, consequentemente, a parcela referente as ondas sonoras recirculantes e evanescentes (subsonicas). O trabalho apresenta uma breve revisão teorica dos fundamentos da holografia acustica plana usando a transformada de Fourier e sua extensão para obtenção da Intensidade Acustica Supersonica. Com base no NAH para sistemas em coordenadas Cartesiano (holografia plana) implementou-se em linguagem MatLab um algoritmo do calculo da IAS e simulações em estrutura plana do tipo placa foram realizadas. Os resultados simulados foram verificados atraves de medições experimentais em uma placa real com as mesmas propriedades, dimensões, condições iniciais e de contorno. Os resultados obtidos são analisados e discutidos
Abstract: This work presents an experimental implementation and evaluation of the acoustic parameter named Supersonic Acoustic Intensity (SAI) which permits determining the part of the acoustic intensity of sound source that will be radiate to farfield. This parameter permits quantify precisely the radiation efficiency or acoustic radiator to solve the vibroacoustic problems. SAI had origin from Nearfield Acoustic Holography (NAH) it has as objective identify the regions of the sound source that contribute to the sound power radiated to the far field (supersonic) filtered out as a result the part of the sound recirculating and evanescence waves (subsonic). The work presents a brief theoretical review of the planar acoustic holography fundaments using the Fourier Transformed and its extension to obtain the supersonic acoustic intensity. With base in the NAH for coordinates systems (planar holography) it was implemented in MatLab language an algorithm from the SAI calculus and simulation in planar structure type plate were achieved. The simulated results were verified through experimental measurements in a realistic plate with the same properties, dimension, initial conditions and boundaries. The results obtained are analyzed and discussed.
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica

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Hänßler, Olaf C. [Verfasser], Didier [Akademischer Betreuer] Théron, and Sergej [Akademischer Betreuer] Fatikow. "Multimodal sensing and imaging technology by integrated scanning electron, force, and nearfield microwave microscopy and its application to submicrometer studies / Olaf C. Hänßler ; Didier Théron, Sergej Fatikow." Oldenburg : BIS der Universität Oldenburg, 2018. http://d-nb.info/1157010199/34.

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Hänßler, Olaf C. Verfasser], Didier [Akademischer Betreuer] Théron, and Sergej [Akademischer Betreuer] [Fatikow. "Multimodal sensing and imaging technology by integrated scanning electron, force, and nearfield microwave microscopy and its application to submicrometer studies / Olaf C. Hänßler ; Didier Théron, Sergej Fatikow." Oldenburg : BIS der Universität Oldenburg, 2018. http://d-nb.info/1157010199/34.

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Watada, Shingo Kanamori H. Kanamori H. Anderson Don L. "Part I. Near-source acoustic coupling between the atmosphere and the solid earth during volcanic eruptions. : Part II. Nearfield normal mode amplitude anomalies of the Landers earthquake /." Diss., Pasadena, Calif. : California Institute of Technology, 1995. http://resolver.caltech.edu/CaltechETD:etd-10302007-082547.

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Vasudevan, Namboodiri Mahesh [Verfasser], Arnulf [Akademischer Betreuer] Materny, Veit [Akademischer Betreuer] Wagner, and Günter [Akademischer Betreuer] Flachenecker. "Time Resolved Spectroscopy in the Nearfield and Farfield: Probing Ultrafast Molecular Dynamics and Subwavelength Resolution Imaging / Mahesh Vasudevan Namboodiri. Betreuer: Arnulf Materny. Gutachter: Arnulf Materny ; Veit Wagner ; Günter Flachenecker." Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2013. http://d-nb.info/1087274834/34.

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Mignuzzi, Sandro. "Near-field optical spectroscopy of two-dimensional materials." Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/nearfield-optical-spectroscopy-of-twodimensional-materials(2e5e7a6b-d2b5-4242-bab7-3a66bd6c8c25).html.

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Real materials contain structural defects which significantly affect their properties. Defects, in a general sense, are ubiquitous and encompass the diverse variety of elements capable of disrupting the continuity and translational symmetry of a crystalline lattice, both in terms of its structural morphology, and in terms of local modulation of its electrical and optical properties. In this perspective, atomic vacancies, line vacancies, atomic rearrangements, local doping inhomogeneity, chemically adsorbed adatoms, all fall within the broad category of defects. Thus, the nanoscale details of surface structure plays a pivotal role in understanding the impact defects may have on the overall properties of the material, and this is particularly true for "all-surface" materials such as two-dimensional (2-D) crystals. Even the interface between two atomically thin layers has a strong impact on the electronic and optical properties of few-layered stacks; therefore, also the interface associated with stacking and layer orientation can be viewed as an extend defect in two dimensions. While macroscopic morphological characterization methods can provide averaged information over a lateral extent defined by their spatial resolution, high resolution (i.e. nanoscale) imaging has the potential to unveil important insights into the role of defects that dominate several aspects of surface chemistry and physics. On the one hand, defects in 2-D materials can be seen as deleterious as they may alter their electrical, chemical, magnetic and mechanical properties. On the other hand, the intentional creation of nanoscale defects may offer an additional degree of freedom for engineering their properties. In this perspective, having structural defects can be either detrimental or beneficial, depending on the targeted application. Despite the ever expanding literature on the study of the interplay between defects and the optical, electrical and mechanical properties of two dimensional materials, direct and non-destructive imaging of defect formation at the nanoscale remains a significant challenge. Although techniques such as electron microscopies or scanning tunnelling microscopy can be used to resolve individual lattice defects, they may be destructive or restricted to specific (e.g. conductive) substrates. This thesis presents a nanoscale optical investigation of 2-D materials, such as graphene and single-layer MoS2, with a particular focus on the characterisation of defects. The field enhancement at the tip-apex of a metal-coated atomic force microscopy (AFM) tip is used to decrease the spatial resolution beyond the diffraction limit. In the case of the investigation of Raman scattering, this near-field optical technique is known as tip-enhanced Raman spectroscopy (TERS). TERS is here demonstrated to be a valid technique to probe the distribution of point-like defects at the nanoscale, especially in the case of barely defective graphene. An analytical model to describe near-field imaging of pointlike Raman scatterers, which is of general applicability to zero-dimensional scatterers such as molecules, is presented. The near-field image, constructed from the Raman intensity, is found to depend on the Raman tensor and the orientation of the scatterer. The model can be also used to explain the different values of near-field Raman enhancement observed for different Raman bands. Motivated by the successful optical characterization of defects in graphene by means of Raman spectroscopy, it is now timely to expand the study of structural defects to other 2-D materials, such as semiconducting transition metal dichalcogenides. MoS2 is one of the most prominent members of this newly discovered category of chalcogenide monolayers. Defect-induced Raman scattering of single-layer MoS2 is studied by means of a controlled introduction of defects using ion-bombardment. Phonon confinement is used to explain the evolution of peak widths and shifts, and a metric based on Raman intensities is proposed to quantify defects. To gain insight into the defect-induced Raman processes, polarised and resonance Raman spectroscopy are employed.

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Parisot-Dupuis, Hélène. "Application de l'holographie acoustique en soufflerie par mesures LDV." Thesis, Toulouse, ISAE, 2012. http://www.theses.fr/2012ESAE0035/document.

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L’ Holographie acoustique de champ proche (NAH) est une méthode d’imagerie acoustique robuste, mais son application en écoulement peut être limitée par l’utilisation de mesures intrusives de pression ou de vitesse acoustique. Dans cette étude, une procédure holographique applicable en écoulement utilisant des mesures de vitesse non-intrusives est proposée. Cette méthode est basée sur le théorème intégral de Kirchhoff-Helmholtz convecté. La fonction de Green convectée est alors utilisée pour déterminer des propagateurs spatiaux convectés définis dans l’espace réel et incluant l’effet d’un écoulement subsonique uniforme. Les transformées de Fourier discrètes de ces propagateurs permettent alors d’évaluer les champs acoustiques à partir de la mesure du champ de pression ou de vitesse acoustique normale. Le but étant de développer une méthode de caractérisation de sources aéroacoustiques à partir de mesures de vitesse non-intrusives, cette étude se concentre essentiellement sur les propagateurs réels convectés basés sur la mesure de vitesse acoustique. Afin de valider cette procédure,des simulations ont été menées dans le cas de combinaisons de sources monopolaires et dipolaires convectées corrélées ou non. La procédure holographique développée donne de bons résultats par comparaison aux champs acoustiques théoriques. Une comparaison des résultats obtenus par les propagateurs convectés réels, développés dans cette thèse, avec ceux obtenus par leurs formes spectrales, développés par Kwon et al. fin 2010 pour des mesures de pression acoustique, montre l’intérêt d’utiliser la forme réelle pour la reconstruction de la pression acoustique à partir de la mesure de vitesse acoustique normale. L’efficacité de la procédure développée est confirmée par une campagne de mesure en soufflerie avec un haut-parleur affleurant rayonnant au sein d’un écoulement à Mach 0.22, et des mesures non-intrusives effectuées par Vélocimétrie Laser Doppler (LDV). Les champs de vitesse acoustique utilisés pour la procédure holographique sont dans ce cas extraits des mesures LDV par corrélation avec un microphone de référence. La faisabilité de prendre en compte des variations de l’écoulement dans la direction de reconstruction holographique est également vérifiée
Nearfield Acoustic Holography (NAH) is a powerful acoustic imaging method but its application in flow can be limited by intrusive measurements of acoustic pressure or velocity. In this work, a moving fluid medium NAH procedure using non-intrusive velocity measurements is proposed. This method is based on the convective Kirchhoff-Helmholtz integral formula. The convective Green’s function is then used to derive convective realspace propagators including uniform subsonic airflow effects. Discrete Fourier transforms of these propagators allow then the assessment of acoustic fields from acoustic pressure or normal acoustic velocity measurements. As the aim is to derive an aeroacoustic sources characterisation method from non-inrusive velocity measurements, this study is especially focused on real convective velocity-based propagators. In order to validate this procedure, simulations in the case of combinations of monopolar and dipolar sources correlated or not, radiating invarious uniform subsonic flows, have been performed. NAH provides very favorable results when compared to the theoretical fields. A comparison of results obtained by real convective propagators, developed in this work, and those obtained by the spectral ones, developed by Kwon et al. at the end of 2010 for acoustic pressure measurements, shows the interest of using the real-form for NAH acoustic pressure reconstruction from normal acoustic velocity measurements. The efficiency of the developed procedure is confirmed by a wind tunnel campaign with a flush-mounted loudspeaker radiating in a flow at Mach 0.22 and non-intrusive Laser Doppler Velocimetry (LDV) measurements. Acoustic velocity fields used for the NAH procedure are in this case extracted from LDV measurements by correlation with a reference microphone. The feasibility of taking into account mean flow variations in the direction of NAH reconstruction is also checked

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Silva, Gerson Albuquerque da. "Estudo acústico de moedas." reponame:Repositório Institucional da UFABC, 2014.

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Orientador: Prof. Dr. Mário Minami
Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Engenharia da Informação, 2014.
Determinar as características de um objeto é essencial para conhecê-lo e pode ser útil para colocá-lo em um sistema de classificação. Este trabalho pretendeu investigar as frequências naturais de moedas nacionais - as quais, do ponto de vista estritamente físico, tratam-se de discos metálicos- com o auxílio das ferramentas de Processamento Digital de Sinal. O método utilizado consistiu em excitar moedas fixas de modo a fazê-las vibrar segundo suas frequências naturais. Da teoria de Vibração de Discos, as propriedades acústicas de tais discos se relacionam com suas propriedades físicas, com o material de que tais discos são compostos e com as condições de contorno de suas partes componentes. Moedas, mesmo de geometria semelhante, mas feitas de diferentes materiais apresentam conjuntos diferentes de frequências naturais. Assim, moedas de um real fabricadas antes de 2002- quando se deu a mudança dos materiais empregados na cunhagem das moedas ¿ apresentam frequências nitididamente diferentes de uma moeda produzida a partir de então. Para atingir o objetivo proposto, utilizou-se aqui da técnica acústica de campo próximo. Dadas as pequenas dimensões do objeto, foi construído um array de microfones de capsulas de eletreto. O dispositivo foi responsável pela captação da vibração e por sua transdução para ondas sonoras. A caracterização acustica de moedas nacionais talvez possa ser útil no controle de seu processo de cunhagem e, também, para evitar fraudes.
The Determination of the characteristics of an object is essential to understand it and it can be helpful to build a system of classification. This work aims to investigate the natural frequencies of brazilian coins ¿ which are, from a purely physical standpoint,a kind of small plate metal- with the help of Digital Signal Processing tools. The method used was to excite clamped coins in order to make them vibrate according to their natural frequencies. According to the Vibration Theory, the acoustics properties of such plates are related to their physical properties, as well as with the material from which they are made of and the boundary conditions of its component parts. Coins even of similar geometry but made of different materials have different sets of natural frequencies. Thus, a real coin manufactured before 2002 - when there was a change of materials used in the minting of coins - has different set of frequencies from a coin produced since then. To achieve the goal that was proposed, we used here the acoustic near-field technique.Given the small size of the object, a microphones electret capsules array was built. They was responsible for the vibration capture and its transduction to the sound waves. The acoustic characterization of the national coins in circulation in Brazil, might be useful for controlling the process of minting and also to prevent frauds.

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Gregorio, Helvio Prevelato. "Modelagem numérica da dispersão da pluma do emissário submarino de Santos." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/21/21132/tde-19012010-165632/.

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A dispersão dos efluentes do emissário submarino de Santos foi estudada por meio de modelagem numérica, acoplando-se modelos hidrodinâmico, de dispersão no campo próximo e no campo distante. As simulações foram realizadas para o projeto original do emissário de 1979, para a nova configuração de 2009 e para terceiro arranjo sugerido por este estudo, que dobra o comprimento do duto em relação ao projeto original. As diluições foram modeladas em cenários ambientais com propriedades marinhas e estuarinas climatológicas de verão, juntamente com forçantes atmosféricas climatológicas da mesma estação, simulando ausência de vento, presença de vento médio e presença de vento médio seguido por passagem de frente fria climatológica (obtida por este estudo). Com as devidas validações do modelo hidrodinâmico, a diluição, tanto no campo próximo quanto no campo distante, foi fortemente regida pela estratificação da coluna dágua e pela velocidade das correntes. O cenário sem vento apresentou as maiores estratificações, menores velocidades e originou as menores diluições em oposição ao cenário que simulou a passagem de frente fria. Dentre os projetos de emissário analisados, aquele proposto por este estudo apresentou plumas com menores comprimentos horizontais e menores profundidades, atingindo a costa uma só vez. O projeto original e o novo que será implantado em 2009 apresentaram, comparativamente, plumas mais extensas e profundas, interceptando a costa em diversas situações.
Sewage plume dispersion for the Santos outfall was studied using numerical models, coupling hydrodynamic, near field and far field models. Experiments were conducted for the 1979 original outfall design, for the new 2009 outfall configuration and also for a third arrangement suggested here, which duplicates the emissary length comparatively to the original 1979 project. Dilutions were modeled in environmental sceneries with summer climatological estuarine and marine properties, together with climatological atmospheric forcing for the same season, simulating no wind conditions, mean wind forcing and mean wind followed by a climatological cold front (developed at this study) passage. After the appropriate hydrodynamic numerical model validation, the dilution, at the near field as well as at the far field, was strongly determined by the vertical water stratification and by the current velocities. The no-wind scenery presented the highest stratifications, smallest velocities and originated the smallest dilutions, in opposition to the cold-front-scenery. Among the sewage outfall projects considered, the one presented at this study showed the shallowest plumes, with the smallest horizontal lengths, reaching the coast only once. The original 1979 project and the 2009 configuration showed, comparatively, the deepest and widest plumes reaching the coast in several situations.

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Escuder, Silla Eva María. "Estudio del comportamiento acústico de estructuras multicapa mediante nah." Doctoral thesis, Universitat Politècnica de València, 2008. http://hdl.handle.net/10251/1860.

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El objeto de esta tesis se centra el estudio del comportamiento acústico de estructuras multicapa, utilizando como herramienta, entre otras, la denominada "Holografía acústica de campo cercano" (NAH, Nearfield Acoustical Holography). Las conclusiones obtenidas y las herramientas desarrolladas en este estudio tienen implicaciones en dos ámbitos, el aislamiento acústico con particiones ligeras multicapa, y la optimización de la radiación de sistemas electroacústicos basados en la vibración de un panel provocada por un elemento excitador de tipo dinámico (caso de los altavoces planos). El proceso para conseguir predicciones acertadas del comportamiento de estructuras multicapa, tanto desde el punto de vista de la aplicación acústica de la edificación, como el electroacústico (mejora de prestaciones de altavoces), debe partir, necesariamente de un conocimiento preciso de las características acústicas de los componentes, es decir, cada una de las capas. Este estudio constituye la primera fase de la investigación y del trabajo. La validación de las teorías sobre el aislamiento acústico lleva contigo el ensayo de diferentes materiales y configuraciones. El objeto es aumentar al máximo el índice de aislamiento de una cierta configuración, intentado disminuir en lo posible los costes. El estudio del comportamiento acústico de distintas configuraciones suele realizarse en cámara de transmisión. Los resultados de las medidas en estas condiciones no tienen por qué coincidir con los obtenidos con medidas "in situ", ya que las condiciones de montaje son hasta cierto punto incontrolables. Existen diversos trabajos donde se desarrollan los diferentes modelos, teorías y técnicas de medición con este fin, desde modelos y teorías para caracterizar materiales absorbentes hasta métodos de caracterización de materiales absorbentes medidos en el tubo de Kundt. También existen medidas de una determinado variable acústica, permiten obtener los parámetros de entrada necesarios para los progr
Escuder Silla, EM. (2005). Estudio del comportamiento acústico de estructuras multicapa mediante nah [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/1860
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23

Hedia, Sassia. "Identification des sources de perturbations par retournement temporel : application à la compatibilité électromagnétique en champ proche." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST021.

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Le progrès technologique, en particulier la montée en fréquences et l’intégration des systèmes embarqués, crée des interférences électromagnétiques (EMI) et des problèmes critiques. D’où la présence de multiples sources de perturbation pouvant affecter le bon fonctionnement des circuits électroniques et électriques. C’est pourquoi la caractérisation de ces sources est devenue essentielle permettant ainsi l’évaluation des émissions rayonnées et la prédiction du comportement des dispositifs électroniques. Les travaux présentés dans cette thèse s’intéressent à l’élaboration de modèles de rayonnement équivalents qui permettent de prendre en compte les aspects CEM pour réduire les perturbations EM. Premièrement, l’étude réalisée consiste à la mise en œuvre d’une méthode inverse temporelle basée sur le retournement temporel électromagnétique en utilisant le champ proche mesuré au-dessus du système. Ensuite, nous avons exploité la méthode proposée pour analyser des structures qui émettent des signaux transitoires. Une validation de la méthode proposée a été réalisée dans une première étape en se basant sur des cartographies de champs EM calculés avec les équations analytiques qui décrivent le champ EM rayonné.Dans ce cas, les structures sous tests contiennent des sources de rayonnement connues à l’avance et qui sont excités chacune par un signal temporel de type gaussien. En deuxième étape, la validation expérimentale de la méthode a été effectuée en utilisant des mesures en champ proche au-dessus des structures réelles et en utilisant des signaux d’excitation judicieusement choisis et qui sont riches en fréquences. Les résultats obtenus ont pu montrer la robustesse de notre méthode vis-à-vis des erreurs de mesures. En plus des validations sur des circuits académiques, nous avons appliqué la méthode proposée à un circuit de l’électronique de puissance : un convertisseur de commerce de type AC/DC. Enfin, pour évaluer la performance de la méthode inverse temporelle basée sur le retournement temporel électromagnétique, nous avons mené une étude comparative avec la méthode inverse classique basée sur les algorithmes génétiques dans les deux domaines fréquentiel et temporel. Les résultats obtenus ont montré les performances et l’efficacité de la méthode proposée à fournir un modèle équivalent du système étudié sur de larges bandes de fréquences en un temps de calcul restreint
The technological progress, in particular the increase in frequencies and the integration of embedded systems, creates critical problems of electromagnetic interference (EMI). Hence, the presence of multiple disturbance sources may affect the proper functioning of electronic circuits. Therefore, the characterisation of these sources becomes essential for the evaluation of radiated emissions and the prediction of the behaviour of electronic devices. The main purpose of this thesis is to study the development of equivalent radiation models that allow EMC considerations and reduce EM disturbances. First, the implementation of the inverse time domain (TD) method based on the electromagnetic time reversal technique has been carried in the near field. The aim here is to use the proposed method for structures that emit transient signals. A validation of the proposed method has been performed based on EM field maps calculated with analytical equations that describe the radiated EM field.In this case, structures under test contain radiating sources that are controlled in advance and excited by a Gaussian type signal. In addition, an experimental validation of the proposed method has been also performed using near field measurements in two different cases of real structures and using a well-chosen excitation signal, which contains many frequencies of resonance. Furthermore, in addition to the academic circuits, we have carried out an experimental application of the proposed method using a power electronics circuit (AC/DC converter). Finally, in order to evaluate the performance of the inverse TD method based on electromagnetic time reversal, a comparative study has been conducted using the classical inverse method based on genetic algorithms in both frequency and time domains. Predicted resulted have shown the high performance and the efficiency of the proposed method and demonstrated that it provides an adequate equivalent model of the device under test on a wide frequency band and in a limited calculation time

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Friede, Sebastian. "Elementare optische Anregungen in Molekülen, Hybridsystemen und Halbleitern." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2015. http://dx.doi.org/10.18452/17410.

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Methoden der optischen Spektroskopie gestatten es, über die Licht-Materie-Wechselwirkung Aussagen über verschiedene Materialsysteme zu treffen. Im Zuge dieser Arbeit wurde das Potential von stationären und transienten optischen Methoden– u.a. der Nahfeldmikroskopie– zur qualitativen und quantitativen Analyse prototypischer Materialsysteme genutzt. Die Kombination von aufeinander abgestimmten organischen und anorganischen Materialien führt auf so genannte Hybridsysteme. Die Vielzahl verschiedener Halbleiter- und Molekülsysteme lässt eine Vielzahl möglicher Hybride zu. Diarylethene (DTE) bilden eine Klasse photochromer molekularer Systeme. In der Arbeit wird der Frage nach den fundamentalen optischen Eigenschaften und dem Schaltverhalten des hier vorliegenden prototypischen DTE nachgegangen. Die zweite untersuchte Klasse von Systemen sind Hybride, welche aus dem anorganischen Halbleiter Zinkoxid (ZnO) und einer molekularen Bedeckung bestehen. Bei den Untersuchungen dieser Hybride wurde der Frage nach den optisch induzierten physikalischen Prozessen an bzw. in der Grenzschicht zwischen der molekularen Bedeckung und dem anorganischen Halbleiter nachgegangen. Im Speziellen wurde ein exzitonischer Oberflächenzustand (SX) beobachtet. Die Anwendung zeitaufgelöster Tieftemperaturnahfeldmikroskopie deckt die Transporteigenschaften der SX entlang der Oberfläche auf. Weiterhin wurden prototypische Laserdioden auf der Basis des Halbleiters Galliumnitrid (GaN) untersucht. Der Unterschied zwischen den hier untersuchten GaN-Bauelementen liegt in der Materialzusammensetzung der in die Bauelemente integrierten Wellenleiter. Eine Optimierung der Wellenleiter kann zu einer Steigerung der Effizienz der Bauelemente führen. Die Analyse der Bauelemente erfolgte mit Methoden der Nahfeldmikroskopie. Die Experimente decken Unterschiede in der Struktur der Bauelemente auf und erlauben Messungen der in den Wellenleitern geführten Lasermoden.
Methods of optical spectroscopy allow for the investigation of diverse material systems via the interaction between light and matter. Stationary and transient methods of optical spectroscopy were exploited– particularly near-field scanning optical microscopy– for qualitative and quantitative analyses of prototypical material systems. The combination of organic and inorganic materials which are adapted to each other yields a so-called hybrid system. The wide range of different semiconductor materials and molecular systems available results in a multitude of hybrid systems. Diarylethenes (DTE) form one class of photoswitchable molecular systems. This work focuses on the fundamental optical properties and the photochromic switching behavior of a prototypical DTE species. The second class of investigated prototypical sample systems consists of the inorganic semiconductor zinc oxide (ZnO) covered with molecular monolayers. The studies performed on this sample system focus on optically-induced physical processes localized at the interface between the inorganic semiconductor and the organic adlayer. In particular, a surface-excitonic state (SX) was investigated. The application of time-resolved low-temperature near-field scanning optical microscopy enables the monitoring of lateral SX transport along the organic-inorganic interface. The third prototypical sample class considered consists of two gallium nitride (GaN) diode lasers. The difference between the two investigated prototypical diode lasers is the different material composition of the waveguides integrated within the lasers. An optimization of the waveguide material composition may be used to increase the laser efficiency. Near-field scanning optical microscopy was used to analyze the two different diode lasers. The experiments show the structural differences between the distinct laser architectures and revealed the mode profiles of the waveguides within the diode lasers.

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Mcnaughton, James. "Turbulence modelling in the near-field of an axial flow tidal turbine in Code_Saturne." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/turbulence-modelling-in-the-nearfield-of-an-axial-flow-tidal-turbine-in-codesaturne(54c9b513-2472-4c61-a521-8ef73428465b).html.

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This Thesis presents simulation of flow past laboratory-scale and full-scale tidal stream turbines (TST) using EDF's open-source CFD solver Code_Saturne. The work shows that detailed results may be obtained with confidence and that greater information on the loading and wake structure is available than other methods, such as blade element momentum theory.Results are obtained using a new sliding-mesh method that has been implemented in Code_Saturne as part of this work. The sliding-mesh method uses internal Dirichlet boundary conditions with values on the interface prescribed via a halo-point method. Parallel performance is optimised by a carefully-chosen method of exchanging information between specific processes. Validation is provided for flow past a rotating cylinder and a sphere.For the laboratory-scale TST, Reynolds-Averaged Navier-Stokes models are used to model turbulence. The k-omega-SST and Launder-Reece-Rodi (LRR) models yield good agreement with experimental values of power and thrust coefficients as a function of tip-speed ratio (TSR). The standard k-epsilon model is shown to perform poorly due to an overprediction of turbulent kinetic energy upstream of the rotor plane. The k-omega-SST model is then used to examine wake behaviour for parametric studies of turbulence intensity and TSR. Increased turbulence levels are shown to reduce the downstream propagation of the wake because of increased mixing. The near wake is influenced by the TSR, whilst the far wake is independent of TSR.The predicted effect of tidal conditions typical of the EMEC test site are considered for flow past Tidal Generation Limited's 1MW TST. The effect of sheared-velocity profiles leads to an increase in loading on an individual turbine blade at the point of a rotation where velocity shear is greatest. The effect of increased yaw angle leads to large fluctuations of the power coefficient, but smaller fluctuations of the thrust coefficient. Mean values of thrust and power decrease as a function of the cosine of the yaw angle and yaw angle squared respectively.

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Schröder, Tim. "Integrated photonic systems for single photon generation and quantum applications." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16723.

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Im Rahmen der vorliegenden Dissertation wurden neuartige integrierte Einzelphotonenquellen (EPQ) und ihre Anwendung für die Quanteninformationsverarbeitung entwickelt und untersucht. Die Erzeugung von Einzelphotonen basiert auf einzelnen Defektzentren in nanometergroßen Diamantkristallen mit einzigartigen optischen Eigenschaften: Stabilität bei Zimmertemperatur ohne optisches Blinken. Diamantkristalle mit Größen bis unter 20nm wurden mit neuartigen „pick-and-place“ Techniken (z.B. mit einem Atomkraftmikroskop) in komplexe photonische Strukturen integriert. Zwei unterschiedliche Ansätze für die Realisierung der neuartigen EPQ wurden verfolgt. Beim ersten werden fluoreszierende Diamantkristalle in nano- und mikrometergroße Faser-basierte oder resonante Strukturen in einem „bottom-up“ Ansatz integriert, dadurch werden zusätzliche optische Komponenten überflüssig und das Gesamtsystem ultra-stabil und wartungsfrei. Der zweite Ansatz beruht auf einem Festkörperimmersionsmikroskop (FIM). Seine Festkörperimmersionslinse wirkt wie eine dielektrische Antenne für die Emission der Defektzentren. Es ermöglicht die höchsten bisher erreichten Photonenzählraten von Stickstoff-Fehlstellen von bis zu 2.4Mcts/s und Einsammeleffizienzen von bis zu 4.2%. Durch Anwendung des FIM bei cryogenen Temperaturen wurden neuartige Anwendungen und fundamentale Untersuchungen möglich, weil Photonenraten signifikant erhöht wurden. Die Bestimmung der spektralen Diffusionszeit eines einzelnen Defektzentrums (2.2µs) gab neue Erkenntnisse über die Ursachen von spektraler Diffusion. Spektrale Diffusion ist eine limitierende Eigenschaft für die Realisierung von Quanteninformationsanwendungen. Das Tisch-basierte FIM wurde außerdem als kompakte mobile EPQ mit Ausmaßen von nur 7x19x23cm^3 realisiert. Es wurde für ein Quantenkryptographie-Experiment implementiert, zum ersten Mal mit Siliziumdefektzentren. Des Weiteren wurde ein neues Konzept für die Erzeugung von infraroten EPQ entwickelt und realisiert.
The presented thesis covers the development and investigation of novel integrated single photon (SP) sources and their application for quantum information schemes. SP generation was based on single defect centers in diamond nanocrystals. Such defect centers offer unique optical properties as they are room temperature stable, non-blinking, and do not photo-bleach over time. The fluorescent nanocrystals are mechanically stable, their size down to 20nm enabled the development of novel nano-manipulation pick-and-place techniques, e.g., with an atomic force microscope, for integration into photonic structures. Two different approaches were pursued to realize novel SP sources. First, fluorescent diamond nanocrystals were integrated into nano- and micrometer scaled fiber devices and resonators, making them ultra-stable and maintenance free. Secondly, a solid immersion microscope (SIM) was developed. Its solid immersion lens acts as a dielectric antenna for the emission of defect centers, enabling the highest photon rates of up to 2.4Mcts/s and collection efficiencies of up to 4.2% from nitrogen vacancy defect centers achieved to date. Implementation of the SIM at cryogenic temperatures enabled novel applications and fundamental investigations due to increased photon rates. The determination of the spectral diffusion time of a single nitrogen vacancy defect center (2.2µs) gave new insights about the mechanisms causing spectral diffusion. Spectral diffusion is a limiting property for quantum information applications. The table-top SIM was integrated into a compact mobile SP system with dimension of only 7x19x23cm^3 while still maintaining record-high stable SP rates. This makes it interesting for various SP applications. First, a quantum key distribution scheme based on the BB84 protocol was implemented, for the first time also with silicon vacancy defect centers. Secondly, a conceptually novel scheme for the generation of infrared SPs was introduced and realized.

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Wang, Chen-Yu, and 王振宇. "Microwave Imaging by Nearfield Measurement." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/73511867658414296368.

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碩士
大葉大學
電機工程研究所
88
The experiment in this paper is conducted with Electromagnetic Anecchoic chamber, HP8720D(Vector Network Analyzer) , and near field measurement system recover the microwave images of the scatterers . In the paper ,We have used two different methods to get microwave images of the scatterers.one is the method of Linear SAR(Linear Synthetic Aperture Radar),the other is the method of ISAR (Inverse Synthetic Aperture Radar). Besides microwave images recovery, we also step further to improve the quality and resolution of imaging.

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Margraves, Charles H. "From Nearfield Nanoparticle Tracking To Intracellular Vesicle Tracking." 2008. http://trace.tennessee.edu/utk_graddiss/469.

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The initial goal of this research was to measure the hindered Brownian motion of nanoparticles (100 nm to 500 nm in radii), in varying salinities of water, in order to compare the normal and tangential motion with existing theory. Using techniques developed from this work, brain cancer cells containing vesicles loaded with Nonsteroidal anti-inflammatory drug-Activated Gene-1 (NAG-1), tagged with a Green Fluorescent Protein (GFP), were examined to see what effect the glass cover slip played in hindering their motion. Several microscopy techniques have been used in this work including Total Internal Reflection Fluorescent Microscopy (TIRFM) and Differential Interference Reflection Microscopy (DICM). TIRFM in is a method used to examine an area approximately 1micrometer from the cover slip, while DICM can be used to examine the coverage area of a cell. Included in this work are several digital image processing techniques that were developed for tracking nanoparticles and biological vesicles, as well as software to examine cellular and focal adhesion coverage area using DICM and Interference Reflection Contrast Microscopy (IRCM), a technique that is especially useful in examining cell substrate interactions. Results of nanoparticle tracking showed that the tangential motion of the particles followed very closely to the theory proposed by Goldman et. Al., while the normal motion was substantially different than that proposed by Brenner. However it should be noted that Brenner’s theory does not include electrostatic forces that are significant in this work and therefore it should not be concluded that the theory is incorrect. Rather it was concluded that an additional term is needed to account for this added force. For intracellular vesicle tracking in cancer cells three types of motion were apparent: directional, Brownian, and caged. It was observed that the majority of the motion was either directional or caged and that hindrance values due to hydrodynamic effects were small compared with other hindrance effects. Also a method was established to estimate the average vesicle size base on the observed motion. This method is believed to have potential for use in determining fluid viscosity as well as nanoparticle sizes in future studies.

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Ryh-Shin, Tsai, and 蔡日興. "Nearfield and farfield emission characteristics of microdisk lasers." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/22738888075664801367.

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碩士
國立交通大學
光電(科學)研究所
83
In this thesis, we discuss the resonance cavity modes of microdisk lasers and the corresponding farfield emisssion patterns. Besides conventional circular microdisk lasers, we introduce the point matching method to solve the cavity modes of noncircular microdisks. And we further discuss how the changes in disk shape influences the farfield emission pattern of microdisk lasers.

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WANG, YI-AN, and 王一安. "Enhancement of nearfield acoustic holography for sound radiation analysis." Thesis, 1991. http://ndltd.ncl.edu.tw/handle/48603806381104105237.

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Abhayapala, Thushara. "Modal Analysis and Synthesis of Broadband Nearfield Beamforming Arrays." Phd thesis, 1999. http://hdl.handle.net/1885/46049.

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This thesis considers the design of a beamformer which can enhance desired signals in an environment consisting of broadband nearfield and/or farfield sources. The thesis contains: a formulation of a set of analysis tools which can provide insight into the intrinsic structure of array processing problems; a methodology for nearfield beamforming; theory and design of a general broadband beamformer; and a consideration of a coherent nearfield broadband adaptive beamforming problem. To a lesser extent, the source localization problem and background noise modeling are also treated. A set of analysis tools called modal analysis techniques which can be used to a solve wider class of array signal processing problems, is first formulated. The solution to the classical wave equation is studied in detail and exploited in order to develop these techniques. Three novel methods of designing a beamformer having a desired nearfield broadband beampattern are presented.

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Lehmann, Eric Andr{u00E9}. "Real-time implementation of a nearfield broadband acoustic beamformer." Master's thesis, 2000. http://hdl.handle.net/1885/147462.

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Chen, Ching-Cheng, and 陳勁誠. "Noise source identification for machine tools using nearfield and farfield microphone arrays." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/95350551949657448061.

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博士
國立清華大學
動力機械工程學系
102
Farfield and nearfield microphone arrays are proposed for noise source identification (NSI) and sound field visualization (SFV). Farfield acoustic imaging algorithms including the delay and sum (DAS) algorithm, the minimum variance distortionless response (MVDR) algorithm and the multiple signal classification (MUSIC) algorithm are employed to estimate direction of arrival (DOA). Results show that the MUSIC algorithm can attain the highest resolution of localizing sound sources positions. In the nearefield array signal processing, one formulation derived from discretizing the simple layer potential is termed the indirect equivalent source model (ESM)-based nearfield acoustical holography (NAH), while another formulation derived from discretizing the Kirchhoff-Helmholtz integral equation is termed the direct ESM-based NAH. In the use of ESM NAH, the choice of parameters including retract distance and average area of element is of vital importance. These parameters are optimized, with the aid of the golden section search and parabolic interpolation (GSS-PI) algorithm and the simulated annealing (SA) algorithm, for the direct and indirect ESM formulations. Instead of directly solving the inverse problem, the forward problem is solved in a recursive manner akin to the approach adopted by using recursive Wiener filtering. The approaches proposed are based on a state-space formulation employing the Kalman filter-based state observer and particle filter-based state estimator. The state observer and estimator are adaptive in nature and capable of tracking dynamic variation of sound field, even in the presence of noises and perturbations. Optimum weighting coefficients and inverse filters for microphone arrays can be accomplished, with the aid of a systematic methodology of mathematical programming. Both farfield and nearfield array problems are formulated in terms of compressive sampling (CS) and convex optimization (CVX) formalisms. CVX is applied to beamformer design, pressure field reconstruction, source separation and modal analysis with satisfactory performance in both nearfield and farfield microphone arrays. Design of optimal beamformers that withstand system errors such as channel mismatch, sensor position error, and pointing error has been a key issue in real-world applications of arrays. This thesis also examines the effects of system errors on beamformer performance from a statistical perspective. In practical applications where only patch array with scarce sensors are available, the ESM-based interpolation (ESM-IP), under-determined ESM (UD-ESM), direct basis function model (D-BFM) and BFM-based interpolation (BFM-IP) are proposed to reconstruct source velocity with sound filed interpolation. These methods were compared with the direct ESM (D-ESM) method. In the BFM-based NAH, basis functions including planar and spherical wave functions are used. CS is exploited in the BFM-IP and the D-BFM in light of CVX method. It is desirable to enhance the image resolution based on a sparse array configuration. As indicated by the simulation and experiment results, the proposed technique proved effective in identifying sources of many practical examples, including wooden box experiment, noncontact modal analysis of plate and machine tools.

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Wang, Chun-kai, and 王俊凱. "Superdirective microphone array with application in nearfield acoustical holography and supersensitive sound pickup." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/78727869214292849640.

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碩士
國立交通大學
機械工程學系
99
There are two topics in this thesis: one is supersensitive sound pickup and the other is super directive microphone array with application in nearfield acoustic holography. The former contains horn and curved array, and we will discuss the theory, design method and the result. Final, the device is applied to the application in a distant recording. Conventional nearfield acoustical holography (NAH) is generally based on the free-field assumption, which can cause errors when interfering sources are present in practical environment. Although the measurement of particle velocity as the input to NAH provides certain advantage, the noise problem of finite difference estimation of particle velocity can nullify the velocity-based reconstruction that is better conditioned than the pressure-based process. Alternatively, this paper examines the feasibility of using directional sensors in each channel of the microphone array such that the robustness of inverse reconstruction is enhanced against reflections from boundaries. With two microphones in each channel, the directivity of each array element is tailored according to various design criteria of first-order differential microphones. Directivity index, front-to-back ratio and constant beam-width are employed as the objective functions for optimizing array filters. The proposed methods are utilized in an Equivalent Source Model (ESM)-based NAH. The proposed techniques are verified by numerical simulations and experiments, with interfering source positioned at various directions. Sound field is reconstructed using the pressure input and the particle velocity estimated by the finite difference method.

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Tseng, Chih-Wen, and 曾智文. "Microphone array imaging systems with application in nearfield source identification and comparative study of the algorithms." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/12702083815752492146.

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碩士
國立交通大學
機械工程學系
98
Noise source identification (NSI) techniques using microphone arrays can be divided into two categories: Nearfield Acoustical Holography (NAH) and Beamforming. This thesis compares several algorithms of the methods derived from NAH and the methods derived from Beamforming in the nearfield. In the methods derived from NAH, this paper revisits traditional Fourier NAH and Nearfield Equivalent Source Imaging (NESI) proposed previously by the authors. The techniques and applications of the NESI that implemented in frequency domain termed as FDNESI are introduced and discussed by simulations and experiments. In FDNESI, acoustical variables including sound pressure, particle velocity, and active intensity are reconstructed by using multichannel inverse filters. A virtual microphone approach is employed to improve imaging resolution and minimize edge effects by using interpolation and extrapolation when sparse microphones are available. In the methods derived from Beamforming and direction of arrival (DOA) estimation: the delay and sum algorithm (DAS), the time reversal (TR) algorithm, the minimum variance distortionless response (MVDR) algorithm, and the multiple signal classification algorithm (MUSIC) are discussed and compared. As application in nearfield, the algorithms above are based on the assumption that the incoming waves are spherical waves. All the algorithms were compared and discussed by several numerical simulations and experiments in the nearfield.

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36

Hodeck, Kai Friedrich [Verfasser]. "Development of a scanning nearfield optical microscope for low-temperature investigations of semiconductor nanostructures / vorgelegt von Kai Friedrich Hodeck." 2009. http://d-nb.info/994341504/34.

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37

Ward, Darren Brett. "Theory and application of broadband frequency invariant beamforming." Phd thesis, 1996. http://hdl.handle.net/1885/49259.

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Abstract:

In many engineering applications, including radar, sonar, communications and seismology, the direction of impinging signal wavefronts can be used to discriminate between competing sources. Often these source signals cover a wide bandwidth and conventional narrowband beamforming techniques are ineffective, since spatial resolution varies significantly across the band. In this thesis we consider the problem of beamforming for broadband signals, primarily when the spatial response remains constant as a function of frequency. This is called a frequency invariant beamformer (FIB). ¶ ...

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38

Watada, Shingo. "Part I. Near-source acoustic coupling between the atmosphere and the solid earth during volcanic eruptions. Part II. Nearfield normal mode amplitude anomalies of the Landers earthquake." Thesis, 1995. https://thesis.library.caltech.edu/4331/1/Watada_s_1995.pdf.

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NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.

This thesis consists of two chapters. In the first chapter the normal mode theory of a spherical Earth model is extended to include the atmosphere and the theory is applied to understand the observation of air-ground acoustic coupling during volcanic eruptions and to construct synthetic ground motions. In chapter II, the fully developed normal mode theory of 3D Earth is applied to the nearfield amplitude anomalies of the surface waves of the Landers rearthquake. Synthetic seismograms for the recently-available three dimensional seismic global Earth models are constructed using the normal mode theory and compared with observations. The horizontal scale and the location of lateral seismic velocity variations which caused the amplitude anomalies are examined in detail.

Part I:

Long-period harmonic Rayleigh waves were observed by worldwide seismographic networks during the eruption of Mt. Pinatubo in 1991. It has been suggested that these Rayleigh waves were excited, through atmospheric-solid Earth coupling, by atmospheric oscillations set off by the eruption. We investigated this problem using the Earth's normal modes computed for a spherically symmetric Earth model with the solid (elastic) Earth, ocean and atmosphere. These normal modes represent Rayleigh waves in the solid Earth, tsunamis in the ocean, and Lamb waves, internal acoustic waves and internal gravity waves in the atmosphere. Since the atmosphere has a low sound velocity channel below the thermosphere (altitude 90 km), two characteristic acoustic modes with periods of 230 and 270 s exist. The energy coupling between atmospheric acoustic waves and Rayleigh waves is efficient because of the proximity of the horizontal phase velocities of these waves. The energy distribution suggests that a low altitude volcanic eruption would excite the 230 s mode more strongly than the 270 s mode. This is consistent with the observation for the Pinatubo eruption. In contrast, the internal gravity mode has a period of 300 s. The barographic oscillation at a period of 300 s observed for the 1980 Mt. St. Helens eruption is probably this mode. However, because of its slow phase velocity, it would not couple to Rayleigh waves efficiently, and cannot be detected with seismographs.

Part II-A:

The 1992 Landers earthquake ([...]=7.3) occurred in the middle of the TERRAscope network. Long-period Rayleigh waves recorded at TERRAscope stations [...] after travelling around the Earth show large amplitude anomalies, one order of magnitude larger than spherical Earth predictions up to a period of about 600 s. The ground motions over the epicentral region at and after the arrival of R4-5 are in phase at all stations. These observations are inconsistent with the nearly vertical strike slip mechanism of the Landers earthquake. Synthetic seismograms for a rotating, elliptic and laterally heterogeneous Earth model calculated by the variational method agree well with the observed waveforms. Calculations for various 3D Earth models demonstrate that the amplitudes are very sensitive to the large scale aspherical structure in the crust and the mantle. The anomalies for modes shorter than 300 s period can be explained by lateral heterogeneity shallower than the upper mantle. Rotation of the Earth and lower mantle heterogeneity are required to explain mode amplitudes at longer periods. Current whole mantle seismic tomographic models can fully explain the observed amplitudes longer than 300 s. To assess the effect of the high order lateral heterogeneity in the mantle, more precise estimate of the crustal correction is required.

Part II-B:

We modeled the interaction of the source mechanism and the station location with large-scale lateral heterogeneity using the splitting matrix of an isolated multiplet and the 'source-receiver function' whose spherical harmonic coefficients are given by [...] where s and t are angular and azimuthal order numbers respectively. For a short period of time waveform perturbation is proportional to the integral of products of the splitting function with harmonic coefficients [...] and the 'source-receiver' function. For the Landers earthquake and TERRAscope stations source-receiver geometry, the 'source-receiver function' is dominated by the low-order components, paticularly l = 2, m = ±2 in the epicentral coordinates. This beach-ball like pattern is the same for all the near-source stations located in different quadrants of the strike-slip mechanism. The two maxima of the 'beach ball' pattern coincide with the locations of the degree 2 maxima of the splitting functions; western Pacific and east of South America. These features explain the weak dependence of the waveforms on higher order lateral heterogeneity and similarity of waveforms over the epicentral region. The location and the source mechanism of the Landers earthquake relative to the large scale lateral heterogeneity l = 2, including the variations of the cruatal structures, are responsible for the cause of amplitude anomalies near the epicenter. However, the amplitude near the epicenter of an earthquake with a thrust fault type mechanism, for example the Northridge earthquake, is explained well with a spherical Earth model.

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Dissertations / Theses on the topic 'Nearfield'

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