The analysis and development of robust sensing platforms based on solidly-mounted ZnO bulk acoustic wave devices was proposed. The exploitation of acoustic energy trapping was investigated and demonstrated as a method to define active sensing areas on a substrate. In addition, a new "hybrid" acoustic mode experiencing acoustic energy trapping was studied theoretically and experimentally. This mode was used as an explanation of historical inconsistencies in observed thickness-shear mode velocities. Initial theoretical and experimental results suggest that this mode is a coupling of thickness-shear and longitudinal particle displacements and, as such, may offer more mechanical and/or structural information about a sample under test. Device development was taken another step further and multi-mode ZnO resonators operating in the thickness-shear, hybrid, and longitudinal modes were introduced. These devices were characterized with respect to sample viscosity and conductivity and preliminary results show that, with further development, the multi-mode resonators provide significantly more information about a sample than their single-mode counterparts. An alternative to resonator-based platforms was also presented in the form of bulk acoustic delay lines. Initial conceptual and simulation results show that these devices provide a different perspective of typical sensing modalities by using properly designed input pulses, device tuning, and examining overall input and output signal spectra.

Seismic hazard and microzonation of cities enable to characterize the potential seismic areas that need to be taken into account when designing new structures or retrofitting the existing ones. Study of seismic hazard and preparation of geotechnical microzonation maps will provide an effective solution for city planning and input to earthquake resistant design of structures in an area. Seismic hazard is the study of expected earthquake ground motions at any point on the earth. Microzonation is the process of sub division of region in to number of zones based on the earthquake effects in the local scale. Seismic microzonation is the process of estimating response of soil layers under earthquake excitation and thus the variation of ground motion characteristic on the ground surface. Geotechnical site characterization and assessment of site response during earthquakes is one of the crucial phases of seismic microzonation with respect to ground shaking intensity, attenuation, amplification rating and liquefaction susceptibility. Microzonation mapping of seismic hazards can be expressed in relative or absolute terms, on an urban block-by-block scale, based on local soil conditions (such as soil types) that affect ground shaking levels or vulnerability to soil liquefaction. Such maps would provide general guidelines for integrated planning of cities and in positioning the types of new structures that are most suited to an area, along with information on the relative damage potential of the existing structures in a region. In the present study an attempt has been made to characterize the site and to study the seismic hazard analysis considering the local site effects and to develop microzonation maps for Bangalore. Seismic hazard analysis and microzonation of Bangalore is addressed in this study in three parts: In the first part, estimation of seismic hazard using seismotectonic and geological information. Second part deals about site characterization using geotechnical and shallow geophysical techniques. An area of 220 sq.km, encompassing Bangalore Municipal Corporation has been chosen as the study area in this part of the investigation. There were over 150 lakes, though most of them are dried up due to erosion and encroachments leaving only 64 at present in an area of 220 sq. km and emphasizing the need to study site effects. In the last part, local site effects are assessed by carrying out one-dimensional (1-D) ground response analysis (using the program SHAKE 2000) using both borehole SPT data and shear wave velocity survey data within an area of 220 sq. km. Further, field experiments using microtremor studies have also been carried out (jointly with NGRI) for evaluation of predominant frequency of the soil columns. The same has been assessed using 1-D ground response analysis and compared with microtremor results. Further, Seed and Idriss simplified approach has been adopted to evaluate the liquefaction susceptibility and liquefaction resistance assessment. Microzonation maps have been prepared for Bangalore city covering 220 sq. km area on a scale of 1:20000. Deterministic Seismic Hazard Analysis (DSHA) for Bangalore has been carried out by considering the past earthquakes, assumed subsurface fault rupture lengths and point source synthetic ground motion model. The seismic sources for region have been collected by considering seismotectonic atlas map of India and lineaments identified from satellite remote sensing images. Analysis of lineaments and faults help in understanding the regional seismotectonic activity of the area. Maximum Credible Earthquake (MCE) has been determined by considering the regional seismotectonic activity in about 350 km radius around Bangalore. Earthquake data are collected from United State Geological Survey (USGS), Indian Metrological Department (IMD), New Delhi; Geological Survey of India (GSI) and Amateur Seismic Centre (ASC), National Geophysical Research Institute (NGRI),Hyderabad; Centre for Earth Science Studies (CESS), Akkulam, Kerala; Gauribindanur (GB) Seismic station and other public domain sites. Source magnitude for each source is chosen from the maximum reported past earthquake close to that source and shortest distance from each source to Bangalore is arrived from the newly prepared seismotectonic map of the area. Using these details, and, attenuation relation developed for southern India by Iyengar and Raghukanth (2004), the peak ground acceleration (PGA) has been estimated. A parametric study has been carried out to find fault subsurface rupture length using past earthquake data and Wells and Coppersmith (1994) relation between the subsurface lengths versus earthquake magnitudes. Further seismological model developed by Boore (1983, 2003) SMSIM program has been used to generate synthetic ground motions from vulnerable sources identified in above two methods. From the above three approaches maximum PGA of 0.15g was estimated for Bangalore. This value was obtained for a maximum credible earthquake (MCE) having a moment magnitude of 5.1 from a source of Mandya-Channapatna-Bangalore lineament. Considering this lineament and MCE, a synthetic ground motion has been generated for 850 borehole locations and they are used to prepare PGA map at rock level. The past seismic data has been collected for almost 200 years from different sources such as IMD, BARC (Gauribidanur array), NGRI, CESS, ASC center, USGS, and other public domain data. The seismic data is seen to be homogenous for the last four decades irrespective of the magnitude. Seismic parameters were then evaluated using the data corresponding to the last four decades and also the mixed data (using Kijko’s analysis) for Bangalore region, which are found to be comparable with the earlier reported seismic parameters for south India. The probabilities of distance, magnitude and peak ground acceleration have been evaluated for the six most vulnerable sources using PSHA (Probabilistic Seismic Hazard Analysis). The mean annual rate of exceedance has been calculated for all the six sources at the rock level. The cumulative probability hazard curves have been generated at the bedrock level for peak ground acceleration and spectral acceleration. The spectral acceleration calculation corresponding to a period of 1sec and 5% damping are evaluated. For the design of structures, uniform hazard response spectrum (UHRS) at rock level is developed for the 5% damping corresponding to 10% probability of exceedance in 50 years. The peak ground acceleration (PGA) values corresponding to 10% probability of exceedance in 50 years are comparable to the PGA values obtained in deterministic seismic hazard analysis (DSHA) and higher than Global Seismic Hazard Assessment Program (GSHAP) maps of Bhatia et.al (1997) for the Indian shield area. The 3-D subsurface model with geotechnical data has been generated for site characterization of Bangalore. The base map of Bangalore city (220sq.km) with several layers of information (such as Outer and Administrative boundaries, Contours, Highways, Major roads, Minor roads, Streets, Rail roads, Water bodies, Drains, Landmarks and Borehole locations) has been generated. GIS database for collating and synthesizing geotechnical data available with different sources and 3-dimensional view of soil stratum presenting various geotechnical parameters with depth in appropriate format has been developed. In the context of prediction of reduced level of rock (called as “engineering rock depth” corresponding to about Vs > 700 m/sec) in the subsurface of Bangalore and their spatial variability evaluated using Artificial Neural Network (ANN). Observed SPT ‘N’ values are corrected by applying necessary corrections, which can be used for engineering studies such as site response and liquefaction analysis. Site characterization has also been carried out using measured shear wave velocity with the help of shear wave velocity survey using MASW. MASW (Multichannel Analysis of Surface Wave) is a geophysical method, which generates a shear-wave velocity (Vs) profile (i.e., Vs versus depth) by analyzing Raleigh-type surface waves on a multichannel record. MASW system consisting of 24 channels Geode seismograph with 24 geophones of 4.5 Hz capacity were used in this investigation. The shear wave velocity of Bangalore subsurface soil has been measured and correlation has been developed for shear wave velocity (Vs) with the standard penetration tests (SPT) corrected ‘N’ values. About 58 one-dimensional (1-D) MASW surveys and 20 two-dimensional (2-D) MASW surveys has been carried out with in 220 sq.km Bangalore urban area. Dispersion curves and shear velocity 1-D and 2-D have been evaluated using SurfSeis software. Using 1-dimensional shear wave velocity, the average shear wave velocity of Bangalore soil has been evaluated for depths of 5m, 10m, 15m, 20m, 25m and 30m (Vs30) depths. The sub soil classification has been carried out for local site effect evaluation based on average shear wave velocity of 30m depth (Vs30) of sites using NEHRP (National Earthquake Hazard Research Programme) and IBC (International Building Code) classification. Bangalore falls into site class D type of soil. Mapping clearly indicates that the depth of soil obtained from MASW is closely matching with the soil layers in the bore logs. The measured shear wave velocity at 38 locations close to SPT boreholes, which are used to generate the correlation between the shear wave velocity and corrected ‘N’ values using a power fit. Also, developed relationship between shear wave velocity and corrected ‘N’ values corresponds well with the published relationships of Japan Road Association. Bangalore city, a fast growing urban center, with low to moderate earthquake history and highly altered soil structure (due to large reclamation of land) is been the focus of this work. There were over 150 lakes, though most of them are dried up due to erosion and encroachments leaving only 64 at present in an area of 220 sq km. In the present study, an attempt has been made to assess the site response using geotechnical, geophysical data and field studies. The subsurface profiles of the study area within 220sq.km area was represented by 170 geotechnical bore logs and 58 shear wave velocity profiles obtained by MASW survey. The data from these geotechnical and geophysical technique have been used to study the site response. These soil properties and synthetic ground motions for each borehole locations are further used to study the local site effects by conducting one-dimensional ground response analysis using the program SHAKE2000. The response and amplification spectrum have been evaluated for each layer of borehole location. The natural period of the soil column, peak spectral acceleration and frequency at peak spectral acceleration of each borehole has been evaluated and presented as maps. Predominant frequency obtained from both methods is compared; the correlation between corrected SPT ‘N’ value and low strain shear modulus has been generated. The noise was recorded at 54 different locations in 220sq.km area of Bangalore city using L4-3D short period sensors (CMG3T) equipped with digital data acquisition system. Predominant frequency obtained from ground response studies and microtremor measurement is comparable. To study the liquefaction hazard in Bangalore, the liquefaction hazard assessment has been carried out using standard penetration test (SPT) data and soil properties. Factor of Safety against liquefaction of soil layer has been evaluated based on the simplified procedure of Seed and Idriss (1971) and subsequent revisions of Seed et al (1983, 1985), Youd et al (2001) and Cetin et al (2004). Cyclic Stress Ratio (CSR) resulting from earthquake loading is calculated by considering moment magnitude of 5.1 and amplified peak ground acceleration. Cyclic Resistant Ratio (CRR) is arrived using the corrected SPT ‘N’ values and soil properties. Factor of safety against liquefaction is calculated using stress ratios and accounting necessary magnitude scaling factor for maximum credible earthquake. A simple spread sheet was developed to carryout the calculation for each bore log. The factor of safety against liquefaction is grouped together for the purpose of classification of Bangalore (220 sq. km) area for a liquefaction hazards. Using 2-D base map of Bangalore city, the liquefaction hazard map was prepared using AutoCAD and Arc GIS packages. The results are grouped as four groups for mapping and presented in the form of 2-dimensional maps. Liquefaction possibilities are also assessed conducting laboratory cyclic triaxial test using undisturbed soil samples collected at few locations.

No description available.

Two separate problems are to be investigated in this thesis. The first problem is the propagation of waves through a short rod (or slug) of viscoelastic material. The second problem is the study of impact of a short viscoelastic rod (or slug) on a stationary semi-infinite viscoelastic. rod. The viscoelastic materials are modelled as standard linear solids which involve 3 material parameters and the motion is treated. as one-dimensional. For the first study, a viscoelastic slug is placed between two semi-infinite elastic rods and a wave initiated in the first rod is transmitted through the slug into the second rod. The objective is to relate the transmitted signal to the material parameters of the slug. We solve the governing system of partial differential equations using the Laplace transform and we examine the propagating velocity discontinuity using discontinuity analysis and the limit theorem of the Laplace transform. We then approximate the solution of the propagating disturbance using the regular perturbation method. We invert the Laplace transformed solution numerically to obtain the transmitted signal for several viscosity time constants and ratios of acoustic impedances. We compare the results obtained using the above techniques. In the second problem, we first model the impact and solve the governing system of partial differential equations in the Laplace transform domain. Then we examine the propagating stress and velocity discontinuities using discontinuity analysis. We approximate the solutions of the propagating stress and velocity using the regular and multiple scales perturbation methods. In this problem, we first consider the slug is elastic and the rod is viscoelastic. Secondly, we consider the slug is viscoelastic and the rod is elastic and thirdly, we consider both materials are viscoelastic. Numerically we invert the Laplace transformed solutions for the interface stress and interface velocity for several viscosity time constants and ratios of acoustic impedances to determine whether the slug and the rod part company or remain in contact. Then we compare the results obtained using the discontinuity analysis, regular and multiple scales perturbation methods.

Une brosse de polymères est une matrice dense de macromolécules greffées à une surface donnée. Au-delà des brosses synthétiques réalisées en laboratoire, on trouve des exemples très variés dans la nature: un exemple emblématique est le glycocalyx endothélial, décorant la surface interne des vaisseaux sanguins des mammifères. L'interaction de cette structure avec le plasma et les cellules sous écoulement n'est encore que très partiellement explorée. La présente thèse propose, grâce à des simulations de "Dissipative Particle Dynamics", un modèle coarse-grained pour une analyse auto-cohérente d'une brosse polymérique dense sous écoulement parabolique. Cette étude mésoscopique met en évidence l'importance des effets collectifs entre molécules, entraînée par l'hydrodynamique, et propose des nouvelles interprétations à la phénoménologie du système brosse-écoulement. Des résultats préliminaires sont également produits pour l'interaction sous écoulement entre un objet mésoscopique déformable (prototype d'un globule rouge) et les polymères greffés. / Polymer brushes are dense matrices of grafted macromolecules. In addition to brushes finely designed in laboratory, various examples are offered by Nature, as the endothelial glycocalyx, decorating the lumen of mammalian blood vessels. The interaction of such network with the flowing plasma and cells is still partially unknown.The present thesis, by mean of Dissipative Particle Dynamics simulations, proposes a coarse-grained model for the self-consistent analysis of a dense polymer brush under parabolic flow. Our mesoscale investigation highlights the relevance of collective effects, driven by hydrodynamics, and proposes novel interpretations regarding the rich phenomenology of the brush-flow system.Preliminary results are also provided for the interplay between a mesoscopic deformable flowing object (prototype of a red blood cell) and the grafted polymers.

Le sujet de ma thèse est l’étude de la diffraction par des trous sub-longueur percés dans des films métalliques, ainsi que la compréhension du rôle des plasmons de surface (SPs) dans la diffraction en champ lointain. Nous avons construit un goniomètre « fait maison » de haute qualité. Une série de trous unique percés dans un film opaque et variant continûment de k • r >> 1 à k • r << 1 ont été explorées. Ici, k est le vecteur d'onde de l'onde incidente et r est le rayon du trou. Les résultats expérimentaux indiquent que la diffraction de la lumière par un trou unique peut être séparée en quatre régimes, dépendant de la polarisation incidente. Une expression analytique simple révèle pour la première fois, l’implication de deux facteurs compétitifs: l'un lié aux plasmons de surface, et l'autre provenant du couplage du champ aux modes de guide d'onde de l'ouverture. Lorsque le trou est entouré par des corrugations concentriques (structure d'oeil de boeuf), et est illuminé avec les rainures sur le côté de sortie, l'effet de collimation est observé: la diffraction en champ lointain est confinée dans un très petit angle solide. L’influence des paramètres géométrique sur la figure de diffraction de l’œil de bœuf a été étudié et des motifs de diffraction dont la largeur est inférieure à 1 ° dans le champ lointain ont été atteints. Un autre mode de surface (CWs), différent des SPs, a été étudié sur des films de tungstène. Il a été démontré que les CWs permettent également d’obtenir un effet de collimation. À titre de comparaison, nous avons montré que la transmission exaltée est bien plus faible pour les CWs que pour les SPs sur nanostructures. / The theme of my thesis is to investigate the diffraction behavior of subwavelength holes in metal films, and to understand the surface plasmons’ (SPs) role in aperture far-field diffraction. We have built a home-made goniometer setup with high-level quality. A series of single hole continuously ranging from k•r>>1 to k•r<<1 in a flat opaque film were explored, where k is the wavevector of the incident wave and r is the radius of the hole. The experimental results indicated that the diffraction of single hole can be classified into four regimes, depending on the input polarization. A simple analytical expression reveals for the first time the subtle interplay of two competing factors: one related to surface plasmon excitation and the other originating in the coupling of the field to the waveguide mode of the aperture. When the hole is surrounded by concentric grooves (bull’s eye structure) and is illuminated with the grooves on the output side, the beaming effect occurs: far-field diffraction is confined in very small solid angle. The effects of geometrical parameters on bull’s eye diffraction have been studied and the diffraction patterns with the width less than 1° in the far field have been achieved. Another surface waves (CWs) different from SPs on tungsten films were studied. It was demonstrated that the CWs have beaming effect as well. By comparison we showed that CWs display much weaker enhancement in transmission than SPs through nanostructures.

La caractérisation et le monitoring des ressources en eau souterraine et des processus d'écoulement et de transport associés reposent principalement sur la mise en place de forages (piézomètres). Mais la variété des échelles auxquelles se déroulent ces processus et leur variabilité dans l'espace et dans le temps limitent l'interprétation des observations hydrogéologiques. Dans un tel contexte, l'hydrogéophysique fait appel aux méthodes de prospection géophysique afin, notamment, d'améliorer la très faible résolution spatiale des données de forage et de limiter leur caractère destructif. Parmi les outils géophysiques appliqués à l'hydrogéologie, les méthodes sismiques sont régulièrement utilisées à différentes échelles. Mais la réponse sismique dans le contexte de la caractérisation des aquifères reste complexe. L'interprétation des vitesses estimées est souvent délicate à cause de leur variabilité en fonction de la lithologie de l'aquifère (paramètres mécaniques intrinsèques et géométrie des milieux poreux le constituant, influence du degré de saturation, etc). La perméabilité du milieu a également un effet sur la géométrie d'un réservoir hydrologique dont les contours peuvent varier en espace comme en temps, compliquant ainsi l'interprétation des données sismiques.Les géophysiciens cherchent à pallier ces limites, notamment à travers l'étude conjointe des vitesses (Vp et Vs) des ondes compression (P) et de cisaillement (S), dont l'évolution est par définition fortement découplée en présence de fluides. D'un point de vue théorique, cette approche se révèle appropriée à la caractérisation de certains aquifères, en particulier grâce à l'estimation des rapports Vp/Vs ou du coefficient de Poisson. L'évaluation de ces rapports peut être pratiquée de manière systématique grâce à la tomographie sismique en réfraction en utilisant parallèlement ondes P et S. Mais d'un point de vue pratique, la mesure de Vs reste délicate à mettre en oeuvre car les ondes S sont souvent difficiles à générer et à identifier sur les enregistrements sismiques. Une alternative est proposée par l’estimation indirecte de Vs à partir de l’inversion de la dispersion des ondes de surface, réalisée à partir de mesures de la vitesse des ondes de surface contenues dans les enregistrements sismiques classiques. Bien que généralement proposée pour la caractérisation de milieux 1D, la prospection par ondes de surface peut être déployée le long de sections linéaires dans le but de reconstruire un modèle 2D de distribution des Vs du sous-sol.Une méthodologie a été mise au point afin d'exploiter simultanément et de façon optimale les ondes P et les ondes de surface à partir des mêmes enregistrements sismiques. Lors de sa mise en oeuvre sur le terrain, cette acquisition « en ondes P » a été systématiquement suivie d'une acquisition « en ondes SH » afin de comparer les vitesses Vs obtenues par analyse de la dispersion des ondes de surface et par tomographie en ondes SH. L'utilisation de cette méthodologie dans différents contextes géologiques et hydrogéologiques a permis d'estimer les variations latérales et temporelles du rapport Vp/Vs, en bon accord avec les informations géologiques a priori et les données géophysiques et piézométriques existantes. L'utilisation de l'interférométrie laser a également permis de mettre ces techniques de traitement en application sur des modèles physiques parfaitement contrôlés afin d'étudier la propagation des ondes élastiques dans des « analogues » réalistes de milieux poreux partiellement saturés. / Characterisation and monitoring of groundwater resources and associated flow and transport processes mainly rely on the implementation of wells (piezometers). The interpretation of hydrogeological observations is however limited by the variety of scales at which these processes occur and by their variability in space and in time. In such a context, using geophysical methods often improves the very low spatial resolution of borehole data and limits their destructive nature. Among the geophysical tools applied to hydrogeology, seismic methods are commonly used at different scales. However, the seismic response in the context of aquifer characterisation remains complex. The interpretation of the estimated velocities is often difficult because of their variability depending on the aquifer lithology (intrinsic mechanical parameters and geometry of the constituting porous media, influence of the degree of saturation, etc). The permeability of the medium also affects the geometry of a hydrological reservoir whose contours may vary in space and in time, thus complicating the interpretation of seismic data. Geophysicists seek to overcome these limitations, especially through the joint study of compression (P-) and shear (S-) wave velocities (Vp and Vs), whose evolution is by definition highly decoupled in the presence of fluids. From a theoretical point of view, this approach proves suitable for the characterisation of aquifers, especially by estimating Vp/Vs or Poisson's ratio. The evaluation of these ratios can be systematically carried out with seismic refraction tomography using both P- and S-waves. However, retrieving Vs remains practically delicate because S-waves are usually difficult to generate and identify on seismic records. As an alternative, indirect estimation of Vs is commonly achieved thanks to surface-wave dispersion inversion, carried out from measurements of surface waves phase velocities contained in typical seismic records. Although it is usually proposed for the characterisation of 1D media, surface-wave prospecting can be deployed along linear sections in order to build 2D models of Vs distribution in the ground. A specific methodology has been developed for the combined and optimised exploitation of P- and surface waves present on single seismic records. When deployed on the field, this "P-wave" acquisition has been systematically followed by a "SH-wave" acquisition in order to compare Vs models obtained from surface-wave dispersion analysis and SH-wave refraction tomography. The use of this methodology in several geological and hydrogeological contexts allowed for estimating Vp/Vs ratio lateral and temporal variations in good agreement with a priori geological information and existing geophysical and piezometric data. Laser-based ultrasonic techniques were also proposed to put these processing techniques in practice on perfectly controlled physical models and study elastic wave propagation in partially saturated porous media.

In this study, ambient noise wavefield was used for the first time to image spatial and temporal upper crustal seismic structures in NW-Bohemia/Vogtland region. The data come from 111 stations and were collected from continuous recordings of the permanent station networks of Germany and Czech Academy of Sciences as well as temporary stations of the BOHEMA and PASSEQ experiments. Rayleigh and Love waves travelling between each station-pair are extracted by cross-correlating long time series of ambient noise data recorded at the stations. Group velocity dispersion curves are obtained by time-frequency analysis of cross-correlation functions between 0.1 and 1 Hz, and are tomographically inverted to provide 2-D group velocity maps. At shorter periods Rayleigh wave group velocity maps are in good agreement with surface geology where low velocity anomalies appear along Mariánské Lázně Fault and Eger rift. A low velocity zone is observed at the northern edge of Mariánské Lázně Fault which shifts slightly to the south with increasing period and correlates well with the main focal zone of the earthquake swarms at 5 s period. We invert the 2-D group velocity maps into a 3-D shear wave velocity model. In this step Love waves were excluded from further analysis because of their high level of misfit to modelled dispersion curves. Horizontal and vertical sections through the model reveal a clear low velocity zone above the Nový Kostel seismic focal zone which narrows towards the top of the seismic activity and ends above the shallowest hypocenters at 7 km depth. We investigate temporal variation of seismic velocity within and around the Nový Kostel associated with 2008 and 2011 earthquake swarms by employing Passive Image Interferometry method using 7 continuous seismograms recorded by the WEBNET network. The results reveals stable seismic velocities without a clear post seismic velocity change during earthquake swarms in the Nový Kostel area.

Thesis (M.S.)--Joint Program in Oceanographic Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 1997. / Includes bibliographical references (p. 65-66). / The Surface Suspended Acoustic Receiver (SSAR) is a free-drifting platform intended for use as a receiver in large scale acoustic tomography experiments. Early prototypes of the SSAR exhibited very poor signal-to-noise ratios in the frequency band of the hydrophones. This thesis details efforts to reduce the hydrophone noise level by combining the analysis of experimental data with the results from numerical models. Experiments were conducted to quantify both the frequency content and magnitude of noise generated on the SSAR. Through a program of sea trials and pond testing, two noise sources were identified. The dominant source of noise in the SSAR is velocity dependent flow noise that results from turbulent pressure fluctuations on the hydrophones. A second noise source results from the acceleration sensitivity of the hydrophones in conjunction with high frequency accelerations present in the hydrophone array cable. These high frequency accelerations also show a velocity dependence. The presence of the acceleration-induced noise leads to correlations between the signals from adjacent hydrophones, thus distorting the typical picture that flow noise should be uncorrelated along an array. The primary methods of eliminating the noise are encapsulating the hydrophone in a flow shield, eliminating the array cable, and slowing the system down by replacing the wave following surface buoy with a spar buoy. Using the experimental results, empirical relationships between hydrophone velocity and expected noise level are formed for both shielded and unshielded hydrophones. The numerical models developed as a part of this effort are then used to predict the velocities for a wide range of possible SSAR configurations. The models can also provide information, such as system tensions, that is useful in evaluating the longevity and survivability of SSARs. Modeled design fixes include subsurface component changes as well as comparing a wave following surface buoy to a spar buoy. / by Jason I. Gobat. / M.S.

Surface acoustic wave (SAW) sensors offer a wireless, passive sensor solution for use in numerous environments where wired sensing can be expensive and infeasible. Single carrier frequency SAW sensor embodiments such as delay lines, and resonators have been used in single sensor environments where sensor identification is not a necessity. The orthogonal frequency coded (OFC) SAW sensor tag embodiment developed at UCF uses a spread spectrum approach that allows interrogation in a multi-sensor environment and provides simultaneous sensing and sensor identi- fication. The SAW device is encoded via proper design of multiple Bragg reflectors at differing frequencies. To enable accurate device design, a model to predict reflectivity over a wide range of electrode metallization ratios and metal thicknesses has been developed and implemented in a coupling of modes (COM) model. The high coupling coefficient, reflectivity and temperature coefficient of delay (TCD) of YZ LiNbO3 makes it an ideal substrate material for a temperature sensor, and the reflectivity model has been developed and verified for this substrate. A new concept of pseudo-orthogonal frequency coded (POFC) SAW sensor tags has been investigated, and with proper design, the POFC SAW reduces device insertion loss and fractional bandwidth compared to OFC. OFC and POFC sensor devices have been fabricated at 250 MHz and 915 MHz using fundamental operation, and 500 MHz and 1.6 GHz using second harmonic operation. Measured device results are shown and compared with the COM simulations using the iii enhanced reflectivity model. Additionally, the first OFC devices at 1.05 GHz were fabricated on 128o YX LiNbO3 to explore feasibility of the material for future use in OFC sensor applications. Devices at 915 MHz have been fabricated on YZ LiNbO3 and integrated with an antenna, and have then been used in a transceiver system built by Mnemonics, Inc. to wirelessly sense temperature. The first experimental wireless POFC SAW sensor device results and predictions will be presented.