Sound radiation from an acoustic source typically exhibits directional behavior, as is the case for the human voice, musical instruments, and loudspeakers, to name just a few. The necessity of directional data for many applications, such as sound source modeling, microphone placement, room acoustical design, and auralization, motivates directivity measurements. However, these measurements require careful understanding and implementation to produce the most meaningful results. Accordingly, this dissertation addresses several topics relevant to directivity theory, measurement, processing, and application. It first expands and amends previously published concepts of an acoustic source center and demonstrates the close relationship between the center and a source's far-field directional response. This relationship subsequently leads to an acoustic centering method that improves source placements within directivity measurement arrays. The dissertation then addresses several measurement considerations, including the required numbers of sampling positions for directivity measurements, quadrature rules applicable to standardized dual-equiangular sampling schemes, and a source's far-field response from arbitrarily shaped microphone arrays. Selected directivity results for the human voice and musical instruments illustrate applications of the developed measurement theories for procuring high-resolution results over a sphere. Compiled voice and musical instrument directivities now appear in an open-source database for use in room acoustical modeling, microphone placements, and other applications. To better elucidate and help predict sound source radiation, this work proposes several theoretical models, including equivalent point-source models, low-frequency radiation from a radially vibrating cap set on a rigid spherical shell with a circular aperture, and radiation from a vibrating cap on a rigid sphere with imposed mode shapes. Finally, this dissertation presents two microphone placement methods for audio and other applications. The first method approximates the measurement of a source's sound power spectrum through a single-channel measurement; the second considers microphone placement for maximum perceived loudness. The work's various developments, results, and conclusions will assist researchers and practitioners in better evaluating, predicting, and applying sound source directivities for many uses.

В данной выпускной квалификационной работе стоит цель разработать антенную систему МС, в которую войдут одна антенна: секторная или кольцевая ФАР, с возможностью сканирования пространства в горизонтальной плоскости в диапазоне от 0 до 360 градусов. Обязательное требование, предъявляемое к антенне с электронным сканированием – при отклонении ДН на определённый угол уровень равносигнального направления между соседними ДН не должен быть ниже -2 дБ. Это позволит стабилизировать связь при переключении между соседними каналами с метеорологическим зондом, который может находиться в любом направлении относительно стационарного пункта наблюдения на МС. / In this final qualifying work is the aim to develop an antenna system MS, which will include one antenna: sector or ring of lights, with the ability to scan space in a horizontal plane in the range from 0 to 360 degrees. Mandatory requirement for the antenna with electronic scanning – rejecting days to a certain angle the level of the equisignal direction between adjacent days should not be below -2 dB. This will allow to stabilize the connection when switching between adjacent channels with a meteorological probe, which can be in any direction relative to a stationary point of observation on the MC.

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Two rotor configurations with different non-uniform inflows were studied: a rotor ingesting the wake of an upstream cylinder and a rotor ingesting a thick axially symmetric boundary layer from an upstream centerbody. In both cases, the undisturbed inflow was measured without the rotor present in order to characterize the inflow, in particular to calculate the unsteady upwash velocity distribution at the location of the rotor. In addition, detailed acoustic measurements were completed using a 251-channel large-area microphone array. In all, over 400 conditions covering different advance ratios, angles of yaw, and inflow conditions were measured. Measurements of the sound show that the source has a complex directivity, different from that of a streamwise aligned dipole, due to the inhomogeneous unsteady upwash distribution. In addition, observers at different far field locations will perceive sources from different locations on the rotor disk. The directivity is a function of both the rotor geometry and turbulent inflow. A simplified model of the sound source was developed using these inputs and accurately predicts trends observed in the far field noise. For the cylinder wake ingestion case, on-blade measurements of the flow field show that the wake is drawn to the center of the rotor disk with increasing thrust. This is particularly noticeable if the wake does not strike the center of the rotor disk. The effects of this flow distortion on the far field directivity are well predicted by the model. The effects of yaw to rotate the produced sound field can be inferred from this model as well. A novel beamforming procedure was used to isolate sources across the face of the rotor for the cylinder wake ingestion case for an upstream observer position. This method may be used to isolate different sound sources on a rotor if multiple sources are present or if different regions of the rotor disk need to be isolated. The directivity of a rotor ingesting an axially symmetric boundary layer is far less complex than the ingestion of a two-dimensional cylinder wake, but measurements still show the perceived source location shift with observer location. Overall, the proposed noise modeling technique is an efficient method to predict the directivity of turbulence ingestion noise for inhomogeneous inflows. This can enable quick absolute noise predictions at all far field locations using only a single point measurement or far field noise prediction to establish absolute levels. / Doctor of Philosophy / In many engineering applications, rotors interact with turbulence. Aircraft and ships with rear mounted propellers can have upstream appendages or discontinuities that generate turbulence that travels downstream and is drawn into the propeller. Wind turbines interact with turbulence in the atmosphere and with turbulent wakes from other turbines. Interaction of a rotor with turbulence results in unsteady loading on the rotor blades that can radiate as sound, causing unwanted community noise or vehicle detection. As such, prediction and reduction of noise due to turbulence ingestion is highly desirable and remains an active area of research. Turbulence ingestion noise is well understood from first principles and can be successfully predicted provided an accurate description of the turbulent inflow and unsteady aerodynamic response of the rotor blades. Much work has focused on homogenous, isotropic turbulence ingestion noise, however, in practical applications, the rotor inflow is often non-uniform, anisotropic, and can change dramatically with the thrusting condition of the rotor. Research efforts to develop noise predictions considering these more complex, but practical inflows have focused on the inflow modeling and measurement and have relied on a small subset of sound measurements for validation. The present study seeks to provide new physical insight into inhomogeneous, anisotropic turbulence ingestion noise through wind tunnel experiments. In particular, two rotor configurations with different practical non-uniform inflows are studied: a rotor ingesting the wake of an upstream cylinder and a rotor ingesting a thick axially symmetric boundary layer from an upstream center body. In both cases, the undisturbed inflow was measured without the rotor present in order to characterize the inflow, and detailed acoustic measurements were completed using a 251-channel large-area microphone array. In all, over 400 rotor operating conditions were measured. The acoustic directivity in each case is examined in detail as a function of rotor operating condition. A simplified directivity model is developed and validated with measurements. Ultimately, the directivity model can provide a good engineering approximation of the full directivity with reduced computational time or can be used to extrapolate measured results to positions in the far field where placement of sensors is not possible. The results can also be used to guide the analysis and interpretation of single point or microphone array measurements in the acoustic far field of a rotor.

A broadside radiating, linearly polarized, electrically small Huygens source antenna system that has a large impedance bandwidth is reported. The bandwidth performance is facilitated by embedding non-Foster components into the near-field resonant parasitic elements of this metamaterial-inspired antenna. High-quality and stable radiation performance characteristics are achieved over the entire operational bandwidth. When the ideal non-Foster components are introduced, the simulated impedance bandwidth witnesses approximately a 17-fold enhancement over the passive case. Within this -10-dB bandwidth, its maximum realized gain, radiation efficiency, and front-to-back ratio (FTBR) are, respectively, 4.00 dB, 88%, and 26.95 dB. When the anticipated actual negative impedance convertor circuits are incorporated, the impedance bandwidth still sustains more than a 10-fold enhancement. The peak realized gain, radiation efficiency, and FTBR values are, respectively, 3.74 dB, 80%, and 28.01 dB, which are very comparable to the ideal values.

Dans ce travail de these, nous étudions comment des nano-structures métalliques modifient le processus d'émission spontannée d'objets fluorescents et jouent ainsi un rôle d'antenne. Ces structures supportent des modes optiques confinés aux interfaces metal-diélectrique: ce sont des modes plasmoniques.De par leur fort confinement, ces modes modifient la densité locale d'états optiques et permettent notamment d'accélérer le processus d'émission spontannée (facteur de Purcell). Nous étudions le cas d'une structure planaire metal-isolant-métal de type patch couplée à un ensemble de nanocristaux colloïdaux fluorescents. Nos mesures, soutenues par des calculs numériques, montrent une acceleration de l'émission fluorescente d'un facteur 80 ainsi qu'une augmentation de la directivité de l'émission. Nous décrivons ensuite le procedé de fabrication d'une structure patch metal-semiconducteur-métal pour laquelle la source fluorescente est un puits quantique émettant dans le proche infra-rouge. Nous montrons que l'antenne permet d'augmenter l'extraction fluorescente d'un facteur 8. Enfin, nous considérons le cas d'une structure sphérique composée d'un unique nanocristal fluorescent au centre d'une bille de silice entourée par une fine coquille métallique. Cette structure plasmonique accélère l'émission d'une facteur 10 et permet de supprimer le scintillement caractéristique de l'émission des nanocristaux. La coquille métallique permet également d'isoler chimiquement le nanocristal de l'environnement, assurant ainsi une grande photostabilité et une toxicité réduite. L'émetteur ainsi obtenu est donc un candidat prometteur pour des applications de marquage de fluorescence in-vivo. / The present work focuses on the modification of spontaneous emission of fluorescent emitters using metallic nano-structures. These structures support confined plasmonic modes that strongly increase the local density of optical states. Consequently, the plasmonic structure enhances the spontaneous decay rate of the emitter. We use both numerical simulations and experimental results to demonstrate the potential of plasmonic antennas as tools to control spontaneous emission. First, we study a metal-dielectric-metal planar structure called patch antenna. This structure is coupled to an ensemble of quantumdots emitting visible light. We show that, in the presence of the patch antenna, the fluorescent emission is accelerated by a factor 80 and that its directivity is increased. Then, we use a similar plasmonic structure coupled to a quantum well emitting in the near infrared. Using an ad hoc hyperspectral imaging setup, we show that the antenna increases the extracted light by a factor 8. Finally, we study a spherical geometry composed of a single fluorescent quantum dot at the center of a silica bead coated with a thin gold shell. This plasmonic structure

In some antenna applications, having high directivity while keeping the antenna dimensions small is desired, which can be obtained by use of superdirective arrays. Superdirective arrays have been popular in academic world since a superdirective array provides higher directivity than the uniformly excited antenna array of same length. In this thesis, superdirective arrays are investigated by making high precision numerical computations. Superdirective array element excitations, array factors and directivities are inspected for different number of elements. Superdirective array pattern and directivity features are compared to uniformly excited array pattern and directivities. Superdirective array tolerance is investigated by examination of array element excitation sensitivities. Bandwidth of superdirective arrays is also inspected. Multiple Precision Toolbox is used during numerical computations in Matlab.

Assessment of potential ground motions in seismically active regions is essential for purposes of seismic design and analysis. Peak ground motion intensity values and frequency content of seismic excitations are required for reliable seismic design, analysis and retrofitting of structures. In regions of sparse or no strong ground motion records, ground motion simulations provide physics-based synthetic records. These simulations provide not only the earthquake engineering parameters but also give insight into the mechanisms of the earthquakes. This thesis presents strong ground motion simulations in three regions of intense seismic activity. Stochastic finite-fault simulation methodology with a dynamic corner frequency approach is applied to three case studies performed in D&uuml / zce, L&rsquo / Aquila and Erzincan regions. In D&uuml / zce study, regional seismic source, propagation and site parameters are determined through validation of the simulations against the records. In L&rsquo / Aquila case study, in addition to study of the regional parameters, the limitations of the method in terms of simulating the directivity effects are also investigated. In Erzincan case study, where there are very few records, the optimum model parameters are determined using a large set of simulations with an error-minimization scheme. Later, a parametric sensitivity study is performed to observe the variations in simulation results to small perturbations in input parameters. Results of this study confirm that stochastic finite-fault simulation method is an effective technique for generating realistic physics-based synthetic records of large earthquakes in near field regions.

Previous studies have shown that spectral analysis based on force data can elucidate fundamental physical phenomena during chemical mechanical planarization (CMP). While it has not been literally described elsewhere, such analysis was partly motivated by modern violinmakers and physicists studying Old Italian violins, who were trying to discover spectral relations to sound quality. In this paper, we draw parallels between violins and CMP as far as functionality and spectral characteristics are concerned. Inspired by the de facto standard of violin testing via hammer strikes on the base edge of a violin's bridge, we introduce for the first time, a mobility plot for the polisher by striking the wafer carrier head of a CMP polisher with a hammer. Results show three independent peaks that can indeed be attributed to the polisher's natural resonance. Extending our study to an actual CMP process, similar to hammered and bowed violin tests, at lower frequencies the hammered and polished mobility peaks are somewhat aligned. At higher frequencies, peak alignment becomes less obvious and the peaks become more isolated and defined in the case of the polished wafer spectrum. Lastly, we introduce another parameter from violin testing known as directivity, , which in our case, we define as the ratio of shear force variance to normal force variance acquired during CMP. Results shows that under identical polishing conditions, increases with the polishing removal rate.

Les dimensions d’une antenne sont inversement proportionnelles à leurs fréquences de fonctionnement. De plus, la miniaturisation d’une antenne entraîne la dégradation de ses performances électriques et de rayonnement. Par conséquent, il est important pour le concepteur de trouver un bon compromis entre le taux de miniaturisation et les performances souhaitées. L’objet de cette thèse est de proposer une antenne miniature possédant les meilleures caractéristiques possibles dans la bande UHF de la RFID (860MHz – 960MHz), facile à réaliser et à moindre coût d’industrialisation. Les travaux de cette thèse ont montré qu’un couplage magnétique d’une cellule de métamatériaux avec une demi-boucle permet d’obtenir des structures antennaires intéressantes de par leurs dimensions de l’ordre de λ0/10, leur efficacité et leur fonctionnement en multibande. Différentes techniques sont appliquées pour améliorer les performances des antennes développées à savoir le gain, la directivité et la polarisation circulaire et/ou elliptique. / Antenna dimensions are inversely proportional to their operating frequencies. Besides, the antenna miniaturization degrades its electrical and radiation performances. Therefore it is important for the antenna designer to find a good compromise between the miniaturization rate and the desired performances. The purpose of this thesis is to obtain a miniature antenna which has good characteristics in the UHF band of RFID (860MHz - 960MHz), easy to implement and with low industrialization cost. The works described in this thesis showed that a magnetic coupling of a metamaterial cell with a half loop provides interesting antennas in terms of dimensions of about λ0/10, efficiency and multiband behavior. Different techniques are applied to improve the performances of realized antennas as gain, directivity and circular and/or elliptical polarization.